In accordance with GOST 2.703 - 68 on the kinematic diagram, it is necessary to depict the entire set of kinematic elements and their connections, all kinematic connections between pairs, chains, etc., as well as connections with sources of motion.
The kinematic diagram of the product should be drawn, as a rule, in the form of a sweep. It is allowed to depict diagrams in axonometric projections and, without violating the clarity of the diagram, move elements up or down from their true position, as well as rotate them to positions that are most convenient for the image. In these cases, the conjugated links of the pair, drawn separately, should be connected by a dashed line.
All elements of the circuit must be depicted with conventional graphic symbols in accordance with GOST 2.770 - 68 (Fig. 10.1) or simplified external outlines.
The elements of the scheme should be depicted:
shafts, axles, rods, etc. - with solid main lines of thickness S;
elements depicted in simplified external outlines (gear wheels, worms, pulleys, sprockets, etc.) are solid thin lines with a thickness of S / 2;
the contour of the product, in which the circuit is inscribed, is in solid thin lines with a thickness of S / 3;
kinematic links between the mating links of the pair, drawn separately, - dashed lines with a thickness of S / 2;
the extreme positions of the element that changes its position during the operation of the product - thin dash-dotted lines with two points;
shafts or axles covered by other elements (invisible) - dashed lines.
To each kinematic element should be assigned a serial number, starting from the source of movement. The shafts are numbered in Roman numerals, the rest of the elements are numbered in Arabic. Elements of purchased or borrowed mechanisms (for example, gearboxes) are not numbered, a serial number is assigned to the entire mechanism.
The serial number is put down on the shelf of the leader line. Under the shelf, it is necessary to indicate the main characteristics and parameters of the kinematic element:
electric motor power, W and frequency of rotation of its shaft, min -1 (angular velocity, rad / s) or power and frequency of rotation of the input shaft of the unit;
torque, Nm, and speed, min -1 of the output shaft;
the number and angle of inclination of the teeth and the module of gears and worm wheels, and for the worm - the number of entries, the module and the diameter coefficient;
belt drive pulley diameters; number of sprocket teeth and chain pitch, etc.
If the diagram is overloaded with images of links and kinematic links, the characteristics of the elements of the diagram can be indicated on the drawing field - the diagram in the form of a table. It provides a complete list of constituent elements.
Let us explain some aspects of the process of reading and executing kinematic diagrams, and, first of all, with the accepted conventions when creating kinematic diagrams.
1. It is customary to depict the kinematic scheme in the form of a sweep. What does this word mean in relation to the kinematic scheme?
The fact is that the spatial arrangement of the kinematic links in the mechanism for the most part is such that it is difficult to depict them on the diagram, since individual links obscure each other.
This, in turn, leads to misunderstandings or misconceptions about the schema. To avoid this, the schemes use the conditional method of the so-called expanded images.
On fig. 10.1, a picture of two pairs is shown gear wheels. Since it is customary to depict gears in the form of rectangles on kinematic diagrams, it is easy to imagine that with a given spatial arrangement of gears, their images will overlap in pairs.
To prevent such overlays, regardless of the spatial arrangement of the kinematic links in the mechanism, it is customary to depict them in expanded form, that is, the rotation axes of all mating gears must lie in the same plane, parallel plane images (see Fig. 10.1, b).
An example of a sweep of kinematic links in a diagram.
2. The transition from a constructive scheme to a kinematic one facilitates the figurative perception of the latter (Fig. 10.2). From this diagram it can be seen that the crank 1 has a rigid support, which is marked with a thick main line with hatching; piston 2, shown in the kinematic diagram in the form of a rectangle, has a gap with the cylinder walls, which, as fixed elements, also have one-sided shading. The gap indicates a possible reciprocating movement of the piston.
Structural and kinematic diagrams of an internal combustion engine
3. In all diagrams, shafts and axles are depicted with the same thick main line (Fig. 10.3). The difference between them is as follows:
a) the shaft supports are represented by two dashes with a gap on both shaft stops; since the shafts rotate together with the gear wheels (pulleys) mounted and connected to them by keys, the bearings are plain bearings or rolling bearings. In cases where it is necessary to clarify the type of shaft supports, the standard provides for special designations based on the given dashes;
b) the axis is a fixed product, therefore its ends are embedded in fixed supports, marked in the diagram by line segments with one-sided hatching. The gear wheel mounted on the axle rotates freely when the driven wheel rotates on the shaft.
Shafts and axles in kinematic diagrams
4. Some rules for reading kinematic diagrams:
a) for the most part, the drive gear (pulley) is the smaller of the mated pair, and the larger one is the driven one (Fig. 10.4). The letters n 1 and n 2 indicated in the diagram are the designation of the gear ratio or the ratio of the rotational speed n of the driving and driven wheels: n 1 / n 2;
Drive shaft and driven shaft on kinematic diagrams
b) in fig. 10.5 shows a reduction gear, since n 1 > n 2. In a gear train, the mating gears are made in one module, so the larger of the gears has more teeth. Gear ratio of the gear train:
where Z 1 and Z 2 - the number of teeth of the gears;
Reduction gear
c) in fig. 10.6 shows an overdrive, since n 1< n 2 ;
d) in fig. 10.7 shows three speed transmissions: a stepped pulley transmission with a flat belt and a gearbox with a movable block of gears.
In a belt drive, for the use of one belt at all stages, the following condition is provided: d 1 + d 2 \u003d d 3 + d 4 \u003d d 5 + d 6, where d 1, d 2, d 3, d 4, d 5, d 6 - pulley diameters in mm.
Rotation is transferred from shaft I to shaft II (n I and n II).
Rotation frequency:
n II \u003d n I d 1 /d 2; n II \u003d n I d 3 /d 4; n II \u003d n I d 5 /d 6.
Overdrive gear
Three speed gears
On fig. 10.7, b shows a gearbox for three speeds of rotation with a movable block of gears Z 1 - Z 3 - Z 5 that can move along the shaft key I; on shaft II, the wheels are rigidly connected to the shaft with keys.
Shaft speed II:
n II =n I Z 1 /Z 2 ; n II =n I Z 3 /Z 4 ; n II \u003d n I Z 5 / Z 6 .
where Z 1 , Z 2 , Z 3 , ..., Z 6 is the number of teeth of the wheels.
Since the gears of one module, then
Z 1 + Z 2 \u003d Z 3 + Z 4 \u003d Z 5 + Z 6.
5. It should be noted that the “scale-free” schemes are a relative sign. So, for basic kinematic diagrams, the ratio of the sizes of the conventional graphic symbols of the interacting elements in the diagram should approximately correspond to the actual ratio of the sizes of these elements.
This can be seen from the consideration of the principal kinematic diagrams of the conical differential of the gear hobbing machine, shown in orthogonal and axonometric projections (see Fig. 10.8). In these diagrams, the geometric dimensions of the bevel gears 3...6 are the same.
Kinematic circuit diagram of a bevel differential:
a – orthogonal projection; axonometric projection.
On fig. 10.9 shows an example of a schematic kinematic diagram, which consists of conditional graphic designations of elements, connections between them and alphanumeric positional designations of elements, as well as constituent elements of the circuit, made in the form of a table. The image can be used to represent the sequence of transmission of movement from the engine to the actuator. The table shows the designations of the constituent elements, their explanations and parameters.
Example of a kinematic circuit diagram
| Name | visual image | Symbol |
| Shaft, axle, roller, rod, connecting rod, etc. | ||
| Sliding and rolling bearings on the shaft (without specifying the type): a - radial b - thrust one-sided | ||
| The connection of the part with the shaft: a - free during rotation b - movable without rotation c - deaf | ||
| Shaft connection: a - blind b - articulated | ||
| Clutch couplings: a - single-sided cam b - double-sided cam c - double-sided friction (without specifying the type) | ||
| Stepped pulley mounted on the shaft | ||
| Flat belt transmission open | ||
| Chain transmission (without specification of chain type) | ||
| Gear gears (cylindrical): a - general designation (without specifying the type of teeth) b - with straight c - with oblique teeth | ||
| Gear transmissions with intersecting shafts (bevel): a - general designation (without specifying the type of teeth) b - with straight c - with spiral d - with circular teeth | ||
| Rack and pinion transmission (without specifying the type of teeth) | ||
| Screw that transmits motion | ||
| Nut on the screw that transmits the movement: a - one-piece b - detachable | ||
| electric motor | ||
| Springs: a - compression b - tension c - conical |
As can be seen from the table, the shaft, axle, rod, connecting rod are indicated by a solid thickened straight line. The screw that transmits the movement is indicated by a wavy line. Gears are indicated by a circle drawn by a dash-dotted line on one projection, and in the form of a rectangle circled by a solid line, on the other. In this case, as in some other cases (chain transmission, rack and pinion gears, friction clutches, etc.), general designations (without type specification) and private designations (with type indication) are used. On a general designation, for example, the type of gear teeth is not shown at all, but on private designations they are shown with thin lines. Compression and extension springs are indicated by a zigzag line. To depict the connection of the part with the shaft, there are also symbols.
Conventional signs, used in diagrams, are drawn without adhering to the scale of the image. However, the ratio of the sizes of the conventional graphic symbols of the interacting elements should approximately correspond to their actual ratio.
When repeating the same signs, you need to perform them in the same size.
When depicting shafts, axles, rods, connecting rods and other parts, solid lines of thickness s are used. Bearings, gears, pulleys, couplings, motors are outlined with lines about twice as thin. Axes, circles of gears, keys, chains are drawn with a thin line.
When performing kinematic diagrams, inscriptions are made. For gears, the module and number of teeth are indicated. For pulleys, their diameters and widths are recorded. The power of the electric motor and its rotational speed are also indicated by an inscription like N \u003d 3.7 kW, n \u003d 1440 rpm.
Each kinematic element shown in the diagram is assigned a serial number, starting from the engine. The shafts are numbered in Roman numerals, the rest of the elements in Arabic.
The serial number of the element is put down on the shelf of the leader line. Under the shelf indicate the main characteristics and parameters of the kinematic element.
If the diagram is complex, then the position number is indicated for the gears, and the specification of the wheels is attached to the diagram.
When reading and drawing up diagrams of products with gears, one should take into account the features of the image of such gears. All gears, when they are depicted as circles, are conditionally considered transparent, assuming that they do not cover the objects behind them. An example of such an image is shown in Fig. 10.1, where in the main view the circles show the engagement of two pairs of gears. From this view, it is impossible to determine which of the gears are in front and which are behind. This can be determined from the view on the left, which shows that the pair of wheels 1 - 2 is in front, and the pair 3 - 4 is located behind it.
Rice. 10.1.Gear Diagram
Another feature of the image of gears is the use of so-called expanded images. On fig. 10.2, two types of gearing scheme are made: non-deployed (a) and deployed (b).
Rice. 10.2. Gear images in the diagram
The location of the wheels is such that, in the left view, wheel 2 overlaps part of wheel 1, which may result in ambiguity when reading the diagram. To avoid errors, it is allowed to do as in Fig. 10 .2 , b, where the main view is preserved, as in Fig. 10.2, a, and the left view is shown in the expanded position. In this case, the shafts on which the gears are located are spaced from each other at a distance of the sum of the radii of the wheels.
On fig. 10.3, b shows an example of a kinematic diagram of a gearbox of a lathe, and in fig. 10.3, and its visual image is given.
Reading kinematic diagrams is recommended to start with the study of the technical passport, according to which they get acquainted with the device of the mechanism. Then they proceed to reading the diagram, looking for the main details, while using their symbols, some of which are given in Table. 10.1. Reading the kinematic diagram should start from the engine, which gives movement to all the main parts of the mechanism, and go sequentially along the transmission of motion.
The concept of detail and product
In the process of any work, a person always strives for
facilitating its implementation. As a result, daily
new complex devices and machines appear in the world,
capable of producing useful things or performing certain work faster and better.
Technological development:
a) woodworking;
b) metalworking;
c) agricultural;
d) textile.
Machinery, mechanisms and other items made
as a result of human technological activity, are called products.
A product is an item or set of items manufactured by an enterprise.
The product is the result of a manufacturing process
The product may consist of simpler parts,
Which are called details.
A part is a product made from one
piece of material, such as a shaft, gear,
nut, screw, etc.
In modern technology, parts are divided into two
major groups
The first includes details that are widely
are used in most machines (bolts, nuts, washers, etc.), they are called typical.
The second group is the details that are used
only in some individual machines (aircraft propeller, ship propeller, sewing machine foot, etc.). They are called special, or original.
Parts manufacturing methods
Parts are made from different materials
ways. The most common of these is cutting. On turning, milling and other machines, the cutter cuts off an extra layer from the material, leaving the desired shape and dimensions of the part.
Manufacturing
cutting details:
on lathes;
on drilling machines;
on sawmills
Parts manufacturing methods
A common economical production method
parts is casting.
Molten metal is poured into molds
for further solidification and formation of cast
Casting parts:
a) industrial casting;
b) casting scheme
Parts manufacturing methods
Stamping is the process of making parts.
Required sizes and shapes under the action of mechanical
Loads on a workpiece placed in a special device - a stamp.
In mechanical engineering, a product is an object of production to be manufactured. The product is a machine, device, mechanism, tool, etc. and their components: assembly unit, detail. An assembly unit is a product, the components of which are to be connected at the enterprise separately from other elements of the product.
An assembly unit, depending on the design, can either consist of individual parts or include assembly units of higher orders and parts. There are assembly units of the first, second and higher orders. The assembly unit of the first order enters directly into the product. It consists either of single parts or of one or more second-order assembly units and parts. The assembly unit of the second order is broken down into parts or assembly units of the third order and parts, etc. The assembly unit of the highest order is broken down only into parts. The considered division of the product into its component parts is carried out according to the technological feature.
A part is a product made from a material that is homogeneous in name and brand without the use of assembly operations. characteristic feature details - the absence of detachable and one-piece connections in it. A part is a complex of interconnected surfaces that perform various functions when operating the machine.
The production process is a set of all the actions of people and tools necessary for a given enterprise for the manufacture and repair of products. For example, the production process of manufacturing a machine includes not only the manufacture of parts and their assembly, but also the extraction of ore, its transportation, transformation into metal, and the production of blanks from metal. In mechanical engineering, the production process is part of the overall production process and consists of three stages: obtaining a workpiece; converting a workpiece into a part; product assembly. Depending on the specific conditions, these three stages can be carried out at different enterprises, in different workshops of the same enterprise, and even in the same workshop.
Technological process - a part of the production process, containing purposeful actions to change and (or) determine the state of the object of labor. A change in the state of the object of labor is understood as a change in its physical, chemical, mechanical properties, geometry, appearance. In addition, the technological process includes additional actions that are directly related to or accompanying a qualitative change in the production object; these include quality control, transportation, etc. For the implementation of the technological process, a set of production tools is required, called technological equipment, and workplace.
Technological equipment is a means of technological equipment, in which materials or blanks, means of influencing them, as well as technological equipment are placed to perform a certain part of the technological process. These include, for example, foundry machines, presses, machine tools, test benches, etc.
Technological equipment is a means of technological equipment that complements technological equipment to perform a certain part of the technological process. These include cutting tools, fixtures, measuring instruments. Technological equipment, together with technological equipment, and in some cases a manipulator, is commonly called a technological system. The concept of "technological system" emphasizes that the result of the technological process depends not only on the equipment, but also, to a lesser extent, on the fixture, tool, workpiece.
A blank is an object of labor, from which a part is made by changing the shape, size, surface properties or material. The workpiece before the first technological operation is called the initial workpiece. The workplace is an elementary unit of the structure of the enterprise, where the performers of work and serviced technological equipment, lifting and transport vehicles, technological equipment and objects of labor are located.
For organizational, technical and economic reasons, the technological process is divided into parts, which are commonly called operations.
A technological operation is a completed part of the technological process performed at one workplace. An operation covers all the activities of equipment and workers on one or more items of production to be assembled. When processing on machine tools, the operation includes all the actions of the worker who controls the technological system, the installation and removal of the object of labor, as well as the movements of the working bodies of the technological system. The content of operations varies over a wide range - from work performed on a separate machine tool or assembly machine in conventional production, to work performed on an automatic line, which is a complex of technological equipment connected by a single transport system and having a single control system in automated production. The number of operations in the technological process varies from one (production of a part on a bar machine, production of a body part on a multi-operation machine) to dozens (manufacture of turbine blades, complex body parts).
The operation is formed mainly according to the organizational principle, since it is the main element of production planning and accounting. All planning, accounting and technological documentation is usually developed for the operation. In turn, the technological operation also consists of a number of elements: technological and auxiliary transitions, setup, positions, working stroke.
Technological transition - a completed part of a technological operation, performed by the same means of technological equipment under constant technological conditions and installation.
An auxiliary transition is a completed part of a technological operation, consisting of human and (or) equipment actions that are not accompanied by a change in the properties of objects of labor, but are necessary to perform a technological transition (for example, installing a workpiece, changing tools, etc.). The transition can be performed in one or more work passes. The working stroke is a complete part of the technological transition, consisting of a single movement of the tool relative to the workpiece, accompanied by a change in the shape, dimensions, surface quality and properties of the workpiece. When processing a workpiece with the removal of a layer of material, the term "allowance" is used.
The technological process of machining is a part of the production process that is directly related to changing the shape, dimensions or properties of the workpiece being processed, performed in a certain sequence. The technological process consists of a number of operations.
An operation is a completed part of the technological process of processing one or more simultaneously processed workpieces, performed at one workplace by one worker or team. The operation begins from the moment the workpiece is installed on the machine and includes all its subsequent processing and removal from the machine. The operation is the main element in the development, planning and regulation of the technological process of processing workpieces. The operation is performed in one or more settings of the workpiece.
Installation - a part of the technological operation, performed with the constant fixing of the workpieces being processed. In the installation, separate positions of the workpiece are distinguished.
Position - a fixed position occupied by a fixed workpiece together with a fixture relative to a tool or a fixed part of the equipment to perform a certain part of the operation.
A technological operation can be performed in one or several transitions.
The transition is the part of the operation, which is characterized by the constancy of the cutting tool, the processing mode and the surface to be machined. In turn, the transition can be subdivided into smaller elements of the technological process - passages. During the pass, a layer of material is removed without changing the machine settings.
The development of all these elements of the technological process largely depends on the nature of the workpiece and the allowances for its processing.
A workpiece is an object of production from which a part is made by changing the shape, size, roughness and properties of the material. Blanks are produced in foundries (castings), forging shops (forgings, stampings) or blanking shops (cut from rolled products). The method of producing blanks depends on the design requirements for the parts, material properties, etc.
When developing a technological process, it is very important to choose the right technological (installation and measuring) bases.
Under the mounting base is understood the surface of the workpiece on which it is fixed and on which it is oriented relative to the machine and the cutting tool. The mounting base used in the first operation is called the rough base, and the base that was formed as a result of initial processing and is used to fix and orient the workpiece during further processing is called the finishing base.
Measuring bases are the surfaces of the workpiece, from which the dimensions are measured when monitoring the results of processing.
When choosing technological bases, they are guided by the rules of unity and constancy of bases. According to the first rule, the same surfaces should be used as installation and measuring bases whenever possible. The second rule requires that as many surfaces as possible be processed from one base. Compliance with these rules ensures higher processing accuracy. For a rough installation base, they usually take the surface that is not subject to further processing or has the smallest allowance for processing. This avoids marriage due to insufficient allowance for this surface.
The surfaces selected as mounting bases must allow the workpiece to be securely fastened.
The development of the technological process begins with the analysis of the initial data - the working drawing and the dimensions of the batch of parts (the number of workpieces of the same name to be processed). At the same time, the availability of equipment, fixtures, etc. is taken into account.
Based on the working drawing and batch sizes, the type and dimensions of the workpiece are determined. So, for a single production, workpieces are usually cut from sectional or sheet metal (in this case, the locksmith must determine the dimensions of the workpiece, taking into account processing allowances). In serial and mass production, blanks are usually obtained by casting, free forging or stamping.
For the selected workpiece, technological bases are outlined: first - roughing, then - the base for finishing.
Based on typical technological processes, the sequence and content of technological operations for processing a particular part are determined. When the processing sequence is determined and the operations are scheduled, for each of them select necessary equipment, technological equipment (working and measuring tools, devices) and auxiliary materials (means for painting workpieces during marking, cooling and lubricants, etc.).
In the case of processing parts on machine tools, processing modes are calculated and assigned. Then the technological process is normalized, i.e., the time limit for the execution of each technological operation is determined.
State standards established the Unified System for Technological Preparation of Production (USTPP). The main purpose of the ECTPP is to establish a system for organizing and managing the process of technological preparation of production. ECTPP provides for the widespread use of progressive standard technological processes, standard technological equipment and means of mechanization and automation of production processes.
A locksmith shop at an industrial enterprise is an independent production unit of the shop, which occupies a significant area and is equipped with workbenches, tools, basic and auxiliary equipment.
The staff of the site consists of several tens or even several hundred people. Depending on the size of the enterprise, independent assembly and locksmith shops can be organized, which may include production units (tool pantry, pantry of materials and components, control department and a number of other production and auxiliary units).
Separate parts of machines and devices manufactured at other sites are delivered to the fitter and assembly site. From these parts, site workers assemble assembly units, kits or units from which machines are mounted. The products of the fitting and assembly section of the workshop can be presented in the form of parts. However, the site, as a rule, does not perform other services for servicing the workshop or plant.
The locksmith section of the workshop should be equipped with workbenches equipped with a vice, manual and mechanical drilling machines, tool sharpening machines, mechanical saws, lever shears, straightening and lapping plates, marking plate, portable electric grinders, machines and tools for soldering, mechanization equipment lifting and transport works, racks and containers for parts, waste containers, tool pantry.
Occupational Health, Safety and Health
Work is safe if it is performed under conditions not life threatening and health of workers.
At industrial enterprises, the heads of the enterprise, workshop, section (director, foreman, foreman) bear full responsibility for labor protection and safety. Each enterprise should organize a labor protection department that monitors compliance with the conditions for safe work and implements measures to improve these conditions.
Employees are required to comply with the requirements of labor protection instructions.
Before starting work, the employee must be instructed in labor protection.
Occupational hygiene is a section of preventive medicine that studies the impact of the labor process and factors of the working environment on the human body in order to scientifically substantiate the standards and means of preventing occupational diseases and other adverse effects the impact of working conditions on workers.
An employee starting work must be healthy and neatly dressed. Hair must be tucked under a headdress (beret, scarf).
Locker rooms must have adequate lighting in accordance with current regulations. Distinguish between natural (daylight) and artificial (electric) lighting. Electric lighting can be general and local.
The floor in the locksmith's room should be laid out from end checkers, wooden beams or asphalt masses. Contamination of the floor with oil or grease should be avoided as this may cause an accident.
In order to avoid accidents at the enterprise and at the workplace, safety requirements must be observed.
All moving and rotating parts of machines, equipment and tools must have protective screens. Machinery and equipment must be properly grounded. Sources of electricity must comply with current technical requirements. In the places where fuses are installed, special protective equipment must be used.
Maintenance and repair of equipment and fixtures must be carried out in accordance with the instructions for use and repair. The tool must be correct.
Informational (for example, “Water for drinking”, “Changing room”, “Toilets”, etc.), warning (for example, “Attention - train”, “Stop! High voltage”, etc.) and prohibiting (for example, "No smoking!", "Grinding without glasses is prohibited", etc.) pointers.
Steel and hemp ropes of various handling equipment and accessories, seat belts should be systematically tested for strength.
Fire and access roads, walkways for pedestrians (both on the territory of the enterprise and inside the premises) must be safe for traffic.
Do not use damaged ladders. Open channels and manholes should be well marked and protected.
At the enterprise and at the workplace, the thoughts of the employee should be focused on the work entrusted to him, which must be completed quickly and efficiently. At work, violations of labor and production discipline, alcohol consumption are unacceptable.
At the end of the work, you should tidy up the workplace, put the tools and accessories in the tool box, wash your hands and face with warm soapy water or take a shower.
Overalls should be put away in a closet specially designed for this purpose.
Each site or workshop must be equipped with a first aid kit (first aid station). The first aid kit should contain sterile bandages, cotton wool, disinfectants, plasters, bandages, tourniquets, sterile bags, triangular scarves, splints and stretchers, valerian drops, painkillers, cough tablets, ammonia, iodine, pure alcohol, baking soda.
Teams (links) of rescuers or sanitary instructors are formed from among specially trained workers at an enterprise or in a workshop.
The rescuer or health instructor provides the victim with first aid in case of accidents, calls for emergency assistance, transports the victim home, to the clinic or hospital and does not leave the victim until the necessary medical care is provided to him.
Employees of enterprises and locksmith shops working with metal most often experience the following occupational injuries: cuts or damage to the surface of tissues with a sharp tool, eye damage from metal fragments or shavings, burns, electric shock.
A burn is damage to body tissues that have been in direct contact with a hot object, steam, hot liquid, electric current, acid.
There are three degrees of burns: the first degree is reddening of the skin, the second is the appearance of blisters, the third is the necrosis and charring of tissues.
For minor burns (first degree), first aid is provided with cleansing agents. Do not compress with oil or any ointment, as this may lead to further irritation or infection, requiring long-term treatment. The burnt area should be bandaged with a sterile bandage. A victim with first, second and third degree burns should be immediately sent to the hospital.
In case of electric shock, the victim is first of all released from the source of damage (to do this, it is necessary to break the connection, turn off the voltage or drag the victim away from the place of damage, while wearing dielectric shoes and gloves) and lay on a dry surface (boards, doors, blanket, clothes), unfasten clothing that squeezes the throat, chest and stomach.
Clenched teeth must be unclenched, tongue extended (preferably with a handkerchief) and a wooden object placed in the mouth to prevent the mouth from spontaneously closing. After that, begin to do artificial respiration (15-18 shoulder movements or breaths per minute). Artificial respiration should be interrupted only on the recommendation of a doctor or if the victim begins to breathe on his own.
The most efficient method artificial respiration is the mouth-to-mouth and mouth-to-nose method.
In the event of a fire, stop work, turn off electrical installations, equipment, ventilation, call the fire brigade, inform the management of the organization and start extinguishing the fire with the available fire extinguishing equipment.
Safety measures when performing certain types of work are briefly discussed in the relevant sections.
Works on the construction of buildings and structures, installation of technological, sanitary, electrical equipment, automation and low-voltage devices are carried out in accordance with the design and estimate documentation specially developed for each object. During the construction of industrial facilities, working drawings must contain sets of architectural, construction, sanitary, electrical and technological documentation.
During electrical work, working drawings of the electrical part of the project are used, including technical documentation for external and internal electrical networks, substations and other power supply devices, power and lighting electrical equipment. When accepting working documentation, it is necessary to pay attention to taking into account the requirements of the industrialization of installation work, as well as the mechanization of cable laying, rigging of units and blocks of electrical equipment and their installation.
When developing project documentation, the requirements of the technology of electrical installation production of the organization that will carry out the installation are taken into account. In the installation area (directly at the site of installation of equipment and laying electrical networks in workshops, buildings), installation work consists in installing large blocks of electrical devices, assembling nodes and laying networks. Therefore, working drawings are completed according to their purpose: for procurement work, i.e. for ordering blocks and assemblies at manufacturing plants or in workshops of electrical assembly workpieces (MEZ), and for the installation of electrical devices in the installation area.
Openings, niches, holes for electrical installation must be taken into account in the drawings of the architectural and construction part of the project. Channels or pipes for laying wires, niches, nests with embedded parts for installing switch cabinets, sockets, switches, bells and call buttons should be provided in the working drawings of building structures (reinforced concrete, gypsum concrete, expanded clay concrete floor panels, wall panels and partitions, reinforced concrete columns and crossbars of factory production). Installation sites for electrical equipment and routes for laying electrical networks should be linked to installation sites for technological and sanitary equipment and routes for other engineering networks. Installation of off-shop cable and overhead lines is carried out according to the drawings for laying the indicated line routes with their binding to the coordinate grids of the building and structure. As a rule, overhead line supports, their foundations, intersections of cable lines and cable structures are performed according to standard drawings. For the installation of power electrical equipment, floor plans of the building and workshops are developed with the indication and coordination of the routes for laying supply and distribution power networks and the placement of busbars, power supply points and cabinets, electrical receivers and ballasts, for the installation of electric lighting - with the indication and coordination of the supply lines on them. and group networks, lamps, lighting points and shields.
The electrical installation department receives project documentation from the customer and orders the manufacture of blocks and assemblies of electrical installations at manufacturing enterprises and at the bases of installation organizations. On the working drawings transferred to the installation organization, they put a stamp or inscription: “Permitted for production” signed by the responsible representative of the customer. The customer also transfers to the installation organization the diagrams and installation instructions received from the equipment manufacturers.
Continuation of the table. 3.1
Continuation of the table. 3.1
The end of the table. 3.1
Among the transmissions of motion from the drive to the working bodies of the machine, mechanical transmissions are most widely used (Fig. 3.1).
According to the method of transferring motion from the driving element to the driven element, mechanical transmissions are divided as follows: gears with direct contact (gear - Fig. 3.1, a; worm - Fig. 3.1, b; ratchet; cam) or with a flexible connection (chain); friction transmissions with direct contact (friction) or with a flexible connection (belt - Fig. 3.1, c).
The main kinematic parameter that characterizes all types of mechanical transmissions of rotational motion is the gear ratio - the ratio of the number of teeth of a larger wheel to the number of teeth of a smaller one in a gear, the number of teeth of a wheel to the number of worm entries in a worm gear, the number of teeth of a large sprocket to the number of teeth of a small one in a chain transmission, as well as the diameter of a large pulley or roller to the smaller diameter in a belt or friction drive. The gear ratio characterizes the change in speed in the transmission
where and - the speed of rotation of the driving I and driven shafts II, min -1 or s -1 (see Fig. 3.1, a, b and c).
So, for gear (see Fig. 3.1, a) and chain drives
where is the number of teeth of the larger gear or sprocket; - the number of teeth of the smaller gear or sprocket.
For worm gear (see fig. 3.1, b)
where is the number of teeth of the worm wheel; - the number of visits of the worm.
For belt drive (Fig. 3.1, c)
where is the diameter of the driven (larger) transmission pulley, mm; - diameter of the driving (smaller) transmission pulley, mm.
To convert rotational motion into translational or vice versa, rack and pinion are used (Fig. 3.1, G) or screw (Fig. 3.1, e) transmission. In the first case, the axis of rotational motion and the direction of translational motion are perpendicular, and in the second, they are parallel.
Gears that convert rotational motion into translational motion are characterized by the distance that the moving element translates in one revolution of the drive shaft.
In a rack and pinion (see Fig. 3.1, d), the rack moves in one revolution of the gear (gear)
where is the number of teeth of the wheel; - engagement module.
Rice. 3.1. Gears in machine tools: a - gear: I - drive shaft; - number of gear teeth; - frequency of rotation of the drive shaft; II - driven shaft; - number of teeth of the wheel; - frequency of rotation of the driven shaft; b - worm: and - rotational speed and number of worm entries, respectively; and - frequency of rotation and the number of teeth of the wheel, respectively; c - belt: and - frequency of rotation of the drive roller and its diameter, respectively; and - frequency of rotation of the driven roller and its diameter, respectively; g - screw: - screw pitch; - the direction of movement of the nut; d - rack: - direction of movement of the rail; - rack teeth pitch; - number of teeth of the wheel; - wheel rotation direction
A screw-nut pair is used in the feed mechanisms of almost all machine tools. Turning the screw one turn moves the nut to the right or left (depending on the thread direction) one step. There are designs in which the nut is fixed and the screw rotates and moves, as well as designs with a rotating and moving nut. For screw-nut transmission, the translational movement of the moving element
where - screw pitch, mm; - number of screw starts.
When several gears are arranged in series, their total gear ratio is equal to the product of the gear ratios of the individual gears
where is the total gear ratio of the kinematic chain; - gear ratios of all elements of the kinematic chain.
The speed of the last driven shaft of the kinematic chain is equal to the speed of the drive shaft, divided by the total gear ratio,
Travel speed (mm/min) of the finite element (node) of the kinematic chain
where is the frequency of rotation of the drive shaft of the initial element; - displacement of a translationally moving element per revolution of the drive shaft, mm.
The mathematical expression of the connection between the movements of the leading and driven elements (initial and final links) of the kinematic chain of the machine is called the kinematic balance equation. It includes components that characterize all elements of the chain from the initial to the final link, including those that transform movement, for example, rotational into translational. In this case, the balance equation includes the unit of measurement of the parameter (lead screw pitch - when using the screw-nut transmission or module - when using the gear-rack transmission), which determines the conditions for this transformation, millimeter. This parameter also allows you to coordinate the characteristics of the movement of the initial and final links of the kinematic chain. When transmitting only rotational motion, the equation includes dimensionless components (gear ratios of mechanisms and individual gears), and therefore the units of measurement of the motion parameters of the final and initial links are the same.
For machines with the main rotational movement, the limiting values of the spindle speed and provide the processing of a workpiece with a diameter of the machined surfaces in the range from to.
The spindle speed control range characterizes the operational capabilities of the machine and is determined by the ratio of the highest speed of the machine spindle to the lowest:
The rotational speed values from to form a series. In the machine tool industry, as a rule, a geometric series is used in which adjacent values differ by a factor of (- the denominator of the series: ). The following values of the denominator 1.06 are accepted and normalized; 1.12; 1.26; 1.41; 1.58; 1.78; 2.00. These values form the basis of the table series of spindle speeds.
3.2. Typical parts and mechanisms of machine tools
Beds and guides. The carrier system of the machine is formed by a set of its elements, through which the forces that arise between the tool and the workpiece during the cutting process are closed. The main elements of the carrier system of the machine are the frame and body parts (crossbars, trunks, sliders, plates, tables, calipers, etc.).
Bed 1 (Fig. 3.2) serves for mounting parts and assemblies of the machine, moving parts and assemblies are oriented and moved relative to it. The bed, as well as other elements of the carrier system, must have stable properties and ensure the possibility of processing workpieces with specified modes and accuracy during the service life of the machine. This is achieved the right choice the material of the bed and the technology of its manufacture, the wear resistance of the guides.
Rice. 3.2. Machine beds: a - screw-cutting lathe; b - lathe with program control; in - surface grinding; 1 - bed, 2 - guides.
For the manufacture of frames, the following basic materials are used: for cast frames - cast iron; for welded - steel, for the beds of heavy machine tools - reinforced concrete (sometimes), for high-precision machines - an artificial synthetic material made from crumbs of mineral materials and resin and characterized by slight temperature deformations.
Guides 2 provide the required relative position and the possibility of relative movement of the nodes that carry the tool and the workpiece. The rail design for moving the assembly allows only one degree of freedom of movement.
Depending on the purpose and design, there is the following classification of guides:
By type of movement - main movement and feed movement; guides for rearranging mating and auxiliary units that are stationary during processing;
Along the trajectory of movement - rectilinear and circular motion;
In the direction of the trajectory of the movement of the node in space - horizontal, vertical and inclined;
By geometric shape - prismatic, flat, cylindrical, conical (only for circular motion) and their combinations.
Rice. 3.3. Examples of sliding guides: a - flat; 6 - prismatic; in - in the form of a "dovetail"
Sliding guides and rolling guides are the most widely used (in the latter, balls or rollers are used as intermediate rolling bodies).
For the manufacture of sliding guides (Fig. 3.3) (when the guides are made as one piece with the frame), gray cast iron is used. Wear resistance of guides is increased by surface hardening, hardness HRC 42…56.
Steel guides are made overhead, usually hardened, with hardness HRC 58…63. Most often, steel 40X is used with HDTV hardening 1, steels 15X and 20X are followed by carburizing and hardening.
Reliable operation of the guides depends on protective devices that protect the working surfaces from dust, chips, dirt on them (Fig. 3.4). Protective devices are made from various materials, including polymers.
Spindles and their supports. The spindle - a type of shaft - serves to secure and rotate the cutting tool or fixture that carries the workpiece.
To maintain the accuracy of processing during a given service life of the machine, the spindle ensures the stability of the position of the axis during rotation and translational motion, the wear resistance of the supporting, seating and basing surfaces.
Spindles, as a rule, are made of steel (40Kh, 20Kh, 18KhGT, 40KhFA, etc.) and subjected to heat treatment (carburizing, nitriding, bulk or surface hardening, tempering).
To secure a tool or fixture, the front ends of the spindles are standardized. The main types of machine tool spindle ends are shown in Table. 3.2.
Rice. 3.4. The main types of protective devices for guides: a - guards; b - telescopic shields; c, d and e - tape; e - harmonica-shaped furs
Sliding and rolling bearings are used as spindle supports. The structural diagram of adjustable plain bearings made in the form of bronze bushings, one of the surfaces of which has a conical shape, is shown in fig. 3.5.
Spindle bearings use a lubricant in the form of a liquid (in hydrostatic and hydrodynamic bearings) or gas (in aerodynamic and aerostatic bearings).
There are single and multi-wedge hydrodynamic bearings. Single wedges are the simplest in design (sleeve), but do not provide a stable position of the spindle at high sliding speeds and low loads. This disadvantage is absent in multi-wedge bearings, which have several bearing oil layers covering the spindle neck evenly from all sides (Fig. 3.6).
Table 3.2
The main types of ends of machine spindles
Rice. 3.5. Adjustable plain bearings: a - with a cylindrical spindle neck: 1 - spindle neck; 2 - split sleeve; 3 - body; b - with a tapered neck of the spindle: 1 - spindle; 2 - solid sleeve
Rice. 3.6. Grinding wheel spindle support with hydrodynamic five-piece bearing: 1 - self-aligning liners; 2 - spindle; 3 - clip; 4 - screw; 5 - rolling bearings; 6 - screws with a spherical support end; 7 - cuffs
Hydrostatic bearings - plain bearings, in which the oil layer between the rubbing surfaces is created by supplying oil under pressure from the pump to them - provide high accuracy of the position of the spindle axis during rotation, have high rigidity and provide a liquid friction mode at low sliding speeds (Fig. 3.7 ).
Gas-lubricated bearings (aerodynamic and aerostatic) are similar in design to hydraulic bearings, but provide lower friction losses, which allows them to be used in high-speed spindle bearings.
Rolling bearings as spindle supports are widely used in machine tools of various types. Increased requirements are imposed on the accuracy of rotation of spindles, therefore, bearings of high accuracy classes are used in their supports, installed with a preload, which eliminates the harmful effects of clearances. Preload in angular contact ball and tapered roller bearings is created when they are installed in pairs as a result of axial displacement of the inner rings relative to the outer ones.
This displacement is carried out with the help of special structural elements of the spindle assembly: spacer rings of a certain size; springs that ensure the constancy of the preload force; threaded connections. In roller bearings with cylindrical rollers, the preload is created by deforming the inner ring 6 (Fig. 3.8) when it is tightened onto the tapered neck of the spindle 8 using a bushing 5 1. The bearings of the spindle bearings are reliably protected from contamination and leakage of lubricant by lip and labyrinth seals 7 .
Rolling bearings 4 are widely used as thrust bearings that fix the position of the spindle in the axial direction and perceive the loads arising in this direction. The preload of ball thrust bearings 4 is created by springs 3. The springs are adjusted with nuts 2.
Rice. 3.7. Hydrostatic bearing: 1 - bearing shell; 2 - spindle neck; 3 - a pocket that creates the bearing surface of the bearing (the arrows show the direction of supply of lubricant under pressure and its withdrawal)
Rice. 3.8. Front support of the lathe spindle on rolling bearings: 1 - nuts; 2 - adjusting nuts; 3 - springs; 4 - thrust bearings; 5 - bushings; 6 - roller bearing inner ring; 7 - seals; 8 - spindle
An example of using angular contact ball bearings to absorb axial loads is shown in fig. 3.6. The preload is created by adjusting the position of the outer
bearing rings 5 with nut 4.
Typical mechanisms for the implementation of translational movement. Translational motion in the machines under consideration is provided by the following mechanisms and devices:
Mechanisms that convert rotational motion into translational: a gear wheel or a worm with a rack, a lead screw - a nut and other mechanisms;
Hydraulic devices with a pair of cylinder - piston;
Electromagnetic devices such as solenoids, used mainly in drives of control systems. Let us give examples of some of these mechanisms (see Table 3.1 for symbols).
The gear-rack pair has a high efficiency, which determines its use in a wide range of rack speeds, including in the drives of the main movement, which transmit significant power, and in the drives of auxiliary movements.
A worm-and-rack gear differs from a gear-rack pair in increased smoothness of movement. However, this transmission is more difficult to manufacture and has a lower efficiency.
The mechanism of the lead screw - nut is widely used in drives of feeds, auxiliary and installation movements and provides: a small distance that the moving element moves in one revolution of the drive; high smoothness and accuracy of movement, determined mainly by the accuracy of manufacturing the elements of the pair; self-braking (in pairs of sliding screw-nut).
In the machine tool industry, six accuracy classes have been established for lead screws and sliding nuts: 0 - the most accurate; 1, 2, 3, 4 and 5 classes, with the help of which they regulate the permissible deviations in pitch, profile, diameters and surface roughness parameter. The design of the nuts depends on the purpose
mechanism.
Pairs of lead screw - sliding nut due to low efficiency are replaced by rolling screw pairs (Fig. 3.9). These pairs eliminate wear, reduce frictional losses and can eliminate gaps by preloading.
The disadvantages inherent in pairs of sliding screw-nut and screw-rolling nut, due to the peculiarities of their operation and manufacture, are excluded in the hydrostatic screw-nut transmission. This pair works in friction with a lubricant; The transmission efficiency reaches 0.99; oil is supplied to pockets made on the sides of the nut thread.
Typical mechanisms for the implementation of periodic movements. In the process of work in some machines, periodic movement (change of position) of individual nodes or elements is required. Periodic movements can be carried out by ratchet and Maltese mechanisms, cam mechanisms and overtaking clutches, electric, pneumatic and hydraulic mechanisms.
Ratchet mechanisms (Fig. 3.10) are most often used in the feed mechanisms of machine tools, in which the periodic movement of the workpiece, cutting (cutter, grinding wheel) or auxiliary (diamond for dressing the grinding wheel) tool is performed during the overrun or reverse (auxiliary) stroke (in grinding and other machines).
In most cases, ratchet mechanisms are used for rectilinear movement the corresponding node (table, caliper, quill). With the help of a ratchet gear, circular periodic movements are also carried out.
Couplings are used to connect two coaxial shafts. Depending on the purpose, there are non-disengaging, interlocking and safety clutches.
Non-disengaging couplings (Fig. 3.11, a, b, c) are used for a rigid (deaf) connection of shafts, for example, a connection using a sleeve, through elastic elements or through an intermediate element that has two mutually perpendicular protrusions on the end planes and allows you to compensate for the misalignment of the connected shafts .
Rice. 3.9. A pair of rolling screw-nut: 1, 2 - a nut consisting of two parts; 3 - screw; 4 - balls (or rollers)
Rice. 3.10. Ratchet Diagram: 1 - ratchet; 2 - doggy; 3 - shield; 4 - thrust
Interlocking couplings (Fig. 3.11, d, e, f) are used for periodic connection of shafts. The machines use interlocking cam clutches in the form of disks with end teeth-cams and gear clutches. The disadvantage of such coupled clutches is the difficulty of their inclusion with a large difference in the angular velocities of the driving and driven elements. Friction clutches do not have the disadvantage inherent in cam clutches, and allow them to be switched on at any speed of rotation of the driving and driven elements. Friction clutches are conical and disc. In the drives of the main movement and feed, multi-plate clutches are widely used, which transmit significant torques with relatively small overall dimensions. The compression of the leading disks with the driven ones is carried out using mechanical, electromagnetic and hydraulic drives.
Rice. 3.11. Couplings for connecting shafts: a - rigid bushing type; b - with elastic elements; in - cross-movable; g - cam; d - multi-disk with a mechanical drive: 1 - washer; 2 - pressure plate; 3 - balls; 4 - fixed bushing; 5 - sleeve; 6 - nut; 7 - springs; e - electromagnetic: 1 - slotted bushing; 2 - electromagnetic coil; 3 and 4 - magnetically conductive disks; 5 - anchor; 6 - sleeve
Safety couplings (Fig. 3.12) connect two shafts when normal conditions work and break the kinematic chain when the load increases. A chain break can occur when a special element is destroyed, as well as as a result of slippage of mating and rubbing parts (for example, discs) or disengagement of the cams of two mating parts of the coupling.
As a destructible element, a pin is usually used, the cross-sectional area of \u200b\u200bwhich is calculated to transmit a given torque. The disengagement of the mating elements of the clutch occurs under the condition that the axial force arising on the teeth, cams 1 or balls 5
, during overloads exceeds the force generated by the springs 3 and regulated by the nut 4. When displaced, the movable element 2 of the coupling acts on the limit switch, which breaks the electric power circuit of the engine
drive.
Overrunning clutches (Fig. 3.13) are designed to transmit torque when the kinematic chain links rotate in a given direction and to disconnect the links when rotating in the opposite direction, as well as to transmit rotations of different frequencies to the shaft (for example, slow - working rotation and fast - auxiliary ). The overrunning clutch allows you to transfer additional (fast) rotation without turning off the main chain. In machine tools, roller-type clutches are most widely used, which can transmit torque in two directions.
Ratchet mechanisms are also used as overtaking clutches.
Rice. 3.12. Schemes of safety clutches: a - ball; b - cam; 1 - cams; 2 - movable element of the clutch; 3 - springs; 4 - nut; 5 - balls
Rice. 3.13. Overrunning roller clutch: 1 - clip; 2 - hub; 3 - rollers; 4 - driving fork; 5 - springs
3.3. Drives for main movement and feed movement
A set of mechanisms with a source of movement, which serves to actuate the executive body of the machine with given characteristics of speed and accuracy, is called a drive.
Metal-cutting machines are equipped with an individual drive; on many machines, the main movement, feed movement, auxiliary movements are carried out from separate sources - electric motors and hydraulic devices. The change in speed can be stepless and stepped.
As drives for metal-cutting machines, electric motors of direct and alternating current, hydraulic motors and pneumatic motors are used. Electric motors are the most widely used as machine tool drives. Where stepless regulation of the shaft speed is not required, asynchronous AC motors are used (as the cheapest and simplest). For stepless speed control, especially in feed mechanisms, thyristor-controlled DC motors are increasingly being used.
The advantages of using an electric motor as a drive include: high rotation speed, the possibility of automatic and remote control, as well as the fact that their operation does not depend on the ambient temperature.
Among the transmissions of motion from the engine to the working bodies of the machine, mechanical transmissions are most widely used. According to the method of transmission of movement from the leading element to the driven, mechanical transmissions are divided as follows:
Gears by friction with direct contact (friction) or with flexible connection (belt);
Direct contact gears (gear, worm, ratchet, cam) or with flexible connection (chain).
Friction transmissions with a flexible connection include belt transmissions (Fig. 3.14). In these gears, the pulleys of the drive and driven shafts are covered by a belt with a certain tension force, which ensures the appearance of a friction force between the belt and the pulleys necessary to transmit the force. The tension, limited by the strength of the belt, is regulated by pushing the shafts apart or by a special tensioner.
Belts are made of leather, rubberized fabric, plastic, they have a different cross-sectional shape. Belts with a flat section (Fig. 3.14, b) is used when transmitting high speed (50 m/s and above) with relatively little effort. Large power is transmitted by several V-belts (Fig. 3.14, c) or a poly-V-belt (Fig. 3.14, d). Gears with belts with a circular cross section (Fig. 3.14, e) are used for small relative forces and in gears between cross shafts. V-ribbed belts are widely used (see Fig. 3.14, d) to increase the friction force (at the same tension as for flat belts).
In friction and belt drives, slippage always occurs between rubbing surfaces, so the real gear ratio for them is:
where is the theoretical gear ratio; - slip coefficient.
To prevent slippage, toothed belts are used (Fig. 3.14, e).
Rice. 3.14. Scheme of belt transmission (a) and transmission with a flat belt (b), V-belt (c), poly-V-belt ( G), round belt (d), toothed belt ( e): 1 - pulling metal cable toothed belt; 2 - the base of the toothed belt made of plastic or rubber; 3 - pulley; - leading roller; and - the center of rotation and the diameter of the drive roller, respectively; - driven roller; and - the center of rotation and the diameter of the driven roller, respectively; - belt tension force; - distance between the centers of rotation of the driving and driven rollers
Chain drives (Fig. 3.15) (for lubrication and cooling systems), like toothed belt transmission, transmit rotation speed to the driven shaft more stably and can transmit high power.
Rice. 3.15. Chain drive: - drive sprocket; - driven sprocket
The gear train (Fig. 3.16) is the most common gear, as it provides high stability of rotation speeds, is capable of transmitting high powers and has relatively small overall dimensions. Gears are used to transmit rotation between shafts (parallel, intersecting, crossing), as well as to convert rotational motion into translational (or vice versa). The movement from one shaft to another is transmitted as a result of mutual engagement of gears forming a kinematic pair. The teeth of these wheels are specially shaped. The most common gearing is in which the profile of the teeth is outlined along a curve called the involute of a circle or simply involute, and the gear itself is called involute.
The drive with gear boxes is the most common drive for the main movement and feed movement in machine tools and is called the gearbox and feed box respectively.
Gearboxes (Fig. 3.17) are distinguished by their layout and by the method of switching speeds. The layout of the gearbox determines the purpose of the machine and its size.
Gearboxes with replaceable wheels are used in machine tools with a relatively rare drive setting. The box is characterized by simplicity of design, small overall dimensions.
Gearboxes with movable wheels (Fig. 3.17, a) are widely used mainly in universal manual machines.
Rice. 3.16. Gear types for rotational movements: a and b - spur gear of external and internal gearing, respectively; in - helical cylindrical gear of external gearing; g - spur bevel gear; d - chevron wheel; e - worm gear
Rice. 3.17. Kinematic diagrams of gearboxes: a - with movable wheels: - gear wheels; b - with cam clutches: 0, I, II, III, IV - gearbox shafts; - gear wheels; - electric motor; Mf1, Mf2, MfZ, Mf4 - friction clutches; - claw clutch
The disadvantages of these boxes are: the need to turn off the drive before changing gears; the possibility of an accident in case of violation of the blocking and the simultaneous inclusion of two gears of the same group between adjacent shafts; relatively big sizes in the axial direction.
Gearboxes with cam clutches (Fig. 3.17, b) are characterized by small axial displacements of the clutches during switching, the possibility of using helical and chevron wheels, and low switching forces. The disadvantages include the need to turn off and brake the drive when switching speeds.
Gearboxes with friction clutches, unlike boxes with dog clutches, provide smooth gear shifting on the go. In addition to the disadvantages inherent in boxes with cam clutches, they are also characterized by a limited transmitted torque, large overall dimensions, reduced efficiency, etc. Despite this, boxes are used in lathes, drilling and milling groups.
Gearboxes with electromagnetic and other clutches that allow the use of remote control are used in various automatic and semi-automatic machines, including CNC machines. To unify the drive of the main movement of such machine tools, the domestic machine tool industry produces unified automatic gearboxes (AKS) of seven overall dimensions, designed for a power of 1.5 ... 55 kW; number of speed steps - 4... 18.
Depending on the type of mechanisms used with gears that serve to adjust the feeds, the following feed boxes are distinguished:
With replaceable wheels at a constant distance between the axes of the shafts;
With movable wheel blocks;
With built-in stepped cones (sets) of wheels and exhaust keys;
Norton (with cap gear);
With guitars of interchangeable wheels.
To obtain feed boxes with desired characteristics, they are often designed using several of the listed mechanisms simultaneously.
Norton boxes are used in feed drives of screw-cutting machines due to the possibility of accurately implementing the specified gear ratios. The advantages of boxes of this type are a small number of gears (the number of wheels is two more number gears), disadvantages - low rigidity and accuracy of pairing of the included wheels, the possibility of gear clogging if there is a cutout in the box body.
Feed boxes with interchangeable wheel guitars (Fig. 3.18) make it possible to adjust the feed with any degree of accuracy. The features of guitars with interchangeable wheels make them suitable for use in various types of machine tools, especially in serial and mass production machines. Such machines are equipped with appropriate sets of interchangeable wheels.
Rice. 3.18. Kinematic scheme (a) and design (b and c) of the guitar of replaceable gears: 1 - backstage; 2 - nut; 3 - screw; K, L, M, N - gears
3.4. General information about the technological process
machining
The process of creating wealth is called production.
The part of the production process that contains purposeful actions to change and (or) determine the state of the object of labor is called the technological process. The technological process can be attributed to the product, its component parts or to the methods of processing, shaping and assembly. The objects of labor include blanks and products. Depending on the execution method, the following elements of technological processes are distinguished:
Shaping (casting, molding, electroforming);
Processing (cutting, pressure, thermal, electrophysical, electrochemical, coating);
Assembly (welding, soldering, gluing, nodal and general assembly);
Technical control.
The completed part of the technological process, performed at one workplace, is called a technological operation. The definition of these terms is given in GOST 3.1109-82.
In production, a worker most often encounters the following types of descriptions of technological processes in terms of their level of detail:
A route description of a technological process is an abbreviated description of all technological operations in a route map in the sequence of their execution, without specifying transitions and technological modes;
Operational description of the technological process, a complete description of all technological operations in the sequence of their execution, indicating transitions and technological modes;
Abbreviated description of technological operations in the route map in the sequence of their execution, with full description individual operations in other technological documents is called a route-operational description of the process.
The description of manufacturing operations in their technological sequence is given in compliance with the rules for recording these operations and their coding. For example, cutting operations performed on machine tools are divided into groups. Each group is assigned certain numbers: 08 - program (operations on machine tools with program control); 12 - drilling; 14 - turning; 16 - grinding, etc.
When recording the content of operations, use established titles technological transitions and their conditional codes, for example: 05 - bring; 08 - sharpen; 18 - polish; 19 - grind; 30 - sharpen; 33 - grind; 36 - mill; 81 - fix; 82 - configure; 83 - reinstall; 90 - remove; 91 - install.
Part of the technological operation, carried out with a constant fixing of the workpieces, is called at camp. A fixed position occupied by a workpiece that is invariably fixed in a fixture relative to a tool or a fixed piece of equipment to perform a certain part of an operation is called a position.
The main elements of the technological operation include transitions. A technological transition is a completed part of a technological operation performed by the same means of technological equipment under constant technological conditions and installation. An auxiliary transition is a completed part of a technological operation, consisting of human and (or) equipment actions that are not accompanied by a change in the properties of the object of labor, but are necessary to complete the technological transition.
When registering technological processes, a set of technological documentation is created - a set of sets of documents of technological processes and individual documents necessary and sufficient to perform technological processes in the manufacture of a product or its components.
unified system technological documentation (ESTD), the following documents are provided: route map, sketch map, operational map, equipment list, material list, etc. Description of the content of technological operations, i.e. a description of the route technological process is given in the route map - the main technological document in the conditions of a single and pilot production, with the help of which the technological process is brought to the workplace. In the route map, in accordance with the established forms, indicate data on equipment, tooling, material and labor costs. The presentation of the operational technological process is given in operational maps compiled in conjunction with sketch maps.
A technological document can be graphic or textual. It alone or in combination with other documents defines the technological process or operation of manufacturing the product. A graphic document, which, according to its purpose and content, replaces the working drawing of a part in this operation, is called an operational sketch. The main projection on the operational sketch depicts the view of the workpiece from the side of the workplace at the machine after the operation. The machined surfaces of the workpiece on the operational sketch are shown by a solid line, the thickness of which is two to three times the thickness of the main lines on the sketch. The operational sketch indicates the dimensions of the surfaces processed in this operation and their position relative to the bases. You can also provide reference data indicating "dimensions for reference". The operational sketch indicates the maximum deviations in the form of numbers or symbols of the tolerance and fit fields according to the standards, as well as the roughness of the machined surfaces, which must be ensured by this operation.
The rules for recording operations and transitions, their coding and filling the cards with data are defined by standards and teaching materials the parent organization for the development of ESTD.
test questions
1. Give formulas for determining the cutting speed during the main rotary motion.
2. How are the gear ratios of kinematic pairs of machine tools found?
3. What is the regulation range?
4. What are the requirements for machine beds and guides?
5. Tell us about the purpose and design of spindle assemblies and bearings.
6. What couplings are used in machine tools?
7. Define a drive and tell us about the drives used in machine tools.
8. What are the main elements of machine tool drives do you know?
9. Tell us about the types and designs of gearboxes.
10. What designs of feed boxes are used in machine tools?
11. What is called the technological process? Name the components of technological processes.
In order to schematically depict the main components of a machine or other mechanism, kinematic diagrams are used.
In such diagrams, nodes, details, ways of interaction of individual elements of the mechanism are depicted conditionally. Each type element has its own designation.
How to read kinematic diagrams of machine tools
In order to learn how to read kinematic diagrams, you need to know the designations of individual elements and learn to understand the interaction of individual components. First of all, we will study the most common designations of the most common elements, the symbols on the kinematic diagrams are presented in GOST 3462-52.
Shaft designation
The shaft on the kinematic diagram is indicated by a bold straight line. The spindle diagram shows the tip.
Designation of bearings in the diagrams
The designation of the bearing depends on its type.
Plain bearing depicted in the form of conventional brackets-supports. If the thrust bearing supports are depicted at an angle.
ball bearings on the kinematic diagrams of the machines are depicted as follows.
Balls in bearings are conventionally depicted as a circle.
In conditional images roller bearings the rollers are shown as rectangles.
Schematic designation of parts connections
Kinematic diagrams depict various types of shaft and component connections.
The symbol of the coupling depends on its type, the most common of them are:
- cam
- frictional
The designations of one-way couplings on the kinematic diagrams of the machines are shown in the figure.
The designation of a two-way coupling can be obtained by mirroring the one-way layout horizontally.
Designation of gears on machine diagrams
Gears are one of the most common elements of machine tools. The symbol allows you to understand what type of transmission is used - spur, helical, chevron, bevel, worm. In addition, according to the diagram, you can find out which wheel is larger and which is smaller.
| Name | Designation | Name | Designation | |
| Shaft | Gears: | |||
| Connection of two shafts: | cylindrical wheels | |||
| deaf | ||||
| blind with overload protection | bevel wheels | |||
| elastic | ||||
| articulated | screw wheels | |||
| telescopic | ||||
| floating clutch | worm | |||
| gear clutch | ||||
| Shaft connection: | ||||
| free to rotate | rack | |||
| movable without rotation |  | |||
| with pull-out pin | Lead screw transmission with nut: | |||
| deaf | one-piece | |||
| Plain bearings: | detachable | |||
| radial | Couplings: | |||
| cam one-sided | ||||
| cam double-sided | ||||
| Rolling bearings: | conical one-sided | |||
| radial | ||||
| angular contact one-sided | disk one-sided | |||
| double-ended angular contact | disc double-sided | |||
| Belt drives: | electromagnetic unilateral | |||
| flat belt | ||||
| electromagnetic double-sided | ||||
| overrunning unilateral | ||||
| V-belt | ||||
| overrunning double-sided |  | |||
| Brakes: | ||||
| conical | ||||
| chain transmission |  | |||
| shoe | ||||
| disk |
with wheel z6 it is necessary that the block freely passes by the wheel z8 without hitting it with a wheel z9. This is possible if z7 – z9 > 5. Otherwise, it is necessary to apply the transmission scheme shown in Fig. 2.15, b. On fig. 2.15, in brute force transmission is shown. Shaft I can receive rotation from the wheel z5 when turning on the cam clutch of the wheels z1 and z4. With the clutch disengaged and the wheel engaged z4 With z3 rotation on the shaft I is transmitted through gears z1/z2, shaft II and wheels z3/z4 .
Rice. 2.15. Gear box mechanisms: a─ with two
mobile blocks; b─ with a three-crown block;
in─ with enumeration; G─ with friction double-sided clutch
Transmissions with sliding blocks and dog clutches are simple in design, reliable in operation and easy to control, but do not allow switching during rotation and are large in the axial direction. On fig. 2.15, G a transmission is given that is devoid of these shortcomings. wheels z2 and z4 freely mounted on the shaft II and are constantly engaged with the wheels z1 and z3, rigidly fixed on the shaft I. The transfer of motion to the shaft II from the shaft I occurs when the friction double-sided clutch is turned on, which rigidly connects the wheels to the shaft II z2 and z4. In this case, the speed can be changed on the go.
In modern machine tools with automatic gearboxes, one and two-way friction electromagnetic clutches are used.
On fig. 2.16, a shows the mechanism of the meander with a captive wheel z0, which allows you to double the gear ratios when you turn on the adjacent pair of gears. If we accept shaft I as the leading one, and shaft II as the driven ones, and z \u003d z 2 \u003d z 3 \u003d z 6= 56, and z 1 = z 4 = z 5 = z 7= 28, then we get the gear ratios of the mechanism:
Rice. 2.16. Mechanisms meander feed boxes:
a ─ with a captive wheel; b ─ with a movable wheel
The meander mechanism is also called the “multiplying mechanism”. The cap wheel mechanism has the disadvantage that it does not provide a constant center distance between the cap wheel z0 and z2, since the swivel lever 2 is fixed with a non-rigid movable cylindrical latch 1.
On fig. 2.16 b a more perfect design of the meander mechanism is shown, from which the cap wheel with a swivel lever is excluded.
The connection with the wheels of the blocks is made by a movable wheel z, which ensures the constancy of the center distances.
Norton's mechanism (Fig. 2. 17) is a cone made of gears with a cap wheel mounted on a rotary lever with a cylindrical lock. Cap wheel z0 can alternately engage with all the wheels of the cone ( z1 – z6) and transfer motion from shaft I to shaft II. Thus, six different gear ratios can be obtained. The choice of the number of teeth of the cone wheels is not related to the constancy of the center distance between the driving and driven shafts. The advantage of this mechanism is compactness, the disadvantage is low rigidity. The main purpose of this mechanism is to create an arithmetic series of gear ratios. Mainly used in universal screw-cutting lathes.
Shown in fig. 2.15, a The scheme of a six-speed gear box is a conventional multiplier structure, consisting of one kinematic chain with a series connection of movable blocks (gear groups), and provides a geometric series of circular output shaft speeds. This structure allows you to successfully create rational drives of the main movement. However, in some cases, for example, in universal screw-cutting lathes, with an increase in the range of speed control, it is impossible to create a simple drive that meets the requirements on the basis of such a structure. Therefore, in the machine tool industry, so-called folded structures are used. Folded is the structure of a multi-speed stepped drive, consisting of two, less often three kinematic chains, each of which is a conventional multiplier structure. One of these circuits (short) is for higher drive speeds, the others (longer) for low speeds. As an example, in fig. 2.18 shows a diagram of a gear box for 12 spindle speeds (output shaft), which has a folded
