Machine parts: the concept and their characteristics. Basic concepts of machine parts Requirements for technical objects

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PROFESSIONAL SCHOOL №22

Discipline abstract

"Technical Mechanics"

on the topic: "Machine parts: the concept and their characteristics"

Completed by: Rozhko Svetlana

Saratov-2010

Basic definitions and concepts

A part is a product obtained from a material of a homogeneous grade without assembly operations.

Assembly unit - a product obtained using assembly operations.

The mechanism is a complex of parts and assembly units, created in order to perform a certain type of movement of the driven link with a predetermined movement of the leading link.

A machine is a set of mechanisms created to convert one type of energy into another, or to perform useful work, in order to facilitate human labor.

mechanical transmissions.

Gears are mechanisms designed to transmit movement.

1. According to the method of transmission of movement:

a) gearing (gear, worm, chain);

b) friction (friction);

2. According to the method of contact:

a) direct touch (tooth, worm, friction);

b) with the help of a transmission link.

Gear - consists of a gear and a gear and is designed to transmit rotation.

Advantages: reliability and durability, compactness.

Disadvantages: noise, high demands on the accuracy of manufacturing and installation, depressions - stress concentrators.

Classification.

1. Cylindrical (axes 11), conical (axes crossed), helical (axes cross).

2. According to the tooth profile:

a) involute;

b) cycloidal;

c) with the Novikov link.

3. According to the method of engagement:

a) internal;

b) external.

4. According to the location of the teeth:

a) straight-toothed;

b) helical;

c) mevron.

5. By design:

a) open;

b) closed.

They are used in machines, cars, watches.

The worm gear consists of a worm and a worm wheel, the axes of which are crossed. Serves for transmission by a rotation wheel.

Advantages: reliability and durability, the ability to create self-braking transmission, compactness, smoothness and noiselessness of operation, the ability to create large accessory numbers.

Disadvantages: low-speed, high transmission heat, the use of expensive anti-friction materials.

Classification.

1. By the type of worm:

a) cylindrical;

b) globoidal.

2. According to the profile of the worm tooth:

a) involute;

b) covolute;

c) Archimedes.

3. By the number of visits:

a) one-way;

b) Multi-pass.

4. In relation to the worm to the worm wheel:

a) with the bottom;

b) with the top;

c) with the side.

They are used in machine tools, lifting devices.

The belt drive consists of pulleys and a belt. Serves for transmission of rotation at a distance of up to 15 meters.

Advantages: smooth and quiet operation, simple design, the possibility of smooth adjustment of the gear ratio.

Disadvantages: belt slippage, limited belt life, need for tensioners, cannot be used in explosive environments.

It is used in conveyors, machine tool drives, in the textile industry, in sewing machines.

Instrumentation.

Belts - leather, rubber.

Pulleys - cast iron, aluminum, steel.

A chain drive consists of a chain and gears. Serves to transmit torque over a distance of up to 8 meters.

Advantages: reliability and durability, no slippage, less pressure on shafts and bearings.

Disadvantages: noise, high wear, sagging, lubrication difficult.

Material - steel.

Classification.

1. By appointment:

a) trucks

b) tension,

c) traction.

2. By design:

a) roller

b) sleeve,

c) serrated.

Are applied in bicycles, drives of machine tools and cars, conveyors.

Shafts and axles.

A shaft is a part designed to support other parts in order to transmit torque.

During operation, the shaft experiences bending and torsion.

An axle is a part designed only to support other parts mounted on it; during operation, the axle experiences only bending.

Shaft classification.

1. By appointment:

a) straight

b) cranked

c) flexible.

2. By shape:

a) smooth

b) stepped.

3. By section:

a) solid

Shaft elements. Shafts are often made of steel-20, steel 20x.

Shaft calculation: kr=|Mmax|\W<=[ кр] и=|Mmax|W<=[ и] Оси только на изгиб. W - момент сопротивления сечения [м3].

Couplings are devices designed to connect shafts in order to transmit torque and ensure the unit stops without turning off the engine, as well as protecting the operation of the mechanism during overloads.

Classification.

1. Non-releaseable:

a) tough

b) flexible.

Advantages: simplicity of designs, low cost, reliability.

Disadvantages: can connect shafts of the same diameter.

Material: steel-45, gray cast iron.

2. Managed:

a) toothed

b) friction.

Advantages: simplicity of design, different shafts, it is possible to turn off the mechanism in case of overload.

3. Self-acting:

a) safety

b) overtaking,

c) centrifugal.

Advantages: reliability in operation, transmit rotation when a certain speed is reached due to inertia forces.

Disadvantages: design complexity, high wear of the cams.

Made from gray cast iron.

4. Combined.

Couplings are selected according to the GOST table.

Permanent connections

One-piece connections are such connections of parts that cannot be disassembled without destroying the parts included in this connection.

These include: riveted, welded, soldered, adhesive joints.

Rivet connections.

Rivet connections:

1. By appointment:

a) durable

b) dense.

2. According to the location of the rivets:

a) parallel

b) in a checkerboard pattern.

3. By the number of visits:

a) single row

b) multi-row.

Advantages: withstand shock loads well, reliability and strength, provide visual contact for the quality of the seam.

Disadvantages: holes are stress concentrators and reduce the tensile strength, make the structure heavier, noisy production.

Welding connections

Welding is the process of joining parts by heating them to a melting temperature, or by plastic deformation in order to create an integral connection.

a) gas

b) electrode,

c) contact

d) laser,

d) cold

e) explosion welding.

Welded connections:

a) corner

b) butt,

c) overlap

d) tee,

e) point.

Advantages: provides a reliable hermetic connection, the ability to connect any materials of any thickness, noiseless process.

Disadvantages: change in physical and chemical properties in the weld area, warping of the part, difficulty in checking the quality of the weld, highly qualified specialists are required, they do not withstand repeated variable loads, the weld is a stress concentrator.

Adhesive connections.

Advantages: does not make the structure heavier, low cost, does not require specialists, the ability to connect any parts of any thickness, the noiselessness of the process.

Disadvantages: "aging" of the adhesive, low heat resistance, the need for pre-cleaning the surface.

All permanent connections are calculated for shear.

Тср=Q\A<=[Тср].

Threads (classification)

1. By appointment:

a) fasteners

b) running,

c) sealing.

2. By the corner at the top:

a) metric (60),

b) inch (55).

3. By profile:

a) triangular

b) trapezoidal,

c) stubborn

d) round

e) rectangular.

4. By the number of visits:

a) one way

b) multi-entry.

5. In the direction of the helix:

a) left, the detail of the mechanism is one-piece connection

b) right.

6. By surface:

a) external

b) internal,

c) cylindrical,

d) conical.

Threaded surfaces can be made:

a) manually

b) on machines,

c) on automatic rolling machines.

Advantages: simplicity of design, reliability and strength, standardization and interchangeability, low cost, does not require specialists, the ability to connect any materials.

Disadvantages: thread - stress concentrator, wear of contact surfaces. Material - steel, non-ferrous alloys, plastic.

Keyed connections.

Keys are: prismatic, segmented, wedge.

Advantages: simplicity of design, reliability in operation, long dowels - guides.

Disadvantages: keyway - stress concentrator.

Slotted connections.

There are: straight-sided, triangular, involute.

Advantages: reliability in operation, uniform distribution over the entire section of the shaft.

Disadvantages: difficult to manufacture.

R=sqr(x^2+y^2) - for fixed supports,

x - cos of the given angle

by y - sin of this angle or cos (90-angle)

if the longest side of the triangle is 2/3

if small then - 1/3

d'Alembert's principle: F+R+Pu=0

Literature

Textbooks and study guides

1. Yablonsky A.A., Nikiforova V.M. Course of theoretical mechanics. Parts 1, 2 Publishing house "Higher school", M.: 1996

2. Voronkov I.M. Course of theoretical mechanics. State. publishing house of technical and theoretical literature. M: 2006

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As a result of studying this section, the student must:

know

• methodological, normative and guidance materials related to the work performed;
• fundamentals of designing technical objects;
• problems of creating machines of various types, drives, operating principles, technical characteristics;
• design features of the developed and used technical means;
• sources of scientific and technical information (including Internet sites) on the design of parts, assemblies, drives and general-purpose machines;

be able to

• apply the theoretical foundations for performing work in the field of scientific and technical design activities;
• apply the methods of conducting a comprehensive technical and economic analysis in mechanical engineering for sound decision-making;
• independently understand the normative methods of calculation and adopt them to solve the problem;
• choose structural materials for the manufacture of general-purpose parts, depending on the working conditions;
• search and analyze scientific and technical information;

own

• skills to rationalize professional activities in order to ensure safety and protect the environment;
• discussion skills on professional topics;
• terminology in the field of designing machine parts and general-purpose products;
• skills to search for information about the properties of structural materials;
• information on the technical parameters of the equipment for use in the design;
• modeling skills, carrying out structural work and designing transmission mechanisms, taking into account compliance with the terms of reference;
• the skills of applying the information received in the design of machine parts and general-purpose products.

The study of the elemental base of mechanical engineering (machine parts) - to know the functional purpose, image (graphical representation), methods of design and verification calculations of the main elements and parts of machines.

Studying the structure and methods of the design process - to have an idea about the invariant concepts of the system design process, to know the stages and methods of design. Including - iteration, optimization. Obtaining practical skills in the design of technical systems (TS) from the field of mechanical engineering, independent work (with the help of a teacher - consultant) to create a project of a mechanical device.

Mechanical engineering is the basis of scientific and technological progress, the main production and technological processes are carried out by machines or automatic lines. In this regard, mechanical engineering plays a leading role among other industries.

The use of machine parts has been known since ancient times. Simple machine parts - metal pins, primitive gears, screws, cranks were known before Archimedes; rope and belt transmissions, cargo propellers, articulated couplings were used.

Leonardo da Vinci, who is considered the first researcher in the field of machine parts, created gears with intersecting axes, articulated chains, and rolling bearings. The development of the theory and calculation of machine parts are associated with many names of Russian scientists - II. L. Chebyshev, N. P. Petrov, N. E. Zhukovsky, S. A. Chaplygin, V. L. Kirpichev (author of the first textbook (1881) on machine parts); Later, the course “Machine Parts” was developed in the works of P. K. Khudyakov, A. I. Sidorov, M. A. Savsrin, D. N. Reshetov and others.

As an independent scientific discipline, the course "Details of Machines" took shape by the 1780s, at which time it was separated from the general course of building machines. Of the foreign courses "Machine Parts", the works of K. Bach, F. Retscher were most widely used. The discipline "Machine parts" is directly based on the courses "Strength of materials", "Theory of mechanisms and machines", "Engineering graphics".

Basic concepts and definitions. "Machine Parts" is the first of the calculation and design courses in which they study design basics machines and mechanisms. Any machine (mechanism) consists of parts.

Detail - a part of a machine that is made without assembly operations. Parts can be simple (nut, key, etc.) or complex (crankshaft, gearbox housing, machine bed, etc.). Details (partially or completely) are combined into nodes.

Knot represents a complete assembly unit, consisting of a number of parts that have a common functional purpose (rolling bearing, coupling, gearbox, etc.). Complex nodes may include several simple nodes (sub-nodes); for example, a gearbox includes bearings, shafts with gears mounted on them, etc.

Among the wide variety of machine parts and assemblies, there are those that are used in almost all machines (bolts, shafts, couplings, mechanical transmissions, etc.). These parts (assemblies) are called general purpose parts and study in the course "Details of machines". All other parts (pistons, turbine blades, propellers, etc.) are special purpose parts and study in special courses.

General-purpose parts are used in mechanical engineering in very large quantities; about a billion gears are produced annually. Therefore, any improvement in the methods of calculation and design of these parts, which makes it possible to reduce material costs, lower production costs, and increase durability, brings a great economic effect.

Car- a device that performs mechanical movements in order to convert energy, materials and information, for example, an internal combustion engine, a rolling mill, a crane. A computer, strictly speaking, cannot be called a machine, since it does not have parts that perform mechanical movements.

performance(GOST 27.002-89) units and parts of machines - a state in which the ability to perform specified functions is maintained within the parameters established by regulatory and technical documentation

Reliability(GOST 27.002-89) - the property of an object (machines, mechanisms and parts) to perform the specified functions, maintaining the values ​​of the established indicators over time within the required limits, corresponding to the specified modes and conditions of use, maintenance, repair, storage and transportation.

Reliability - the property of an object to continuously maintain operability for some time or some operating time.

Refusal - This is an event consisting in a violation of the health of an object.

MTBF - operating time from one failure to another.

Failure rate - number of failures per unit of time.

Durability - the property of a machine (mechanism, part) to remain operational until the limit state occurs with the established system of maintenance and repairs. The limiting state is understood as such a state of the object when further operation becomes economically unfeasible or technically impossible (for example, repairs cost more than a new machine, part, or may cause an emergency breakdown).

maintainability- the property of the object, which consists in adaptability to the prevention and detection of the causes of failures and damages and the elimination of their consequences in the process of repair and maintenance.

Persistence - the property of an object to remain functional during and after storage or transportation.

Basic requirements for the design of machine parts. The design excellence of a part is judged by its reliability and economy. Reliability is understood the property of a product to maintain its performance over time. Profitability is determined by the cost of the material, the cost of production and operation.

The main criteria for performance and calculation of machine parts are strength, rigidity, wear resistance, corrosion resistance, heat resistance, vibration resistance. The value of one or another criterion for a given part depends on its functional purpose and operating conditions. For example, for mounting screws, the main criterion is strength, and for lead screws, wear resistance. When designing parts, their performance is mainly ensured by the choice of the appropriate material, a rational structural form and the calculation of dimensions according to the main criteria.

Features of the calculation of machine parts. In order to compile a mathematical description of the calculation object and, if possible, simply solve the problem, real structures in engineering calculations are replaced by idealized models or calculation schemes. For example, in strength calculations, essentially non-continuous and inhomogeneous material of parts is considered as continuous and homogeneous, supports, loads and the shape of parts are idealized. Wherein calculation becomes approximate. In approximate calculations, the correct choice of the calculation model, the ability to evaluate the main and discard secondary factors are of great importance.

Inaccuracies in strength calculations are compensated mainly due to safety margins. Wherein the choice of safety factors becomes a very important step in the calculation. An underestimated value of the margin of safety leads to the destruction of the part, and an overestimated value leads to an unjustified increase in the mass of the product and waste of material. The factors affecting the margin of safety are numerous and varied: the degree of responsibility of the part, the homogeneity of the material and the reliability of its tests, the accuracy of the calculation formulas and the determination of the design loads, the influence of the quality of technology, operating conditions, etc.

In engineering practice, there are two types of calculation: design and verification. Design calculation - preliminary, simplified calculation performed in the process of developing the design of a part (assembly) in order to determine its dimensions and material. Check calculation - a refined calculation of a known structure, performed in order to check its strength or determine the load standards.

Estimated loads. When calculating machine parts, a distinction is made between the calculated and rated load. Estimated load, e.g. torque T, is defined as the product of the nominal torque T p on the dynamic coefficient of the load mode K. T \u003d KT p.

Rated moment T n corresponds to the passport (design) power of the machine. Coefficient TO takes into account additional dynamic loads associated mainly with uneven movement, starting and braking. The value of this factor depends on the type of motor, drive and driven machine. If the mode of operation of the machine, its elastic characteristics and mass are known, then the value TO can be determined by calculation. In other cases, the value TO choose based on recommendations. Such recommendations are based on experimental studies and operating experience of various machines.

Material selection for machine parts is a critical design stage. Correctly chosen material largely determines the quality of the part and the machine as a whole.

When choosing a material, the following factors are mainly taken into account: compliance of the material properties with the main performance criterion (strength, wear resistance, etc.); requirements for the mass and dimensions of the part and the machine as a whole; other requirements related to the purpose of the part and the conditions of its operation (anti-corrosion resistance, friction properties, electrical insulating properties, etc.); compliance of the technological properties of the material with the structural form and the intended method of processing the part (formability, weldability, casting properties, machinability, etc.); cost and scarcity of material.

AND FUNDAMENTALS OF DESIGN AND CONSTRUCTION

Basic concepts and definitions

Detail- a part of a machine made of a homogeneous material without the use of assembly operations. Details can be simple (nut, key, etc.) and complex (crankshaft, gearbox housing, machine bed, etc.).

Details are general and special purpose.

Assembly unit - a product obtained from parts using assembly operations.

Knot- a complete assembly unit, consisting of parts that have a common functional purpose (bearing, support assembly).

Mechanism- a kinematic chain for the transmission and transformation of movement (for example, a crank mechanism). The mechanism consists of parts and assemblies.

Car- a mechanism or a set of mechanisms designed to perform the required useful work (conversion of energy, materials or information in order to facilitate labor). Any machine consists of a motor, transmission and actuator. Operating the machine requires the presence of an operator.

Machine- a machine that works according to a given program without an operator.

Robot- a machine that has a control system that allows it to independently make performance decisions in a given range.

1.1.1 Classification of machine parts

Machine parts study details, knots and mechanisms general purpose(bolts, screws, shafts, axles, bearings, couplings, mechanical transmissions, etc.), i.e., which are used in all mechanisms.

Parts and components of machines are classified into typical groups according to the nature of their use:

· Transmissions - transmit the movement from the source to the actuators;

Shafts and axles - carry rotating gear parts;

Supports - serve to install shafts and axles;

Couplings - connect shafts together and transmit torque;

Connecting parts (connections) - connect parts to each other.

Elastic elements - soften vibration, jerks and shocks, accumulate energy, provide constant compression of parts;

· Body parts - organize inside themselves the space for placing other parts and assemblies, provide their protection.

1.1.2 Design and construction

The process of developing machines is called designing. It consists in creating a prototype of an object representing in general terms its main parameters.

Under designing understand the whole process from the idea to the production of the machine. The purpose and end result of design is the creation working documentation, according to which it is possible to manufacture, operate, control and repair the product without the participation of the developer.

Machine design is a creative process. The main task of design is to create products that are most profitable from an economic point of view. In other words, the creation of products that provide the performance of certain functions (useful work with the required productivity), at the lowest cost for their manufacture, operation, maintenance and disposal of these products at the end of their service life.

When starting to design, the designer must clearly identify three positions:

1. Initial data - any objects and information related to the case (“what do we have?”);

2. Goal - expected end results, values, documents, objects (“what do we want to get?”);

3. Means to achieve the goal - design methods, calculation formulas, tools, sources of information, design skills, experience (“what and how to do?”).

A thorough analysis of this information will allow the designer to correctly build the logical chain “Task - Goal - Means” and complete the project as efficiently as possible.

Main design features:

· multivariate solution of any problem. The same design problem can usually be solved in many ways. A comparison of competing options is made and one of them is selected - the optimal one based on certain criteria (mass, price, manufacturability);

coordination of decisions made with the general and specific requirements for the design, as well as with the requirements of GOSTs (regulating not only the design, dimensions and materials used, but also terms, definitions, symbols, measurement system, calculation methods, etc.) ;

· Coordination of decisions made with the existing level of technology for manufacturing parts.

The requirements for the design can be both those imposed by the customer and the requirements formulated on the basis of an analysis of the conditions of manufacture, operation, maintenance, disposal, as well as the requirements of regulatory documents.

1.1.3 Basic requirements for the design of machine parts.

When designing a machine or mechanism from a designer, except functionality, it is required to provide reliability and economy.

Functionality - ability to fulfill its purpose. Functionality criteria: Power, performance, efficiency, dimensions, energy consumption, material consumption, accuracy, smooth running, etc.

Reliability- the property of the product to maintain its performance over time, i.e. the ability to perform its functions, maintaining the specified indicators for a specified period of time. Reliability can be strength and tribological (wear).

Economy determined by the cost of the material, the cost of production and operation.

Main reliability criteria: strength, rigidity, wear resistance, corrosion resistance, heat resistance, vibration resistance.

The value of one or another criterion for a given part depends on its functional purpose and operating conditions. For example, for fastening screws, the main criterion is strength, for lead screws - wear resistance. When designing parts, their performance is ensured mainly by the choice of the appropriate material, a rational structural form and the calculation of dimensions according to the main criteria.

Strength is usually the main criterion for the performance of most parts. The part must not collapse or receive permanent deformation under the influence of the working load. It should be remembered that the destruction of machine parts can lead not only to downtime, but also to accidents.

Strength condition: Stresses in the material of the part must not exceed the allowable:

In some cases, it is more convenient to check the strength by determining the safety factor:

Rigidity characterized by a change in the size and shape of the part under load. The calculation for stiffness provides for limiting the elastic displacements of parts within the limits permissible for specific operating conditions. For example, insufficient rigidity of shafts in gearboxes leads to their deflection, which worsens the quality of gear engagement and the operating conditions of bearing assemblies.

Rigidity condition: The movement of the points of the part (deformation) under the influence of working loads must not exceed the permitted value, which is determined by the conditions of normal operation. For example, the beam deflection arrow should not exceed the allowable value:

The twist angle of the shaft must not exceed the permissible value:

Wear resistance. Wear is the process of gradual change in the size and shape of parts as a result of friction. At the same time, the gaps in bearings, guides, in gears, in the cylinders of piston machines increase, and this reduces the quality characteristics of the machines - power, efficiency, reliability, accuracy. Parts that are worn out more than the norm are rejected and replaced during repair. With the current state of technology, 85-90% of machines fail as a result of wear and tear and only 10-15% for other reasons.

Wear condition: The pressure on the rubbing surfaces must not exceed the allowable value:

Corrosion resistance. Corrosion is the process of destruction of the surface layers of a metal as a result of oxidation. Corrosion is the cause of premature failure of many structures. Due to corrosion, up to 10% of the volume of smelted metal is lost annually. Anti-corrosion coatings are used to protect against corrosion nickel plating, zinc plating, bluing, cadmium plating, painting) or manufacture parts from special corrosion-resistant materials ( stainless steel, non-ferrous metals, plastics).

Heat resistance. Heating of machine parts can cause: a decrease in the strength of the material and the appearance of creep, a decrease in the protective ability of oil films, and therefore an increase in wear, a change in gaps in mating parts, which can lead to jamming or seizing. To avoid harmful consequences, thermal calculations are carried out and, if necessary, appropriate design changes are made (for example, artificial cooling).

Vibration resistance. Vibrations cause additional alternating stresses and, as a rule, lead to fatigue failure of parts. In some cases, vibrations reduce the quality of machines, for example, the accuracy of machining machine tools and the quality of the machined surface. In addition, there is additional noise. The most dangerous resonant vibrations.

In addition to the reliability criteria during design, the following requirements are imposed on the details:

Economy. The design of the machine, the shape and material of its parts must be such as to ensure the minimum cost of its manufacture, operation, maintenance, disposal.

Manufacturability. The shape and material of the parts must be such that the manufacture of the part requires minimal labor, time, and money.

Safety. The design of parts must ensure the safety of personnel during the manufacture, operation and maintenance of the machine.

Machine parts (from French détail - detail)

elements of machines, each of which is a single whole and cannot be disassembled without destruction into simpler, component parts of machines. Mechanical engineering is also a scientific discipline that deals with the theory, calculation, and design of machines.

The number of parts in complex machines reaches tens of thousands. The execution of machines from parts is primarily due to the need for relative movements of the parts. However, fixed and mutually fixed parts of machines (links) are also made from separate interconnected parts. This makes it possible to use optimal materials, restore the performance of worn-out machines, replacing only simple and cheap parts, facilitates their manufacture, and provides the possibility and convenience of assembly.

D. m. as a scientific discipline considers the following main functional groups.

Body parts ( rice. one ), bearing mechanisms and other machine components: plates supporting machines, consisting of separate units; beds carrying the main components of machines; frames of transport vehicles; cases of rotary machines (turbines, pumps, electric motors); cylinders and cylinder blocks; cases of reducers, gearboxes; tables, sleds, calipers, consoles, brackets, etc.

Gears - mechanisms that transmit mechanical energy over a distance, as a rule, with the transformation of speeds and moments, sometimes with the transformation of the types and laws of motion. Gears of rotational motion, in turn, are divided according to the principle of operation into gears that operate without slipping - gears (See. Gear) (rice. 2 , a, b), worm gears (See. Worm-gear) (rice. 2 , c) both chain and friction transmissions - belt transmissions (See. Belting) and friction with rigid links. According to the presence of an intermediate flexible link, which provides the possibility of significant distances between the shafts, transmissions by flexible connection (belt and chain) and transmissions by direct contact (gear, worm, friction, etc.) are distinguished. According to the mutual arrangement of the shafts - gears with parallel shaft axes (cylindrical gear, chain, belt), with intersecting axes (bevel gear), with intersecting axes (worm, hypoid). According to the main kinematic characteristic - the gear ratio - there are gears with a constant gear ratio (reducing, overdrive) and with a variable gear ratio - stepped (gearboxes (See. Transmission)) and stepless ( Variable speed drive s). Gears that convert rotational motion into continuous translational motion or vice versa are divided into gears screw - nut (sliding and rolling), rack - rack gear, rack - worm, long half nut - worm.

Shafts and axles ( rice. 3 ) serve to support rotating gears. There are gear shafts that carry gear parts - gears, pulleys, sprockets, and main and special shafts, which, in addition to gear parts, carry the working parts of engines or machine tools. Axles, rotating and fixed, are widely used in transport vehicles to support, for example, non-driving wheels. Rotating shafts or axles are supported by Bearing and ( rice. 4 ), and progressively moving parts (tables, calipers, etc.) move along the guides (See. Guides). Sliding bearings can work with hydrodynamic, aerodynamic, aerostatic friction or mixed friction. Ball rolling bearings are used for small and medium loads, roller bearings for significant loads, needle bearings for cramped dimensions. Most often, rolling bearings are used in machines; they are manufactured in a wide range of outer diameters from one mm up to several m and weight from shares G up to several T.

Couplings are used to connect the shafts. (Cm. Coupling) This function can be combined with manufacturing and assembly error compensation, dynamic damping, control, etc.

Elastic elements are intended for vibration isolation and damping of impact energy, for performing engine functions (for example, clock springs), for creating gaps and interference in mechanisms. There are coil springs, coil springs, leaf springs, rubber springs, etc.

Connecting parts are a separate functional group. Distinguish: one-piece connections (See. Permanent connection), which do not allow separation without destruction of parts, connecting elements or connecting layer - welded ( rice. 5 , a), soldered, riveted ( rice. 5 , b), adhesive ( rice. 5 , c), rolled; connectors (See Detachable connection), allowing separation and carried out by the mutual direction of parts and friction forces (most detachable connections) or only by mutual direction (for example, prismatic connections Key mi). According to the shape of the connecting surfaces, connections are distinguished by planes (most) and by surfaces of revolution - cylindrical or conical (shaft - hub). Welded joints have received the widest application in mechanical engineering. Of the detachable connections, threaded connections made by screws, bolts, studs, nuts ( rice. 5 , G).

The prototypes of many D. m. have been known since ancient times, the earliest of them are the lever and the wedge. More than 25 thousand years ago, man began to use a spring in bows for throwing arrows. The first transmission with a flexible connection was used in a bow drive for making fire. Rollers based on rolling friction have been known for over 4,000 years. The first parts approaching modern conditions in terms of working conditions include the wheel, axle and bearing in wagons. In antiquity and in the construction of temples and pyramids, gate ami and Block ami. Plato and Aristotle (fourth century BC) mention in their writings metal trunnions, gear wheels, cranks, rollers, and chain hoists. Archimedes used a screw in a water-lifting machine, apparently known before. The notes of Leonardo da Vinci describe helical gears, gears with rotating pins, rolling bearings and articulated chains. In the literature of the Renaissance, there is information about belt and cable drives, cargo propellers, couplings. D.'s designs were improved, new modifications appeared. At the end of the 18th - beginning of the 19th centuries. riveted joints in boilers and railway structures were widely used. bridges, etc. In the 20th century riveted joints were gradually replaced by welded ones. In 1841, in England, J. Whitworth developed a system of fastening threads, which was the first work on standardization in mechanical engineering. The use of flexible transmissions (belt and cable) was caused by the distribution of energy from the steam engine through the floors of the factory, with the drive of transmissions, etc. With the development of an individual electric drive, belt and cable drives began to be used to transfer energy from electric motors and prime movers in drives of light and medium-sized machines. In the 20s. 20th century V-belt transmissions became widespread. A further development of transmissions with flexible connection are multi-V-belts and toothed belts. Gears were continuously improved: the pin gear and the gear of a straight-sided profile with fillets were replaced by cycloidal, and then involute. An essential step was the appearance of the circular screw gearing by M. L. Novikov. From the 70s of the 19th century. rolling bearings began to be widely used. Hydrostatic bearings and guides, as well as air lubricated bearings, are widely used.

Materials of mechanical materials to a large extent determine the quality of cars and make up a significant part of their cost (for example, in cars up to 65-70%). The main materials for D. m. are steel, cast iron and non-ferrous alloys. Plastic masses are used as electrically insulating, antifriction and frictional, corrosion-resistant, heat-insulating, high-strength (fiberglass), and also as having good technological properties. Rubbers are used as materials with high elasticity and wear resistance. Responsible D. m. (gear wheels, heavily stressed shafts, etc.) are made of hardened or improved steel. For D. m., the dimensions of which are determined by the conditions of rigidity, materials are used that allow the manufacture of parts of perfect shapes, for example, non-hardened steel and cast iron. D. m., working at high temperatures, are made of heat-resistant or heat-resistant alloys. On the surface of D. m., the highest nominal stresses from bending and torsion, local and contact stresses, and wear occur, therefore D. m.

D. m. must, with a given probability, be operable for a certain service life at the minimum necessary cost of their manufacture and operation. To do this, they must satisfy the performance criteria: strength, rigidity, wear resistance, heat resistance, etc. Calculations for the strength of D. m. operating mode variability. The most reasonable can be considered the calculation for a given probability and failure-free operation. Calculation of D. m. for stiffness is usually carried out on the basis of the condition of satisfactory operation of the mating parts (the absence of elevated edge pressures) and the condition of the machine's performance, for example, obtaining accurate products on a machine tool. To ensure wear resistance, they seek to create conditions for fluid friction, in which the thickness of the oil layer must exceed the sum of the heights of microroughnesses and other deviations from the correct geometric shape of the surfaces. If it is impossible to create liquid friction, the pressure and speeds are limited to those established by practice or wear is calculated based on similarity according to operational data for units or machines of the same purpose. Calculations of dynamic meters are developing in the following areas: computational optimization of structures, development of computer calculations, introduction of the time factor into calculations, introduction of probabilistic methods, standardization of calculations, and use of tabular calculations for centralized manufacturing of diesel meters. The foundations of the theory of calculating mechanical dynamics were laid by research in the theory of gearing (L. Euler, Kh. I. Gokhman), the theory of friction of threads on drums (L. Euler, and others), and the hydrodynamic theory of lubrication (N. P. Petrov, O. Reynolds, N. E. Zhukovsky and others). Research in the field of D. m. in the USSR is carried out at the Institute of Mechanical Engineering, the Research Institute of Mechanical Engineering Technology, Moscow State Technical University. Bauman;

The development of the design of dynamic materials takes place in the following areas: increasing the parameters and developing high-quality dynamic materials, using the optimal capabilities of mechanical with solid links, hydraulic, electrical, electronic, and other devices, designing dynamic materials for a period up to obsolescence machines, increasing reliability, optimizing forms in connection with new technological possibilities, ensuring perfect friction (liquid, gas, rolling), sealing interfaces of D. m., Making D. m., Working in an abrasive environment, from materials whose hardness is higher than hardness abrasive, standardization and organization of centralized production.

Lit.: Machine parts. Atlas of structures, ed. D. N. Reshetova, 3rd ed., M., 1968; Machine parts. Handbook, vol. 1-3, M., 1968-69.

D. N. Reshetov.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

See what "Machine parts" is in other dictionaries:

A set of structural elements and their combinations, which is the basis of the design of the machine. A machine part is a part of the mechanism that is manufactured without assembly operations. Machine parts are also scientific and ... Wikipedia

machine parts- — Topics oil and gas industry EN machine components … Technical Translator's Handbook

1) otd. component parts and their simplest connections in machines, instruments, devices, fixtures, etc.: bolts, rivets, shafts, gears, keys, etc. 2) Nauch. a discipline that includes theory, calculation and design ... Big encyclopedic polytechnic dictionary

This term has other meanings, see Key. Mounting the key in the groove of the shaft Key (from Polish szponka, through it Spon, Span sliver, wedge, lining) an oblong-shaped machine and mechanism part inserted into the groove ... ... Wikipedia