Shapes of shafts and axes. Shafts and axles. General information

Shafts and axles serve to support rotating parts (gears, couplings, pulleys, sprockets, rotors, etc.) and transmit loads from these parts through supports to the housing. Axes can be both rotating and stationary; they perceive the actions of bending moments and longitudinal forces. Shafts, unlike axles, can only be rotating. They are subject to longitudinal forces, bending and torsional moments.

The structural shape of shafts and axles depends on many factors - the purpose of the mechanism, the purpose and shape of the parts mating to the shaft or axle, the nature of the loads, manufacturing and assembly technology.

There are shafts straight, cranked And flexible. This tutorial covers only the most common straight shafts. Axes are only available with a straight geometry axis.

Shafts and axles can be solid And hollow. When using hollow shafts and axles, the weight of the structure can be significantly reduced. For example, a hollow shaft with a ratio of hole diameter to outer shaft diameter of 0.75, with almost equal strength as a solid shaft, has a mass that is 50% less. In this regard, in aircraft mechanisms, shafts and axles large diameter(more than 10...12 mm) are usually made hollow. Input and output shafts are designed with blind holes to seal the internal cavity of the mechanism or with holes closed with plugs.

Shafts and axles vary in shape: smooth And stepped. By choosing a stepped shape that is more difficult to manufacture, it is possible to ensure uniform stress distribution along the length of the shaft and the necessary strength and rigidity under the action of internal force factors. In addition, with a stepped form, Better conditions for assembling parts with a shaft and for fixing them relative to the shaft in the axial and radial directions. The axles, due to their greater simplicity, are often made smooth, and the shafts, as a rule, are stepped, with each part corresponding to its own step on the shaft, machined with the required accuracy and roughness.

Shafts are made in the form individual part(Fig. 13.1, a) or integrally with cylindrical gears (Fig. 13.1, b, d) y bevel gear (Fig. 13.1, c).

In aircraft mechanisms, shafts are often made integral with gear parts, which, due to the absence of connecting elements, reduces the total weight of the structure and increases its reliability. However, a monolithic shaft design is not always advisable, since it is not always necessary to make the shaft and the part from the same material. In addition, this option eliminates the possibility of replacing a shaft or part during operation. When manufacturing a monolithic structure from a large-diameter workpiece, one should take into account the fact that the strength properties of the material decrease with increasing diameter of the workpiece. Monolithic construction It is economically advantageous if the diameter of the part is not much larger than the diameter of its own shaft, as well as in conditions of single production or obtaining a workpiece by forging (for example, forming part elements located at the end of the shaft using an upsetting operation).

Shafts can be made with teeth (Fig. 13.1,6), with keyways (Fig. 13.1, a), with annular grooves for support rings (Fig. 13.1, a), with threaded sections (Fig. 13.1, 6, V) and grooves for locking threaded parts (Fig. 13.1, V). The shafts can have axial ones (Fig. 13.1, b) and radial (Fig. 13.1, V) holes, as well as grooves for exit

grinding wheel (Fig. 13.1, a, c), areas where the cutter exits when cutting teeth (Fig. 13.1, b), as well as grooves for the tool to exit when cutting threads (Fig. 13.1, c).

Axes can be fixed (Fig. 13.2, a) and rotating (Fig. 13.2, boo smooth (Fig. 13.2, A) and stepped (Fig. 13.2, b). Axles, like shafts, can have teeth (splines), grooves, grooves, grooves, threads and holes. Smooth axles are standardized. Fixing these axes in the axial direction is most often

carried out with a cotter pin (Fig. 13.3, a). For axes (mainly stationary), fixation with a cylindrical or conical pin is used (Fig. 13.3, b), set screw (Fig. 13.3, V) or a saddle holder with a bolt (Fig. 13.3, G). Fixed axles are installed using a transitional fit (for example, K7/I6) or an interference fit (for example, R7/h6).

Moving axes and shafts in both radial and axial directions are fixed in bearings, which in turn are installed in the housing. Precise fixation of shafts and axes in the radial direction is carried out by fitting them into bearings and fitting bearings into the housing. In the axial direction, shafts and axles with parts mounted on them are connected to bearings in one of the ways shown in Fig. 13.4. The most widely used method is simple and cheap fixation with spring rings (Fig. 13.4, A): eccentric 1 or concentric 2 . The presence of a gap 5 between the ring and the bearing leads to inaccurate installation of parts and to sliding of the surfaces of parts and the shaft, i.e. to their wear. Using an intermediate ring 3 (Fig. 13.4, b) with adjusting its thickness by grinding the end or a set of shims 4 from foil (Fig. 13.4, V) allows you to reduce the size of the gap 5 to a minimum. The shims are not placed near the spring ring to prevent the shims from getting into the ring groove. When fixing at the end of the shaft, it is convenient to use a standard end washer 5 (Fig. 13.4, d)> secured with a screw 6 and secured against turning with pin 7. The screw is secured against unscrewing with a washer 8. For significant axial loads, a washer is used, secured with two screws (Fig. 13.4, d).

Before you understand how a shaft and an axle differ from each other, you should have a clear idea of ​​what these parts actually are, what and where they are used and what functions they perform. So, as you know, shafts and axles are designed to hold rotating parts on them.

Definition

Shaft- this is a part of a mechanism that has the shape of a rod and serves to transmit torque to other parts of this mechanism, thereby creating a general rotational movement of all parts located on it (on the shaft): pulleys, eccentrics, wheels, etc.

Axis- this is a part of a mechanism designed to connect and fasten together the parts of this mechanism. The axle only supports transverse loads (bending stress). Axes can be fixed or rotating.

Comparison

The main difference between an axle and a shaft is that the axle does not transmit torque to other parts. It is subject to only lateral loads and does not experience torsional forces.

The shaft, unlike the axle, transmits useful torque to the parts that are attached to it. In addition, the axes can be either rotating or stationary. The shaft always rotates. Most shafts can be divided into geometric shape axles into straight, crank (eccentric) and flexible. There are also crankshafts or indirect shafts, which are used to convert reciprocating movements into rotational ones. Axes, in their geometric shape, are only straight.

Conclusions website

1. The axis carries the rotating parts of the mechanism without transmitting any torque to them. The shaft transmits useful torque to other parts of the mechanism, the so-called rotating force.
2. The axis can be either rotating or stationary. The shaft can only be rotating.
3. The axis has only a straight shape. The shape of the shaft can be straight, indirect (cranked), eccentric and flexible.

Shafts and axles

PLAN LECTIONS

General information.

Materials and processing of shafts and axles.

Criteria for performance and calculation of shafts and axes.

Calculations of shafts and axes.

General information

Shafts- these are parts that serve to transmit torque along their axis and hold other parts located on them (wheels, pulleys, sprockets and other rotating machine parts) and perceive the acting forces.

Axles- these are parts that only hold the parts installed on them and perceive the forces acting on these parts (the axle does not transmit useful torque).

Classification of shafts and axles

C lassification V alov groups the latter according to a number of characteristics: by purpose, by form cross section, by the shape of the geometric axis, by the external outline of the cross section, by the relative speed of rotation and by location in the node .

By purpose they are distinguished:

gear shafts, on which wheels, pulleys, sprockets, couplings, bearings and other gear parts are installed. In Fig. eleven, A The transmission shaft is shown in Fig. eleven, b– transmission shaft;

main shafts(Fig. 11.2 - machine spindle), on which not only gear parts are installed, but also the working parts of the machine (connecting rods, turbine disks, etc.).

The following are made according to the cross-sectional shape:

solid shafts;

hollow shafts provide weight reduction or placement inside another part. In large-scale production, hollow welded shafts made from wound tape are used.

According to the shape of the geometric axis they produce:

straight shafts:

A) constant diameter(Fig. 11.3). Such shafts are less labor-intensive to manufacture and create less stress concentration;

b) stepped(Fig. 11.4). Based on the strength condition, it is advisable to design shafts of variable cross-section, approaching in shape to bodies of equal resistance. The stepped shape is convenient for manufacturing and assembly; the ledges can absorb large axial forces;

V) with flanges. Long shafts are composite, connected by flanges;

G) with cut gears(gear shaft);

crankshafts(Fig. 11.5) in crank gears serve to convert rotational movement to reciprocating or vice versa;

flexible shafts (Fig. 11.6), which are multi-lead torsion springs twisted from wires, are used to transmit torque between machine components that change their relative position in operation (portable tools, tachometer, dental drills, etc.).

According to the external outline of the cross section, the shafts are:

smooth;

keyed;

splined;

profile;

eccentric.

According to the relative speed of rotation and location in the unit (gearbox), shafts are produced:

high-speed And input (leading)(pos. 1 rice. 11.7);

medium speed And intermediate(pos. 2 rice. 11.7);

slow-moving And weekend (slave)(pos. 3 rice. 11.7).

Rice. 11.2 Fig. 11.3

Rice. 11.7 Fig. 11.8

Classification. The axes can be stationary (Fig. 11.8) or rotating together with the parts mounted on them. Rotating axles provide better operating conditions for bearings; stationary axles are cheaper, but require bearings to be built into parts rotating on the axes.

Designs of shafts and axles. The most common is the stepped shaft shape. Parts are secured on shafts most often with prismatic keys (GOST 23360–78, GOST 10748–79), straight-sided splines (GOST 1139–80) or involute splines (GOST 6033–80) or fits with guaranteed interference. The supporting parts of the shafts and axles are called axles. The intermediate axles are called necks, the end axles are called tenons. The supporting areas that take the axial load are called heels. Thrust bearings serve as supports for the heels.

In Fig. 11.9 are given structural elements shafts, where 1 – prismatic key, 2 – splines, 3 – axle, 4 – heel, 5 – cylindrical surface, 6 – conical surface, 7 – ledge, 8 - shoulder, 9 – groove for the stop ring, 10 – threaded section, 11 – fillet, 12 – groove, 13 – chamfer, 14 – center hole.

The journals of shafts and axles operating in rolling bearings are almost always cylindrical, and in plain bearings they are cylindrical, conical or spherical (Fig. 11.10.)

The main application is cylindrical journals (Fig. 11.10, A, b) as simpler ones. Conical journals with small taper (Fig. 11.10, V) are used to regulate the clearance in bearings and sometimes for axial fixation of the shaft. Spherical journals (Fig. 11.10, G) due to the difficulty of their manufacture, they are used when it is necessary to compensate for significant angular displacements of the shaft axis.

a B C D

Landing surfaces under the hubs various parts(according to GOST 6536–69 from the normal series), mounted on the shaft, and end sections shafts are made cylindrical (pos. 5 rice. 11.9, GOST 12080–72) or conical (pos. 6 rice. 1.9, GOST 12081–72). Conical surfaces are used to ensure quick release and a given tension, increasing the accuracy of centering of parts.

For axial fixation of parts and the shaft itself, use ledges(pos. 7 rice. 11.9) and shoulders shaft (pos. 8 rice. 11.9, GOST 20226–74), conical sections of the shaft, retaining rings(pos. 9 rice. 11.9, GOST 13940–86, GOST 13942–86) and threaded sections (pos. 10 rice. 11.9) under nuts(GOST 11871–80).

Transitional areas from one section of the shaft to another and the ends of the shafts are made with grooves(pos. 12 rice. 11.9, fig. 11.11, GOST 8820–69), chamfered(pos. 13 rice. 11.9, GOST 10948–65) and fillets. Radius R fillets of constant radius (Fig. 11.11, A) choose less than the radius of curvature or the radial size of the chamfer of the mounted parts. It is desirable that the radius of curvature in highly stressed shafts be greater than or equal to 0.1 d. It is recommended to take fillet radii as large as possible to reduce load concentration. When the radius of the fillet is severely limited by the radius of the rounding of the edges of the mounted parts, spacer rings are installed. Fillets of a special elliptical shape and with an undercut or, more often, fillets outlined by two radii of curvature (Fig. 11.11, b), used when transitioning fillets to a step of smaller diameter (makes it possible to increase the radius in the transition zone).

Application of grooves (Fig. 11.11, V) can be recommended for non-critical parts, since they cause significant stress concentrations and reduce the strength of shafts under variable stresses. Grooves are used for the exit of grinding wheels (significantly increasing their durability during processing), as well as at the ends of sections with threads for the exit of thread-cutting tools. The grooves must have the maximum possible radii of curvature.

a B C

The ends of the shafts, in order to avoid crushing and damage to the hands of workers, are made with chamfers to facilitate fitting of parts.

Mechanical processing shafts are produced in centers, therefore, center holes should be provided at the ends of the shafts (pos. 14 rice. 11.9, GOST 14034–74).

The length of the axles usually does not exceed 3 m; the length of solid shafts, according to the conditions of manufacture, transportation and installation, should not exceed 6 m.

Axes serve to support various machine parts and mechanisms rotating with them or on them. The rotation of the axis, together with the parts installed on it, is carried out relative to its supports, called bearings. An example of a non-rotating axis is the axis of a lifting machine block (Fig. 1, a), and a rotating axis is a carriage axle (Fig. 1, b). The axes take the load from the parts located on them and bend.

Designs of axles and shafts.

Shafts, unlike axles, are designed to transmit torques and, in most cases, to support various machine parts rotating with them relative to the bearings. The shafts that carry the parts through which torque is transmitted receive loads from these parts and, therefore, work simultaneously in bending and torsion. When axial loads are applied to parts mounted on shafts (bevel gears, worm wheels, etc.), the shafts additionally work in tension or compression. Some shafts do not support rotating parts ( cardan shafts cars, connecting rolls rolling mills etc.), so these shafts only work in torsion. According to their intended purpose, they distinguish between gear shafts, on which gears, sprockets, couplings and other gear parts are installed, and main shafts, on which not only gear parts are installed, but also other parts, such as flywheels, cranks, etc.

The axes represent straight rods(Figure 1, a, b), and the shafts are distinguished straight(Fig. 1, c, d), cranked(Fig. 1, e) and flexible(Fig. 1, f). Straight shafts are widespread. Crankshafts in crank transmissions serve to convert reciprocating motion into rotational motion or vice versa and are used in piston machines (engines, pumps). Flexible shafts, which are multi-lead torsion springs twisted from wires, are used to transmit torque between machine components that change their relative position during operation (mechanized tools, instruments remote control and controls, dental drills, etc.). Crankshafts and flexible shafts are special parts and are studied in the relevant special courses. Axes and shafts in most cases are of a solid round, and sometimes of an annular cross-section. Individual sections of the shafts have a round solid or annular section with a keyway (Fig. 1, c, d) or with splines, and sometimes a profile section. The cost of axles and shafts of an annular section is usually higher than that of a solid section; they are used in cases where it is necessary to reduce the mass of the structure, for example in aircraft (see also the axes of the satellites of the planetary gearbox in Fig. 4), or to place another part inside. Hollow welded axles and shafts, made from a tape located along a helical line, reduce weight by up to 60%.

Axles of short length are made of the same diameter along the entire length (Fig. 1, a), and long and heavily loaded axles are made shaped (Fig. 1, b). Depending on the purpose, straight shafts are made either of constant diameter along the entire length (transmission shafts, Fig. 1, c), or stepped (Fig. 1, d), i.e. various diameters in separate areas. The most common are stepped shafts, since their shape is convenient for installing parts on them, each of which must pass freely to its place (for gearbox shafts, see the article “Gear reducers” Fig. 2; 3; and “Worm gear” Fig. 2 ; 3). Sometimes shafts are made integral with gears (see Fig. 2) or worms (see Fig. 2; 3).

The sections of axles and shafts with which they rest on bearings are called axles when perceiving radial loads, and heels when perceiving axial loads. End journals operating in plain bearings are called spikes(Fig. 2, a), and the axles located at some distance from the ends of the axles and shafts - necks(Fig. 2, b). The journals of axles and shafts operating in plain bearings are cylindrical (Fig. 2, a), conical(Fig. 2, c) and spherical(Fig. 2, d). The most common are cylindrical panels, as they are the simplest, most convenient and cheapest to manufacture, install and operate. Conical and spherical journals are used relatively rarely, for example, to adjust the clearance in bearings of precision machines by moving the shaft or bearing shell, and sometimes for axial fixation of the axis or shaft. Spherical journals are used when the shaft, in addition to rotational movement, must undergo angular movement in the axial plane. Cylindrical journals operating in plain bearings are usually made of a slightly smaller diameter compared to the adjacent section of the axle or shaft, so that, thanks to the shoulders and shoulders (Fig. 2, b), the axles and shafts can be secured against axial displacements. The axle and shaft journals for rolling bearings are almost always cylindrical (Fig. 3, a, b). Conical journals with small angle tapers to regulate clearances in rolling bearings by elastic deformation of the rings. On some axles and shafts, for fixing rolling bearings, threads for nuts are provided next to the journals (Fig. 3, b;) or annular grooves for fixing spring rings.

The heels operating in sliding bearings, called thrust bearings, are usually made annular (Fig. 4, a), and in some cases - comb (Fig. 4, b). Comb heels are used when large axial loads are applied to shafts; in modern mechanical engineering they are rare.

The seating surfaces of axles and shafts on which rotating parts of machines and mechanisms are installed are cylindrical and much less often conical. The latter are used, for example, to facilitate the installation and removal of heavy parts from the shaft with increased accuracy of centering of the parts.

The surface of a smooth transition from one stage of an axis or shaft to another is called a fillet (see Fig. 2, a, b). The transition from steps of a smaller diameter to a step of a larger diameter is made with a rounded groove for the exit of the grinding wheel (see Fig. 3). To reduce stress concentration, the radii of curvature of fillets and grooves are taken as large as possible, and the depth of the grooves is taken to be smaller (GOST 10948-64 and 8820-69).

The difference between the diameters of adjacent steps of axles and shafts should be minimal to reduce stress concentration. To facilitate the installation of rotating machine parts on them and to prevent injury to hands, the ends of the axles and shafts are chamfered, i.e., slightly ground to a cone (see Fig. 1...3). The radii of curvature of the fillets and the dimensions of the chamfers are normalized by GOST 10948-64.

The length of the axles usually does not exceed 2...3 m, the shafts can be longer. According to the conditions of manufacture, transportation and installation, the length of solid shafts should not exceed 6...7 m. Longer shafts are made into composite parts and their individual parts are connected by couplings or using flanges. The diameters of the landing areas of axles and shafts on which rotating parts of machines and mechanisms are installed must be consistent with GOST 6636-69 (ST SEV 514-77).

Materials of axles and shafts.

Axles and shafts are made from carbon and alloy structural steels, as they have high strength, the ability to be surface and volumetrically hardened, and are easy to produce by rolling cylindrical blanks and good machinability on machines. For axles and shafts without heat treatment, carbon steels St3, St4, St5, 25, 30, 35, 40 and 45 are used. Axles and shafts for which increased requirements To bearing capacity and durability of splines and journals, they are made of medium-carbon or alloy steels with an improvement of 35, 40, 40Х, 40НХ, etc. To increase the wear resistance of the journals of shafts rotating in plain bearings, the shafts are made of steels 20, 20Х, 12ХНЗА and others, followed by carburization and hardening of axles. Critical, heavily loaded shafts are made from alloy steels 40ХН, 40ХНМА, 30ХГТ, etc. Heavily loaded shafts complex shape, for example, engine crankshafts are also made from modified or high-strength cast iron.

4.1. Which part is called the shaft and which is called the axis?

Shaft is a rotating part of a machine that transmits torque from

one detail to another. Rotating parts are installed on the shaft and secured to it. During operation, the shaft experiences bending and torsion, and in some cases additional tension or compression.

An axle is a part of a machine designed to support the parts installed on it. Unlike a shaft, an axle does not transmit torque and therefore does not experience torsion.

4.2. Types of shafts and axles.

According to their geometric shape, shafts are divided into:

● Direct 1 and 2.

● Flexible 3.

● Elbows 4.

By design, straight shafts and axles are divided into:

● Smooth 1.

● Stepped 2.

Axes can be rotating or stationary.

4.3. Structural elements of shafts and axles.

●
Trunnion is the supporting part of a shaft or axle.

● A tenon is a pin at the end of a shaft or axle.

● A journal is a journal in the middle of a shaft or axle.

● A shoulder is a ring-shaped projection on a shaft or axle.

● Fillet is a smooth rounded transition from one surface to another.

4.4. Basic criteria for shaft performance.

● Strength .

● Rigidity .

● Vibration resistance .

4.5. Three stages of calculation and design of the shaft.

● Design calculation. The diameter of the end section of the shaft is determined from the torsional strength condition. The resulting diameter value is rounded to the nearest standard size according to GOST “Normal linear dimensions”.

● Shaft design. Its dimensions are determined based on design considerations.

● Verification calculation. The strength of the designed shaft is checked: the loads on the shaft are determined, a design diagram of the shaft is drawn up, the support reactions of the shaft are determined and diagrams of bending and torsional moments are constructed, stresses in the dangerous section are calculated and the strength is checked.

5. Shaft and axle supports

5.1. What do the shafts and axles rest on in a running machine?

Shafts and rotating axles are mounted on supports that provide rotation, absorb loads and transmit them to the base of the machine. The main part of the supports are bearings, which can absorb radial, radial-axial and axial loads.

Based on the principle of operation, they are distinguished:

● Sliding bearings.

● Rolling bearings.

5.2. What is a plain bearing?

The simplest plain bearing is a hole bored directly into the machine body, into which a bushing (liner) made of antifriction material is usually inserted. The shaft journal slides along the supporting surface.

5.3. Advantages and disadvantages of plain bearings.

Advantages:

● Small dimensions in the radial direction.

● Good susceptibility to shock and vibration loads.

● Can be used at very high shaft speeds.

● Can be used when working in water or aggressive environments.

Flaws:

● Large dimensions in the axial direction.

● Significant consumption lubricant and the need for systematic monitoring of the lubrication process.

● The need to use expensive and scarce antifriction materials for liners.

5.4. Basic requirements for materials used in plain bearings.

The materials of the liners paired with the trunnion must provide:

● Low coefficient of friction.

● High wear resistance.

● Good run-in.

● Corrosion resistance.

● Low coefficient of linear expansion.

● Low cost.

None of the known materials possesses the full range of these properties. Therefore, various antifriction materials are used, the best way meeting specific operating conditions.

5.5. Main materials used in plain bearings.

Liner materials can be divided into three groups.

● Metal. Babbitts (tin- or lead-based alloys) have high anti-friction properties and good wearability, but are expensive. Bronze, brass, and zinc alloys have good antifriction properties. At low speeds, anti-friction cast irons are used.

● Metal-ceramic. Porous bronze-graphite or iron-graphite materials are impregnated with hot oil and used when it is impossible to provide liquid lubrication. These materials are able to work for quite a long time without the supply of lubricant.

● Non-metallic. Polymer self-lubricating materials are used at significant sliding speeds. Fluoroplastics have a low coefficient of friction, but a high coefficient of linear expansion. Bearings with rubber liners are used with water lubricant.

5.6. Performance criteria for plain bearings.

The main criterion iswear resistance rubbing couple.

The work of frictional forces in the bearing is converted into heat, so another criterion isheat resistance .

5.7. What is a rolling bearing?

A finished unit, which consists of outer 1 and inner 2 rings with raceways, rolling elements 3 (balls or rollers) and a separator 4 that separates and guides the rolling elements.

5.8. Advantages and disadvantages of rolling bearings.

Advantages:

● Low friction losses.

● High efficiency.

● Slight heating.

● High load capacity.

● Small overall dimensions in the axial direction.

● High degree of interchangeability.

● Easy to use.

● Low lubricant consumption.

Flaws:

● Sensitivity to shock and vibration loads.

● Large dimensions in the radial direction.

● Noise at high speeds.

5.9. How are rolling bearings classified?

● The shape of the rolling elements is ball and roller, and roller: cylindrical, conical, barrel-shaped.

● In the direction of the perceived load - radial (perceive radial loads), radial-thrust (perceive radial and axial loads) and thrust (perceive axial loads).

● According to the number of rows of rolling elements - single-row, double-row and multi-row.

5.10. The main reasons for the loss of performance of rolling bearings.

● Fatigue chipping after prolonged use.

● Wear – with insufficient protection against abrasive particles.

● Destruction of cages, typical for high-speed bearings, especially those operating with axial loads or with ring misalignment.

● Splitting of rings and rolling elements - under unacceptable shock loads and distortions of the rings.

● Residual deformations on the raceways in the form of dimples and dents - in heavily loaded low-speed bearings.

5.11. How is rolling bearings selected?

When designing machines, rolling bearings are not designed, but selected from standard ones.

There are different types of bearings:

● According to basicstatic load capacity to prevent residual deformation - at a rotation speed of no more than 10 rpm.

● According to basicdynamic load capacity to prevent fatigue failure (chipping) - at a rotation speed of more than 10 rpm.