Clamping fixtures. Clamping devices of fixtures (wedge and lever clamps). Installation elements of devices
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4. Purpose of clamps and features of their designs depending on the device design
The main purpose of clamping devices is to ensure reliable contact of the workpiece with the mounting elements and to prevent its displacement and vibration during processing.
Clamping devices are also used to ensure correct positioning and centering of the workpiece. In this case, the clamps perform the function of mounting and clamping elements. These include self-centering chucks, collet clamps and other devices.
The workpiece may not be secured if a heavy (stable) part is being processed, compared to the weight of which the cutting forces are insignificant; the force generated during the cutting process is applied in such a way that it does not disturb the installation of the part.
During processing, the following forces can act on the workpiece:
Cutting forces, which can be variable due to different processing allowances, material properties, dullness of the cutting tool;
Workpiece weight (at vertical position details);
Centrifugal forces resulting from a displacement of the center of gravity of a part relative to the axis of rotation.
The following basic requirements apply to fixture clamping devices:
When securing the workpiece, its position achieved by installation must not be violated;
The clamping forces must exclude the possibility of movement of the part and its vibration during processing;
Deformation of the part under the action of clamping forces should be minimal.
The crushing of the base surfaces should be minimal, so the clamping force should be applied so that the part is pressed against installation elements fixtures with a flat base surface rather than a cylindrical or shaped one.
Clamping devices must be fast-acting, conveniently located, simple in design and require minimal effort from the worker.
Clamping devices must be wear-resistant, and the most wearable parts must be replaceable.
The clamping forces must be directed towards the supports so as not to deform the part, especially a non-rigid one.
Materials: steel 30ХГСА, 40Х, 45. Working surface should be processed in 7 square meters. and more precisely.
Terminal designation:
Clamping device designation:
P – pneumatic
H – hydraulic
E – electric
M – magnetic
EM – electromagnetic
G – hydroplastic
In individual production, manual drives are used: screw, eccentric, etc. In mass production, mechanized drives are used.
5. CLAMPING THE PART. INITIAL DATA FOR DRAFTING A SCHEME FOR CALCULATING THE CLAMPING FORCE OF THE PART. METHOD FOR DETERMINING THE CLAMPING FORCE OF A PART IN A DEVICE. TYPICAL DIAGRAMS FOR CALCULATING FORCE, REQUIRED VALUE OF CLAMPING FORCE.
The magnitude of the required clamping forces is determined by solving the statics problem of the equilibrium of a rigid body under the influence of all forces and moments applied to it.
Clamping forces are calculated in 2 main cases:
1. when using existing universal devices with clamping devices that develop a certain force;
2. when designing new devices.
In the first case, the calculation of the clamping force is of a testing nature. The required clamping force, determined from the processing conditions, must be less than or equal to the force that the clamping device of the universal fixture used develops. If this condition is not met, then the processing conditions are changed in order to reduce the required clamping force, followed by a new verification calculation.
In the second case, the method for calculating clamping forces is as follows:
1. The most is selected rational scheme installing the part, i.e. the position and type of supports, places of application of clamping forces are outlined, taking into account the direction of cutting forces at the most unfavorable moment of processing.
2. In the selected diagram, arrows indicate all forces applied to the part that tend to disrupt the position of the part in the fixture (cutting forces, clamping forces) and forces that tend to maintain this position (friction forces, support reactions). If necessary, inertial forces are also taken into account.
3. Select the static equilibrium equations applicable to the given case and determine the desired value of the clamping force Q 1 .
4. Having accepted the fastening reliability coefficient (safety factor), the need for which is caused by inevitable fluctuations in cutting forces during processing, the actual required clamping force is determined:
The safety factor K is calculated in relation to specific processing conditions
where K 0 = 2.5 – guaranteed safety factor for all cases;
K 1 – coefficient taking into account the state of the workpiece surface; K 1 = 1.2 – for rough surface; К 1 = 1 – for finishing surface;
K 2 – coefficient that takes into account the increase in cutting forces from the progressive dulling of the tool (K 2 = 1.0...1.9);
K 3 – coefficient that takes into account the increase in cutting forces during intermittent cutting; (K 3 = 1.2).
К 4 – coefficient taking into account the constancy of the clamping force developed by the power drive of the device; K 4 = 1…1.6;
K 5 – this coefficient is taken into account only in the presence of torques tending to rotate the workpiece; K 5 = 1…1.5.
Typical diagrams for calculating the clamping force of a part and the required clamping force:
1. The cutting force P and the clamping force Q are equally directed and act on the supports:
At a constant value of P, force Q = 0. This scheme corresponds to broaching holes, turning in centers, and counterbore bosses.
2. The cutting force P is directed against the clamping force:
3. The cutting force tends to move the workpiece from the mounting elements:
Typical for pendulum milling and milling of closed contours.
4. The workpiece is installed in the chuck and is under the influence of moment and axial force:
where Q c is the total clamping force of all cams:
where z is the number of jaws in the chuck.
Taking into account the safety factor k, the required force developed by each cam will be:
5. If one hole is drilled in a part and the direction of the clamping force coincides with the direction of drilling, then the clamping force is determined by the formula:
k M = W f R
W = k M / f R
6. If several holes are drilled simultaneously in a part and the direction of the clamping force coincides with the direction of drilling, then the clamping force is determined by the formula:
In serial and small-scale production, equipment is designed using universal clamping mechanisms (CLM) or special single-link ones with manual drive. In cases where required great forces for securing workpieces, it is advisable to use mechanized clamps.
In mechanized production, clamping mechanisms are used in which the clamps are automatically retracted to the side. This ensures free access to the installation elements for cleaning them from chips and ease of reinstallation of workpieces.
Lever single-link mechanisms controlled by a hydraulic or pneumatic drive are used when securing, as a rule, one body or large workpiece. In such cases, the clamp is moved or turned manually. However, it is better to use an additional link to remove the stick from the workpiece loading area.
L-type clamping devices are used more often to secure body workpieces from above. To rotate the clamp during fastening, a screw groove with a straight section is provided.
Rice. 3.1.
Combined clamping mechanisms are used to secure a wide range of workpieces: housings, flanges, rings, shafts, strips, etc.
Let's look at some standard designs clamping mechanisms.
Lever clamping mechanisms are distinguished by their simplicity of design (Fig. 3.1), a significant gain in force (or movement), constancy of the clamping force, and the ability to secure the workpiece in hard to reach place, ease of use, reliability.
Lever mechanisms are used in the form of clamps (clamping bars) or as amplifiers of power drives. To facilitate the installation of workpieces, lever mechanisms are rotary, folding and movable. According to their design (Fig. 3.2), they can be rectilinear and retractable (Fig. 3.2, A) and rotary (Fig. 3.2, b), folding (Fig. 3.2, V) with a swinging support, curved (Fig. 3.2, G) and combined (Fig. 3.2, 
Rice. 3.2.
In Fig. 3.3 shows universal lever CMs with a manual screw drive, used in individual and small-scale production. They are simple in design and reliable.
Support screw 1 installed in the T-shaped groove of the table and secured with a nut 5. Clamp position 3 The height is adjusted using screw 7 with a support foot 6, and spring 4. The force of fastening to the workpiece is transmitted from the nut 2 through the clamp 3 (Fig. 3.3, A).
In ZM (Fig. 3.3, b) workpiece 5 is secured with a clamp 4, and the workpiece 6 clamping 7. The fastening force is transmitted from the screw 9 for sticking 4 through the plunger 2 and adjusting screw /; to the clamp 7 - through the nut fixed in it. When changing the thickness of the workpieces, the position of the axes 3, 8 easy to adjust.
Rice. 3.3.
In ZM (Fig. 3.3, V) frame 4 clamping mechanism is secured to the table with a nut 3 via bushing 5 with threaded hole. Curved Clamp Position 1 but the height is adjusted with a support 6 and screw 7. Clamp 1 there is play between the conical washer installed iod the head of screw 7, and the washer, which is located above the locking ring 2.
The design has an arched clamp 1 while fastening the workpiece with a nut 3 rotates on an axis 2. Screw 4 in this design it is not attached to the machine table, but moves freely in a T-shaped slot (Fig. 3.3, d).
The screws used in clamping mechanisms develop a force at the end R, which can be calculated using the formula
Where R- the force of the worker applied to the end of the handle; L- handle length; r cf - average thread radius; a - thread lead angle; cf - friction angle in the thread.
The moment developed on the handle (key) to obtain a given force R
where M, p is the friction moment at the supporting end of the nut or screw:
where / is the sliding friction coefficient: when fastening / = 0.16...0.21, when unfastening / = 0.24...0.30; D H - outside diameter rubbing surface of a screw or nut; s/v - screw thread diameter.
Taking a = 2°30" (for threads from M8 to M42, angle a changes from 3°10" to 1°57"), f = 10°30", g avg= 0.45s/, D, = 1.7s/, d B = d u/= 0.15, we obtain an approximate formula for the moment at the end of the nut M gr = 0.2 dP.
For flat end screws M t p = 0 ,1с1Р+ n, and for screws with a spherical end M Lr ~ 0.1 s1R.
In Fig. 3.4 shows other lever clamping mechanisms. Frame 3 universal clamping mechanism with a screw drive (Fig. 3.4, A) secured to the machine table with a screw/nut 4. Sticking b during fastening, the workpiece is rotated on axis 7 with a screw 5 clockwise. Clamp position b with body 3 Easily adjustable relative to the fixed liner 2.
Rice. 3.4.
Special lever clamping mechanism with an additional link and a pneumatic drive (Fig. 3.4, b) used in mechanized production to automatically remove the stick from the workpiece loading area. While unfastening the workpiece/rod b moves downwards, while the sticking 2 rotates on an axis 4. The latter together with the earring 5 rotates on an axis 3 and occupies the position shown by the dashed line. Sticking 2 removed from the workpiece loading area.
Wedge clamping mechanisms come with a single-bevel wedge and wedge-plunger ones with one plunger (without rollers or with rollers). Wedge clamping mechanisms are distinguished by their simplicity of design, ease of setup and operation, ability to self-braking, and constant clamping force.
To securely hold the workpiece 2 in adaptation 1 (Fig. 3.5, A) wedge 4 must be self-braking due to the angle a of the bevel. Wedge clamps are used independently or as an intermediate link in complex clamping systems. They allow you to increase and change the direction of the transmitted force Q.
In Fig. 3.5, b shows a standardized hand-operated wedge clamping mechanism for securing the workpiece to the machine table. The workpiece is clamped with a wedge / moving relative to the body 4. The position of the moving part of the wedge clamp is fixed with a bolt 2 , nut 3 and a puck; fixed part - bolt b, nut 5 and washer 7.
Rice. 3.5. Scheme (A) and design (V) wedge clamping mechanism
The clamping force developed by the wedge mechanism is calculated using the formula
where sr and f| - friction angles on the inclined and horizontal surfaces of the wedge, respectively.
Rice. 3.6.
In the practice of mechanical engineering production, equipment with rollers in wedge clamping mechanisms is more often used. Such clamping mechanisms can reduce friction losses by half.
The calculation of the fastening force (Fig. 3.6) is made using a formula similar to the formula for calculating a wedge mechanism operating under the condition of sliding friction on contacting surfaces. In this case, we replace the sliding friction angles φ and φ with the rolling friction angles φ |1р and φ pr1:
To determine the ratio of friction coefficients during sliding and
rolling, consider the equilibrium of the lower roller of the mechanism: F l - = T - .
Because T = WfF i =Wtgi p tsr1 and / = tgcp, we obtain tg(p llpl = tg the upper roller, the formula is similar. In the designs of wedge clamping mechanisms, standard rollers and axes are used, in which D= 22...26 mm, a d= 10... 12 mm. If we take tg(p =0.1; d/D= 0.5, then the rolling friction coefficient will be / k = tg 0,1 0,5 = 0,05 =0,05. Rice. 3. In Fig. Fig. 3.7 shows diagrams of wedge-plunger clamping mechanisms with a double-plunger plunger without a roller (Fig. 3.7, a); with a two-support plunger and a roller (Fig. 3.7, (5); with a single-support plunger and three rollers (Fig. 3.7, c); with two single-support (cantilever) plungers and rollers (Fig. 3.7, G). Such clamping mechanisms are reliable in operation, easy to manufacture and can have the property of self-braking at certain wedge bevel angles. In Fig. Figure 3.8 shows a clamping mechanism used in automated production. The workpiece 5 is installed on the finger b and fastened with a clamp 3.
The clamping force on the workpiece is transmitted from the rod 8
hydraulic cylinder 7 through a wedge 9,
video clip 10
and plunger 4.
Removal of the clamp from the loading zone during removal and installation of the workpiece is carried out by a lever 1,
which turns on an axis 11
projection 12.
Sticking 3
easily stirred by lever 1
or springs 2, since in the axle design 13
rectangular crackers are provided 14,
easily moved in the grooves of the clamp. Rice. 3.8. To increase the force on the rod of a pneumatic actuator or other power drive, hinged lever mechanisms are used. They are an intermediate link connecting the power drive with the clamp, and are used in cases where greater force is required to secure the workpiece. According to their design, they are divided into single-lever, double-lever single-acting and double-lever double-acting. In Fig. 3.9, A shows a diagram of a single-acting articulated lever mechanism (amplifier) in the form of an inclined lever 5
and roller 3,
connected by an axis 4
with lever 5 and rod 2 of pneumatic cylinder 1.
Initial strength R, developed by a pneumatic cylinder, through rod 2, roller 3 and axis 4
transmitted to the lever 5.
In this case, the lower end of the lever 5
moves to the right, and its upper end turns the clamp 7 around fixed support b and secures the workpiece with force Q. The value of the latter depends on the strength W and grip arm ratio 7. Strength W for a single-lever hinge mechanism (amplifier) without a plunger is determined by the equation Force IV, developed by double lever hinge mechanism(amplifier) (Fig. 3.9, b), equal to Strength If"2
,
developed by a double-lever hinge-plunger mechanism of one-sided action (Fig. 3.9, V), determined by the equation In the given formulas: R- initial force on the motorized drive rod, N; a - angle of position of the inclined link (lever); p - additional angle that takes into account friction losses in the hinges ^p = arcsin/^П;/- coefficient of sliding friction on the roller axis and in the hinges of the levers (f~ 0.1...0.2); (/-diameter of the axes of the hinges and roller, mm; D- outer diameter of the support roller, mm; L- distance between lever axes, mm; f[ - sliding friction angle on the hinge axes; f 11р - friction angle rolling on a roller support; tgф pp =tgф-^; tgф pp 2 - reduced coefficient zhere; tgф np 2 =tgф-; / - the distance between the hinge axis and the middle of the friction, taking into account friction losses in the cantilever (skewed) plunger 3/ , the plunger guide sleeve (Fig. 3.9, V), mm; A- length of the plunger guide sleeve, mm. Rice. 3.9. actions Single-lever hinged clamping mechanisms are used in cases where large workpiece clamping forces are required. This is explained by the fact that during fastening of the workpiece, the angle a of the inclined lever decreases and the clamping force increases. So, at an angle a = 10°, the force W at the upper end of the inclined link 3
(see Fig. 3.9, A) amounts to JV~ 3,5R, and at a = 3° W~ 1 IP, Where R- force on the rod 8
pneumatic cylinder. In Fig. 3.10, A An example of the design of such a mechanism is given. The workpiece / is secured with a clamp 2.
The clamping force is transmitted from the rod 8
pneumatic cylinder through a roller 6
and length-adjustable inclined link 4,
consisting of a fork 5
and earrings 3.
To prevent rod bending 8
a support bar 7 is provided for the roller. IN clamping mechanism(Fig. 3.10, b) The pneumatic cylinder is located inside the housing 1
fixture to which the housing is attached with screws 2
clamping Rice. 3.10. mechanism. While securing the workpiece, the rod 3
pneumatic cylinder with roller 7 moves upward, and the clamp 5
with link b rotates on an axis 4.
When unfastening the workpiece, the clamp 5 takes the position shown by the dashed lines, without interfering with the change of the workpiece.
The designs of clamping devices consist of three main parts: a drive, a contact element, and a power mechanism.
The drive, converting a certain type of energy, develops a force Q, which is converted into a clamping force using a power mechanism R and is transmitted through contact elements to the workpiece.
The contact elements serve to transfer the clamping force directly to the workpiece. Their designs allow forces to be dispersed, preventing crushing of the workpiece surfaces, and distributed between several support points.
It is known that rational choice of devices reduces auxiliary time. Auxiliary time can be reduced by using mechanized drives.
Mechanized drives, depending on the type and source of energy, can be divided into the following main groups: mechanical, pneumatic, electromechanical, magnetic, vacuum, etc. The scope of application of manually controlled mechanical drives is limited, since a significant amount of time is required for installation and removal of workpieces. . The most widely used drives are pneumatic, hydraulic, electric, magnetic and their combinations.
Pneumatic actuators work on the feed principle compressed air. Can be used as a pneumatic drive
pneumatic cylinders (double-acting and single-acting) and pneumatic chambers.
for cylinder cavity with rod
for single acting cylinders
The disadvantages of pneumatic drives include their relatively large overall dimensions. The force Q(H) in pneumatic cylinders depends on their type and, without taking into account friction forces, it is determined by the following formulas:
For double-acting pneumatic cylinders for the left side of the cylinder
where p - compressed air pressure, MPa; compressed air pressure is usually taken to be 0.4-0.63 MPa,
D - piston diameter, mm;
d- rod diameter, mm;
ή- efficiency, taking into account losses in the cylinder, at D = 150...200 mm ή =0.90...0.95;
q - spring resistance force, N.
Pneumatic cylinders are used with an internal diameter of 50, 75, 100, 150, 200, 250, 300 mm. Fitting the piston in the cylinder when using o-rings 
or 
, and when sealed with cuffs 
or 
.
The use of cylinders with a diameter of less than 50 mm and more than 300 mm is not economically profitable; in this case, it is necessary to use other types of drives,
Pneumatic chambers have a number of advantages compared to pneumatic cylinders: they are durable, withstand up to 600 thousand starts (pneumatic cylinders - 10 thousand); compact; They are lightweight and easier to manufacture. The disadvantages include the small stroke of the rod and the variability of the developed forces.
Hydraulic drives compared to pneumatic ones they have
the following advantages: develops great forces (15 MPa and above); their working fluid (oil) is practically incompressible; ensure smooth transmission of the developed forces by the power mechanism; can ensure the transfer of force directly to the contact elements of the device; have a wide range of applications, since they can be used for precise movements of the working parts of the machine and moving parts of devices; allow the use of working cylinders of small diameter (20, 30, 40, 50 mm v. more), which ensures their compactness.
Pneumohydraulic drives have a number of advantages compared to pneumatic and hydraulic ones: they have high working forces, speed of action, low cost and small dimensions. The calculation formulas are similar to the calculation of hydraulic cylinders.
Electromechanical drives are widely used in CNC lathes, aggregate machines, and automatic lines. Driven by an electric motor and through mechanical transmissions, forces are transmitted to the contact elements of the clamping device.
Electromagnetic and magnetic clamping devices They are carried out mainly in the form of plates and faceplates for securing steel and cast iron workpieces. Magnetic field energy from electromagnetic coils or permanent magnets is used. The technological capabilities of using electromagnetic and magnetic devices in conditions of small-scale production and group processing are significantly expanded when using quick-change setups. These devices increase labor productivity by reducing auxiliary and main time (10-15 times) during multi-site processing.
Vacuum drives used for fastening workpieces made of various materials with a flat or curved surface, taken as the main base. Vacuum clamping devices operate on the principle of using atmospheric pressure.
Force (N), pressing the workpiece to the plate:
Where F- area of the cavity of the device from which air is removed, cm 2;
p - pressure (in factory conditions usually p = 0.01 ... 0.015 MPa).
Pressure for individual and group installations is created by one- and two-stage vacuum pumps.
Power mechanisms act as amplifiers. Their main characteristic is the gain:
Where R- fastening force applied to the workpiece, N;
Q - force developed by the drive, N.
Power mechanisms often act as a self-braking element in the event of a sudden failure of the drive.
Some standard schemes designs of clamping devices are shown in Fig. 5.
Figure 5 Clamping device diagrams:
A- using a clip; 6 - swinging lever; V- self-centeringprisms
Clamping elements are mechanisms directly used to secure workpieces, or intermediate links in more complex clamping systems.
Most simple view universal clamps are those that are activated by keys, handles or handwheels mounted on them.
To prevent the movement of the clamped workpiece and the formation of dents on it from the screw, and also to reduce the bending of the screw when pressing on a surface not perpendicular to its axis, swinging shoes are placed on the ends of the screws (Fig. 68, α).
Combinations screw devices with levers or wedges are called combination clamps and, a variety of which are screw clamps(Fig. 68, b), The device of the clamps allows you to move them away or rotate them so that you can more conveniently install the workpiece in the fixture.
In Fig. 69 shows some designs quick release clamps. For small clamping forces, a bayonet device is used (Fig. 69, α), and for significant forces, a plunger device is used (Fig. 69, b). These devices allow the clamping element to be retracted to long distance from the workpiece; fastening occurs as a result of turning the rod through a certain angle. An example of a clamp with a folding stop is shown in Fig. 69, v. Having loosened the handle nut 2, remove the stop 3, rotating it around its axis. After this, the clamping rod 1 is retracted to the right at a distance h. In Fig. 69, d shows a diagram of a high-speed device lever type. When turning the handle 4, the pin 5 slides along the bar 6 with an oblique cut, and the pin 2 slides along the workpiece 1, pressing it against the stops located below. Spherical washer 3 serves as a hinge.
The large amount of time and significant forces required to secure the workpieces limit the scope of use of screw clamps and, in most cases, make quick-release clamps preferable. eccentric clamps . In Fig. 70 shows disk (α), cylindrical with L-shaped clamp (b) and conical floating (c) clamps.
Eccentrics are round, involute and spiral (along the Archimedes spiral). Two types of eccentrics are used in clamping devices: round and curved.
Round eccentrics(Fig. 71) are a disk or roller with the axis of rotation shifted by the eccentricity size e; the self-braking condition is ensured when the ratio D/е≥ 4.
The advantage of round eccentrics is the ease of their manufacture; The main disadvantage is the variability of the lifting angle α and clamping forces Q. Curvilinear eccentrics, the working profile of which is carried out according to an involute or an Archimedes spiral, have a constant angle of elevation α, and, therefore, ensure a constant force Q when clamping any point of the profile.
Wedge mechanism used as an intermediate link in complex clamping systems. It is simple to manufacture, easily placed in the device, and allows you to increase and change the direction of the transmitted force. At certain angles, the wedge mechanism has self-braking properties. For a single-bevel wedge (Fig. 72, a) when transmitting forces at a right angle, the following relationship can be accepted (with ϕ1 = ϕ2 = ϕ3 = ϕ where ϕ1…ϕ3 are friction angles):
P = Qtg (α ± 2ϕ),
where P is the axial force; Q - clamping force. Self-braking will take place at α<ϕ1 + ϕ2.
For a two-bevel wedge (Fig. 72, b) when transmitting forces at an angle β>90, the relationship between P and Q at a constant friction angle (ϕ1 = ϕ2 = ϕ3 = ϕ) is expressed by the following formula:
P = Qsin(α + 2ϕ)/cos (90° + α - β + 2ϕ).
Lever Clamps used in combination with other elementary clamps, forming more complex clamping systems. Using the lever, you can change the magnitude and direction of the transmitted force, as well as simultaneously and uniformly secure the workpiece in two places. In Fig. Figure 73 shows diagrams of the action of forces in single-arm and double-arm straight and curved clamps. The equilibrium equations for these lever mechanisms have next view; for a single-arm clamp (Fig. 73, α):
direct double-arm clamp (Fig. 73, b):
curved clamp (for l1 where p is the friction angle; ƒ - friction coefficient. Centering clamping elements are used as installation elements for the external or internal surfaces of rotating bodies: collets, expanding mandrels, clamping bushings with hydroplastic, as well as membrane cartridges. The cone angle of the compression sleeve is made 1° less or greater than the collet cone angle. The collets ensure installation eccentricity (runout) of no more than 0.02...0.05 mm. The base surface of the workpiece should be processed according to the 9th...7th accuracy grade. Expanding mandrels various designs (including designs using hydroplastic) are classified as mounting and clamping devices. Diaphragm cartridges used for precise centering of workpieces along the outer or inner cylindrical surface. The cartridge (Fig. 75) consists of a round membrane 1 screwed to the faceplate of the machine in the form of a plate with symmetrically located protrusions-cams 2, the number of which is selected within the range of 6...12. A pneumatic cylinder rod 4 passes inside the spindle. When the pneumatics are turned on, the membrane bends, pushing the cams apart. When the rod moves back, the membrane, trying to return to its original position, compresses the workpiece 3 with its cams. Rack and pinion clamp(Fig. 76) consists of a rack 3, a gear 5 sitting on a shaft 4, and a handle lever 6. By rotating the handle counterclockwise, lower the rack and clamp 2 to secure the workpiece 1. The clamping force Q depends on the value of the force P applied to the handle. The device is equipped with a lock, which, jamming the system, prevents the reverse rotation of the wheel. The most common types of locks are: Roller lock(Fig. 77, a) consists of a drive ring 3 with a cutout for roller 1, which is in contact with the cut plane of the roller. 2 gears. Drive ring 3 is attached to the handle of the clamping device. By rotating the handle in the direction of the arrow, rotation is transmitted to the gear shaft through roller 1*. The roller is wedged between the bore surface of the housing 4 and the cut plane of the roller 2 and prevents reverse rotation. Direct Drive Roller Lock the moment from the driver to the roller is shown in Fig. 77, b. Rotation from the handle through the leash is transmitted directly to the 6th wheel shaft. Roller 3 is pressed through pin 4 by a weak spring 5. Since the gaps in the places where the roller touches ring 1 and shaft 6 are selected, the system instantly jams when the force is removed from handle 2. By turning the handle in the opposite direction, the roller wedges and rotates the shaft clockwise . Conical lock(Fig. 77, c) has a conical sleeve 1 and a shaft with a cone 3 and a handle 4. The spiral teeth on the middle neck of the shaft are engaged with the rack 5. The latter is connected to the actuator clamping mechanism. At a tooth angle of 45°, the axial force on shaft 2 is equal (without taking into account friction) to the clamping force. * Locks of this type are made with three rollers located at an angle of 120°. Combination clamping devices are a combination of elementary clamps of various types. They are used to increase the clamping force and reduce the dimensions of the device, as well as to create greater ease of control. Combination clamping devices can also provide simultaneous clamping of a workpiece in several places. Types of combined clamps are shown in Fig. 78. The combination of a curved lever and a screw (Fig. 78, a) allows you to simultaneously secure the workpiece in two places, uniformly increasing the clamping forces to a given value. A conventional rotary clamp (Fig. 78, b) is a combination of lever and screw clamps. The swing axis of lever 2 is aligned with the center of the spherical surface of washer 1, which relieves pin 3 from bending forces. The clamp with an eccentric shown in Fig. 78 is an example of a high-speed combined clamp. At a certain lever arm ratio, the clamping force or stroke of the clamping end of the lever can be increased. In Fig. 78, d shows a device for securing a cylindrical workpiece in a prism using a hinge lever, and in Fig. 78, d - diagram of a high-speed combined clamp (lever and eccentric), providing lateral and vertical pressing of the workpiece to the supports of the device, since the clamping force is applied at an angle. A similar condition is provided by the device shown in Fig. 78, e. Hinge-lever clamps (Fig. 78, g, h, i) are examples of high-speed clamping devices actuated by turning the handle. To prevent self-release, the handle is moved through the dead position to stop 2. The clamping force depends on the deformation of the system and its rigidity. The desired deformation of the system is set by adjusting pressure screw 1. However, the presence of a tolerance for size H (Fig. 78, g) does not ensure constant clamping force for all workpieces of a given batch. Combined clamping devices are operated manually or by power units. Clamping mechanisms for multiple fixtures must provide the same clamping force in all positions. The simplest multi-place device is a mandrel on which a package of blanks “rings, disks” is installed, secured along the end planes with one nut (sequential clamping force transmission scheme). In Fig. 79, α shows an example of a clamping device operating on the principle of parallel distribution of clamping force. If it is necessary to ensure the concentricity of the base and machined surfaces and to prevent deformation of the workpiece, elastic clamping devices are used, where the clamping force is uniformly transmitted by means of a filler or other intermediate body to the clamping element of the device within the limits of elastic deformations). Conventional springs, rubber or hydroplastic are used as an intermediate body. A parallel clamping device using hydroplastic is shown in Fig. 79, b. In Fig. 79, in shows a device of mixed (parallel-series) action. On continuous machines (drum-milling, special multi-spindle drilling) workpieces are installed and removed without interrupting the feed movement. If the auxiliary time overlaps with the machine time, then clamping devices can be used to secure the workpieces various types. In order to mechanize production processes, it is advisable to use Automatic clamping devices(continuous) driven by the feed mechanism of the machine. In Fig. 80, α shows a diagram of a device with a flexible closed element 1 (cable, chain) for securing cylindrical workpieces 2 on a drum milling machine when processing end surfaces, and in Fig. 80, 6 - diagram of a device for securing piston blanks on a multi-spindle horizontal drilling machine. In both devices, operators only install and remove the workpiece, and the workpiece is secured automatically. An effective clamping device for holding workpieces made of thin sheet material during finishing or finishing is a vacuum clamp. The clamping force is determined by the formula: where A is the active area of the device cavity limited by the seal; p = 10 5 Pa - the difference between atmospheric pressure and the pressure in the cavity of the device from which air is removed. Electromagnetic clamping devices used for securing workpieces made of steel and cast iron with a flat base surface. Clamping devices are usually made in the form of plates and chucks, the design of which takes as initial data the dimensions and configuration of the workpiece in plan, its thickness, material and the necessary holding force. The holding force of the electromagnetic device largely depends on the thickness of the workpiece; at small thicknesses, not all the magnetic flux passes through the cross section of the part, and some of the magnetic flux lines are scattered into the surrounding space. Parts processed on electromagnetic plates or chucks acquire residual magnetic properties - they are demagnetized by passing them through a solenoid powered by alternating current. In magnetic clamping In devices, the main elements are permanent magnets, isolated from one another by non-magnetic gaskets and fastened into a common block, and the workpiece is an armature through which the magnetic power flow is closed. To detach the finished part, the block is shifted using an eccentric or crank mechanism, while the magnetic power flow is closed on the device body, bypassing the part. The main purpose of fixture clamping devices is to ensure reliable contact (continuity) of the workpiece or assembled part with the installation elements, preventing its displacement during processing or assembly. Lever clamps. Lever clamps (Figure 2.16) are used in combination with other elementary clamps, forming more complex clamping systems. They allow you to change the magnitude and direction of the transmitted force. Wedge mechanism. Wedges are very widely used in clamping mechanisms of devices, this ensures a simple and compact design and reliable operation. The wedge can be either a simple clamping element acting directly on the workpiece, or it can be combined with any other simple element to create combined mechanisms. The use of a wedge in the clamping mechanism provides: an increase in the initial drive force, a change in the direction of the initial force, self-braking of the mechanism (the ability to maintain the clamping force when the force generated by the drive ceases). If the wedge mechanism is used to change the direction of the clamping force, then the wedge angle is usually equal to 45°, and if to increase the clamping force or increase reliability, then the wedge angle is taken equal to 6...15° (self-braking angles). o mechanisms with a flat single-bevel wedge ( o multi-wedge (multi-plunger) mechanisms; o eccentrics (mechanisms with a curved wedge); o end cams (mechanisms with a cylindrical wedge). 11. The action of cutting forces, clamps and their moments on the workpiece During the processing process, the cutting tool makes certain movements relative to the workpiece. Therefore, the required arrangement of the surfaces of the part can be ensured only in the following cases: 1) if the workpiece occupies a certain position in the working area of the machine; 2) if the position of the workpiece in the working area is determined before the start of processing, on the basis of this it is possible to correct the shaping movements. The exact position of the workpiece in the working area of the machine is achieved during its installation in the fixture. The installation process includes basing (i.e. giving the workpiece the required position relative to the selected coordinate system) and securing (i.e. applying forces and force pairs to the workpiece to ensure constancy and immutability of its position achieved during basing). The actual position of the workpiece installed in the working area of the machine differs from the required one, which is caused by the deviation of the position of the workpiece (in the direction of the maintained size) during the installation process. This deviation is called the installation error, which consists of a basing error and a fixing error. The surfaces belonging to the workpiece and used in its basing are called technological bases, and those used for its measurements are called measuring bases. To install a workpiece in a fixture, several bases are usually used. To put it simply, the workpiece is considered to be in contact with the fixture at points called support points. The arrangement of reference points is called a basing scheme. Each reference point determines the connection of the workpiece with the selected coordinate system in which the workpiece is processed. 1. If there are high requirements for processing accuracy, the precisely machined surface of the workpiece should be used as a technological basis and a basing scheme should be adopted that ensures the smallest installation error. 2. One of the simplest ways to increase basing accuracy is to adhere to the principle of combining bases. 3. To increase processing accuracy, the principle of constancy of bases should be observed. If this is not possible for some reason, then it is necessary that the new databases be processed more accurately than the previous ones. 4. As bases, you should use surfaces of simple shape (flat, cylindrical and conical), from which, if necessary, you can create a set of bases. In cases where the surfaces of the workpiece do not meet the requirements for bases (i.e., their size, shape and location cannot provide the specified accuracy, stability and ease of processing), artificial bases are created on the workpiece (center holes, technological holes , plates, undercuts, etc.). The basic requirements for securing workpieces in fixtures are as follows. 1. Fastening should ensure reliable contact of the workpiece with the supports of the devices and ensure that the position of the workpiece remains unchanged relative to the technological equipment during processing or when the power is turned off. 2. Clamping of the workpiece should only be used in cases where the processing force or other forces can displace the workpiece (for example, when pulling a keyway, the workpiece is not secured). 3. Fastening forces should not cause large deformations and collapse of the base. 4. Securing and releasing the workpiece must be done with a minimum of time and effort on the part of the worker. The smallest fixing error is provided by clamping devices that create constant clamping force (for example, devices with pneumatic or hydraulic drive). 5. To reduce the clamping error, base surfaces with low roughness should be used; use driven devices; Place workpieces on flat head supports or precision machined support plates. Ticket 13 Clamping mechanisms of fixtures Clamping mechanisms are called mechanisms that eliminate the possibility of vibration or displacement of the workpiece relative to the installation elements under the influence of its own weight and forces arising during the processing (assembly). The main purpose of clamping devices is to ensure reliable contact of the workpiece with the mounting elements, to prevent its displacement and vibration during processing, as well as to ensure correct installation and centering of the workpiece. Calculation of clamping forces The calculation of clamping forces can be reduced to solving the statics problem of equilibrium of a solid body (workpiece) under the action of a system of external forces. On the one hand, gravity and forces arising during processing are applied to the workpiece, on the other hand, the required clamping forces - reaction of the supports. Under the influence of these forces, the workpiece must maintain balance. Example 1. The clamping force presses the workpiece against the fixture supports, and the cutting force that arises during the processing of parts (Figure 2.12a) tends to move the workpiece along the supporting plane. The forces acting on the workpiece are: on the upper plane, the clamping force and the friction force, which prevents the workpiece from shifting; along the lower plane, the reaction forces of the supports (not shown in the figure) are equal to the clamping force and the friction force between the workpiece and the supports. Then the equilibrium equation of the workpiece will be where is the safety factor; – coefficient of friction between the workpiece and the clamping mechanism; – coefficient of friction between the workpiece and the fixture supports. Where Figure 2.12 – Schemes for calculating clamping forces Example 2. The cutting force is directed at an angle to the fastening force (Figure 2.12b). Then the equilibrium equation of the workpiece will be From Figure 2.12b we find the components of the cutting force Substituting, we get Example 3. The workpiece is processed on a lathe and secured in a three-jaw chuck. Cutting forces create torque, tending to rotate the workpiece in the jaws. Frictional forces arising at the points of contact between the jaws and the workpiece create a frictional moment that prevents the workpiece from turning. Then the equilibrium condition of the workpiece will be The cutting torque will be determined by the magnitude of the vertical component of the cutting force Friction moment Elementary clamping mechanisms Elementary clamping devices include the simplest mechanisms used to secure workpieces or acting as intermediate links in complex clamping systems: screw; wedge; eccentric; lever; centering; rack-and-lever. Screw terminals. Screw mechanisms (Figure 2.13) are widely used in devices with manual fastening of workpieces, with a mechanized drive, as well as on automatic lines when using satellite devices. Their advantage is simplicity of design, low cost and high operational reliability. Screw mechanisms are used both for direct clamping and in combination with other mechanisms. The force on the handle required to create the clamping force can be calculated using the formula: where is the average thread radius, mm; – key offset, mm; – thread lead angle; Friction angle in a threaded pair. Wedge mechanism. Wedges are very widely used in clamping mechanisms of devices, this ensures a simple and compact design and operational reliability. The wedge can be either a simple clamping element acting directly on the workpiece, or it can be combined with any other simple element to create combined mechanisms. The use of a wedge in the clamping mechanism provides: an increase in the initial drive force, a change in the direction of the initial force, self-braking of the mechanism (the ability to maintain the clamping force when the force generated by the drive ceases). If the wedge mechanism is used to change the direction of the clamping force, then the wedge angle is usually equal to 45°, and if to increase the clamping force or increase reliability, then the wedge angle is taken equal to 6...15° (self-braking angles). The wedge is used in the following design options for clamps: mechanisms with a flat single-bevel wedge (Figure 2.14b); multi-wedge (multi-plunger) mechanisms; eccentrics (mechanisms with a curved wedge); end cams (cylindrical wedge mechanisms). Figure 2.14a shows a diagram of a two-angle wedge. When clamping a workpiece, the wedge moves to the left under the influence of force. When the wedge moves, normal forces and friction forces arise on its planes (Figure 2.14, b). A significant disadvantage of the considered mechanism is the low coefficient of efficiency (COP) due to friction losses. An example of using a wedge in a fixture is shown in To increase the efficiency of the wedge mechanism, sliding friction on the wedge surfaces is replaced by rolling friction using support rollers (Figure 2.14, c). Multi-wedge mechanisms come with one, two or more plungers. Single- and double-plunger ones are used as clamping ones; multi-piston ones are used as self-centering mechanisms. Eccentric clamps. An eccentric is a connection in one part of two elements - a round disk (Figure 2.15e) and a flat single-bevel wedge. When the eccentric rotates around the axis of rotation of the disk, the wedge enters the gap between the disk and the workpiece and develops a clamping force. The working surface of the eccentrics can be a circle (circular) or a spiral (curvilinear). Cam clamps are the fastest-acting of all manual clamping mechanisms. In terms of speed, they are comparable to pneumatic clamps. The disadvantages of eccentric clamps are: small stroke; limited by the magnitude of eccentricity; increased fatigue of the worker, since when unfastening the workpiece the worker must apply force due to the self-braking property of the eccentric; unreliability of the clamp when the tool operates with shocks or vibrations, as this can lead to self-detachment of the workpiece. Despite these disadvantages, eccentric clamps are widely used in fixtures (Figure 2.15b), especially in small-scale and medium-scale production. To achieve the required fastening force, we determine the maximum moment on the eccentric handle where is the force on the handle, – handle length; – eccentric rotation angle; – friction angles. Lever clamps. Lever clamps (Figure 2.16) are used in combination with other elementary clamps, forming more complex clamping systems. They allow you to change the magnitude and direction of the transmitted force. There are many design varieties of lever clamps, however, they all boil down to three power schemes shown in Figure 2.16, which also provides formulas for calculating the required amount of force to create a workpiece clamping force for ideal mechanisms (without taking into account friction forces). This force is determined from the condition that the moments of all forces relative to the point of rotation of the lever are equal to zero. Figure 2.17 shows the design diagrams of lever clamps. When performing a number of machining operations, the stiffness cutting tool and the entire technological system as a whole turns out to be insufficient. To eliminate deflections and deformations of the tool, various guide elements are used. Basic requirements for such elements: accuracy, wear resistance, replaceability. Such devices are called conductors or conductor bushings and are used for drilling and boring work .
The designs and dimensions of conductor bushings for drilling are standardized (Fig. 11.10). Bushings are permanent (Fig. 11.10 a) and replaceable Rice. 11.10. Designs of conductor bushings: a) permanent; b) replaceable; c) quick-change with a lock (Fig. 11.10 b). Permanent bushings are used in single production when processing with one tool. Replacement bushings are used in serial and mass production. Quick-change bushings with a lock (Fig. 11.10 c) are used when processing holes with several sequentially replaced tools. With a hole diameter of up to 25 mm, the bushings are made of U10A steel, hardened to 60...65. With a hole diameter of more than 25 mm, the bushings are made of steel 20 (20X), followed by case hardening and hardening to the same hardness. If the tools are guided in the bushing not by the working part, but by cylindrical centering sections, then special bushings are used (Fig. 11.11). In Fig. 11.11a shows a bushing for drilling holes on an inclined 15. Adjustment elements of devices. -Setting elements
(height and angular settings) are used to control the position of the tool when setting up the machine.) - Setting elements
, ensuring the correct position of the cutting tool when setting up (adjusting) the machine to obtain the specified dimensions. Such elements are high-rise and angular installations of milling devices, used to control the position of the cutter during setup and sub-adjustment of the machine. Their use facilitates and speeds up the setup of the machine when processing workpieces by automatically obtaining specified dimensions Setting elements perform the following functions
: 1) Prevent tool drift during operation. 2) They give the instrument an exact position relative to the device, these include settings (dimensions), copiers. 3) Perform both functions stated above, these include conductor bushings and guide bushings. Conductor bushings are used when drilling holes with drills, countersinks, and reamers. There are different types of conductor bushings: permanent, quick-change and replaceable. Constant with a collar and without a seal when the hole is processed with one tool. They are pressed into part of the body - the conductor plate H7/n6. Replaceable bushings are used when processing with one tool, but taking into account replacement due to wear. Quick-change notes when a hole in an operation is processed sequentially with several tools. They differ from replaceable ones by a through groove in the collar. Special jig bushings are also used, having a design that corresponds to the characteristics of the workpiece and the operation. Extended bushing Bushing with an inclined end Guide bushings that perform only the function of preventing tool withdrawal are made permanent. For example, on turret machines it is installed in the spindle hole and rotates with it. The hole in the guide bushings is made according to H7. Copiers are used for precise positioning of the tool relative to the fixture when processing curved surfaces. Copiers come in overhead and built-in types. The invoices are placed on the workpiece and secured together with it. The guiding part of the tool has continuous contact with the Copier, and the cutting part performs the required profile. Built-in copiers are installed on the device body. A tracing finger is guided along the copier, which, through a specially built-in device in the machine, transmits the corresponding movement to the spindle with the tool for processing the curved profile. Installations are standard and special, high-rise and corner. High-rise installations orient the tool in one direction, angular in 2 directions. Coordination of the tool according to the settings is carried out using standard flat probes with a thickness of 1.3.5 mm or cylindrical probes with a diameter of 3 or 5 mm. The installations are located on the body of the device away from the workpiece, taking into account the penetration of the tool, and are secured with screws and fixed with pins. The probe used to adjust the tool for installation on the assembly drawing of the device is indicated in the technical requirements, and is also allowed graphically. To set (adjust) the position of the machine table together with the device relative to the cutting tool, special installation templates are used, made in the form of plates, prisms and squares of different shapes. The units are fixed to the body of the device; their reference surfaces should be located below the workpiece surfaces to be processed so as not to interfere with the passage of the cutting tool. Most often, installations are used when processing on milling machines configured to automatically obtain dimensions of a given accuracy. There are high-rise and corner installations. The first serve to correctly position the part relative to the cutter in height, the second - both in height and in the lateral direction. Manufactured from steel 20X, carburized to a depth of 0.8 - 1.2 mm, followed by hardening to a hardness of HRC 55...60 units. Setting elements for cutting tools (example)
Comprehensive production research into the accuracy of operation of existing automatic lines, experimental research and theoretical analysis should provide answers to the following basic questions in the design of technological processes for the production of body parts on automatic lines: a) justification for the choice of technological methods and the number of sequentially performed transitions for processing the most critical surfaces of parts, taking into account the specified accuracy requirements b) establishing the optimal degree of concentration of transitions in one position, based on loading conditions and the required processing accuracy c) selection of installation methods and schemes when designing installation elements of automatic line devices to ensure processing accuracy d) recommendations for the use and design of automatic line units, providing direction and fixation of cutting tools in connection with the requirements for processing accuracy e) selection of methods for setting machines to the required dimensions and selection of control means for reliable maintenance of the adjustment size f) justification of requirements for the accuracy of machines and for the accuracy of assembling an automatic line according to parameters that directly affect accuracy processing g) justification of requirements for the accuracy of black workpieces in connection with the accuracy of their installation and clarification during processing, as well as the establishment of standard values for calculating allowances for processing h) identification and formation of methodological provisions for accuracy calculations when designing automatic lines. 16. Pneumatic drives. Purpose and requirements for them.
A pneumatic drive, like a hydraulic drive, is a kind of “pneumatic insert” between the drive motor and the load (machine or mechanism) and performs the same functions as a mechanical transmission (gearbox, belt drive, crank mechanism, etc.). The main purpose of the pneumatic drive
, as well as a mechanical transmission, - transformation of the mechanical characteristics of the drive motor in accordance with the requirements of the load (transformation of the type of movement of the motor output link, its parameters, as well as regulation, overload protection, etc.). Mandatory elements of a pneumatic drive are a compressor (pneumatic energy generator) and a pneumatic motor Depending on the nature of the movement of the output link of the pneumatic motor (the shaft of the pneumatic motor or the rod-pneumatic cylinder), and, accordingly, the nature of the movement of the working element, the pneumatic drive can be rotary or translational. Pneumatic actuators with translational motion are most widely used in technology. Operating principle of pneumatic machines
In general terms, energy transfer in a pneumatic drive occurs as follows: 1. The drive motor transmits torque to the compressor shaft, which imparts energy to the working gas. 2. The working gas, after special preparation, flows through pneumatic lines through control equipment into the pneumatic motor, where pneumatic energy is converted into mechanical energy. 3. After this, the working gas is released into the environment, in contrast to a hydraulic drive, in which the working fluid is returned through hydraulic lines either to the hydraulic tank or directly to the pump. Many pneumatic machines have their design analogues among volumetric hydraulic machines. In particular, axial piston pneumatic motors and compressors, gear and vane pneumatic motors, pneumatic cylinders are widely used... Typical pneumatic drive diagram Typical pneumatic drive diagram: 1 - air intake; 2 - filter; 3 - compressor; 4 - heat exchanger (refrigerator); 5 - moisture separator; 6 - air collector (receiver); 7 - safety valve; 8- Throttle; 9 - oil sprayer; 10 - pressure reducing valve; 11 - throttle; 12 - distributor; 13 pneumatic motor; M - pressure gauge. Air enters the pneumatic system through the air intake. The filter cleans the air in order to prevent damage to drive elements and reduce their wear. The compressor compresses the air. Since, according to Charles’s law, the air compressed in the compressor has a high temperature, before supplying the air to consumers (usually air motors), the air is cooled in a heat exchanger (in a refrigerator). To prevent icing of pneumatic motors due to the expansion of air in them, as well as to reduce corrosion of parts, a moisture separator is installed in the pneumatic system. The receiver serves to create a supply of compressed air, as well as to smooth out pressure pulsations in the pneumatic system. These pulsations are due to the operating principle of volumetric compressors (for example, piston compressors), which supply air into the system in portions. In an oil sprayer, lubricant is added to the compressed air, thereby reducing friction between the moving parts of the pneumatic drive and preventing them from jamming. A pressure reducing valve must be installed in the pneumatic drive, ensuring the supply of compressed air to the pneumatic motors at constant pressure. The distributor controls the movement of the output links of the air motor. In an air motor (pneumatic motor or pneumatic cylinder), the energy of compressed air is converted into mechanical energy. Pneumatic actuators are equipped with:
1. stationary devices mounted on tables of milling, drilling and other machines; 2. rotating devices - chucks, mandrels, etc. 3) devices installed on rotating and dividing tables for continuous and positional processing. Single- and double-acting pneumatic chambers are used as the working body. With double action, the piston is moved in both directions by compressed air. With one-sided action, the piston is moved by compressed air when securing the workpiece, and by a spring when unfastening it. To increase the fastening force, two and three-piston cylinders or two and three-chamber air chambers are used. In this case, the clamping force increases by 2... 3 times An increase in the fastening force can be achieved by integrating amplifier levers into the pneumatic drive. It is necessary to note some advantages of pneumatic drives of devices. Compared to a hydraulic drive, it is clean; there is no need to have a hydraulic station for each device if the machine on which the device is installed is not equipped with a hydraulic station. The pneumatic drive is characterized by its speed of action; it surpasses not only manual, but many mechanized drives. If, for example, the flow rate of oil under pressure in the pipeline of a hydraulic device is 2.5...4.5 m/sec, the maximum possible is 9m/sec, then the air, being at a pressure of 4...5 MPa, spreads through pipelines at speeds of up to 180 m/sec or more. Therefore, within 1 hour it is possible to carry out up to 2500 operations of the pneumatic actuator. The advantages of a pneumatic drive include the fact that its performance does not depend on fluctuations in ambient temperature. The big advantage is that the pneumatic drive provides a continuous action of the clamping force, as a result of which this force can be significantly less than with a manual drive. This circumstance is very important when processing thin-walled workpieces that are prone to deformation during fastening. Advantages · unlike a hydraulic drive, there is no need to return the working fluid (air) back to the compressor; · lower weight of the working fluid compared to a hydraulic drive (relevant for rocket science); · lower weight of actuators compared to electric ones; · the ability to simplify the system by using a compressed gas cylinder as an energy source; such systems are sometimes used instead of squibs; there are systems where the pressure in the cylinder reaches 500 MPa; · simplicity and efficiency due to the low cost of working gas; · response speed and high rotation speeds of pneumatic motors (up to several tens of thousands of revolutions per minute); · fire safety and neutrality of the working environment, ensuring the possibility of using a pneumatic drive in mines and chemical plants; · in comparison with a hydraulic drive - the ability to transmit pneumatic energy over long distances (up to several kilometers), which allows the use of a pneumatic drive as a main drive in mines and mines; · unlike a hydraulic drive, a pneumatic drive is less sensitive to changes in ambient temperature due to the lower dependence of efficiency on leaks of the working medium (working gas), therefore changes in the gaps between parts of pneumatic equipment and the viscosity of the working medium do not have a serious impact on the operating parameters of the pneumatic drive; this makes the pneumatic drive convenient for use in hot shops of metallurgical enterprises. Flaws · heating and cooling of the working gas during compression in compressors and expansion in pneumatic motors; this disadvantage is due to the laws of thermodynamics, and leads to the following problems: · possibility of freezing of pneumatic systems; · condensation of water vapor from the working gas, and therefore the need to dry it; · high cost of pneumatic energy compared to electrical energy (about 3-4 times), which is important, for example, when using a pneumatic drive in mines; · even lower efficiency than that of a hydraulic drive; · low operating accuracy and smooth operation; · the possibility of explosive rupture of pipelines or industrial injuries, due to which small working gas pressures are used in an industrial pneumatic drive (usually the pressure in pneumatic systems does not exceed 1 MPa, although pneumatic systems with a working pressure of up to 7 MPa are known - for example, in nuclear power plants), and, as a result, the forces on the working parts are significantly less compared to a hydraulic drive). Where there is no such problem (on rockets and airplanes) or the size of the systems is small, pressures can reach 20 MPa and even higher. · to regulate the amount of rotation of the actuator rod, it is necessary to use expensive devices - positioners.
Collets They are split spring sleeves, the design varieties of which are shown in Fig. 74 (α - with a tension tube; 6 - with a spacer tube; c - vertical type). They are made from high-carbon steels, for example, U10A, and are heat treated to a hardness of HRC 58...62 in the clamping part and to a hardness of HRC 40...44 in the tail parts. Collet cone angle α = 30…40°. At smaller angles, the collet may jam.
Cam lock(Fig. 77, d) consists of a wheel shaft 2 on which an eccentric 3 is jammed. The shaft is driven into rotation by a ring 1 attached to the lock handle; the ring rotates in the housing bore 4, the axis of which is displaced from the shaft axis by a distance e. When the handle rotates in reverse, transmission to the shaft occurs through pin 5. During the fastening process, ring 1 is wedged between the eccentric and the housing.
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Figure 2.14, d.
Pneumatic drive (pneumatic drive)- a set of devices designed to drive parts of machines and mechanisms using the energy of compressed air.