Machine clamping devices
TO category:
Metal cutting machines
Machine clamping devices
The process of feeding automatic machines with workpieces is carried out with close interaction between loading devices and automatic clamping fixtures. In many cases, automatic clamping devices are part of the machine design or an integral part of it. Therefore, despite the existence of special literature devoted to clamping devices, it seems necessary to briefly dwell on some characteristic designs,
The moving elements of automatic clamping devices receive movement from corresponding controlled drives, which can be mechanical controlled drives receiving movement from the main drive of the working body or from an independent electric motor, cam drives, hydraulic, pneumatic and pneumohydraulic drives. The individual moving elements of the clamping devices can receive movement from both a common and several independent drives.
Consideration of designs special devices, which are mainly determined by the configuration and dimensions of the specific workpiece, are not included in the scope of this work, and we will limit ourselves to familiarizing ourselves with some clamping devices for general purposes.
Clamping chucks. Available big number designs of self-centering chucks in most cases with piston hydraulic and pneumatic drives, which are used on lathes, turrets and grinding machines. These chucks, while providing reliable clamping and good centering of the workpiece, have a low consumption of jaws, which is why, when moving from processing one batch of parts to another, the chuck must be rebuilt and ensure high precision centering process the centering surfaces of the cams in place; in this case, hardened cams are ground, and raw cams are turned or bored.
One of the common designs of a chuck with a pneumatic piston drive is shown in Fig. 1. The pneumatic cylinder is secured with an intermediate flange at the end of the spindle. The air supply to the pneumatic cylinder is carried out through an axle box sitting on rolling bearings on the shank of the cylinder cover. The cylinder piston is connected by a rod to the clamping mechanism of the cartridge. The pneumatic chuck is attached to a flange mounted on the front end of the spindle. The head, attached to the end of the rod, has inclined grooves into which the L-shaped protrusions of the cams fit. When the head moves forward together with the rod, the cams move closer together, and when moving backward, they diverge.
On the main jaws, which have T-shaped grooves, overhead jaws are fixed, which are installed in accordance with the diameter of the clamped surface of the workpiece.
Thanks to the small number of intermediate links that transmit movement to the cams, and the significant size of the rubbing surfaces, cartridges of the described design have relatively high rigidity and durability.
Rice. 1. Pneumatic chuck.
A number of pneumatic chuck designs use lever gears. Such cartridges have less rigidity and, due to the presence of a number of hinged joints, wear out faster.
Instead of a pneumatic cylinder, a pneumatic diaphragm drive or a hydraulic cylinder can be used. Cylinders rotating with the spindle, especially when high number spindle revolutions require careful balancing, which is a disadvantage of this design option.
The piston drive can be mounted stationary coaxially with the spindle, and the cylinder rod is connected to the clamping rod by a coupling that ensures free rotation of the clamping rod together with the spindle. The fixed cylinder rod can also be connected to the clamping rod by a system of intermediate mechanical transmissions. Such schemes are applicable if there are self-braking mechanisms in the drive of the clamping device, since otherwise the spindle bearings will be loaded with significant axial forces.
Along with self-centering chucks, two-jaw chucks with special jaws that receive movement from the above drives and special chucks are also used.
Similar drives are used when securing parts to various expanding mandrels.
Collet clamping devices. Collet clamping devices are a design element of turret machines and automatic lathes designed for the manufacture of parts from rods. At the same time, they are also widely used in special clamping devices.
Rice. 2. Collet clamping devices.
In practice, there are three types of collet clamping devices.
The collet, which has several longitudinal cuts, is centered with its rear cylindrical tail in the spindle hole, and with its front conical tail in the cap hole. When clamping, the pipe moves the collet forward and its front conical part fits into the conical hole of the spindle cap. In this case, the collet is compressed and clamps the rod or workpiece. This type of clamping device has a number of significant disadvantages.
The centering accuracy of the workpiece is largely determined by the coaxiality of the conical surface of the cap and the axis of rotation of the spindle. To do this, it is necessary to achieve coaxiality of the conical hole of the cap and its cylindrical centering surface, coaxiality of the centering collar and the axis of rotation of the spindle, and a minimum gap between the centering surfaces of the cap and the spindle.
Since fulfilling these conditions presents significant difficulties, collet devices of this type do not provide good centering.
In addition, during the clamping process, the collet, moving forward, grabs the rod, which moves along with the collet, which can
lead to changes in the dimensions of the processed parts along the length and to the appearance of large pressures on the stop. In practice, there are cases when a rotating rod, pressed with great force against a stop, is welded to the latter.
The advantage of this design is the possibility of using a small diameter spindle. However, since the diameter of the spindle is largely determined by other considerations and primarily by its rigidity, this circumstance in most cases is not significant.
Due to these disadvantages, this version of the collet clamping device is of limited use.
The collet has a reverse cone, and when the material is clamped, the pipe pulls the collet into the spindle. This design ensures good centering, since the centering cone is located directly in the spindle. The disadvantage of the design is that the material moves along with the collet during the clamping process, which leads to a change in the dimensions of the workpiece, but does not cause any axial loads on the stop. Some disadvantage is also the weakness of the section in place threaded connection. The spindle diameter increases slightly compared to the previous version.
Due to the noted advantages and simplicity of design, this option is widely used on turret machines and multi-spindle automatic lathes, the spindles of which must have a minimum diameter.
The option shown in Fig. 2, c, differs from the previous one in that during the clamping process the collet, abutting the front end surface against the cap, remains motionless, and the sleeve moves under the action of the pipe. The conical surface of the sleeve is pushed onto the outer conical surface of the collet, and the latter is compressed. Since the collet remains motionless during the clamping process, with this design there is no displacement of the processed rod. The sleeve has good centering in the spindle, and ensuring the alignment of the inner conical and outer centering surfaces of the sleeve does not present technological difficulties, due to which this design ensures fairly good centering of the processed rod.
When the collet is released, the pipe is retracted to the left and the sleeve moves under the action of the spring.
To ensure that the friction forces arising during the clamping process on the end surface of the collet blades do not reduce the clamping force, the end surface is given a conical shape with an angle slightly greater than the friction angle.
This design is more complex than the previous one and requires an increase in the spindle diameter. However, due to the noted advantages, it is widely used on single-spindle machines, where an increase in the spindle diameter is not significant, and on a number of models of turret machines.
The sizes of the most common collets are standardized by the corresponding GOST. Large collets are made with replaceable jaws, which allows you to reduce the number of collets in the set and, when the jaws wear out, replace them with new ones.
The surface of the jaws of collets operating under heavy loads has a notch, which ensures the transfer of large forces to the clamped part.
Clamping collets are made from steels U8A, U10A, 65G, 9ХС. The working part of the collet is hardened to a hardness of HRC 58-62. Tail
the part is tempered to a hardness of HRC 38-40. Case-hardened steels are also used for the manufacture of collets, in particular steel 12ХНЗА.
The pipe moving the clamping collet itself receives movement from one of the listed types of drives through one or another system of intermediate gears. Some designs of intermediate gears for moving the clamping pipe are shown in Fig. IV. 3.
The clamping tube receives movement from the crackers, which are part of the bushing with a protrusion that fits into the groove of the spindle. The crackers rest on the tail protrusions of the clamping tube, which hold them in the required position. The crackers receive movement from levers, the L-shaped ends of which fit into the end recess of sleeve 6 sitting on the spindle. When the collet is clamped, the sleeve moves to the left and, acting with its inner conical surface on the ends of the levers, turns them. The rotation occurs relative to the points of contact of the L-shaped protrusions of the levers with the recess of the bushing. In this case, the heels of the levers press on the crackers. The drawing shows the mechanisms in the position corresponding to the end of the clamp. In this position, the mechanism is closed, and the bushing is unloaded from axial forces.
Rice. 3. Clamping tube movement mechanism.
The clamping force is adjusted using nuts that move the sleeve. To avoid the need to increase the diameter of the spindle, a threaded ring is mounted on it, which abuts against the half rings that fit into the groove of the spindle.
Depending on the diameter of the clamping surface, which can vary within a tolerance, the clamping tube will occupy different positions in the axial direction. Deviations in the position of the pipe are compensated by deformation of the levers. In other designs, special spring compensators are introduced.
This option is widely used on single-spindle automatic lathes. There are numerous design modifications, differing in the shape of the levers.
In a number of designs, the levers are replaced by propping balls or rollers. At the end of the clamping pipe, a flange sits on a thread. When the collet is clamped, the flange along with the pipe moves to the left. The flange receives movement from the sleeve acting through the roller on the disk. As the case moves to the left, its inner conical surface causes the barrel rollers to move toward the center. In this case, the rollers, moving along the conical surface of the washer, shift to the left, moving the disk and flange with the clamping pipe in the same direction. All parts are mounted on a bushing mounted at the end of the spindle. The clamping force is adjusted by screwing the flange onto the pipe. In the required position, the flange is locked using a lock. The mechanism can be equipped with an elastic compensator in the form of disc springs, which allows it to be used for clamping rods with large diameter tolerances.
The movable sleeves that perform clamping receive movement from the cam mechanisms of automatic lathes or from piston drives. The clamping tube can also be directly connected to the piston drive.
Drives of clamping devices of multi-position machines. Each of the clamping fixtures of a multi-station machine may have its own drive, usually a piston drive, or the moving elements of the clamping fixture may be driven by a drive installed at the loading position. In the latter case, the clamping mechanisms that fall into the loading position are connected to the drive mechanisms. At the end of the clamp, this connection is terminated.
The latter option is widely used on multi-spindle automatic lathes. In the position in which the rod is fed and clamped, a slider with a protrusion is installed. When the spindle block is rotated, the protrusion enters the annular groove of the movable sleeve of the clamping mechanism and, at appropriate moments, moves the sleeve in the axial direction.
A similar principle can in some cases be used to move the moving elements of clamping devices installed on multi-position tables and drums. The earring is clamped between the fixed and movable prisms of a clamping device mounted on a multi-position table. The prism receives movement from a wedge-bevel slide. When clamped, the plunger, on which the gear rack is cut, moves to the right. Through the toothed gear, the movement is transmitted to the slider, which moves the prism to the prism using a wedge bevel. When the clamped part is released, the plunger moves to the right, which is also connected to the slider by a gear.
The plungers can be driven by piston actuators mounted in the loading position or by corresponding cam links. Clamping and release of the part can also be done while the table is rotating. When clamping, a plunger equipped with a roller runs against a stationary fist installed between the loading and first working positions. When released, the plunger runs into the fist located between the last working and loading positions. The plungers are located in different planes. To compensate for deviations in the dimensions of the clamped part, elastic compensators are introduced.
It should be noted that such simple solutions are not used enough when designing clamping fixtures for multi-position machines when processing small parts.
Rice. 4. Multi-position machine clamping device, powered by a drive installed in the loading position.
If there are individual piston motors for each of the clamping devices of the multi-station machine, compressed air or pressurized oil must be supplied to the rotary table or drum. The device for supplying compressed air or oil is similar to the rotating cylinder device described above. Application of rolling bearings in in this case unnecessary, since the rotation speed is low.
Each fixture may have an individual control valve or spool, or a common distribution device may be used for all fixtures.
Rice. 5. Distribution device for piston drives of clamping devices of a multi-position table.
Individual taps or distribution devices switched by auxiliary drives installed in the loading position.
The general switchgear sequentially connects the piston drives of the jigs as the table or drum rotates. An approximate design of such a distribution device is shown in Fig. 5. The housing of the distribution device, installed coaxially with the axis of rotation of the table or drum, rotates along with the latter, and the spools, together with the axis, remain stationary. The spool controls the supply of compressed air to the cavities, and the spool controls the supply of compressed air to the cavities of the clamping cylinders.
Compressed air enters through the channel into the space between the spools and is directed with the help of the latter into the corresponding cavities of the clamping cylinders. Exhaust air escapes into the atmosphere through openings.
Compressed air enters the cavity through the hole, arc groove and holes. As long as the holes of the corresponding cylinders coincide with the arc groove, compressed air enters the cavities of the cylinders. When, during the next rotation of the table, the hole of one of the cylinders is aligned with the hole, the cavity of this cylinder will be connected to the atmosphere through an annular groove, a channel, an annular groove and a channel.
The cavities of those cylinders into which compressed air enters must be connected to the atmosphere. The cavities are connected to the atmosphere through channels, arc groove, channels, annular groove and hole.
Compressed air must enter the cavity of the cylinder located in the loading position, which is supplied through the hole and channels.
Thus, when the multi-position table is rotated, the compressed air flows are automatically switched.
A similar principle is used to control the flow of oil supplied to the clamping devices of multi-position machines.
It should be noted that similar distribution devices are also used on continuous processing machines with rotating tables or drums.
Principles for determining the forces acting in clamping devices. Clamping fixtures are usually designed in such a way that the forces generated during the cutting process are absorbed by the stationary elements of the fixture. If certain forces arising during the cutting process are perceived by moving elements, then the magnitude of these forces is determined based on the equations of friction statics.
The method for determining the forces acting in the lever mechanisms of collet clamping devices is similar to the method used to determine the activation forces of friction clutches with lever mechanisms.
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 operate on the principle of supplying 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 over pneumatic and hydraulic ones: they have high labor force, 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 typical designs of clamping devices are shown in Fig. 5.
Figure 5 Clamping device diagrams:
A- using a clip; 6 - swinging lever; V- self-centeringprisms
The purpose of clamping devices is to ensure reliable contact of the workpiece with the installation elements and to prevent its displacement and vibration during processing. Figure 7.6 shows some types of clamping devices.
Requirements for clamping elements:
Reliability in operation;
Simplicity of design;
Ease of maintenance;
Should not cause deformation of workpieces and damage to their surfaces;
The workpiece should not be moved during its fastening from the installation elements;
Fastening and detaching workpieces must be done with minimum cost labor and time;
The clamping elements must be wear-resistant and, if possible, replaceable.
Types of clamping elements:
Clamping screws, which are rotated with keys, handles or handwheels (see Fig. 7.6)
Fig.7.6 Types of clamps:
a – clamping screw; b – screw clamp
Fast acting clamps shown in fig. 7.7.
Fig.7.7. Types of quick release clamps:
a – with a split washer; b – with a plunger device; c – with folding stop; g – s lever device
Eccentric clamps, which are round, involute and spiral (along the Archimedes spiral) (Fig. 7.8).
Fig.7.8. Types of eccentric clamps:
a – disk; b – cylindrical with an L-shaped clamp; g – conical floating.
Wedge clamps– the wedging effect is used and is used as an intermediate link in complex clamping systems. At certain angles, the wedge mechanism has the property of self-braking. In Fig. Figure 7.9 shows the calculated diagram of the action of forces in the wedge mechanism.
Rice. 7.9. Calculation diagram of forces in the wedge mechanism:
a- one-sided; b – double-skewed
Lever Clamps used in combination with other clamps to form more complex clamping systems. Using the lever, you can change both the magnitude and direction of the clamping force, as well as simultaneously and uniformly secure the workpiece in two places. In Fig. Figure 7.10 shows a diagram of the action of forces in lever clamps.
Rice. 7.10. Diagram of the action of forces in lever clamps.
Collets They are split spring sleeves, the varieties of which are shown in Fig. 7.11.
Rice. 7. 11. Types of collet clamps:
a – with a tension tube; b – with a spacer tube; c – vertical type
Collets ensure concentricity of workpiece installation within 0.02...0.05 mm. The base surface of the workpiece for collet clamps should be processed according to accuracy classes 2…3. Collets are made of high-carbon steels of type U10A with subsequent heat treatment to a hardness of HRC 58...62. Collet cone angle d = 30…40 0 . At smaller angles, the collet may jam.
Expanding mandrels, the types of which are shown in Fig. 7.4.
Roller lock(Fig. 7.12)
Rice. 7.12. Types of roller locks
Combination clamps– combination of elementary clamps various types. In Fig. 7.13 shows some types of such clamping devices.
Rice. 7.13. Types of combined clamping devices.
Combination clamping devices are operated manually or by power devices.
Guide elements of devices
When performing some operations machining(drilling, boring) rigidity of the cutting tool and technological system in general it turns out to be insufficient. To eliminate elastic pressing of the tool relative to the workpiece, guide elements are used (guide bushings when boring and drilling, copiers when processing shaped surfaces, etc. (see Fig. 7.14).
Fig.7.14. Types of conductor bushings:
a – constant; b – replaceable; c – quick-change
Guide bushings are made of steel grade U10A or 20X, hardened to a hardness of HRC 60...65.
Guide elements of devices - copiers - are used when processing shaped surfaces complex profile, whose task is to guide the cutting tool along the processed surface of the workpiece to obtain the specified accuracy of the trajectory of their movement.
MINISTRY OF EDUCATION AND SCIENCE OF UKRAINE
Donbass State Academy of Construction
and architecture
METHODOLOGICAL INSTRUCTIONS
for practical classes in the course "Technological Fundamentals of Mechanical Engineering" on the topic "Calculation of Devices"
Minutes No. of 2005 were approved at a meeting of the department "Cars and Automotive Industry"
Makeevka 2005
Methodological instructions for practical classes in the course "Technological fundamentals of mechanical engineering" on the topic "Calculation of devices" (for students of specialty 7.090258 Automobiles and automotive industry) / Comp. D.V. Popov, E.S. Savenko. - Makeevka: DonGASA, 2002. -24 p.
Basic information about machine tools, design, main elements are presented, and a methodology for calculating devices is presented.
Compiled by: D.V. Popov, assistant,
E.S. Savenko, assistant.
Responsible for the release S.A. Gorozhankin, associate professor
Devices4
Elements of devices5
Installation elements of devices6
Clamping elements of fixtures9
Calculation of forces for securing workpieces12
Devices for guiding and determining the position of 13 cutting tools
Housings and auxiliary elements of devices14
General methodology for calculating devices15
Calculation of jaw chucks using the example of turning16
Literature19
Applications20
DEVICES
All devices based on technological characteristics can be divided into the following groups:
1. Machine tools for installing and securing workpieces, depending on the type of machining, are divided into devices for turning, drilling, milling, grinding, multi-purpose and other machines. These devices communicate the workpiece with the machine.
2. Machine tools for installing and securing the working tool (they are also called auxiliary tools) communicate between the tool and the machine. These include cartridges for drills, reamers, taps; multi-spindle drilling, milling, turret heads; tool holders, blocks, etc.
Using the devices of the above groups, the machine-workpiece-tool system is adjusted.
Assembly devices are used to connect mating parts of a product, used for fastening base parts, ensuring the correct installation of connected elements of a product, preliminary assembly of elastic elements (springs, split rings), etc.;
Control devices are used to check deviations in size, shape and relative position of surfaces, mating of assembly units and products, as well as to control design parameters obtained during the assembly process.
Devices for capturing, moving and turning heavy, and in automated production, GPS and light workpieces and assembled products. Devices are the working parts of industrial robots built into automated production and GPS systems.
There are a number of requirements for gripping devices:
reliability of gripping and holding the workpiece; basing stability; versatility; high flexibility (easy and fast changeover); small overall dimensions and weight. In most cases, mechanical gripping devices are used. Examples of gripping diagrams for various gripping devices are shown in Fig. 18.3. Magnetic, vacuum and elastic chamber gripping devices are also widely used.
All described groups of devices, depending on the type of production, can be manual, mechanical, semi-automatic and automatic, and depending on the degree of specialization - universal, specialized and special.
Depending on the degree of unification and standardization in mechanical engineering and instrument making in accordance with the requirements of the Unified System of Technological Preparation of Production (USTPP), approved
seven standard machine fixture systems.
In the practice of modern production, the following systems of devices have developed.
Universal prefabricated devices (USF) are assembled from finally processed interchangeable standard universal elements. They are used as special reversible short-acting devices. They provide installation and fixation of various parts within the dimensional capabilities of the USP kit.
Special prefabricated devices (SRP) are assembled from standard elements as a result of their additional mechanical processing and are used as special irreversible long-term devices made from reversible elements.
Non-separable special devices (NSD) are assembled using standard parts and assemblies for general purpose as long-term irreversible devices made from irreversible parts and assemblies. They consist of two parts: a unified base part and a replaceable nozzle. The devices of this system are used for manual processing of parts.
Universal non-adjustment devices (UPD) are the most common system in mass production conditions. These devices provide installation and fixation of workpieces of any small and medium-sized products. In this case, the installation of a part is associated with the need for control and orientation in space. Such devices provide a wide range of processing operations.
Universal adjustment devices (UNF) provide installation using special adjustments, fixation of workpieces of small and medium dimensions and performance of a wide range of processing operations.
Specialized adjustment devices (SAD) provide, according to a certain basing scheme with the help of special adjustments, the fixation of parts related in design to carry out a typical operation. All of the listed device systems belong to the unified category.
ELEMENTS OF DEVICES
The main elements of devices are installation, clamping, guides, dividing (rotary), fasteners, housings and mechanized drives. Their purpose is as follows:
installation elements - to determine the position of the workpiece relative to the fixture and the position of the processed surface relative to the cutting tool;
clamping elements - for securing the workpiece;
guide elements - to implement the required direction of movement of the tool;
dividing or rotating elements - to accurately change the position of the workpiece surface being processed relative to the cutting tool;
fastening elements - for connecting individual elements to each other;
housings of devices (as base parts) - for placing all elements of devices on them;
mechanized drives - for automatic securing of the workpiece.
Elements of devices also include gripping devices of various devices (robots, GPS transport devices) for gripping, clamping (unclamping) and moving workpieces being processed or assembled assembly units.
1 Installation elements of devices
Installation of workpieces in fixtures or on machines, as well as assembly of parts includes their basing and fastening.
The need for fastening (force closure) when processing a workpiece in fixtures is obvious. For precise processing of workpieces it is necessary: to carry out its correct location in relation to equipment devices that determine the trajectories of movement of the tool or the workpiece itself;
ensure constant contact of the bases with the reference points and complete immobility of the workpiece relative to the fixture during its processing.
For complete orientation in all cases, when fastening, the workpiece must be deprived of all six degrees of freedom (the six-point rule in basing theory); In some cases, a deviation from this rule is possible.
For this purpose, main supports are used, the number of which must be equal to the number of degrees of freedom that the workpiece is deprived of. To increase the rigidity and vibration resistance of the workpieces being processed, auxiliary adjustable and self-aligning supports are used in the fixtures.
To install a workpiece in a fixture with a flat surface, standardized main supports are used in the form of pins with spherical, notched and flat heads, washers, and support plates. If it is impossible to install the workpiece only on the main supports, auxiliary supports are used. As the latter, standardized adjustable supports in the form of screws with a spherical bearing surface and self-aligning supports can be used.
Figure 1 Standardized supports:
A-e- permanent supports (pins): a- flat surface; b- spherical; V- notched; G- flat with installation in the adapter sleeve; d- support washer; e- base plate; and- adjustable support - self-aligning support
The mating of supports with spherical, notched and flat heads with the body of the device is carried out according to the fit 
or 
. Installation of such supports is also used through intermediate bushings, which are mated with the housing holes according to the fit 
.
Examples of standardized main and auxiliary supports are shown in Figure 1.
To install a workpiece along two cylindrical holes and a flat surface perpendicular to their axes, use
Figure 2.Schemebased on the end and hole:
a – on the high finger; b – on the low finger
standardized flat supports and mounting pins. To avoid jamming of the workpieces when installing them on the fingers along the exact two holes (D7), one of the installation fingers must be cut off and the other cylindrical.
Installation of parts on two fingers and a plane has found wide application in the processing of workpieces on automatic and production lines, multi-purpose machines and in GPS.
Schemes for basing on a plane and holes using mounting fingers can be divided into three groups: on the end and hole (Fig. 2); along the plane, end and hole (Fig. 3); along a plane and two holes (Fig. 4).
Rice. 19.4. Scheme of basing on a plane and two holes
It is recommended to install the workpiece on one finger according to the fit 
or 
, and on two fingers - each 
.
AND 
From Fig. 2 it follows that installing the workpiece along the hole on a long cylindrical uncut pin deprives it of four degrees of freedom (double guide base), and installation on the end deprives it of one degree of freedom (support base). Installing the workpiece on a short pin deprives it of two degrees of freedom (double support base), but the end in this case is an installation base and deprives the workpiece of three degrees of freedom. For complete basing it is necessary to create a force closure, i.e. apply clamping forces. From Fig. 3 it follows that the plane of the base of the workpiece is the installation base, the long hole into which the cut finger with an axis parallel to the plane enters is the guide base (the workpiece is deprived of two degrees) and the end of the workpiece is the support base.
Figure 3. Based onplane, Figure 4 Based on
end and hole of the plane and two holes
In Fig. Figure 4 shows a workpiece that is installed along a plane and two holes. The plane is the installation base. The holes centered with the cylindrical pin are the double support base, and those centered with the cut pin are the support base. The applied forces (shown by the arrow in Fig. 3 and 4) ensure alignment accuracy.
The finger is a double support base, and the cut finger is the support base. The applied forces (shown by the arrow in Fig. 3 and 4) ensure alignment accuracy.
To install workpieces with the outer surface and the end surface perpendicular to its axis, support and mounting prisms (movable and fixed), as well as bushings and cartridges are used.
Elements of fixtures include settings and probes for setting the machine to required size. Thus, standardized settings for cutters on milling machines can be:
high-rise, high-rise end, corner and corner end.
Flat probes are made with a thickness of 3-5 mm, cylindrical ones with a diameter of 3-5 mm with an accuracy of 6th grade (h6) and subjected to hardening 55-60 HRC 3, ground (roughness parameter Ra = 0.63 µm).
The actuating surfaces of all installation elements of devices must have high wear resistance and high hardness. Therefore, they are made from structural and alloy steels 20, 45, 20Х, 12ХНЗА with subsequent carburization and hardening to 55-60 HRC3 (supports, prisms, mounting pins, centers) and tool steels U7 and U8A with hardening to 50-55 HRG, ( supports with a diameter of less than 12 mm; mounting pins with a diameter of less than 16 mm; installations and probes).
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 work area 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 most simple ways increasing 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 must ensure reliable contact workpieces with fixture supports and ensure that the position of the workpiece remains unchanged relative to the technological equipment during processing or during a power outage.
2. Workpiece securing should only be used in cases where the processing force or other forces could displace the workpiece (for example, when pulling 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 the workpiece.
Calculation of clamping forces
The calculation of clamping forces can be reduced to solving a statics problem for equilibrium solid(blanks) under the influence 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 fastening force presses the workpiece against the supports of the device, 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 lathe and is fixed 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 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).
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 double-angled 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
Figure 2.14, d.
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 a large number 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 worker, since when unfastening a 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 shortcomings eccentric clamps widely used in devices (Figure 2.15, b), 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 come down to three power circuits 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 design diagrams lever clamps.
When performing a number of machining operations, the rigidity of the 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 , providing correct position 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 conductor bushings are also used, having a design corresponding to the characteristics of the workpiece and 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 ones serve for correct location parts 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.
Pneumatic drive (pneumatic drive)- a set of devices designed to drive parts of machines and mechanisms using the energy of compressed air.
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 the hydraulic drive, in which working fluid it returns 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 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 high temperature, then before supplying 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 moves in both directions 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 the pneumatic drive include the fact that its performance does not depend on temperature fluctuations environment. The great advantage is that the pneumatic drive provides continuous action of the clamping force, as a result of which this force can be significantly less than with 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 on chemical production;
· 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 deficiency 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 in connection with this 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.
