What defects are needed to write off a lathe. Repair of lathes - general principles

During the operation of the lathe, sooner or later you will encounter some kind of malfunction. The probability of breakdown is especially high if you use a unit with a considerable “mileage” in your work. In this case, you need to be prepared not only for minor malfunctions, but also for the possible need to overhaul the lathe, and this is a very, very costly undertaking.

Fortunately, the design of most units (especially those produced during the Soviet era) is simple enough for you to cope with the repair of a lathe without the involvement of a third-party specialist. Below, using the example of model 1K62, we will consider the most common breakdowns, their causes and methods of elimination. If in practice you encounter the described problems, most likely you will be able to carry out repairs on your own, following the recommendations below.

The main breakdowns, causes and methods for their elimination

The initial cause of most malfunctions in the operation of a lathe is improper operation and maintenance of the equipment. The master should know how to maintain the unit. This will save a lot of money in the future, since the overhaul of lathes is not cheap, even if you repair it yourself.

Experts recommend that before you start working on the machine for the first time, study in detail the operating recommendations and other documentation that comes with the equipment. If you are purchasing a used machine without instructions, then it makes sense to find all the documentation regarding the 1K62 unit or any other model on your own online.

Now that you have learned about the intricacies of operating your "assistant", it is time to study the most common breakdowns and how to fix them. For ease of perception, here are tips for repairing a 1K62 lathe in the form of a list:

• The machine does not turn on. The most common and easiest problem to solve. It is most likely due to the lack of mains voltage. The master is recommended to check the presence and indicators of voltage.
• Unable to shift the gear cluster with the handle, the unit makes a typical slipping sound. This kind of problem is due to the fact that the block is not brought out of the idle position. It is recommended to start the electric motor again and to carry out the inclusion of the gear "freewheel".
• The electric motor spontaneously turns off during operation. Most likely, this triggers a relay that protects the power unit from excessive load. In this case, the master should reduce the intensity of cutting or feed.
• Insufficiently high spindle torque, which does not reach the limit specified in the documentation. The problem may be that the belts are not tight enough. By increasing it, you will increase the torque. Another reason for the manifestation of the problem may be a poorly tightened friction clutch, increasing the tension of which, you will also be able to increase the torque.
• Slow spindle deceleration. In most cases, the cause of this malfunction is insufficient tension on the brake band. By increasing this parameter, you will notice that the braking has become more dynamic.
• The caliper feed amplification does not reach the indicators specified in the documentation. To cope with the problem, experts recommend tightening the overload device spring more tightly.
• The cooling pump is not working. Usually the occurrence of this problem is associated with an insufficiently high level of coolant in the system. Topping it up, in most cases, you will be able to fix the problem. Also, the cause of this problem may be the failure of the fuses. The usual replacement with new ones will solve the problem that has suddenly arisen before you.
• Excessive machine vibration during operation. There may be several reasons for this. The first is the incorrect installation of the unit according to the level. In this case, you need to calibrate the machine. The second possible reason is the wear of the joint of the caliper guides. Tighten the clamping wedges and slats, and most likely the situation will improve. Also, excessive vibrations are often associated with incorrect selection of the cutting mode or with improper sharpening of the cutting tool.
• The workpiece processing accuracy is unsatisfactory. There are four main reasons for this problem. This is the transverse displacement of the tailstock, excessive overhang of the structure fixed in the chuck, insufficiently rigid fixation of the cutter or cartridge holder. In the first case, you need to adjust the position of the headstock, in the second case, you need to press the structure with the center or support it with a steady rest. In the third and fourth cases, you should tighten the cutter holder handle or the chuck holding straps.

Often, a 1K62 lathe needs to be repaired due to a malfunction in the lubrication system. If there is no weak jet of lubricant in the oil indicator, then this indicates that the pump lever stop screw is not set. The master needs to adjust the position of the plunger.

If there is a jet of oil, but it is very weak, then most likely the reason is filter contamination. The problem is solved by banal washing of the filter.

In addition, a malfunction of the plunger pump spring can lead to the complete absence of a lubricant jet in the oil gauge. Replacing the spring will fix the problem. If the lubricant is not supplied to the guide beds, then the reason most likely lies in the contamination of one of the valves of the plunger pump. Again, the repair is a thorough flush.

Results

As you can see, you can repair lathes yourself if you understand how to eliminate basic malfunctions. We hope that the information provided will save you money and a lot of time.

And invented in 650 BC, lathe has undergone revolutionary changes, and is nowadays an integral equipment of any machine-building production. Considering this type of equipment from the point of view of reliability, it should be noted that they are complex technical systems with hard feedbacks, and consist of a mechanical and electrical component, which are characterized by deterioration of technical parameters during operation.

This, first of all, is expressed in a natural change in geometry, as such, i.e. details lathe, subjected to mechanical and erosive influences, change in size over time. As a result, their relative position in space does not correspond to the design documentation, and the parallelism in the design is violated, which, of course, affects the rigidity of the machine as a whole, its individual elements and leads to breakdowns of the lathe.

The most severe physical impact is primarily on the driving elements - hydraulic systems and electric drives. Moreover, precisely hydraulics is the main "sore" place in any lathe. The cause of breakdowns in hydraulics and related systems is quite banal: seals, gaskets and seals are extremely unreliable and leak very quickly. Industrial oil begins to flow, falling on the floor and causing danger to the worker or into the coolant tank. The coolant at the same time thickens, is poorly pumped, as a result of which the tool overheats, has a harder effect on the workpiece, causing overheating and even a breakdown of the electric drive.

In Russian machines of all types, all kinds of backlash, crushing, vibration most often occur, which adversely affect the quality of the processing of the part, or make it impossible for the machine to work.

Sudden loads on the motor during turning work lead to to electrical breakdowns. In addition, the oil being poured does not always meet the requirements (it may be more viscous, including due to cold weather). industrial premises), and, as a result, does not provide lathe high-quality centralized lubrication, increasing the wear of rubbing surfaces, provoking overheating of pumps, jamming and destruction of machine components.

Another cause of breakdowns caused by pressure drop in hydraulic system and which must be voiced, is to loosen the clamping of the part, and this can lead to knocking out the workpiece and an accident. This problem should be solved by sensors and pressure controllers, but they do not always work in a timely manner.

As an example related to malfunctions in the hydraulic system, the production workers called the journalist www.site frequent breakdowns in centerless lathes 9A340F1 and KZh9340, the operation of which is characterized by significant dynamic loads:

• violation of the supply of lubricating oil to the spindle assembly, causes premature destruction of the cuffs in the "Oil-air" systems;
• for the same reason, the destruction of the bearings on the feed rollers can be caused by the fall of the workpiece on the rollers;
• lack of pressure in the clamping hydraulic cylinder, causes the workpiece to scroll in the yew;
• overheating of the oil station due to lack of oil, substandard oil, the presence of random parts between rubbing surfaces.

In the final stage, this can lead to damage to hydraulic pumps and / or pump in the cooling system.

In addition to hydraulics and electric motors, which are a risk zone for performance lathes, attention should be focused on the "driving" mechanics - rolling bearings and gears. As a result of the influence of high frequency vibration possible processes of grazing and cavitation. If, for example, there are defects in the gearbox on the gears, then there is a high probability of grazing and jamming, which can lead to the failure of the corresponding pair.

Studying the special literature, the analyst of the www.site portal nevertheless turned to the workshop to interview specialists involved in the repair of domestic lathes. As it turned out, in Russian machines of all types, all kinds of backlashes, crushing, vibrations most often occur, which adversely affect the quality of the processing of the part, or make it impossible for the machine to work.

Such repairs are simple, as well as the replacement of various bearings, and the adjustment of the coordinates of the machine. More complex ones include restoration measures for the wedge carriage and calipers, as well as for worn screw pairs of the caliper slide drive, tool holder and tailstock lifting drive shaft. For jobs that require significant costs, refer to the correction of the geometry of the lathe as a whole. Quite often in lathes repair the headstock, gearbox, machine apron. In automatic lathes and CNC machines, tool heads often fail and position sensors lose their accuracy.

Maintenance of CNC machines is a set of measures aimed at maintaining machine equipment in working condition and eliminating possible problems. CNC machines are complex devices that provide autonomous or semi-autonomous processing of workpieces with high accuracy.

Due to the complex design, any problem can lead to a deterioration in the accuracy of the task being performed, which will require repair of CNC machines.

Maintenance

Maintenance is carried out when the CNC machine is still in good condition. The purpose of maintenance is to prevent breakdowns.

Maintenance is also required when:

• machine storage;
• transportation;
• preparation for use.

Full service maintenance of the equipment can be provided by the manufacturer. In addition to standard work, maintenance includes checking compliance with the standard for equipping the room in which the unit is used.

At maintenance machine work is carried out by a whole group of professionals, consisting of:

• repairmen;
• electricians;
• electronics specialists;
• operators;
• lubricants.

In the absence of narrow specialists, the work is assigned to the adjuster. Maintenance can be scheduled or unscheduled. If scheduled maintenance is carried out periodically in accordance with operating standards, it will not be necessary to resort to the second type of maintenance. If, during the inspection of the equipment, breakdowns are detected, repairs are needed. The service company can provide it.

Troubleshooting Methods

CNC machines are devices that have a complex system of work. It is difficult to find a malfunction on your own, so this task is handled by service center. There are three ways to accurately detect damage:

• logical;
• practical;
• test.

The first method involves analytical work. It is carried out by specialists who know the device of the CNC machine well. The logical method allows you to analyze the operation of the machine as a whole, and separately and the CNC unit. After that, the slightest inaccuracies will be revealed, on the basis of which it will be possible to determine the cause and eliminate it.

The second method is carried out using a specially designed scheme. The system on the machine is divided into several parts, after which they are separately diagnosed. If a malfunction is detected in some part, it is divided into several more parts. Each of them is also analyzed. This scheme is used until the exact cause of the breakdown is found. Only then will it be possible to choose ways to eliminate it.

The third method is used in production conditions. It involves the use of a special program that analyzes the operation of the unit. When a full analysis is carried out, the program will indicate exactly what problems there are in the operation of the unit and how they can be eliminated. The advantage of this method lies in the rapid troubleshooting without dismantling and transportation of the machine.

Repair types

Repair of CNC machines is of two types: current and capital. The first type involves partial troubleshooting, and the second - a full repair of the device components. Previously, instead of current repairs, medium or small repairs were carried out. But later they were merged in order to provide a better repair. The complex of repair works is divided into three stages:

• restoration of the geometry of the guides, repair of drives, adjustment of parts responsible for the movement of the tool;
• restoration of the electrical system (wiring, sensors, and other details);
• CNC rack repair (boards, controllers, wiring).

Before starting the repair, a defective list must be drawn up. It is the owner of the equipment. Based on the documentation, a complex will be planned repair work. After the repair is completed, the device is tested. The machine is returned to the owner if the problems found are corrected. With a quality repair, it is possible to restore the characteristics of the unit to the indicators corresponding to the technical passport of the device.

In some cases, emergency repair activities are also carried out on machines. It is performed when defects were made in the production of equipment. Also, this type of repair is necessary if the operation of the device has been violated.

Causes

The CNC machine consists of two parts: the instrument itself and the numerical control system. Diagnostics is also carried out separately. First, the machine is examined, and then the CNC system. The most common causes of failure of devices of this type are:

• improperly adjusted nodes and working tools;
• machine overload;
• non-compliance with the norm of operation;
• wear or damage to components;
• improper repair of the unit.

If the check number is incorrectly punched, an error will occur in the punched tape. In this case, it will have to be replaced. If the rules are not taken into account when storing punched tape, or if oil gets on it, it will quickly become faulty. The problem is also solved by replacing it. If moisture, dust, or dirt enters the optical system, the photoreadout will no longer perform its function. You can fix the situation by wiping the lens with alcohol.

A failed tape drive is a more serious problem. It will immediately affect the reading equipment and punched tape. To solve the problem, cleaning, lubricating and adjusting the tape drive is required.

If technical malfunctions occur in a numerical control system, the consequences may be characterized by errors in the operation of the machine equipment.

The problem can be solved by refurbished electronics and the introduction of a new program.

Prevention

Prevention involves the diagnosis of a serviceable unit in order to maintain and identify possible technical malfunctions. Preventive work can be carried out by people with special training. The set of actions includes:

• lubrication of components;
• cleaning the structure from dirt;
• cleaning or replacing air filters and electronic systems.

The last task is carried out with the help of electronics. Lubrication is required for parts that are subjected to the greatest friction during operation. Vaseline or industrial oil 30 is used for lubrication. Along with the machines, there is documentation that indicates how to use them. Malfunctions can occur even if the standard of use is observed.

A very important issue for maintaining the normal quality of work of CNC machines is the choice of the most rational method of troubleshooting.

In practice, three search methods are mainly used.

1. The logical method is based on knowledge of the composition and operation of the equipment, analysis of the issuance of actual information and its comparison with a given control program, knowledge of the procedure for processing information on the nodes and blocks of the device, the correct identification of characteristic and uncharacteristic errors in the control program and malfunctions in CNC devices on the very machine. Based on the analysis of the action of the input and the results of the output information, a logical conclusion is made about the existing defects and ways to eliminate them to ensure the normal operation of the CNC machine.

2. The practical method of troubleshooting is carried out by means of special measuring instruments. In this case, the defective chain is divided into two parts. Then the part in which a malfunction is detected is divided again. And so on - until a faulty board is found that needs to be replaced. After that, a general check of the device is carried out and a conclusion is made about the quality of the CNC system and the machine as a whole.

3. The test method for troubleshooting on CNC machines is applied in the workshop. In this case, the operation of the CNC device as a whole or its individual units is checked, which perform the completed micro-operations by influencing them with the appropriate test programs. The test method allows you to relatively quickly identify the defect and take the necessary measures to eliminate it.

Malfunctions of the input unit with a photoreader, as well as a linear interpolator and a speed setting unit are the most typical for CNC systems used on modern metal-cutting machines. The most common causes of failures in the input unit are the aging of the photodiodes or contamination of the optics of the photoreader and the tape drive.

For the preparation and control of control programs at factories and associations where CNC machines operate, specialized sections equipped with the necessary equipment have been created.

When using CNC machines, there are also increased requirements for the electrical equipment installed on them. It should provide the ability to quickly eliminate interference in the places of their occurrence, as well as be able to reliably control high-current equipment and electric motors by means of weak signals or contacts.

CNC machine tools, unlike conventional machines, are equipped with a separate feed drive for each controlled movement coordinate, which operates from the control system and should provide high positioning accuracy and sufficient speed. For this, high-speed drive motors are used - hydraulic, electro-hydraulic (stepping or servo) and electric. Structural and technological methods ensure the maximum elimination of the gap in the kinematic chain (for example, by replacing conventional screw gearings with ball screw pairs) and reduce friction in the guides to a minimum, select the optimal masses of moving units, etc.

Particular attention should be paid to the care of the hydraulic drive. The type of oil for filling into the hydraulic system must comply with the requirements of the instruction manual for this equipment. The oil must be clean, filtered and homogeneous (it is not recommended to mix different brands of oils). Violation of the tightness of the hydraulic system, leakage and a decrease in the permissible oil level must not be allowed. Before starting the machine, it is necessary to turn on the hydraulic system for a while to warm up the oil.

According to the current situation, all measures for preventive maintenance of equipment and apparatus, as well as for other types of maintenance of CNC machines, should be carried out only by specially trained personnel with the appropriate permit, and the machine operator is prohibited from independently performing any operations on the machine that are not included in his duties. Nevertheless, the operator must not only know when and what activities are provided for by the maintenance schedules of the CNC machine on which he works, but also systematically monitor their implementation in accordance with the established schedules, and also, if necessary, directly participate in them, providing every possible assistance and assistance to maintenance personnel of repairmen.

Taking this into account, it is advisable for production workers servicing CNC machines not only to know the features of these machines and the method for detecting faults on them, given above, but also to familiarize themselves in general terms with characteristic reading errors and methods for their elimination on CNC devices (Table 6) .

Table 6 Reading errors and methods for their elimination when working on CNC machines

Note. Preventive repairs, adjustment and other work on CNC devices can be performed independently only by those specialists and workers who have undergone the necessary training and received the relevant documents.

Defects- deviations from the quality of the material provided for by the technical specifications in terms of chemical composition, structure, continuity, surface condition, mechanical and other properties.

Defects that occur during the operation of equipment can be divided into three groups:

1) wear, scratches, risks, nadir;

2) mechanical damage (cracks, tooth chipping, breakage, bending, twisting);

3) chemical and thermal damage (warping, shells, corrosion).

Most large and medium mechanical defects are detected during external examination. In some cases, the check is carried out with a hammer: a rattling sound when the part is tapped with a hammer indicates the presence of cracks in it. To detect small cracks, various methods of flaw detection can be used. The simplest are capillary methods that allow you to visually determine the presence of cracks. The method of magnetic flaw detection with longitudinal or rotational magnetization is more complicated. Defects located inside the material are determined by fluoroscopic or ultrasonic methods. Ultrasound can also be used to detect cracks.

Wear(wear) - a change in size, shape, mass or state of the surface due to the destruction of the surface layer of the product. The following types of wear are distinguished: permissible, critical, limiting, premature, natural, and many others, the name of which is determined by physical and chemical phenomena or the nature of the distribution over the surface of the part.

Of all the possible types of wear, the main ones in machine tools are mechanical, seizing and oxidative.

At mechanical wear there is abrasion (cutting) of the surface layer of the jointly working parts. It is often exacerbated by the presence of abrasive dust, solid particles, chips, wear products. In this case, the rubbing surfaces are additionally destroyed due to scratches. Mechanical wear occurs at zero and different relative speeds of mating surfaces, in the presence of long-term loads, high specific loads, and a number of other factors. Proper design and processing can significantly reduce this wear.

Seizure wear occurs as a result of the setting of one surface with another, deep pulling out of the material. This happens with insufficient lubrication and significant specific pressure, when molecular forces begin to act. Seizure also occurs at high sliding speeds and high pressures, when the temperature of the rubbing surfaces is high.

Oxidative wear manifests itself in machine parts that are directly affected by water, air, chemicals and directly temperature.

The wear of parts and assembly units can be judged by the nature of their work (for example, noise), surface quality, shape and size of the machined part.

To reduce the wear of the mating surfaces, liquid lubrication (including gas lubrication), rolling friction, a magnetic field and special anti-friction linings, gaskets and materials are used.

Monitoring the wear of critical interfaces of machine tools is necessary to determine the need for repairs, to assess the quality of machine operation, and to develop measures to improve the durability of the machine.

Wear can be measured during operation (especially during scheduled inspections), during periods of scheduled repairs or when testing machines.

There are various methods for measuring wear, which can be divided into the following groups:

1) integral methods, when it is possible to determine only the total wear on the friction surface, without setting the amount of wear at each point of the surface, these include weighing, the use of radioactive isotopes;

2) the method of micrometering, based on measuring the part with a micrometer, indicator or other devices before and after wear; micrometerage, especially measurement using indicator devices, is often used when machine parts are worn out in production conditions; the method does not always give an accurate idea of ​​the shape of the worn surface;

3) the method of "artificial bases" used to assess the wear of the friction surfaces of the base parts of the machine; it consists in the fact that holes of a certain shape are pre-applied on the wear surfaces, which have practically no effect on the change in the friction mode, since their dimensions are small; according to the first method (imprint method), holes 2 are applied to the friction surface either by indentation of a diamond pyramid 1 (Fig. 8.4, a), or a rotating carbide roller 3 (Fig. 8.4, b). The second method, which is called the "wipe" method, more precisely because of the absence of expanded metal.

Rice. 8.4. Forms of prints

4) the surface activation method, as well as the “artificial bases” method, is used in automatic lines due to the large number of controlled equipment and limited access to rubbing surfaces; the essence of the method is that the working sections of guides, spindle assemblies, gear and worm gears, screw gears and other critical mechanisms are subjected to surface activation in cyclotrons by a beam of accelerated charged particles (protons, deuterons, alpha particles); the depth of the activated layer must correspond to the expected value of the linear wear of the part; for large parts, pre-activated special inserts are used. The amount of wear of the activated surfaces is judged by periodically measuring the radiation energy.

The choice of method depends on the purpose of the test and the required measurement accuracy. The allowable wear of the guide beds of screw-cutting and console-milling machines is normalized depending on the required machining accuracy and the dimensions of the part. If the wear of the guides exceeds 0.2 mm, the vibration resistance of the machine is significantly reduced, and although, under the conditions of ensuring the specified accuracy of parts, it is permissible to continue the operation of the machine, it is necessary to stop it for major repairs due to deterioration in the quality of the machined surface (traces of vibration) or loss of productivity.

Permissible wear of the guides of longitudinal planers and longitudinal milling machines is determined by the formula

U max \u003d d (L o / L 1) 2,

where d is the machining error on the machine (tolerance for the part); L o and L 1 - the length of the guides of the bed and the workpiece, respectively.

For flat guides, wear is equal to the distance from some conditional straight line passing through points at the non-worn ends of the guides to the worn surface.

For machines with V-guides or triangular guideways with base angle α permissible wear

U max \u003d dcos α (L o / L 1) 2.

The wear of the frame guides, depending on the mode of operation of the machine and proper operation, is 0.04 ... 0.10 mm or more per year.

The wear of the bed guides of lathes and turrets operating in the conditions of individual and small-scale production is on average about 30% of the wear of the guides of machine tools employed in the conditions of large-scale and mass production.

The main consequence of the wear of the guides of heavy machine tools, such as longitudinal planers, longitudinal milling machines, boring machines, carousels, etc., as well as medium-sized machines with high speeds movement along the guides is a contact setting - jamming. Accompanying it in this category of machine tools is abrasive wear.

To check the guides, universal bridges are used. They are installed on machine guides of various shapes and sizes. With the help of two levels, the straightness and twisting (i.e., deviation from parallelism in the horizontal plane) of the guides are simultaneously checked, and the parallelism of the surfaces is determined with indicators.

The bridge is located approximately in the middle part (along the length) of the frame so that four supports are located on the prismatic part of the guides. Then, levels are fixed on the upper platform with a division value of 0.02 mm per 1000 mm of length and the position of the levels is adjusted using screws so that the bubbles of the main and auxiliary level ampoules are located in the middle between the scales. Next, the device is shifted along the guides and returned to its original place. In this case, the bubbles of the main ampoules should return to their original position. If this does not happen, it is necessary to check the fastening of the columns and thrust bearings.

The guides are checked when the bridge is stopped sequentially through sections equal in length to the distance between the bridge supports. According to the level set along the guides, the non-straightness is determined. The twisting of the surfaces is determined by the level located perpendicular to the guides.

The level readings in micrometers, measured in individual sections, are recorded in the protocol and then a graph of the shape of the guides is built.

On fig. 8.5, a an example of checking the guides of a triangular profile (often found on the beds of turret lathes) is given. Indicator 4 determines the parallelism of the left guide base plane; according to level 2, located across the guides, their twisting is established. The second side of the right guide can be checked by level by installing support 3 on this side, or, without moving the support, by the indicator (in the figure this is shown by a dashed line).

Rice. 8.5. Guide test patterns

On fig. 8.5, b shows the installation of a fixture on the bed of a lathe to check with indicator 4 the parallelism of the middle guides of the base surface, i.e. from the plane under the rack and check the helical twisting level 2.

To check the beds of grinding and some other machines with a similar combination of guides (Fig. 8.5, v) for straightness and twisting, four supports 1 are placed between the generatrix of the guide V-profile, and one support 3 - on the opposite flat guide. Testing is carried out at level 2.

When the dimensions of the guides do not allow placing devices between them that form all the supports (Fig. 8.5, G), then only two supports 1 are installed.

On fig. 8.5, d supports 1 are moved apart in accordance with the size of the prismatic guide frame.

When checking the flat guides of the bed (Fig. 8.5, e) two of the supports 1 abut against the side surface, the other two and support 3 are placed on horizontal planes. This ensures stable level 2 readings.

Using a universal bridge, using various holders for mounting the indicator, you can control the parallelism of the axis of the lead screw and the guides of the lathe bed. The scheme for checking the parallelism of the axis of the screw of the jig boring machine with the guides of the bed is shown in fig. 8.6.

Rice. 8.6. Scheme for checking the parallelism of the axis of the screw of the jig boring machine with the guides of the frame

The design of the universal bridge is simple, so setting up the device takes no more than 5 minutes. It is handled by a medium-skilled locksmith.

Corner bridge. Angular bridges are used to check guides located in different planes (for example, the guide surfaces of the traverse of a coordinate boring machine model KR-450).

On fig. 8.7 shows a diagram of such a device for measuring with an angular bridge.

The short arm 3 is located perpendicular to the elongated 5. The roller 1 is fixed, and the roller 4 can be moved and installed depending on the size of the guide. When this rollers 1 and 4 are placed in V-shaped guides or cover the surface of the prismatic guide. The support 7 is reinstalled along the groove of the shoulder 5 and adjusted in height.

An adjustable block 2 is installed on the shoulder 3 along the guides. level and check their straightness. The twisting is checked when the level is perpendicular to the guides. Using indicators 6 determine the non-parallelism of the surfaces, as well as the non-parallelism of the axis of the screw to the guides.

It is convenient to check the parallelism of the guides of the dovetail form, as well as other forms, using special and universal devices equipped with indicators.

The guide can be checked for parallelism with indicator devices only after the preparation of the base ones. Shown in Fig. 8.8 A fixture is used to check the parallelism of male and female guides. various forms and dimensions with contact on the upper or lower surfaces.

Rice. 8.8. Schemes for checking the dovetail guides

The device consists of a beam 3 with a hinged lever 1 and an adjustable measuring rod 8 , stands 2 with indicator and interchangeable swivel support 5 with control roller 6 . The support 5 can be installed at various angles and on any part of the bar 3 along its groove. The position of the support 5 is fixed with a bolt 4 .

When checking the guides of the dovetail form with contacts along the lower plane, a replaceable support is selected with a roller diameter that provides contact approximately in the middle of the height of the inclined plane (Fig. 8.8, a and v). Support 9 is adjusted along its groove and also fixed with a bolt (not shown in the figure). On the cylindrical surface of the measuring rod there is a scale, which determines the value of the division of the indicator, depending on the difference in distances a and b(Fig. 8.8, a). In this case, the value of one division of the indicator scale is 0.005 ... 0.015 mm , which must be taken into account when measuring.

Various methods are used to restore parts (Table 8.1). When choosing a restoration method, it is necessary to assign a repair, repair free or repair regulated size.

Table 8.1

Detail recovery methods

Repair is the size to which the worn surface is processed when restoring the part. Free repair size - a size whose value is not set in advance, but is obtained directly during processing, when wear marks are removed and the shape of the part is restored. The corresponding size of the mating part is adjusted to the resulting size by the individual fit method. At the same time, it is impossible to pre-manufacture spare parts in a finished form. Regulated repair size - a predetermined size to which the worn surface is processed. At the same time, spare parts can be manufactured in advance, the repair is accelerated.

Methods for restoring parts during repairs are discussed in detail in the technical literature, some of them are shown in the diagrams in Fig. 8.9. The use of one or another repair method is dictated by the technical requirements for the part and is due to economic feasibility, depends on the specific conditions in production, on the availability necessary equipment and repair times.

Widespread for the restoration of parts received methods using polymer materials. This requires injection molding equipment that is simple and materials such as polyamides that have sufficient adhesiveness to metal and good mechanical properties.

In a bored bushing (Fig. 8.9, a) make radial holes, then the sleeve is heated, placed on the press table, pressed against the nozzle (Fig. 8.9, b) and pressed. The restored sleeve is shown in fig. 8.9, v.

To restore a worn shaft journal (Fig. 8.9, G) it is pre-cut (Fig. 8.9, d), and then the process is repeated, as in the previous case (Fig. 8.9, e).

Rice. 8.9. Schemes for the restoration of machine parts

Restoration will be of high quality only if the casting conditions and process technology are observed.

Sliding screw drives can be restored using self-hardening acrylic plastics (styracryl, butacryl, ethacryl, etc.), consisting of two components - a powder and a monomer liquid. After mixing the powder with the liquid, the mixture hardens in 15–30 minutes.

Broken shaft (Fig. 8.9, well) can be restored by pressing in a new part 1 (Fig. 8.9, h) or welding method (Fig. 8.9, m) with subsequent turning of the weld.

Worn thread in the body part (Fig. 8.9, To) are reamed and reamed, a sleeve is pressed into the resulting hole, which, if necessary, is fixed with a locking screw 2 (Fig. 8.9, l). In a similar way, they proceed when repairing smooth holes.

An exact fit on the sides of a worn splined shaft can be restored if, after annealing the shaft, the splines are expanded with core blows, followed by hardening and grinding of the sides (Fig. 8.9, m).

The inner diameter of the bronze bushing can be reduced from d 1 to d 2 by upsetting, i.e. reduce its height with a constant outer diameter. The draft is carried out under pressure (Fig. 8.9, n).

The technology for restoring sliding screw gears may be as follows. Restore the constancy of the pitch of the sliding lead screw of the slotted thread. The thread in the lead nut is cut off and bored to a diameter of 2 ... 3 mm larger than the outer diameter of the lead screw. The surface to be bored is, if possible, ribbed. The repaired lead screw is heated to 90°C and immersed in molten paraffin. After cooling, a thin paraffin film remains on the surface of the screw. The paraffin-coated screw is mounted with a bored nut, simulating the working condition of the transmission. The ends of the nut are sealed with plasticine. Then, the newly prepared mixture is poured into the side, specially drilled hole of the nut with a syringe. After a few minutes the mixture hardens and the screw can be removed from the nut.

Ball screws are repaired if the wear of the screw thread is more than 0.04 mm. Recovery technology is as follows. Fix the center holes of the screw by grinding or lapping. If there are nicks and dents in the center holes, then they bore and install plugs with center holes on the glue. After restoring the centers, if necessary, the screw is straightened according to the indicator in the centers. Then the accuracy of the thread pitch is restored by machining. During processing, the thread groove is expanded along the entire length of the screw to the width at the most worn area. The outer and inner thread diameters remain unchanged. The axial clearance is chosen by adjusting the nuts. Nuts are most often not repaired, but if necessary, they are interchanged.

Correction of worn guide beds is carried out in the following ways: 1) manually; 2) on machines; 3) with the help of devices.

Correction manually by sawing and scraping is used for guides with a small surface area with a small amount of wear. Scraping guide beds can be done in two ways: 1) using a control tool; 2) according to a pre-scraped or ground mating part.

When the wear of the guide beds exceeds 0.5 mm, they are repaired by machining. For this, special grinding, longitudinal planing and longitudinal milling machines are used.

When the guide beds are worn 0.3 ... 0.5 mm at some plants, they are processed by the finishing planing method. The accuracy of processing by this method allows you to almost completely abandon scraping and limit yourself to only decorative scraping.

By grinding, the bed guides are repaired on special grinding machines or longitudinal planing or longitudinal milling machines with special stationary devices.

Large beds that cannot be machined must be machined with fixtures. Appliances, when properly used, provide sufficient high quality processed surfaces. Processing is carried out without dismantling the frame, which reduces the repair time and reduces its cost. Portable devices move, as a rule, along the frame that they process. A specially prepared plate or sometimes a part of a repaired machine is used as a base for a fixture (carriage).

The most widespread are planing and grinding devices.

Processing with fixtures does not require special equipment. The disadvantage of the method is lower productivity compared to machining on machines and the need for handmade base preparation. The advantage of machining with fixtures is that it saves time for dismantling, transporting and re-assembling the bed, which is inevitable when machining on machines.

Of great importance for the restoration of guides is the selection of technological bases. According to the nature of the bases, the beds can be divided into four main groups.

1) Beds in which spindles are mounted (horizontal milling machines, vertical milling machines with an integral head, some types of gear shaping, etc.). When repairing the beds of this group, alignment is carried out from mandrels installed in the machine spindle, materializing the axis of rotation.

2) Beds with non-working surfaces, machined along with the workers (longitudinally milling, longitudinal planing, circular and intra-shaft grinding).

3) Beds with partially worn guides. As a base, working surfaces are taken that wear out little and not all the way during operation. In such frames, first, little-worn surfaces are restored, then, based on them, the rest of the worn-out working surfaces are restored. Typical for this group are the beds of lathes, turret machines with a detachable headstock, etc.

4) Beds with separate unworn sections of the guides. This group includes beds that do not have other processed surfaces, except for wear workers (gear and thread milling machines). Unworn or slightly worn sections of working surfaces to be corrected are taken as a base.

To restore the required properties of the guide beds, they are subjected to heat treatment. From the variety of methods, here are some of the most common.

Surface hardening with induction heating by high frequency currents ( HDTV ) . The quality of the cast iron layer hardened by HDTV depends on the frequency of the current, power density, heating time, design of the inductor, the gap between the inductor and the hardened surface, as well as on the cooling conditions. The initial state of the cast iron (its chemical composition and microstructure) also affects the final results of hardening.

When gray cast iron is heated for the purpose of subsequent hardening, part of the carbon dissolves in austenite, while the rest remains in a free state in the form of graphite inclusions. As a rule, cast iron must have a pearlitic structure before hardening. If the initial structure of cast iron is unsatisfactory for surface hardening, then the concentration of bound carbon should be increased (increase the content of pearlite in the structure) by preliminary heat treatment— normalization.

The maximum achievable hardness of cast iron, obtained after hardening of high-frequency current at a temperature of 830 ... 950 ° C (depending on the composition of cast iron), is HRC 48-53. A further increase in the hardening temperature leads to a decrease in hardness.

The cooling rate during quenching has little effect on hardness. When quenched in oil, the hardness of cast iron decreases only by 2-3 units. HRC compared to water hardening.

Surface hardening with heating of high-frequency modified cast iron makes it possible to obtain greater hardness and layer depth compared to hardening of conventional pearlitic cast iron. In terms of microstructure, hardened modified cast iron practically does not differ from pearlitic cast iron.

Before hardening lathe beds, the following must be done:

1) install the frame on the table of the planer and align it for parallelism with the base surfaces with an accuracy of 0.05 mm and then bend it by 0.3 ... 0.4 mm (value of deformation during hardening);

2) plan all guide beds until they are parallel to the table travel. After detaching the frame (from the table), due to elastic deformation, a bulge is formed corresponding to the deflection value;

3) install the frame (without alignment) on the hardening platform, edged with a cement shoulder to collect the used hardening water;

4) install a portable machine on the guides of the bed, fix two brackets on both sides of it; connect the roller chain with the machine drive sprocket;

5) adjust the gap between the inductor and the hardened bed using the vertical and horizontal support of the machine. Then supply water to the inductor;

6) turn on the current and harden. Since the hardened surface of the frame is located in a horizontal plane, cooling water floods a flat, not yet fully heated area and thereby makes hardening difficult. As a rule, the depth of the hardened layer at the top of the prism is greater than in the flat area (3...4 mm at the prism, 1.5...2.5 mm in the flat area).

Example. The mode of hardening the guides of the bed of a screw-cutting lathe mod. 1K62.

Generator voltage, V ……….………………………………. 600-750

Current strength, A………………………..…………………………………. 95-120

Capacitor battery capacity, uF ….…………………….. 300-375

Used power, W ………………………………………. 55-70

Gap between the inductor and the hardened bed, mm ………..2.5-3.5

Inductor movement speed during heating, m/min….. 0-24

Bed surface heating temperature, °С …………………850-900

Hardening depth, mm …………………………………………………..3-4

HRC ……………………………………………………….…………. 45-53

Bed hardening time, min………………………………….……. 60-70

The leash of the bed after hardening (toward the concavity), mm ... 0.30-0.50

During hardening, the guide beds sag, while compensating for the bulge obtained during planing. Thus, a small metal removal is ensured during the subsequent grinding of the guides.

fiery surface hardening

For surface hardening of guide beds by flame hardening, stationary and mobile installations are used in repair practice. The former are usually installed in special areas of mechanical repair shops. In this case, the beds must be delivered there for heat treatment and subsequent recovery. For frames that cannot be removed from the foundation for production reasons (lack of lifting equipment and transport, the need to preserve the foundation, etc.), mobile units are used.

Flame surface hardening of guide beds can be carried out with an oxy-acetylene or kerosene-oxygen flame. Heating with an acetylene-oxygen flame is more intense than with kerosene-oxygen, since with the help of the first one it is possible to heat up to 3150 ° C, and with the help of the second - only up to 2400 ° C. As a combustible mixture, propane-butane and oxygen or natural gas mixed with oxygen are also used.

The quenching medium is water. The flame hardening plant is simple in design and reliable in operation, it is operated by one worker.

Tempering with a snake . In some factories, instead of continuous hardening of the guide beds of lathes, the so-called serpentine hardening is practiced, in which crossed zigzag hardened strips are formed on the surface of the guides by heating with a gas burner.

During the hardening process, a crossed zigzag line 6 ... 12 mm wide is applied to the guide surfaces of the frame With step 40 ... 100 mm (Fig. 8.10).

Rice. 8.10. Hardening snake pattern

The hardening pattern is done by hand and usually has an irregular shape. The distance from the edge of the bed to the hardening line must be at least 6 mm . Torch travel speed along guide rails approx. 0.5 m/min , which provides heating up to 750…800 °C.

The hardening pattern is recommended to be applied like this. First, you should apply a zigzag line in one pass on the first guide, and then move on to the second guide. During the application of a zigzag line on the second guide, the first one cools down to 50 ... 60 ° C, and a crossed hardening line is applied to it.

Therefore, it is necessary to carefully monitor the heating process and timely adjust the speed of the burner relative to the hardened surface of the guide frames, preventing the metal from melting.