RU2740874C1 - Apparatus for evaluating tribological properties of lubricating materials - Google Patents

Abstract

FIELD: monitoring and measuring equipment.SUBSTANCE: device relates to research of resistance to wear or abrasion of materials in lubricant by application of forces to them and can be used in scientific and industrial laboratories when studying tribological properties of oils and greases. Proposed plant comprises four-ball friction machine equipped with electric motor, testing unit, limit torque limiter and loading unit connected with test assembly by means of lever, comprises a friction torque sensor, a program sequence control unit, and an electric motor rpm controller, and a compressed air source. Loading assembly is made in the form of a pneumatic cylinder, the rod of which is connected to the large arm of the lever, above-piston cavity of the pneumatic cylinder is connected to the compressed air source by the pneumatic line with installed in it electro-pneumatic pressure converter in the above-piston cavity, and motor rpm controller, electropneumatic pressure converter in over-piston cavity, limit torque limiter and friction force sensor are connected to corresponding inputs of sequence control program unit, corresponding control outputs of which are connected to motor rpm controller and actuator of electropneumatic pressure converter in above-piston cavity of pneumatic cylinder.EFFECT: higher reliability and speed of obtaining a result while simultaneously expanding the list of determined indicators by enabling continuous dynamic loading of the test assembly, change of engine rpm and registration of determined parameters directly during test.1 cl, 2 dwg, 2 tbl

Description

The invention relates to the field of research of resistance to wear or abrasion of materials in a lubricant by applying efforts to them and can be used in scientific and industrial laboratories in the study of the tribological properties of oils and greases.

The tribological properties of lubricants, regulated by current standards (for example, GOST 9490), are such indicators as critical load (Pk), weld load (Pc), scuffing index (Iz) and wear scar diameter (Di).

The authors were faced with the task of creating a device that makes it possible to evaluate the tribological properties of lubricants under conditions as close as possible to their operation in real friction units.

Known laboratory machines designed to determine the lubricating properties of materials, having a friction unit with linear contact of working elements. These are various options for roller machines. The working unit of such machines allows simulating the operating conditions of a number of mechanisms: gear drives, roller bearings, cam mechanisms, friction drives, rolling variators, etc. Roller machines have a number of positive qualities. They make it possible to carry out studies with sliding under various loads, realized by changing the load rollers. However, the rollers themselves, as a rule, are non-standard parts, which creates difficulties in obtaining the required number of samples of identical quality and the resulting variation in results. The main disadvantage of the roller machines under consideration is the low test accuracy due to the difficulty of determining the load with its stepwise change and the impossibility of ensuring the constancy of its rate of increase [SU # 567117, G01N 3/56].

The closest in technical essence and taken as a prototype is a four-ball friction machine (CFM), consisting of a metal case with an electric motor installed on it with a built-in electromagnetic brake and a manual release device, a limiter that turns off the electric motor when a certain torque is exceeded (limiter

limiting torque), a test unit consisting of three fixed lower and one upper rotating balls, a lever for creating axial loads in the friction unit, a weight holder for installing weights (loading unit) [Four-ball friction machine ChMT-1. Manual. HMEK.441131.001 RE. JSC RNTP "Neftekhimmashsystems", Ryazan, 2008.

In the course of tests on the BSM, the test lubricant is used to lubricate balls, one of which (upper) is rotated by an electric motor in contact with three other (lower) fixed balls immersed in the test grease. The load is applied to the balls by means of disc weights placed on the arm. A series of tests is performed, discretely increasing the load until the balls are welded, fix the welding load, turn off the machine and measure the diameters of the wear spots on the balls. The data obtained are used to evaluate the tribological properties of the test material.

Thus, the use of CSM makes it possible to predict the tribological properties of oils and greases to predict the wear of rubbing parts without performing expensive operational tests in a simple and reproducible way. The method is used to assess the tribological properties of oils and lubricants in the current domestic (GOST 9490) and in a number of foreign standards.

The main disadvantage of the described design of the BSM is the discreteness (discontinuity) of the loading of the tested unit, which does not meet modern requirements for laboratory bench tests of lubricants operating in real friction units in most cases under conditions of continuously changing dynamic loads, the impossibility of regulating engine speed, as well as the duration of the result (at the end of the test).

The technical result is an increase in the reliability and speed of obtaining the result while simultaneously expanding the list of determined indicators by providing the possibility of continuous (stepless) dynamic loading of the test unit, changing the engine speed and registering the determined parameters directly during the test.

The specified technical result is achieved in that the known device containing a four-ball friction machine with an electric motor, a test unit, a limit torque limiter and a loading unit connected to the test unit by means of a lever, according to the invention, the installation additionally contains a friction force sensor, a program control unit for the sequence of operations , an electric motor speed regulator and a source of compressed air, and the loading unit is made in the form of a pneumatic cylinder, the rod of which is connected to a large lever arm, the above-piston cavity of the pneumatic cylinder is connected to a compressed air source by a pneumatic line with an electro-pneumatic pressure converter installed in the above-piston cavity, while the engine speed controller , an electro-pneumatic pressure transducer in the above-piston cavity, a limit torque limiter and a friction force sensor are connected to the corresponding inputs of the program control unit. The range of operations, the corresponding control outputs of which are connected to the speed controller of the electric motor and to the actuator of the electro-pneumatic pressure converter in the above-piston cavity of the pneumatic cylinder.

FIG. 1 shows a block diagram of an installation for evaluating the tribological characteristics of lubricants;

fig. 2 - graphical dependences of the friction force (Ftr) on the load (p); for lubricants: "a" - CIATIM-221, "b" - CIATIM-201 and "c" - Litol-24.

The installation for evaluating the tribological properties of lubricants contains: 1 - a program block for controlling the sequence of operations; 2 - source of compressed air; 3 - electro-pneumatic pressure transducer in the above-piston cavity of the pneumatic cylinder; 4 - pneumatic cylinder; 5 - lever; 6 - BShM; 7 - test unit (does not differ from the working unit of the BSM); 8 - electric motor; 9 - electric motor speed regulator; 10 - friction force sensor; 11 - limiter of the limiting torque;

All units of the installation are based on standard parts and diagrams.

The loading unit is a lever 5 driven by a pneumatic system. The pneumatic system includes well-known components: compressed air source (compressor) 2, loading pneumatic cylinder 4, electro-pneumatic pressure transducer in the above-piston cavity of the pneumatic cylinder 3 (for example, type ER 104-5 011 / 2X Camozzi with an operating range of 0-5 bar

[https://www.camozzi.ru/images/pdi2015/series_er100.pdf,27.02.2020]).

The software block for controlling the sequence of operations with the software for maintaining the set parameters and processing the results 1 consists of a programmable logic controller (for example, PZh 150 [WWW.owen.ru, 02/27/2020]) connected to an electro-pneumatic pressure converter 3, a frequency converter 9 ( for example, type Micromaster 420 Simens, adjustable range 0-3000 rpm [https://www.automaticasystem.ru/templates/autosystem/docs/manual_micromaste r_420.pdf, 02/27/2020]), torque limiter 11 (end switch), a friction force sensor 10 (for example, of the LIR-19A type with a measuring force of no more than 2N, an indication resolution of 0.1 μm [https://www.skbis.ru/catalog/linear/gauge/lir-19а, 27.02. 2020]).

This installation allows testing both in the static loading mode and sliding speeds, and in the dynamic one.

The installation works as follows (dynamic mode).

With the help of the program control unit of the sequence of operations 1, into which, for example, by means of a computer, a program code with predetermined programs of continuous change in the load and the speed of rotation of the electric motor 8 is entered, control signals are generated to the electro-pneumatic pressure transducer 3 in the above-piston cavity of the pneumatic cylinder 4 and the frequency regulator engine speed 9. They, in turn, maintain the required speed of the upper ball of the test unit 7 and the pressure in the pneumatic cylinder 4, which actuates the lever 5. The friction force sensor 10 records the corresponding parameters and transfers them to the programmable control unit of the sequence of operations 1, where registration and processing of input signals and transmission of the received data by means of feedback to a recording device (not shown), for example, to a computer memory for display on a monitor.

The static mode of operation of the installation differs from the dynamic one in that the programmable control unit for the sequence of operations in accordance with the program provides a discrete, stepwise change in the load on the test unit as it occurs in the prototype under the action of the weights.

To assess the accuracy of the measured parameters, comparative tests of Litol-24, TsIATIM 201, Shch1ATIM-221 greases were carried out in static mode on the developed device and on the well-known ChShM installation in the amount of GOST 9490 in terms of: wear scar diameter (D _and ); critical load (P _k ), welding load (P _s ) and seizure index (I _z ).

Example 1. Lubricants Litol-24, CIATIM 201, CIATIM-221 (static mode).

In the control unit of the sequence of operations 1, the program code was entered with the given programs of stepwise change in the load in accordance with a number of loads in accordance with GOST 9490 and a constant speed of rotation of the electric motor 8. Four steel balls were placed in the test unit 7 of the CShM 6, three of which were immersed in a cup and one was set in a collet fixed in the machine spindle. The test lubricant was placed in a cup with three balls, after which the balls were fixed. The cup was installed in ChShM 6 and the installation was started. In accordance with the program code previously entered into the control unit sequence of operations 1, the electric motor 8 was started with a constant rotation speed of 1475 min ^-1 , supported by the frequency controller of engine speed 9. At the same time, air under pressure was supplied to the above-piston cavity of the pneumatic cylinder 4 from the compressed air source 2 via the pneumatic line controlled by an electro-pneumatic pressure transducer 3 and providing, by acting on the cylinder rod and the associated lever 5, a step-changing load on the test unit 7. Achievement of the welding load was fixed by the limit torque limiter 11 with a corresponding signal to the control unit of the sequence of operations 1, according to the signal from which the electric motor 8 was turned off and the load was removed from the loading unit 7. The tribological properties (Р _к , Р _с ) were determined at the end of the measurement and entered into table 1.

Example 2. Under the conditions of example 1, the tribological properties of Litol-24, TsIATIM 201, TsIATIM-221 lubricants were tested on a prototype device (Four-ball friction machine ChMT-1) by stepwise loading of the lever with metal weights in accordance with a number of loads according to GOST 9490.

The results of the comparative tests are presented in table 1.

As can be seen from the presented results of comparative tests, the obtained values of the estimated indicators are close (the discrepancies of all determined indicators do not exceed the allowable ones according to GOST 9490), which indicates the adequacy of measurements on the proposed installation to measurements on a CSM in a static mode.

Example 3. Under the conditions of example 1, the lubricants Litol-24, CIATIM 201, CIATIM-221 were tested in a dynamic loading mode.

In the control unit of the sequence of operations 1 was entered the program code with the given programs of continuous dynamic change in the load and the rotational speed of the electric motor 8. Four steel balls were placed in the test unit 7 of the CHShM 6, three of which were immersed in the cup and one was installed in the collet fixed in the spindle of the machine. The test lubricant was placed in a cup with three balls, after which the balls were fixed. The cup was installed in ChShM 6 and the installation was started. In accordance with the program code previously entered into the control unit sequence of operations 1, the electric motor 8 was started with a constant speed of 1475 min ^-1 , supported by the frequency controller of engine speed 9. At the same time, air under pressure was supplied to the above-piston cavity of the pneumatic cylinder 4 from the compressed air source 2 via the pneumatic line controlled by an electro-pneumatic pressure transducer 3 and providing, by acting on the cylinder rod and the associated lever 5, uniformly increasing at a rate of 100 N / s load on the test unit 7. The values of the friction force on the balls were measured by the friction force sensor 10 and fed to the control unit sequence of operations 1 for processing and transmission in the form of a graphical dependence on the magnitude of the load on the monitor. Achievement of the welding load was recorded by the limit torque limiter 11 with a corresponding signal to the control unit of the sequence of operations 1, on the signal from which the electric motor 8 was switched off and the load was removed from the loading unit 7. Indicators of tribological properties (P _k , P _s , F _tr average, F _stp ) was determined from the graph of the friction force (Fig. 2) directly during the measurement.

The results of determining the tribological characteristics of greases on the developed installation in the dynamic mode in comparison with the determination on the BSM are presented in Table 2.

As seen from the table, when tested in dynamic mode, the example parameters P _k and P _s, increasing the accuracy of determination due stepless loading, and it becomes possible to define additional parameters - the frictional force at different loads (in the table shows the average F _TP at working loads of 150-400N) and breakaway force (F _ctp ).

Studies of the tribological characteristics of greases have shown that in the load range of 150-400N the test unit operates in a steady friction mode without scuffing during testing of most brands of greases. Therefore, to assess the antifriction properties of greases in this friction mode, the average friction force in the load range of 150-400N was chosen.

The breakaway force (F _stp ) is the most important starting characteristic of greases, which determines the possibility of starting movement, especially in low temperatures in the Arctic and the Far North.

FIG. 2 shows the graphs of the dependence of the friction force on the load at a linear sliding speed of 0.3 m / s, a load increase rate of 100 N / s and an initial load of 100 N for CIATIM-201, CIATIM-221 and Litol-24 lubricants.

The graphs show the characteristic areas of the operation of lubricants in the friction unit of the utility model.

Load 100-150 N (for CIATIM-221 grease) - starting area. Despite the low load, the friction force at the first moment of the test time increases, compared with the values at higher loads in the steady state, which corresponds to the peak at the beginning of the curve. On the graphs for lubricants, the boundary film of which does not have sufficient bearing capacity to prevent scuffing (TsIATIM-201, TsIATIM-221), the peak characterizing the jump in the friction force at the moment of starting the machine is more pronounced than on the graph of Litol-24 lubricant, which indicates about the best starting properties of the latter at the specified friction mode, since it is the value of the starting friction force that characterizes the starting properties of lubricants.

Load 150-450 N (for CIATIM-221 lubricant) - steady-state friction mode, at which the required rate of lubricant supply to the friction zone is provided, the continuity of the boundary lubricant layer is restored and the friction force is stabilized. Its slight increase can be associated with a change in the surface microgeometry as a result of wear processes and is uniform. The average value of the friction force in this segment can be chosen as a characteristic of the antiwear properties of lubricants.

Load 450-525 N (for CIATIM-221 grease) - scuffing. To determine the bearing capacity of the lubricant film, an estimated indicator P _{k is} adopted. In the dynamic loading mode, this value of the load precedes the welding load, at which an increase in the friction force is observed by more than 5 N when the load changes by no more than 50 N, and / or for 1 sec. On the graphs, the scuffing phenomenon is manifested by a peak characterizing a sharp jump in the friction force.

Load 525-1275 N (for CIATIM-221 grease). After reaching the critical load, the area of the wear spot of the lower balls increases several times, the specific load decreases, as a result of which the supply of lubricant to the friction zone is accelerated and the continuity of the boundary lubricant layer is restored, while the friction force decreases sharply. However, the change in roughness that occurred at the moment of seizure changes the friction conditions and the values of the friction force do not return to the level of the previous steady state. The efficiency and durability of the friction unit under conditions of significant changes in the linear dimensions of parts of real machines, changes in roughness, temperature conditions, and tribotransformations in the lubricant can be assessed by this segment of the lubricant's work schedule in the friction unit of a utility model.

The welding of the balls is the last jump in the frictional force in the graphs where the welding stop shuts down the motor. For example, for _a P-221 CIATIM lubricant is 1326 N.

Since the registration of experimental data is carried out graphically directly during testing, the time to obtain a result is significantly reduced.

From the presented data, it follows that the application of the invention makes it possible to carry out tests in continuously changing modes of loads and sliding speeds in the process of studying the antifriction properties of oils and greases, thereby simulating the operating modes of real friction units during operation, and also to additionally determine the friction force for any load intervals and breakaway force for various lubricants.

Thus, the stated set of essential features, each of which is necessary, and all together are sufficient, makes it possible to achieve a super-cumulative effect of increasing the accuracy and speed of measurements of the tribological properties of oils and greases, while simultaneously expanding the boundaries of the determination method using FSM and, therefore, to solve the problem posed.

Claims (1)

An installation for evaluating the tribological properties of lubricants, containing a four-ball friction machine (CFM) with an electric motor, a test unit, a limit torque limiter and a loading unit connected to the test unit by means of a lever, characterized in that the unit additionally contains a friction force sensor, a software control unit sequence of operations, an electric motor speed controller and a source of compressed air, and the loading unit is made in the form of a pneumatic cylinder, the rod of which is connected to a large lever arm, the above-piston cavity of the pneumatic cylinder is connected to the compressed air source by a pneumatic line with an electro-pneumatic pressure converter installed in it in the above-piston cavity, while the regulator speed of the electric motor, electro-pneumatic pressure transducer in the above-piston cavity, limiter torque limiter and friction force sensor are connected to the corresponding inputs of the program control unit a sequence of operations, the corresponding control outputs of which are connected to the speed controller of the electric motor and to the actuator of the electro-pneumatic pressure converter in the above-piston cavity of the pneumatic cylinder.

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