INVESTIGATION OF THE COEFFICIENT OF FRICTION AND WEAR OF ABRASIVE-FILLED COMPOSITE POLYMER MATERIALS FOR TRIBOTECHNICAL PURPOSES

ABSTRACT

The article presents the results of research in the field of research of composite thermoplastic polymer materials filled with solid organomineral fillers and coatings based on them in a dry and lubricating environment. At the same time, it was found that the change in the antifriction properties of polymer coatings significantly depends on the nature, type and content of organic-mineral fillers.

АННОТАЦИЯ

В статье представлены результаты исследований в области исследования композиционных термопластичных полимерных материалов, наполненных твердыми органоминеральными наполнителями и покрытиями на их основе в сухой и смазывающей среде. В то же время установлено, что изменение антифрикционных свойств полимерных покрытий существенно зависит от природы, вида и содержания органоминеральных наполнителей.

Keywords: antifriction properties, composition, polymer, coatings, modification, abrasive fillers, wear, coefficient of friction.

Ключевые слова: антифрикционные свойства, композиция, полимер, покрытия, модификация, абразивные наполнители, износ, коэффициент трения.

Introduction. The development and application of composite polymer and metal polymer materials used in friction units of parts of working bodies of machines and mechanisms for various purposes is of increased interest in the world.

At the same time, the field of application of metal polymer materials has significant resources. An increasing number of works appear in the field of research on friction and wear of polymer and metal polymer materials. However, the physico-chemical processes that occur when a polymer is rubbed against a metal are extremely complex. Suffice it to say that the nature of the supramolecular structure, the size of individual and complex formations, as well as their distribution largely determines the static and fatigue strength, relaxation characteristics, the amount of mechanical hysteresis and many other parameters on which the nature of the external friction of polymers directly depends. And in dynamics, a qualitative and quantitative relationship between the parameters of the structure and the main characteristics of friction can be obtained by penetrating into the atomic-molecular level of processes occurring on rubbing surfaces [1]. For example, it has been shown that the size of spherulites significantly affects the coefficient of friction, even within a single spherulite, the coefficient of friction is not a constant value [2].

The complexity of the study of friction processes also lies in the fact that during the static and dynamic action of the indicator, deformation and destruction of supramolecular structures occur in the surface layers of the polymer. During operation, the shape of the spherulites and the boundaries between them may change, but the integrity of the sample is not violated, and after removing the loads, they can restore their original shape.

Research and experience in the use of metal-polymer materials have shown that the modification of polymers by the introduction of various fillers can significantly increase the wear resistance and load capacity of the studied materials, and is also a good reserve for creating materials for specified working conditions [3-7].

In this regard, this paper presents the results of a study and analysis of the role of filler in a filled polymer coating in the search for ways to create friction surfaces that implement the properties of machine-building materials most effectively. To this end, the role of the filler in giving the material high antifriction characteristics is studied, and the conditions for the implementation of the mode of selective transfer during friction, the possibility of polycaproamide coatings with steel friction surfaces are also considered.

The purpose of this work is to study the effect of fillers on the anti-friction and wear-resistant properties of composite polymer materials and coatings based on them.

The object method of research. The objects of research are powdered thermoplastic polymers (polycapromide, pentaplast, polyethylene)  dispersion up to 250 microns. 45 steel was used as a substrate. Various organic and inorganic fillers were used as fillers, as well as dispersed abrasive materials (diamonds, white electrocorundum, silicon carbides, etc.) with particle sizes from 15 to 40 microns. Neazon D was used as a polycaproamide heat stabilizer . The introduction of fillers and other dispersed modifiers was carried out by their mechanical mixing.

Research methods. The strength of the adhesive joint of the coating with metals was evaluated by the methods of normal separation (ZD – 4 machine, at a constant loading speed) and peeling at an angle of 1800 (ZD – 40 machine). In the dissertation work, for a comprehensive study of the physical and mechanical properties of metalworking materials and coatings, for the study of friction and wear, the upgraded MI-1 and SMC-2 machine, the ZD-4 bursting machine, the PMT-3 microhardometer devices, the upgraded PR-05 machine, the horizontal microscope NLI-2 were used. To study oxidative processes, structural components, as well as other physicochemical changes in the polymer and metal of the adhesive compound, the MIM-8 microscope, the OD-102 derivatograph, the URS-50 IM diffractometer, and chemical analysis methods were used.

Research results and their analysis. Studies show that the antifriction properties of the filler under dry friction in the averaged limit affect the friction in the case of filling the coating with them, the results of which are shown in (Table 1).

Table 1.

Influence of the degree of filler on the coefficient of friction of thermoplastic polymer coatings under air-dry friction (v = 1.0 m/sec, ore = 0.75 mn/m²)

As can be seen from the above data, when graphite is introduced into polycaproamide in a small amount (5-10), it does not essentially change, and with an increase in the percentage of filling, it increases the coefficient of friction of the filled polymer. At the same time, the adhesive bond strength of the PAS graphite-filled polymer coated (with an addition of 15-20% by weight) is 20-25% higher than that of the modified coating [8].

At the same time, it seems that the increase in the coefficient of friction is associated with an increase in the graphite content in the coatings in a change in the cohesive strength of the composition for the specific properties of graphite itself, since similar results were obtained not only for other polymers [8,9], but also for metal bearings [11,12].

It was shown [5,6] that the addition of graphite to a thermosetting polymer based on ED-6 resin increases the coefficient of friction by 10 to 80%, and the brittleness of the composition is destroyed even at a load of 4.0-6.0 Mn/m². It also notes the non-monotonic nature of the friction moment from the graphite content in chlorosulfated polyethylene. When 10% graphite (by weight) was introduced into this resin, the friction moment decreased compared to the friction moment for pure resin. A consistent increase in the amount of graphite to 20, 40, 50% invariably increased the value of the friction moment.

Studies [13] carried out to determine the coefficient of friction of porous ferro-graphite bearing materials depending on the graphite charge showed that with an increase in its content, the coefficient of friction decreases, reaching the lowest value of the mass fraction of graphite 5. A further increase in the graphite content leads to an increase in the coefficient of friction. Bearings made of a charge with a mass fraction of graphite of 3% can withstand the greatest extreme loads, and with a mass fraction of graphite of 4%, a sharp decrease in strength occurs.

Thus, graphite, well-known for its antifriction properties, when introduced into the composition, has a complex effect on the properties of the latter.

With boundary friction and with friction without lubrication, due to the release of a large amount of heat on the contacting surfaces, irreversible processes of transformation in the metal occur (oxidation, dispersion, fatigue failure or destruction due to structural changes). A thin adsorbed layer of lubricant or a layer of oxides are not able to protect the surface layer of the metal from deformation, hardening in destruction and gives a large amount of friction [13-17].

Currently, there are quite a lot of methods that reduce the influence of irreversible transformation processes on the contact surface [18]. However, these methods, for example, artificially created non-film surfaces, cannot prevent or compensate for wear or other damage, lead to the destruction of the metal. And from this point of view, the most effective and progressive method of preventing irreversible processes occurring on contacting surfaces during friction is the implementation of selective transfer under conditions of boundary friction [19-20].

We have conducted studies on the possibility of realizing the effect of atomic transfer in the case of friction of a filled polymer coating on a steel surface in a glycerine medium and with CIAFAO-201 lubrication.

At the same time, polymer coatings were filled with copper oxide, lead, and lead oxide.

The experimental results confirm the possibility of the formation of a copper surface film in the case under consideration. In the case of friction in a glycerine medium of a polycaproamide coating filled with lead or lead oxide, the formation of a lead film on the steel surface is also observed, which is confirmed by a low coefficient of friction and abnormally high wear resistance (Fig. 1, 2).

1-PCA is not modified, 2 – PCA-Ai-2 (PCA + 30% copper oxide), 3 – PCA-Ai-4 (PCA + 30% lead oxide), 4-PCA-Ai-6 (PCA + 20% lead).

Figure 1. Dependence of the coefficient of friction from the specific pressure for filled coatings when lubricated with glycerin (TNPM = 525 K, Ʊ-0.5 m/sec)

1-PKA not modified (Ore=10mn/m), 2- PKA+1.5% heat stabilizer, 3-PKA-Ai-2(PKA+30% copper oxide), 4-PKA-Ai-2(30% copper oxide +5% graphite), 5-PKA-Ai-4(PKA+30% lead oxide),6-PKA-Ai-6 (PKA+20% lead).

Figure 2. Dependence of wear intensity during glycerin lubrication (TPNM-525 K, Ore=20mn/m²)

Figure 3 shows experimental data confirming the implementation of the selective transfer effect in the cases under consideration. A comparison of the dependencies for MS-20 oil (boundary friction) and glycerin (selective transfer) shows a change in the coefficient of friction over time with the sudden application of an additional load. In the case of friction in MS-20 oil, filled coating under sudden loading, the coefficient of friction increases abruptly and only after a long time passes to steady friction (Fig.1, curve 1,2). For the case of selective transfer, relatively small sudden loads are not sensitive, and with large sudden loads, the steady-state friction is restored very quickly (Fig.3, curves 3,4). For the case of selective transfer, relatively small sudden loads are not sensitive, and with large sudden loads it recovers very quickly.

1,2,5,6 - copper oxide; 8,4 - lead oxide; 1,2 - friction in MS-20 oil; 3,4,5,6 - friction in glycerin (1,3,5-steady-state friction, 15=0.75 Ʊ/sec; Ore=14 mn/m²; 2,4,6 - friction after sudden application of load, Ʊ=0.75 m/sec, Ore = 22mn/m²)

Figure 3. Change in the coefficient of friction over time of filled polycaproamide with sudden application of additional specific pressure

As can be seen from the research results, steady-state friction is clearly observed on (Fif. 3, curves 3,4).

X-ray diffraction and spectroscopic methods of investigation also confirmed that in all cases of selective wear, the formation of a sulfur-screw film on the contacting surfaces is observed.

The analysis of the state of the surface of the steel roller shows that on hardened surfaces and with a sufficiently high purity class, the selective transfer mode is most quickly established. The experiments were carried out during friction tests using a steel counter body with a different nature of preliminary heat treatment (Table 2).

Table 2.

Friction tests using a steel counterbody with a different character of preliminary heat treatment

Based on the analysis of the ratio of the mechanical properties of the surface layer and the substrate in [20,21], it was shown that an increase in the hardness of the substrate should lead to an improvement in the antifriction characteristics. This conclusion is confirmed by the results of our experimental studies during antifriction tests in the use of copper alloys of different hardness in a steel shell with a different character of preliminary heat treatment (Table 2).

Conclusions. Thus, the analysis of the data obtained shows that although when introducing abrasive solid fillers that are or are not antifriction materials, there are general patterns in changing the physico-mechanical and antifriction properties of thermoplastic polycaproamide polymer coatings, but there are also significant factors influencing the properties of fillers. In further studies, we will show that solid fillers are not only used in filled antifriction coatings. With the contact interaction of abrasive-filled polymer coatings, it is possible to create friction surfaces that are effective from the point of view of realizing optimal performance characteristics of the material in friction nodes when honing metal surfaces of machine parts.

References:

1.  Abed-Negmatova N., Negmatov J., Gulyamov G., Negmatov S., Khodjimuradov D. Composite polymer materials and parts made of them for cotton machines and mechanisms. Advanced Materials Research 413, pp. 535-538.2012.Egorenkov N.I. Investigation of some issues of adhesion of polyethylene in metals.. PhD thesis, Riga, 1970
2. Abed-Negmatova, N. Negmatov S.S., Gulyamov G., Negmatov Yu.N. Antifriction wear-resistant composite materials and parts made of them for the working bodies of cotton machines and mechanisms. Advanced Materials Research 616-618, pp. 2005-2008
3. Beliy V.A., Sviridenok A.I., Petrokovets M.I., Savkin V.G. Friction and wear of polymer-based materials. Publishing house ”Science and Technology” Minsk 1976
4.  Bely V.A. Abstract of the candidate's dissertation, Minsk, 1980.
5. Bilik Sh.M. Experience in the use of plastics in friction units of railway rolling stock. Collection "Plastics in sliding bearings", Moscow, 1965.
6. Bilik Sh.M. Metal-plastic friction pairs in machines and mechanisms. M., 1965
7.  Egorenkov N.I. High-molecular compounds, 1 1980, p. 83.
8. Eirikh, Mark “Chemistry and technology of polymers"* No. 3, 16, 1961
9. Friction, wear and lubrication. Handbook, book 2, M., Mechanical Engineering, 1979
10.  Gagin L.A. Contact problems of elasticity theory, M., 1955.
11.  Garkunov D.P., Kragelsky I.V., DAN of the USSR, vol. 113, No. 2, 1957.
12. Garkunov D.P., Lozovsky V.N., Polyakov A.A. DANN USSR, vol. 133 No. 3, 1960
13.  Garkunov D.P., Lozovsky V.N., Polyakov A.A. Selective transfer in friction nodes. Ed. “transport", Moscow, 1969.
14.  Karegelsky I.V. Friction and wear, M., 1968.
15. Makushok E.M., Kalinovskaya T.V., Bely A.V. Mass transfer in friction processes. Ed. “Science and Technology”, Minsk, 1978
16. Mandelkern V.M. Crystallization of polymers. Izd. “Chemistry", 1966.
17. Martynov A.N., Gridin A.N. Polishing of the inner surfaces of spinning rings with a compacted flow of free abrasive. In the collection ”Issues of technology, accuracy and reliability in Mechanical Engineering", No. 3, Penza, 1111I, 1974.
18. Musabekov D., Abed-Negmatova N., Gulyamov G., Khodzhimuradov D., Negmatov S. Effective composite materials for friction pairs of working bodies of cotton gins. Advanced Materials Research 413, pp. 548-550.2012
19. Negmatov S., Ulmasov T., Karshiev M., ...Abdulaev O., M Matsharipova. Adhesive-strength and tribotechnical properties of composite polymer coatings for mechanical engineering. E3S web conference successfully, 2021.
20. Negmatov S., Ulmasov T., Navruzov F., Dzhovliev S. Vibration-damping composite polymer materials and coatings for engineering purposes E3S Web of Conferences, , 2021
21. Sergienko V. P. et al. The influence of a high-frequency electromagnetic field on the dynamic mechanical and tribotechnical characteristics of friction composites with a thermosetting polymer matrix //Journal of Friction and wear. - 2021. – p. 42. – No. 6. – p. 401-407.
22. Sviridenko A.I. Investigation of frictional interaction of polymer and metal polymer materials and structures. Abstract of the doctoral dissertation, Minsk, 1975