SUBSTANCE: antifriction coat can be used in gear pumps for reducing friction and wear resulted from corrosion or mechanical effects in tribojoints under effects of chemically active reagents, high temperature and loads on engaged parts to ensure required stable gaps between the said parts. The antifriction coat consists of three layers, i.e. inner, intermediate and upper layers. Note here that the inner layer represents a composition comprising 90 wt % of a polyimide varnish and 10 wt % of chromophosphatealuminic bond, the intermediate layer being made from 100 wt % of a pure polyimide varnish. Finally, the top layer represents a composition containing 90 wt % of polyimide varnish, 8 wt % of colloid graphite and 2 wt % of lecithin. Thickness of the aforesaid inner layer is within the limits of from 8 up to 10 mcm, thickness of the intermediate layer is within the limits of from 16 up to 20 mcm, thickness of the top layer is within the limits of from 24 up to 30 mcm, while the required thickness of the coat is provided by grinding the top layer.
EFFECT: longer life of friction assembly units and parts operated in chemically active environments.
The invention relates to the field of engineering, namely, anti-friction coatings used in gear pumps to reduce friction and corrosion and mechanical wear between the drive shaft and the pump casing and in other tribocharging when exposed to the mating parts of chemically active reagents, high temperatures and loads, and the need to safeguard the stability of the gaps in tribocharging.
Known antifriction self-lubricating material used for coating, which is used as a binder of epoxy resin and fillers are polyamide and silica fabric, molybdenum disulfide, bronze powder and polytetrafluoroethylene (see patent RU No. 2155198, CL F16C 33/20, 27.08.2000).
The main disadvantage of such coatings is the high coefficient of friction.
Known anti-friction coating containing a solid lubricant is molybdenum disulfide, graphite, boron nitride and a binder based on epoxy resin, in the following ratio of components, parts by weight: molybdenum disulfide - 25-58, graphite - 25-58, boron nitride 7-16, binder - 30-70, when this coating is applied on the metal surface a thin film of a mixture of solid lubricant and a binder (see US patent No. 5482637, CL F02B 77/02, 09.01.1996).
This composition may be used in which the quality of anti-friction wear-resistant coatings in the nodes mechanisms, operated in the regime of dry friction at loads up to 10 kg/mm2. However, this coating has a high porosity and does not protect the metal substrate from corrosion during operation of the mechanism in aggressive environments.
Closest to the invention to the technical essence and the achieved result is an anti-friction coating containing a solid lubricant is molybdenum disulfide and graphite, molybdenum and binder based on epoxy resin, and the coating consists of three layers, the lower of which is adjacent to the metal substrate made of molybdenum, an intermediate layer made of a binder without fillers, and the upper layer made of a binder, in which, as the solid lubricant introduced graphite (see patent RU 2211260, CL SS 28/00, 27.08.2003).
This coating provides excellent wear resistance and low coefficient of friction of adjacent pairs, the shear strength when working in non-aggressive environments. However, this coverage does not reduce corrosion and mechanical wear of friction pairs in the operation of the mechanism in aggressive environments, such as alkali and hydrochloric acid. Along with this, the floor, as previous analogs having a relatively low hardness, very poorly mechanical grinding and polishing, which does not allow to use it for promyshlennogo the manufacture of precision parts of friction, for example, gear pumps, pumping aggressive solutions.
Task to be solved by the present invention is directed, is the improvement of tribological characteristics of the coating and give it the properties of a corrosion inhibitor conjugate coated metal friction pairs, with high hardness, toughness and adhesion to the metal substrate.
The technical result is to increase the durability of anti-friction coatings, durability counterface and, respectively, of the friction mechanism as a whole.
This problem is solved and the technical result is achieved due to the fact that the anti-friction coating consists of three layers - the inner, intermediate, and upper, and the inner layer is made of a composition containing a polyimide varnish - 90 parts by weight and alumbramiento bunch - 10 parts by weight, the intermediate layer is made of pure polyimide varnish - 100 parts by weight and the upper layer is made of a composition containing a polyimide varnish - 90 parts by weight, colloidal graphite - 8 parts by weight and lecithin - 2 parts by weight, the thickness of the inner layer is in the range from 8 to 10 μm, the thickness of the intermediate layer is ranging from 16 to 20 μm, and the thickness of the upper layer is in the range from 24 to 30 μm. The top layer is polished to the desired thickness.
In anti-friction coating each SL the St and its components have its own function.
First of all, the use of polyimide varnish PAK as the matrix of the coating layers allows the floor to work in the friction nodes used in chemically active environments at temperatures up to 300°C.
High physical-mechanical properties of polyimides in comparison with other polymers, including hardness and ultimate tensile strength, allow for mechanical grinding and polishing polyimide coatings. This, in turn, allows the manufacture of industrial parts precision machinery, such as pumps, with a steadily recurring dimension of the gaps in tribocharging.
High wetting properties of polyimide varnish and related uniform thickness allow the coating process by using conventional methods, for example by dipping, brush or spray gun.
The inner layer of the cover - "adhesive" is used to increase the adhesion of the polymer coating to the metal surface such as the surface of the drive shaft gear pump. Introduction alumbramiento ligaments related to inorganic adhesives, polyimide matrix helped to create the inner layer with high adhesion to the metal substrate that can withstand up to 300°and stores in the high hardness. This layer by its physical-mechanical properties, including compressive strength, tensile, impact and Flexural significantly higher than the characteristics of other organic coatings.
The intermediate layer coating - "compensation", made entirely of polyimide varnish, plays the role of a pressure compensator in the case of a temperature increase in tribojunction, for example, when the temperature of the pumped by the pump environment.
The top layer of the coating is "anti-friction" that performs multiple functions. The composition of colloidal graphite s-1 with a polyimide varnish gives the coating properties salesmanagement. Introduction in the polyimide matrix method, which is a corrosion inhibitor, allows you to create friction on the surface of the counterface thin film that prevents corrosion and mechanical wear, such as wear of the gear housing of the dosing pump when rotating in him the drive shaft on the floor. It is the top layer of the coating is subjected to mechanical precision grinding, and precision products polishing to achieve the rated accuracy of the dimensions of the cover and roughness of its surface.
During the performed tests indicate that the physico-mechanical and tribological characteristics of the thickness of each layer of antifriction pok is itia. The best results were achieved when the thickness of the inner layer was in the range of from 8 to 10 μm, the thickness of the intermediate layer was in the range of from 16 to 20 μm, and the thickness of the upper layer ranged from 24 to 20 microns.
The main elements of technology for anti-friction coatings are:
- preparation of the compositions of the layers;
- the formation of layers on steel surfaces with step thermoimidization intermediate layers;
- high-temperature heat treatment;
- precision grinding of the upper layer (in the case of manufacturing precision products - polishing).
The preparation of the composition of the inner layer of the coating comprises combining and mixing 90 parts by weight of polyimide varnish and 10 parts by weight of alumbramiento ligaments in the stirrer vane type liquid polymers with a characteristic viscosity of 0.6...1.2 V for 10-15 min until complete homogenization.
The preparation of the composition of the top layer includes combining and mixing 90 parts by weight of polyimide varnish, 8 parts by weight of graphite and 2 parts by weight of lecithin in the mixer of the same type for 15-20 min until complete homogenization.
The formation of the inner layer of the coating is carried out by applying the composition with a brush on the metal surface, the exposure to full spreading and termoemcali at 427°C for 1 h is CA. The thickness of the layer is in the range of 8 to 10 μm.
The formation of the intermediate coating layer is 2 to receive:
- application 1-layer net polyimide lacquer brush on the surface of the inner layer of the coating, exposure to full spreading and termoemcali at 427°C for 1 hour. The thickness of the 1st layer is in the range of 8 to 10 μm;
- drawing 2-layer polyimide lacquer brush on the surface of the 1st layer, the exposure to full spreading and termoemcali at 427°C for 1 hour. The thickness of the 2nd layer is in the range of 8 to 10 μm, and the thickness of the intermediate coating layer is in the range 16...20 microns.
The formation of the upper layer coating is carried out in 3 doses:
- application 1-layer composite brush on the surface of the intermediate layer coating, exposure to full spreading and termoemcali at 427°C for 1 hour. The thickness of the 1st layer is in the range of 8 to 10 μm;
- drawing 2-layer composite brush on the surface of the 1st layer, the exposure to full spreading and termoemcali at 427°C for 1 hour. The thickness of the 2nd layer is in the range of 8 to 10 μm;
- application of 3-layer composite brush on the surface of the 2nd layer, the exposure to full spreading and termoemcali at 427°C for 1 hour. The thickness of the 3rd layer is within the 8 to 10 μm, and the thickness of the top layer of the coating is within 24-30 ám.
This layering of paint and the compositions of the intermediate layers 8 to 10 μm and their thermoimidization at a temperature of 427°allows us to produce a coating with high physical-mechanical characteristics with virtually no internal stress after the heat treatment.
After formation of the coating is high temperature heat treatment by heating and aging of coatings in vacuum at temperatures of 250°C (1 hour)300°C (1 hour), 350°C (1 hour) and 400°With (30 min).
After cooling the product is covering up to 20±2°is made With precision grinding of the upper layer (in the case of manufacturing precision products - polishing).
If necessary, the coating on the body of rotation, for example on the shaft of gear pump, polyimide varnish and composition of the layers applied to the shaft of the brush, after which the shaft is installed on the device and is driven with a speed of 300 rpm With this method of molding is ensured uniformity and thickness of the coating layers to the extent necessary.
Performed laboratory and pilot testing of anti-friction coatings in comparison with its prototype.
Laboratory tests of the coating was carried out on the end machine friction. Covered the e was applied on a metal substrate of steel H, and as counterbody used gear pumps of the same steel. Sliding speed V=0.05 m/s, pressure P=15 MPa, Wednesday - acidic solution of aramid fibers, containing 1.5% hydrochloric acid. The floor of the prototype was applied in accordance with the description EN 2211260, CL SS 28/00, 27.08.2003. In table 1 and table 2 show the results of the tests. Linear wear was determined by the base points on optimate with multiplier 1 μm. 1, 2, 3 is the number of samples.
|Floor||Hardness, conventional units, GOST 5233-76||Ultimate tensile strength, MPa|
|Floor||The coefficient of friction||The wear rate of the coating, 1·10-9||The intensity of wear of the counterbody, 1·10-9|
From the results of laboratory tests, it follows that the tribological characteristics of anti-friction coatings is higher than that of the prototype. This is especially noticeable in the analysis of the wear counterface, which confirms the effectiveness of the introduction of the coating of the corrosion inhibitor of lecithin. The hardness and ultimate tensile strength of the proposed coating is higher than that of the coating of the prototype, which probably allows the mechanical grind and Polish the proposed coverage.
Pilot testing of anti-friction coatings show is on gear pumps-dosing, pumping aggressive solutions aramid fibers at JSC "the company". Anti-friction coating and coating-the prototype was applied to the drive shaft of the pump, and operating time were determined their effectiveness. The counterbody was a cast iron housing. As a result, the operating time of the pump with the shaft, covered with anti-friction coating, amounted to 768 hours, coated prototype - 1778 hours.
Thus, the proposed anti-friction coating has a high level of properties and ensure the reliability and durability of the friction gear pumps and other machinery operating in harsh environments.
As can be seen from the description of the proposed anti-friction coating involves an inventive step and can be protected by a patent of the Russian Federation.
Anti-friction coating consisting of three layers: an inner, an intermediate and a top, wherein the inner layer is made of a composition containing a polyimide varnish 90 parts by weight and alumbramiento a bunch of 10 parts by weight, the intermediate layer is made of pure polyimide varnish 100 parts by weight and the upper layer is made of a composition containing a polyimide varnish 90 parts by weight, colloidal graphite 8 parts by weight and lecithin 2 parts by weight, and the thickness of the inner layer is in the range from 8 to 10 μm, the thickness of the intermediate layer is within 16 to 20 microns, the thickness of the upper layer is in the range from 24 to 30 μm, and the required thickness of the coating is achieved by grinding the top layer.
SUBSTANCE: invention concerns composite materials used in manufacturing of antifriction parts for friction units in automotive industry, e.g. of ball joint pads. Polymer material for "Lyugam" friction units contains, mass %: polyamide-6 34-70, high-pressure polyethylene 10-16, fiber carbon filler 12-35, and oil additive 7-15. The other is a composition based on a mineral oil, surfactants, functional additives and crushed crystal graphite.
EFFECT: improved performance characteristic of the material due to higher elasticity enabling better durability against impact loading, and to lower friction factor.
SUBSTANCE: invention concerns production of antifriction epoxy moulding materials used in manufacturing of inserts for bearing bushings with binary friction surface, i.e. greases, as well as construction material and electric insulator in electrical engineering and other technical fields. The method involves forge rolling of solid pre-polymer with fluorine rubber capable of curing by an amine, in the ratio of 90:10 to 60:40 at the temperature of 60-90°C for 5-30 minutes. Here pre-polymer is a product of interaction of epoxidised novolac (A) with epoxy diane resin of molecular mass 360 to 540 (B) and with 3,3'-dichlor-4,4'-diaminodiphenylmethane (C) in the A:B:C ratio of 85:10:5 to 5:80:15, obtained by heating at 60-130°C for 30-120 minutes. Further to 100 mass parts of forge-rolled mix 15.0-50.0 mass parts of arylamine as curative, 5.0-50.0 mass parts of polytetrafluoretylene and 10.0-100.0 mass parts of chopped fiber as filler, and 2.0-6.0 mass parts of antiadhesive are added. The composition is additionally forge-rolled at 40-80°C for 5-15 minutes, then the resulting mass is cooled and crushed.
EFFECT: improved antifriction properties of moulding material.
2 tbl, 8 ex
SUBSTANCE: invention pertains to compositions of high-molecular compounds, in particular, to compositions of homopolymers of vinyliden fluoride. Description is given of the composition based on polyvinyliden fluoride, containing polyvinyliden fluoride, as well as an elastomer, in the form of butadiene-styrene thermoplastic elastomer, in quantity of 15-30% of the mass, and extra 3-8% mass of high pressure dispersed polyethylene, irradiated in an oxygen containing medium, to an absorbed dose of 100-400 kGY.
EFFECT: increased tribotechnica characteristics, reduction of frictional coefficient and increased wear resistance of the composition based on polyvinyliden fluoride.
1 cl, 2 tbl, 7 ex
SUBSTANCE: invention pertains to polymer composite materials for anti-frictional purposes, which can be used for making component parts of friction assemblies of machines and equipment. Description is given of the polymer composition, containing polytetrafluoroethylene and aluminium oxide with particle size of 9-11 nm as filler material, with the following ratio of components: nano-size aluminium oxide - 0.1-2.0 mass %, polytetrafluoroethylene constitutes the remaining percentage.
EFFECT: increased wear resistance, carrying capacity, reduction of coefficient of friction with retention of stress-strain properties of the composite material based on polytetrafluoroethylene.
1 cl, 1 ex, 1 tbl
FIELD: technological processes.
SUBSTANCE: invention is related to the field of materials science, in particular, to polymer composite materials (PCM) based on polytetrafluorinethylene (PTFE) and may be used for making parts of metal polymer friction units of different equipment. Technical result is achieved by using energy of ultrasonic vibrations with frequency of 20±3 KHz and vibrations amplitude within the range of 8-12 microns during pressing of composite mixture. At that vibrations continuously affect the pressing puncheon during 2÷3 minutes. Preliminarily mixture powders are mixed in the mixer with knives rotation frequency of at least 2800 min-1. Cold pressing of composition is made in closed mould under the pressure of 50±5 MPa. Pressed stock is heated in the furnace up to the temperature of 360±5°C with the rate of 1.5-2.0 degrees/min. Then it is soaked at this temperature for 8÷9 min per 1 mm of item wall thickness and cooled down to 327°C with the rate of 0.3-0.4 degrees/min and then from 327°C down to room temperature together with the furnace.
EFFECT: improves mechanical and tribotechnical properties of composite material and increases economy of technological process of items production.
2 cl, 2 tbl
FIELD: polymer materials.
SUBSTANCE: invention provides powdered composite extender for elastomer materials intended for manufacturing articles operated under dry friction or increased wear conditions and applied in engine, compressor, and pump manufacture industries as well as in other industry fields. Extender particles contain at least one metal oxide nucleus and polymeric shell of thermoplastic having modulus of elasticity between 1.5 and 5.0 GPa, volume percentage of nuclei in extender particle ranging from 1 to 10%. Method of preparing composite powder extender consists in that metal oxide particles are activated in mechanochemical activator at mechanical energy supply intensity 1 to 5 kW/kg and dose from 30 to 1000 kJ/kg in medium selected from air, nitrogen, argon, and vacuum between 1 and 10-2 atm to obtain particles with average size no higher than 15 μm, after which shell polymer is added to mechanochemical activator and metal oxide particles are modified with intensity of mechanical energy supply from 1 to 5 kW/kg and dose from 30 to 100 kJ in above indicated medium.
EFFECT: reduced coefficient of friction and lowered summary rate of wear of friction couple under hydroabrasive wear conditions.
4 cl, 2 dwg, 3 tbl
SUBSTANCE: invention proposes composition polymeric material of tribotechnical designation based on polytetrafluoroethylene, coke and activated magnesium spinel and can be used in machine and mechanisms heavy-loaded friction units. The composition polymeric material comprises the following components, wt.-%: coke, 13.0-14.5; magnesium spinel activated in planetary mill AGO-2 for 2 min, 0.5-2, and polytetrafluoroethylene, the balance. Using the invention allows enhancing longevity and working ability of friction units based on high abrasion resistance, low friction coefficient that are determined by the composition structure.
EFFECT: improved and valuable properties of material.
FIELD: composite materials.
SUBSTANCE: invention provides structural- and antifriction-destination six-block polyamide-based polymer material, which is, in particular, intended for manufacturing parts with low coefficient of friction and meeting requirements of shock and thermal stability. According to first embodiment, in polyamide composite material composed of six-block polyamide matrix and matrix-modifying carbon additive, said carbon additive is fullerene C60 or fullerene C70, or mixture thereof in amounts from 0.0001 to 1.5%. According to second embodiment, in polyamide composite material composed as above, said carbon additive is fullerene soot containing 3-16% fullerene C60 or fullerene C70, or mixture thereof and used in amount 0.01 to 3.0%.
EFFECT: addition of fullerene materials results increased strength and elasticity, reduced coefficient of friction with metals and wear, increased softening, melting and in-air destruction temperatures, and increased heat conductivity without deterioration in density and moisture absorption.
2 cl, 1 dwg, 2 tbl, 6 ex
FIELD: chemical industry; production of the polymeric antifrictional composite materials.
SUBSTANCE: the invention is pertaining to the polymeric antifrictional composite materials intended for manufacture of details of the friction assemblies of abrasion of the machines and aggregates. The technical result of the invention is to improve the mechanical characteristics and the wear-resistance properties in combination with the reduction of the labor input of manufacture of the composite material. The invention offers the polymeric antifrictional composite material including (in mass %): olytetrafluoroethylene (81.5-87.0), molybdenum disulfide (1.5-2.0), cryptocrystalline graphite with the specific surface area of 50-75 m2 /g (6.0-10.0), the carbonic filler with the filament length of 0.05-0.5 mm (4.0 - 7.0).
EFFECT: the invention ensures the improved mechanical characteristics and the wear-resistance properties in combination with the reduction of the labor input of manufacture of the composite material.
1 cl, 1 tbl, 4 ex
FIELD: chemical industry; radiation-chemical methods of the production of the polymeric materials with the improved complex of properties.
SUBSTANCE: the invention is pertaining to the field of the radiation-chemical methods of production of the polymeric materials with the improved complex of properties. The invention presents the description of the method of the radiation-chemical modification of the polytetrafluorethylene providing for treatment of the articles made out of the polytetrafluorethylene with the gamma-rays exceeding the temperature of the fusion point of the crystalline phase differing that the block and the film articles are subjected to this radiation and this radiation is conducted at presence of the molecular oxygen, at the oxygen tension of 102 - 1 mmHg. The invention also presents the description of the substance produced by the above indicated method. The technical result of the invention is production of the substance possessing the high indexes of the wear-resistance and creepage.
EFFECT: the invention ensures production of the substance possessing the high indexes of the wear-resistance and creepage.
3 cl, 3 tbl, 7 dwg, 2 ex
SUBSTANCE: contamination protector contains fine particles of nitrogen dioxide, aqueous solvent containing alcohol dispersing specified particles of nitrogen dioxide, surface-active substance and splash modifier chosen among alkali metal compound, alkaline-earth metal compound, phosphorus compound, clay mineral and mixtures thereof. Specified contamination protector enters into the composition of specified aqueous solvent. It can be applied onto building board coating.
EFFECT: contamination protector and its adhesion to building board coating are enhanced.
3 cl, 30 dwg, 3 tbl, 30 ex
FIELD: anti-adhesion materials.
SUBSTANCE: invention relates to a composition comprising 0.1-4% of mixture of perfluoropolyoxaalkylene carboxylic acids of the general formula: wherein n = 3-50. For preparing colloidal solution of perfluoropolyoxaalkylene acid the composition comprises additionally 1-2% of amidoalcohol of the general formula: wherein n = 0 or 1; m = 1 at q = 1 and m = 2 at q = 0 that is prepared by interaction of dimer and/or trimer of hexafluoropropylene oxide with mono- and/or diethanolamine and water, up to 100. After treatment with the proposed composition surface of solid bodies acquires water-oil-repelling properties and the gluing seam rupture strength is reduced by two orders that accords with strength levels providing by the nearest analog representing a mixture of perfluoropolyoxaalkylene acids in coolants. Invention can be used for decreasing adherence of moldable plastic, crude rubber articles and other polymers to a tool and press-forms.
EFFECT: improved and valuable technical properties of composition.
1 tbl, 2 ex
FIELD: machine engineering, namely modification of rubbing surfaces of kinematic pairs.
SUBSTANCE: method comprises steps of placing between rubbing surfaces disintegrated mineral composition containing synthetic modification of serpentine produced by diluting in water mixture of α-quartz and magnesium hydroxide at temperature 120 - 170°C and pressure 1.2 - 15.0 at for further formation of crystals. Chrysotile having monocline syngony with coordination numbers 5.0< a< 7.3A°, 9.0<b< 9.2A°, 7.0<c< 7.3A° and with angles β between positive directions of crystallographic axes 90° or 93° is used as seed for producing crystal of synthetic modification of serpentine. Summed value of molar masses of α-quartz and magnesium hydroxide corresponds to molar mass of synthetic modification of serpentine. Composition includes in addition homologs of fullerenes Cm where m ≥ 60 at next relation of components, mass %: synthetic modification of serpentine, 70 - 90; homologs of fullerenes Cm, 10 - 30. Invention allows to form coating with receive friction factor lowered to 0.001, increased hardness HRC 90 - 95.
EFFECT: enhanced wear resistance, increased useful life period of coating, possibility for realizing method with use of oil lubricant and also without any lubricant.
SUBSTANCE: method comprises securing means of the anchor fastening to the surface, applying the lining material on the surface, solidifying the lining, AND drying the lining at a temperature sufficient to the melting of the coating at the means of anchor fastening. The device for anchor fastening is proposed.
EFFECT: enhanced reliability.
16 cl, 1 tbl, 3 ex
FIELD: processes to apply liquid or fluent material to obtain an anti-friction or anti-adhesive surface, particularly to produce siliconized wrapping paper.
SUBSTANCE: method involves mixing organopolysiloxanes-based silicone composition components; applying the obtained composition on movable paper substrate; heat-treating the obtained coating up to full coating hardening. Above paper substrate is wet-strength paper web with 6-8% moisture content. The paper is preliminary subjected to calendaring operation to obtain 1.0-1.1 g/cm3 density and 250-400 sec. smoothness. Silicone composition is applied by doctoring method, wherein silicone composition from local bath is applied on paper web moving between doctor blade and rear support. At least part of rear support surface in contact area between doctor blade and rear support is resilient. Degree of paper web bending during doctor blade introduction in the rear support is regulated by change in rear support surface resiliency. Unit for silicone composition application comprises doctor and rear support having changeable resiliency at least in contact area between rear support and doctor blade. Doctor blade is installed at acute angle to line perpendicular to rear support base and passing through contact line between rear support and doctor blade. Local bath is arranged in space defined by doctor blade and paper web.
EFFECT: increased application properties and strength of the paper, provision of reliable peeling force to paper separation from adhesive layer within wide temperature range, increased quality of composition application due to increased fullness of composition introduction in surface layer of paper web.
13 cl, 2 dwg
FIELD: processes for applying fluent materials to surfaces to obtain anti-friction surface with the purpose to reduce hydraulic and aerodynamic friction of vehicle moving in liquid and to reduce friction in friction assemblies of machines and mechanisms working in aqueous medium.
SUBSTANCE: method involves obtaining and applying antifriction coating on vehicle body so that specific coating surface energy along liquid streamlines (streamline surface) has negative gradient.
EFFECT: reduced friction due to provision of friction resistance control.