Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
  • B05D5/08—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
  • F02F3/00—Pistons 
  • F02F3/10—Pistons  having surface coverings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/32—Processes for applying liquids or other fluent materials using means for protecting parts of a surface not to be coated, e.g. using stencils, resists

Definitions

• the present invention relates to a method for coating a surface, in particular a piston skirt of an internal combustion engine, with a dry lubricating film with high mechanical resistance and low coefficient of friction.
• the object of the invention is mainly to reduce friction between the skirt of the piston and the cylinder. It is in fact known that the main function of the piston skirts is to guide the piston in the cylinder while avoiding any risk of seizure, the upper part of the piston being composed of ring holders which seal between the chamber and the lower part of the engine. The friction between the skirt and the resulting cylinder is therefore a source of noise, loss of energy and damage to the surfaces. In order to remedy these drawbacks, several solutions have been considered.
• patent application EP0380415 describes a composite coating, based on a resin from the family of sulfonic polymers, which is fixed to the skirt of the piston by screwing, shrinking or gluing. This invention has the disadvantage of adding an assembly step between the piston skirt and the very restrictive coating in terms of manufacture and mechanical strength.
• patent FR2808461 proposes a process for depositing pure polyaryietherketone by pure thermal spraying on the piston skirt, but it has the drawback of being restrictive in terms of equipment, since it requires the use of projection torches.
• patent EP0614416 proposes a solution which consists in coating by transfer pad the piston skirt with a paste comprising a dry moistened lubricant then in drying the paste.
• the dry lubricant is composed of a fluoropolymer or graphite or molybdenum disulphide mixed with a binder and a very volatile organic solvent such as acetone.
• the object of the present invention is to propose a method for coating a surface, in particular a piston skirt of an internal combustion engine, with a dry lubricating film with high mechanical resistance and low coefficient of friction. overcoming all or part of the drawbacks noted in the prior art detailed above.
• said process consists in: - coating the surface of a paste produced in an aqueous solvent and comprising a polymer with low coefficient of friction, - heating said film at a temperature T for a period t, of so that said film has an amorphous structure,
• the step of coating the surface with the paste can be followed by a step of drying said paste so as to obtain a dry lubricating film.
• the step of heating said film can be followed by a step of cooling said film so that said film largely retains its amorphous structure.
• Said low friction polymer is preferably a polyaryiether ketone.
• said paste can be produced from a mixture of water, a binder in the proportions of 2 to 5% by mass, a dispersant in the proportions of 1 to 3% by mass, of an anti-foaming agent in the proportions of 5 to 30 ppm, to which is added the polymer with a low coefficient of friction in the proportions of 60 to 80% by mass.
• Said paste can also contain non-organic compounds with a lubricating property, and preferably in proportions of less than 10% by mass.
• Said inorganic compounds are one or more of the following compounds: molybdenum disulphides, carbon, carbon nanotubes, silicon carbides or even graphite.
• the step of coating the surface with said paste can be preceded by a step of preparing the surface which comprises at least a first step of cleaning said surface using a solvent or 'A detergent.
• the temperature T is preferably between 350 ° C and 450 ° C.
• the duration t is preferably between 5 s and 15 s.
• the cleaning can be followed for example by a sandblasting operation which consists in spraying silica grains at high speed on the skirts 7a, 7b so as to create small impacts which favor the attachment of the film 3.
• a sandblasting operation which consists in spraying silica grains at high speed on the skirts 7a, 7b so as to create small impacts which favor the attachment of the film 3.
• this operation is optional insofar as the skirts 7a, 7b admit a base roughness of approximately 20 microns which allows sufficient attachment of the film 3 to said skirts.
• the preparation of the dough is carried out from a mixture of water, a binder in the proportions of 2 to 5% by mass, a dispersant in the proportions of 1 to 3% by mass, of an anti-foaming agent in the proportions of 5 to 30 ppm, to which is added a polymer with a low coefficient of friction in the proportions of 60 to 80% by mass.
• the proportions by percentage by mass refer to the total mass of the paste consisting of the mixture of water, binder, dispersant, anti-foaming agent, polymer with a low coefficient of friction.
• the polymer with a low coefficient of friction is preferably a polyaryiether ketone sold under the name of Poly Ether Ether
• Ketone PEEK TM. It is a semi-crystalline polymer, the basic formula of which is as follows: oxy-1, 4-phenylene-oxy-1, 4-phenylene-carbonyl-
• Polyaryietherketone is a polymer with a low coefficient of friction which gives tribological properties to film 3 and which therefore makes it possible to significantly reduce the friction observed between the piston skirts and the cylinder. More precisely, compared with the results obtained with dry lubricating films comprising fluorinated polymers, graphite or molybdenum disulphide, a reduction of up to 20% in friction is observed in hydrodynamic lubrication regime, which allows a gain in consumption. in fuel of at least 1%. It was also chosen for its high chemical inertness and good mechanical performance, especially at high temperatures. In hydrodynamic regime, it indeed admits a surface energy at least twice lower than fluoropolymers, graphite and molybdenum disulfide.
• the binder it is advantageous to use two ultra-fine powders of low viscosity, either with an average particle size of 25 ⁇ m, or with an average particle size of 10 ⁇ m.
• RHODOVIOL 25/140 TM which is a polyvinyl alcohol obtained by hydrolysis of polyvinyl acetate. It helps to promote the adhesion of the paste on the surface to be coated.
• anti-foaming agent it is advantageous to use the
• BEVALOID 581 B TM It is a mixture of aliphatic hydrocarbons and nonionic surfactants. It avoids the foaming phenomena that appear when mixing PEEK TM powder in water. Regarding the dispersant, it is advantageous to use SINNOPAL OP11 TM. It is a non-anionic surfactant (Octylphenol ethoxyl), which avoids the settling of the PEEK TM powder in solution.
• the preparation of the dough is carried out according to the same recommendations as those described in the first embodiment, except that one or more non-organic compounds with lubricating property are added in proportions less than 10% by mass.
• the percentages by mass refer to the total mass of the paste made up of the water, binder, dispersant, anti-foaming agent, polymer with low friction coefficient, non-organic compounds with lubricating properties.
• non-organic compounds with lubricating properties it is advantageous to use molybdenum disulphides, carbon nanotubes, carbon, silicon carbides or even graphite in proportions of less than 10% by mass.
• These inorganic compounds are in the form of powder admitting an average particle size, G, in accordance with that specified in the table below:
• the presence in the paste of one or more of these non-organic compounds is particularly desirable, insofar as they optimize the mechanical properties in terms of friction and of the wear resistance of the film 3.
• the addition of molybdenum disulfide or carbon nanotubes in proportions of 10% by mass makes it possible to reduce by around 15% the coefficient of friction corresponding to a film obtained according to the first embodiment of the paste, that is to say with a paste produced from a mixture of water, a binder in the proportions of 2 to 5% by mass, a dispersant in the proportions of 1 to 3% by mass, an anti-foaming agent in the proportions of 5 to 30 ppm, and of the polyaryiether ketone in the proportions of 60 to 80% by mass.
• the addition of molybdenum disulphides, carbon nanotubes, carbon, silicon carbides or even graphite in proportions of 10% by mass makes it possible to increase resistance to wear corresponding to a film obtained according to the first embodiment of the paste.
• the process for depositing the dough on the skirt 7a, 7b can be carried out by a process of the screen printing type, which consists in rotating the piston 1 around its axis 2 and in bringing the skirt 7a, 7b into contact with a sieve, not shown in Figure 1, through which flows said dough.
• a process of the screen printing type which consists in rotating the piston 1 around its axis 2 and in bringing the skirt 7a, 7b into contact with a sieve, not shown in Figure 1, through which flows said dough.
• a thermal spraying process it is not necessary to mask the area of the grooves 5 of the piston 1 provided for the segments, to prevent the dough from being deposited there.
• the piston 1 it is advantageous to heat the piston 1 to a temperature of approximately 200 ° C. in order on the one hand to dry the dough so as to obtain the dry lubricating film 3 and in order on the other part of avoiding the thermal shocks which result from the heat treatment which will follow and which is located at the level of said film 3 and not over the entire thickness of the skirt 7a, 7b.
• a temperature T for a duration t.
• the heating device can use YAG laser technology or C02 lasers with a power between 800 and
• the temperature T is between 350 ° C and 450 ° C.
• the duration t is between 5 s and 15 s. So that the film 3 largely retains its amorphous structure, it must then be cooled. Using the YAG laser heater as described above, simple cooling with ambient air results in a semi-crystalline structure. According to the method described above, the thickness of the film 3 is from 20 to 100 ⁇ m. According to an alternative sintering method, the film can be sintered by means of a heating device other than the laser, such as an induction heating device. The temperature T is then between 380 ° C and 450 ° C and the duration t is reduced to an interval of 4 to 8 s.
• the cooling advantageously comprises a first air quenching intended to cool the surface of the skirt 7a, 7b to a temperature of approximately 260 ° C. then a second quenching with water, intended to bring the film 3 to the room temperature, while retaining an amorphous structure.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Pistons, Piston Rings, And Cylinders (AREA)

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• 2005
  • 2005-05-11 WO PCT/FR2005/050312 patent/WO2005114038A2/fr not_active Ceased
  • 2005-05-11 EP EP05762671A patent/EP1745205A2/de not_active Withdrawn

Non-Patent Citations (1)

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