Self-lubricating mower blade and method for manufacturing same

[0102] Such as figure 1 As shown, the cutting module 1 used for the hair or hair electric clipper generally includes two knives 2 and 3, and the two knives 2 and 3 are moved by a non-illustrated and in the industry in an alternate translational movement relative to each other. Well-known mechanism drive. Often the lower cutter 2 is fixed relative to the base of the clipper, while the upper cutter 3 is movable relative to the lower cutter 2.

[0103] The fixed cutter 2 includes a main body 4 from which a set of teeth or blades 5 extend, and the set of teeth or blades 5 each have a substantially triangular shape, such as figure 1 Shown. Similarly, the movable cutter 3 includes a main body 6 which carries a set of teeth 7 each of which is also substantially triangular in shape. Unlike the blade 5 of the fixed knife 2, the teeth 7 of the movable knife 3 each have two sharp edges according to the example, the two sharp edges forming corresponding triangle edges. Of course, the teeth 5 of the fixed tool 2 may also have sharp edges.

[0104] The teeth 7 of the movable tool 3 are arranged substantially above the teeth 5 of the fixed tool 2, and the lower surface of the teeth 7 is at least partially supported on the upper surface of the teeth 5. In addition, the main body 6 of the movable cutter 3 has a flat surface at the lower surface 10 that contacts the flat surface of the upper surface 11 of the fixed cutter 2.

[0105] In order to limit friction, the present invention proposes to use a self-lubricating material to make at least one tool or even two tools 2 and 3, and the self-lubricating material is formed with a matrix in which solid lubricant is dispersed. The matrix can be metal, ceramic or also the properties of a cermet composition, which is also called a cermet.

[0106] Therefore, according to the present invention, the matrix is ​​therefore formed of a material selected from the group consisting of metals, metal alloys, ceramics, ceramic mixtures, cermet compositions, mixtures of these materials.

[0107] More precisely, the structural solid is selected from:

[0108] -steel,

[0109] -stainless steel,

[0110] -Low-alloy steel,

[0111] -Metal alloys (for example: iron-based, nickel-based, copper-based, cobalt-based, titanium-based metal alloys),

[0112] -Magnetic alloy,

[0113] -High temperature resistant metal,

[0114] -Hard metals,

[0115] -Ceramics (for example: based on alumina, zirconia, calcium oxide, magnesium, silicon dioxide and various nitrides and carbides, especially tungsten carbide),

[0116] -A mixture of these materials.

[0117] Preferably, the constituent material of the substrate is stainless steel, for example, stainless steel of the generally designated variety 316L.

[0118] The solid lubricant is preferably selected from: molybdenum disulfide MoS 2 , Boron nitride BN, graphite, tin Sn or copper Cu or zinc Zn or lead Pb or alloys of these metals, silver Ag, mixtures of these materials.

[0119] More particularly preferably, the solid lubricant used is molybdenum disulfide MoS 2.

[0120] The tool using this self-lubricating material according to the present invention is manufactured on the basis of powder injection molding technology, and its English abbreviation is PIM (Powder Injection Molding). In the case of metal matrix, this technology refers to metal injection molding, and its English abbreviation is MIM (Metal Injection Molding), and in the case of ceramic matrix, this technology refers to ceramic injection molding, and its English abbreviation is CIM (Ceramic Injection Molding). Molding).

[0121] According to the preferred but non-exclusive manufacturing method of the self-lubricating material cutter of the present invention, the manufacturing process involves the preparation of particles of solid compounds used in the injection molding stage, which will appear below. However, according to the present invention, the preparation of solid compound particles can be achieved by a third party who provides these particles to the manufacturer of the clipper cutter according to the present invention or the mechanical parts made of self-lubricating material according to the present invention. In traditional powder injection molding methods, the solid mixture that makes up the particles is often called "feedstock."

[0122] The particle preparation of the solid compound involves heating-related mixing or stirring of at least three components, namely:

[0123] -Structured solid particles used to form the matrix,

[0124] -Particles of solid lubricant used to form particles of solid lubricant dispersed in the matrix, and

[0125] -A binder, which is used to ensure the bonding of the structural solid and the particles of the solid lubricant in the injection molding step, and is used to be removed after this step, which will appear below.

[0126] The binder can be of any suitable kind and is selected, for example, from:

[0127] -Based on thermoplastic polymers (for example: polyethylene, polypropylene, polystyrene, polyamide, polyméthacrylate de butyle, polycarbonate,...) or waxes (for example: natural wax, paraffin wax, acrylic Ethyl diamide (ethylènediamide wax) adhesive,

[0128] -Polyacetal adhesive (for example: polyoxymethylene),

[0129] -Water-soluble adhesives (for example: polyethylene glycol, or polyvinyl alcohol/polyvinyl acetate copolymer (copolymère alcool de polyvinyle/polyacétate de vinyle)),

[0130] -Gelling or cross-linking binders (for example: polysaccharides, agar, methyl cellulose, (methoxy) polyethylene glycol (glycol de (méthoxy) polyéthylène), acrylic polymer),

[0131] -glass,

[0132] -A mixture of the above adhesives.

[0133] When the solvent is water, the binder may be, for example, more precisely an organic base or a base organique ou aqueuse. The binder may mainly contain some of the above polymers, but may also contain additives in a smaller proportion, such as other waxes, stearic acid, oleic acid, esters, glycerin, boric acid, phthalic acid esters, or guanidine. These additives can, for example, have: the function of a dispersant, which is used to avoid too coarse aggregates of solid particles; the function of a reagent, which wets the powder, is used to ensure uniform packaging of the solid particles during stirring; the function of a plasticizer, It is used to reduce the viscosity of the fluid obtained by heating the particles of the solid mixture; or it also has the function of a reagent, that is, the function of debinding, which facilitates the removal of different components of the binder between the forming step and the sintering step.

[0134] The ideal properties of adhesives studied by different ingredients can be, for example: the adhesive makes the powder well dispersed and wetting; the adhesive allows the mixture to have a small viscosity at low temperatures for injection; the adhesive has heat resistance to molding The adhesive is chemically inert and stable; and the adhesive is easily removed during the corresponding steps.

[0135] The powders of structural solids and solid lubricants used for preparing particles of solid compounds preferably include a size less than or equal to 100 μm, preferably a size between 0.1 μm and 50 μm, and more particularly preferably between 1 μm and 20 μm Of particles. The size of less than 1μm can be preferred, so that the applied powder reacts greatly in the subsequent sintering step; this can allow lowering the sintering temperature and reducing the sintering duration, or relying on obtaining very fine particle sizes Structure to increase the corrosion resistance of the final part.

[0136] The size distribution of the constituent particles of the powder can be selected in a wide range of ways in order to increase the compactness of the final part. In fact, small particles occupy the gaps between the largest particles. The geometry of the particles can also be selected according to the desired effect. In fact, the roughly spherical shape of the particles facilitates molding, while the angular or more irregular shape helps the molded parts to bond after the binder is removed and before sintering. Therefore, it is possible to mix regular-shaped particles and irregular-shaped particles. In this respect, when the structural solid is an iron alloy, the powder obtained by atomization of liquid water includes approximately spherical particles, and the powder obtained by gas atomization includes irregularly shaped particles.

[0137] In order to ensure on the one hand the fluidity required for the injection and molding of the heated mixture without inhomogeneity or bubbles, and on the other hand to obtain an intermediate part after the injection molding step is completed, and the intermediate part has enough to ensure its The firmness and the cohesiveness that allows its operation should ensure that the solid particles are evenly wrapped with the adhesive, while using the smallest amount of adhesive and ensure the large compactness of the solid particles in the subsequent molded parts.

[0138] The volume of the structured solid and solid lubricant particles called "taux de charge" corresponds to between 40% and 75% of the volume of the solid mixture before particle manufacture, preferably between 55% and 60%. between. The packing rate is preferably selected to correspond to a volume percentage slightly less than the "critical packing rate", which ratio makes all the particles of the structural solid in contact with other binding and lubricating components filling the gap. If the critical filling rate is exceeded, injection will no longer be possible. The volume of the adhesive is equivalent to the volume complement.

[0139] The volume percentage of the binder is preferably selected such that, on the one hand, the particle surface of the structural solid and the solid lubricant in the particles is completely covered, and on the other hand, the amount of the binder is sufficient to ensure that the mixture is suitable for injection and molding. Fluidity without excessive amount of adhesive, so as not to cause defects, such as lack of adhesion and durability of parts after adhesive removal, and lack of uniformity of molded parts and The existence of bubbles.

[0140] During the stirring, the mixture is heated to a temperature located in the melting zone of the binder, and preferably around the melting temperature of the binder. Stirring is ensured during a duration sufficient to allow the particles of structural solids and solid lubricants to be uniformly encapsulated by the binder. Stirring can be achieved by means of a mixer or extruder, which induces viscous mixing at a strong shear rate, which allows a homogeneous mixture to be obtained.

[0141] After stirring, the mixture thus obtained is cooled either in an accelerated manner or by natural cooling of free air, until one or more blocks of larger size are formed.

[0142] The mixture in solid form is ground to produce particles of solid compounds or solid mixtures, which include particles of structural solids, particles of solid lubricants, and binders.

[0143] The particles of the solid compound can be stored for a long or short period of time before its implementation. The implementation of these particles is used to manufacture molded parts made of self-lubricating materials, such as the cutter of the clipper according to the present invention.

[0144] The molding of the molded part is performed in a pressure injection press, such as a press used for plastic injection molding. In this press, the particles of the solid mixture are first stirred and heated to a temperature that is greater than or equal to the melting temperature of the binder and on the one hand less than the melting temperature of the structural solid and on the other hand less than the solid lubricant The melting temperature. The viscous fluid thus obtained is pressure-injected into a mold that has a shape corresponding to the shape of the part at the end of the manufacturing process, while taking into account the shrinkage phenomenon that will occur during processing after molding.

[0145] The molded part is cooled to a temperature less than the melting temperature of the adhesive under pressure inside the mold to solidify the adhesive and thus impart a durability to the part that allows it to shrink from the mold or Demould without risk of deformation.

[0146] After this cooling, the molded part is therefore preferably removed from the mold by an automatic device, in order to avoid its alteration. In fact, molded parts are brittle when they are integrally formed of structural solids and solid lubricant particles, and the structural solids and solid lubricant particles are held between each other by a binder.

[0147] After demolding, the molded part undergoes a step of removing the adhesive, which is sometimes referred to as "debonding." This step, which is performed in a way that does not damage the geometry of the part, can be performed in different ways.

[0148] By thermal methods, if possible, under controlled atmospheric pressure, the part undergoes one or more controlled temperature change steps (temperature rise or fall rate, temperature retention level during a certain duration, etc.). The different components of the binder that have a lower physical transition temperature than structural solids and solid lubricants can be removed, for example, by evaporation, decomposition or even pyrolysis.

[0149] By chemical methods, the components of the adhesive can be achieved by using solvents such as water, organic solvents or supercritical CO 2 To remove. The removal of certain components of the binder can also be achieved from a catalytic reaction, for example in the trademark of BASF In the case of the commercially available particle series binder, chemical depolymerization at 120°C under nitric acid.

[0150] Combinations or combinations of different treatments for removing all components of the adhesive are also possible. In fact, the adhesive may consist of at least two components, one of which is for example wax, which drains more quickly and therefore allows the internal passage to the external pores to be opened to facilitate the removal of other components and possibly other components. This discharge occurs without overpressure, which may damage the parts or even cause the parts to burst.

[0151] At the end of the step of removing the binder from the molded part, a very porous part formed of particles of structural solid and particles of solid lubricant is obtained. The part can actually contain residues of the adhesive, which allow the solid particles to be held between each other. The porous part is particularly brittle and does not have the mechanical properties required for its implementation for targeted applications.

[0152] Then, a sintering operation is implemented in which the reducing agent is heated in a controlled atmosphere, for example, to avoid corrosion of the metal. It should be noted that if residues of the binder still exist after the removal operation, the removal of these residues is ensured in the sintering furnace in view of the high temperature required to achieve this step. In this respect, the binder removal step and the sintering step can be carried out in the same furnace, which further avoids moving very brittle porous parts.

[0153] During sintering, the parts are densified and reinforced due to solid diffusion and particle growth. Sintering can involve one or more heating stages, if possible, one or more stages maintained at a certain temperature and one or more cooling stages. During sintering, the molded part is heated to a high temperature, but the high temperature is preferably slightly less than the melting temperature of the structural solid and slightly less than the melting temperature of the solid lubricant.

[0154] The selected sintering temperature can be, for example, between 1000°C and 1200°C. When the structural solid is stainless steel and the solid lubricant is molybdenum disulfide MoS 2 At this time, the sintering temperature may be between 900°C and 1250°C, preferably between 1000°C and 1185°C. Therefore, the sintering temperature may be about 1100°C.

[0155] During sintering, the molded part undergoes isotropic shrinkage generally between 10% and 20%, so that the size of the mold used in the injection step should be considered.

[0156] After the sintering step, the mechanical parts can be subjected to further processing if possible, for example, through hot isostatic pressing (HIP (Hot Isostatic Pressing) in English) to finally determine the density to 100%, heat treatment, coating or processing applications . However, note that after sintering, the part has mechanical properties that allow it to be implemented in targeted applications. Therefore, within the scope of the present invention, after sintering, the clipper cutter can be directly assembled to form figure 1 The clipper cutting module shown. This final part is not porous and has a density greater than 95% of the theoretical density of the structural solid, which imparts good mechanical properties to these parts, which are comparable to those of bulk parts obtained using other manufacturing methods. Performance is comparable.

[0157] It should be noted that the method according to the present invention can be used to manufacture mechanical parts other than clippers.

[0158] According to the above-mentioned embodiment, the teeth of the cutter have a triangular shape. However, the teeth of the tool may have any other suitable shape, such as a diamond shape connected to the tool body through the top or other more complex shapes.

[0159] Of course, various modifications can be made to the manufacturing method according to the invention and the clipper cutter according to the invention within the scope of the appended claims.