FR2747753A1 - Non-magnet friction material for brake pads - Google Patents

Abstract

The non-magnetic friction material has a thermo-hardening binder, a non-magnetic fibrous armature, a friction modifying organic additive, a solid lubricant and a charge of calcium fluoride. The calcium fluoride content is between 2 and 35% of the total weight of the friction material. The binder resin is between 5 and 15% by weight and the organic additive between 3 and 20% by weight. The solid lubricant is between 3 and 15% by weight and the mineral charge is between 25 and 70% by weight. The fibrous armature is between 3 and 15% by weight.

Description

 The present invention relates to a friction material which contains calcium fluoride. More specifically, the invention relates to friction materials without asbestos which can be used in brake pads, brake linings, clutch linings and other types of friction materials for industrial machines, for railway vehicles , for commercial vehicles and for cars and which have a clearly reduced noise creation while having a high profitability.

 Friction materials (such as brake pads, brake and clutch linings) for brakes and clutches generally contain the following essential ingredients: binders of a thermosetting resin, for example phenolic resin, friction-modifying adjuvants, for example resin dust, mineral fillers, such as barium sulphate, and fibrous asbestos-free reinforcing materials, such as organic, mineral and metallic fibers (see, for example, United States patent United States of America No. 4,785,029).

 One of the most important performance conditions of friction materials is the noise properties (limited creation of noise when braking). Since a significant part of the disc brake and similar market requires noise reduction, reduced noise creation is considered to be an essential consideration in practical applications, so that the reduction of noise creation risks (good properties of noise) is one of the most important characteristics of friction materials.

 Various attempts have already been made to develop friction materials having excellent noise properties. Two conventional methods are the addition of solid lubricants, such as graphite and molybdenum disulphide, intended to give regular friction which reduces the risk of creating noise, and the addition of friction-modifying adjuvants, such as mahogany dust, so that the damping characteristics of the friction material are better and reduce the risk of noise creation due to the friction material.

 These methods can give some reduction in noise, but none of them is completely satisfactory, and there is still a need to develop a friction material with better noise properties.

 The subject of the invention is therefore the production of an asbestos-free friction material which has excellent noise properties and which is also satisfactory from the point of view of profitability.

 Following extensive studies carried out for this purpose, the inventors have found that this object can be achieved by using calcium fluoride as an ingredient in the friction material. The invention was made on the basis of this discovery.

 The invention therefore relates essentially to an asbestos-free friction material which contains a binder of a thermosetting resin, a non-asbestos fibrous reinforcement, an organic friction-modifying adjuvant, a solid lubricant, a mineral filler and calcium fluoride.

 In a preferred embodiment of the invention, the content of calcium fluoride is between 2 and 35% of the total weight of the friction material.

 In another preferred embodiment of the invention, the thermosetting resin binder is present in an amount of 5 to 15 k by weight, the fibrous reinforcement in an amount of 3 to 15 W by weight, the organic friction-modifying adjuvant at a rate of 3 to 20 W by weight, the solid lubricant at a rate of 3 to 15 k by weight, and the mineral filler at a rate of 25 to 70 Oo by weight relative to the total amount of the friction material.

 By using calcium fluoride as an additional ingredient, an asbestos-free friction material can be produced at low cost which reduces friction vibrations and also reduces noise. In addition, satisfactory wear resistance is maintained, and the attack of various cooperating surfaces can be reduced.

 We now describe an embodiment of the invention.

 The asbestos-free friction material according to the invention contains a binder of a thermosetting resin, a fibrous reinforcing material, a solid lubricant, a mineral filler and an organic friction-modifying adjuvant, as essential ingredients, and it also contains calcium fluoride.

The calcium fluoride (CaF2) used as an additional ingredient according to the present invention is generally called "fluoride" and it is not subject to any particular restriction; however, more specifically, it preferably has an apparent density of between 1.4 and 1.8 g / cm3 ("CB-0010", particle size less than 300 μm), a true density of between 2 and 3.3 (measured with respect to air), a hardness equal to 4 on the scale
Moh, and a melting temperature of 1350 OC.

 The particle distribution of the calcium fluoride is such that the maximum of the particle size is preferably close to 300 ssm or less, preferably 45 µm or less.

 Calcium fluoride which meets these conditions is commercially available from various manufacturers, for example from Kinseimatec Co. Ltd. under the trademark "Hotaruishi Y".

 The calcium fluoride content is preferably between 2 and 35% by weight and advantageously between 5 and 15 k of the total weight of the friction material. When the calcium fluoride content is within these ranges, satisfactory noise properties can be preserved without increasing the wear range.

 The role of the thermosetting resin binder used according to the invention is to maintain the other ingredients of the friction material in cooperation in the form of a single mass and they may be phenolic resins (unbranched phenolic resins, as well as rubber and other modified phenolic resins), melamine resins, epoxy resins, cyanate ester resins, etc. Among these resins, phenolic resins are preferable. The thermosetting resin binder is for example used in an amount between 5 and 15 W of the total weight of the friction material.

 The fibrous reinforcement used according to the invention consists, for example, of metallic fibers such as copper, brass and steel fibers, organic fibers, for example aromatic polyamide (for example aramid fibers) and flame retardant acrylic fibers, and asbestos-free mineral fibers such as potassium titanate fibers, glass fibers, alumina fibers, carbon fibers and rock wool. These fibers can be used alone or in combination.

The fibrous reinforcement is preferably used in an amount between 3 and 15 W and very advantageously between 3 and 10 k of the total weight of the friction material.

 The organic friction-modifying adjuvant used according to the invention consists for example of resin dust (mahogany dust and melamine resin dust), rubber dust, etc. These modifying adjuvants can be used alone or in combination. The organic friction-modifying adjuvant is preferably incorporated in an amount of between about 3 and 20 W and preferably between 3 and 10 W of the total weight of the friction material.

 The solid lubricant used according to the invention can be for example graphite, molybdenum disulfide, etc. These substances can be used alone or in combination. The solid lubricant is preferably incorporated in an amount of between approximately 3 and 15% by weight and advantageously between 3 and 10% by weight relative to the total weight of the friction material.

 The mineral filler used according to the invention can consist, for example, of particles of hard metal oxides (for example of alumina, of silica and of zircon) of metallic particles (for example of copper, of brass, of iron or of zinc ), mineral materials in the form of scales (for example "Vermiculite" and mica), and mineral compounds (for example barium sulphate, calcium carbonate and magnesium oxide). These substances can be used alone or in combination. The mineral filler is preferably incorporated in an amount of between approximately 25 and 70 W and preferably between 25 and 60 k of the total weight of the friction material.

 The asbestos-free friction material according to the invention can be produced by dry or wet-type treatment.

In the dry process, the raw material powders of all the ingredients described above are uniformly mixed, and the resulting mixture is shaped by heating under pressure (more precisely, the mixture is previously shaped in a mold, transferred in a heated mold in which a support plate has been mounted, hot pressed to form an integral part of the support plate, then polymerized later). In the wet-type process, the powders of all the ingredients are mixed as a uniform wet mass in the presence of a solvent (wetting agent), and the resulting wet mixture is dried and then hot pressed.

 The wetting agent used in the wet type process is not limited to a particular type, but a flocculating and binding agent in the form of a water-alcohol solvent system is advantageously used. A particular operation carried out in the wet type process with such a flocculating agent forming a binder is as follows: while the abovementioned ingredients are being dry-mixed, the flocculant forming a binder in the form of a water-alcohol solvent system is added and mixed with the ingredients for the preparation of a wet and viscous mixture which is then granulated and dried for the formation of dry granules.

The use of the water-alcohol solvent system has the advantage, even when the aforementioned operation of granulation of the wet mixture for feeding and drying the granules is adopted to avoid the formation of dust in the drying step, of not not allow the granules to break during granulation or drying due to mechanical operations such as transfer and vibration. The resulting dry granules are subjected to hot compression in a heated mold in which a support or support plate has been incorporated, so that the granules are shaped so that they are integral with the support plate, and the part obtained undergoes a subsequent polymerization intended to produce the desired friction material. The known conditions can be used for the execution of the molding operations which have just been described (see for example the patent of the United States of America No. 5,433,907).

 We will now describe examples of implementation of the invention.

(1) Preparation of friction material samples
The following table indicates the types and quantities (in percentages by weight) of the ingredients used for the preparation of samples of the friction material of Examples 1 to 6 and of Comparative Example 1. Calcium fluoride, forming an additional ingredient , is available from Kinseimatec Co. Ltd under the trademark "Hotaruishi Y" and has the following properties: 80 W of CaF2, apparent density 1.4 to 1.8 g / cm3, true density 3.0 to 3 , 3, hardness on the Moh scale 4, melting temperature 1 350 OC, particle size number 88 to 95 (that is to say nominal size = 45 µm).

 The ingredients indicated in the table were subjected to dry mixing in a mixer in the presence of an added solvent system formed of water and ethanol (10 mol of water per mole of ethanol), and the resulting wet mixture is passed through an extrusion granulator for the formation of granules having an average granular dimension of 5 mm and an average length of 10 mm, then the granules were dried at approximately 105 ° C. until their moisture content was less than or equal at 1.0 k; the dry granules were stacked in a hot mold having a temperature setting of 150 OC, then underwent hot compression at a pressure of 400 bar, then a polymerization subsequent to 250 OC allowed the preparation of samples of the material friction in the form of brake pads. These samples had a thickness of 10 mm and each of them had a friction surface of 50 cm2.

(2) Assessment of noise properties
The brake pads thus prepared (as samples of the friction material) were mounted on a vehicle driven at a speed of 40 km / h and the noise properties were evaluated by a subjective test of the level of noise created by vibration for a deceleration equal to 0.4 G. The noise level was classified into five levels and the criteria for evaluating the noise properties were as follows s for the values from 1 to 2, O for a value of 3, X for a value from 4 to 5. The results are shown in the table below.

Board
Examples Example
Compa ingredient
1 2 3 4 5 6 rat 1
Fibrous reinforcement
Aramid fibers 5 5 5 5 5 5 5
Binder
Phenolic resin 10 10 10 10 10 10 10
Modi organic admixture
friction cracker
Mahogany dust 10 10 10 10 10 10 10
Solid lubricant
Graphite 7 7 7 7 7 7 7 7
Mineral filler
Barium sulfate 28 28 28 28 28 23 28
Calcium carbonate 25 20 10 - 28 - 25
Mica 5 5 5 5 5 5 5
Copper powder 5 5 5 5 5 5 5
Alumina powder - - - - - - 5
Calcium fluoride 5 10 20 30 2 35
Total 100 100 100 100 100 100 100 Noise level ooe @ e O e X
As clearly indicated in Table 1 in which the numerical values are given in percentages by weight, the friction material samples containing calcium fluoride gave only low levels of vibration and therefore had satisfactory noise properties.

 The asbestos-free friction material according to the invention has excellent profitability and yet satisfactory noise properties. In addition, it has satisfactory wear resistance and the attack is reduced on various cooperation surfaces.

 Of course, various modifications can be made by those skilled in the art to the friction materials which have just been described solely by way of nonlimiting example without departing from the scope of the invention.

Claims (7)

 1. Friction material without asbestos, characterized in that it comprises a thermosetting resin binder, a fibrous reinforcement without asbestos, an organic adjuvant modifying friction, a solid lubricant, a mineral filler and calcium fluoride.  2. Material according to claim 1, characterized in that the content of calcium fluoride is between 2 and 35% of the total weight of the friction material.  3. Material according to claim 1, characterized in that the thermosetting resin binder is contained in an amount between 5 and 15% by weight, the fibrous reinforcement in an amount between 3 and 15% by weight, the modifying organic adjuvant friction in an amount between 3 and 20% by weight, the solid lubricant in an amount between 3 and 15% by weight and the mineral filler in an amount between 25 and 70% by weight relative to the total amount of friction material .  4. Material according to claim 2, characterized in that the thermosetting resin binder is contained in an amount between 5 and 15% by weight, the fibrous reinforcement in an amount between 3 and 15 Oc by weight, the modifying organic adjuvant friction in an amount between 3 and 20% by weight, the solid lubricant in an amount between 3 and 15% by weight and the mineral filler in an amount between 25 and 70% by weight relative to the total amount of friction material .  5. Material according to claim 1, characterized in that the content of calcium fluoride is between 5 and 15 W of the total weight of the friction material.  6. Material according to claim 1, characterized in that the thermosetting resin binder is contained in an amount between 5 and 15% by weight, the fibrous reinforcement in an amount between 3 and 10 W by weight, the modifying organic adjuvant friction in an amount between 3 and 10% by weight, the solid lubricant in an amount between 3 and 10% by weight and the mineral filler in an amount between 25 and 60 Oc by weight relative to the total amount of friction material .  7. Material according to claim 1, characterized in that the thermosetting resin binder is contained in an amount between 5 and 15% by weight, the fibrous reinforcement in an amount between 3 and 10% by weight, the modifying organic adjuvant friction in an amount between 3 and 10% by weight, the solid lubricant in an amount between 3 and 10% by weight and the mineral filler in an amount between 25 and 60% by weight relative to the total amount of friction material .