MIXTURE COMPOSITION FOR FRICTION MATERIAL

Abstract: A mixture composition for friction material is described, comprising: a base alloy including elements such as zirconium, titanium (in the form of oxides) and a solid lubricant formed from a mixture of graphite and molybdenum (in the form of disulphide); phenolic resins in powder form, including friction powders; copper sulphide; baryta; amorphous graphite; and nitrylic type powdered rubber.

Description: MIXTURE COMPOSITION FOR FRICTION MATERIAL DESCRIPTION BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to the composition of a mixture for friction material and more specifically to a mixture for brake material suitable to be applied in the field of brake materials for light and heavy vehicles. An object of the present invention is to provide a mixture of this kind that contains no substances that are toxic or harmful to the health. 2. Description of The Prior Art It is known that brake material, more commonly known as friction material, is made up of a composition of materials comprising a base structure of brake material and also chemical additives typical for the field of use of the brake material itself. The fields of use may be divided into three sectors: a. Low load field of use: this is the field generally comprising light vehicles such as mopeds, cars, etc. in which the characteristics required of the mixture are those of having a high friction coefficient, as short stopping distances or times are required. The heat developed over a short time dissipates in an equally short time. b. Medium load field of use: this field includes uses of medium severity such as brakes for industrial machinery, brakes for cranes, etc., in which a higher temperature resistance and a lower friction coefficient is required compared to the low load field mentioned above; in fact in this case the braking loads involved are higher and the stopping times are longer. c. High or serious load field of use: this field includes the use of serious loads such as trains, military armoured vehicles, speed brakes for cranes, etc. in which a high temperature resistance is required due to the large amount of heat developed, along with a low friction coefficient because short braking times and distances are not required. In any case in all these fields of use, the mixture used according to the prior art contains as basic materials, although in variable proportions, asbestos, lead and zinc, which are notorious environmental pollutants and constitute a health risk. It is also known that the chemical and physical characteristics of these braking materials containing asbestos do not give a satisfactory response to the phenomenon known as "FADE", which consists in a fall in the friction coefficient level due to the increase in temperature and the failure to recover the original level of said coefficient in time for the next braking operation. SUMMARY OF THE INVENTION In view of the problems illustrated above, the present invention has the object of providing a mixture composition for friction material that does not have among its component materials asbestos, lead and zinc, so that it does not cause environmental pollution and above all does not damage the health. Another object, no less important than the above, is to provide a mixture composition of friction material that substantially solves the problems of "FADE" , and the materials of which do not crystallise during working, even in critical conditions such as high speeds or heavy loads . An object of the present invention is a mixture composition for friction material comprising, in percentage by weight with reference to said mixture : from 24% to 32% of a base alloy including (in percentage by weight with reference to said alloy) : from 25% to 35% of zirconium oxide Zr02; from 30% to 40% of titanium oxide Ti02; from 25% to 35% of a solid lubricant for friction material formed of a mixture of graphite and molybdenum disulphide/ from 21% to 24% of a mixture of phenolic resins in powder form, which polymerise at between 155° and 160°, including approximately 30% in weight, with respect to the weight of said mixture, of a friction powder; from 11% to 15% of copper sulphide; from 7.5% to 9.5% of baryta or barite; from 21% to 28% of silver or amorphous graphite; and from 3.5% to 4.5% of nitrylic type rubber in power form, heat resistant and with a granulometry of between 200μm and 300μm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will now be described in greater detail with the addition of examples that clarify and illustrate further advantages offered by the present invention. According to the present invention the mixture composition for friction material is made up of a base alloy and additive materials. The base alloy comprises, with reference to the weight of the alloy itself, in percentage by weight: zirconium, present as a dioxide, between 25% and 35%. This material is a temperature stabiliser and at high speed allows the friction coefficient to increase; titanium, present as a dioxide, between 30% and 40%. This material greatly reduces wear on the braking surface and is an excellent temperature stabiliser at low and high speed; a solid lubricant present in the alloy in a percentage by weight of between 25% and 35%, made up of a mixture if graphite and molybdenum sulphide. This mixture is of fundamental importance to give effective lubrication at high speeds and to stabilise the friction coefficient. A commercially available solid lubricant material of this type is known by the trade name of "Lubolid" . The base alloy described above replaces in the present invention the braking alloys known from the state of the art, based on asbestos, lead and zinc. The base alloy according to the invention is used in an amount of between 24% and 32% by weight with respect to the total weight of the mixture, together with a mixture of phenolic resins and other additives. The phenolic resins in this mixture are resins in powder form that polymerise at between 155°C and 160°C and serve, along with a usual friction powder, to bind the components in the base alloy together to form the braking material . The amount of phenolic resins and friction powder used in the mixture according to the present invention is between 21% and 24% by weight with respect to the total weight of the mixture. The friction powder forms approximately 30% of the mixture of resins and powder. As phenolic resins, a resin may be used that forms an excellent binding agent for the metallic ingredients in the powders. An indication of a resin of this type is a phenolic resin J 1506 H produced by Massara, Bollate (MI) , Italy, which has a viscosity at 25°C of 200/220xlθ "6 m 2 /sec, a pellet flow of 30/50 m/m at 135°C, a nitrogen content of 3.4/4.0%, a specific weight of approximately 1.26, a gelling time at 150°C of 1 minute, a moulding temperature of 150-160°C at a pressure of 120/200 kg/cm 2 . It is also possible to use a phenolic resin in powder to bind the components in fibre form. A resin of this type is the resin J 1109 H produced by Massara, Bollate (MI) , Italy. This resin has a viscosity at 25°C of 54/72xl0 "s m 2 /sec, a hexamin content of 7.3 - 7.9%, a pellet flow at 150°C of approximately 60 m/m, a gelling time at 150°C of approximately 2 and 3/4 minutes, a specific weight of approximately 1.42, a vulcanisation temperature of 150- 160°C at a pressure of 120-200 kg/cm 2 . A preferred ratio for use of these two resins J 1506 H and J 1109 H is approximately 1:2. As a friction powder it is possible to use a powder manufactured by Massara, Bollate (MI) , Italy under the trade name J 4106 D, which has a suitable granulometry, a maximum solubility in acetone of 20% and a specific weight of approximately 1.12. The friction powder is used as a reagent integrating the base alloy to ensure optimum distribution of the braking properties and to guarantee that the friction coefficient for braking is restored in sufficient time. The mixture also contains, as stabilising additives, the following: copper, in the form of a sulphide, in a percentage by weight of between 11% and 15% and, for preference, between 12% and 13% with respect to the weight of the mixture. This is used to control the temperature, as it ensures a uniform and progressive decrease of the temperature developed during operation, and, in particular, at high speeds; baryta (or barite) , in a percentage by weight of between 7.5% and 9.5% with respect to the total weight of the mixture. This is used in the mixture as a "charge" to reduce wear of the friction material and noise during braking; silver (or amorphous) graphite, in a percentage by weight of between 21% and 28% and, for preference, between 24% and 25% with respect to the total weight of the mixture. This is used in combination with the baryta to develop and support the characteristics of the latter; nitrylic type rubber in power form, heat resistant and preferably with a granulometry of between 200μm and 300μm, in a percentage by weight of between 3.5% and 4.5% and, for preference, 4.0% with respect to the weight of the mixture. This is used to give the friction material the necessary softness and elasticity, greatly reducing noise. The proportions of rubber indicated above with respect to the other components is sufficient to ensure that the "FADE" effect is not produced. The composition as described in precedence is particularly suited for application in the field of medium loads. For application in the field of low loads, which require a high friction coefficient, the following are added to the composition as illustrated above : aluminium in powder form, in a percentage by weight with respect to the total weight of the mixture of between 4.0% and 6.0%. Addition of this material has a purely electromagnetic function, breaking the magnetic waves created during braking. Furthermore, this material does not attack the braking surface; brass in flakes, in a percentage by weight of between 5% and 7% and, for preference, 6.0% with respect to the total weight of the mixture. The addition of this material ensures a perfect mechanical seal between the component materials and, furthermore, distributes the working temperature in a uniform manner over the whole braking surface. Should application of the mixture composition as described above be in the field of heavy or severe loads, the following materials should be added to said composition: iron wool, for preference with fibres of between 2mm and 3mm in length, in a percentage by weight of between 17.0% and 20.0% with respect to the total weight of the mixture and, for preference, in a percentage by weight of between 17.5% and 19.0%. This is used to give the mixture the necessary mechanical strength and seal of all the component materials in the mixture; corundum (or emery powder) , in a percentage by weight of between 0.09% and 0.15% and, for preference, between 0.10% and 0.12% with respect to the total weight of the mixture. This is used to increase the friction coefficient. It should be noted that an excessive amount causes increased noise during operation, as well as scratches on the braking surface. To obtain the braking material, the base alloy comprising zirconium, titanium and the "Lubolid" type solid lubricant is mixed together with the synthetic graphite, the special phenolic resins and the other components of the composition in the required proportions. The mixture is then vulcanised in special oleodynamic hot presses ensuring continuous monitoring of correct and constant vulcanisation, polymerisation and temperature control. Before being mixed, all the components are carefully checked and made to undergo tests to ensure that the resulting proportions will be correct and to guarantee the total absence of humidity. During mixing it is of essential importance that the presence of any humidity be checked as, for example, a humidity level of over 60% might seriously alter the chemical characteristics of the working components. To avoid this phenomenon, a component with a high dehydration factor is added to the mixture, in a proportion suited to react with the other components. In effect during operation at a temperature of 180° in the presence of water the hydrogen molecules can cause small explosions, which are the cause of damage to the braked surface. This damage is invisible to the naked eye, but causes cracks and splits in the brake surface during continued use. In the composition described above, according to the present invention, the materials are combined in such a way as to ensure that they do not crystallise, even under heavy working conditions, thus improving efficiency and maintaining their characteristics intact over a period of time. Furthermore, given the presence of diamagnetic materials, the negative effects of magnetisation of the braking surface, which are seen in the mixture compositions of friction materials according to the prior art and which result in blockage of one surface on the other during operation, are avoided. Another advantage of the present invention is the elasticity of the braking materials obtained in this way, which is such that it allows perfect the braking element to adapt perfectly to the braking surface. This makes it possible to distribute the braking action homogeneously over the whole surface area, optimising effectiveness and also obtaining a homogeneous distribution of the heat generated, thus avoiding any excessive local concentration of heat that might result in cracking and splitting of the mixture of materials. Another advantage lies in the fact that, unlike the braking materials according to the prior art, which are subject to corrosion because of the high percentages of metallic materials they contain, thus resulting in serious damage to the braking surfaces, as well as high noise levels during operation and sparking, according to the present invention these problems are solved, as the materials used to form the mixture are not subject to corrosion. A further advantage lies in the fact that according to the invention the mixture obtained has a specific weight reduced by 25% when compared with cast iron brakes, and by 65% when compared with synthetic ones. This gives greater manoeuvrability during installation and replacement operations. A further advantage lies in the fact that the mixture according to the invention is subject to less wear during operation that the mixtures according to the prior art. Examples will now be given of tests carried out on the mixture for friction materials according to the invention. The mixtures used in the tests given below are mixtures for use in medium load applications, in the sense defined in the above description. Example 1 Procedure for tests carried out on "Ranzicuna" test tesnεh A sample of the friction material under examination was made to operate against a rotating metal drum, pressing it against said drum at a pressure varying during the course of the test, so as to maintain the braking moment and the final test temperature constant. The speed of rotation of the drum was adjustable in order to enable tests to be carried out at different temperatures. Drum characteristics: Material: cast iron, with the following typical chemical composition: Ca = 3 . 25 Si = 2 . 10 Mn = 1 . 3 Cr = 0 . 20 - 0 .40 Mo = 0 .20- 0 .40 P = 0 . 10 s — 0 . 25 Brinnell Hardness: HB 197-225 Structure: perlytic, uniformly distributed layers of graphite, no cementite. Size: 0149.50 mm State of surface: Ra = 0.4-0.8 Test characteristics: Working surface: 6 cm (adapted to suit the surface of the drum) Initial thickness: 7.60 mm The test was made up of three periods of operation, alternating with cooling periods. For each period the machine operates for a time enough to create a friction level of 166,000 kgm, so as to give a total operation over the three periods of 498,000 kgm. As the braking moment of the machine is known, and is 100 kgm. , it is possible to calculate the duration of each test period. Results of the test: PERIOD DURATION SPEED min. f av. f max.f TEMP. minutes (km/h) (°C) I 92 8 0.32 0.38 0.41 190 II 60 12.5 0.35 0.39 0.40 240 III 42 18 0.36 0.38 0.39 290 Duration transient equivalent to 5,000 turns of the machine, due to test-contratest adaptation. The results were obtained after this transient. The average friction coefficient (av.f) refers to the duration of the test and not to an average of the values (max.f) and (min.f) , which are instantaneous values. Thickness of the test element at the end of test : 7.30 mm Wear on test element: 0.030 mm Specific wear: U = 12 x S = 12 x 0.030 = 0.36 cm 3 /10 e kgm (valid relation on the basis of the size of the test element and the test characteristics) State of test element surface: very smooth, absence of cracks or scratches Final diameter of drum: 149.50 mm Wear on drum: practically unappreciable State of the surface of drum: very smooth, absence of cracks or scratches Friction coefficient with constant progress over long periods Noise level: very low Kxam le 2 Method used for tests with Ranzi L.R.C. machine achine characteristics: n = 7200 rpm (92 km/h) Operating speed j = 0.250 kg.cm/sec 2 Flywheel moment of inertia K = 0.1 mm/turn Scale constant R = 1:8=0.125 Leverage ratio Mn = 1.65 kg.cm Machine internal moment of inertia Mt = 1130/1 Braking moment, dependent on the stopping space "1" given in the test Test element characteristics: r = 1.35 cm Average radius of braking track A = 7 cm Working surface S = 7.00 mm Initial thickness of test element Four series of five braking operations each were carried out; interval between each operation approximately 20 sec, with a pressure adjustable by application of an applied weight (P) in kg and the specific weight (p) in kg/cm is as follows: P = 0.875 x p By calculating the pressure, using the surface area (A) of the test element, the force (F) acting thereon is obtained: F = p x A For each single braking operation the test machine picks up the temperature by means of a thermo-couple inserted in the contratest element, as well as the stopping distances. The friction moment of the braking material is the following: Mr = Mt - Mn = 1130 - Mn lm (lm being the average stopping distance for a series of braking operations) . The average friction coefficient is the following: fm = Mr/F x r Test results : P P F lm av. .f Max.T (kg) (kσ/cm2 ( kσi (mm) CO 7 8 56 45 0.35 150 8 9.14 64 39.0 0.37 200 9 10.28 72 34 0.39 230 10 11.43 80 31 0.39 250 State of the test element surface: very smooth, without cracks or splits. State of the controtest element surface: very smooth, without cracks or splits. Thickness of the test element after testing: 7.00 mm Wear on test element: not appreciable Specific wear: U = A/EK x d/N x 10 x d/N = 0.00 in which: A = working surface EK = cynetic energy of flywheel d = reduction in thickness in hundredths of mm N = number of braking operations carried out Wear in contratest element: not appreciable Sparking: absent Smoke: absent. Conclusions From example 1 (constant moment) it is possible to see • the variation in friction coefficient with temperature. The variation in average friction coefficient with pressure can be seen from example 2. As can be clearly seen, the average friction coefficient initially tends to increase as the specific pressure increases, but then stabilises at a value of around 0.39. From a comparative analysis of the values in the two tests it is possible to deduce that the friction coefficient increases within a fairly restricted range of values with speed, remaining extremely constant at low speeds. From the results of the tests it is possible to deduce that the braking materials object of the present invention are fully capable of providing all the advantages indicated. The present invention is not restricted to the embodiment described herein, but comprises all alternative versions thereof, obtained using equivalent technical methods, included in the scope of the following claims.

Claims: CLAIMS 1. A mixture composition for friction material comprising, in percentage by weight with respect to said mixture: between 24% and 32% of a base alloy including, in percentage by weight with respect to said alloy: between 25% and 35% of zirconium oxide Zr0 2 ; between 30% and 40% of titanium oxide Ti0 2 ; between 25% and 35% of a solid lubricant for friction material made up of a mixture of graphite and molybdenum disulphide; between 21% and 24% of a mixture of phenolic resins in powder form, polymerising at between 155°C and 160°C, including approximately 30% by weight, with respect to the weight of said mixture, of a friction powder; between 11% and 15% of copper sulphide; between 7.5% and 9.5% of baryta or barite; between 21% and 28% of silver, or amorphous, graphite; and between 3.5% and 4.5% of nitrylic type rubber in powder form, heat resistant and having a granulometry of between 200μm and 300μm. 2. Composition according to claim 1, suitable for applications involving a high friction coefficient, in particular for light-weight braking operations, further comprising, in percentage by weight with respect to the total weight of the mixture: between 4% and 7% of aluminium in powder form; and between 5% and 7% of brass in flakes. 3. Composition according to claim 1, suitable for applications involving a low friction coefficient, in particular for heavy-weight braking operations, further comprising, in percentage by weight with respect to the total weight of the mixture: between 17% and 20% of iron wool; and between 0.1% and 0.15% of corundum.

Inventors: BELLICOSO ANTONIO CARMINE, BELLICOSO, ANTONIO, CARMINE
Applicants: BELLICOSO ANTONIO CARMINE, BELLICOSO, ANTONIO, CARMINE
Application year: 1996
Main classification: F16D69
IPC codes: F16D69