Making Brake Pad Material

FIELD OF THE INVENTION

The invention relates to the sphere of production of friction materials that can be used in the making of brake pads for passenger automobiles and freight trucks, as well as in the other sphere such, for example, as the railway transport and the making of other frictional load facilities.

BACKGROUND OF THE INVENTION

As is well known, the material intended for brake pads is made using the organic and inorganic raw material; for ensuring the respective characteristics, especially in the making of pads resistant to the aggressive medium and possessing structural resistance, the material composition is determined by selecting the respective raw material. The natural or manmade fiber is used for these purposes. The natural stone-based mineral fiber is prioritized. The tendency of offering the brake pad material made of the natural stone-based fiber has been observed lately. It is evidenced, for example, by the invention described in the published in 2012 US patent No. 8167097 "Friction Material", which reflects the latest development tendency of the given sphere, directed at the use of the fiber produced from the mentioned raw material. To achieve the goal set in the present patent, namely, to ensure the high coefficient of friction and wear factor, it is offered to base the friction material on chopped continuous basalt fiber of 5-25 microns in diameter and 1 -20 mm in length. The length of chopped basalt fiber within this range depends on the formulation/composition of the specific friction material. The share of such basalt in the material's composition is 1-20 percent by weight, the weight of the additive provided therein makes 0.5- 30%, while the filler is added in the amount of 1 - 15 weight %.

The friction material described in the US patent has a number of advantages as compared with other known materials, but it should be also bom in mind that it is characterized by some noteworthy disadvantages. In particular, according to the mentioned US patent, the disadvantage of the invention is that the lower chopping limit of the continuous fiber is limited to the length of 1 mm, or under the patent the length of the chopped fiber should not be less than 1mm. Better frictional properties are achieved exactly by the chopped fiber of less length. However, the use of stone wool of the given size represents the main disadvantage of the mentioned patent. For improving the frictional properties of pads, the patent does not consider the continuous basalt fiber as an alternative tothe useof stone wool in the range of 0.15-1.0 mm. In this range of sizes the use of chopped continuous basalt fiber with a higher temperature gradient is of importance. Basalt is known to have the thermal gradient 1.5-2-times higher than the glass fiber.As regards the basalt stone wool, it is not only the basalt stone-based product. Given its manufacturing method, it, in addition to basalt, contains many different mineral admixtures and does not represent fibers of the continuous diameter and length. Correspondingly, the pads made of the materials containing the stone wool-based fibers chopped in the range of bellow 1 mm lengths are characterized by overheating of the breaking area , compared with this invention.

Another shortcoming of the known friction materials that will be eliminated by the proposed invention is that the non-coated textile fiber in more than 6 mm length poorly get mixed with the friction mass andleads to balling of fibers. Although using the chopped fibers upon 6 mm length the mechanical properties of pads (the flexural modulus and the flexural strength) increase. Therefore, the use of chopped fibers in the length of 6 mm and more, for example up to 20 mm, is deemed to be rather desirable, for it is known mat the increase in the length of the used fiber leads to the improvement of such mechanical properties as the flexural modulus (seeN. Subramaniam, Brijnreshr. Sinha, Frank D. Blum, Young-Rwei Chen and L. R. Dharani, Glass Fiber Based Friction Materials.Intern. J. Polymeric Mater., 1991, Vol. 15, pp. 93-102).

Theaforesaid disadvantages are absent in theproposed invention, the essence of which is that the use of continuous basalt fiber is the component ensuring the desirable frictional properties of the friction material, which is sized by a non-silane sizing, resistant to the aggressive medium, for example the anionic/non-ionic polycarbonate-polyether urethane polymer-based Baybond XP 2728 or the non-ionic polyether urethane polymer-based Baybond PU 406, or their combination and is so chopped that the below length limit is within the sizes of 0,15-1 mm.The fiber chopping length is determined according to the suitable specific length by the formulation/composition of the material, which depends upon the target characteristics of the pads to be made. According to this form of the invention, the sizing should necessarily be resistant to the aggressive medium and selected from the number of non-silane substances.

In addition to the above, the offered invention differs also by the fact that the continuous basalt fibers sized by the non-silane or silane sizing to be used for making the brake pad friction material to improve the mechanical properties are coated, dried and chopped into pieces not less than 6 mm in length according to a specific composition. At that the lubricated fiber is necessarily dried in two stages under conditions of a divided process, in the first stage of which preheating takes place at the temperature of 150-160°C, while in the second stage - the drying proper is carried out at the temperature of 180-200°C. Coating is a non-silane material, which increasesthe resistance to the aggressive mediumand rigidityof fibers.For example, the one based on styrene butadiene;in particular, suchpoIymerasLefasol VG 92/1 is comparable to the described one.

The principal and lucky find of the present invention as per claim 1 is the proposal of the basalt fiber sizing with a non-silane sizing being resistant to the aggressive medium in order to ensure the use of chopped basalt fibers in the friction material composition for enhancing the frictional properties within the below limit length range of 0.15-1 mm.

According to claim 3, the principal inventive idea of making this invention is to cope with the problem of mixing the chopped basalt fibers in the mentioned range of length with other components of the brake pad material so that the above-mentioned disadvantages of the known art are eliminated. The idea-ensuring find is the proposal of the basalt fiber coating with a non-silane coating, such, for example, as styrene butadiene-based Lefasol VG 92/1 and, in addition, the proposal of dividing the drying process into two stages - the pre-heating and the drying stages proper, with the observance of the temperature conditions. According to this form of the invention, continuous basalt fiber can be sized with any earlier widely used silane and non-silane sizing, the selection of which depends upon the obtaining of properties suitable to the end use of brake pad material.

The continuous basalt fiber designated for making brake pads under the given invention presented for patenting is produced as follows: under the technology described in the Patent of Georgia No. P 2003 3024 B "Method of Producing Fiber from Mineral Raw Material" basalt continuous fiber is extruded and is concurrently sized. The fibers can be lubricated by both theknown silanesizing as well as the non-silane one being resistant to the aggressive medium. For example, we selected for the purposethe anionic/non-ionic polycarbonate-polyether urethane polymer-based Baybond XP 2728 and the non-ionic polyether urethane polymer-based Baybond PU 406. A combination thereof can also be used.

After the aforesaid, the direct non-coated basalt low-tex (70-800 tex) fiber rovings are assembled into the high-tex (2400-9800 tex) rovings, following which they are chopped to size in the range of 0.15-1.0 mm of length on condition that the strands aresizedwith a non-silanesizing resistant to the aggressive medium, or of 1.0-6.0 mm where the strands are sized with the silanesizing. For the sizing process both the silane and non-silane above-mentioned sizingsare used for sizingthe direct rovings of the low-tex fiber strands, according to the pre-heating, drying and chopping flow sheet. In this case the fibers are chopped to size in the length over 6.0 mm, in accordance with brake pad material formulation/composition.

Based on the above, the chopped continuous basalt fibers of three different parameters can be used for making brake pads, every one of which independently improves the specific characteristics of the brake pads. These, in particular, include:

The basalt fiber chopped according to the formulation of using on a specific length in the range of 0,15-1,0 mm, sized with a lubricant ,resistant to the aggressive medium, in particular the anionic/non-ionic polycarbonate-polyether urethane polymer-based Baybond XP 2728 or the non- ionic polyether urethane polymer-based Baybond PU 406, or with a combination thereof. The application of such fibers improves the frictional properties of the pads;

The basalt fiber chopped according to the formulation of using on a specific length in the range of 1.0-6,0 ^' mm,sizedwith the silane sizing. Such fibers can be used in the pads to retain the characteristics of the acceptable noise, vibration and harshness (NVH) levels in the pads and to improve the thermal resistance parameters;

The basalt fiber in a length over 6.0 mm (e.g. up to 20.0 mm), chopped according to the specific formulation, coated with the non-silane coating, for example, the styrene butadiene-based one. The application of such fibers improves the frictional properties of pads.

As a result of implementation of the proposed method, all the aforementioned disadvantages will be eliminated and continious basalt fibers could be applied in the friction material, the below chopping limit of which will be in the length range of 0.15 mm; additionally, it will also be possible to apply in the friction material the continuous basalt fibers chopped to size from 6 to 20 mm and over, for the problem of their mixing with other components will no longer exist.

The continuous basalt fiber produced under the described invention, which is manufactured according to the foregoing technology is ready for mixing into the friction material. It is desirable that the composition (formulation) of the friction material is as follows: phenolic resin- 8%; friction dust - 3%; potassium sulfide - 4%;molybdenum disulfide - 4%; ferric oxide - 4%; the continuous basalt fiber chopped to size 0.35 mm in length lubricated with the non-silane sizing - 3%; the continuous basalt fiber chopped to size 4.0 mm in length sizedwith the silane sizing - 4%; the choppedcontinuous basalt fiber to size 9 mm in length coatedwith the non-silanecoating - 3%; aramid pulp - 3%; copper fiber - 8%; graphite - 7%; limestone - 3%; vermiculite - 3%; barium - 20%; potash - 14%; wollastonite - 5%; coke - 3%. The application of the present invention may save material. For example, to improve the frictional properties of brake pads, the stone wool-based Rock Brake RB 297 is frequently used. It contains up to 18% non-fiber inclusions, therefore the use of 20% less basalt fibers chopped to size within 0-15 to 1 mm, in particular 0.3 mm in length is possible instead of the RB 297, because the basalt fibers chopped into the 0.3 mm lengths contain only up to 1% of non-fiber material in the form of a lubricant resistant to theaggressive medium.