Technical field

[001] The invention relates to the field of mechanical engineering, namely to heavily loaded friction units, such as brake systems of sports cars and other ground equipment.

Background Art

[002] There is known method of obtaining 2D composites by laying layers of fabrics, felt or other reinforcing elements, followed by impregnation of their binder US5205888A]. The main disadvantage of this method for producing carbon-carbon composites [CCC] is the low interlayer strength of the resulting material, leading to delamination and reduced reliability of the resulting products under operating conditions.

[003] There is also known a method for producing a friction disc, which involves laying out layers of fabric with their subsequent needling to obtain a connected frame, which is subsequently compacted to achieve the required density [US6691393B2]. The disadvantage of this method is the increased cost due to the need to use a complex and expensive needling technology, which also does not ensure the uniformity of the properties of the resulting material due to the localization of transversely oriented fibers.

[004] A known method for the manufacture of carbon fiber [W02019000957A1], which involves pre-perforation of the workpiece to improve the process of product quality, however, it does not provide the production of CCC and their use in friction units.

[005] A known method of manufacturing friction materials for friction units based on chopped fibers and pitch binder [EP1724245A1], involving the production of discretely reinforced friction material. The main disadvantages of this method are the use of dry mixing of components, which can lead to uncontrolled grinding of carbon fibers and the formation of inhomogeneities in the structure of the material, as well as the use of a long and expensive pyrolytic compaction operation, which also leads to low values of the final density [1.75-1. 78 g/cm ³ ) due to the peculiarities of gas-phase sealing.

Disclosure of the Invention

[006] The technical result of the invention is to increase the interlayer strength of the carbon-carbon friction material while maintaining its fine structure without the use of expensive reinforcing materials and labor-intensive needle-punching and needle-sewing operations due to the preliminary perforation of the carbon fabric layers and ensuring the introduction of discrete carbon fibers into the material structure at the molding stage.

[007] The technical result is achieved by:

- initially, a carbon fabric based on polyacrylonitrile [PAN] fibers of any weave [plain, twill, satin or other weave, preferably with a warp to weft ratio of 1:1 to 3:1) preimpregnated with a binder, preferably based on pitches, or in the initial state, it is subjected to a given perforation by forming holes on it [preferably essentially round in shape) with a linear size significantly exceeding the diameter of the carbon fiber filament, while the ratio of the linear size of the hole to the diameter of the filament L/d>100;

- then, in a perforated sleeve, a press pack is assembled by alternating laying of fabric cuts and sucking through them an aqueous suspension containing a powder of a pitch binder and carbon fiber filaments with a length of not more than 750 mkm; moreover, during the laying of the layers, the holes of the perforations of the layers of carbon fabric are placed either in such a way as to avoid their overlap or partial overlap, or coaxially with each other; moreover, the preferred ratio of water, pitch binder powder and carbon fiber filaments is from 100:5:1 to 100:15:3, and the ratio of carbon fabric and carbon fiber filaments is from 1:2 to 2:1;

- the resulting wet press pack is compressed in the sleeve by at least % of the original height and dried in a fixed state at the melting temperatures of the pitch binder to a constant weight, after which it is cooled to room temperature;

- the resulting press pack is removed from the sleeve and loaded into a mold, after which it is pressed at a temperature not less than twice the melting temperature of the pitch binder to the required thickness, taking into account the provision of the optimal degree of reinforcement of the composite, after which the workpieces are carbonized, compacted, heat treated and mechanically processed in accordance with the drawing. [008] As a result of perforation followed by suction under optimal conditions at the stage of molding the press pack, carbon fiber filaments are partially infiltrated into the layers of the fabric, which provides an increase in the shear strength of the composite material without the needle-punching operation and eliminates its delamination during operation. Practice has shown that the effect of perforation is more pronounced if it is carried out along concentric circles or radii of a circular workpiece with a step between holes from 10 to 100 mm. After suction of an aqueous suspension containing carbon fiber filaments, the effect of the integration of layers is enhanced in the process of pressing the press pack and is fixed as a result of cooling it in a fixed state to room temperature after drying at the melting temperature of the pitch binder. At the pressing stage, there is an additional compression of the press pack and the final formation of the structure of the composite material with the integration of carbon fiber filaments into the fabric layers. [009] Performance characteristics are formed at the stages of impregnation, compaction, intermediate and final heat treatments according to specially developed modes. At the same time, the interlayer strength of the resulting composite is not inferior to the known variants of similar materials and reaches 25-30 MPa. The proposed method provides the possibility of a given control of the friction coefficient in the range of 0.3-0.5, while the wear resistance is not inferior to similar materials. The duration of the technological cycle is 30-40% less than known analogues, which ensures a lower cost of production.

Brief Description of Drawings

[010] Fig. 1. - examples of perforating circular cuts of fabric;

Fig. 2 - scheme for forming a workpiece from perforated fabric cuts;

Fig. 3 - the proposed reinforcement scheme of the press pack.

[Oil] Fig. 1 shows possible schemes for perforation of a circular cutting of fabric with a circular and a radial arrangement of perforations. Fig.2 shows the scheme of molding the workpiece, during which the perforated cuttings of the fabric [1] are laid out [perforation is conventionally not shown] followed by the suction of an aqueous suspension [2] containing the pitch binder powder and carbon fiber filaments through them. Fig. 3 shows the resulting reinforcement scheme of the press pack, which shows the relative positioning of the layers of carbon fabric [1], pitch binder powder [3] and carbon fiber filaments [4].

[012] A more detailed description is illustrated by the following examples:

Examples of the Implementation of the Invention

[013] Example 1. Initially, circular cuts of twill weave carbon fabric are made, after which they are impregnated with coal-tar pitch with a softening temperature of ~85°C, after which circular perforation of the fabric layers is carried out with round holes 10 mm in diameter, located at a distance of 10-30 mm. Then, the molding of the press pack is carried out by laying out circular cuts of the fabric and sucking through them an aqueous suspension containing a powder of pitch binder with a fraction of <1 mm and carbon fiber filaments with a processing temperature of 1400 ° C with a length of not more than 750 mkm in the ratio of water : powder of pitch binder : carbon filaments fibers - 100:5:1. After molding, the press package is compressed by % of the original height and fixed in a metal mandrel, then dried to constant weight at a temperature of ~85°C. After drying, the press pack is reloaded into a mold and the circular worpiece is pressed at a temperature of ~200-220°C, after which it is carbonized at a maximum temperature of 900°C, liquid-phase compaction with a pitch binder at a vacuum of -0.9 atm, followed by carbonization at 650°C under pressure of 32 MPa, heat treatment at a temperature of 2000°C and mechanical treatment.

[014] Example 2. It repeats Example 1, but the cuttings of the fabric are not preimpregnated with a pitch binder.

[015] Example 3. Repeats Example 1, but perforation of fabric cuts is carried out with holes with a diameter of 2 mm.

[016] Example 4. Repeats Example 1, but perforation of fabric cuts is carried out with holes with a diameter of 40 mm.

[017] Example 5. Repeats Example 1, but perforation of fabric cuts is carried out with holes with a diameter of 10 mm, located at a distance of 120-150 mm from each other. [018] Example 6. Repeats Example 1, but the aqueous suspension contains carbon fiber filaments 2-4 mm long.

[019] Example 7. Repeats Example 1, but the aqueous suspension contains the pitch binder powder and carbon fiber filaments in the ratio water:pitch binder powder: carbon fiber filaments - 100:2:0.4.

[020] Example 8. Repeats Example 1, but the aqueous suspension contains the pitch binder powder and carbon fiber filaments in the ratio water:pitch binder powder: carbon fiber filaments -100:20:4.

[021] Example 9. Repeats Example 1, but after molding, the press pack is not subjected to preloading before fixing.

[022] Example 10. Repeats Example 1, but after fixing the press pack is dried to constant weight at a temperature of ~50°C. [023] Example 11. Repeats Example 1, but after fixing the press pack is dried to constant weight at a temperature of ~160°C.

[024] Example 12. Repeats Example 1, but the weight ratio of carbon fabric to carbon fiber filaments is 1:3.

[025] Example 13. Repeats Example 1, but the weight ratio of carbon fabric to carbon fiber filaments is 3:1.

[026] Table. Comparative characteristics of materials obtained in accordance with the examples

[027] As can be seen from the table, the material according to the proposed method has identical performance characteristics as the known material according to the technical solution described in EP1724245A1, including the required interlayer strength of ~30 MPa due to the effective suction of an aqueous suspension through the fabric layers. In the case of using fabric cuts not impregnated with a pitch binder [Example 2), there is a significantly greater variation in physical and mechanical characteristics, in particular, the bending strength takes values from 30 to 120 MPa, which is associated with technological difficulties in forming the workpiece - unimpregnated fabric has significantly lower rigidity and is capable of deforming when an aqueous suspension is sucked in, forming so-called folds, which leads to a significant heterogeneity of properties over the volume. When changing the nature of the perforation of the cuts [Examples 3-5), there is also a significant deterioration in the stability of the properties obtained, associated with the lower uniformity of the resulting composite. In this case, in Examples 3 and 5, there is a significant decrease in interlayer strength to values of 15-21 and 11-17 MPa, respectively, due to the small size of the perforation holes and a significant distance between them and, as a result, poor mutual penetration of tissue layers. The use in the process of molding a suspension with a longer length of carbon fiber filaments [Example 6) leads to a deterioration in frictional properties and, in particular, to a significant increase in wear to 1.5-3.1 mkm/braking, the resulting material due to a rougher structure. With a decrease in the concentration of the pitch binder powder and carbon fiber filaments in Example 7, a significant increase in the linear wear of the material up to 2.4-5.0 mkm/braking can be noted, associated with a low content of discrete carbon fibers on the friction surface and the associated decrease in strength during interlayer shift up to 11-19 MPa. With an increase in the concentration of the powder of the pitch binder and carbon fiber filaments in an aqueous suspension [Example 8), a decrease in physical and mechanical characteristics is observed, in particular, the bending strength to 50-75 MPa, along with a significant decrease in the interlayer strength to 13-16 MPa due to the formation a thicker intermediate layer containing carbon fiber filaments, which is not capable of providing a strong bond between the fabric layers. Also, in the absence of compression during overload, there was no sufficient binding of the press pack during drying, which led to its delamination [Example 9). In Example 10, due to the drying of the press pack at a low temperature, the press pack delaminated due to insufficient temperature for melting the pitch binder and forming a bounded press pack, and in Example 11 the temperature was too high, which led to a strong decrease in the viscosity of the binder and its partial leakage from press pack, which subsequently led to density instability over the volume of the workpiece (values were obtained in the range of 1.69-1.83 g/cm ³ ) and to a significant decrease in strength and friction characteristics, for example, the bending strength was 35-85 MPa, and wear fluctuated within 0.9-2.9 mkm/braking. In Example 12, where the weight ratio of carbon fabric to carbon fiber filaments was 1:3, there is a significant decrease in strength, for example, the bending strength was 20-75 MPa, and the interlaminar shear strength was 7-22 MPa, as well as fluctuations in density by volume due to uneven deposition of carbon fiber filaments in the volume of the workpiece and, as a result, the heterogeneity of the obtained properties. In Example 13, where the weight ratio of carbon fabric to carbon fiber filaments was 3:1, delamination of the workpiece occurred due to the extremely low interlaminar strength resulting from a significant reduction in the volume fraction of discrete carbon fibers in the volume of the workpiece.