Method for manufacturing friction disks with ceramic materials with improved friction layer

Abstract

Method for manufacturing friction disks with ceramic materials with at least one friction layer, with a matrix containing silicon carbide, silicon and carbon, in the first step a mixture of a fine silicon and/or fine particles of other carbide-forming elements with at least one other component selected from a resin in particulate form and a binder selected from resins, pitches and mixtures of them, being prepared, in the second step, the mixture being deaerated and at an elevated temperature of up to 280° C. being pressed and hardened into a cylindrical or cylindrical annular disk, in the third step the hardened disk being treated by heating to a temperature of approx. 750° C. to approx. 1300° C. with the exclusion of oxidizing agents, the binders decomposing with the formation of a carbon residue, and a porous carbon body remaining, in the fourth step, the porous carbon body being heated to above the melting point of the silicon or other carbide-forming elements, their reacting with the carbon formed and yielding an alveolar structure with a skeleton of formed carbides and unreacted residues of carbon or carbide-forming elements, and in the fifth step additional silicon being added at a temperature above its melting point, at least some of the pores of the structure being filled with elementary silicon, and unreacted carbon of the alveolar structure reacting with silicon to form silicon carbide, and use of the friction disks produced in this way as brake disks or clutch driving disks.

Description

EXAMPLE 1

Production of a Mixture for the Friction Layer

500 g of a silicon granulate (®Silgrain, Elkem Co., particle diameter up to 70 μm) were premixed with 400 g of a dry phenolic resin powder (®Bakelite 223, Hexion Co.) in an intensive mixer from Eirich at 300/min⁻¹. Then, at an increased rpm of 1200/min⁻¹ within 5 minutes 300 ml of an aqueous solution of polyvinyl alcohol (mass concentration in the solution: 5 g in 100 g) were added. A lumpy mass referred to as a “granulate” forms. It is dried in a drying cabinet to a residual moisture of approx. 2.5% (remaining mass proportion of water in the granulate).

EXAMPLE 2

Production of a Molded Body for a Friction Layer

350 g of the dried granulate from example 1 were placed in a cylindrical press mold with an outside diameter of 350 mm and a diameter of the inner cylinder of 180 mm to the same height, and pressed for ten minutes at a pressure of 170 MPa and a temperature of 150° C. After curing, a cylindrical annular disk with an outside diameter of 350 mm and an inside diameter of 180 mm, 3 mm thick, was obtained.

EXAMPLE 3

Production of a Carrier Body

Coated short graphite fibers were produced according to the description in patent application DE 197 10 105 A1. With these fibers a press body was prepared from 25 kg of a fraction of the indicated fibers with a length range from 1 mm to 2 mm, 6 kg of a fraction of the indicated fibers with a length range of up to 0.5 mm, and 4 kg of a fiber fraction with a length range from 0.5 mm to 1 mm, and 10 kg of a phenolic resin (®Norsophen 1203), this mixture having been homogenized in an intensive mixer from Eirich for eight minutes at an rpm of 500 min⁻¹. 3.2 kg of the press body produced in this way were placed in a mold in the form of a cylindrical ring with an outside diameter of 360 mm and an inside diameter of 160 mm. Plastic cores with shape of the desired cooling channels were inserted into the mold during filling. In a hot flow press at a pressure of 2.5 N/mm² and a temperature of up to 180° C. the mass was hardened into a green compact which was then carbonized at approx. 900° C. with the exclusion of oxidizing agents and with the formation of a porous, fiber-reinforced carbon body. The body experiences a mass loss of 12.5% relative to the charge mass. The body was machined to the selected final geometry.

EXAMPLE 4

Production of a Composite Disk from a Carbonized Carrier Body and Two Cylindrical Pressed Slabs According to Example 2

Two pressed slabs according to example 2 were heated in a furnace at a heating rate of 2 K/min under a protective gas (argon) to a temperature of 900° C., the hardened phenolic resin portions having been converted to amorphous carbon. These disks were fixed after cooling and removal from the furnace onto each of the cover surface of a cylindrical carrier body according to Example 3 with a phenolic resin adhesive. By hardening in a press at 140° C. and a pressure of 100 MPa, a composite disk with a mass of approx. 2200 g was produced. The disk was placed in a graphite crucible on three porous carbon wicks, the crucible was filled with 2800 g of a silicon granulate (grain size up to 2 mm) and heated in a vacuum furnace to a temperature of approx. 1700° C. at reduced pressure (approx. 5 mbar). The heat-up rates were 5 K/min to 1420° C., and 2 K/min up to 1700° C.; the silicon melted starting at 1420° C. and penetrated via the open pores into the composite body where it reacted with carbon to form SiC. After cooling, the C/SiC component which had formed was removed and optionally ground on the free cover surfaces.

Claims

1. Method for manufacturing friction disks with ceramic materials with at least one friction layer, with a matrix containing silicon carbide, silicon and carbon, the method comprising, in sequence: mixing a fine silicon and/or fine particles of other carbide-forming elements with at least one other component selected from the group consisting of a resin in particulate form and a binder selected from resins, pitches and mixtures thereof;deaerating the mixture and pressing and hardening the mixture at an elevated temperature of up to 280° C. into a cylindrical or cylindrical annular disk,treating the hardened disk by heating to a temperature of approx. 750° C. to approx. 1300° C. with the exclusion of oxidizing agents, whereby the binders of the formation of a carbon residue decompose, and a porous carbon body remains,heating the porous carbon body to above the melting point of the silicon or other carbide-forming elements, and reacting with the carbon formed and yielding an alveolar structure with a skeleton of formed carbides and unreacted residues of carbon or carbide-forming elements,adding additional silicon at a temperature above its melting point, at least some of the pores of the structure being filled with elementary silicon, and unreacted carbon of the alveolar structure reacting with silicon to form silicon carbide.

2. The method according to claim 1, wherein the porous carbon bodies produced in the treating step are placed on a previously separately produced carrier body of carbon reinforced with fibers on its two ring-shaped cover surfaces, then heated jointly and infiltrated with liquid silicon, silicon carbide being formed from the silicon and carbon on the applied porous carbon body and the carrier body.

3. The method according to claim 2, wherein the porous carbon body and the carrier body before heating and infiltration are fixed to one another by surface or spot cementing or by pinning together.

4. The method according to claim 1, further comprising adding short carbon fibers to the mixture of the mixing step.

5. The method according to claim 1, wherein the mixture of the mixing step contains fine silicon and a phenolic resin in particulate form.

6. Friction disks produced according to claim 1.

7. The method according to claim 1, wherein the porous carbon bodies produced in the treating step are placed on a previously separately produced carrier body of carbon reinforced with fibers of carbon on its two ring-shaped cover surfaces, then heated jointly and infiltrated with liquid silicon, silicon carbide being formed from the silicon and carbon on the applied porous carbon body and the carrier body.