A PISTON

Abstract: Disclosed is a piston (1) having a cylindrical body made from a thermosetting molding compound. The body has a central well (3) and a molded-on metal cap (2) having sides that extend downward over the exterior of the body and into the well. There is thermal insulation (8, 9) under and in contact with the metal cap.

Description: A PISTON This invention relates to a metal capped piston having insulation under the cap. In particular, it relates to a piston for use in a vehicle braking system made from a thermosetting molding compound that has a molded-on metal cap under which is insulation. Pistons for use in vehicle braking systems are commonly made by molding phenol formaldehyde molding compound into the shape of the piston, then grinding the rough piston to the precise piston dimensions. Metal caps are often molded onto the top of the piston which is to engage a brake pad or brake shoe to prevent degradation of the phenolic compound from the heat generated in the brake pad or shoe during braking While a metal cap will extend the life of a piston, the phenolic material under the metal cap will eventually degrade, resulting in the failure of the piston According to one aspect of this invention there is provided a piston comprising (A) a cylindrical body made from a thermoset molding compound having a central well at one end, (B) an annular metal cap having sides that extend downward over the outside of said cylindrical body and into said central well, molded onto said cylindrical body, and (C) insulation under and in contact with said metal cap The insulation is thermal insulation Preferably said thermoset molding compound is a phenolic molding compound. Conveniently said metal cap is made of steel In one embodiment said insulation is air Preferably said air is about 0.024 to 0.076 mm (about 0 001 to 0.003 inches) thick. Conveniently a washer-shaped spacer is molded to tne end of said cylindrical body and said air insulation is between said spacer and said metal cap. In an alternative embodiment said insulation is silicone Preferably said piston has an external annular groove to receive a dust boot. According to another aspect of this invention there is provided a brake piston comprising (A) a cylindrical body made from a phenolic molding compound having a central well at one end, (B) an annular metal cap having sides that extend downward over the outside of said body and into said well, molded onto said cylindrical body; and (C) insulation between said metal cap and the end of said cylindrical body. According to a further aspect of this invention there is provided a brake piston comprising (A) a cylindrical body made from a phenol-formaldehyde molding compound having a central well at one end, (B) an annular metal cap having sides that extend downward over the outside of said body and into said well, molded onto said cylindrical body; and (C) insulation in between said steel cap and the end of said cylindrical body. Heat degradation of metal capped pistons made out of thermosetting molding compounds can be greatly reduced or even eliminated if there is thermal insulation under and in contact with the metal cap. This can be easily accomplished in the molding process with little or no additional cost. It has been found that brake pistons made according to this invention can withstand heat that degrades identical pistons that do not have such thermal insulation under the metal cap. The invention will be described by way of example with reference to the accompanying drawings in which: Figures 1 , 2, and 3 are side views partially in section showing various embodiments of brake pistons according to this invention. Figure 1 show a side view partially in section of a molded piston 1 for use in a vehicle braking system, the piston 1 has a molded-on metal cap 2. The piston 1 has a cylindrical interior well 3 for the purpose of saving material and making the piston lighter. Metal cap 2 has an interior flange 4 that extends into well 3 and an exterior flange 5 that extends over the outside of piston 1. Also shown is an annular groove 6 for receiving part of a dust boot provided for the purpose of keeping road dust out of the brake. Under metal cap 2 is molded a washer-shaped metal spacer 7. There is a thermal insulating air gap 8 of about 0.0024 to about 0.076 mm (about 0 0001 to about 0 003 inches) in between metal cap 2 and metal spacer 7 which acts as thermal insulation Alternatively the gap may be about 0.024 to about 0 076 mm (about 0 001 to about 0.003 inches). Figure 2 is identical to Figure 1 except that air gap 8 has been replaced by about 0.13 to about 0.5 mm (about 0 005 to about 0 02 inches) of thermally insulating material 9, which may consist of materials such as fiberglass, silicone, or carbonized organic resin Figure 3 is identical to Figure 1 except that metal spacer 7 and air gap 8 have been replaced with thermally insulating material 9 This invention applies to any type of piston, including hydraulic pistons, and pneumatic pistons, but it is particularly applicable to brake pistons The pistons are made out of a thermosetting molding compound, such as melamine formaldehyde or phenol formaldehyde Most commonly, phenol formaldehyde is used for brake pistons, but the invention is applicable to any molded compound that will degrade when heated The invention applies to pistons that have metal caps on the open or hot side of the piston. The metal caps are intended to contact brake pads or brake shoes, the pads or shoes become heated during braking and the heat is transferred, by conduction, to the metal-capped ends of the pistons the other end of the piston is received in a hydraulic or pneumatic cylinder so that pressure can thereby be applied to the piston to effect braking These metal caps are generally molded-on are more effective than snap-on caps The caps are annular and extend downward over both sides the body of the piston The pistons are almost always cylindrical and are usually made with a well to reduce cost and weight The cap can be constructed of various metals, such as steel, stainless steel, copper, brass, and aluminum The piston can be made by placing the cap, insulation, and spacer (if one is used) in a mold If compression molding is used to make the piston, a preformed molding compound is placed into the mold prior to compression molding. If injection molding is used, the molding compound is forced into the mold. For phenolic molding compounds, a typical practice is to heat for about 2 minutes at 171 to 176°C (340 to 350°F), place the rough piston into an oven, age it for up to 16 hours at 204 to 232°C (400 to 450°F), and then grind it to the final dimensions Typical brake pistons are about 4 76 to 7 62 cms (about 1 7/8 to 3 inches) in diameter

Claims: CLAIMS: 1. A piston comprising (A) a cylindrical body made from a thermoset molding compound having a central well at one end; (B) an annular metal cap having sides that extend downward over the outside of said cylindrical body and into said central well, molded onto said cylindrical body; and (C) insulation under and in contact with said metal cap. 2. A piston according to Claim 1 wherein said thermoset molding compound is a phenolic molding compound. 3. A piston according to Claim 1 or 2 wherein said metal cap is made of steel. 4. A piston according to Claim 1 , 2 or 3 wherein said insulation is air. 5. A piston according to Claim 4 wherein said air is about 0.024 to 0.076 mm (about 0.001 to 0.003 inches) thick. 6. A piston according to Claim 4 or 5 wherein a washer-shaped spacer is molded to the end of said cylindrical body and said air insulation is between said spacer and said metal cap 7. A piston according to Claim 1 , 2 or 3 wherein said insulation is silicone. 8. A piston according to any one of the preceding Claims wherein said piston has an external annular groove to receive a dust boot 9. A brake piston comprising (A) a cylindrical body made from a phenolic molding compound having a central well at one end, (B) an annular metal cap having sides that extend downward over the outside of said body and into said well, molded onto said cylindrical body; and (C) insulation between said metal cap and the end of said cylindrical body 10. A piston according to Claim 9 wherein said metal cap is made of steel 11. A piston according to Claim 9 or 10 wherein said insulation is air 12. A piston according to Claim 11 wherein said air is about 0.0024 to 0.076 mm (about 0.0001 to 0.003 inches) thick. 13. A piston according to Claim 11 or 12 wherein a washer-shaped spacer is molded to the end of said cylindrical body and said air insulation is between said spacer and said metal cap. 14. A piston according to Claim 9 or 10 wherein said insulation is silicone. 15. A piston according to any one of Claims 9 to 14 wherein said piston has an external annular groove to receive part of a dust boot. 16. A brake piston comprising (A) a cylindrical body made from a phenol-formaldehyde molding compound having a central well at one end; (B) an annular metal cap having sides that extend downward over the outside of said body and into said well, molded onto said cylindrical body; and (C) insulation in between said steel cap and the end of said cylindrical body. 17. A piston according to Claim 16 wherein said insulation is air. 18. A piston according to Claim 17 wherein said air is about 0.024 to 0.076 mm (about 0.001 to 0 003 inches) thick 19. A piston according to Claim 16 wherein said insulation is silicone 20. A piston according to any one of Claims 16 to 19 wherein said piston has an external annular groove to receive part of a dust boot

Inventors: MEYER LEON G, MEYER, LEON, G.
Applicants: OCCIDENTAL CHEM CO, STEPHENS DINAH, OCCIDENTAL CHEMICAL CORPORATION, STEPHENS, DINAH
Application year: 1999
Main classification: F02F
IPC codes: F16D65, F16J1