In studying and making sintered disc brake linings, this project aimed to: control the coefficient of friction within the 0.15 to 0.55 range; reduce wear via action of a viscous transfer coating and realize a substantial gain versus loses due to braking; reduce total braking system weight by reducing rubbing surfaces; and improve disc life. The project found that the presence of copper and bronze fibres enhanced mechanical strength during braking. It also found that mechanical strength decreases when the dimensions of graphite particles decrease. Furthermore, a large drop in rupture strength occurs for all grades at temperatures above 500 C. Thermal conductivity increases with temperatures up to 500 C a contrast with the usual decrease in the thermal conductivity of metals, while it decreases drastically at higher temperatures. The substitution of ceramics by glass forming alloys does not significantly affect mechanical properties but increasing graphite content appears more detrimental. Particle morphology does not affect damping capacity. It seemed possible to obtain a desired coefficient of friction at low speeds by combining the effects of composition and morphology. At high speeds, it seemed difficult to control the formation mechanism of the transfer layer and obtain the desired friction coefficient. The last part of this project showed that it could be possible to obtain a given coefficient of friction by using materials with different friction coefficients in different segments of a single pad, and to control closely the coefficient of friction at high speeds. The resulting friction and wear at all speeds is the same as that found by combining the contributions of each material in proporrtion to the number of segments and their positions.
A study has been conducted on the use of sintered materials for high energy and/or high power dissipation during braking on steel discs.
3 particular areas were investigated:
the influence of particle morphology on mechanical, thermal and tribological properties of the brake pads;
the influence of intrinsic properties of ceramics and metallic glass forming alloys on the coefficient of friction, wear and thermal exchange at the rubbing surfaces;
mathematical modelling of the disc pad system including the viscous layer.
THE PROJECT CONSISTS IN THE STUDY AND PRODUCTION OF SINTERED LININGS FOR HIGH-ENERGY AND/OR HEAVY-DUTY DISC BRAKES ON BRONZE BASE FRICTION MATERIALS. IN THESE AREAS OF APPLICATION THE PERFORMANCE OF SINTERED LININGS SHOULD BE VERY PROMISING FOR THE FOLLOWING REASONS:
- ADDITION OF NEW MATERIALS TO THE COMPOSITION OF THE LININGS SUCH AS ALLOYS LIKELY TO FORM AMORPHOUS-STRUCTURE METALLIC GLASSES AND SPECIAL CERAMICS. THESE MATERIALS, WHICH DETERMINE THE CHARACTERISTICS OF THE AMORPHOUS, VISCOUS TRANSFER COATING BASICALLY AFFECTS THE COEFFICIENT OF FRICTION, WEAR, AND HEAT TRANSFER FROM THE RUBBING SURFACES.
- USE OF METALLIC FIBRES IN ORDER TO OBTAIN MICROSCOPIC STRUCTURES GIVING MECHANICAL AND PHYSICAL PROPERTIES WHICH ARE WELL MATCHED TO TRIBOLOGICAL APPLICATIONS.
- USE OF NEW TECHNIQUES SUCH AS HOT FORGING AND HOT ISOSTATIC PRESSING FOR THE FABRICATION OF SINTERED LININGS.
THE MAJOR AIMS OF THE PROJECT, WHICH REPRESENT A CLEAR TECHNOLOGICAL ADVANCE AS COMPARED WITH CURRENT PRACTICE ARE:
- CONTROLLING THE COEFFICIENT OF FRICTION WITHIN THE RANGE 0.15 - 0.55 - REDUCING WEAR VIA THE ACTION OF THE VISCOUS TRANSFER COATING, AND HENCE A SUBSTANTIAL GAIN VERSUS LOSSES DUE TO BRAKING.
- REDUCTION IN THE TOTAL WEIGHT OF THE BRAKING SYSTEM BY REDUCING THE RUBBING SURFACES
- IMPROVEMENTS TO DISC LIFE.
THREE ITEMS OF RESEARCH ARE DEFINED:
- INFLUENCE OF PARTICLE MORPHOLOGY ON MECHANICAL, THERMAL AND TRIBOLOGICAL PROPERTIES OF PADS.
- INFLUENCE OF INTRINSIC PROPERTIES OF CERAMICS AND METALLIC GLASS FORMING ALLOYS, ON THE COEFFICIENT OF FRICTION , WEAR AND THERMAL EXCHANGE AT THE RUBBING SURFACES.
- MATHEMATICAL MODELLING OF THE DISC/PAD SYSTEM INCLUDING THE VISCOUS LAYER.