Automotive Applications of Metal Powders

Carbon Brushes


In the context of electric motors and related machinery, a brush is a device used to maintain a circuit between a fixed and rotating or moving part.  The brush is affixed to the moving or rotating component and maintains constant contact with some stationary piece within the system.  A common scenario is in direct current motors where a central armature, or magnetised rod, spins about its axis between two magnets.  This spinning shaft, which converts electrical energy into mechanical energy, must remain in constant contact with an electric current in order to function.  Graphite is used to construct these brushes in order to maintain a low coefficient of friction, but require metal powder additives in order to maintain sufficient conductivity to carry current across the two parts.  Copper – graphite sintered composites have the added advantage of possessing a porous structure which allows diffusion of lubricants into the brush component reducing wear under especially strenuous conditions.


Friction (brakes and clutches)


The inherent porous structure of sintered metals and alloys make them ideal materials in high friction environments such as those encountered in braking systems.  This porosity provides two advantages.  First, void spaces within the metal matrix accommodate thermal expansion of the material without fracturing when they rapidly become heated as a result of the immense friction generated when stopping.  Second, it enables the impregnation and diffusion of lubricants into and throughout the metal, which additionally alleviates friction-related stresses.  Because copper and bronze powders are both well suited for the sintering process and highly resistant to common sources of corrosion, they are in turn ideal materials for use in the manufacture of brake pads, and clutch buttons which routinely encounter similar stress.  

     

Engine Bearings


A crankshaft converts released chemical energy from the combustion process within the pistons of an engine into mechanical energy.  In order to maintain stability while doing so, main bearings are required to keep the shaft fixed about its spinning axis and to do so without generating detrimental levels of friction as the moving surface of the rotating crankshaft remains in contact with the inner surface of the cylindrical bearing.  Copper powders and its alloys are employed in both cast and sintered bearing components to achieve an adequate balance of low-friction, characteristic of soft materials, and high load capacity, characteristic of hard materials.  Also, in this case, high thermal conductivity aids in heat transfer away from the metal interface, which also reduces wear.     

    

Bearings and Bushings


There are an array of designs with varying complexity of bearings, but the essence of their function is to “bear” the mechanical stress resulting from contact between dynamic and stationary components.  Commonly this is a spinning or rotating shaft resting on a bearing within a motor or wheel.  Bushings are essentially a simplified bearing, with no moving parts of its own, in contrast to say ball bearings.  Bushings can be a single circular design or a dual component system consisting of two half circles.  In either case, the key to material selection for fabrication is to maintain a balance between low-friction and high strength characteristics, which is accomplished through the use of varying levels of copper, bronze, and tin powders in both cast and sintered bushings.


Sintered Components


See the applications of metal powder in sintered components for construction.


Filters 

 

Ensuring that the fuel stream flowing into an engine remains contaminant free is crucial to the longevity of an automobile.  Fuel filters require the utilisation of especially robust materials to stand up to operational pressures within fuel lines.  Also, the filtering media must remain chemically inert for prolonged exposure times to the hydrocarbon fuel.  Copper and bronze-based systems are well suited due to their corrosion resistance and ease to which they can be sintered.  The sintering process enables fabrication of porous filter media from these inert metals.  Maintaining control of the particle size and distribution of the constituent metal powders facilitates better control over the porosity of the resulting filter system.  

Bronze-Filled PTFE Seals


Seals are used to prevent movement of fluid or seal the seam between moving and stationary parts, not be confused with a gasket which serves the same function between two stationary components.  PTFE, or more commonly known by its brand name Teflon®, is an excellent material employed in the construction of seals due its extremely inert nature.  In some applications good heat transfer across the seal is required.  Since PTFE is a poor conductor of heat, bronze powders are sometimes blended in prior to fabrication to accommodate this need.