Development prize: New materials
Sintered bearing for a shaft in a door closure motor
Diamet Corporation received an award in the New Materials category for the development of a sintered bearing to be used on the output shaft in an automotive door closure motor.
An Fe based or Fe-Cu based material is the normal material of choice for sintered bearings for the low-speed and high load conditions of door closure motors. However, because of grease lubrication, corrosion of the sintered bearing was an issue. A phosphor bronze-based material was therefore developed as the material was expected to exhibit both high strength and corrosion resistance.
In this development, the contents of Sn and P were optimised to achieve high strength and hardness and to suppress deformation during sintering. However, dimensional accuracy was reduced because of the excessive volume of liquid created during sintering. Therefore, this excessive volume of liquid was decreased by optimising raw powder and sintering conditions, resulting in an improvement in dimensional accuracy.
The phosphor bronze-based material with high strength, high dimensional accuracy and corrosion resistance has been successfully developed and the mass production of the sintered bearing for the output shaft in the door closure motor has been achieved.
Valve guide material with high wear resistance generated by a dispersion of hard particles
Hitachi Chemical Co. Ltd received an award for its development of a high wear resistance valve guide material. The valve guide supports the open/close motion of valves in combustion engines. The move to smaller, turbocharged engines has resulted in higher operating temperatures and potential wear problems on the valve guides. Therefore, a higher wear resistant material for valve guides was required.
In this new material a dispersion of hard particles was adopted to increase wear resistance. Cr-type hard particles were selected based on both their effect on wear resistance and their cost. Machinability is an important factor as the inner diameter is machined during the engine manufacturing process. Because machinability is generally reduced through the addition of hard particles, dispersion of a soft phase (Cu-phase) in the matrix was also used to improve the machinability.
It has been confirmed that the new material offers 50% less wear than the company’s conventional material without machinability deterioration.
Net shape reactor core with a newly developed insulating lubricant
Hitachi Chemicals Co. Ltd received a further award for a pure iron Soft Magnetic Composite (SMC) reactor core for a Photovoltaic device which is used for voltage boosting and rectification inside the inverter.
The hardness of pure iron SMC itself is low and therefore, in the compaction process, pure iron powders tend to undergo plastic flow, leading to destruction of the insulation films. In this condition, the original magnetic characteristics are unavailable because of a drastic increase in eddy current loss. The company therefore developed a new lubricant for SMC which can prevent the plastic flow from a sliding surface as well as improving the insulation properties.
A pure iron SMC core (Fe: 99%, others ≦ 1%) was used, with the powders particles being coated with insulation films comprising both inorganic and organic elements. In order to achieve high density and strength, the die-wall lubrication method was used. One of the lubricant elements slides between metal powders and the die, protecting the metal particle shape and preventing plastic flow, whereas, one of insulation elements combines with insulation films preferentially and improves the insulation properties of the sliding surface.
Equivalent specific resistivity values were achieved for the sliding surface and compaction surface and low core losses were also maintained. Manufacture of the net-shape reactor core was achieved with the developed lubricant without surface finishing.