Sintered screw nut used in a medical syringe pump
A further Porite Corporation award was for a non-circular sintered screw nut used in a medical syringe pump, equipment that provides small amounts of liquid medicines continuously. The nut is required to transmit the lead screw rotation to the plunger accurately. It is also required to support the lead screw while rotating at low speed with low friction and high accuracy.
This part was originally a molybdenum-coated material, manufactured by a machining process and needed to use grease. The adoption of the sintered bearing material, selected for the condition of high-load and low-speed, met the required smoothness and durability without needing to use grease.
In addition, this product’s design was required to prevent tooth jumping. This requirement was met by the adoption of the serration tooth shape, after discussion with the customer. As a result, cost is reduced to one third of the original. Also, as this is a grease-free product, the former problem of scattered grease was solved.
High-density sprocket with low cost and compaction without a die lubricant
Fine Sinter Co. Ltd. secured a second award for a two-step engine sprocket with a high density of 7.35 g/cm3 achieved by normal compaction and mesh-belt sintering.
In order to produce high-strength products, various methods (such as warm die compaction, die-wall lubricated warm compaction and high temperature sintering) have been adopted that require the addition of nickel, an expensive alloying element. In contrast, for the purpose of cost reduction, this development used the hybrid Mo steel powder (pre-alloy with Mo and diffusion bonded with Mo fine powder) that does not contain nickel. Although this raw material powder has relatively good compressibility, it is necessary to apply high compaction pressure in order to achieve a density of over 7.35 g/cm3. This required the optimisation of tool breakage by using CAE analysis.
In addition, the achievement of green density levels over 7.35 g/ cm3 also contributed to cost reduction through the ability to employ inexpensive mesh belt sintering, because expensive high temperature sintering is no longer necessary to achieve the high density.
By this development, compared with the conventional die-wall lubrication compaction method, a cost reduction of around 22% was achieved.