Application Digest

Corrosion-resistant PM stainless steel

Louis Desrosiers, Presidetn, Prectitech, Inc., Quebec, PQ, Canada

The corrosion resistance of stainless steel, combined with the unique economy of the powder metal (PM) process, makes PM stainless steel an attractive material for many types of parts. Recent developments in high-temperature sintering make it possible to manufacture corrosion-resistant stainless PM parts, opening a much wider range of cost-effective solutions for design engineers.

The inherent porosity of PMparts tends to increase crevice corrosion. A number of ap-proaches are being explored to improve corrosion resistance, and altering the sintering pro-cess promises to be the most cost-effective.

Corrosion resistance (as evidenced by the length of time before visible corrosion occurs) increases as sintering temperature rises. Sintering stainless steel parts at 2,350F (1,288C) promotes the deoxidation/reduction of oxides that inhibit metal-to-metal bonding of powder particles. In addition, controlling the sintering atmosphere to optimize nitrogen absorption results in significant improvements in me-chanical properties and corrosion resistance.

Traditionally, sintering is performed at a temperature of 2,050F (1,121C) because the metal belts used to transport the product through the furnace have a significantly reduced life above this temperature. High- temperature sintering--processing over 2,100F (1,150C)--can be performed in a pusher, walking beam, or vacuum furnace, eliminating the limitations imposed by the belt.

To contact a Precitech applications engineer, call 418-658-5335, or fax 418-658-5336.

Self-calibrating liquid level sensors

Will Atkinson, Product Manager KDI, Commercial Products Division, Cincinnati, OH

When measuring oil or fuel levels, factors such as degradation, contamination, difference in type and brand and, to some degree, lot-to-lot variation, can often cause capacitive liquid-level sensors to give inaccurate readings. This occurs simply because the majority of these sensors use a fixed reference and cannot allow for such factors.

The Commercial Products Division of KDI Precision Products has developed and patented a new capacitive liquid-. level sensing technology that continuously self-calibrates, thereby eliminating the fixed-reference problem. By locating a series of transmitting plates along the length of the device's sensing region, the KDI sensor can obtain capacitive measurements for liquid, air, and the liquid/air interface point several times/second.

Using these constantly updated readings, the oil level can be very accurately calculated. Just how accurately depends on the size of the transmitting plates but, in a typical application, accuracy to within a millimeter is obtainable.

In addition, KDI's microprocessor-based sensors are low power (less than 50 mW), rugged enough to withstand harsh operating environments, able to filter level variations caused by liquid sloshing, and can be factory-programmed with tank geometry to provide actual volume measurements.

To speak with a KDI representative, call 800-377-3334, extension 2047.

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