Commercial Powder Heating and Delivery Systems

Successful utilization of the warm-compaction process necessitates that the powder, powder shuttle, and compaction tooling be heated to the proper temperature. Recommended temperature control of the heated powder and tooling is ±2.5 °C. It is imperative that the temperature of the powder not exceed 170 °C (320 °F); above this temperature the lubricant and binder degrade, resulting in diminished powder flow. Heating of the tooling is accomplished using cartridge heaters embedded in the stress ring of the die. Typically, eight to twelve 500 W cartridge heaters are required to heat the tooling to 150 °C (300 °F) in approximately 30 min. Heating of the powder shuttle is necessary to maintain the powder temperature during the transfer of the powder into the die cavity. Top-punch heating is recommended to eliminate the possibility of a tool binding between the top punch and core rod(s). Heating the core rod and lower punches is not necessary; where practical, incorporating a cartridge heater in the core rod will provide greater temperature uniformity.

Currently, three commercial powder heating and delivery systems are available. Each system is capable of delivering heated powder at the proper temperature. Additionally, each has the capability of heating and controlling temperatures in the die, the punches, and the powder shuttle system. The three systems are:

• Cincinnati Inc. El Temp System

• Abbott Furnace Company Thermal Powder Processor

• Slotheater

The Cincinnati Incorporated El Temp system utilizes an auger to both heat and transport the powder from the powder feed hopper to the heated shuttle (Ref 18). The auger operates within a resistively heated shell; additionally, the auger is hollowed, allowing preheated air to provide for additional heating capability. The amount of powder heated is determined by the part weight and press speed. Production systems are available that heat up to a maximum of 9 kg/min (20 lb/min). A unique feature of the El Temp system is its direct interface with the Cincinnati computer operating system of the press, allowing for control of all press and heating functions from a single touch screen.

The Abbott Furnace Company Thermal Powder Processor, TPP 300 (patent pending) uses a low-pressure fluidizing air 35 kPa (5 psi) to heat the powder within a sealed reactor. Heating of the powder is accomplished in a stream of air that passes across resistively heated elements. As powder is withdrawn from the bed into the delivery system, additional powder is drawn into the reactor. This system uses a stand-alone programmable logic controller (PLC) controller to heat the powder, die, and powder shuttle. Units are available that can deliver powder up to 3.5 kg/min (8 lb/min) and 3.5 to 9 kg/min (8 to 20 lb/min). The TPP 300 is portable and can be adapted to any press. These units have no moving parts, thus minimizing maintenance.

The Slotheater uses the principle of direct contact of the powder with the heated surfaces of an oil-filled slotted heat exchanger (Ref 4). The powder flows via gravity from the press feeder hopper into the slot heater where it is heated and then flows into the powder delivery system. The temperature of the heated oil is controlled to a temperature approximately 4 °C (7 °F) hotter than the desired temperature of the powder. To achieve uniform temperature of the powder, the residence time of the powder in the heater must be at least 5 min. Commercial units are available that can deliver 3.5 kg/min (8 lb/min) of hot powder. However, the design is scalable to achieve up to 9 kg/min (20 lb/min).

Considerable attention has been given to the actual mechanism of heating the powder; however, attention must also be given to the powder shuttle system. Although no commercial systems exist, it is a relatively easy task to design and build a hot powder feed shoe. Heating of the feed shoe is accomplished by embedding cartridge heaters and a thermocouple in the aluminum feed shoe. Temperature control of the feed shoe is necessary to prevent any heat loss during the residence time of the powder in the shoe. Both a closed shoe and an open shoe have been successfully used. Unlike conventional powder shoes, the amount of powder in the feed shoe is critical. Excessive amounts of powder in the feed result in a long residence time within the feed shoe, possibly resulting in a temperature drop causing excessive part-to-part weight variations.

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