Copper permanent molders discuss casting conversions.

Arriving from the U.S., South America, Asia, Africa and Europe, 70 copper-alloy metalcasters gathered in Ottawa, Ontario, Canada, October 15-16 for the [1.sup.st] International Workshop on Permanent Mold Casting of Copper-Base Alloys. The workshop was co-sponsored by AFS, the International Copper Assn., the Copper Development Assn. (CDA), CANMET Materials Technology Laboratory, and the Brass and Bronze Ingot Manufacturers, and featured 15 technical presentations highlighting all aspects of the copper-alloy permanent mold process and a tour of the CANMET research foundry and laboratory.

Functional Components

During his presentation "Value Added Design Solutions - The Future of Permanent Mold Casting of Copper-Base Alloys," Karl Schweisthal, Piad Precision Casting Corp., said it was important to recognize and market the unique advantages of copper-alloys cast by the permanent mold process. Piad has built its customer base by converting parts to permanent mold castings. When Piad was established in the U.S. in the 1960s, there was little opportunity for copper permanent mold, said Schweisthal. As a result, Piad marketed itself on the manufacturing and selling of functional components - parts having a specific geometry, functional precision and application related engineering properties. According to Schweisthal, Piad then set out to convince prospective customers that copper permanent molding offers distinct advantages in the manufacture of functional components.

The permanent mold process, said Schweisthal, offers customers high repeatability, excellent surface finish, improved mechanical properties and pressure tightness, and the ability to produce parts to close tolerances ([+ or -] 0.005 in.) without taper. Additionally, the process provides quick production cycles, comparatively low tooling cost and is environmentally friendly.

Schweisthal then discussed the advantages of the permanent mold process when combined with the property advantages of copper alloys. He cited the excellent electrical and thermal conductivity of copper alloys, in addition to superior corrosion resistance, wear, bearing, cryogenic and brazing/welding properties. Schweisthal concluded that copper permanent molding offers the customers the most value for the manufacture of their functional components.

"The future of permanent mold casting of copper lies in the continuous improvement of the competitive advantages of the process-alloy combination," said Schweisthal.

Copper Motor Rotors

Reporting on an unique application that shows the conversion potential and versatility of copper casting, John Cowie, CDA, and Jack Daugherty, Thermo Trex Corp. (TTC), discussed the production of copper motor rotors. The induction rotors used in commercial motors currently are pressure diecast using aluminum as the conductor material. The U.S. Dept. of Energy (DOE) has found that motors consume 60% of the electricity generated in the U.S., and that medium horsepower motors (1-125 hp) use 60% of the electricity supplied to electric motors. Since copper's electrical conductivity is twice that of aluminum, the increased efficiency and resulting reduction in electricity consumption creates a significant economic advantage to cast these rotors in copper.

The technical barrier to conversions to copper has been the lack of a durable and cost-effective mold material. A significant quantity of copper is required to make a rotor (approximately 1120 lb for a 10-20 hp motor). The shot temperature of high purity copper would be about 1225F (662C), and this high temperature, coupled with the high energy storage and thermal conductivity of liquid copper, creates a severe thermal load to mold materials. The CDA, DOE and TTC are funding a development program to find an economic solution for mold materials for copper rotor diecasting.

Recent analysis by two U.S. motor manufacturers shows that the economics of motor operation and production would favor the use of copper if die life in the pressure diecasting process could be extended to 20,000 shots. Extensive computer modeling of flow and heat transfer to predict temperatures and temperature gradients was performed by TTC, and testing of copper rotor casting has begun.

To establish a baseline for the mold test, castings were run in die inserts made of H-13 steel. Previous tests with H-13 were not successful, however, an extended run of 800 castings was produced with steel mold inserts. The success is attributed to a dry mold release system, a fast cycle time that minimizes heat input to the mold and the use of advanced computer controlled casting equipment.

This success has provided encouragement for the second phase of the research,

which will test several materials that show considerable promise for mold materials, such as beryllium-nickel alloys and nickel-based superalloys, as well as materials not in current use as mold materials such as tungsten and molybdenum.