Bi-Metal Castings

The bi-metal casting of gear blanks is a technology developed and later patented by William H. Miller, founder of Miller Centrifugal Casting Company. It is a process whereby two alloys are poured and centrifugally cast into one metallurgically bonded gear blank. The outer rim of the blank where the gear teeth are cut is composed of tin bronze. The inner portion where the shaft is to be keyed or splined or an iron spider bolted is manganese bronze.

Bi-metal casting allows two different metals to be combined in one gear while maintaining the distinct advantages offered by the constituent alloys.

The optimism and encouragement with which major producers of gear sets and drive units accepted bi-metal casting led to the construction of a new foundry by MCC. The foundry is tailored specifically to the melting, handling, and pouring of two alloys. Today, MCC is planning further expansion to accommodate the demand for its bi-metal product.

Bi-metal casting begins with the controlled melting and alloying of nonferrous materials. All melting is done in modern coreless induction furnaces. Melting procedures have been established and are carefully monitored by managers trained in metallurgy. Every heat of molten metal is laboratory controlled before it is poured to assure that all customer specifications are met.

The emphasis on defined procedure is as important in casting quality metal as it is in melting it. Centrifugal casting has long been recognized as a superior method for producing quality gear blanks. The ability to control the direction of solidification and draw all impurities to the bore of the cast part enables centrifugal casters to produce blanks free of defects.

Castmanship

At MCC we take pride in our "castmanship." Our molding and pouring procedures have been derived through a solid understanding of theory and years of practice.

MCC's unique casting process achieves a rapid rate of heat transfer from the tin bronze portion of the bi-metal blank through the mold medium and result in a fine equiaxed grain structure in the solidified bronze. The fine grain configuration will give the finished worm gear a superior capability to smear into the worm, minimizing friction between the mating surfaces. Reducing friction will lower operating temperatures in a drive unit.

The conformability and strength of the copper-tin matrix in quality tin bronze has made this alloy the standard material for the manufacturing of worm gears and has led to the nomenclature, "gear bronze." These physical characteristics are not, however, the most desirable properties for the inner, shaft-mounted portion of the worm gear. This section must be able to withstand the torque of starting and the load of operating a drive unit. MCC 90,000 T .S., 45,000 Y.S. manganese bronze is tailored for these requirements. The manganese bronze is metallurgically bonded to the gear bronze in one centrifugal casting, and the two are absolutely inseparable under any operating conditions.

Casting Quality

Quality is the foremost but certainly not the only reason for specifying bi-metal The use of manganese bronze for the hub material allows MCC to offer the bi-metal blank at a price substantially below that for the same piece in straight gear bronze. The percentage of copper in manganese bronze is considerably less than the percentage in gear bronze, making the bi-metal a less expensive gear blank to produce. These cost savings in the foundry are passed on to MCC customers in the form of lower prices for the finished blank.

MCC design engineers have been working with major producers of speed reducers, drive units, and gear sets to incorporate bi-metal worm gears into their own designs. Blanks once made of straight gear bronze and bolted on to iron spiders are now made with manganese bronze in the inner flange.

Today, many gear manufacturers are taking the bi-metal concept a step further by purchasing MCC blanks cast directly to specified shaft sizes. These parts are supplied to the customer machined complete on modern numerically controlled equipment ready to be broached or key slotted and shaft mounted. By purchasing double hub gear blanks cast directly to shaft size, MCC'customers have reduced their costs for inventorying spiders and related hardware and labor necessary to affix them to a bronze rim.

Programs have been negotiated with several of our leading customers to supply bi-metal parts in specified quantities on specified dates during the course of the year. We promote these packages with prompt deliveries, lead times below the industry average, and a spirit of cooperation in improving delivery dates for vital parts. Our present capacity allows us to produce blanks in the range 6" to 48" center distance.

In summary, bi-metal casting is a unique foundry technology which has enabled MCC to offer into the worm gear market a gear blank with superior quality at an economical price. Through our achievement, we are certain we can help you eliminate many of your worm gearing problems and build a better machine.