Handbells
Handbells are most often asso- ciated with religious services and church choirs, but the melodic noisemakers rely on a recogniz- able casting to produce their musical brilliance. Because of the exacting specifi cations of the metal that is used in the production of instrument- quality bells, the process has changed very little over time. Bells feature a special bronze
Handbells rely on the sand casting process to meet strict specifi cations.
alloy of 80% copper and 20% tin (with trace amounts of con- taminants). T e tin produces the bell’s beautiful sounds but it also makes it extremely hard and brittle (take the Liberty Bell, for example). Several casting processes have been
tested for their ability to improve the grain structure and subsequent sound quality of bells, but sand casting is the preferred process. Finishing bells remains tedious and manual, and scrap is common considering the instru- ment’s necessary fi ne grain structure for acoustic resonance.
Bells are cast with excess metal on the inner surface, which will be struck by the clap- per. To tune them, trained acousticians machine away layers of metal, judging by ear when the bell produces the desired sound. Unfortunately, in the course of this process, subsurface defects can be found. But the cost of metalcasting scrap is minimal enough to avoid the need for non-
destructive testing prior to machining. T e inner surface of a concert bell
is machined to a pitch about 40% higher than the desired note. T is gives the bell maker a bit of leeway when the outer surface undergoes multiple rounds of sanding.
Woodwind Components Clarinets and fl utes have intricate-
ly designed sets of keys and rods that allow musicians to hit all the neces- sary notes. T e fl ute, for instance,
requires some 120 diff erent compo- nents to produce a fi nal set of 20 keys. While these can be stamped or forged, the highest quality keys are investment cast in alloys containing nickel, brass, silver and/or gold. T e process begins with the injec-
tion of hot wax into a plaster mold of the particular cast component. Multiple molds are arranged in a clustered tree and dipped into a plaster- or ceramic- based material. After the plaster has set, the wax is burned out leaving a hollow cavity into which the metal is poured. After cooling, the ceramic is
removed and discarded. T e cast components are broken off the tree and machined and polished. Some are plated with other alloys before fi nal installation on the instrument. Similar to the investment cast-
ing process, many saxophone keys are diecast, which uses a steel die in place of the ceramic mold. Diecast keys and components have improved strength and feel compared to stamped keys, with price often dictating the method of production.
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26 Different Meehanite Metals Meehanite specifications cover a whole range of cast irons from easily machinable grades to high strength ductile irons. Select the type of Meehanite best suited to your application on the basis of metallurgical structure and physical property values.
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• Heavy-Duty Applications Austempered Ductile Iron
• General Engineering Applications Flake Graphite and Nodular Types
• Heat-Resisting Applications • Wear-Resisting Applications • Corrosion Resisting Applications
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Sept/Oct 2014 | METAL CASTING DESIGN & PURCHASING | 23 5/16/13 11:37 AM
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