FORMING OPERATIONS

Although zirconium can be formed using standard shop equipment, it does have a tendency to react with gases in the air at elevated temperatures and to gall and seize under sliding contact with other metals. A thin oxide layer, acting as a lubricant, protects against galling in forming operations. If additional lubricant is needed, use any oil or grease that does not contain halogen or sulfur (with the exception of molydisulfide).

A. Bending

Sheet or strip zirconium can be easily bent on conventional press brake or roll forming equipment to a 5T bend radius at room temperature and to 3T at approximately 200¡C. For cold forming zirconium tube, a minimum bend radius of 3 times the OD dimension is advisable. For smaller radius bends, hot forming at temperatures from 200¡C to 425¡C or the use of special bending techniques is required. When bending zirconium tube, spring back may be encountered due to its work hardening behavior. Also, both the inside and outside surfaces at the bend area must be in tension during any bending operation to prevent buckling and wall thinning.

B. Punching

Zirconium requires high plate pressures or excessive side flow occurs during punching operations. Very close punch and die tolerances, 1 to 2 percent of the metal thickness, provide the best results. It is essential that the dies remain sharp when punching zirconium. There is a tendency for zirconium to build up on the punch sides thus making stripping difficult. A die lubricant will minimize galling and reduce die wear.

C. Drawing and Spinning

Despite its work hardening characteristics, zirconiumÕs formability by hot and cold operations is good. Designs that eliminate severe or abrupt section changes, and allow generous radii are a must. Dies of non-galling material with tolerances and clearances comparable to those used for austenitic stainless steels should be employed. As in the case of tube bending, die designs should allow for the spring back tendency of the material.

SAFETY

There is one major precaution that must be considered when working with zirconium. It is non-toxic, but because of its very high heat-producing reaction with oxidizing elements such as oxygen, zirconium is pyrophoric. Large pieces of sheet, plate, bar, tube, and ingot can be heated to high temperatures without burning, however, small machine chips and filings are easily ignited and will burn at extremely high temperatures. Therefore, it is necessary to prevent large accumulations of chips or other small pieces of zirconium, and care should be taken to store this material in non-flammable containers and isolated areas. Zirconium chips and filings should be frequently cleared from machines and moved to a proper storage container.

An effective method of storage for zirconium chips and filings is to keep the material covered with water in the containers, with a layer of oil on top of the water to prevent evaporation. It is important to keep any storage container covered to prevent stray sparks from igniting the zirconium. If a fire does start in zirconium, ordinary fire extinguishers or water must not be used. Only dry sand, powdered graphite or special Metal-X powder should be used.

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