GEA's Global HVAC Technology Blog

Editor's Note: CR4 would like to thank PJ Sikorsky for contributing this blog entry, which complements his last post about material selection.

Continuing the investigation of common materials selection issues, let's discuss the importance of regularly reviewing material selections. Things change! The graph below shows changes in the relative cost of aluminum, copper and zinc over the past 10-15 years on a per pound basis. (The costs are normalized to the cost of aluminum on August 1, 1998 which was about $1400 / tonne.)

All three of these metals are often used in applications where corrosion resistance to water is important. There are a whole host of factors which need to be considered when selecting the "right" material. Strength, density, resistance to specific contaminants, etc., all can influence a material choice, but cost is obviously an important parameter. If in 1998 our analysis showed that copper was the right choice for a given application when it was on cost parity with aluminum and zinc, is it still the right choice in 2011 when the price of copper has risen four times as rapidly as the cost of the other two metals?

Cost, obviously, is not the only thing that changes with time. Technology changes, too. New materials are being commercialized daily. Originally, charred oak was the material of choice for plain bearing applications. Have you seen many wooden bearings lately? Of course not, but we still do see a lot of lead-tin, or antimony-tin Babbitt bearings. Are these the right materials when metal matrix composite bearings are stronger, lighter, and often more cost effective? They may or may not be the right choice today, but we can't know without doing the analysis.

New technology in manufacturing is allowing us to use "old" materials in new ways. For example, for many, many years gray cast iron was not used in some bearing and sealing applications because it was not possible to obtain the required surface finish. But as machining technology improved, it became possible to utilize this old, inexpensive material in new applications.

Clearly, the point is that the materials world changes. The material we chose for a given application years ago, may not only be sub-optimum today, it may be absolutely wrong and we may be letting our competition get an unnecessary advantage in the marketplace if they are more nimble than we are at changing materials as the times change. If we only consider new or alternative materials when we design new equipment, we're missing out on opportunities to reduce cost, improve profitability and solve technical problems on existing equipment.

- PJ Sikorsky