April 2006 Mechanical Engineering Departments: Tech Focus, Pt. 2

This section was edited by
Executive Editor Harry Hutchinson.

Fluid Handling and
Fluid Power

Wet Jet for the Jet Set
by Michael Abrams

For years, aerospace vehicles have been built with composites, while their close cousins, passenger jets, have continued to be made with more traditional materials. But now, with fuel prices soaring, the switch to the lighter and more efficient composites has become more obviously cost effective. And with the switch in material comes a switch in the tools to cut the material. Airbus's recent multimillion contract with Flow International Corp. in Kent, Wash., illustrates the point.

Water jets can cut cleanly through composite wings, like the virtual one shown here in gray.

The Airbus A350 is made with more than 50 percent composite materials, and the routers and laser cutters that once were used for the cutting are no longer sufficient. Routers can cause delamination and cracking when used with composites, and laser cutting can produce toxic fumes.

Flow makes water jets that cut using a pressured stream of water with a little abrasive. The method avoids problems with lasers and routers.

"It's a Waterpik on steroids," said Mike Ruppenthal, Flow's vice president of marketing and product development. He claimed other advantages of water cutting—that the tool doesn't wear, there's no dust, and there's no need for heavy fixtures to hold what's being cut.

"Every major aerospace company that uses composites uses water jets," Ruppenthal said. "Composites just haven't been used in passenger planes till recently."

Michigan Manu- facturer Goes Against a Trend
by Harry Hutchinson

A manufacturer of hard chrome-plated steel bars for hydraulic systems seems to be bucking a trend: Its factory is in Michigan and it's expanding.

The company, Stelmi America, based in Marshall, Mich., uses a proprietary closed-chamber plating process to produce corrosion-resistant steel bars and tubes used as hydraulic and pneumatic piston rods. The company says it will add machinery to increase its output capacity by more than half. The equipment will be made by an Italian company, Stelmi S.p.A. of Milan, which developed the chrome-plating process.

According to its managing director, Steven Dodge, Stelmi America began operating in 2003 and has been booked to capacity for the past two years. "This expansion represents a capacity increase well in excess of 50 percent and is targeted toward OEM producers of mobile hydraulics," he said.

The company's process plates bars in enclosed machines, which permit tight control over emissions from the process, Dodge said.

Chrome plating of bars takes place in the enclosed central chamber on this line at Stelmi America's plant in Marshall, Mich. Emissions from the process pass through a scrubber.

The hexavalent chromium—or, bonding to six atoms—that used in industry is a suspected carcinogen. There is also trivalent chromium, which is considered an essential trace nutrient that helps the body metabolize fats and carbohydrates.

According to a description of the process on the company's Web site, stelmiamerica.com, "Using an automated material handling system, which also transfers the required electrical contact to each bar, the bars advance and rotate, driven one by one through a series of circular anodes in the chrome plating machines. The ground and polished bars enter the machine from one side and exit, fully plated, from the other."

There are two process lines to a machine and one bar to a line. The smaller scale permits better control than does batch plating in open tanks, Dodge said. Emissions from the plating chambers pass through a scrubber system. Dodge said the products are priced competitively with other plated bar. The company sells bars in 24-foot lengths.

The Michigan operation started as an affiliate of Stelmi S.p.A., and later purchased the rights to the process and equipment for North and South America. Dodge said it is now "American- and Canadian-owned."

The machinery maintains negative internal pressure to curb emissions. According to Dodge, chromium emissions from the process are within the new limits set by the U.S. Occupational Safety and Health Administration.

Kar Laboratories of Kalamazoo, Mich., conducted tests at the Stelmi America plant in June 2004. According to Garrett Ervin, Kar's senior project manager, tests turned up less than 0.02 microgram of chromium per cubic meter, which was the reporting limit of the instruments.

OSHA has published new rules for chromium exposure, due to take effect at the end of May. The maximum permissible exposure limit is an average of 5 mg of chromium per cubic meter over an eight-hour period. OSHA originally proposed a limit of 1 mg, but decided after hearing comment that in many industrial applications, the limit was unrealistically low.

The previous exposure limit for chromium had been 52 mg/m³. The rules take effect 90 days following their publication in the Federal Register, where they appeared at the end of February.