Turning over a new leaf: State Brass Foundry and Machine was able to bring back a former customer by enhancing the centrifugal casting technology in use at its facility.
State Brass Foundry and Machine, Salt Lake City, Utah, has been dabbling in centrifugal casting for about 25 years, and its commitment to the process has allowed it to regain at least one job it had previously lost to low cost suppliers.JBT Aerotech, also of Salt Lake City, first approached State Brass in the 1970s. The OEM produces, among other things, the ramps airline passengers walk across to enter commercial jets--alternately called jetways or airbridges--and it needed two large, round brass castings to brace the column that links them to the airport terminal and allows them to pivot. One of the castings would be used on the upper side of the hydraulic columns, the other on the lower side.
At the time, State Brass was a primarily green sand metalcaster that used a horizontal centrifugal casting machine sparingly. The company quoted and won the rotunda job on its green sand line, mostly on the strength of the price it offered. The large cylindrical castings were poured in CDA 836 brass and weighed 73 lbs. (lower) and 57 lbs. (upper), each with similar dimensions at 34 x 27.5 x 7 in. They weren't State Brass's crown jewel, but rather low-yield, porous structures that took a long time to make. After time-consuming mold making and pouring, the castings required a two-hour cool down before shakeout, with shot blast and grinding room cleanup adding another hour per piece.
[ILLUSTRATION OMITTED]
Nevertheless, State Brass continued to make the castings in green sand, and JBT continued to buy them for about two decades. Rut in the early 1990s, another green sand casting supplier offered the airbridge producer a lower price, and the buyer accepted.
"Every year, we re-bid our parts," said JBT materials manager Nicholas Manning. "We always are looking for lower cost, quality suppliers that can deliver on time."
In the succeeding years, State Brass won its customer back. The company installed a vertical centrifugal caster, which allowed it to deliver JBT a bid that was even lower than the green sand competition, without sacrificing quality or lead time. The company was rewarded for its efforts with a best-in-class supplier award in 2000, and a year later, it became a certified supplier to JBT.
[ILLUSTRATION OMITTED]
"It was kind of the Field of Dreams theory," said Don Archer, a fourth generation employee of State Brass. "If you build it, they will come."
Going Upright
Centrifugal casting machines are ideal for customers seeking cylindrical parts with microstructures and mechanical properties superior to those made in static casting methods. The process, which is often linked to the production of ductile iron pipe, also can produce large parts in unexpectedly intricate patterns.
State Brass began operating a small horizontal centrifugal casting machine in 1985. In 1995, the company installed a vertical centrifugal casting machine for about $500,000. The machine is capable of reaching outside diameter sizes of 72 in., and according to Archer, it offers significant advantages for the metalcaster's cleaning room. In addition to sending more consistent parts to finishing, centrifugal components are made without the use of a gating and risering system, which takes time to grind away from green sand castings. This alleviation of cleaning room requirements--as well as a reduction in cooling time provided by centrifugal casting--is critical for the 14-employee staff at State Brass.
"In centrifugal, you cast [a part] and pull it out of the mold in less than 15 minutes," Archer said. "Then, you throw it in the [shot blast] and send it over to the machine shop."
Today, State Brass boasts a near zero scrap rate on its centrifugally cast parts. While this is primarily due to the inherent benefits of solidification during spinning, the company also has retrofitted a ceramic sprue to hold a filter for parts where it needs an added level of cleanliness in the melt. In addition, it only uses certified alloys for parts poured on the machine.
The vertical centrifugal casting machine also allows State Brass to produce parts with considerably lower draft than can be produced in static casting. Because castings shrink away from the walls of the mold in a centrifugal machine as they cool, the draft can be as low as 1 degree, with 3 degrees being the standard.
"A lot of it depends on how big the part is," Archer said. "The taller the part, the more draft you would want on it."
Take Two
For casting buyer JBT, a company-wide policy of re-bidding all of its components every year allowed it to discover the centrifugal casting process. The OEM heard that State Brass had installed its larger vertical centrifugal machine in 1995, and after it sent out its requests for quote, the metalcaster's new bid came back lower and with shorter lead times than it had previously offered.
[ILLUSTRATION OMITTED]
Thanks to the centrifugal casting process and its ability to limit porosity, shrinkage and inclusion defects, State Brass now produces more quality bearing castings for JBT with less scrap, which in itself saves both companies time and money.
"They were able to produce the part [in centrifugal casting] for a lower-cost, and we were happy to go back to them," Manning said. "It's now of very good quality, and it's always on time."
The new process also has allowed State Brass to yield more parts per hour. Where in the green sand process the metalcaster produced the two parts in roughly three hours, State Brass can now pour both pieces in one mold in about half an hour, quickly blast it and then send it directly to the machine shop, where it is cut into two parts.
According to Archer, the centrifugal process has saved two hours per casting (which includes a molding time reduction in addition to the lower cooling time), allowing State Brass to go from three to four green sand castings to 16 centrifugal castings in the same eight-hour shift. Improved casting yield also has saved 50-75 lbs. of metal per part, which Archer said was critical for a casting that starts out as a 385-lb. piece and is machined into the 73- and 57-lb. components.
[ILLUSTRATION OMITTED]
State Brass also has trimmed the amount of value-added services it performs on the part, further highlighting the mold-to-customer strategy it has taken on the job.
"We were casting them, machining and then assembling them, and pressing them onto the rotunda column, which we would also machine," Archer said. "Now, they do the assembly."
State Brass has been able to expand its centrifugal casting business in the wake of the vertical machine addition. Because of its larger size compared to the horizontal machine, the company finds it is only limited on the parts it can produce by its pouring capacity, which is about 2 tons.
"Now, I believe we do some of the heaviest wall thicknesses on the West Coast," Archer said.
And as long as the company continues to produce those large centrifugal pieces at a high level of quality, customers like JBT give it reason to believe it can grow that side of the business even more.
"State Brass has been a really good vendor for us," said JBT mechanical engineer Chris Hansen. "We've had other vendors of other components that [produce] parts with porosity, and we have to reject them. But to my knowledge, we've never had any issues with this bearing from State Brass."
[ILLUSTRATION OMITTED]
For More Information
"Centrifugal Casting," N. Janco, American Foundry Society Publications, 2007.
Shea Gibbs, Senior Editor
 Printer friendly
 Cite/link
 Email
 Feedback
| |
| Author: | Gibbs, Shea |
|---|---|
| Publication: | Modern Casting |
| Date: | Oct 1, 2010 |
| Words: | 1251 |
| Previous Article: | Know the environmental impact of your additives: step one in pollution prevention is reviewing the additives in your green sand molds. |
| Next Article: | The necessity of Leadership: a metalcasting veteran examines what it will take for the future leaders of the industry to overcome the crises it faces. |
| Topics: | |