Barrel Plating Continuous Improvement

Article From: Products Finishing, , from Products Finishing

Posted on: 3/1/2006

Process improvements, overall line improvements; barrel plating is not a static technology, as these companies reveal...

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barrel plate zinc die casting

The Zinc Die Cast Department is well known for having the capability to barrel plate zinc die casting to withstand prolonged high temperature with no blistering.

In the late 1800s, just after the Civil War, there was an increased need for finishing, particularly large lots of smaller parts. It was about this time that barrel plating began, with platers using wooden barrels to finish parts. Until the 1940s, there were no significant improvements in barrel plating; however, after WWII, chemically resistant plastics were available for manufacturing the barrel plating systems.

This was an incredible boom to the business, since plastic barrels would not wear out as quickly as wooden ones because the solutions could not be absorbed into the plastic barrels. Also, the plastic barrels better withstood the tumbling of metal parts. However, since this first great improvement, barrel plating has progressed even more.

Today, companies such as New Brunswick Plating, New Brunswick, New Jersey, develop better plating processes designed to accommodate the specific needs of its customers. The company is dedicated to working with customers to specifically define and develop the best finish for a particular part. This dedication pays off for its other clients as well, who benefit from the new plating process developments and improved processing methods.

For example, the company developed a barrel plating process on zinc die-cast for Bell Labs’ optical fiber data link. The gold finished item, which was purchased by IBM, had to withstand 3,000 hrs at 85% humidity and not blister under 400°F prolonged heat. Also, the data link has to meet a 0.0003-inch bore tolerance.

To obtain the specific parameters, New Brunswick Plating (NBP) started by examining its casting machine. Release time, temperature, overflow venting and other factors were tightly controlled to minimize porosity, flash and cold shut on the zinc casting. The die was designed steel safe, allowing for dimensional adjustments.

A trial plating run determined the amount of chemical mill necessary to remove laminate surfaces, clean up minor flash and open any surface pores, especially around the parting lines and cold shut areas. The trial plating run also determined the amount of copper required to seal microscopic pores on the casting. This amounted to about a 0.001 to 0.0015 inch thickness, with a 0.0002 inch final electroless nickel plate.

Although today most job requirements are not as stringent, the procedure developed then now lends itself to barrel plating that yields superior plated finishes on zinc die-cast, steel and copper-based alloys today. This benefits New Brunswick Plating’s customers in the telecommunication, medical, electronic and automotive industries.

Barrel plating generates 75% of New Brunswick Plating’s sales. Of the 75%, zinc die-cast-based material accounts for 65%, with the remainder being steel and copper-based alloys. Parts are plated with copper, nickel, electroless nickel, tin, tin alloys, cobalt and nickel alloys, zinc, gold, indium, silver and brass. Usually, however, the job requires that a combination of these metals be plated.

Normally, incoming zinc die-cast parts go through a 0.0003 inch chemical milling process, with dimensional loss being made up by an additional copper plate thickness. Chemical milling is an important step in the barrel plating process at NBP, because removing 0.0003 inch of material not only removes zinc oxide and carbonate on the surface of the parts, but also removes any minor base laminate surface that would produce a casting blister and minor flash. The loose laminate is not visible on the raw part, but would manifest itself as a casting blister when the highly stressed intermetallic is formed between the zinc base and the copper plate.

Every die-cast part undergoes a chemical milling sequence, with a removal limit of 0.00125 inch. This limit was established after tests showed that additional milling would expose minute internal air pockets in the casting. The chemical milling process was developed by Bob Sica, then a plating chemist at NBP and now its CEO, and Allan Cook, a Bell Labs engineer who coordinated the die-cast changes necessary around the plating sequence.

The milling process at NBP initially impacted its waste treatment. This made it too expensive to use on all castings; however, a method was developed to treat the milling solution off line. Zinc is precipitated as its carbonate. The mix goes through a filter press to yield a dense, semi-dry cake. Each week, one ton is recycled and the remaining filtrate is sent to waste treatment where NBP also recycles its F006 waste.

As exemplified by NBP, there have been significant advances in barrel plating technology. The company’s greatest strength is its adaptability to change. In the 1930s, NBP was a decorative plating company. During WWII, plating was 100% industrial. In the 1950s, the company plated wave-guides and became an FAA repair station for hard chromium and cadmium plating on landing gears. In the 1960s, NBP had the largest hard chromium plating tanks on the East Coast, and the company was heavily into aerospace plating. NBP had the contract to gold plate retrorockets on the Surveyor Space Craft and satellite work from RCA Astro. When heavy machine manufacturing moved offshore, the company’s hard chromium plating jobs dwindled. Now the company has no hard chromium in either of its plating facilities. Today the company is heavy into barrel plating, although at one time barrel plating was restricted to smaller lots and never the preferred choice for plating. The company is ready to adapt again should demands or the economy necessitate it.

Other Barrel Plating Improvements

There also have been improvements in waste treatment among barrel platers. Technical Plating, Inc., Brooklyn Park, Minnesota, which was featured in a previous Products Finishing article, has been able to save more than $45,000 a year by improving flow control and reusing effluent, which saved more than two million gallons of water a year.

Technical Plating’s work ethic is simple—turn out reliable, consistent, high quality work at all times and maintain a clean shop. This enabled the company to increase its customer base, which, in turn, increased its water use and subsequent wastewater discharge.

On the barrel plating line, MnTAP intern Eric Tsai, a chemical engineering junior at the University of Minnesota, determined baselines for water use on the rinses. The research determined that the flows on different barrel plating lines varied and flows varied according to the time of day. Tsai determined that the variability was partially caused by ball valves, which were used to control flow.

Flow meters were installed on the rinses of one barrel plating line. Water use decreased by 5,000 gpd, saving more than $4,000 in sewer and water costs.

Also, barrels were modified to accommodate internal rinsing. Tests comparing internal barrel rinsing with traditional two-tank counterflow rinsing showed that internal rinse barrels require 30 seconds more rinse time; however, water consumption was reduced 1,400 gpd. Technical Plating’s first year savings was $45,550.

MnTap has a variety of technical assistance services to help Minnesota businesses.

Barrel plating is not a stagnant technology. It continues to develop new plating solutions and methods as well as innovative designs for lowering water consumption and decreasing costs related to waste use and waste generation.

 



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