Dana Keeps Zinc Plating Under Control

Article From: Products Finishing, , from Products Finishing

Posted on: 2/1/1997

Three recently installed zinc plating lines feature state-of-the-art controls...

A farmer will not wake up without an alarm clock (or a rooster). A farm will not produce without a farmer and a tractor. The tractor will not run without gears and hoses. And the hoses will not work without the proper fittings.

This is where the Dana Corporation, Antwerp, Ohio, enters the picture. Dana Corporation manufactures hoses, fittings and the equipment to put them together. These hoses and steel fittings are used in a variety of markets, including mobile off-highway (large earth movers), agricultural and truck and trailer.

Hoses are manufactured at the company's facility in Hohenwald, Tennessee. The equipment for crimping the fittings onto the hoses is made in Columbia City, Indiana. The Antwerp facility has the responsibility for manufacturing and finishing the myriad of fittings for the hoses.

The finishing line at the Antwerp facility was getting old. It had been in service for 25 years. When the system went down, spare parts could take up to six weeks to arrive. "It became obsolete," stated Joe Williams, manufacturing manager. "Spare parts just were not available. We needed a more reliable system."

Mr. Williams contacted Corrotec, Inc., in Springfield, Ohio, to design, manufacture and install replacement lines for the two barrel and one rack zinc plating lines currently in production.

Ordinary replacements were not all Dana Corporation was considering, however. It wanted reliability, since its production averages 7,500,000 pieces per month. Corrotec's Dave Stratton knew how to execute the order. He contacted MABCO in Old Castle, Ontario, Canada. Within the new lines, Corrotec incorporated the Flex Cycle system from MABCO. This provided Dana the reliability it needed.

Flex Cycle runs the finishing lines from Windows 95. It has the capability to program each barrel or rack of parts to a particular sequence. From a diagram on the computer, set up near each line, operators can determine and program time in tank, tank temperatures, rectifier voltage, pH and tank chemistry as well as sequencing. Not only can the operators see what is going on, but he/she has the ability to change any parameter necessary. If the barrels need a longer dwell over a certain rinse, that is easily programmed.

Barrels on the barrel plating lines can also be programmed for rotational speed. Barrels have an 800-lb capacity. The 14-inch barrel plating line is used to plate parts that may be damaged in the 18-inch barrels. Other parts that require gentler cycling are plated on the rack line.

The rack line features eight-ft wide tanks and a six-station zinc plating bath. One rectifier controls the voltage in all six stations. The control system compensates for the size and density of the products so that the rectifier amperage is consistent for good plating in each station. One bath may contain 100 half-inch hose fittings, while another contains only 48 one-inch fittings. The rectifier compensates for the difference and provides the correct amount of amperage to each.

Another feature of the control system is an ability to remember where processing ended. This is beneficial if there is an unexpected shutdown or even a coffee break. The system will start the process at exactly the same location with same parameters as before the shutdown.

The control system also has the benefit of "Look Ahead." With this feature, the control system "knows" the number processes or tanks that must be available before a workbar will be moved. For example, a workbar cannot remain in an acid etch beyond a certain time. So, in the recipe step before the acid etch, the Look Ahead is set to two. This ensures that both the acid etch and the next tank are available before the workbar is moved to the acid etch. At the end of the acid etch, the workbar will always be able to move to the next tank. The system can put itself in a "safe" mode if it anticipates trouble down the line. It then can place racks or barrels in "safe" positions, until the problems are corrected.

Each rack or barrel of parts goes through the same cleaning, plating and chromating cycles on its respective line: Uni Kleen 10 heavy-duty alkaline soak cleaner at 180F; Electro-Kleen SP alkaline electrocleaner for three min at 180F; Lustra-Zinc PCZ-5000 acid chloride zinc; and Duracoat 1237 yellow chromate. Parts are then treated with Watershed, a water-soluble rust inhibitor that passivates the steel, leaving a dry, non-oily film.

Chemical additions of zinc, chloride and brighteners are made daily to maintain consistency in the brightness and color of the plated finish. Baths are continuously filtered and treated for iron using hydrogen peroxide. Each Monday, bath samples are sent to the supplier, Heatbath, for analysis. Kirk Parker, plating supervisor, tests baths weekly, particularly for iron content. He also titrates cleaners daily.

Pre-production tests were done on the bath chemistry prior to installation. Because the majority of the work is plated in barrels, Dana wanted a low-foaming, low-dragout product. It also required that finished parts be defect free and free of red rust after 120 hrs salt spray testing (as well as meeting SAE J514 standards).

Much of the testing is required because the water in northeastern Ohio is full of heavy metals and minerals. Also, this, and environmental regulations moved the company to install a multi-million dollar state-of-the-art Unipure wastewater treatment system. John Tuto runs the wastewater treatment system. First, wastewater from the plating system enters a holding tank where it is batch treated for chromium reduction, followed by a pH adjustment. From there it is pumped into a holding tank for flow equalization and then directly into a clarifier. A polymer is injected into the clarifier that drops out the solids, mostly chromium and zinc. Then John adjusts the pH and injects ferrous sulfate and air. The solution is pumped into a second clarifier where more polymers are injected. The clean effluent is discharged into the Maumee River. The sludge runs into two settling tanks and is pumped through a JWI filter press and dryer. The system handles 80 gpm, and Dana Corporation discharges 100,000 gpd. The EPA limit on zinc is 0.34 mg/liter. However, Dana Corporation is consistently under that limit in its discharge water quality.

Now Dana has a complete state-of-the-art facility, from finishing to waste treatment. The 250,000-sq-ft facility runs more efficiently because there are no breakdowns. There are no effluent worries because the wastewater treatment system effectively keeps zinc below EPA limits.

 


TABLE I--Zinc Chloride Plating Process (barrel and rack)
SOLUTION COMPOSITION

Component Optimum Range
pH 4.8 to 5.8
Zinc Metal 4.0 to 5.5 oz/gal
Total Chloride 16 to 22 oz/gal
Boric Acid 4 to 5 oz/gal
Make-up Additive 3 to 4 pct
Brightener 0.1 pct


OPERATING PARAMETERS

Parameter Barrel Rack
Temperature 70 to 100F 70 to 100F
Cathode Current Density 2 to 10 asf 20 to 40 asf
Voltage 10 to 12 v 4 to 6 v
Cathode Efficiency 98 pct 98 pct
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