A New Spin on Zinc Post-Treatment

Automated processing can improve quality, reduce waste.
#plating #pollutioncontrol


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Many electrogalvanized parts require a chromate sealer or other additional processing to improve corrosion resistance or other performance characteristics. In the past, chromate and other post-treatments would have been performed in the barrel line, on multiple manual lines, or using a combination of the two.

More recently, increased chemical costs associated with trivalent passivation chemistries, the desire to reduce wastewater treatment and customer demands for improved quality have led platers to consider automating their post-treatment processes. According to WMV Dip Spin Automation Coating Equipment (Sylvan Lake, MI), one approach to automation is to use a dip-spin-tilt transfer hoist to move baskets of parts through post-finishing, reorienting them as needed and providing automatic material handling to control the entire process.

The company's Aron Lorenz says use of dip-spin-tilt equipment can provide multiple benefits in some post-treatment applications. "One of the major benefits is increased finish quality due to part manipulation and process control based on specific recipes," he explains. "Other benefits include reduced chemical usage and water consumption, reduced work in process inventory, lower waste treatment requirements and reduced effluent sent to public wastewater treatment facilities."

According to Lorenz, a major concern for platers required to produce high-quality finishes is preventing damage to parts during transfer from the plating barrel to post-treatment. WMV's dip-spin-tilt equipment addresses this issue by transferring parts through a water-filled funnel and basket.

"The water buffers the impact of parts while they are being transferred into the centrifuge basket," he explains. "Transferring the parts through water to the centrifuge basket also typically eliminates one rinse station on the plating line, because loading the parts to the centrifuge basket will function as a final rinse."

Dip-spin-tilt equipment also works well for complex parts with design features such as cupped areas, blind holes, internal cavities and recesses, which are prone to head fill, puddling, and uneven coating. WMV's equipment alleviates potential problems with complex parts by allowing the basket to be dipped and tilted while it rotates in the post-treatment solution. Tilting the basket up to a 60° angle reorients parts and maximizes solution turnover around them. The system can also oscillate the basket up and down while it remains vertical or tilted.

After post-treatment or rinsing, the hoist raises the basket above the treatment bath and spins it at up to 160 rpm to centrifuge off excess solution. This step can reduce drag-out into the next process tank by up to 90%, Lorenz says.

The system lets users set all treatment parameters in the part process recipe to ensure that a variety of different parts are processed as required to optimize quality and productivity for each batch. User-programmable parameters include basket or barrel loading weight, time in solution, rotation speed under solution, spin-off time and centrifuge speed, and number of repetitions desired.