Heat Treatment and Zinc Plating of Grade 8 Cap Screw for the Construction Industry

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This grade 8 carbon steel cap screw is so simple looking, yet it presented Elm Plating Company with an interesting two-fold challenge. A large supplier of fasteners for the construction industry was eliminating hexavalent chromium, a potentially harmful toxin, from their part finishes. They wanted to migrate to a finishing process that used trivalent chromium, a more environmentally friendly and human-healthy option, but required that it deliver comparable corrosion resistance. Secondly, the part had to maintain its unique yellow color, which was critical to the identification of its strength grade.

Embracing the challenge, our skilled technicians began an ongoing process of prototyping and testing a variety of color formulations to find the one that best matched the original yellow. Although we quickly came close, the color was fine-tuned over a year-long period to achieve the best match possible. Simultaneously, the finishing process was also being developed and refined, and after extensive DOE testing, Elm's new process using a trivalent chromium finish proved capable of 120 hours to white corrosion and 144 hours to red corrosion for a non-baked part, and 96 hours to white corrosion, 120 hours to red corrosion for a baked part when tested to ASTM B117.

For this customer, the finishing process is streamlined to handle large volume production on a typical 5-day turnaround. After heat treating the carbon steel cap screw, a .0002" thick zinc base coat is applied and the part is baked with a trivalent yellow chromate finish. Samples are continually subject to 144 hour salt spray testing at an onsite accredited laboratory, and Elm Plating annually processes over a million pieces, with a large range in cap screw lengths and diameters, for this customer.

Heat Treatment and Zinc Plating Project Highlights

Product Name	Grade 8 Cap Screw
Product Description	This grade 8 cap screw is used within a construction application.
Capabilities Applied/Processes	Heat Treatment Zinc Coating Baking Trivalent Yellow Chromate Coating
Overall Part Dimensions	Zinc Coating Thickness: .0002" Zinc Overall Length: 4.00"
Material Used	Carbon Steel
Material Finish	Yellow
In process testing performed	Salt-Spray Testing 144 Hours
Industry for Use	Construction
Volume	1,000,000+
Turn Around Time	5 Days
Standards Met	Customer supplied specifications ASTM F1941 5C 96/96
Delivery Location	Indiana

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