Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Continuous Chromating Machines
Q. Hello,
My company is looking to start chromating our own aluminium parts. They are small pins and bobs on the size scale of screws and bolts. I am wondering if there are any continuous chromating machines available, or if there are only the dip process style. I also wonder if there is anything more scientific that can be used to determine if the parts have been in the alkaline etch or deox long enough besides for "ehh they look ok". I appreciate your responses in advance.
Thank you,
Dan NathanManufacturing - Telford, Shropshire, England
2004
A. "Continuous" and "dip process style" don't strike me as opposites, so I'm not quite sure what kind of continuous machine you are picturing that would apply to small discrete parts. Would you be thinking of what some people call a 'bandolier' machine, where 'cartridge belts' go through the process and you automatically insert the components to be chromated into the belt?
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Thank you Ted for your quick reply. I would like to be able to chromate small Aluminum bolts and nut style parts. I think the threads would be damaged in a horizontal rotating chromaters. I will be processing them in rather high volume (smaller and bigger parts, roughly same volumes but different part quantities), and was hoping I could chromate them on a conveyor belt. A bandolier process or any other process is suitable, as long as it can adapt to different sizes and can be automatically loaded and unloaded. What I meant by dip style was where you have perforated baskets full of parts and lift them in and out of large tubs of chemicals. What is the best way to do a quality check on the chromating job, is it salt spray? Are there ways to actively determine the optimum time in each bath, or going through each process while the machine is running? Thank you, - Dan
Dan Nathan-RobertsManufacturing - Telford, Shropshire, England
2004
A. I have not seen such a machine, but custom machine builders will conceive, design, and manufacture a solution if you can afford it. Be aware that chromating requires good agitation (usually air agitation), and that the rinse tanks should also be agitated ... so it's probably not as simple as placing the parts on a conveyor belt. I've seen machines (not chromating machines) that use two parallel round belts that you place the parts between. I think some people call them "rubber band conveyors"; that might have some possibilities if you are thinking of developing a machine.
Salt spray testing is probably the best quality control.
I doubt that any of the process steps will require an immersion time of more than 90 seconds, but allowing 120 seconds might be a good idea--any of the suppliers of chromating processes (Chemetall Oakite, Macdermid for example) will be happy to run test parts and advise you. One problem with a fixed-cycle machine like a conveyor belt is that it is difficult if not impossible to independently adjust immersion times in the various processes, so you would need to determine how much etch time and desmut time to allow, and then live with it.
I think I'd go with racks or baskets (but not rotating baskets) instead of a conveyor belt.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004
Q. Ted,
Thanks again for the reply. The ideas you came up with are excellent. What did you mean when you said you'd go with baskets, but not rotating baskets?
Thanks again,
Dan Nathan-RobertsManufacturing - Telford, Shropshire, England
2004
A. You were concerned about the possibility of parts damage from rotating baskets, but it is possible to chromate parts in simple stainless steel wire baskets, carried from tank to tank by hand, or with the help of a monorail hoist, or via programmed cranes.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004
Thank you Ted, I appreciate your help.
Manufacturing - Telford, Shropshire, England
2004
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