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topic 60510

What kind of coating for washing machine's aluminum spider arm?

September 15, 2017

Q. I am looking into coating a washing machine part called a spider arm. AFAIK, it's made of die cast aluminum.
The part bolts to a stainless steel drum, which it spins. The drum is of course where you put your clothes. This setup is (afaik) always on a front load washer.

The thing is, the spider always corrodes and breaks - mine did in just 3 years. It's inevitable. Lots of theories as to why that happens...galvanic corrosion, water PH levels, too little detergent, too much detergent, using cold water, keeping the washer door closed...and so on.

60510-1a 60510-1b

I am getting ready to put in a new spider-arm and i would like to treat/coat it so that i could get at least 10 years out of it. The coat of course has to be durable, adheres well to die cast aluminum (with the right prep work), resistant to alkaline water, soap, heat (100 °C/212 °F), bleach and bio-films.

What do you guys suggest?

More pics from google: https://www.google.com/search?q=spider+arm+corrosion&safe=strict&client=opera&hs=ocg&source=lnms&tbm=isch&sa=X&ved=0ahUKEwif2dmc8KXWAhXBcRQKHanTDLMQ_AUICigB&biw=1517&bih=745

Elliott Wright
- Thuwal, Jeddah, Saudi Arabia


September 2017

A. Hi Elliott. As you say, this is a perennial problem for buyers of front-loading washing machines. A similar question was asked in the early days of finishing.com 20 years ago, and it seems that no washing machine manufacturer has much interest in fixing the problem as long as it makes it through the warranty period and the repair cost shifts to the consumer. If there were a class action suit, I think the manufacturers would have to admit that it's a known design/manufacturing defect :-(

Alodine 1201

The right answer of course is to make the spider arm from a stainless steel stamping, and some home craftsmen have done second best and made them from stainless steel weldments. Short of that, the aluminum can be epoxy coated, preferably after thorough cleaning and Alodining, which ought to somewhat extend it's life, although I don't think "at least 10 years" is likely no matter how you paint the aluminum. It would be theoretically possible to electroless nickel plate it, but I think you would find the cost prohibitive. Good luck.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


September 17, 2017

Q. Thanks for your input Ted!

Since I've posted this question a few days ago, I've been looking into powder coating. I hear it's superior to 2k exoxy paint. I'm open to suggestions.

I am not sure though what kind of powder coating to go with - if powder coating would indeed be a better option.
Thermoset or thermoplastic? Fluidized bed method by heating the part, or electrostatic fluidized bed method? And if fluidized bed method instead of spraying, then what kind of powder...nylon? PCV? If using a gun, then again...what kind of powder?... Epoxy? polyester etc.?

What about pre-treatment? I hear conversion coating is best...but what kind?... Phosphate? Chromate? Oxide?

The conditions the spider will be in is basically aquatic - lots of soap and water, occasional bleach, and heat (100 °C/212°F).

Elliott Wright [returning]
- Thuwal, Jeddah, Saudi Arabia


September 2017

A. Hi. Alodine is chromate conversion coating, and the best pretreatment for aluminum.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


September 18, 2017

Q. When it comes to die cast aluminum, what is the best way to clean the surface before chromate conversion? What kind of a deoxidizer will do the job, so there would not be any traces of silicon, copper, etc. to ruin the end result, which is powder coating?

A step-by-step instruction would be so greatly appreciated!

Elliott Wright [returning]
- Thuwal, Jeddah, Saudi Arabia


September 2017

A. Hi again Elliott. In a production situation the component would be vibratory finished, then immersed in a mild alkaline cleaner, then immersed for light etching in strong sodium hydroxide, then de-smutted before the chromate conversion. But the best de-smutter will depend on the exact alloy: for example, nitric acid to deal with copper, fluoride to deal with the silicon, but most often a tri-acid desmutter.

Topic 45313 offers many perspectives on the subject of pretreatment for chromate conversion coating, but people do not use these techniques and extremely aggressive chemicals for one-off treatments in a home environment, but only in an industrial factory after they have received hands-on haz-mat training and have been supplied with appropriate personal protection equipment, and also have appropriate disposal facilities for the chemicals.

If I were you, I would scrub it with pumice powder and detergent, rinse it, dry it, Alodine it, rinse it, and paint it with 2K epoxy.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


September 19, 2017

Q. Thanks Ted!

If i were to go with what you suggested at the end, wouldn't NOT properly cleaning it (desmutting etc.) before Alodining cause problems with the paint (epoxy) later?

Elliott Wright
- Thuwal, Jeddah, Saudi Arabia



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