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topic 52468

Pretreatment for Powder Coating - Extruded Aluminum & Sand Castings


A discussion started in 2009 but continuing through 2018

June 23, 2009

Q. Hi,
How can I treat (the process and the chemical) the aluminum windows and doors with minimum space; can I use a manual spray method?
Also, can the same process work for aluminum sand cast parts?
Thanks,

Rayed Mohammed
Powder Coat Shop - Saudi Arabia


July 1, 2009

A. Yes, it's possible to treat Aluminium doors and windows; the process is:

* Aluminium degreasing
* Water wash
* DESMUTTING
* Aluminium Chromotizing
* Waterwash

Drying and Coating.

the same process holds good for sand cast aluminium, and we are successfully doing it.

Shankar Omprakash Khandelwal
- Coimbatore, TAMILNADU, INDIA



April 21, 2012

Q.
WE ARE DOING POWDER COATING OF EXTRUDED PROFILE BUT WE ARE RECEIVING THE COMPLAINTS OF PEELING & ALSO CORROSION AT PEELED PLACE FROM OUR CUSTOMERS, WHO ARE SITUATED NEAR SEA SHORE.
THANKS & REGARDS

Sanjay Kumar
- Lagos, Nigeria, Africa


April 24, 2012

A. Hi Sanjay.

This is probably a pretreatment problem. Are you properly chromate conversion coating the extrusions before powder coating?

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


April 24, 2012

A. There could be many reasons for poor performance:
(A) Check the quality of raw extrusions received.
Most Al extrusions are of 6000 series Al alloys.
However there have been occasions where the metallurgy of extrusions does not comply. This has been particularly noticeable with extrusions sourced from China.
(B) Check that extrusions are not contaminated with lubricant residues which will not dislodge with your degreasing process.
Beeswax is commonly used as a lubricant with Al cutting processes and is difficult to remove (MEK helps).
(C) Ensure your pretreatment process is adequate eg:
Caustic wash
Freshwater rinse
Acid etch
Freshwater rinse
Chromate
Freshwater rinse
Immersion DI water rinse
Halo DI Rinse.
(D) Ensure your pretreatment process is maintained.
In particular that detritis is skimmed from tank surfaces at least daily.
(E) Select a premium grade architectural Polyester powder not a run of the mill TGIC-free offering.
(F) Ensure that powder is applied to correct film thickness.
(G) Ensure that the correct cure schedule is maintained in particular that time at temperature is time at actual metal temperature.
With all that under control you should be looking pretty good.
Hope that helps.
Regards,
Bill

William Doherty
Trainer - Salamander Bay, Australia


April 26, 2012

A. Whoops,
I neglected to mention that it is important to integrate your various chemical treatment processes.
In other words, choose a single supplier and work with them.
Some I have had success with include Henkel, Chemetall & Macdermid.

Also it is important that the drying process after Chemical pre-treatment is handled appropriately.
Never exceed 70° centigrade and use air volume and velocity rather than temperature to dry the work prior to powder application.
Regards,
Bill

William Doherty
trainer - Soldiers Pt., Australia


January 31, 2018

Q. We face a problem of powder peel off on aluminium painted profiles (6063 alloy). We checked the pre-treatment, which is okay as a result of etching rate 1.5 - 1.8 and chrome free conversion layer. The curing oven is ok in respect of curing temperature.

The profiles pass Qc -mechanical adhesion -cross hatch , impact ...

The Problem: after one or two days the products have peel off !!

If we reheat the the profiles, it becomes passing.

What is the Problem?
Does anybody have an idea how to find the cause?
The product is aluminium profiles -- how to check if the problem is in pre-treatment or powder ?

Regards,

R A.A.
- amman , Jordan


February 3, 2018

A. Could you please explain the statement:
"If we reheat the ...it becomes passing" ?
Could you also please elaborate your complete pre-treatment process and cure schedule.
These could assist us to assist you.
Regards,
Bill

William Doherty
trainer. - salamander bay nsw australia



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