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Pretreatment of LM24 and LM6 aluminum for powder coating
Q. We manufacture ceiling fans. The end shields of the motor are diecast from LM24 and LM6 alloys.
Can I know what precautions are recommended for cleaning before powder coating and what I must do to reduce orange peel effect?
electrical - Ponda, Goa, India
2003
A. Dear Sashi Prabhu,
Orange peel can be reduced by controlling the paint thickness; control it between 50-60 mic, check your oven profile and match with the paint supplier recommendation. The best pretreatment for aluminum lm-24 is Precleaning (MTO) - degrease (non caustic) - deoxidise - chromate - dry - coat.
- Delhi, India
2003
A. Hi Sashi,
There are a number of ways to reduce the orange peel effect. As Rakesh suggested, film thickness and oven profiles can be contributing factors to this phenomenon but there are more fundamental causes. The most common is particle size distribution -- if you use a reclaim system you must regulate your virgin to reclaim ratios. Other causes include incorrect spraying: you should spray at least 30 cm away from the object you are spraying and have your kV set at 70. We also have to consider the quality of the powder itself ... if there is insufficient flow agent in the powder or the PVC is too high this can also lead to a poor finish.
Hope this helps.
- North Lincolnshire, U.K.
2003
Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)
Q. Can someone advise me as to what pretreatment is required before powder coating LM24 and LM6 die cast components that will finally be used on ceiling fan motors? The present practice is that the components are rinsed in turpentine [on eBay or Amazon] and then cleaned with air to remove chips. The components are then heated up to 220 °C for 20 minutes to cleanse the castings for absorbed Dakota and oil during die casting. The next step is mounting these components on a rotating fixture and polishing them with a polish paper so that inherent casting defects come to surface, and bite is provided for powder coating process. I use epoxy polyester powder and I have problems of shade variation and orange peeling (my thermocouple is calibrated). Can I have some suggestions please.
Sashi Prabhu- Ponda-Goa, India
2003
A. Sashi,
Out of various causes for orange pilling, the most common is excess coating thickness, and as far as the problem of shade variation, though your thermocouple is calibrated, the actual body temperature of the products at various levels & sides inside of your oven could be the root cause. The temperature variation at various positions is a very common reason for these kind of shade variation problems, so I would suggest you to have your oven calibrated at various points and see that the air & heat circulation is proper.
Best luck
Atul Bhide
jobshop / applicator - Mumbai, India
2003
A. Are you not doing any other pretreatment prior to powder coating Aluminum?
Sandeep Kundramanufacturers of metal pretreatment chemicals - Bombay, Maharashtra, India
2003
A. Your letter shows that you are using die-cast material & I hope that if it is aluminium you may go for solvent based cleaners, then desmutting with 5% nitric acid + chromatising + powder coating. But prior to this I want to know the composition in that die-casting. So that according to the properties of the diecast material I can suggest you the cleaners & chromate conversion coating. Regular powder coatings orange peel problems are visible mostly in glossy shades. But it is better to refer to the powder suppliers. As I know some of the powders have very invisible orange peel.
Sudhir.J- Chennai, Tamilnadu, India
2003
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