Required Pretreatment before E-Coating on Aluminum

A. That is for the person that you are painting it for to determine, or in many cases the OEM that he is building the part for.

A. Do non-chrome coating (Oxsilan:Chemetall / Bonderite:Henkel) prior to E-Coat.

THANKS
SURYA

A. Hi,

Except Degreasing & Phosphating process, the pre-treatment process is almost similar for both aluminium casting & Mild steel components.

Usually, high temperature & strong alkaline Degreasing chemical can cause smut over aluminium components which will affect further Pre-treatment process leading in to quality problems (Poor phosphate coating)

Hence:

1. Aluminium degreasing process temperature must be lower than the mild steel degreasing stage. Less than 55 °C is preferred for Aluminum casting but 60 -70 °C usually maintained for mild steel degreasing.

2.Degreasing chemical should be weak alkaline, preferably Caustic-free alkaline chemicals recommended for Aluminum casting products, whereas Strong alkaline chemicals are used for mild steel components.

3.Some additives should be added in the Phosphating process while processing the aluminium components.

If you are doing CED coating with any of the job coater plants in Chennai, the degreasing chemical suitability & Phosphate process must be studied. In case if you are planning own facility the ideal process will be

Hot water rinse --> Degreasing --> Rinse 1 --> Rinse 2 --> Surface Activation -->Phosphating --> Rinse 3 --> Rinse 3 --> Fresh DI Rinse --> CED --> UF rinse 1 --> UF rinse 2 --> Final DI rinse

Thanks

A. Hi,
Usual Pre treatment process for Cast Aluminum is as follows:
1.Alkaline Degreasing (weakly alkaline)
2.Rinses
3.Desmutting (usually Nitric Acid)]
4.Rinses
5.Non Chrome / Chrome consisting - Chromatizing Process
6.Rinses
7.E.Coat
8.UF rinses
9.Oven Baking
Above process will help you in E-Coating of Aluminum castings, the E-Coat thickness and Baking schedule can be received from your E-Coat suppliers.

A. Hi Viviek.

Metals require pretreatment for a host of reasons including better paint adhesion, resisting filiform corrosion, minimizing galvanic hot spots, etc. The E-coating does not obviate the need for pretreatment.

Steel parts cannot be chromated because chromate will not react with steel; it will not form the required corrosion resisting compounds. Aluminum parts can be phosphatized, but chromate pretreatments are more corrosion resistant.

Please try to flesh out your question with who you are and what your situation is, and we can probably answer more fully and satisfactorily. Good luck.

Regards,

A. Hi Jatin. The basic reactions in a cleaning/degreasing tank usually involve saponification, wetting & emulsifying, deflocculation, chelating & sequestration, buffering, and inhibition ... for starters. Phosphating creates metal phosphates compounds on the surface of steel parts; they may be iron phosphate, zinc phosphate, or manganese phosphate -- often with additional trace compounds that improve the surface. Aluminum can be zinc phosphated. Chromating forms aluminum chromate conversion compounds on aluminum parts. Each of those topics has been the subject of whole books :-)

Good luck.

Regards,

A. Hi Ananto. Proprietary alkaline cleaners are the most common way to remove the oil. On steel parts you can use strong solutions and high temperatures. If necessary you can add ultrasonics or DC electricity, turning the soak cleaner into an electrocleaner. In that case, scrubbing bubbles of hydrogen or oxygen form on the surface of the workpiece and help to carry away the oil. Good luck.

Regards,

A. Hi Sachin. Chromate conversion coating.

Regards,