Lets talk about the first step of the powder coating process. The very first thing to do is thoroughly clean and degrease your item. Even if it is brand new, it should be cleaned.After cleaning your part, check out this article for the following steps: "How to Prep for Powder Coating". The first thing you need to do is figure out what its made out of. Steel, aluminum, etc. Some metals like aluminum are very sensitive to certain cleaners and it can cause can corrosion and damage on a microscopic level. I will explain the steps I use to clean below.
Step 1. Pressure Wash
My very first step for any part that I am powder coating is to pressure wash the part. The pressure washer removes a lot of the loose debris like dirt and grease chunks with ease. Pressuring washing can replace a lot of manual scrubbing and the part is usually clean the touch after. My pressure washer is not anything fancy, but it works great and has great pressure for a smaller unit. It is a 1900 psi electric model. I prefer the electric pressure washers because of how frequently I use it. If it was a gas powered pressure washer, I would have to start it up each time. If you are a powder coating small parts occasionally, an electric pressure washer is fine. Having a pressure washer is also extremely useful in every day life. It makes short work of cleaning anything that can handle the pressure.
As long as the part doesn't have any very delicate areas or is thin enough to bend, I set the pressure washer on the "pencil" setting. This focuses all the pressure into point and is very strong. I have actually managed to cut my skin with the water using this setting, so be careful. I just run this stream over the entire part until I no longer see the dirt coming off. I wear safety goggles while doing this because it splashes everywhere when hitting something irregularly shaped like a car part. If you really want to make short work of cleaning with the pressure washer, look at the gas-powered options. They are capable of a much higher pressures and can get your parts cleaner. Just be careful not to damage anything. This gas pressure washer puts out 2.5 gallons of water per minute. That's nearly double the electric pressure washer.
Step 2. Soak with Cleaner
After the loose dirt and crud is off, I spray the part down with an aluminum safe cleaner. I am very selective about what I use to clean aluminum. A lot of normal household cleaners can corrode aluminum. After a lot of research on the right cleaner for aluminum, I decided on Simple Green Extreme: Aircraft and Precision Cleaner. It states all over the bottle that it was formulated specifically for aluminum and precision tools. I checked the MSDS and it is, in fact, not just relabeled simple green. After testing it out, I am very happy with it. Its not too expensive, but online is the only place I could find it. It cleans great. I also tested it by spraying on some scrap cast aluminum pieces I had, and just letting it sit for a couple of days. When I came back to the part and wiped off the cleaner, there was no signs of corrosion at all.
I used the simple green cleaner on this head. Unfortunately, I didn't get a good before picture, but in the picture, you can see the area I cleaned, vs the area I didn't clean yet. The 2nd picture shows it almost completely clean.
|Cleaning cast aluminum with Simple Green Extreme|
|Head cleaned with Simple Green Extreme|
How to Clean Steel & Iron
Super Clean, formerly Castrol Super Clean which is amazing. Purple Power works okay too, just not quite as strong. I do not dilute the cleaner when using it on greasy iron or steel parts.
I did mention there are things that you have to watch out for with steel. What you need to watch out for is using any acid based cleaners on hardened steels. Most acidic household cleaners use weaker acids so it is not as big of an issue, but the chemical rust removers and things like that contain phosphoric acid or muriatic acid which can can cause something called Hydrogen Embitterment in hardened steel and even cast iron parts. Without getting to into it, basically hydrogen atoms can be absorbed into the steel, changing the internal structure which can lead the hardened steel part to break. This doesn't come up too much in the powder coating process but its something that's good to know. If I can help it, I don't use acid based cleaners on steel parts.
Step 3. Scrub
After spraying down the aluminum part with Simple Green Extreme or the iron/steel part with Super Clean, I let it soak for about 5 minutes, I spray a little more cleaner on the part and scrub it down with various nylon brushes. gun cleaning brushes are great for getting into bolt holes. A parts washer is a great place to do this task. Its the most convenient place to clean anything, it contains the mess, and constantly sprays cleaner out of the little nozzle. They come complete with a stand or you can get a bench-top model to save some space.
Step 4. Rinse & Repeat
After scrubbing the part thoroughly. I rinse it off with the pressure washer. I then repeat the scrubbing process and give it a very thorough final rinse with the pressure washer. I bring the part for a final rinse in hot water and then blow the part off with air to dry it.
Time Saver: Ultrasonic Cleaner
Another method I use for smaller parts, is an ultrasonic cleaner. I say smaller parts because the larger ultrasonic cleaners can be very expensive. They are coming down in price so I am looking into a bigger one. If the part fits in my ultrasonic cleaner, I will use it. Its a great way to outsource some labor. I use the same cleaning solutions inside the ultrasonic cleaner that I mentioned above. Although a very good ultrasonic cleaning solution recipe is 50% vinegar, 50% water, a couple drops of dawn dish soap and some baking soda. This solution will clean steel perfectly down to bare metal. It removes rust, zinc plating, and everything else. I don't bother making the solution because of the possible Hydrogen Embitterment issues(vinegar is an acid, although mild) and I just don't have a need for it anymore since I added the sandblasting cabinet to my garage, you may though...
This my ultrasonic cleaner below. It also has a heating function which I'm sure does a good bit of the cleaning by itself. It works well for me, I use it for small parts and fasteners. I have cleaned heater cores, throttle bodies, brake master cylinders in it too, just have to flip the parts over to keep them submerged. It can clean where I can't reach with any brush. Sometimes I will think a part is clean, until I put it in the ultrasonic cleaner, and then the water starts to turn black. You can see the results below.
|Ultrasonic cleaner in progress.|
|Fresh out of the Ultrasonic Cleaner.|
Step 5. Bake / Outgas in the Oven
I then bake the part in the oven. This not only dries the metal completely from any moisture that may have been remaining, but it also outgasses the part. Cast aluminum and cast iron are porous. Grease, oils, and other impurities can soak into the metal over time. These impurities can also be in the part from the casting process itself. Outgassing the aluminum or iron consists of baking it at a slightly higher temperature and a little bit longer time than your cure schedule.
For example, say a powders cure schedule is 400 degrees for 10 minutes. I will outgas the aluminum at 425 degrees for 20 minutes. I do not start the 20 minute timer until the actual aluminum part is 425 degrees though. I check the temperature with a non-contact infrared thermometer. If you don't know why you should own an infrared thermometer while powder coating, read this article, they are essential for powder coating. For cast metal parts, you can actually see the part smoking in the oven, these are the oils evaporating out of the metal. If at 20 minutes, the part is still smoking, I will leave it in until the smoking is done and then an extra 5 minutes for good measure. I outgas every part I powder coat just to be thorough, but it is usually okay to only do it on cast items. I don't notice the extra oven use on my electric bill, but a powder coating shop that has large ovens would notice it.
The reason why you outgas a part before powder coating is to prevent it from happening during the curing stage. If those oils are left inside the cast aluminum, and you powder coat it and put it in the oven to cure, as the heat cures the powder, it also heats up the oils, causing them to expand. This expanding causes them to escape out of the part, leaving a nice pinhole in your powder coating finish which looks like:
Outgassing parts in the oven does solve about 90% of the outgassing problems when powder coating. However there are some parts out there that want to outgas no matter how long you bake it before hand. For parts like these, special powder coat primers and outgas forgiving powder coats need to be applied, but I will cover that a bit later.
Now that your part is clean, degreased, and outgassed. It is ready for media blasting (sand blasting). Stay tuned for the next post and leave a comment if you find the sight helpful. For a thorough explanation of the remaining steps, head on over to "How to Prep for Powder Coating".