Today at the Pittsburgh Tech Shop, I took a class in sand blasting and powder coating. Powder coating is a fantastic technique for painting just about any metal you can think of. Not only that, it's fairly straightforward, safer than other methods, and gives you a nice glossy finish. This Instructable is the documentation of the class in which I powder coated a sheet of metal and a key that I had lying around.
I will discuss the process from start to finish beginning with material preparation, the sandblasting cabinet, cleaning the material, the painting process, and baking.
More information about the Pittsburgh Tech Shop can be found at http://techshop.ws/
I made it at TechShop!
Step 1: Before you start: The Setup
Powder coating is a straightforward process but requires access to certain resources (which the TechShop happily provides). Make sure that you have access to all of the following tools and materials before beginning:
Time: about 2 hours for a small project
-compressed air (dry and filtered)
-air supply (regulated from 30-90 psi)
-appropriate media for the blasting cabinet
-powder coating gun
-spray booth with filtration system
-curing oven large enough for your piece
-heat resistant gloves
-powder coating media
-polyester tape (for masking)
-wire (for hanging)
-paper (for filling holes you don't want sandblasted, e.g. threaded areas)
-trisodium phosphate (for cleaning steel) OR Simple Green (for other materials)
It is also advisable to wear a long sleeved shirt made of a natural material such as cotton as well as closed toed shoes.
[Source: TechShop course handout #FIN105, available at the front desk upon class signup]
Step 2: First question: What do you want to paint?
Choose something to paint. You can paint anything from scrap metal to bike frames to car parts to tools with powder coating. It should be conductive and be able to withstand temperatures of about 400 degrees Fahrenheit. Choosing a metal is your best bet. I was given a piece of metal to paint; I also decided to paint an old Master Lock key I had on me.
Step 3: Sand Blasting: Intro
Sand blasting, or abrasive blasting, is the first step in the powder coating process. Its purpose is to remove any rust and impurities from the surface of your material as well as providing a good surface for the powder to stick to.
A blasting cabinet like this is a good resource for this process. The enclosed space allows you to work without spreading much particulate and keeps your hands safe from the blast.
Step 4: Sand Blasting: Placing your parts
Open the door and place your piece in the cabinet. If your piece is difficult to pick up with the gloves, it helps to prop it up on another piece of metal as shown in the picture.
Step 5: Sand Blasting: Small pieces
If there's a possibility of your piece slipping through the grill (like my key), it might help to attach a piece of metal wire to prevent it from being lost.
Step 6: Sand Blasting: Activating the spray
On this particular cabinet, the spray is powered by a floor pedal. The cabinet that you are using may have a different setup; if you are unsure, ask a TechShop employee or other qualified person for assistance.
Step 7: Sand Blasting: Blast away!
When you're ready to begin, close and lock the door to the cabinet. Put your hands in the gloves, pick up your piece and the gun, and press the floor switch to activate the flow. Hold the gun a few inches from your piece to get a nice, even coat of roughened surface. Be careful not to spray the viewing glass and avoid directing the spray at the gloves more than is necessary.
If this is your first time using a sand blaster, you should practice scrap metal before you try it on any pieces you care about. The particulate may be too rough for your piece and it may destroy fine detail if you aren't careful.
Step 8: Sand blasting: Done!
When you are finished blasting, turn off the machine, unlock the door, and take out your piece. It should have a roughened texture. Feel free to try a few coats to get an even texture but be careful not to take off too much material.
Step 9: Rinsing and cleaning: Intro
Now that you're done sand blasting, your piece is probably covered in leftover particulate and oil from your hands. Before you powder coat, you want to remove these impurities by washing them off with a chemical cleaning material. From this point onwards, it would be a good idea to wear Latex gloves (or another material if you are allergic) to avoid transferring more impurities to your piece.
Step 10: Rinsing and cleaning: Steel
If your material is made of steel, you should clean your material using a small amount (about a teaspoon for a small piece) of trisodium phosphate mixed with water. Mix the TSP powder with a some water, dip a clean scrub brush in the solution, and scrub gently to remove excess particulate. Rinse off the material with water when you are done.
If you are using another material, skip this step and go to "Rinsing and cleaning: Other materials".
Step 11: Rinsing and cleaning: Other materials
If you're using other materials such as aluminum or brass, it might be a good idea to use Simple Green instead. Spray your material, scrub gently with a scrub brush, and rinse off with water to clean it of impurities.
Step 12: Hang your piece
In order to get an even coat, you should hang your material by a piece of metal wire. You should give some thought as to how you will hang your piece to avoid patches in your finished color. The wire will serve both to hang your piece while you're coating it and to hang it in the oven to bake.
Step 13: Preheating your pieces
After rinsing, you should dry and preheat your material for powder coating. Preheat the powder coating oven to 400 degrees (this may depend on the material and size of your part) and hang your part inside for between five and thirty minutes.
The oven may have a fan; turn it on for the duration of the preheating but be sure to turn it off and open the door slowly to avoid getting blasted in the face by hot air.
Step 14: Powder coating: Choosing your powder
Powder comes in many colors, specularities, and grits. You should be sure to do some research on the type you're using to make sure you have the oven set to the right temperature and are applying the right thickness to your material. The bottle should have information about the powder; it would be a good idea to read it.
Step 15: Powder coating: The powder booth
Powder coating should be done in a booth; it has appropriate grounding and a filtration system. Make sure the booth that you're using is for powder coating; at the TechShop, there is one booth for spray paint and one for powder coating. Hang your piece from the bar on top or a piece of metal wire attached to the bar.
Step 16: Powder coating: Setting up the gun (Part 1)
Make sure the machine is off before beginning prep; while the shock won't kill you (unless you have a pacemaker, in which case you should take extra precaution or ask your doctor), you should prepare your powder with no current going through the gun.
Powder coating works by positively charging the powder in the gun and shooting it at a grounded metal material; the positively charged particles will be attracted to the material and stick to the surface. The powder can still be easily removed with any touch until it is baked, though, so if you make any mistakes you can brush or blow the powder off and start over.
Likewise, if there is still powder on the gun, you can use a pressurized air gun or shop vac to clear the powder off.
Step 17: Powder coating: Setting up the gun (Part 2)
Pour your powder into a jar compatible with the gun. It should fill about a third of the bottle. Too much can leave lumps, so only put in as much as you need. Screw it onto the base of the gun.
Step 18: Powder coating: Setting up the gun (Part 3)
If you are unsure of the settings, ask a machine monitor or someone else familiar with the process.
Step 19: Powder coating: Test the gun
Turn on the powder coating system. The booth should be grounded, the gun should work, and an air filtration system should pull excess powder toward a vent. From this point onward, do not touch the tip of the gun--it contains a charge and will hurt you.
Test the gun by pulling the trigger while pointing at the filter. It should create a fine cloud of powder.
Step 20: Powder coating: Actually powder coating
Hold the trigger down a few inches from your piece to coat it with powder. You want to achieve a nice, even coat. Do not touch any of the coated material or it will rub off. When you are done, return the gun and turn off the machine.
Step 21: Powder coating: Done!
Pick up the piece by the wire you hung it on, being careful not to touch the powder. It should have a nice, even, matte coat.
Step 22: Baking
Put on a pair of heat resistant gloves and hang your piece inside the oven. Close the door, turn on the fan, and leave it for 15 minutes or more, depending on the piece. (Unrelated note: ovens can double as funhouse mirrors)
Step 23: Wait for them to cool!
After your piece is done baking, take it out of the oven and leave it to cool for a few minutes before you handle it. When they are cool to the touch, you may take your piece off of its wire. You're done powder coating. Enjoy your new piece!
Step 24: My finished product
I coated my key in red and mixed two powders, red and yellow, to get the speckled effect on the piece of sheet metal.