Monthly Archives: July 2016

Proper Grounding Techniques for Powder Coating

Powder Coated Parts After CuringOne of the keys to successful powder coating application is proper grounding. A good ground acts like glue to the powder being sprayed on the part, making it easy to get a uniform, high-quality finish with high transfer efficiency. A weak ground can cause a host of issues, such as light coverage areas, Faraday cage problems, larger hook marks, generally uneven powder application, dirtier spray booth filters, and poor transfer efficiency. In extreme cases, improper grounding can cause the operator to get shocked.

How to Get Proper Grounding for Your Powder Coating Gun

There are four main areas where your grounding technique needs to be addressed:

Grounding Rod. We have mentioned in previous articles that the best starting ground for manual spray applications is a 6’ to 10’ copper grounding rod installed just outside of the powder spray enclosure. Permanently attach a ground strap of at least a 14-gauge wire with a good clamp on the end that will be used to ground parts. When the ground rod is in rather sandy or dry soil, a small amount of water can be poured into the grounding rod hole and allowed to soak in prior to powder coating.

Clamp And Copper Grounding Rod For Powder Coating

For the best ground, make sure your clamp (left) is attached to a copper grounding rod outside the spray booth (right).

When using this grounding method, the powder will stick to the part like glue. The powder will resist being shaken off when moved or when encountering mild air movement.

IMPORTANT: Using just the grounding clamp supplied with the gun unit is inferior to using a grounding rod, but it’s better than nothing until you get your grounding rod installed.

Parts Rack or Cart. You will need good metal-to-metal contact from the grounding rod clamp to the part. If you clamp the cart in the same place each time, be sure to blow or wipe off the powder around the clamp attachment area each time BEFORE the cart enters the curing oven. This will prevent you from having to grind off this area every time you use the cart.

Custom Parts Racks For Powder Coating

When parts are attached directly to the rack or cart frame, metal-to-metal contact is usually achieved by the part shielding the rack’s contact points. It’s important to note that if you do not hang parts on every contact point, powder will accumulate on the exposed points and will have to be removed before using the rack again. Some operators use high temp tape or other masking agents to protect areas of the rack from powder that can become baked over the exposed metal.

If you use racks that have movable hooks to attach the parts using a bar or similar contact points, you need to grind the tops of the bars every 5-6 coating cycles. This will ensure a good ground and proper transfer efficiency. If you hear popping sounds while applying the powder or see small instances of electrical arcing from hook to rack, flag that rack to be cleaned via grinding or stripping before using it in the next coating cycle.

Racks can usually be manufactured by any local metal fabrication shop. Many job shops make their own. When designing racks or carts, remember to concentrate parts so they are two feet from the floor to about six feet high. This will allow the operators to spray all areas fairly easily.

HParts Being Powder Coated On Hooksooks. As with the cart, you need good metal-to-metal contact with the cart and the parts. Most shops can get 5-6 uses from a hook before it starts becoming insulated by baked-on powder. Some powder coaters just replace the hooks with new ones, but others have them cleaned. Cost analysis will tell you which is more efficient. If you are getting arcing and the rack has been cleaned, then you need to clean or replace your hooks. Mighty Hook is a great source for hooks, plugs, and tape. http://www.mightyhook.com/default.aspx

Parts. Not all parts ground well. Because of their mass, some parts can be tough to ground properly. Also, if parts have been coated before, they can be more challenging to ground. Sometimes the racks don’t ground parts adequately because the parts hang too far from the grounding point. In these cases, you can clamp directly to the part in question. After spraying the powder, just remove the clamp and spray the clamped section last to keep from getting surface defects.

If you’re worried that you might not be getting a good ground, use a megohmmeter (often called a “megger” after the company that makes these types of test instruments: http://us.megger.com/) to check the resistance from area to area. If the resistance exceeds 1 megohm from ground to part, work backwards at all the contact points to determine where the loss of ground is occurring.

Using professional quality powder coating equipment can solve many of your coating issues. All of Reliant Finishing Systems’ equipment is designed to provide the best finishes possible for today’s powder coating operations. Find out more about Reliant equipment here, or give one of our systems specialists a call today.

Tips For Touching-Up A Powder Coated Finish

Pump Casting With Powder Coated FinishOne of the many advantages powder coating has over wet paint is the variety of ways you can fine-tune and rework a powder coated finish. This article discusses some of the different touch-up techniques you can use to clean up your work and get the best overall quality for your powder coating projects.

Why Should You Touch-Up Your Powder Coated Finish

Visual Appeal. This is the obvious reason for fixing a powder coated finish. To most customers, if it doesn’t look right, it isn’t acceptable.

Performance. Some powder coatings are purely functional, so they don’t need to be aesthetically perfect. Usually there are one or more standards (such as corrosion resistance) that have to be met. A defect can compromise the finish integrity and cause a part to fail to meet a specific customer’s standards.

Warranty. If the powder coated part has any sort of warranty, then special care should be made to make sure the part passes end-of-the line QC testing. A part may look great and have no apparent defects, but if it does not pass the customer’s minimum testing standards, a repair or rework is needed.

When Is The Right Time To Do Touch-Up Work?

The best time to catch your coating mistakes is prior to curing the powder. The powder can easily be blown off with compressed air or wiped off and then reapplied with very little hassle. Get in the habit of checking your parts for application errors before you start the curing process. Every mistake you catch here will save you time, effort and money later.

Common Powder Coating Touch-up Techniques After Curing

It’s not always possible to catch coating errors, especially if there are overbaking or underbaking issues with your oven. When dealing with a defective finish, you should ask yourself: will a touched-up surface be acceptable -both visually and from a performance standpoint-or should you repaint? In either case, if you have to resolve a finish problem, here are some of the most effective techniques to use once a powder coated part has been cured using Reliant’s products:

Liquid Paint Touch-Up

Many manufacturers use color-matched liquid enamels to cover hook marks, missed areas, Faraday areas, re-welds, sanded spots, handling damage and other defects.

Pros – cheap, fast, least labor intensive, little skill required

Cons – not visually appealing on a class A part, visual “halo” around repair, repair is not as durable as the rest of finish, repair may fade or chalk faster than surrounding powder coated finish

Usable with most decorative finishes. This repair method is fine except for on the primary surface a customer can see.

Re-coating

In some instances, your powder process can allow for a repainted finish to go over a previously painted part with no prep work. Usually the part must be freshly powder coated with no contamination on the surface.

Some chemistry is not compatible with this method and the surface will need to be abraded (blasted with abrasive grit or scuffed with sandpaper) and then wiped down with alcohol. If the part has been cured for more than a week, it will almost always need to be abraded and cleaned before re-coating. 

Pros – Less expensive and faster than stripping, better corrosion protection than liquid enamel

Cons – Adhesion risk (always do a test part and check adhesion), too much film build-up could cause issues (weight, measurement tolerances, extreme temperature checking)

Many small parts manufacturers will re-run parts after inspection if they have light powder coverage or other easily repaired surface defects. In the closet hardware and racking industries it is especially common for facilities to repaint parts once or twice if they are having an acceptable amount of rejects.

Tip: Remember to use your powder gun’s re-coat settings to properly apply a second coat

Sanding And Buffing

Sanding and buffing the powder finish can eliminate surface trash and some defects. This also helps smooth out orange peel that naturally occurs with most powder coatings on parts where the powder thickness is excessive in a particular area. Sanding companies like 3M have a series of abrasive and buffing compounds that allow shops to sand out defects and then bring the surface back to a smooth shine.

Pro’s – Mirror-like finish, faster to buff than to repaint

Con’s – Burn-throughs will need to be repainted or touched up with a liquid paint, labor-intensive, requires moderate skill

In the automotive and other transportation industries, manufacturers will sometimes sand and buff out Class A type parts such as hoods or panels that need to have a mirror-like defect free finish. This is similar to work done with wet paint. It takes some experimentation to develop a successful sanding and buffing process.

Tip: The sooner you buff after curing, the easier it is to work with the finish. Power coating gets very hard 1-3 days after curing.

IMPORTANT! Be sure to have the buffing operation isolated from the finishing operation. Many of the waxes and compounds used for buffing and polishing do not react well with painting and powder coating processes and can cause defects like “fish-eyes.”

 Fillers And Putties

There are many products like Bondo and Lab-metal that can be used to fill gaps and seal holes prior to powder coating. Before adding a filler to your process, make sure it is compatible with 400° to 450° F curing temperatures and that it is recommended for powder coating.

Pros – Eliminates re-welding for small areas, surface defects are much less noticeable if repaired prior to powder coating, parts do not need to be taken off-line for repair

Cons – Powder may have trouble being electrostatically attracted to the repair, in a large area adhesion can be suspect, may cause powder finish to “shimmer” or look different over repair

Trailer companies often use filler-putty to bridge gaps in their dump-style trailers. Tiger Drylac has a two-component filler that has some conductive elements for good results when used under a powder coated finish. Here is a link to their data sheet:

http://www.tiger-coatings.us/fileadmin/user_upload/downloads_us_new/product-data-sheets/tiger-drylac/special-products/Epo_Strong_Series_93-70080_Epoxy_Repair_Kit.pdf

Total Strip And Repaint

If there is a catastrophic finish failure, starting over after taking the finish off down to the bare metal can sometimes be the only solution. Major powder coating issues, like severe adhesion problems in high-performance parts, often require a total repaint. Pretreatment failures, parts contamination after pretreatment, underbaking, and overbaking can also cause problems that are so bad that the only answer is to totally strip the coating off and redo the process (after you have identified and corrected the fault in the process). Remember, the finish is only as strong as its weakest layer, so if you notice flaking once the finish is cured, it will need to be completely redone.

Pros – Once the process is fixed, you have high quality parts going to the customer and you don’t have to worry about field failures and the possibility of costly claims in the future

Cons – Costliest and most time-consuming solution

For demanding projects like government contracts, high-performance industrial components, engine parts, military equipment, parts that will be exposed to a highly corrosive environment or impact/abrasion in the field, the only way to insure quality compliance for parts that have badly defective finishes is to re-work the parts down to the metal.

The Nail Polish Fix

We’ve just outlined the most common touch-up and re-work methods, but there is another technique that can sometimes get positive results. An uncommon method for fixing small finish imperfections is to put a small amount of the powder in a clear lacquer and use it as touch-up paint. It’s possible to use hair spray, nail polish and other lacquers in a hobby situation, but bulk materials will be needed in a professional environment. Although the touched-up area will visually match the cured powder paint, the repaired area will not have the same durability as the cured surface. Remember, if you need the same surface integrity and durability in your touch-up areas as you do with the powder coated finish, you will probably need to use a two-component catalyzed topcoat and possibly a zinc-rich epoxy primer for appropriate corrosion resistance.

Meet Expectations With The Right Powder Coated Finish

To retain business and keep customers happy, you need to know exactly what each customer expects from the powder coated finish you are providing. Once you know that, you can develop a process that includes a repeatable touch-up system that addresses defective finishes of all types. Proper touch-up and re-work techniques help ensure great finished products.

Using professional quality equipment can solve many of your coating issues, including overbake and underbake problems associated with outdated or inferior quality ovens. All of Reliant Finishing Systems’ equipment is designed to provide the best finishes possible for today’s powder coating operations. Find out more about Reliant equipment here, or give one of our systems specialists a call today.