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Plastic Pointers - Volume 3 Number 2

click here to view the Adobe Acrobat version of Plastic Pointers

Repairing Cracked Nylon Radiator Tanks

Although the 5600HT Mini-Weld Model 6 Airless Plastic Welder is most commonly thought of as a bumper repair tool, it can also be used to repair a wide variety of plastics elsewhere on the car.One example is in repairing cracked plastic radiator tanks. As everybody knows, a cracked or pinholed tank can be a real headache. Oftentimes, a radiator shop won't even quote replacement of the tank; you have to buy an entire radiator just to fix a simple crack. Even if they do replace the tank, you're looking at a $50 to $100 repair bill. This is just the kind of problem our plastic welder was designed to solve! One or two repairs on such parts will pay for the welder, paving the way for more and more profitable repairs down the road.

Radiator Tanks are a Challenge

Radiator tanks present one of the biggest challeges for the repair technician for several reasons. First, the repair has to withstand high operating temperatures (200 degrees and up).

Second, the repair has to contain hot, pressurized coolant, making it immediately obvious when your weld is less-than-perfect.

Because of the harsh operating conditions, the radiator tanks are made from glass-reinforced nylon, a plastic that features a high-softening point which easily withstands the pressure and temperatures involved.

Adhesives don't stand a chance in such an environment. There's no way an adhesive bond can hold on over the long run at such temperatures with high-pressure water behind it.

The only true way to repair a radiator tank is with a true fusion weld. The 5600HT airless plastic welder enables you to melt pure nylon fill material directly into the base material, creating a seamless, strong repair that will last for the long haul.

Creating a durable weld repair is not as easy on the radiator as it is on other plastic parts because of the high melting point of the nylon and the harsh operating conditions. However, by following the simple step-by-step procedure we have outlined here, you will be making quality repairs in no time.

Making the Repair, Step by Step.

Of course, the first step in any plastic repair is (do we really have to tell you anymore!?!) to clean the surface. Wash with soap and water, dry it, then clean with 1000 Super Clean plastic cleaner.

Prepare for the weld by melting in a v-groove with the 6200VG V-Groovin' Tool. You'll notice that the plastic sizzles when you melt it; that's the glass reinforcement in the nylon. You can also cut the v-groove with a 6121-T teardrop cutter bit. Here's the critical step for welding nylon.

Step 3

Because it has such a high melting point, you have to preheat the material with a heat gun before welding. It takes an incredible amount of patience to transfer enough heat with just the welder tip. You'll speed up the work and create a better repair if you pre-heat it first.

Using the 6500VT High Temperature Heat Gun on its highest setting, direct hot air onto the v-grooved area. Have patience--it takes a fair amount of time to get the plastic up to the proper temperature. Preheat a two inch section at a time on longer cracks. Heat until the plastic begins to turn glossy. You may even see some areas soften and melt slightly. At that point, you've pumped enough heat into the plastic to make it easy to get a good fusion weld.

With the welder set at the highest heat setting, begin to feed 5003R6 nylon welding rod through the 6027HT Tube Welding Tip into the v-groove. The welding rod should come out of the bottom of the welding foot completely melted but not discolored. It's normal for the nylon rod to turn a bit brown, however, so don't worry about that. Nylon has a pretty pungent odor, so work in a well ventilated area and use a NIOSH respirator rated for organic vapors if you're especially sensitive to the welding smoke.

Step 4

After laying some welding rod into the v-groove, you'll notice quite a contrast between the white color of the welding rod and the brownish- black color of the tank. Take the welding rod out of the welder tip, andwork the welding rod and base material together until the white color disappears completely. A good weld will be about the same color as the tank and uniform in appearance. Keep pushing, spreading, tamping, and smoothing until the welding rod is completely mixed with the base material. Add more weld rod if it looks like you need it.

Work in a one or two inch area at a time. It's impossible to keep a larger area hot with the welder tip, so take on a small area at a time. On longer cracks, finish welding one section, then preheat the next section with the heat gun before you start welding it. The key to a quality repair is to keep the heat on it and melt the rod and base together compeletely. Using this as a simple guideline, you should be able to save a few of those cracked radiators that you thought you'd have to throw away.

Film-Coated TPO Bumpers Can Be Repaired and Refinished

Back in the Winter 1998 issue we had an article describing a new technology that would eliminate the painting process on bumper covers with an in-mold film technology.

The question mark at the time was whether or not the material could be refinished since it uses a slippery acrylic fluoropolymer clearcoat layer.

Thanks to Dale Moore and Janusz Dryja of Visteon Automotive Systems, we were able to get some samples of the new film-coated bumper materials to test our refinishing procedures on.

The film-coated bumpers are easy to tell apart from their painted cousins because there's no overspray at the edges or on the back.

The color coat will show a sharp but curving and uneven edge along the outer edges of the bumper. Because the bumpers are molded from standard TPO (in Ford's case Dexflex D161B), the repair process is very straightforward. We suggest using the 5003R8 Uni-Weld Ribbon and the thermoplastic method of repair as described in our Book of Automotive Plastic Repair.

The refinish steps pose a little bit of a challenge, but we were able to get very good results from typical materials and processing steps. The main problem is that the clearcoat film doesn't feather on the basecoat film. Of course, when you do a repair, you're going to have to break through the clearcoat, so the issue is how to refinish it.

We found the following basic steps gave a very good result.

Step 1 - Clean the plastic with 1000 Super Clean plastic cleaner before repairing.

Step 2 - Repair with 5003R8 Uni-Weld Ribbon and smooth with 2000 Flex-Filler 2 flexible epoxy filler if necessary. Sand with 80 and 180 in a DA, then block sand the repair and surrounding area with 220 and 320 grit.

Cross Section of Film Coated TPO Repair

Step 3 - Spray 1050-A Plastic Magic adhesion promoter on the repair and surrounding area.

Step 4 - At this point, you'll have a halo around your repair area defined by the edge of the clearcoat film layer. Spray 3000 Light Gray Flexible Primer Surfacer over the repair and surrounding area. Apply 5 to 10 light coats, allowing each coat to flash. This will build up the area inside the halo.

Step 5 - Allow primer to dry thoroughly to allow shrinkage to occur. Block sand with 320 grit paper in an X pattern. Feather out over the clearcoat layer so that the halo is completely hidden.

Step 6 - Use 1040-T Flexible Spot Putty to fill any minor surface imperfections. Block sand with 320 again after spot putty has dried. Apply more 3000 primer if necessary.

Step 7 - Sand bumper overall with 180 or 220 grit in a DA to prepare for paint. Be careful not to break through clearcoat. Blow dust free, then spray 1050 Plastic Magic adhesion promoter overall.

Step 8 - Apply 3000 Light Gray Flexible Primer Surfacer overall, block sand, seal with 3250 Flexible Sealer, then apply a matching topcoat with 3750 Flex-All 2 flex additive. We have also tested this procedure with our soon-to-be-released Waterborne Black Flexible Primer Surfacer (watch this space next time for details!) with excellent results. Cross-hatch adhesion test results showed absolutely no peel between the clearcoat film and the overlying refinish layers. Furthermore, these results were achieved without elevated temperature cure. As new plastics and finishing technologies are developed, look toward Urethane Supply Company to remain at the forefront of new repair techniques.

Miata Rears Are Strange Looking, but They're TPO

One of our customers called and said he couldn't get anything to stick to a '95 Mazda Miata rear bumper. He sent a sample of the bumper for us to analyze. Indeed, it is a bit weird looking. It has the feel and appearance of a TPO, but the color is a light gray, which is unusual.

We usually recommend repairing TPO with 5003R8 Uni-Weld Ribbon, but this bumper had such a long tear (about 12 inches), we decided to try our standard 5003R5 TPO rod. It's a little more difficult to work with, but it's a bit faster than the Uni-Weld on longer tears. The key to welding with the 5003R5 TPO rod is to keep the heat on the weld and keep working the rod into the base material. At first the rod acts like candle wax, not seeming to want to stick to the substrate. Keep working the rod and the bumper together; it will eventually start to melt in and create a strong weld.

Plastic Pointers Tenth Issue

It's hard to believe that it's been two and a half years since the first issue of Plastic Pointers came out.

Thanks for the tremendous response to the newsletter. It shows us that there's a real demand in the market for some useful technical information about plastic repair.

Plastic Pointers is the only regularly published bulletin in the automotive plastic repair industry. That's fitting because Urethane Supply is the only company in America that focuses only on automotive plastic repair.

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