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Plastic Pointers - Issue 19

IMPORTANT NOTE: The Plastic Pointers newsletter is a printed newsletter that is sent to thousands of customers. Some things are "lost" in the translation to HTML web format. To see the Plastic Pointers as it was originally printed, you need to view the Adobe Acrobat version by clicking here.

Speed the Welding Process on TPO Bumpers with our New R13 Polypropylene Strip

Way back when Jimmy Carter was president, the only way to repair plastic bumper covers was to use a hot air welder. Fortunately, there weren’t too many plastic bumper covers back in those days.

Hot air welding technology has been around since the dawn of the plastics age back in the 1950’s. It got its start in industrial welding and fabrication.

Crossing the industrial-based hot air welder over to automotive plastic repair was not pretty, as most of the plastic bumpers back in the 80’s were thermoset polyurethane (PUR), which is virtually impossible to repair using a hot air welder.

That’s why Urethane Supply Company invented the airless welding process back in 1983 and has been its main proponent ever since. Airless welding allows you to control the heat input into the substrate, so you can “weld” PUR easily. (Actually, this is more like a brazing process since the substrate is not melted).

The main disadvantage of airless welding is speed, or rather lack of it. A six inch tear in an ABS motorcycle side fairing can be hot air welded in about 30 seconds, but the same repair will take about five minutes with the airless welder.

We still recommend the airless welder to most body shops because it is still easier to use and less expensive than the hot air welder. This is especially true if you’re only doing the occasional plastic repair.

But if you do a lot of plastic repair, like our bumper recycling customers, the hot air welder could save you some time. Why? Because over 90% of late model bumper covers are made from PP blends (TPO, TEO, PP/EPDM, etc) instead of the old PURs. That means the old hot air welder can be used with great success.

Plastic tab repair With our new R13 series of polypropylene strips, hot air welding has never been easier or stronger! We’ve found the stickiest PP resin on the market and extrude it into a flat ribbon profile that’s 7/16” wide by 1/16” thick.

The flat ribbon has several advantages over the standard round rod. First of all, it has a much broader contact area with the substrate, making for a stronger fusion weld.

Second, because the molecules in the strip are largely unmolested, they retain the strength gained in the extrusion process. The enormous pressure generated in the extrusion process aligns the polypropylene molecules, giving the strip excellent tensile strength. The airless welding process mixes the filler rod, invariably creating air voids which jumble up the molecules. As a result, an airless weld using a standard round rod is much less strong than the same repair using the R13 strip and the hot air welder.

We have developed a repair method we call the “hybrid welding method,” which combines the best features of both hot air and airless welding. This works by first laying the strip down using the hot air welder. The airless welder is then immediately used while the strip and substrate are still hot to burnish down the edges of the strip and shape the repair area.

Combining the methods combines the advantages of both-- the speed of hot air with the ability to physically press on the surface using the airless welder tip. The sidebar in this issue of Plastic Pointers will focus on use of the hybrid welding method using the R13 PP strip.

The R13 doesn’t feather out as nice as our FiberFlex rod, so you can combine the methods by welding with the R13 on the back then use the FiberFlex on the frontside for easier sanding and finishing.

The R13 strips are available in both black and natural in both 30 ft rolls and 1.3 lb. spool. Suggested User prices for body shop customers are as follows:

Part No.	Price
5003R13B 30ft. roll, Black	$15.95
5003R13W 30ft. roll, Natural	$15.95
R13-B, 1.3 lb. spool, Black	$76.00
R13-W, 1.3 lb. spool , Natural	$76.00

Buy one of our hot air welders (either the 6050HA or the 6055) today to try out this speedy new repair technique!

Using the Hybrid Welding Method with R13 PP Strip to Repair Honda Tab

Step 1. Grind plastic on both sides of the missing plastic bar with a 50 grit Roloc on both sides. Taper down to a point.
Step 2. Apply a piece of 6481-2 aluminum body tape across the gap to support the softened welding rod during the repair process.
Step 3. Premelt the base material with the hot air welder, then stick the R13 down and slowly feed the strip down onto the base plastic as you make your pass.
Step 4. Bridge the strip across the gap without melting it, then pick up the weld pass on the other side. Melt the R13 down for at least 1/2” on the other side.
Step 5. Put the hot air welder down and immediately burnish the hot R13 strip into the bumper using the 6028RT round tip and the airless plastic welder.
Step 6. Repeat the process on the opposite side. Use the airless welder to shape the plastic to nearly the final shape and melt it in with the base material very well.
Step 7. Using a Dremel tool and the 6121-T Teardrop Cutter Bit and a DA sander, final shape the plastic bar to the finished dimensions.
Step 8. When finished, the bar can support the entire weight of the bumper! This is a very strong repair considering how little area you’ve got to work with.