Welding plastic is really easier than you think

Instead of trying to use crazy glue for all non-metal repairs, consider welding. It is fairly simple and can save you money on machinery repairs

by KEITH BERGLIND

There was a time when I tried to glue plastic pieces together and used crazy glue for all non-metal repairs. Then I learned how to weld plastic.

The project I'm showing today is a typical job of repairing damaged plastic parts. I use this technique for repairing everything from auto and farm machinery parts to kids' toys. The repairs are solid and do not fail again, like glue that dries out.

To start, you need to accept that this welding is the fusion of two surfaces together, using a filler rod and heat to cause the two surfaces to become one - fused and bonded together and not just connected with a bonding agent, such as a glue.

With adhesives, the material grips two surfaces, and holds them together, with a wall of adhesive in the centre. The two walls remain intact. Welding is the fusion of the material. When we weld with an arc welder, two pieces of metal are heated to the melting point with filler rod added, and the whole pool fuses into one. We will do the same with this plastic welder.

The tool I use is made by Northwest Polymers. It looks like a regular soldering iron, but with a feeder tube on top of the heat shoe for adding the plastic welding wire into the welding pool. The fusion-grade plastic welding wire, also from Northwest Polymers, is custom-built with a plastic welding wire that matches each type of plastic.

The welding process has a few simple steps, which you have to follow. The actual welding is easy, and you will learn quickly. I will explain this in detail in later issues. Stay tuned. You may want to buy a welder soon and learn as we go along.

But, to start any repair job, the plastic you are going to work with has to be identified. This is done with a burning test and a specific gravity test. I will go into these details in future issues of Better Farming. Northwest Polymers makes and sells all the popular fusion wires you'll need.

For today's repair project, I am going to repair, by plastic welding, the tub from a household washing machine. The tub was worn badly in two areas, after some base mounting bolts worked out. A new tub would have cost me about $150 delivered. I fixed it for less than $5.

After I pressure-washed it, I could see the wear spots (Figure 1. subscibers please see page 66 of our March 2007 Issue).

Next, I identified the plastic. It was polypropylene (PP). I'll explain how I did this in the next issue. It took about five minutes to do the identification test. Then I selected a roll of polypropylene welding wire.

This tub was about 1/8-inch thick, but there was some thinning on each side of the slots now worn in the tub. This meant I had to build up some of the thin areas before closing the gap.

If you have ever brazed metal, you can picture the process. This welder has an adjustable heat range. I started at about three-quarter heat and made slight changes to keep the fusion wire flowing into the tub wall.

Basically, I held the shoe on the tub wall (Figure 2 subscibers please see page 67 of our March 2007 Issue) and, when the plastic started to flow around the shoe, I just fed in the welding wire. I can move the shoe around to spread the heat, and also vary the rate at which I feed in the wire.

As the plastic cools behind the moving tip, it is now part of the tub wall. I just moved along the worn area, building up the wall thickness. When the gap was closed, I went back and re-did the process, moving cross-ways over the weld area, with a light application of welding wire. This ensures all pin holes are filled.

After the whole area looked smooth, without holes or gaps, I repeated the process on the inside of the tub. This eliminates any weld edges that could become cracks or pin-hole leaks.

In future issues, watch for the plastic identification process and more welding projects and welding techniques. BF

Keith Berglind is a licensed heavy-duty mechanic. Agricultural engineer