A nitrogen hot air welder uses compressed nitrogen gas to eliminate oxygen from the weld area. The nitrogen acts as a shielding gas and allows for a contaminant-free weld with less smoke, which creates a stronger weld (see Figure 1). This type of welder can also switch to compressed air so that when preheating, or cooling down the heating element, it does not waste the nitrogen.

A fusion weld is made when the welding rod and plastic melt and mix together. This type of weld can only be done on thermoplastics. Thermoplastics, such as polypropylene/thermo plastic polyolefin (PP/TPO), which is used to make most bumper covers today, work very well with this type of welder.

Making a Repair

Figure 2 - Whenever possible, match the ISO code on the part to the filler material.

Before any sanding or grinding starts, the part must first be cleaned with soap and water, followed by cleaning with the recommended cleaner. It is also recommended to wipe in one direction to help reduce static. If this step is skipped, the repair may fail due to contamination in the repair area. Once the plastic has been abraded, no solvent cleaners should be used because if any of the solvents become trapped under the repairs it could bubble the repair area in the bake cycle or when it is exposed to the sun.

Identification

When making a nitrogen hot air plastic weld, the need for plastic identification is essential to a successful repair. The plastic identification is primarily used to determine which rod will match the plastic part. It is also helpful to know how the plastic will melt because different plastics will melt at different temperatures. One way to identify the type of plastic is to look at the ISO code that should be located on the backside of the part (see Figure 2). If the ISO code cannot be found, the vehicle maker may have a listing of the types of plastic their parts are made of and may even have a recommended repair procedure.

Once the base material is identified, the technician can select the filler rod to use. Plastic welding rods are usually made of a pure plastic like polypropylene (PP), acrylonitrile butadiene styrene (ABS) or thermoplastic olefin (TPO). Therefore, they may not match a specific blend of plastic base material. They are available in different diameters and shapes. Some are round rods and others are a flat ribbon. There are also different widths of flat ribbon with the wide ribbons used on the backside as a reinforcement and the more narrow ribbon used as a filler on the front side.

Figure 3 - Protective gloves are recommended in order to prevent burns from the high heat of the nitrogen hot air welder.

Repair

After the part has been cleaned and the base material and filler rod have been identified, the part being repaired can be realigned and held in place using aluminum tape. Once the front side is realigned, the backside of the part can be sanded with about P80 grit. Following sanding, the area should be blown clean with clean, oilfree compressed air.

After the nitrogen hot air plastic welder is preheated, the nitrogen gas is turned on and the base material and the welding ribbon are preheated. As the base material and ribbon start to melt, the ribbon is pushed into the base material (see Figure 3). The ribbon will start to fuse to the base material and begin to squeeze out the sides of the ribbon. If a tear goes to an edge of a part, a second smaller ribbon can be laid down across the tear to form a "T" pattern at the edge of the part to add extra strength. Watch the video for a short demonstration of this process (see video).