Material characteristics, types of damage and basis of decision
Material characteristics, types of damage and basis of decision |
For the most part, plastic components are made up of three elements: plastic, reinforcing fibre and filling material.
About 15 different types of plastic are currently used in the auto industry. Most are found on the exterior of our cars. Plastics are usually divided into two categories, thermoplastics and thermoset plastics.
Thermoplastics soften or dissolve when solvents and/or heat are applied. They can be glued, welded or thermoformed. As a rule, they consist of: 70 - 90% plastic raw material, 10 - 30% reinforcing fibre and 10 - 20% filling material. Another characteristic of thermoplastics is that they strive to resume the shape they were given when made moulded if heated to just the right temperature.
Thermoset plastics do not discernibly soften or dissolve when solvents and/or heat are applied. They can be glued, but not welded or thermoformed. For this reason, thermoset plastics will not be discussed in any further detail in these instructions.
Identifying plastics |
It is thermoplastics that can be welded. When welding, however, you must use the correct filler material, i.e. when welding cast iron or aluminium, you must use welding wire intended for cast iron or aluminium.
The same principle applies when welding thermoplastics: you must have the right filler material, i.e. you must identify the type of plastic to be able to use the correct filler material, in this case, the correct welding wire.
There are currently ten types of thermoplastics used in the auto industry, e.g. ABS - PP, PE - etc. Saab has narrowed its use of plastic (and welding wire) types to five. These are enough to repair most plastic components, especially those most vulnerable to damage. See Plastic code table
The content of a plastic component, i.e. the plastic type, is stamped into the component on later model cars. The mark may appear as follows: >PP / EPDM<. This makes identification easy.
Determining the correct plastic type of components on older model cars may cause slight problems. If there is no marking, try the following: find the component in our list of material in the plastic components of different models. This list indicates the code of each components. If the component is not on the list, we advise against welding it. Note that the plastic components, e.g. bumper, of some models cannot be welded. The plastic types that can be welded are listed in the table. See Plastic codes, temperature and welding wire .
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Types of damage |
The different types of damage that may require repair are primarily scratches, cracks and small holes in plastic components. Warps and “buckles” can also be successfully straightened by heat treating the damaged component.
Repair or replace? |
When it comes time to decide whether to repair or replace a component, you must determine if the amount of time required for the procedure is reasonable when cost is considered. A general guideline can be to repair cracks that are no longer than approx. 50 mm and scratches that are no longer than 150 mm. If there is a hole in the plastic, it should be repaired if the diameter is less than approx. 30 mm. Tip: Even if the component is replaced, the discarded one should be kept for practice or to replace material that is missing from components that can be repaired. This especially applies to mounting lugs for components such as grilles and headlight inserts.