Characteristics, types of damage and basis for assessment
Characteristics, types of damage and basis for assessment |
Roughly speaking, plastic components comprise three constituents; plastic, reinforcing fibres and filler.
At the present time, there are around 15 different types of plastic being used in the automobile industry. Most of them can be found on the outside of our cars. Types of plastic are normally categorized as thermoplastic or thermosetting plastic.
Thermoplastic softens or dissolves when affected by solvents and/or heat and can be glued, welded or thermoformed. They generally consist of: 70 - 90% raw plastic, 10 - 30% reinforcing fibre and 10 - 20% filler. Thermoplastic is also characterized by it tendency to return to the form it had when it was moulded if it is heated to a suitable temperature.
Thermosetting plastic is a type that does not soften or dissolve to any appreciable extent when affected by solvent and/or heat. It can be glued but not welded or thermoformed. Consequently, thermosetting plastic will not be discussed further in these instructions.
Identifying plastic
Accordingly, it is thermoplastic that can be welded. To be able to weld the material, the correct agent must be used, i.e. to weld cast iron or aluminium you must use welding rods for cast iron or aluminium.
The same principle applies also to welding thermoplastic: the correct agent must be used, i.e. the type of plastic must be identified so that the correct agent can be used = the correct welding rod.
There are approximately ten different types of thermoplastic used in the automobile industry today, ABS - PP - PE - etc. As far as Saab is concerned, there are five different types of plastic (and welding rod). These suffice to repair most plastic components and especially those that are most susceptible to damage. See .
The content in a plastic component, i.e. the type of plastic, is stamped on the component in modern cars. The actual marking can look like this: >PP / EPDM<. This makes identification easy to do.
Older models of car contain plastic components that can cause problems when trying to identify the type of plastic. If there is no marking, try the following: Find the component in our summary of plastic materials used in various models. This will supply you with a code for the respective component. If the component cannot be found in the list, we do not recommend welding it. Bear in mind that plastic components in some models, e.g. the bumper, cannot be welded. The types of plastic that can be welded are shown in the table, see .
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Types of damage |
The different kinds of damage that can be considered for repair are principally scores, cracks and small holes in the plastic component. Deformities and “dents” can also be repaired with good results by heat-treating the damaged component.
“Repair or replace?” |
When assessing whether to repair or to replace a component, it must be considered whether or not the time required for the repair is acceptable with regard to cost.
As a rule of thumb, cracks that are not longer than approx. 50 mm and scores not longer than approx. 150 mm are worth repairing. If there is a hole in the component, this should not exceed approx. 30 mm in diameter.
Tip: Even if you have decided to replace the component you should try to save the discarded material for training purposes or to replace material on other components that can be repaired. This applies especially to fixing lugs on grilles or headlamp inserts.