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Thermoplastics in cars. Identification and welding.

Updated on May 14, 2012

What isathermoplastic andwhere it is applied:

Is a synthetic origin material which changes its physical state by the action of temperature, but do not change their properties with those changes of state.
There are also duroplast which are a type of plastics which do not react to temperature.

Currently automobiles incorporate a large number of plastic parts, such as for example fuel tanks, water tanks, brake fluid deposits, optical, bumpers, batteries, parts of the carrier, grids, etc..

Different plastic types:

There is a lot of types of plastics, this is due to the different characteristics and attributes of each.
In a vehicle can find a great number of types of plastics, as:
- Acrylonitrile (ABS) in the mirrors
- Polyamide (PA) on material from the heat exchanger of the engine coolant
- Polypropylene (PP) in the optical headlight and fuel tanks
- Polyethylene (PE) on the bumpers and tanks

However On the market there more types of plastics:
- polyurethane (PUR)
- Polycarbonate (PC)
- Polybutylene terephthalate (PBT)
- Polypropylene (PP / EPDM)
- Polyvinyl Chloride (PVC)
- Acrylonitrile polymer (ABS / PC)
- Glass fiber lastic (GRP / SMC)

How to identifyeach type of plastic:

Each type of plastic may be identified by four different tests and not by their color, are only some of these tests to determine whether two plastics are equal, it is possible for only a good quality welding if two materials to treat the same.
The four tests are:

- Place a small welding with a rod, to show the welding of the same material are solid.
- Burning a small sample of the material and then examining the flame and smoke odor.
- Black smoke and acrid smell: PVC
- Blackened Smoke, with flakes of sweet smell: ABS
- Yellow smoke and sweet smell: PC
- No smoke and smell of burnt oil: PP
- No smoke and smell of burnt bone: PA
- No smoke and smell the wax: PE

- Make the cutting of a small strip of material and by two chip form if they are different or the same materials are also respectively equal or different.
- Place a piece of each type of material and observe their stay at the surface or not, if the behaviors are also different materials are.

Plasticswelding techniques:

Factors influencing the quality of a weld:
- welding temperature
- welding speed
- welding pressure (between the two parts to be welded or between the rod and the material)
Control of these three factors when a welding is necessary for it to be of good quality.

Welding processes:

- For contact (deprecated)
- For high frequency (25.12 Hz)
- By ultrasonic
- Friction (circular surfaces)
- For leisure
- For hot air (most used in the automotive sector)

Hot air process:
1 º Identifying the type of plastic;
2 º Surface preparation: cleaning of all areas to be welded and removing objects stuck with the welding zone;
3 º Tapping the crack: to better receive the cord, this should make a bevel angle of about 90 °. It is also usual to make some holes at the ends of the cracks to prevent its spread.
4 º Welding (1st stage), welding the base on both sides of the crack by contact, this allows perfect alignment of both parties.
5 º Main Welding (2nd phase): deposition of material within the cleft stick. This deposition can be done in two ways, either using a commercial itself (when possible) or by the method of commuting (ideal for areas with closed corners).
The first is the simplest and least error probability, introduces the welding rod in the accessory and the perfect temperature when you slide the tool along the cleft.
In accordance with the welder will directing the stream of heat for the welding and pressing the rod against the cleft (at an angle of about 85 degrees), the jet will be directed in a pendulum.

The plastics welding in general is simple to perform and prune it to be profitable for a company, but the people involved in the world of motor vehicle, except for some sectors (repairing motorcycles panels, etc..) Are not informed or even suitable for this process, preferring the use of new material.


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