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Be Careful When Identifying Your Plastic Type Using A Burn Test

When doing a burn test, please be careful. Drips can cause flames to spread. Use small amounts of plastic. Also, don't directly inhale the smoke; simply note the general odor.



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Identifying What Kind of Plastic You Have

In order to make a good repair on your plastic, it is critical that you know which kind of plastic you have. The kind of plastic you have makes a huge difference on how to make the repair properly.

To start, there are two "rules of thumb" for deciding whether you should use a plastic welder or a chemical (epoxy) weld. "If it melts, weld it." "If it doesn't melt, use a chemical weld." Adhering to these truths will take you a long way towards a succesful repair.

Aside from these general statements, there are two basic ways to find out what kind of plastic you have; using the plastic manufacturer's labels and using a burn test. These tests will identify some common types of plastic; however, with an increasing use of composites in plastics, these tests are by no means complete.

The following plastics are easily welded using one of our welding kits.

Manufacturer's ID Label

This symbol indicates that the plastic is Polyethylene Terephthalate. This plastic is chemically inert, and so is often used for sprayer and water tanks, gas cans, etc. This plastic is easily welded using one of our welding kits.

This symbol indicates that the plastic is High Density Polyethylene. This plastic is often flexible and tough, although this depends on the amount of plasticizer used. This plastic is easily welded using one of our welding kits.

This symbol indicates that the plastic is Vinyl or Polyvinyl Chloride. This plastic is often in plumbing situations, and can be flexible, depending on the amounts of plasticizer used. This plastic is easily welded using one of our welding kits.

This symbol indicates that the plastic is Low Density Polyethylene. This plastic is much more flexible than High Density PE and is often found in flexible bottles and plastics. As compared to HDPE, LDPE will float while HDPE will sink. This plastic is easily welded using one of our welding kits.

This symbol indicates that the plastic is Polypropylene. This plastic is flexible and tough, does not crack when bent repeatedly, and is difficult to scratch with your fingernail. This plastic is often found in car parts like radiators. This plastic is easily welded using one of our welding kits.

This symbol indicates that the plastic is Polystyrene. This plastic is often formed and in sheets. The sheets will turn white when bent or stressed, and it makes a metallic noise when struck. This plastic is easily welded using one of our welding kits.

This symbol indicates that the plastic is a single plastic, or a combination of two or more plastics. These plastics often need to be chemically welded. Please see our RapidPatch line.

Burn Test for Plastics

It is often difficult to find the manufacturer's ID label, and so other tests may be required. You may be able to call the manufacturer to identify the plastics. If this isn't possible, you may want to try the burn test. This is a simple test in which you bring a small piece of the plastic in contact with a flame. The follwing chart shows reactions of different plastics.

Burn Reactions for Common Plastics
Burns but goes out on removal of flame Continues to burn on removal of flame
Thermoplastic Material Odor Color of Flame Drips Odor Color of Flame Drips Speed of Burn Remarks
ABS Acrid blue edges Yellow No       Slow Black sooty smoke in air
Acrylics       Fruity Blue, yellow tip No (cast) yes (molded) Slow Flame may spur if rubber modifiers added
Polycarbonates Faint, sweet, aromic, ester Orange Yes         Black smoke with soot in air
Polyethylenes       Parafins Blue, yellow tip Yes Slow Little smoke, floats in water
Polystyrenes       illuminating gas Yellow Yes Rapid Dense black smoke with soot in the air
Polyurethanes       Non descript Yellow No Slow Black smoke
Vinyls or PVC Hydrochloric Acid Yellow with green spurts No         Chars, melts some
Polyesters       nondescript Yellow, blue edges No Slow Cracks and breaks
ABS/PVC Acrid Yellow, blue edges No         Black smoke, soot in air
PVC, Acrylics Fruity Blue, Yellow tip No         Black smoke, soot in air
                 
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