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Let's start with the most important level in plastic welding, "plastic identification and welding rod selection" . Most plastics have an ID abbreviation stamped somewhere on them, take the time to locate it. You may have to clean or scape the entire part to find it, but it will save you a tremendous amount of time and resources. (click here for a list of plastics acronyms) If you cannot find the ID Stamp,then you are not up the creek just yet , there are still some ways to determine the plastic type. You can call the manufacturer of the machine that you have and ask them to look up the ID stamp for you,(some will, some won't ), you can purchase a sample pack of various types of plastic types and do a trial and error procedure, or you can send a sample of the part into the welding rod factory and have them ID the type of plastic and suggest a matching welding rod. Getting the exact or as close to exact welding rod is really the most important part of the entire job, because whatever you weld will only be as strong as the two plastic types' bonding strength . If you use a weld rod that does not have the same density, not only will they not bond well but you may be taking away from the part's integrity , strength or flexibility that it was designed to have. If you would like to take the chance on determining the plastic type on your own there is always the popular burn test . Take a small torch or heat a piece of clean steel to a temp. of around 500 degrees F. Polyethylene (PE) Plastic type is a real common plastic on most machines with wheels. There are three basic PE types: High Density Polyethylene (HDPE) , Low Density Polyethylene (LDPE) and Linear Low Density Polyethylene (LLDPE) . When burning the HDPE type it will start to melt fast,meaning it has a low melt point. HDPE will also molten up but will keep some of its composure. LDPE and LLDPE will also start to melt quick but , unlike HDPE they will be stringy and tacky and start to run . Polypropylene (PP) is another popular plastic type used. When heated, there will be a noticable difference from the PE because it has a higher melting point, it will molten up and will become almost waxy or silky looking . You should be able to tell the difference between the two types just by melt temperature. Polyvinylchloride (PVC) type plastic is a ridgid plastic; when burned it will turn black and produce black smoke. Oh yea, it stinks really bad too . Polyurethane (TPU) will also start to melt rather quickly like LDPE and LLDPE but it will drip and become more like hot glue . After determining the plastic type and proper weld rod, you are ready to prepare the part's surface for the welding procedure.
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