There are many different methods used to weld PVC or other types of plastics in use today. Not all of these methods can be used on the same forms of plastic, it is important to know which methods are appropriate for the material you are going to be working with.
Hot gas welding is a technique which requires a specially designed heat gun called a hot air welder. This produces a stream of hot air that will soften the plastic so that it can be joined. It is important that the pieces you are joining be of a similar type of plastic. This method is primarily used in the manufacturing of water tanks, plumbing fittings and chemical tanks.
Speed tip welding uses a plastic welder that is similar to a soldering iron in appearance and wattage. The speed tip heats the rod while pressing the molten weld rod into position. A bead of softened plastic is then laid into the joint which are fused together by the rod fuse. With some plastics the melted welding rod must be combined with the semi-melted base material in order to create a strong connection between the two materials.
Hot plate welding is a technique which is similar to contact welding. This welding process is used to weld larger parts or parts with a lot of joint connections. The two pieces that are to be joined are placed in the tooling attached to the two opposing platens of a press. A hot plate that has the same shape as the parts to be joined is then placed between the two parts. The heat produced will cause the two pieces to soften and then melt together forming a sound connection. After the pieces have cooled the weld produced by this method creates a permanent bond.
These are only a few of the methods used to join PVC, there are other methods used depending on the connections that need to be made. Some are specialized forms of welding that require special knowledge of a particular aspect of the process.