Heat fusion, also called heat welding or plastic welding, is an industrial process that uses heat to join two or more pieces of a given material to create one solid piece. Using the heat fusion process, the individual pieces are heated to the point where the material begins to soften, and then they are pressed together. When done properly, the separate pieces form a bond and become one unified part. This manufacturing process is used to join a variety of materials, including plastic, glass and metal.
The industrial practice of heat fusion relies on a principle called the heat of fusion. As a material is heated, the molecular bonds begin to break down, and the material begins to turn into a liquid. This is commonly called the melting point, and when melting begins to occur, the heat of fusion has been reached. At this point, two pieces of melting material can be put together under pressure, and the molecules of each piece will pair together to form a solid piece as the fused joint cools. After the joint has cooled, the two pieces are permanently joined and are indistinguishable.
Heat fusion, as used in manufacturing, presents a number of advantages. Using heat fusion to join parts ensures a watertight and airtight seal between the parts. The melting and joining of the parts using the heat fusion process will create a stronger permanent bond than that which could be achieved using adhesives, because the two parts essentially become one solid piece. By melting pieces together to form new plastic that can be used in the manufacturing process, heat fusion makes it possible to recycle materials that might otherwise be discarded.
The process of heat fusion is used in a variety of applications, from the creation of glass art to coins and plastic products. In the plastic manufacturing industry, small pieces of plastic are heated and joined to make solid sheets of the material. In other cases, individual thermoplastic parts are joined using a heat fusion machine to create a solid product.
The most common industrial use of heat fusion is the connection of thermoplastic pipes and joints. This is done by using heat to melt the ends of the plastic pipe before pressing them together or placing them into the joints. Melting the ends of two pipes and then pressing them together without a joint is called butt plate welding. If a joint is used to connect the two pieces, it is called socket fusion.