PTFE glass tape or fabric is applied to weld plates to allow for heat to pass through the tape to accomplish a joint weld. The melted PVC will not adhere to the tape or fabric surface which allows for a clean weld. 

The equipment used for this process can vary in size and complexity. The simplest equipment is referred to as a single point welding. This equipment allows the operator to weld one window corner at a time. It is typically used for custom window profiles, or by small companies with relatively low volumes of window production. The next style of equipment is semi-automated and is referred to as a two-point welding.  As expected, this equipment allows the operator to weld two window corners at one time. The most popular style of equipment is used for high volume facilities – the equipment is referred to as a four-point welding. This equipment is usually more automated and allows for the sealing of a complete 4 corner window or door in one step.

The moving image shows a hot platen which is covered with PTFE-glass tape on both sides. The angle edge of the PVC profile becomes molten against the platen. The platen is then automatically removed and the two molten ends are pushed together and held in place while the molten plastic is held in place, forming the corner of a PVC window frame.