utilize moving belts over heating elements. Impulse heat sealers- have heating elements (one or two) of Nichrome placed between a resilient synthetic rubber and a release surface of film or fabric. The heating elements are not continuously heated; heat is generated only when current flows. When the materials are placed in the heat sealer, they are held in place by pressure. An electric current heats the heating element for a specified time to create the required temperature. the Jaws hold the material in place after the heat is stopped, sometimes with cooling water: this allows the material to fuse before stress can be applied. Hot melt adhesive can be applied in strips or beads at the point of joining. It can also be applied to one of the surfaces during an earlier manufacturing step and reactivated for bonding. Hot wire sealing – involves a heated wire that both cuts the surfaces and joins them with a molten edge bead. This is not usually employed when barrier properties are critical. Induction sealing is a non-contact type of sealing used for inner seals in bottle caps. Induction welding heat sealing by non-contact induction Ultrasonic welding uses high-frequency ultrasonic acoustic vibrations to workpieces being held together under pressure to create a weld. A type of heat sealer is also used to piece together plastic side panels for light-weight agricultural buildings such as greenhouses and sheds. This version is guided along the floor by four wheels. Seal quality Good seals are a result of time, temperature and pressure for the correct clean material. Several standard test methods are available to measure the strength of heat seals. In addition, package testing is used to determine the ability of completed packages to withstand specified pressure or vacuum. Several methods are available to determine the ability of a sealed package to retain its integrity, barrier characteristics, and sterility. Heat sealing processes can be controlled by a variety of quality management systems such as HACCP, statistical process control, ISO 9000, etc. Verification and validation protocols are used to ensure that specifications are met and final materials/packages are suited for end-use. Seal Strength Testing The efficacy of heat seals is often detailed in governing specifications, contracts, and regulations. Quality management systems sometimes ask for periodic subjective evaluations: For example, some seals can be evaluated by a simple pull to determine the existence of a bond and the mechanism of