Heat sealing welding

See also induction welding dielectric heat sealing/welding vibration welding spin welding. 

See also dielectric heat sealing/welding dielectric curing or heating. 

PFA has the advantage over PTFE in that it can be thermoformed, heat sealed, welded, and heat laminated. This makes the material much easier to produce a lining from than that of PTFE. PFA can be bonded to a metal substrate. It is also used to line pipe. 

Other Techniques. The FEP resin is bonded to metal surfaces by the appHcation of heat and pressure it can be heat sealed or hot-gas welded. Heating FEP at 260°C and allowing it to cool slowly results in stress relieving, or annealing. The FEP film is used to weld PTFE-coated surfaces. 

PTFE mouldings and extrudates may be machined without difficulty. Film may be obtained by peeling from a pressure sintered ring and this may be welded to similar film by heat sealing under light pressure at about 350°C. 

Figures 10-7, 10-7A, 10-7B, and 10-7C illustrate the general arrangements of most manufacturers, although several variations of plate flow pattern designs are available to accomplish specific heat transfer fluids temperature exchanges. Also, the gasket sealing varies, and some styles are seal welded (usually laser) to prevent cross-contamination. Note that Figure 10-7C has no interplate gaskets and is totally accessible on both sides, yet easy to clean.

TPEs can be bonded to other materials by adhesive, heat bonding, electromagnetic filling, radio frequency, heat-sealing lamination, friction and spin welding, and ultrasonic welding. For TPUs, the most widely used techniques are radio frequencies, and ultrasonic and hot stamping. A few typical applications include football bladders, valves, and conveyer belts. 

Because SPMDs have high sampling rates (Rs s) for vapor phase contaminants, all SPMDs are assembled in an environmentally controlled room equipped with an activated carbon air filtration system for the removal of airborne contaminants. SPMDs of almost any length can be prepared after allowance of space for the molecular welds or heat seals (i.e., 2.5 cm for each end). However, different... 

Strip Packs. Usually two laminates of paper and/or soft temper aluminum and various plastics have been used as clear cellophane (i.e., coated rather than a laminate). This process uses two rolls of either laminate or film which at the point of coming together have the product (usually tablet or capsule) placed between the rolls and heat sealed inside the rolls by means of a hot knurled roller, thereby welding the inside layers of the laminate together. The essential point of this method is that the product itself helps to form the pocket. The number of packed tablets or capsules required is then cut off the strip. 

Articles may be assembled from plastics by adhesive bonding, heat sealing and welding (which are reviewed in subsequent chapters), and by a variety of physical methods of fixing including sewing with filament, thread, or wire. 

Blister Packs. This type of pack can be produced by heat-sealing rigid transparent or translucent film to pre-coated card but vinyl thermoformings can be welded more quickly and the welding technique is more versatile. 

Transparent Boxes. Boxes can be made in translucent or transparent acetate or rigid vinyl film, with creasing by application of heat and welds at the final tear-seal. 

Zade, H.P., Heat Sealing and High-Frequency Welding of Plastics. Temple Press Limited, London, (1979), P. 79. 

Plastic sections, which are too thick to be heat-sealed, may usually be welded. There are three major methods in commercial use heat, solvent, and ultrasonic. In general, these methods are limited to use with thermoplastic materials. These welding techniques have done much to lower the total cost of using plastics in the construction and other industries. 

The second sheet lining is also a fluorocarbon—Halar , but made entirely of this basic material. Though quite expensive, this material has probably the best overall chemical resistance of any of the generally available sheet linings. It is adhered to the substrate with a rubber-type adhesive, and though Halar can accept surface temperatures of 300°F and above without damage, the use of the sheet must be limited to the 220°F range due to the thermal limit of the elastomer adhesive. Joints are butted, tooled to accept a weld strip, and then a narrow strip is heat-sealed over the joint. Full data on the material, its installation and chemical resistance is available from the manufacturer. 

All the above processes can also be used in a form fill seal process with, for example, thermoforming and cold forming blister packs. Rommelag type bottle pack systems use an extrusion process where the container is formed by either blowing or vacuum (smaller sizes). Immediately after this, containers are filled, and the pack is sealed (welded) by using the residual heat in an extension to the main body of the container. 

Welding/heat sealing—involves the direct and indirect application of heat, usually under pressure, for a given time (dwell) followed by a cooling period, so that a bond is made between two materials. 

Filling end. Heat seal, heat weld with cooling jaws usually essential (avoid presence of product). Also ultrasonic welding, hot air sealing, plus cooling jaws, etc. 

---