The common Flatband is an old stand-by configuration that was originally developed to make seals with widths wider than that which could be made with round wire. In most applications, the Flatband has been replaced by the Wulstband or the Hollowband. The Flatband has the disadvantage of sharp edges that cut in and weaken the film in the zone immediately adjacent to the seal.
This band, usually called Wulstband, is the contemporary version of the Flatband. On this band the edges have been tapered down to a very thin edge. This produces two advantages. The tapering removes the sharp outer edge that presses into the film while heating. It also acts to reduce the temperature of the band along its outer edges. Without tapering, the band edge will cause a thinning of the film along the edge of the seal thereby reducing the strength of the package. Failures that result are called "zipper failures".
This is an excellent band for thick materials, hard to seal materials and vacuum packaging. Because of the convex configuration of the band it only makes edge contact with its backing. This minimizes heat loss and provides more energy for the sealing of the film. This band is also excellent for liquid sealing because the convex face acts to squeeze the liquid out of the seal zone as the seal is made.
This very popular band is used for cutting the film layers and concurrently sealing along both sides of the cut line. It is made with tapered edges as well and comes in a wide variety of sizes. The space behind the bead does not come in contact with the backing material. As a result, the bead is hotter than the adjacent edges thereby effecting a cutting action without overheating the sealed edges of the film.
These bands are made from solid extruded stock. It has a significant mass per unit of length. It is relieved in the back to minimize contact with the backing. This band retains its heat and is excellent for concurrently sealing and cutting multi-layers of film or thick film.
The Waveband is used to make two perfectly parallel narrow seals. Double seams, although rarely needed, produce the impression of greater integrity. They are useful in sealing liquids or other hard to seal materials.
Heatseal bands can be constructed with segments along their length that remain cool while other segments reach sealing temperatures. These so called "Zebra" bands can have one or many hot and cool zones. They are used for making intermittent seals for sealing a multiplicity of small packages or for making vent openings along a seal. They are all custom designed.