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Heat Sealing Equipment

Different heat-sealing devices are commonly used on packaging machinery intended to deal with plastic films. While some devices tend to gravitate towards one specific machine type, discussing them will allow the reader to clearly understand/discern their similarities and differences.

Meanwhile, each of these devices is designed to combine two different layers of film, heat them until the creation of a seal, and then get them separated, which paves the way for continued film travel. Some heating jaws entail the use of a sharp blade which slits the seal to separate the finished package.

Impulse Sealing

These sealers contain lightweight jaws to which a resistance wire covered in Teflon gets affixed. Electric current swiftly gets the wire heated to a temperature that is strong enough to melt the plastic within the area of seal. After switching off the current, the jaws keep the seal intact until it is cool enough to be released. However, the drawback of this sealing technique is that it is confined to the width of the seal that can be made: wide seal widths are known to take a long time to cool off.

Heated Jaw Sealing

Here, the jaw is kept hot, whereas the time of contact between the film and jaw is adjusted in order to produce a satisfactory seal. Since these devices typically include cool jaws they work more rapidly than impulse sealers because they usually keep the seal intact without deferring the further use of heated jaws, and work more swiftly than impulse sealers. The jaws can run in a returning or a rotatory manner.

Hot Air Sealing

Under this method, a blast of hot air is utilized to impart the required heat. Notably, this method is generally used for heavy duty bags comprising of products like fertilizer since it does not employ any mating surfaces that run the risk of getting contaminated with the packaged product. Dust particles that get entrapped in the seal area are unable to negatively impact its hermetic property since they are engulfed by molten plastic.

Hot Wire Sealing

In this method, devices provide heat using an unsupported hotwire which ends up cutting the film. Typically, it is employed on shrink wrapped packages since it forms an unobtrusive seal that is aesthetically attractive. Additionally, its inherently lower seal strength, which is attributed to the extremely narrow seal width, is not counted as a disadvantage on shrink wrapped packages that are not required to sustain the weight of products dropping into the package.

Ultrasonic Sealing

Under this method, an ultrasonic head (referred to as a horn) transmits vibratory energy via two separate pieces of plastic film kept in contact with each other. Since the vibratory energy gets converted into heat at the film interface, it creates a near immediate weld. This conversion is attributed to the fact that the two film surfaces create a strong friction at the frequencies employed, thereby generating heat.

Generally, this technique can only join similar plastics; however, this is not regarded as a significant disadvantage. Since only the interface is heated, it is especially helpful for low melting rigid plastics or for oriented film.

This method is also helpful in cases where there is a need to make the seals between surfaces that are contaminated by oils and fats. It is also useful in situations where thick layers of paper are sealed in unison by placing thin plastic coatings on their surfaces.

However, one major drawback of this method is its tendency to be far slower as compared to the previously mentioned radiant heat methods.