Square Root of Negative One

Heat Sealing 101

Posted in EnS, inflatable by cheng on December 21, 2009

[http://heatsealing.blogspot.com/]
 
Heat sealing is a term used to define a method of attaching one or more layers of thermo-plastic synthetic material to itself. Other options exist for non-thermo-plastic materials such as sewing, adhesives, heat activated tapes and mechanical means. However, for thermo-plastic materials, heat sealing is the most cost efficient method producing the best quality seam in the least amount of time.

For most applications, heat sealing processes include two critical components – application of heat under pressure followed by a cooling cycle or no heat under pressure. Depending on the method used, heat sealing can be used to seal 2 or more layers of material, similar and/or dissimilar materials, ie. Polyethylene to polyethylene, or polypropylene to polyester; and a wide range of material thicknesses (or weights).

R.F. or High Frequency Heat Sealing
Uses high frequency energy to seal dielectric materials , i.e. vinyl. Typically high frequency sealing uses a bar of varying lengths and widths (1/4″ to 2″). The dimension of the sealing bar creates the sealing pattern — straight or curved. This process creates very nice looking seals, although high frequency sealing is relatively slow, expensive and only works with a limited range of materials, and does not work well with dissimilar materials.

Ultrasonic Heat Sealing
Uses noise energy to seal thermo-plastic materials. Noise frequencies vary from approximately 15KHz (loud noise – larger sealing area) to 40 KHz (relatively quiet –small sealing area). Typical seam widths range from 1/4″ to 1″. Ultrasonic sealing can either be accomplished with a bar sealer or a rotary sealer. Not all materials can be ultrasonically sealed, although the material range is much greater than high frequency sealing.

Wedge Welding
Uses a heated platen located between the layers to be welded. The heated platen or wedge moves between the layers with very little friction and therefore wedge welding is, perhaps, the fastest method for welding long lengths of material. Wedge welding can be used to produce straight and curved sealing patterns. Works very well with almost all thermo-plastic materials from plastics to synthetic textiles. Works better with thicker or heavier materials (over 20 mil per layer). Wedge welding used predominantly to weld vinyl or pvc coated textiles, high density materials (20-80 mil HDPE), synthetic textiles including polypropylene, polyester and nylon. For more information on wedge welding and wedge welding suppliers to the industry, go to:
http://www.wedgewelding.com/.

Impulse Sealing
Uses a heated nichrome wire under pressure to seal a wide range of materials. Takes the form of a bar sealer and is used predominantly to produce straight sealing patterns. Works best with thin materials ranging from under 5 to 10 mil to produce a seam width ranging from 1/8″ to 1/2″ on materials such as supported or unsupported vinyl, polyethylene, and many flexible materials.

Pulse Sealing
Very similar to Impulse Sealing, however pulses the heated nichrome wire. The pulsing action emulates High Frequency and Ultrasonic heat sealing at significantly less cost. The method developed by
Novaseal is commonly used to make outdoor signs, billboards, posters and drapery systems, among other industrial uses where reduced sealing time is important. Works best with lightweight materials including polyethylene, vinyls and other thermoplastic materials ranging from 5 to 30 mil in thickness. Seam width ranges from 1/4″ to 1″, where 1″ is the most popular.

Hot Air Sealing

Uses heated air directed between the two materials followed by a pressure means to heat seal materials. Sold in various forms from heat gun (looks like a hair dryer) to large industrial systems. Relatively inexpensive method, however prone to heating coil damage (down time) and heat sealing voids (sections of material that appear to be sealed but are not sealed). Two companies are leaders in sales of Hot Air sealing systems … Leister and Miller Weldmaster. Hot Air sealing can be used with virtually all thermoplastic materials.

Heated Platen Sealing

Perhaps the oldest known form of heat sealing, this method uses one or two heated platens (also known as dies) to come into contact with one or both layers of thermoplastic materials. Most commonly used to heat seal curved or complex patterns. Drawback is that the heat is always on which may create safety and handling issues.

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