Seaming Methods


Seaming Methods

Fabrico Sun Domes uses a variety of technologies for industrial fabric seaming. These include radio frequency (RF) welding, hot air welding, wedge welding, gluing and industrial sewing. Below we summarize the features of each of these methods for joining the pieces of industrial fabrics to form a finished product. Ask us about the most appropriate and cost effective means of assembling your product (click on the Contact button above).

Radio Frequency (RF) Welding
RF welding is also called “dielectric welding” and “high frequency welding”. It is the most effective means of producing a bond, or weld, between certain thermoplastic polymeric materials, either as a coating or laminate on a fabric base (or scrim), or in the form of a film. These materials can range in thickness from as little as .005” to 3/16” (0.1875”) or more. RF welding is a process in which two sheets of the material are placed together, under pressure, between two electrically conductive electrodes. An electric field, alternating between positive and negative at a frequency (typically around 27 MHz, or 27 million cycles per second) in the radio portion of the electromagnetic spectrum (hence the name “radio frequency welding”), is applied between the electrodes. The dielectric constant and dipole characteristics of the molecules of certain thermoplastic materials result in the excitation of the molecules at the surfaces of the two pieces of material, generating heat, which in turn causes the polymeric material at the interface between the two pieces of material to melt and merge together. When the applied voltage is discontinued, with the pressure still applied, the melted material at the interface between the two pieces of material solidifies, producing a weld. RF welding is the most common means used by Fabrico for forming air tight, liquid tight seams between pieces of industrial fabric, and is the means of producing the best, most reliable seam (see our list of machinery for details about our RF welding machines).

The advantages of RF welding include:

  • An air and liquid tight seam is formed.
  • The seam is almost perfectly uniform, provided that the operator(s) make the weld correctly (Fabrico’s RF welding operators have an average of 15+ years of experience).
  • The seam is stronger than the base material; in other words, a properly made RF weld, when placed in a tensioning device and stretched until the point of failure, will remain intact when the material itself breaks.
  • The electrodes can be made in relatively complex shapes, and can therefore produce welds of nearly unlimited complexity.
  • Every seam is identical.
  • Depending on the power rating of the RF welding apparatus, a large number of welds can be made with each cycle of the welding process, which takes from 30 seconds to a few minutes for each cycle (Fabrico’s RF welding machines at power levels ranging from less than 1 kilowatt (kW) to 50 kW, allowing us to use the machine which is best suited to the product being manufactured).

The disadvantages of RF welding include:

  • A limited number of polymers can be welded using this method, mainly various formulations of polyvinyl chloride (PVC, commonly known as vinyl) and polyurethane; a handful of other, specially formulated polymers (such as certain formulations of nylon, polyethylene terephthalate – PET, ethylene vinyl acetate – EVA, polyethylene vinyl acetate – PEVA and acrylonitrile butadiene styrene – ABS) can also be joined by RF welding, but the overwhelming majority of RF welding is done with vinyl and urethane materials.
  • Electrodes made in complex shapes are relatively expensive, so a minimum number of assemblies must be ordered to justify the price of the electrodes.

Note: RF welding should not be confused with ultrasonic welding, although both methods are sometimes referred to as “high-frequency” welding. Ultrasonic welding uses high-frequency sound waves to agitate the molecules at the surfaces of two parts, causing them to melt and thereby form a weld. It is an entirely different process from RF welding and has limited applicability. Fabrico does not use ultrasonic welding.

Hot Air Welding

Hot air welding is accomplished by running two pieces of material between two rollers which apply pressure. Just before the materials pass between the rollers, a stream of air, heated to temperatures of up to 600°F, is blown across the surfaces to be joined by a device resembling a blow dryer, causing them to melt. After passing between the pressurized rollers, the weld cools and becomes permanent.

The advantages of hot air welding include:

  • No electrodes are required, so a small number of parts can be made with little or no tooling cost.
  • Polymers which cannot be welded using RF can be welded using this technology, as long as the melting point of the polymer is sufficiently less than 600°F.

The disadvantages of hot air welding include:

  • The consistency of the welds from one piece to the next is dependent on the skill and experience of the operator.
  • Hot air welds tend to be weaker and less consistent than RF welds, although they are air and liquid tight when properly made.

Heated Wedge Welding

Heated wedge welding uses a process which is similar to hot air welding, with the exception that the heat source is a heated metallic wedge, over which the materials to be welded are passed before passing between the pressurized rollers. Its advantages and disadvantages are similar to those associated with hot air welding, although it is somewhat more effective when welding unsupported films, which can develop pinholes when they are welded with hot air.


Industrial fabric “Gluing” is a catch-all phrase for a number of different processes. These fall into two main categories: chemical bonding and contact cementing. When two or more pieces of fabric with the same (or similar) polymeric formula are chemically bonded, a solvent is applied to the surfaces which are to be joined. The solvent dissolves the outer layers of the two parts, and when they are placed in contact (usually under pressure), the material at the surfaces of the parts mix together. When the volatile parts of the solvent evaporate, what is left is, essentially, a chemical weld between the parts. As noted above, this method is typically used when bonding parts of the same polymeric composition, and can be used on a number of polymers, including PVC, polyurethane, silicone and a number of other polymers. Contact cements, such as rubber cement, so-called “super glue,” etc. are used when the two materials to be joined are made from differing polymers, for which no single solvent is available which will dissolve both materials.

The advantages of gluing (or cementing) include:

  • A seam can be formed between dissimilar materials.
  • Under certain conditions, it is a faster way of joining especially large pieces.

The disadvantages of gluing include:

  • A glued seam is typically not as strong as a seam made using heat.
  • The quality of the seam is dependent on the skill of the operator, and the amount of care taken to ensure that the adhesive material is properly applied to the entirety of the surfaces to be joined.
  • Many solvents and contact cements contain volatile organic compounds (VOCs) and other noxious and potentially poisonous ingredients, so special safety precautions must be taken to protect the workers performing the gluing operation.

Industrial Sewing

Industrial sewing is the seaming method with which the general population is most familiar. The American Society for Testing and Materials (ASTM) has published a standard which describes dozens of different types of seams and stitches, which are used in different manufactured products, depending upon the most effective way to create a sewn seam for the particular product.

The advantages of sewn seams include:

  • Sewing can be the fastest way to create a seam between two of more pieces of fabric.
  • Sewing can be used to join materials of differing compositions and thicknesses.
  • Special tooling, such as folding attachments, can increase the speed at which a seam is made.
  • Dual-needle sewing machines are available which can make two parallel seams, at a fixed separation difference, at the same time. Fabrico owns several such machines with varying separation distances between the two seams, and dual-needle sewing machines with various separation distances between the two needles, can be purchased at a relatively low price, for use in a particular application.
  • Specialized, programmable sewing machines can quickly make specialized stitching patterns, such as box stitches and bar tacks, by pressing a single button.
  • Sewing thread is available in an extremely wide variety of constructions, sizes, colors and materials (nylon, polyester, Kevlar, Teflon and Teflon-coated fiberglass, among others). The U.S. Defense Department has a number of specifications for threads used in products for the various branches of the armed services. The most common thread types are nylon and polyester.

The disadvantages of sewn seams include:

  • Sewn seams are neither air or liquid tight, unless a sealant is carefully applied to the seam to prevent the passage of air or fluids through the stitching holes in the fabric.
  • The quality of a sewn seam is highly dependent on the skill of the sewing machine operator. Fabrico’s sewing operators have 15 to 25 years of experience, ensuring the best possible sewn seams.