Types of Industrial Fabric Welds

April is National Welding month and we want to take this time to break down the types of coated fabric welding we offer, starting off with Radio Frequency (RF) Welding and Hot Air Welding. While at times both can be applied to the same application it does not mean that the methods are the same or that you are choosing the right one for your application. This makes it important to know the difference between the two welds so that you can make an informed decision on which is best for your next project.

What is RF welding?

RF welding or radio-frequency welding is a process that is used to join materials, in our case coated fabrics, by heating up the material on the inside using high-frequency electromagnetic energy (27.12 MHz) to fuse the two materials together. This process is achieved by using an RF welding machine. The heat is created by sending radio frequency energy through layers of plastic material. The dielectric loss (resistance of the molecules against oscillation) creates the heat which is generated on the inside of the material, not through the surface. Pressure is exercised at the same time, and after the weld cycle is finished, the pressure is maintained through a cooling cycle.

Pros:

The biggest benefit of RF welding is the consistency of the process. Through test welds, the settings can be finetuned and once the settings for a particular combination of materials and weld size are determined, repeated welds will be consistently high quality.

Another benefit is that multiple layers can be welded at the same time.

Because the RF energy is delivered through a metal die that presses on the material, the material is stationary during welding, and complex welding geometries can be accomplished.

When RF welding is done with a traveling welder, the process of welding long straight seams becomes very efficient.

The 2 most popular brands for traveling welders are FIAB and Forsstrom.

Profile view of RF welding
RF welding Side view

 

 

 

 

 

 

 

When should RF welding be used?

For any type of overlap weld with coated fabrics where the coating is a polar type polymer (PVC, PU)

Projects we have used RF welding on:

    • Fabric panels for frame supported fabric structures

When should this type of weld not be used?

One condition for RF welding to work is that the material is polar. Non-polar polymers, like polyethylene, can generally not be welded with RF welding.

What is Hot Air welding?

Hot air welding or hot gas welding is the process using a designed heat gun that blows hot air in between two fabric membranes which softens the coating. Pressure is applied, and when the two fabric membranes cool there will be a permanent seam between them. In cases where the fabric is difficult to weld, a welding tape can be applied, which is a layer of thermoplastic material that melts more easily and joins the two layers of fabric when melted by hot air. Hot air welding is used in different configurations:

    • Rotary: the welder is stationary and the materials move through the welder
    • Floor welding: the material is stationary and the welder moves along the weld line on the floor
    • Handheld
    • Track welding: the material is stationary and the welder moves along a track at a predetermined speed

Pros:

Hot air welding is applicable to any thermoplastic material such as  PVC coated fabric, polyethylene, and polypropylene. Hot air welding can be used for improved aesthetics of projects because the weld happens on the inside of the materials, which can reduce the visibility of the seam. It also allows for more dynamic “creations” due to the ability to move the heat gun freely.

When should hot air welding be used?

We recommend hot air welding for finishing on a building because it can be done with a handheld hot air gun, for materials where other methods fail, for complex tridimensional shapes and for high-speed welding of simple larger projects.

Projects we have used Hot Air welding on:

    • Industrial Curtains
    • Finishing details
    • Polyethylene projects

When should this type of weld not be used?

When there are multiple layers to be welded

Diagram of wedge welder used for hot air welding
Hot Air wedge welding diagram

What is Hot Wedge welding?

Hot wedge welding is the process using a heated wedge that slides between two fabric membranes which softens the coating. Pressure is applied, and when the two fabric membranes cool there will be a permanent seam between them.

Pros:

Hot wedge welding is also applicable to materials such as PVC coated fabric, polyethylene, and polypropylene. Hot wedge welding is more reliable and more precise in where the heat is applied compared to hot air welding. Some welding equipment offers the option to switch between hot air and hot wedge on the same equipment.

When should hot wedge welding be used?

We recommend hot wedge welding for long straight welds where the ability to reproduce consistent weld strengths is important

Projects we have used Hot Wedge welding on:

    • Industrial Curtains
    • Polyethylene projects

When should this type of weld not be used?

When there are multiple layers to be welded, and when a weld is required away from the edge of the fabric.

What is Hot Bar welding?

Hot bar welding is the process using a heated metal bar that heats the coated fabric from the outside. Pressure is applied, and when the two fabric membranes cool there will be a permanent seam between them. The process is rather slow since the heat has to be transferred through the thickness of the fabric to the inside between 2 layers, using conductive heat transfer.

Pros:

Hot bar welding is applicable to advanced technical fabrics such as PTFE/glass. It can be used for many thermoplastics but is generally only used when other weld methods are unsatisfactory, because of the slow speed of the hot bar. The hot bar is used for many advanced technical textiles such as PTFE coated fiberglass fabric and other fluoropolymers. With PTFE/glass, an FEP welding tape is inserted between the layers to be welded.

When should hot bar welding be used?

We recommend hot bar welding for any advanced technical textile where other methods do not offer satisfactory results.

Hot bar welding on PTFE fabric profile view example
Hot bar welding profile view

 

Projects we have used Hot Bar welding on:

    • PTFE/glass tensile projects

When should this type of weld not be used?

When more efficient methods are available.

Other fabric joining  methods:

Adhesives

In certain applications, adhesives can be used effectively, especially when the materials are difficult to weld otherwise, and when the process is continuous and repeatable so that setting can be optimized.

Impulse welding

Impulse welding is another form of bar welding where the temperature is controlled digitally at the surface of the welding bar, for a very precise welding temperature.

Ultrasound welding

Ultrasound welding is used both in rotary and bar welding equipment, to weld materials that are difficult to weld otherwise. Ultrasound energy excites the molecules and creates a bond in a diverse range of fabrics.