Welding a special Waterbed-PVC-Foil to manufacture the watermattress.

Welding processes are often categorized and identified by the heating method that is used. All processes can be divided into two general categories: intemal heating and external heating. Internal heating methods are further divided into two categories: internal mechanical heating and internal electromagnetic heating. For manufacturing a waterbed or watermattress we produce most mattress parts by internal heating categories like Radio Frequency, Microwave and for some customers Laser technics.

• Heated Tool
• Hot Gas
• Extrusion
• Implant Induction
• Implant Resistance

There are following categories of Internal Heating:

• Mechanical:
  Ultrasonic
  Vibration
  Spin
• Electromagnetic
  Radio Frequency
  Infrared and Laser
  Microwave

External heating methods rely on convection and/or conduction to heat the weld surface. These processes include: hol tool, hot gas, extrusion, implant mduction, and implant resist-ance welding.Internal mechanical heating methods rely on the conversion of mechanical energy into heat through surface friction and intermolecular friction. These processes include: ultrasonic, Vibration, and spin welding.
Internal electromagnetic heating methods rely on the absorption and conversion of electro-magnetic radiation into heat. These processes include: infrared, laser, radio frequency, and microwave welding.
Radio Frequency Welding

Radio Frequency (RF) welding, which is also often referred to äs "dielectric welding" is a process that relies on internal heat generation by dielectric hysteresis losses of mermoplas-tics. It is most commonly used to weld PVC bladders such äs intravenous drip bags for the medical industry. It is also used to weld book and binding covers äs well äs blister packages.
For waterbeds and parts of it we use foils with a thickness between 0,3 and 0,7 mm. Most good waterbeds are manufactured with a foil of 0,5 or 0,6 mm.

Radio Frequency welding has the advantages that it is a relatively fast process with typical cycle times of less than 2 to 5 s. It also does not require any special joint designs and produces relatively the weldings.
RF welding is almost exclusively used for welding relatively min sheets or films. Thick-ness' usually ränge from 0.03 to 1.27 mm, depending on the material and the application. The welding of films is limited because a strong electric field must be generated and this can only be achieved when the welding electrodes are brought together in close proximity, 0.03 to l .27 mm. If the welding electrodes are significantly further apart, the electric field density is too low to effectively heat and melt the plastic.

Another limitation of the process is that the material being joined must have the proper electrical properties. One such property is a relatively high dielectric constant, typically greater than two. This allows more current to flow through the material, which promotes heating, at a lower electrode voltage.
The major restriction on materials to be welded by RF is the fact that the material must have a relatively high dielectric loss, i.e., the material must have the ability to convert the alternating electric field into heat. The most common thermoplastics that can be effectively heated with RF welding are:
• PVC
• CPVC
• Polyurethane
• Nylons (polyamide)
• Cellulose acetate
• PET, PETGA

Relatively high dielectric breakdown voltage (dielectric strength) in the material is also important to reduce the possibility of arcing through the material. This property is usually less of a restriction for material selection with RF welding, because most plastics are good electrical insulators and mherently have high dielectric breakdown voltage. In some cases, a third material can be added to the bond Ime to allow for matenals, which naturally cannot be heated by RF to be welded.


Joining of Plastics and Composites for manufacturing a waterbed or Watermattress  

Welding a special Waterbed-PVC-Foil to manufacture the watermattress.

Process Description of welding a waterbed or watermattress with Radio Frequency