Welding of plastics
Welding of thermo plastics :Thermo plastics only are weldable by some processes namely : 1. Hot air welding 2. Gas welding 3.Ultrasonic welding 4.Friction welding 5.Other special processes.
1.Hot air welding uses a welding gun to supply heated air of required temperature to heat or melt plastic.When plastic is melted and solidified the original molecular structure is disturbed
and the strength of joint reduces as compared to original plastic before welding.
2.Hot gas welding :Heated nitrogen gas provides oxygen free atmosphere to some of the plastics like HDPE and LDPE to prevent oxidation.Highly skilled welders are required for various applications:Tubes,pipes,containers,ducts etc.
3.Ultasonic welding : Commercially available machines with sufficient power can be used for many industrial applications to improve productivity.Mechanical vibrations (20-70 kHz)with amplitude of 0.5 and pressure provide frictional heat to melt plastic.On solidification the joint acquires strength suitable for intended service. Some of the typical applications include:Automotive components, medical ,electrical,electronics,computers,toys etc.http://www.ewi.org
4.Friction welding (Spin welding):This mass production process can be employed to weld variety of components where one part should be circular.The other part can be of any other cross section.Some applications include :Aerosol bottles, floats and other circular parts.
5.Other processes: a) Hot plate welding – Hot plate is kept between surfaces and when sufficient heat is generated on surfaces, the plate is removed and contact is established under pressure to establish the joint.Applications to include: Washing machines,Dish washers,Vacuum cleaners,Automotive components,pipes b)Vibration welding – Heat is produced between surfaces to be joined by creating vibrations with high frequency and amplitude and under pressure.
This process has several applications : The components of complex shapes made by various moulding methods can be welded .
There are very important standards on welding of plastics which
give guidance for fabrication of plastics.EN13067 gives details on training and qualification of plastic welders.
Thermoplastic composites also find wide use industrially.These are welded by ultrasonic welding and Induction welding processes
and machines are commercially available.