Plastic Welding: Important Facts and Developments
Md Shakibul Haque*, Mohd. Anees Siddiqui
Department of Mechanical Engineering, Integral University, Lucknow, INDIA
To cite this article:
Md Shakibul Haque, Mohd. Anees Siddiqui. Plastic Welding: Important Facts and Developments. American Journal of Mechanical and Industrial Engineering. Vol. 1, No. 2, 2016, pp. 15-19. doi: 10.11648/j.ajmie.20160102.12
Received: August 24, 2016; Accepted: September 8, 2016; Published: September 22, 2016
Abstract: This paper provides an introduction to some important facts and developments in the plastic welding field for assisting the developments in future in plastic welding. Plastic manufactured part are regularly used in many industries. The parts made of polymeric materials and polymeric composites fulfilled very demanding criteria now-e-days. Plastics have good corrosion resistance, excellent strength to weight ratio and ability to take good finish. Plastics can be categorized as thermosets and thermoplastics. Only the thermoplastic is weld able among these two. A chemical reaction occurs during processing and curing in case of thermo sets resin, that is, as a result of irreversible cross-linking reaction in the mold. Both molded thermosets and vulcanized elastomer components cannot be reshaped by applying heat, because of the irreversible reaction that occurs. And thus in this case joining can be obtained by mechanical fastening and adhesive bonding only. In this paper few selected welding processes are discussed like hot gas welding, friction welding, hot plate welding, etc. Various important Poly Vinyl Chloride welding parameters such as welding techniques, welding temperature, welding speed, equipments requirements have also been discussed. Recent developments in this field are also discussed.
Keywords: Poly Vinyl Chloride, P.V.C. Welding, Friction Welding, Hot Air Technique
Plastics are used in day to day life for manufacturing of toys, utensils and complicated part such as heart valve for medical use etc. Plastic parts are frequently used in many industries . Plastics have ability to take good finish, excellent strength to weight ratio and good corrosion resistance. There are two types of plastics, thermosets and thermoplastics out of which only thermoplastic is able to be welded A chemical reaction occurs during processing and curing in case of thermosets resin, that is, as a result of irreversible cross-linking reaction in the mold. . Molded thermosets components cannot be reshaped by applying heat, because of the irreversible reaction that occur . And thus in this case joining can be obtained by mechanical fastening and adhesive bonding only. But, thermoplastics are able to be softened and remolded by means of heating, and can fusion welded. Therefore thermoplastics are able to be welded by following three methods (a) Thermal, (b) Friction (c)Electromagnetic. Further the types of Thermal plastic welding are (a) Hot air technique (b) Hot tool method (c) Laser beam heating (d) Infrared heating. PVC plastics are different from other geomembrane like HDPE, LLDPE, and FPP because it is primarily amorphous while others are semi-crystalline . When PVC is heated it will soften [5,6], that allow alimited amount of chain entanglements to assure a strong bond.
2. Hot Tool Welding
Hot tool welding is a technique in which surfaces to be joined by direct contact with a heated metallic tool. When it is required to join the pipes, the surfaces to be joined are flat hence the tool is a hot plate. However in many applications, such as in automotive rear light and headlamps, because of doubly curved joined interface it require complex tool that allow the hot surface to match the contours of the joint interface.
3. Hot Gas Welding
When the external heating method is applied the technique is called hot air technique. In the process of welding the welding rod and a weld groove are simultaneously heated with a hot gas stream until they soften sufficiently to fuse together; and then the welding rod is pressed into the weld groove to complete welding process. A stream of hot air is directed toward the filler and the joint area using a hot air torch. A filler rod of a similar composition as the polymer being joined is gently pushed into the gap between the substrates (Fig1). The round cross-section filler rod is used, but it is also available in oval, triangular and rectangular cross section . During welding, the hot air temperature can range from 200 to 600°C, depending upon polymer being joined . The table 2 shows a list of plastic welding temperature  for different type of plastics. The melting temperature of PVC is not well-defined, owing to the large distribution in crystalline particle size  this results broad melting range. Hot gas welding can be used for most thermoplastics but PVC is the major material being assembled by this technique . Apart from PVC, there are some more plastic which can be welded by this techniques are polyethylene, polypropylene, acrylics, polystyrene, and polycarbonate .
|• Temperature||Temperature of hot gas|
|• Gas||Composition of hot gas(air, carbon dioxide, hydrogen, oxygen or nitrogen)|
|• Angle||Include angle between weldment and rod, angle between gas nozzle and weldment.|
|• Travel Speed||Rate at which weld is being deposited|
|• Weld force||Amount of force applied to the filler rod|
|• Filler rod||Composition of filler rod|
|• Gap distance||Distance between gas nozzle and workpiece|
|• Weld joint||butt joint and double strap fillet joint.|
|• Pressure of hot • air/gas||Pressure of gas at which it coming out from nozzle|
|• shoe||Design and size of welding nozzle|
4. Welding Procedure in Hot Gas Technique
The hot air gun is used for hot air welding. The gun consists of a main body which contain heating element. This is anon contact soldering for high requirements. The air mass flow and the temperature can be adjusted in a prescribed range; the basic element of hot air gun is shown in the figure 2. The nozzles can be easily replaced so that each component is soldered by using the suitable nozzle, air and temperature setting .
The melting temperature of PVC is not well-defined, owing to the large distribution in crystalline particle size  this results broad melting range. Most thermoplastic can be joined via hot gas welding but PVC is the major material being assembled by this technique . Apart from PVC, there are some more plastic which can be welded by this techniques are polyethylene, polypropylene, acrylics, polystyrene, and polycarbonate.
|Acrylonitrile Butadiene Styrene||350°C|
In figure 3 the graph is shown between Gap distance between torch and the job versus temperature of hot air with application of different pressures.
Md Shakibul Haque et.al. develop a experimental setup and performed experiments and find that The poly vinyl chloride can be successfully welded by using their fabricated setup in workshop. Their setup is user-friendly because of easy controlling of air flow, air temperature, welding speed, less weight and portable. and eco- friendly also because of no harmful fumes, gases, radiationsand flames are generated .
Md Shakibul Haque et.al.has been carried out the work to study the effect of welding parameters on hardness of butt welds, made on poly vinyl chloride sample using hot air technique. These parameters are Temperature, welding speed and airflow. They are varied at two levels higher and lower. From their study conclusion is drawn that the better hardness of the welded joint is obtained at higher level of temperature .
Md Shakibul Haque et.al.has been workedon the study of the effect of input welding parameters on Tensile strength of butt welds, made on poly vinyl chloride sampleusing hot air technique. The parameters, Temperature, welding speed and airflow are varied at two levels higher and lower. From these studyit is found that the better tensile strength of the welded jointis obtained at higher level of temperature.Better weld factor was obtained i.e. from 0.46 to 0.69. Betterresult of tensilestrength was obtainedmaximumof 11.25MPa .
Hoomam Ahamad et al. carried the review for plastic welding, it can be concluded that there is huge scope for research in order to investigate the parameters responsible for high quality welding of plastic. Nitrogen gas and other inert gases can be used in order to prevent oxidation. Proper jigs and fixtures as well as roller can be used to increase the welding pressure applied on welding rod for proper fusion .
5. Hot Plate Welding
Hot plate welding isone of the simplest welding techniques making it highly reliable and common place in industry. The processworks by bringing the faying surfaces to be joined in contact with a heated tool. The tool can have relativelycomplex geometries to allow the welding of complex interfaces. In addition, the tool is often coated with anon-stick material (often PTFE, product name: Teflon) to act as a release agent. In the initial phase (matching phase), pressure is applied to promote squeeze flow of the faying surfaces to assure that the faying surfaces arewell defined and all part irregularities are removed. Once sufficient matching displacement is achieved, the pressure is removed by mechanical stops or pressureregulators, so that a relatively thick melt layer is developed. After a pre-selected heating time, the parts are retracted from the tool, the tool is quickly displacedaway from the parts and the parts are brought together to allow the two molten interfaces to weld. Again, the amount of displacement during the cooling phasemay be limited by mechanical stops to prevent excessive squeeze out which would force the majority of melt out of the weld zone leaving a cold weld .
6. Recent Developments
6.1. Ultrasonic Welding
Ultrasonic welding is a verypopular technique for fusion bonding of thermoplastics and thermoplastic composites. Welding is accomplished by applying low amplitude (1 to 250 lm) highfrequency (10 to 70 kHz) mechanical vibration to parts. This results in cyclical deformation of the parts, primarily at the faying surfaces (joining surfaces) and surfaceasperities. The cyclical energy is converted into heat – within the thermoplastic – through intermolecular friction. This issimilar to the heating that occurs in a metal wire that is bent back and forth repeatedly, or in general, tothe effect occurring when materials are subjected to cyclical loading. The heat, which is highest at thesurfaces (because asperities are straining more than the bulk), is sufficient to melt the thermoplastic and to fuse the parts. Usually, a man-made asperity in the form of a triangularprotrusion is molded into one of the parts to improve the consistency of heating and welding. Thisprotrusion, which is also called an energy director or concentrator, experiences the highest levels of cyclical strain producing the greatest level of heating. Therefore, theenergy director melts and flows to join the parts. There is a wide range of joint designs that concentrate the energyat the faying surfaces, including shear joints, mesh joints, knife edge joints among others that can be used inconjunction with roughened surfaces to enhance welding. It is beyond the scope of this paper to reviewthese alternative joint designs .
6.2. Friction Welding
Four main variations of frictionwelding are linear, orbital, spin and angular welding. Or bital and linear welding are similar in thatthey are amenable to a wide range of geometries, while in contrast, angular and spin welding are primarily suitable for circular weld geometrics. All four processes rely on relative motion between the two parts that are tobe joined, which results in frictional heating. The only major difference between these processes is the geometry of the relative motion. It is important to note that in all cases, the angular velocity of the displacement is in radians/s . In addition, in the case of angular welding the angle of rotation is defined in radians. With thevelocities, it is possible to estimate power dissipation based on the fundamental assumption that power is equal to velocity multiplied by friction force as detailed in Grewell, D at all work. Linear vibration welding allows welding of surfaces that are able to be moved in one direction. However, with linear vibration welding thereis the risk that relatively weak welds can result with walls that are aligned transversely to the vibration direction. This is due to that fact that without propersupport, either internally with stiffening ribs or externally with built-in features in the fixtures, the walls can deflect and reduce the relative motion of the interfaces. Orbital welding, produces a relatively constant velocitybecause of its elliptical or circular motion  assuming the amplitudes in both directions are equal. This constant velocity dissipates more energy at the jointfor a given weld time and amplitude compared with linear vibration.
The major use of Plastic welding are to repair polyolefin tank, container and welding of Polyvinylchloride, ABS, PE and PP pipe section  Apart from this it is also used to repair of bumper in automotive industry, construction, sealing and packaging of material etc.
In the present paper the different techniques of welding of plastics is reviewed with the help of available relevant literature. As this is the period of plastic age, joining of plastics is a challenge to young researchers and scholars working in the area of welding technology. Although there are several methods that are reported to join two plastic pieces but hot air gun technique is most reliable and techno-commercially beneficial from research as well as production point of view and more work is required in this area in order to understand effect of different process parameters on the main response parameters. So, after this review there is a need to take initiative for the experiments for making the results more favorable. Further response parameters such as tensile test, hardness test and grain size can be analyzed.
We would like to thank Prof. (Dr.) M.I. Khan, Integral University for the patient guidance, encouragement and advice. We would also like to thank Er. Ajitanshu Mishra, HoD, Mechanical deptt., Inverstis University who helped us in our work.
Md Shakibul Haque is a Senior Lecturer in Mechanical Engineering Department at Integral University, Lucknow, India. He has completed M Tech in Mechanical Engineering from Invertis University Bareilly in year 2015. He has more than six years teaching experience and published more than ten papers in reputed International Journals.
Mohd. Anees Siddiqui is a Lecturer in Mechanical Engineering Department at Integral University, Lucknow, India. He has completed M Tech in Mechanical Engineering from Integral University Lucknow in year 2015. He has more than four years teaching experience and published more than fifteen papers in reputed International Journals.