Heat fusion

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HDPE pipe fusion

Heat fusion (sometimes called heat welding, butt welding or simply fusion) is a welding process used to join two different pieces of a thermoplastic. This process involves heating both pieces simultaneously and pressing them together. The two pieces then cool together and form a permanent bond. When done properly, the two pieces become indistinguishable from each other. Dissimilar plastics can result in improper bonding. [1] [2]

Contents

Applications

This process is commonly used in plastic pressure pipe systems to join a pipe and fitting together, or to join a length of pipe directly to another length of pipe. Generally, polyolefins (such as polypropylene, polyethylene, and polybutylene) are used for these applications.

Types

Butt welding is usually performed using one of several methods. The first, and most common, is butt welding or butt fusion, which is a type of hot plate welding. This technique involves heating two planed surfaces of thermoplastic material (typically polyethylene) against a heated surface. After a specified amount of time, the heating plate is removed and the two pieces are pressed together and allowed to cool under pressure, forming the desired bond. Butt welding outside of manufacturing is usually performed to join pipes. [3] [4] [5] [6]

The other major technique is socket fusion. It is distinguished from butt-welding by using custom-shaped and -sized heating plates rather than a basic flat surface. These heads allow for more surface contact, reducing the time needed to heat and fuse the pipe. Socket fusion joins pipe and fittings together, rather than simply joining pipe to pipe. It requires less pressure than butt-welding and is more commonly used on smaller sizes of pipe (4" or less). Socket welding has additional advantages of requiring less machinery and is more portable than the heavier equipment required for butt fusion. [7]

A third method of thermoplastic welding is called sidewall fusion, or saddle fusion. Sidewall fusion is, like butt fusion and socket fusion, another process based on hot plate welding. Sidewall fusion differs from either socket, or butt fusion methods by performing fusion into the side of the pipe wall in a transverse orientation to the main pipe, rather than in line with the pipe. Sidewall fusion is typically employed in conjunction with either socket or butt fusion methods as a complementary process and many fusion machines designed for butt fusion are also equipped for sidewall fusion. Adaptor plates that match the outside diameter of the main pipe are applied to the heating plate to perform this type of fusion. [8]

Another method used is referred to as electrofusion. Electrofusion is a method of joining HDPE and other plastic pipes with special fittings that have built-in resistive wire which is used to weld the joint together. The pipes to be joined are trimmed, cleaned, inserted into the electrofusion fitting (with a temporary clamp if required) and a voltage (typically 40V) is applied using a device called an electrofusion processor. The processor controls how much voltage is applied, and for how long, depending on the fitting in use. As current is applied to the resistive wire, the coils heat up and melt the inside of the fitting and the outside of the pipe wall which weld together producing a very strong homogeneous joint. The assembly is then left to cool for a specified time. The joints produced tend to be more reliable than threaded fittings sealed with O-rings. [9]

Related Research Articles

<span class="mw-page-title-main">Welding</span> Fabrication or sculptural process for joining materials

Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as brazing and soldering, which do not melt the base metal.

<span class="mw-page-title-main">Plastic welding</span> Welding of semi-finished plastic materials

Plastic welding is welding for semi-finished plastic materials, and is described in ISO 472 as a process of uniting softened surfaces of materials, generally with the aid of heat. Welding of thermoplastics is accomplished in three sequential stages, namely surface preparation, application of heat and pressure, and cooling. Numerous welding methods have been developed for the joining of semi-finished plastic materials. Based on the mechanism of heat generation at the welding interface, welding methods for thermoplastics can be classified as external and internal heating methods, as shown in Fig 1.

<span class="mw-page-title-main">Hot plate</span> Portable self-contained tabletop small appliance

A hot plate is a portable self-contained tabletop small appliance cooktop that features one or more electric heating elements or gas burners. A hot plate can be used as a stand-alone appliance, but is often used as a substitute for one of the burners from an oven range or a kitchen stove. Hot plates are often used for food preparation, generally in locations where a full kitchen stove would not be convenient or practical. They can also be used as a heat source in laboratories. A hot plate can have a flat surface or round surface. Hot plates can be used for traveling or in areas without electricity.

Electric resistance welding (ERW) is a welding process where metal parts in contact are permanently joined by heating them with an electric current, melting the metal at the joint. Electric resistance welding is widely used, for example, in manufacture of steel pipe and in assembly of bodies for automobiles. The electric current can be supplied to electrodes that also apply clamping pressure, or may be induced by an external magnetic field. The electric resistance welding process can be further classified by the geometry of the weld and the method of applying pressure to the joint: spot welding, seam welding, flash welding, projection welding, for example. Some factors influencing heat or welding temperatures are the proportions of the workpieces, the metal coating or the lack of coating, the electrode materials, electrode geometry, electrode pressing force, electrical current and length of welding time. Small pools of molten metal are formed at the point of most electrical resistance as an electrical current is passed through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are limited to relatively thin materials.

<span class="mw-page-title-main">Heat sealer</span>

A heat sealer is a machine used to seal products, packaging, and other thermoplastic materials using heat. This can be with uniform thermoplastic monolayers or with materials having several layers, at least one being thermoplastic. Heat sealing can join two similar materials together or can join dissimilar materials, one of which has a thermoplastic layer.

Cross-linked polyethylene, commonly abbreviated PEX, XPE or XLPE, is a form of polyethylene with cross-links. It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, insulation for high tension electrical cables, and baby play mats. It is also used for natural gas and offshore oil applications, chemical transportation, and transportation of sewage and slurries. PEX is an alternative to polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) or copper tubing for use as residential water pipes.

<span class="mw-page-title-main">Pipe (fluid conveyance)</span> Tubular section or hollow cylinder

A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipe is far stiffer per unit weight than solid members.

<span class="mw-page-title-main">Electrofusion</span>

The word electrofusion is also used when fusing cells with electricity.

<span class="mw-page-title-main">Piping and plumbing fitting</span> Connecting pieces in pipe systems

A fitting or adapter is used in pipe systems to connect straight sections of pipe or tube, adapt to different sizes or shapes, and for other purposes such as regulating fluid flow. These fittings are used in plumbing to manipulate the conveyance of water, gas, or liquid waste in domestic or commercial environments, within a system of pipes or tubes.

<span class="mw-page-title-main">Butt welding</span> Welding of metal pieces placed end-to-end (butt joint)

Butt welding is the principal method for creating a join between two ends of material. This can include but is not limited to various metals, plastics and other materials. A butt weld requires three key elements under carefully controlled parameters - these include temperature, time and pressure.

<span class="mw-page-title-main">Plastic pipework</span> Tubular section or hollow cylinder made of plastic

Plastic pipe is a tubular section, or hollow cylinder, made of plastic. It is usually, but not necessarily, of circular cross-section, used mainly to convey substances which can flow—liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipes are far stiffer per unit weight than solid members.

Hot plate welding, also called heated tool welding, is a thermal welding technique for joining thermoplastics. A heated tool is placed against or near the two surfaces to be joined in order to melt them. Then, the heat source is removed, and the surfaces are brought together under pressure. Hot plate welding has relatively long cycle times, ranging from 10 seconds to minutes, compared to vibration or ultrasonic welding. However, its simplicity and ability to produce strong joints in almost all thermoplastics make it widely used in mass production and for large structures, like large-diameter plastic pipes. Different inspection techniques are implemented in order to identify various discontinuities or cracks.

<span class="mw-page-title-main">AGRU Kunststofftechnik</span>

agru Kunststofftechnik Gesellschaft m.b.H. is a company with global operations in engineering plastics based in Bad Hall, Austria, and was founded in 1948 by Alois Gruber senior. AGRU manufactures and supplies pipeline systems, semi-finished products, concrete protection liners, and geomembranes made of engineered plastics. As one of the 130 largest industrial companies in Austria, and one of Upper Austrias' TOP 50 biggest Companies, AGRU employs 1020 staff and has global sales of EUR 375 million (2017). In addition to the five factories at the global headquarters in Bad Hall, the company operates production sites in the United States, Germany, Poland and China. The export share is over 90%. Sales partners in more than 150 countries distribute products from AGRU, for which approximately 100,000 tons of plastic are processed annually.

Electrofusion welding is a form of resistive implant welding used to join pipes. A fitting with implanted metal coils is placed around two ends of pipes to be joined, and current is passed through the coils. Resistive heating of the coils melts small amounts of the pipe and fitting, and upon solidification, a joint is formed. It is most commonly used to join polyethylene (PE) and polypropylene (PP) pipes. Electrofusion welding is the most common welding technique for joining PE pipes. Because of the consistency of the electrofusion welding process in creating strong joints, it is commonly employed for the construction and repair of gas-carrying pipelines. The development of the joint strength is affected by several process parameters, and a consistent joining procedure is necessary for the creation of strong joints.

Extrusion welding is one of the processes used to weld thermoplastics and composites, developed in the 1960s as an evolution of hot gas welding. It can be a manual or automated process.

Advanced thermoplastic composites (ACM) have a high strength fibres held together by a thermoplastic matrix. Advanced thermoplastic composites are becoming more widely used in the aerospace, marine, automotive and energy industry. This is due to the decreasing cost and superior strength to weight ratios, over metallic parts. Advance thermoplastic composite have excellent damage tolerance, corrosion resistant, high fracture toughness, high impact resistance, good fatigue resistance, low storage cost, and infinite shelf life. Thermoplastic composites also have the ability to be formed and reformed, repaired and fusion welded.

HDPE pipe is a type of flexible plastic pipe used for fluid and gas transfer and is often used to replace ageing concrete or steel mains pipelines. Made from the thermoplastic HDPE, its high level of impermeability and strong molecular bond make it suitable for high pressure pipelines. HDPE pipe is used across the globe for applications such as water mains, gas mains, sewer mains, slurry transfer lines, rural irrigation, fire system supply lines, electrical and communications conduit, and stormwater and drainage pipes.

IR welding is a welding technique that uses a non-contact heating method to melt and fuse thermoplastic parts together using the energy from infrared radiation. The process was first developed in the late 1900s, but due to the high capital cost of IR equipment the process was not commonly applied in industry until prices dropped in the 1990s. IR welding typically uses a range of wavelengths from 800 to 11,000 nm on the electromagnetic spectrum to heat, melt, and fuse the interface between two plastic parts through the absorption and conversion of the IR energy into heat. Laser welding is a similar joining process that applies IR radiation at a single wavelength.

Implant resistance welding is a method used in welding to join thermoplastics and thermoplastic composites.

Implant induction welding is a joining method used in plastic manufacturing. The welding process uses an induction coil to excite and heat electromagnetically susceptible material at the joint interface and melt the thermoplastic. The susceptible material can be contained in a gasket placed between the welding surface, or within the actual components of a composite material. Its usage is common for large, unusually shaped, or delicate parts that would be difficult to weld through other methods.

References

  1. ASTM Standard D2657, 2007, "Standard Practice for Heat Fusion Joining of Polyolefin Pipe and Fittings", ASTM International, West Conshohocken, PA, 2007, doi : 10.1520/D2657-07, www.astm.org.
  2. ASTM Standard F2620, 2009e1, "Standard Practice for Heat Fusion Joining of Polyethylene Pipe and Fittings", ASTM International, West Conshohocken, PA, 2009, doi : 10.1520/F2620-09e1, www.astm.org.
  3. Chasis, David A. (1988), Plastic piping systems (2nd ed.), Industrial Press, p. 49, ISBN   978-0-8311-1181-6.
  4. "Анимации". Archived from the original on 2013-04-30. Retrieved 2012-12-20.
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  6. "DVS Technical Codes on Plastics Joining Technologies" (PDF). dvs-media.eu. 2011. Retrieved 9 April 2023.
  7. "Aquatherm Greenpipe Fusion Connections". Archived from the original on 2011-11-28. Retrieved 2009-06-01.
  8. "- - Worldpoly". Archived from the original on 2019-02-02. Retrieved 2022-02-07.
  9. "Electrofusion Jointing of PE Pipe and Fittings for Pressure Applications | the Plastics Industry Pipe Association of Australia". Archived from the original on 2018-03-14. Retrieved 2015-05-06.