Microwave welding

A number of other deposition methods have been used for growing diamond, with varying degrees of success. These include oxyacetylene welding torches, arc jets and plasma torches, laser ablation and hquid phase crystallisation, but none of these yet reahstically compete with the hot filament or microwave systems for reliability and reproducibility. 

Polymethylpentenes have very weak loss factors, about 2 X 10 , and do not heat up under high-frequency current. They can be used for microwave ovenware but cannot be welded by the high-frequency technique. 

Other examples of microwave property applications have been given in the field of thermoplastic welding by using conductive polymers at the interface [4b,98] or in microwave equipment [99]. 

Fig. 16 Foam composite material made by means of microwave welding...

The sources of risk identified include radio gears and homing aids to support the aviation, military radio equipment, optoelectronic systems, back-up electric power sources, electric generators, central monitor panel, microwave communication centres and cellular phones, computer networks including power supply imits, computers and monitors, telephone switchboard, welding equipments, transformer stations, electric power distribution and various appliances including domestic ones (Kubicek, L. 2008). The stay of unit employees in the NIEMF of radar side lobes was assessed as a critical risk subjected to a more detailed examination. 

The possibility of using microwaves to weld thermoplastics has existed since the development of the magnetron in the 1940s. In 1993, TWl built a research facility to explore... 

Most thermoplastics do not experience a temperature rise when irradiated by micro-waves. However, the insertion of a microwave-susceptible implant at the joint line allows local heating to take place. If the joint is subjected simultaneously to microwaves and an applied pressure, melting of the surrounding plastic results and a weld is formed. Suitable implants include metals, carbon or a conducting polymer. The particular advantage of microwave welding over other forms of welding is its capability to irradiate the entire component and consequently produce complex three-dimensional joints. Welds are typically created in less than one minute. 

The technique is still in the development stages, and as such, there are currently no reported industrial applications. However, it is anticipated that microwave welding may prove to be suitable for joining automotive under-body components and domestic appliance parts. 

Welding plastics - electromagnetic radiation A BUXTON IR microwave, high frequency, etc. 

A low dissipation factor is important for plastic insulators in high-frequency applications such as radar equipment and microwave parts smaller values mean better dielectric materials with less dielectric heating. A high dissipation factor is important for polymers that are to be heated in a radio frequency or microwave oven for welding, drying, etc. 

A typical dielectric welding tool consists of two platens that are electrically connected to a generator that imposes an alternating electric field. The platens are used both as electrodes and apply pressure to the joint area. Various parameters will affect the quality of the dielectric weld. These include the type of fibre in the fabric, its propensity to heat in a dielectric field (called the material s dielectric loss), the thickness of the fabric, and the melt temperature of the fabric. Time, pressure, and field frequency (directly related to temperamre) will also affect the quality of the joint. The frequency of the field being generated can be from the radiofrequency range (13—100 MHz) up to microwave frequency (2—20 GHz). 

Sensors Electromagnetic shielding Electrochromic screens or windows Lithography Conductive textiles Microwave welding of plastics Electrolytic capacitors... 

Intrinsically conductive polyaniline (PANI) composite gaskets were used to microwave (2.45 GHz) weld high density polyethylene (HOPE) bars [ 148]. Two composite gaskets were made from a mixture of HDPE and PANI (50 and 60 wt%) powders in different proportions. The mixtures were compression molded in a hot (180 °C) press. Adiabatic heating experiments were used to estimate the internal... 

Table 18. Microwave welding of thermoplastics using inherently conducting polymers. Reprinted from (1993) Polymer 34 3105 [148] with permission ...

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