Working coil

RF-Plasma Torch Reactor. A diagram of a radiofrequency (RF) plasma torch reactor (25) is shown in Figure 8.1.3. The apparatus consists of an RF-plasma reactor with frequency of 4.0 MHz, a powder feeder, a gas supply system, and an exhaust system. The torch is composed of a work coil and three concentric quartz tubes for three independent gas flows outer, inner, and center carrier gas flows. For TiN UFPs synthesis, N2 is added to the outer flow of Ar, and titanium powder sieved in advance to a size less than 25 p.m is fed into the plasma by the carrier gas of Ar... 

Fig. 8.1.3 Rcaclor chamber designed for powder processing studies (1) torch head. (2) three concentric quart/ lubes. (3) work coil, (4) water-cooled Pyrex cylinder. (5) water-cooled copper quenching plate. (6) window, (7) to generator, (8) water in, (9) water out. (10) to exhaust system. (Reprinted front J Mater Sci, 65. The synthesis of ultrafine titanium nitride in an r.f. plasma. Copyright 1979. with kind permission from Kluwer Academic Publishers.)...

Risk of overcuring the adhesive especially with adhesives that have a high exotherm Fixturing difficult relative to the working coil and geometry restraints... 

The technique and past history of skull melting has been described in several articles from this and other laboratories.12-19 Basically, radio frequency power from a commercial power supply (50 KW at 3-5 MHz) is transferred to a work coil tightly wrapped about a skull crucible consisting of a set of cold fingers that... 

Fig. 2. A schematic diagram of the skull melting apparatus. Not shown are protective screens around the vacuum cylinders, a transparent fused silica sleeve between the skull crucible and the r.f work coil, and a fume hood above the apparatus. (1) Skull crucible (2) work coil (3) to r.f. generator (4) 12-port vacuum collar (J) vacuum quick-connect coupling (6) Teflon insulating flange (7) water supply (in and out) for crucible (S) motor-driven gear system for lowering crucible (9) base plate and supporting frame, (10) 45.7-cm diameter X 30.5 cm high Pyrex vacuum cylinders (11) aluminum top plate (12) to mechanical pump.

High-frequency generator, heating coil, and inserts (generally 0.02 to 0.04 in thick). Hooked up to automated devices, speeds are high. Work coils, water cooling for electronics, automatic timers, multiple-position stations may also be required. 

A water-cooled copper work coil designed to establish the magnetic field pattern along the bond line... 

A holding fixture —manually or electrically controlled mechanism to locate the workpiece uniformly within the work coil... 

Electromagnetic hot melts are also used. Standard hot melt applicators dispense the hot melt between the two substrates to be bonded with their subsequent reactivation through an RF work coil. This permits maintaining the ultimate hot melt temperatures without heat losses due to open time and heat sink through the substrate. 

The distance between the work coil and the electromagnetic material should be as close as possible, generally, between 1/32 in. to 3/32 in. In many applications, the work coil is set into a non-conductive holding fixture and acts as a pressure medium with direct contact on the surface of the plastic to be bonded. 

An alternative approach with a horizontal cold boat system with RF induction heating is to traverse the melt out of the work coil, thus driving a solid-liquid interface through the material. This method is sometimes referred to as the Chalmer s method or horizontal Bridgman technique. A cold finger can be introduced at one end to provide a specific nucleation site. This method has not found wide application for rare earth compounds. 

Important determinants of bond quality in induction welding are the joint design and work coil design. Proper coil and joint designs are essential for good welds and determine whether or not electromagnetic welding can be used successfully. Other parameters... 

For bonding thermoplastic parts made from the same material, the matrix is generally the same material as in the part and can be matched on melt flow. For dissimilar materials, a blend of the two thermoplastics is used. Type and cross-section of the EMA material (ferromagnetic filler -i- thermoplastic matrix) are dependent on the size and shape of the parts to be welded and on the position of the work coils. EMA material is supplied in many different forms (Fig. 14.33) strands and extruded profiles (continuous reels and precut), tapes and strips up to 30 cm wide, stampings and in-j ection-molded parts. 

Figure 14.34 A typical induction welder, showing components of the welding process induction generator, work coils, fixtures or nests, and the electromagnetic material. The inset shows the joint area, with placement of work coils and electromagnetic material.

The furnace work coil should have a minimum output of SOO W the minimum input rating of the furnace must be 1000 W. With the correct amount of iron chips. 

---