Inductive curing

The induction curing process is illustrated in Fig. 14.4. Four basic components comprise the induction heating process ... 

Speed is the most important feature of induction heating. Workpiece heating rates greater than 40°C/s are possible. One supplier of induction curing epoxy adhesives claims production speeds of 600 parts per/hour are possible.21... 

For high-power applications, the conductors in the workpiece may have to be cooled with water. Typical power supplies for induction curing applications range from 1 to 5 kW, depending on the parts and application requirements. 

Although speed may be the most important factor in considering induction curing, this curing method is also characterized by a uniform heat distribution within a sharply defined boundary and by unique, precisely controlled temperature. Thus, the quality of the joint can be better and more consistent with induction curing than with other heating methods. 

Induction Curing Adhesives. Typically one-component epoxy adhesive systems are used for induction bonding of structural parts. However, two-component adhesives have also been used. The properly designed induction cured adhesive should provide the following application and performance properties ... 

When induction curing a one-part thermosetting adhesive, one has the choice of taking the adhesive to full strength or only to partial strength in the induction field (complete cure... 

Overheating of the adhesive is always a critical concern with induction curing. This is especially true when the adhesive cures with a high exotherm, such as epoxy-dicyandiamide systems. Several proprietary epoxy curing agents have been developed that provide lower exotherm yet faster cure rate than typical dicyandiamide reactions.27,28 Tertiary amines and modified polyamines29 are often used to accelerate the cure of dicyandiamide-epoxy... 

One of the advantages of using a two-component room temperature curing adhesive system is that induction curing can be used to spot-cure the adhesive in a joint (similar to a spot-welding process). The adhesive that is not spot-cured by induction will then fully cure at room temperature as the part moves down the assembly line. 

Turi, D., Supplier/User Cooperation Yields Beneficial Induction Cure Epoxy, Adhesives Age, June 1993, p. 22. 

Figure 7. Calculated cure curves for systems of Figure 6, for inductive cure. Nominal temperature 300 C, time constant 1 sec.

Table I. Comparative Fluidity Values for vs. Inductive Cure Conditions. "Normal"...

Curing by means of electrical processes (inductive curing, resistance, high-frequency and microwave curing)... 

In inductive curing an induction coil is located close to a metallic workpiece and generates eddy currents in the latter. The workpiece therefore becomes hot and the paint is heated from beneath the film solvent loss or curing occurs. 

Figure 7. Bonding metal to glass by means of electrical induction curing of a film adhesive.

Epoxy - One-part Epoxy One-part, induction cure ... 

Manufacturers Comments Self-levelling epoxy. Fast moderate Manutecturers Comments Fast induction curing, aluminium filled. ... 

New technologies which will impact the growth of adhesives in assembly line applications are robotics and induction curing. 

The process of building door assemblies requires the application of a structural adhesive to the outer door panel. The next step in the assembly of doors is the joining of the inner and outer panels. Finally, a hemming die is used to turn a small section of the outer panel over the inner panel to form a hem. Accurate bead placement and uniform material deposition are critical to achieve a structural bond. These requirements, combined with high production speeds, make hem flange bonding well suited for robotic automation. Fig. 11 depicts the entire door assembly line process complete with hemming die and induction cure fixture. The induction cure fixture applies localized... 

Joining of metallic parts (induction curing) or of metallic with nonmetal-lic substrates... 

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