Resistance Wire And Induction Welding

RESISTANCE WIRE AND INDUCTION WELDING:

1. A wire of high electrical resistance (nichrome wire) is placed between the mating surfaces of the two thermoplastic parts.

2. Current flow in the wire generates heat to soften the adjacent plastic surfaces which can be pressed together to complete the joint

3. The wire will remain in the joint

4. High speed welding process.

5. Any thermoplastic could be welded.

An electrically conductive wire or braid is placed in the joint interface. 

The wire is connected to an electric circuit and an electric current generates heat in the weld zone through resistance losses. 

The heat generated depends on the electrical resistance and is expressed by the equation: 

Where, E is the heat energy, I is the current, R is the electrical resistance of the wire and t is the time that the current is applied

The two parts are joined under pressure and the plastic that surrounds the wire is softened or melted by the heat. 

The plastic solidifies when the electric current is switched off and the bond is formed. 

DIELECTRIC OR HIGH FREQUENCY HEAT SEALING

1. Involves the use of electronic waves from an AC generator passing through a plastic sheet or film.

2. These waves causes high level molecular friction with in the plastic so that heat is generated with in the plastic and the plastic will melt at the point of contact.

3. By applying pressure at this point and allowing sufficient cooling time, a permanent bond is formed. Plastics commonly used ABS, PVD, PMMA.

4. Biggest use vinyl films  raincoats, inflatable etc.

Advantage

1. Suitable for very large parts due to the minimal equipment requirements

2. Reversible process, which permits repair of misaligned joints and defective components, and also improves recyclability.

Disadvantage

1. A sacrificial heating wire is required, which remains in place after welding, adding to the process costs. 

2. The presence of the wire in the weld may have a negative influence on the weld strength.