Section 8 - Evaluating Quality

Production of high-temperature insulated wire is sensitive to a number of variables: raw material quality, extrusion temperature, curing rates, machine calibration and others. Up-to-date quality control measures such as statistical process control will ensure that high-quality standards are met.

Material Quality: Determine how well the wire manufacturer inspects raw materials. Conductors should be carefully checked for tensile strength and dimensional accuracy before use in wire construction. Insulating materials also should be tested frequently - lot by lot - for specific gravity, hardness and tensile strength.

Processing Controls: Question the supplier closely about processing controls. Make sure that thermoplastic or thermoset compound ingredients are metered and mixed properly. Poor blending causes surges and pulses during extrusion, resulting in displaced or "wandering" conductors, inconsistent wall thicknesses and alternating soft and brittle zones in the wiring insulation. In addition, explore how other production variables are handled. Undercuring can cause progressive shifting of the conductor and loss of tensile strength; overcuring produces spotty adhesion, termination problems in assembly and reduced thermal performance. Braiding, serving and taping equipment also require close control of calibration.

Saturants: Saturants or binders must be applied to glass or other braid materials in correct amounts to avoid such problems as porosity residual splinters on the wire surface, fraying and pushback. Wire should strip cleanly.

Conductor: Conductor cost and performance depends on type of stranding and on coating material and thickness, as well as basic conductor material. As an example, for greater crush resistance, concentric stranding is often specified, as opposed to less costly bunch stranding, which consists of wires twisted together without regard to orientation of individual strands. Or, to enhance soldering and assembly operations, a tinned copper treatment known as Tinned Prebond is used.