Multi-pass cold drawing through tungsten carbide and single-crystal diamond…
Drawing Process
Cold Drawing Sequence
- Rod in — hot-rolled wire rod (φ5.5 mm) enters the multi-pass drawing machine.
- Draw — each pass reduces the cross-section by 15–25% through progressively smaller tungsten carbide dies, with lubricant applied at every die entrance to control friction and temperature.
- Anneal — intermediate H₂/N₂ annealing between passes restores the ductility that cold work removes.
- Finish — after 13 passes the wire reaches φ0.025 mm, thinner than a human hair, held to ±0.005 mm.
Equipment
- Multi-block continuous drawing line — 13 dies
- Tungsten carbide dies (roughing, φ5.5→0.5 mm)
- Single-crystal diamond dies (finishing, φ0.5→0.025 mm)
- In-line laser micrometer — ±0.001 mm resolution
- Eddy current surface inspection — 100% coverage
Why diameter tolerance matters
Thermocouple wire diameter directly affects thermal response time (halving diameter ≈ 4× faster response), electrical resistance (φ0.025 mm Type K ≈ 1,900 Ω/m vs φ1.0 mm ≈ 1.2 Ω/m), and mechanical service life (doubling diameter ≈ 3× longer fatigue life).
For aerospace engine testing where millisecond response is critical, we supply wire at the fine end of that range. For industrial furnaces with multi-year service intervals, φ1.0–3.0 mm is standard. Our drawing capability spans the full range from one extreme to the other — all from one in-house process with full traceability.
Frequently Asked Questions
What diameter range can be drawn in-house?
φ5.5 mm hot-rolled rod down to φ0.025 mm finished wire — thinner than a human hair — with custom diameters from φ0.015 mm to φ8.0 mm available on request.
What tolerance is held on finished diameter?
±0.005 mm on finished wire, measured by an in-line laser micrometer with ±0.001 mm resolution, with 100% eddy-current surface inspection.
How many drawing passes does it take and why does that matter?
φ5.5 mm to φ0.025 mm takes 13 passes, each reducing cross-section by 15–25%, with intermediate H₂/N₂ annealing between passes to restore ductility. Without that annealing the wire work-hardens and the EMF drifts.
How does diameter affect thermocouple performance?
Halving the diameter makes response roughly 4× faster but shortens fatigue life, and resistance rises sharply at fine sizes — φ0.025 mm Type K is about 1,900 Ω/m against 1.2 Ω/m at φ1.0 mm.
Bottom line: Drawing is a ductility problem before it is a diameter problem: 13 passes from φ5.5 mm rod to φ0.025 mm wire, with intermediate H₂/N₂ annealing between each pass to prevent work-hardening. The payoff is a single in-house process holding ±0.005 mm across the full range, from millisecond-response fine wire to multi-year industrial diameters.