5 furnace setups, Box Furnaces: Type K, φ0.5–2.0 mm
| Application | Typical conditions | Recommended wire |
|---|---|---|
| Box Furnaces | Batch heat treatment of tools, dies and components. Steady-state temperature control for carburising and hardening cycles. | Type K, φ0.5–2.0 mm |
| Vacuum Furnaces | Low-pressure heat treatment of aerospace alloys and tool steels. Requires minimal outgassing and stable EMF in vacuum. | Type N, φ0.25–1.0 mm |
| Pit Furnaces | Vertical furnaces for large shafts, tubes and wire coils. Long immersion lengths — stranded wire for vibration resistance. | Type K stranded, φ1.0–3.0 mm |
| Continuous Annealing Lines | Wire, strip and tube pass continuously through a heated zone. Fast-response bare wire for rapid temperature tracking. | Type K, φ0.1–0.5 mm |
| Ceramic Kilns | Batch and tunnel kilns for tableware, technical ceramics and refractories. Oxidising atmosphere, 900–1300 °C. | Type K or N, φ0.5–1.5 mm |
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Atmosphere
Endothermic gas (carburising): Type K. Vacuum or reducing (nitriding): Type N. Type K develops green rot in low-oxygen atmospheres above 800 °C.
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Temperature uniformity
AMS 2750 (aerospace) requires ±3 °C uniformity. Choose Class 1 / Special Limits tolerance wire and calibrate at the furnace survey interval.
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Mechanical life
Furnace charging and thermal cycling flex the wire repeatedly. Stranded wire lasts 3-5× longer than solid in pit and box furnace installations.
Frequently Asked Questions
Which thermocouple type suits a vacuum furnace?
Type N, φ0.25–1.0 mm. Type K develops green rot in low-oxygen atmospheres above 800 °C, so the vacuum processes used for aerospace alloys and tool steels call for Type N.
Why is stranded wire used in pit furnaces?
Charging and thermal cycling flex the wire repeatedly over long immersion lengths. Stranded Type K, φ1.0–3.0 mm, lasts 3–5× longer than solid wire in pit and box furnace service.
What tolerance is needed for AMS 2750 uniformity surveys?
Class 1 / Special Limits wire, holding ±3 °C uniformity across the survey and calibrated at the furnace survey interval.
What diameter is used on continuous annealing lines?
φ0.1–0.5 mm Type K bare wire. The thin section tracks the heated zone fast enough to follow line-speed changes.
Bottom line: Match the alloy to the atmosphere first: Type N for vacuum and reducing furnaces, Type K for carburising and clean oxidising service. Then match the form to the mechanics — stranded wire for pit and box furnaces where charging flexes the conductors, thin bare wire where line speed demands fast response.