Vulcanising press and edge iron check
Edge iron thickness and the platen length and width a splice needs, for a press set on the bias or square.
Result
How it works
Edge irons hold the splice width and set its finished thickness; they are made slightly thinner than the belt so the platens can apply pressure. The press platens must cover the whole splice plus an overhang at each end and side.
If the press is set square to the belt instead of on the splice bias, it must also cover the bias run-out. The undersize and overhangs are values from your press and splice-kit maker.
Formula
Edge iron thickness = belt thickness − undersize δ Platen length, press on the bias ≥ L + 2 × end overhang Platen length, square press ≥ L + La + 2 × end overhang Platen width ≥ B + 2 × side overhang
| Symbol | Meaning | Unit |
|---|---|---|
| L | Splice length | mm |
| La | Bias offset | mm |
| B | Belt width | mm |
| δ | Edge iron undersize from the maker (about 0.8–2 mm) | mm |
Worked example
Inputs: Measured belt thickness = 12 mm; Edge iron undersize (maker) = 1 mm; Belt width B = 800 mm; Splice length L = 740 mm; Bias offset La = 240 mm; Overhang at each end (maker) = 200 mm; Overhang at each side (maker) = 75 mm; Platen length = 1200 mm; Platen width = 1000 mm.
- Edge iron = 12 − 1 = 11.0 mm
- Press on the bias: 740 + 2 × 200 = 1140 mm ≤ 1200 → OK
- Square press: 740 + 240 + 2 × 200 = 1380 mm > 1200 → too short (needs 2 platens or moves)
- Width: 800 + 2 × 75 = 950 mm ≤ 1000 → OK
Assumptions and limits
- The 12 mm thickness and the overhangs are illustrations. Measure your belt and use your press and kit maker values.
- Edge irons must be straight, clean and the full splice length.
- Thermocouples on every heating element; follow the cure time, temperature and pressure in your instruction.
Screening estimate, not a design approval. Verify measured inputs, current standards, manufacturer limits and site procedures before purchasing, cutting or installation. Isolate and lock out equipment before any hands-on measurement.
Questions
How thick should edge irons be?
Slightly thinner than the belt — makers give about 0.8 to 2 mm undersize. Use your instruction’s value.
Why does a square press need to be longer?
Because the splice runs along the bias, a press square to the belt must also cover the bias offset.
Source notes
- Edge irons thinner than the belt (0.8–2 mm): NILOS, Sempertrans, Dunlop and Mercurio splice instructions. Platen oversize examples: NILOS 200 mm each end and 75 mm each side; Dunlop L + 300 / W + 200 mm; Ferroflex L + 200 / W + 100 mm. Summarised in original words.
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