Recovery
Installing heat shrink tube: heat, distance and stroke order
125 °C is published against the material, never against a tool. No tube datasheet in this range gives a setting, a distance or a dwell — three cap sheets do, and this page works from those.
Four things settled before any heat arrives
Cut length. Longitudinal change is capped at −10 percent maximum on every tube sheet here — thin wall, vented, dual wall, medium and heavy wall, 5:1 and double layer alike. A 300 mm piece can finish near 270. The cap sheets ask for sufficient overlap at each end, and the missing 30 mm eats that overlap first. Maximum cut length on GMW and GHW is 1200 mm, where the same percentage is 120 mm of travel.
Position. Slide every length onto the run and park it clear before a lug is crimped. Nothing gets past a finished connection, and a recovered wall will not slide.
Substrate. Cut the end straight and even, then clean and de-grease every surface the wall or the sealant will touch. Both torch sheets open on that instruction and neither offers an alternative to it.
Size. The manufacturer's own selection rule is a tube that recovers to slightly smaller than the thing it goes on. Recovered ID under the smallest diameter on the run, supplied ID over the largest, enough wall left afterwards. Bands for every series are on the heat shrink size chart.
What the sheets publish about heat
| Series | Shrink temperature | Continuous limit | Heat shock | Method |
|---|---|---|---|---|
| GSC, GLC thin wall | Not published | −55 to +125 °C | 250 °C, 4 hrs | IEC 216 |
| GLC-SV vented thin wall | Not published | −40 to +125 °C | 250 °C, 4 hrs | IEC 216 |
| GDW dual wall, outer wall | Not published | −55 to +125 °C | 250 °C, 4 hrs | IEC 216 |
| GMW medium wall, GHW heavy wall | 125 °C | −40 to +110 °C | 250 °C, 30 min | IEC 216, ESI 09-11 |
| GMW 5x | Not published | −40 to +110 °C | 250 °C, 30 min | IEC 216, ESI 09-11 |
| GDLT double layer | 135 °C | −40 to +100 °C | 250 °C, 30 min | IEC 216, ESI 09-11 |
Every figure here is measured on the material. Not one of them is a setting for a tool.
Two rows above carry a shrink temperature. Four do not.
GMW and GHW give 125 °C, GDLT gives 135 °C, and that is the whole list. The thin wall, vented, dual wall and 5:1 sheets each carry a complete thermal block with no recovery figure anywhere in it. What they give instead is the heat shock row, which is an oven result and an upper bound — not a target to work to. Do not borrow the 125 °C off the medium wall sheet into a method statement for thin wall. Ask for the figure in writing.
The only published recovery band: 100 °C to 130 °C, on GDLT
The double layer sheet is the one part in this range that says where recovery starts and where it completes — minimum shrink temperature 100 °C, minimum fully shrink temperature 130 °C. Thirty degrees separate a tube that has begun moving from a tube that is done. Nothing else in the range prints that pair, which is why every finishing test below is dimensional or visual rather than thermal.
Not published: an installation sheet for tube
Search the ten tube datasheets in this range for the word instruction and it returns nothing. Step-by-step sequences exist on exactly three sheets — Polecap, Dock Pile Cap and InsulCap-Live — and all three parts have a closed end, which is precisely where their sequence says to begin. A tube has two open ends and no closed one. Kits are different again: a joint or termination kit lists an Installation Instruction Manual among its supplied components, and a spool of bulk tube does not. What follows is those three sheets read onto a tube. Where a line is this site's rather than theirs, it says so, and anything packed with a kit overrides all of it.
Stroke order
Seven moves. The manufacturer's own wording is set in italics; the rest is marked extension.
Set the flame before it touches the work
Use a propane (preferred) or butane gas torch. Then: adjust the torch to obtain a soft blue flame with a yellow tip. Pencil-like blue flames should be avoided. Work with the outer 3-4 inch tip of the flame with a rapid brushing motion — the sheets' own unit, and the only working distance published anywhere in the range.
Begin at one end, never at both
The published sequence starts at the closed end and working towards the Pole: one direction, no return. A tube has no closed end, so pick one and commit to it. Extension — the sheets never rule out closing both ends first, because on a cap the choice does not exist.
Keep it moving
Keep the flame moving continuously to avoid scorching the material. That sentence is on both torch sheets and it is the only defect-prevention instruction the manufacturer publishes. Do not park the tip, do not orbit a fixed point, and do not go back over a section already down.
Turn the work, not the heat
Extension. Rotate the cable or the bolt so every face takes the same pass at the same distance. A cap is heated all round a single closed end, so nothing published covers a second face.
On adhesive-lined tube, keep going
Polyolefin recovers first and the hot melt beneath it moves second. The sheets give the signal but not the timing: adhesive will be visible at ends. Until it is, the outer wall is finished and the lining may not have started. Extension — carrying on past the point the profile stops changing is this site's line, because no flow temperature for the lining appears on any sheet.
Stop at recovered ID
Two published acceptance criteria, both visual: the part should be smooth and conform to what it covers, and smooth and without wrinkles. Neither is a temperature. Check the result against the recovered diameter on the row you ordered, not against how tight it feels.
Leave it alone until it is cold
Allow the cap to cool before applying any mechanical strain closes both torch sheets. No pull, no bend, no clamp, no cable dragged through. Warm polyolefin still moves and warm hot melt has not set.
Adhesive-lined work, and the one tube that ignores the wrinkle problem
GDW recovers 0.35 mm of hot melt against the substrate at size 3/1 and 0.9 mm at 50/17. The lining is the product; the outer wall carries it.
- The bead is the only inspectable thing. Adhesive will be visible at ends is the acceptance criterion, and it has to show all the way round at both. Nothing on the outside of the tube reports on what the layer underneath did.
- Recovered is not sealed. A GDW length gripping hard with clean dry ends has done the insulating half and none of the sealing half — the IP 68 claim sits on the lining. Sizes and adhesive thicknesses: dual wall adhesive lined tubing.
- A plain wall seals nothing by closing. GSC, GLC, GMW and GHW without a lining recover onto the substrate and stop there. GMW, GHW and the 5:1 series each take an optional hot melt lining to IP 68 — order it and the end bead becomes your finishing signal too.
- GLC-SV is the exception on bends. An internal air-vent groove in the bore lets it recover wrinkle-free over a bend without grease or any other lubricant, at 2:1. Eight sizes, 20/10 to 70/35, leaving 0.78 to 1.10 mm of wall. A design feature of the part, not a licence to move faster.
Five families, five finishing signals
The last column is the one that costs money.
| Series | Ratio | Finished looks like | What it does not prove |
|---|---|---|---|
| GSC, GLC thin wall | 2:1 | Wall down on the substrate, no shoulder bridged | Nothing about sealing — there is no lining to flow |
| GLC-SV vented | 2:1 | A bend coming out wrinkle-free, no lubricant used | Nothing about the thread or fastener underneath |
| GMW, GHW | 3:1 | Bore closed to the published recovered ID, ends laid flat | Whether an optional lining flowed, if one was ordered |
| GMW 5x | 5:1 | One length down over a connector and its cable together | That the step underneath was inside the 5:1 range |
| GDW dual wall | 3:1, 4:1 | Adhesive standing proud right round at both ends | Nothing about abrasion on the outer wall |
Asked at the bench
Torch or hot air gun?
Why does the surface scorch before the wall comes down?
It did not go down fully. Can it be re-heated?
Why did the ends pull back off what I measured?
Where this sits in the sequence
Sizing comes before this page. Diagnosis comes after it.
- Shrink ratio explainedWhat each ratio buys, before a size code is picked.
- How heat shrink tubing worksCrosslinking, expansion, and why recovery runs one way.
- Why a recovered tube failsFive faults, most of them made inside the first minute of heat.
- Heat shrink size chartEvery series named here, by diameter and by wall.
- The jointer's sequence, on cablejointkit.comCutback, screen, stress control, earth path — the MV order of work, on a sister site in this network.
Send two diameters and the substrate
Little of this is settled with a torch in hand. Send what the tube must clear at its widest, what it must close onto, the finished length, the substrate, and whether a flame is permitted on site.