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I'd like a lesson in Types of Heat Shrink Please


Hybrid_From_Hell
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Good Grief :blink:

I thought heat shrink was heat shrink, but now know otherwise.

What I don't know is that other than getting types with glue liners and non glue liners there are a selection of materials

Anyone explain to me in simple terms what is best for a Harness and to be still flexible, I THINK I should be going for ELASTOMER (flexible and Chemical resistant Non Glue Lined) , but not 100% sure ?

Types seem to be :

Polyolefin

Elastomer I fink :blink: is highly flexible

Flouropolymer - is this semi rigid from memory ?

Polyvinylidene - no idea ?

Nige

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I've worked in electronics for 20 years & I've never seen any that would remain flexible after shrink.

I dont see how it could, you are compressing the wires together.

If you want to leave a flexible loom, use a plastic braid sleeving.

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Guest diesel_jim

Whenever i make looms for my LR's (or mates LR's)... and i make quite a lot of them! i just wrap them up in black electricians tape.

cheap as chips, easy to do, /fairly/ flexible, easy to undo if you need to.

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Sorry I have to disagree. (Now) :ph34r:

My Mate has a loom I gave him from some S/H Eales Stuff I bought from a 4.8 engine,

The loom is an absolute masterpiece - a real work of art,

Every joint is completed sealed as is the harness and it is heatshrinked

After some 4 1/2 hours trwaling the net I have identified the maker of the components (and a chat with the retired harness maker) and got part numbers

Its the MIL Spec heatshrink, made in sizes (3.2mm up to 76mm) with a 1/3 max reduction on heat shinking - goes up in tiny amounts and it doesn't shrink that much from the specs - thats why you have to buy a size correct for the wires in the loom.................. and yes is espensive :blink::lol:

There are a vast number of sizes, (all in black) and the harness matey has on his racer is amazingly flexible,

The MIL Spec does not have glue in side it, but the joints do, but can bend like thick trailer cable.

I have now spoken to someone in the states and is a "radiation cross-linked Elastomer material" (sounds posh - and thus justifies the expense :lol: ) "designed for military applications to MIL-DTL-23053 for anti chaff anti oil fuel water fuild on wirning harness etc ....whilst keeping flexibility greater than normal PVC coverings or tubings"

Just need to capture Mr Piggy-Bank :lol: who after the call when I put the phone down went pale, shook and ran out not seen since :D

Nige

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PM'd to me by 02GF74 - posted here for benefit of forum

I didn't realise there was more than one type, the stuff sold in maplins - so you have push the bounds of heatshrink knowledge.

I am not sure what you will gain using it for the whole loom - all car looms I have ever seen use tape. (but then cost is an issue and most don't go wading).

For water proofing perhaps? well the wire is covered in plastic so putting another coat isn't gonna make it any better - the points that need it at are any connection points - and as you are starting a loom from scratch, there shouldn't be any joins - connectors being at the ends e.g. lamps and such.

heatshrink is expensive - but just because it costs more, doesn't mean it is better - life also will ge interesting for the heatshrink when you have wires coming off the main loom so the loom diameter changes - easly accomodated with tape but you'll need diferent dia. h/shrink.

It'll be interesting to find out what is use on aircraft - not that waterproofing is an issue and also on milatiry vehciles, if LR are anything to go by, then tape is the way.

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Most of the aircrarft I have worked on both large and small don't use much to cover the loom's. The older original fit looms are usually just string tied with a nomex string.

Newer looms for modifications and updates are some time sleeved in woven expanded sleeve (Snake Skin) which helps prevent chafing and seperates the looms for electro magnetic reasons, (apparently).

Splices in wires coming in a huge variety from shielded heatshrink envioronmental ones to bombtales with no sealing at all depending on where they are being used.

Some heatshrink is used but it tends to be for Ident labels and wire numbers (as most wires are white.)

Hth

Pete.

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As you have found out, there are a load of different types of heat-shrink; however all are manufactured to the same basic principle. The tube is first extruded at its final shrunk size, it is then irradiated (with gamma radiation usually as far as I can understand) to form crosslinks between the polymer chains. The last step is to heat the tube again and expand it (using air) up to the full size. Moulded parts are manufactured in a similar way except that they are injection moulded first.

A large range of polymers can be treated in this way, but the majority are traditional thermoplastics. A large proportion of elastomers are already crosslinked (vulcanised) as it is this property that is critical to their elastic behaviour, this is therefore likely as to why there is a small range of choice when it comes to elastomer heatshrinks.

By choice of material, and control of process, a range of different properties can be achieved such as variations in shrink ratio, temperature range, stiffness, wall thickness, fire retardancy etc.

The flexibility of the final loom is influenced by a range of factors;

Material of the heat-shrink, which elastomers are generally the most flexible

Wall thickness- a combination of shrink ratio and initial wall thickness

Adhesive lining- generally adhesive lining will increase stiffness

Loom makeup- Wire type, twist of loom (twisting with fillers to give a round loom improves flexibility), taping (some cables will have a thin non-adhesive tape wrapping the loom prior to shrinking to allow the tubing to slide over the bundle)

So onto different types-

This is all based on info from the Tyco/ Raychem catalogue- probably about the biggest manufacturer of these materials. Unfortunately it is not really easy to categorise the properties dependent on material, as there is such a wide range of options! The following is therefore a generalisation.

Polyolefin Typical 2:1 to 4:1 ratio -40°C to 80°C operating Flexible & semi-rigid versions

Elastomer Typical 2:1 ratio -75°C to 150°C operating Very flexible, Good diesel resistance

Flouropolymer Typical 2:1 ratio -55°C to 175°C operating Flexible & semi-rigid versions

Neoprene Typical 2:1 ratio -70°C to 120°C operating Very flexible

Polyvinylidene fluoride Typical 2:1 ratio -55°C to 175°C operating Semi-rigid

Silicone Typical 2:1 ratio -75° to 180°C operating Very flexible

PTFE Typical 1.8:1 ratio -67°C to 250°C operating Semi-rigid

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Loom makeup- Wire type, twist of loom (twisting with fillers to give a round loom improves flexibility),

Absolurely spot on

I have had a long conv today with a loom specialist, apart from probably having an obscene amount of money from me on my visit I will get a lesson in loom making........THATS what makes the difference, however I have another prob in that Raychem DR25 has a heat shrink level in excess of the normal wires heat limits :lol:

So will have to decide what to do...............

Ho hum

Watch this space

Nige :unsure:

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Absolurely spot on

I have had a long conv today with a loom specialist, apart from probably having an obscene amount of money from me on my visit I will get a lesson in loom making........THATS what makes the difference, however I have another prob in that Raychem DR25 has a heat shrink level in excess of the normal wires heat limits :lol:

So will have to decide what to do...............

Ho hum

Watch this space

Nige :unsure:

sounds like yer a bit FUBARed then, spiral wrap it is then :rolleyes:

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