Plastic heater control lever.

[Tinkley]

Plumbers adhesive is meant for PVC pipefittings and it is specific to PVC. Most likely the heater stuff is Polypropylene for which there is a specific adhesive as it is one of the most difficult plastics to glue. It should somewhere on the part have the designation PP usually in the recycling triangular shape or near the date stamp (normally some circular design with month/year). In my experience the PP glues are not that good but they may have improved more recently. If it has the designation PE its polythene or polyethylene (both names are used - same stuff), and this will not glue at all. If the part floats its either one of the two, almost all other plastics sink in water.

For a stiff part like the lever I would expect the material to be 10% glass filled Polypropylene (PP). It is aslo possible that its Nylon 6 or 66 which also can be glass filled but its 3 times the cost.

Personally if repairing it, I'd make a splint as suggested and with epoxy and glass cloth wrap around the repair to hold it in place. Just glueing it on end is a butt joint, one of the worst you can have, so spreading the load with a structure will ensure it (the part) continues to do its job.

[Vanny]

Most likely the heater stuff is Polypropylene.

I know this is verging on going off topic, and i might need some re-education, but i thought polyprop is a thermo plastic, (can be remoulded with heat), and goes soft in the 60c* to 100c* range, and brittle at -20c*.

To me this sounds like a dreadful material to make a heater case out of, given that before coolant goes through it, a vehicle can see under dash temperatures of -40c to 120c just sitting outside (obviously not in Wales!).

I'd have thought a heater case would be made from a thermoset or something like HDPE?

I can't think i've ever seen a material marker on a BX part, i assumed they where too old for the recycling laws to have come in, but i'm intrigued to see what its made from now).


*thermal properties are from memory so could be well off the mark!

[Tinkley]

There is a large range of Polypropylene available for different applications. You are correct it is a thermoplastic. Your plastic kettle (if you have one) will be PP. It is a long chain polymer like PE. It is used for those cheap blue tow ropes right through to the fan blades on fairly serious paint extractors. Different additives can change the properties quite a lot, you have talc, glass beads, glass strand and other 'alloys' that improve impact resistance. I've been part of a team designing a couple of large suitcases and they are a high impact resistance PP. Of course it is used in its more basic form for packaging, little pots etc.
I bet BX radiator fan blades are PP with glass (strand) fill, whereas the air box stuff will be purer. The important thing is to select an appropriate heat range and allowable distortion for the application.
Since around 1995 a commercial glue for polypropylene has been available. It is not the easiest stuff to glue and dinghies such as the Topper are usually rewelded (yes its made of a foamed PP injection moulded) because this is generally a better long term fix. I would guess almost all 'plastic' car bumpers that have been injection moulded use a PP base. Some are quite sophisticated with the paint finish sprayed inside the mould prior to injecting the plastic.

As for temp range, if that lever (shown in photos) is exposed to 120° all the time it will be nylon. If it is only 105-110 at peak there is a good chance it will be PP. When testing proximity to heat sources we have found an air gap of 6-7mm from a 400°C non exposed flame source will give sufficient drop for the use of either Nylon or PP. Each application is slightly different so its worth testing in the real world with prototypes. Right first time is a nice idea but if you get it 95%+ right your doing OK. You need to check the Vicat softeneing temperature of the grade your using before selecting it.

You will find HDPE is very similar in performance to PP and it is often used as an alternative being approximately the same cost. Generally (and I stand to be corrected) it is not quite as heat resistant as PP, ie it becomes a bit softer earlier, but not by much.

The other joy of PP is chemical resistance - its very good. Regrettably this why most of the rubbish on our beaches is PP or PE because its cheap and takes a long time to break down, all the more reason to dispose of it properly. It can be recycled up to 5 times but you loose some properties each time so the load/application is a lower one each time. Best example is the grit bins at the side of the road, roto moulded in PP or PE and last phase recycling.

[Vanny]

Thanks for that Tinkley.

I have to ask, why are you putting suit cases next to a 400°C flame? Thats some serious air port security measure!

[Tinkley]

Cheers Vanny, actually note I said non naked flame heat source. In one case it was for an electric kettle with an underfloor external element. You don't really want the kettle base to collapse! Or for fun catch fire!. We also tested other ones and similar for toasters etc and often found problems with badly designed appliances (yes they had CE marks) whereby the plastic (whichever polymer used) distorted, bubbled or even charred. I consider some to be dangerous.

With the suitcases we had a 'baggage handler' test. Imagine a 3.25 metre (10ft in old money) tumble drier, now put in say a 100ltr suitcase with 30Kg inside it. The test was 30 minutes continuous tumbling with no broken latches, wheels, handles etc. Whilst I will admit our designs were not perfect first time, but with a very small ammount of tweaking they passed with flying colours. Client admitted the best they had experienced compared with previous designs (not ours), so having designed most of the mechanisms I was pretty chuffed. A lot of good design you don't notice, but boy do you notice bad design when it goes 'tits up'.
BTW the handles (on the cases) were filled Nylon because PP ones only did 10,000 pulls on the test rig before breaking. Nylon ones were still sound after 50-60,000 pulls....nuff said. Trouble is if you can't find the material marking you won't know. Also done things like laptop hinges and printed circuit connectors to do 150,000+ open/shut scenarios without failure.