How to glue plastics

Hi

I am asking for help please? How to glue polyethylene to stainless steel. I have i think a polyethylene injection moulded pulley wheel shalt with a damaged gear shaft I want to bond a new gear cog over the boss what glue can is best to do this. The loads are not heavy. I have a photo if I can attach it to the link!

Many thanks

Nigel Jaques

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Thank you B

I don't know how to upload the photo I took of the parts.

Nigel

Some plastics are notoriously difficult to glue reliably. Polythene (= polyethylene) is such a material. If you can arrange a fairly robust mechanical joint, it may help to 'improve' the situation with a Loctite type product. but are you sure your shaft is Polyethylene and not polypropylene or nylon or acetal (etc) ?

Cheers, Tim

Hi Tim

Thank you for your reply I have a photo of the parts which I don't know how to load so help is sort The photo would explain a lot. I am not sure which plastic it is but I believe it is an injection moulding the cog will slide over the plastic< make a firm push fit

ThanksNigel

Posting photos - not obvious! Read all about it here.

Dave

Hi Everyone,

I have managed to load a photo of the parts

Nigel

1. Looking at your pic I am assuming that there are two remnants of teeth on the pulley wheel boss 180* apart ?

2. Is the ID of the replacement gear larger than the OD of the remaining teeth;

In which case you could place the new gear over the boss & epoxy resin / JB weld infill the space remaining. If not alternatively remove the remaining teeth fit the new gear cog & if there is sufficient gap between the two Loctite with Loctite 638 retainer.I would also mechanically lock the two together.. e.g.drill & tap through the root of one tooth for 3-4mm grub screw. Gorilla glue is surprising strong as well.. usual disclaimer applies.

George.

You can glue most hard plastics except ABS (which requires a specialist glue)

Model suppliers will have the best range.

Hi. I've not got time at the minute to check the spec sheets - but 3M do some adhesive that should do the job. From memory DP8005 should do the job......check their site.

Rgds.

Mike

Hi do not want to put a downer on this but if you are trying to bond polyethylene you are going to be disappointed as there are, to my knowledge, no conventional adhesives that will bond to polyethylene with any degree of adhesion under normal conditions.

Your best bet is to find a way to mechanically fix the gear such that it is keyed in some way.

First I would check what material the pulley is made of. Plastics that are characterised as olefins are notoriously difficult to bond to. Other plastics can be bonded but it is important to find what the material is.

Steve

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Barrie,

The link you attached makes for interesting reading. Coming from the plastics industry I am aware and have used corona treatment prior to printing or applying coatings to plastics. Flame treatment was always something that was hit or miss and potentially dangerous in the environments in which we used to work and therefore was not suitable.

I would take issue with the accuracy of the document since it clearly states " The material itself is not particularly high performance and will deform and melt at high temperatures and be easily attacked by solvents. This makes solvent welding, ultrasonic or infrared welding or induction heating a good method of bonding polyethylene (to itself)"

I am not aware of any commonly available solvents for polyethylene - hence why it is used for packaging acetone and other highly volatile solvents and is used for the storage of hydrofluoric acid.

Flame treatment is a method that works but requires a fairly high level of skill to reduce the surface tension of the PE yet not melt or deform the base material.

Steve

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Ok, here I cannot have my mouth shut. I suppose in that sentence a 'not' is missing.

ABS is one of the easiest plastics to glue. It can be dissolved in Acetone (every 3D-printer knows that), and bonds also to Epoxies and Acrylics.

For 'most hard plastics', the secret lies in the preparation. I see that the flame treatment has already been mentioned, and with this method I glued two plates from (I suppose) Polypropylene, and it would be very hard to separate them again.

The method consists of 'brushing' the parts with a Propane torch or similar, without melting the plastic, but it becomes then hydrophilic (in contrary to the water-repellent or hydrophobe surface the plastic usually has).
It is best to try this before if you have an offcut , if water builds a film instead of dropping off, you got it right.

I think I saw this method in one of the well-known Dan Gelbart videos.

Regards,
Hans

I worked in the plastic pipe industry, making PE and PP pipes, all the purple pipe you see down motorways etc is mainly PE and is flame treated so that the print will stick to the pipe. Flame treat was phased out and we went to a plasma treatment and finally the ink producers made an ink that would stick and meet the requirements for print adhesion.

Not much will stick to PE or PP.

There is no point guessing what the plastic is you need to have a better idea. Looking at the photo I think Polyethylene is unlikely to be the material, it is too soft to make a ridid wheel lik the one shown. A couple of quick checks could be carried out on a sample (one of the remaining teeth would do). First is to try disolving it in an aggresive solvent like acetone (nail varnish remover if you don't have the pure kind). If it softens or dissolves it's unlikey to be PE, PVC or polypropylene and can for your application be glued with epoxy, just abrade the surfcae well.

If it does not dissolve try the tests here:

https://www.twi-global.com/technical-knowledge/faqs/faq-how-using-simple-manual-tests-can-i-identify-an-unknown-plastic-material

If the wheel runs on a shaft, whatever plastic it is, if you cut LH and RH grooves in the surface an epoxy would probably make a adequate mechanical joint regardless of surface adhesion. There is big surface area and the joint is in shear both of which are good for a bonded joint.

Robert G8RPI.

I agree with Robert ....

For ease of reference, I have copied Nigel’s photo to my Album and posted it here:

.

The choice of background colour is perhaps unfortunate, but the ejector pin marks are quite evident and there is some identification numbering visible [which appears to have been in the tool before the spokes were created]

It is impossible to tell from the photo, but: to me, this doesn’t look like a polyethylene moulding.

... and the snapped-off gear teeth certainly suggest something much more brittle !

My guess would be either polystyrene or ABS

MichaelG.

Edited By Michael Gilligan on 08/06/2020 09:03:32

Going to the expense of generating a Stainless Steel gear would better be served by manufacturing the rest of the finished object from a material suited to mechanically fixing the parts together. Watch wheels and pinions are a good example in this case.ie. make a backplate and pulley from metal and join the two.

Regards Ian