The Granville silicone adhesive that I initially recommended does not exhibit the 'floppiness' of the neutral cure silicone you have used.
The Granville may have done the job well after taking the precaution of protecting the bare copper junction with a layer of paint or varnish.
However, I hesitate from encouraging you to experiment with the Granville as I have not used it in a situation where there is continual movement.
The Granville may have done the job well after taking the precaution of protecting the bare copper junction with a layer of paint or varnish.
However, I hesitate from encouraging you to experiment with the Granville as I have not used it in a situation where there is continual movement.
The Arbomeric MP20 sealant to which you linked in post #19 cures to form "a tough but elastic rubber".
That is precisely what the Granville adhesive does.
Note that the Sugru product to which you also linked "does not bond to oily plastics like polypropylene", so is not suitable for your polypropylene cone.
That is precisely what the Granville adhesive does.
Note that the Sugru product to which you also linked "does not bond to oily plastics like polypropylene", so is not suitable for your polypropylene cone.
Thanks @Galu. I was hesitant about the Granville last week, because it's an acetoxy cure silicone, (although I note that its datasheet says it's suitable for electrical connections - and I guess varnish first would help). But I'm now more wary of silicone in general, in this application.
It's not only Sugru. Polymers, silicones, cyanoacrylates and hot glues are all classed as being unsuitable for polypropylene, it seems. As far as I can tell the only glues claiming suitability are specialist industrial products. Priming appears to be the recommended workaround.
After my experience so far, I'm concerned about the need to hold the joint in place without flexing, so that it moves as one with the cone at all times. All silicones are flexible, even the high modulus ones (and the Granville datasheet says nothing about modulus). Also the polymer products I mentioned previously, including Sugru, cure to form a synthetic rubber - which is still quite elastic.
However hot glue, once set, is not really flexible at all - but I guess not so brittle that it can't cope with the cone vibrations. I'm now leaning towards using it, second time around. While it's true that the original hot glue blob failed, it's still the case that some variety of hot melt glue was chosen by the driver manufacturer originally (and other plastic cone driver manufacturers, going by what @Stuey says), and I guess they knew what they were doing. I haven't read of any similar failures on Usher drivers. (I know there's been an issue with some Scanspeaks, but that seems to be a corrosion problem, primarily, rather than an adhesion one.)
My remaining hesitation is simply because I don't know whether the hot glue sticks widely available, and usable in the manner @Stuey suggested, are going to adhere well to the cone, even once it's been treated with a primer.
Anyway, I've removed the silicone. The solder joint gave way, so that will need to be re-done. There's no visible residue on the cone, and I've scraped off some hot melt residue that I left on last time. I'm not going to risk using a silicone solvent, incase it damages the cone. (In any case, its primary use is to remove visible silicone.) I think I'm going to use the Loctite SF 770 primer, and I'll clean with isopropyl alcohol, first.
All observations welcome!
I wonder if it is worthwhile to hold the tinsel lead to the cone with a small stitch of thread through the cone. Hate to resort to that but adhesive failures seem to be a problem in this case.
I read that polypropylene has a very low surface energy, which means that most glues can't adhere to the material.
Apparently, for a successful bond, the surface energy of the adhesive must be lower than that of polypropylene.
To back up your use of a primer, chemical pre-treatment can enable the use of non-specialist glue*.
However, I've found a specialist, low surface energy, primerless polypropylene glue: https://www.forgeway.com/products/purok/vx90
Unfortunately, it may not be available in small quantities.
Learning all the time!
P.S. The problem with what daqvin_carter has just suggested is that the process of drilling holes through the polypropylene could weaken it.
*P.P.S. The Loctite SF 770 primer sounds just the job as it makes low energy surfaces suitable for bonding with non-specialist adhesives.
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It's a thought - if the primer/hot melt method doesn't work, I might have to resort to that.
I've discovered another potential hitch, however: most hot melt glue seems to need to be near 200 degrees celcius to work. But the melting point of polypropylene is about 160 degrees. Not good.
Fortunately there are versions of holt melt glue that work at around 135 celcius - sold as 'cool melt' glue sticks. I think I'll go for those.
For the purpose of reference:
I found this link that describes the range of adhesives used in loudspeaker assembly: https://ctaltd.co.uk/loud-speaker-adhesives/
There are a two mentions regarding the bonding of polyolefin plastics such as polypropylene.
P.S. Elsewhere I read that hot glue has a low bond strength and may not adhere properly to the material of the cone. Additionally, hot glue can become brittle over time, causing the bond to fail.
I found this link that describes the range of adhesives used in loudspeaker assembly: https://ctaltd.co.uk/loud-speaker-adhesives/
There are a two mentions regarding the bonding of polyolefin plastics such as polypropylene.
P.S. Elsewhere I read that hot glue has a low bond strength and may not adhere properly to the material of the cone. Additionally, hot glue can become brittle over time, causing the bond to fail.
Brilliant thanks. Really interesting info, and many products available in small quantities. Some of the info is a bit confusing - e.g. they suggest Hernon Supertacker 358 for polyolefins (which includes polypropylene) and for gluing lead out wires to cones, but the datasheet for 358 says it's not recommended for polypropylene. It's a bit of a minefield. I might email them.
Sorry I hadn't noticed this thread before.
Yes you can be successful with this.
Do not attempt to use anything silicone based. None of them are suited for this application and have very poor long term adhesion to polypropylene.
You need a glue gun (very inexpensive at your local discount store).
You need specific polypropylene based glue sticks, not available everywhere. Super Tac 500 is one I have used but I am sure there are others. I am also quite certain that is what the driver manufacturer used.
You do not need a primer, you need a proper, non residue cleaner such as Isopropyl alcohol or methyl hydrate. Both work if the surface is free of residual silicone. It should be, as it never bonded fully to begin with.
Good luck with it. I know there are lots of choices being offered but I am seeing speculation when I think we have a tried and true method here.
Yes you can be successful with this.
Do not attempt to use anything silicone based. None of them are suited for this application and have very poor long term adhesion to polypropylene.
You need a glue gun (very inexpensive at your local discount store).
You need specific polypropylene based glue sticks, not available everywhere. Super Tac 500 is one I have used but I am sure there are others. I am also quite certain that is what the driver manufacturer used.
You do not need a primer, you need a proper, non residue cleaner such as Isopropyl alcohol or methyl hydrate. Both work if the surface is free of residual silicone. It should be, as it never bonded fully to begin with.
Good luck with it. I know there are lots of choices being offered but I am seeing speculation when I think we have a tried and true method here.
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SuperTac 500 "high temp hot melt" doesn't seem to be available in the UK: https://www.hotmelt.com/products/plastics-hot-melt-glue-sticks
However, the link mentions some comparable glue sticks including the 3M 3731 which is available in the UK and has the capability to bond to low surface energy substrates. It requires a temperature setting of 4 or 5 on an EC heat gun (is that cool enough?): https://www.zoro.co.uk/shop/adhesives-and-sealants/hot-melt-adhesives/hot-melt-adhesive-3731-pg-tan-1-in-x-3-in-22-lb-case/p/ZT5136187S?utm_source=awin&utm_medium=affiliates&utm_campaign=unknown&utm_content=39135959115 | 0&pub_a_id=1454694&awc=27732_1736457826_c938c7cd1058df996777db25c378bc0f
Full details of the 3M product are here: https://www.3m.co.uk/3M/en_GB/p/d/b40065542/
Thanks! I've found some Bosch glue sticks for plastics, including polypropylene apparently: https://www.amazon.co.uk/gp/aw/d/B00SJ8RO0E/ref=ox_sc_act_image_2?smid=A30DC7701CXIBH&psc=1
They need a temperature of at least 160 C. I've found a gun that takes that size of stick and operates at 165 C: https://www.amazon.co.uk/gp/aw/d/B004MKMWSW/ref=ox_sc_act_title_1?smid=A3P5ROKL5A1OLE&psc=1
Cost is modest. I think I might be in business.
They need a temperature of at least 160 C. I've found a gun that takes that size of stick and operates at 165 C: https://www.amazon.co.uk/gp/aw/d/B004MKMWSW/ref=ox_sc_act_title_1?smid=A3P5ROKL5A1OLE&psc=1
Cost is modest. I think I might be in business.
The last repair I did was bridging a crack in the cone. It was done on the back of the cone. I did not use a scrim, just the glue and of course it was tooled flat with my finger covered in parchment paper.
And yes, I did the same thing on the opposite side of the cone that was not damaged, for balance.
And yes, I did the same thing on the opposite side of the cone that was not damaged, for balance.
Hehe, boy am I glad we've never met face to face. Your kind thoughts might go right out the window 🙂
We use a blow lamp or heat gun on polypropylene before printing, either pad or screen, it is good for about ten minutes.
A brief puff like pass, just enough to gently wipe the surface with heat.
Another alternate chemical is called 'surfacer' here, it is used to prepare car bumpers for painting, it is a liquid.
Car bumpers are mostly filled polypropylene, 'PP' for us plastics people.
Hot glue is mostly modified LDPE, same as for plastic bags, will stick to PP if the PP is not coated or old, which may need a brief puff of hot air, or cleaning either mechanically or by solvent.
Third method is the glue used to coat sticker sheets, that sticks...we get stickers printed on coated sheets, which are then die cut, we peel off the stickers, and stick them to the containers.
The adhesive sheets are backed by release paper, it is white top, then adhesive, then backing paper.
For jewelry boxes, we used to make a laminate of velvet fabric, sticker adhesive, LDPE foam, release paper and die cut when dry (next day).
That is a sample...I make them off and on at my plant, no need to show off really.
A brief puff like pass, just enough to gently wipe the surface with heat.
Another alternate chemical is called 'surfacer' here, it is used to prepare car bumpers for painting, it is a liquid.
Car bumpers are mostly filled polypropylene, 'PP' for us plastics people.
Hot glue is mostly modified LDPE, same as for plastic bags, will stick to PP if the PP is not coated or old, which may need a brief puff of hot air, or cleaning either mechanically or by solvent.
Third method is the glue used to coat sticker sheets, that sticks...we get stickers printed on coated sheets, which are then die cut, we peel off the stickers, and stick them to the containers.
The adhesive sheets are backed by release paper, it is white top, then adhesive, then backing paper.
For jewelry boxes, we used to make a laminate of velvet fabric, sticker adhesive, LDPE foam, release paper and die cut when dry (next day).
That is a sample...I make them off and on at my plant, no need to show off really.
The brand of sticker adhesive we used here was 'Emdilith", it looks like PVA wood adhesive, but smells different, and cannot be diluted with water, you need screen printing ink solvent to dilute it
.
.
No ties to the brand, it was given to help you find a similar product in your country if needed.
The sticker on top of the container was printed on ready 'gum sheets' which claimed to be coated with 'hot glue'.
Such an adhesive may be available in handy packs in your country, here the smallest I could find was a kilo...ask in shops selling printers' supplies.
The sticker on top of the container was printed on ready 'gum sheets' which claimed to be coated with 'hot glue'.
Such an adhesive may be available in handy packs in your country, here the smallest I could find was a kilo...ask in shops selling printers' supplies.
Can the glue sticks come in black? I notice the cone is shiny, and I have IR heating in mind. What is the other side? is cooling an option. It would be nice to get in there and really melt the glue, but obviously the temps are close. Foil tape or simply foil might be of use, while you move in with a hot iron. I have worked hot glue into puddles with an iron held close. Getting it deep into plastic mouldings, the gun couldn't. Perhaps an old iron, with no tip, and a little insulating wrap, would give a 10mm hot disk to get near the glue with. Wet tissue on the other side would be very useful. You must of seen the pub trick with a paper bank note and cigarette on somebodies arm.
Just some thoughts..
Superglue all plastics? It's supplied with a surface preparation fluid. Listed for these types of plastics.
Just some thoughts..
Superglue all plastics? It's supplied with a surface preparation fluid. Listed for these types of plastics.