Author Topic: Joining polypropylene  (Read 11105 times)

Offline picclock

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Joining polypropylene
« on: October 16, 2010, 03:38:56 AM »
I need to fabricate a part out of polypropylene. This is a part which has internal vanes and rotates and the exterior is cone shaped so although it could be milled out of solid it would be very difficult. I'm looking for a good way to weld/glue the constituent parts.

Any advice much appreciated.

picclock

« Last Edit: October 17, 2010, 05:50:04 PM by picclock »
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Offline DMIOM

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Re: Joining polypropylene
« Reply #1 on: October 16, 2010, 04:33:00 AM »
I have done this a little, but with improvised equipment; all involved using a dry heat source.

After tacking just using the hot bit from an old Weller soldering iron, first attempts to actually hot-air weld were made using a paint stripper hot air gun and then a more controlled source from my heat-shrink sleeving gun to heat two adjacent edges sufficiently to get them to weld together - very hard to get enough, but not too much, focussed heat. Improvising more constricted nozzles and using filler rod (initially thin 3mm square cut from the edge of a sheet, then proper rod) gave better results but the speed of movement along the weld line had to be quite high to avoid over-heating.  Sectioning it showed defects and the rod sitting in the apex or alternatively the weld pool had been blown away.

The breakthrough for me was switching to a lower-volume air source using my hot air soldering/rework station which has a highly controllable hot air flow (temp & flow rate) and a range of nozzles. At first I thought the air flow rate was too low, but the slower, more measured work rates allow a far better weld. I did find though that having enough hot air in the vicinity to keep the two workpieces sufficiently hot meant that the filler rod was too soft to get it pushed into the apex, so eventually I modified a soldering nozzle for welding by adding a one-inch filler rod sized metal tube alongside the hot air nozzle to (a) guide the rod down to the weld point, (b) shield the rod from most of the heat until it emerged to the weld pool, and (c) with a flared 'shoe' at the exit point to keep pressure on the rod into the corner. Using this rig I have been able to weld polyprop for various small covers, cases, low-stress fittings etc. (including running multiple beads) but nothing that I've ever done has been for use with chemicals or at pressure etc...

As with heating any plastics - needs good ventilation and usual spatter protection.

Dave
« Last Edit: October 16, 2010, 05:02:07 AM by DMIOM »

Offline Bogstandard

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Re: Joining polypropylene
« Reply #2 on: October 16, 2010, 04:35:26 AM »
Apart from heat welding, I don't think that there are any chemical ways of doing it (well none available to the general user), so to my way of thinking it with have to be done mechanically, such as threaded joints, or close tolerance fits and pinning.

Here are a couple of search engine 'hits'

Quote
There is NO adhesive for 'butt joining' Polyethylene (or Polypropylene, for that matter). Were someone to invent a good 'glue' for Pe they'd be an immediate billionaire!

There are two ways only of making a successful joint.

The first one is butt fusion. This requires a Teflon coated heating plate & pressure. After getting the material to the right 'fusion' temperature, one forces the two pieces together. For small diameters, this can be done by hand. For large diameters, you need a machine, ie. CHEVRON, U.S.A. amongst others makes h.d. Pe pipe up to 4 feet diameter. They use butt fusion machines to get around 100% weld strengths.

But to contradict both mine and the above, I found this.

http://www.highbeam.com/doc/1G1-108837737.html


Bogs

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Offline HS93

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Re: Joining polypropylene
« Reply #3 on: October 16, 2010, 05:03:04 AM »
have a look at  http://www.glue-shop.com/

Universal Bonding Pack!
  Special adhesive that bonds
ANY METAL, ANY PLASTIC
ANY RUBBER, ALL CHINA
ALL STONE ,ALL GLASS
ALL BONE

EVEN TEFLON (PTFE)!, EVEN ABS!
EVEN NYLON!, EVEN POLYPROPYLENE!
EVEN POLYETHYLENE!, EVEN DELRIN!


Simply wipe surfaces to be bonded with the special primer, then bond with the special adhesive.
Sets in 5 to 10 seconds!

this a link to there shop and the glue is on the left

http://www.ekmpowershop9.com/ekmps/shops/shop4glue/index.asp
Shelf life 2 yrs at cool room temp.
Up to 7 yrs in the freezer.

Resists temperatures up to 180 deg C
Resists water, heat, light, most solvents, oils, petrol, diesel,steam etc
Resists vibration and impact induced fatigue.

 
 
Peter
« Last Edit: October 16, 2010, 05:05:08 AM by HS93 »
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Offline DMIOM

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Re: Joining polypropylene
« Reply #4 on: October 16, 2010, 05:42:05 AM »
and I've just (after being prompted by Bogs' & Peter's posts) remembered having seen that 3M have Scotchweld 4693H that claims to secure polyprop as well. (though as well as sticking the two faces together you might still then need to brace it with buttresses or stick-in a cold-profiled fillet either side of the T join if your joint needs any significant strength)

EDIT: and I've just done a search and it's even available from Amazon

Dave
« Last Edit: October 16, 2010, 06:03:03 AM by DMIOM »

Offline Brass_Machine

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Re: Joining polypropylene
« Reply #5 on: October 16, 2010, 08:36:18 AM »
I have never tried any of the adhesives. I have done a ton of 'welding' though. I don't have any hotair sources so I used an old soldering iron. I cut up a small strip of poly to use as filler rod and carefully plastic soldered the two pieces together. Works like a champ if you take your time.

If you use one of the chemicals, please let us know how it goes. I for one would like to know.

Eric
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Offline picclock

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Re: Joining polypropylene
« Reply #6 on: October 17, 2010, 04:52:52 AM »
Many thanks for the info.

The adhesive method would work better for me but I am fairly sceptical about how good the adhesives are. I think its likely the 4693H will be better because its a flexible adhasive. The shop4glue product appears to be a cyanoacrylate product which is likely to fail due to its inflexibility.

I tried bogstandards link http://www.highbeam.com/doc/1G1-108837737.html but you need a subscription which you cancel.

http://multimedia.3m.com/mws/mediawebserver?mwsId=66666UuZjcFSLXTtnxfVmXs6EVuQEcuZgVs6EVs6E666666--
is the data sheet on Scotch-Weld 4693H. Its a synthetic rubber type adhesive.

The Shop4Glue.com site has a very wide range of adhesives but I'm slightly put off by the name 'KAPOW' on the bottle label. It appears to be an activated cyanoacrylate product. I couldn't find any associated data sheets.

However, I will do some tests on the two adhesives and see if they work as well as they say. When I have the info I will post the results.

Many thanks

picclock
Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Offline HS93

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Re: Joining polypropylene
« Reply #7 on: October 17, 2010, 05:40:17 AM »
E-Mail the guy he is very knolable or just ring him he is very helpfull and will explain all about it.I have started using his flexi epozy and super Glues as they do not got britle and so you can knock them of if the parts are a bit flexable as in model hulls it is great stuff but is is a bit slower than he says it is, but not by much.

Peter
I am usless at metalwork, Oh and cannot spell either . failure

Offline Bogstandard

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Re: Joining polypropylene
« Reply #8 on: October 17, 2010, 05:40:58 AM »
I have been trying to find a good bonding agent for perspex and other derivatives for years and have only found one that is to my liking, even though everyone says that their glue will stick it.

I think that is the main problem with these adhesive types, they will etch into the surface and stick the bits together, but the bond strength is only as good as the adhesive strength, not the original material strength.

It is for that reason I would still recommend some sort of mechanical fixing as well, just to make sure that the original material is physically acting between themselves, rather than just relying on the glue strength alone.


Bogs
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Offline andyf

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Re: Joining polypropylene
« Reply #9 on: October 17, 2010, 06:39:43 AM »
I have been trying to find a good bonding agent for perspex and other derivatives for years and have only found one that is to my liking, even though everyone says that their glue will stick it.....


Though this is a bit off Picclock's topic, I've had good results with ether (diethyl ether), if you can get hold of some. It dissolves it, so you end up with a weld-type joint, rather than a layer of adhesive between two surfaces. Probably best done outdoors, to avoid anaesthetising yourself.

Wikipedia says it's poly(methyl methacrylate) originally sold as Plexiglas and now known by various trade names including Perspex and Lucite. The article says it "can be joined using cyanoacrylate cement, more commonly known as superglue, with heat (melting), or by using solvents such as di- or trichloromethane* to dissolve the plastic at the joint which then fuses and sets, forming an almost invisible weld."

* I think that might be chloroform. Sleepy business, this.

Andy

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Offline ken572

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Re: Joining polypropylene
« Reply #10 on: October 17, 2010, 03:04:53 PM »
Hello picclock,

If you have a lathe, you can spinweld two pieces of polypro together with the
inner piece being .006" to .010" larger then the ID., of the outer piece. One piece in
the chuck and hold the other by hand while pushing it in with the tail stock screw.
Spin it slow, and just use hand to guide it, DON'T GRAB IT or it will peel some skin
off or give a nice friction burn. :thumbup:

Hot Air Welder with filtered, oil free, dried air, or substitute Nitrogen for the air and
you can get professional results. :thumbup:

Ken.
« Last Edit: October 17, 2010, 03:07:39 PM by ken572 »
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