The Shop > Composites & Plastics
Joining polypropylene
picclock:
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
DMIOM:
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
Bogstandard:
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.
--- End quote ---
But to contradict both mine and the above, I found this.
http://www.highbeam.com/doc/1G1-108837737.html
Bogs
HS93:
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
DMIOM:
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
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