OT Plastics Repair

Please forgive the off-topic post. I know this has nothing to do with metalworking but I also know that the range of experience and knowledge
of subscribers to this group is legendary.
I have a very limited time to complete the repair of a large dog kennel, the kind that is often used to move animals by airplane. It is two pieces, moulded, sort of "clamshell" style. I believe it is polypropylene but stand to be corrected. It has suffered a blow to one corner, maybe when it was very cold and has several cracks radiating from the point of impact. The damaged area is maybe 6 inches across.
I'm have drilled holes at the ends of the cracks to prevent further propagation. I am thinking of using what I have on hand which is fiberglass cloth and epoxy resin. (West System 106). I have no idea if the epoxy will bond with this plastic. Maybe polyester resin would be more suitable? I don't feel like I have time to do a test run.
Thanks for any suggestions.
Kevin in Nova Scotia
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
kartwood wrote: > I have a very limited time to complete the repair of a large dog

I would make an alternate guess of vinyl and try a small test spot of PVC "joint weld" goop from a local plumbing supply place. It will partially dissolve the two sides of the crack and let them re-form together.
Getting any Plastic A to stick well to Plastic B is always a crapshoot. Small fast tests are the rule, then only sink time into something that works.
--
Fred R
"It doesn't really take all kinds; there just *are* all kinds".
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi Fred,
Thanks for the info. I found some 5 minute epoxy and tried a test. It didn't look like it would bond very well. I dug around the basement and found some CPVC pipe cement. I'm still waiting for the results. I bet welding would be the way to go if I could get my OA torch cool enough. :-) Maybe the ol' bernz-o-matic would work.
K.
Fred R wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
It will be a bitch to fix by welding or adhesives. I would wrap the thing with duct tape and/or nylon filament tape. By adding a second layer of material to the shell you are not depending on the base material to provide the strength. Duct tape is used on Nascar race cars to hold fenders on at 200mph. It should keep a dog crate together for a few hours airplane flite.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Um, it ain't Duct tape they use, but Racers Tape, a fiberglas reinforced material with superb adhesive backing. Available from Pegasus Racing, use google, try ebay.
/mark
daniel peterman wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Look for a two-part epoxie product called "Plastic Welder". It should be displayed with the other two-part epoxies such as the five-minute stuff, and it comes in a two-part mixing syringe.
This is made by Devcon, but sold under a number of brands such as Loctite.
It is the ONLY two-part epoxy that I've ever seen specifically stating on the package that it WILL work on plastics.
Most say they WON'T!
Around my neighborhood, they use a lot of the stuff to repair ABS snowmobile hoods.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If it is PP or PE it should be fairly easy to fix by welding. You can buy plastic welding kits to do it on ebay with a hot air gun and rods. The only time i've done it I borrowed a mates gas powered hot air soldering iron and used some bits of HDPE milk bottle caps for the filler. The process is much like OA welding but much cooler.
That said you might try asking in a body shop as car plastic bumpers these days are often welded and it might cost you less to do that than get the kit to do it yourself.
kartwood wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
David,
Thanks for the suggestion. I think welding would be a good solution in this case. I fear I don't have access to the correct tool to heat the joint. The other concern is getting the two sides of the work to line-up. I can "rob" filler material from elsewhere on the piece so I might give it a try.
Kevin
David Billington wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
kartwood wrote:

Check the local craigslist, grocery store bulletin board, or bargain finder paper. You can buy a used good crate for peanuts. Much less than buying a welding kit for plastic (unless you just need a reason to have one) , and for a fraction of what a bumber shop is gonna charge out on an hourly rate.
Cheers Trevor Jones
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Good 'ol Weller soldering gun as a welder... stinks, smokes, etc., but will melt the two plastics together (along with a little bit of "stirring" with the tip of the gun). Ken.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Nothing sticks to polyethylene or polypropylene. Either weld it, stitch it with copper wire, or replace it.
Joe Gwinn
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Or simply pop rivit an aluminum patch, inside and out sandwich
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Joseph Gwinn writes:

3M disagrees.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I would flip the box over and look at the marks on it. There is a recycling symbol that is three bent arrows forming a triangle with a number inside and an abbreviation like abs, pe, hdpe, etc.
Once you know what kind of plastic the box is made from then you can effect a repair.
One way that would work regardless of the type of plastic is to make a fiberglass corner inside and out and rivet the sandwich together.
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Roger Shoaf wrote:

Good idea. If the plastic is PE or HDPE, then adhesive will not work unless you modify the surface. One method is to use plasma to oxidize the plastic surface. Don't use a plasma torch as they are much too hot. But if you just happen to have a neon sign transformer handy, you can rig something with it. The other method that I know is to run a propane torch over the area where you want the adhesive to stick. Don't get it too hot, but hot enough for the surface to oxidize.
Stiching with wire and then some good cloth backed tape is probably the best bet. Don't use cheap duct tape, use the good stuff with a cloth back.
Dan
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
kartwood wrote:

Don't piss around with the glass and resin .
Drill 1/16 inch size holes about every 3/8 of an inch along the splits and lace it together with wire. Use picture hanging wire or black iron wire from crappy tire.
I usually use aircraft safety wire, cause I have a pile, but pretty much any wire that you can lace through the holes will do.
Cheers Trevor Jones
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Plastic is usually welded with a special hot air gun. Just google for plastic welding, and you will find more information than you can use.
Steve R.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I agree with the posters who say welding is the only way to go unless you want a mechanical patch (pop rivets) or wire stitching.
The best way is with a sharply focussed hot air gun, but they tend to be pricy for the type that will produce the temperatures and small focus required. A paint peeling heat gun will just melt big holes.
The alternative is a soldering iron. The result will be messy and ugly, but probably reasonably strong. I've done it on a number of repairs.
You can get a tip for a soldering gun (weller, I think) that is smashed out to a thin, flat, round, spreading blade of about 3/8" diameter. This is far better than an ordinary pointed soldering tip for plastic welding. The same shape is available in a tip that screws into a conventional weller soldering iron that accepts screw-in tips. Check with your local electronics supply store or plastics supply store.
The advantage of the iron over the soldering gun is that you could adjust temperature for optimum workability and to avoid burning, whereas with a soldering gun the temperature is all over the place as you try to modulate it with the trigger and you (I) burn areas due to attention focussed elsewhere.. Use an ordinary lamp dimmer for temperature control and experiment in an out of the way area first.
You can probably buy plastic "welding rod" about 1/8" diameterat a plastics supply store, but the plastic of the object stolen from some other area of the object is best. Don't forget that you may be experiencing damage due to long-term exposure. to UV from the sun, in which case your repair will be short-lived.
I generally try to slide the hot blade down the crack and squeeze the parts together as the blade passes, but that is often difficult to accomplish before the plastic freezes. The alternative is to melt small areas and "smoosh" the soft plastic around with the blade to get the smoothest, well blended joint. You generally have to do that anyway, even after you run the blade down the crack.
Good luck.
awright

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Many thanks for all the suggestions and useful information. It was apparent early-on that the epoxy was not going to bond to the plastic. In spite of the fact that I DO have a neon sign transformer, my lack of time steered me away from experimenting in that direction. I have had bad luck with welding plastics but I know that is because I didn't take my time to make sure all the material in the join was hot enough to flow.
I took the easy way out and put a two ply epoxy layup on each side using quite heavy cloth and pop-riveted the heck out of the whole thing.
If the dog wins some best-in-shows, I will buy him a new travel crate.
Thanks again to all,
Kevin
Anne Irving wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.