Plastic Welding

[zoiks]

You could try mixing in pvc with acetone to create a plastic sludge. Apply the sludge to the area and mold it in. I used this to create the stereo enclosure in my car.
Check out mp3car.com in the Fabrication section for more info.

 

[BoomerD]

http://www.malcomheatguns.com/

http://www.youtube.com/watch?v=dQi-Kbsr_6o

http://video.google.com/videos...roperty-revision&cd=1#

 

[lokiju]

Isn't that what super glue is for?

 

[dullard]

Originally posted by: PottedMeat
I've fused broken plastic parts together with a few drops of MEK before. The result was surprisingly strong - the joint on my Sony headphones lasted more than a year of heavy use before they snapped again in the same place. At first I used some cheap epoxy that didn't even last a day.

Good call. Solvent welding (see BoomerD's link) is always my first resort. I haven't tried MEK, but many different solvents do the trick. Methylene chloride is usually the solvent I use.

Solvent welding works similar to using a glue. Dab/rub on a little of the solvent, place the parts together, and they weld themselves. I haven't found anything better looking that is as strong.

 

[OdiN]

MIGHTY PUTTY TO THE RESCUE!!!!!

 

[rpanic]

Originally posted by: OdiN
MIGHTY PUTTY TO THE RESCUE!!!!!

Oh hell yeah, with that stuff you can just build a whole new part, just form and sand.

 

[Rubycon]

Originally posted by: CycloWizard

It can be done safely and effectively, but the heating should be very slow and a low maximum temperature is helpful to prevent complete melting. A lot of polymer rigidity comes from tangles between the polymer chains, which are lost during fracture. Melting two pieces together will return some of the stiffness, but the part will be brittle because the entaglement density will be lower than the surrounding material.

And it's this very reason that makes it such a challenge!

Originally posted by: rpanic
Heat up an old flat head screwdriver on the stove and use it to melt the pieces back.

Hehe I have a Hexacon soldering station with several cutter tips that work well. The trickiest part is selecting a temperature that's right.

Originally posted by: zoiks
You could try mixing in pvc with acetone to create a plastic sludge. Apply the sludge to the area and mold it in. I used this to create the stereo enclosure in my car.
Check out mp3car.com in the Fabrication section for more info.

Wow I hope that was done in a well ventilated area free of any kind of ignition sources! Those fumes can be ignited by something as tiny as a spark from a static shock and a fire will flash everywhere there are fumes!

Originally posted by: lokiju
Isn't that what super glue is for?

If the break has sufficient surface area and the (bending) stresses are not too high it's a good choice. I've used glass fibers with gelled CA and "kicker" (anything sprayed on liquid CA to flash cure it - baking soda works in a bind albeit messy looking) for strong areal bonds, etc. If time permits a build up and sand down with metal reinforced epoxy putty is very strong too.

The problem often occurs in high stress areas where the plastic fails completely and an equal strength repair (either with welding or adhesives) is difficult. Murphy's law.

 

[Swagman]

It is clear that you have a good creative mind, but just to throw some more out here . . .

As you know, some plastics will dissolve (to different degrees) with the application of acetone. With that, a very good bond can be created using epoxy, where otherwise purt near impossible.

Even with rather small pieces, shallow holes can be drilled that allow stubs of wire, from paperclip diameter on down, to help reinforce.

In certain cases, when the configuration has allowed, holes can be drilled where thread (I'm partial to upholsterer's nylon) can be laced through and around the repair. A coat of adhesive over the thread can be the finishing touch.

[Swagman - Repairer of RC toys (and more) since the transition period from vacuum tubes and dry cells in transmitters.]

 

[aircooled]

We used to "spin weld" or "friction weld" threaded inserts into polyethylene.

 

[Gothgar]

Originally posted by: OdiN
MIGHTY PUTTY TO THE RESCUE!!!!!

Text

 

[RU482]

alot of times, if you don't care how it looks but just want to retain structure, you can use a soldering iron. put the peices back together, then use a quick swiping motion with the iron. Works pretty well for repairing bosses inside plastic cases

 

[Rubycon]

Originally posted by: redly1
alot of times, if you don't care how it looks but just want to retain structure, you can use a soldering iron. put the peices back together, then use a quick swiping motion with the iron. Works pretty well for repairing bosses inside plastic cases

Yep in low stress this generally works well. I broke a tab on a fan holder on a SAS cage and this method did not work. I cranked the iron up to 750F and used a piece of sprue as filler and it worked well - strong and fairly ugly but it's out of sight.

 

[BackFlow]

Originally posted by: DrPizza

Originally posted by: Indolent

Originally posted by: Jeff7
but it doesn't stick at all to polyethylene or polypropylene.

Random fact: These are the only two types of plastic that float in water.

The kind toy boats are made out of and the type that rubber duckies are made out of? Milk jugs, they float too. j/k, I knew you meant "there are only two types of plastic with a density less than 1g/cm^3

I have done hundreds of socket & saddle heat fusion on polyethylene tubing (mostly for water/glycol lines & a few gas lines).

 

[BackFlow]

It can be done safely and effectively, but the heating should be very slow and a low maximum temperature is helpful to prevent complete melting. A lot of polymer rigidity comes from tangles between the polymer chains, which are lost during fracture. Melting two pieces together will return some of the stiffness, but the part will be brittle because the entaglement density will be lower than the surrounding material.

If done in a control manner the fusion bond should be just as strong as the original plastic area. And, most fusion joints are at least 2X the strength of the original material area because the joints tend to be thicker than what it was.

 

[BackFlow]

Originally posted by: Rubycon

Originally posted by: redly1
alot of times, if you don't care how it looks but just want to retain structure, you can use a soldering iron. put the peices back together, then use a quick swiping motion with the iron. Works pretty well for repairing bosses inside plastic cases

Yep in low stress this generally works well. I broke a tab on a fan holder on a SAS cage and this method did not work. I cranked the iron up to 750F and used a piece of sprue as filler and it worked well - strong and fairly ugly but it's out of sight.

Find out the type of plastic and its melting temperature then slowly bring it up to temperature to prevent coking the surface.

280-290F is the temperature that we set the fusion iron for polyethylene.

 

[Throckmorton]

The stuff they make for welding PVC pipes works on some other plastics. I also know for a fact that Home Depot doesn't sell that stuff, or anything else you'd actually NEED.

 

[CallMeJoe]

The Eastwood Company has a plastic welder that may be just the thing.

 

[Evadman]

Plastic Welder