Plastic Repair

[Britton30]

Yeah, test each method first on a hidden place or the old part. Many glues and adhesives will break down when heated. Have we mentioned JB Weld for plastic before?

 

[seekermeister]

No, but I'm somewhat familiar with it, however my knowledge of it is more about using it on metallic surfaces, rather than plastic. The Plastic Welder that I mentioned is a VersaChem product. I don't know how good it is, but I have heard mentioned a number of times before, so I figure it is worth a shot.

 

[carwiz]

Epoxy probably won't stick to the ABS very well. I've tried making repairs using fiberglass/resin and it doesn't hold for long. You'll need to use a solvent glue like pipe cement. There's more often than not, a oil-based mold release on the panels too. Clean the area with solvent before using the glue.

 

[seekermeister]

Won't know until I try it, but the first item on the list for application is ABS. I don't see the term epoxy anywhere on the packaging, but I suspect that it is one. At least it comes in a two part ejector, which requires mixing prior to application. It also mentions bonding metal to plastic, so I may try putting a metal washer sandwiched between the plastic components.

It doesn't say anything about using a cleaning solvent, only to roughen the surfaces first.

 

[jekeesl]

All of the methods that heat two plastic surfaces for joining require that both surfaces are raised a bit above their melting points. Those melted surfaces are then brought together, under pressure, and cooled. If done properly, as in plastic pipe, the welded areas are stronger than the original cross-section. ABS typically melts at around 220F (if memory still serves). The welding technique, whether done via sonic welding, heated plates, hot air, etc., must be done properly or the surfaces won't bond. If the surfaces aren't melted deeply enough (heated too fast), then proper mixing of the two can't occur when pressed. And if the surfaces become too hot, then degradation occurs and the surfaces will not bond. If you do attempt a contact heating method, , like a soldering iron, then the best surface temperature range for ABS welding is roughly 350-450F. Sonic welding works best on two flat, parallel surfaces, and may not be applicable here.

That said, I'm thinking that you can go to web sites for the primary plastic sheet suppliers, and get their recommendations for ABS solvents and adhesives. They probably sell adhesives and have product data sheets online, or can email them to your attention. Those data sheets should have descriptions of how to apply the adhesive, along with information on expected results. If you google "plastic sheet", you'll see several suppliers (see below for link). I'd pull up the web sites for the larger ones, like Tap Plastics or US Plastics Corp. to get phone numbers. Ask for technical assistance with bonding, and they should get you to an appropriate resource.

plastic sheet - Google Search

 

[seekermeister]

Thanks, but I've ruled out sonic welding due to cost factors. I'm not certain if I should apply your comments regarding temperature sensitivity to using a soldering iron or not? I know that the soldering iron that I have doesn't have any kind of temperature control, so I guess that I would need another one. How accurate are those types on their temperature control usually?

 

[seekermeister]

I Googled for the temperature factors on ABS, and this is what I found:

1. Maximum Temperature: 176°F 80°C

2. Minimum Temperature: -4°F -20°C

3. Autoclavable: No

4. Melting Point: 221°F 105°C

5.Tensile Strength: 4,300 ps

The tensile strength of Plastic Welder is only 3500 psi, so I guess it would be the weakest link.

 

[carwiz]

Somewhere on the packagte it should say the surface should be free of oil, dirt, dust, rust or some similar phrase. Just trying to save you a headache but I'm betting the fix detaches. In any case, good luck with it.

 

[seekermeister]

Not all plastics are equal. Plastic Welder does warn that it doesn't work on polyethylene or polypropylene plastics, but it does list fiberglass, among others on it list of appropriate uses. I'm not saying that it wouldn't be a good idea to clean the surfaces as you suggested first, only that the packaging of the product doesn't say anything regarding it. Still, all insights and opinions are welcome.

 

[Britton30]

Is there a lot of force applied to the area you want to fix seeker?

I also would recommend cleaning with a highly volatile solvent like MEK or acetone.

 

[seekermeister]

As that the repair is at the mounting point for a door pull, which obviously involves some slamming for closing, I would tend to say that yes, there is an impact factor, but I don't know how to measure how much. Since this is a very common point of breakage in the Chevy Blazer models, I can only say that the original design wasn't strong enough.

 

[jekeesl]

If you see something glow a very dull red color, that usually indicates something in the 700F degree range. If it glows bright red, then the surface is probalby about 1000F. If it glows reddish-white, then it's even hotter. The problem with soldering irons isn't so much temperature control, because the plastic's surface temperature can be regulated by the amount of time it contacts the iron. The real problem is that you can't get even temperatures to large surfaces with a soldering iron, so bonding will be uneven. The soldering iron may work for very small areas, but should probably be avoided for most complex or larger areas.

As to various gluing and solvent welding techniques, some of those should work. As stated earlier, see if you have a local plastic sheet supplier (yellow pages), and talk to them. They can probably look at your part to confirm that it's ABS. Actually, you can do that if a small fragment is available. Polyethylene and polypropylene both have specific gravity values in the 0.920-0.965 g/cc range, (just under the value for water), so will float on water. ABS has specific values around 1.03 g/cc, so will very slowly sink if you put the fragment in a bowl of water and depress it to break the water's surface tension. The other plastics used in engineering applications mostly have specific gravity values greater than 1.2 g/cc, so will sink rapidly to the bowl's bottom. If it sinks slowly, then it can probably be glued or bonded with any decent material designed for ABS. As stated earlier, I'd try to get a bonding agent from the plastic sheet suppliers, since their customers deal with bonding applications on a frequent basis. They can also supply a test specimen, so you can confirm adequate bonding before messing up your part.

 

[Britton30]

A point like that does have to endure a lot of stress. Is it possible to fashion a metal reinforcement arounf the screw hole? It may not be pretty but would be duable at least.
Coming from the taxi business, I've seen this done a lot on taxi doors, arm rests, consoles, glove box doors, etc.

 

[seekermeister]

If you see something glow a very dull red color, that usually indicates something in the 700F degree range. If it glows bright red, then the surface is probalby about 1000F. If it glows reddish-white, then it's even hotter. The problem with soldering irons isn't so much temperature control, because the plastic's surface temperature can be regulated by the amount of time it contacts the iron. The real problem is that you can't get even temperatures to large surfaces with a soldering iron, so bonding will be uneven. The soldering iron may work for very small areas, but should probably be avoided for most complex or larger areas.

I don't think that my little soldering iron is capable of getting hot enough to glow at any color. However, from the specs that I posted above regarding the temperature qualities of ABS, I don't think that it needs to.

As to various gluing and solvent welding techniques, some of those should work. As stated earlier, see if you have a local plastic sheet supplier (yellow pages), and talk to them. They can probably look at your part to confirm that it's ABS. Actually, you can do that if a small fragment is available. Polyethylene and polypropylene both have specific gravity values in the 0.920-0.965 g/cc range, (just under the value for water), so will float on water. ABS has specific values around 1.03 g/cc, so will very slowly sink if you put the fragment in a bowl of water and depress it to break the water's surface tension. The other plastics used in engineering applications mostly have specific gravity values greater than 1.2 g/cc, so will sink rapidly to the bowl's bottom. If it sinks slowly, then it can probably be glued or bonded with any decent material designed for ABS. As stated earlier, I'd try to get a bonding agent from the plastic sheet suppliers, since their customers deal with bonding applications on a frequent basis. They can also supply a test specimen, so you can confirm adequate bonding before messing up your part.

There is no doubt about it being ABS, because it is printed directly on the backside of the door panel, and the plastic on the door pull looks exactly the same. It would be useless to try to test for the specific gravity, because a door deal of the material covering it is foam and vinyl, so I don't doubt that it would float.

 

[seekermeister]

A point like that does have to endure a lot of stress. Is it possible to fashion a metal reinforcement arounf the screw hole? It may not be pretty but would be duable at least.
Coming from the taxi business, I've seen this done a lot on taxi doors, arm rests, consoles, glove box doors, etc.

Pretty is not really a factor, since the repair will not be in an area that is not visible. As mentioned previously, I intend to place a metal washer between the layers of ABS, so I guess that would be equal to what you have suggested.

EDIT: What I have in mind doing is to bond a .060" layer on the backside of the door panel, plus two .125" thick layers on the inside. The combined thickness of the patch will be ~ 3/8" inch thick, plus whatever the thickness of the washer is. Surely, that must be stronger than original, because it was only ~.060" for the door panel, plus another .060" for the door panel, or ~1/8" total.

 

[Britton30]

Sounds good, the idea is to spread the force over a much larger area. That seems like a good reinforcment.

 

[seekermeister]

I'm pretty sure that it will work, because the fellow that I bought the door panel from, wanted $50 dollars for it (which I thought was a good deal), he lowered the price to $20 when he saw the break, which had only used metal washers to hold it on, which apparently worked, since he didn't know about it. He also included the switch panel, which is normally sold separately from the door panel, so it would have been impossible to beat the price.

Even though the panel's color is called graphite in both models, it is somewhat darker on the new panel than on the old, so I'm hoping that he hasn't sold the other panels yet, so I can get a matching set.

 

[Britton30]

Nice buy! The switch panel is probably outrageous to buy new.
Found this http://jbweld.net/products/jbweld.php at the bottom it says for PVC/ABS. There are several flavors to choose from. Apparently all epoxy or polyurethane formulations since there are two parts to mix.