Plastic welders

[ajmcforester]

I'm trying to find an alternative to using glue. On my prior 240z I used ABS glue and any time I put any pressure on the panel near the repaired crack I'd hear a crackle. The plastic near the repair seem to get stiffer, witch I don't know if that is a good thing. Just to let you know I had white interior so I used clear ABS glue, maybe the black would be better.

I do like the idea of using backing like fiberglass or acrylic fabric with a resin or epoxy and you can find one that flexes more than others so the panel stays pliable without separating.

I was wishing we would get some more examples of people that have tried a plastic welder, but hay their are a lot of good ways to make repairs. So lets get them out their so people can read them.

[ajmcforester]

These are made of either mineral-filled polypropylene (PP) or glass/mineral-filled nylon 66. If it's PP, there's no glue that will adhere unless you etch the surface with a corona discharge (not in anyone's tool kit). If it's nylon, you should be able to get an epoxy to stick. Thus, it sounds like it's PP. You will have to weld this or fabricate a plastic strap to bridge the crack and screw it into the shroud.

If I remember polypropylene when burned releases an oily like substance usually plastics with that characteristic will not glue well. That is a trick my grandfather gave me about gluing plastics.

[Seppi72]

I cannot disagree with your desire to hear from more folks about plastics welding. I've worked in polymer and plastics R&D for almost 30 years now (my god, am I really that old?) and I have a pretty good idea of what these materials are like and how they respond to outside "forces."

The problem with plastics welding is that, just as with metal welding, you need to have experience to be good and most of us generally S-U-C-K at welding because we lack that experience.:sleepy: I certainly know that I do and I am thankful that I have a greatly experienced body guy to do my welding for me.

The thing to remember about plastics is that all of them soften to a greater or lesser degree as they are heated - amorphous polymers like ABS and PVC soften much more than semi-crystalline ones like PP or nylon - which is something that is not a significant issue when welding metals simply because metals have much greater initial stiffness (modulus). Plastics also have much, much poorer thermal condiuctivity than do metals. So, if you take too long to get your plastic welding rod and workpieces up to the proper temperature using the typical hot air source, you run the risk of gravity causing the workpieces to distort.

In fact, the best way to weld plastics is to use a plasma discharge torch that heats a stream of plastic powder (appropriate to the base plastic, of course) and blows it onto the workpieces as it almost instantaneously heats only their surfaces. All the melted plastics become quite intimate and you get a weld quickly and without the same risk of distortion. But only high-powered plastics welding operations could afford to have such plasma welders, so we hobbyists are screwed.

[Seppi72]

Just to address your experience when gluing your panels, here's something to consider.

A glue like ABS (or PVC) cement works by dissolving the plastic in the workpieces. If you have a truly clear ABS glue; i.e., transparent and colorless, it does NOT contain any ABS. If it did, it would, at least, have to be translucent if not opaque. Thus, using that glue would simply dissolve the plastic surfaces that it touched. Polymer molecules would entangle forming connections between the various pieces, but it would only be a thin surface thing on something such as an interior panel crack.

Black ABS glue has some black ABS already dissolved into it. Thus, when it eventually dries, it not only has those molecules from the part surfaces, it also has the ones that were in the glue to begin with. You therefore have more solid material in that joint.

[ajmcforester]

Just to address your experience when gluing your panels, here's something to consider.

A glue like ABS (or PVC) cement works by dissolving the plastic in the workpieces. If you have a truly clear ABS glue; i.e., transparent and colorless, it does NOT contain any ABS. If it did, it would, at least, have to be translucent if not opaque. Thus, using that glue would simply dissolve the plastic surfaces that it touched. Polymer molecules would entangle forming connections between the various pieces, but it would only be a thin surface thing on something such as an interior panel crack.

Black ABS glue has some black ABS already dissolved into it. Thus, when it eventually dries, it not only has those molecules from the part surfaces, it also has the ones that were in the glue to begin with. You therefore have more solid material in that joint.

That would explain the crackling I would get and how come the section got stiffer.

[WalterMondale]

I feel for you if this is a matter of trying to save some dough. At times, I have found dissapointment trying to make a repair that brings a new learning curve, new special tools, and lot's of time. Contrary to that, I bought my first mig welder, spent lot's of time practicing, and now make quite a bit of money welding special projects. I guess you have to ask yourself if your up to the challenge, and if going forward is worth the investment of time and money.

Which plastic panels are you looking to repair? Perhaps you could find "better" ones.

I by no means want to dismiss you original questions about making the repairs plastic. I have found some of the information on this thread enlightning. If you do find yourself making these repairs, please post some before and after pictures. I wish you the best of luck!

Edited February 16, 2009 by WalterMondale
more words.

[ajmcforester]

I wanted to get more insight I have not been a big fan of gluing old parts it just seems to make them more brittle, and plastics get more brittle over time. It just exacerbate the problem of cracking.

I've been good with TIG welding, my grandfather thought I was a natural. I think if I set up things and take my time it would come out OK my concern is it going to have the same problems as glue? If that is the case the investment would be a waist of money.

I have some good panels with most only having 1-2 cracks about .25"-1" in length. The thing is if I'm going to get a dash restored, repair the vinyl, put new seat covers on, rechrome plastic parts (may use chrome paint became allergic to chrome), have new carpets, and have the body redone, I should put the same attention in the plastic parts and do them right.

At one time I did restoration judging on Corvettes and I'm looking into what some of them have done. The problem is the aftermarket for Corvettes is much better and new parts usually just bolt on if the car is straight, and almost every plastic part is made.

If I decide to get a plastic welder I'll post pictures, and tips for everyone. I hope others will do the same.

Edited February 16, 2009 by ajmcforester

[WalterMondale]

I have some good panels with most only having 1-2 cracks about .25"-1" in length. The thing is if I'm going to get a dash restored, repair the vinyl, put new seat covers on, rechrome plastic parts (may use chrome paint became allergic to chrome), have new carpets, and have the body redone, I should put the same attention in the plastic parts and do them right.

The original plastic trims I have are so brittle now, I have great concern about putting them back in when the time comes. I have been thinking I may try my hand at fiberglass (carbon fiber) replacements. However, $300 will buy the four pieces of Quarter Trim from http://www.datsunrestore.com/catalog.html

I have been threating to stop at the vacuum plating place on Church Rd in Moorestown and see if they would do chrome plating on some plastic pieces for me.

[ajmcforester]

OK I did get the plastic welder and like it better than glue. One nice thing is I can add reinforcement to the plastic like fiberglass strands. Also the plastic in the area welded seems to gain some of its original characteristics back.

Cons it will distort panels just like welding thin metal so plan to have stuff to reshape the panel, and a heatgun. I found doing 1/4" sections at a time best with the thin panels. Also on panels that are not painted you can only weld one side than two sides, like recommended in the instruction. I'll try to get pictures up sometime this month.

[FastWoman]

Reviving an old thread here...

I need to repair/replace a few interior trim parts on my '78. Among these are my A-pillar trim pieces, which have distorted over time, and which have the screw recesses broken off. I'm considering the following approach and would appreciate any insights as to whether this is a good approach:

(1) Lay the panels out, and hit them carefully with a heat gun, so as to work out the distortions and put them back into the proper shape.

(2) Sand the backsides with coarse sandpaper.

(3) If I can find any solvent that will attack the plastic, brush it over the backside, and then immediately overcoat with a brushing of West System epoxy.

(4) Brush a layer of unthickened West System on the backside (either as the first coat or as a follow-up coat to #3). Add a layer of fine-weave fiberglass, and wet out.

(5) Possibly overlay a layer of chopped fiber mat for strength, wherever thickness is not a problem.

(6) Finish with another layer of fine weave over any chopped fiber mat.

(7) Let cure, sand smooth, and paint any exposed epoxy black. Re-drill holes, and mount back in place.

Thoughts?

Edited January 3, 2011 by FastWoman

[Seppi72]

I'm not familar with the '78 model. All my Zs are '72s and they do not have this type of A-pillar finisher parts. However...

I am familar with automotive plastics and if these are rigid parts they are undoubtedly made from ABS plastic. For many decades, most interior trim parts have been made from ABS of one sort or another. There are, literally, hundreds of variations in the formulations that have been used worldwide.

You can find a pretty good solvent system for ABS in the plumbing department of any hardware or home inprovement store. Get the stuff for cleaning the surfaces prior to gluing parts together. That will mildly attack the surface, removing grime without causing dimensional distortions like swelling and make it more amenable to further bonding.

If, in fact, you have the screw bosses, you might consider then using an ABS glue mixture (from the same plumbing department) to reattach them to the main part. After drying for a while, say, 12 hours, you could then bolster the joint by light sanding and coating with the epoxy.

[ajmcforester]

Reviving an old thread here...

I need to repair/replace a few interior trim parts on my '78. Among these are my A-pillar trim pieces, which have distorted over time, and which have the screw recesses broken off. I'm considering the following approach and would appreciate any insights as to whether this is a good approach:

OK I got a plastic welder and I came up with a great way to fix that area. That is simpler.

(1) Lay the panels out, and hit them carefully with a heat gun, so as to work out the distortions and put them back into the proper shape.

Good idea use a feathering motion with the heat gun you will see a restoration of the color that is when it becomes playable and not to soft. try not to touch the front side in-case it gets to hot.

(2) Sand the backsides with coarse sandpaper.

Not a good idea use heat to help create bite.

(3) If I can find any solvent that will attack the plastic, brush it over the backside, and then immediately overcoat with a brushing of West System epoxy.

Just use a little paint prep or alcohol to clean the oil off a good idea before applying any heat

(4) Brush a layer of unthickened West System on the backside (either as the first coat or as a follow-up coat to #3). Add a layer of fine-weave fiberglass, and wet out.

It is ABS plastic either melt some ABS plastic or use ABS glue it will fill in

(5) Possibly overlay a layer of chopped fiber mat for strength, wherever thickness is not a problem.

I added support with fiberglass drywall mesh to add support melted it into the original plastic on the back and added more ABS plastic; Without a welder I would heat the plastic up lay into the surface the mesh and use ABS glue to cover and make it thicker. The fiberglass mat won't move like the plastic. On the early 240Z you will not most with original center counsel has small cracks, because it's fiberglass mat backed over plastic.

(6) Finish with another layer of fine weave over any chopped fiber mat.

Not Good same as 5

(7) Let cure, sand smooth, and paint any exposed epoxy black. Re-drill holes, and mount back in place.

Thoughts?

Things I've learned is ABS gets brittle on the surface and can cause cracking heat will bring chemicals inside the plastic up and make it more durable (don't have a clue how many times that trick might work and I bet the sun and other heat sources will shorten the amount of times). ABS glue works well on mending the crack so you can't see it on the front side, it does not help the plastic be less brittle in that area. New plastic welded to back to make it stronger and adding the new plastic seems to reinvigorate the plastic in that area. Looking at other things made of ABS now days they are a lot thicker, about the same thickness as the ABS plastic headlights or thicker. Also some more, but ask away I was going to do a wright up but who am I kidding I don't seem to ever find the time for that:rolleyes: