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Old 11-16-2019, 02:55 PM   #1 (permalink)
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Any one know how to chemically weld motocross fairings

My dirtbike’s fairing broke (rear mudguard) and I would like to chemically weld it back to one.

I tried acetone and it had no effect, so I am assuming it is not ABS.

It could be polypropylene or polyethylene, but I do not know what is a good solvent for those. If I succeed, could make a few bucks repairing fairings for others.

I have some Methyl ethyl ketone on order will try that next but i am doubtful.

(Bike is a 2007 yamaha YZ450F which may or may not have original plastics)

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Old 11-16-2019, 07:12 PM   #2 (permalink)
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Quote:
Originally Posted by teoman View Post
My dirtbikes fairing broke (rear mudguard) and I would like to chemically weld it back to one.
Those plastics are probably condensates or thermo-setting. There is no solvent. There may be chemicals that disintegrate the plastic, like paint stipper, which generally contain MEK. If you really want to attempt a repair its going to be thermal.
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Old 11-17-2019, 06:07 AM   #3 (permalink)
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Thank you for the info. I have been looking at the chemical compatibility charts for some time now. But it just says incompatible without an explanation, does it melt or disintegrate...

Some solvents are not easy to get a hold of.

1,2,4 trichlorobenzen is a solvent. But i think it may need high temperatures.


https://www.researchgate.net/post/Wh..._Polypropylene
3rd post has a downloadable pdf where they try to dissolve PE PP and PS for spin coating.

"Polyethylene and polypropylene have high crystallinity degree structures, which means that to ensure dissolving of polymer pellets in solvent, the solution should be heated above the polymer melting temperature. These are 120-130 C for polyethylene and 160-165 C for isotactic polypropylene. To ensure fast polymer dissolving, the solvent must have a boiling point that is higher or comparable with the above mentioned temperatures and so decaline, anhydrous 99 % purity (Sigma Aldrich, mixture of cis and trans) was used (boiling point range of 189-191 C). It should be pointed out that solutions of polyethylene and polypropylene in tetrahydrofuran and toluene are possible but require more than 6 hours to be obtained. When decaline was used as a solvent and the temperature was above 160 C, complete polymer dissolving in both PE and PP cases were obtained in less than 3 hours. After the solution has been obtained, great care must be taken with its handling. The droppers used to transport the solution to the wafer need to be heated to 120 C. The spin coater chuck should be heated up to 60-80 C as well. The Si wafers should also have temperatures above 160 C to ensure uniform surface wetting. If the temperature is below this value, PP and PE solutions adhere non- uniformly due to the high solution viscosity, as shown in Figures 5 and 6 respectively."


The process seems a bit too involved for my taste.
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Old 11-17-2019, 06:05 PM   #4 (permalink)
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Most solvents and glues are adhesive. A few mollusks produce a glue with chemical action, and they are being studied.

DDG/?q=mollusk+chemical+bond+adhesive

Quote:
Adhesion & Cohesion - adhesives.org
[Search domain http://www.adhesives.org/adhesives-s...sion-cohesion] https://www.adhesives.org/adhesives-...esion-cohesion
Chemical bonds, however, only form for very few substrate/adhesive combinations, e.g. between silicone and glass, polyurethane and glass, and epoxy resin and aluminum. For some of these bonded joints it has been demonstrated that chemical bonds account for up to 50% of all the interactions.
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Old 11-23-2019, 12:03 PM   #5 (permalink)
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Quote:
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1,2,4 trichlorobenzen is a solvent. But i think it may need high temperatures.
It doesn't - it'd evaporate very quickly at higher temps and atmospheric pressure

Toxic and highly flammable
Don't heat & breathe it

All the stuff you named, can be glued with commercially available glues


Better find out what it is first
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Old 11-23-2019, 12:22 PM   #6 (permalink)
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Can you plastic weld, meaning use heat and similar plastic to fuse it?

JB weld or other epoxy?
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Old 11-23-2019, 04:29 PM   #7 (permalink)
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Have to ask, why do you want to weld it instead of just replacing it?
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Old 11-25-2019, 12:43 AM   #8 (permalink)
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Harbor Fright sells a plastic welding kit that is pretty cheap and might work. I've heard that it works halfway decent.
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Old 11-25-2019, 01:49 AM   #9 (permalink)
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Quote:
Originally Posted by iikhod View Post
Have to ask, why do you want to weld it instead of just replacing it?
Parts availability. The bike is a 2007 model that was not too popular over here. So it will take a long time for the part to arrive.

There are also friends bikes with broken fairings that could do with a bit of fixing.

But most of all it would be a good learning experience. Add something to the skill set.

Last edited by teoman; 11-25-2019 at 01:56 AM..
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Old 11-26-2019, 12:56 AM   #10 (permalink)
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You may be thinking of cement used for styrene in models. I use epoxy on fairings.

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