How to repair styrene split on TK helmet?
- Thread starter Spankuh
- Start date
That’s a really common spot to see a tear like that, plastic gets very thin in that area. A small piece of cotton saturated with super glue will work, it’s like a poor man fiber glass job. Fiberglass itself could be used or a reinforce it with a piece of plastic behind and some styrene good to fill the crack.
@ part epoxy putty can be used, scuff up the inside with 180 grit paper, then carefully apply the putty.
TazMan2000
Master Member
I'd go with a piece of plastic to reinforce the area. Two part epoxy glues yellow over time and can blemish the part.
TazMan2000
TazMan2000
If the helmet, is in fact polystyrene, or a thermo-plastic like ABS or PETG, then a solvent cement is the ideal material for the repair. "Weld-On" is one brand, of this type of cement.
All the above suggestions are a dissimilar glues, which, with proper surface prep, may work. Although I would avoid cyanoacrylate adhesives, as most of them will embrittle styrene.
Solvent cements are specifically engineered for each thermal plastics, and come in different types, depending on your type of plastic. (Acriylic, ABS, PVC, Styrene, PETG, Kydex....) These are most common in clear, but ABS & PVC cements are available in black.
These solvent cements will melt the base material, and once the solvent in them has evaporated, you are left with the same base material, in this case styrene. Note; solvent cements only work on thermal-plastics, and will not work on thermal-set plastics, Epoxy, polyurethanes and so on.
The best and most stable way to repair a crack like this, is to get a thin piece of the same plastic, .030" (1/32") and fabricate a patch, which is a plate, that can be bonded to the inside of the helmet. It should be 1/4-1/2" bigger than the crack. If the area to be repaired is on a compound curve, then use a heat gun to soften the patch and form it to the inside area over the crack. Use masking tape on the outside, to hold the split area together, and keep the surfaces lined up and flush.
Solvent cements come generally in 2-3 "thicknesses" (viscosities).The thicker versions have dissolved quantities of the base plastic in them.
The water thin versions of the solvents should only be used when you have 2 surfaces perfectly matched and held snug (like the seams of a display case).
For this repair, I'd use the ticker version of the solvent. BUT! do not use too much, as the solvent with melt both the helmet and your patch and if you use a big glob of the solvent cement, it can soften the thin material of the helmet enough to distort it. Since these cements contain solvent, which evaporates quickly, you want a nice match to you patch, and the inside of the helmet, and a way to clamp the pieces together, or a weight that can keep the patch in contact with the helmet. This can be something as simple as a plastic bag fill with sand (lead shot is better) If the patch fits nicely, and doesn't move around easily, you can also just hold it by hand.
Apply the solvent to both pieces, and quickly apply you patch over the crack.
Once the solvent has evaporated, the helmet has been repaired with, styrene. So it should not split again, even with temperature changes and repeated flexing. Which may cause the other suggested repair methods to fail.
All the above suggestions are a dissimilar glues, which, with proper surface prep, may work. Although I would avoid cyanoacrylate adhesives, as most of them will embrittle styrene.
Solvent cements are specifically engineered for each thermal plastics, and come in different types, depending on your type of plastic. (Acriylic, ABS, PVC, Styrene, PETG, Kydex....) These are most common in clear, but ABS & PVC cements are available in black.
These solvent cements will melt the base material, and once the solvent in them has evaporated, you are left with the same base material, in this case styrene. Note; solvent cements only work on thermal-plastics, and will not work on thermal-set plastics, Epoxy, polyurethanes and so on.
The best and most stable way to repair a crack like this, is to get a thin piece of the same plastic, .030" (1/32") and fabricate a patch, which is a plate, that can be bonded to the inside of the helmet. It should be 1/4-1/2" bigger than the crack. If the area to be repaired is on a compound curve, then use a heat gun to soften the patch and form it to the inside area over the crack. Use masking tape on the outside, to hold the split area together, and keep the surfaces lined up and flush.
Solvent cements come generally in 2-3 "thicknesses" (viscosities).The thicker versions have dissolved quantities of the base plastic in them.
The water thin versions of the solvents should only be used when you have 2 surfaces perfectly matched and held snug (like the seams of a display case).
For this repair, I'd use the ticker version of the solvent. BUT! do not use too much, as the solvent with melt both the helmet and your patch and if you use a big glob of the solvent cement, it can soften the thin material of the helmet enough to distort it. Since these cements contain solvent, which evaporates quickly, you want a nice match to you patch, and the inside of the helmet, and a way to clamp the pieces together, or a weight that can keep the patch in contact with the helmet. This can be something as simple as a plastic bag fill with sand (lead shot is better) If the patch fits nicely, and doesn't move around easily, you can also just hold it by hand.
Apply the solvent to both pieces, and quickly apply you patch over the crack.
Once the solvent has evaporated, the helmet has been repaired with, styrene. So it should not split again, even with temperature changes and repeated flexing. Which may cause the other suggested repair methods to fail.
TazMan2000
Master Member
Generally I agree on most of what you say, but I think using solvent on already thin plastic is asking for trouble.
I recommend if one is go this way to test it with a similarly thin and cracked piece of styrene to ensure that only enough solvent is applied. It is too easy to apply too much one isn’t familiar on how to apply it.
CA glue doesn’t penetrate or melt the styrene. By using thicker gel, it would fill most gaps between the surface and the patch. Depending on the curvature of the material, thin styrene can also be stretched and formed by hand. Using successive patches will make the repair even stronger.
Of course every repair has its risks.
TazMan2000
TheWolfhound
Active Member
You could try Miliput, it's a two part adhesive putty. You can get it in white for pottery and china repair. Scuff the area with wet and dry, Mix the Miliput 1 to 1 and make sure it is mixed well. Press it to the inside overlapping the broken section. It can be smoothed over with wet fingers to get it the right shape. If it pushes through the break smooth it on the outside and leave to dry for 24 hours. The putty drys hard as stone and has great adhesive properties. Hope this helps.
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