If you're in a rush jump to the Soldering step, which will be enough for many cases.
Para meus colegas de língua portuguesa tem um vídeo tutorial no youtube.
Plastic is the material of the 21st century. After learning how to fix broken plastic I realized how plastic is everywhere. A huge number of day to day things that we use are made of different polymers that most people just throw away as they get broken... and they break all the time. I've turned myself into an addict of soldering plastic. I often take a soldering iron in my back pack and offer to fix people's plastic everywhere. It's impressive the number of things that are just discarded and that could still be useful:
- refrigerator drawer
- hair brushes
- car parts
- electronic cases
The list is endless. So, let's learn how they can be welded!
I will show you one of various techniques I've seen to fix plastic. This is the most generic and will fit most cases. This will fix plastics that have some thickness. You won't be able to weld plastic bags or other flexible plastic.
To finish this introduction I would like to ask everyone to correct any misspelled or misused words. As I'm not a native English person I have made mistakes. Just make a comment and I will fix it. Thanks! And I must say that many people have already sent suggestions and corrections. Thank you very much!
For most cases you will only need:
- A soldering iron, those simple ones, used in electronics with tin solder
- A respirator or other way to avoid breathing plastic gases (a fan to blow fumes away is agood idea, especially if you can be outside)
- Optional: a flat tip for your iron
The optional flat tip will improve the results, but it's possible to do without it.
If your plastic is thin, missing a piece, needs to be sealed for liquid, or under tension, you may also need:
- Disposable plastic strips
- Staple or wire
- Instant glue, soldering arms or other way to keep parts in place that you are welding
Sometimes, when the plastic is too thin or you might have lost some piece or need to seal it for liquids or if the piece suffers big tensions you might need those items. I'll explain better in further steps.
Note: some plastic are already in a decomposition state, they break quite easily, almost crumbling by itself. Decomposition is more common to see in plastic exposed to sun and rain, but can happen to indoor plastic as well. In these cases the welding process won't work at all.
Step 1: Preparation 1: What Is the Best Iron and Tip?
Choose the main tool for the job
If you already have a soldering iron, just use it. A flat tip will be better. I'll talk more about it below.
There are many types of soldering irons and stations. Besides ordinary ones, which you just plug on electricity, you can choose one in which you can set the temperature. If the plastic reaches too high temperatures it can loose its original properties and get weaker, breaking easier. High temperatures applied on polymers also produces toxic smoke. See next step on toxicity.
Portable soldering irons are also good to use at work, caring on your bag or far from plugs. I love a gas iron I have and use to help many friends with it, fixing their plastic things.
Choosing or making the tip better
When choosing an iron to buy, try to find a relatively flat tip for it or one that can get flattened. Usually cheaper irons have easier removable tips that are just a metal stick. If you think about making your own tip, those will make your life easier. See the video I've put here showing how I make my flat tips for soldering plastic.
More advanced irons or soldering stations may require more elaborated DIY tips and might be worth to buy a new one. You can wait to see if you will get addicted to fixing plastic as me to spend money on it ;) although they are really cheap.
Instead of making a flat tip you can also think about flatten the one that came with the iron. I've done that in some. A few hammered and a file or grinder can do the job. It's not a problem if you reach the internal copper layer.
Step 2: Preparation 2: When Extra Material Is Needed
Is your plastic too thin or have holes?
I can't give an exact measure, but when the plastic is too thin, like 0,5 mm (0,02 in) or even thicker ones, and the iron is too hot, it just make a hole in the plastic instead of weld it. In this cases you will need some spare plastic parts to add material to the original plastic.
I usually have this problem with broken tupperware, but have been able to fix them with extra plastic.
The best option is to take strips of a plastic of the same type of the one you will weld. You can identify your plastic type by the number printed on it inside 3 arrows, like shown in the image above or in this page.
Some suggestions to make plastic strips:
- cut from thin plastic pieces, like shampoo bottles, pet bottles, ...
- use plastic zip ties
- use that plastic strip from below pet bottle lids
Step 3: Preparation 3: When Metal Can Guarantee the Fixing
Will your plastic suffer some tension after being welded?
In spite of having already done very strong plastic weldings, in some cases even a small permanent tension can break it again. It's hard to say exactly when it will happen.
I would say you can choose between:
- make the welding as strong as you can
- make it simple. If it break then make it again, stronger
In any case, to make the welding stronger you can use more plastic, as with the plastic strips suggested before, or you can insert some metal inside the plastic. Suggested metal parts may depend on the job to be done. I've already used staple (the one I use most), bent wire (on thicker parts) and small strips of metal sheet (in glasses arms). There was a time when common 1.5V batteries were covered with a metal sheet that you could cut with ordinary scissors. Surely aluminium cans can also be cut with common tools. Try to find the things you can find easier. For me the staples are the most accessible.
Step 4: Preparation 4: a Helping Hand
Is it difficult to keep parts together?
If it's hard to hold the parts to be welded together you can try to use some soldering arms, just like in tin electronic soldering, or you can use instant glue to put them in place before soldering. In this case be careful with the soldering smoke in your eyes. If possible, use a mask on them too. I'll talk more about it in the next step.
Step 5: Preparation 5: Take Care of Yourself
Many people will probably talk about the toxicity of the plastic and instant glue smokes. I'm not an expert on the subject but, from what I've read, even usual soldering like the one made with tin on electronics and also professional metal soldering smokes are all highly toxic. In all cases you should try to avoid breathing or get your face exposed to the smoke.
With tin soldering you should also be careful with your hands if you manipulate the tin without gloves: it contains lead.
Here are some suggestions to avoid the smoke:
- Use a respirator
- Do the job in a level above your head (smoke will go up)
- Use any fan as an exhaust fan
After reading some comments made here, I suggest that, if you are concerned about the toxicity, and you should, mainly if you think you will do this often, choose an iron with settable temperature. As you see smoke burning from the plastic, reduce the temperature. Some polymers are more toxic than others and people advised me to be extra careful with PVC, which stands for Poly Vinyl Chloride, listed as carcinogen.
Alternatively to the settable temperature iron you can make a plug connected to a dimmer to reduce the iron power and temperature. I had the spare items necessary to make this at home, maybe you're also lucky :) (don't really know if it's called "dimmer" in English. We call it "dimmer" in Brazil. It is a potentiometer. That in the picture is from a ceiling fan).
You can search the internet for the SDS (formerly MSDS - Material Safety Data Sheet) of the desired polymer. Some have the specification of the recommended respiration protection, like N95 Cartridge, for example. More details at Plasteek and Pgs070947 comments below.
If you have other suggestions, let me know ;)
Gloves can protect you from getting burned. Some irons reach temperatures near 600°C (1112°F).
Note on glasses:
I've already welded a couple of them. Be sure to protect the lenses. Remove them if you can. The heat can damage them permanently. Many lenses are made of polymers nowadays, which will melt with any accidental touch of the hot iron or even only with its proximity.
Step 6: Soldering (Finally!)
This is the main step and in many cases can be the only one. Once you get used to it you will can do it very fast. I'm saying that because the big tutorial can intimidate some people, but the main process is very fast.
The secret is to melt the plastic in the joint so that both melted parts get together, welding themselves. This is how I do it:
- insert the iron in the joint with its flat tip line crossing the joint
- push it forward a little bit, to form a small plastic mass along the joint
- do it again behind the last pushed part to make other mass beside the previous
At the end you should have a nice weld bead, just like the one made in metal welding. Watch the video for a better understanding.
Adding more plastic
I usually add more plastic when the fixed parts are too thin or to complete some missing part. Sometimes they start to shrink and some holes appear during soldering. You can cover it with additional plastic, just like people do with tin on electronic soldering. I've embed a video here showing plastic addition.
You can put a plastic strip over the piece to be fixed and weld them together with the iron coming from above the strip until it melts. You need to feel when the plastic below starts to melt. If it doesn't melt at all, then the soldering will be bad and the parts tend to separate after sometime. If you push it too much maybe you will open a new hole on the plastic.
Remember the preparation about it: it is recommended that you use a similar polymer to improve the result.
As I've written: add a metal part can make the soldering stronger. I've already used it in buckets (people are never careful with them) and many other fixings.
You need to put the metal, let's say a staple, crossing the soldering line and press it with the iron until it enters the plastic by melting it. After finishing you may want to add more plastic over it so the metal don't stay exposed.
Remember to check the other side to see if the metal hasn't crossed the plastic. If it has you can cover the other side with plastic too.
Sometimes the plastic is to thin and even inserting only a staple it can't get all inside the plastic. I recommend that you cover it with additional plastic (as written above) to avoid rust.
After doing the weld bead you can try to make the surface smooth again by passing the iron over it. A flat tip will do this job better. The glass on the first picture has been finished this way and it has a staple inside it. After smoothing I have painted the front with a permanent marker.
It's a good idea to test the work after finishing. It's also a good idea to wait for it to cool down completely before testing. Try to make as much pressure or tension as you think it will suffer when used.
Some plastic suffer great tensions, as plastic chairs. A good way to test them is to really use them in extreme situations, like putting all your weight on it, not letting your legs on the floor, and maybe also jumping a little bit over it. Just be prepared for a sudden break.
Another conclusion I took from experimenting is that the final resistance will also depend on the polymer fixed. Some are just pretty stronger after soldering than others:
- The drawer puller I've shown in some pictures has shown itself quite weak. A simple fall down from low altitude have broke it, so I had to remake the soldering about 4 times until it gets resistant enough with 8 pieces of metal inserted.
- A PET bottle cap I've cut in half just to solder and test has shown itself really strong. I couldn't break it again with all my arms power (ok, I'm not that strong, but also not that weak guy)
- The PVC tube I've used in this video have also become really strong after fixed, even doing hard tests on it
What if it breaks on the test? Well, do it again, but now stronger! Add more metal, add more plastic, melt it deeper and so on.
Again, sorry for any misused word. Tell me about any mistake or strange phrase written here, please. I'm not a native English, so much probably there are better ways to write many things here.
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