Plastic welding is used across many different industries, whether it is for small construction or harbor freight. The process, which sees thermoplastics joined together through the application of heat, is relatively straightforward in theory. However, more is required than you may realize. To ensure you know how to master the basics, this guide covers the essential steps during the plastic welding process.
Get Prepared
Preparation is the key to a successful welding project. That starts with having the right hot air tool for plastic welding. Air tools need to produce heat, but the job can be done more effectively when the device incorporates additional features and ergonomic handling. Also, think about other equipment to go along with your hot air tool, including accessories such as nozzles and safety gear.
Another aspect of preparation is having a clean, well-ventilated space to complete your welds. As with wearing protective gear, the right area setup can greatly maximize your safety. Ventilation prevents you from inhaling hazardous fumes, and at the same time, a clean environment limits potential accidents occurring.
Pick Your Plastic
It’s important to know what plastic you are working with before welding. This is because only “like” materials can be welded. For instance, if you are working with polypropylene (PP), you can only use a plastic welding rod made from polypropylene. Trying to combine two different plastic types isn’t compatible, and it only results in unsuccessful welds.
Plastic will typically feature identifiers in the form of letters. PP is polypropylene; PE is polyethylene; PVC stands for polyvinyl chloride. You get the picture. Another way to identify the plastic you have is with a welding rod test kit. These kits include rods made of different plastic types. Simply melt a rod and attempt to join it with your plastic item. If they stick together, that means they’re made from the same material and compatible.
Surface Preparation
Before you start melting the plastic, it is vital you prepare the surfaces correctly. It can be easily overlooked, but the wrong preparation will result in welding failures. As for what preparation involves, this generally revolves around ensuring the surfaces of the plastic components are clean.
The removal of all soil from the surfaces is imperative. Dirt, oils, greases, paints, even UV degradation – you must get rid of all these before welding. For instance, if you have any painted surfaces, these should be cleaned back to the parent material. A sanding disc or grinding disc can do the job in that regard.
Joining The Plastic
Now it’s time to cover the welding process’s main aspect: joining the plastic together. This begins by preheating your hot air tool. Plastic welding machines typically get up to the necessary heat after two or three minutes. As for what heat needs to be achieved, this depends on what plastic material you’re using. Typically, the temperature will fall between 200°C (390°F) to 300 °C (570°F).
You want to get this temperature right. Go too low, and you won’t reach the necessary temperature that heats the plastic up. On the other hand, going too high can lead to an ineffective melt – and possibly even burn the plastic. As a result, ensure you know the melting point for your plastic of choice.
Securing the plastic together can be done with tack welding. This is where the join ends of the plastic pieces are melted and pinned together. With a specialist tack welding nozzle attached to your hot air tool, you apply heat until the plastic begins to melt. Once melted, the pieces are joined together. Going this route during the welding process stops any unnecessary movement with the plastic.
To produce a steady, smooth weld, it is recommended you trim down the ends of the welding rods. This can be done with the use of pliers or a trimming knife. Plastic welders will also tell you the importance of inserting a new rod before you begin welding again. This can help avoid a big bubble of plastic forming when you restart welding.
Getting the speed right
“Speed welding” is a technique you can use – and it is recommended for long weld runs. However, when we talk about getting the speed right, this is about how you move the hot air tool over the plastic. If you go too quickly, the plastic won’t melt sufficiently – and the opposite will occur if you’re too slow.
A gradual speed is necessary from top to bottom of the weld joint. Having the gun positioned at a 45-degree angle helps with the procedure. Furthermore, having the nozzle’s edge next to the plastic is another step to take. Although this can be tricky to maintain when using a hand held heat gun, it is helpful to use a lightweight tool with ergonomic handling. You can also acquire an automatic or semi-automatic machine for added efficiency and accuracy.
Finishing the weld
When it comes to adding the finishing touches, there are a few things to consider after you have completed the weld. The first step is being patient and leaving the plastic to cool. This should be done for at least five minutes. Fortunately, plastic doesn’t take long to get back to room temperature. When it’s producing zero heat, you know it is ready to be worked on further.
However, before you allow the plastic weld to cool off completely, make sure it is completely smooth and up to standard. If not, you can add welding rods before it hits room temperature and completely solidifies. Sanding is another method to add consistency and smoothness to a welded joint.
Using sandpaper is a simple – and effective – method to iron out rough ridges and produce a level joint. Additionally, it stops any of the surrounding plastic from being scratched. Rather than do this manually, you should attach the sandpaper to a rotary tool. This assists with significantly speeding up the process of delivering a smooth, finished plastic weld.