Thermoplastics are common products found all around us this day and age. Thermoplastics have to be heat sealed and one method to do so is with an impulse sealer. Naturally, there are many other methods that are used to seal plastic. An impulse sealer has derived its name from the way in which heat is created. First, a plastic layer is placed on a large fixed coil. This is to generate a huge burst of heat, which is then followed by a huge burst of cool. Through this process, the thermoplastic is immediately sealed and then cooled again, which leads to a bond that will last for ages. In general, it is far easier to bond plastic rather than to bond any other type of substance. This is mainly because plastic has very high levels of uniformity. Because of this, one part of plastic can almost not be told apart from another part in the same plastic. In other words, when a plastic goes through a bonding process, it in essence melts into itself. Because the part that is melted basically bonds with itself, it looks and acts as if it was a single piece to begin with. There is almost no joint, and the joint that is there is far stronger than any other type of bond.
The Bonding Process
Bonding through heat is the preferred process that is used on plastic. An impulse sealer is used for this and it has been proven time and again that this offers the best results. Some manufacturers use a chemical bonding agent instead. However, these release highly toxic fumes and the end result is a lot less strong than those that have gone through an impulse sealer. Heat is the most common agent available and it is being used in a variety of ways to bond a plastic. If it is used within a process of assembly, there are three main types of sealers that can be used. These are continuous heat sealers, spot sealers and impulse sealers.
Continuous Heat Sealers
Continuous heat sealers form a part of the whole assembly process. This part is always heated to very high temperatures. Whether you use a continuous heat sealer, an impulse sealer or a spot sealer, the temperatures are always very high. Hands off, in other words, unless you want to burn your fingers. With a continuous heat sealer, the plastic moves through the hot area and bonds while they are on the move. This is a very easy way of sealing, often described as “no frill”. It is a reasonably reliable manner of sealing as it is rare that something goes wrong. However, if something does go wrong, this is often not picked up on because there is no room for quality control by using this method. It is a very cost effective method and therefore often chosen by manufacturing processes.
The next way of heat sealing on a manufacturing level is known as spot sealing. Just like continuous heat sealing, it uses a constant heat. However, unlike an impulse sealer, it only bonds one part at a time. Rather than having an entire heated area, like with the continuous heat sealer, it uses a hot metal rod that is at a constant temperature. Once a part moves past the rod, it is touched in a specifically designated spot. This method is far more accurate than continuous heat sealing. On the downside, however, a rod can only touch a relatively small area, whereas a continuous heat sealer can heat up a huge area. This process does require some quality control, because the slightest miscalculation in the heat settings can lead to the plastic burning through or not melting sufficiently.
The last method that is commonly used is impulse sealing. An impulse sealer is usually part of the end of the production line. The system is designed to fuse a range of thermoplastic sheets together at one time. Often, the sheets themselves contain a substance that has to be hermetically sealed in between the layers of thermoplastic. Regardless of whether or not something has to be inside, impulse sealers heat and seal a complete area in one go. In look and design, these machines are very similar to a press. The plastic goes inside the machine and sits at the top of a heating coil that is inactive. The top of the machine has a similar coil and is placed on top of the plastic. Both coils then heat up (this only takes a second or two), which then bonds the layers of plastic together. After this, cold water is pumped through to drop the temperature and hence harden the plastic.