Plastic extrusion welders can generally be divided into two categories: screw-based extruders and non-screw-based extruders.
Learn our top 5 tips for properly caring for your hot air welding tools and minimizing maintenance.
Every plastic has a set of parameters (temperature, pressure, time/speed) at which it should be welded. However, the perfect temperature for the application can vary depending on environmental conditions. If you are welding in a less than ideal environment, the only way to find the perfect welding temperature for your project is trial and error. If welding is taking place outdoors be sure to perform test welds periodically throughout the day to ensure your temperature is set correctly, as the environment can change over time.
It’s important to evaluate each plastic weld to ensure your final product is strong and resilient. Particularly when speed welding with a hand tool, small defects in a single weld can be magnified as beads are built up to the base material’s thickness. Several key indicators allow you to evaluate your welds without the need for destructive tests.
Broadly, there are two types of hot air plastic welding tools: manual tools and extrusion welders. Manual tools are ideal for very small fabrication work, detailed projects, and repair work. Extrusion welders are suited for larger fabrication projects such as tanks, chutes, liners, and piping.
It's important to identify the plastic you're welding as only like plastics can be joined. The simplest way is by performing a burn test.
Inside every Leister hot air tool is a heating element composed of a ceramic honeycomb supported resistance wire filament (See below). Electric resistance wire heaters work on the principle that when electrical current passes through a conductor heat is generated, and the amount of heat generated is related to the resistance of the conductor.
Some resistance wire heaters are able to function without airflow because they have been designed in such a way that they will not reach temperatures above their safe operating limits. Examples include: a toaster, some ovens, wrap heaters, some space heaters, etc.
However, Leister heaters are designed to operate at very high temperatures—most are designed to heat airflows up to 650°C, and some up to 900°C—and as a result require airflow at all times. To reach these high air temperatures, the heating element must be capable of reaching even higher temperatures. Without adequate airflow, the element will heat up unchecked and will exceed safe limits, leading to the destruction of the element.
When PVC is melted or burned, it emits hydrogen chloride (HCl) fumes. At room temperature HCl is a colorless gas, although it will form white fumes of hydrochloric acid upon contact with atmospheric water vapor. When welding PVC the work area should be well ventilated, either naturally or through a forced air system.
PVC should only be used with an extrusion welder that specifies compatibility with the material. Components that will be exposed to PVC plastic or HCl fumes in these extruders should either be made with different materials or have a corrosion resistant coating. Using PVC with any extrusion welder without specified compatibility will result in signification corrosion to the internal components in contact with the plastic and fumes (see photos below). In the photos, the corrosion damage to the extruder screw is evident. This costly repair was completed in the STANMECH Service Centre and required the replacement of the extruder screw, extruder tube, and extruder nozzle. The damage could have been avoided by using a tool designed for use with PVC.
While Laser IR Thermometers are an extremely common tool, they are entirely ineffective for measuring the outlet temperature of an air heater. To understand why, we must first understand how this tool works. Laser IR Thermometers measure the surface temperature of an object by measuring the thermal energy emitted by the target. Knowing the amount of thermal energy discharged and the emissivity of an object’s surface, the object's temperature can be determined by the device.
When measuring a heater’s output air temperature, the largest issue with these tools is that they measure surface temperatures. As the heated air is transparent, the measurement will always be the surface temperature of a nozzle or a component of the heater housing; and frequently it will be an exterior surface. These items will always be cooler than the heated air, often by a significantly larger margin than the user would expect. To accurately measure the output temperature of an air heater you must measure air temperature and laser IR thermometers are incapable of doing so.
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