Extrusion is complicated. There are countless variables and different processes, and machine sizes vary greatly. Although the following tips can help all extrusion processors, people working on larger machines will see the greatest benefits. Plants that extrude sheet, blown film, profile, piping, wiring, or tubing (among others) will be familiar with this situation: You start up your large extruder and are close to your processing temps, but find some issues with cold zones that are causing carbon.
What a nightmare. We can see it in this example.
Maintenance arrives at 5:00 am, turns on the resistors and other related equipment. Production arrives at 7:00 am for their morning meeting before going to the machines. Suddenly, there is a change in the production schedule. Instead of Nylon, now they'll be running PE, so the first machine must be adjusted. Also, an adjustor didn't show and there's nobody to cover, so the second machine must be turned off. Finally, on the 3rd machine, the dryer does not work so it will be necessary to wait a few more hours to be able to feed the ABS and start production.
All three are large machines and they started early because there are some areas that take a long time to raise the temperature. So, the last zone of the extruder has already been burning resin for about five hours and the die zone has not yet reached the set point. As it passes 10:00 am and production begins, you can see the contamination in the black spec and degradation that comes routinely at each start. Finally, you're running good production after noon.
If this sounds familiar, here are some tips to have faster start-ups for large extruders.
1. Power up equipment and heaters in sequence
Start with whatever will take you the longest to reach your processing temps. Sometimes this might be a machine that processes at higher temps. Other times, it may be machines with parts that take longer to reach processing temps than the extruder zone. Consider heads, dies, and accessories.
2. Double-check to make sure that your heating and cooling systems are working properly
It would not be good to realize two hours later that we have a resistance overheating due to a badly installed thermocouple or that the refrigerant does not circulate.
3. As soon as you review your production schedule with your personnel who showed up, immediately continue turning on other necessary equipment
For this section, consider:
a. The most urgent production.
b. Machines that require lower temperatures to start production.
c. Also, remember the machines that require higher temperatures that are adjusted in steps. Start with a low temp to gain time, and raise the temps only when an adjuster is ready and dedicated to start the machine. Consider that there may be distractions at start-up. It's common for a machine to be left waiting to start for extended periods of time. If you started raising the temperatures past a certain point at the beginning, you may be more likely to experience contamination.
4. Good start-ups are dependent on how the machines were shut down
Even if you do everything right the morning of your production run, a bad shut down could lead to contamination issues because resin oxidizes in the barrel. Fortunately, purging compounds are designed to avoid this oxidation and will help you start-up with perfect parts in a fraction of the time. Sealing with a purging compound like Asaclean's U Grade could get you on the right track to earlier, and longer, production runs.
Ready to reduce your production downtime to protect your profits? Learn more about how purging compounds and process efficiency work in tandem.