Barrel temperature overshoots
i am facing a typical problem of barrel temp overshoot, we process polycarbonate, abs and pp. machine is 130 ton g2 series toyo. when we turn on heaters parameter cut off at right temperature ie set @220 cut off at 220 but once the machine starts it’s cycle the temp starts overshooting i.e. set@ 220 actual is 235 in mid 3 zones of the five. as if barrel is generating the heat on it’s own
to further rule out screw bend problem 1. we formed lumps and free refilling (ie. at the time of refill we allowed material drooling from barrel) with different backpressure and injection rate there was no overshooting temperature remained stable. we tried this on pp and abs at least 20 cycles each and no overshooting at all even of 1deg at any zone
2.next step we formed lumps and this time we made a nozzle touch with mold to stop drooling and the temperature started overshooting again with almost 1 deg rise at 2-3 shot gaps and by 15 – 20 shots we were overshooting by almost 4-7deg in middle 3 zones
what we have tried to solve all this is
1 checked all the thermocouples
2 checked all heaters
found nothing amiss…. now before opening screw set i want to double check if i am missing onto something
if anyone can guide me on this that would be great
to be sure you can check one more thing.
This temperature increase would be quicker and higher in case of more viscous material.
The Easiest way to solve this problem is by cooling the barrel with the help of fan air during operation,
so temperature may get down quickly
but this way your electrical power consumption may increase.
Although some smaller sized screw and barrels you have to run with a tighter clearance
such as 22mm and below. These have to run with less clearence 0.006. This is becauce the checkrings are soo small they actually expand during injection and too much clearance will cause the check ring to crack.
Also check your residence time in the dryer to ensure the temp of the chip is all the way through the chip, not just on the surface. Do the cycle time and part weight calculation to see what the hourly throughput is. Get the bulk density of the residence and based on height in the dryer and hopper volume make sure you are getting the minimum the resin mfg'er recommends. If it is marginal raise your dryer hopper level. We always tried to get as much energy into the chip as we could before the compression zone because sheer caused us other problems.