A question recently came in regarding an older post about running high-temperature materials in normal machinery: High Temp Machinery
Question:
We run high temp resin in newer electric presses. i do not believe our injection units were retrofitted with any special materials. the main resin put through our units is PAEK with 30% glass reinforcement, which is a tannish color. we have been experiencing “black streaks” on the part surfaces, and no one in house can seem to figure out the root cause. These streaks are usually dark brown, (despite the symptom name) and really seems to be burnt up resin at the edge of degradation to me… but whether or not our steel can handle the constant high heat cycles has been the main focus of attention. any thoughts from your end that could possibly help us out? we keep the rear zones at about 700*F on these jobs.
My Response:
The most important thing to do first is to compare the actual melt temperature with the manufacturer’s suggested temperature and verify the material is being melted properly. I have seen machines set at 750°F with a resulting melt temperature of only 675°F. In this example, we were able to increase the cooling time and significantly slow down the recovery speed to get the melt temp up to 710°F. This material was still 15° below the recommended temp, but acceptable parts were able to be produced for the while better heater bands were ordered.
Hi Andy,
Thanks for getting back to me. What is your method of performing melt temperature test? We use a needle melt pyrometer using the 30/30 method. This method just seems very unreliable to me as the readings can jump around quite a bit, and very rapidly. Our engineer has found in the past that our thermocouple reading was much lower than what we were actually getting, and so since then we have lowered the nozzle heats in relation to the difference between the readings and actual. I believe his findings were the results of a 30/30 melt temp test. Our problem with streaking subsided but is now back with vengeance.
I think we will revisit this melt temp thing as you suggested. If your method is the same as our, maybe our pyrometer is not top notch?
Thanks,
TOOLFANATIK
Hello,
The newer K type fine needle probes are very fast and accurate. With these, you no longer have to preheat and wait 30 seconds. With the thin probes, you insert the probe, slowly move it around, and record the highest temperature reading. We get the most consistency with this method. The important aspects are to wipe off the probe immediately after it leaves the melt so it remains clean, and have a spare probe in case you suspect the measurement to be false.
-Andy
OK thanks. we have some older type K’s and some newer type J’s. the type J’s are what we’ve been using lately. i’ll give this a go. thanks again for your help.
TOOLFANATIK
Hello,
The J type is just too slow to make good measurements. 15 years ago, the thin K types were too delicate, but the technology has improved immensely. We use K-Type needle probes (.072″ diameter 4″ long) in our labs, but there are many good options available.
-Andy