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High Temperature Materials…

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.

Measuring Preform Temperature…

There is no true ‘preform temperature’ because there is dynamic range of temperatures along the entire length of the preform.

Question: What should the finish temp be on the preform as it leaves the oven?
My Response: There is no specific temperature, but typically a profile this is specific to the material, mold, and equipment you are processing. For this reason, there may be an average temperature recommendation such as 100°C which might be used, but it can be very misleading. There is a range of temperatures which typically vary between 80-110° along the length of the preform. One of the most important aspects is to ensure you are measuring different locations on the preform at the exact same location each time. A hand-held probe will not give you repeatable, reliable, or useful results.
-Andy

Transferring with Temperature Sensors…

All the Scientific Molding principles apply when developing a process for V-P transfer using a temperature probe as with a process developed with position transfer.

Question: How does the development of a process differ when using a position transfer vs.a transfer via temperature sensor?
My Response:  The purpose of transferring using a signal from a temperature sensor is to establish a consistent mold cavity filling volume each shot. The first step is to build a good process using position transfer. Once you have established a good reliable process, you know the desired injection volume necessary to make a good part. From this point on, you adjust your temperature sensor transfer settings to get the same fill volume as your established process. This technology does not replace good process development, it just just provides you a method of better repeating that acceptable process.
Additional Thoughts: There is a large amount of processing technology available, but they do not replace god processing. The best use of this technology is to build a good reliable process which compensates for most variation, and then use the technology to reduce variation from that established process.
-Andy

Should Employees Train at Home?

Salaried employees are much more likely to train outside of the office since they can pick locations/times which are much more convenient for themselves.

Question: How common is it to have employees take the online training at home?
My Response: Salaried employees tend to be more motivated to train on their own time. If the training is required for the job function, hourly employees are very unlikely to train on their own time. It is best to make time during their shift or provide access before or after their shift.
After the required training is completed, some companies have had success getting hourly employees to conduct advancement training on their own time… but these company typically have other incentives such as bonuses or pay increases after the training is complete. Such incentives make this additional effort worthwhile.
-Andy 

Purging Co-Extrusion Dies…

When using mechanical purging compounds to purge co-extrusion dies, it is important to not purge all the extruders through the die at once to prevent excessive die pressure buildup.

Question: I have been told “For co-extrusion it is important to purge from first to last and not all at once”. Could you explain this?
My Response: Every co-extrusion die is constructed differently, but the main point is to avoid purging all the extruders with a mechanical compound at once if the die is somewhat restrictive. Since non-abrasive mechanical purging compounds tend to increase the die pressure, filling the die with compound from each extruder all at once may result in damage to the die. Some companies have had the die blown right off of the extruders when they have purged concurrently.
Safe procedures for using mechanical purging compounds in co-extrusion dies would involve purging one extruder at a time. This can either be purging to either the final material, a virgin resin, or a more neutral material such as polypropylene before moving on to the next extruder. Many molders will also reduce the RPM of all the extruders to help reduce pressure buildup.  This reduces the pressure spikes in the die making it safer and less stressful to the die when purging.
-Andy

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