Sticky pellets

[jayglo]

Hi new to this board. Thanks in advance for any advice I might get. Currently running a flexible PVC natural compounder single screw. Has a hot face die cutter. I'm seeing a problem with excessive sticky pellets after about 8 hours of running. Not too familiar with hot die face cutters, but wondered if cooling the face with compressed air might help solve this? Appreciate any advice.


Thanks

Jayglo

[Len]

Jay,

Use forced (cool) air on the cutter face and fluidized bed cooling, bring the pellet temp down to about 110F or less, then package. You should be okay, unless there is something migrating out of the pellet formulation that is causnig agglomeration, after the pellets cool. Check your formulation for ingredients that bloom or migrate, replace them w/ more compartable ingredients, if necessary.

I've seen some stickiness after packaging f-PVC w/ face cut pellets. Under water pelletizer is a better way to go for TPE and f-PVC to avoid sticking/agglomeration. Even so, the set up conditions and formulation have an effect on these soft polymers.

Len

[jayglo]

Len,

Thank you so much for your input. Forced air can be in form of those venturi tubes that blow cold air out one side and hot out the other? My melt temp is currently about 180 C. the formulation is fairly stable, I agree with you about the temp lowering. I an not very familiar with hot face cutters, this particular one has 4 blades. We have a pellet cooling system of 3 cyclone style coolers (air). I don't think that the blower in the face cutter unit is not helping enough in cooling down the pellets. If you can offer some advice after reading my situation I would greatly appreciate it! Does agglomeration happen at the cutter surface?

Thank you

Jay

[Len]

Jay,

Check your pellets, carefuly. Inspect them as to the type of agglomeration: tails, twins, clusters, size of agglomerate, for example. You brain storm your own classes and degree of acceptability for agglomerated pellets.

Weigh out a specific amount of pellets, then count the number in each of your classes/proposed catagories in this sample. Divide the cut pellets into classes/types of defect or agglomerate. Rate the acceptability and then log/track the type of defect. This will establish a bench mark for changes in your porcess and allow you to rate/evaluate if process changes move you in a better direction. Stats on the pellet class population per sample acceptability constitute; go/no go levels of agglomeration or defect and establish a metric for improvement.

Some Questions: Does agglomeration get worse after running for a period of time? What is that time period? Does this suggest some process change that will allow you to run longer w/out agglomeration? Does pellet size effect the agglomeration? You might be able to vary the blade speed and throughput to change the pellet size and gain an advantage. Keep asking questions of yourself and those involved in the process.

Venturi tubes are great for generating localized cool air, and although I've not used them, could work to lower the initial cut pellet temperature. Test your hypothsis w/ some experiments. Temperature, air volume, air angle, for example might be critical.

Also, you should rig up some method for measuring the bulk temperature of your freshly cut pellets, as soon as possible after the 3 cyclone cooler. Track this temperature at the same time period for a better read on your progress toward a cooler/less agglomerated pellet blend. If you can lower this bulk temp, as you know, you will have less pellet agglomeration. You can them rate pellet temp and pellet quality via these metrics.

It could be that you will need to look not only at the cool air flow (temp and volume) at the face cutter, but also Blade Conditions: blade sharpness/condition and clearance between the blades and the die face. Other areas of interest will arise as you better understand your pelletizer output.

I hope these suggestions are helpful. Good luck, happy hunting. BTW - luck favors those how practice their craft.

Len

[jayglo]

Len,

Thank you so much for your wonderful insight. I have a great place to start now. I sicerely appreciate your feedback. I will try all of yor suggestions and move forward. I'll keep you posted on my progress.


All the best

Jay.