Need advice on managing regrind

Buzz - Morning Skip - it's been a while since we posted here - lots of things going on in various forums and hopefully as this spring unfolds we can get back onto a regular contribution schedule, but for now, another important question cropped up on use of regrind -

"We realize every heat cycle deteriorates the integrity of plastic resin. We have a few parts that can be made from 100% regrind. These parts require very little strength or cosmetic requirements. How do you manage regind of regrind? What do you do with the runner and sprue composed of 100% regrind? Regrind a second time, sell? It seems it can become a material management nightmare quickly. THANKS"

Skippy - Morning Buzz - well let's go through a couple thoughts-

a) some materials "live on" despite being regrind better than others

Buzz - right, and some materials can have a small amount of "sweeteners" to add as processing aids in subsequent passes through a machine. Size reduction equipment is likely to yield better "flow" and better process stability

Skippy - exactly so - next

b) work to establish a "use ratio" of "regrind aka sprues and runners and less than acceptable parts and start up scrap" that is slightly larger in intent than generation aka use a goal of 21% "regrind" when you generate a total of 20%.

Buzz - the obvious advantage in controlling a steady "process" is that this keeps things very close and as you get better, you may find that you need to reduce the percentage of what you classify as regrind as you get better -

Skippy - spot on, so to continue,

c) Generally "100% regrind" is still suspect for process "ability variability" unless it is (continually) well blended - keep an eye on aspect ratio (size of and percentage of each size) in the mixes and gravity induced separation -


Buzz - thinking this one through -- ask if the runner and sprue are say 20% of the shot weight, then use these as the "regrind" portion of an 80/20 mix with 80% being the "first pass" material and the 20% being the "second pass regrind".

Skippy - Right; just like mapping a "virgin and regrind" process, only a tiny percentage of the material on a descending basis remains and keeps moving forward as the "regrind of the regrind" becomes a portion as "regrind".

just our two cents -
Skippy and Buzz

for more on this discussion see it here:

http://www.linkedin.com/groupItem?view=&srchtype=discussedNews&gid=155135&item=42931513&type=member&trk=EML_anet_ac_pst_ttle