Welcome!

Note: High RPM grinders typically rotate a set of blades at a very high speed. When the rotating blades pass by the stationary bed, they cut the part giving the familiar rat-tat-tat sound. The motors on these grinders tend to be over sized… and they often consume a significant amount of energy relative to the amount of material they consume since they have to maintain a very high RPM to work effectively.

In most cases, I prefer the low RPM grinders because they consume less energy than high RPM grinders… especially if it is running constantly. Low RPM grinders use a heavier set of stepped blades which operate more by maintaining the momentum of the blades to steadily chew up the plastic. Over time… theses grinders tend to be less expensive to operate and maintain… especially if they are in constant use.

Most grinders are best used in applications where the amount of material being fed into the grinder is close to the maximum amount it can consume. A grinder which consumes only 10-25% of it’s capacity can waste a large amount of energy over time.

-Andy

First, you are correct that your process will be more solid and reliable if it is short during first stage. This is critical to compensating for material variation… which will always save you money over the long term.

Second, your first stage injection pressure will show an increase as the material reaches the end of fill. If you look at the injection pressure integral for the entire cycle, you will find that the energy applied to the polymer will be virtually equal in either case.

You should always approach your processing in a logical manner… regardless of whether the machine has an all-electric, hydraulic, or a hybrid design.

-Andy