I received a series of follow-up questions from yesterday's blog entry. I will do my best to paraphrase and answer...
Blog Reader
One machine has a 30mm screw (3100 bar max pressure), and one has a 40mm screw (1800 bar max pressure). Both have the same size injection cylinders. When I transfer from the 30mm to the 40mm machine, do I need a higher pressure pump to move the screw the same distance.
My Response
In reality, the larger diameter screw changes all the aspects of pressure, velocity, and distance.
Since the surface area of the 30mm screw is 56% of the 40mm screw, you need to approach the process with the following assumptions:
- To maintain the same injection volume, the 40mm screw will need to travel approximately 56% of the distance.
- To maintain the same injection rate, the 40mm screw will need to travel at a speed approximately 56% of the 30mm screw.
Additional Thoughts
Basically, this is why it is critical to document your process based on process outputs such as fill time, part weight at the end of fill, and plastic pressure at transfer. Such an approach will eliminate the need to make such conversions.
-Andy
Hello Andy.
Can I find out that my process is pressure limited from machine's pressure curve?
Is there any different between these curves?
Milan
Milan,
The pressure limited process will have a plateau on the pressure curve, and a drop in the velocity at the time of pressure limiting.
-Andy