Published Injection Press capacity specifications: Is Max Shot Size at Melt density or Solid density?
Most specifications for injection molding presses give a max shot size in ounces or grams of PS polystyrene. Is this value at melt density or solid density? Then is there a formula to convert melt density to solid density and vice versa? I know its not as simple as a conversion factor due to the # of variables involved, but is there a formula that gets close? I found an article by Beaumont that discusses this and they give a rule of thumb regarding Amorphous and semi Crystalline materials, but they also caveat it by saying its just a generalization. Thank You.
Re: Published Injection Press capacity specifications: Is Max Shot Size at Melt density or Solid density?
Hi,
The best way to find out the shot capacity is to go the machine find the max distance the screw will move back and calculate the volume. Once you have the volume take the published shot weight from the machine manufacturer and divide that by the volume. Weight divided by volume will give you the density they are using. You will then know if it is melt or solid.
Hope this helps.
Regards,
Suhas
Re: Published Injection Press capacity specifications: Is Max Shot Size at Melt density or Solid density?
Hello,
Suhas has got you on the right track here. Most of my machines give specs in inches so I end up calculating the volume as Suhas suggested. Once you have your volume for the barrel, you then can use the melt density to determine the appropriate shot size and more importantly, can you fit that shot size into this machine. Now for safety, (if your previous calculations tell you that you can fit in said machine) I would do another calculation and reduce your calculated volume by 80% to prevent an over calculation that would end up flashing out your tool in the first shot and causing you a lot of head aches.
Hope this helps
Husky
Re: Published Injection Press capacity specifications: Is Max Shot Size at Melt density or Solid density?
At one shop we used one resin and a 1/4" suck back plus max screw stroke, purged onto a pice of cardboard that had been tarred on the scale, shot the resin out and weighed it. We did it for every press and put it into a spreadsheet.
Rick.
Re: Published Injection Press capacity specifications: Is Max Shot Size at Melt density or Solid density?
Agreed with Rick - great idea to find the melt density. Note that the back pressure will play a role.
Regards,
Suhas
