Blow Molding 1

[chicopee]

I recently reviewed prints for blow molding a bottle.
The prints did not show vents. In order to inject the molten plastic, vents had to be incorporated and my question is, if vents are no longer incorporated into the design ,is the mold under a partial vacuum to allow the plastic melt to evenly distribute throughout the mold?

 

[jbel]

On our injection mold prints , very often there are no callouts for vents in the molds. It is usually left up to the mold maker to add vents as necessary. While this may not be a technically correct print drawing, we have found that it works well provided you are working with a skilled mold maker. If this is not the case and you are required to call out vent location, it is advisable that you put the vents as far away from the material nozzle as possible. As the material expands inside the mold cavity it will push the air away from it. In order to fill out the whole cavity, the maximum venting is required at the point farthest from the injection nozzle. This is not to say that venting will not be required at other locations on the mold, but the most difficult place to remove the air from is the farthest point from the nozzle, due to a decrease in the injection pressure as a result of proximity to the nozzle. Unless the machine you are using is somewhat exotic and provides for vacuum molding cavities it sounds like your molds need venting. Hope this helps!!!

 

[chicopee]

jbel, thank you for your comment.

 

[TheTick]

I've never specified where vents should be. On some occasions, I will specify where they shouldn't be, usually for cosmetic reasons.

All this machinery making modern music can still be open hearted.

 

[brengine]

For any molds made out-of-house, we only provide the bottle cavity shape and mold (machine) size. All actual mold design is left to the mold maker.

Ken