Why control melt decompression? Just shut it off

September 08, 2011

That's the question, and succinct answer, that MD Plastics Inc. (Columbiana, OH), has for injection molders who normally have to control their resin melt via decompression to eliminate stringing and drooling. MD Plastics President Michael F. Durina says his company's Mini-Shut provides an inexpensive, automatic, miniature nozzle shut-off tip that not only eliminates stringing and drooling, but also the need for melt decompression itself.MD Plastics Mini-Shut shutoff nozzle

The Mini-Shut, for which a U.S. patent is being sought, was engineered to ensure repeatable part weight distribution, while also reducing surface imperfections. Designed to fit on the majority of nozzle bodies, MD Plastics says the Easy Nozzle is easy to install and remove and can run reliably at temperatures above 750F. In addition to ensuring low pressure drop and shear, the Mini-Shut also allows for the simultaneous operation of the clamp and the screw to boost productivity and can be cleaned using conventional purging methods.

Durina told PlasticsToday that the miniaturization of the device, as well as its cost ($225-$300), make it very unique from anything else that has been invented. Durina noted that melt decompression has been used since the invention of the reciprocating screw as a method to minimize drooling and stringing, but that it is decompression that can create other issues such as splay, melt cushion and shot inconsistency, as well as shifting of the solids bed along the screw axis, which can create screw slippage, bubbles/voids in the melt pool, and shear when the screw is called to rotate during the next phase of the cycle.

"My challenge is to provoke processors to critically look at what they have been doing and offer them a solution to a problem that most of them don't know they have," Durina said. "Up until now, the solution has been a shutoff nozzle that costs between $1500 and $9000 and has been plagued with maintenance problems, excessive length, and a short life span so most processors don't think of using a shutoff nozzle."

Md Plastics distributes the product in the U.S. through its own offices, as well as through DME Molding Supplies. SE System Engineering AG (Däniken, Switzerland) is its exclusive distributor throughout Continental Europe, while Cooper Technology (Bangor, Northerin Ireland) distributes Mini-Shut in both the U.K. and Ireland.


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