Who needs this fancy-smancy stuff?

Many molders are afraid to run thermoplastic elastomers, urethanes, or PVC. The reason they tell you is that they are either messy or they burn too many parts.  Many molders are even afraid of the Nylon families of materials.  This fear comes from the ease of running very forgiving materials and not paying attention to the special requirements of the non forgiving ones.

If you are going to have long-term contracts for any part where you'll essentially be dedicating one machine to a material and a mold, buy a custom built screw, check ring, and nozzle specifically designed for that material.  Why?  General Purpose is a compromise.  While I've run all these materials on conventional equipment with nothing special on the machine you have to pay close attention to what you are doing because the screw, check ring, and nozzle really want to mis-process your material.

On that note, if you have a job that runs optically clear resin or one with an especially difficult time to change materials, sometimes the best investment is a separate screw, barrel nozzle.  Instead of having to clean everything out, the newer machines only require a few bolts and unlocking a bayonet lock to remove the entire barrel.  This saves the two days and hundreds of pounds of mixed material when you are purging.

OK, you say.  I have a profitable job in one of these touchy materials but the profit isn't there to have the savings of using a separate barrel or custom components in the barrel offset their cost.  What do I do?  The best solution will cost you no more than $50 US.  Materials burn and degrade as a function of shear.  The highest source of shear is the nozzle.  Go to your local machine component catalog and buy a specialty nozzle with the taper on the inside, the orifice outside and whatever anti drool mechanisms might exist for your material.

The only problem here is a nozzle designed for Delrin will destroy PVC.  It is good form to remove your specialty nozzle and keep it with your mold until the next time.

Knowledge is power.  It's this knowledge that gives you your competitive edge over the competition.  Think about it.

Contact me with questions put in the subject line QUESTIONS.
Bill Tobin, WJT Associates, E-mail: bill4012@hotmail.com