Best Practices (Secrets of Molding)

During my career there was a constant search for best practices or maybe even the “Secrets of Molding”. It seems that there was a continuous flow of snake oil salesmen floating around trying to sell you something you didn’t know you needed. In many cases they were successful; however, I sometimes think back on the pieces of equipment we bought that didn’t do the job or didn’t perform as advertised.

Perhaps in the most extreme case a significant number of pieces that were to automate our process were completely unacceptable and even sent back to the manufacturer for a refund. Once a salesman came in to sell material additives to enhance the properties of the materials we were molding. We invited him in for a trial and quickly encountered problems. The long story short was that his product was actually starting to melt in the drying hopper and caused bridging- not only rendering the process unstable, but causing a need to completely clean the dryer and spreader cone. This is the only time I ever “threw someone out”. What’s more surprising is that this person is still selling this kind of product or enhanced version. How will someone ever find out about this? No doubt a respectable company would be very careful about naming someone’s product defective at the risk of a lawsuit!

There must be people out there using this stuff and buying it on a regular basis. It was not for us. Situations such as these reveal that technologies can be very different and concepts that apply to some do not necessarily work in others. Hence my favorite words as an instructor, “It depends”.

The committee for the Technician’s Toolbox struggled with a Best Practice that wasn’t necessarily best for everyone. The question was, “When shutting down a machine, where does one leave the injection screw after purging out the barrel?” There are two distinct factions out there:

1. We always left the screw in the completely forward position. This allowed heating the machine up in a more uniform way and decreased the amount of material that may have burned on the barrel walls in the front zone.
2. Some molders argued that there was too much opportunity to break off screw tips when starting up, so the screw should NEVER be left in the forward position!

As the Editor for the Toolbox, my goal was to present more than one way to apply a technology and expect that the wisdom of the user would determine how to approach a situation. So, given the scenario, how do you approach this situation? My answer is, “It depends.”

One reason screw tips break off at start up is that the screw was installed improperly into the injection unit. There should be a small clearance between the end of the screw tip and the barrel end cap (We used .030 inch). It should be obvious that if the screw assembly and barrel are touching that under some circumstances the screw tip would shear off. Another tool to prevent this from happening would be what we called a pre-soak timer. This assumes that the barrel temperatures are proper. The presoak timer activates when the setting is reached and the heat permeates the injection unit, making sure that all of the plastic is melted inside.

Trick Question, “When standing in front of the machine nozzle, which way does the screw rotate?”. Answer – It depends. Actually some manufacturers build machines with the “left handed screws”. I remember once when the machinists were trying to remove the nozzle from one machine and actually coupled a chain hoist to the wrench – with the pipe handle- to loosen the nozzle, only to find out the nozzle was threaded in the opposite direction! In a worst-case scenario I was busily waiting for a machine installation to be completed and after pushing the start button, determined that the motors were turning the wrong way. This happens with 3-phase installations (another story). I asked the control systems technician to “correct” this, and he did, along with the dryer that was plugged into the machine circuit breaker. Upon further examination we determined that the original rotation was indeed proper, and needed to go back to its original state – and so did the dryer.

Maybe these are not good analogies, but what rings true after so many years is that there are just as many ways to do things as there are companies doing them. Some procedures work better than others for different people for different reasons. One should keep this in mind when touring a facility. Although sometimes it appears that management has learned the Secrets of Molding, what you may be witnessing is managements identifying some best practices and then adapting their philosophies to enable effective means of implementing them. It’s not healthy to spot what appears to be a good idea and then proceed to enumerate the reasons why it couldn’t be done elsewhere. The point is that one must ask questions and then determine what has to be done to implement the scheme – and then DO IT! Who knows, it may just become one of YOUR best practices, and then you start learning the Secrets of Molding. This could be the most important aspect of membership in Nebraska SPE, so go tour a facility and learn from the experience!

HOMEWORK ASSIGNMENT! Let's have some fun with this! No matter what the circumstances are, when you open the drain on your sink, tub or whatever watch the direction of the vortex. Does it spin clockwise or counterclockwise (anti-clockwise)? Send your answer to Golubki@cox.net and I'll let you know what we find out.

Jerry Golmanavich