May 2011 Archives

Recently I was asked about manufacturers of larger molding machines...

Your recommendation on the best performing large all-electric presses - 2300 to 3000 ton range?

My Response
There are only a couple manufacturers who produce all-electric molding machines at this size range and I provided those names. My suggestion was to wait until NPE2012 if possible, since it is likely that more manufacturers will join the ranks of the 'big molding machine' manufacturers.

This question came across my desk last week...

If I want to measure the flow rate in the mold cooling system, should I measure the water coming IN the mold or the water going OUT of the mold?

My Response
Either is OK. Unless there is a leak, the IN and OUT flow rates should be the same.

Additional Thoughts
Some companies will also check the flow of each water line (during initial mold testing) just to ensure there are no significant restrictions or imbalances.

I received this question via email last week...

I am new to plastics technology and am looking for input on how to do an in-mold rheology test.

My Response
Although there is much training centered around the in-mold rheology curve, the basics are as follows:

  • Fill the mold as fast as you can with a short shot during 1st stage velocity controlled injection
  • Record the fill time and injection pressure at transfer
  • Repeat this process using incrementally slower speeds
  • Use 1/(fill time) for apparent Shear Rate
  • Use (Pressure)*(Fill Time) for Relative Viscosity
  • Graph Relative Viscosity (X axis) vs. Shear Rate (Y axis)
Additional Thoughts
For more posts about rheology, just type rheology in the search box in the upper right hand corner of this page.

I was recently asked this question...

We have been experiencing problems with excessive flash on a new silicone part. We are injecting a liquid silicone into a mold and letting it set. Could you give any insite to what may be causing this problem?

My Response
lash is a common issue that must be dealt with in silicone injection molding. The low viscosity of the silicone prior to curing allows it to get out of the smallest spaces of the mold including the parting line, mold vents, and ejector pins. In order to prevent flash in silicone injection molding a few different things can be done to counteract the problem.

First, ensure your shot size is not to large. An excessively large shot size will contribute to flash because the silicone expands as it cures. Unlike traditional injection molding the mold does not usually need to be 95-98% full during first stage fill. Second, check your mold tonnage and ensure both platens are evenly applying the appropriate force. This can be verified with spotting fluid. Also, try increasing the mold temperature or preheat the silicone more prior to injection. This should reduce your curing and cycle times and also increase the silicones viscosity in the mold.


New Hire Training

Andy Routsis
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I recently had this question asked via email...


If I am considering training should I require all new hires to take your introductory courses even if they have some past injection molding experience?

My Response
Yes. When establishing a training system in your company it is important to give every employee an introduction. It is also important to get everyone on board with the training and familiarize them with the system and its benefits. After participants with prior injection molding experience are familiarized with our training you can custom tailor a plan for them to include more in depth content to increase their skill level. 

I received a few emails after my last post on machine guarding and wanted to follow-up...

We have an older pneumatic molding machine at our facility, OSHA has not commented on it, should I still add guarding to it?

My Response
Personally, I would ensure there is some protection to the machine. On most of these machines, there are very few moving parts on this machine, so you basically need to protect the heater bands and clamping unit (if it is not already protected).

Since these machines are very small, I have also seen companies just place a small Plexiglas enclosure around the whole machine.

Recently, I was at a customer site and saw a 'tabletop' machine from a machinery supplier who is no longer in business. The excellent thing about this machine is that the customer added full guarding around the machine. This was pretty simplistic and inexpensive, but it served the purpose very well and I made a point of thanking them for the effort.

So, if you have a machine which has much older and inadequate guarding, remember that safety is not grandfathered in. Even though the machine was built when lower standards were in place, there is no reason to allow the machine to continue being unsafe. Always keep this in mind when you purchase a machine used machinery, or from a country which has a significantly lower safety standard.

I have seen a lot of confusion about this topic...

SCORM Compliance
According to Wikipedia: Sharable Content Object Reference Model (SCORM) is a collection of standards and specifications for web-based e-learning.

Basically, this is not a standard data protocol or format. Any SCORM-compliant course can be played by a SCORM-compliant player. This does not mean the course meets any specification regarding content quality, but it does meet a specific playback protocol.

For comparison, a PDF,  'Portable Document Format',  file is a standardized document which can be opened using a compatible .PDF reader. The.PDF does to relate to the quality of information in the file, just the way it can be viewed.

I was in some online discussions lately and this question came as a follow-up via email...

I have an older {brand name} molding machine and it has a very large & heavy injection unit. What is the best way to compensate for overshoot?

My Response
Once the machine transfers, the ideal result would be for the screw to go directly into packing. Unfortunately, the inertia of the injection unit can cause additional material to be injected during 1st stage. In most cases, you can just transfer from 1st stage to 2nd stage early to compensate. Unfortunately, the inertia creates force applied to the screw resulting in a pressure-controlled situation. Although the slowdown is typically consistent, some high-precision applications need more precise control near the end of fill.

If more control is required, and you cannot change machines, then you can create a slowdown profile at the end of fill. In this situation, the profile should closely match the natural slowdown of the screw using a couple steps. The benefit to this approach is that you have a more consistent slowdown than just allowing the screw to slow down.

Additional Thoughts
This correction should only be used when the natural slowdown of the screw provides inadequate consistency during transfer.


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This page is an archive of entries from May 2011 listed from newest to oldest.

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