Join Andy Routsis, founder and president of A. Routsis Associates, as he presents many aspects the typical injection molder overlooks.
When optimizing the injection molding process, many injection molders stop their efforts after adjusting a few parameters such as cooling time.
Andy will focus on often overlooked concepts such as the proper use of injection profiling, appropriate cushion sizing, and material preparation.
This seminar can benefit any engineer, processor, supervisor, technician, or die setter as well as anyone involved in managing a molding operation.
Q: Do you see any difference when molding different colors?
A: Yes, lighter colors tend to flow easier than dark colors. Keep in mind this will affect both mold filling and cushion size.
Q: Can you give more examples on sizing a cushion with respect to different materials?
A: Yes, Semi-crystalline and engineering polymers exhibit a melting temperature and their density tends to be more consistent in the barrel. As a result, they benefit from smaller cushions which provide better control of the process. As for amorphous resins, they tend to require a larger cushion to compensate the variations in melt density.
Q: Are there any special cushion requirements for low durometer materials?
A: Since these materials tend to be highly compressible with a large amount of packing required... they tend to require larger cushions around 10% of the shot size.
Q: Are the slides of this webinar available online?
A: They should be available for download on this page.
Q: Could I see this webinar again?
A: It should be available for download on this page.
Q: Could you discuss a little more about cushion and how it affects the molding process?
A: A cushion places additional material in front of the screw. Since the packing of the material is pressure-controlled, the amount of screw travels varies from shot to shot during this process. Inadequate cushion can lead to variability in packing... especially if the screw bottoms out.
Q: Can you elaborate more on clamp tonnage?
A: Generally speaking, we like to use only the amount of tonnage that is necessary. This causes less wear and tear on the machines, molds and process will run more consistently.
Q: Could you please review how to pinpoint gate seal again?
A: The stabilization of the gate seal curve is where the gate seals. We recommend selecting a time shortly after this point to ensure the gate remains sealed.
Q: Could you talk a little bit more about Machine Evaluations?
A: We discussed this in much more detail in the previous 'Scientific Molding' and 'Scientific Troubleshooting' webinars, also available on IDES. We go into great detail in our Intelligent Molder Series.
Q: Do your training products cover purging?
A: Yes, many of our products cover the importance of purging. If your company does a significant amount of purging, you may want to create a procedure to ensure this is performed properly.
Q: Do you have any information regarding scratch and Mar resistance additives and how do they affect resin flow?
A: Most non-reinforcement additives and colorants have a lower molecular weight than the base polymer. As a result, they tend to reduce the viscosity and increase the heat sensitivity of the polymer. Also ask your material supplier if they have any Technical Service Bulletins [TSB] on this matter.
Q: During the gate freeze study, how important is it to adjust the cooling time along with hold time to maintain a consistent cycle time?
A: If you process of material is very sensitive, they you may want to add cooling time as you reduce second stage time to ensure a consistent cycle time.
Q: During the molding of HDPE crates for the food industry, how important is the packing pressure and time in reducing the amount of stresses built in to the base of the crate.
A: To reduce stresses, a lower packing pressure may need to be used. In most cases, controlling the degree of crystallinity may be more important to the dimensional stability of the part. You should check the density at the gate and measure as you move away.
Q: How can i prevent flow marks on my moldings?
A: Although there are different causes for flow marks, they are most likely caused by poor adhesion of the material to the mold surface. Increases to the injection speed, melt temperature, and mold temperature can generally improve the situation.
Q: How do you determine if you are heating your material with 80% from shear and not from high heater band settings?
A: To start... in an autothermic process, where all the heating is provided by the screw, the heater bands will not even turn on. A properly configured process will have heater bands which turn on and off occasionally, but use 60-80% less power than when the barrel is heating up from a cold-start.
Q: How long before you can take an accurate melt temperature?
A: Although 30 seconds is a general rule, some resins will cool faster, and some pyrometers respond much faster. We recommend that you perform some tests to determine what method provides the most consistent measurement with your materials and equipment.
Q: How would you achieve the best color concentrate mixing (within the barrel) without special equipment or compromising part strength?
A: The first concern is to ensure that the rear zone temperature is optimized so the material is conveyed quickly and efficiently to the transition zone of the screw. Once this is optimized, you can better control the melting and mixing of the material by the screw.
Q: Parts to be 95% filled comparing to packed part (1-st stage filling)?
A: If you completely fill the part during velocity-controlled, first-stage injection... then any variation in material density or viscosity will cause a flash or short condition during fill. By leaving some of the filling to be completed by second stage, pressure-controlled packing... you ensure the mold is filled the same way each shot and starts packing immediately after the mold cavity if full.
Q: Viscosity curve and gate seal test - should it be redone every time the melt temperature changes?
A: If you choose a fill time which falls in the shear-thinning region of the viscosity curve, then temperature will not significantly affect the viscosity curve. If you choose a second stage time which takes place after the gate seal, then your gate seal worksheet only needs to be performed if a large temperature change occurs.
Q: What effect does running an LSR molding process with no cushion have?
A: Any process without a cushion invites variability if any degree of packing is required.
Q: How does venting affect the process? And can you over vent?
A: Remember, increasing the depth of the vent can cause flash, but increasing the number of vents has no negative effect on the process. In some applications you could even consider using a vacuum vent.
Q: What is approach on gate seal with valve gates?
A: You should perform a similar study, but you will be looking for a stabilization of the graph rather than a flat line.
Q: What problems come from running rear zone too low all the time?
A: If you perform a tacking temperature study, then you are using the temperature which optimizes material conveyance and melting. In this case, the optimal temperature may be high, low, or in-between.
Q: What pressure should be used for gate seal study?
A: You should first determine the optimal pressure using a long pack and hold time... then optimize the second stage time for that pressure.
Q: Would you please tell us what kind of cost for those training mentioned? Is there any more discounts when more training are combined together?
A: The pricing is available using the link provided above... Combination packages and plant-wide training packages are best handled by contacting me directly at 978.957.0700 or andyr@raininteractive.com.
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