Tag: drnick
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Ask Dr. Nick: Are There Guidelines for Vent Sizes?
During a recent “What’s Your Problem?” session, we were asked whether any guidelines existed relating to the sizing vents for rotomolding tools. This subject is covered in the ARM webinar series on “Operator Training.” I have reproduced the most relevant slides below: The first slide shows a “rule of thumb” that has been cited by…
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Ask Dr. Nick: What issues should I expect with mold pressurization?
Question: We have a question about molding with pressure inside the mold. We have rock & roll machine making medium sized parts. We have been experiencing significant warpage, especially on flat surfaces and it has been suggested that we should apply air pressure inside the mold, to improve our parts. Please could you provide some…
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Ask Dr. Nick: Particle Size Test Method Specifics
Question: I’m looking for information to go along with the Test Method for Particle Size of Rotational Molding Powders. What type of shaker do you need to use? Is it acceptable to shake the screens manually? Dr. Nick: In North America, the “Rotap” system is normally used. This imparts a horizontal swirling motion, with a…
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Don’t Forget Your Venting
Last year I wrote a blog for ARM that pointed out the importance of adequate venting and the bad consequences of not ensuring that your venting for each tool is adequate. This is VITAL to making a quality part. While I’m sure that many of you are fully aware of this subject, I still get…
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Temperature Conditioning for ARM Impact Testing
(and a few other practical tips) Minus 40º (actually the same number in ºF or ºC) is specified as the conditioning temperature prior to drop dart testing, according to the ARM protocol (“Low Temperature Impact Test”, Version 4.0, July 2003). This relatively low temperature has been chosen because it provides a better differentiation between different polyethylene grades and…
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Ask Dr. Nick: Is Dry Blend Color Good Enough for Roto?
Q: I see dry blend color has an advantage of quick color change without waste vs. compounding. Is this significant in your view? Can dry blend be “good enough” for roto? Dr Nick: Dry blend is still common in North America, mainly because of cost and convenience. It can be “good enough” for some non-critical…
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Ask Dr. Nick: Using thinner while flame treating parts
Member Question: In order to finish our parts we are using thinner along with gas flaming. Our process is not very safe and we have had a few events of rags catching on fire due to flame and thinner. Is there a standard way to finish rotomold parts (PE), maybe using non-flammable chemicals? Dr. Nick…
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What causes oven fires and how to respond
A rotomolder member of ARM asked about recommended actions in relation to fires in rotomolding ovens. These fires are typically caused by powder spilling out of a mold during the cooking process. This can be due to: Incorrectly closed clamps, or clamps that fail, causing the mold to open as it rotates A missing vent…
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Will future rotomolders be gas-free?
As a representative of ARM, I was recently asked in a discussion with some other ARMO groups about whether electromagnetic induction heating could be suitable for rotomolding. The issue was raised because of how the Emissions Reduction Plan of New Zealand may limit rotomolders’ ability to use gas to power their rotomolding machines. Today there…
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What constitutes ADEQUATE venting?
When I train machine operators, I tell them that, most likely, venting problems are the biggest cause of scrap parts they will come across. This statement was originally based on a survey conducted by the ARM many years ago. After 30 years in this business, the statement still holds true, as far as I’m concerned.…