Tag: drnick
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Ask Dr. Nick: What’s the difference between hexene and butene?
Question: I have been discussing rotomolding resin made from butene versus hexene and have received mixed feedback. Is there a real difference between the two and are there applications where one is preferred over the other? Or is it just a question of price and availability, when it comes to using prime material in natural…
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Ask Dr. Nick: XLPE v. PE heating and cooling cycles
Question: What are typical heating cooling cycles compared between XLPE and PE? Dr. Nick: Crosslinkable polyethylene (XLPE) rotomolding grades work in a different way to standard linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) grades. During the cook stage of rotomolding standard PE grades, two separate things need to be achieved: Sintering – ensuring…
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“The Seven Stages of Rotomolding” Questions and Comments
As part of ARM’s on-going commitment to member service, we are ramping up our webinar program for 2020. The latest webinar was presented on March 19 by Dr Gareth McDowell of 493K. I thoroughly recommend that, if you missed the live show, you catch up with it on the ARM website. Many of you will be…
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Ask Dr. Nick: Warpage in a polypropylene tank
Question: In a cylindrical tank made of PP powder, we have experienced a problem of warpage (internal and external waves). I wonder if you could give me your technical opinion. The inside part of the mold is welded with an additional metal stripe and in this part of the mold we are facing warpage in…
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Ask Dr. Nick: A Basic Review of Foam in Rotational Molding
ARM often receives questions about the foaming process as it relates to rotomolded parts and we thought a basic review might be useful. A number of different foam products have been used in conjunction with rotomolded articles, in order to impart enhanced properties. These include: Polyurethane (PU) Foam, injected into a cavity in the final…
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Why is there (what looks like) orange contamination in my powder?
Bizarre as it may seem, in the past few weeks, I’ve had two different consultancy customers report powders with this same problem. They sent me samples and parts but, even before they arrived, I suspected that the problem was gas fading. Some of you may have experienced this phenomenon before, and wondered why it happens:…
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Ask Dr. Nick: Why does the same mold need different cook times in a different rotomolding machine?
Rotomolders who have multiple machines often find that, if they move a mold from one machine to another, an adjustment in cooking conditions is invariably required. The differences between machine performance can be considerable. Whilst this may be expected when moving from one style of machine to another, an adjustment may even be required when…
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Ask Dr. Nick: How does cold weather affect the rotomolding process?
You may have heard that in England, when we’re not obsessing about Brexit, we often discuss the weather. This is odd, when you consider that, other than a lot of rain, we don’t see extremes of weather that often. Recently, we’ve experienced what we Brits would regard as some cold weather, although it’s been nothing…
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Ask Dr. Nick: Can I fix gaps in a parting line?
A badly fitting parting line is a regular pain in the neck, for a number of reasons. The most notable annoyance is that, as the mold rotates in the initial stages of heating, powder spills out from any gaps that exist. This wastage of powder can cause an under-weight part and, even if the spillage…
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Ask Dr. Nick: Avoiding “Angel Hairs”
On ARM’s most recent What’s Your Problem? teleconference, there was a question asked about powder piping systems, especially about avoiding and dealing with “angel hairs”. I provided some follow up to the molder after the call, which we’re happy to share here for everyone’s use. My first recommendation was to contact ARM’s mainstream pulverizer supplier members, who should be able to offer good advice. They are…