President’s Message: ARM is Engaging Members in New Ways


Rick Carlsen

For the rest of the messages I write this year, I will continue to record some numbers that are affecting my thinking, just like I did when I wrote my last message on 3/21/20.  

Today is 05/11/20 (happy belated Mother’s Day to all the moms!).  The US has 1,334,951 confirmed COVID-19 cases (up from 6,519 on 3/21).  There have been 4,142,97 cases worldwide (up from 204,000), and the DJIA is at 24,333 (up from 20,315).  Schools, restaurants, bars, and other “non-essential” businesses remain closed.  For all intents and purposes, face masks are mandatory while injecting disinfectants into patients seems like a prudent medical strategy.

In the last 50 days, ARM enacted its plan to engage with its members in a different way.  ARM has more frequent emails going out to membership with updates on topics ranging from PPE (personal protection equipment) to the PPP (Payroll Protection Program).  Webinars are occurring more frequently with many more planned.  ARM is working hard to engage in a social distancing environment.

Membership feedback has been crucial during this time.  We are getting suggestions from members about what type of information they need to navigate the storm.  As quickly as possible, we are acting on suggestions and putting reliable content in front of members.  This model seems to be working.

We continue to value and act on the feedback received, so please keep it coming.

Based on travel restrictions and social distancing guidelines, ARM is modifying the format of the Summer Regional Meetings this year.  Rather than hosting three to four meetings around the US this year, ARM is going to host an online Regional Meeting.  While we are giving up the face to face meetings that membership finds so valuable, we are moving to a format where more participants can view and access presentations and information.  I am hopeful that this format proves to be as effective as other regional meetings.

The details for the event will be communicated and promoted when the details and logistics are finalized.

Finally, I want to remind you that ARM’s knowledge library is accessible to our members.  The knowledge library has information on almost any topic that applies to your business.  This is a great resource to help train and educate your employees. 

Thank you for your continued support of ARM!


Rick Carlsen
Solar Plastics, LLC
ARM President

ARM Leak Testing Summary


Dr. Nick Henwood

On Thursday April 30, 2020 ARM held a discussion on Leak Testing, moderated by Education Committee Chairman Ron Cooke (ExxonMobil)  and Sandy Scaccia (Norstar Aluminum Molds).  The session was very well attended and the discussion between everyone on the call was excellent.  There was so much useful information exchanged that we decided to try to capture all the salient points.

We began by talking about the methods that are commonly used for leak testing of rotomolded parts, then discussed some more unusual methods that had been tried.  Then we talked about whether leaks can be rectified and what can be done to stop the leaks happening in the first place.  This led us into a very interesting detailed discussion about issues with metal inserts, which is one of the most common causes of leak problems. Continue reading

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 or color?


Dr. Nick Henwood

This is a question that I’m asked quite frequently.  There isn’t a simple “bad / good / better” answer, it’s a bit more complicated than that.  In the description below, I’ll try to concentrate on what molders really need to know, so my description could be viewed by some polymer chemists as a bit superficial.  Others may think it’s over-complicated… I’ve tried to steer a middle way!

Butene and hexene (strictly speaking: butene-1 and hexene-1) are examples of comonomers that are used during the production of different polyethylene (PE) grades, including roto grades.  They do essentially the same thing for PE, but their presence can cause some differences in grade performance. Continue reading

Ask Dr. Nick: XLPE v. PE heating and cooling cycles

Question: What are typical heating cooling cycles compared between XLPE and PE? 


Dr. Nick Henwood

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 that powder particles melt and fuse together in a solid mass.  For standard roto grades, sintering is typically completed by the time that the Internal Air Temperature (IAT, the air temperature inside the mold) reaches approx 265 degF.
  • Consolidation – allowing sufficient time and temperature for the gases in trapped air bubbles to dissolve into the molten polymer matrix.  For standard roto grades, consolidation is typically sufficiently accomplished by the time that the IAT reaches 390 degF.

During the cook stage of rotomolding XLPE grades, the above two mechanisms need to be achieved, followed by another additional one:

  • Crosslinking – XLPE grades contain a special package of additives, based on organic peroxides, which form side links and create a network structure from the individual polymer chains.  This network structure provides improved short- and long-term physical properties.  BUT – and it’s a big but – this won’t happen unless sufficient time and temperature is provided.

The requirements for individual XLPE grades may vary, but one general recommendation that I have seen is that, during the final stages of cooking, the IAT should be above 390 degF for several minutes.  An additional processing benefit of the best XLPE grades is that over-cooking does not result in the usual catastrophic loss of impact strength due to chain scission.

I recommend that, if possible, you set up your cook cycles for XLPE using a device that can measure IAT and that you follow the guidelines above, in the absence of anything more specific from your material supplier.  A more rough-and-ready guideline might be to add two or three minutes on to the cook cycle you would use for standard PE,

However –

Depending on the formulation, over-cooking XLPE can result in some undesirable effects, that you will want to avoid.  One common effect is known as coining – the appearance of a locally depressed area on the surface of the part, as though a large coin had been pressed into the surface while the polymer was soft.  Reducing the oven temperature is the usual expedient to eliminate such defects, but then you may affect crosslinking.  Hence my main recommendation, to use available control tools to achieve as much precision in set-up as you possibly can.

Hope that helps; happy rotomolding!

Dr Nick Henwood serves as the Technical Director for the Association of Rotational Molders. He has more than 30 years of experience in rotomolding, specializing in the fields of materials development and process control. He operates as a consultant, researcher and educator through his own company, Rotomotive Limited, based in UK.

“The Seven Stages of Rotomolding” Questions and Comments


Dr. Nick Henwood

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 familiar with Dr Gareth’s lively presentation style from his many presentations at ARM conferences. He was able to bring this approach to the very different format of an on-line event and, as a result, we saw a high level of reaction from the live audience, in terms of comments and questions.

Unfortunately, we simply ran out of time to address everyone’s needs, so I’m doing a wrap-up via my Technical Director’s Blog.  The length of my Blog reflects the number of questions, but feel free to dip in and out of it, if you don’t have time for a long read!

Thanks again to Gareth for a really excellent webinar.   Continue reading

President’s Message: ARM is adapting to unprecedented change


ARM President Rick Carlsen

To give this message context, I am writing this on 03/18/20.  The US has 6,519 confirmed COVID-19 cases, there have been 204,000 cases worldwide, and the DJIA is at 20,315.  Schools, restaurants, bars, and other “non-essential” businesses are closed nationwide. Tom Brady just signed with the Tampa Bay Buccaneers; the world is in chaos.

We made the decision to postpone the Spring Executive Forum three weeks ago today.  At the time, there were fewer than 500 confirmed cases in Italy. We were hearing rumblings of border closures and quarantines.  As crazy as it felt, we thought there was a risk of ARM members getting stuck abroad, so we made the decision to postpone. What seemed like a possible overreaction three weeks ago seems like a simple decision today.  Things are changing quickly.

As we are facing unprecedented changes in our daily lives, ARM is working hard to adapt to this fluid situation.  We are working to determine how ARM can deliver value to its members in the world of social distancing. Personal interaction between members will be limited for a period of time, which is very unfortunate given that we constantly hear that “networking” is one of the greatest ARM values.

ARM has hosted webinars for more than 10 years.  These sessions are free and available online to our members to view at their leisure.  This has proven to be a successful way to interact with our members, and we see this as a continued viable meeting method in the near term.

In addition to webinars, ARM has built an impressive knowledge library that is accessible to our members.  The knowledge library has information on almost any topic that applies to your business. I encourage you and your team to explore its offerings. 

In my last letter, I wrote that ARM’s goals remained unchanged; we are dedicated to making incremental and sustainable changes that increase the value that ARM offers its members.  The COVID-19 pandemic doesn’t change this. ARM’s delivery methods and personal interactions are going to be different for a period of time. ARM will try some new ways to interact with its members, some of which will work and some that will teach us what to do better next time.  

Finally, ARM is on solid financial ground.  We have worked diligently to build cash reserves in preparation for times like this.  We have analyzed our projected cashflows, and we know we will weather this storm and come out the other side in great shape.

Thank you for your continued support of ARM!


Rick Carlsen
Solar Plastics, LLC
ARM President

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 the molded part. The warpage area is focused in the middle part of the welded metal stripe. In the warped area, the wall thickness is between 7.5 – 8.5 mm. In order to eliminate the warpage problem, our customer has added externally a metal plaque to prevent overheating. The part is cooled up to 80-85 degC (176 – 185 degF) inside the mold. Then, the part is moved from the mold and is left for cooling in the environmental temperature.


Dr. Nick Henwood

Dr: Nick:  I’ll try to give an opinion on this problem. 

  1.       I’ve previously seen warpage problems when molding a particular grade of PP.  The shape I was molding was a simple cylinder. The material supplier told me that PP has “natural lubricity”, by which I understood that something in the polymer migrates to the mold surface and provides what amounts to an internal release agent.  However, I have successfully molded many other grades of PP, without seeing the problem.
  2.       Generally, PP shrinks less than PE, so you would expect that warpage problems (which are caused by unequal shrinkage rates in different sections of the molded part) would be less.
  3.       Warpage effects tend to occur more often with thick parts; at 7.5 – 8.5 mm, I would consider your part to be pretty thick.
  4.       The area of the mold containing the welded metal stripe may result in a different heating condition compared to the rest of the mold surface.  This may result in a lesser or greater wall thickness building up at the stripe. It’s not clear from your description which it is, although the fact that the problem was fixed by reducing the heat to the stripe area (by adding the external metal plaque) indicates that the stripe area was previously heating up more than the rest.  Did you measure the wall thickness of the part in this area, compared to the rest of the part?  In any case, thickness variation around the part is another cause of warpage.
  5.       You’ve not mentioned anything about mold release agent (mra); your choice and level of application may be a factor.  If the PP grade you’re using has this natural lubricity (see note 1 above), then reduce the level of mra applied. You can immediately reduce the release properties of an existing surface (ie one which already has mra applied) by gently abrading with a scotch pad or similar non-metallic product.
  6.       Slower cooling can reduce warpage; you don’t specify how you cooled or the cooling rate.  In extremis, don’t apply any external cooling and allow the mold to cool naturally in ambient conditions.  Worth trying, just to see if it helps, even if this is not practical in production.

I hope the above list gives you some pointers to the problem.  Whilst the root causes of warpage are similar across production, the way these causes come together to manifest a particular warpage problem can be complicated.

Dr Nick Henwood serves as the Technical Director for the Association of Rotational Molders. He has 25 years-plus experience in rotomolding, specializing in the fields of materials development and process control. He operates as a consultant, researcher and educator through his own company, Rotomotive Limited, based in UK.

ARM Tours Italy: Attendee Info

ARM regrets to announce that we will be postponing our tour of Italian rotomolders and our collaborative meeting with IT-RO, the Italian rotomolding organization. The meeting had been scheduled for March 29 – April 3.

We are working with the venues in Italy and those we have booked for our next spring meeting to determine when we will reschedule. We expect to hold the meeting in 2021 or 2022 and will make an announcement in the coming weeks.

Details for the postponed meeting follow…


More than 60 attendees (including more than 25 ARM members) have already registered for our unique event in Italy.

The meeting begins with a tour of the rotomolders of high-end, complex parts in northern Italy. Then we join our Italian counterparts for a day and a half of education and networking on Lake Garda.

Below we’ve included some information about the meeting for planning purposes. We’ll update this post as the event approaches.


March 29: Arrive in Milan; Overnight at Villa Malpensa Hotel
March 30: Tour Rototech and Metallurgiche Cornaglia; Dinner included at Roof Garden in Bergamo; Overnight at Mercure Hotel in Bergamo
March 31: Tour Persico and Acerbis; Overnight at Hotel Caesius
April 1: Tour Ve.Ca and Moulding Services and the Ferarri Museum; Overnight at Hotel Caesius
April 2: Conference at Hotel Caesius; Dinner included at Hotel Caesius
April 3: Half-Day Conference and Optional Wine Tour

  • Lunch is included on tour stops and during the conference.
  • Our Sunday night hotel, Villa Malpensa Hotel, is located a few minutes away from Milan’s Malpensa airport. The tour will depart from Villa Malpensa Hotel early Monday morning.
  • If you’re departing Italy from Hotel Caesius, Milan’s Linate airport is the closer of the two Milan airports. Verona airport is the closest to Hotel Caesius but offers fewer flights.

Airport Transfers and more
The Hotel Caesius offers private cars and coaches to the airports and the train stations. Their price list is available here. In the next couple of weeks, we will send a form to see if it’s feasible to organize group transfers to the airport.

Education Program
We are organizing the education sessions with our Technical Director and IT-RO. A key portion of the program will be based on our group’s feedback from the tours. ARM members will complete comment cards after each part of the tour and Nick Henwood will use that feedback to lead a discussion during the conference about what we liked, what we learned, and what we want to know more about. We’re making good progress and will be able to share more about the remainder of the program soon.

You should plan for your own voice/data cellular service while in Italy. However, we are ordering multiple pocket wifi servers. We’ve never used it before but hope it will improve connectivity for everyone on the tour.



President’s Message: ARM’s approach, offerings, and goals remain steadfast



ARM President Rick Carlsen

In an attempt to understand how long New Year’s Resolutions last, a social networking firm called Strava analyzed over 30 million fitness records from its users.  The results show that most New Year’s Resolutions start to derail on the second Friday in January. This year, most people’s resolutions lasted just 10 days.


A reason for short-lived resolutions is that many of them are viewed as temporary, thus, expendable.  To make sustainable changes, experts advise that you should make small additions to your routine that don’t result in a perceived hardship.

I am happy to report that ARM made 0 New Year’s Resolutions this year.  Continue reading