Category Archives: Uncategorized

“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

ARM Members Can Watch These 65 On-Demand Roto Training Webinars

ARM webinars were viewed 3,600 webinar times in 2019.  This number combines live webinar views — where members were able to partake in Q&A — and on-demand webinar views — where members were accessed our 10+ years of webinars at their convenience on the ARM website.

We have offer 65 webinars available on-demand for members. Members can access all of these titles immediately. Non-members can join here.

In addition to a variety of new webinar topics in 2020, we plan to organize a new series based on the Introductory Guide to Designing Rotomolded Parts.

  • Operator Training Program (25 Videos) presented by Nick Henwood, Dru Laws, and more Click for the detailed contents
  • Burner Maintenance presented by Adam Covington
  • Considerations When Light-Weighting Rotomolded Parts presented by Henry Hay
  • Cooling Fixtures presented by Ron Joannou Jr. and Joey Morsi
  • Determining Your True Cost presented by Steve Osborn
  • The Effect of Pigments and Warpage on HDPE Rotomolded Parts by Mike Haubert
  • EPCRA Reporting & Combustible Dust (with Roto 101 Intro) presented by EPA & OSHA
  • Finishing Parts with Robots (Case Study) presented by Dru Laws
  • Finishing Series (4 videos): Secondary Finishing Operations, Graphics, EPS Molding, and PU Foaming presented by Jason Brownell, Rick Carlsen, Corey Eystad, Nick Henwood, and Scott Saxman
  • Finite Element Analysis: The Basics presented by Michael Paloian
  • Improving Rotational Molded Insert Performance presented by Glenn Larkin and Jon Ratzlaff
  • In-Process Rotational Foam Molding presented by Dru Laws
  • Infrared Thermography presented by Bill Spenceley
  • Lengthening the Life of Your Mold presented by Tony Short
  • Making the Most of Trade Shows by Melissa Shearer
  • Making the Most of Your Marketing Budget presented by Melissa Shearer
  • Mold Clamping Methods – Pros and Cons presented by Erik Adams and Bob Mueller
  • Mold Release presented by Even Silo & Scott Waterman
  • Prop 65 for Rotomolders presented by Mike Haubert
  • Proper Sampling Techniques presented by Josh Hunsberger and Dave Loeffler
  • Rebranding Your Business (Case Study) presented by Tom Innis
  • Resin Rotomation by Rob Miller
  • Rotational Molding & the Evolving Structural Part Processing Business presented by Dr. Peter Mooney
  • Roto 101 presented by Rick Carlsen & Ron Joannou Jr.
  • Safety in Rotomolding & OSHA Compliance presented by Dave Schwoerer
  • Save Energy & Save Money presented by Bill Spenceley
  • Selecting the Right PE Grade for Your Part presented by Nick Henwood
  • Solve Cosmetic Part Problems presented by Jon Ratzlaff
  • Stiffness Models and Options for Multi-Layered Parts presented by Dr. Nick Henwood
  • Test Method for Flowability (Dry Flow Rate) of Polyethylene Powders Using a Specified Funnel presented by Ron Cooke & Jon Ratzlaff
  • Ten Actionable Business Topics by Tom Kammerait
  • Troubleshooting Your Rotomolding Operation from a Shop Floor Perspective presented by Ron Cooke
  • Turning a 4% Bottom Line into a 10% Bottom Line presented by Al Bates
  • Understanding the Molding Cycle presented by Gareth MacDowell
  • Unwanted Holes in Rotomolded Parts by Nick Henwood
  • Vent Plug Materials, Techniques, and Installations by Sandy Scaccia
  • What Does Internal Air Mold Temperature Have to do with Quality presented by Gareth McDowell
  • What’s Your Problem (2 videos) presented by Ron Cooke & Sandy Scaccia

President’s Message: The People of ARM


ARM 2018 – 2019 President Dru Laws

As my final message as the president of ARM, please forgive a different (and more personal) approach.  Instead of talking about the processes and programs that make up our association. I’d like to focus on the people that populate it.

It has been my complete honor to serve all of you as ARM President.  You have each made it a great experience for me! I am particularly grateful for those whom I get to rub shoulders with on the Board of Directors.  You can all rest assured that each one of these board members is an honorable industry ambassador. And a sincere thank you to those who serve on and lead the committees.  It’s encouraging to watch so much time freely and selflessly given to better the association. I would highly recommend you each consider how you can be a part of these fine groups of individuals and volunteers.

I can’t help but express my gratitude for the ARM leaders of yesteryear.  What an amazing community they helped build. I feel fortunate to have been able to carry that leadership baton for the past 2 years, and I am excited to now pass it on to those better qualified than I to carry us onward and upward.

And a big thank you to the amazing team that manages our association, on a day-to-day basis.  They do far more than any of us realize.

I love the variety of meetings the association holds throughout the year.  Some of those are remote, while others are in person. Regardless of the format, I love them mostly because of the people I get to associate with … you.  I look forward to shaking hands with new faces, and exchanging stories with old friends.

As I reflect on my ARM membership, I’m reminded of an old quaker proverb … “Thee lift me, and I’ll lift thee, and we’ll ascend together”.  This has certainly been my experience. Every time I extend help to someone else in the industry, I seem to benefit more so. What a great personal investment it has been for me, and I owe that to so many of you.

Now, in conclusion, please allow a short and heart-felt two-word benediction.

Thank you!

Dru Laws is the President of ARM and the Senior Vice President of Seljan Company in Lake Mills, Wisconsin.