Archive for the 'Rotomolding' Category

Sorry Guys, Rotomolding Is Not Dead

I thought this was interesting when it was posted in early April, but decided not to pile on to the responses. Every once in a while, the folks at Core77 do step in it and their faithful readers are only too glad to point it out.

When frequent contributor hipstomp posted about some nifty watering cans, quizzing readers to see who could figure out how these hollow products were produced, his reveal was somewhat anti-climatic:

Rotational molding! I’d practically forgotten this technique even existed; we see it so rarely, probably because you could accurately describe it as being “expensive, and takes freaking forever.”

For those of us who design products utilizing a wide range of materials and processes, it wasn’t that rotomolding was the chosen process that was notable in his post, it was hipstomp’s apparent surprise that rotomolders weren’t extinct. As many respondents reminded our dear poster, rotational molding is still very much alive and kicking. I have personally worked on several rotomolded products in the last year and know that most molders and mold builders are quite busy indeed.

One of the reasons why you don’t see rotomolding as often as other processes might have something to do with the poor job the rotomolding industry has done promoting its process to the design community. True, rotomolding isn’t appropriate for high-volume applications, but for specific situations requiring the kind of rugged parts this process can produce, there are few other processes that can do the same as cost-effectively. Perhaps watering cans aren’t the best example of that as some observed–perhaps blow molding might have been a better choice (depending on the production volumes), but there would still be a fair amount of scrap generated by that design.

Hipstomp goes on to suggest that RP processes might be more appropriate for the creation of hollow parts. I’m not saying that these products can’t be produced using rapid prototyping methods like Polyjet, but I guess I still question why. As commenter Dave observed:

RP materials and processes are improving, but this is a question that should be posed to people with knowledge of roto-molding and other processes, as well. RP is not a silver bullet, despite what seems like an ID fascination with having a one-size-fits-all answer to manufacturing. As for surface finish, there are RP machines (polyjet) that do pretty high resolution (.0006″ layer thickness). With texture built into the build file, maybe surface finish will eventually not be an issue of “can we make it this way?” “Should we make it this way?” will remain though.

A more fundamental limitation comes into play. RP methods require high precision movements of the RP machine for every part. Roto-molding, like injection molding, blow molding, etc. requires high precision to build the tool, then much lower precision to build the parts.

To be clear, I’m not beating up on hipstomp; I myself am a moderator of the Materials and Processes discussion forum on Core and I’ve re-posted many of his articles on this blog. But it does say something about how we as a design community looks at M&P as the foundation of what we do as industrial designers. True, not all ID’s engage in the development of artifacts, but many of us still do and not all of them are mass-produced to justify infection molding or so custom as to warrant using RP processes regardless of how novel that might be. I think it’s worth taking the time to properly educate our students and continually educate ourselves and our community on the materials and manufacturing technologies (old and new) that are being (still) used today and where each fits in the broad spectrum.

Take a look at the post as well as the comments and let me know what you think.

[Core77 post]

What’s That?: Rotomolded Utility Cart Door

The sickness strikes again… I’m walking on NC State campus and notice a utility cart used the landscaping crew has… The doors catch my attention because while the entire cart looks nice enough, the doors have a bit ‘o styling that I would expect in a product like this. Anything too flashy or complicated wouldn’t be appropriate for a cart intended to haul dirt or recently-killed wildlife…

BANG! It’s a rotomolded door.

So here’s a reasonably decent-sized part that’s both rugged (that plastic can take a lickin’ without any dents), functional (it can get cold and rainy in NC, you know) and has a bit of style (checkout those Batman-esque details at the bottom). The doors help to elevate the aesthetics of what might otherwise be a hum drum utility cart.

Stay tuned for more materials and processes sightings in the wild…

What’s That?: Rotomolded Upper Section of Parking Meter

It’s a sickness, I know it is…

I’m walking down the street with some friends in Portland, OR. I’m there attending the IDSA International Conference and I notice the parking meters… Nothing really out of the ordinary. “Nice, clean design” I think as my eye traces the lines of the human-statue-sized meter that line the streets. I ‘m draw to how everything fits together to make up a complete product. I notice where the parts meet, how they match up, the radii, the different materials… What a minute: that upper section’s rotomolded

While the bulk of the meter is constructed of painted metal castings, the upper section–the one that holds the solar panel (of course this thing is solar-powered, this is Portland), is rotationally molded plastic. There are several styles of these meters throughout the city and it’s difficult to tell if these are retrofits or part of the original design to use rotomolding for this upper section. I suspect that perhaps it was easier to bolt in the relatively light solar panel and run the wires through the hollow part and doing something more complex out if metal. Also (this is pure conjecture), rotomolding might have provided a way to add some visual interest to the meter where to part cost and tooling was less expensive using this process. But, again, that’s just a guess…

I’d love to hear the story behind the design of this thing.  I actually found some information about it here, in the form of a “Green Purchasing Case Study.” According to the study, these SmartMeters have a 10-watt solar panel and cost about $7500 each.  Parkeon and Cale manufacturers the SmartMeter, but I can;t find any additional information about them. If anyone has the inside scoop, I’d love to hear about it.

I told you it was a sickness…

Rotomold Your Own Toys



I came across this and I know it’s a few years old, but it’s still really cool…

JESTER of J6Studios documented a toy project he did using Smooth-On Smooth-Cast 325 which is a castable liquid polyurethane. After designing his toy in sketches, he built up the form in clay and created silicone molds for molding the polyurethane.

This is a bit different from the kind of rotomolding used to make the kids toys you’re used to seeing in your back yard, but the design approach is pretty much the same.  The big difference is that this uses a chemical process to convert a liquid material (the Smooth-Cast) to a rigid part using a catalyst. Traditional rotomolding uses heat to melt (actually sinter if you want to be really accurate) a powdered plastic using heated molds. But in both cases you do need to rotate the molds (thus the name) while the material distributes itself around the mold.

There’s lots of images showing his technique. Enjoy.

Rain-based Plant Watering System


[Via Core77]

Bas van der Veer’s “A Drop of Water” is a simple rain-collection system that connects into your gutter’s downspout. With an integrated plant-watering bottle, the barrel is large enough to catch a considerable amount of water and offers a tap at the bottom which lets you refill the bottle. While the product looks like a prime candidate for rotational molding in production, the recent Design Academy Eindhoven graduate built a prototype out of gel-coated fiberglass using MDF mold machined from a 3-D model.


[More pictures and van der Veer’s other work]

DIY Rotational Molding Machine


(Via Designboom)

Industrial design students Andrew Duffy, Craig Tyler and Edward Harrison from the University of Rochester constructed a minature rotational molding machine out of scrap materials and a cordless drill. From their YouTube post:

Continue reading ‘DIY Rotational Molding Machine’