Looking for a resin to use in a consumer athletic product

[desipius]

It's basically a monolithic tripod with a pedestal on top. About 45cm overall height, and the base fits within a 35cm diameter circle. The tripod legs stop about 1/3 of the way up.

Outdoor use all over the world
by occasionally angry/competitive athletes
should survive being landed on (ideally can be crushed and will spring back -- can have warping, stretch marks, etc. after)
paintable and bondable

Premium consumer grade materials are OK (the product is for high-end consumers, so some cost is acceptable. Ideally a cheap, common consumer product resin, though).

If the unit is tipped over one leg will be pointing up. From a safety standpoint this leg needs to buckle under the weight of a human body. From a customer satisfaction standpoint, it should spring back to at least usable shape (keeping the cosmetics would be a bonus) after unloading. This will be a rare event, but it will almost certainly happen.

I had a recommendation for Nylon 6/6 before the buckling requirement was added, and another recommendation for an ABS/PP blend after. Do either of these sound reasonable? Alternatives I should consider?

Thanks!!

 

[Pud]

Is it the tripod legs that need to recover?
(I'm afraid your 1000 words are not as good a picture...)



www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[MikeHalloran]

A rubber traffic cone might be a better starting design.


Mike Halloran
Pembroke Pines, FL, USA

 

[desipius]

Pud: Yes, the leg needs to buckle when loaded from the side. And preferably recover. I've attempted to attach an image which should clarify things.

Mike: Yes, the engineers on this project (I am one of them) wanted to go with a traffic cone shape, but it turns out that shape isn't something people will pay a premium price for.

 

[Pud]

Have a look at amorphous Nylon 11* or Nylon 12*. They tend to be fairly stiff but have a very good recovery when strained. They are also have very good chemical resistance and can be got with UV stabiliser in. A very hard (Durometer hardness) polyurethane might also work.

Perhaps extruded tubing with a rigid joining piece? All will be available in extrusion grades as it's used for oil pipelines amongst other things.

* e.g. PA11 = "Rilsan" trade name, PA12= "Grilamid TR90UV" and there are others.

Cheers

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[MikeHalloran]

The general shape guarantees that one leg or the pedestal will always be pointing up.
That's a liability, not an asset.

If you make it from a material and in a shape that's rigid within the service temperature range (not stated so far), you are also guaranteeing a puncture wound on the field of battle.
When, not if, that happens, you are looking at a lawsuit, at least.
Talk to your insurance carrier before proceeding much further with this product in this shape.

Alternatives include four traffic cone shapes joined by a generally spherical hub, in the general topology you want, but thin walled and flexible, maybe even inflatable.
... or a Schmoo derivative, a single pedestal projecting upward from a sphere, with ballast in the bottom of the sphere, so the apparatus is self-righting. ... and also flexible or inflatable.



Mike Halloran
Pembroke Pines, FL, USA

 

[ornerynorsk]

I'd be looking at urethanes, quite honestly. Most nylons and ABS blends would make a very neat improvised bayonet, which is not desirable.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[desipius]

Thank you all for the input.

I've talked with our mold shop in China and it sounds like the cost for Nylon 11 or 12 would be roughly 3x the cost to use Nylon 6/6. Does that sound correct to you, Pud?

Mike: We are aware of the safety issues involved, and I have no intention of sending a dangerous product out into the market. The shape of the actual product vs. the stick figure may be a bit misleading, we have rubber bumpers on the end of each leg, and the use case is closer to a course marker than, say, a track hurdle (which is likely more dangerous than this product).

I like the idea of using urethane. Assuming the material is chosen properly it seems like it will always get out of the way as well as spring back like we want. I'm currently looking into the costs to make the lower portion out of urethane or some other semi-stiff rubber. The product 'snaps' together using a slip fit joint just above where the 3 legs meet. I don't think that will work with rubber on one side, so we would either need to do an overmold or bond the rubber to a rigid plastic fitting.

 

[Pud]

the cost for Nylon 11 or 12 would be roughly 3x the cost to use Nylon 6/6

The amorphous versions are probably a bit more than that - but it's a completely different sort of material to straight Nylon 12, which is more like the usual nylon 6 (apart from it's excellent chemical resistance).

If you think a synthetic rubber might do, have a look into SEBS. It's about the cheapest of the elastomers, but I'm not sure of harder grade specs.


www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[desipius]

Our mold shop says they can do a SEBS overmold in a harder durometer, and I think the cost is manageable.

I'm currently wondering if I should be worried about creep. These will in some instances be sitting out all day in hot parking lots, and while they don't weigh that much the elevated temperatures might be a problem. Wouldn't want them to 'wilt'.

Should I be worried? Looks like there are some additives or certain formulations that have improved creep resistance. As near as I can tell the UV resistance is good already.