Injection Molded Bicycle Wheels 4

[ornerynorsk]

Hello All,

Just wondering if anyone knows what material is common to bicycle wheels. These are the typcial utility style rims as found on sidewalk bikes, childrens bikes, and the low-end BMX style. Cost and toughness are primary considerations, so I was thinking maybe a toughened unfilled 6/6.

This particular application is low speed <10 rpm's, 12.5 x 1.75 nominal rim size, max loading in either static or dynamic will be about 250 lbs, and will operate slightly out of perpendicular to the floor (max 8 degrees). Tire selection will either be solid urethane (foamed center) or 58 psi max pneumatic tire/tube. Impact during usage will be nil, but should be able to withstand incidental impact of handling, loading in and out of vehicle, etc.

Any thoughts?

 

[insideman]

I'm gonna write it before anyone else has a chance: Don't reinvent the wheel! There has to be wheels available at low cost, so you need not go through design, mold build, first shots, mold revision etc.....

 

[KENAT]

Anything of use here

http://www.skywaywheels.com/about.htm

either material (nylon composite) or existing design.

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[ornerynorsk]

Thanks Insideman,

For our unique application, we do, this time, have to literally re-invent the wheel, or at least redesign it a bit. The conglomeration of sprockets, hardware, and other attachments that we would have to put together would not only be prohibitively expensive, but would end up looking like Rube Goldberg gone mad.

We've already justified all the associated costs of doing it ourselves, and have management's blessing on it, so we will be proceeding.

Would much rather have practical advice from the people who've done it before to back up our material selection than to rely solely on vendor recomendation.

 

[ornerynorsk]

Thanks Kenat,

Skyway was the first company we checked out!

 

[MacGyverS2000]

<10rpm? That's a slooooow wheel...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[ornerynorsk]

Hey Macgyver,

Yes it is. It's on a piece of handicap mobility equipment, so we don't any speed records being set! Strictly manual stuff, no motorization.

 

[patprimmer]

BMX bikes used super tough glass filled nylon 6.6, but toughened nylon 6 would do just as well and be easier to mould.

Cheaper bycycles that are designed for small children use unfilled nylon 6 or even glass filled polypropylene.

If you want them round and with no weld lines at the most stressed point (like in the rim 1/2 way between spokes) you need to very carefully consider gate position. A diaphram gate in the hub will not work well.

I can provide details if required.

Regards
Pat
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[dwightdixon]

What material to use will depend on whether you want it: weatherable, or durable for a long time, or worried about it taking a set after being bent or setting at high temperature in the trunk of a car. The easiest way to refine your choices is to look at your competitors in a similar application and copy what they use. They have likely make some mistakes before the settled on the final material. You can check what they are using by looking at the recycle marks or conducting a simple burn test.

 

[patprimmer]

Dwight

I agree in principle, but I have seen a number of such wheels. They have all been nylon or PP

I will stand naked on the town hall steps if one of those two is not eminently suitable.

Regards
Pat
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[ornerynorsk]

Thanks Everyone,

Pat, our current design will not allow a diaphragm gate, but I'm glad you mentioned it, because we had talked about it at one point. We are now considering either fan gating at several points around the periphery or just going to hot runner. There are 3 convenient countersunk bolt holes which would allow for hot runner injection points, I'm just not experienced enough to know how it will affect the part regarding weld lines, warpage, and such. Surface finish or splay should be not a major consideration as we will have some heavy texturizing (IBM #8) on the cosmetic face. We are pointed toward unfilled toughened 6/6, also.

I would love to post a drawing but cannot due to IP considerations.

Pat, if you do, indeed, find yourself standing naked at city hall, let me know and I'll arrange to be comfortably seated . . . at a pub on the other end of town :>)

All comments regarding gating are well appreciated.