Elastic cord replacement material

[cthompson68]

I have an application where I am in need of an elastic cord. Similar products on the market are the Goody elastic cords (

http://www.goodycomfort.com/main.taf?p=1,4)

used which are used as hair bands, and are only available in a few sizes. I have considered using an o-ring as various standard sizes are available for a 1/8” (.125) cross-section width. The o-ring would need to have a good resilience (rebound), and weather resistance. From the chart in an o-ring products book Neoprene appears to be the best choice of material as natural rubber is rated poor in weather resistance.

As rubber bands typically have a 35A durometer, and several o-ring manufacturers have the capability of manufacturing 40A durometer o-rings, this would appear to be a good alternative to the Goody elastic cords. The application is for a consumer good product, and the typically bungee cords are too high in cost.

If anyone else has other elastic cord / material recommendations, I would be interested in hearing about those as well.

 

[MikeHalloran]

Do you need the toroidal shape of a hairband or o-ring, or do you need linear cord?



Mike Halloran
Pembroke Pines, FL, USA

 

[cthompson68]

I was thinking of a toroid (doughnut) shape, such as an o-ring, as it would be lower in cost, and perhaps readily available off-the-shelf. An open-ended linear cord (circular cross-section) is also an option, but may have higher associated costs.

I am looking to use an elastic cord in an assembly to join parts together. An example would be a portable bicycle pump to its mounting bracket to prevent it from slipping-off (not the actual application). Are there any torus-shaped bungee cords on the market?

The hair band bands are too short, and the head wraps are too long in regards to the O.D. As o-rings are available in various O.D. or I.D. sizes (ex: AS 568A-226,-242,-258, etc.), I have not yet determined the size needed. If will depend on the design of the injection-molded plastic parts.

As I mentioned, the elastic cord would need to be low-cost, and available as an off-the-shelf component if possible. With an o-ring, this may requiring a special order due to possible need of a lower durometer material. The typical o-ring durometer of 70A will not have the degree of elasticity as required. I am open to hearing about other suggestions.

 

[Compositepro]

There is not much cost difference between O-ring stock and shock-cord. Solid rubber cord is more prone to breaking when stretched because of notch sensitivity to tearing. Shock-cord is made from multiple strands of rubber so tears do not propagate from strand to strand. The fiber braid around the rubber is far stronger than the rubber itself and causes the rubber to stretch uniformly rather than mostly at the weakest point.

If your product requires more than about 10 to 20% stretch on a frequent or continuous basis I would recommend shock cord.

 

[unclesyd]

Checkout you local hobby or fabric store for elastic cords.
Some stores carry a very good cross section sizes and shapes.

Here is a site that has round cord and loop

http://elasticconnections.com/loops.html

 

[cthompson68]

Thanks for all the responses, and the comment about the notch sensitivity of a solid elastomeric core was a good point. So why is tearing typically not a problem with rubber bands under normal use (light-duty)?

The linear bungee / shock cord typcially found in stores have hardware (hooks, balls, barb, etc.) on the ends of a linear cord which may not be needed for my application. This is the reason why I was looking at the Goody headwraps is the ends are joined together without hardware in a similar fashion as an o-ring. However, the ID size is not correct for my purpose unless other sizes are available in the range of a 3 to 4 inch I.D., and 1/8 inch cross-section (similar o-ring size: AS 568A-234 to AS 568A-242).

Some other possible manufacturers I located are:

* LexcoCable:

http://www.lexcocable.com/bungee-cords.html

* Phoenix Roper & Cordage:

http://www.phoenixrope.com/elastic.html

* American Cord & Webbing (ACW):

http://www.acw1.com/

* HNW:

http://www.hnwelastic.com/products.htm#cords

If you know of any other manufactures that provides off-the-shelf elastic shock cords close to the sizes I had previously mentioned, then let me know. I need to get some samples to test in a prototype assembly.

I had tried a local hobby store but nothing was close ti what I was looking for was available.

 

[unclesyd]

Have you looked at latex tubing like that used for sling shots, spearguns, and medical. This tubing has the highest elasticity and is too notch sensitive. I don't think it amenable to bonding.
You also might look at SBR tubing which I believe is bondable

http://www.brownells.com/.aspx/pid=1221/Product/SURGICAL_TUBING

http://www.spearitco.com/index.php?main_page=index&cPath=88

http://www.kentelastomer.com/

http://www.opticsplanet.net/vwr-amber-latex-rubber-tubing-2408-50-coil-length.html

Here is a source of SBR and also rubber bands.

http://www.aerorubber.com/tubing.htm

 

[cthompson68]

Thanks for the ideas, and the latex tubing used in sling shots is also a good idea. I will need to review those links to see what is available.

Here is a product similar to what I am looking for from UMX Inc. Lanyard Supply:

* LY-WR-401EC 1/8”(D) x 14”(L) Elastic Round Cord (approx 4 ½” I.D.):

http://www.lanyardsupply.com/lanyards/ring/wrist/wrist-ring-lanyard-material-view.htm

Not sure if this material would classify as an elastic shock cord, but I will try to get some samples for evaluation.