Plastic Springs?

Most plastics creep under load, so must have a normal condition of zero or close to it, load. In addition, temperature dramatically increases this effect.

Polypropylene may do it but I suspect the 100C temp will beat it.

Some of the nylons may also work, but again temperature may reduce it's life.

Some of the thermosets may be your best bet.

You could look at phenol formaldehyde, urea formaldehyde.

I assume this is to be a production part, so cost will be impotant.

You will probably need to fiddle with fillers (glass etc) to get the right properties.

Good luck

I agree with ronsargent about the use of acetal AKA Delrin. I have designed some very interesting springs to use for actuating a pixi-point without damaging it. It is easy to adjust the tension by adjusting the thickness. There are no materials yet available for use with SLA models that will give you the characteristics of a machined or molded part. Also ABS is definitely not the material for a spring. If you need a material that will withstand a lot of heat, then you might want to consider one of the polycrystalline materials. I don't remember the names, but they shouldn't be hard to find. I used one that was carbon fiber filled for a snap on assembly that was subject to 200+ degrees. The material had a 500deg. molding temperature so the heat was not a problem.

I think one of the materials Garyceng is thinking of is an LCP, like Vectra. The main problem I see with making the springs one piece with the frame is that the best material for the frame may not necessarily be the best spring material. ABS is definitely not a good material for a spring that is under constant load. Without knowing details of the overall design and requirements, it is hard to recommend a material.

send us your detail with the drawing on www.cgenterprise.in we can give some better information for the same.

First, let me say that I have no knowledge or experience in this area so just ignore me if I'm being stupid.

What about cutting "fingers" in the PCB and letting the FR4 do the flexing.

Not stupid at all! We considered this, but a primary consideration is space. This is small assembly of about 1" total and there is no room for the 'fingers' on the pcb.

Thanks,

Dave

What about plastic coated metal springs?

I'd go to DuPont, GE Plastics, ICI or any large supplier and ask the guys who REALLY know their products.

Don't undersatnd exact application you discribed, but just for your information PU springs are beeing widly used in press tools, and work better then metal one,

Good answer (and so rated). Another possible approach is use of conductive epoxy or similar adhesive, eliminating need for deflection. This is highly dependent upon layout, components themselves, and volume, though. Frame would only need to position switches initially.

Follow-up: this came in a different newsletter that I just saw: http://www.cotronics.com/vo/cotr/ea_electricalconductive.htm#125. Look at the data sheet.

Stop trying to give the world another cheap oiece of garbage that will fail two weeks after purchase. Use proper metal springs and proper electrical contacts.

Cheap to build doesn't mean poor performance/reliability. If you think about the design he's described; assuming that he gets it right: it should be simple, and, therefore very reliable.

We currently use silver plated berrylium copper springs. They work well, but are very small, hard to handle, costly, and take up valuable space. So, we are exploring a lot of different approaches. Since product reliability/durability is priority #1, we may end up with the metal springs again if we fail to imagine/create something better.

Since reliability is the #1 issue, possibly staying with the beryllium copper springs, but mold them into the frame. A molder that does overmolding could mold over the pre-formed springs that come all together on a strip or sheet. Then the metal could be pierced to make them electrically isolated. If it is high volume, the springs could be supplied on a strip on a reel. The strip of springs would be fed into the mold, the plastic molded around it, the connections between the springs pierced, and either the carrier strip cut off and parts drop into a chute, or the assembly wound onto another reel.

Hi, Non-ME!

Would a spring configured as a plastic plate with a flexible center work?

The plate can be made in any size/shape with any sized perimeter 'frame' to maintain the distance required above/below the spring contacts; and that distance would ensure a long-term usage life for the flexible portion so long as your plastic material has a low creep coefficient. Hmmm. Maybe not, considering that you still haven't found the plastic that is work wear and temperature resistant yet. Still, an idea.

Mark