flexible plastic plate

[opticsman]

Hi all, I want to produce a circular plate (70 mm in diameter ) that is flexible in the central area ( 45 mm diameter but the annular part is rigid. I want to keep the number of parts to a minimum so hoping to avoid a a three component solution where I sandwhich a thin rubber sheet in between two rigid annular rings. I was wondering if I could use nylon ( or something similar ) and make the central section much thinner. I would appreciate any suggestions. Also for the rubber / flexible part what sort of material would give high number of repeat "flexes" without failing? I was hoping i could deflect the plate by 10 mm or more at the centre. Many thanks in advance opticsman.

 

[Pud]

Any chance of a pic?

I don't think on a 70mm dia plate you will get 10mm or more deflection.

Polypropylene "live hinges" are good for over 2M flexes.

Any idea of loads?

H

http://www.tynevalleyplastics.co.uk

 

[opticsman]

Hi Pud, this is like a push button so whatever pressure a finger can exert . Its only the inner 45 mm i want to be flexible, Thanks opticsman.

 

[patprimmer]

Like Harry says.

Further to that, over moulding polyurethane with nylon or even glass filled nylon will produce a disk with hard and soft elements and good durability. I can't say if that will allow 10mm movement, but it will allow a reasonable amount and will have good fatigue resistance in each material. I don't know the durability of the wed. I would suspect good but I have no data to back it up. A pair of prototype moulds should be dead easy to prove the concept and run durability tests.

The same principle can be used with PP over Santoprene or equivalent or PBT over Hytrel or Arnitel elastomers, or with some fancy silicone elastomers from Wacker or Dow. Wacker and Dow have data and bond strength of various hard resins with there special over mouldable siicones

I would expect the best result from the nylon/PU or I think from memory a special silicone from Wacker and PBT.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[opticsman]

Thanks all, Pat. I think you have helped me in the past (I tend to mainly ask questions on materials/mechanics as its not my area). Can overmoulding be over a certain area only (45 mmdia?) otherwise i assume composite would have same flexibility throughout. How does overmoulding work? is it expensive in terms of tooling /piece part relative to normal injection moulding? Opticsman.

 

[patprimmer]

It can work over part of the are only.
Typical examples are handles with soft rib in a hard matrix such as the rend in razor handles, ball point en bodies, tooth brush handles and screw driver handles and tyres moulded to wheels.

The material cost is a bit more and the moulding time is about double as it is really two mouldings welded together.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[MikeHalloran]

For 10mm stroke on 45mm diameter, you probably need to include some bellows type convolutions in your flexible part to get decent life.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I really did drop some letters in my last post and I was a bit brief on some details.

I have copied it and replaced the missing letters and expanded thecontent. I hope this makes it more sensible.


It can work over part of the areA only.
Typical examples are handles with soft rib in a hard matrix such as the Trend in razor handles, ball point Pen bodies, tooth brush handles and screw driver handles and tyres moulded to wheels

The material cost is a bit more and the moulding time is about double as it is really two mouldings welded together DURING THE OVER MOULDING PROCESS.

The most typical wheel tyre over moulding is shopping trolley wheels.

The higher melting point material should be used as the second material as it welds better that way.

Mikes idea is good and is the normal proven way to increase stroke on diaphragms.

With the correct design I have seen durable bellows type diaphragms made out of straight unfilled extrusion grade nylon. These had a rigid centre for actuator attachment and flexible outer ring much like an old fashioned automotive fuel pump diaphragm.

If you can change the design to solid centre and have some flexibility on exact sizes, I can probably put you in contact with an existing manufacturer. They use them as the actuators in a pnumatic control valve system.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[opticsman]

Hi Pat Yes i can have it as you suggest. Does that make a 10mm deflection easier to achieve? Cheers opticsman

 

[patprimmer]

Not specifically, but the parts already exist with a very simple bellows that should allow that stroke.

Contact me at

http://www.Duromer.com

or

http://www.ccplastics.com

and I will send you a few mouldings for appraisal.

They may work as such or they may give design ideas that you might take to a more local moulder such as Harry for discussion of the manufacture of prototypes. For some reason (maybe language use and spelling), I think you are located in GB.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[unclesyd]

Take a look at the design of these diaphragms. I would use Santoprene if possible. We have had very good sucess replacing different diaphragm materials with Santoprene.

http://www.rulon-meldin.com/Data/El..._line_edit.asp?ele_ch_id=L0000000000000001656

 

[patprimmer]

Unclesyd is right, Santoprene makes a good diaphragm good enough most times. PU is better but probably more than you need.

With a correct bellows design, PP is probably good enough and nylon is certainly good enough. A elastomer will not be required.

A lot depends on environment and service life expected.

The sample I will send you will be straight nylon with a simple bellows. I can probably also get stroke and durability testing results.

My customer here is Goyen Controls (now part of Tyco and Southcorp)and the UR is

http://www.tycoflowcontrol.com.au/TES_Goyen_Dust_Filter_Cleaning_Systems/products

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers