Plastic Part design with Integrated hinges 3

[arsenal75]

Hi, I am currently looking for technical specs and design guides for integrated hinges for plastic mouldings. Doe anyone have a website or link to a good source for this kind of information?

 

[peglor]

Don't know where to get that information, but I do know only a limited number of plastics, such as Polypropylene are suitable for this application.

 

[insideman]

1. Use polypropylene. Other plastics will only work for quite limited number of flexes. like three.
2. Design the part so it is molded with the melt flowwing across the hinge.
3. Start with hinge thickness = 0.005 inches. After first shots increase it if needed.
4. Instruct the mold operator to flex the hinge as soon as possible after the part is ejected.
5. Material strengh is increased dramatically in the hinge. typically in non-hinge areas, s=8000 psi. in the hinge s=80,000 psi.

 

[TheAnswerGuy]

arsenal75,

I am not aware of any guide for polymer hinges.

Maybe I should write one. Since I have worked on many closures. Many of the hinge designs are patented so I can not give any details regarding them. Although it may be a good idea for you to just go to your local store and take a look at the many designs that are being used. Common hinge designs are:
Bow-tie
Simple (single) strap
Multi-strap

The most perplexing problem with incorporating a hinge into your design is to properly put the design into the mold.

One place that you may want to try for a book is at the Society of Plastic Engineers website.

 

[mloew]

TheAnswerGuy,

Why would you not be able to include information from patented technologies? As long as they are properly referenced, I see no problem including this information. Patents are part of the public domain in terms of access to the information, but obviously not the use without permission from the assignee. The US Patent & Trademark Office website (

http://www.uspto.gov)

is a good source for information.
Best regards,

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Bavarian]

Our need is for a strip (2"x1/8" cross section) of suitable hinge type plastic where there are a total of six hinge notches across the width of the strip. A web search with Google (Plastic Hinges) shows two suppliers at the top of the search results. They offer short hinges and piano type hinges (come in a roll of 50')which are apparently of molded design in the first case and possible extrusion in the ssecond case. I have a Craftsman (Sears) set of Allen wrenches where the container is a clam-shell like design (one piece!) with two "life" hinges on one side. Looks like a supremely expensive mold. I guess with Sears selling quite a few of these, the cost of this mold is amortised by the vendor who sells to Sears.

Anyone have an idea about getting around the mold cost (we are a small company and need to know start-up cost for a new item to establish sales price.

 

[MikeHalloran]

Given a small company's mold budget, I'd forget the living hinges. Getting the melt flow right in one hinge in a part is not too difficult; six is way more than six times as difficult.

How about multiple identical modules, hinged to each other with drive pins?



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[rmetzger]

Dow has a small section on their website with some info - proved useful to me in the past.

http://www.dow.com/polyolefins/pptechctr/design/int.htm

 

[Bavarian]

Mike, you are right... whoever made the clam shell container for SEARS must be very experienced in making a one part mold with two hinges. We are now looking into using a sheetmetal part with 6 individual segments with each end formed (like a door hinge) with pins connecting same. Cost would be for punching and forming the end just like standard hinges.

 

[Iskit4iam]

If all you need is a strip with six hinges in it why don't you use an extrusion? Profile tooling is much cheaper than molding tooling.

 

[hbarea]

Here are some links with information:

http://www.huntsman.com/polymers/Media/Living_Hinge_Tips.PDF

http://www.plasticsresource.com/downloads/design_guide.pdf

http://www.geplastics.com/resins/global/pdf/design_guides/productdesignsec4.pdf

Why 6 hinges and not just 1 long one?

 

[BillPSU]

Living hinges can be fabricated using strip heaters and forming the hinge into the plastic. Polypropylene is the best material to use as it will withstand an enormous amount of cycles before failure. Polyethylene has been used with limited success.

Bill

 

[DanStro]

arsenal75,

I came across a web site about "living hinges". I think that just means that it is integrated, but I could be wrong. I have never actually designed any of these, it just came up when I was looking for something else.

http://engr.bd.psu.edu/pkoch/plasticdesign/living_hinge.htm

Hope this helps.
Dan