HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
<<  <  Page 4/4
Rob Spiegel
User Rank
Blogger
Re: Is it the plastic?
Rob Spiegel   8/17/2012 11:37:56 AM
NO RATINGS
That certainly helps with clarity, Dave. That's a major change in stiffness with just a relatively small change in temperature. Also seems odd that stiffness alone would affect the latch.

Dave Palmer
User Rank
Platinum
Re: Is it the plastic?
Dave Palmer   8/17/2012 11:31:31 AM
NO RATINGS
@Rob: It sounds like the problem isn't expansion of the plastic but, as Brooks says in the article, the change in stiffness with temperature.

I'm not sure what material this door latch is made from, but often plastic parts that are designed to flex in operation are made from polypropylene.  The elastic modulus of polypropylene changes by a factor of five between room temperature and 100°C, i.e. it is five times less stiff at 100°C than at room temperature.  I'd guess that, even from room temperature to 90°F, it might change by as much as 50%.

The mechanical properties of plastics are highly dependent on temperature and strain rate.  Design engineers need to keep these effects in mind.  When designing a steel part, it's usually safe to assume that the elastic modulus, yield strength, tensile strength, and ductility are the same from room temperature to at least 300°F.  With plastics, you can't assume that the properties listed on the datasheet are the same properties the material will have in your application.

Several years ago, Joseph Ogando wrote a great article for Design News regarding the use and abuse of plastics datasheets.  It points out many of the parameters that affect the properties of plastics.  I've sent it to a lot of people over the years as a reference.

Rob Spiegel
User Rank
Blogger
Is it the plastic?
Rob Spiegel   8/17/2012 10:43:43 AM
NO RATINGS
Sounds like the hook should have been designed to be free of the plastic even as the plastic expanded. Even so, should the plastic on this microwave -- which is expected to get hot -- expand so easily? At merely 80 degrees? Seems the plastic may be part of the culprit.

<<  <  Page 4/4


Partner Zone
Latest Analysis
Major changes are happening in the world of 3D printing and additive manufacturing materials, machines, and software. If the industry -- and the design engineers and OEMs it serves -- are to grow, all three areas must become much more tightly integrated.
Americans spent more than $60B on their pets in 2015. Folks are definitely spending their money on more than dog food. We’re spending on things like dog spas and fancy toys, and as you can imagine, the wearables market is becoming well represented here.
Collaborating researchers in Australia and the United States have discovered nanotechnology for thermophotovoltaic cells that could boost solar-energy harvesting.
Time was when sports equipment was made only from common, everyday, low-tech materials. But now sports equipment has a new, high-tech ingredient that is helping players take their game to the next level.
Every now and then Design News likes to revisit some of our favorite Gadget Freak projects. Robotic hands, manipulated Kindles, and smart recycling cans round out the latest crop.
More:Blogs|News
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6 |  7 | 8 | 9


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Next Course September 29-October 1:
Sponsored by Proto Labs
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Technology Marketplace

Copyright © 2016 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service