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
From wearables to design changes to rumors of a car, Apple has multiple things cooking up in its kitchen. Here are six possibilities from Apple next week, with likely more than one coming to light.
The key to the success of alt energy is advanced automation, which is still relatively new to the energy scene.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
New fastening and joining methods are making it possible to join multiple materials and thinner sheets in consumer and medical portable electronics, as well as automotive and aviation systems.
An upcoming Digi-Key Continuing Education Center class on designing motor control using MCUs and FPGAs will show you how to choose the best hardware and tools to speed up your development time.
More:Blogs|News
Design News Webinar Series
2/25/2015 11:00 a.m. California / 2:00 p.m. New York
12/11/2014 8:00 a.m. California / 11:00 a.m. New York
12/10/2014 8:00 a.m. California / 11:00 a.m. New York
11/19/2014 11:00 a.m. California / 2:00 p.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Mar 9 - 13, Implementing Motor Control Designs with MCUs and FPGAs: An Introduction and Update
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  67


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.
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2015 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service