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
This Gadget Freak Review looks at a keyless Bluetooth padlock that works with your smartphone, along with a system that tracks your sleep behavior and wakes you at the perfect time in your sleep cycle to avoid morning grogginess.
Siemens released Intosite, a cloud-based, location-aware SaaS app that lets users navigate a virtual production facility in much of the same fashion as traversing through Google Earth. Users can access PLM, IT, and other pertinent information for specific points on a factory floor or at an outdoor location.
Since 1987, teams of engineers around the world have built solar cars to participate in a road race around Australia called the World Solar Challenge, being tested on the race time, kilometers traveled, practicality, and energy used by the vehicles they invent.
An Israeli design student has created a series of unique pieces of jewelry that can harvest energy from default movements of the body and even use human blood as a way to conduct energy.
Made By Monkeys highlights products that somehow slipped by the QC cops.
More:Blogs|News
Design News Webinar Series
7/23/2014 11:00 a.m. California / 2:00 p.m. New York
7/17/2014 11:00 a.m. California / 2:00 p.m. New York
6/25/2014 11:00 a.m. California / 2:00 p.m. New York
5/13/2014 10:00 a.m. California / 1:00 p.m. New York / 6:00 p.m. London
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Aug 18 - 22, Embedded Software Development With Python & the Raspberry Pi
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6


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 Class: September 30 - October 2
Sponsored by Altera
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service