peek-photoOne of the topics I usually bring up to engineers when trying to define what material they need for an application is to consider what their Application Operating Temperature is going to be and determine what physical properties are required at that temperature (I usually carry a chart with such illustrations with me). 

A common mistake I find in the field is for an engineer to look at a data sheet with physical properties tested at Room Temp. (73F) but intend to use the material at a higher temperature say 200F, 350F or 500F and are surprised by how much a thermoplastics physical properties are reduced in the higher temperatures. 

Let’s take three fairly common materials designers/engineers may typically work with; 

The 1st Graph illustrates an Acetal Copolymer with a continuous use temperature of up to 180F,  has a Tensile Yield Strength of 8,800psi @ 73F but a Tensile Yield Strength reduced to around 4,000psi @ 180F (which still isn’t too bad). 

figure7_1-1-08.jpg  Click On Chart to View

The 2nd Graph illustrates an Ultem 1000 PEI with a continuous use temperature of 338F and has a Tensile Strength of 15,200psi @ 73F but it’s Tensile Strength reduced to around 6,000psi @ 350F. 

figure8_1-1-08.jpg  Click On Chart to View

The 3rd Graph illustrates Victrex PEEK (unfilled) with a continuous use temperature of up to 500F and a Tensile Strength of 14,500psi @ 73F but it’s Tensile Strength reduced to around 1,900psi @ 500F. But, add 30% Carbon Fiber (another topic later) and it retains it’s Tensile Strength to around 8,800psi @ 482F. 

figure3_1-1-08.jpg  Click On Chart to View

The point I’m try to make is… when designing with Thermoplastics, study and scrutinize the data sheets carefully against how you intend to use them ie; if you were for instance looking at an Acetal for an application with light/moderate loading at 225F you may want to either look at either adding a Glass/Carbon reinforcement or upgrade your material choice to a material with better properties at your given temperature ie: Ultem PEI, PPS,PPA, PET, PBT, Polyamide etc.

- Lonny Miller

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