Plastic Sheets and Rods: Build them smart, build them to last Hayden Hess December 13, 2013 Some people think the most powerful force on Earth is 'Love'. While Love is certainly powerful, a force known as Coefficient of Thermal Expansion is more powerful. All materials grow and shrink with temperatures regardless of pressures or weight. (Newswire.net -- December 13, 2013) Anaheim, CA -- We know by now that plastics are great and versatile materials. We can use plastics in many ways for many different applications. Plastics are used in a variety of everyday materials from cogs and gears for machinery in warehouses, to medical components and packing materials. When these amazing materials are used improperly, they can get a bad Plastics Affected By Temperatures rap.
One critical property we need to be aware of is something called the Coefficient of thermal expansion.
What is the coefficient of thermal expansion?
Simply put, the coefficient of thermal expansion is the amount a material will expand or contract as the temperature changes. As the temperature rises, the material will grow or expand. As the temperature drops, the material will contract. All materials have this quality, some may have a large change in shape, and others may have a small change. The common examples are metals compared to plastics. Metals are known to move about 6 – 10 times less than plastics under the same temperatures and conditions (see chart below).
Why is this important?
Let us say that you are building a outdoor cabinet from HDPE. Let’s say you are going to build your cabinet at 8 a.m. when it is 32 degrees Fahrenheit. You lay down your HDPE sheets to fit perfectly, edge to edge, with no space in between sheets. Then you leave, a job well done, and move on to something else. When you come back, your HDPE sheets are warped, twisted or cracked. It is now noon, and the temperature is 90 degrees Fahrenheit. The HDPE has warped
due to the coefficient of thermal expansion. The increase in temperature has caused the plastic sheets to expand, and with nowhere to go, no “wiggle room,” the plastic can only bend up or down, causing the twist or warp.
Using the chart above, we can determine the amount a plastic will move. As an example, a part of Acetal that measures exactly 72.0” long at 40 degrees Fahrenheit with measure 72.294” at 100 degrees Fahrenheit. Calculation is .000068 X 72”= .00489” per degree x 60 degrees increase is .294” growth.
How can we fix this?
The solution to this problem is easier than you might think. By allowing a little room to grow or shrink, some “wiggle room,” you can effectively solve this problem. When drilling your holes for bolts, it is better to drill oversized or oblong holes. These larger holes will allow the room necessary for the plastic to expand and contract, without damaging the plastic sheets. In addition, many people feel the need to tighten bolts until their muscles ache. This can also be damaging to your project. Over tightening your bolts restrict the plastics ability to swell or grow thus restricting the needed “wiggle room,” and can snap or crack your HDPE sheets at the drill holes. The easy solution is to tighten your bolts down enough to hold in place, and use rubber washers, but not over tightened. The last step you should take into account is spacing the sheets to allow that swelling to take place. You do not have to space the sheets inches apart with gaps that you could fall through, but you do need to take into account that, like all materials from wood to metal, plastic will expand and contract in temperature change.
All materials, including all plastics, have a coefficient of thermal expansion. Each material has a slightly different rate of expansion. To find out which plastic may best suits your needs, feel free to contact Industrial Plastic Supply, and chat with one of our qualified Plasticologists.
~~~~~~~~~~~~~~~~~~~~~~~~
Industrial Plastic Supply, Inc. 2240 S. Dupont Drive Anaheim, CA 92806 7149783520 info@iplasticsupply.com http://www.iplasticsupply.com