Thursday, 18 June 2015

5 common Plastic fasteners mistakes

Common mistakes people make with plastic fasteners

There’s nothing more frustrating than purchasing plastic fasteners and having them fail after you install them in your application.  
Plastic can fail in a multitude of ways, from cracking, creeping and deforming to fading.  Different kinds of plastics are vulnerable to a wide array of elements, including UV rays, processing chemicals, water and saltwater, and more.  Unlike metal, which bends before breaking, giving the user a warning that the part needs to be replaced, plastic fasteners will snap if they are put under too much pressure.
So what can you do to try to avoid plastic fastener failure? 
Of course, you want to select a manufacturer whom you trust to provide you with high quality parts.  You are not completely at the mercy of the plastic manufacturer, however.  There are certain mistakes people make when they purchase and install plastic fasteners. 
Let’s take a look at them:
1)      Not doing your research.
Most people do not understand the sometimes nuanced differences between the many different types and grades of plastics available.  Reliable mechanical properties and chemical resistance data sheets can be hard to track down.  Plastic resin manufacturers do not always pay for extensive testing on all the grades of plastic they put on the market.  So let’s say you go to buy plastic hardware and you have only heard of a few types of commercially available plastic materials.  It is a mistake to just choose a familiar name without really considering the specifics of your application.  Not all plastics will work in all environments.
2)      Being cheap.
So let’s say you’ve done your research and you know what kinds of properties you’re looking for.  Sometimes customers will balk at the price tags on some high performance plastics.  You might think that you can just go with an inexpensive material like nylon and you’ll probably be fine.  Well, you might be, but you also might not be.  The only way to ensure that your plastic components won’t fail is to pay to have them made in the proper material.  If you don’t, you may end up having to buy the more expensive material anyway after the cheaper product fails.
3)      Not testing samples.
Remember how I mentioned that most resin manufacturers don’t spend a lot of money on testing their products?  Well, they certainly don’t pay to have their materials tested 10,000 feet under water after a period of 30 years.  They only do the most basic level of testing and the information they release may just not be enough for you to really know if a material will work for you.  So if plastic failure is a major concern, you should consider doing your own testing.  Most manufacturers can provide samples for you to test.  If they do not have your part in stock, sometimes they can provide you with a similar part made from the same material.
4)      Not designing for plastic.
Many customers make the mistake of buying plastic parts just as if they were metal without allowing for the differences between the two types of materials in their design.  For example, just making a plastic screw thicker will not necessarily make it stronger the way it might with a metal screw.  There are also limitations on how thick different materials can be molded.  For example, some glass-reinforced TPU’s and many thermosets can be molded to almost one inch in thickness under the right circumstances.  Other compounds, such as CPVC, can be molded only with difficulty in thin sections.  So you may want to do a little research as you’re designing you application with plastics in mind, which brings us to mistake #5…
5)      Not consulting someone who is familiar with plastics.
So I was tempted to write “not consulting a plastics expert” but I thought maybe that’s a little intimidating.  You don’t need an expert-you just need someone to check your work.  I don’t want you to do all that research and then still end up with plastic failure because of a small mistake.  Many years ago, we had a customer who ordered thousands of Celcon Polyester rollers to be used in an oven.  He was dismayed to find that, after installation, the rollers were melting.  Upon consulting with our engineers, he discovered that in reading the mechanical properties for Celcon Polyester he had mistaken the glass transition temperature for the maximum service temperature.  Oops!  So take an extra moment to ask the plastic manufacturer if he thinks you’re making the right material choice.  Most plastic manufacturing engineers will be happy to consult with you for free.  They have many years of experience working with plastics, so let them help!

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