I got into a recent debate with a group of maintenance engineers on what is the best rubber to use for our applications. The debate centered around whether we should be using silicone rubber in our facilities or should we be using Viton ® (FKM Fluoroelastomer) rubber.
As you might guess, there was no easy answer to the debate. We all have slightly different needs in our plants depending on what types of processes we are doing, what chemicals are present and our operating environments. In some cases, neither of these materials are ideal, but since we were only debating the two, let us stick to them for now.
Silicone rubber was favored by some of the maintenance engineers. Their biggest argument was about the crazy temperature ranges silicone rubber can be used in. It can withstand temperatures that range from -67 °F to 572 °F. There are almost no working conditions where that will not work.
Viton ® (FKM Fluoroelastomer) rubber on the other hand has an impressive temperature range of -15°F to +440°F and can go higher for short periods of time. It is the bottom number that concerned the silicone advocates. Cold winter temperatures for components being used outside can dip below -15 in northern states. Of course, does the equipment they are using the seals on sit outside?
The Viton ® (FKM Fluoroelastomer) rubber advocates argued against the softness of silicone rubber. They felt it was less durable than Viton ® (FKM Fluoroelastomer) in most applications. Viton ® (FKM Fluoroelastomer) is definitely a harder rubber than silicone.
The talk finally swung around to what is really important in many situations. Which is better for resistance to the materials they are going to be used around. Both rubbers are used for seals, o-rings and gaskets, but which one will stand up better to chemicals.
If we are talking about a simple cross-section, Viton ® (FKM Fluoroelastomer) rubber would be the winner. It has a high-resistance to a wide variety of solvents, oils, petroleum products, fuels, acids, animal fats and even vegetable oils. Silicone rubber on the other hand only has a moderate resistance to these same chemicals.
This is one area where we all agreed you had to start digging deep. You cannot randomly choose between silicone, Teflon™, Viton ® (FKM Fluoroelastomer) or other other formulations of rubber for your application. You need to dig into the actual chemicals they will come in contact with and determine their resistance to them. Viton ® (FKM Fluoroelastomer) is excellent to use in automotive, aerospace and other applications where it comes in contact with fuels, but can fail miserably with other chemicals.
As a good example of chemical resistance or failure, silicone receives a fair rating for use with ammonia. It can be used for seals in ammonia transfer hoses and containers. Viton ® (FKM Fluoroelastomer) on the other hand receives an unsatisfactory mark. Viton ® (FKM Fluoroelastomer) will fail quickly in environments with ammonia.
On the opposite side of the spectrum, using a silicone seal with automatic transmission fluid would be a disaster, but Viton ® (FKM Fluoroelastomer) rubber is considered an excellent choice with a top rating.
Hydraulic fluid is something all maintenance departments battle on a regular basis. Silicone seals will survive with normal hydraulic fluid but have a quick death with synthetics. Viton ® (FKM Fluoroelastomer) excels with regular fluid and can be used just as easily for synthetics.
Part of the debate between the two materials needs to come down to how you are going to use the materials. Silicone seals are usually molded to fit. Silicone is more prone to breakage and tearing compared to Viton ® (FKM Fluoroelastomer).
Viton ® (FKM Fluoroelastomer) rubber can be molded, but is also available in sheet form that can be used to cut gaskets and seals with machines or even be hand cut for custom seals.
Both silicone rubber and Viton ® (FKM Fluoroelastomer) offer good levels of fire resistance, so we felt that one was a draw in our debate.
What was our final conclusion as to which rubber was superior? We did not decide. We all recognize seals have to be chosen based upon the needs of a specific application. Most of us agreed that Viton ® (FKM Fluoroelastomer) rubber had a wider range of application for most of our purposes, but that silicone rubber still had its place. We carefully evaluate the type of rubber for a seal based upon the equipment manufacturers recommendations and chemical resistance charts that help us choose seals that are safe for our environment.