When designing a seal, chemical compatibility is one of the two important factors, the other is the size. Your rings should be compatible with the chemical they come into contact with. Choosing the right compound can make or break your seal and to the general designer,
from a good supplier. There are many rubber o-ring suppliers with compound families and hundreds of chemicals to sell, so how can you know whether your seal is going to hold up with the chemicals you are going to use?
Chemical compatibility important when selecting seals and o-rings -
Chemical compatibility is an important factor to keep in mind when selecting seals and O-rings. Both the material to be dispensed and the materials that the dispensing equipment is constructed from and how they react with each other is important to the performance of the dispensed equipment.
Outline some of the most common effects that these could have -
Corrosion of metal parts in the dispensing equipment:
This leads to the premature failure of equipment resulting in the production downtime, the need for costly renovations, and even new dispense equipment. The way this can be avoided is to make sure that the rubber O-rings supplied and the silicon O-ring supplied are constructed from are compatible. Most of the applications are stainless steel parts and they are most corrosion-resistant. Having knowledge of chemical compatibility will save you on the corrosion of metal parts.
Seal failure that will cause leakage and ratio imbalance:
Some chemicals contained within products attack the X-rings supplied material causing them to break down, or swell, and disintegrate. This leads to leaks that are time-consuming and difficult to clean up that they create in both the product lost and the time wasted. In metering systems, seal failure can cause a ratio imbalance. Thus having rings and seals that are compatible with the chemicals at hand will be of great help.
Premature polymerization of adhesives resin is also another issue and can be caused by incompatible materials:
This results in dysfunctional Viton O-ring supplied as it is full of the cured material, meaning countless hours of work involved to strip back and clean down the machinery. Not to mention the time lost to the production lines as the dispensing equipment is out of action. This is also an issue that often occurs when the correct hoses are not specified. For example, if a moisture curing material such as an MS Polymer is being dispensed, the hoses must be lined with Teflon to avoid any moisture absorption and the potential for material in the hose to cure. Many other potential issues could arise from chemicals incompatibly.
How do you know which O- rings are compatible with which chemicals? Fortunately, you can contact your O-rings supplier to give you all the details on chemical compatibility.
Let's take an example where we assume the x-ring supplied is going to be in contact with a mixture of 50% water, 20% ethylene glycol, and 30% anhydrous ammonia. How would you figure out what compound family would be best for this seal? A good rule is to use this method with EPDM, Nitrile, and FKM. The three stand for the general spectrum of chemical compatibility. EPDM is highly compatible with water-based chemicals, FKM is likely compatible with oil/hydrocarbon-based chemicals, and nitriles are just in the middle.
In conclusion, it is wise if you choose the right silicon O-ring supplier who will supply materials that are compatible with each other. This will save your money that would have been used to replace the damaged rings.