Top 5 Questions on Vulcanized O-rings

Having trouble finding the proper size o-ring for your application?  Maybe the size you are looking for is not available from stock.  Maybe the size you are looking for is too large to be molded.  Is the volume too low to consider a minimum run of molded parts?  Vulcanized o-rings may be a solution.

Top 5 Questions on Vulcanized O-Rings

1. Is a vulcanized o-ring right for you?

The first thing you want to ask yourself is whether this is a dynamic application (moving parts coming into contact with the o-ring) or a static application (no moving parts coming into contact with the o-ring).  If there are any moving parts around the o-ring, then we would not recommend a vulcanized o-ring for your application.  If it is a static application, then a vulcanized ring may be your solution.

Vulcanized o-rings are most often used in the filtration, and pharmaceutical industries, but they can be used anywhere there is a flange or a lid that needs to be sealed.  The application does not need to be round.  You may need to seal a lid on a rectangular container; a vulcanized o-ring will work for that, as long as the groove is designed properly.

2. What is the difference between a spliced o-ring and a vulcanized o-ring?

When customers think of vulcanized o-rings, many think of what we call spliced o-rings.  A spliced o-ring is when you take extruded o-ring cord stock, cut it to length, and then bond the two ends together with cyanoacrylate (Super Glue TM).  This works fine in a pinch and can give you a successful seal, but that is not what we mean by vulcanized.  Vulcanized rings utilize uncured rubber compound, mixed with adhesive, to provide the bond.  So if your o-ring is EPDM for example, the adhesive would consist of uncured EPDM compound and adhesive, if it is Viton ™, it would be uncured Viton compound and adhesive, etc.  Using the uncured compound mixed with adhesive gives you the best bond.

3. What is the process used to vulcanize an o-ring?

What we do first is determine the length of cord we need to cut in order to provide the proper inside diameter (ID) or outside diameter (OD) of the o-ring.   In order to do that the customer must provide us with two dimensions.  We must be provided with either the ID and the cross section (CS), the OD and the CS, or the cut length and the CS.  Click Monroe Seal vulcanized-spliced o-ring formulas for formulas to determine the 3rd missing dimension, using the dimensions provided.

Once we have the cord cut to the proper length, we apply the proper adhesive, for the compound we are vulcanizing, to each end of the cord.  We exclusively use the butt splice method, which is a straight cut through the cord and bonded (see figure 2).  Some customers will argue that a 45 deg. angle splice gives you a better bond because there is more surface area to be bonded.  We have found it is much too difficult, with the 45 deg. angle splice, to get the two surfaces on each end to match up perfectly and most times you cannot get them to match up perfectly at all.   After 20 years of doing the butt splices, we feel the strongest and best bond is the butt splice.

The vulcanization process utilizes uncured compound, adhesive, heat, pressure, and time to cure a joint.  This is accomplished by placing the two mating ends of the cord material in a special splicing jig that is machined to the proper size of the cord (or in some cases a custom profile).  The die is heated up in the press and the press is locked down for a few minutes to cure the bond.  After a few minutes the o-rings are removed, the bond is cleaned up for any excess rubber, and you have a finished vulcanized o-ring.  See figure 3 for the splicing jigs and figure 4 to see o-rings being vulcanized in the press.

vulcanized oring collages

Figure 2 (Left) Butt splice method ——————- Figure 3 (Middle) Splicing jigs ——————- Figure 4 (Right) O-rings being vulcanized

4. What are your available sizes? 

We can vulcanize cross sections of 0.070” to 1.000” in diameter.  For cross sections of 0.070” to 0.250”, the inside diameter must be at least 3” in order to get the cord around our equipment.  For larger cross sections above .250” and up to 1.000”, the inside diameter must be at least 4” in order to get around the equipment.  There is no limitation on how large the inside diameter can be.

5. How do you inspect a vulcanized joint?

If you try hard enough, a vulcanized joint will come apart every time.  If they did not come apart, they could be used in dynamic applications.  There is a proper inspection you can do and if it passes you can feel comfortable that the o-ring will perform as needed once it is locked into its application.  To properly inspect a vulcanized o-ring, locate the splice joint on the ring.  First, place your fingers on either side of the joint.  Then give the o-ring a quarter twist in either direction.  Don’t twist too far or the joint will break.  Then give it a little tug.  Again, don’t tug too hard or it will break.  If it passes the twist and tug test, then install it, lock it down, and it will be fine.  Absolutely do not bend the o-ring at the joint, which will break it every time.   The o-ring will not be bent in application, so there is no reason to do so.

The other thing to look for would be a crack or tiny pinhole in the joint.  If there is a crack or a tiny pinhole, it is best to reject the ring because eventually it will come apart and there will be a failure.

Need Help?

If you think a vulcanized o-ring will work for you, or if you have any questions regarding vulcanized o-rings or vulcanized custom profiles, please call our knowledgeable sales staff at 877-740-0349. We will be more than happy to help you out.   We stock most standard and metric size cord diameters in nitrile(buna n), Viton, EPDM, silicone, and Neoprene.  Our turnaround time on vulcanized rings is same or next day if we have the material in stock.

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