Vulcanized O-Rings Q and A

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 your application?

The first thing you want to ask yourself is whether this is a dynamic application or a static application like a gasket. 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 storage tanks, filtration, pool and gasket applications, 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 cold spliced O-Ring and a heat vulcanized O-Ring?

When customers think of vulcanized o-rings, many think of what we call a 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 Rubber Toughened Cyanoacrylate adhesive. This works great for soft durometer or in pinch for 70-90 durometer compounds 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 Fluorocarbon FKM, it would be uncured Fluorocarbon FKM 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.

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. This provides the best cord seam alignment and most consistent of all vulcanized seals.

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-Ring are removed, the bond is cleaned up for any excess rubber, and you have a finished vulcanized o-ring.

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 5” in order to get the cord around our equipment without a flat spot. For larger cross sections above .250” and up to 1.000”, the inside diameter must be at least 6” in order to get around the equipment without a flat spot. 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.

Spliced & Vulcanized O-Rings

Spliced and vulcanized O-Rings are available online and a viable solution when standard o-rings cannot be used. Vulcanized O-Rings or Rubber Toughened Cyanoacrylate Bonded O-Rings are great for a custom design or a unique size that is not included on the standard charts. One of The O-ring Store's specialties is fabricating special sized o-rings in house for fast delivery, normally shipping in 2-5 days. Our vulcanizing department can make just about any non-standard size from 5" inside diameter and up.

The O-Ring Store LLC stocks an assortment of O-ring cord in standard and square cut profiles for use in our vulcanizing department. Vulcanized O-rings are an excellent replacement for any non-standard static O-ring.


Applications:         Static
Pressure:              Up to 1200 psi Max.
Requirements:       24 hours to cure


The O-Ring Store LLC stocks O-ring cord for both splice & vulcanizing and for
the sale of custom lengths. The following materials are available:

  • Nitrile
  • EPDM
  • Fluorocarbon FKM
  • Silicone

Vulcanized/Spliced O-ring Formulas
(determining the size or cut length of a vulcanized/spliced o-ring)

Determine the inside diameter if you know the cut length and the cross section:

  • (cut length ÷ 3.1416) – 1(cross section) = inside diameter
  • e.g. –   124.375” cut length and a .313” cross section
  • (124.375 ÷ 3.1416) -1(.313) = 39.276” inside diameter

Determine the outside diameter if you know the cut length and the cross section:

  • (cut length ÷ 3.1416) + 1(cross section) = outside diameter
  • e.g. –   124.375” cut length and a .313” cross section
  • (124.375 ÷ 3.1416) +1(.313) = 39.902” outside diameter

Determine the cut length if you know the inside diameter and the cross section:

  • (inside diameter + 1X the cross section)*3.1416 = cut length
  • e.g. -    19.750” inside diameter X .500” cross section
  • (19.750 + .500)*3.1416=63.617” cut length

Determine the cut length if you know the outside diameter and the cross section:

  • (outside diameter - 1X the cross section)*3.1416 = cut length
  • e.g. -    19.750” inside diameter X .500” cross section
  • (20.750 - .500)*3.1416=63.617” cut length

Information within is believed to be accurate and reliable. However, The O-Ring Store, LLC makes no warranty, expressed or implied, that parts supplied in this material will perform satisfactorily in specific applications. It’s the customer’s responsibility to evaluate the material prior to use.


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1847 Wilma Dr, Clarkston WA 99403
Phone 208-413-6377 - Fax 208-413-6719