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Method of Splicing Cured High Temperature Perfluoroelastomer Parts Disclosure Number: IPCOM000201145D
Publication Date: 2010-Nov-09
Document File: 3 page(s) / 24K

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This procedure describes a method for splicing cured perfluoroelastomer o-ring cord resulting in ultimate tensile strength that is equivalent to that of molded o-rings that have not been spliced.

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This is the abbreviated version, containing approximately 48% of the total text.

Page 01 of 3

Method of Splicing Cured High Temperature Perfluoroelastomer Parts

     Perfluoroelastomer (PFE) manufacturers are seeking improved methods of splicing parts such as o-rings, gaskets, etc. Typically parts such as o-rings made from perfluoroelastomer compounds are compression molded in one piece using a continuous OD/ID preform or extruded cord cut to fit the mold cavity dimensions. However in some cases splicing of o-ring cord after curing is necessary. This is usually done when the required o-ring size is too large to fit in existing molds or presses. It may also be done to better control o-ring dimensions (PFE's shrink more than most elastomers after molding) or to minimize perfluoroelastomer compound waste.

     There is concern from o-ring manufacturers and end-users that o-rings that have been spliced are not as strong as o-rings molded in one piece without a splice. If the spliced section is weak, it could split apart in service which could result in the o-ring seal failing. Since PFE o-rings are typically used in severe service conditions, a seal failure could have catastrophic consequences.

     A common splicing technique used currently is to mold a piece of uncured perfluoroelastomer compound in between the cured ends of the o-ring cord to be spliced as shown above but without using a primer to pretreat the cured o-ring ends or using a tie coat such as in US20090018275.

     A new method has been discovered to splice high temperature (nitrile cure site containing) PFE parts. The method improves bond strength vs. previous methods. The method involves the use of a catalyst/hydrofluoroether (HFE) solvent solution to pretreat cured PFE parts. The catalyst may include amidines, amidoximes and amidrazones that are soluble in the solvent. Other solvents capable of swelling the PFE and solubilizing the catalyst may also be used.

     This splicing method is used to form an o-ring (or other shape to form a continuous seal) of desired OD/ID dimensions with no loss in tensile strength compared to a molded (not spliced) o-ring. This is achieved by dissolving an amidine catalyst in a hydrofluoroether (HFE) solvent capable of swelling the cured perfluoroelastomer compound. The ends of the o-ring cord are first soaked in this catalyst/solvent solution. Then the o-ring splice is formed by placing an uncured piece of the original PFE compound between the ends of the cord and remolding the splice section under heat and pressure. The resulting spliced o-ring has tensile strength equivalent to a molded o-ring that is not spliced.

Figure 1

Figure 2

Figure 3

Cured O-ring cord to be spliced

= tensile strength

Uncured PFE before splicing

catalyst solution

Cured O-ring Cord

ends soaked in

O-ring section before splicing

Spliced O-ring

Molded O-ring

Page 02 of 3

Spliced o-ring specimens were made as follows:

1) PFE o-rings (AS214 size) were molded for 15' @ 177°C.
2) A section of the o-ring was cut from the molded ring as shown in Figure 2.
3) The cut o-ring ends of the...