The Parker Gask-O-Seal, now more than 55 years old, enjoys a leading role as a world class sealing concept.
Profoundly simple, yet enviably reliable, a uniquely designed elastomeric element is molded directly into groove(s) to produce an integrated sealing solution for a virtually endless array of challenging static face type applications.
The Parker Gask-O-Seal, now more than 55 years old, enjoys a leading role as a world class sealing concept. Profoundly simple, yet enviably reliable, a uniquely designed elastomeric element is molded directly into groove(s) to produce an integrated sealing solution for a virtually endless array of challenging static face type applications.
Under pressure of assembly, the rubber compound is deformed from a round configuration to a square or oblong shape as shown in the figure. By predetermining and manufacturing the proper ratio between the volume of the molded in voids and the volume of the crown, controlled confinement is obtained. The Gask-O-Seal is designed so that the elastomer is deformed against the faying surfaces, affecting the seal by the inherent “memory” or resiliency of the elastomer as it tries to return to its original molded shape. There are many features and benefits that come with Gask-O-Seal design in static face seal applications.
Once the operating parameters and leak rate criteria have been established and the appropriate sealing materials selected, the actual design for the GaskO-Seal can be started. This section provides basic guidelines for designing the seal.
1. Edge Distance
Using standard metals and manufacturing techniques, the desired seal groove to edge distance is .060″ minimum. The seal groove to hole distance can be as small as .050″ minimum, providing the parts are not blanked. Blanked parts in low carbon steel require an edge distance at least as great as the thickness of the part. This is necessary because of the “roll” that occurs on the edges of blanked parts in this material.
2. Groove Design
It is good practice to use larger groove widths and higher crown heights for larger parts and higher pressures. It is recommended that customer’s contact the Composite Sealing Systems Division’s engineering department if the available land area is minimal. If adequate land area is available, .100″ width is recommended.
3. Metal Thickness
Whenever possible, the metal thickness should be specified as a standard gauge call out with an accompanying standard stock thickness; i.e., Steel 11 gauge (.120″ stock). This allows Parker to use materials that are readily available from suppliers and are most economical in producing the finished Gask-O-Seal. Metals with a thickness of less than .090″ should be discussed with the Composite Sealing Systems Division’s engineering department.
4. Dimensional Tolerances
In developing the overall design and establishing tolerances, the noncritical features, such as outline or outside dimensions, should have wide tolerances to reduce manufacturing costs. Bolt holes should have sufficient clearance around the bolts to permit reasonable locating tolerances. However, when the seal groove is located in relation to the bolt holes, the holes should be located within O.014 on small parts (<10 inches). Broader location tolerances can be used if the groove width can be increased to allow for the resulting misalignment.
In order to achieve optimum sealing, it is essential to provide sufficient flange preload and proper bolt size and spacing to create a metal to metal contact between the Gask-O-Seal retainer and the mating parts. Under all service conditions, such as out-of-flat, system pressure, and rubber strength, the separation between flanges should not exceed .003″ in order to prevent extrusion and damage to the elastomer. The force required to compress the seal is generally between 30 and 150 pounds per linear inch of seal, depending on the rubber durometer, material, and the configuration used for larger gaps, contact the Composite Sealing Systems Division’s engineering department.
6. Surface Roughness
Surface roughness of the Gask-O-Seal retainer itself is not critical to sealing. When a sheet metal retainer is used, the “as received” condition of the metal is satisfactory. On machined surfaces, Parker will maintain a roughness value of 125 micro-inch Ra or better. Callouts for finishes of the Gask-O-Seal retainer with roughness less than 125 Ra can add unnecessarily to the part cost. For mating surfaces that the Gask-O-Seal is to seal against, a 125 Ra or better will provide good sealing surfaces for almost all applications. The only noteable exceptions are seals for gaseous media where diffusion type leakage must be kept to a minimum. For these installations, the mating surface should have a finish of 32 Ra or better.
7. Flatness and Parallelism
In most cases, no particular attention needs to be given to flatness and parallelism requirements. Occasionally a Gask-O-Seal is used between two halves of a device that must be accurately aligned such as a gear box housing. For this, the mating surfaces must be parallel within close tolerances. If the Gask-O-Seal is molded directly into one of these rigid parts, which would often be a casting, a flatness requirement is generally acceptable.
8. Types of Bond
There are two types of bonding to retain sealing element in groove(s); mechanical and chemical.
- Mechanical Bonding: In a double sided retainer with back-to-back grooves, it is convenient to provide cross holes in the web portion at planned intervals. During the molding process, the rubber compound flows through these holes, mechanically locking and holding the seal elements in place.
- Chemical Bonding: A chemical bonding agent is applied to the groove(s) prior to molding. During the molding process, the rubber compound interacts with this bonding agent, a process called co-vulcanization, to chemically bond the seal element in place. Gask-O-Seal Design Considerations, Continued
9. Finite Element Analysis (FEA)
The study of elastomer stress and its relationship to seal effectiveness has been dramatically enhanced with the advent of finite element analysis. FEA is a numerical modeling technique used to predict a deformation and stress concentration of a given seal cross section. Parameters such as cross section geometry and material property data are factored into the modeling equation to produce a stress concentration model of the seal. FEA is effective as a predictor of seal performance only when it is used in conjunction with historical seal and material data and specific performance testing. Please consult the division if FEA is being considered as a tool for seal design.
The retainer permits extremely fast and sure installation. In fact, where volume dictates, the placement of the seal can be fully automated on a completely foolproof basis.
- Bolt retention: The rubber can be molded on the bolt holes for positive pre-assembly gripping and transporting. Retainer fits conveniently over bolts to hold the seal in place during assembly.
- Fast assembly
- Visually detectable after assembly
This warranty comprises the sole and entire warranty pertaining to items provided hereunder. seller makes no other warranty, guarantee, or representation of any kind whatsoever. All other warranties, including but not limited to, merchant ability and fitness for purpose, whether expressed, implied, or arising by operation of law, trade usage, or course of dealing are hereby disclaimed. Notwithstanding the foregoing, there are no warranties whatsoever on items built or acquired wholly or partially, to buyer’s designs or specifications.
Limitation of remedy: Seller’s Liability arising from or in any way connected with the items sold or this contract shall be limited exclusively to repair or replacement of the items sold or refund of the purchase price paid by buyer, at seller’s sole option. In no event shall seller be liable for any incidental, consequential or special damages of any kind or nature whatsoever, including but not limited to lost profits arising from or in any way connected with this agreement or items sold hereunder, whether alleged to arise from breach of contract, expressed or implied warranty, or in tort, including without limitation, negligence, failure to warn or strict liability.
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