Parker Hannifin’s O-Ring & Engineered Seals Division, based in Lexington, Ky., has published the 2018 O-Ring Material Offering Guide (ORD 5712). It is a condensed version of the company’s comprehensive O-Ring Handbook seal catalog. The newly updated edition is filled with quick references and technical details, including material and design recommendations and specifics on part sizes and tolerances.
The 74-page guide is intended as a sealing resource and tool suitable for all markets and applications. A short introduction discusses Parker’s capabilities in manufacturing precision-engineered O-rings and custom seals and its emphasis on quality assurance. That includes the Controlled Batch Identification program and use of the latest inspection techniques to ensure material consistency and dimensional control. In addition, on-site R&D labs develop new material formulations and compounds to meet customers’ needs for mechanical, physical and environmental performance.
The company has also developed FEA software specifically designed for elastomeric evaluation. This lets engineers predict seal performance in a variety of media, temperatures and pressures before actually making parts. This eliminates the need for costly tooling, speeds production and ensures the selection of the right material and geometry for a customer’s application.
Product lines include O-rings manufactured to U.S. and international standards including AS568, ISO 3601, DIN 3771, JIS and metric; custom sizes of almost any dimension; miniature O-rings; and large special O-rings, and continuously molded and spliced cord. Besides the seals themselves, related offerings include Parbak back-up rings that prevent extrusion in high-pressure applications, and accessory products like assembly greases and lubricants, sizing cones and extraction tools.
The guide’s 24-page materials section explains that Parker’s O-rings can be molded in a wide range of compounds in durometers ranging from 40 to 95 Shore A. These materials include:
• Acrylonitrile-Butadiene (NBR)
• Butyl (IIR)
• Chloroprene (CR)
• Ethylene Acrylic (AEM)
• Ethylene Propylene (EPDM)
• Fluorocarbon (FKM)
• Fluorosilicone (FVMQ)
• Hydrogenated Nitrile (HNBR)
• Perfluoroelastomer (FFKM)
• Polyacrylate (ACM)
• Silicone (VMQ)
Each grouping includes a general description of the material. It then lists the compound number of each formulation, the application it is recommended for, the temperature range and color.
Specific compounds are formulated to meet the most stringent industry standards, including NSF, Underwriters Laboratories (UL), Military (MIL-SPEC), Aerospace (AMS), NASA, FDA, USDA, USP, and many customer-specific requirements.
For example, the Food and Drug Administration (FDA) has established a list of rubber compounding ingredients which tests have indicated are neither toxic nor carcinogenic. Rubber compounds produced entirely from those ingredients and which also pass the FDA extraction tests are said to “meet the FDA requirements.” The FDA does not approve rubber compounds. It is the responsibility of the manufacturer to compound food grade materials from the FDA list of ingredients and establish whether they pass the necessary extraction requirements. Similar standards are established by the U.S. Dept. of Agriculture.
Additional requirements have been imposed upon seal manufacturers regarding food and beverage service. Parker has developed several materials that are certified to NSF 51, Food and Beverage Standard. In critical medical applications, seals often must be made from an even “cleaner” list of ingredients. The U.S. Pharmacopoeia (USP) Class VI outlines requirements for system toxicity and intracutaneous toxicity for these “cleaner” compounds. The USP Class VI compounds must be made from ingredients with clear histories of biocompatibility that meet tighter requirements for leachates. Typical applications for FDA, NSF 51 and USDA materials are disposable medical devices, surgical instruments and medical fluid dispensing components, as well as a wide variety of food and beverage handling equipment.
The guide includes extrusion charts that show allowable limits for O-rings based on the fluid pressure, total diametral clearance, and Shore hardness. It then details proper gland designs for static as well as dynamic sealing applications, including cases for internal or external pressure, and shows dimensions, tolerances, surface finishes and other machining data. It also discusses undercut or dovetail grooves, which provide a mechanical means for holding an O-ring in place during assembly and maintenance. The design has proven beneficial in many applications but, according to Parker engineers, is an expensive groove to machine and should only be used when absolutely necessary.
Following on are sizing charts that provide dimensions for products made of standard-shrinkage materials. These correspond to AS568 dimensions. A vast number of seals are listed by size, detailing the cross section, ID and tolerance in both inch and metric dimensions. The guide also lists dimensional information for Parbak back-up rings.
Finally, other research and design tools and resources are listed, including Parker’s O-Ring eHandbook, Seal Solutions eGuide, Mobile inPHorm O-Ring Calculator and the O-Ring Selector. These software programs and mobile apps are designed to assist with material selection, fluid compatibility, gland/seal calculations and overall design analysis.