R & D
- Does Parco use MIL-STD-417 and MIL-R-3065?
- Why do test values for a physical property of the same compound vary?
- How does Parco test hardness?
- Does Parco have compounds approved by the National Sanitation Foundation (NSF)?
- Does Parco have compounds listed by Underwriters Laboratories, Inc. (UL)?
- What causes some compounds to craze plastic?
- What is the shelf life of Parco compounds?
Does Parco use MIL-STD-417 and MIL-R-3065?
MIL-STD-417, Classification System and Tests for Solid Elastomeric Materials, was a method for classifying elastomers and desired properties. The standard was canceled without replacement in December 1995. MIL-R-3065, Fabricated Rubber Products, was the document that cited dimensional and visual quality requirements for rubber products. That specification was canceled in January 2000. The cancellation notice has a cross reference from MIL-STD-417 product references to ASTM D2000 designations.
Parco prefers to quote to active specifications whenever possible. We encourage customers to revise their requirements associated with MIL-STD-417 and MIL-STD-3065 to active ASTM D2000 designations.
Why do test values for a physical property of the same compound vary?
In most cases, rubber test results are affected by the variables associated with material age, laboratory environment, specimen preparation, test machine accuracy and maintenance, and operator consistency.
Cumulatively, those variables make test results differ from time-to-time, operator-to-operator and laboratory-to-laboratory. The expected amount of variation is documented in the ASTM Test Method associated with a particular test. For example, ASTM D412 states that dumbbell tensile strength test results from two laboratories must differ by more than 18% of their average to have come from different populations.
How does Parco test hardness?
Parco tests the hardness of batches using a standard hardness test specimen and Shore A durometer on a test stand. Parco tests some standard hardness specimens and other shapes on hardness testers like the Shore M and International hardness IRHD, as specified by material specifications and associated test methods.
Refer to SAE Aerospace Recommended Practice (ARP) 4738, Hardness Testing of Elastomeric O-rings, for a detailed description of popular hardness test methods and the causes of differences resulting from hardness testers and specimen geometry.
Does Parco have compounds approved by the National Sanitation Foundation (NSF)?
Parco has several compounds approved to NSF Standard 61. To view the listings, use the link below to NSF Product and Service Listings, then enter "Parco, Inc." in the field for Manufacturer's Name.
www.nsf.org/Certified
Does Parco have compounds listed by Underwriters Laboratories, Inc. (UL)?
Parco has several UL listings. To view the listings, use the link below to go to the UL Online Certifications Directory. Search by Company Name/Location and enter "Parco" into the field for Company Name.
www.ul.com/clients/index.html
What causes some compounds to craze plastic?
Compounds containing aromatic plasticizers craze (produce minute cracks) the surface of plastics. Fluorocarbon and silicone compounds do not craze plastic because they have no plasticizers. Parco offers other compounds that contain no plasticizers or that contain plasticizers compatible with plastic.
What is the shelf life of Parco compounds?
For compounds using most elastomers, Parco recommends the shelf life stated in SAE Aerospace Recommended Practice (ARP) 5316, Storage of Aerospace Elastomeric Seals and Seal Assemblies Which Include an Elastomer Element Prior to Hardware Assembly. For compounds using elastomers not listed in that document, Parco recommends the shelf life stated in MIL-HDBK-695, Rubber Products: Recommended Shelf Life.
For compounds using elastomers not listed in either of those two documents, Parco's R & D laboratory recommends a shelf life based on recommendations from our polymer supplier and experience. Many Parco customers have their own shelf life specifications based on their experience with particular applications. You can view Parco’s recommended shelf life by elastomer and compound by using the O-ring Shelf Life Tool in the Compounds section of our web site.
