Quality
- What quality certifications does Parco have?
- What does AQL mean in acceptance sampling?
- Why do I receive defective parts when I order parts to C = Zero sampling?
- What are the advantages and disadvantages of various measurement methods?
- What are Class I inside diameter tolerances?
- What is the difference between a batch and a lot?
- What tests do you perform on batches and finished parts?
- Why do O-rings fail?
What quality certifications does Parco have?
Parco has the following certifications:
ISO 9001
Det Norske Veritas Certification, Inc. (DNV) has certified that Parco's quality management system meets the requirements of ISO 9001, Quality Management Systems – Requirements. ISO 9001 is the internationally recognized standard for a basic quality management system.
ISO/TS 16949
DNV has certified that Parco's quality management system meets the requirements of ISO Technical Specification (TS) 16949, Quality Management Systems – Particular requirements for the application of ISO 9001:2000 for automotive production and relevant service part organizations. ISO/TS 16949 incorporates the requirements of ISO 9001 and adds requirements specific to the automotive industry.
AS9100B
DNV has certified that Parco's quality management system meets the requirements of AS 9100B, Quality Management Systems – Aerospace – Requirements. AS 9100 incorporates the requirements of ISO 9001B and adds requirements specific to the aerospace industry.
AS7115
The Performance Review Institute (PRI), an affiliate of the Society of Automotive Engineers (SAE), has certified that Parco meets the requirements of AS 7115, National Association of Defense Contractors Accreditation Program (NADCAP) Requirements for Elastomer Seals. AS 7115 describes certain manufacturing and quality requirements. Elastomer seal manufacturers must have accreditation to AS 7115 to be included on aerospace-defense Qualified Products Listings (QPLs).
What does AQL mean in acceptance sampling?
AQL is an acronym for Acceptable Quality Level. It is the percent nonconforming that, for purposes of sampling inspection, can be considered satisfactory as a process average. The AQL alone does not describe the protection to the consumer for individual lots. Rather, it describes the expectation from a series of lots. For more information on Acceptable Quality Levels please see ANSI/ASQC Z1.4-1993, Sampling Procedures and Tables for Inspection by Attributes.
Why do I receive defective parts when I order parts to C = Zero sampling?
No sampling plan offers assurance of 100 percent conformance. Sampling plans are designed statistically to be more or less stringent. Stringent process controls are required to meet more stringent sampling plans. If the process average conforming is less than that accepted by the sampling plan, lots must be reworked or sorted to pass that sampling plan.
There are two main differences between C = Zero sampling and AQL sampling. First, the number of defects allowed in the sample is always zero in C = Zero sampling plans. Second, C = Zero sample sizes are significantly smaller than AQL sample sizes.Parco's C = Zero sampling plan is approximately equal to a .65 AQL sampling plan. Therefore, the average percent conforming will be 99.35% or more for a series of lots when C = Zero sampling is invoked.
What are the advantages and disadvantages of various measurement methods?
There are many different methods used to measure rubber seals. Those measurement methods may be categorized as either Contact or Non-Contact.
Contact Measurement - Examples of contact measurement methods include micrometers, calipers, go/no-go gauges, and measurement pins (pin gages). These methods all suffer from the same disadvantage. Any time you touch a piece of rubber with a gauge, you deflect it. The amount of deflection varies by rubber hardness and operator feel and experience. Therefore, operator-to-operator variability is prevalent with contact measurement methods.
The main advantage of contact measurement methods is speed. Contact measurement methods are best suited for measuring large sample sizes associated with production and receiving inspection.
Non-Contact Measurement - Examples of non-contact measurement methods include microscopes, optical comparators, and video coordinate measuring machines. Non-contact measurement removes the variability associated with rubber hardness and operator feel. As a result, the measurements are more consistent.
Generally, non-contact measurement is much slower than contact measurement. Non-contact measurement is best suited for measuring small sample sizes associated with mold approval, problem-solving, and referee measurements.
What are Class I inside diameter tolerances?
Please see Parco's O-ring Size Chart for an explanation of dimensional tolerances.
What is the difference between a batch and a lot?
A batch is the amount of material run through a mixer at one time. At Parco, a batch of compound weighs between 50 and 240 pounds, depending on the size of the mixer and the specific gravity of the compound. The mixing department assigns each batch a sequential five-digit batch number. We put the batch number on packages, packing lists, and certifications as evidence of traceability of the material to acceptance test results.
After the laboratory approves a batch, the mixing department distributes the batch to work orders. If a work order is for a large quantity of seals, it may take an entire batch to mold the parts. Usually, the batch will be distributed to several work orders. Work orders are uniquely numbered and bear the number of the batch.
A lot is all the same size parts made from the same batch of rubber that are run through the plant together. At Parco, the term lot is used to describe all the parts associated with a particular work order.
What tests do you perform on batches and finished parts?
Parco's laboratory tests the following physical properties of every batch of compound:
- Shore A hardness
- Tensile strength
- Ultimate elongation
- Modulus at 50 and 100% elongation
- Specific gravity.
All of those properties must pass Parco's specification, which is based on the most stringent requirements to which Parco sells the compound.
The laboratory tests other batch physical properties (low temperature resistance and compression set, for example) and finished parts as dictated by the customer's purchase order and certification requirements.
O-rings and other seals leak for many reasons. A defective seal may cause some leaks. However, most leaks are associated with other factors such as installation method, gland design, and sealing environment.
The Society of Automotive Engineers publishes Aerospace Information Report (AIR) 1707, Patterns of O-ring Failures. That report can often help a user to determine the cause of an O-ring failure.
