We operate an in-house metallurgical laboratory for the metallographic examination of rolled threads, conformant with aerospace, military, and commercial specifications. These specifications require threads be inspected both destructively and non-destructively. Non-destructive testing checks the thread’s profile dimensionally (major, minor and effective diameters) and also checks the form of the crest, flanks and root. Destructive testing verifies the thread is free from cracks, laps and surface irregularities as well as ensuring the grain flow is smooth and continuous.
During a production run, multiple specialised methods are employed to measure the thread’s dimensions and form. These methods include, shadow graph, thread micrometer, calliper gauges and go/no go ring gauges. The thread rolling operators use these measurements to monitor thread rolling processes and make the necessary adjustments. Die wear, material properties and other factors affect the rolling process; once a machine is set, the process is consistent, repeatable and fast.
A destructive thread inspection method is used at Redcliffe to formally verify quality of product. Representative samples are tested at the beginning and end of each new set up, as well as periodically during the course of a production run.
The destructive testing process requires that the thread be cut from the rest of the part, bisected longitudinally and mounted in a phenolic resin. This specimen is then ground and lapped to a three-micron mirror finish before being etched to reveal the micro structure. The microstructure is analysed using a microscope supported by metrology software, allowing measurements and images to be made.
Each specimen is uniquely identified and stored. Inspection reports are documented to produce a certificate of conformance; these, along with digital thread rolling examination can be sent to the customer. Our laboratory also provides metallurgical testing services for external companies.
Micro test laboratory facilities
Typical microstructure test samples