Coiling Technologies, Inc., is known for the superior quality products that we deliver to our customers. We are always keen that each delivered product is tested under our standard testing methodology and special inspection is done before the springs are moved to our warehouse.
Some of the testing methods we follow are:
Load Testing:
In load testing, a load is applied to the spring and then the displacement of the spring is checked. Alternatively, the spring can be compressed to a known distance and then the load checked at that point, if the parameters match the requirement, then the spring can be marked as OK, otherwise the sample shall be rejected. We are able to test up to 48,000 pounds.
Magnetic Particle Inspection:
This technique is capable of producing more accurate and sensitive testing results. This is mainly followed to detect fatigue cracks at an early stage of development. This helps to identify microcracks with widths of 0.001 mm and depths of 0.01 mm or more.
Liquid Penetrant Testing:
This is also known as the color check method. The surface of the material is coated with a liquid under penetrating forces, and this liquid flows into the open flaws by which we can detect the cracks on the surface of your spring.
Please contact us, if you have any questions about our testing methods.
Non-Destructive Testing of Springs FAQs
What is non-destructive testing on a spring, and why does it matter?
Non-destructive testing evaluates a spring without damaging or consuming it, which means the part that gets inspected is the part that ships. Destructive testing tells you about a sample. Non-destructive testing tells you about the spring in your hand. For springs the value is finding surface discontinuities before the part enters service, because fatigue cracks in springs initiate at the surface and a crack too small to see will still propagate under cyclic load. Coiling Technologies tests delivered product under a standard testing methodology, with special inspection performed before springs move to the warehouse.
Which non-destructive test methods does Coiling Technologies use?
Three are published: load testing, magnetic particle inspection and liquid penetrant testing. Load testing verifies mechanical performance by applying a load and checking deflection, or by compressing to a known distance and checking the load at that point, with a stated capacity up to 48,000 pounds. Magnetic particle inspection finds surface and near-surface cracks in ferromagnetic material. Liquid penetrant testing, also called the color check method, reveals surface-breaking flaws on materials magnetic particle cannot handle. If your specification calls for a method outside those three, raise it during the quote rather than after the purchase order.
What can magnetic particle inspection actually detect?
It is used mainly to catch fatigue cracks at an early stage of development, and the published sensitivity is microcracks with widths of 0.001 mm and depths of 0.01 mm or more. That resolution is far past what visual inspection can resolve, which is why the method is worth specifying on high-cycle or safety-relevant springs. The limitation is material. The technique depends on magnetic flux leaking at a discontinuity, so it works only on ferromagnetic material. Carbon steel, alloy steel and martensitic grades respond well. Austenitic and nickel-based material does not respond at all.
When should liquid penetrant be specified instead of magnetic particle inspection?
Whenever the spring material is not ferromagnetic. Austenitic stainless grades, the Inconel and nickel alloy family, Monel, copper-based alloys and titanium are all effectively non-magnetic, so magnetic particle inspection has nothing to work with on them. Liquid penetrant is indifferent to magnetic properties. A penetrating liquid is drawn into open surface flaws, then brought back out to make the flaw visible. The tradeoff is that penetrant finds only discontinuities that break the surface, while magnetic particle can also pick up flaws sitting just beneath it.
How does spring load testing work, and what capacity is available?
Two approaches, and your drawing decides which applies. A known load is applied and the resulting displacement measured, or the spring is compressed to a specified distance and the load at that point recorded. Either way the measured value is compared against the requirement, and a sample outside the parameters is rejected rather than shipped. Coiling Technologies can test up to 48,000 pounds, which covers the large and heavy-duty compression spring work the shop specializes in. Load test data is one of the documents available with your order.
When should I specify non-destructive testing on my spring drawing?
Call it out when a spring failure carries consequences: suspension and other high-cycle parts, springs in valve or pressure service, military work, and anything installed where the assembly cannot easily be accessed for replacement. Name the method instead of writing inspect for cracks, since magnetic particle and liquid penetrant suit different materials and find different things. Add the acceptance criteria, the sampling plan, and whether you need results as a deliverable. Coiling Technologies can supply dimensional inspection reports with measured values against drawing tolerances, first article inspection documentation and load test data on request.
