Imagine you bought a pair of jeans and the color faded the first time you put them through the wash. It’s fair to say that the product wasn’t fit to be sold and hadn’t been tested. The same concept applies to seals. Companies perform comprehensive testing so that industrial seals don’t fail under expected conditions in an application. There are many factors that need to be analyzed, but the research and development process itself can broadly be divided into three main parts: material development, seal development, and product testing.
Selecting the right material for the job
This is clearly the starting point. If you’re using a seal in an application that experiences high temperatures, the seal needs a material that can withstand these conditions. In my experience, the first thing the manufacturer must do is assess what the seal will be used for and whether the seal material supports this. As experts, they have an in-depth understanding of which materials are suitable for different applications.
Transforming concepts into reality
The design department works closely with the material department when defining the seal design. Based on the FEA calculations, pre-selection of suitable seal design is performed. The best ones with different geometries are then chosen for prototyping. At SKF, we produce prototypes with the SKF SEAL JET system. Especially for the purpose of seal testing, I find this particularly beneficial, as injection molding tools are not required, and the seal can be manufactured according to different specifications very quickly.
What comes after producing prototypes?
After the seal prototypes have been produced, the testing phase begins in earnest. The prototypes are tested under different conditions (pressure, speed rate, temperature, stroke length, testing time, etc.) that are similar to the real application conditions or – in case of benchmark testing – characteristic for the selected seal type.
The different seal types require totally different testing methods. Take hydraulic seals as an example. Different hydraulic seal test rigs are used that simulate hydraulic cylinders to cover all different seals in a hydraulic sealing system like piston seals, rod and buffer seals as well as wiper seals. The main criteria for evaluating the overall seal performance for hydraulic seals are friction force, leakage behavior, wear and, last but not least, the compression set of seals. This is the remaining deformation after applying high loads.
For rotary seals, specially designed rotary seal test rigs are used. They are suitable for different lubricants, such as grease, oil, and water-based fluids. For these, real–life conditions are simulated for lots of different industry applications. These include wind turbines, marine applications, metal industries, and also heavily contaminated environments like we see in the mining, mineral processing, and cement industries.
In addition to those common tests, there are many other tests necessary to fulfil the very specific requirements for some selected industries, like the oil and gas industry. Due to the extreme requirements regarding safety, the seals are tested under extreme conditions according to API 6A and NORSOK standards.
After the internal verification of the seal products, a real-life validation or factory acceptance test (FAT) is conducted once the customer begins using the seal. During this factory acceptance test, the client provides feedback on seal performance. If the seal works as it should, it could be a perfectly working unique solution according to sometimes very demanding, special application conditions. Alternatively, it could end up as a standard product resp. catalogue seal.
With a unique combination of machining capabilities, specially developed sealing materials and a pre-selection of seal profiles, polymeric seals can be produced on the SKF SEAL JET DD system in virtually any dimension and any design, for virtually any industrial application.
And that’s my rundown of how and why industrial seals are tested. This is how companies like SKF make sure the seals it sells will be reliable when used in applications. Naturally, every company has its own practices for certain parts of the process, but I would say that these methods are somewhat standard. From what I’ve seen at SKF, years of experience, a large number of test rigs, numerous facilities, and the SKF SEAL JET system contribute to designing seals that will be durable and reliable.
Author: Silvio Schreymayer