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Customised analysis

Damage analysis / Determination of causes of failure / Analysis of material defects / Component tests / Material analysis

For decades, we have learned to understand plastic and to bring together the knowledge acquired in the areas of polymers, tribology and mechanical engineering, in order to use high performance & engineering polymers as machine element successfully.

We want to provide our customers with this knowledge, supported by the tests/analyses that we can carry out with our laboratory equipment, as a service to support them in determining the causes of errors by carrying out damage analyses.

In the event of damage, we can determine the cause of the failure as far as possible through mechanical, thermal, micro or macroscopic examinations of the defective parts and suggest the necessary measures to remedy or prevent it. Optionally, we recommend the suitable ZEDEX® engineering or high-performance polymer.

Failure of plastic components

can have different causes, e.g.

  • mechanical or thermal overload
  • influence of chemicals
  • material defects
  • processing errors
  • environmental influences (e.g. UV radiation)

     

There may be external signs of this

  • discoloration
  • cracks, ruptures
  • excessive wear
  • plastic deformation, warpage
  • melted areas

Example

Melted areas due to too high sliding speed and at the same time too high mechanical stress.

Damage analysis

Problem
A spherical cap (bonded segmental sliding sheets) made of ZX-324 is used for the storage of the main undercarriage
of the world‘s largest excavator.

During operation, strong creaking noises were detected, so the sphere was removed for an inspection. It was found that the sliding layer was provided with a brown substance that closed the holes for the grease supply, thus preventing re-lubrication. At the sphere, the chrome was chipped here and there.

At these locations, severe corrosion was seen.

Mining excavator

Spherical cap (installed state)

Sphere

Spherical cap (after disassembly)

Task
It should be analysed , why it came to failure.

Damage (detail)

Experiments performed at Wolf’s
Here is a second example of a failure analysis. Here was about to find the best material for this application.

Here you can be seen what was going on …..

In the laboratory of the corporate Wolf were tested different ZEDEX® plastics, that could have been used for this application.
Friction and wear tests, in function of the counter material, the lubricant and the surface roughnesses were
performed.

SRV-experimental apparatus

Evaluation of the wear measurement

Cause of the problem
Thanks to the test results was demonstrated, that the material pairing was not the best and especially the used lubricant had a negative impact on the wear behaviour.

Even in dry running conditions the wear would have been lower by several times.

Problem solving
Based on the test results, the usage of a better lubricant was recommended, which was also significantly inexpensive in comparison to the one used previously.

In addition, another material has been proposed as spherical cap.

Status
The customer has switched over to the new lubricant. As a next step , the recommended material change is planned.

Damage analysis & component testing & material selection

Problem
At the customer’s different seals made of PEEK were used. Some of these broke even with low mechanical stress.

Task
Failure analysis needed and at the same time the friction properties have to be improved.

Experiments performed at Wolf’s
On the samples provided by the customer following tests were performed:

  • Compression
  • bending
  • melt viscosity
  • thermal analysis
  • optical inspection.

Axial compression test

Radial compression test

Example: Pressure test (axial and radial) on sealing rings made of ZX-324. It has been found at which load a permanent deformation occurs and at which load the rings brake.

Cause of the problem
The carried out experiments have shown that the errors were present in the material. Within different batches, some severe quality variations were observed. By looking at the breaking point under the microscope, it was found that the semi-finished product for the parts was made by the compression moulding process, and that the temperature was possibly not correctly set.

Breaking point at the parts supplied
by the customer

Example: Determination of the switching torque of a ball valve with ball seals made of ZX-324 at extreme temperatures from –196°C up to +200°C

Problem solving
As comparison, sealing rings made of ZX-324V2T were manufactured from an extruded semifinished product. These ones obtained significantly better results in the compression tests.

Even with extreme experiments, in which ZX-324V2T rings was squeezed in a bench-vice until its stop, there was no rupture.

The customers were provided with sample parts made of ZX-324V2T for his tests and with a detailed inspection report.

 

Status
Customer makes a working life tests with a test bench.

Seal made of ZX-324V2T, squeezed in a bench-vice

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