Extruding, Forging & Heat Treatment
The highly competitive aluminum can market depends on very clean aluminum sheet of consistent quality. Several investigations have been performed by Touchstone using the Scanning Electron Microscope (SEM) to identify failure initiation sites in defective can bodies.
The following examples illustrate some of our contributions to this business sector:
- Touchstone was contacted by a manufacturer of ultra-high pressure (60,000 psi) stainless tubing regarding fatigue life. Evaluations of finished material found longitudinal cracks on the ID that acted as notches and progressed to failure in a short time. The cracks were formed during the cold-drawing operation used to form the tube. Removal of the cracks extended the fatigue life beyond that needed for satisfactory service.
- A large industrial air compressor failed catastrophically when the end cap separated from the main bearing. The failure was traced to the initial failure of one cap screw that broke under normal load. The screw was specified as a grade 8 fastener, but the rolled threads had been formed before heat treatment instead of after. While the roll threading did eliminate the problems associated with cut threads, the benefit of cold work to the threads in terms of fatigue life was lost during heat treatment. A recommendation for future orders was to specify that threads be rolled after final heat treatment.
- A problem with leakage in the seat area of valve bodies was brought to the attention of Touchstone engineers. A process known as “thermal deburring” was used to clean the bodies prior to shipment. Based on the metallographic evaluations, it was decided that the thermal process might have been introducing stress and irregularities in the seat area and actually causing the leak problem by deforming the seat area.
- A problem concerning cracking in a forged steel roll was examined metallographically. The presence of iron oxide scale in the crack and the configuration of the crack indicated that quench cracking was the probable cause of the defect.
- The highly competitive aluminum can market depends on very clean aluminum sheet of consistent quality. Several investigations have been performed by Touchstone using the Scanning Electron Microscope (SEM) to identify failure initiation sites in defective can bodies. Frequently, the cause is an inclusion that presents a weak spot that causes the failure in the drawing operation. SEM analysis of the inclusions allows plant operators to determine where in production the foreign material is introduced and, therefore, how to prevent recurrence of the defect.
- The failure of a gear, manufactured from a forged steel blank, was traced to a “lap” in the original forging. Using standard metallographic techniques, the gear was examined in the area of the failure and a lap was identified that had provided the origination site for the failure.
- The manufacturer of roll-formed, line-coated steel panels concerned about defects that were seen along the formed edges contacted Touchstone. In the manufacturing process used for this product, coated steel sheet is passed through successive forming rolls until the final product shape is reached. The defect was a split in the coating at the location of the sharpest bend in the panels. Evaluation found two conditions that could lead to the defect: an excessively thick layer of brittle zinc-iron alloy and a small forming roll radius.
- A producer of automotive body panels experienced breakage of tool steel punches. SEM evaluation of two broken punches found that the fractures were brittle. Microstructural evaluation indicated insufficient tempering after quenching in the manufacture of the die. Since no use history records were available, the question of suitability for the purpose arose, which centered on two possibilities: either the manufacture of the die had changed, or the punching operation and/or material being punched had changed over time.
The above examples are only a sample of our work in this area. We would be pleased to provide any additional information you may require. We also invite you to review examples on our website of work that we have performed in support of other business sectors.
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