Touchstone performed a comparative evaluation of the edge quality resulting from several different cutting systems including: Blanking press, wire EDM, Laser, Turret punch, and abrasive water jet cutting systems.
The following examples illustrate some of our contributions to this business sector:
- Repeated, explosive failures of heating elements in commercial coffee vending machines led to the evaluation of both new and failed heating elements. The elements were inconel-sheathed, resistance elements and after only a short service were seen to burst when the machine began to heat water. The failures clearly appeared to be the result of bursting, probably under steam pressure, but no corrosion was seen which might have allowed water to seep into the element. Metallographic evaluation found the elements to have a uniform, fine-grained microstructure with no obvious defect. Examination of the element exterior did not find any cracks or obvious manufacturing defects that would explain the failure. A discussion of the problem with the vending machine manufacturer found that, as part of their quality control, each new element was tested by powering it until it became orange hot to assure the element was operational. Immediately afterward the hot element was then plunged into cold water. Metallographic examination of new “untested” elements revealed that the units were supplied with the sheath in an annealed state. The annealed structure allowed for normal expansion when the element was used. Quenching has rendered the sheath hard and relatively inflexible. During initial heating the sheath would crack and allow water to seep into the element. During a subsequent heating cycle the element would burst from steam pressure.
- A computer manufacturer requested that Touchstone help to solve problems with the surface quality of their galvanized computer chassis. Touchstone determined the thickness of the zinc plating, the type of chromate conversion coating and the nature and cause of the white stains. The coatings were found to meet appropriate requirements, and the stain was found to be caused by an inorganic acid coming into contact with the chassis in a post forming operation.
- An analysis was performed on a plated, copper wire sample using a scanning electron microscope in the EDS mode to determine the type of plating present.
- A fastener manufacturer wanted a detailed engineering and cost analysis which compared the laser cutting or turret punch systems versus the method which incoporates either press blanking or a wire-edm process. Touchstone performed a comparative evaluation of the edge quality resulting from several different cutting systems including: Blanking press, wire EDM, Laser, Turret punch, and abrasive water jet cutting systems. While the Abrasive Water Jet produced the best result in terms of the characteristics evaluated, areas for improvement of this system were identified.
- Repeated failures of screws in computer chassis led the manufacturer to contact Touchstone. Broken screws were frequently the source for complaints of “rattling” noises and electrical shorts. Examination of the fracture surfaces found intergranular, faceted fracture surfaces typical of hydrogen embrittlement. A production check found that the screws were plated, but not baked to remove hydrogen.
- Touchstone performed an evaluation of brass plating on exterior light fixtures in order to determine the cause of corrosion and to suggest changes in manufacture which would assure the satisfactory performance of new units. TRL concluded that the rusting on the light fixtures was due to very thin plating, which did not provide adequate protection of the base metal. The rusting on the globe fastener screw was also due to the same conditions as the fixture.
- Workmen for a telephone company opened a manhole to begin repairs and noticed a strong odor emanating from the opening. Also, an orange surface layer was seen covering the floor of the storm drain. Touchstone was contacted by the Telephone Company. An investigation found that the odor was due to decomposition of leaves and other organic debris that washed in during recent rainstorms. Methane was detected in the atmosphere by GCMS analysis of air samples. The color (orange) was caused by iron-rich debris sandblasted from a nearby interstate bridge during repainting operations that had covered the organic debris.
- Eleven metal samples from guitars were sent to TRL for evaluation. These included a pole piece and a gap piece from a speaker, 3 round headed wood screws, 3 spacer bars and 3 pieces suspected of being alnico magnets. The speaker parts were to be examined to determine what type of metal was used in their manufacture, how they were manufactured, their density and what type of plating might be present. The remaining samples were evaluated to determine what metal alloy was used in their manufacture.
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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