DN Staff

September 4, 2006

3 Min Read
The Case of the Stressful Stripper

Surface preparation is a necessary prelude to a successful refinishing job. In years past, refinishers were limited to putty knives, scrapers, sanding blocks and other hand-operated devices, all of which made for slow going. Even then, flying paint chips were a threat to the eyes.

Scene of the Crime

Somewhere along the line, someone devised a rotary stripper powered by an electric drill. Hard-drawn steel wires pivot loosely as the device rotates and rapidly scratches paint, rust, varnish and whatever off the surface. In the present case, a wire detached from a stripper, entering the operator's eye with dire results. The subject stripper is shown in the figure. Seventeen wires had fractured during use. The first 16 wires flew off harmlessly - the 17th did the damage. Most of the other wires had fractured just earlier and were strewn about the floor at the accident scene. The injured was not wearing eye protection.

The Investigation

The wire that entered the eye had been lost. This was no problem, as it had been the 17th wire to fracture. Had this particular wire been weaker than the other 29, it would have fractured first. My failure analysis was rather simple, involving only scanning electron microscopy of the fracture surface and metallographic examination of a longitudinal section of one wire. Scanning electron microscope study showed the fracture to be of the progressive fatigue type with no evidence of cracks or other defects that would have caused premature failure.

A section of one wire was mounted in plastic and polished along one side. Examination in an ordinary optical microscope showed that the steel grains were highly elongated due to drawing through a wire die. Such drawing is a widely used way of strengthening, being used in piano wire, for one example. The wire was entirely appropriate for the use.

Instructions with the stripper tell the operator to use a light touch, never bear down and to always wear eye protection. Instructions were given for sharpening the ends of the wires. The operator had obviously ignored all the instructions. The ends of the wires had become dull, and instead of sharpening them per the instructions, the operator put pressure on the stripper, leading to heavy bending stresses and - predictably - fatigue failure. A light touch would not have caused the wires to fracture. Eye protection would have prevented the errant wire from damaging the eye.

The figure shows the subject stripper has from zero to four wires per pivot. An exemplar stripper had five wires on each of six pivots. Thus, 17 of 30 wires have broken off near the pivot. The operator ignored these danger signs and continued to operate the stripper without eye protection.

The Smoking Gun

Product law has what is called the doctrine of foreseeable misuse. The product should perform safely even though misused in a "foreseeable" manner. In the present case, the doctrine would be one of "imaginable idiocy." The injured operator flew in the teeth not only of the explicit and repeated instructions, but of common sense. Continued misuse of the stripper with fractured wires flying about and no eye protection boggles even my jaded mind.

The preceding sounds as if I were making the case for the stripper manufacturer. Not so. This was a plaintiff's case pursued by a blue-blood Boston law firm. They apparently felt that their client had not been properly warned. The case dragged on for years. I never learned the outcome.

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