Biomedical Engineering Reference
In-Depth Information
10.4.4 Aftermath
Returning to the factory with the recommendation that moulding be stopped
to reset the moulding machines, did indeed save the situation. The change
in conditions moved the weld lines away from the hinges, and samples were
again taken for testing. The strength of the new samples averaged 12 N m and
was much more consistent. Far from being a material problem, the moulders
should have taken greater care in monitoring their moulding conditions, and
inspecting their products to eliminate the damaging weld lines. A systematic
approach to troubleshooting the problem revealed the cause of the premature
failures, led directly to remedial measures and a solution to a problem which
had caused a great deal of concern as well as loss of production. such action
would strengthen the guards to such an extent that they would survive harsh
handling during transport and any casual vandalism, so as to reassure the
final user, the hospital technician, that the cylinder contents remained intact
and tamper-free.
10.5 Breathing tube failures
The medical appliances market has developed greatly in recent years with
the demand for ever better patient care both in hospital for acute cases, and
at home for patients with chronic ailments. Respiratory illnesses are among
the most common such ailments, and often require breathing apparatus for
supplying the patient with humidified air or oxygen in a controllable way.
The breathing equipment for such applications must be made to a very
high standard, so that bacterial contamination of the bore is impossible.
The case reported here concerns the quality of a large transparent sight
tube developed for use in breathing apparatus, the material being injection
moulded polysulfone.
The alleged defects related to the quality of finish of the tubes, rather
than any structural or functional problems in use. The manufacturer of the
breathing apparatus brought an action against the toolmaker, alleging that
the tool for making the tubes was incapable of moulding sight tubes in
polysulfone.
10.5.1 Development of sight tube
The breathing equipment was already in existence when the decision was
made to develop a moulded sight tube. The tube sat at the top of a longer
metal pipe, and enclosed a float giving visual indication of flow rate in the
tube (Fig. 10.16). The float must not fall below the lower marker so as to
ensure air or oxygen is being sent to the patient. The transparent tube was
machined from acrylic resin (high molecular weight PMMA) to a high quality,
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