Appeal No. 99-0158
Application 08/616,787
caps and the tube when the assembly is heated to the
superplastic forming temperature of the tube. Fields makes no
mention of the coefficients of thermal expansion of the tube
(tubular blank TB) and end caps (plug members 23 and 24)
disclosed therein, or of any heat-induced gas-tight seal
between the tube and end caps.
The examiner’s reliance on Greacen to overcome these
deficiencies is not well taken.
Greacen discloses an element 20 designed to plug a
defective tube in a heat exchange apparatus to avoid the
necessity of removing the apparatus from service to replace or
repair the tube. To this end, the plug is made of a shape
memory alloy “whereby it can be physically deformed into a
reduced diameter for insertion into the tube end and
thereafter induced to assume its original diameter to thus
secure the plug within the tube” (Abstract). Greacen explains
that
there is provided a method of plugging a defective
tube by means of a plug formed from the above
material comprising the steps of forming the plug
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