Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2000-01-12
2001-06-05
Kastler, Scott (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C072S062000
Reexamination Certificate
active
06241832
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes and apparatuses for creep-sizing annular-shaped structures. More particularly, this invention relates to a thermal creep-sizing process that employs a mandrel configured to be installed and then expanded within a hoop structure, so that a subsequent thermal treatment diametrically expands the hoop structure as a result of thermal creep.
BACKGROUND OF THE INVENTION
Hoop structures and various other components with annular-shaped sections at times must be diametrically expanded to attain or restore desired diametrical conditions, such as during the manufacturing or reconditioning of shrouds and nozzle supports of gas turbine engines. For relatively ductile materials, sizing can be accomplished by hydraulic expansion methods while the component is at or near room temperature (“cold sizing”). However, a component can be susceptible to tensile fractures during cold-sizing if formed from certain materials, including superalloys commonly employed in gas turbine engines. For these materials, sizing must be performed at an elevated temperature. One such method is generally referred to as hot creep sizing, and involves a high mass fixture with a coefficient of thermal expansion (&agr;) that is relatively constant for the temperatures used and equal to or higher than the structure being sized. A difficulty with hot creep sizing is the requirement for slow and tightly controlled heating and cooling rates in order to match the growth of the fixture with the component being sized, which slows processing throughput. Another thermal creep-sizing method is known as warm sizing, and involves expanding a preheated component on a mandrel that is maintained at a lower temperature throughout the sizing operation. With many materials including superalloys, the component must be heated to very high temperatures, e.g., 1800° F. (about 980° C.) or more, which may pose a hazard to the operator.
In view of the above, it would be desirable if an improved method were available for sizing a hoop structure that avoided the disadvantages of prior art methods.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a method and device for thermal creep-sizing an annular-shaped structure, including hoop structures and components with annular sections. The invention provides a method by which controlled sizing of an annular-shaped structure is achieved with a creep-sizing device that is mechanically expanded in a manner that provides controlled and accurate sizing of the structure during a thermal treatment.
According to this invention, the creep-sizing device includes a ring member having inner and outer diametrical boundaries relative to the axis of the ring member. Through-holes are present in the ring member between the inner and outer diametrical boundaries, with through-slots extending from each through-hole through the ring member to either the inner or outer diametrical boundary. Finally, pins are provided that are sized to be received in the through-holes. Each pin has a diameter approximately equal to one of the through-holes when the ring member is in a free-state, i.e., not deformed by any force applied externally to the ring member.
The method of this invention made possible by the above-described creep-sizing device generally entails placing the ring member (without pins) within an annular-shaped structure so that the outer diametrical boundary of the ring member is adjacent an inner surface of the annular-shaped structure. The pins are then inserted into the through-holes in the ring member, which causes the outer diametrical boundary of the ring member to diametrically expand. The annular-shaped structure and the device of this invention can then be heated so that the mechanically expanded ring member causes the structure to undergo thermal creep-sizing at a temperature at which the material of the structure is ductile and therefore less likely to fracture.
In view of the above, it can be seen that a significant advantage of this invention is that it entails sizing an annular-shaped structure at an elevated temperature, thereby significantly reducing the risk of tensile fractures as compared to cold sizing methods. Furthermore, the ring member employed by this invention can be of relatively low mass, and its desired sizing effect is mechanically induced instead of relying on a high coefficient of thermal expansion. As a result, the ring member can be heated relatively rapidly without stringent control of the heating and cooling rates as compared to hot creep-sizing methods. Finally, and in contrast to warm creep-sizing methods, the thermal creep-sizing method of this invention can be performed without any requirement to handle the creep-sizing device or the structure being sized while at an elevated temperature.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
REFERENCES:
patent: 3920175 (1975-11-01), Hamilton et al.
patent: 3934441 (1976-01-01), Hamilton et al.
patent: 5551790 (1996-09-01), Melton
General Electric Company
Gressel Gerry S.
Hess Andrew C.
Kastler Scott
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