US3008688A

US3008688A - Overspeed safety check for turbines

Info

Publication number: US3008688A
Application number: US663683A
Authority: US
Inventors: Makowski Jerzy
Original assignee: Fairchild Stratos Corp
Current assignee: Fairchild Stratos Corp
Priority date: 1957-06-05
Filing date: 1957-06-05
Publication date: 1961-11-14
Anticipated expiration: 1978-11-14

Description

Nov. 14, 1961 J. MAKOWSKI OVERSPEED SAFETY CHECK FOR TURBINES Filed June 5, 1957 INVENTOR JERZY MAKOWSKI 3,008,688 OVERSPEED SAFETY CIECK FOR TURBINES Jerzy Makowski, Babylon, N.Y., assignor to Fairchild Stratos Corporation, a corporation of Maryland Filed June 5, 1957, Ser. No. 663,683 8 Claims. (Cl. 253-59) This invention relates to safety means for providing overspeed protection for turbines.

It is well known that runaway turbines are highly dangerous due to the possibility of failure of the turbine wheel. Because of the extremely high rotational speeds at which failures occur, it is not unusual for bullet-like fragments to be projected with sufficient force to penetrate the housing within which the turbine wheel is situated. It is apparent that such failures present an extreme hazard to both personnel and equipment stationed nearby. In addition, there is the imminent danger of fire as a result of the excessive growth of the runaway turbine wheel due to the effects of heat expansion and centrifugal force. A turbine wheel which has experienced excessive growth eventually rubs against the interior walls of the turbine housing and generates intense heat which further adds to the danger of turbine failure, unless the runaway condition is checked.

The present invention is directed to safety means to check an overspeed condition in a runaway turbine. This safety means provides a plurality of passage means capable of directing streams of a fluid under pressure against the turbine wheel in opposition to the direction of rotation of the turbine wheel, and temperature sensitive means normally closing said passage means to prevent the flow of fluid therethrough. In the event of a runaway condition, the exorbitant growth of the turbine wheel brings the turbine wheel into frictional contact with the housing, generating heat Which causes the temperature sensitive means to open the plurality of passages, thereby slowing down the speed of the turbine wheel within the safe range.

In the preferred embodiment of the present invention, the turbine housing is equipped with a number of holes spaced apart and arranged in an orderly fashion about the outer perimeter of the turbine housing. These holes are drilled or cast in a direction having a component opposite to the direction of rotation of the turbine wheel. These holes communicate with a source of fluid under pressure, such as, for example, the impelling fluid which drives the turbine. The holes are then filled with a material having a melting point relatively low in comparison to the melting point of the material from which the housing is made. When the turbine overspeeds the turbine wheel undergoes expansion, and the frictional engagement between the outer ends of the turbine blades and the surface forming the inner periphery of the housing generates heat which melts the filling material so that the fluid under pressure is admitted through the holes, exerting a force on the turbine wheel in a direction opposite to the direction of rotation of the turbine wheel. As a result, the speed of the turbine wheel will be greatly reduced, although the turbine will continue to operate.

For a complete understanding of the present invention, reference may be made to the detailed description which follows, and to the accompanying drawing in which:

FIGURE 1 is a fragmentary perspective view, partially in cross-section, of a turbine wheel and housing therefor equipped with the safety features of the present invention;

FIGURE 2 is an elevational view in cross-section taken along a plane normal to the axis of the shaft, illustrating the parts shown in FIGURE 1; and

Patented Nov. 14, 19,61

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FIGURE 3 is a view in cross-section taken along the line 3-3 of FIGURE 2, looking in the direction of the arrows.

Referring to the drawing, a rotatable turbine wheel 10 is mounted on a shaft 12 suitably supported in bearings. The turbine wheel carries a plurality of turbine impeller blades 13 spaced around the outer periphery thereof. The turbine wheel is enclosed within a conventional turbine housing 14.

In conventional axial flow turbines, the impelling fluid is conducted through an inlet duct or scroll 15 and through the annular passage 16 into contact with the surfaces forming one side of the impeller blades 13. A plurality of stationary vanes 17 is interposed in the passage 16 to direct the flow of fluid through the passage and toward the blades 13 in the desired direction.

In accordance with the present invention, a plurality of holes 18 are formed in the housing 14 around the outer periphery of the turbine Wheel 10. The holes 18 connect the interior of the inlet scroll 15 with the in-v terior of the turbine housing 14. The holes 18 are canted or angularly inclined so as to admit the fluid under pressure within the inlet scroll 15 into the interior of the housing, directing the fluid against the side of the blades 13 opposite to the side against which the impelling fluid is directed by the vanes 17 in the inlet passage 16. In other words, the fluid under pressure iS directed by the holes 18 against the blades 13 of th turbine wheel in a direction having a component which is opposite to the direction of rotation of the turbine wheel.

In normal operation, the holes 18 are closed by a fusible filling material 19 which has a melting point substantially lower than the melting point of the housing material. The selection of the housing material is usually determined by temperatures of the gases entering the turbine. Housing materials of aluminum may be fitted with plugs of eutectic lead alloys with cadmium silver or similar metals. For higher temperatures and housings of steel, plugs can be of pure lead aluminum or other suitable melting point metals.

It is characteristic of cverspeeding or runaway turbines for the turbine wheels to expand due to the effect of centrifugal force, as well as to the effect of temperature increase in the overspeed turbine wheel. When a turbine wheel undergoes excessive expansion, it is not unusual for the outer ends of the turbine blades to come into contact with the inner surface of the housing. When this occurs, the friction between the blades and the housing generates heat which melts the filling material, thereby opening the holes 18 to direct jets or streams of fluid against the turbine wheel to oppose the rotation thereof. In addition, the holes or passages 18 serve to relieve the pressure of the impelling fluid and to provide a bypass, for the impelling fi uid around the impeller blades. These have the effect of slowing down the turbine to within safe limits, without causing a complete shutdown thereof; consequently, the turbine will continue in operation, although the efliciency of operation is somewhat reduced.

The reference to the frictional engagement between the blades and the housing is intended to include frictional engagement between the turbine wheel and any part of the housing itself or any part connected to the housing, including frictional engagement between the turbine wheel and the filling material 19.

The invention has been shown in preferred form and by way of example only, and obviously many variations and modifications may be made therein without departing from the spirit of the invention. The invention, therefore, is not to be limited to any specified form or embodiment, except in so far as such limitations are set forth in the claims.

I claim:

1. In a turbine, a turbine housing, a turbine wheel accommodated within said housing and safety means for checking overspeed operation of the turbine Wheel, said safety means comprising a source of fluid under pressure, a plurality of passage means preformed in said turbine housing and in communication with the source of fluid under pressure for directing streams of the fluid against the turbine wheel in opposition to the direction of rotation of the turbine wheel, and temperature sensitive means for closing said passage means, said temperature sensitive means being in heat exchange relation with the turbine housing so that when the turbine wheel expands excessively due to the overspeed condition, the heat generated by friction between the turbine wheel and the housing opens said passage means to slow down the speed of rotation'of the turbine wheel.

2. A turbine comprising a rotatable turbine Wheel, a plurality of turbine blades mounted around the outer periphery of the turbine wheel, a housing surrounding the turbine wheel, a fluid duct in communication with the outer surface of said housing for a fluid under pressure, the outer surface of said housing forming part of said fluid duct, an inlet passage in communication with said fluid duct for directing the fluid under pressure against one side of the blades mounted to the turbine wheel, a plurality of passages formed in said housing around the turbine wheel, the outer ends of said passages being in communication with the fluid in said fluid duct, said passages directing streams of the fluid toward the rotor in directions to brake the speed of rotation of the rotor, and filling material closing said passages, said filling material having a low melting point in relation to the melting point of the material from which the housing is made, whereby the overexpansion of the turbine wheel due to an overspeed condition thereof produces friction between the housing and the turbine wheel and the heat generated thereby causes melting of the filling material to open the passages.

3. A turbine as set forth in claim 2 wherein the holes are angularly inclined with respect to the radii of the axis of the turbine wheel, so that the fluid will be directed against the turbine wheel with a component in opposition to the direction of rotation of the turbine wheel.

4. A turbine comprising a rotatable turbine wheel, impeller blades carried by said rotatable turbine wheel, a turbine housing, a source of fluid under pressure, means forming passages through the turbine housing and in communication with said source of fluid under pressure for directing streams of the fluid against the turbine wheel in directions to oppose the rotation of the turbine wheel, means normally closing said passages, said means having a rela tively low melting point so that heat generated as the result of an overspeed condition of the turbine wheel causes said closure means to melt, opening the passage means, which, in turn, acts to slow down the speed of rotation of the turbine wheel.

5. A rotary apparatus comprising a rotor, a wall in close proxmity to the outer periphery of the rotor, a fluid duct adjacent the outer surface of said wall, a preformed passage through the wall, the outer end of the passage communicating with the fluid within said fluid duct, the

passage being angularly disposed with respect to the radius of the rotor so as to direct fluid passing therethrough against the rotor with a component thereof in opposition to the direction of rotation of the rotor, and a closure for the passage, said closure including a fusible material which opens the passage when subjected to heat generated by friction between the outer perimeter of the rotor and the wall resulting from growth in the size of the rotor at high speeds of rotation, whereby fluid from the duct passes through the housing and exerts a braking effect on the rotor.

6. A rotary apparatus comprising a rotor, a wall in close proxmity to the outer periphery of the rotor, a fluid intake in communication with a source of fluid under pressure for supplying an impelling fluid which impinges on the rotor to drive the rotor, a pro-formed passage through the wall, the outer end of said passage communicating with a source of fluid under pressure, said passage directing a stream of fluid against the rotor in a direction to exert a braking force on the rotor, and a closure for the passage, said closure including a fusible material which opens the passage when subjected to heat generated by friction between the rotor and the wall resulting from growth in the size of the rotor at high speeds of operation.

7. An overspeed safety check for turbines comprising a turbine rotor, a wall in proxmity to the turbine rotor but normally out of contact therewith, the outer surface of said wall being in communication with a source of fluid under pressure, a passage through the wall for directing a stream of the fluid toward the rotor in a direction to brake the speed of rotation of the rotor, and a temperature responsive closure for the passage which normally prevents flow of the fluid through the passage but opens when subjected to heat generated by friction between the rotor and the wall.

8. An overspeed safety check for turbines comprising a turbine rotor, means defining a passage which is in communication with a source of fluid under pressure and capable of directing a stream of said fluid against the rotor to brake the speed of rotation of the rotor, a temperature responsive closure normally preventing flow through the passage but opening when subjected to heat, and means normal-1y out of contact with the rotor and in heat-exchange relationship with the closure, whereby heat generated by frictional contact between the rotor and said last-mentioned means as a result of enlargement of the rotor during an overspeed condition causes the closure to open.

References Cited in the file of this patent UNITED STATES PATENTS 1,634,897 Davis July '5, 1927 1,836,388 Olsen Dec. 15, 1931 2,684,227 Seewer July 20, 1954 2,685,429 Auyer Aug. 3, 1954 2,697,326 Featonby Dec. 21, 1954 2,742,224 Burhans Apr. 17, 1956 FOREIGN PATENTS 57,833 Switzerland Oct. 9, 1911