US3567942A

US3567942A - Nucleonic measuring apparatus with automatic fire safety radiation source shutter closing and locking means controlled by a fusible element which melts at high temperatures

Info

Publication number: US3567942A
Application number: US634366A
Authority: US
Inventors: Richard E Bach
Original assignee: Industrial Nucleonics Corp
Current assignee: Industrial Nucleonics Corp; ABB Automation Inc
Priority date: 1967-04-27
Filing date: 1967-04-27
Publication date: 1971-03-02
Anticipated expiration: 1988-03-02

Abstract

A nucleonic measuring instrument wherein a housing contains a radiation source and has an aperture controlled by a shutter which is spring loaded to a closed position for confining and shielding the radiation and is movable by a linear actuator to an open position for releasing the radiation, the actuator power being applied through a heat sensitive fuse so that it is deenergized and the shutter closes in response to a predetermined high ambient temperature such as may be caused by a fire, and including a spring-biased shutter locking pin retained in a retracted position by a meltable metal barrier which melts to release the pin in response to attainment of a predetermined higher ambient temperature and lock the shutter in the closed position.

Description

United States atent Richard E. Bach Hilliard, Ohio Apr. 27, 1967 Mar. 2, 1971 Industrial Nucleonics Corporation Inventor Appl. No. Filed Patented Assignee NUCLEONIC MEASURING APPARATUS WITH AUTOMATIC FIRE SAFETY RADIATION SOURCE SHUTTER CLOSING AND LOCKING MEANS CONTROLLED BY A FUSIBLE ELEMENT WHICH MELTS AT HIGH TEMPERATURES Primary Examiner-Ralph G1 Nilson Assistant Examiner-Morton J. Frome AttorneysMarechal, Biebel, French & Bugg, William T.

Fryer, III, C. Henry Peterson and James .I. OReilly ABSTRACT: A nucleonic measuring instrument wherein a housing contains a radiation source and has an aperture controlled by a shutter which is spring loaded to a closed position for confining and shielding the radiation and is movable by a linear actuator to an open position for releasing the radiation, the actuator power being applied through a heat sensitive fuse so that it is deenergized and the shutter closes in response to a predetermined high ambient temperature such as may be caused by a fire, and including a spring-biased shutter locking pin retained in a retracted position by a meltable metal barrier which melts to release the pin in response to attainment of a predetermined higher ambient temperature and lock the shutter in the closed position.

PATENTED "AR 2 I97! SHEET 1 OF 2 0 W M A n B A. a M D R m m R v! 8 H6 3 O 6 a 5 5 NUCLEONIC MEASURING APPARATUS WITH AUTOMATIC FIRE SAFETY RADIATION SOURCE SHUTTER CLOSING AND LOCKING MEANS CONTROLLED BY A FUSIBLE ELEMENT WHICH MELTS AT HIGH TEMPERATURES RELATED INVENTIONS BACKGROUND OF THE INVENTION Nucleonic measuring gauges have been provided with source housings having apertures controlled by shutters which are operated by an electric solenoid or by an air motor, or the like, for retracting and permitting the release of the radiation from a suitable nucleonic source within the housing. Examples of such shutters are shown in the US. Pat. No. 2,858,450 ofv 1958 to Holben and US Pat. No. 2,932,744 of 1960 to Lehman, each assigned to the assignee of this invention. These shutters are normally made of heat resistant material and also act as an effective block or shield for the rays emanatingfrom the source, so that when the shutter is closed, the source cap-. sule is effectively sealed within-its housing and no substantial radiation emanates through the aperture.

Normally, the shutter mechanism are fail-safe so that upon deenergization of the operating motor, the shutter automatically returns to the closed position such as by the'use of retraction springs or the like. In the event of a disaster or conflagration, it is important to maintain the integrity of the source housing and to confine all radiation within the housing; This is accomplished by assuring that the shutter returns to the closed position under such conditions and remains there.

SUMMARY OF THE INVENTION The present invention relates to nucleonic gauging and measuring apparatus, and more particularly, to such apparatus in which a movable shutter is positioned in relation to the exit aperture for a nucleonic source, and to apparatus for closing and locking the shutter in the event that certain predetermined temperature limits are exceeded.

The invention employs motor means, such asan electric solenoid, for moving the shutter between a closed positionwhere it effectively shields radiation from the source of radioactive material and an open position where the aperture is uncovered. Normally, during the operation of the gauge, the shutter is maintained in its open position with respect to the aperture, by continuously energizing the solenoid. However, it is within the scope of this invention to use other means such as an air-operated motor shown in the Holben and Lehman patents mentioned above.

The invention further includes means responsive to the occurrence of a first predetermined temperature for causing the shutter to close and seal the source capsule within its housing to render it relatively harmless in the event of fire or the like. This means includes a temperature responsive element, such as a fuse, to interrupt the power to the solenoid so that the shutter is returned to its closed position by the shutter retraction springs.

The present invention also provides for locking the shutter in the closed position upon the occurrence of a still higher predetermined temperature, and specifically employs a pin which is spring loaded in a retracted position where it is retained by a solder barrier. The barrier is adapted to melt when a predetermined ambient temperature occurs and thereby release the pin to engage and lock the shutter in its closed position.

Thus as a primary, object, the present invention provides a nucleonic gauge with a shutter which moves to a closed position upon the occurrence of a high ambient temperature and which is thereafter locked in its closed position by a locking member which becomes operative in response to the melting of a solder barrier with the occurrence of a still higher ambient temperature.

A more specific object of this invention is the provision of a shutter for a nucleonic source housing and which is opened against the bias of springs by an operator which becomes deenergized with the occurrence of abnormally high heat, and a spring loaded pin is released when the ambient temperature further increases to the melting temperature of a solder barrier and thereby locking the shutter in its closed position.

These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a nucleonic thickness gauging system including a shutter assembly and lock constructed in accordance with the invention;

FIG. 2 is an elevational viewof the radiation source head partially broken away;

FIG. 3 is a view of the shutter assembly and its operating mechanism as taken generally on the line 3-3 of FIG. 5;

FIG. 4 is a section taken generally on the line 4-4 of FIG. 3;

FIG. 5 is a bottom view ofthe apparatus shown in FIG. 3;

FIG. 6 is a fragmentary section of the shutter lock as taken generally on the line 6-6 of FIG. 3 and taken before the lock is released;

FIG 7 is a fragmentary section similar to FIG. 6 and showing the shutter look after it is released;'

FIG. 8 is a fragmentary section taken generally ontthe line 8-8 of either FIG. 5 or 6; and

FIG. 9 is a fragmentary section showing the interlocking-of the shutter and its supporting plate.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a nucleonic thickness measuring gauge 10 is connected to an electronic equipment cabinet 12- through flexible cables 13 and an intermediate disconnect box, 14. A conduit 15 leads from the cabinet 12 to a combined recorder and remote control unit 16 located at an operators station.

The thickness measuring gauge 10 may be of any suitable type utilizing radioactive material as the source, and may be constructed as shown in Chope U.S.'Pat. No. 2,790,945 of 1957 and US. Pat. No. 2,829,268 of 1958, both assigned to the same assignee as this invention. Furthermore, it is within the scope of this invention to employ a backscatter gauge as shown in the above mentioned Holben patent.

As shown in FIG. 1, the gauge 10 includes a C-shaped frame 20 having an upper leg 21- and a lower leg 22 supported by a carriage 23 mounted for traversing movement on a supporting rail 24. A housing 25 is mounted on the rail 24 and encloses a motor which is connected to move the frame 20 in directions as indicated by the arrow 26.

.A radiation source head 30 is mounted on the lower leg 22 of the frame 20 and a detector head 31 is mounted on the upper leg 21 directly above the head 30. The

heads

30 and 31 cooperate to form a gap or space through which a traveling web W of material is directed. Referring to FIG. 2, the source head 30 includes a member 33 supporting a plate 34.which forms a cover for a cylindrical shaped housing 35 containing a radiation source 36. The plate 34 has a U-shaped opening or aperture 37 (FIG. 3) through which the radiation is directed upwardly towards the detector head 31 as indicated generally by the arrow 38.

The source 36 is preferably of the penetrative radiation type wherein a source of beta, gamma, bremsstrahlung or other type radiation is produced to irradiate the material to be measured. The radiation detector in the detector head 31 may be a scintillation detector or an ionization chamber which is effective to determine the amount of radiation passing through the web W of material. The choice of radiation depends on the character and the density of the material being measured. That is, a useful detector response results from the use of beta or bremsstrahlung radiation for light weight materials but there would be substantially no absorption of a more penetrating radiation such as gamma. On the other hand, it is desirable to use a gamma source in measuring a relatively dense material. Typical examples of beta emitters are Strontium 90 and Krypton 85, while Americium 241 and Cesium 137 are suitable gamma emitters.

Referring to FIGS. 35, a milled groove 39 is formed within the plate 34 around the aperture 37 and forms a guideway for supporting a shutter 40 having an outwardly projecting rib or flange 41 which projects into the groove 39. Thus the shutter 40 is slidably supported for movement between a closed position, as shown in full lines, and an open position where the shutter is retracted to the left in FIGS. 3 and 4 to open the aperture 37. In the closed position, the flange 41 on the forward end of the shutter 40 is received within the corresponding portion of the groove 39 so that the cooperation between the interfitting flange 41 and the groove 39 form an effective seal between the shutter 40 and the plate 34.

The shutter 40 is made of suitable material which resists exceedingly high temperatures such as would occur in a fire and also forms an effective shield to block radiation from the source 36. Suitable materials for the shutter are defined in the Holben and Lehman patents mentioned above.

Means for moving the shutter 40 within the guideway 39 to open the aperture 37 include a solenoid 50 which has its operating coil 51 mounted on an extension plate 52 bolted to the under surface of the plate 34 by screws 53. The solenoid 50 has a T-shaped armature 55 having, at its forward end, a pair of flanges 56 which receive a vertically extending block 57 therebetween. The block 57 supports, at its upper end, a threaded rod 58 which extends generally in the direction of movement of the solenoid armature. An arm 60 (FIG. 3) is mounted on the shutter 40 by screws 61 and depends downwardly to receive the rod 58 projecting through a hole formed within the arm 60. A pair of lock nuts 63 are mounted on the bolt 58 on opposite sides of the arm 60 and provide means for adjustably positioning the shutter 40 in relation to the solenoid armature 55.

The shutter 40 is moved to its closed position upon the deenergization of the solenoid 50 by a pair of retraction or tension springs 65 each having one end secured to the plate 34 by a spring retainer bracket 66 (FIG. 4), The opposite ends of the spring 65 are connected to the solenoid armature 55 by means of a hat bracket 70 which is secured to the flanges 56 by a bolt 71 extending through aligned holes formed within the bracket 76, flanges 56 and block 57. Thus when the solenoid is energized, the assembly including the block 57, the shutter arm 60 and the shutter 40 move to the left (FIG. 3) causing the extension of the springs 66 and the opening of the aperture 37. When the solenoid is deenergized, the springs 66 return the shutter 40 to a position closing the aperture 37 The invention includes means responsive to the occurrence of a predetermined high temperature for deenergizing the solenoid 50. Preferably this means comprises a heat sensitive or responsive fuse 80 mounted on the plate 52 by suitable fuse clips 82 and wired in series with the coil 51. The heat responsive fuse 80 may be the type TFX manufactured by Bussman Manufacturing Division of McGraw-Edison Company, of St. Louis, Missouri, and will interrupt the flow interrupt the flow of current to the solenoid when the ambient temperature reaches approximately 300 F. The fuse 80 is provided in the event that electrical power to the solenoid still exists at this temperature, although it can be reasonably expected that by the time this temperature has occurred, either the solenoid itself will have become inoperative or the electrical lines to the solenoid would have become disrupted or otherwise deenergized.

Referring more particularly to FIGS. 69, a cylindrical, transversely-aligned bore or opening 85 is formed within the plate 34 and extends from a counterbore threaded portion 86 on an outside edge surface of the plate 34 inwardly in intersecting relation with the shutter opening in the plate 34. Thus, the hole or bore 85 joins coaxially and concentrically with a smaller diameter hole 88 which opens into the groove 39 forming a portion of the shutter guideway, forming an annular inner abutment or shoulder 89 at the junction of the bore 85 and the hole 88.

An elongated pin or plunger 90 is inserted through the larger open end of the bore 85 at the threaded portion 86 and has a stem-like elongated cylindrical portion 91 extending into the hole 88. The portion 91 of the plunger 90 is of somewhat reduced diameter as compared to that of the hole 88. The forward end of the plunger 90 is terminated in a somewhat en larged cylindrical tip portion 92 which forms with the stem portion 91 an annular, inwardly-facing shoulder 93. The diameter of the tip portion 92 is such that it forms a relatively loose fit when inserted within the hole 88.

A cylindrical collar 94 is formed on the inner end of the plunger 90 and has an outer diameter which conforms approximately with that of the bore 85 to form a relatively loose fit therewith. The collar 94 is formed with a short inwardly-extending, spring-locating boss 96.

An annular, tapered, ring-like shoulder of a suitable eutectic alloy or solder composition is formed on the plunger in surrounding relation to. an axial portion of the stem 91. The ring 95 is thus essentially frustoconical in space with its base being formed in abutment with the collar 94 and having a diameter at its base substantially greater than that of the hole 88. The outer frustoconical surface of the ring 95 is proportioned to engage the shoulder 89 and thus forms a block or a barrier which retains the plunger 90 and the tip portion 92 in a retracted or inner position. A compression coil spring 98 is positioned within the bore 85 and has its inner end located over the boss 96 and in abutment with the collar 94. The spring is retained in its compressed or stressed condition within the bore 85 by a plug 99 which is threaded into the threaded counterbore 86 and engages the end of the spring.

A notch 100 having a diameter which is somewhat greater than that of the hole 88 is formed within the flange 41 of the shutter 40 and is positioned to be in alignment with the hole 88 when the shutter 40 is in its closed posi ion. Referring to FIG. 8, a weep hole 102 extends vertically upward from the underneath surface of the plate 34 in intersecting relation with the bore 85 and close to the position of the solder ring 95.

As an example, the ring 95 may be formed of a solder composition including approximately 95 percent tin, 3.5 percent silver and 1 percent antimony so that it has a eutectic melting temperature at approximately 430 F. However, any metal alloy material may be used which has sufficient resistance against cold flow to hold its shape over extended periods of use at temperatures below the eutectic temperature, and which melts at a predetermined or predictable temperature to release the plunger 90 for locking movement into engagement with the shutter 40.

Thus when the ambient temperature surrounding the gauge increase to approximately 300 F, the fuse 80 blows to break the circuit to the solenoid so that the springs 65 move the shutter 40 to its closed position. However, at this temperature, the power to the solenoid may already have been removed, and the fuse 80 accordingly acts as a backup or safety device to assure that the shutter closes.

If the ambient temperature continues to increase and reaches a temperature of approximately 430 F, the solder of the ring 95 melts and the molten material flows outwardly through the weep hole 162. The melting of the ring 95 thus removes the barrier holding the plunger 90 in its retracted position and the spring 98 forces the tip portion 92 of the plunger 90 into the notch 100 formed within the shutter flange 41. As a result, the shutter 40 is positively locked in its closed position. As shown in FIG. 9, the plunger 90 will become canted or tilted in the hole 88 such as by mechanical jarring, or by slight movement of the shutter toward its open position, so that the shoulder 93 engages the plate 34 just outwardly of the hole 88, and prevents the plunger from retracting even if the ambient temperature exceeds the point where the spring 98 loses its effectiveness.

The locking system constructed in accordance with the present invention provides a simple, dependable and economical means for locking the shutter in its closed position in the event of excessive heat such as would occur in a fire. Thus, the shutter locking system of the present invention provides means for closing the shutter upon the attainment of a first predetermined temperature by the blowing of the fuse 80 and the operation of the retraction springs 65, followed by barrier means which is removable upon the attainment of a second and higher predetermined temperature to permit a movable element to move into locking relation with the shutter. In the locked position, all possibility of radiation being released by the accidental opening of the shutter after it has been closed and locked as described above is eliminated.

The shutter locking system of this invention is entirely selfcontained, and while in the preferred embodiment it is shown as being incorporated within the plate 34 comprising the guide for the shutter 40, it is obvious that the relative position of the parts can be reversed. In other words, the movable parts of the locking mechanism could be placed wholly within the shutter 40, with the pin 90 moving outwardly into locking engagement with the shutter guide.

It is also within the scope of this invention to employ any suitable motor for the opening and closing of the shutter 40. Preferably, a single acting motor is used, such as the solenoid disclosed, and it is also within the scope of this invention to employ an air-operated motor, such as a piston motor. If an air motor is used, it will be deenergized when the air supply line to the motor ruptures or breaks with heat. A short section of plastic tubing can conveniently be incorporated in the air line as an equivalent or of the fuse 80 used in this embodiment.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

Iclaim:

1. A nucleonic radiation measuring instrument comprising a housing enclosing a source of nuclear radiation and having an aperture for releasing radiation from said housing for measurement purposes, a shutter for said aperture, means supporting said shutter for movement between an open position to release radiation from said aperture and a closed position effectively confining the radiation within said housing, bias means urging said shutter to said closed position, motor means for moving said shutter from said closed position to said open position, means responsive to the occurrence of a first predetermined high ambient temperature for deenergizing said motor means so that said bias means moves said shutter from said open position to said closed position, lock means associated with said shutter and including a member movable between a retracted position to permit movement of said shutter and an extended position locking said shutter in said closed position, means urging said member toward said extended position, thermal responsive barrier means retaining said member in said retracted position, and being responsive to a predetermined ambient temperature higher than said first temperature for releasing said member for movement to said extended position locking said shutter in said closed position.

2. An instrument as defined in claim 1 wherein said barrier means comprises a eutectic alloy having a predetermined melting point so that said barrier means melts and flows to release said member when said higher temperature occurs.

3. An instrument as defined in claim 2 wherein said urging means comprises a spring normally held in a stressed condition and movable upon the melting of said barrier means to effect locking of said shutter in its said closed position.

4. An instrument as defined in claim 2 wherein said shutter includes an outwardly projecting flange, said supporting means for said shutter including means defining a guideway receiving said flange, means defining an opening within said supporting means for said shutter, said member comprising a pin mounted for axial movement within said opening, said barrier means comprising a solder ring surrounding said pin, means defining a slot within said flange, and said slot being in alignment with said opening when said shutter is in said closed position for receiving said pin.

5. An instrument as defined in claim 4 including means defining an annular shoulder within said opening formed within said supporting means, said solder ring having an outer surface engaging said shoulder for retaining said pin in said retracted position, said urging means comprising a compression spring mounted within said opening and engaging said pin, and plug means for retaining said spring within said openmg.

6. An instrument as defined in claim 4 wherein said pin includes a head portion forming an external shoulder engageable with said supporting means at said opening for securing said pin in said extended position in response to slight movement of said shutter toward said open position.

'7. A nucleonic radiation energy measuring instrument having a source of nuclear energy and incorporating a temperature responsive safety lock in which a shutter member is mounted on a guide member for movement between a retracted position defining an opening for radiation measurement purposes and a closed position effectively confining radiation from said source, the improvement in shutter locking mechanism comprising means defining an essentially rigid movable locking member mounted in one of said shutter and guide members and being movable between a retracted position permitting movement of said shutter member between its said positions, and an operative extended position in which said locking member is in locking engagement with the other of said shutter and guide members, and metal barrier means having a predetermined melting temperature retaining said locking member in its said retracted position and flowable upon the attainment of said temperature to release said locking members for movement into its said operative position.

8. The instrument of claim 7 in which said locking member includes a spring normally held by said metal barrier in a stressed condition and released upon the melting of said barrier for moving said locking member into said operative position.

9. The instrument of claim 8 in which said locking member further comprises a plunger in said guide member, means forming a head on said plunger, a recess formed in said shutter member aligned with said head in the closed position thereof, said head being proportioned to be received in said recess in its said operative position.

10. The instrument of claim 9 in which said metal barrier means comprises an annular ring of eutectic material carried on said plunger, and means in said guide defining a shoulder normally in engagement with said ring and permitting movement of said plunger therepast upon the melting of said ring.

Claims

5. An instrument as defined in claim 4 including means defining an annular shoulder within said opening formed within said supporting means, said solder ring having an outer surface engaging said shoulder for retaining said pin in said retracted position, said urging means comprising a compression spring mounted within said opening and engaging said pin, and plug means for retaining said spring within said opening.

7. A nucleonic radiation energy measuring instrument having a source of nuclear energy and incorporating a temperature responsive safety lock in which a shutter member is mounted on a guide member for movement between a retracted position defining an opening for radiation measurement purposes and a closed position effectively confining radiation from said source, the improvement in shutter locking mechanism comprising means defining an essentially rigid movable locking member mounted in one of said shutter and guide members and being movable between a retracted position permitting movement of said shutter member between iTs said positions, and an operative extended position in which said locking member is in locking engagement with the other of said shutter and guide members, and metal barrier means having a predetermined melting temperature retaining said locking member in its said retracted position and flowable upon the attainment of said temperature to release said locking members for movement into its said operative position.