US2945675A

US2945675A - Drawworks

Info

Publication number: US2945675A
Application number: US692069A
Authority: US
Inventors: Fischer William
Original assignee: California Research LLC
Current assignee: California Research LLC
Priority date: 1957-10-24
Filing date: 1957-10-24
Publication date: 1960-07-19
Anticipated expiration: 1977-07-19

Description

W. FISCHER July 19, 1960 DRAWWORKS Filed Oct. 24. 1957 3 Sheets-Sheet 1 F l G. 1

INV ENTOR WILL/AM FISCHER ATT RNEYS W. FISCHER July 19, 1960 DRAWWORKS 3 Sheets-Sheet 2 Filed Oct; 24. 19 57 R E m NF F- AT N E YS July 19, 1960 w. FISCHER 2,945,675

' DRAWWORKS Filed Oct. 24, 1957 3 Sheets-Sheet 3 F|G.4 INVENTOR WILL/AM FISCHER United States Patent DRAWWORKS William Fischer, Fullerton, Califi, assignor, by mesne assignments, to California Research Corporation, San Francisco, Calif., a corporation of Delaware Filed Oct. 24, 1957, Ser; No. 692,069

7 Claims. (Cl. 254-185) This invention pertains to a drawworks for use in well drilling apparatus and more particularly to an improved drawworks for drilling offshore wells from a floating vessel.

In one method of offshore drilling, a floating vessel is used to support a rotary drilling rig by which a well is drilled into the bottom of the ocean. The vessel. is anchored at the drilling site, but nevertheless will to some degree move with the surface of the water. Of particular pertinence to the drilling operation is the vertical motion induced in the vessel by Wave action which causes it periodically to change its elevation relative to the bottom.

It will be appreciated that if the drill string, for instance, is supported in the derrick by lines which are relatively fixed in position for periods of time while the lice The substantially constant weight control. of thedrawworks of this invention has advantages in offshore appli, cations in well operations other than drilling. For example, when making a formation test this system provides a means for compensating for the motion 'ofthe vessel to keep substantially constant weight on the packer, thereby enabling the test to be made successfully. Also, on fi l 1,- ing jobs the drawworks of this invention will automatically control the tension in the lines to prevent it; from becoming excessive and damaging as the shiprises with the surface of the water. Furthermore, the automatically controlled tension of the supporting lines isof great advantage in maintaining the position of submerged Wellhead controlequipment substantially constant relative to the ocean bottom to prevent overstraining the lines; while the equipment is being attached to orreleased from its connection with a submarine well opening by remote operation from the drilling; vessel.

The drawworks of this invention is devised, in, a manner to be described, to reduce selectively, in; accordance with varying conditions of drilling prqceure, the inertia of the rotating masses of the system to provide a quick response'of the operating portions of the apparatus to the control mechanism. The system includes winch drums which are driven from an engine through amultispeed transmission and torque converter which provides bit is cutting into the subterranean formations, as is usual in oil field practice to land, the motion of the floating vessel will periodically cause the bit to be lifted from the bottom to spin freely in the hole and alternately be forced against the bottom with a greater pressure than desired for maximum drilling efiiciency, or perhaps with sufiicient pressure to damage the apparatus. In these circumstances it is desirable to provide some means for controlling the derrick lines supporting the drill string so that they will be operated in accordance with the vertical motion of the floating vessel to cause the bit to remain at the bottom of the hole and with a constant weight acting on it.

In the relatively static conditions of onshore drilling, automatic feed-off devices have been found to compensate for the changing weight which occurs as the bit of the drill string assembly cuts into the earth. The principal requirement for such a device is to control the action of the drawworks in one direction, and, at the relatively slow rate of bit penetration, to feed off line. The particular environment of offshore drilling from a floating vessel, wherein the vessel is constantly in motion relative to the ocean bottom, presents a situation which is much more difficult to cope with. If constant weight is to be held on the bit under this latter condition through the operation of the drawworks, a system is required which is sensitive and responsive to such a degree that it will continuously haul in and feed out line as required by the relatively rapidly and constantly changing position of the vessel in the water.

Under ordinary offshore drilling conditions the greater amount of vertical motion induced in the floating vessel by the water is periodic in character, thevessel rising and falling with wave motion. If the compensating control of the derrick lines is to be effective, the drawworksmust respond more. rapidly than the period of boat motion. If its response is relatively sluggish, the control system can get out of phase with the boat motion, and rather than correct for the motion may add to it and thuscause it the bit to pound on the bottom of the hole. Obviously this condition aggravates ratherthan cures the difiiculties attendant the offshore drilling operation.

an automatically controlled, selectively'preset torque out.- put.. The two principal winch drums, that is, the sand line drum and the casing line drum, can be independently and individually connected to and disconnected from the output side of the transmission. Th drive toJthe, cat heads does not go through the multispeed, transmission, and thus the inertia of these parts does not affect the sensitivity of the control of line tension by the, output torque of the transmission.

The desired on-bottom bitweight for a particular depth and with a' particular weight of drill string is maintained by. selecting the transmission gear ratio setting and input shaft speed which will cause the output, shaft 'of the torque converter to be stalled when a predetennined hook load is achieved. If then the vessel drops with the surface of the water, thereby increasing the weight on the bit, the weight on the hook will be decreased and the output shaft of the torque converter will immediately turn inits normal forward direction to haul in line to maintain the predetermined hook load. Conversely, as the vessel rises with the surface of the water the weight on the hook will be increased, and the resultant back drive through the system will overpower the preset torque on the output shaft of the torque converter to turn it in a.reverse direction. The slippage in the torque converter occurs at substantially the preset torque so that while. line is being payed out to compensate for the changing elevation of the vessel the hook load remains substantially constant. Thus a continual state of rotational reversals exists in the components of the system from the torque converter output shaft through the line drum.

In accordance with this invention, such a system is made practically operative byremoving from the operating portions as much as possible of such masses as would resist rapid acceleration and deceleration of it. For example, in furtherance of this objective, the brake for the casing line drum is made to be disconnected'from the drum by a clutch. During an ordinary drilling operation the drum brake is uncoupled from the line drum to divorce its heavy mass from the rotatingparts connected to the output of the. transmission; The clutch for the brake drum is automatically controlled by move ment of the brake handle to couple the brake, drum with,

the line dr-umwhen a braking action is" desired and to uncouple the drums when theJbIaki'ng action is released.

Ordinarily during drilling the sand line drum will be disconnected from the system, as will be the brake drum for the casing line drum. Thus the casing line drum will be essentially directly connected to the output of the torque converter without any unnecessaryinertia masses interveninggto reduce thesensitivity of the, casing line tension systemf i -It is an object of this invention to provide a novel draw-' Works which will operate automatically to hold a constant tension in the derrick lines of well drilling apparatus. It is a further object of this invention to provide a drawworks for olfshore drilling from a floating vessel which will automatically control the tension in the lines supporting drilling apparatusin the derrick to compensate for changes in the elfective weight of the apparatus induced by the motion of the vessel with the surface of the water. A still further object of this invention is to provide a drawworks for use in oifshore drilling from afloating vessel which will be controlled automatically to prevent stresses from being placed in the lifting lines of such magnitude as to cause damage to the equipment. The accompanying drawings, which are a part of this specification, illustrate an exemplary embodiment of this invention.

In the drawings: r I Fig. l is a schematic representation of a plan view of a drawworks embodying this invention. j

Fig. Zrepresents in front elevation and partly in section an embodiment of a casing line drum assembly constructed in accordance with this invention. 7 V

Fig. 3 represents in side elevation and partly in section a detail of the main brake apparatus. 7 Fig. 4 illustrates in side elevation and partly in section a detail of the emergency brake apparatus.

The drawworks illustrated in Fig. 1 comprises a source 'of motive power 10, which may be, for instance, a diesel or any other suitable engine, connected througha clutch 12 to a sprocket 14. The sprocket is connected bya chain 16 to a sprocket assembly :18rotatably mounted on the input shaft 20 of a multispeed transmission22. This transmission has in it a gear system which is shifted manually by the driller and an automatic fluid-operated torque converter, and will function to provide a substantially constant preselected torque output for a given engine speed, as is well known to the art. The sprocket assembly may be coupled to, the shaft through the clutch 24.

The output shaft of the transmission is connected by a sprocket 26 through a chain 28 -to an idler sprocket assembly 30, which rotates freely on the shaft of the sand line drum 32, but can be attached to the shaft by means of the clutch 34 to rotatethe drum. The idler sprocket assembly is connected by chain 36 to sprocket 38 which is rotatably mounted on the shaft 40,0f the casing line drum assembly; This latter sprocket can be clutched to the shaft to rotate the drum. Returning now to the engine, as stated, the initial drive to the input side of the transmission is imposed on the idler sprocket assembly 18. This assembly includes the sprocket 42 which is connected by chain 16 to the output shaft of the engine and a second sprocket 44 fixed to the first sprocket in a unitary manner and which is connected by a chain 46 to another idler sprocket assembly 48. The drive from the latter sprocket assembly is directed by chain 50 to the sprocket 52 which is unitarily mounted on the cat shaft 54. The cat shaft will, of course, rotate the cat heads 56 and 58.

From the foregoing description, it will be seen that the sand line drum and the casing line drum can be selectably and individually connected to the output side of the transmission, and the cat shaft takes its drive relatively directly from the output side of the engine without the drive passing through the transmission. The importance of this feature will become apparent as the description of the apparatus proceeds hereinafter.

Referring now to Fig. 2, the casing line drum 60 is rotatably mounted by bearings 62 and 64 on the shaft 66. A second shaft 40 is rigidly fixed to the drum and extends outwardly from it in coaxial alignment with the first shaft. The shafts 66 and 40 are supported on the

bearings

68 and 70 so that this assembly may rotate as a unit. Additionally, because of the above-described construction the casing line drum may rotate relative to the first shaft 66.

The drive sprocket 38 for the drum is rotatably supported on the shaft 40 by bearings 72 and 74. It has fixed to it an outwardly disposed cylindrical projection 76 which has an internal spline 78. The spline receives the

friction discs

80 and 82 of the clutch 84 in sliding engagement.

It will be appreciated that the clutch structure described is presented by way of example only and to give a clear teaching of one embodiment of an element which may be used in the apparatus of this invention.

The hub 86 of the clutch is keyed to the shaft 40 and has a radially extending flange 88 against which the friction disc 82 will abut with a friction drive when the clutch is actuated. The hub has an external cylindrical spline 90 on which the annular plaates 92 and 94 are fitted with a sliding connection. The axially outer portion 96 of the clutch housing has an inner annular chamber 98 of which one wall is formed by the annular flexible diaphragm 100. An air passage 101 leads from the chamber to a rotary seal means 102 mounted on the end of shaft 40. An annular ring assembly 103 is interposed between the diaphragm and the clutch plate 92. Pressurized air introduced into the chamber will cause the diaphragm to force the ring 103 against the clutch plate and disc assembly, and the adjacent complementary surfaces of the plates and discs will contact each other with sufficient friction to transmit the drive from the sprocket '38 to the shaft 40 and thus rotate the casing line drum. Of course, when the air pressure is released from the chamber 98, the frictional contact between the clutch plates is removed, and the sprocket will no longer drive the shaft but will rotate freely on it.

In accordance with this invention, means are provided for disconnecting the main brake assembly 104 from the casing line drum to separate the mass of the brake drum from the winch drum to reduce the inertia of the casing line drum assembly. This arrangement increases the speed and sensitivity of response of the winch drum in compensating for changes in on-bottom bit weight. A clutch may be used for this purpose similar to that described heretofore as connecting the drive sprocket to the shaft 40.

In the clutch assembly 106 the

friction discs

108 and 110 slidably engage an internal spline 112 in the cylindrical projection 114 which is atfixed to and extends axially from the flange 116 of the line drum. The hub 118 of the clutch is keyed to the shaft 66 so that it will rotate with it. The hub has a radially extending flange .120 which will form a frictional contact surface for the friction disc 108, and an external spline 122 on which the clutch plates 124 and 126 are slidably mounted to present interposed abutting surfaces for the friction discs. The axially outwardly portion 128 of the hub housing has an internal annular chamber 130 which is connected by an air passage 131 to a rotary seal 132 on the end of shaft 66. One wall of the chamber is formed by the flexible diaphragm 133. An annular ring assembly 134 is interposed between the diaphragm and the clutch plate assembly to transmit the force of pressurized air from the chamber to the clutch plates and the friction discs.

The brake drum 136 is fixed to the clutch housing 128 and hence will rotate with it and with the shaft 66. When the clutch is disengaged, that is, when air pressure is released from the chamber 130, the winch drum will rotate on and relative to the shaft 66. Of the clutch assembly, only the masses of the cylindrical projection 114 and the friction discs '108 and 110 which are splined to itwill becarried' in: rotation by the winch drum. The major portion of the mass of the, clutch apparatus as well as the brake drumwill 'be: free of the Winch drum and will. not impose their hiertial effects on its operation.

Braking force is applied to. the main drum by manipulating the lever. 138 to pull the brake. band 140 against its In accordance with this invention the clutch 106 will automatically be actuated to connect the brake drum to the winch drum when a braking force is to be applied to the latter. As' illustrated in Fig. 3, the brake lever maybe formed with a radiah'arm 142 projecting from it near its pivot I143. This is connected to the end of the brake band to force it against the brake drum and create a braking force. .A cam 144 is formed on the brake lever and projects laterally from it. The cam actuates an air valve 146 in the compressed air line 148 to theclutch and. will open the valve to permit pressurized air to flow to the clutch, immediately engaging it as the lever is displaced to apply the brake.

As illustrated schematically in the drawings, the clutch valve may have an actuating pin 150'which is biased by a. spring 152 against the cam 144.. When the brake lever is displaced to abraking position, its initial movement will cause the cam to depress the pin and open the air valve to connect the line 148 with a source of compressed air through the conduit 153. Thus, the clutch will immediately engage the brake drum with the winch drum before the frictional force of the brake band is applied. As the braking force is released from the brake drum, the movement of the cam 144 away from the valve will permit the spring .152 to retract the pin from the air valve to close it. Thus, as the braking 'force is released from the brake drum the air pressure will be removed from the clutch assembly, and the brake drum will be uncoupled from the winch drum.

During some steps of a drilling operation, such as when lowering apparatus into the well bore or lifting it therefrom, it is desirable to have the brake drum continuously connected with the winch idrum regardless of the position or the brake lever. The air valve 146 is constructed to accomplish this. The control lever 154 acting through the linkage 155 can be operated to hold the air valve open against the. action of spring 152 regardless of the position of the brake lever, and the air will be supplied continuously to the clutch to maintain the coupling of the brake drum with the winch drum. A means, such as -a pawl and rachet mechanism, is provided to hold the control lever 154 in the retracted position.

An emergency brake is provided for the casing line drum as a means for controlling it if the main braking apparatus should fail to function fromv loss of air pressure. The operation of the emergency brake is integrated with that of the clutch 106 to cause the emergency brake to be applied immediately and automatically if the air pressure is not sufiicient to actuate the clutch to couple the main brake drum to the winch drum. The emergency brake has a drum i156 rigidly attached to the rim of an end flange of the casing line drum. A brake band 158 may be manually actuated by a lever 160 to apply or release the braking force. However, it is very desirable to have the. emergency brake applied automatically to prevent the line drum from running away if the coupling of the main brake apparatus should fail to function. One means for accomplishing this is shown in Fig. 4. The emergency brake. lever is connected to an air motor (162' which automatically will operate it in accordance with the operating potential of the air pressure to clutch means 106 to withhold or apply a braking force to the emergency brake drum.

The air motor may be constructed with a piston 164 which is connected by a rod 166 and pin 168 to a clevis 170 formed on the end of the radial arm 171 of the emergency brake lever. The piston is biased by a spring 172 of sufiicientcompressi've force to retract the rod with the added weight. increased tension in the casing line will cause a back drive 166 within the: cylinder and rotate. the lever about its pivot point 174 to apply the brake band: to the brake drum. During normal operation of'the drawworks, pressurizedvair is introduced into the cylinder through the conduit 176 to cause the piston to overpower the spring and rotate the lever 161) in a direction to release the braking force.

In-the exemplary embodiment of the invention illustrated in Fig. l, the various clutches and the emergency brake air motor are operated by pressurized air derived from the air compressor 178. The pressurized air leaves the compressor through the

conduits

180 and 182 and thence through appropriate, valves and rotary seals to the respective assemblies of the apparatus. The drawing represents a schematic arrangement of. the air lines. It is desirable, and within the skill of the art, to place the control valves at the drillers station so that they will be readily accessible to him.

The air conduit 176 to the emergency brake motor 162 and the air conduit 153 to the clutch control 146 are both connected to the conduit 180 from the air compressor. When the air pressure from the compressor falls below that necessary to operate the clutch 106, it will be also below the pressure necessary to cause the piston 164 to overpower the spring 172. Thus, if failure of the air supply prevents the operation of the clutch 106, the emergency brake automatically will be applied to prevent the winch drum from running away under a linev load. it is intended that this brake will be used primarily for stopping the winch drum under emergency conditions, and hence the braking surface and the mass of the rotating parts, are-considerably less than that. required for the main brake.

The construction of the clutch mechanism on the sand linedrum shaft may be similar to that described heretofore for the clutches in the casing line drum assembly. When the sand line drum is uncoupled from the system, only a: small part of the mass of the clutch structure rotates with the sprocket assembly 30. As. noted previously, the drive to the cat. heads is derived .from the. input side of the transmission 22, and hence their rotational inertia does not impose a load on the output torque. Thus the inertia of the rotating parts in the drive train to the casing line drum is reduced to a minimum. Since the mass of the rotating portions of the casing line drum assembly can be reduced substantially by disconnecting the main brake apparatus from it, these features combine to permit the casing line. drum to respond readily' in, whatever direction of rotation and magnitude of travel is required to hold on-bottom bit weight at a sub: stantially constant value.

It has: been explained heretofore that the transmission L is constructed to give a substantially constant preselected torque output. During an ofishore drilling operation from a floating vessel, when the vessel sinks with the surface of the water and decreases its elevation relative to the bottom, the bit bears more heavily on the bottom of the hole, releasing weight from the derrick lines and decreasing the tension in them. When the drawworks of this invention is used, the drive through the transmission will automatically rotate the casing line drum in a direction to maintain the derrick lines at their preselected tension and support the bit with a predetermined weight on the bottom. When the vessel rises With the water and increases its elevation relative to the bottom, the bit will tend to be lifted from contact with the bottom of the hole, and the tension in the derrick lines will increase Under these circumstances the to the transmission. In this case the torque converter in the transmission will slip when the preset torque output of the transmission is exceeded, and the back drive from the casing line drum to the transmission will be absorbed in the latter while the hue is being payed an the drum at substantially the preselected tension. It is apparent, then,

that the drawworks of this invention provides'a means for holding a substantially constant weight on the bit while the floating drilling vessel rises and falls with the surface of the water. The low inertia characteristics and ready response to control enables a substantially constant line tension to be maintained, even under the aggravated conditions of offshore use.

The function of this apparatus in releasing overloads in the casing line at constant tension is particularly useful when the lines are attached to any tools or apparatus which are fixed relative to the ocean bottom. This would apply, for instance, to a fishing operation when the fishing tool supported by the derrick lines becomes secured to a portion of the drilling apparatus which is stuck in the bore hole. Under such conditions, if some means are not provided for releasing the overload tension in the lines as the drilling platform is carried upwardly by a wave, the stress placed on the apparatus can well exceed the amount it is able to withstand. Similar conditions arise when wellhead control equipment supported by the derrick is being attached to or detached from a submerged wellhead fixed relative to the bottom of the ocean. Here, obviously, it is necessary to maintain the wellhead control equipment stationary relative to the submerged fixed apparatus while the connection is being manipulated from the vessel. The drawworks of this invention permits the torque output of the transmission to be set to apply a constant value of lifting force to the submerged wellhead control equipment and pay out or take up the derrick lines in accordance with the motion of the drilling vessel to keep the wellhead equipment stationary relative to the fixed apparatus at the bottom of the ocean. Again, in such operations as formation testing, this apparatus permits the packers to be set and remain stationary in the well bore without being disturbed from their position by the heaving of the vessel acting on the supporting lines.

Although the apparatus of this invention has been described as applied primarily to a drawworks for drilling off-shore wells from a floating drilling vessel, it will be apparent that the invention is not limited to this specific use. The quick response of the apparatus to compensate for changes in tension in the derrick lines, and the ability of it to hold a substantially constant tension in the lines, whether the weight suspended from the lines is increased or decreased, makes the apparatus readily applicable to land drilling operations where it is desired to have a winch mechanism supply a constant value of lifting force when the effective load suspended from its lines is continuously changing. Therefore, it is not intended that the invention be limited to the specific exemplary embodiment described and illustrated herein, but that the concept include all equivalents within the scope of the appended claims.

I claim:

1. In a drawworks comprising a driving motor, a multispeed transmission having an automatically controlled preselected torque output and connected to said motor for operation thereby, and a winch drum operably connected to said transmission to be rotated by the output torque thereof, the improvement comprising a brake separable from said Winch drum, a brake drum in said brake, a clutch means selectively operable to connect said brake drum to said winch drum for rotation therewith and to disconnect said brake drum from said winch drum, and

means to operate said clutch means and said brake simultaneously to engage said brake drum with said winch drum as braking action is applied to said brake.

2. A casing line drum assembly for a drawworks comprising a first shaft, a casing line drum rotatably mounted on said first shaft, a second shaft afiixed to said line drum and extending therefrom in coaxial alignment with said first shaft, a sprocket rotatably mounted on said second shaft, clutch means for engaging and disengaging said sprocket and said second shaft, means to drive said sprocket to rotate said line drum when said clutch means engages saidspr'ocket 'with said second shaft, a brake drum affixed to said first shaft and positioned adjacent said line drum, 'a clutch means for engaging and disengaging said brake drum and said line drum, means to apply 'a braking force to said brake drum, and means for simultaneously actuating the last said clutch means to engage said brake drum and said line drum as the brak ing force is applied to said brake drum.

3. A casing line drum assembly for a drawworks comprising a rotary shaft, a casing line drum. rotatably mounted on said shaft, a brake drum afiixed to'said shaft and positioned in coaxial alignment with and adjacent to said line drum, a clutch means for engaging and disengaging said brake drum and said line drum, means to apply a braking force to said brake drum, and means to automatically actuate the said clutch means to engage the said brake drum with the said line drum as the braking force is applied to said brake drum and to disengage the said brake drum from the said line drum when the braking force is released from said brake drum.

4. An assembly in accordance with claim 3 including means to actuate said clutch means to maintain the engagement of said brake drum with said line drum when the braking force is released from said brake drum.

5. In a drawworks a casing line drum assem'bly comprising a rotatably mounted shaft, a line drum mounted on said shaft for rotation relative thereto, a first brake drum atfixed to said line drum, a second brake drum afiixed to said shaft, clutch means for engaging and disengaging said second brake drum and said line drum, means to apply a braking force to said second brake drum, means to automatically actuate the said clutch means to engage the said second brake drum and the said line drum as the braking force is applied to said second brake drum, means to apply a braking force to said first brake drum, and means coordinated with the actuating means of said clutch to automatically apply braking force to said first brake drum when said actuating means fails to actuate said clutch.

6. 'In a drawworks a casing line drum assembly comprising a rotatably mounted shaft, a line drum mounted on said shaft for rotation relative thereto, a first brake drum affixed to said line drum, a second brake drum afiixed to said shaft, pressurized air actuated clutch means for engaging and disengaging said second brake drum and said line drum, a source of pressurized air for actuating said clutch, means to apply 'a braking force to said second brake drum, means to automatically actuate the said clutch to engage said second brake drum and said line drum as the braking force is applied to said second brake drum, means to apply a braking force to said first brake drum, pressurized air actuated means operatively connected to said source of pressurized air to prevent the application of braking force to said first brake drum, and means to automatically apply braking force to said first brake drum when the pressure in said source of pressurized air is insuflicient to actuate said clutch means.

7. A winch mechanism comprising a driving means, and an adjustable speed transmission means operatively connected to said driving means, an output torque control means associated 'With said transmission [1168115, -a plurality of winch drums operably connectible to the output shaft of said transmission means, means to selectively connect and disconnect each of said plurality of winch drums and said transmission means to selectively disconnect the inertial load of each of said winch drums from the output shaft of said tansmission means, a brake means associated with one of said plurality of 'winch dr-ums, means to selectively connect and disconnect said brake means and said one of said winch drums to selectively disconnect the inertial load of said brake means from the output shaft of said transmission means, means to operate the winch mechanism with said. onewinch References Cited in the file of this patent UNITED STATES PATENTS Ferris June 21, 1932 Rockwell May 9, 1950 Ljungkull Jan. 30, 1951 OLeary Mar. 11, 1952 Young Aug. 25, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2945 675 July 19 1960 William Fischer It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 32, for "to" read on line 45, for found read used column 2 line 21 for "proceure" read procedure column 5,, line 5 after "main" insert brake column 8, line 60, strike out "and'h Signed and sealed this 27th day of December 1960 (SEAL) Attest: a KARL H. AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Oificer