US3011653A

US3011653A - System for operating rail- or cablecrane carriages

Info

Publication number: US3011653A
Application number: US622984A
Authority: US
Inventors: Larsen Botolv
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-11-21
Filing date: 1956-11-19
Publication date: 1961-12-05
Anticipated expiration: 1978-12-05
Also published as: GB809149A

Abstract

809,149. Overhead travellers; winding apparatus; rope railways. LARSEN, B. L. Nov. 21, 1956 [Nov. 21, 1955], No. 35552/56. Classes 78 (4), 78 (5) and 104 (2). A crane carriage, mounted to run on cables or rails, is hauled in opposite directions by two cables with winches connected to separate driving means comprising positive displacement hydraulic motors which are controlled by valves so that one driving means is hauling while the other acts as a brake and also as a pump, restoring power to the hauling means. As shown, the carriage 10, Fig. 1, is hauled along the cable 16 by cables 5, 11 connected to winches 3, 4. The winch 3 is driven by a fluid motor 27, Fig. 2, and the winch 4 by two fluid motors 25, 26, each of which is less powerful than the motor 27, though together they are more powerful. Each of the motors is of the displacement type, and may also act as a pump. Pressure fluid is supplied by a pump 28 driven by an engine 19, and is controlled by two manually-operated valves 29, 30. When the lever 42 is moved to the left, the motors 26 and 27 rotate in the hauling direction (the fluid moving in the direction of the arrows in Fig. 2) until the hook 14, Fig. 1, makes contact with the carriage 10, after which the weaker motor 26 is entrained in the opposite direction by the cable 11 and acts as a pump supplying part of the fluid to motor 27, the carriage 10 moving to the left as viewed in Fig. 1 and the motor 25 idly pumping fluid in a closed circuit 53, 54. With both levers 42 and 50 moved to the right, the motor 25 receives pressure in the unwinding direction (i.e. against the arrow in Fig. 2) and forces the weaker motor 26 to act as a pump, thereby lowering the hook 14. A lowering of the hook under gravity may be achieved by keeping the lever 42 in its central position and moving the lever 50 only part-way to the right, so that all four entries to the valve 30 are inter-connected. With both levers turned to the left, all three motors act in a winding direction, so that the load is first hauled up to the carriage and then moved to the right as seen in Fig. 1, the motor 27 being thus entrained by the cable 5 and forced to work as a pump. By slightly adjusting the lever 42 so that some fluid escapes through the conduit 33, the pressure supplied to the motors may be varied and the log or other load may be dragged along the ground. In another embodiment (Fig. 3, not shown), the cable or rail 16 is dispensed with, the carriage running on the upper stretch of cable 5. With this arrangement the carriage and hook may both be lowered to the ground by varying, the tension in the cables, using lever 42 in the manner referred to above. The hook may be attached to the cable 11 at a point some distance behind the carriage, so that on lowering the carriage to the ground the hook may be attached to objects laterally displaced from the cable. A modification for lifting heavy loads is shown in Fig. 6, the two carriages 101, 10<SP>11</SP> being spaced apart by a rigid bar 58. A tackle such as 20<SP>11</SP> may be used with the other embodiments described above. The required ratios between the hauling powers of the motors 25, 26, 27 may be achieved by using motors of different volumetric capacities, or by using different diameter winch drums or different transmission ratios.

Description

B. LARSEN 3,011,653

STEM FOR OPERATING RAIL-0R CABLECRANE CARRIAGES Dec. 5, 1961 3 Sheets-Sheet 1 Filed NOV. 19. 1956 Dec. 5, 1961 B. LARSEN 3,011,653

SYSTEM FOR OPERATING RAIL-OR CABLECRANE CARRIAGES Filed Nov. 19, 1956 3 Sheets-Sheet 2 m/w/vrm: 507041/ 44/95:-

Dec. 5, 1961 B. LARSEN 3,011,653

SYSTEM FOR OPERATING RAIL-OR CABLECRANE CARRIAGES Filed Nov. 19, 1956 3 Sheets-Sheet 5 Arr; (I,

United States Patent Ofiice 3,011,653 Patented Dec. 5', 1961 3,611,653 SYSTEM FOR OPERATING RAIL- R CABLECRANE CARRIAGES Botolv Larsen, Faere, Voss, Norway Filed Nov. 19, 1956, Ser. No. 622,984 Claims priority, application Norway Nov. 21, 1955 11 Claims. (Cl. 212--91) The invention relates to systems for operating rail or cablecrane carriages, which are actuated in opposite directions by two cables with winches connected to separate driving means.

The invention pirman'ly consists in that the driving means comprise volumetric hydraulic motors, especially gear motors, which by means of valve means are adapted to be connected so that alternatively one driving means may be operative for hauling while the other exerts a braking action, or vice versa, and that a motor comprised in that driving means which at the moment exerts a braking action during transport along the transport course, can operate as a pump in a recirculating path for the other driving means for recuperating braking power. In this manner a transport system is obtained which operates very economically and at the same time permits flexible operation in adaptation to various possibilities of application, and which especially permits a control of speed and pulling force to be effected easily while maintaining a des red adjustable cable tension, which is of particular importance if, as is the case with preferred embodiments of the invention, the cables are subjected to the load of the freight carrier so that the height of the latter above the ground (or for example the sea, according to where the system is used) at any point of the transport course will vary with the total unwound length of the cables.

Further features and advantages of the invention will appear from the following specification having reference to the attached drawings which illustrate the system in a convenient embodiment with certain modifications and adaptations.

FIG. 1 diagrammatically illustrates the system as used for transporting timber, and with a separate supporting cable for the carriage.

FIG. 2 is an example of a hydraulic connection diagram for hydraulic driving means with control valves capable of being used with the system in FIG. 1 and likewise with the systems of the following figures.

FIG. 3 is a diagrammatic view similar to that of FIG. 1 of the system as used without separate supporting cable.

FIG. 4 illustrates a modified manner of suspending the freight hook in the embodiment of FIG. 3.

FIG. 5 illustrates the dragging of a timber log by means of a system according to FIG. 3.

FIG. 6 illustrates a further modified suspension method suitable for transporting particularly long objects while using two travelling carriages, in an embodiment which in other respects may be similar to that of FIG. 3.

FIGS. 7 to 12 are diagrammatic views corresponding generally to FIG. 2 but showing the conditions of the hydraulic system for various valve positions.

In the embodiment shown in FIG. 1 the system is assumed to be used for transporting timber logs 1 a piling place 2. is the crane carriage which, by means of a pair of pulleys or rollers 15 is suspended from a supporting cable 16 stretched between the extremities of the transport course. The carriage 10 is operated by means of a pair of

cables

5 and 11, the latter of which is passed from the freight hook 14 over a pulley or roller on the carriage onto a pulley or roller 12 adjacent the piling place 2, and therefrom down to a winch 4, whereas the cable 5 is attached to the carriage and passed therefrom to a pulley or roller 9 suspended as indicated by 8 at the opposite end of the course and therefrom backwards to a roller 7 mounted on the same block 6 as the roller 12, and down to a Winch 3.

The

winches

3 and 4 are driven through a hydraulic system which will be more fully described with reference to FIG. 2, for example from the motor of a car as indicated by 18 in FIG. 1, on which the winches and driving means may be mounted and which, if desired, may be used for moving the Whole plant from place to place.

As indicated by dash-and-dot lines in FIG. 2 the winch drum 4 is connected to a hydraulic driving means comprising two

hydraulic motors

25 and 26, and the drum 3 is connected to a driving means comprising a hydraulic motor 27. The

motors

25, 26 and 27 are of the rotating volumetric type having positive fluid displacement therethrough and are reversible, being capable of operating as motors or as pumps according to the requirements and with liquid flow in one sense or the other. In FIG. 2 the directions of liquid flow through the hydraulic motors during hauling of the

cables

11 and 5 respectively are assumed to be from the left to the right. The volumetric capacity of these motors calculated as the volume of liquid flowing therethrough per unit of cable hauling length ought to have a certain inter-relation, which may be realized in various ways using difierent drum diameters, transmission ratios between driving means and drums etc. However, for the sake of simplicity it will be assumed that the

drums

3 and 4 have the same diameter and are driven by the appurtenant hydraulic motors with the same transmission ratio, so that the mutual ratios of the volumes of liquid flowing through the motors per unit of cable hauling length will be equal to the mutual ratios of the volumetric capacities of the motors expressed in volume of flow per unit of time for a certain rotative speed, or in other words will be equal to the mutual ratios of the turning moments developed by the hydraulic motors under the action of a given pressure. More particularly the volumetric capacity of the motor 26 is less than that of the motor 27, yet preferably greater than one half thereof, while the capacity of the motor 25, which preferably is stronger than the motor 26, plus the capacity of the motor 26 is greater than the capacity of the motor 27. Preferably the ratio of the sum of the capacities of the

motors

25 and 26 to the capacity of the motor 27 is substantially equal to the ratio of this latter capacity to that of the motor 26, this ratio being for example 3 :2. For example, there may be assumed a volume of fiow for the motor 25 of cmfi, for the motor 26 of 60 cm. and for the motor 27 of cm. per drum revolution.

The operation of the

hydraulic motors

25, 26, 27 is effected from a volumetric pump 28, for example a gear driven pump, connected to a mechanical driving source 19, such as the car motor. The pump 28 is controlled by means of two

valves

29 and 30 equipped with turning

slides

41 and 49, respectively, and levers 42 and 50 respectively.

By means of the pump 28 a driving liquid, for example 011, is pumped from a sump 31 through a conduit 32 to a central inlet 40 for the valve 29. From the valve 29 there extends a return conduit 33 to the sump 31, a conduit 38 to the motor 27 and two

conduits

36 and 37 which are connected in parallel and pass partly to the motor 26 and partly through a conduit 39 to a central inlet 48 for the Valve 30. The

motors

26 and 27 both discharge into the sump 31. Both sides of the motor 25 are connected to the valve 30 through

conduits

53 and 54 respectively. The valve 30 has a discharge to the sump through the conduit 55.

In the position of the lever 42 shown in the drawing the turning slide 41 of the valve 29 opens a connection between the inlet 40 and the outlet 33, but closes the

conduits

36, 37 and 38, so that the pump 28 is running idly. If the lever 42 is swung to the right the slide 41 will throttle the discharge 33 and open the conduit 36. If the lever is swung to the left from the position shown, it will likewise throttle the discharge 33 while at the same time opening the

conduits

37 and 38. When the lever 50 is in the position shown, the turning slide 49 of the valve 30 will cut off the connection from the inlet 48 to the

conduits

53, 54 and 55, although these conduits are mutually connected through the valve. If the lever 50 is turned to the left, it will open the connection between inlet 48 and conduit 53, while the connection of the latter with

conduits

54 and 55 is throttled. When the lever 50 is turned to the right, the valve 49 will throttle the connection of the conduit 54 to the

conduits

53 and 55 but open the connection from inlet 48 to conduit 54.

It may now be assumed that the carriage 10 is at the lower extremity 6 of the course and is to travel idly upwardly along the course to some desired point in order to fetch a load 1. After the pump 28 has been coupled to the motor 19 and started with the valves in the positions shown so that it runs idly, the lever 42 is turned to the left to the position shown in full lines in FIG. 7, whereby conditions of flow are established as indicated by arrows in full lines in the figure. Due to the throttling of the discharge conduit 33 a pressure is developed within the valve, which through the

conduits

37 and 38 is applied to the

motors

26 and 27 respectively, which start hauling the lines 11 and respectively. The motor 26 entrains the motor 25, which now runs idly as a pump, the path therethrough being short-circuited through the valve 30. Due to the hauling effect the total wound-out length of the cables is shortened so that the hook 14 is pulled upwards until it is stopped by the carriage 10. The cables are then tensioned, forming a loop with the carriage acting as a joint therebetween, until the pulling force in the cables corresponds to the turning moment of the weaker driving means, i.e. in this case the moment of the motor 26. This moment will of course in turn be dependent on the pressure in the valve 29, so that the tension can be adjusted by means of the lever 42. From now on the motor 27 will be means of the cable loop entrain the motor 26 with opposite sense of rotation and with the turning moment and hence the cable tension unchanged and the flow conditions in the hydraulic system will change as indicated by the dotted arrows in FIG. 7. Since the

motors

26 and 27 are now running in synchrom'sm the liquid flow from the motor 26 through the conduit 37 will add itself to the current from the conduit 32 in the valve 29 and together with this latter current be forced through conduit 38 and motor 27, with or without a branching through the conduit 33, according to whether the latter is completely closed or not. Thus the motor 27 will with unchanged turning moment be accelerated to a higher rotative speed whereby the braking effect of the motor 26 is recovered. The carriage is pulled upwards along the course with a force corresponding to the difference of the turning moments of the

motors

27 and 26. Since the increased velocity of the motor 27 causes a correspondingly increased backward liquid flow through the motor 26, acceleration of the system will proceed till the difference of the currents through the

motors

27 and 26 equals the current supplied (deducting a throttling leakage, if any). In the example chosen this will mean that the current through the motor 27 becomes three times as great as the current supplied through the conduit 32, whereas initially, when the

motors

26 and 27 were connected in parallel, it was only Vs of the supplied current, in other words the speed is five times as great when the outlet 33 is closed.

The carriage is thus travelling to the left in FIG. 1 while the speed can be controlled by lever 42. When it has arrived at the desired point the lever 42 is placed in the central position (see FIG. 2) so that the circuits through the

motors

26 and 27 are blocked and the carriage will stop and be kept locked. Assuming for the present that the freight hook 14 is so heavy that it can sink while overcoming the weight of the cable 11 in the considered position of the carriage, the lowering of the hook can take place in the following manner:

The lever 50 is moved to the right to a position such as that shown in full lines in FIG. 8, opening the connection from inlet 48 to conduit 54 and throttling the connection of conduit 54 with the

conduits

53 and 55. So long as the latter connection is not completely blocked, circuits will be established through the

motors

25 and 26 respectively and the valve 30, so that by the action of the pulling force in the cable caused by the weight of the freight hook both these motors can rotate in the unwinding sense, operating now as pumps.

It is, however, also possible to accelerate the lowering in the following manner:

The lever 50 is turned to its extreme right hand position indicated in dotted lines at 543 in FIG. 8 so that the connection of the

conduits

53, 55 with the conduit 54 is blocked. Due to the action of the cable pull the motor 25 will tend to operate as a pump and force the motor 26 to operate as a motor, but both motors are blocked due to the fact that they are coupled mechanically and have different volumetric capacities so that the motor 26 is not capable of admitting the current which the motor 25 would force through it. If, however, the lever 42 is now turned to the right, as shown in FIG. 9, the

motors

25 and 26 through conduit 36 will be subjected to pressure from the pump 28 and receive a supply of liquid from the latter. Under the action of cable pull and liquid pressure the motor 25 is thereby started in the unwinding sense and the weaker motor 26 will be forced to operate as a pump in a circuit through conduit 39, inlet 48, conduit 54, motor 25, conduit 53, conduit 55 back to motor 26. Thereby the drum 4 will be accelerated to a rotative speed at which the difference of the currents through

motors

25 and 26 corresponds to the increment supplied from pump 28 through conduit 36, which can easily be controlled by means of lever 42 for adjusting the unwinding speed of cable 11. While this is going on the carriage is kept stationary all the time, the drum 3 of cable 5 being held by motor 27, the circuit of which is blocked by the turning slide 41.

When the hook 14 has been lowered by unwinding cable 11 to the desired length, the lever 42 is placed in the central position and the lever 50 turned to the left, as shown in FIG. 10, whereby both cables are again blocked. The freight is attached and for hoisting, if the carriage is desired to remain stationary, the lever 42 may be turned to the right, as shown in FIG. 11, whereby the

motors

25 and 26 will operate in parallel in the rewinding sense until the hook approaches the carriage. Thereafter the lever 42 is turned to the left whereupon the three

motors

25, 26 and 27 will all operate in parallel connection in the rewinding sense, as illustrated by the arrows in full lines in FIG. 12. Or the lever 42 may be placed in its left hand position from the beginning, so that all motors start working at the same time. The liquid current will now be divided on the

motors

25, 26 and 27 in the ratio 2 /2 22:3 so that the lifting of the hook upwardly towards the carriage will take place at a low speed under the control of the lever 42, and when the cables are tightened by the hook engaging the carriage, due to the transmission of the pulling force from drum 4 through

cables

11 and 5 to drum 3 the

motors

25 and 26 will force the motor 27 to rotate backwards as a pump, as indicated by the arrows in dotted lines in FIG. 12. Thus, the carriage 10 will now move to the right along the course, the braking power being recovered in a similar manner as before, and the cable tension corresponding to the braking moment of the motor 27 determined by the actual position of the lever 42.

When hoisting with all motors operating, it is possible, if desired, to adjust the moment of the motor 27 so that V it is not quite suflicient to hold the carriage back on complete lifting of the log 1 off the ground, whereby the log will be dragged along the ground in a manner similar to that which will be described later with reference to FIG. 5.

When the log has arrived over the piling place 2 the

levers

42 and 50 are placed in their central positions so as to stop the carriage whereafter lowering takes place in a manner corresponding to that previously described for an empty hook, except that of course care is taken to adjust the

valve

29 or 30 respectively with such a small opening that the lowering will take place quietly and under full control.

In the embodiment of FIG. 3, in which the same reference numbers as in FIG. 1 have been used for corresponding parts, the supporting cable 16 has been omitted and instead the carriage travels with the roller in the return stretch of the cable 5. In other respects the arrangement is unchanged and can be manipulated in the same manner as described above, except that in this case it is not necessary for the hook 14 to be capable of overcoming the weight of the cable 11 in order to be lowered, since the cables are loaded by the weight of the carriage, and the carriage and hook will be raised or/and lowered by the cable stretches on both sides of the carriage adjusting themselves any time at an angle dependent on the weight of the carriage and that of the freight and on the adjusted tension. Besides, in FIG. 3 there is shown an additional device in the form of an additional carriage 21 travelling with a roller 17 on the return stretch of cable 5 and attached to the cable 11 by clamps 22 and provided with a hook 23 to which the freight carrier 14 may be hooked when unloaded. As indicated by dash-and-dot lines at 11 a free end portion of the cable 11 is thereby placed at the disposal of the operator when the carriage has been lowered onto the ground, so that on disconnecting the hook 14 he may carry it with him in order to attach it to a load laterally displaced with respect to the course of travel.

A specific advantage of .a cable crane made without a supporting cable as shown in FIG. 3 and operating according to the invention with a certain adjusted tension when loaded, while permitting unwinding and rewinding, is that in this case the tension will be independent of the distance between the extremities of the course, so that this distance may vary under load without the cables being overloaded. Such plants are remarkably well suited for the transport of men and goods in suspended chairs between ships in rough sea and will thereby be a good help in rescuing operations.

Since a plant without separate supporting cable as described is independent of the load from the freight hook for recovering loads from the ground, the arrangement is particularly suited for being used with the hook suspended from a tackle as shown at in FIG. 4, for lifting heavy loads.

FIG. 5 illustrates how a dragging of the timber log 1 along the ground can take place with an arrangement as shown in FIG. 3 when the tension on the return cable 5 is adjusted so that the motor 27, as previously described, starts operating as a pump before the log 1 is lifted ofl the ground.

FIG. 6 illustrates a modification of the embodiment shown in FIG. 4 adapted for the transport of long and heavy objects 1', for example poles or pipes. In this case the freight is carried by two

tackles

20 and 20", each of which is suspended in one of two travelling

carriages

10, 10" by means of the cable 11, and which are kept at a desired mutual distance by a connecting rod 58.

The arrangement according to the invention may of course be modified in various manners difiering from those shown, so as to comply with various demands. Thus the invention may also be used for rail cranes in which the crane rails will have a function corresponding to that of the supporting cable 16 in FIG. 1. It will also be obvious, without having to be described in detail, that the systems described may be used for the transport of freights, not only from the extremity 8 to the extremity 6, but also in the opposite direction, and that the freight carrier 14 instead of being connected to the direct pulling cable 11 may also be connected to the looped pulling cable 5, while the cable 11 is connected to the carriage.

I claim:

1. A transportation system comprising a first support, a second support placed from said first support, a carriage, means supporting said carriage for travel between said first and second supports, first and second pulleys mounted on said first support, a third pulley mounted on said second support, a pair of winches positioned adjacent said first support, a first cable interconnecting one of said winches and said carriage and extending over said first pulley and said third pulley, a second cable interconnecting the other of said winches with said carriage and extending over said second pulley, separate driving means for each of said winches, one of said driving means comprising two hydraulic motors mechanically connected to the other of said winches, another of said driving means comprising another hydraulic motor having less power than the combined powers of said two hydraulic motors but greater than the power of one of said two hydraulic motors, conduits interconnecting said motors, and valves controlling flow of fluid in said conduits, whereby said motors may be selectively interconnected by said valves to exert difierential polls on the cables for moving said carriage in a direction to either of said supports, the driving means exerting the weaker pull on its associated cable acting as a pump to drive fluid to the remaining driving means having the stronger pull and transferring energy from the associated cable to said remaining driving means.

2. A transportation system as defined in claim 1, Wherein the ratio of the capacity of the driving means exerting the stronger pull to the capacity of the driving means exerting the weaker pull is always substantially the same irrespective of which driving means is exerting the stronger pull, the capacity of each driving means being measured in rate of fluid flow therethrough per unit of cable hauling length.

3. A transportation system as defined in claim 2, wherein said two hydraulic motors have different powers, the ratio of the sum of the capacities of the two hydraulic motors to the capacity of said other hydraulic motor being approximately 3:2, the ratio of the capacity of said other hydraulic motor to the capacity of the weaker motor of said two hydraulic motors also being approximately 3:2, the capacity of each motor being measured in rate of fluid flow therethrough per unit of cable hauling length.

4. A transportation system comprising a first support, a second support spaced from said first support, a carriage, means supporting said carriage for travel between said first and second supports, first and second pulleys mounted on said first support, a third pulley mounted on said second support, a pair of winches positioned adjacent said first support, a first cable interconnecting one of said winches and said carriage and extending over said first pulley and said third pulley, a second cable interconnecting the other of said winches with said carriage and extending over said second pulley, separate driving means for each of said winches, said driving means comprising positive fluid displacement hydraulic means, said hydraulic means being reversible to be driven as motors by said fluid in one mode of operation and to drive said fluid as pumps in another mode of operation, a hydraulic power source for creating hydraulic pressure in said fluid, conduits interconnecting said hydraulic means and said source for supplying hydraulic pressure to the hydraulic means for driving the same, said conduits being connected to provide recirculating paths for said fluid to said hydraulic means, and valves controlling flow of said fluid in said conduits, said valves. having one operating condition wherein one of said driving means efiectively dominates the other of said driving means so that the other driving means supplies power through its recirculating path to the first driving means to assist driving thereof, said valves having a second operating condition wherein the other driving means .dominates said first driving means so that the first driving means supplies power through its recirculating path to the other driving means to assist driving thereof.

5. A transportation system as claimed in claim 4, wherein said other driving means includes a motor loaded by an associated cable and winch so as to act as a pump for supplying power through the recirculating path of said other driving means to the first driving means.

6. A transportation system as claimed in claim 4, wherein said other driving means includes two motors, one motor being loaded by an associate cable and winch so as to act as a pump for supplying power through the recirculating path of said other driving means to the first driving means in the one operating condition of said Valves, the other motor in said one position of the valves being short circuited through its recirculating path to permit the said other driving means to be dominated by said one driving means.

7. A system as defined in claim 4, wherein a roller is provided in said carriage, one of the cables being unattached to the carriage and extending over said roller, and freight engaging means located at the lower free end of said one cable.

8., A system as defined in claim 4, wherein a third cable interconnects said supports and wherein said carriage is supported by said third cable.

9. A system as defined in claim 5, wherein the ratio of the capacity of the dominating driving means to the capacity of the motor of the other driving means is substantially the same, irrespective of which driving means has the highest capacity, the capacity being measured in rate of fiuid flow per unit of cable hauling length in the dominating driving means and said motor.

10. A system as defined in claim 4, wherein the carriage is supported on a part of the first cable extending between said first pulley and said third pulley.

11. A system as defined in claim 4, wherein said valves have a third operating condition in which one of said valves has a position wherein it causes the blocking of liquid flow through one of the hydraulic means While the other of the hydraulic means is operable by means of another of said valves for selectively hoisting and lowering a load while said carriage remains stationary.

References Cited in the file of this patent UNITED STATES PATENTS 564,186 Dickinson July 21, 1896 1,024,833 Dickinson Apr. 30, 1912 1,262,227 Miller Apr. 9, 1918 1,404,358 Frink Jan. 24, 1922 1,624,545 Dickinson Apr. 12, 1927 1,826,303 Dickinson Oct. 6, 1931 2,318,218 Grabinski May 4, 1943 2,374,588 Doran Apr. 24, 1945 2,395,302 Slomer Feb. 19, 1946 2,736,170 Huse Feb. 28, 1956 2,750,153 Lindgren June 12, 1956