US2874436A

US2874436A - Slip assembly

Info

Publication number: US2874436A
Application number: US495575A
Authority: US
Inventors: Allen Herbert
Original assignee: Cameron Iron Works Inc
Current assignee: Cooper Industries LLC
Priority date: 1955-03-21
Filing date: 1955-03-21
Publication date: 1959-02-24
Anticipated expiration: 1976-02-24

Description

Feb. 24, 1959 H. ALLEN I 2,874,436

SLIP ASSEMBLY Filed March 21, 1955 5 Sheets-Sh'eet 1 f" I INVENTOR.

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Feb. 24, 1959 H. ALLEN 2,874,436

SLIP ASSEMBLY Filed March 21, 1955 5 Sheets-Sheet 2.

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SLIP ASSEMBLY Filed March 21, 1955 5 Sheets-Sheet 4 A EPBEN flu E/V IN V EN TOR.

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United States Patent SLIP ASSEMBLY Herbert Allen, Houston, Tex., assignor to Cameron Iron Works, Inc., Houston, Tex., a corporation of Texas Application March 21, 1955, Serial No. 495,575

9 Claims. (Cl. 24-263) This invention relates in general to slip assemblies and more particularly to an arrangement employing wedges of the type commonly referred to as slips for locking two relatively movable members against movement with respect to each other in one direction. One of the most common uses for such type of suspension is in the suspending of long strings of pipe such as either casing or tubing in deep wells such as oil or gas wells.

Slip assemblies have been employed for suspending pipe in oil and gas wells and the like for many years and have generally consisted of a plurality of segmental wedges tapered downwardly and provided on their inner "surfaces with horizontally extended wickers or teeth adapted to cut into and engage the pipe with a non-sliding engagement but provided on their outer surfaces with relatively smooth faces adapted to sliding engage within a tapered, usually conical, seat in a casing head or the like, such seat being customarily referred to as a bowl or a slip bowl. in such arrangements, when the string of pipe has been lowered through the slip bowl to the point where it is desired that it be suspended, the slips or segmental wedges are dropped in place around the pipe so that the wickers on their inner faces engage the pipe. Thereupon a further lowering of the pipe will cause these wedges to be forced to slide downwardly within the slip bowl, thereby providing a radial compressive force urging the slip segments against the pipe until the wickers or teeth thereon bite into the pipe a sufficient amount to enable them to support the weight of the string of pipe.

However, as strings of pipe have become longer and heavier due to increase in the depths of wells being drilled, difiiculty has been encountered in that the compressive forces exerted by the slips on the pipe have become so great that they have caused an inward deflection of the pipe wall beyond tolerable limits. Efforts to avoid this difficulty by changing the slope of the walls of the slip bowl have not been practical because such changes, or any other changes which tend to reduce the rate of increase of the compressive force of the slips against the pipe during the initial stages of placing weight on the slips, prevent the slip teeth from digging into the pipe sufiiciently to support the pipe. Neither can the problem be solved by providing a definite stop for downward movement of the slips within the bowl because manufacturing tolerances in external diameter of a nominal size of pipe cause the slips to initially engage the pipe at various levels within the slip bowl and a positive stop for downward movement of the slips may either prevent sufii- 'cient downward movement in the case of a pipe of minimum actual external diameter or permit too great a down ward movement in the case of a pipe of maximum actual external diameter for a given nominal pipe size.

In view of the foregoing, it is an object of this invention to provide a slip suspension in which the compressive force exerted by the slip against the object suspended will be prevented from exceeding a predetermined maximum.

Another object is to provide such a suspension in which the rate of increase of compressive force exerted by the slips against the object suspended will be high during the initial stages of increase of weight placed on the slips until the engagement of the slip wickers with the object suspended is great enough to support the weight of the object but such compressive force is less than a predetermined maximum, and in which further increase in such compressive force will be substantially inhibited with further increase in the weight placed on the slips.

Another object is to provide such a suspension in which the desired compression variation and inhibition will be substantially the same regardless of variations of dimension of the object suspended due to manufacturing tolerances.

Another object is ot provide such a suspension in which the tapered surface against which the slips are adapted to seat will not be damagedin normal use so as to prevent reuse.

Another object is to provide a suspension which may be employed for long, heavy strings of pipe without subjecting the pipe to an external compressive force greater than that which would produce a tolerable predetermined degree of deflection of the pipe wall.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings in which is set forth by way of illustration and example one embodiment of the invention.

In the drawings:

Fig. l is a longitudinal cross-section through a slip assembly and bowl and a packing associated therewith, showing the manner in which the slip assembly is retained within the bowl prior to being actually put in use;

Fig. 2 is a view similar to Fig. l but taken at right angles thereto and substantially along the line 22 of Figure l; v

Fig. 3 is a transverse cross-section of the structure illustrated in Fig. 1 taken along the line 3-3 thereof;

Fig. 4A is an elevational view of one of the slip segments illustrated in Figs. 1 to 3 which are constructed in accordance with this invention, showing the surfaces thereof which are adapted to engage the interior of the slip bowl;

Fig. 4B is an elevational view of the structure shown in Fig. 4A looking in the direction shown by the arrows 4B4B of Fig. 4A;

Fig. 4C is an enlarged view showing a portion of the surface of the slip segment of Fig. 4B which is adapted to engage the slip bowl;

Fig. 5 is a diagrammatic view illustrating with some exaggeration for illustration purposes the relatio-nshipof the curvatures and dimensions of the slip segment of this invention with respect to the pipe and slip bowl with which it is intended to cooperate;

Fig. 6 is a view similar to Fig. 5 but on a reduce scale and illustrating a slip segment and a segmental portion of the pipe and slip bowl with which it cooperates in the position these parts occupy at the point of initial contact between them when the slips are dropped into place preliminary to suspending the pipe;

Figs. 7 and 8 represent fragmentary longitudinal crosssections of the structure illustrated in Fig. 6 taken along the lines 77 and S8 thereof, respectively;

Fig. 9 is a view similar to Fig. 6 but illustrating the parts in the position they occupy after a portion of the weight of the pipe has been placed upon the slip assembly and the assembly moved downward within the slip bowl sufiiciently to cause the slip wickers to dig or bite into the pipe to a substantial degree;

Fig. 10 is a longitudinal cross-section taken along the line 10-10 of Fig. 9;

Fig. 11 is a view similar to Figs. 6 and 9, but showing the parts in the position they occupy after the full weight of the pipe has been placed upon the slip assembly; and

Figs. 12 and 13 are longitudinal fragmentary crosssections taken along the lines 12-12 and 1313 respectively of Fig. 11.

It is contemplated that in this particular embodiment of the invention there will be provided a slip bowl generally designated as 1 which will be seated in the tapered upper end portion of the casing head structure normally employed as a part of the well head equipment of oil and gas wells. This bowl is made in two sections, 2 and 3, each substantially semi-circular so that it may be separated for ease of putting in position around a pipe to be suspended. The semi-circular portions of the bowl may be secured together around the pipe in any suitable fashion as by cap screws 4 and 5 so as to provide a bowl which is in effect a complete circular structure having an outer tapered surface 6 and an inner tapered surface 7 substantially parallel to each other.

At each lateral edge of the section 2 there is provided a plate which operates as a slip retainer as indicated by the

numerals

8 and 9. Similar plates 10 and 11 are employed on the lateral edges of the bowl segment 3. Inasmuch as these plates are interposed between the lateral edges of these bowl segments respectively, each of the bowl segments without the plates is slightly less than a semi-circular member in transverse cross-section. The

plates

8, 9, 10 and 11 are secured to the lateral edge faces of the segments 2 and 3 in any suitable fashion as by providing holes 12 through the plates and welding inside of these holes about the edges thereof, thereby providing a welded connection at each hole between the plate and the edge face of the segment of the bowl.

The slip retainer plates are each cut away as indicated at 13 and 14 for the purpose of permitting the extension of aligning dowels between the slip segments in the manner presently to be described.

If desired, there may be employed on the upper end of the slip bowl a packing ring 15 which forms a complete circle of deformable packing material except for being split at 15a on an angle so that upon removal of the cap screws 4 and 5 the packing ring may be separated along the line 15a and flexed at the opposite side of the assembly so as to provide in effect a sort of hinge connection enabling the assembly to be spread apart and placed around a pipe and then brought together and secured in place by the cap screws 4 and 5. The packing ring is held in place on the upper ends of the slip bowl segments 2 and 3 by means of a split holddown ring comprised of

segments

16 and 17, each having

countersunk holes

18 and 19, respectively, for the purpose of receiving countersunk cap screws 20 as clearly shown in Fig. 1. These cap screws 20 are threaded adjacent their lower ends as at 21 into tapped openings in the upper ends of the slip bowl segments 2 and 3.

Located inside the slip bowl formed by the segments 2 and 3 are four slip segments or assemblies indicated re spectively by the

numerals

22, 23, 24 and 25. Adjacent its upper end and at one lateral extremity each of these segments is provided with a drilled hole 26 into which is press fitted a dowel pin 27 extending toward the adjacent edge of the next slip segment and projecting into a larger drilled hole 28 in such adjacent segment, the dowels 27 fitting loosely each in one of the holes 28. Prior to being put into use the four slip segments are held in an upper position within the bowl 1 by means of cap screws 29 extending through the bowl segments 2 and 3 and threaded into the slip segments respectively as shown at 30. Retainer pins 31 are press fitted into openings in the bowl and extend inwardly between

slips

22 and 23 and between slips 24 and to separate and retain them in the bowl.

For the purpose of facilitating the handling of the entire assembly which includes the slip bowl with the slip assembly inside of the bowl, there is also secured in place with respect to the outside of the slip bowl by means of the cap screws 29 a pair of handle members 32, which, as illustrated, extend around each of the slip bowl segments from one screw 29 to the other and have portions spaced from the bowl between the screws 29 to provide handle grips. These provide handles by which two men may lift the entire assembly and manipulate it for the purpose of putting it in place around the pipe and within a well head fitting.

Attention is now directed to the illustration of the individual slips in Figs. 4A and 4B. In this illustration it will be seen that the exterior surface of each of the slips is provided on a substantial area on each side of the central section thereof with a roughened surface 33, this surface preferably being formed by means of very small grooves or machine tool marks extending laterally with respect to the axis of the slip. These constitute surfaces providing high frictional characteristics with substantially any other surface with which they might come in contact, and particularly provide surfaces which will give high frictional resistance to sliding in a downward direction within slip bowl 1 when engaged with the inner surface '7 of such bowl.

Intermediate the two areas 33 which possess relatively high frictional characteristics is an area 34 extending substantially from the top to the bottom of each slip which is preferably substantially smooth and provides relatively low frictional characteristics when in contact with a surface such as the interior surface of the slip bowl indicated at 7.

Referring now to Fig. 5, the pipe to be suspended by the slip assembly of this invention is indicated at 35 and the inner surface of the slip bowl is indicated at 7 with a slip segment or assembly disposed between them in the position which it would occupy when first released by the removal of the cap screws 29 and the handles 32. It will be seen that the slip segments themselves have wickers or pipe-engaging teeth 36 on their inner faces which, as clearly shown in Figs. 1, 2 and 4B are directed upwardly so that when the edges of these wickers are dug or cut into the surface of the pipe they will prevent downward movement of the pipe with respect to the slip segments. These wickers, however, are interrupted by means of a groove or slot 37 illustrated as located substantially midway between the side extremities of the slip segment and extending a substantial por-- tion of the distance from the interior surface to the exterior surface of the segment so as to substantially weaken the segment at this point against forces tending to flatten it out or increase its over-all radius. essential, it is preferred that the segments are so proportioned and made of a sufiiciently elastic material that the flexing within the grooved portion or slot 37 as hereinafter described will be within the elastic limit of the material.

The nature which the roughened areas 33 may have is more clearly indicated in the enlarged section appearing as part of Fig. 4B and is shown to be formed of grooves 38 having ridges or teeth 39 between them both extending in a lateral direction. It will be understood that the surface need not necessarily take this specific form but that it is desired that the surface be one which will afford a frictional resistance against sliding against the interior wall 7 of the bowl when in contact therewith which is much higher than that afforded by the smooth surface 34 and that one way of achieving this result is by a coarse machining producing a surface of the form illustrated. It has been found that when these ridges and grooves are formed on a small or fine pitchless than the expected sliding of these surfaces within the bowlthe inner surface of the bowl will not be damaged by the seating of the slips so as to prevent reuse of the bowl.

On further reference to Fig 5 it will be seen that initially the slip segments will have their outer faces on Although not which the surfaces 33 and the bowl.

34 are formed, shaped to a radius r2 which is substantially shorter than the radius r1 of the inner surface of the bowl at approximately the position where the slip is adapted to come to rest in the tapered space between the bowl and the pipe. For this reason, the slip will engage the inner surface of the bowl initially only over a relatively narrow area 40, the surface of which lies within the smooth surface 34 and which is disposed substantially opposite from the groove 37. This smooth surface 34 may be formed by first rough machining the entire outer face of the slip then grinding smooth the central area thereof. This will make this central area of a slightly longer radius than the radius r2 which is the over-all radius of the outer sur face of the slip. As will be seen, this radius r3 of the central smooth area 34 is both longer than the radius 1'2 and shorter than the radius r1 of the interior of This is a preferred condition though 'not an essential in the operation of this invention.

At the same time that contact is made with the inner surface of the bowl along the area 40, the only contact between the wickers 36 and the outer surface of the pipe will be substantially at the extreme ends of these wickers as indicated at 41. As Will be seen, the pipe will have its inner and outer surfaces concentric and on radii r4 and r5 respectively. These surfaces are all also concentric with the inner surface of the bowl, whereas the over-all radius of the wickers r6 is concentric with the outer surfaces of the slips.

Figs. 5 and 6 illustrate the parts in the position they occupy just after the slips have been lowered into engagement with the pipe and the inner surface of the bowl and before any of the weight of the pipe has been placed thereon and it will be seen that at this point there will be a substantial space 42 left between the slip and the inner surface of the bowl at the lateral extremities of the slip and a substantial space 43 left between the wickers and the outer surface of the pipe along the intermediate portion of the slip.

The operation of the slip assembly of this invention is more clearly illustrated in Figs. 6 to 13, inclusive, in which the contacts between the slip assemblies and the slip bowl at the points 40 and the slip assemblies and the pipe at the points 41 are clearly apparent, as well as the spaces between the slip assemblies and the slip bowl at the points 42 and the clearance between the slip assemblies and the pipe at the points 43 In the position of the parts as they appear in Figs. 6, 7 and 8 without any of the weight of the pipe having been placed on the slips, it will be seen that the only contact between the slips and the slip bowl is along the smooth area 34.

If the pipe now be moved downwardly the slip will slide downwardly along the smooth surface 34 which is in engagement with the inner surface of the bowl, r

thereby causing greater pressure to be exerted on the corners of the slips against the pipe causing these corners to bite into the pipe and thereby provide a greater and greater engagement with the pipe so as to enable them to take more and more of the weight of the pipe. As additional weight of the pipe is placed upon the slips and greater pressure thereby exerted by the slips against the pipe, the slips will become squeezed into the narrower lower portion of the wedge-shaped space between the pipe and the slip bowl and will flex along the weakened line left by the'groove 37, putting more and more pressure against the pipe by the wickers 36 until these wickers have bitten into the pipe firmly at the corners as illustrated at 45 and the smooth surface 34 begins to leave the inner surface of the bowl as indicated at 44 (Fig. 9). At this time also the clearances between the lateral extremities of the slip and the inner surface of the bowl will become less as shown at 46 and the clearance between the central portions of the tral portions of the wickers come into contact with the pipe as shown at 47. All this will result in a change in the portion of the slip in contact with the slip bowl from one which is entirely smooth until a portion of the rough outer face 33 of the slip comes in contact with the bowl. As pressure increases through the downward movement of the slip as the weight of the pipe is placed on the slip the frictional resistance to downward sliding movement of the slip against the slip bowl will increase and finally by the time the pressure on the pipe has increased sufficiently to force the wickers 36 to bite into the pipe as shown in Figs. ,11, 12 and 13 along the entire lengths of the wickers, the smooth central surface of the slips will have moved out of contact with the slip bowl as shown at 48 in Fig. 11 and the wickers will not only be fully engaged with the pipe at their ends as shown at 49 but the slip will also be in engagement with the slip bowl over the major portions of the roughened outer areas 33 of the slip and the wickers will be fully engaged adjacent their central portions as shown at 51. By this time also with nearly the entire roughenedouter face portions of the slip in engagement with the slip bowl the resistance to downward movement of the slip and the slip bowl will have become so great as to substantially stop such downward movement even for great increases in weight of pipe placed on the slips. Inasmuch as the inward pressure of the slips against the pipe tending to compress the same is directly proportionalto the amount of downward sliding movement of the slips in the slip bowl, the engagement of the roughened outer areasof the slip with the slip bowl will substantially limit the compressive forces exerted against the pipe and prevent intolerable reduction in diameter of the pipe by excessive compressive forces thereon;

It will be appreciated that while the slip assembly of this invention has been described as useful in connec tion with the suspension of strings of pipe in a well, .it might be used likewise for suspending pipe or any other cyiindrical member within a tapered opening or for securing together two members, one of which is cylindrical and passes through another which is tapered, and that I it might be used with obvious modification for securing against movement with respect to each other in one direction any two members which have a wedge-shaped space between them, the essential features being that the slip assembly be designed to grip one member and move with it toward tighter wedging engagement with the other member and that with respect to such other member it be so formed that it will initially present to such other member only an area of low frictional characteristics so as to permit free sliding movement with respect thereto and that after it has slid far enough to provide sufiicient compressive force to cause the requisite tight engagement between its gripping surface and the first member it will present to such other member another surface of much higher frictional characteristics so as to greatly retard further sliding movement with respect to such other member-and thereby limit the compressive force upon the first member.

From the foregoing it will be seen that this invention is one Well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

it will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombin-atio'n's. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it 18 to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

. The invention having been described, what is claimed 18:

1. Apparatus for fixedly locating one member against movement in one directional sense relative to an oppositely facing and angularly disposed surface of another member, comprising wedge-shaped slip means disposable within the tapered space between said members and having teeth on the inner surface thereof for gripping said one member to resist its movement in said one directional sense, a part on the outer surface of said slip means having low friction characteristics to permit movement of the teeth in said one directional sense and in a path substantially parallel to the oppositely facing surface of said other member as gripping of the teeth with said one member resists movement of said one member in said one directional sense, said part being initially positioned to engage the oppositely facing surface of said other member, and means including another part on said slip means having higher frictional characteristics than said first part, and being initially positioned with respect to said first part so as to be out of engagement with the oppositely facing surface of said other member and movable relative to said first mentioned part to a position to engage the oppositely facing surface of said other member when a predetermined wedging load has been placed on said slip means to increase the resistance to movement of said one member in said one directional sense.

2. Apparatus for hanging a pipe, comprising a bowl having a downwardly and inwardly tapered seat, a wedgeshaped slip means disposable between the pipe and bowl and having pipe gripping teeth on the inner surface thereof, a part on said slip means having low friction characteristics initially engageable with said seat upon placement of said slip means in the bowl to permit movement of the teeth downwardly in the bowl and in a path substantially parallel to the taper of the seat as gripping of the teeth with the pipe resists movement of said pipe downwardly, and means including another part on said slip means having higher friction characteristics than said first mentioned part initially positioned with respect to said first mentioned part so as to be held thereby out of contact with the seat and movable relative to said first mentioned part when a predetermined wedging load has been placed upon said slips to a position into frictional engagement with the seat to increase the resistance to downward movement of said pipe, said higher friction part facing oppositely to said teeth and being effective, upon said increased resistance, to prevent further substantial downward movement of the pipe.

3. A slip assembly for fixedly locating one member against movement in one directional sense relative to an oppositely facing and angularly disposed surface of another member, comprising a Wedge-shaped body having wickers on one face for gripping said one member and a substantially smooth low friction surface on an opposite face to permit sliding of the body along the surface of said other member, and a second surface having higher frictional characteristics than said smooth surface movable with regard to said smooth surface and responsive to the placement of a predetermined wedging load upon the body from an initial position ineffective to retard sliding of said smooth surface in said one direction to a position effectively increasing the resistance to sliding of said body.

4. A slip assembly comprising a wedge-shaped flexible body having wickers on one face adapted to engage and bite into one of a pair of surfaces disposed at an angle to each other which is substantially the same as the angle of the faces of said wedge, said body having a substantially smooth area on an opposite face to slide with respect to the other of said surfaces, and said body having another area with higher frictional characteristics than said smooth area and movable with respect to said smooth area in response to flexing of the body upon the placement of a predetermined wedging load upon the body from an ineffective position to a position to provide engagernent between said body and said other surface and to limit said sliding to a predetermined amount.

5. A slip segment for fixedly locating one member against movement in one directional sense relative to an oppositely facing and angularly disposed surface of another member, comprising a tapered body having wickers along one face for gripping said one member and having on its opposite face a longitudinally extending portion with lower frictional characteristics than the remainder thereof, said body being substantially rigid under less than a predetermined stress tending to alter its contour in a lateral direction so as to dispose said longitudinally extending portion in initial engagement with the surface of said other member and the remainder of its opposite face out of engagement therewith, and yieldable under said predetermined stress to change its overall lateral contour and move said remainder of its opposite face itno engagement with said surface.

6. A slip segment for hanging a pipe within a downwardly and inwardly tapered seat of a bowl, said slip seg ment having a generally cylindrical inner face with pipe engaging teeth thereon and a generally conical outer face coaxial with the inner face and with a longitudinally extending area remote from its lateral edges smoother than the areas on each side thereof, said segment being substantially rigid under less than a predetermined stress so as to dispose said longitudinally extending area in initial engagement with the seat and the areas on each side thereof out of engagement therewith and yieldable under said predetermined stress to an overall greater radius of curvature to move said areas on each side of the longitudinally extending area into engagement with said seat.

7. A slip assembly for suspending a pipe in a well head comprising, in combination, an annular bowl adapted to seat in such well head and having a longitudinally tapered inner surface, and a plurality of slip segments within said bowl, each of said segmentsv having an outer surface with a longitudinal taper substantially corresponding to the taper in said bowl and of a shorter radius than said inner surface of the bowl in transverse cross section and having a central longitudinally extending part of said outer surface with lower frictional characteristics than the parts on either side thereof for sliding over the tapered inner surface of the bowl, and each segment having pipe gripping wickers on the inner surface for gripping the pipe, said wickers having their lateral extremities closer to the axis of said bowl than their intermediate portions, and said segments each being substantially rigid under less than a predetermined stress so as to dispose said longitudinally extending part in initial engagement with the surface of the bowl and the parts on either side thereof out of engagement therewith, and yieldable under said predetermined stress along a longitudinal portion remote from its lateral edges to move said parts into engagement with the surface of the bowl.

8. The assembly as set forth in claim 7 in which the annular bowl is formed in segments and in which each bowl segment has radially extending parts adjacent the opposite lateral edges of each slip segment disposed therein for retaining the slip segments in the segments of the bowl respectively.

9. The assembly as set forth in claim 8 in which each bowl segment has radially extending parts positioned to hold said slip segments in the upper portion of said bowl segments and retractable from engagement with said slip segments to permit said slip segments to move inwardly and downwardly within said bowl.

References Cited in the file of this patent UNITED STATES PATENTS 1,099,453 Kline June 9, 1914 1,436,246 Grieve Nov. 21, 1922 1,556,094 Fletcher Oct. 6, 1925 1,559,932 Bogen Nov. 3, 1925 (Other references on following page) UNITED STATES PATENTS 2,237,683 Minbr Apr. 8, 1941 1, 41,457 Adair Sept 5 27 21340-597 Kfilley 1, 1944 1,735,937 Shaffer Nov. 19, 1929 315741614 13, 1951 1,849,216 Adair Mar. 15, 1932 $33,046 Allen July 1954 1 59,5 1 Hawonh May 24, 32 6 2,712,455 Nellon y 1955 1,860,062 Taylor May 24, 1932 2,086,652 Volpin July 13, 1937 FOREIGN PATENTS 2,207,469 Roye July 9, 1940 687,691 Great Britain of 1953 2,230,712 Bendeler et a1. Feb. 4, 1941