US 2749054 A
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Description (OCR text may contain errors)
June 1956 J. M. CROM, JR 2,749,054
APPARATUS FOR LOW POWER TENSIONED WINDING OF CONCRETE ARTICLES Filed May 21, 1952 4 Sheets-Sneet 1 INVENTOR Jam/1mm Jr:
ATTORNEYS June 5, 1956 2,749,054
J. M. CROM, JR APPARATUS FOR LOW POWER TENSIONED WINDING OF CONCRETE ARTICLES Filed May 21. 1952 4 Sheets-Sneet 2 ATTORNEYS un 1956 J. CROM, JR 2,749,054
APPARATUS FOR LOW POWER TENSIONED WINDING OF CQNCRETE ARTICLES Filed May 21. 1952 4 Sheets-Sneet I5 J n 5, 9 .1. M. CROM. JR
APPARATUS FOR LOW POWER TENSIONED WINDING OF CONCRETE ARTICLES 4 Sheets$neet Filed May 21, 1952 Jain/M 61mm ab:
ATR WNFYS APPARATUS FOR LOW POWER TENSIONED WIND- ING OF CONCRETE ARTICLES This invention relates to an apparatus for continuously prestressing concrete articles.
Heretofore in the prior art, methods and apparatus have been advanced for the continuous prestressing of concrete articles. These methods and apparatus, while producing the desired result, have, nevertheless, been extremely costly by reason of the equipment involved and have also required the consumption of considerable power. In some of these methods and apparatus where wire has been continuously tensioned while paying out from a source of supply to effect prestressing, the load which caused tension has had to act over the entire length of the wire. The work done by these methods and apparatus, therefore, is equal to the product of the length of the wire and the load applied. This results in the expenditure' of a large amount of work.
In contradistinction to the above methods and apparatus of continuously prestressing, the linear prestressing of beams and the like by tensioning wires is generally affected by stressing from one end only. The load in this instance acts only over a relatively short length to produce the stretch desired. The Work done, therefore, is equal to the product of the change in length of the wire and the mean load applied.
It follows from the foregoing then that the theoretical work necessary to stress wire as illustrated by the linear prestressing method is considerably less than when the load acts over the entire length of wire, as is usually the casein continuous prestressing methods and apparatus.
By the present invention, an apparatus for continuously prestressing pipes, tanks, roads, or the like is advanced which provides a means for prestressing that does not require the load to act over the entire length of the wire.
It is an object of this invention to provide an apparatus for continuously prestressing concrete bodies that results in expending less work to effect the prestressing than methods which have heretofore been available.
It is another object of this invention to provide an apparatus for continuously prestressing that will be more economical and eflicient than apparatuses which have heretofore been available.
It is another object of this invention to provide an apparatus for continuously stressing wires which involves the consumption of less power and by which apparatus wires can be stressed with greater facility and speed than has heretofore been available.
Other objects and advantages of the present invention will become apparent from a study of the following specification when considered in conjunction with the drawings, in which:
Figure 1 is a plan view showing the method of this invention as applied to the continuous prestressing of concrete pipes;
Figure 2 is a vertical section of the clutch assembly taken along line 22 of Figure 1;
nited States Patent Figure 3 is a vertical section of the clutch assembly taken along line 3-3 of Figure 2;
Figure 4 is a schematic representation illustrating the theory of this invention;
Figure 5 is a view in side elevation of a modification of this invention showing the method applied to the continuous prestressing of concrete pipes;
Figure 6 is a plan view of the modification showniu Figure 5;
Figure 7. is a schematic representation of the modification shown in Figure 5;
Figure 8 is a view in side elevation of a further modification showing the method applied to the continuous prestressing of concrete pipes while in a vertical position;
Figure 9 is a view in side elevation of a further modification showing the method applied to the continuous prestressing of concrete tanks;
Figure 10 is a plan view of the modification shown in Figure 9;
Figure 11 is a view in side elevation of a further modification showing the method applied to the continuous prestressingof concrete roads; and
Figure 12 is a view in front elevation of the modification shown in Fig. 11.
Before referring to the drawings for a detailed description of the invention, Figures 1 and 4 will be discussed to enable a clear understanding of the theory by which this invention operates. As can be seen in Figure l, the wire 20 which is ultimately to be wound on a concrete pipe 21 is first wound several turns around a tapered braking drum 22. Wire 20 is wound on drum 22 with a small initial back-tension to prevent the wire from slipping uncontrollably around tapered drum 22. This backtension can be produced by passing the wire initially through a small draft die, lightly gripping wooden blocks,
wheels that cold work the wire, drive an electric generator, or hydraulic pump or any such similar device. Both the pipe 21 and the drum 22 are mounted upon a common shaft 23 to which power is supplied by means of an electric motor 24. The drum diameter is slightly smaller than the pipe diameter. One rotation of the pipe 21 will require a length of wire equal to the pipe circumference. However, one rotation of the pipe results in wire being payed out from the drum-22 in a length equal to the circumference of the drum. Inasmuch as the drum is of smaller diameter the amount of wire released by the drum is insufiicient to go around the pipe. Consequently the wire 20 must be stretched if it is to go around the pipe 21. Therefore, by controlling. the relative diameter of the drum and pipe it is possible to obtain the exact desired stress in the wire. Stated in another way, for a pipe of a given diameter there is theoretically a corresponding drum of smaller diameter that will cooperate with the pipe to produce the proper stress in the wire. As the variables of the problem are the diameters of the pipe and drum and the stress in the wire, the establishment of any two variables will determine the third. In Figure 4 is shown a schematic representation of the forces produced by the tensioned wire and their direction. Since the tensioned wire is common to both the drum and the pipe, the forces exerted on the wire with respect to the drum and pipe are equal and in a direction opposed to the tension in the wire. Hence Ta, the force exerted on the drum is equal and opposite to Tb, the force exerted on the pipe.
The wire is-wound on the drum and pipe so that torque raTrz opposes torque rbTb. Consequently, the force required to turn the pipe is equal to the torque of (rb-ra) Ta. This force is greatly less than that of previous meth-, ods'of wire winding a-pipe where the load which caused J Patented June 5, 1956 3 the tension has had to act over the entire length of the wire.
Referring now to the drawings in detail, Figures 1, 2 and 3 show the manner by which the pipe 21 is wound or wrapped with tensioned wire 20. The wire is first presented to drum 22 where it is wound thereon several turns as indicated at 25. The wire is then passed over wheels 26 and 27 and Wound on pipe 21. Wheel 27 is mounted on a threaded shaft 28 which is rotated by means not shown to advance the wire 20 during the winding operation. The drum 22 and pipe 21 are mounted co axially on shaft 23. Power is supplied by means of motor 24 to drive shaft 23.
The drum 22 acts as a torque regulating device to provide slippage when the tension on wire 20 is excessive. This will enable the wire to be wound on the pipe at constant tension.
It will be understood from the above discussion that a torque regulating device is theoretically not necessary.
However, in practice it has been found difiicult to attain the theoretical size of the drum to produce the proper stress.
This is readily apparent when it is considered that both the diameter of the drum and pipe must be maintained I absolutely constant in order to properly stress the wire.
In practice it is difficult to maintain the exact working ratios between the drum and pipe due to several factors. For example, the pipe may vary in diameter as in the case of a bell end pipe or creep of the wire around the drum may result in the wire being too loose, with attendant low stress when applied to the pipe.
Accordingly, this practical difiiculty is overcome by selecting a drum of smaller diameter than is necessary to properly stress the wire. This will result in the wire being overstressed. A torque regulating device is employed with the drum to permit slippage thereof to relieve the overstress in the wire to the desired point. By this arrangement it is possible to select a drum size which would normally overstress the wire to or over the breaking point. The torque regulating device would, under this condition, permit the drum to slip relative to the pipe thereby relieving the overstress. Consequently, a drum of small enough diameter can be used with a variety of pipe diameters. The drum operates to stress the wire beyond the proper stress and the torque regulating device serves to assure constant tension on the payed out wire to the proper degree.
The torque regulating device can be any suitable apparatus that will function as desired. It has been found that a brake is suitable for this purpose. While any of the well known types of brakes can be used as a controllable torque device to provide slippage to dissipate any desired portion of the power, the most common types are the mechanical dry friction type, the fluid coupling type, the magnetic-fluid type, the electromagnetic and electrostatic clutch. Of the above types of brakes the mechanical dry friction and magnetic fluid types are preferred. As shown in the drawings, Figures 2 and 3, the drum 22 is provided with a mechanical dry friction clutch which is designed to slip continuously with very dependable torque controlling characteristics to reduce the overstressed wire to a constant tension with the desired stress. As with any dry clutch, its static friction is greater than its moving frictiou. Therefore, in order to prevent chattering, the clutch is operated to slip at least several R. P. M. under normal operating conditions to bring it into the range of dynamic friction. As the slippage is kept small, the power dissipation is correspondingly small and hence the overall load is not appreciably increased.
Figures 5, 6 and 7 show a modified form of this invention. The pipe 30 to be wire wound is mounted on rubber rollers 31 and turned thereon. The weight of the pipe on the rollers develops sufficient friction so that the pipe may be turned by the rollers against the pull of tcnsioncd wire 32. Offset from the pipe and running laterally there to is a splined shaft 33. Carried thereon is a tapered brake drum 34 which is free to slide longitudinally along the splined shaft 33 but engages the splines so that the drum and shaft can rotate as a unit. A motor supplies the small force necessary to drive the pipe 30 and drum 34. The motor 35 rotates the splined shaft 33 which causes the pipe 39 to turn by means of a chain drive consisting of sprockets and 46 and chain 47.
In order to advance the wire 32 during the winding operation and to support the splined shaft 33, a rail or beam 36 of considerable rigidity is mounted beneath the splined shaft 33 so that the axes of the shaft and rail are substantially parallel. The drum 34 is mounted with a carriage 37 which rolls on the rail 36 by means of wheels 38. Passing through the carriage 37 and fixed nuts 40 is a threaded shaft 39 whereby the traversing of the drum is effected. This shaft 39 is rotated by means of motor 35 and a chain drive from the shaft 33 consisting of sprockets 42 and 43 and chain 44. As can be seen the rate at which wire will be payed out from drum 34 will be less than the take up rate of the pipe 30. This will impart a stress to wire 32. The relative diameters of the drum and pipe are such that wire 32 will be overstressed; a clutch similar to that shown in Figures 2 and 3 is contained within drum 34 and serves to relieve the overstress and maintain the tension on wire to a constant degree.
In Figure 8 is shown a scheme for winding pipe vertically. The pipe to be wound is placed vertically upon a turntable 51 which is mounted in a pit 52 in timber flooring 53 by means of a centering pin 54. On the turntable 51 is a sprocket 55. Located beneath the turntable 51 are turntable rollers 56. A chain drive is provided to supply power to turn the pipe 50 and it consists of sprocket 55, sprocket 58, and a chain 59 linking the two sprockets together. A speed changer 60 is mounted above sprocket 58 and the two are connected by a vertical shaft 61. A horizontal input shaft (not shown) extends from the speed changer 60 upon which is mounted a tapered drum 62 provided with a brake assembly similar to that shown in Figures 2 and 3. Power is supplied to turn the drum 62 and pipe 50 through the input shaft to the speed changer 60. A wire roll 63 on a swift 67 is suitably mounted to pay wire 64 to the tapered drum 62 and through guide rollers 65 to pipe 50 where it is wound. The guide rollers 65 are mounted on a screw traversing mechanism 66 in order to evenly feed the wire 64 along the length of the pipe 50. Consequently, as the various parts are so chosen as to effectively take up and wind the wire 64 on pipe 50 faster than it is payed out by drum 62, the wire 64 will be stressed. Also as the directions of rotation are pre-selected in accordance with the discussion in conjunction with Figures 1 and 4, the winding is carried out with the minimum expenditure of power. The wire 64 is normally overstressed by drum 62 and pipe 50. Therefore a clutch relieves the overstress and keeps the tension on the wire constant.
A method and apparatus for producing a stress in wire when winding on a tank with a low-power consumption is shown in Figures 9 and 10. A roller chain 70 is placed in frictional engagement with the face 71 of a tank wall 72. The chain 70 also meshes with a drive sprocket 73 located on a truck frame 74 provided with rear wheels 75 on axle 77 and a front wheel 76. The sprocket 73 is mounted on a shaft 78 which is driven by a motor 79. Also mounted on the shaft 78 is a tapered drum 80 containing a clutch assembly similar to that shown in Figures 2 and 3. Also mounted on a shaft 81 projecting from frame 74 is a wire roll 82 on a swift 83. The wire 84 is payed out from the roll 82 and passes several turns around the tapered drum 80 and then wrapped around the tank wall 72. Since the drive sprocket 73 is of greater diameter than the drum 80, the rate of linear forward movement of the truck relative to the wall will exceed the linear rate that wire 84 is payed out from drum 80; consequently, the wire will be stressed during the winding.
The manner by which multiple wire linear stressing can be accomplished for a roadbed, airstrip, beam or the like is shown in Figures 11 and 12. A car 90, provided with flanged wheels 91 on axles 98, rides on rails 92 which straddle the road surface or the like to be paved. The car 90 has a frame 93 which forms a platform 94. On the platform 94 are a series of wire rolls 95 each mounted on a swift 96. On the ends of a horizontal shaft 97 located centrally of the car 90 are driven sprockets 99.
Chains 100 mesh with the drive sprockets 99. One end 105 of the chains 100 is dead-ended at a distant point ahead of the car 90. The other end 101 of the chains 100 is connected to a tractor, winch, or other suitable device. The wire 102 on swift 96 passes between a pair of rollers 103 for initial braking, then several turns around a tapered drum 104 mounted on shaft 97 and finally is payed out onto the roadbed. The drum 104 is provided with a brake assembly similar to that described in conjunction with Figures 2 and 3. A drum 104 and a pair of rollers 103 are provided for each wire roll 95. Inasmuch as the drive sprockets 99 are of greater diameter than the drums 104, the wire 102 will be payed out at a slower rate than the rate of forward motion of car 90 when end 101 of chain 100 is pulled or take up of wire by the road. Consequently, the Wire 102 will be stressed during its pay-out. As the sprocket and drum tend to normally overstress the wire, the brake in drum 80 will permit it to slip and thereby relieve the overstress and maintain the tension on wire 102 to a constant degree.
In each of the assemblies shown in Figures 1, 5 and 8-10 inclusive the wire leading to the tapered drum is provided with a small initial back tension by any suitable means as explained with reference to Figures 1 and 4 for the purpose of preventing the wire from slipping uncontrollably around the tapered pay-out drum.
The tapered drum is the preferred form of a pay-out device. However similar devices may be employed depending upon the wire to be payed out. By way of example, in the case of paying out flat wire a tapered drum would be unsatisfactory and it would be necessary to use a conventional pay-out device for flat wire.
Although this invention has been shown in specific embodiments, it is nevertheless understood that various changes and modifications obvious to one skilled in the art may be made without departing from the spirit and scope of this invention.
1. Apparatus for continuously prestressing a concrete pipe comprising support means to hold a concrete pipe for rotation, a shaft, a drum rotatably mounted on said shaft, drive means connected to drive said shaft and said support means to rotate the concrete pipe, a source of wire, said wire leading from said source, being wrapped several turns around said drum and then being anchored to the concrete pipe, said drum having a diameter less than the diameter of the concrete pipe so that the wire is payedout from said drum at a rate less than the rate of wire take-up by the concrete pipe such that the wire tends to be excessively overstressed, and a slipping clutch located within the drum and drivingly connecting said shaft and said drum to enable said drum to slip relative to said shaft to reduce the stress of the wire to a predetermined value.
2. Apparatus for continuously prestressing a concrete pipe as defined in claim 1 wherein said support means is a rotatably mounted turntable.
3. Apparatus for continuously prestressing a concrete pipe as defined in claim 1 wherein said support means includes two pairs of rollers with one roller connected to be rotated by said drive means.
4. Apparatus for continuously prestressing a concrete pipe as defined in claim 1 wherein said drum and the concrete pipe are coaxially supported on a common shaft with the concrete pipe fixed to rotate with said common shaft and said drive means is connected to rotate said common shaft.
References Cited in the file of this patent UNITED STATES PATENTS 1,180,232 Brown Apr, 18, 1916 1,249,809 Noble Dec. 11, 1917 2,175,479 Miller et al Oct. 10, 1939 2,215,361 Miller et a1 Sept. 17, 1940 2,498,681 Hirsh Feb. 28, 1950 2,573,793 Kennison Nov. 6, 1951