US 3139663 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
July 7, 1964 J. BoswELL ETAL 3,139,653
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United States Patent 3,139,663 CONCRETE CASTING MACHINE Joseph I. Boswell, Vicksburg, and Tiiden Burke, Greenville, Miss., George F. Dixon, Jr., Carlisle, Pa., and Goode S. Lee, Warren County, Miss., assignors to the United States of America as represented by the Secretary of the Army Filed Sept. 29, 1961, Ser. No. 141,914
6 Claims. (Cl. 25-2) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.
The present invention relates to improvements in automatic apparatus for casting, on a production line basis, articulated concrete revetment mats employed to protect river banks and flood control levees from hydraulic erosion.
In particular, the present invention relates to improvements in casting plants of the type described in U.S. Patent No. 2,835,016, entitled Concrete Casting Machine, issued to George F. Dixon, l r., on May 20, 1958. Although concrete castings of virtually any shape could be produced in accordance with the present invention, the castings to be formed by the embodiment herein described in detail are of the standardized size and construction used by the U.S. Army Corps of Engineers in connection with flood control projects on the Mississippi River. The articulated mat castings are described in detail in the above-mentioned patent. Each casting is approximately four feet Wide, twenty-live feet long and three inches thick. Each casting covers approximately one-hundred square feet installed and is commonly referred to as a square Each articulated square is comprised of twenty concrete slabs approximately one foot Wide extending transversely of the casting and interconnected by a continuous Wire fabric embedded in the concrete at a plane about the midpoint of the thickness of each slab. When installed, the squares are connected end to end and side to side to form a continuous flexible mat of any desired size.
While the above-cited patent discloses the general concept of a machine for producing cured concrete castings on a production line basis Within a building to provide all- Weather operation by mechanical forming means using vibration compacting and low Water-cement ratios with accelerated curing in a kiln, the embodiment therein described has proven inefficient and therefore uneconomical to operate. This inefficiency is primarily caused by a low production rate due at least in part to the fact that the described apparatus required manual instigation of each of the various mechanical movements, with the conveyor system being stopped during each forming operation.
Therefore, the object of the present invention is to provide a substantially automatic casting apparatus of the type described having an increased output and therefore greater economy of operation.
Many additional objects and novel features of construction which directly contribute to an eicient and economic apparatus and the advantages which result therefrom Will be obvious from a reading of the following detailed description in which:
FIGS. la, lb and lc, taken together, show a plan layout of a concrete casting plant constructed in accordance with the present invention;
FIG. 2 is a side elevation of a chain sprocket and asociated structure located at the slack take-up works shown in FIG. lc;
FIG. 2a is a detailed plan vieW of an expansible rail joint shown in FIG. 2;
FIG. 2b is a detailed side elevation of the eXpansible rail joint of FIG. 2a; Y
FIG. 3 is a sectional elevation taken on line 3-3 bf FIG. 2;
FIGS. 4a, 4b and 4c are schematic illustrations of the operation of the casting forming station of the plant shown in FIG. la;
FIG. 5 is a time and sequence chart for the'casting forming station illustrated in FIGS. 4a, 4b and 4c;
FIG. 6 is a schematic illustration of the motion of a part of the casting station during operation;
FIG. 7 is a detailed diagrammatic elevational view, partly in section, of the casting station for the plant shown in FIGS. la, lb and 1c;
FIG. 8 is a detailed diagrammatic, transverse elevational view of the casting station, shown partly in section, taken on line 8 8 of FIG. 7;
FIG. 9 is Ian enlarged view showing details of construction, partly in section, of the nesting guides hereafter described in detail;
FIG. 10 is an enlarged view of the casting station as viewed from the left end of FIG. 8 showing details of construction, partly in section;
FIG. 1l is a top view of a portion of the casting forming station of the plant shown in FIG. 7;
FIG. 12 is an enlarged longitudinal sectional view showing details of construction of the casting forming station; l
FIG. 12a is a detailed top view of a part of a conveyor chain shown in FIG. 12;
FIG. 13 is a schematic diagram of the hydraulic system for actuating the various working elements of the casting forming station of the plant shown in FIG. 7;
FIGS. 14a and l4b, taken together, comprise a Wiring diagram of the electrical system for controlling the sequential operation of the hydraulic system shown in FIG. 13 and hence the operation of the castingY forming station;
FIG. 15 is a plan View of a device for engaging and removing cured concrete castings from the conveyor system of the casting plant; H
FIG. 16 is a side elevation of the device of FIG. 15;
FIG. 17 is a sectional end elevation taken on line 17-17 of FIG. 15 with a concrete mat in phantom outline;
FIG. 18 is a diagrammatic perspective of the concrete casting removal station; i
FIG. 19 is a detailed horizontal cross section of the cradle lifter guide shown generally in FIGS. 7 and 8; and
FIG. 20 is a detailed sectional view taken on line 20-20 of FIG. 19. ,A
In accordance with the present invention, a continuously moving conveyor system transports a large number of flat pallets successively to a forming or casting station Where a concrete casting is formed on each pallet. The pallets are then transported through a curing kiln Where a relatively high temperature and maximum humidity is maintained, to a casting removal station where a novel hoist removes the cured castings from the pallets, past a pallet cleaning brush Which removes concrete fragments which may remain on the pallets, to a station where two operators manually position a Wire fabric on the pallets, past an oiling station where oil is dripped onto the pallets to prevent the concrete from sticking to the pallets, and once again to the forming station to complete the' cycle. The entire operation is continuous and substantially automatic in that it requires only an operator for the conventional concrete mixing plant which supplies the forming station with plastic concrete, an operator stationed at the forming station to supervise and act in the event of a malfunction of the plant, an operator for the casting removal hoist, and two operators for positioning the Wire fabric on the pallets.
FIGS. 1a, 1b and 1c taken together show a plan viev`v` of a plant layout in accordance with the present invention.
aisaeea A suitable building indicated generally by 300 is of conventional design using vertical I beam columns 301 supported by a concrete foundation 302 and with siding 303 attached thereto. The building is divided into two general compartments, the rst being that shown in FIG. la which houses the casting forming and the removal stages of the operation, and the second shown in FIGS. 1b and y 1c which comprises a curing kiln.
The kiln begins at the partition 300:1 which has two openings therein to receive a conveyor system and includes all of the building structure shown in FIGS. lb and 1c. The kiln is properly insulated in a suitable manner so thatthe area can economically be maintained at a high temperature by five heating units with blowers, located generally at 30017. A steam generator is also provided at 300e` to maintain the humidity within the kiln as high as practicable. The heaters, steam generator and kiln building structure can be of any conventional type as the details of these components are not critical to the present invention. In an actual embodiment, the kiln is maintained at V180 F. at the entrance and 210 F. at the take-up works lwith a humidity of approximately 90 percent.
A concrete mixing plant of conventional design is shown generally at 305 and provides a volume of plastic concrete as demanded by the casting operation. The actual embodiment has four 50Vcubic feet capacity batch mixers capable of mixing 37 cubic feet every every four minutes, and suitable concrete and sand silos and a water tank.
An endless conveyor system for transporting the flat Vpallets upon which concrete castings are formed extends substantially the entire length ofthe building 300 and has an upper reach which travels from the part of the building shown in FIG. 1a into the kiln and a lower reach directly thereunder which travels in the opposite direction. By
using this system, the freshly formed castings carried by the system travel'twice the length of the kiln to provide ya longer curing time.
The conveyor system has two endless chains 336 and 307. The two chains are of the same link construction. Each link is comprised of a pair of parallel plates 308 which are interconnected by a pair of bradded bolts 308e which pass through spacer bushings 308b as shown in FIG. 12a. The successive links are pivotally connected at adjacent ends by pins 309. A roller 310 is journalled on cach pin 309. The rollers travel on chain tracks 311 which support the weight of the chains along both the upper and lower reaches. A side plate 312 extends along the outside of each chain track to maintain the chain on the track.
Synchronous movement of the two chains is provided by four separate electric driving mechanisms, each being of substantially identical construction. Two of the drives are in superimposed relation so that only one can be seen in FIG. la, generally at 332. One drives the upper reach of the conveyor system and the other drives the lower reach. Similarly, two drives are shown in superimposed relation in FIG. 1b generally at 383 with one driving the upper. reach and the other the lower reach of the conveyor system.
Now, describing one of the four drive systems, reference is made to FIGS. la, 1b, 12a, and 18 wherein an electric motor 331 drives a shaft 380 by means of a chain and sprocket arrangement. At each end of the shaft 330, which extends transversely across the building, a chain 384 drives a sprocket 385e on a shaft 386e which drives another sprocket 387a which drives lug chains Sa having lugs which mesh between the two spacer bushings 308b of each chain link and thereby drive the chains. Since each of the drive mechanisms for the two parallel chains uses a single motor with interconnected speed reduction gearing, the two chains must remain synchronized.
The ilelds of the four motors 381 which drive the reduction gearing are individually controlled by rheostats which are manuallyadjusted in a conventional manner to disl tribute equally the load between the four drive motors so that chain slack is fed to the take-up sprockets.
The conveyor system also includes a large plurality of cradles indicated generally at 365, each of which supports a pallet 460 upon which the concrete castings are formed. Each cradle is suspended like a seat on a Ferris Wheel from a pair of two-wheel dollies shown generally at 370 and 372 in FIG. 8. As shown in FIG. 10, the cradle frame is formed of two end plates 367 which are interconnected by I-beams 366 to form an open rectangular structure. Axles 36S protrude horizontally from the end members 367 and are journaled in a rectangular chassis frame 369. A pair of wheels 370a are disposed within the chassis and rotate on axles connected within the chassis frame 369.
The dollies 370 and 372 travel on cradle dolly tracks 356 which are located between and slightly below the chain tracks 311. On the upper reaches of the conveyor system, the cradle dolly tracks are indicated at 357 as in FIG. 7. The dollies, it will be noted, are so constructed as to operate in one position as the cradles are traversing the upper reach and in an inverted position as the cradles are traversing the lower reach. v
Each of the two endless chains has a plurality of pairs of corresponding lugs 38S, best shown in FIGS. 10 and 12, spaced at uniform intervals of about four and one-half feet. The lugs on the chains are so arranged that two opposing lugs are always in alignment as the chains are synchronously propelled by the driving means. Each dolly of each cradle has an inverted angle iron arm 386 extending outwardly from the chassis toward the chains. A right triangular wedge-shaped plate 387 is vertically disposed and connected to the end of arm 386. The vertical edge of the wedge plate 337 is aligned with the center of the stub axle 368 of the dolly. A pair of corresponding lugs 385 of the chain engages the vertical edges 388 of the two wedges 387 of a cradle and push the cradle along the cradle tracks.
As previously mentioned, each of the four turn around sprockets are of identical construction, with only the support structure for the various sprockets being different. The sprocket illustrated in FIGS. 2 and 3 has an axle 335 which extends outwardly from the conveyor system and is journaled in two bearings 333 and 334 which are supported by suitable I-beam structure hereafter described. Each sprocket has an inner radial flange 338 and an outer radial flange 337 which are supported by suitable spoke structure radiating from the axle. A plurality of teeth 339 are equally spaced around the periphery of the outer radial ilanges so that generally U-shaped notches 371:1 in the outer ends thereof will receive each roller of the chain as the chain passes around the sprocket. Teeth 371 are spaced around the inner radial flange to receive the axles 3238 of the cradles. The notches 371a of the teeth 371 are tapered so that the cradles are set slightly ahead of the chain as the two pass around the sprocket to insure that the chain lugs do not interfere with the cradle lugs and that the chain readily re-engages the cradles as they are released on the lower reach by the sprocket teeth- A curved continuation of each cradle track is attached to each sprocket support structure. Referring specifically to FIGS. 2 and 3, for example, the cradle tracks 357 of the upper reach extend from a curved portion 357:1 completely around the sprocket to straight portion 35717. This curved continuation is supported by plates 358 and 358b positioned between the two sets of teeth on the sprocket which plates are supported by structure 358e. The lower cradle track begins in a curved portion 373 and curves around to a straight portion 356 which is the lower reach.
As the cradles are engaged by the sprocket teeth, the curved continuation of the upper track 357 slowly turns the chassis frame from the horizontal. As the cradle approaches the horizontal position with the sprocket axle, the dollies slide outwardly into engagement with the lower track extension 373 and are lowered at a constant rate` until they are inverted and released on the lower reach 356 where they are re-engaged by the chain lugs and moved along the lower reach. Similar curved tracks for the chains 306 and 307 are not required because tension on the chain will keep the chains engaged with the sprocket teeth. Substantially the same operation occurs at the head-works sprockets, except of course the conveyor is moving the cradles from the lower reach to the upper reach.
Each of the four sprockets is associated with similar curved track and support structure as described heretofore. However, the support structure at the head-works, shown in FIGS. 1a and 18, is stationary while the takeup support structure located in the kiln, FIG. 1c, is horizontally movable to provide a means for taking up slack in the chains due to thermal expansion. A generally rectangular floating structure bounded by members 328, 329 and 327 supports the track continuations of both the upper and lower reaches. This rectangular structure has lower beams 321 and 322 which ride on sets of rollers 317 and 318, respectively, as shown in FIG. 3. The axles of rollers 317 are interconnected by bars 319 and 319rz and the axles of rollers 318 are similarly interconnected by bars 320 and 320a. These roller sets travel on I-beams 309C and 310e', respectively, which rest on concrete foundation 303e. Transverse beams 315 support a third I-beam 316. Brackets 324 are connected to cross beams 323 of the riding structure and embrace and slide along beam 316 to maintain the riding sprocket structure in proper alignment on rollers 317 and 318.
A cable 339:1 is connected to eyelet 340 of the riding structure and passes outside the kiln to weight tower generally indicated at 341, shown in FIG. 1c. The cable passes under a sheave 342 and over a second sheave 344 and supports a weight 345. The weight 345 continually exerts a force on the riding sprocket structure in such a manner as to keep the chains taut during thermal expansion and contraction. A similar take-up sprocket, riding support and weight tower therefor is provided for the other chain.
Each of the two chain tracks and each of the trolley tracks has an expansible joint between the permanent structure 374 in both the upper and lower reaches to permit free movement of the take-up works and yet provide a continuous uninterrupted track for the rollers. One type of expansible joint which has proven successful is shown in FIGS. 2a and 2b. A plurality of flat plates 375 are turned on edge, separated by spacers 376 and are connected to the riding structure by pins 377. A similar set of ilat plates 378 are alternately disposed between plates 375 within channel 330. Plates 378 are alternately separated by spacer plates 379 and are connected to stationary conveyor system support structure 374 by bolts 37451. Plates 375 slide relative to plates 378 as the floating take-up structure moves and continually provide a level track for the chain or cradle rollers as the case may be.
The conveyor system continuously transports the casting pallets in a complete cycle, which for convenience of discussion can be considered as beginning at the fabric station. As the pallets approach the fabric station, they are clean and ready for the casting operation. A platform 700 extends transversely of the conveyor system above the upper reach of the chain. A sliding access door 702 in building 300 provides a means where a bail of preformed fabric units can be conveniently placed on the platform by a suitable traversing hoist. Each preformed fabric element is comprised of copper coated steel wire and has three parallel longitudinal links interconnected at spaced intervals by ten rectangular loops extending transversely thereof as can readily be seen at 704 in FIG. la. Each pallet is provided with three spring loaded, boomer-type snatch latches at each end thereof which engage the ends of the long strands of the fabric. Two operators manually place a fabric element on each pallet as it emerges from under the platform.
The pallets with fabric latched thereon proceed under an oiling station 706 where a small quantity of oil is dripped from a perforated tube onto the surface of the pallets to prevent the concrete from sticking thereto. A suitable reservoir (not shown) feeds oil to the tube by gravity. Of course some oil will wet the fabric wires also, but since the wires are completely encased by concrete, this is unimportant, and oiling the pallets after the fabric station provides cleaner working conditions for the fabric operators.
Next the pallets proceed to a casting station where a concrete square is cast on each pallet. The operation of the casting station is schematically illustrated in FIGS. 4a, 4b, and 4c taken in conjunction with time and sequence chart FIG. 5.
Referring specifically to FIG. 4a, the conveyor system is moving from left to right as indicated by the arrow. Cradle D, position V, has a freshly formed casting thereon and is being transported away from thecasting station. Cradle C is resting at the casting station, position III, after having a casting formed thereon and is waiting to be re-engaged with the conveyor system. Cradles A, position I, and B, position II, are being transported by the conveyor and are approaching the casting station.
As cradle B reaches position II, a pair of limit switches are actuated which causes the transfer rod 10a to rapidly move both cradles B and C in advance of the normal chain travel. Cradle C is moved to position IV where it is almost immediately re-engaged by the chain lugs. Cradle B is moved to the casting forming station, position III. Six seconds are required to set the two cradles forward as can be seen by reference to operation No. 1, FIG. 5.
When the cradles reach the set forward position, additional limit switches are actuated which cause rod 10a to return to the original position, that shown in FIG. 4b. Two Y-shaped clamps 11a, one positioned at each end of the cradle, are raised by hydraulic motors and engage cradle stub axles 368 to clamp the cradle in position III.
Lifter head 12a is then raised by hydraulic motors 12 and passes through the open rectangular frame of the cradle and engages and lifts the pallet 460, pressing it against the bottom of mold box 9 as shown in FIG. 4b. The mold box is an outline of the castings to be formed. Aprons 9a and 9b are flush with the top of the mold box 9 and extend horizontally therefrom. The pallet 460 comprises the bottom of the casting mold, the mold box forms the sides, and the top of the mold is open.
Plastic concrete is deposited in hopper 13b and falls downward into feeder drawer 13a. The volume of concrete in the feeder drawer 13a is precisely that required to till the mold box 9 to the desired level. Feeder 13a is then forced outwardly across the mold box to the position shown in FIG. 4b. As the feeder passes over the mold box, the plastic concrete is deposited and fills the mold. The feeder immediately returns to the initial position in register with hopper 13b where it is refilled with plastic concrete for the next cycle. An apron 13C, which is flush with the top of the feeder drawer, serves as a valve on the bottom of the hopper 13b as the feeder passes over the mold box.
As the feeder returns to its dwell position, operations Nos. 6 and 7, FIG. 5, begin simultaneously. The upper vibrator 14a is lowered into the top of the plastic concrete in mold box 9, as shown in FIG. 4c. At the same time the upper vibrator 14a. begins to lower, eccentric vibrators connected to lifter head 12a start to vibrate. The lower vibrators on lifter head 12a serve to begin settling the plastic concrete and insure that the upper vibrator 14a' will be properly seated within the mold box. As the upper vibrator reaches the down position it also starts vibrating,
alsaeea operation No. 8. The lower vibrator stops vibrating three seconds after the upper vibrator starts. The upper vibrator vibrates for a total of nineteen seconds to thoroughly compact the plastic concrete into a homogeneous mass.
When the upper vibrator stops vibrating, the lifter 12a starts down, operation No. 9. The weight of the upper Vibrator remains on the plastic casting for one second and aids in forcing the freshly formed casting from the mold. Then the upper vibrators return to the up position, operation 11. When the lifter head and the upper vibrator have reached their dwell positions, those shown in FIG. 4a, clamps 11a. are lowered, operation 12. The casting station remains inoperative with all elements in the positions shown in FIG. 4a until cradle A is advanced by the normal motion of the chain to position II. Then the cycle repeats with transfer rod a moving cradle A into position III where a casting will be formed thereon and moving cradle B into position IV where it will be reengaged by the conveyor system and moved into the kiln.
After the cradles with the freshly formed castings thereon are re-engaged by the conveyor system, they proceed along the upper reach into the kiln where the temperature upon entrance is maintained at approximately 180 F. The cradles continue along the upper reach to the take-up sprockets where the temperature rises as high as 230 F. and then back along the lower reach to the kiln exit. The trip through the kiln requires less than two hours depending upon the speed of the chain. As previously mentioned, the humidity in the kiln is maintained as high as possible.
' The semicured castings then cool as they proceed along the lower reach to the mat removal station, hereafter described in detail FIGS. 7-13 show various detailed views of the casting station. The two transfer rods 16a can be seen above the upper reach on opposite sides of the cradles in FIG. 8. Each transfer rod 10a has two legs indicated generally at 10c and 10d. Referring to FIGS. 10 and 12, each lug is comprised of a wedge 391 pivotally carried on an axle 392 which is connected to a pair of vertical plates 392a on arm 390. Arm 390 is welded to rod 10a. Each wedge also has an arcuate slot 394 through which a pin 39? passes. The pin 393 is also secured to the plates 39251. This construction permits upstanding spikes 395 and 396 connected to the cradle dollies to pass under the inclined portion of the wedge 391 thereby pivoting the wedge upward until the wedge drops down behind the upstanding spike so that the rod can move the cradle dollies forward.V
Each of the four transfer rod lugs are of identical construction.
A rack and pinion arrangement is provided to insure that the two transfer rods 10a are always synchronized in movement. A rack 397 is mounted on top of each rod. A shaft (not shown) extends from one gear rack 397 transversely of the conveyor system to the other gear rack mounted on the other transfer rod. Pinions (not shown) are splined on each end of the shaft and mesh with the gear racks 397 to insure that motion of one transfer rod is mechanically transmitted to the other. This arrangement insures that the movement of the rods is synchronized despite unequal forces which might be exerted by the two hydraulic motors 10, shown in FIG. 13.
As previously mentioned, the transfer rods simultaneously set two cradles in advance of the chain travel. The forward cradle is re-engaged with the chain while the rear cradle is disengaged from the chain and left at the casting station. The chain track as it passes the casting station is raised so that chain lugs 385 pass over the triangular cradle lugs 383 which are connected to the dollies. To insure that tension does not lift the chain too soon and disengage a cradle before it reaches position II, upper rail 355b is positioned above the rollers to hold the chain As a cradle is moved from the casting station of the triangular cradle lug 387 connected to the dolly actually wedges under the chain lug 335, forcing it upwardly until the chain lug drops down behind Vertical edge 383.
Several means are employed to decelerate the cradles which are moved rapidly by the transfer rods to a stop at the casting station. At each end of the cradle, a drag brake 398 rides against plate 399 Which is connected to the bottom of angle iron extension 386 which extends outwardly from each cradle dolly. The drag brake is supported by levers 40d and 451 which are pivotally mounted on suitable support structure at 402 and 403, respectively, and are pivotally connected to the drag brake shoes at 404 and 405, respectively. Weights 406 and 407 are suspended at the other ends of the levers 4d() and 401, respectively, and continually urge the drag brake upwardly against plate 399.
Also provided at each end of the .cradle is a spring biased detent device having an arm 468 which is pivotally mounted at one end 499 and is` biased outwardly by spring 414B into engagement with the leading edge of the cradle. A cylindrical llobe 411 retains the cradle as it engages the leading edge thereof until the detent is depressed by eX- cessive force exerted on the cradle, which force occurs when the transfer rod moves the cradle from the casting station to the point of re-engagernent with the chain.
Y-shaped clamps 11a are provided at each end of the cradle and slide in sleeves 413 when raised and lowered by hydraulic motors 11. The clamps are raised into engagement with the stub axles 36S of the cradles to hold the cradles in position at the casting forming station.
The lifter head 12a is comprised generally of a rectangular frame which is raised and lowered by two hydraulic motors 12 supported by transverse beam 352. Four channel beams 423, 424, 425, and 426 extend longitudinally of the lifter head and are supported in spaced relation by triangular plates 427, 423, 429, and 430. Plates 427 and 428 are interconnected by spacer plates 431 and 432 which form a trunnion for pin 433 which is connected to rod 434 of one motor 12. Similar spacer plates and a pin pivotally .connect the piston rod 437 of the other motor 12 to the lifter head.
Ten vibrator segments are spring supported on the rectangular lifter frame. Each vibrator section has end plates 440 and 441 and plates 442 and 443 shown in FIG. 12 which are so spaced as to embrace the longitudinal beams 423, 424, 425 in close-fitting, sliding engagement to permit independent vertical movement of each vibrator section. Each Vibrator section also has cross bracing members 445, 446, 447, and 448 which extend longitudinally of the lifter head and cross braces 449, 45t), and 451 which extend transversely of the lifter head, and a fiat, horizontally disposed plate 452. Each vibrator section is supported by stiff coil springs 453 and 454 which are connected to channel beam braces 455. A conventional vibrator (not shown) comprised of an electrically driven eccentric is mounted on each spring supported vibrator section.
Each lifter head vibrator section has side lugs 456 and 45er: and a center lug 457 projecting above the plate 452. The lifter head -is so dimensioned as to pass through the cradle between the longitudinal beams 366 of the cradle and engage and lift the pallet 460 carried by the cradle. Pallet 460 is reinforced by cross braces 451 which are tapered at each end so that the pallet will align itself between the I-beams 366 to a certain extent. Pallets 460 have slots (not shown) which register and receive the lugs 456, 455g, and 457 of each vibrator section of the lifter head, so that the lugs protrude through the pallets and support wire fabric 476 at a height above the pallet corresponding to the midpoint of the casting.
A pair of guideposts 43) and 481 which are connected to the lifter head 12a are shown in FIGS. 8, 19, and 20. A wide flange 483 is rstiffened by flanges 483m and 483b