CA1169635A - Concrete railroad crosstie casting and handling system - Google Patents

Abstract

ABSTRACT
Concrete railroad crossties are mass-produced by slip-forming concrete using a specially adapted continuous casting machine (70, 230) to deposit concrete over a plurality of forms (34, 210) arranged side by side end end to end above an elongated casting bed (32, 209). Each group of side-by-side casting forms is preferably supported above the bed on a carriage (214) longitudinally moveable on rollers (220), thereby permitting relative movement of adjacent end-to-end carriages to compensate for concrete contraction when pretensioned wire strands in the concrete are detensioned and for a slight recoil action when adjacent end-to-end crossties are separated by sawing. An apparatus (140, 270) for lifting side-by-side crossties in groups is also disclosed. The apparatus (270) preferably is equipped with hydraulic jacks (282) for forcibly ejecting the concrete crossties from their forms.

Description

CONCRETE RAILROAD CROSSTIE CASTING AND HANDLING SYSTEM

The present invention pertains to high volume concrete casting and handling techniques, and more particularly to improved techniques for sli~forming prestressed concrete railroad ties.
It is a general object of the present invention to provide a system that overcomes the limitations of the prior art that have effectively prevented the mass production of concrete railroad crossties by slip-forming.
The prestressed concrete crosstie for supporting rails has found wide acceptance in the railroad industry as a substitute for ln the traditional wooden railroad tie. Until now, however, there has been only limited success in adapting state-of-the-art techniques for mass production of concrete crossties. Although casting by slip-forming has become common place in the production of prestressed concrete products having regular cross-sectional shapes such as building panels and structural beams and columns, slip-forming of the industry standard concrete crosstie has not yet been widely attempted. Rather, it is still the predominant practice in the industry to manufacture concrete crossties using conventional wet casting techniques wherein concrete is poured into molds of the desired shaped.
Those skilled in the art will appreciate that slip-forming provides m any advantages over such conventional wet casting techniques. Wet casting requires full forms around the sides and ends of the concrete product, thereby not only adding to the cost, but also tending to allow air bubbles and voids to form along the sides of the product. Slip-forming, on the other hand, employs moving side forms which tend to eliminate air bubbles and voids by virtue of the traveling effect of the form along the sides of the product being cast.

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~- 2 -When the product being cast is a crosstie, prestressed cables must be employed, thus requiring bulkheads and seals at the ends of each form or mold used in a wet cast process. Slip-forming of concrete crossties, however, permits the elimination of bulkheads since the crossties are formed continuously end-to-end and later separated by sawing. In addition to the very favorable economic advantages of mass-producing crossties by slip-forming, those skilled in the art will appreciate that a number of practical benefits are also derived from the continuous end-to-end formation. For example, in conventional wet casting systems using full forms for each crosstie, an undesirable sieving effect occurs at the ends of the crossties such that concrete tends to squirt through the spaces around the prestressed cables within the endwalls of the forms. Such sieving action adversely affects the integrity of the concrete at the ends of the crossties where the best possible concrete is required for forming a good bond with the prestressed cables. Such deficient bonds are eliminated by the present method of continuous end-to-end formation and separation-by sawing.
An additional advantage of slip-forming is that the very high strength requirements needed for concrete crossties are more readily achieved using low slump concrete which can readily be slip-formed but is difficult to wet cast due to its relatively low water content.
In accordance with an aspect of the invention there is provided a system for slip-forming concrete crossties, comprising an elongated casting bed, a plurality of molds arranged side by side and end to end on the casting bed, each mold having a casting plate supported above the casting bed by a frame, a continuous casting machine movable along the bed while the molds remain stationary, the machine having means for forming a casting chamber above each casting plate, said means making a `~2 3'5 - 2a -slidable fluid seal at points of sliding engagement of the casting chamber means with each casting plate as the machine moves along the bed.
In accordance with a first embodiment of the inventive casting system, a plurality of molds are positioned side by side and end to end on an elongated casting bed, each mold having an upper surface conforming to an irregular shaped surface of the crosstie to be formed thereon, the upper surface varying in height in the direction of the length of the bed. Then wire strands are arranged in precise patterns over the molds and stressed to a predetermined tension. Next, low slump concrete material is slip-formed over the molds to the shape of crossties in inverted orientation and then allowed to harden. The wire strands are then detensioned and the concrete is cut at the ends of adjacent molds to form separate crossties.

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The slip-forming of crossties is performed using a continuous casting machine specially adapted in accordance w;th the present invention to fluidize low slump concrete to permit slip-iorming of crossties in inverted orientation. The machine is equipped with a casting hopper for maintaining a predetermined concrete hydrostatic head pressure, internal vibrators for fluidizing low slump concrete below the casting hopper, a generally horizontal pressure plate rearward from the casting hopper and a plurality of legs extending generally downward from the pressure plate to form the sides of the crossties while slideably and sealably engaging the edges of the molds upon which the crossties are slip-formed.
- From experimental tests using the first embodiment of the inventive casting system, it has been found that the forms or molds upon which the crossties are slip-formed have a tendency to move by a small but significant amount both upon the detensioning of the prestressed cables at the ends of the casting bed and upon separating adjacent end-to-end crossties by sawing. It has also been found that resistance to the movement of the forms can damage the forms as well as the crossties themsleves. Furthermore, uncontrolled movement of the forms makes their realignment for the next casting operation more difficult and time consuming. It would therefore be desirable to provide a technique for eliminating the resistance to the relative movement of adjacent end-to-end forms over short distances during the detensionsing and sawing steps of the process while maintaining general alignment of the forms on the casting bed.
Another area of difficulty concerns the task of removing finished crossties from their forms. It has been found to be difficult and very awkward to remove the concrete crossties from their forms due to the tendency of the concrete to stubbornly adhere to the surfaces of the forms even when a release agent has been used.
Accordingly, it would be desirable to provide 8 technique for quickly removing crossties side by side in groups from their forms for transport to a stacking area or the like without dislocating or damaging the forms.

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"' These additional objectives are accomplished in accordance with a second embodiment of the inventive casting system. Briefly, each group of adjacent side-by~ide forms is mounted on a carriage assembly above the casting bed, each carriage S assembly being intercoupled with an adjacent carriage assembly to provide a plurality of carriage assemblies arranged end to end longitudinally along the bed, each carriage assembly being supported by rollers or the like so that adjacent carriage assemblies are freely moveable relative to each other within controlled limits. Removal of the crossties from their forms is accomplished by means of an improved hoist apparatus having a plurality of parallel bars slidable between adjacent side-by-side crossties for lifitng the crossties by contacting sloping portions of their sides, the improved hoist apparatus including hydraulic jacks or the like for breaking the crossties loose from their forms prior to lifting and transporting them from the casting bed.
Additional features of the present invention may be understood best by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein:
FIGURE 1 is a view in perspective of a prestressed concrete crosstie mass produced in accordance with the present invention;
FIGURE 2 is a side elevational view thereof;
FIGURE 3 is an end view thereof;
FIGURE 4 is a view in perspective of a portion of a casting bed with a plurality of molds arranged thereon in accordance with the inventive system;
FIGURE 5 is a plan view of a plant layout for mass producing concrete crossties in accordance with the inventive system;
FIGURE 6 is a side elevational view of one of the molds shown in FIGllRE 4;
FIGURE 7 is an end view thereof;
FIGURE 8 is an enlarged view of a portion of FlGURE
6;

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l.~t>~3635 FIG URE 9 is a plan view of the portion of the mold shown in FlGURE 8;
FlGURE 10 is a vertical cross section through a portion of a casting machine and underlying molds during casting of concrete crossties on a casting bed in accordance with a first embodiment of the inventive system;
FIGURE lOA is an enlarged view of a portion of FIGURE
10;
FIGURE 11 is a partially sectioned side view of a portion of the casting machine as it moves from right to left on a casting bed, the view illustrating a casting hopper and one of a plurality of stinger vibrators;
FIGURE 12 is a cross section taken along line XII-XII of FIGURE lOA;
FIGURE 13 is a side elevational view of a portion of freshly cast concrete at an end joint between two molds of the type shown in FIGURE 6;
FIGURE 14 is a view in perspective of a first hoist apparatus for removing concrete crossties from a casting bed;
FIGURE 15 is an end view of the hoist apparatus of FIGURE 14 shown in engagement with eight side-by-side concrete crossties just prior to being lifted from their molds;
FIGURE 16 is a view in perspective of an apparatus for inverting the orientation of a plurality of side-by-side crossties shown on a railroad flat car;
FIGURE 17 is a plan view of the apparatus of FIGURE 16 shown separately;
FIGURE 18 is an enlarged view in perspective of a corner portion of the apparatus of FIGURE 17;
FIGURE 19 is a side elevational view of a plurality of crossties stacked atop each other in their end-use orientation;
FIGURE 20 is a side elevational view of a portion of a casting bed illustrating carriage-mounted forms disposed thereon for casting concrete railroad ties in inverted orientation in accordance with a second embodiment of the inventive system;

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FIGURE 21 is a vertical cross-section taken along line 21-21 of FIGURE 20;
FIGVRE 22 is a vertical cross-section similar to FIGURE 21 but with the inclusion of a continuous casting machine depicted during the inventive process of slip-forming concrete crossties, the section being taken along line 22-22 of FIGURE 28;
FIGURE 23 is a vertical cross-section similar to FIGURES 21 and 22 at a subsequent stage of the inventive process illustrating four side-by side crossties after slip-forming;
FIGURE 24 is an enlarged fragmentary side view, partially in elevation and partially in section, illustrating a typical joint between ends of adjacent carriages;
FIGURES 25-27 are end elevational views schematically illustrating the operation of an improved hoist apparatus during steps in a process for removing concrete crossties from their forms in accordance with the invention, the various background features being left out for sake of clarity;
FIGURE 28 is a vertical cross-section through the corltinuous casting machine of FlGURE 22 and the underlying forms and casting bed, the view being taken longitudinally through the center of one of four pairs of end-to-end forms; and FIGURES 29 and 30 are vertical cross-sections taken respectively along lines 29-29 and 30-30 of FIGURE 28.
Now referring to the drawings, presently preferred embodiments of the invention as well as various modifications and alternatives thereof will be described in detail, similar reference - numerals designating similar parts in the various figures.
With reference to FlGURES 1-3, a concrete railroad crosstie, which is mass produced in accordance with the present invention, is designated generally by reference numeral 10. The crosstie 10 has a flat base 12, upstanding ends 14, inwardly leaning sides 16, and 8 top 18 that gives the crosstie 10 an irregular height dimension varying along its length. The top 18 comprises seven planar r ,i . - ........................ . .
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l~`t9635 surfaces 20 having chamfered edges 21 adjoining the sides 16 as shown.
The planar surfaces 20 vary both in orientation and height above the base surface 12. In accordance with a unique feature of the present invention, the sides 16 of the crosstie 10 each have a dual-planar configuration including sloping surface portions 16a for optimum stress distribution and vertical surface portions 16b specially adapted to facilitate slip-forming the crosstie 10 using a continuous casting machine, as will become apparent from the following description thereof. Both side surface portions 16a and 16b extend the entire - 10 length of the crosstie 10. The vertical surface 16b, which varies in height, is about 1/2 inch at its narrowest points in the center area denoted as 16b. Although the geometry of the crosstie 10 as illustrated is presently preferred, it will be appreciated from the following description that a variety of alternative shapes can be produced in accordance with the invention to achieve both cost reductions and performance improvements in the state of the art of concrete crossties.
Fastening of the rails (shown in phantom in FIGURE 2) to the crosstie 10 is achieved in a conventional manner using iron inserts 22, each rail being mounted between an inner and an outer insert separately denoted in FIGURE a by the appended letters "a"
and "b", respectively. The inserts 22 each have a stem portion 24 (see FIGURES 2 and 3) anchored in the concrete crosstie 10 and a h~ad portion 26 extending out the top 18, each head portion 26 including an eyelet 28 for retaining a rail fastening clip (not shown). The inserts 22 are precisely located in relationship to top surface portions 20a and 20b, upon which the rails are mounted in the slightly sloped manner shown in PlGURE 2. Eight pretensioned wire strands, collectively designated by numeral 30 in FIGURE 3, are arranged in a precise pattern for prestressing the crosstie 10 acording to conventional techniques to enable it to withstand the superimposed loads of rail traffic. It will be appreciated that various other arrangements and numbers of wire strands can be used with satisfactory results, one alternate arrangement being shown in FIGURES 22-24 described below.

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li~'3~35 Referring to FIGURE 4, the crossties lO are cast side by side and end to end in inverted orientation on a casting bed 32 of several hundred feet in length using a plurality of prearranged molds 34 with inserts 22 installed therein as shown. The molds 34 are disposed directly on the bed 32 in accordance with one casting system of the present invention. An alternate casting system of the present invention wherein casting forms are mounted on carriages which are supported above a casting bed is described in detail below with reference to FIGURES 20-30. Mass production of crossties lO in accordance with the inventive casting system is achieved by slip-forming using a specially adapted continuous casting machine, the pertinent details of which are described below. The casting bed 32 is equipped with Gshaped side channels 36 for guiding such a casting machine along the length t1 ereof.
1, Now referring to FIGllRE 5, a preferred concrete casting plant layout for mass producing crossties lO is schematically illustrated and designated generally by reference numeral 50. The plan 50 is arranged with pairs of casting beds 32 disposed adjacent to auxiliary rail line or tracks 52, which are joined to a main track 54, for delivering finished crossties 10 to a railroad system. A first group of overhead cranes 56 is cooperatively disposed in relation to the casting beds 32 such that each crane 56 serves a pair of beds 32 and an adjacent rail line 52. Located at the ends of the beds 32 nearest the main track 54 are stacking areas 58 for temporary storage of crossties 10. A second group of overhead cranes 60 is cooperatively disposed in relation to the stacking areas 58 such that each crane 60 serves one stacking area 58 and an adjacent rail line 52 as shown.
Flat bed railroad cars 62 are used to carry finished crossties 10 from the beds 32 to the stacking areas 58.

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1l69635 Prior to casting the crossties 10, wire srands are drawn from coils 64 and strung through heads 66 at opposite ends of each bed 32, the heads 66 being constructed to provide eight precise patterns of wire strands 30 as mentioned above in conjunction with PIGURE 3. Hydraulic rams, schematically represented by the triangular shapes 68 in FIGURE 5, are then used to pretension the wire strands 30 according to conventional techniques.
Once the wire strands 30 are pretensioned in place over the molds 34 with the iron inserts 22 properly arranged therein, slip-forming of crossties 10 can proceed using a continuous casting machine, schematically illustrated in FIGURE 5 and designated by reference numeral 70. The machine 70 is supplied with low slump concrete by a concrete delivery vehicle 72, having a suitable chute 74 for such purpose. By low slump concrete is meant concrete having a lS slump measurement of less than about two inches as determined in a standard concrete consistency test. The casting machine 70 is equipped with a first hopper 76 for receiving concrete through the chute 74 and 8 second hopper 78, referred to in the art as a casting hopper, for forming an appropriate hydrostatic head pressure to permit momentary fluidization of the concrete during the casting process. Concrete is transferred from the first hopper 76 to the second hopper 78 by conveyor means as will be described more fully below.
Now referring to FIGURES 6-9, the details of the mold 34 used in one embodiment of the inventive casting system will be described. The mold 34 comprises a casting plate 80, which is supported by an underlying frame 82. The plate 80 has upper surfaces 84 that conform in precise complementary fashion to the top 18 of the crosstie 10. The surfaces 84 are treated with a release agent in a 3~ conventional manner prior to casting. The plate 80 has vertical outer edges 86 separated by precisely the same distance flS are the opposed vertical surfaces 16b of the crosstie 10. Included in the plate 80 at four locations are openings 88, two of which are seen in FIGURE

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9, for receiving the iron inserts 22 as exemplified in FIGURE 4. The inserts 22 are precisely located in the openings 88 in accordance with a unique feature of the present invention to be described below.
The frame 82 of the mold 34 comprises first and second supports 90 and 92, which are preferably L-shaped as seen most clearly in the view of FlGURE 7. The supports 90 and 92 are mechanically interconnected such as by welding to metal webs 94 located at spaced intervals. Some of the webs 94 conveniently extend above the supports 90 and 92 to engage the casting plate 80 as seen in F~GURES 6 and 8. The casting plate 80 is also supported at spaced intervals as seen in FIGURE 6 by ~shaped metal angles 96. The casting plate 80 is preferably supported at its ends and near each of six points along its length where a change in slope occurs.
A first method of mass producing crossties 10 in accordance with the invention will now be described in conjunction with ~IGURE 10, which schematically illustrates crossties 10 being cast by slip-forming. The view of FIGURE 10 is a cross section taken through a rear pressure plate 100 of the continuous casting machine 70 and underlying molds 34 and casting bed 32 along a line of outer inserts 22b looking in a direction toward the ends of the molds 34 nearest the inserts 22b. Seen in the background is a frame member 102 equipped with rollers 104 engaging the side channels 36 for supporting and guiding the mach~ne 70 as it travels along the length of the bed 32. The pressure plate 100 is located at a precise height above the bed 32 and rigidly secured to the machine 70 in a suitable manner, such as by attachment to the frame 102 as shown. Rigidly affixed to the pressure plate are downwardly extending legs 106, which resiliently engage the edges 86 of the molds 34 to form a fluid seal therewith. Thus, it will be appreciated that the molds 34 in combination with the pressure plate 100 and legs 106 form a plurality of casting chambers, each of which conforms to the precise outline of a crosstie 10 in inverted orientation.

~1~;'3ti35 In accordance with a presently preferred technique, the lower portions of the legs 106 are resiliently forced against the edges of the molds 34 by means of pneumatically operated hoses 105, which are longitudinally disposed along the legs 106 in the manner depicted in FIGURE 10. Alternatively, the legs 106 can be resiliently forced against the edges of the molds 34 by means of convention springs (not shown).
A presently preferred technique for fluidizing the concrete in the casting chambers wiIl now be described with reference to FIGURE 11, which illustrates the casting hopper 78 and one of a plurality of stinger vibrators 107. The vibrators 107 are located in the concrete below the casting hopper 78 and just ahead of the rear pressure plate 100. The casting hopper 78 is filled with concrete by conveyor means, which preferably comprises an auger 108 equipped to convey the concrete at a controlled rate. The stinger vibrators 107 produce localized internal vibration within the region of concrete below the casting hopper 78 to cause the concrete to become fluidized as it passies under the rear pressure plate 100 to ensure that the casting chambers will be completely filled with concrete as shown in FIGURE 10. As the vibrators 107 move away the concrete becomes less fluidize~ until it is sufficiently rigid to retain its shape, whereupon it slips out of the casting chambers at the rear of the casting machine 70. It will be appreciated that additional vibrators (now shown) can be employed to advantage up within the casting hopper 78 or downstream from the casting hopper 78 within the casting chamber or both as deemed desirable for the consistency of concrete being cast. It will also be appreciated that a special screen (not shown) can be empoyed if desired at the downstream end of the pressure plate 100 to give the crossties a striated base surface for improved surface contact with ballast in a railroad bed.

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An important feature of the legs 106 is ~lustrated in greater detail in the enlarged view of FIGURE lOA. The legs 106 each have stoping portion 106a and a vertical portion 106b for forming the respective sloping and vertical surfaces 16a and 16b of the crossties 10. As the machine 70 moves down the length of the bed 32, the legs 106 slide along the molds 34 such that the variable height edges 86 of the casting plate 80 rise and fall in sliding engagement with the vertical portions 106b of the legs 106. Thus, the unique shape of the crosstie 10 shown in FIGURES 1-3 permits slip-forming of the concrete while main-taining a fluid-tight seal at the edges 86 of the casting plate 80.
Now referring to FIGURE 12 in conjunction- with FIGURE lOA, a preferred technique for precisely locating the iron inserts 22 in the openings 88 of the molds 34 will be described. An elastomeric locating and sesling member 109 is placed in each opening 88 as shown, and then the inserts 22 are laid in place therein. The elastomeric member 109 is supported by metal rests 110, which are securely fastened to the ~shaped supports 90 and 92. The member 109 has an inner surface 112 generally conforming to the edges around the opening 88 of the plate 80. Thus, the member 109 serves both to locate the insert 22 and form a surrounding fluid seal with the plate 80. The member 109 preferably comprises a moldable, weather-resistant rubbery polymer such as polyisoprene, polybutadiene, or butadiene-styrene copolymer, but most preferably a polyisoprene such as neoprene.
According to a unique feature of the present invention, the inserts 22 are secured in place in the molds 34 by means of locating pins 116, which also serve to make a fine adjustment for precise positioning of the inserts 22. The supports 90 and 92 are provided with holes 118, seen clearly in FIGURE 8, adapted to receive the locating pins 116 at a precise level for positioning the inserts 22 relative to the casting plate 80. Accordingly, the centers of the holes 118 are located at a precise predetermined distance below the sloped .~ .
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surface of the casting plate 80. The elastomeric member 109 is constructed to hold the inserts 22 initiaUy slightly above their final position. Each locating pin has a tapered leading edge 120 flS shown in PIGURE lOA to facilitate insertion of the pin 116 into the eyelet 28 in its initial offset position. After passing through the first support 90 and the member 109, the leading edge 120 of the pin 116 encounters the insert 22 in the eyelet 28 at a point designated by numeral 122. Then, as the pin 116 is driven into the eyelet 28 the insert 22 is pulled down slightly into proper position. With the pin 116 extending through the hole 118 of the second support 92, the insert 22 is securely held in precisely the proper position by the pin 116 and the elastic force of the member 109.
The locating pins 116 are preferably arranged in gang fashion as seen in FIGVRE 10, wherein each pin 116 is secured to a control rod 124 by connecting bars 126. The control rod 124 is equipped with a head piece 128 to facilitate mechanical actuation of the rod 124 and gang of locating pins 116. Thus, each row of inserts 22 can be secured and precisely positioned in the molds 34 prior to casting by driving the rod 124 from left to right in the view of FIGURE 10 so that the locating pins 116 pass through the supports 90 and 92 and the inserts 22 therebetween. Initial installation of the control rod 124 and gang of pins 116 under the casting plates 80 of adjacent molds 34 is achieved by passing the control rod 124 through ,elongated openings 130 in the supports 90 and 92. The openings 130 are sufficiently wide to permit the connecting bars 126 to pass therethrough when the rod 124 and gang of pins 116 are oriented 90 degrees from that shown in FIGURE 10.
Now referring to FIGVRE 13, a typical joint at adjacent ends of two molds 34 will be described. Freshly cast crossties 10 are shown in integral end-to-end relationship prior to separation by sawing along a line designated by numeral 132. lnterposed between the two molds 34 and forming a fluid seal therewith is an elastomeric spacer 134, which preferably comprises a suitable weathe~resistant material similar to that of the member 109 described above. The spacer ~.

63~3 134 terminates flush with the edges 86 of the casting plates 80 (see also FIGURE 4) so as not to interfere with the legs 106 of the casting machine 70 as it slip-forms the concrete crossties 10 in situ thereover in the manner previously described. After the concrete has been allowed to harden to a sufficient strength, the wire strands 30 are detensioned at the ends of the bed 32. The resulting stress applied to the crossties 10 along the length of the bed 32 causes a slight contraction of the concrete, which is compensated for between adjacent molds 34 by contraction of such elastomeric spacers 134.
Thereafter, the prestressed concrete is sawed through along each line 132 in accordance with known techniques. The elastomeric spacers 134 preferably extend upward beyond the ends of the molds 34 to abut the lowermost wire strands 30 to provide a clean break between crossties when the lowermost wire strands are cu-t.
After separation, the crossties 10 are removed from the casting bed 32 in accordance with another mportant feature of ths present casting system as will now be described in conjunction with FIGURES 14 and 15. Referring in particular to FIGURE 14, a unique hoist apparatus, generally designated by reference numeral 140, comprises a plurality of bars 142 assembled in a fork-like configuration. Cross braces 144 support the bars 142 from above and maintain a parallel alignment and precise spacing thereof as shown.
The apparatus 140 is equipped to be lifted by one of the overheadcranes 56 in a suitable manner, such as by cables 146 and eye bolts 148, which are preferably secured to opposite ends of the braces 144 as shown.
With particular reference to FIGURE 15, a group of eight finished crossties 10, which have been separated at their ends by sawing, are shown just prior to being lifted out of their molds 34 by the hoist apparatus 140. It will be appreciated that the crossties 10 present handling problems due to their weight, shape and close-packed arrangement on the casting bed 32. In particular, the sawed ends of adjacent end-to-end crossties 10 would be quite difficult to access without widening the space therebetween, which would otherwise be only as wide as the saw blade used to cut the concrete `~

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9~i35 into separate crossties 10. Thus, in accordance with the present casting system, the crossties 10 are removed from the bed 32 using the hoist apparatus 140 by sliding the bars 142 between the free ends of adjacent side-by-side crossties 10 and then lifting the apparatus l40 until the bars 142 engage the sides of the crossties I0. The bars 142 preferably have sloped edges giving them a generally wedge shape configuration such that they conform to the sloping portions of the sides of the crossties 10, as seen in FIGURE 15. Thus, a large area interface 150 is formed beween each bar 142 and each crosstie 10.
~hen the apparatus 140 is raised using the cables 146, the crossties 10 are lifted out of their molds 34 with the bars 142 contacting only the sides of the crossties 10. Accordingly, it will be appreciated that the hoist apparatus 140 permits removal of crossties 10 from the bed 32 without having to contact the ends 14 of the crossties 10 and without having to move the molds 34 from their original positions. Using the hoist apparatus 140, the bed 32 may be cleared of crossties 10 in groups of eight while working from one end of the bed 32 to the other in a systematic manner. It will be appreciated that the hoist apparatus 140 may be modified for carrying greater or lesser numbers of crossties 10, an alternate hoist apparatus for carrying four side-by-side crossties being described below with reference to FIGURES 25-27.
After the crossties 10 are removed from the casting bed 32, they are loaded on railroad cars 62 for transport to the stacking areas 58 located nearby as depicted in FIGURE 5. Once the bed 32 is completely cleared of crossties 10, the molds 34 are returned to their original positions and alignments since, as mentioned above, releasing the stress on the wire strands 30 causes the crossties 10 flnd molds 34 to move to compensate for the shock of the stress release.

i9635 Certain details of the hoist apparatus 140 deserve further exp3sition. ln order that the bars 142 may be slipped between the sides of adjacent crossties 10 without jamming, attachment of the braces 144 to the bars 142 is achieved by extensions 152, which are 5 constructed so that when the bars 142 engage the crossties 10 as shown in FIGURE 15, the braces 144 will be positioned a few inches above the crossties 10. The extensions 152 are narrower than the distance between the uppermost edges of the crossties 10, so that the apparatus 140 may be lowered to permit the braces to lie directly on the crossties 10. In addition, the lowermost edge of each bar 142 is narrower than the distance between adjacent molds 34, so that the molds 34 will not interfere with the sliding movement of the bars 142 therebetween when the apparatus 140 is in its lower sliding position.
Now referring to FIGURES 16-18, a unique apparatus for transporting and inverting the orientation of crossties 10 is illustrated and designated generally by reference numeral 160. The apparatus 160 comprises a frame 162 rotatably mounted in an overhead trussed assembly 164. The frame 162 is equipped to lift a plurality of side-by-side crossties 10 from a rsilroad car 62, and invert the orientation of the crossties 10 from that shown in FIGURE 16 by 180 degrees for stacking in upright orientation in the stacking areas 58 (see also FIGURE S). Groups of eight side-by-side crossties 10 are removed from the railroad car 62, then inverted and stacked atop each other as depicted in FIGURE 19 using spacers 166 to prevent damage to the inserts 22.
The procedure for removing the crossties 10 from the railroad car 62 is as follows: The apparatus 160 is first lowered into position with the frame 162 surrounding a group of eight crossties 10 as shown in FIGURE 16. Then hydraulic jacks 168 are actuated to 30 bring plates 170 into contact with the opposite ends of the crossties 10. The plates 170 are slidably mounted in side walls 172 of the frame 162 in a suitable manner. Each plate 170 has a lower lip 174, best seen in FIGURE 18, for alignment with respect to the ends of the crossties .~

6~s 10 prior to actuation of the jacks 168. After aligning the lips 174 under the edges of the crossties 10, the jacks 168 cause the plates 170 to be driven forcefully against the ends of the crossties 10 so that the weight of the crossties 10 can be supported by friction alone at the ends tllereof. It will be appreciated that each of the crossties 10 of the group of eight are nearly identical in length by virtue of being sawed side by side on the casting bed 32 as discussed above.
However, should slight variations in length within groups of crossties 10 prevent adequate friction contacting force with shorter ones of the crossties 10, a hard rubber cushion (not shown) can be installed on each plate 170 for obviating such problems.
With the plates 170 forcefully engaging the ends of the crossties 10, the apparatus 160 is lifted by means of a hook 176 to remove the group of eight crossties 10 from the flat car 62. The trussed assembly 164 that carries the frame 162 is equipped with a cross beam 178 disposed between vertical beams 180 at a height sufficient to permit the frame 162 to be rotated through an angle of 180 degrees, thereby inverting the crossties 10. The frame 162 is caused to be rotated in a suitable manner such as by an appropriately controlled motor 182 disposed at one side of the frame 162 as depicted. The motor 182 is equipped to rotate a shaft 184 using gears 186 and 188, the shaft 184 being axially joined to the frame 162 to provide a balanced load. When the frame 162 has been rotated by 180 degrees to invert the orientation of the crossties 10, the frame 162 is lowered into position over the stacking area 58 so that the crossties 10 come to rest on the stacking area 58 or on spacers 166 above a previously unloaded group of crossties 10. Then, the jacks 168 release the plates 170 so that the apparatus 160 can be lifted away from the stack of crossties 10 and returned to the nat car 62 for the removal of additional crossties 10. Thus, it will be appreciated that the apparatus 160 is capable Or inverting groups of crossties 10 to their end-use orientation during the removal and stacking process just described. It will also be appreciated that, although the above-described sequence of events is preferred, the step of rotating the crossties 10 can be performed at any convenient time in the process ~ 9635 as, for example, after stacking during loading of crosstîes lO onto railroad cars for shipment from the plant 50 to their place of installation.
Now referring to FIGURES 20 and 21, an improved 5 system is illustrated for slip-forming concrete crossties above an elongated casting bed 209. The improved system includes an arrangement of casting forms 210 disposed side by side and end to end above the length of the casting bed 209. The forms 210 each have an upper surface 211 of varying height upon which the concrete crossties 10 are cast in accordance with the invention. The upper surface 211 of each form 210 has upwardly angled edges 212 to provide chambered corners on the crossties. In the particular example shown, the forms 10 are arranged side by side in groups of four as seen in FIGURE 21.
Four metal inserts 213 extend upward from the casting surface 211 of each form 210 as seen best in the view of FIGURE 20. The inserts 213 become anchored in the concrete, as will be appreciated from the subsequent figures, to provide a means for fastening rails (not shown) to the crossties as explained above with reference to FIGURE 2.
Each group of four side-by-side forms 210 is supported by a carriage assembly, designated generally by reference numeral 214. Each carriage assembly 214 comprises a plurality- of longitudinally spaced cross beams 216 secured at their ends to a C-shaped side support 218. Each carriage assembly 216 is supported at its four corners by rollers 220, which are journaled in base members 222 situated atop the casting bed 209, the rollers 220 being flanged to prevent lateral movement of the carriages 214. It is presently preferred for ease of alignment that the rollers 220 and associated base members 222 will be provided in assemblies 224 as seen in the view of FlGURE 20 wherein each roller assembly 224 supports the opposed corners of adjacent carriage assemblies 2}4.

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Each carriage assembIy 214 is preferably provided with eight of the transverse cross beams 216, two at each carriage end and six at various intermediate positions corresponding to points where casting surfaces 211 of the superimposed forms 210 change slope. The 5 shape of the forms 210 is dictated by the preferred shape of the upper surface of the concrete crossties, which are slip-formed in inverted orientation on the forms 210. An example of a preferred crosstie is described above with reference to FlGURES 1-3. In order to support the higher intermediate portions of the forms 210, braces 226 extend upwardly from intermediate cross beams 216 to the under surfaces of the forms 210. The braces 226 do not extend beyond the side edges of the forms 210 since that would interfere with the slip-forming process as will become apparent from the description that follows.
Referring now to FlGURE 22, four side-by-side concrete crossties 228 are illustrated during casting by sli~forming using a specially adapted continuous casting machine, designated by reference numeral 230. It will be appreciated that the machine 230 is similar in certain respects to the machine 70 previously described with reference to FIGURES 10-12. Additional details of the machine 230 are described below with reference to FIGVRES 28-30. Referring briefly to FIGURE 28 in conjunction with FIGURE 22, the machine 230 includes a casting hopper 232 having a trflnsverse dimension sufficiently wide to deposit low slump concrete 228' on each of the side-by-side casting forms 210, which in this illustrative example number four per carriage 214. The casting hopper 232 has front and rear transverse walls 233a and 233b, which are inclined so that the width of the hopper 232 increases very slightly in moving downward to prevent concrete bridging within the hopper 232. The machine 230 has a suitable frame which is very schematically depicted as including front and rear transverse support members 234a and 234b, corner columns 235 and sidewalls 236. Rollers 237 are provided at selected points along the sidewalls 236 for supporting and guiding the machine 230 as it travels along the bed 209, the forward direction of travel being from left to right in the view of FIGURE 28.

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For each end-to-end string of forms 210 there is provided within the machine 230 a casting chamber conforming to the shape of the concrete crosstie 228, as best seen in the view of FIGURE 22. Preferably, eflch casting chamber comprises a separate forming member or mold 238 having an inverted U-shape provided by a horizontal wall portion or top plate 23g and downwardly extending Ieg portions 240. It is presently preferred thst the molds 238 be fabricated from relatively heavy gauge sheet metal, such as 0.229 inch steel plate. The molds 238 are mechanically interconnected and suspended both forwardly and rearwardly of the hopper 232 and at a precise height above the bed 209 in a suitable manner, such as by means of plates 241 extending horizontally out to the sidewalls 236, in the manner depicted. As seen clearly in FlGURE 22, the corners of the crossties 228 formed at the interfaces of the top plates 238 and the respective generally vertical legs 240 are rounded, preferably with a 0.50 inch radius, to resist chipping during subsequent handling.
It will be appreciated that such rounded corners would be difficult to fabricate using a prior-art wet-casting system, but are formed automatically in accordance with the present invention.
The hopper 232 can be permanently affixed to the horizontal plates 241 as indicated by the weld joints 242, or can be provided separately in a suitable manner so long as a fluid tight seal is maintained at the ,interface between the hopper 232 and the horizontal walls 239 and plates 241.
- The downwardly extending legs 240 slidingly engage the side edges of the form 210 as the concrete crossties 228 are sli~
formed top side down on the forms 210. In accordance with a presently preferred technique, the lower portions of the legs 240 are resiliently forced against the side edges of the forms 210 by means of pneumatically operated hoses 243. The hoses 243 are controlled by connection to a common pres~sure source (not shown). As will be appreciated by those skilled in the art, concrete having a relatively ~'` .

~6~;3~ -., low slump measurement must be érnployed so that the crossties 228 will retain their shape as depicted ;n FIGURE 23 after the machine 230 has moved away down the casting bed 209.
An inherent advantage of the present system is that the 5 casting of the crossties 228 is done at a relatively high level above the casting bed 209, thereby providing a relatively large open area or wash space below the carriages 214 for ease of clean-up after each casting operation.
As mentioned above, the roller assemblies 224 support the opposed corners of adjacent carriages 214. FIGURE 24 depicts additional details of the preferred system at a typical joint formed between the opposed ends of adjacent carriages 214. In order to keep adjacent carriages 214 in longitudinal alignment, they are coupled together on each side by a guide bar 244 slidably retained in slotted channels 246 mounted at the ends of the side supports 218 as shown.
Stops 248 are secured to the ends of the guide bar 244 in order to limit the relative movement of adjacent carriages so that the ends of the carriages 214 will not travel beyond their respective rollers 220.
The guide bars 244, channels 245 and stops 248 at each corner joint of adjacent carriages are collectively designated as coupling means 249 in FIGURES 21-23 and 29.
In accordance with an important aspect of the invention, specially adapted spring seals 250 are disposed between the opposed ends of corresponding forms on adjacent carriages 214 as best seen in FIGURES 24 and 29. Each spring seal 250 comprises an inner elastomeric member 252 retained within a thin outer cover 254. The member 252 preferably comprises a moldable, weather-resistant rubbery polymer such as polyisoprene, polybutadiene or butadiene-styrene copolymer, but most preferably a polyisoprene such as neoprene. A pattern of strands or cables 256 is shown in the concrete, the actual number of cables 256 being variable among several diff erent designs employed in present practice. The elastomeric members 252 are wide enough so that they will deform with ease and permitadjacent carriages 214 to move toward each ~ , _..... . ... . .. .

1~6~6~5 other upon detensioning of the cables 256 with the resulting contraction or shortening of the concrete. Actual experience indicates that each crosstie will shorten about one-sixteenth of an inch upon detensioning. Each elastomeric member 252 tapers from its widest dimension between the ends of adjacent forms 210 to a generally pointed upper edge 258 situated just below the lowest of the cables 256. The cover 254 preferably comprises 0.062 inch thick stainless steel sheet general~y conforming to the shape of the elastomeric member 252 as shown. Each side of the cover 254 is provided with a protruding lip 260 as best seen in FIGURE 24 to provide a means for holding the seals 250 in place between the opposed ends of adjacent forms 210. The lateral edges of each spring seal 250 terminate flush with the edges of the forms 210 as best seen in FIGURE 29 so as not to interfere with the legs 240 of the casting machine 230 while making a fluid seal for the respective casting chamber as it passes over each respective joint between the opposed ends of adjacent forms 210. The protruding lips 260, however, are preferably not flush with the edges of the forms 210 but instead are cut back slightly from the edges so that the lips 260 will lie flat against the horizontal portions of the upper surfaces 211 of the forms 210 and not ride up on the angled edges 212 (FlGURE 21). It will be appreciated that the lips 260 if properly dimensioned will nest within the angled edges 212 to provide a convenient mechanism for a curate self-alignment of the lateral edges of the seals 250 with the edges of the forms 210. As an alternate means of aligning and supporting the seals 250, a single transverse member (not shown) supporting all four of the seals 250 can be mounted between the opposed ends of adjacent carriages 214, provided such a transverse supporting member is located low enough so that it would not interfere with the passing legs 240 of the casting machine 230. Such a transverse supporting member could conveniently be provided as an integral portion of the elastomeric members 252 and could conveniently be supported on the guide bars 244 of the coupling means 249.

-._ .. ... . . _ , ., ~ gain referring to FIGURE 24, additional aspects of the joint between adjacent carriages 214 will be described. When the concrete has gained sufficient strength, the prestressed cables 256 are detensioned at the opposite ends of the casting bed 209, thereby S causing the concrete to contract by a small but significant amount.
For example, in the case where thirty crossties 228 are included in each of the four continuous end-to-end strings, a contraction of about two inches occurs. This contraction occurs with a minimum of resistance from the casting forms 210 and carriages 214, since the carriages 214 with their slotted channels 246 sliding on the guide bars 244 are free to move toward each other on the rollers 220 while compressing the elastomeric members 252.
In the next stage of the process, the concrete is sawed through above the joints between carriages 214 to separate the concrete into discrete crossties 228. The dashed line 262 in FIGURE
24 depicts the point at which the saw cut would be made. When the concrete is sawed through, the newly freed crossties 228 tend to bow upward and recoil slightly, thus moving a short distance from the point of the saw cut 262. The guide bars 244 are long enough to 20 permit the carriages 214 to move longitudinally in order to compensate for such recoil action without interference from the stops 248 on ~he ends of the guide bars 244. In addition, the coupling povided by the guide bars 244 and slotted channels 246 tends to resist the bowing action of the crossties 228 as their ends break free, thus 25 stabilizing the carriages 214 and keeping them in general alignment.

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. , It ~.vill be appreciated that each spring seal 250 preferably extends upward to a point just under the lowest of the prestressed cables 256, thereby allowing the newly separated crossties 228 to pull free of each other with a clean break 5 immediately upon sawing through the lowest of the prestressed cables 256. It has been found that when the seals 250 are not provided with a portion extending up on into the concrete to just under the cables 256, the concrete tends to have.an irregular break below the cables 256 caused when the concrete pulls apart as the last cable is cut - 10 through.
An additional advantage of the presently preferred construction of the spring seals 250 is that the metal cover 250 resists bending as the concrete is deposited during slip-forming. It is believed that an elastomeric member without such a cover would tend 15 to bend out of position during sli~forming.
Referring now to FIGURES 25-27, an important aspect of the invention pertaining to the removal of crossties from their .forms will now be described. With particular reference to FlGURE
25, a hoist apparatus, designated generally by reference numeral 270, 20 is depicted just after being positioned for engaging a group of four side-by-side crossties 228. It will be appreciated that the crossties 228 at this stage in the process have already been separated by sawing in the abov~described manner at their ends from the other crossties (not shown) mass-produced in the same casting operation.
25 It will also be appreciated that the crossties 228 have at least one free end in front of which the hoist 270 can be positioned prior to sliding it into place between and above the crossties 228 as depicted in FIGURE 25. The hoist 270 is an adaptation of the similar hoist apparatus 140 previously described in conjunction with FIGVRES 14 30 and 15.

i35 The presently preferred hoist apparatus 270 comprises five bars 272 arranged in a fork-like manner at precise lateral SpRCings so that the bars 272 can be inserted between each of the four crossties 228 and along the outer surfaces of the two outer crossties 228. The bars 272 are supported in parallel alignment from above by at least one brace or frame member 274 using interconnecting members 276. The hoist apparatus 270 is adapted to be lifted from above by an overhead crane (not shown) in a suitable manner, such as by means of cables 278 and eyebolts 28û. The hoist 270 further comprises hydraulic jacks 282 carried by the frame 274 for purposes of aiding in releasing the crossties 228 from their respective forms 211 by means of selectively extendable rams 284 in a manner to be described more fully below.
It will, of course, be understood that the hoist 270 is intended for use with crossties 228 having sloping side portions such as shown in FIGURES 25-27. The dimensional details of a similar crosstie 10 are described above in conjunction with FIGURES 1-3. For best results, the surfaces of the bars 272 that engage the crossties 228 are sloped in the same manner as the sloping sides of the crossties 228. The bars 272 &-e wide enough so that they will engage the sloping sides of the crossties 228 when the hoist 270 is lifted upward in the manner depicted by FIGURE 27. On the other hand, the bars 272 and interconnecting member 276 are narro,w enough so that they will slide freely between the crossties 228 when the hoist 270 is lowered slightly into the position depicted in FIGURE 25. It will be appreciated that the unique shape of the crossties 228 with their sloping sides permits the effective operation of the hoist apparatus 270 herein described.
With the hoist 270 properly positioned as depicted in FIGURE 25, removal of the crossties 228 from their respective froms 210 can proceed as will now be described with particular reference to FIG~lRE 26. First, the hoist 270 is lifted so that the bars 272 come into contact with the crossties 228. Then the hydraulic jacks 282 are "

;9~;~5 ~Co actuated to cause the rams 284 to extend down into contact with the carriage 214, preferably at the top surfaces of the side supports 218 as shown. As the rams 284 push with increasing force on the carriage 214~ the crossties 228 are soon forcibly ejected from their respective forrns 210. In the presently most preferred embodiment of the hoist apparatus 270, four jacks 282 are employed (two of which are obscured from view directly behind the two explicitly shown) so that the ejecting force can be applied evenly at each of the four corners of the carriage 214. In this regard, it will be appreciated that the In operation of the jacks 282 can easily be synchronized using a common hydraulic driving pump (not shown) in accordance with conventional techniques. It is also preferred that the rams 284 each have sufficient extension to be able to raise the crossties 228 at least about two inches from their forms 210, thus permitting the inserts 213 to clear the forms 210. Once the crossties 228 have been separated from their respective forms 210 in the foregoing manner, the hoist 270 can be lifted from above as depicted in FlGURE 27 to facilitate transport of the group of four crossties 228 to a suitable transport car (not shown) at the side of the casting bed 209 or to a suitable nearby 2 0 storage area.
From the foregoing description of the invention, it will be appreciated that a number of significant improvements have been made in the state of the art of mass-producing prestressed concrete crosst~ies. For example, the present invention eliminates the expense and complications associated with full-sided casting forms employed in conventional wet casting operations since the sides of the crossties 228 of the present invention are slip-formed using the specially adapted continuous casting machine 230. Furthermore, providing casting forms 210 side by side on common carriages 214 and allowing adjacent carriages 214 to move relative to each other has reduced the incidence of damage to the forms 210 and crossties 228 and has minimized realignment problems between casting operation. In addition, the washout of concrete spillage between casting operations has been made easier due to the rather large open area provided under the carriages 214.

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Another imporlant advantage of the present invention is the elimination of bulkheads and seals between the opposed ends of adjacent crossties 228, as has been the practice in wet casting crossties end to end in full-sided molds. When a large number of crossties 228 are slip-formed in integral end to end strings in accordance with the present invention, the fact that no bulkheads are provided (except at the opposite ends of the casting bed 209) presents the problem of maintaining the prestressed cables 256 in precise predetermined positions in the crossties 228. It will be appreciated that even though tremendous tension is applied to the cables 256, there is still a small but significant sagging effect due to the weight of the cables 256 themselves. Accordingly, when a large number of crossties 228 are sli~formed end to end, the presently preferred casting machine 230 is adapted to guide the cables 256 into proper alignment just prior to their being embedded in concrete as will presently be described.
Referring now to FIGURES 28 and 30, it will be seen that the machine 230 is equipped with four guide plates 290, one for eflch of the four strings of crossties 228 in the particular example illustrated. Each guide plate 290 is provided with Q plurality of holes in the precise pattern of the cables 256, which are strung through the holes in the manner depicted. The guideplates 290 are supported from above at a convenient position ahead of the flowing concrete 228'. Each guide plate 290 is preferably suspended from the forward most edge of the corresponding mold 238 by means of an assembly of two vertical alignment bars 292 and an interconnecting horizontal alignment bar 294, all of which abut the guide plate 290 and push it forward as the machine 230 moves forward down along the bed 209.
Each guide plate 290 is maintained at a precise height by means of an insert pin 296 which extends from the horizontal bar 294 into a cooperating hole in the plate 290, as best depicted in FIGURE 30.
Such an arrangement permits the assemblies of the bars 292 and 294 to be removed by disengaging the insert pins 296 from the guide plates 290, thereby permitting the machine 230 to pass over ,~ " . ~

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the bulkheads (not shown) at either end of the casting bed 209. It will be appreciated that the guide plates 290 lift the cables 256 into proper position just prior to the cables 256 being ernbedded in the crossties 228 being formed to the rear thereof.
Finally, as will be appreciated from FIGURES 28 and 29, a plurality of stinger vibrators 298 are provided at the bottom of the hopper 232, preferably one vibrator 290 per casting chamber, for locally fluidizing the relatively low slump concrete using the technique previously described with reference to FlGURE 11.
From the foregoing description, it will be appreciated tliat the present invention provides an innovative advance in the state of the art of mass-producing concrete railroad crossties. Although illustrative embodiments of the invention have been described in detail, it is to be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
What is claimed is:

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Claims (19)

Claims:

1. A system for slip-forming concrete crossties, comprising:
an elongated casting bed, a plurality of molds arranged side by side and end to end on the casting bed, each mold having a casting plate supported above the casting bed by a frame, a continuous casting machine movable along the bed while the molds remain stationary, the machine having means for forming a casting chamber above each casting plate, said means making aslidable fluid seal at points of sliding engagement of the casting chamber means with each casting plate as the machine moves along the bed.

2. The system of claim 1 wherein each casting plate has upper surfaces of a variable height above the casting bed in the direction of movement of the casting machine, the upper surfaces conforming to the shape of a top surface of a crosstie formed in inverted orientation thereon.

3. A system for slip-forming concrete crossties in inverted orientation on an elongated casting bed, each crosstie having a plurality of prestressed cables embedded in the concrete, the system comprising:
a plurality of casting forms arranged side by side and end to end above the casting bed, each side of each casting form being disposed in an upright plane to sealingly engage depending sides of a relatively moving slip-form casting machine;
a plurality of carriage assemblies arranged end to end above the casting bed, each carriage assembly supporting a group of side-by-side casting forms;
means for supporting the carriage assemblies while permitting relative longitudinal movement of adjacent carriage assemblies; and resilient sealing means disposed between the adjacent ends of the casting forms and forming a fluid seal therebetween, the sealing means extending to the upright planes to also form a fluid seal with the depending sides of the casting machine.

4. The system of claim 3, wherein the supporting means comprises a plurality of rollers arranged to support at least the four corners of each carriage assembly on revolving surfaces of the rollers, each roller being journaled for rotation on an axis directed transversely to the casting bed.

5. The system of claim 4, further comprising means for coupling the opposed corners of adjacent carriages to maintain the carriages in substantial longitudinal alignment while permitting relative longitudinal movement of adjacent cariages.

6. The system of claim 5, wherein the coupling means at each pair of opposed corners of adjacent carriages comprises a first channel secured at one corner of one of the carriages, a second channel secured at the opposed corner of the other carriage, the channels having longi-tudinally aligned slots, a guide bar slidably retained in the slots of the first and second channels, and means at the ends of the guide bar for limiting the maximum separation distance between adjacent carriages.

7. The system of claim 3 wherein each sealing member extends upward from the end edges of the respective pair of forms to a point just under the lowest of the-prestressed cables.

8. The system of claim 7 wherein each sealing member comprises an inner elastomeric member retained within a thin metal cover.

9. The system of claim 8 further comprising means for supporting each sealing member in a predetermined position relative to its respective pair of forms.

10. A machine for slip-forming prestressed concrete railroad crossties on a plurality of casting forms arranged side by side and end to end above a generally horizontal casting bed, the machine comprising a plurality of casting chambers each having a top plate and downwardly extending legs, each chamber cooperating with an underlying casting form to slip-form a concrete railraod crosstie in inverted orientation on the casting form as the machine moves longitudinally down the casting bed, a casting hopper for depositing relatively low slump concrete into the casting chambers, means for guiding prestressed cables into the concrete in precise predetermined positions at a point just ahead of where the cables are embedded in the concrete and pneumatically actuable means for urging the downwardly extending legs with a uniform force against cooperating edges of the respective forms to maintain an essentially fluid tight seal therebetween.

11. The machine of claim 10, further comprising means for locally fluidizing the concrete in the bottom of the casting hopper.

12. The machine of claim 10, wherein each casting chamber is provided with rounded corners at the interfaces of the top plate with each of the downwardly extending legs.

13. The machine of claim 10, wherein the top plate and downwardly extending legs of each casting chamber comprise integral portions of a single sheet-metal mold.

14. A system for slip-forming concrete cross ties, comprising:
an elongated bed, a plurality of casting frames arranged side by side and end to end on the casting bed each casting frame supporting a casting plate above the casting bed, a continuous casting machine movable along the bed while the casting plates remain stationary, the machine having means for forming a casting chamber above each casting plate, each casting plate having upper surfaces of a variable height above the casting bed in the direction of movement of the casting machine, the upper surface conforming to the shape of a top surface of a cross tie formed in inverted orientation thereon, each casting plate having outer edges each of which is disposed in a generally vertical plane along the entire length of the casting plate, said means making a fluid seal at points of sliding engagement with each casting plate as the machine moves along the bed, said means comprising a horizontal pressure plate attached to the casting machine rearward of a source of fluidized concrete, and downwardly extending legs affixed to the pressure plate, each leg having an upper sloping portion and a lower generally vertical portion, the lower vertical portions slidably and sealably engaging corres-ponding outer edges of the variable height surfaces of the casting plates.

15. A system for slip-forming concrete products having an irregular surface, comprising:
elongated casting bed means supporting a plurality of casting plates arranged side by side and end to end above the casting bed, a continuous casting machine movable along the bed means while the casting plates remain stationary, the machine having means for forming a casting chamber above each casting plate, each casting plate having upper surfaces of a variable height above the casting bed means in the direction of movement of the casting machine, the upper surfaces conforming to the shape of the irregular surface of the products, each casting plate having outer edges disposed in generally vertical imaginary surfaces along the entire length of the casting plate, said means forming the casting chamber making a fluid seal at points of sliding engagement with the outer edges of each casting plate as the machine moves along the bed, said means comprising a horizontal pressure plate attached to the casting machine rearward of a source of fluidized concrete, and downwardly extending legs affixed to the pressure plate, each leg having a surface conforming to the generally vertical imaginary surface and slidably and sealably engaging corresponding outer edges of the variable height surfaces of the casting plates.

16. A machine for slip-forming concrete products of irregular geometry, the concrete products being formed on casting plates arranged side by side and end to end on a generally horizontal casting bed, each vertical edge lying in a vertical plane along the entire length of its respective casting plate, the machine comprising:
a generally horizontal pressure plate held at a predetermined height above the casting bed, a plurality of legs extending downward from the pressure plate to form a casting chamber above each casting plate, the legs having lower generally vertical portions of sufficient dimension to slidably and sealably engage the generally vertical edges as they rise and fall in relation to the machine as it moves down the length of the bed, and means for resiliently urging the legs against the respective vertical edges of the casting plates.

17. The machine of claim 16 further comprising:
a casting hopper for depositing low slump concrete on the casting plates ahead of the pressure plate in the direction of movement of the machine during slip-forming, and means for fluidizing the concrete as it passes under the pressure plate.

18. The machine of claim 17 further comprising:
means for controlling the amount of concrete in the casting hopper to maintain a predetermined hydrostatic head pressure therein.

19. The machine of claim 17 wherein the fluidizing means comprises stinger vibrators located generally below the casting hopper.