Apparatus for inserting dowel bars within the pan of a concrete slip forming machine

An apparatus for inserting dowel bars into a concrete slab in association with a slip forming machine of a type having a frame with a mold attached thereto for shaping uncured concrete into a continuous concrete slab. The mold having a front and rear pan portion with a space therein completely across the mold. Dowel bar retainers are disposed above this space in the pan for holding dowel bars in readiness to be inserted into the concrete slab. A dowel bar inserter having individual fork assemblies is disposed above the dowel bar retainers for pushing the dowel bars down into the formed concrete slab, preferably all at one time. The dowel bar inserter is adjustable and removable. If removed, the forward and rear pan portions of the mold can be bolted together instead of being spaced apart.

CROSS-REFERENCE TO RELATED APPLICATIONS 
This application is a continuation-in-part of the Gary L. Godbersen 
application Ser. No. 08/689,795 filed Aug. 13, 1996, which application is 
incorporated herein by reference. 
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
Not Applicable. 
MICROFICHE APPENDIX 
Not Applicable. 
BACKGROUND OF INVENTION 
1. Field of Application 
The present invention relates generally to an apparatus for slip forming 
concrete using a pan which initially begins the concrete forming process 
of such a machine and to an apparatus for inserting dowel bars for a 
concrete slip forming machine, and more particularly to such a method and 
apparatus which inserts dowel bars directly between spaced apart portions 
of the pan of such machine, instead of utilizing a separate dowel bar 
insertion device disposed behind the pan, which has been the custom of the 
prior art. 
2. Description of Prior Art 
In concrete slip forming machines used for constructing roads and the like, 
it is customary to form joints therein at predetermined intervals. One of 
the reasons for these joints is to transfer stresses between adjacent 
sections of the concrete slabs through the use of dowel bars placed within 
the slab. Another reason for the joints is to allow for expansion and 
contraction of the slabs, which occurs during freezing and thawing cycles. 
The joints are generally perpendicular with respect to the length of the 
slab and direction of forward movement of the machine. The joints may also 
extend across the width of the slab at an angle, which is commonplace in 
present day road construction so that each set of tires of a vehicle does 
not hit the joint at precisely the same time, thereby lessening the 
thumping problem that often occurs when the concrete joints are 
perpendicular to the direction of the movement of the vehicle traveling 
thereon. 
The dowel bars are typically inserted into the concrete at one-third to 
one-half the depth of the slab down from the top surface of the slab and 
are generally aligned with the forward movement of the machine. The dowel 
bars are also usually epoxy coated to prevent rusting of the bars and are 
usually coated with a film oil to prevent the concrete from bonding to the 
surface of the bars. After the concrete has set, a saw is used to cut a 
joint in the concrete above and perpendicular to the dowel bars. The 
saw-cuts control the shrinkage cracking of the concrete during the final 
curing stage of the concrete by allowing the concrete to crack more easily 
along the saw cut joints. The concrete slabs are therefore able to move 
independently as they expand and contract during temperatures changes but 
the dowel bars joining the slabs are still able to transfer the shear 
stresses from slab to slab as motor vehicles pass over the slabs. 
The aforementioned concrete slip forming machines have for many years used 
dowel bar insertion mechanisms to place the dowel bars within the concrete 
as the slab is being formed, for example like those shown in U.S. Pat. 
Nos. 4,798,495 and 4,799,820, both by Laeuppi, et al., both of which are 
incorporated herein by reference. 
Conventional dowel bar inserting equipment is attached to the frame of a 
slip forming machine behind the pan or mold, for example as shown in U.S. 
Pat. No. 5,190,397 to Bengford, which patent is incorporated herein by 
reference. By utilizing this prior art technology with the dowel bar 
insertion mechanism located behind the pan, the concrete slab, which has 
already been formed, shaped and smoothed by the pan, is disturbed 
considerably by the insertion of the dowel bars therein. This disruption 
of the smoothed concrete surface is often referred to in the industry as 
"scaring" of the surface. The scaring of the surface, due to the insertion 
of the dowel bars into the formed, slab creates a need for an additional 
troweling procedure following the dowel bar insertion mechanism to repair 
the scaring. Such a trowel is shown in U.S. Pat. No. 5,061,115 to 
Godbersen, et al. Additionally, a vibrating screed or tamper bar must 
precede the trowel on such a machine in order to consolidate the concrete 
back around the inserted dowel bar. 
The need to have this dowel bar inserting apparatus and accompanying trowel 
mechanism makes it necessary to lengthen the machine by a considerable 
amount. This additional length creates many problems such as making the 
machine more difficult to move and requiring much more time to assemble 
and disassemble as these machines are moved from one job site to the 
other. Additionally, on roads that have sharp vertical curves up or down, 
if the paver is too long, it may not correctly pave the surface 
thereunder. For example, on a sharp downward vertical curve, the paver may 
span completely across such a low spot resulting in the paver not being 
capable of reaching low enough to maintain a uniform slab thickness. 
Alternatively, on a sharp upward vertical curve, the paver may extend 
completely across the high spot leaving only a thin layer of concrete. 
Furthermore, a machine which has a conventional dowel bar inserter thereon 
and a follow-up trowel mechanism almost always needs to be a four-track 
machine, which increases the costs of manufacture and use over that of a 
two-track machine, and also causes the aforementioned problem relating to 
the difficulty of being able to pave roads which have sharp vertical 
curves up and down. 
U.S. Pat. No. 5,209,602, issued May 11, 1993 to Gary L. Godbersen, which is 
incorporated herein by reference, solved many of the aforementioned 
problems. The present invention is an improvement thereto since it has 
been determined that it is better to form a wide space in the pan than to 
merely have openings which extend therethrough for inserting dowel bars. 
Consequently, there is a need for a method and apparatus for inserting 
dowel bars on a concrete slip forming machine which will overcome the 
aforementioned disadvantages of the prior art. 
SUMMARY OF THE INVENTION 
The present invention relates generally to an apparatus for inserting dowel 
bars into a concrete slab in association with a slip forming machine of a 
type having a frame with a pan attached thereto for forming uncured 
concrete into a continuous concrete slab. The pan itself has a space 
disposed therein completely across the pan. Dowel bar retainers are 
disposed above this space in the pan for holding dowel bars in readiness 
to be inserted into the concrete slab. A dowel bar inserter is disposed 
above each of the dowel bar retainers for pushing the dowel bars down. The 
dowel bars may be pushed into the concrete slab all at one time or 
alternatively one at a time if it is desired to form a diagonal or skewed 
joint. 
An object of the present invention is to provide an improved method and 
apparatus for inserting dowel bars into a concrete slab in association 
with the use of a concrete slip forming machine. 
Another object of the present invention is to provide a dowel bar inserting 
apparatus which does not disturb the concrete slab after it has been 
formed by the pan of a slip forming machine. 
A still further object of the present invention is to provide a dowel bar 
inserting apparatus within the pan to eliminate the need for a separate 
troweling operation of the top of the concrete slab after dowel bars have 
been inserted. 
A still further object of the present invention is to provide a dowel bar 
inserting apparatus which permits a slip forming machine to be much 
shorter and also permit such a machine to be a two-track machine instead 
of a longer, more awkward and expensive four-track machine. 
A still further object of the present invention is to provide a concrete 
slip forming machine with a dowel bar insertion apparatus disposed above a 
space between front and rear portions of the pan. 
A still further object is to provide an apparatus of the aforementioned 
type which has a device for adjusting the distance between dowel bars and 
the distance between insertion forks so that an entirely different pan 
does not need to be used as would be the case if different distances 
between dowel bars were required in the above mentioned '602 patent. 
Still another object of the invention is to provide an apparatus which can 
have the aforementioned objects achieved and still have an arrangement 
where a dowel bar inserter can be used or not used in a split pan 
arrangement. 
Other objects, advantages, and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings wherein like reference numerals designate 
identical or corresponding parts throughout the several views, FIGS. 6 and 
6a respectively show a four-track and a two-track concrete slip forming 
machine (10) of the present invention. The machine (10) is comprised of a 
frame (12) which includes horizontal frame members (15) supported by 
vertical legs (16). The machine (10) is movable in a forward or rearward 
direction by hydraulically driven tracks (13) attached to the vertical 
legs (16). The tracks (13) are pivotally attached to the vertical legs 
(16) such that the frame (12) remains relatively parallel to the road bed 
at all times. The frame supports the engine, fuel tank, hydraulic fluid 
holding tank, as well as all the components and mechanisms used for slip 
forming the concrete slab (14). In the four-track embodiment of FIG. 6, 
the vertical legs (16) are placed at the four comers of the machine (10). 
The legs (16) are pivotally attached to the horizontal frame members (15) 
to enable each pair of front and rear vertical legs (16) to be turned in 
unison by hydraulic cylinders and linkages (not shown) such that the 
machine (10) can follow the road bed along horizontal curves. In the 
two-track embodiment of FIG. 6a, the vertical legs (16) are rigidly fixed 
to the frame (12). When it is desired to turn the two-track machine (10) 
along a horizontal curve, the track (13) on the outside of the curve is 
caused to rotate faster than the track (13) on the inside of the curve, 
thus causing the machine (10) to turn about the slower moving track (13). 
Throughout this specification, references are often made to "forward" and 
"rearward" directions. It should therefore be understood that any 
reference to "forward" or "forwardly" refers to the direction of forward 
movement of the machine (10) denoted by arrows (11), whereas a reference 
to "rearward" or "rearwardly" refers to the direction away from the 
forward movement of the machine (10). 
FIG. 7 shows a rear view of the present invention (10) and FIG. 8, is a 
cross-sectional view of the concrete slip forming machine (10), taken 
along lines 8--8 of FIG. 7. In FIG. 8, operably attached to the forward 
end of the frame (12) is a first auger (18), followed by a strike-off bar 
(19). Bent paving vibrators (20) are positioned behind the strike-off bar 
(19), followed by a second auger (21). Following the second auger (21) is 
the concrete form or mold. The mold includes a split-pan form (17) and 
side forms (17c) (best viewed in FIG. 9). The split-pan form (17) is 
comprised of a front pan portion (17a) and a rear pan portion (17b). 
Referring now to FIG. 2, showing a more detailed side elevation view of 
the split-pan form (17), the front and rear pan portions (17a and 17b) 
have concrete pan forming surfaces (23a and 23b) which form the top 
surface of the concrete slab (14). It should be understood that the 
concrete pan forming surfaces (23a and 23b) share a common plane that is 
substantially parallel with the frame (12) and the surface of the road 
bed. 
The thickness of the concrete slab (14) is controlled by the height of the 
split-pan form (17) above the road bed. By hydraulically raising or 
lowering the frame (12) on the vertical legs (16) of the machine (10), the 
height of the frame (12) above the road bed is raised or lowered. 
Because the split-pan form (17) is operably connected to the frame (12) by 
hangers (133) the split-pan form (17) moves up and down with the frame 
(12) thereby varying the thickness of the slab (14) being laid. 
The side forms (17c) are continuous along the length of the machine (10) 
and act to contain the concrete within a predetermined width as the slab 
(14) is being formed. The side forms (17c) are operably connected to the 
front and rear pan portions (17a and 17b) by side form mounts (22a and 
22b) as shown in FIG. 9. The side form mounts (22a and 22b) include 
bolting flanges (123). The bolting flanges (123) have apertures (124) 
formed therein which align with mating apertures in the bolting flanges of 
the side forms (17c). Hydraulic cylinders (125) mounted at the ends of the 
front and rear pan portions (17a and 17b) can be actuated to raise or 
lower the side forms (17c) relative to concrete pan forming surfaces (23a 
and 23b). The rear pan portion (17b) is comprised of modular sections of 
predetermined width which can be bolted together to create a rear pan 
portion (17b) of a desired width. The internal structure of each modular 
section of the rear pan portion (17b) includes a plurality of cross braces 
and stiffeners (91) and gussets (90) to add rigidity. The concrete pan 
forming surface (23b) of the rear pan portion (17b) includes a rearward 
adjustable portion (23b') preferably made of stainless steel (see FIG. 1). 
The rearward adjustable portion (23b') is adjusted by the form finish 
bolts (96). The form finish bolts (96) extend between a first set of 
horizontal plates (93) rigidly fixed to the adjustable pan portion (23b') 
and a second set of plates (92) rigidly fixed to the gussets (90). By 
turning the nut (95) on the form finish bolts (96), the form finish bolts 
(96) will extend or retract, thereby forcing the adjustable concrete pan 
forming surface (23b') up or down to create the desired bevel. The 
movement of the adjustable concrete pan forming surface (23b') is shown in 
hidden lines greatly exaggerated in FIG. 1. 
Also mounted within the rear pan portion (17b) are a plurality of 
hydraulically actuated pan vibrators (97). When in use, these vibrators 
(97) cause the concrete pan forming surface (23b) to vibrate which assists 
in the finishing process of the concrete as the concrete pan forming 
surface (23b) passes over the concrete. The preferred pan vibrators are of 
the type manufactured by Minnich Manufacturing Co., Inc. of Mansfield, 
Ohio. It should be understood that the vibrators are not limited to 
hydraulically actuated vibrators. Pneumatic or electric pan vibrators will 
also work for this application. 
The front pan portion (17a) is also comprised of modular sections of a 
predetermined width which can be bolted together to create a front pan 
portion (17a) of a desired width. Each modular section of the front pan 
portion (17a) includes a plurality of gussets and stiffeners (142) to add 
rigidity to the structure. It should be noted that the forward end of the 
front pan portion (17a) includes a higher front plate (143) to prevent 
concrete from spilling over onto the front of the pan (17a). Attached to 
the rear of the front pan portion (17a) is a rail (144). The rail (144) 
supports the brackets (145) of the vertical struts (33). Attached to the 
brackets (145) is a trolley support rail (70). 
Referring again to FIGS. 2 and 9 in conjunction with FIGS. 10 and 13, at 
the forward end of the front and rear pan portions (17a and 17b) are 
tamper bar assemblies (110a and 110b) respectively. The tamper bar 
assemblies (110a and 110b) are used to further level the concrete and 
bring the cement to the surface of the concrete slab for better finishing. 
A motor (111) (best viewed in FIG. 9) rotates a wheel (112) to which is 
attached an arm (113). The rotation of the wheel (112) by the motor (111) 
causes the arm (113) to move in an elliptical direction both up and down 
and left to right. The other end of the arm (113) is pivotally linked to a 
shaft (114) which oscillates within shaft guides (115). Attached to the 
shaft (114) is a plurality of tamper bar linkages (116) which transfer the 
oscillating motion of the shaft (114) to the tamper bar (117b) through 
bolted brackets (118). The tamper bar (117b) therefore oscillates 
transversely to the forward direction of the machine (10) across the width 
of the slab (14). The rear tamper bar assembly (110b) also includes a 
vibrating means. A vibrator (120) is mounted to the rear pan portion (17b) 
to vibrate the tamper bar (117b) through a bracket (122) rigidly attached 
to the tamper bar (117b). The action of this oscillating and vibrating 
tamper bar (117b) creates a roll of concrete before the rear pan portion 
(17b) which has been shown to provide a smoother finish to the slab (14) 
as the concrete pan forming surface (23b) passes over it. As shown in FIG. 
13, the front pan portion (17a) has a similar tamper bar assembly (110a), 
however the oscillating action is in more of a vertical direction than a 
horizontal direction. This vertical action is achieved by the use of a 
motor (151) (best viewed in FIG. 9) which rotates a wheel (152) to which 
is attached an arm (153). The rotation of the wheel (152) by the motor 
(151) causes the arm (153) to move in an elliptical direction both up and 
down and left to right. The other end of the arm (153) is pivotally 
attached to a vertically disposed linkage (154) which converts the 
oscillating action of the arm (153) into a more vertical movement. The 
vertically disposed pivotal linkage (154) is in turn pivotally connected 
by a rocker arm (158) to a vertical shaft (155) which is attached to the 
tamper bar (117a) through bolted brackets (159). 
Wear bars (121a and 121b) secured to the front and rear pan portions (17a 
and 17b) respectively protects the pan portions from wear due to the 
oscillating action of the tamper bars (117a and 117b). 
Referring back to FIG. 2, between space "A" is a dowel bar insertion 
mechanism (27), a trolley (36) and dowel bar retainers (24). The trolley 
(36) is of the type shown in U.S. Pat. No. 5,209,602 to Godbersen, which 
is incorporated herein by reference, and U.S. Pat. No. 5,190,397 to 
Bengford, et al., which is also incorporated herein by reference. This 
structure shown is constructed more like the Bengford, et al., device 
except that in the preferred embodiment, the dowel bars are inserted in a 
straight line perpendicular across the length of the slab instead of at an 
angle as shown in both the Bengford, et al, and the Godbersen preferred 
embodiments of the aforementioned patents. It would be possible to modify 
the present invention to enable the dowel bars to be inserted at an angle 
as shown in the aforementioned Bengford, et al and Godbersen patents by 
lengthening the machine to accommodate the extra space requirements for 
such a device. It is also possible to insert the dowel bars at an angle by 
using the Godbersen '602 device with individual actuators for each fork 
assembly (80) (to be discussed later). The following specification 
however, is limited to discussing only the perpendicular dowel bar 
insertion mechanism. 
The trolley (36) rides on rollers (71) along a rail (70) positioned above 
dowel bar retainers (24). The rail (70) is supported by brackets (145) 
attached to the rear of the front pan portion (17a). The trolley (36) 
deposits dowel bars (49) into dowel bar retainers (24) at predetermined 
intervals to be discussed later. When the trolley (36) is not depositing 
dowel bars (49) into the dowel bar retainers (24), it is positioned 
outside the side form (17c), out of the way of the dowel bar inserting 
mechanism (27) (best illustrated in FIG. 7). 
A detailed perspective view of two embodiments of the dowel bar retainers 
(24) is shown in FIGS. 11 and 11a. In FIG. 11, the retainers (24) are 
comprised of rearwardly cantilevered brackets (72) attached to a beam (30) 
by bolts (73). The beam (30) is attached rear of the front pan portion 
(17a). The beam (30) has openings (29) therein spaced along its length. 
Two transverse brackets (74) are bolted to and supported by the cantilever 
bracket (72). Attached to the ends of the transverse brackets (74) are 
inwardly projecting resilient spring tabs (26) that are positioned to 
support the dowel bars (49) between adjacent transverse brackets (74). 
Also attached to each end of the transverse brackets (74) are L-shaped 
projections (75) used to longitudinally position the dowel bars (49) 
within the dowel bar retainers (24). The transverse brackets (74) are 
adjustable within slotted holes (76) to accommodate different lengths of 
dowel bars (49). For additional adjustment slotted holes (77) are also 
included in the L-shaped projections (75). 
If it is desired to adjust the lateral distance between adjacent dowel bars 
in the concrete (14), for the embodiment shown in FIG. 11, the dowel bar 
retainers (24) can be adjusted by removing the bolts (73) and putting them 
into different openings (29). In the alternative embodiment, shown in FIG. 
11a, the rearwardly cantilevered brackets (72) are clamped to a beam (30') 
through the use of a clamping plate (78) and bolts (73). This arrangement 
allows the retainers (24) to be clamped in any number of positions rather 
than in the predetermined locations set by the spacing of the openings 
(29). It should be understood that any lateral adjustment to the position 
of dowel bar retainers (24) requires a corresponding adjustment in the 
lateral position of the insertion forks (28) (discussed below). 
Referring to FIGS. 1, 2, 3, 7 and 9 longitudinal beams (32) at each end of 
the machine (10) are disposed above the space "A" between front and rear 
pan portions (17a and 17b) and are supported by vertical struts (33) 
attached to said front and rear pan portions (17a and 17b) (best 
illustrated in FIGS. 2 and 9). The beams (32) act as rails for a 
transverse beam (41) which supports the dowel bar insertion mechanism (27) 
as best illustrated in FIG. 1. The transverse beam (41) is supported at 
its ends by rollers (31) which ride along the flanges of the longitudinal 
beams (32) and is therefore moveable, front to rear, along the length of 
the longitudinal beams (32) by a gear and toothed rail mechanism (42 and 
43). Disposed below the length of the transverse beam (41) is a rod (34) 
(see FIGS. 3, 6 and 7). This rod has a gear (42) rigidly attached to each 
end thereof. This gear (42) engages a toothed rail (43) mounted to the top 
of longitudinal beams (32) at each end of the machine (10). A motor (44) 
through a chain sprocket (45) rotates the rod and therefore the gears (42) 
which in turn moves the transverse beam (41) along the toothed rail (43) 
front to rear within the space "A". FIG. 2 illustrates the movement of the 
dowel bar insertion mechanism (27) from a rearward position (shown in 
hidden lines) to a forward position (shown in solid lines). The motor (44) 
is connected to a computer controller (55) as shown in FIG. 4. The 
controller (55) monitors the speed and position of the tracks (13) through 
an encoder (56) connected to the controller (55) by signal cable (67). 
This information is fed into the computer controller (55) to operate the 
motor (44) and hydraulic cylinders (25) at appropriate times. This 
procedure is discussed in further detail below. 
The dowel bar insertion mechanism (27) is comprised of a pair of 
telescoping arms (35) actuated by hydraulic cylinders (25). The downward 
end of the telescoping arms (35) terminate onto a second transverse beam 
(40), to which is attached multiple fork assemblies (80). The fork 
assemblies (80) are mounted to the bottom flange of the second transverse 
beam (40) by brackets (39) and bolts (37). 
As best shown in FIG. 12, each fork assembly (80) includes a set of front 
and rear forks (28) mounted to the body of the fork assembly (80). Each 
fork (28) includes a vertical rod (81) having a threaded upward projecting 
end (82) and a downward projecting end (83). The threaded upward 
projecting end (82) of the rod (81) is attached to the body of the fork 
assembly (80) by a nut (89). Rigidly attached to the downward projecting 
end (83) of the rod (81) is a V-shaped plate (84) oriented transversely to 
the direction of the dowel bars (49) within the dowel bar retainers (24). 
A second plate (85) is also rigidly attached to the downward projecting 
end (83) of the rod (81) perpendicular to the V-shaped plate (84). These 
second plates (85) having one end terminating in a finger-like projection 
(86) are oriented on each set of forks (28) such that the finger-like 
projections (86) oppose each other. The two plates (84 and 85) are 
designed to fit over the dowel bars (49) within the dowel bar retainers 
(24) such that the dowel bars (49) are restrained within the V-shaped 
plates (84) laterally and within the finger-like projections (86) 
longitudinally, (as shown in FIG. 2) thereby enabling the dowel bars (49) 
to be positioned within the concrete slab (14) within very strict 
tolerances. 
It should be understood that the distance between adjacent dowel bar 
retainers (24) is sufficient to clear the width of the V-shaped plate (84) 
as the insertion forks (28) are forced downwardly between the adjacent 
dowel bar retainers (24). This operation is discussed below. It should 
also be understood that any adjustment to the position of dowel bar 
retainers (24) requires a corresponding adjustment in the lateral position 
of the fork assemblies (80) which can be done by moving the bolts (37) to 
a different opening in brackets (39) as shown in FIG. 1, or by other 
mechanisms to make the adjustment correspond to the position of the dowel 
bar retainers (24). 
In addition to the above elements of the fork assembly (80), each 
individual fork assembly (80) includes hydraulically actuated form 
vibrators (87) mounted thereto. The preferred form vibrators are of the 
type manufactured by Minnich Manufacturing Co. Inc. of Mansfield, Ohio. 
Although hydraulic vibrators are preferred, pneumatic or electric 
vibrators may be used. It is necessary to vibrate the insertion forks (28) 
to consolidate the concrete around the dowel bars (49) as they are being 
inserted into the concrete. As best shown in FIG. 12, each bracket (39) is 
isolated from the body of the fork assembly (80) by annular resilient 
cushioning rings (88) (preferably a rubber type material) to dampen the 
effects of the vibrating forks on the mounting brackets (39). 
In regard to the vibration of the fork assemblies (80), it has been 
determined that round bars are preferred for the vertical rods (82) of the 
fork assemblies (80) rather than rectangular bars. Round bars are 
preferred because they are symmetrical about their longitudinal axis and 
therefore the vibrating action of the round bars is unrestricted, thereby 
creating a 360 degree conical vibration pattern. A rectangular bar 
however, will tend to vibrate only side to side, because the vibrating 
action will be dampened in the direction of the long side of the bar. 
As mentioned previously, it should be understood that the horizontal frame 
members (15) are moveable up or down along the vertical legs (16) by 
hydraulic cylinders (not shown). Therefore, all the components and 
mechanisms which are used to form the concrete slab (14) and insert the 
dowel bars, likewise move up or down with the horizontal frame members 
(15), since they are all operably connected to the horizontal frame 
members (15), thereby enabling the machine (10) to lay various thicknesses 
of concrete slabs. Additionally, because the pan mold forms (17a and 17b) 
are modular, the paving width of the machine (10) can be increased by 
adding additional sections of the front and rear pan portions (17a and 
17b) as discussed above, along with additional sections to transverse 
beams (40 and 41), and trolley rail (70) and the retainer support beam 
(30), along with additional fork assemblies (80) and dowel bar retainers 
(24). 
In operation, and referring to FIGS. 2, and 8, the forward direction of the 
machine (10) is shown by arrow (11). As the machine moves forward, the 
fresh concrete previously placed in front of the machine (10) is 
distributed across the width of the machine (10) between side forms (17c) 
by a first auger (18). A strike-off bar (19) is positioned behind the 
first auger (18) to level the concrete to a uniform thickness. A plurality 
of bent paving vibrators (20) following the strike-off bar (19) 
consolidates the concrete creating an even more uniform thickness. The 
preferred bent paving vibrators (20) are of the type manufactured by 
Minnich Manufacturing Co. Inc. of Mansfield, Ohio. A second auger (21), 
following the bent paving vibrators (20) is positioned to redistribute the 
concrete from any high spots to any low spots. A vertically oscillating 
tamper bar assembly (110a) following the second auger (21) and mounted to 
the forward end of the front pan portion (17a) tamps the concrete as the 
machine (10) moves forward. 
As the slip forming machine (10) moves in a forwardly direction, the 
concrete is molded by the side forms (17c) and the concrete pan forming 
surface (23a) of the front pan portion (17a). The pan forming surface 
(23a) creates a smooth top surface to the concrete as it passes. The 
continued forward movement of the machine (10), exposes the concrete in 
the space "A" between the front and rear pan portions (17a and 17b). 
At this time, the dowel bar insertion device (27) is in a rearward 
position, just ahead of the rear pan portion (17b). While the machine (10) 
is moving forward, a signal is sent from the controller (55) to actuate 
the trolley (36) which travels across the width of the machine (10) on 
rails (70), best seen in FIGS. 1 and 2, automatically depositing dowel 
bars (49) in the dowel bar retainers (24) in the manner shown in the 
Bengford, et al., patent referred to above. After the dowel bars (49) have 
been deposited into the dowel bar retainers (24), the trolley (36) returns 
to its original starting position outside of the side forms (17c) and out 
of the way of the dowel bar insertion device (27). 
After the trolley (36) has deposited the dowel bars (49) in the dowel bar 
retainers (24), the controller (55) will send a signal through a signal 
cable (63) (shown in FIG. 4) actuating the motor (44) and chain sprocket 
(45) thereby causing the rod (34) positioned below the transverse beam 
(41) to rotate. The gears (42) rigidly attached to the ends of the rod 
(34) will engage the toothed rail (43), mounted to the longitudinal beams 
(32), thereby causing the transverse beam (41), supporting the dowel bar 
inserter (27), to move forwardly along the horizontal beam (32) until the 
dowel bar inserter (27) is positioned over the dowel bar retainers (24), 
holding the previously loaded dowel bars (49). When it is time for the 
dowel bars to be inserted into the slab (14), the computer controller (55) 
will send a signal through a signal cable (66) (see FIG. 4) to open the 
hydraulic fluid directional control valve (62). Hydraulic fluid will flow 
to and from the hydraulic cylinder (25), connected to the telescoping arm 
(35) of the dowel bar insertion device (27), to and from the directional 
control valve (62) through hydraulic lines (60 and 61). Note, lines (64) 
and (65) are pressure and return lines respectively which are connected to 
the hydraulic fluid holding tank mounted on to the frame (12). The 
movement of the hydraulic fluid to and from the cylinder (25) causes the 
piston of the hydraulic cylinder (25), connected to the telescoping arm 
(35) of the dowel bar insertion device (27), to extend, thereby forcing 
the second transverse beam (40), to which is mounted the fork assemblies 
(80), to move downwardly. The forks (28) of the fork assemblies (80) 
engage the dowel bars (49) within the dowel bar retainers (24). The 
continued downward movement of the forks (28) forces the dowel bars (49) 
through the spring tabs (26) of the dowel bar retainer (24) and into the 
concrete (14). This action is similar to that shown in FIG. 5 of the 
Godbersen Pat. No. 5,209,602. The resilient spring tabs (26) will spring 
back to their original position, ready to receive another dowel bar. When 
the dowel bars (49) are inserted into the concrete (14) at the desired 
depth (see FIG. 2), the controller (55) closes the directional control 
valve (62) stopping the downward movement of the forks (28). At the same 
time that the dowel bars (49) enter the concrete, the controller (55) 
again sends a signal to the motor (44) actuating the rod (34) and gears 
(42) to rotate in the opposite direction as before, thereby moving the 
transverse beam (41) and dowel bar insertion device (27) rearward along 
the longitudinal beam (32) at the same speed but in the opposite direction 
as the forward motion of the machine (10). Thus, the forks (28) will 
remain stationary within the concrete slab (14) relative to the point of 
insertion while the machine (10) continues its forward movement. This 
action prevents the dowel bars from being dragged along within the 
concrete slab as the machine (10) continues its forward movement. 
As soon as the dowel bar (49) reaches the desired depth within the 
concrete, a signal is sent by the controller (55) to the dowel bar 
inserter mechanism (27) to actuate the hydraulic cylinder (25), causing 
the telescoping arm (35) of the dowel bar insertion device (27) to 
telescope up, thereby removing the forks (28) from the concrete slab (14), 
leaving the dowel bars (49) behind within the concrete slab (14) at the 
appropriate depth. As the forks (28) are being withdrawn from the 
concrete, the dowel bar inserter (27) continues to move rearwardly along 
the toothed rail (43) until it reaches the end. The removal of the forks 
(28), leaves the once smooth concrete surface scarred where the dowel bars 
(49) were inserted. This scarred surface is corrected by the action of the 
second vibrating and oscillating tamper bar assembly (110b) and the 
concrete pan forming surface (23b) of the rear pan portion (17b) as it 
passes over the concrete, leaving behind it once again a smooth, formed 
concrete surface. This procedure is repeated again and again along the 
length of the slab (14). 
When it is desired to utilize the slip forming machine without utilizing 
the dowel bar inserter (27), the front and rear pan portions (17a and 17b) 
are unbolted from the overhead structure and the dowel bar inserter (27) 
is removed. The rear pan portion (17b) is then attached to the front pan 
portion (17a) by bolts or threaded fasteners (46) as shown in FIG. 5. In 
the FIG. 5 configuration, the slip forming machine (10) can be utilized 
without inserting dowel bars. The advantage of this adjustment is that the 
slip forming machine (10) can be purchased in the FIG. 5 configuration 
without the additional expense of the dowel bar inserting mechanism (27) 
and then, at a later time, the insertion mechanism (27) can be purchased. 
Alternatively, a contractor who knows that he may need to use a dowel bar 
inserter at some time but knows that it is not required at other times can 
derive significant economic benefit from having this adjustable feature 
which allows the dowel bar inserter to be used or not used. 
Accordingly, it will be appreciated that the preferred embodiment shown 
herein does indeed accomplish the aforementioned objects. Obviously many 
modifications and variations of the present invention are possible in 
light of the above teachings. It is therefore to be understood that, 
within the scope of the appended claims, the invention may be practiced 
otherwise than as specifically described.