Ballast cleaning machine with preliminary sifting conveyor

In a ballast cleaning machine which comprises a machine frame, a ballast excavating and conveying chain mounted on the machine frame, the chain having a discharge end for the excavated and conveyed ballast, ballast screening apparatus arranged to receive the ballast from the discharge end of the chain and to separate a waste component from the clean ballast, a conveyor band system mounted below the screening apparatus for receiving the clean ballast component and redistributing it to the track, and an endless conveyor band mounted below the screening apparatus for receiving and conveying the waste component: a sifting conveyor band mounted between the discharge end of the chain and the screening apparatus, the sifting conveyor band having an upper stringer receiving the excavated and conveyed ballast from the discharge end and defining openings permitting a portion of the waste component to pass through the sifting conveyor band, and a drive connected to the sifting conveyor band for driving the band whereby partially cleaned ballast is conveyed from the discharge end of the chain to the screening apparatus.

The present invention relates to a track working machine, particularly a 
ballast cleaning machine, capable of receiving bulk material, particularly 
ballast, including a waste component from the track, cleaning the received 
bulk material and conveying the bulk material, which comprises a machine 
frame, a bulk material excavating and conveying chain mounted on the 
machine frame, the chain having a discharge end for the excavated and 
conveyed bulk material, bulk material screening apparatus arranged to 
receive the bulk material from the discharge end of the chain and to 
separate the waste component from the clean bulk material, a conveyor band 
system mounted below the screening apparatus for receiving the clean bulk 
material component and redistributing it to the track, and an endless 
conveyor band mounted below the screening apparatus for receiving and 
conveying the waste component. 
UK patent application No. 2,116,233 A, published Sept. 21, 1983, discloses 
a mobile ballast cleaning machine of this type wherein a vibratory 
screening installation for cleaning the ballast succeeds the ballast 
excavating and conveying chain in the operating direction of the machine, 
and two conveyor bands pivotal in a plane parallel to the track for 
redistributing the cleaned ballast as well as an endless conveyor band for 
removing the waste component are arranged below the screening 
installation. The bottom of the ascending guide channel holding the 
ballast excavating and conveying chain defines slots for pre-screening the 
excavated ballast. 
U.S. Pat. No. 2,142,208, dated Jan. 3, 1939, relates to apparatus designed 
only for cleaning the ballast in the track shoulders with two endless 
excavating chains arranged in series at each shoulder. Two screening 
grates defining round holes are arranged under the leading excavating 
chain for respectively depositing smaller ballast stones and the waste on 
the exposed subgrade of the shoulder. A conveyor band is associated with 
the trailing excavating chain and a vibratory, obliquely arranged 
screening grate is mounted below the upper discharge end of this conveyor 
band for separating the waste from the ballast. While the cleaned ballast 
is redistributed to the ballast bed by a chute leading from the lower end 
of the screening grate to the ballast bed, the waste is removed by a 
conveyor. This machine and its ballast cleaning system is complex in 
structure while being inefficient wherefore it has not had any commercial 
success. Cleaning the ballast over the entire width of the track is not 
possible with this machine. 
U.S. Pat. No. 4,178,995, dated Dec. 18, 1979, discloses a ballast cleaning 
machine with a ballast excavating and conveying chain, a vibratory ballast 
screen, a waste removal conveyor below the screen and an endless conveyor 
band conveying the excavated ballast from a discharge end of the chain to 
the screen. The cleaned ballast is stored adjacent the point where it is 
excavated and discharged in controlled amounts for redistribution to the 
track. 
U.S. Pat. No. 2,165,068, dated July 4, 1939, relates to a ballast cleaning 
machine wherein excavated ballast is conveyed over an inclined sifting 
grate. 
It is the primary object of this invention to provide a track working 
machine of the first-described type having an enhanced cleaning 
efficiency. 
The above and other objects are accomplished according to the invention 
with a sifting conveyor band mounted between the discharge end of the 
chain and the screening apparatus. The sifting conveyor band has an upper 
stringer receiving the excavated and conveyed ballast from the discharge 
end and defining openings permitting a portion of the waste component to 
pass through the sifting conveyor band, and a drive is connected to the 
sifting conveyor band for driving the band whereby partially cleaned 
ballast is conveyed from the discharge end of the chain to the screening 
apparatus. 
This sifting conveyor produces a pre-screening of the bulk material before 
it is cleaned on the screening apparatus, which greatly increases the 
efficiency of the cleaning operation with a minimal increase in 
construction costs. The sifting conveyor band delivers bulk material 
containing a substantially reduced amount of waste to the screening 
apparatus whereby cleaning of the bulk material in the screening apparatus 
proceeds much more quickly since a reduced portion of the waste component 
must be separated during cleaning. This, on the other hand, substantially 
improves the forward speed of the machine during ballast cleaning and, 
therefore, increases the daily output of the machine. The cleaning 
operation is further facilitated because the friction between the bulk 
material particles during their conveyance along a conveyance path 
extended by the length of the sifting conveyor band is prolonged so that 
waste adhering to the bulk material is loosened, thus making the 
separation of the waste in the screening apparatus easier. This is of 
particular advantage under humid weather conditions tending to promote the 
bonding of waste to the bulk material. The sifting conveyor band may be 
used in track working machines incorporated in track renewal trains and 
standard ballast cleaning machines may be easily retrofitted with such 
sifting conveyor bands.

Referring now to the drawing, FIG. 1 shows a part of a track working 
machine illustrated as ballast cleaning machine 1 capable of receiving 
bulk material, i.e. ballast, including a waste component from track 5 
comprised of rails 3 fastened to ties 4 supported on the ballast, cleaning 
the received ballast and conveying the ballast. The machine comprises 
machine frame 7 mounted on undercarriages 2, 2 for mobility on track 5 in 
an operating direction indicated by arrow 19. Driven ballast excavating 
and conveying chain 8 is mounted on machine frame 7 and has discharge end 
9 for the excavated and conveyed ballast. Chain 8 is linked to the machine 
frame by hydraulic adjustment drives for vertical and lateral adjustment 
in a well known manner. As is conventional, the excavating and conveying 
chain comprises endless excavating chain 11 having a horizontal section 
passing transversely under track 5, an ascending section leading from one 
end of the horizontal section to discharge end 9 and a descending section 
leading from the discharge end to the other end of the horizontal section. 
Drive 10 for chain 11 is mounted at the discharge end. 
A ballast screening apparatus comprised in the illustrated embodiment of 
leading vibratory screening installation 12 and trailing vibratory 
screening installation 20 is arranged on machine frame 7 to receive the 
ballast from discharge end 9 of the excavating and conveying chain and to 
separate the waste component from the clean ballast. Each vibratory 
screening installation has drive 22 for vibrating the installation and a 
series of superposed screens of different mesh size, all of this structure 
being generally conventional. As is also known in this type of ballast 
screening apparatus, conveyor band 21 is arranged between the leading and 
trailing screening installation for longitudinal displacement in the 
operating direction. Conveyor band 21 may be so displaced that the 
excavated ballast is selectively received in one or the other screening 
installation or in both installations at the same time. A conveyor band 
system is mounted on machine frame 7 below screening apparatus 12, 20 for 
receiving the clean ballast component and redistributing it to the track. 
The illustrated conveyor band system comprises a pair of ballast 
redistributing conveyor bands 23 which are pivotal in a plane 
substantially parallel to the track, each conveyor band 23 being 
associated with a respective track rail 3. An input end of each conveyor 
band 23 is aligned below a respective chute discharging a cleaned ballast 
component from leading screening installation 12 and the discharged 
cleaned ballast component is conveyed from the input end to a discharge 
end whence it is thrown onto the exposed subgrade for redistribution. The 
illustrated conveyor band system comprises a further pair of short ballast 
redistributing conveyor bands 24 also associated with the track rails. 
These short conveyor bands below trailing sceening installation 20 receive 
the cleaned ballast component discharged therefrom and convey it to chutes 
which redistribute the cleaned ballast component behind machine 1. Endless 
conveyor band 17 is mounted below the screening apparatus centrally 
between the redistributing conveyor bands for receiving and conveying 
waste component 16. Further conveyors (not shown) receive the waste 
component from an output end of endless conveyor band 17 to load the waste 
component on freight cars preceding machine 1 or dispose of the same in 
any other desired manner, all of which is well known. 
According to this invention, endless sifting conveyor band 14 is mounted 
between discharge end 9 of the chain and screening apparatus 12, 20, the 
sifting conveyor band having an upper stringer receiving the excavated and 
conveyed ballast from the discharge end. The sifting conveyor band defines 
openings 15 permitting a portion of waste component 16 of the ballast to 
pass through the sifting conveyor band. Drive 13 is connected to sifting 
conveyor band 14 for driving the band whereby partially cleaned ballast is 
conveyed from discharge end 9 of the excavating and conveying chain to 
screening apparatus 12, 20. In the illustrated embodiment, the sifting 
conveyor band is mounted directly above endless conveyor band 17 receiving 
and conveying waste component 16 and is arranged to ascend from discharge 
end 9 to the screening apparatus, preferably at an angle of 20.degree. to 
30.degree.. This saves any additional conveyor means between conveyor 
bands 14 and 17 since the waste simply falls through openings 15 into 
conveyor band 17. Because of the inclination of sifting conveyor band 14, 
some waste always remains behind the ballast conveyed upwardly on the 
conveyor band so that a larger portion thereof is removed through openings 
15. 
Machine 1 is operated from control panel 25 arranged in a rear cab on 
machine frame 7. As is conventional, a track lifting device is mounted on 
the machine frame for raising the track off the ballast bed at the point 
of ballast excavation. Also as conventional, a vertically adjustable 
ballast planing device is mounted on the machine frame behind the point 
where the clean ballast component is redistributed from the discharge ends 
of conveyor bands 23 to smooth the redistributed ballast. 
The illustrated embodiment of machine 1 comprises protective housing 18 
mounted on machine frame 7 below sifting conveyor band 14 so that the 
portion of waste component 16 passing through openings 15 falls through 
the protective housing. A series of rollers 30 mounted on protective 
housing 18 support endless sifting conveyor band 14 thereon. Power drive 
31 constituted by a hydraulic cylinder-piston device is connected to 
sifting conveyor band 14 for displacing the same in the direction of its 
longitudinal extension and with respect to screening apparatus 12, 20. The 
illustrated protective housing has protective and limiting walls 33 
alongside the two side edges of the upper stringer of sifting conveyor 
band 14 and the leading end thereof whereby the ballast conveyed on the 
upper stringer is channeled between the walls and prevented from dropping 
off the leading sifting conveyor band end. The protective and limiting 
side walls project beyond a trailing end of the sifting conveyor band 
adjacent screening apparatus 12, 20. In this manner, the protective 
housing covers the two side edges and the leading end of the sifting 
conveyor band. As shown in FIG. 2, protective and limiting walls 33 are 
inclined to operate in the manner of a funnel and extend to the upper 
stringer slightly inwardly of the side and end edges thereof, the upper 
ends of the side walls 33 being affixed to the upper ends of the side 
walls of housing 18. 
The remote-controllable displacement of the sifting conveyor band by drive 
31 enables the conveyance path of the excavated ballast to be rapidly and 
continuously adjusted to adapt the machine operation to prevailing ballast 
conditions. For example, if the screening apparatus is suddenly 
overloaded, delivery of further ballast thereto may be temporarily 
interrupted by so displacing sifting conveyor band 14 that it delivers the 
excavated ballast directly to waste component conveyor band 17 mounted 
directly therebelow. The arrangement of the protective and limiting walls 
prevents any ballast from gliding off the sifting conveyor band even if a 
considerable amount of ballast is conveyed thereon and/or the sifting 
conveyor band is vibrated. The protective housing assures that all of the 
portion of the waste component passing through openings 15 is directed to 
waste component conveyor band 17 and, furthermore, provides a convenient 
support for the sifting conveyor band. 
As shown in FIG. 2, means 26 is connected to sifting conveyor band 14 for 
vibrating the same. The illustrated vibrating means comprises a series of 
crank shafts 27 arranged along the sifting conveyor band in the direction 
of the longitudinal extension thereof and connected to drive 13 by a 
suitable motion-transmitting means, such as a transmission belt or chain. 
The crank shafts as well as rollers 28 about which the sifting conveyor 
band is trained at respective ends thereof are journaled in two lateral 
support ledges 29 mounted for displacement on rollers 30. The piston rod 
of hydraulic displacement drive 31 is connected to the sifting conveyor 
band to displace between a first position shown in full lines in FIG. 1 
and a second position shown in dash-dotted lines, as indicated by the 
arrows pointing in opposite directions. The cylinder end of displacement 
drive 31 is connected to protective housing 18. When the sifting conveyor 
band is displaced into the end position shown in dash-dotted lines, the 
excavated ballast will fall directly from discharge end 9 onto waste 
component conveyor band 17. 
Sifting conveyor band 14 defines openings 15 whose size has been 
exaggerated in the drawing for the sake of clearer illustration. The 
openings are substantially uniformly distributed over the entire width and 
length of the sifting conveyor band, which provides a maximum number of 
openings for a high sifting efficiency while maintaining uniform strength 
for the entire band. 
As shown in FIG. 2, openings 34 and 35 of different sizes are provided, 
which provides an irregular supporting surface for the bulk material to 
enhance the friction between the bulk material particles whereby the waste 
component is loosened. Round openings enable larger waste particles or 
ballast stones which are too small to serve as component of clean ballast 
to be redistributed to the track to pass through the openings and thus to 
be removed. Openings 34 and 35 have a size not exceeding the smallest 
particle size of the ballast still acceptable for the clean ballast 
component, which is about 30 mm so that the opening sizes preferably range 
between 10 and 30 mm. This arrangement provides a maximal and trouble-free 
sifting of the waste component, the selection of the proper opening size 
preventing ballast stones of a size useful for the clean ballast component 
from passing through the openings. 
FIG. 3 shows a sifting conveyor band 36 with elongated slots 37 extending 
in the direction of the longitudinal extension of the band, the slots 
being uniformly distributed in rows. In sifting conveyor band 39 
illustrated in FIG. 4, elongated slots 38 are offset in relation to each 
other in the direction of the longitudinal extension of the band, the 
widths 40, 41 of alternate slots 38 differing from each other. Width 40 
may be about 30 mm while width 41 is about 15 mm. Elongated slot openings 
in the sifting conveyor band enable the waste component to pass 
continuously through the openings over a relatively long conveyance path, 
thus increasing the sifting efficiency. This opening configuration also 
aids in preventing the waste material from clogging the openings. 
In the embodiment shown in FIG. 5, sifting conveyor band 42 defines 
randomly distributed round openings 43 and elongated slot openings 44. The 
round openings are of different sizes, thus producing a highly irregular 
sifting arrangement. Sifting conveyor band 45 shown in FIG. 6 has 
alternating rows of elongated slots 46 and round openings 47, the rows 
extending in the direction of the longitudinal extension of the band. In 
the embodiment of FIG. 7, the openings in sifting conveyor band 48 are so 
arrayed that two elongated slots 49 extending in the direction of the 
longitudinal extension of the band alternate with two shorter slots 50 
extending perpendicularly thereto. In the transverse direction, pairs of 
slots 49 are so offset from adjacent pairs of slots 49 that a respective 
pair of slots 50 is disposed between pairs of slots 49 in the longitudinal 
direction. Finally, FIG. 8 shows a sifting conveyor band 51 comprised of a 
mesh formed by intersecting ropes 52 extending at angles of 45.degree. to 
the direction of the longitudinal extension of the band. The intersecting 
ropes define uniformly arrayed square openings in the band. 
The operation of ballast cleaning machine 1 may be readily derived from the 
above description of its structure and will be described in more detail 
hereinbelow. 
As soon as ballast excavating and conveying chain 8 has been put in place 
and drive 10 is actuated to operate the chain, the bulk material 
consisting of ballast containing a waste component, which fouls the 
ballast, is excavated and conveyed to discharge end 9 whence it is thrown 
continuously onto the leading input end of sifting conveyor band 14. Drive 
13 drives the band and, at the same time, operates vibrating means 26 to 
vibrate the moving sifting conveyor band to convey the bulk material to 
the higher discharge end of the sifting conveyor band while, at the same 
time, sifting the waste component through openings 15 whereby a 
pre-screened bulk material is thrown off the discharge end of the sifting 
conveyor band. Depending on the position of conveyor 21, this pre-screened 
bulk material will be discharged solely into leading screening 
installation 12, partially into the leading screening installation and 
onto conveyor 21 which discharges a portion of the bulk material into 
trailing screening installation 20, or solely onto conveyor 21 for 
complete discharge into the trailing screening installation. Waste 
component 16 sifted through openings 15 in conveyor band 14 falls through 
housing 18 directly onto conveyor band 17 for removal. The pre-screened 
bulk material in screening installations 12, 20 passes through the 
superposed vibratory screens in these installations, the waste component 
of this screening falling onto conveyor band 17 for removal while the 
clean ballast component is redistributed by conveyor bands 23 and 24 on 
the exposed subgrade, all in a well known manner. 
The disposition of sifting conveyor band 14 between the discharge end of 
the ballast excavating and conveying chain and the screening apparatus not 
only considerably enhances the total efficiency of the machine but also 
relieves the screening installations. When cleaning heavily encrusted 
ballast, a large portion of the adhering waste is removed by sifting on 
conveyor band 14 so that the screening apparatus is able to clean the 
pre-screened ballast much more rapidly and better. The danger of clogging 
the vibratory screens in the screening installations by heavy waste is 
also reduced. 
When the ballast is relatively clean, most of the waste component will be 
removed on the sifting conveyor band so that very little cleaning will 
have to be done in the screening apparatus, thus considerably improving 
the efficiency as well as the time required for cleaning the ballast. All 
of these advantages will be accomplished not only in a ballast cleaning 
machine of the illustrated type and using two screening installations in 
series but in any type of track working machine in which bulk material is 
to be cleaned.