The two ends of the luffable and swivelable arms of the gantry of an overburden excavator each have a horizontal bolt for a frame of the drive, on the axis of rotation or drive shaft of which is mounted a rotary cutter in the form of a cutter drum. The rotary cutters are disposed on both sides of a receiving conveyor. The axes of rotation of the shafts rotating the rotary cutters are oriented approximately parallel to the plane of symmetry (longitudinal axis) of the receiving conveyor belt. The angle of the rotary cutter axis can be adjusted in relation to the plane of the roadway by the length adjuster in the form of a hydraulic or pneumatic cylinder, which is located between a bearing lug of the arm and a bearing lug of the frame. The rotary cutters transport the material via transverse conveyors to the converyor belt.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an overburden excavator with a gantry arm which 
can be adjusted vertically and pivoted laterally, and with rotary cutters 
with cutting edges located on both sides of its receiving conveyor. 
2. Description of the Prior Art 
On an overburden excavator of the prior art as described in DE-AS 11 39 
073, the axis of rotation of the rotary cutters is perpendicular to the 
conveyor belt, and the rotary cutters have excavating blades for the 
overburden, whereby the working directions of the rotary cutters can be 
opposite to one another. When the direction of the rotary cutters is from 
top to bottom, there must be extra space below the gantry for the idler 
rolls and the conveyor belt. If some of the material cut off remains ahead 
of the front end of the gantry and is not transported onto the conveyor 
belt, this material left on the ground hinders the movement of the rotary 
cutter on the other side when the gantry pivots laterally. This is also 
true in the opposite direction of rotation, i.e. when the rotary cutters 
are operating from bottom to top. This overburden excavator of the prior 
art is apparently suitable only for use in rather loose ground, because 
the overburden material is further compressed after it is removed. It is 
unsuited, moreover, for cutting and breaking hard rock. 
OBJECT OF THE INVENTION 
The object of the invention is, therefore, an overburden excavator of the 
type with swivelable and luffable gantry arm which makes possible the 
economical breaking and secure removal of even hard overburden material. 
This object is achieved in that the rotary cutters are disposed on both 
sides of a receiving conveyor so that the receiving end of this conveyor 
is placed between the rotary cutters, the axes of rotation of the rotary 
cutters being approximately parallel to the plane of symmetry of the 
receiving conveyor. While the gantry arm is swiveling, the rotary cutters 
cut and break the overburden on the outside extremity of the unit by 
rotation from top to bottom, and simultaneously transport it on the 
opposite, ascending side of the cutters toward the receiving conveyor, 
whereby between the rotary cutters and the receiving conveyor, there can 
be transverse conveyors in the form of deflector plates, or driven 
conveyor belts, which may also be equipped with flight feeders. To the 
side of the transverse conveyors and at the end of the receiving conveyor 
there can be deflector plates for the overburden material. 
SUMMARY OF THE INVENTION 
The rotary cutters are preferably cutter drums, whereby the angle between 
the axis of rotation of each cutter and the roadway plane can be adjusted 
at any time. For this purpose, a drive frame of the rotary cutter is 
connected with bolts to an arm of the gantry, which can have a bearing lug 
pointing upward for a length adjuster, which engages with a bearing lug 
pointing upward on the frame. 
The invention relates broadly to an overburden excavator with a base and a 
swivelable superstructure disposed on the base. The swivelable 
superstructure comprises a gantry apparatus with a rotary cutter 
arrangement being connected to the gantry apparatus at an outer end 
thereof. The rotary cutter arrangement has axes about which the cutting 
action of the rotary cutter arrangement cuts. The rotary cutter 
arrangement also has transverse conveyors disposed on the gantry behind 
the rotary cutters transferring material cut thereby from the rotary 
cutter arrangement to a receiving conveyor disposed on the gantry between 
the rotary cutters. The receiving conveyor transporting material to a 
location on the superstructure inwardly thereof defines a longitudinal 
axis or plane of symmetry disposed along the gantry. The shafts for 
driving the rotary cutters are disposed along the gantry on both sides of 
the receiving conveyor, and each shaft defines its own longitudinal axis. 
The longitudinal axes of the shafts are disposed substantially parallel to 
the longitudinal plane of symmetry of the receiving conveyor. The 
inclination of the shafts can be adjusted by a length adjuster. 
Embodiments of the invention are illustrated in the accompanying drawings 
and are explained in greater detail below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The overburden excavator has a caterpillar track 12 with a rim 13 for the 
swivelable superstructure 14, on which the arms 1 of a vertically movable 
gantry are mounted by means of bolts 15. Between the arms 1 of the gantry 
there is a receiving conveyor 2, which transports the material broken at 
the excavating face A via a discharge funnel 16 onto the conveyor belt 17 
to the discharge point B. 
The ends of the arms 1 of the gantry each have horizontal bolts 3 for a 
frame 4 of a drive, on whose axis of rotation 5a of the drive shaft 5 is 
mounted a cutter in the form of a cutting drum. The rotary cutters 6 are 
disposed laterally on both sides of the receiving end of the receiving 
conveyor 2. The axes of rotation 5a of the rotary cutters 6 are 
approximately parallel to the plane of symmetry (longitudinal center plane 
2a) of the conveyor belt 2. Instead of two cutting drums, other breaking 
and/or transport devices equipped with teeth or cutting edges can also be 
used. The angle of each frame 4 with the rotary cutter 6 can be adjusted 
in relation to the roadway plane by means of a length adjuster 7 (shown in 
FIG. 3) in the form of a hydraulic, or pneumatic, cylinder which is 
located between a bearing lug 8 of the arm 1 and a bearing lug 8a of the 
frame 4. The rotary cutter transports the material via a transverse 
conveyor 9 with a chute 9a visible in FIG. 4 onto the conveyor belt 2. The 
transverse conveyor 9 is disposed substantially tangential to the 
swiveling motion of the gantry 1 around the axis 13a of the rim 13 and is 
preferably a deflector in the manner of a plough blade. To transport the 
material, the rotation of the rotary cutter 6 equipped with the cutting 
edges in the direction of the arrow indicated in FIG. 4 generally 
suffices, in combination with the swiveling motion of the gantry around 
the axis 13a of the rim 13. The material is prevented from sliding off the 
transverse conveyor 9 by a deflector 10 located approximately vertically 
behind it, and by a plate 11 located ahead of the front end of the 
conveyor belt 2 over the idler roller 20 of the conveyor belt 2. Instead 
of a plough blade driven belt conveyors or flight feeders can also be used 
as transverse conveyors (FIG. 3). 
Referring once again to FIG. 2, the axis of rotation 5a of the drive shaft 
5 which runs the rotary cutter 6 is approximately parallel to the 
longitudinal center plane 2a of the conveyor belt. The details of the 
drive which rotates the rotary cutter 6 are not shown in detail in the 
figures but are well known in the prior art and are typically shown in 
U.S. Pat. No. 4,616,720, entitled, "Divided Bucket Type Rotary Excavator", 
U.S. Pat. No. 4,663,868, entitled "Scoop Wheel Having Oscillating Impact 
Cutters"; U.S. Pat. Nos. 3,677,604; 3,746,100; 4,012,856; 4,214,386; 
2,910,274; 3,038,710; and 3,336,989. All of the afore-mentioned patents 
are incorporated by reference as if the entire contents thereof were fully 
set forth herein. 
The conveyor belt 2 is supported by a structure 2b which, among other 
things, maintains the conveyor belt 2 in a stretched position between the 
two rollers 20 and 22, as shown in FIG. 4 and FIG. 1 respectively. 
Referring once again to FIG. 4, the transverse conveyor 9 and the chutes 9a 
are all attached to the supporting structure 2b of the conveyor belt 2. 
The conveyor belt 2 may be termed as a receiving conveyor, since it 
receives material excavated by the cutters 6 which is transported by the 
transverse conveyors 9 and into the chutes 9a for loading onto the 
conveyor belt 2. The supporting mechanism for the transverse conveyors 9 
and the chutes 9a is not shown in any detail but can be any of a number of 
means of attachments such as rods, I-beams and plates for providing 
substantially high rigidity. Each chute 9a is preferably also attached to 
a similar structure or the same structure that supports its transverse 
conveyor 9. The plate 11 located ahead of the front end of the conveyor 
belt 2 is shown on the left side in FIG. 4 and is omitted on the right 
side thereof for simplicity. This plate 11 extends adjacent the transverse 
conveyor 9 and the chute 9a in order to guide the material which has been 
excavated by the cutters 6 and conveyed by the transverse conveyor 9. This 
plate 11 is also attached, preferably, by means of a structure not shown, 
to the structure 2b which supports the conveyor belt 2. This not shown 
structure is similar to that as described above for holding the transverse 
conveyors 9 and the chutes 9a. 
In summing up, the overburden excavator of an embodiment of the present 
invention has a gantry which can move vertically and pivot laterally. The 
lateral pivoting of the gantry is preferably done about the swiveling axis 
13a of the superstructure 14 of the excavator. In relationship to the 
gantry, there is a structure 2b for holding the conveyor belt 2 thereon. 
On both sides of the gantry there are rotary cutters 6 located on both 
sides of the receiving end of the receiving conveyor belt 2. The rotary 
cutters 6 are driven by shafts 5 which are substantially parallel to the 
longitudinal center plane 2a of the conveyor belt 2. 
Behind each of the rotary cutters 6 at least a portion of a transverse 
conveyor 9 is disposed substantially tangential to the swiveling motion of 
the gantry 1 around the axis 13a of the rim 13. A portion of each of the 
transverse conveyors 9 is disposed between the cutters 6. The transverse 
conveyors 9 preferably end over the conveyor belt 2 and transport the 
material cut by the rotary cutter 6 across to the conveyor belt 2. 
Each of these transverse conveyors 9 has a deflection plate 9a disposed for 
guiding the material excavated by the cutters 6 onto the main, or 
receiving, conveyor belt 2. These transverse conveyors 9 can be of 
deflector type or driven as belt conveyors or chain driven flight feeders. 
The transverse conveyors 9 may be driven by hydraulic motors supplied by 
hydraulic pressure from a motor (not shown). This motor is preferably 
disposed in the superstructure 14 and drives also the conveyor belt 2 and 
the axles 5, which drive the cutters 6. Alternatively, other means of 
driving the particular belts and shafts may be used, such as an individual 
transmissions or motors for driving each of the following, that is, the 
main conveyor belt 2, the transverse conveyor belt 9, and the shafts 5 for 
rotating cutters 6. Alternatively, there could be a transmission driving 
the shafts 5 for reversing the rotation of the rotary cutters 6 for under 
certain conditions. 
The transverse conveyors 9 in an embodiment of the invention are equipped 
with chain or flight feeders as shown in FIG. 5. Flight feeders are 
described in U.S. Pat. No. 4,017,241, entitled "Notched Flight Feeder 
Screws for Briquetting Operation" and U.S. Pat. No. 3,901,621, entitled 
"Auger Assembly". Each of the afore-mentioned patents is incorporated by 
reference as if the entire contents thereof were fully set forth herein. 
Each frame 4 is adjusted by the preferably hydraulic, or pneumatic, 
cylinder which comprises the length adjuster 7, as shown in FIGS. 1 and 3. 
In this embodiment of the invention, the angle of the shaft 5 which drives 
the cutter 6 can be adjusted with respect to the ground plane. 
The frame 4 of the rotary cutter 6 is attached with bolts 3 to the arm of 
the gantry. The arm of the gantry has a bearing lug 8 pointing upwardly 
for the attachment of a length adjuster 7, which length adjuster engages a 
bearing lug 8 pointing upwardly from the frame 4. FIG. 5 shows an 
embodiment of the general concept illustrated in FIG. 4, in an 
alternative, with driven transverse conveyors. 
The invention as described hereinabove in the context of the preferred 
embodiments is not to be taken as limited to all of the provided details 
thereof, since modifications and variations thereof may be made without 
departing from the spirit and scope of the invention.