Abstract: The invention relates to a device for protecting selective cutting machines against overload, in which the selective cutting machine has cutting tools, in particular cutting rollers, rotatably supported on a pivotable cantilevered arm, and both the cutting tools and the cutting arm are connected to separate drive mechanisms. At least one strain or deformation measuring sensor is disposed on the pivotable cantilevered arm, and its signals are delivered to an evaluation circuit; the evaluation circuit is connected via control lines at least to the drive mechanisms of the cutting arm and the cutting tool.

Abstract: The bit holder (1) is nonpositively connected to a bit bushing (3) with adherence to a pressure per unit of surface area of >100N/mm.sup.2 between the conical outer surface of the bit bushing (3) and the inner wall of the receiving bore (2) of the bit holder (1). After the bushing has been driven into the receiving bore (2), the conical outer surface of the bit bushing (3), formed by rectilinear generatrices, protrudes beyond the bore (2) by an excess amount (a).

Abstract: For cutting rock by means of cutting head (1) having its bits (24) cooperating over a limited axial shifting stroke (a) with a cylinder-piston-aggregate, for example a valve (18), it is proposed to intermittently subject the cylinder-piston-aggregate to the action of pressurized fluid, thus exposing the bit (24) during its engaging the rock to percussion forces. During the phases lacking any action of pressurized fluid onto the cylinder-piston-aggregate, the bit (24) shall be pushed into its starting position. This embodiment can be realized with both hydraulic and pneumatic cylinder-piston-aggregates, noting that in case of an embodiment having a hydraulic cylinder-piston-aggregate it is preferred to design this cylinder-piston-aggregate as a valve (18) which simultaneously provides the possibility to expel pressurized liquid via a spraying nozzle (32) onto the mine face. (FIG.

Abstract: A hydraulic mine prop includes an inner piston-like prop guided within an outer cylinder-like prop, and a roof fall valve. The interior space of said inner prop communicates freely with the working chamber of the prop, and the roof fall valve is arranged outwardly on the prop and rigidly secured thereon, the valve being connected to the working chamber by an orifice provided in the prop and leading to the working chamber. The cross-sectional area of the roof fall valve in its open position.

Abstract: The telescopically extendable prop (1) has at the periphery of the intermediate prop (3) abutments (30) which cooperate with a valve (15) before the intermediate prop (3) has attained its highest extended position. The valve (15) stops the extending stroke of the intermediate prop (3) and is releasing the beginning of the extending stroke of the top prop (4). As soon as a predetermined pressure is built up in the consolidating conduit (10) of the top prop (4), the valve (27) subjected to this pressure is overacting the valve (15) cooperating with the abutments (30) of the intermediate prop (3), whereupon the consolidating stroke is completed by pressurizing the intermediate prop (3) with pressurizing fluid. (FIG.

Abstract: The mine roof supporting structure comprises hydraulic props (3) which are pressing a swivelling cap (8) against the mine roof. A link lever (5) is pivotally linked to the floor frame (1) and a shield (4) is pivotally linked to the link lever (5) and to the cap (8). The shield (4) is pulled in direction to the floor frame (1) by means of a hydraulic tension strut (14). The working chamber (24) of the tension strut (16), which working chamber includes the piston rod and is facing the pivotal point (12) of the tension strut (16) to the shield (4), can be brought in connection with the supply conduit (19) for feeding pressurized fluid to the props (3) via a spring loaded check valve (22, 23), noting that the opening pressure of the spring (22) is smaller than the final supporting pressure exerted by the props (3). The piston surface of the working chamber (24) is smaller than the piston surface (4) delimiting the working chamber of the props (3).

Abstract: It is an object of the invention to provide an improved shield-carrying roof support unit which has a linkage for adjusting the elevation of the cap while the pivotal connection between the cap and the shield is constrained to move substantially at right angles to the base frame. The provision of auxiliary links having pivotal connections at properly selected points results in a linkage which has a precisely defined configuration and avoids an overloading of the pivotal connections such as could occur in known shield-carrying roof support units of the same kind.

Abstract: A swivel mechanism for kerf-cutting machines comprising a cutter arm, which carries the cutting tool, in which mechanism the cutter arm is pivoted to a swivel head on a horizontal axis for a vertical angular movement, said swivel head is pivoted on an approximately vertical axis to a bearing disc, which is rigidly connected to the frame of the cutting machine and has an outer annular zone that is engaged on both sides by sliding surfaces of the swivel head, and swivel drive means are provided for imparting angular movements to the swivel head, characterized in that the swivel drive means comprise two racks, which are mounted in the swivel head for movement in mutually opposite directions, which are parallel to the vertical center plane of the cutter arm, and a pinion is connected to and coaxial with the bearing disc and is in mesh with said racks at diametrically opposite points of said pinion.

Abstract: A pressure relief valve for hydraulic mine supporting elements, particularly mine props, has a valve member loaded in its closing direction by a spring, a piston is connected to the valve member end sealingly sliding within a cylinder of the valve housing and arranged to be acted upon in closing direction by the pressure prevailing within the space before the seat of the valve member. The valve member has a neck portion of reduced diameter between the valve seat and the piston and the annular cross section, being acted upon in closing direction, between the neck portion and the circumference of the piston is smaller than the annular cross section, being acted upon in opening direction, between the neck portion and the valve seat.