Crane Terminology

AXLE, FIXED - A shaft which is fixed in the end truck and about which the wheel revolves.

AXLE, ROTATING - A shaft which is fixed in the wheel and which rotates on bearings fixed in the end truck.

BEARING LIFE - the B-10 life of an anti-friction bearing is the minimum expected life in hours of 90% of a group of bearings which are operating at a given speed and loading.

BEARING, LIFETIME LUBRICATED - An anti-friction bearing which is provided with seals and a high-stability oxidation-resistant grease to permit operation of the bearing without re-lubrication for not less than the specified B-10 life.

BLOCK, LOAD - The assembly of hook, swivel, bearings, sheaves, pins and frame suspended from the hoisting ropes. In a "short type" block, the hook and the sheaves are mounted on the same member, called the swivel. In a "long type" block, the hook and the sheaves are mounted on separate members. (The supporting member for the sheaves is called the sheave pin and the supporting member for the hook is called the trunnion.)

BLOCK, UPPER - A fixed assembly of sheaves, bearings, pins and frame, located on the trolley cross members, and which supports the load block and its load by means of the ropes.

BOGIE - A short end truck attached to the end of one girder (or to a connecting member if more than one bogie is used per girder). This type of end truck is used when more than four wheels are required on a crane due to the design of the runway.

BOGIE, EQUALIZING - A short end truck which is flexibly connected to one girder (or connecting member) by means of a pin upon which the truck can oscillate to equalize the loading on the two truck wheels. This construction uses a very rigid end tie between the girders.

BOGIE, FIXED - A short end truck which is rigidly connected to one girder. A flexible end tie is used between the girders to permit equalization of the wheel loads by torsional deflection of the girders and flexing of the end tie.

BRAKE, EDDY CURRENT - A device for controlling load speed in the hoisting or lowering direction by placing a supplementary load on the motor. This load results from the interaction of magnetic fields produced by an adjustable direct current in the stator coils and induced currents in the rotor.

BRAKE, PARKING - A friction brake for bridge or trolley, automatically applied when power to the crane is interrupted.
CAMBER- The slight, upward, vertical curve given to girders to partially compensate for deflection due to rated load and weight of the crane parts.

CLEARANCE - The minimum distance from any part of the crane to the point of nearest obstruction.

CONTROL BRAKING MEANS - A method of controlling lowering speed of the load by removing energy from the moving load or by imparting energy in the opposite direction.

COUNTERTORQUE - A method of control by which the power to the motor is reversed to develop torque in the opposite direction to the rotation of the motor.

DYNAMIC - A method of controlling speed by using the motor as a generator, with the energy being dissipated in resistors.


EDDY CURRENT - A method of controlling or reducing speed by means of an electrical induction load brake.

MECHANICAL - A method of controlling or reducing speed by friction.

REGENERATIVE - A method of control in which the electrical energy generated by the motor is fed back into the power system.

CONTROLLER - A device or group of devices which serves to govern in some predetermined manner the power delivered to the motor to which it is connected.

CONTROLLER, MANUAL - A controller having all of its basic functions performed by devices which are operated by hand.

CONTROL PANEL - An assembly of electrical components (magnetic or static) which governs the flow of power to or from a motor in response to signals from a master switch, pushbutton station, or remote control.

COVER PLATE - The top or bottom plate of a box girder.

CRANE, HOT MOLTEN MATERIAL HANDLING (LADLE) - An overhead crane used for transporting or pouring molten material.

CRANE, OUTDOOR STORAGE GANTRY - A special type of gantry crane of long span and with long legs, usually used for the storage of bulk material such as ore, coal, limestone, or sand. This type of crane normally will have one or two cantilevered girder ends with through legs.

CREEP SPEED - A very slow, constant, continuous, fixed rate of motion of the hoist, trolley, or bridge: usually established at 1% to 10% of the normal full load speed.

CRITICAL LOAD - As defined by the Nuclear Regulatory Commission, "A critical load is a load of magnitude or kind that under certain conditions, if dropped, could result in damage leading to unacceptable release of radioactivity or impair the capability to safely shut down the plant."

DEFLECTION, DEAD LOAD - The vertical displacement of a bridge girder due to its own weight plus the weight of parts permanently attached thereto, such as footwalk, drive mechanism, motor and control panels. The dead load deflection is fully compensated for in the girder camber.

DEFLECTION, LIVE LOAD - The vertical displacement of a bridge girder due to the weight of the trolley plus the rated load.

DIAPHRAGM - A vertical plate (or channel) between the girder webs, which serves to support the top cover plate and bridge rail and to transfer the forces of the trolley wheel loads to the webs. Refer to Figure 44 in Part A of Section VII.

DRIFT POINT - A control point on a travel motion which releases the electric brake without energizing the motor.

DRIVE - The assembly of the motor and gear unit used to propel the bridge or trolley.

END TRUCK - An assembly consisting of structural members, wheels, bearings, axles, etc., which supports the bridge girder(s) or the trolley cross member(s)

EXPOSED - Capable of being contacted inadvertently (applies to hazardous objects not adequately guarded or isolated).

FLEET ANGLE - The angle formed by the wire rope and the drum groove or sheave groove in the plane which contains the wire rope and is parallel to the drum or sheave axis. Refer to Figure 90 in Part B of Section VIII.

FOOTWALK - A walkway with handrail and toe boards, attached to the bridge or trolley for access purposes.

GAUGE - The horizontal distance center to center of the bridge rails.

GIRDER, BRIDGE - The principal horizontal beam(s) of the crane, which supports the trolley, is supported by the end trucks, and is perpendicular to the runway.

GIRDER, DRIVE (GIRDER "A"/”G1”) - The bridge girder to which the bridge motor and gearcase(s) are attached. For cranes having a drive on each girder, it is the girder to which the control panels and/or the cab are attached.

GIRDER, IDLER (GIRDER "B”/”G2”) - The bridge girder which does not have the bridge drive attached, but which usually carries the bridge conductors.

GIRDER, RUNWAY - A horizontal beam attached to the building columns GIRDER, Auxiliary (OUTRIGGER)- An additional girder, either solid or latticed, arranged parallel to the bridge girder(s) for supporting the footwalk, control panels, operator's cab, etc., to reduce the torsional forces such loads might otherwise impose.

HOIST, AUXILIARY - A supplemental hoisting unit, usually designed to handle lighter loads at a higher speed than the main hoist.

HOIST, MAIN - The primary hoist mechanism provided for lifting and lowering the rated load of the crane.

HOOK APPROACH, END - The minimum horizontal distance, parallel to the runway, between the centerline of the hook and the face of the wall (or columns) at the end of the building.

HOOK APPROACH, SIDE - The minimum horizontal distance, perpendicular to the runway, between the centerline of a hook (main or auxiliary) and the centerline of the runway rail.

INCH (INCHING) - See "jog". Often used incorrectly to refer to "creep speed" (which see).

JOG (INCH) - To move the hook, trolley, or bridge in a series of short, discontinuous, increments by momentary operation of a controller.

LEFTHAND END - A reference to parts or dimensions on the viewer's left of the centerline of span, established when facing the drive girder side of the crane.

LIFT (HOOK TRAVEL) - The maximum vertical distance through which the hook can move, as determined by the length of rope and/or the number of grooves on the drum.

LIMIT SWITCH - An electrical device which is operated by the bridge, trolley, or hoist motion to disconnect the circuit, to establish a new circuit, or to provide a warning.

LOAD, DEAD - The load(s) on a portion of the crane, which remain(s) in a fixed position relative to the member being considered.

LOAD, LIVE - A load which moves or varies relative to the member being considered. For the trolley, the live load consists of the rated load plus the weight of the block. For the bridge, the live load consists of the rated load plus the weight of the trolley.

LOAD, RATED - The maximum static vertical load for which a crane or an individual hoist is designed.

LOAD FLOAT - A control system which enables Stepless operation of a hoist in either the lifting or lowering direction for a range of about 04% of full rated speed, as well as permitting the load to be suspended stationary for a very short time with the holding brake(s) released.

MASTER SWITCH - A manually operated device which governs the operation of contactors and/or auxiliary devices of an electric control.

MESSENGER TRACK - A horizontal member, mounted along a handrail or girder, supporting movable carriers from which festooned wires are hung. The festooned wires may be used to transmit current from the bridge to the trolley or from the bridge to a pendant control unit.

OVERLOAD - Any hook load greater than the rated load.

PITCH DIAMETER - The distance, measured through the center of a drum or sheave,  from center to center of a rope passed about the periphery of the drum or sheave.

PLUG - To operate a controller in such a manner that the motor line voltage polarity or phase sequence is reversed before the motor rotation has stopped, thereby developing a counter torque which acts as a retarding force.

PLUGGING RELAY - A current relay used on a bridge or trolley control panel which senses current in the motor secondary circuit of an alternating current motor and limits reverse torque of the motor to the first control point until the motor rotation has stopped. In a direct current control panel, the relay performs the same function by establishing a patented sensing circuit at the motor armature. (Sometimes called an anti-plugging relay.)

RAIL, BRIDGE - The track supported by the bridge girder(s), on which the trolley travels.

RAIL, RUNWAY - The track supported by the runway beams, on which the crane travels.

RIGHTHAND END - A reference to parts or dimensions on the viewer's right of the centerline of span, established when facing the drive girder side of the crane.

SECONDARY VOLTAGE - The induced open-circuit voltage in the rotor of a wound-rotor (slipring) motor at standstill, as measured across the slip rings with rated voltage applied to the primary (stator) winding.

SHAFT, CROSS (SQUARING SHAFT) (DRIVE SHAFT) - The shaft(s) extending the length of the bridge, used to transmit torque from the motor to a wheel(s) at each end of the bridge.

SIDE PULL - The portion of the hoist rope pull acting horizontally when the hoist ropes are not operated vertically.

SPAN - The horizontal distance center to center of the runway rails.

SPRING RETURN - A device used on a manual controller, master switch, or pushbutton to cause the unit to return automatically to the neutral position, when released by the operator.

TORQUE, LOCKED-ROTOR - The minimum torque which a squirrel-cage motor will develop at rest, for all angular positions of the rotor, with rated voltage applied at rated frequency. Not applicable to wound-rotor (slipring) motors.

TORQUE, MOTOR BREAKDOWN - The maximum torque which a squirrel-cage or wound-rotor (slip-ring) motor will develop with rated voltage applied at rated frequency, without an abrupt drop in speed.

TORQUE, MOTOR FULL-LOAD - The torque developed by an electric motor (A.C. or D.C.) to produce its rated horsepower at rated full-load speed.

TORQUE, MOTOR PULL-UP - The minimum torque developed by a squirrel-cage or wound-rotor (slipring) motor during the period of acceleration from rest to the speed at which breakdown torque occurs. For squirrel-cage motors with 8% or greater slip, the pull-up torque, the break down torque, and the starting torque are all equal and occur at zero speed.

TWO-BLOCKING - Inadvertent physical contact between the load block and the upper block or other part of the trolley.

WEB PLATE - The vertical plate(s) connecting the upper and lower flanges or cover plates of a girder.

WHEELBASE - The distance from center .to center of the outermost wheels of the bridge or trolley, measured parallel to the rail.

WHEEL LOAD, BRIDGE - The vertical force (without impact) produced on any bridge wheel by the sum of the rated load, trolley weight and bridge weight, with the trolley so positioned on the bridge as to give maximum loading.

WHEEL LOAD, TROLLEY - The vertical force (without impact) produced on any trolley wheel by the sum of the rated load and the trolley weight.