GB1326743A - Lifting tongs - Google Patents

Abstract

1326743 Lifting tongs BRITISH STEEL CORP 1 Dec 1970 [2 Dec 1969] 58899/69 Heading B8H Lifting tongs comprising a pair of primary arms 2, 4 and a pair of secondary arms 9, 10 incorporate an automatic latching mechanism including a latch member pivotally mounted at 21 to the arm 4 for movement between two positions which respectively prevent and allow closure of jaws 8 of the arms 2, 4, in response to successive opening movements of the jaws. The latch member has an opening to receive a projection 26 on the arm 2, the projection being situated at the limit 24 of the opening when the jaws are in their fully closed position as limited by an abutment 36. Upon lowering the tongs into engagement with a load or a surface, the jaws are forced open by the engagement thrust and the projection 26 moves down the latch member opening to a position 30 at which the member is in a position of equilibrium, and upon further downward movement the projection moves into a recess 32 which is shaped such that closing of the jaws is prevented. The jaws cannot be closed until the projection 26 is moved into another equilibrium position 34 of the latch member by further opening of the jaws, after which the projection rides along the profile 40 of the opening allowing closing of the tongs as they are lifted. An abutment 28 limits the amount of opening of the tongs. The gravitational bias of the latch member to either side of the equilibrium positions may be assisted or replaced by an overcentre spring arrangement, and an auxiliary latch member may replace the recess 32 of the latch member.