GB739720A - Improvements relating to lifting tongs and the like - Google Patents

Abstract

739,720. Lifting dogs with automatic control. PRIESTMAN BROS., Ltd. Nov. 3, 1953 [Nov. 11, 1952], No. 28409/52. Class 78 (4). The lifting dog of Figs. 1 and 2 is automatically locked open after it has been lowered to release its load by engagement of a pin 26 on an arm 18 pivoted to a structure 1, 2 carrying the gripping arms 3 with a notch 29 in a member 16 carried by the head 11 by which the dog is raised and the gripping arms closed, and it is subsequently unlocked when the dog is again lowered. As the dog opens to release its load the pin 26 travels up the right hand surface (as seen in Fig. 2) of the member 16 and is then moved into engagement with a projection 27 on a further member 17 on the head 11 by a weight 21 biasing the lever 18 about its pivot 19 so that as the dog is again raised the pin 26 enters the notch 29 and the dog remains open. When the dog is again lowered to engage a load the pin 26 rises to the left of the projection 27 and is moved clear of the notch 29 by the weight 21 which moves the lever 18 into abutment with a stop 22. The stop 22 is carried by a heavily biased lever 23 also pivoted at 19 and normally abutting the base of a channel 2 on the structure 1, 2. As the dog is again raised however the pin 26 engages the left hand surface of the member 16, so turning both levers 18 and 23, until a pin 26 escapes the member 16 and the weight 24 biasing the lever 23 returns the pin 26 for subsequent re-engagement with the left-hand surface of the member 16. As indicated in Fig. 1 the pin 26 preferably projects from both sides of the lever 18 and the members 16, 17 are formed by spaced parallel cam-plates. The head 11 comprises spaced plates 14 guided by members 12 carried by the channel 2 which joins endplates 1. Four gripping arms 3 are provided and are joined in pairs by plates 3A which carry the load engaging devices 5, 6 of Specification 739,719, which is referred to. In the lifting dog of Fig. 11 the arm 18 is normally biased by a weighted lever 39 pivoted at 40 to one of the gripping arms and bearing on a lug 41 on the arm 18 which is thus held in abutment with the end of a lever 42 pivoted at 43 to the other gripping arm and resting on a stop 45. The weighted arms 39, 42 operate similarly to the arms 21, 23 of Fig. 2 to guide the pin 26 around the surfaces of the members 16, 17 which in this construction are carried by a member 30 fast with one of the links 33.