Page 54 - Wire Rope News & Sling Technology - April 2019
P. 54

Denny’s                                     Hoist Self-Adjusting
         crane and                                         Holding Brakes

         rigging notes



                                                                     by Dennis O’Rourke


                                                              the pawl to travel beyond the height of the teeth, they will
                                                              drop into the next tooth from the spring presser. Thereby,
                                                              moving the wheel up a threaded rod and maintaining the
                                                              proper shoe clearance.
                                                               After proper  adjustment, a  keeper  latch  is  snapped in
                                                              place to maintain the adjustment. There lies the problem, to
                                                              “maintain the adjustment” of the shoes.
                                                               If the ratchet wheel is not free to move back and forth,
                                                              each time the brake is set, it will tighten the shoe against
                                                              the brake wheel till no clearance is available. Continual shoe
                                                              drag and overheating occur. Here is a list of possible brake
                                                              adjustment causes;
                                                               1) Lack of adjuster lubrication and cleanliness.
                                                               2) Spring to pawl alignment.
                                                               3) Broken, weak on missing pawl springs.
                                                               4) Ratchet or Pawl worn or broken and don’t pivot freely.
                                                               5) Adjustment keeper worn and not staying engaged.
           Pictured here are “Burned-up” brake shoes, that occurred   The recommended action for cranes in “regular” service is to
         due to poor maintenance.  Our  experience with  the severe   inspect the brake’s clearance on monthly bases along with the
         damage shown here is associated with a self-adjusting type
         — all self-adjusting brakes functions on the same principle
         of operation and for some perform great!
           The top right brake pad is in sharp contrast to the
         “burned and charred” pads when compared alongside this
         new pad. One of the brake material surfaces has separated
         starting a fire.
           Also, the damage to the brake Wheel required resurfacing.
         Cranes up-to 40 ton capacity can be equipped with this “self-
         adjusting” brake design.
           There is a ratchet wheel with evenly spaced “teeth.” The
         height of each tooth is the allowed travel distance the lever-
         ing system requires to set or release the brake shoes. This                                            Photos courtesy of Dennis O’Rourke
         wheel is pulled and allowed to rotate or held in place by the
         grip of two “pawls” which are pressed against the ratchet
         wheel by small springs.
           Once the brake clearance is adjusted, about .045"  max,
         the pawls will set/release the brake within the height of the
         ratchet teeth. When the shoe lining wears enough allowing   ropes and hooks. If problems continual occur, then other types
                                                              of brakes should be considered, and alternates are available.
                                                               Cranes in  “standby “service,  (as those discussed  here)  a
                                                              required “frequent” type OSHA inspection before start-up
                                                              is mandatory, components which include the brakes are in-
                                                              cluded. The additional inspections of a crane equipped with
                                                              self-adjusting brakes are recommended. n
                                                               From the Author: Readers, these published “Notes” are subjects that I
                                                              have experienced over the five decades I’ve spent in the Crane and Rig-
                                                              ging industry as a heavy equipment mechanic, safety engineer, business
                                                              owner, and the former president of Crane Certifiers Association of Amer-
                                                              ica. This information was accumulated over that period. I would appreci-
                                                              ate your comments, additions, or corrections. These are the reflections
                                                              and opinions of one person, on a serious subject.
                                                               Dennis J O’Rourke, (dennis@natlcrane.com)
                                                               DENNIS J. O’ROURKE, CSP, is the Director of National Crane Services, Inc. He has over
                                                              fifty years’ experience in the industrial, maritime, and construction fields working with heavy
                                                              equipment and material handling devices. As a safety engineer, Mr. O’Rourke has developed
                                                              and/or presented over 300 safety-training programs for all representative elements of govern-
                                                              ment and industry.
         54     Wire Rope News & Sling Technology   April 2019
   49   50   51   52   53   54   55   56   57   58   59