Blocking and Cribbing

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Timber  skids  (planks)  are  placed  longitudinally under  heavy  loads  to  distribute  the  weight  over  a greater area. (See fig. 6-35.) The angle of the skids must be kept low to prevent the load from drifting or getting out of control. Skids can be greased only when horizontal movement is involved.  Extreme care must be  exercised.  In  most  circumstances  greasing  is inherently  dangerous,  as  it  can  cause  the  load  to  drift sideways  suddenly,  causing  injuries  to  personnel  and damage  to  equipment. Hardwood   or   pipe   rollers   can   be   used   in conjunction with plank skids for moving heavy loads into position. Planks are placed under the rollers to provide a smooth continuous surface to enable them to roll easily. The rollers must be smooth and round to aid in the ease of movement and long enough to pass completely  under  the  load.  The  load  should  be supported   by   longitudinal   wooden   members   to provide a smooth upper surface for the rollers to roll on. The skids placed underneath must form continuous support.  Normal  practice  is  to  place  four  to  six  rollers under the load to be moved. Several rollers are to be placed in front of the load and the load is then slowly rolled onto these rollers. As the load passes the rollers that are left clear of the load they are then picked up and   moved   in   front   of   the   load.   This   creates   a continuous path of rollers. Turns can be made using rollers;  but,  first  the  front  rollers  must  be  inclined slightly in the direction of the turn and the rear of the rollers in the opposite direction. This inclination of the rollers can be made by striking them sharply with a sledge hammer. Rollers can be fabricated and set on axles in side beams as a semipermanent conveyor for lighter loads. Permanent metal roller conveyors are available  (fig.  6-36)  and  are  normally  fabricated  in sections which can be joined together. BLOCKING AND CRIBBING Block  timbers  are  commonly  used  to  provide  a foundation  for  heavy  loads  or  jacks.  Cribbing  must  be used  when  a  heavy  weight  must  be  supported  at  a height greater than blocking can provide. Cribbing is made up by aligning timber in tiers that run in alternate directions (fig. 6-37). Blocking and cribbing is often necessary  as  a  safety  measure  to  keep  an  object stationary to prevent accidents and injury to personnel working  near  these  heavy  objects. When selecting blocking as a foundation for jacks, ensure it is sound and large enough to support the load safely. It must be free from grease and thoroughly dry. Figure 6-36.—Permanent metal roller conveyor. Figure 6-37.—Examples of the use of cribbing. Additionally, it must be placed firmly on the ground with  the  load  (pressure)  distributed  evenly. A  firm  and  level  foundation  is  a  paramount requirement where cribbing is used. Also, equally as 6-19

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