Transcription of POWER SCREW EXAMPLE PROBLEM - Kettering University
1 POWER SCREW Joyce worm-gearScrew JackPOWER SCREW EXAMPLE PROBLEMR eference: Shigley/page square thread POWER SCREW has a major diameter of 32-mm and a pitch of 4-mm with doublethreads, and it is to be used in an application similar to that of the figure below. Applicable data arethread and collar coefficient of friction equal to , collar diameter of 40-mm, and a load of SCREW . depth, thread width, mean or pitch diameter, minor diameter, and required to rotate the SCREW against the required to rotate the SCREW with the And Acme Threads with Preferred Pitches for Acme ThreadsScrew thread with Thrust CollarddPmmddPmmlnPmmmr= = == = === =232423032428248()()()()TFdlddlFdTTNmRmm mccRR=+ += + + =+=2264000030200080080030003000800086400 0080040215941024262.
2 ,..(a)From the square thread figure above, it can be seen the thread depth and width are the sameand equal to half the pitch, or 2-mm. Also(b)For a square thread , the torque required to raise the load is:() == =FlT2640000082262031,..()()()()TFddldlFd TTNmLmmmccLL= + += + + = +=22640000302008003000080030008000864000 0800402047102498 ,..,..(c)The torque required to lower the load, rotate the SCREW with the aid of the load is:The negative sign in the first term indicates the SCREW alone is not self-locking and wouldrotate under the action of the load except for the fact collar friction is present; and, must beovercome, too. That is, torque required to rotate the SCREW with the load is less thannecessary to overcome collar friction alone.
3 (d)Overall efficiency is.
