Question

Looking for a bit of help with he below question; part C in particular. Thanks in advance!

2 There are two jack screw assemblies both with an ISO Metric Trapezoidal 'Tr 16 x 3' screw, one single-thread and the other double-thread, to raise and lower a load of 450 kg. A ball-thrust bearing forms part of the assembly and therefore collar friction is negligible The coefficient of sliding friction for both screws is 0.08 (a) For each assembly, determine: the pitch, pitch diameter, lead and lead angle (i) (ii) the running torque required to lower the load; able or self-locking? (iii) whether they are back (b) Which assembly is the most efficient in lifting? (c) One way of ensuring that a lifting device can be made to self-lock is to use a thrust collar rather than a ball-thrust bearing. For any of the assemblies found to be back-driveable in (a)(iii), what is the minimum collar diameter required to ensure it/they would self-lock? (Assume the same value of friction coefficient of 0.08 in all situations)

Answer 1

G1iven To 16X 3 Tsapezoia'T) Nominaj diamerer in mm pitch imm P 3 W 45O Kg Coefficient of siiding of Fichiorn Fer assembly First singie- theead Nf pitch 3mm pitch diamejes 1 Lead angie NA dm dE tan tan x3 T 5 -37678 Read The Eunninq torquee eequured to lowersend loary T Wdm ton(d-d) 2. tanLu, CosB o forTsoapezoial thoesad

O 08 COS15 T8T80. Q tan (o08282) 5 4.S ton(4.7346- 3"7678) 540-0 4 N:mm Tosquee Egured to louer the end whetnerY tney 07 47345 3.7678 Frocri ong1e is goeoaers ha lead ongied ona torgye eguire to lowertne load is posiive hence it is seif-ocking

Forr a a4sembly doubie thead NF 2 pitch a mm pitch cliomete dmcP, 16- 4mm head Lead ang ie d: ton" mdm 6 tan T) C14'6) 7.5084 Tosque gequires to louwes load T: 2- L4.54 tan(47345- 7-503) 2- back-dhiveabie os geF LOCK ing they Of e i) Whete: 4.73S 7.SO34 Ficho anqic <* is louwen han lead ongiea, and tergue çeguued to lowr the loaq i negative henre it is back driveabie

lifting i5 tre most efficont Which 06sembly Torquee eequires lift loaq in singie tmeageg Wdm tan +) 4414 S1S ton (47345t 3 7678) 78L. SNMM Tosauee eegue to lift load in louble Treqqc SCrreu Wdm ton -4 L 514°5 ton( L4:7345+ 7:5034 6941.91 .mM TCrquee9uie to lift loaq in dingle tmeade most efficiert SCrew is lowr hem ce. ssembly is which having single thmeade ass-e

double Theoole assem bly is foung a S bock-divaole Fers sef- Loq<ing condition the tosgue Eeauireo to louwes te load in dousie negative threaded assembly shoule ohich is haustcollas Shoud be overcome fricrin torgque 154789 N M Tc but Tc In poblem if is givem vaiue of iction coeffjcdont of o 0g as as6uMe condi tion AecI Rm7 1547'89 im Rm>547-894 S4789 о 08х ч414:5 Rm .382gm inimum colla diomejee is e eo to fersSef loCk is 2X4. 3829 - 8.7659 mn gmm Aprox