Pit & Quarry, July 2009

D R E D G I N G T B Woods longest Deflection of the boom structure was made less problematic owing to the selection of a flexible drive shaft which is actually a combination of six 20 ft long hollow tubular shafts bolted together Gonzales said Also called disc couplings the drive shafts were supplied by T B Woods a manufacturer of large custom engineered drive shafts and specialized couplings for industrial applications in a wide range of industries T B Woods Form Flex couplings were specially modified to run in the vertical position required in the dredging operation and special long taper lock mounted hubs were designed to allow easy field service including axial adjustment at the pump end For DSC and for the dredging industry as a whole this is a truly amazing feat a very impressive machine Wetta said We coupled six drive shafts together for the underwater pump drive line which has never been done in our industry before T B Woods Product Manager John Malik concurred To my knowledge five sections is the longest train of drive shafts weve supplied in the 23 years Ive been in the business I dont recall hearing of any larger projects and you usually hear about things like that Some designers Gonzales said are still using solid shafting and sleeve bearings as a means of driving a piece of underwater equipment However maintenance of the sleeve bearings in an underwater application is difficult and the bearings themselves add significant weight to the overall structure The tubular Form Flex couplings and special hub design solved the maintenance and weight issues What happens is that when the ladder def lects which is unavoidable it pulls the drive shaft with it causing it to def lect Gonzales said When a solid rotating shaft is deflecting it creates a whip So weve been able to circumvent that problem with the Woods couplings For this application T B Woods specially designed a customized hub with a unique flange disc pack and tapered bushing mounting to facilitate ease of installation and adjustment to the underwater pump impeller Because of the abrasive material being pumped axial adjustment of the impeller is necessary when it becomes worn down One of the reasons we selected the Woods couplings was because of their ability to handle parallel offset and angular misalignment and quite a bit of it Gonzales said Theyve done some things with the hubs that have worked really well for us Theyre the guys to call when you need a coupling engineered to your design The thing we like most is the support we know we have from the strong engineering team at T B Woods Six green Form Flex disc couplings from T B Woods Chambersburg Pa connect the underwater suction pump to the 600 hp electric motor on the ladder of the dredge The drive train is long and is specially modified for operation in the vertical position Forty more years Long service life of the couplings and other critical components was also an important issue as the dredge is designed to operate until the year 2049 Wetta noted This dredge will be in the pit for a long time and since you will not be able to access any underwater connections we designed all of the pontoons so they would be bolted together above the water surface he said Another solution DSC adopted to extend the dredges service life was to replace its typical painting process with a metallizing process in which it sprayed a molten aluminum coating on the hull Studies conducted by the U S Army Corps of Engineers indicate the aluminum metallizing process provides a 40 year coating www dscdredge com www tbwoods com Jack Broughton is an account executive with Heinzeroth Marketing Group GLENN MILLER CONSULTING GEOLOGIST 800 USA 3981 517 223 7100 Aggregate Reserves Evaluation Mining Plans Restoration Forensic Geology 30 years of practical applications 18 PIT QUARRY July 2009 www pitandquarry com