Reliable, low cost universal joint shafts
2nd Quarter 2017, Shaft power components
Voith’s CH series universal joint shafts have several features contributing to lower lifecycle costs. These include high fatigue strength under vibration and component lifetime, large torque reserves under overload conditions and a long bearing life.
Fields of application for this type of universal joint shaft are primary drives for rolling mills, mining machinery or systems in which the universal joint shafts are exposed to high or maximum torques. Therefore the universal joint shafts are always individually customised to the specific drive requirements. By employing a revolutionary bearing concept, Voith has over the last three years succeeded in considerably improving its heavy duty universal joint shafts with rotation diameters ranging from 590 to 1460 mm.
One of the decisive factors is the improved bearing technology. Until now, the rolling elements ran directly on the journal cross. In the CH series, Voith has added a newly designed internal bearing ring with integrated axial bearing. The axial bearing on roller bearings ensures maximum deformation resistance and uniform load distribution. The weight forces of the universal joint shaft are reliably handled, even under high lateral accelerations.
The cassette design of the new bearing unit also stands out because of its ease of assembly. In this design, the internal bearing rings and the external ring are assembled as a single unit. This is a plus where life cycle costs are concerned, and Voith estimates these to be 20 to 30% less. This is because bearings are wear parts. With technology currently available on the market, the complete journal cross assembly must be replaced along with the bearings. With the ability to replace just a single bearing, the Voith cassette technology eliminates that need. As a result, operators save on additional costs for acquisition and storage of the journal cross assemblies.
The special configuration of the rolling elements also increases the static load capacity of the radial bearings by up to 18%, giving an additional strength advantage. They are the only heavy duty universal joint shafts without additional screw connections in the bearing unit. There are only two bolts on the bearing cover – without a load-bearing function. This contributes substantially to operational reliability because under a torque load elastic deformation occurs in the joint. This promotes loosening of the screw connections, accompanied by bolt fractures.
Another of Voith’s improvements is the purity of the flange yoke blanks. The problems caused by poor casting quality are only too familiar in industry. For this reason, Voith opted for a forged version of the universal joint shafts. Forged steel increases the fatigue strength under vibration by 20 to 30% over the cast version. Machining provides decided advantages with regard to dimensional accuracy and flexibility in shaping. Complex, cost-intensive wood models – essential for casting – are replaced by the flexible transmission of CAD data to the milling machine.
Over the last three years many operators of steel plants and rolling mills worldwide have relied on the advantages of the new CH series. These include Capital Steel in China, Posco in Korea, Bokaro in India, TMK in Russia, Habas in Turkey, and the Thüringen Steel Works and Nucor Hertford in the USA. The universal joint shafts used at these sites have rotation diameters between 590 mm and 1300 mm. They all prize the benefits of the new CH series, for which Voith also developed the special WearCare 500 lubricant. This produces a non-metallic separation layer to reduce friction and contributes to increased component lifetime.
For more information contact Terry-Lynn McIntosh, Voith Turbo, +27 (0)11 418 4036, firstname.lastname@example.org, www.voith.com