Design and manufacture of forged heavy-duty mill drive shafts

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Roberta Roberts
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1 Design and manufacture of forged heavy-duty mill drive shafts Heavy-duty mill drive shafts and associated equipment impose special criteria and Figure 1 New Trio rolling mill engineering skills regarding design, materials and manufacture and are illustrated by successful implementation in a new rolling mill at Böhler Bleche GmbH in Heribert Bürvenich and Andreas Wons Spicer Gelenkwellenbau At the end of September 2001, Böhler Bleche GmbH in Mürzzuschlag, Austria, a subsidiary company of Böhler Uddeholm AG, commissioned its new triorolling mill for high alloy steel plates and nickel based alloys (see Figure 1). Spicer Gelenkwellenbau Essen (GWB) supplied the main components for the drive, including the cardan shafts, connection flanges and Safeset safety coupling. Trio-stand At the end of 2000, GWB received the order to supply the driving elements for the trio-rolling mill. This stand is the core facility at Böhler Bleche for the manufacture of press sheets for technical and decorative laminates, high-alloy cold-worked steel for tools, high-speed steel for circular saws, and stainless steels and nickel-based alloys for special applications. The intermediate roll is not driven. The old stand consisted of two slipper-type spindles for driving the rolls and a Demag gearbox that had been fitted with new case hardened pinions to be able to transmit higher torques. However, because of increased requirements it became necessary to replace the old installation (see Figure 2) that had been operating for the past 50 years, with a more modern trio-rolling mill. The design and build was done by VOEST-ALPINE Industrieanlagenbau, Linz, Austria. Some old units were integrated into the new milling line. The main drive train (see Figure 3) consists of the following parts: Two identical 1150kW driving motors (old) Figure 2 Old stand before redesigning One middle-symmetrically designed reduction gear (old) with two flywheels located on both pinion shafts One pinion coupling with Safeset SR-PF870-safety coupling (new) One pinion reducing gear (new) Two cardan shafts type each with connection flanges (new) to drive top and lower work rolls

2 Figure 3 Layout of the new trio rolling mill Flange connection diameter Overall length Max. deflection angle Functional limit torque Reversing fatigue torque Connection flange (gear side) Cylindrical slip joint Max/ min. roll gap 76t Max. 4,000t 2,250mm Top/lower roll: 1,040/950mm Intermediate roll: 870/770mm 280/20mm The supply from GWB comprised the following: Heavy cardan shaft Rotation diameter 1,100mm 3,850kg Connection flange (roll side) 1,070mm 4,000kg Flat roll end with 2 sliding plates and 2 centring rings for changing unit Figure 4 Safety coupling Stand details Steel cast housing Roll force Roll length Roll diameter 950mm with hirth serration 2,850mm 10 11t 7,400kNm 3,500kNm Type mm Safeset safety coupling SR- PF 870 (see Figure 4) 1,425mm 5,870kg Cut-out torque 2,150 4,300kNm Planning and manufacturing of these parts was completed in 11/2 years, with a building and assembly time of only eight weeks. The new facility was commissioned at the end of September For the pulsating load, a 4,850kNm maximum torque was established for the cardan shaft from a series of trials. Contrary to common practice with quarto stands, the trio-stand can transmit 80 90% of the entire torque with one shaft. As this project

3 Figure 5 Flange yoke after machining and before heat treatment Figure 7 C r o s s-section of the yoke from 498 series necessitated an extremely high torque requirement at a deflection angle of almost 10, the design required a 950mm rotation diameter with the yokes made as fully forged parts (see Figure 5). The choice of material was a special steel which, in its quenched and tempered condition, has a maximum tensile strength of 1,200N/mm2 and a fatigue strength up to 30% higher than cast steel. The flange, yoke and bearing cap were designed using the latest finite element modelling calculations. FKM guidelines, that have now become a standard in mechanical engineering, are used when proving fatigue resistance. (FKM-Richtlinie Nr. 154: Rechnerischer Festigkeitsnachweis für Maschinenbauteile.) However, elaborate measurements on site are required to be able to calculate any deviation between calculated and actual loads (see Figure 6). Figure 8 Bearing support in flange yokes with closed Figure 9 Bearing support in flange yokes with split Figure 6 Measurement of local stretching at a universal joint in operation

4 Figure 10 Comparison of wear on journal cross from split and closed O n -site measurements confirmed the calculations within +/-10%. The 498 series has been specially designed for tough operating conditions found in specific steel mills. The most innovative features are the design and heat treatment of the drop forged journal cross. This shape, featuring geometrically soft transitions in notch sensitive areas, is selectively induction hardened so as to produce a hard surface in designated areas in order to guarantee low stress gradients. A case depth of up to 25mm is required. The potential for larger torque capacity in the GWB-patented journal cross was optimised by applying FEM calculations. Depending on the deflection angle (5, 10 and 15 ) the diameter of the journal cross can be adapted. The forged bearing cups are hardened to the bearing manufacturers specification and are of notchless design. By minimising the diameter of the trunion of the journal cross, the created space can be used for larger bearing rolls. This results in an adjustment of the lifetime of bearings and torque respectively, tailor-made to customer specification. The high axial forces resulting from centrifugal acceleration of up to 50g are well absorbed by axial bearings made of low friction compound material. The sealing of the bearing is effected by a sealing ring which guarantees a high degree of seal-off due to its complex labyrinth (see Figure 7). Due, in part, to the application of aggressive emulsions, the conditions in the rolling mill are quite demanding, hence grease nipples are made of stainless steel and the yoke is additionally sealed with Figure 11 Detaching the bearing caps after loosening the bolts Figure 12 On location maintenance on a heavy cardan shaft

5 H O T R O L L I N G O-rings. The hirth serrated standard flange is sealed by GWB-patented high grade steel rings. Service There is an ever increasing demand for servicefriendly design of heavy-duty shafts of the 498 type. GWB has 50 years experience in manufacturing propellor shafts of the split- design type. In the vehicle and secondary drive sectors, shafts featuring closed-s are common, but there is now an increase in the use of the split- design in the heavy-duty shafts market. Apart from technological advantages, such as the increased lifetime of bearings, load distribution and torque capacity, the service time to exchange bearings is comparatively low when compared with other designs, such as flange yokes with closed (see Figures 8 & 9). Figure 10 i l l u s t r a t e s the superior performance of the split-. The journal cross on the right (split eye) shows uniform load distribution on the upper bearing surface (shiny surface); whereas the one on the left (closed eye) shows uneven load distribution that reduces bearing life. Because of the limited number of tools required and the ease of repair, inspections can be accomplished worldwide, on location, within a few hours of customers requests. For example the journal cross can be dismantled by loosening the bolts on the bearing cap, enabling a complete journal cross assembly exchange in a single day (see Figures 11 & 12). Summary With the experience gained from this project Spicer Gelenkwellenbau have laid the foundations for the next generation of cardan shaft design. The splitbearing eye system has been further optimised providing higher guaranteed transmission capacity and working life. By continually developing the heavy-duty type 498 shaft as a fully forged variant featuring optimised bearings and the patented inductive hardening journal cross, we are able to provide rolling mills with the means to transfer the highest possible torques and high-bearing lifetime, coupled with an even more improved design featuring splitbearing eye. Heribert Bürvenich is Sales Engineer, Industrial Distribution Department and Andreas Wons is Design Engineer, Industrial Design & Development, both at Spicer Gelenkwellenbau GmbH and Co.KG, Essen, Germany.

SPICER GELENKWELLENBAU. Fully Forged Heavy Duty Shaft with a rotation diameter 950 mm by Böhler Bleche GmbH/Austria

SPICER GELENKWELLENBAU. Fully Forged Heavy Duty Shaft with a rotation diameter 950 mm by Böhler Bleche GmbH/Austria SPICER GELENKWELLENBAU Fully Forged Heavy Duty Shaft with a rotation diameter 950 mm...... by Böhler Bleche GmbH/Austria R SPICER GELENKWELLENBAU Successful commissioning by Böhler Bleche GmbH At the end