Replacing the extremely large rolling bearings used in steelmaking equipment poses significant challenges with regard to the tools, team and strategy deployed. However, this task is not insurmountable, as NSK recently demonstrated in the overhaul of a converter at a major Scandinavian steelworks. Here, NSK and its authorised distributor Nomo supported a Finnish gearbox manufacturer in the replacement of six tapered roller bearings featuring an inner diameter of 1800mm.-Image1.jpeg – Steel industry converters have very large bearings that are subject to high stresses
Nordic and US-based SSAB is a leading European steel manufacturer. The company is principally known for its high-strength steels, which are popular in demanding applications such as crash-related car body sections and heavy-duty construction machinery. SSAB Europe-division, manufactures high-quality strip, plate and tube products.
The entire process chain, from blast furnace to finishing, is covered by SSAB Europe´s four production sites in Scandinavia. As part of a planned maintenance project, three converter gearboxes recently had to be overhauled and equipped with new bearings at the company´s Raahe plant near Oulu, Finland. Gearbox manufacturer David Brown Santasalo was duly commissioned to perform the work, the first stage of which involved removing the gearboxes from the converter and dismantling them at its Jyväskylä factory, some 300km south.
Industry specialists from NSK inspected the bearings and checked the operating data. The Russian-made converter gearboxes were heavy and relatively old, while an added challenge was factoring in the Russian tolerance norms for the gearboxes.
After a full and detailed assessment of the application and its requirements, NSK set about developing bearings with a higher static load rating and user-specific dimensions to replace the existing tapered roller bearings. In total, six 1800mm internal diameter bearings were manufactured, weighing 2250kg each. Prior to shipping, NSK specialists devised a strategy for simultaneously installing the inner and outer ring on the gearbox sprocket wheel with the assistance of a specially designed tool.
The bearings were subsequently shipped to Jyväskylä where NSK supervised their installation using the special tool; this made it possible to adjust the bearing gap exactly.
NSK devised a formula that could define the width of the shims needed for axial bearing clearance after mounting. This had to take into account dimensions such as fixed side bearing assembled width, free side bearing assembled width, fixed side bearing inner ring width, housing diameter, and the distance of the inner ring shoulder to shaft. Following an NSK inspection sheet, each dimension was measured by David Brown Santasalo using a co-ordinate measuring machine.
After checking the measurement values and calculation, NSK was able to recommend an axial bearing clearance of 1800 to 2100µm. Both the mounting of the bearing and adjustment of axial clearance using the shim took place in the vertical position. However, the gap was adjusted again in the horizontal position due to low housing stiffness (split housing) and heavy overall weight. The top part of the gearbox housing alone weighs 11.7 tonnes, while the sprocket wheel fitted with both bearing rings weighs 11.9 tonnes. Once installed, the result (within the required tolerances) was checked by NSK technicians. NSK also asked SSAB to visit David Brown Santasalo´s site to see the mounting procedure take place.
Due to the very high torque involved in the application, the new bearings could only undergo testing after they had been installed at the steelworks. However, the refurbished converter gearboxes with the new tapered roller bearings have been operating satisfactorily under radial loads of up to 150kN.
Throughout the project, Porin Laakeri Oy Oulu part of Nomo Group provided important support services that helped ensure a successful outcome for the client and end user. Thanks to the excellent collaboration between SSAB, David Brown Santasalo, Porin Laakeri and NSK, SSAB Raahe works is now equipped with state-of-the-art converters which are more cost-efficient.
The project also demonstrated NSK´s competence in the steel industry, which is one of the company´s core target sectors. NSK rolling bearings are available to enhance all stages of the steelmaking process, from the preparation of raw material, through smelting operations, right up to the final rolled product. Applications include converters, cold and hot rolling mills, roller beds and cluster mills. Bearings for steelmaking applications feature materials that have been specially-developed by NSK to withstand high operating loads and tough environmental conditions.
The large NSK rolling bearings can be seen in this converter gearbox, which has the top part of its housing removed
The new NSK bearings being prepared for installation
Assembling one of the NSK bearing units at David Brown Santasalo
Bespoke and standard gas struts meet every need
Engineering components and parts manufacturer, WDS Component Parts Ltd. has extended its range of gas struts with new stroke lengths and options. The company can provide standard gas struts by overnight delivery or work with customers to develop bespoke units that perfectly match their application needs.
The extended range now offers stroke lengths between 20mm to 500mm. Rod and body sizes are available from 6mm rod diameter coupled with 15mm body diameter to 14mm rod with 28mm body. The actuation forces available range from 20N to 2,500N, depending on the size of the gas strut.
Each strut is fitted with an adjusting valve so that the internal pressure can be pre-set to the requirements of the application. Once the strut is installed the valve can be used to re-adjust the pressure in situ.
An extended range of end fittings are available, including clevis pin, clevis eye and angle joints. These can be fitted by WDS or supplied separately.
Carbon steel is the usual choice of construction material for the body of the gas struts, but a 316 stainless steel option is available for arduous duty applications.
Both standard and bespoke products can be ordered on line via the WDS website (www.wdsltd.co.uk), where 2D and 3D CAD drawings of the standard units are available. For bespoke struts, the site has an easy to use design wizard where users simply enter the required size, stroke length, thread and force of the spring, along with the preferred materials of construction.
NSK´s new S-HTF ball screws made of “Tough Steel”
Newly-developed S-HTF series ball screws from NSK offer more than double the service life and 1.3 times greater dynamic load capacity than the company´s previous generation product. These performance attributes have been achieved thanks to the use of a new steel material for the screw shaft that delivers an optimised combination of hardness and resilience. Specially developed by NSK, the aptly-named ´Tough Steel´ (TF) is already being used in the company´s rolling bearings with great success.
The S-HTF ball screw has been designed for high-load applications, such as those found in plastic injection-moulding machines and forming presses. With demand for plastic products set to continue growing in coming years, component manufacturers increasingly want machines that operate with shorter cycle times and greater productivity. However, this has consequences for the electric linear drives of the clamping units. They move faster and – depending on the application – with increased clamping force, yet they are expected to last as long, if not longer than existing-generation solutions.
To meet these demands, NSK has developed S-HTF ball screws with screw shafts and nuts manufactured from TF. The high-purity of TF enables – in combination with special heat treatment – the surface of the material to be more resistant. This ensures that no cracks develop from indentations in the material caused by rolling over particles of contamination. Instead, the surface is simply ´smoothed out´ by the roll-over pressure.
Field trials at customers in Japan show that NSK´s S-HTF series high-load ball screws have a service life 2.2 times greater than its predecessor, the HTF series, along with improved load capacity.
The S-HTF series is currently available with shaft diameters from 50 to 100 mm, and leads of 10 to 60 mm (depending on diameter). Overall, there are 21 variants of the new series available. They are not only suitable for the electric clamp axes of injection-moulding machines, but for other high-load applications such as servo presses.
Going beyond all horizons – the S11 with extended functionality
This will particularly please users of the new S11 – the smallest production cylindrical grinding machine in the
STUDER Portfolio: Now they can profit from the diverse advantages of the STUDER standard grinding cycles and the grinding software for offline programming StuderGRIND**. Using the software, StuderWINfocus together with Fanuc control provides the basis for a flexible scope of use, which increases customer benefit significantly.
“The customer naturally still has the opportunity to design his program as flexibly as possible using micro functions. With the STUDER standard grinding cycles, however, he has even more convenience and support with the S11,” explains Christian Josi, Project Manager at
STUDER. The uniform control platform guarantees program consistency on all machines running Windows operating systems. This is regardless of whether the program is programmed directly on the Control or is generated externally with StuderGRIND.
Extended scope of application
The conversion to the new control in the S11 provides even more advantages for users of the small, powerful production cylindrical grinding machine. Up to now, they were only able to work at grinding wheel speeds of 50 m/s (in exceptional cases max. 80 m/s). Today thanks to the combination of a Fanuc Control and StuderGRIND HSG machining is possible with CBN grinding wheels and grinding speeds of up to 140 m/s. A new high-speed spindle has been designed especially for the S11. The S11 achieves an extremely high abrasion performance in a minimum amount of space.
Similarly, the S11 now also enables typical C-axis applications such as thread and form grinding. This is made possible by a new version of the workhead with C-axis function in combination with the software modules StuderThread or StuderForm. The new and reprofiling of grinding wheels thanks to an optimized clearing strategy with StuderDress and machining of longitudinal contours with StuderContour extends the scope of application of the S11.
Above and beyond this, the new S11 also features the SBS Dynamic Balance System. This combined system for contact detection by means of vibration measuring and for semi and fully automatic balancing of the grinding wheels, reduces downtime thanks to less air grinding. It also enables the process to be monitored, for example observation of grinding level noise.
Optimized accessibility and automation casing
STUDER offers the S11 in two different casing designs: The existing version is specially designed for manual loading or to be combined with small handling systems. The new casing is optimized for vertical loading with a top hatch. It is perfect for inter-linked production in which the machines are loaded and unloaded via portal cranes. Both designs stand out with their excellent accessibility and ergonomic features.
* The programming software StuderWIN focus with its standard grinding cycles is perfect for a the most different grinding operations and includes optimized input masks in which the user simply has to enter the application specific grinding parameters.
** The offline programming software StuderGRIND is made up of a variety of modules. The following modules are available on request for the S11:
StuderDress for optimized clearing strategy, for profiling grinding wheels.
StuderThread for thread grinding.
StuderForm for form grinding.
StuderContour for grinding longitudinal contours.
StuderGeoImport for convenient use of workpiece geometry straight from a DXF file.
The S11 gives you great performance in a minimum of space.
With the external tools from StuderGRIND and the new chuck workhead, even threads and polygons can be ground with the S11.
The new HSG spindle enables cutting speeds up to 140 m/s.
Brief portrait of STUDER
Fritz Studer AG, founded in 1912, produces standard machines and individual system solutions in high-precision cylindrical grinding for machining small and medium-sized workpieces. Its customers include the machine construction segment, tool and die makers, automotive engineering, the aerospace industry, Pneumatics/hydraulics, electronics/electrical engineering, medical engineering, the clock and watch industry, as well as job order production. As market and technology leader in universal, external, internal cylindrical and Noncircular grinding , with over 23,000 delivered systems, the STUDER company has stood for precision, quality and longevity for decades. Its products and services include hardware, software and a wide range of services in the Pre- and after-Sales sector – and everything in top Swiss quality.
With a complete tailormade solution for every grinding task, the customer also benefits from our knowledge and expertise in relation to the grinding process. STUDER has over 100 years of experience in the development and manufacture of precision cylindrical grinding machines.
STUDER has around 800 employees (including 78 apprentices).
Media contact at Fritz Studer AG:
+41 33 439 15 90
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