Production of building cement is a complex process that puts enormous demands on the machines that manufacture it. There is demand for reliable torque limiters at many points along the process chain.
What do you think of when you hear the words “bridge construction”? Engineers, steel, excavators, cranes and concrete – things that you see at first glance. There is of course a lot more to it than just that. If you take a closer look just at concrete as an example, it quickly becomes clear how many factors contribute to a successful building project.
Concrete is a composite material, produced predominately from aggregates, water and cement. The latter is an essential raw material. Cement is a hydraulically functioning binding agent that consists mainly of calcium carbonate. Finely ground and mixed with water, it congeals, hardens and maintains this condition. Different grades are used to meet specific job requirements. Sometimes the workability of the building material is of primary importance; at others its ability to retain water is the key factor. Certain aggregates and mixing ratios produce the desired physical characteristics.
From raw stone to effective binding agent
It begins with the extraction of the raw material and ends with bagging and packaging.
“We have worked hard over the years to get our products established along the entire cement production process chain. In doing so, we consider each individual drive element separately and factor in industry-specific requirements. Regular collaboration with customers and the work of our development engineers form the basis of our expertise in the procedures and processes used in an industry,” is how Jörg Stang, Sales Manager at R+W Antriebselemente GmbH, explains the company’s relation to cement processing.
The first step is to break the limestone in a semi-mobile crusher to a minimum grain size of at most 25 mm. As part of this process, other very hard rocks are incorporated into the breaking process alongside the comparatively soft limestone.
The expensive crusher tools have to be protected against peak torque. For this the TORQSET ST1/60 torque limiter was chosen using a flange mounting between a starting coupling and a cardan line shaft that leads to the gearbox. At a defined torque shock of 28,000 Nm, it disconnects the power flow within a few milliseconds and protects the entire gearbox from damage. This saves the plant operator costly repairs and downtimes.
In the next step, the pre-homogenized starting material is dry-ground inside a ball mill. Driven by a high-voltage motor with an output of 800 kW at 500 rpm, balls made of chromium steel process the ground material by means of impacts. An R+W BZ1/450 model gear coupling connects the motor and gearbox. Jörg Stang stresses:
“This compact and extremely robust coupling transfers the rated torque of almost 35,000 Nm and compensates possible misalignments between the shafts. The high-precision interlock of coupling hub and flange component transfers the torque with minimal backlash, IS torsionally stiff and compensates for misalignment.” Since the coupling is designed for a peak torque of 90,000 Nm, it offers sufficient safeguards for temporarily higher torque values e.g., while starting up the mill.
Coping reliably with peak torques
In order to further refine the resulting raw meal, it is filled over crushing units into silos. For these drives, R+W supplied SERVOMAX® EKH/4500 type couplings – once again with the goal of ensuring long-term plant availability. Clinker production follows, during which the meal is so altered by means of a burning process that the cement can harden hydraulically in later applications. So that the cement is chemically reactive, secondary elements like blast furnace slag, fly ash, or calcium sulphate are added in the cement mill. In this ball mill, the connection between the motor and gearbox shafts, like with dry-grinding, is provided by a gear coupling, in this case a BZ1/800. The rated torque is however still higher at 65,000 Nm; at peak torques the coupling will transfer up to 168,000 Nm. In addition to high torques, bridging the comparatively large distance of 1,120 mm between the drive shaft and the output shaft is a requirement of this specific installation situation. This is accomplished by a spacer sleeve fastened by means of a flange, which extends the 358 mm long BZ1/800 to the required length. For the final processing steps, the bagging and packing machines, R+W supplies torsionally rigid and vibration-damping couplings.
Heavy-duty couplings for different industries
“Although it is not immediately apparent in everyday life, R+W technology. Also features in bridges, houses, dams and soccer stadiums,” explains Jörg Stang. “Cement processing is only one example that makes clear the different points at which R+W products are used. Besides this industry, segments such as test bench, printing, bagging and packing technologies as well as the steel processing industry benefit from heavy-duty couplings and our industry expertise.
The complete range of industrial drive solutions can be purchased from Drive Lines Technologies Ltd in the UK. Drive Lines is the official distributor for R+W and can advise and recommend solutions involving couplings, torque limiters and line shaft. Drive Lines also provide Screw Jacks, Gearboxes, Linear Motion, Actuators and more. Take a look at www.drivelines.co.uk