5 years ago

MDA Technologies 4/2015

MDA Technologies 4/2015

Small change, big

Small change, big benefits Christopher Monka Germany, the export based economic powerhouse of Europe currently produces about 43 million tons of crude steel annually. This corresponds to approximately 25 % of the total EU output of approximately 174 million tons and barely 5 % of the output by China, which totals 810 million tons. T o successfully compete on the world market, along with the development and production of high quality specialty steels, in-factory optimizations that result in a sustainable increase in productivity in the manufacturing process are now required more than ever. This “in-factory optimization” does not always have to be the large individual projects. The multitude of small improvements in everyday operating procedure that often appear to be insignificant offers enormous savings potential in this area. Example one: A leading steel producer from the western Ruhr district was able to reduce its operating costs for the steel transport vessel by several tens of thousands of euros in the last five years. The steel removal trolley is a rail-bound vehicle that transports a pan beneath the converter that is filled there with molten crude steel. After that, this vehicle transports the pan with the crude steel to the SMP (secondary metallurgical plant). There, the steel is poured using a crane, e.g. into the vacuum system. The SMP is the device in which the steel receives its quality features through various processes (such as degasification, purity optimization, deoxidation, etc.) before it comes to the continuous casting plant, where it is cast into a solid condition, the slab. The vehicle (Figure1) has a specific weight of 340 tons. A filled pan weighs around 385 tons. The total weight of around 725 tons is driven by 8 slip ring motors having an individual capacity of 30 kW each. Author: Christopher Monka, Area Sales Manager, R+W Antriebselemente GmbH, Klingenberg,Germany n Each of these motors is connected via a simple bolt coupling to a spur gear. After a reduction of i=36.8, the spur gear generates a nominal torque of around 14.85 kNm on its driven shaft. n The driven shaft is connected again via a bolt coupling to a mounted shaft at the end of which a pinion is located. n This pinion in turn engages in the outer ring gear of the gear set that moves the vehicle over the tracks. With 24/7 use in which the pan is filled up to 30 times per day, the primary importance of this device for the overall process quickly becomes clear. When the gears fail In the past, cracked gears repeatedly resulted in the failure of the vessel. This resulted in the vehicle having to be pulled out of the continuous production process, at considerable expense. This became extremely difficult if the pan was also being filled with the crude steel heated to over 1 000 °C. Moreover, there was great expense in releasing the latter from the pan after it hardened. This resulted in enormous costs, consisting of the procurement of a new gear and the associated replacement as well as the repair of the steel pan. Not to mention the costs of the general drop in production. Why the gears fail There were various reasons for the gear failures, but they were always of identical origin: stress too high due to excessive torque. These resulted first of all from blockages on the rail path. Negligently operated third party vehicles, incorrectly deposited material or paths that are just heavily soiled are not uncommon in the giant, dimly lit halls despite maximum safety precautions. Another cause 56 MDA Technologies 4/2015

SUCCESS STORY is the slag and dirt on the gear teeth. Figure 2 shows a gear after a service time of approximately 6 months. Here, it quickly becomes clear that discharging slag gets deposited on the drive components. Eventually, the slag coating is then so solid that the force acting on the gears is simply too great. How to Increase process safety ? At this point, the coupling specialist, R+W Antriebselemente based in Klingenberg, was able to help. The most obvious approach to a solution was the integration of an overload or safety coupling. The purpose of this coupling was to mechanically cut out torque that is present in the drive train at a defined value in a mechanically controlled manner. However, the great challenges in this were: n The extremely restricted installation space relative to the power density of the coupling n The extreme environmental conditions n The cut-off torque, which can be defined only with difficulty n Easy operation or fast restoration in the event of damage For the extremely restricted installation space, R+W therefore developed a special variant of the “TorqSet ST4” Heavy Duty Safety Coupling (Figure 3). This replaces the bolt coupling located between gear and drive pinion shaft. The ST4 has not only the function of overload protection, but also takes on the function of an 02 01 01 The Steel removal trolley, is rail bound and weighs 340 tons 02 A gear after a service time of approximately 6 months 03 For extremely restricted installation space, a special variant of the “Torqset” ST4 Heavy Duty Safety Coupling was developed 03 MDA Technologies 4/2015 57