1 year ago

MDA Technologies 2/2014

MDA Technologies 2/2014

21-ton gear traveled

21-ton gear traveled over 7000 km to be hardened in Bochum Holger Seybold Europe‘s largest plant for protective gas hardening is located in Bochum- Riemke. Machine parts up to 5.2 m in diameter and 5.0 m height are engulfed in one furnace. Gears can even be treated vertically therein and thereby remain highly customized and dimensionally stable. Reason enough to send for an American gear manufacturer to send their 21 -ton gear on the long journey from the USA to Germany. Antriebstechnik was there live during quenching. Hard to believe — but for the American Gear Manufacturer Horsburgh & Scott from Cleveland, Ohio USA, it made good economical and engineering sense to harden a 21-ton gear not in their own country, but more than 7000 km away in Bochum- Riemke. The delivered spur gear with 3 m diameter and a face width of 781 mm is the second of its kind. The first distorted during the heat treating process in the U.S. so badly, that extensive gear machining was 22 MDA Technologies 2/2014

Machine elements required to correct the dimensional errors. Therefore, the Americans decided to entrust the next good piece with Härterei Reese Bochum GmbH. “As a specialist for the heat treatment of large components, we have worked on the edge of our capabilities during the past years. In order to keep our technological leadership and expand, we had to step to the development of a new large furnace plant, for which there are currently no prototypes. ” commented Managing Director Dipl.-Ing. Gerhard Reese his early considerations. Lower grinding costs due to vertical hardening Since then, the company invested a total of around 23 million Euros into the new 4000 m 2 (43,000 sq ft) workshop and is now operating the largest installation for gas carburizing in the Europe. The furnace with a diameter of 5.2 m and a depth of 5.0 m is custom built and has been developed in cooperation with the German company Rohde. It can be loaded with up to 100 tons of material, so that, at the same time, multiple batches can be treated. In this way even large quantities can be handled and processed in a short time. The weight of a single component is only limited by the existing crane with a maximum load capacity of 50 t. To bring this great volume of material to temperature requires a highly-capable heating system. The 24 gas burners, distributed in the furnace wall, produce through soft catalytic combustion heating a capacity of 1920 kW. An electric auxiliary heating in the floor adds another 140 kW. This sum is enough to meet the heating requirements of about 300 single family homes (new construction , approx. 100 m²). Along with the required protective gases, energy costs alone for one hour of operation under load amount to 300 to 400 Euros per hour, or extrapolated from 7200 to 9600 Euro per day. Ovens with such a large diameter were existing even before, however not to this enormous depth. Very distortion sensitive components, such as the USA gear, can now be treated vertically. In the established flatter ovens such components fit horizontal only and must be charged on hardening racks that are themselves unstable at high temperatures. In this way horizontal charging leads to higher dimensional and shape changes - such as runout, ovality and tapering. The resulting higher hardening distortions need to be corrected in the subsequent machining and grinding processes, in which the hardened layer is again more or less removed depending on the amount of the distortion. In contrast, by hardening such a gear vertically, the shape errors are significantly reduced. As a result, the machining and grinding effort are significantly reduced, saving excessive labor and material costs. Customers report up to 60% lower grinding costs. The Hardening Process Not only is the proper fixturing in an oven crucial, the metallurgical and hardening process is a science in itself and requires a lot of expertise, and experience. Through specific time and temperature variations during carburizing, hardening and tempering processes, the material properties can be optimized according to the desired goal. And all that togther is the “Art of Hardening.” The hardening components are to be cleaned at the beginning of the process. Those areas of the workpiece, which should MDA Technologies 2/2014 23


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