CEMEX: New girth gears and drive pinions for two ball mills
SEW‑EURODRIVE safeguards cement production in Prachovice
CEMEX, a major player in the cement industry, has opted for drive technology from SEW-EURODRIVE at its cement plant in the Czech Republic. Highly resilient girth gears and pinions were used to modernize two ball mills.
Limestone has been mined in Prachovice in the Czech Republic since the Middle Ages. Today, this is where CEMEX operates an integrated cement plant. Its capacity is 900 000 metric tons per year .
Two cement mills (ball mills) perform the final production step – grinding the cement clinker. Thanks to SEW‑EURODRIVE, exceptionally robust girth gears and pinions made from high-strength austempered ductile iron (ADI) now keep production running smoothly.
Two new girth gears including installation and startup
Whether it's a family home or a skyscraper, cement provides the basis for almost all construction projects. CEMEX is one of the manufacturers of this basic building material, with annual sales of 14 billion U.S. dollars, making it a major player in the global cement industry. Based in Mexico, the company has a workforce of around 43 000 employees in over 50 countries. One example is in the Czech village of Prachovice, around 100 kilometers east of Prague . This is where CEMEX operates an integrated cement plant, the country's second largest . All production steps – raw material processing, calcination, grinding – are carried out on site.
The production process culminates in two ball mills. Each day, the 15-meter-long machines grind up to 5000 metric tons of clinker – the result is ready-to-use Portland cement. In each mill, two pinions and gear units transfer the force from two 2250-kilowatt asynchronous motors to a girth gear that is directly connected to the ball mill surface.
In spring 2017, an inspection of the drives revealed significant wear in the girth gears and pinions. This rang alarm bells, as a failure would mean a production stoppage, resulting in bottlenecks in delivery and high associated costs. CEMEX therefore opted for a rapid replacement. We provided the cement manufacturer with comprehensive support right from the design phase – from selecting materials and configuration through to startup . Our many years of experience with girth gears in various countries and areas of industry was a compelling factor for CEMEX.
Cutting-edge material technology for wear-free girth gears
When manufacturing girth gears, we exclusively use high-strength austempered ductile iron (ADI) . ADI offers much better material properties than the cast steel previously used in Prachovice. The tensile strength is at least 1000 megapascals, well above the 687 to 785 megapascals of the old girth gears.
In addition to this, the new material has made it possible to design the girth gears to be much more compact and lightweight . In concrete terms, we have reduced the width from 900 millimeters to 300 millimeters. We have also cut the number of teeth from 238 to 180 and increased the module to 40.
A prerequisite for the material's excellent mechanical properties is heat treatment. It changes the microstructure and gives the material impressive strength values. As a result, the new girth gears are much more resilient and less susceptible to material fatigue.
Overall, the superior material properties deliver a number of benefits for CEMEX. Firstly, less material is needed – in other words, the outlay for investment, maintenance and lubrication falls. Secondly, the girth gears are practically wear-free, thanks to the improved strength . A clear advantage for maintenance and repairs.
Segmented design simplifies logistics
Traditional girth gears generally consist of two to four segments. The girth gear from SEW‑EURODRIVE is different – it has multiple parts and comprises several individual compact segments. For instance, the girth gear for Prachovice consists of twelve segments . Depending on the diameter, the individual segments of this design are only one to two meters in size.
The high initial pitch accuracy – complying with the ISO 8 and AGMA 9 standards – means the segmented design offers impressive running characteristics. At the same time, the quality of the girth gear is always the same, regardless of whether the diameter of the finished girth gear is four or 16 meters. This is because we carry out casting, processing, heat treatment and, finally, finishing for each segment individually .
Assembly workers and maintenance technicians are able to handle the individual parts much more easily . For instance, as in the conventional process, installers can preassemble two girth gear halves from the segments before installing the two halves on the mill. However, they can also install the individual segments one by one on the drum. This simplification saves time and resources in cramped production halls.
CEMEX maintenance technicians can also replace individual segments if the gearing is damaged. It is not necessary to completely remove the girth gear to do so. The logistics, too, are easier, as the segmented girth gears fit in standard containers without the need for any further measures.
Our international network of experts was on hand to help CEMEX throughout the project. Along with the head office in Bruchsal, the project involved the Czech subsidiary SEW‑EURODRIVE CZ s.r.o. and the girth gear delivery plant in Tianjin, China, in activities ranging from project planning and selecting the drive components through to installation and startup. Supported and supervised by our experts, the local service provider MZP (Montáže Přerov a.s.) ultimately carried out the installation. Collectively, we performed the test runs and made the radial and axial adjustments for the girth gear. The final stage involved quality assurance measurements.
The results confirmed CEMEX's decision to choose SEW‑EURODRIVE. For example, the vibration measurement on the drive train showed a significant reduction in vibrations throughout the entire system . This cuts the mechanical load of the girth gear and surrounding components. The testing also included a thermal analysis. This did not show any abnormalities and confirmed the accuracy and correct alignment of the overall design.
Since the modernization, the two cement mills have been running perfectly. Stable cement production in Prachovice is therefore assured for the foreseeable future. Our girth gears and professional support played their part in this. And CEMEX agrees – the cement manufacturer has also decided to equip another cement mill with our girth gears .