CEMEX: New girth gears and drive pinions for two ball mills

  • Cement mill with new red girth gear and yellow protection cover

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.

The project at a glance

CEMEX company logo
  • Customer: CEMEX:
  • Where: Prachovice (Czech Republic)
  • Sector: Cement industry
  • Application: Ball mill

Further information about the customer, CEMEX:

  • Number of employees: Around 43 000 worldwide
  • Headquarters: Monterrey, Mexico
  • Active in over 50 countries
  • 1906: Foundation of CEMEX with the opening of the Cementos Hidalgo plant in northern Mexico
  • 1992: CEMEX begins its expansion on the European market by acquiring two Spanish cement companies
  • 1997: Entry into the Asian market with the takeover of Rizal Cement in the Philippines
  • 2005: By acquiring RMC, CEMEX doubles in size and is therefore represented on 20 European markets
  • 2015: CEMEX takes over the cement plant in Prachovice as part of a transaction agreement with Holcim Česko
  • 2016: CEMEX celebrates its 110th anniversary
Ball mill with old girth gear in light gray
Ball mill with old girth gear
  • Replacing girth gears, pinions and girth gear covers for two 15-meter-long ball mills
  • Safeguarding production over the long term
Cement mill with new red girth gear and yellow protection cover
Cement mill with new girth gear and protection cover
  • Two optimized girth gears
    • Material: Austempered ductile iron (ADI) with a minimum tensile strength of 1000 MPa
    • Segmented design with high initial pitch accuracy
    • Width reduced from 900 mm to 300 mm
  • 4 optimized drive pinions made from ADI
  • 2 protection covers for the girth gear
  • Support for the customer every step of the way, from planning and design through to startup
Thermal testing of the drive pinions
Thermal testing confirms smooth operation
  • Practically wear-free operation thanks to the ADI used and its excellent cold work hardening properties
  • Reduced material requirements, leading to lower investment and maintenance costs
  • Fall in vibrations throughout the entire system thanks to the high pitch accuracy and professional alignment work
  • Reduced logistics outlay thanks to segmented design
  • Safeguarding production over the long term

Long history – state-of-the-art technology

Close-up of girth gear and teeth
Girth gears made from wear-resistant ADI material in a segmented design

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.

Impressions of the project

The project in detail

Two new girth gears including installation and startup

A girth gear half on a crane hook
When preassembled in two halves, the girth gear is easier handle

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

The girth gear is installed on the cement mill.
Made from highly resilient ADI and only 300 mm wide

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

Two red girth gears against a white background
The girth gears are always designed in a number of identical segments

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.

Demonstrable improvements

Thermal testing of the drive pinions
The drive pinions are thermally tested

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 .

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Special edition – CEMENT INTERNATIONAL 5/2019

Special edition – CEMENT INTERNATIONAL 5/2019, pages 36-40

"Replacing girth gears for ball mills at the Prachovice cement plant in the Czech Republic"


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