Advances in Drives Benefit Cement Plants
By Zenek Gajewski
The manufacture of Portland cement involves combining the right proportions of limestone, clay and sand at high temperature (up to 1,450C), with the addition of gypsum or fly ash, to achieve a precise consistency. The process requires up to 80 se...
The manufacture of Portland cement involves combining the right proportions of limestone, clay and sand at high temperature (up to 1,450C), with the addition of gypsum or fly ash, to achieve a precise consistency. The process requires up to 80 separate and continuous operations, large quantities of heat and energy, and the use of a variety of heavy machinery and equipment.
It’s a tough environment for all kinds of components, especially those in the power transmission segment. However, state-of-the-art power transmission technology offers significant advantages for every phase of such a manufacturing environment.
From the kilometres-long conveyors that transport crushed material from the quarry to interim storage, to the bucket elevators feeding the huge heat exchangers, to the large-girth gears driving the giant kilns, to the grinders, final packaging machines and palletizers, a diverse range of drive types and capacities is required to keep a modern cement facility up and running. (See chart, which shows some of the drive applications found in a typical cement plant.)
As the demand for cement continues to grow in applications from building, highway and bridge construction, to structural requirements in industry and agriculture, the majority of North American cement plants are still relying on 30-year old equipment. Installed in the 1960s, many of the large drives in these facilities are now wearing out. With efficiency problems, maintenance and energy costs on the rise, more than a few plants are looking to modernize.
The advantages of refitting? Today’s drives deliver increased productivity through greater efficiency and higher outputs, most often from a smaller drive package, which consequently costs less.
By standardizing on one manufacturer, plants not only can get a turnkey solution, but also may realize substantial savings in spare parts inventories. Also, there have been technical advances such as the replacement of fluid couplings with electronic soft-start units that can reduce inrush currents, saving energy.
Without question, there are downtime and cost concerns associated with modernizing. However, experience in the European cement industry has been useful in pointing the way for North American plants. When it comes to power transmission concerns, choosing a drive supplier can be an invaluable first step in making the process easier and less costly.
In the past, cement plants wanting to upgrade have been forced to source their drives in Europe, but now the situation is changing. Global drive manufacturers possessing decades of experience in the European cement industry are now bringing that same level of expertise to the North American market.
These suppliers not only provide on-site applications engineering, supported by a global knowledge base, but also have the local infrastructure and trained technicians to offer round-the-clock service for the complete range of large and smaller drives used in cement applications.
It’s important to work with a drive supplier that can offer in-house expertise to analyze problems and develop long-term solutions that make economic sense. Several approaches are available.
Power transmission alternatives
In many cases it’s possible to refurbish old equipment without the cost of ripping out forms, slabs or steel plate. Large drive manufacturers offer a wide selection of gearing. Using a modular approach, millions of drive configurations are possible. A replacement for virtually any competitor’s drive, old or new, can be built up from off-the-shelf components in little time.
A more costly approach, necessary on occasion, is to custom-manufacture an exact drop-in unit. A substantial part of the additional expense is in the engineering and design, which can amount to $20,000 or more. Then there’s the production downtime to consider. It can take from 18 to 24 weeks to make up the gearing, versus six to eight weeks for an off-the-shelf solution.
As a cost-effective way of improving productivity, many plants are opting to upgrade by replacing their existing drives with new technology. Transition bases can be designed to accommodate today’s smaller drives.
Instead of doing a complete new drop-in, the drive supplier will measure up the existing foundations, modifying adapter plates if necessary to maintain the distance from the base of the reducer to the centre line of the output shaft.
As a result, drives can be purchased ready to go. A wide range of modular drive components is available to get the exact solution needed, while shortening delivery time compared to waiting for a custom unit to be built.
With improvements such as case-hardened, carburized gearing, modern speed reducers offer at least 30% more available torque within the same work envelope, and still provide a 30-year service life. Some manufacturers use shot peening in the gear root to allow for greater bending forces. These advances allow the use of a unit the same size or in many cases smaller than an existing drive, saving on shop floor real estate as well as capital and operational costs.
Standardized options are available to handle aggressive cement plant environments. Innovations such as Taconite, Labyrinth and double-lip seals, as well as spring-loaded, ball-type, dust-proof breathers, make today’s drives virtually impervious to contamination. As well, the latest shrink-disc technology can handle loads well beyond maximum reducer torque ratings while eliminating fretting and corrosion on shafts.
As a specific example, ingress of dust and abrasives at the headshaft of a conveyor can work between shaft surfaces where any deflection might be present. Over time, the resulting corrosion can cause seizing. Special bushings can be installed to solve the problem.
State-of-the-art electronics can also offer certain advantages. In addition to being used on large kiln drives for precise speed control to improve product quality, modern variable frequency drives (VFDs) with built-in overload protection offer improved productivity in packaging applications, where increased palletizing capacities require variable speeds and high starting frequencies.
As an increasing number of cement plants look to modernize operations, they can find a wealth of power transmission options available that can deliver fast payback on the equipment investment. Today’s drives come in a wide range of gearing types and incremental sizes, making it possible to precisely match technical specifications and achieve a low-cost, long-life solution for virtually any cement plant application.
Zenek Gajewski is the product manager for industrial gear at SEW-Eurodrive Co. of Canada Ltd., Brampton, Ont.