Digital Re-print -
May | June 2013
Managing mill maintenance
- Roller mill maintenance
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Innovative extrusion processes without limits. Bühler is the global technology
partner for companies producing breakfast cereals, snack foods, or food in-
gredients on a commercial scale. With its extensive extrusion know-how and
its passion for customized solutions, Bühler is always in a position to generate
added value and success for any product idea. Bühler offers an integral range of
products and services for all process stages – from correct raw material handling,
cooking and shaping through extrusion to drying of the extruded products. And
this for all market segments – from breakfast cereals and snack foods to modified
flours and starches, texturized proteins, or vitaminized rice. In short: extrusion
processes without limits.
Innovations for a better world.
maintenance Roller mill maintenance
by Alice Neal, associate editor, Grain and Feed Milling
Technology, United Kingdom
key concern for all millers is getting outer layer. These rolls are typically made Longer rolls will last longer than a shorter
maximum life and efficiency out by centrifugal casting. In this process, a roll handling the same volume of material.
of equipment while maintaining a hard-metal alloy is fed into a die that spins Similarly, rolls with a bigger diameter will
high standard of product. Roller mills play at high speed. Then the softer gray iron is have a longer working life.
a key part in the milling process and have added. This technique produces rolls with The flutes or corrugations will also affect
a direct influence on subsequent process- a high density and homogeneity which are roll expectancy. Coarse flutes will last longer
es and eventually on the yield and quality crucial for high wear and resistance. The but will produce a chunkier end product
of the end product. Roller mills are a very centrifugal process forces impurities up to whereas fine flutes, which produce a finer
flexible piece of equipment as they can the surface of the roll during manufactur- end product, will need refurbishment sooner.
perform a variety of tasks, be it crumbling ing. Any impurities can be easily removed
pellets, cracking, flaking grain or grinding. before the roll is finished. These features Effective operating
They can also handle many different mean that centrifugal cast rolls last longer The life expectancy of a roll depends
products including corn, wheat, soybean, than static cast rolls. on several variables. First, the products
pellets, and canola. However, despite the Another option is titanium, these rolls are put through the machine will have an
diverse range of applications, the operation harder and more resistant to abrasions than impact on the wear. Large and hard
and maintenance of roller mills general- other materials. Titanium rolls are usually products such as canola or rapeseed will
ly follows a standard procedure. made of cast iron with steel added as an pose more of a challenge to the roller
Image courtesy of Ugur Makina
The manufacturing process alloying element to increase strength and mill than smaller, softer materials such as
The main wear parts in roller mills are wear resistance. corn or wheat.
the rolls. They are set up in pairs and one Cleanliness of the raw materials is also
machine can contain different numbers of Flexibility in design a key consideration. Stones or tramp metal
rolls depending on the application. Most manufacturers offer different rolls can get stuck in the flutes, causing uneven
A high-quality roll represents real value of different hardnesses depending on the wear.
for a miller. A good roll will produce a application. The hardness is important: too In addition, higher volumes of product
consistent product and help minimise costly hard and the roll will lose its grip on the will make a roller mill work harder and rolls
plant downtime and maintenance efforts. product; too soft and the rolls will wear out will therefore wear out faster. No matter
Getting the maximum life and efficiency more easily. how much product a roller mill has to
out of a roller starts with the choice of metal. Just as there are material choices to consider, handle, it is important to ensure an even
A popular option is a two-component there are other areas of roller design which can flow of material through the machine as
chilled iron compound roll with a cast be altered depending on the application. All of inconsistent feeding will lead to one part of
iron inner core with a harder, chilled iron these will have an effect on wear and lifetime. the roll wearing at a disproportionate rate.
44 | may - June 2013 Grain &feed millinG technoloGy
Installing a hopper between the conveyor or replace a full set of rolls than pairs and will flutes are ground smooth before refluting
elevator will stop surges in material entering result in less downtime. while rolls with coarse corrugations can be
the roller mill. refluted using the exisiting flutes as a guide.
Taking time over roller setup will pay Recorrugation/refluting However, deeper corrugations will limit the
dividends in terms of roller life. The key Rolls can be refluted (or recorrugated) number of times a roll can be refurbished.
considerations are making sure the rolls when they are worn out. Manufacturers will
are parallel and level in relation to each be able to provide the best advice but once Other factors to consider
other. again there are roll-specific factors to take Bearings need regular greasing and this
Top rolls will wear quicker than bottom into consideration. task should be built into a maintenance
rolls so switching top and bottom rolls will Rolls with larger diameters can also be schedule. Drives, especially belt drives need
ensure that the set wears evenly. This is refurbished a greater number of times than to be aligned, properly tensioned, and the
a good move, as it is more convenient to a roll with a smaller diameter. Rolls with fine load limitations need to be adhered to.
Maintenance case study
Satisfying highest demands with
Bühler’s FERAN rolls have proven their
worth in the milling industry worldwide
over the last decades. They build the basis
of the milling roll portfolio.
Within the past years a need for even
longer living rolls has been emerging. To
satisfy this need Bühler’s casting experts
have conducted extensive research
efforts based on their long lasting expe-
rience. They came up with a further
developed mixing ratio between the
hard and the soft iron components
in the chilled iron alloy based on a
new metallurgical recipe.
Especially for corrugated rolls that are
subjected to particularly high stressing
TITAN rolls offer great value: they
considerably minimize the main-
Images courtsey of Bühler AG
tenance costs and the undesired
downtime in the grinding process.
This is due to an increase of 30
percent and more in service life
compared to Bühler’s standard FERAN
roll. It is obvious that this leads to a higher
availability of the milling plant since less
roll changes are required. Therefore main-
tenance costs are significantly reduced.
Apart from that the cost of working
capital decreases since less rolls need to
be stocked. Additionally – and nowadays
more and more important in the milling
industry – energy costs are reduced thanks
to the lasting sharpness of the corrugation.
Summing up, TITAN rolls stand for lowest
total cost of ownership for the miller.
The value that was added by TITAN rolls has
been proven in numerous milling companies
all over the world. “We are very satisfied with
the TITAN rolls. Their service life is 60 percent
longer compared to local rolls”, confirms a
Japanese flour milling company who stands
representatively for the large number of TITAN
roll users. Because of their high durability the
TITAN rolls are also very much appreciated by
the oilseed processing and ethanol industry.
Grain &feed millinG technoloGy may - June 2013 | 45
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