Roller Screen, Roll Family

The rolls are the most critical components

The roll is the most critical component of a roller screen and a roller feeder.  It is exposed to high abrasion with the constant contact with the iron ore pellets. It is also subject to impact with hard foreign contaminants discharged on the screens with the pellet load.  They are subject to progressive deterioration which has a direct effect on the roller screen efficiency and consistency of the gapping between the rolls.

Metal 7 is the worldwide specialist in selection of roller material and roller construction. 

Thanks to large investment made in R&D specifically on rollers, we are offering a wide range of roller material and protective coatings which will meet the needs of any customer.


Advantages of Metal 7’s rollers 

-    Less frequent recalibration of the gaps between the rolls.  The “regapping” operation might even be completely eliminated with our special coated rolls;


-    Better consistency of sizing of pellets – no wear with coated rolls;


-    Smallest diameter roller available on the market thanks to the coating which provide extra screening surface;

-    Improved roller rigidity preventing roller sagging;

-    Enhanced pellet transport properties;

-    Less sticking/build-up of material on the roller surface.

Over 40 pellet plants worldwide operate with rollers manufactured by Metal 7 and more are converting every year. Metal 7 has manufactured over 50 000 rolls and counting.

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The rollers are the most important component of a roller screen.  The best design of screen would be useless if its rollers would not provide the required performance. 


The following are the main characteristics sought after for roller screens rolls (same for roller feeder rolls):

-    Quality in the manufacturing (roundness, straightness, surface finish, etc.);

-    Strong shafts and roll assembly;

-    Good pellet conveying surface;

-    Not prone to sticking;

-    Mechanical strength, no bending;

-    Acceptable life through its resistance against abrasion;


The challenge lies in the design of the rolls and the selection of the material for the fabrication of the roller cylinder and the shafts. Many manufacturers compensate for limitations in the properties of the material selected by increasing its diameter and the thickness of the tubes used for the fabrication of the roller. That is the opposite of what their objective should be. Rollers should be as small in diameter as possible.  

Smaller diameter rolls mean more screening gaps and more screening capacity for a roller screen.  The extra capacity is always a plus as it will contribute to a narrower sizing distribution.  Better distribution translates into gains in productivity of the indurating furnace and in the quality of the pellets.

Screening efficiency is also impacted by the wear resistance of the rolls. The abrasion from the contact with the ore and pellets is important. The rollers wear out and have a short life. Production is lost during those maintenances for roller replacement.

The progressive wear of the rolls and enlargement of the gaps also reduces the efficiency of screening. Good pellets are mistakenly returned to the process through the gaps of the fines screening area of the roller screen and oversize pellets pass through the good product gaps. This causes more disruption to the process and lowers the productivity of the pelletizing line.

Frequent shutdowns of the line are required for the calibration of the roller screen. During those “gapping” operations, the rolls are repositioned to compensate the wear and the larger gaps. The periodic interruption of the operation for the gapping of the roller screens or the roller feeder causes loss in production and disruption of the operation.  

Furthermore, in between those stoppages for calibration, a fair amount of good pellets are recirculated through enlarged gaps to the balling system instead of proceeding further to the furnace.  Depending on the frequency of calibration, the loss in productivity caused by this recirculation of good pellets could represent 5 %, 10 % and even more.   It is very significant.

Roller design and strength should reduce the need of shutdowns for roller gapping and roller replacement. They should also have the lowest possible rate of wear to improve the consistency of screening.


Metal 7 manufactures thousands of rollers for iron ore pellet roller screens and roller feeders per year.  They are delivered in 20 countries where all the major iron ore processing plants are located.


This achievement is closely linked to its various solutions developed to optimize the performance of the rolls.  They are the following:

-    Better material for the construction of the rollers;

-    Adapted roller assembly options;

-    High standards in manufacturing;

-    Lowest diameter rolls;

-    Protective coatings and wear resistance options. 


Better material for the construction of the rollers:

Its rollers and roller shafts are made of the best materials in the industry. They provide the strength and the wear resistance allowing Metal 7 to supply the lowest diameter rolls available on the market.


Adapted roller assembly options

Different options of shafts/roller assembly are available to better suit your needs. They include few types of removable shafts designs allowing the fastest replacement of rolls, and particularly for chain driven machine, and perfect concentricity of the shafts and roll assembly (straighter roll). 


Options includes:

-    Fixed press shafts;

-    Welded shafts;

-    Removable bolted flange shafts;

-    Removable central screw taper lock type shafts;

-    Removable central screw shaft/hub arrangement;

-    Etc.


High standards in manufacturing

We are ISO-9001 certified for more than 20 years

All rolls are fabricated 100 % in house.  We control all steps of fabrication and apply the tightest tolerances on all dimensions and quality parameters, including the straightness and the surface finish.

Our own tolerances exceed the ones shown on original prints received from clients.  We know what rollers are for and how important the dimensions are for such calibrated equipment like a roller screen.


Lowest diameter rolls

We are driven by innovation and efficiency improvement.

In any project we are involved with, we always seek at increasing the screening area by the conversion to smaller rolls.  

We have the expertise for this. Metal 7 supplies the smallest rolls of the industry. Depending on the roller length and surface options selected by the client (coated or uncoated rolls), we can go as low as 63 mm (2.5’’) in diameter for the balling line rolls and 83 mm (3.25’’) for roller feeder rolls.

We are currently working on the design of rolls and roller screen components (bearings, sprockets, etc.) to lower the diameter even further.


Protective coatings and wear resistance options

In 1978, Metal 7 introduced an innovation, with the introduction of its ceramic M7-B21 coated rolls.

Since then, the company kept improving this particular coating (which became the M7-C21 some years later) and developing new coating options.

A range of different coatings for roller screen and roller feeder rolls are now available including the:

-    M7-C21 ceramic coating;

-    M7-A19 or C19 – carbide coating;

-    M7-D130- Metallic coating;

Our solutions are custom designed, variations of the above coating families are also considered to really the specific pellet material and conditions of operation in your plant.

The coated rolls extends the life of your rolls by up to 10 times, and even more. Therefore, it has a very positive in your plant operation costs. Reduction in yearly budget for roller replacement, less labour required for the roller replacement and lower losses of pellet production with fewer shutdowns are among the most obvious gains.

However, the maintenance savings are negligible compare to the real benefits in the process the coated wear resistant rolls provide. They do not wear. The gaps between rolls remain constant for all the life of the rolls. The efficiency of screening will stay constant. Many more good pellets are sent to the furnace and the good pellet load is not contaminated by off-size pellets. That is the real contribution of wear resistant rolls.


Smaller rolls

Metal 7 supplies smaller rolls which generate the following benefits:

-    Increased screening area with more gaps on your screen.  Pellet size distribution will be tighter with better pellet bed permeability in the furnace, better firing and quality of the pellets, reduced fuel consumption, etc.

-    Improved shape and strength of the pellets. The more rolls we have on the screen the flatter the surface of the screen is. The pellets travel easier on the machine and we see improvement in the roundness of the pellets and their compressive strength. This is sometimes called the re-rolling effect;

-    Surface speed could be increased with smaller rolls improving even further the pellet segregation and screening efficiency;


Wear resistant rolls / coated rolls 

Metal 7’s success in the market with its rolls is in large part attributable to its wear resistant rolls. They not only last longer but they also contribute to:

-    Increase the productivity of the pelletizing line by reducing the recirculation of good pellets caused by the wear of conventional rolls. The consistency of the gaps is the key contribution. Conversions to our wear resistant rolls have demonstrated gains of 5% to 10 % in the productivity of the pellet plant;

-    Eliminates the need for equipment shutdowns for roller calibration purposes;

-    Decreases maintenance costs. In most cases, it is possible to recycle the coated rolls in replacing the coating on worn rolls. Three lives are possible;

-    Use of protective coating is required to use the smallest possible diameter rolls. Since they do not wear, it is not necessary to add extra material to maintain the strength of the roll;

-    Improved sizing of the pellets will raise pellet quality, and provides better firing of the pellets in the furnace.  

-    Better sizing equals fuel consumption savings.

Metal 7, a partnership that lasts

Metal 7 is one of Canada's biggest players in the metallic and ceramic coating field. Thanks to its leading expertise, the company stands out from its competitors by proposing extremely sophisticated, high-performance solutions. This competitive edge allows the company to thrive on the international market. The products manufactured in its workshops are used in nearly fifty plants in 20 countries, on all five continents. Metal 7 exports over 70% of its annual production outside Canada.

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