Maintaining grooves in rolls
May 8, 2014
by Marco Galli
Inefficient roll grooves have a negative impact on flour mill productivity, thus implicitly generating a series of problems that are not always or timely perceived as such. Actually they imply additional costs and therefore financial losses.
A yield decrease, higher energy consumption and loss in product moisture are several factors that may cause higher costs and losses in the management of a plant, totaling hundreds of thousands of dollars.
Furthermore, there is also the impact of worn out grooves on the finished product quality and on the management of the plant. Less sharp grooves cause a volume increase of the product parameter whose constancy is the key element to guarantee the plant’s reliability over time. To compensate for the volume variations, it is necessary to act on other parameters such as capacity or moisture. It is therefore clear that the most convenient approach is to carefully maintain roll grooves.
Wear and tear of grooves can also negatively impact the quality of the produced flour. One of the most important characteristics of first break flour is the impairment of elasticity, which impacts the balance of straight flour. Inefficient grooves, in fact, mistreat the product, resulting in lower quality flour. Tests carried out on one of Cremona, Italy-based Ocrim’s plants showed an increase of 10%-12% on the P/L value.
Having analyzed the negative consequences related to the poor maintenance of grooves, it is necessary to see what tools are at the millers’ disposal to prevent such problems.
The wear and tear of grooves can be monitored through planned and regular controls. However, there are very few plants that carry out these controls or rely on scientific data collections, such as sifting and energy consumption tests, which can actually ensure objectiveness when dealing with maintenance. Generally it is up to the miller to interpret the sensations received from the mill and decide when to renew the grooves, and this is a major limitation.
Based on experience acquired over the years at Ocrim, software was developed to verify the grooves in the flowsheet.
Starting from known data, such as the number of grooves, dimension of the land and shape of tool, the software is able to calculate the groove depth and, in particular, the product size in the groove. This result helps the miller understand the compatibility of grooves with the production requirements, because an incompatible grinding of the product, for shape and dimensions, will not be suitable. It also prevents rolls from touching before obtaining the required products.
The software is able to simulate various combinations in order to understand the limitation of a groove, before it affects the balance of the diagram in function of the consumption. It is immediately clear that the depth of the groove is the parameter that gives information on the state of wear in a clear and direct way. It is rather complicated to obtain this measurement on a mounted roll.
However, by analyzing the obtained data through such software, it has also been possible to establish a direct relationship between land and depth, because these two parameters are in a constant ratio. It has been established that a limit indicative parameter for the efficiency of grooves can be expressed in doubling the width of the land, measured on the speed roll. Generally, in this condition, the limit dimension of particles inscribed in the groove can be obtained without incurring an imbalance of the diagram, even if the rolls come into contact as previously described.
But in this condition, the width of the land was difficult to measure with the naked eye. Through specialists’ advice, a system of optical image acquisition has been implemented, with a 500-times enlargement factor via a portable microscope. This allows millers to immediately convert the image of the groove in an objective measure, thanks to a reference scale, and in a simple and immediate way establish in real time the state of wear of the groove. Furthermore, there is also the possibility to store the collected data, thus paving the way for future developments.
Today it is almost impossible to scientifically establish the roll duration. Workloads, tool profile, mechanical reliability of the roller mill, competence of the technician in charge, quality of the roll, are only some of the parameters involved in the duration of the roll.
Beside groove prevention and care, it is also very important that grinding rolls are produced according to quality construction criteria in order to make the grooves last longer.
The most evident problem of the roll’s grooves is one of the “shaded bands,” especially in finer grooves. In analyzing a groove with this defect, it is noted that this is nothing but the overlap of grooves. This is mainly caused by the difficulty in realigning the tool with the existing grooves, as a result of necessary sharpening of the same. After the sharpening, some grooves are remade before proceeding to the new ones. If the centering is not extremely precise, there is the risk of inaccurate grooves, thus leading to a lower duration of the groove.
Ocrim has developed a tool system with retrieved insert that allows the substitution of the same insert without having to disassemble the tool. This is the only way to guarantee a perfect centering between groove and tool during the working process. At this point, also having to renew previous grooves is not a problem, especially if the new numerical control grinding machine is used.
It is crucial to be the owner of the whole process in order to know all the processing phases applied to the roll, so as to supply it in the best way. It is important to:
Identify a reliable equipment supplier.
Execute all the involved processes at its workshops.
Execute such processes with its machines.
Marco Galli is Ocrim technologies director. He and Ocrim’s customer service department are available to answer any questions. Galli can be reached at 003903724011 or firstname.lastname@example.org or email@example.com.