Special Requests Lead to Backup Rollers for Straightening Machines

The main market for Unitec ( a company within the Mondial group) has always been the machine tool sector. During the past three years, however, the Piacenza-based company chose to diversify its production and open up to new markets. One of these is the steel industry, where Unitec already completed several projects. During the last few years, a very successful solution has been represented by the backup rollers made to customers’ specifications meant for sheet metal coil straightening machines.

The Mondial group is one of the main distributors for power transmission parts in Italy. The group includes several companies, the most important one being Unitec. The core business of this company, founded in Piacenza in 1974, is the production of special bearings with cylinder rolls for the machine tool segment. Daniele Sergio Bussone, Managing Director, Unitec Special Bearings, explains: “Specifically, Unitec manufactures extra-precise bearings meant for milling heads and tables which by now we consider standard products. We also produce bearings to support machine ground ball screws and crossed roller bearings for various kinds of applications”. Unitec is present in markets all over the world, thanks to the direct presence on the territory of the group’s partner companies: ITM Unitec (a Mondial Group company) is the distributor of Unitec products in Germany, which is the most important market in Europe for the Italian company, while subsidiaries Antifriction, Feyc Rodamientos and RJ International represent the Unitec brand in Great Britain, Spain and France respectively. The level of product customization is high, as Bussone further explains: “Here at Unitec we can produce bearings with an external diameter which may reach 800 mm. One of our assets is the capability of manufacturing bearings to match every precision requirement, based on the client’s specific requests. As manufacturers of customized bearings, we pay special attention to choosing the best possible steel depending on the application for which the bearing is meant. Attention to detail and to production processes (Unitec has been ISO 9001 and ISO 14001 certified since 1996) is acknowledged by the market and much appreciated by all our clients”. A feather in Unitec’s cap (and Mondial’s too) which makes it stand out is its engineering department, as Roberto Valentini, Product Manager, Unitec Special Bearings, confirms: “For the past 25 years, our Technical Manager, Giuliano Mengoz, has been coordinating all of the department’s activities, where 8 engineers and designers work, who are responsible for the products’ development. To guarantee the products’ maximum quality, Unitec employs six persons in the quality control department; quality monitoring occurs step by step throughout the whole production cycle. For a company such as ours, which out of 50 employees has 6 devoted exclusively to quality control, this is a sizeable effort, which however allows us to guarantee the absolute quality of the finished product”.

Not just machine tools

For Unitec, just like for Mondial, the main market has always been the machine tool industry. During the past three years, however, the Piacenza-based company chose to diversify its production and open up to new markets. One of these is the steel industry, where Unitec already completed several projects. During the last few years, a very successful solution has been represented by the backup rollers made to customers’ specifications meant for sheet metal coil straightening machines. Roberto Valentini, product manager, Unitec Special Bearings, explains the philosophy which underlies the project: “The purpose of a sheet metal straightening machine is flatteny, wear easily since they have to work in harsh conditions and dirty environments, and must handle large loads. Since rollers and backup rollers determine the planarity of the coil’s sheet metal, these must present a high quality so as to ensure a longer working life and reduced maintenance. This is why we chose to develop these customized bearings to satisfy the client’s requirements”. Unitec offers two types of backup rollers: the backup roller with chain wheel (without shaft) which represents the ideal choice for maintenance activities on “older” machines; the backup roller with spacer pipe (with line shaft) has been designed for the management of heavy loads. “Being customized products, however, there is no limit to the types of backup rollers which we can offer”, Valentini states. “One example may be sufficient: during the past few years, straighteners greatly evolved, based on the requests coming from the automotive market (a domain where this type of machine is widely used). In this case, coils of high-resilience steel are used; this material has higher elastic modules and needs higher pressure to be straightened. About 85% of backup rollers manufactured by United today are destined to this type of application where very high performances are requested in terms of workload capacity and product working life. We develop our products taking into account well specified requests and needs based on the application where they are meant to be used”.

From a small batch of 5 units up to a 50,000-unit lot Customized is the new standard for Unitec, as Valentini confirms: “Backup rollers are such a niche product that it is impossible to invent a standard which could be used in more than one application. Although Unitec is an important concern on the market, it is small when compared to our multinational competitors, yet we can always guarantee to our clients a product with a high qualitative level and extremely flexible production processes which allow us to produce large and small lots (from a minimum of 5 items to a maximum of 50,000 units). Undoubtedly, for our clients this is a great asset which very few companies can provide”. Talking about customized products, Valentini mentions a special backup roller with lifelong lubrication developed for an important multinational in the steel sector. “On this type of backup rollers, we installed metal guards which protect the rubber washers so as to prevent the lubricant from leaking out. The stainless steel guards are designed to protect the seal form scale, that is, the black dust typical of sheet metal. Using the guards we protect the seal, enabling functioning without particles, while the seal keeps the lubricant within the bearing. By cooperating with the main Italian and European manufacturers of straightening lines, we were able to acquire a very high know-how and to develop an experience in many application segments by designing solutions for high-strength, pickled, stainless steel, coated and other types of sheet metal. The client was very happy with our product, so much so that today Unitec supplies the spare parts required. The spare part business is quite important (suffice it to mention that on a straightening machine hundreds of backup rollers may be fitted, and these need to be replaced over time) Considering the largest sheet metal producers nowadays are mainly abroad, over the past few years we began to turn to the end users of the machines explaining that our customized products may improve the performances of their straightening lines. This policy proved a winning one, since today just by providing spare parts we generate a few million euros worth of sales”. Construction details aligned with the market’s requests Since roughly 85% of backup rollers manufactured by Unitec today are meant for very demanding markets, the company specialized in the making of backup rollers for high-strength steel of considerable thickness. The thicker the sheet metal, the more important the backup roller becomes as a factor of the line’s productivity. “In order to develop these bearings, during the past three or four years Unitec cooperated with some manufacturers of straightening machines so as to enable the product to evolve and stand out with respect to competition”, Valentini remarks. “From this standpoint, our rollers may be customized with some interesting construction details. For instance, they may be configured with an axial framework capable of containing nay axial loads. This may occur during the phase when the machine starts, if the sheet metal entering the machine is not properly cut or rough, thereby generating lateral movements on the working cylinder. Another aspect worth noting is the lubrication process. The working life of a bearing is linked to work conditions but also to the lubricant. For this reason, our backup rollers may be configured with a lubricating unit, or may include manual lubrication if the machine belongs to a previous generation. By means of a grease gun, the bearing may be lubricated from the centre, pushing the lubricant through all revolving bodies. From the lateral openings, the old lubricant is expelled thereby allowing the new one to enter. The lubrication process, which normally occurs when the machine is not working, could actually be automated and programmed at predefined time intervals depending on the requirements of the plant’s manufacturer or user”.

The importance of using rotating bodies with a logarithmic profile

In order to distribute the contact pressure better, the backup rollers for coil straightening machines designed by Unitec may be configured with an external cylindrical ring or with a curve radius with an adequate value which may vary according to the bearing’s external diameter. For its products, Unitec always tries to use revolving bodies with a logarithmic profile, thereby improving the distribution of the contact pressure between the revolving bodies and the shaft, as Valentini explains: “In the backup rollers, the shaft is fixed to the machine while the external ring rotates. On top of the external ring there is a working cylinder. In this type of application, the workload is fixed on the shaft. This means that the shaft is the element of the bearing which always bears the maximum working pressure and, therefore, the greatest stress. Contact pressure changes depending on the curve radius of both the ened steel, which normally has a “fragile core”. As you can see, these are small construction details but they make a difference”. Regarding the straightening machine’s performance, what types of advantages derive from the use of Unitec’s backup rollers with respect to traditional backup rollers? “Comparing the two is very difficult, because there are millions of variables which influence the performance in different ways”, Valentini answers. “Our clients however already noticed their longer life, with varying percentage values according to the operating conditions in which the rollers work. A high added value linked to their use is definitely connected to maintenance times which decreased considerably. This aspect, along with the longer working life of the backup roller, leads to a greater productivity of the straightening machine”.

A small-scale type of production in an automated context

Besides backup rollers, the company develops other products dedicated to the steel industry (a particularly important market for Unitec). Valentini describes them: “Besides backup rollers for coil straightening machines, Unitec also manufactures: self-aligning bearings with a third ring for continuous casting; bearings for rolling mills as a support for the multiroll cylindrical roller working cylinders; bearings for Sendzimir cold rolling mills; bearings for special chains for coil transportation in steel mills; bearings for cardan line shafts; bearings for the mining sector; bearings for screw support; special bearings for planetary drives (Unitec cooperates with the main manufacturers in Italy and in Europe). Unitec also develops bearings for large reduction gears to clients’ specifications”. Unitec stands for special high-quality products but also for production flexibility. How does this type of flexibility show up in the production phase? Bussone replies, “In the workshop, we have more machines which deal with the same activity. Machines equipped with anthropomorphic robots are used to produce large lots, while such equipment as manual grinding machines where an operator is required produce smaller lots (5-10 pieces, 50 at the most). In practice, we are talking about a smallscale type of production within an industrial context. Flexibility at Unitec is therefore the result of an optimal mix between automation and manual work. This is why in our workshop there are many anthropomorphic robots but also many semi-manual or manual machines. By means of this production layout, our operator can manage a machine equipped with an anthropomorphic robot and simultaneously take care of the production of a small lot which still takes place in a traditional way”.