A high-quality material for roller covers
Under the product code of VNP-Viscoelastic Nonwoven Products. FKM produces roll coverings made of nonwoven fabrics for a variety of applications. Any nonwoven material is composed of fibers, that are bonded together to form a randomly oriented fabric. In the case of nonwoven rolls enhanced mechanical strength is required. Therefore, the fiber structure is impregnated with an elastomeric binder material. FKM can design nonwovens with a wide range of hardness, elasticity and porosity. At the same time, the resistance to various chemical media can be optimized.
The extraordinary product characteristics of our VNP roll coverings ensure benefits that have stood the test of time at automotive manufacturers, OEM manufacturers, flat-rolled metal producers, and textile manufacturers.
The production process starts with cutting separate discs out of the nonwoven roll goods. The computer controlled die cutter provides an optimized cutting pattern to avoid unnecessary material consumption.
The geometrical shape of the discs is not tied to a special design, so that the discs can be adopted to any available core cross section.
The discs are pressed onto the roll shaft using special loading procedures, that are based on the given non-woven material. The pressing procedure provides a uniform density and hardness of the covering along the length of the roll face. The die material is then compressed onto the roll shaft at an approximate rate of 1:3.lt is essential to assure a tight interference fit with the shaft eliminating the danger of void formation under the influence of load.
At this point the pressed covering requires turning and grinding to the finished size. For this operation computer controlled equipment is used, because inmost cases crowned roll shapes have to be achieved. The degree of crowning results from the core stiffness and the intended load.
Nonwoven materials for the most part consist of fibers. Therefore, it is plausible that this kind of material is much more resistant to cutting or crack propagation than rubber or polyurethane. Especially in the steel industry, the coverings often are exposed to sharp or irregular strip edges. Under these circumstances, the operational life often is several times the life of a conventional rubber covering.
By an appropriate choice of the fiber base and the incorporation of binder materials it is possible to design and to optimize the elastic properties of a nonwoven material within a wide range. Under load a zone of maximum internal friction will be generated at about a quarter of an inch below the roll surface. The value of the internal friction should be kept as low as possible. This especially holds for squeezing rolls at rolling mills, where the strip speed often exceeds 1500 ft/min. Here, nonwoven coverings are a good choice, because due to their low internal heat generation they can stand the combination of high speed, load, and high environment temperature.
Especially on oily strip surfaces, rubber or polyurethane coverings tend to hydroplaning. Driving or braking rolls often loose their grip, whereas nonwoven rolls still offer a coefficient of friction of about 0.3. The porosity volume near the surface makes it possible.The fluid film is absorbed for the most part, and the covering keeps contact with the strip.
Only as long as the covering keeps contact with the strip, a squeezing roll can provide a good sealing and squeezing effect. Those effects additionally are enhanced by the interaction of porosity and elasticity.When the roll surface leaves the area of the strip contact, the compressed and fluid filled surface zone expands. In this phase some void volume gets free again and is able to suck and transport away a part of the residual oil film.
Roll coverings made from nonwoven can be exposed to various chemical attacks. It is impossible to cover all these different requirements with the use of a single material. Therefore, materials have been developed for acid, neutral and caustic environments. If there is a question concerning the resistance of a nonwoven material regarding a special chemical environment, FKM will test the chemical resistance prior to a possible application.
| Nonwoven Model | VNP09A | VNP09B | VNP09C | VNP09E | VNP10 | VNP12B | VNP12D |
| Color | |||||||
| pH | Neutral | Neutral | Neutral | Neutral | Neutral | 1.5-13 | 0-14 |
| Main industry | Automotive | Automotive / Flat metal | Flat metal | Automotive | Flat metal | Flat metal | Flat metal |
| Feature | Hard / Brittle | Soft / Highly elastic | Soft / Elastic | Medium hardness | Soft | Soft | Soft / Tough |
| Max. operating temperature | 80°C | 70°C | 120-130°C | 80°C | 70°C | 70°C | 90°C |
| Main application | Oiling | Cold rolling at low temperatures | High temperature cold rolling | Oiling | Drain | Mild chemical environment | Strong chemical environments |
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