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Valley Roller Roll Coverings for Industry


Roll Coverings for Industry

Virtually all industries use roll coverings. Rolls ranging in size from small thimbles to rail car dimensions are used in numerous applications. Industries utilizing rolls include paper, printing, steel, textile, wood, tanning, business machines, and plastics. Rolls may be used to feed, squeeze, protect, isolate, insulate, conduct or dissipate an electric charge, etc. All applications have their unique parameters that must be met. Whether it is solvent and chemical resistance or hardness and modulus, each covering must possess attributes which match the requirements of the specific application to be an effective product.

Typically, rolls are covered with elastomeric compositions to allow the creation of a uniform pressure zone called a "NIP". To insure the nip region remains constant, the properties of the roll covering must be stable and not degrade with use. The selection of the roll covering must take into account the physical properties of the covering originally (i.e., static) as well as physical properties of the covering in use (i.e., dynamic). Also an effective covering must not change appreciably in use, as determined largely by the environment (e.g. solvent and chemical exposure), as well as the dynamic properties of the roll covering.

The roll industry uses the widest range of elastomers of any segment of the rubber industry. Rolls are normally exposed to a variety of solvents and/or chemicals and must exhibit certain physical properties. These elastomeric coverings, or rubber compounds, may be modified or tailored to some degree to provide flexibility within their own inherent limitations. By the proper selection of various compounding ingredients, elastomeric coverings may be altered to vary hardness and other physical properties.

Improving the performance of end-use roll applications is essential in most industries today. Our team of specialists offers an extensive background in engineering, covering chemistry and the capability to design coverings to meet the most demanding applications. We can insure our customers get the most suitable covering for the specified application by asking the right questions coupled with our own experience. We guide our customers through the selection process from choice of covering to crown designs and all steps between. This technical expertise and the extensive understanding of roll applications and requirements remains the most important distinguishing characteristic of the company.

We invite you to take a look at the product line Valley Roller Company has assembled for use in industry. We are confident these coverings will improve roll performance and help our customers achieve their goals for improved productivity.

Nitrile Rubber, or NBR, and also referred to as Buna N, is the most commonly used elastomer within the roller industry, primarily due to its excellent resistance to oils as might be encountered in printing inks or in a variety of industrial applications. Nitrile rubber is a copolymer of butadiene and acrylonitrile. It can be formulated over a broad range of hardness's, and can be made in just about any color.

Nitrile/PVC blends have become very popular in the roll industry, and they offer some unique properties. Blending PVC resin into nitrile rubber has been found to improve certain physical properties, such as abrasion resistance, and to dramatically enhance its resistance to ozone. The latter is perhaps the primary reason why nitrile/pvc coverings have been used so extensively in low durometer printing roller applications. As PVC resin is a plastic, when incorporated into nitrile rubber it does bring with it certain disadvantages. Dynamic properties are very poor. Also, hardness, along with other properties, will be severely affected at elevated temperatures.

Carboxylated Nitrile, or XNBR, is a modified nitrile rubber possessing outstanding abrasion resistance and other physical properties, including tensile strength. At the same time it is very similar to nitrile rubber in terms of its chemical and oil resistance. XNBR coverings compare favorably to liquid cast polyurethanes in a hardness range of 45 to 85 in abrasion resistance and in other physical properties. XNBR generally exhibits poor hysteresis properties, and from that standpoint the polyurethanes are better, but in regard to chemical resistance XNBR is considerably superior. For example, XNBR may be used successfully in hot acids or caustics solutions, where even polyether polyurethanes would be unacceptable.

HNBR, or hydrogenated nitrile rubber, is a relatively new elastomer. It differs from nitrile rubber in that the majority of unsaturation sites on the polymer backbone have been eliminated through hydrogenation, thus yielding a more stable elastomer. While it is identical in resistance to oils as regular nitrile rubber, it is much more stable in certain chemical environments, such as ozone, and it also has heat resistance to around 325° F. Outstanding physical properties including abrasion resistance (much better than XNBR or good quality polyurethanes), tear strength and tensile strength are attained with HNBR, in a hardness range of 60-95 durometer Shore A.

EPDM is produced from the polymerization of ethylene and propylene, along with a third monomer. It has a saturated polymer backbone, which accounts for its excellent heat resistance, up to 350° F continuous exposure. EPDM rubber is considered a "non-polar" type polymer thus it has great resistance to "polar" solvents such as ketones and esters. However, EPDM should not be used in "non-polar" materials, such as mineral spirits, kerosene, and most petroleum derived lubricants as it swells severely in this environment.

Hypalon® has good chemical resistance and excellent resistance to ozone. It also has good physical properties, thus making it ideal from many mechanical roll applications. Hypalon® coverings can be formulated specifically for resistance to acids and other hot solutions often used in steel mill applications, such as in squeegee rollers. Also, Hypalon® works well in certain electrical applications such as corona treaters where there is substantial amount of high voltage discharge. It will withstand temperatures up to 300° F.

Neoprene historically is the workhorse of the roller industry. It has good mechanical properties and some resistance to oils. Some applications might include feed rollers of all types, squeegee rollers, wringer rollers, bridle rollers, laminating rollers and embossing rollers. In graphic arts applications neoprenes are frequently used in flexo and gravure printing and on feed rollers. Neoprenes are for general-purpose applications requiring some toughness, but not requiring the properties of urethanes or XNBR.

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© Copyright 2011 Valley Roller Company

WISCONSIN
N257 Stoney Brook Road, Appleton, WI 54915-9444
Phone: (920) 733-1991 | Fax: (920) 733-3722

TEXAS
101 Sentry Drive, Mansfield, TX 76063
Phone: (817) 453-8950 | Fax: (817) 453-1501