Nipped rolls are used in a vast number of continuous process industries including, for example, papermaking, steel making, plastics calendaring and printing. In the process of papermaking, many stages are required to transform headbox stock into paper. The initial stage is the deposition of the headbox stock, commonly referred to as “white water,” onto a paper machine forming fabric, commonly referred to as a “wire.” Upon deposition, a portion of the white water flows through the interstices of the forming fabric wire leaving a mixture of liquid and fiber thereon. This mixture, referred to in the industry as a “web,” can be treated by equipment which further reduce the amount of moisture content of the finished product. The fabric wire continuously supports the fibrous web and transfers it to another fabric called a felt which advances it through the various dewatering equipment that effectively removes the desired amount of liquid from the web. Water from the web is pressed into the wet felt and then can be removed as the wet felt passes a suction box. Dry felts can also be used to support the fibrous web through steam dryers.
One of the stages of dewatering is effected by passing the web through a pair or more of rotating rolls which form a nip press or series thereof, during which liquid is expelled from the web via the pressure being applied by the rotating rolls. The rolls, in exerting force on the web and felt, will cause some liquid to be pressed from the fibrous web into the felt. The web can then be advanced to other presses or drying equipment which further reduce the amount of moisture in the web. The “nip region” is the contact region between two adjacent rolls through which the paper web passes.
The condition of the various wires and felts can cause variations in the amount of liquid and other materials that are removed from the web which can, in turn, alter an amount of nip pressure applied to the web in a nip region. Other components in the papermaking process such as size application stations, coating stations, doctor blades, and oscillating showers can also affect the characteristics of the web. Even nip pressure axially along the roll and stable in time is beneficial in papermaking and contributes to moisture content, caliper, sheet strength and surface appearance. For example, a lack of uniformity in the nip pressure can often result in paper of poor quality. Thus, there remains a need to monitor various components of the papermaking process and account for their potential effect on nip pressure at one or more nip regions.