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When the calender roller group of the papermaking machine is pressurized, because the roller group bears the uniform load generated by its own weight and the external load applied to the bearing, the bottom roller and the top roller will produce flexural deformation, and the maximum deflection will be generated in the middle of the bottom roller and the top roller, thus the pressure distribution of the whole pressure zone is uneven, with small middle and large sides. In order to solve this problem, controllable middle and high rollers are now widely used, such as swimming roller (swimming roll), controllable middle and high roller (controlled crown roll) and partition controllable roller (nip roll). This paper focuses on the design of the electro-hydraulic control system of the controlled roller.

Zoned controllable rollers are generally pressurized by single-acting hydraulic shoe-type or double-acting piston-type pressurizing elements. The roller is divided into a central steel shaft, a roller shell, a pressing element and a rolling bearing or a sliding bearing. The roller is designed to lock the roller shaft to ensure that the nip is closed and loaded when the roller shell moves. Its two ends are spherical journals, which can allow the ends to flex under load. The force of the nip load acts on the roller shell through the hydraulic shoe or slider. The hydraulic pressure applied to the nip can be adjusted in real time, as shown in the figure. The distribution of the pressure zone can also be arranged according to actual needs. In theory, the more pressure zones, the better the calendering effect can be obtained, and selective calendering can be carried out to a large extent on the places that need to improve the transverse distribution of the paper sheet; but too many pressure zones will increase the difficulty of mechanical structure design, and the corresponding control system cost will also increase.

The middle and high volume of the traditional middle and high roller is produced by mechanical processing, which is fixed and cannot be adjusted. However, the modern calender generally adopts the middle and high roller with controllable partition. According to the calculated deflection distribution, the hydraulic pressure shoe is used to realize the correction of the roller deflection, so as to achieve the purpose of uniform distribution of the pressure zone.

Among them, the hydraulic boot pressure circuit adopts Rexroth 3FERE25 series high-frequency control valve, cartridge valve structure, and the outlet pressure is controlled by pilot proportional pressure reducing valve. Through the outlet pressure feedback to the control system, the formation of closed-loop pressure control. When the pressure difference at the valve port is 1MPa(10bar), the P-A flow rate can reach 240L/min and the A- T flow rate can reach 280L/min. The pressure gain curve and frequency response of the valve can meet the functions of rapid pressurization, pressure stabilization and pressure relief of hydraulic shoes.

In addition to meeting the pressure in the nip, the controllable middle and high rollers can generally use hydrostatic sliding bearings to generate a layer of oil film between the roller shell and the bearing. The oil film has good sliding and anti-vibration functions. The roller shell rotates at high speed on the sliding bearing without any wear, because there is no contact between the roller shell and the bearing. Hydrostatic bearing is a kind of sliding bearing. The sliding bearing is formed by the pressure oil transmitted to the small gap between the bearing and the roller shell. It is characterized by extremely high rotation accuracy and high load capacity at any shaft speed. There are many structural forms of hydrostatic bearings, such as small hole throttling, capillary throttling, film feedback, slide valve feedback and other different throttling forms. Its essence is to rely on throttling control elements to maintain a stable oil film. The commonality of these control elements is to change The flow rate compensates for changes in the load on the support.

Loadable sliding bearing structure

Through the transverse measurement of the paper web of the QCS system, combined with the hydraulic system and the automatic control system, a closed-loop banner control system can be formed to ensure the best banner distribution. The advanced electro-hydraulic control system can obtain accurate banner distribution, hydraulic adjustment provides instantaneous response, and equipment maintenance is relatively simple.

When the controllable middle and high roller is running normally, due to the reasonable oil discharge system set in the roller, the excess oil in the roller can be eliminated in time, and the smaller oil amount of the roller can reduce the quality of the roller and reduce the energy consumption of the equipment operation. In addition, through the balance of oil filling and oil discharge in the roller, the temperature distribution of the roller shell can be made very uniform, the temperature can be kept consistent, and the calendering quality of the paper can be ensured.

The technology of partitioned controllable medium and high rollers makes full use of electro-hydraulic integration technology. Through the hydraulic control circuit with load sensitivity and secondary adjustment, the internal loss of the system is reduced, and the use of accumulator circuit is used to save energy consumption and improve working efficiency. The application of proportional valve with high precision and high frequency response and the rational design of electrical control system make equipment maintenance, fault diagnosis and prediction easier and improve the trouble-free running time of paper machine, improved reliability, longevity and safety.