Apparatus for making a paper web with at least one endless screen belt guided by bearing and guide rollers

The present invention relates to a system for producing a paper belt with at least one self-contained sieve belt moved over support or guide rollers, a device for applying a pulp onto the sieve belt, with suction devices arranged along the sieve belt, as well as ceramic scraper strips and, if necessary, with devices for valve-controlled loading of the main web or the squeegees with a coolant, in particular with water.

Known systems of this type have at least one self-contained screen belt which is moved over support or guide rollers. A pulp containing about 1% solids and about 99% water is applied to the screen belt over its entire width by means of nozzles. The sieve belt is guided over suction cheeses and squeegees at a speed of up to 2500 m / min, whereby water contained in the pulp is drawn off.

Since the sieve belt moves over the scraper bars at the beginning of the production process or in the event of production disruptions without a pulp on it, the heat generated by the friction of the sieve belt on the scraper bars is not dissipated. This effect occurs in particular in the areas of the suction boxes in which the screen belt is pressed against the scraper strips located in the suction boxes by the suction effect. This is particularly true in systems in which the pulp is located between two sieve belts, since the two sieve belts cause an increased suction effect and thus an increased contact pressure. Likewise, the deflection of the sieve belt via arched suction boxes creates an additional pressure force acting on the scraper bars, which greatly increases the friction that occurs between the sieve belt and the scraper bars and the heat generated thereby. Since the temperatures caused by this can reach several hundred degrees Celsius, there is a risk of damage to the squeegees. As soon as the pulp is subsequently applied to the screen belt, the squeegee bars are suddenly cooled, which can also damage or destroy them.

In order to avoid these difficulties, it is known to provide spray nozzles in such a system, through which water is applied to the sieve belt or the squeegee bars, whereby the necessary cooling of the squeegee bars is effected at the beginning of the production process or in the event of production disruptions. However, this known measure does not meet the requirements, since the cooling of the wiping strips is carried out without reference to the production conditions, which is why the case may arise that a temperature rise takes place in the ceramic wiping strips up to overheating of the same. For example, the suction effect can be set incorrectly, which is why excessive friction is caused between the sieve belt and the squeegee bars. Likewise, too little water can be sucked off from the pulp, which is why the required cooling is not effected, which likewise results in inadmissible heating of the squeegees. As soon as the spray nozzles are then switched on, there is also the risk of damage or destruction of the ceramic wiper strips due to the sudden cooling of the same.

The present invention is therefore based on the object of avoiding the disadvantages inherent in the known systems for producing a paper strip. This is achieved according to the invention in that at least a part of the squeegee strips is designed with at least one temperature sensor, the output of which is connected to a display device or to a control unit. The outputs of the control unit are preferably connected to the control valves of the devices for applying the coolant to the sieve belt or the scraper bars.

Outputs of the control unit are preferably connected to control valves which are assigned to the suction devices or an output of the control unit is connected to the device for discharging the pulp onto the sieve belt. According to a preferred embodiment, the suction devices are designed with at least one ceramic wiper strip with at least one temperature sensor, the output of which is routed via the control unit to the control valve of the device assigned to the respective suction box for applying the coolant to the sieve belt or the wiper strips.

The temperatures generated in the squeegee bars by the frictional heat are displayed or measured by the temperature sensors, whereby the required controls on the one hand for the device for applying the coolant and on the other hand for the suction forces generated by the suction devices and also the

AT 41 1 536 B

Discharge of the pulp onto which at least one sieve belt can be controlled.

The subject matter of the invention is explained in more detail below with reference to an embodiment shown in the drawing. Show it:

1 shows a system according to the invention, in a schematic representation;

2 and 2a a ceramic wiper strip formed with a temperature sensor, in longitudinal section and in cross section; and

3 shows a suction box in the form of scraper strips according to FIGS. 2 and 2a

Cut.

The system shown in Figure 1 for producing a paper band 10 has two self-contained screen belts 1 and 2, which is placed over a plurality of support or guide rollers 11 and 21, by which the rollers 11a and 21a are driven, whereby these sieve belts 1 and 2 can be moved in circulation at a speed of up to 2500 m / min. A device 3 for applying a pulp is assigned to the first two guide rollers 11 and 21 in the direction of movement, through which the two screen belts 1 and 2 are guided to one another. The pulp, which consists of 1% solids, in particular cellulose fibers, and 99% water, is introduced between them over the entire width of the two screen belts 1 and 2.

In the direction of movement of the two screen belts 1 and 2, two suction boxes 41 and 42 and two groups of scraper strips 44 are arranged. The suction boxes 41 and 42 are also formed with squeegees. In addition, the suction boxes 41 and 42 are each assigned a spray nozzle 61 and 62, through which a coolant, in particular water, can be sprayed onto the sieve belts 1 and 2 or onto the scraper strips provided in the suction boxes 41 and 42. In the course of the movement of the sieve belt 2 after a two common deflection roller 11, 21, another spray nozzle 63 is assigned to the sieve belt 2 and the sieve belt 2 runs over a further suction box 43 formed with squeegees is lifted off the second screen belt 2 by means of a deflection roller 10a, is guided over a pressing device 12 and a drying device 13 and is wound up to form a drum 14.

As explained below with reference to FIGS. 2 and 2a as well as FIG Squeegees are measurable. The outputs of these temperature sensors are connected to an evaluation unit 40 via lines 41a, 42a and 43a. In the same way, the wiper strips of the groups 44 can each be designed with a temperature sensor.

The output of the evaluation unit 40 is connected to a control unit 70 via a line 40a. The outputs 71a, 72a, 73a of the control unit 70 are connected to the control valves 71, 72 and 73 assigned to the spray nozzles 61 to 63, which are located in a line 60 leading to the spray nozzles 61, 62 and 63 for a coolant, in particular water. Further outputs 81a, 82a and 83a of the control unit 70 are connected to control valves 81, 82 and 83, which are located in one of the vacuum lines 80 leading to the suction boxes 41, 42 and 43.

Another output 30a of the control unit 70 is connected to a valve 31, which is located in a feed line 30 to the device 3 for applying the pulp.

The wiper strip 51 shown in FIGS. 2 and 2a consists of a support plate 52, on the upper side of which a plurality of ceramic plates 53 are attached. The support plate 52 is designed with a recess in which a temperature sensor 54 is arranged, the sensor element 55 of which is located in one of the ceramic plates 53. The measured values ​​determined by the sensor element 55 are output via a line 56.

Thermocouples with the material pairing FE-CuNi according to DIN 43 710, class 2 or NiCr-Ni according to DIN EN 60 584 class 2 are preferably used as temperature sensors. Platinum resistors in accordance with DIN IEC 751 can also be used

In Figure 3, the suction box 41 is shown. As can be seen from this, this suction box is divided into two vacuum areas 41b and 41c with different suction effects. In this suction box 41 there are several wiper strips 51 designed with temperature sensors.

The mode of operation of this system is as follows:

By means of the device 3, the pulp is inserted between the two sieve belts 1 and 2

AT 41 1 536 Β brought. The water contained in the pulp is removed from the pulp through the suction boxes 41, 42 and 43 formed with scraper strips 51 as well as the groups 44 of the scraper strips, whereby the paper belt 10 is produced, which can then be lifted off the screen belt 2 and processed further.

Since this is a known technology, it is not explained further.

The temperature sensors 54 contained in the ceramic scraper strips 51 of the suction boxes 41, 42 and 43 measure the temperatures occurring in these due to the friction of the sieve belts 1 and 2 with respect to the scraper strips 51, which are evaluated in the evaluation unit 40. The control signals sent by the evaluation unit 40 to the control unit 70 can be used on the one hand to control the valves 71, 72 and 73 in the water inlet 60 to the spray nozzles 61, 62 and 63 via the lines 71a, 72a and 73a and, on the other hand, to control the valves in the to the suction boxes 41, 42 and 43 leading vacuum line 80 located valves 81, 82 and 83 take place. The valves 71, 72 and 73 act on the sieve belts 1 and 2 or the wiper strips 51 with the coolant, in particular with water, controlled. In this way, on the one hand, overheating of the ceramic wiper strips 51 and, on the other hand, the damaging effects of thermal shocks can be avoided. By controlling the suction effects generated by the suction boxes 41, 42 and 43, the friction occurring between the screen belts 1 and 2 and the scraper bars 51 can be avoided, whereby the heat caused thereby can also be controlled. These two measures can take place simultaneously or alternatively.

In addition, the discharge of the pulp from the device 3 between the sieve belts 1 and 2 can be controlled by the control unit 70. This is advantageous because, if the squeegees overheat, the pulp can cause a temperature shock, which is prevented if no pulp is discharged.

This creates a system by which the temperatures occurring in the ceramic wiper strips are monitored and controlled, thereby preventing damage to the ceramic wiper strips caused by overheating and sudden cooling.

It is essential that at least some of the ceramic wiper strips provided in the system are each designed with at least one temperature sensor, by means of which the temperatures occurring in the wiper strips are measured. These measured values ​​can be fed to a display device, whereupon manual control of the supply of coolant and / or the suction effect of the suction boxes as well as control of the discharge of the pulp can be carried out. These measured values ​​can also be fed to a control unit, by means of which a program-controlled regulation of the supply of coolant and / or the suction effect of the suction boxes and the discharge of the pulp can take place.