Moisture Control Of Felts And Webs In Papermaking Systems

Abstract

An endless movable felt in a paper making machine, is cleaned by applying vacuum to the felt from first and second vacuum boxes adjacent and extending transversely of the felt, sensing a level of vacuum in the first vacuum box, actuating a liquid shower device adjacent and extending transversely of the felt by operating the shower device to apply a shower of liquid to the felt when the level of vacuum in the first vacuum box rises to a predetermined high value and rendering the shower device inoperative when the vacuum falls to a predetermined low value, sensing the variation in the amount of moisture in the felt across the width thereof, and transversely positioning a vacuum zone from the second vacuum box to align the zone with a zone of relatively high moisture content in the felt. The vacuum zone is defined by three relatively transversely movable members, each having a transversely-extending series of apertures cooperating with the apertures in the other members to provide the zone. Also, the moisture content of a paper web is controlled by sensing variations in the amount of moisture in the web across the width thereof, and transversely positioning a liquid shower zone from a liquid shower device adjacent and extending transversely of the web to align the zone with a zone of relatively high moisture content in the web.

Description

This invention relates to paper making machines, this term being used herein to include pulp and board machines.

One problem involved in the production of paper is that of cleaning the wet felts, which in operation collect foreign particles such as tar, wood fibres and size. If such particles are allowed to remain in the felt, the felt will gradually loose its ability to hold water and become hard and less spongy. Various equipment is known for cleaning felts, such as wringer rolls, beater rolls, vacuum boxes, showering systems and chemical solutions therefor. However, the control and operation of such equipment has in the past been somewhat haphazard. The term "felts" is used herein in a general sense to refer to the belts used in paper making machines, and not in a limited sense to define the material of the belts.

It is therefore an object of the invention to provide felt cleaning equipment in which the cleaning operation is at least partly controlled by the condition of the felt.

According to one aspect of the invention, a vacuum box extends across the felt, the box being connected to a source of vacuum and having openings adjacent the felt to remove some of the unwanted material therefrom. A liquid shower apparatus also extends across the felt, and is arranged to be switched on and off according to the level of vacuum in the vacuum box. For example, when the vacuum reaches a predetermined high value indicating a clogged felt, the liquid shower is switched on, and when the vacuum reaches a predetermined lower value indicating a relatively unclogged felt, the liquid shower is switched off. In this manner, an extra cleaning means, namely the liquid shower, is brought into action when the felt is relatively highly clogged.

According to another aspect of the invention, a vacuum box extends across the felt and is provided with adjustable means to enable the vacuum to be applied to the felt at a predetermined position across the width of the felt. A moisture meter is caused to traverse to and fro across the felt to provide a measure of the amount of moisture in the felt at different positions across the width of the felt, the amount of moisture being a function of the amount of clogging of the felt at the transverse position concerned. When the moisture meter detects that the felt is substantially wetter at one transverse portion than elsewhere, i.e. finds a wet streak, the vacuum box is adjusted to supply vacuum to the felt at that position.

The vacuum box can be adjusted manually, or automatically in response to the measurements of the moisture meter. The vacuum box may have three overlaping members, each with a transversely extending series of apertures, one member being fixed, and the other two members being relatively movable. The various apertures can be brought into or out of alignment by relative movement of the members such that the vacuum is applied only to a transversely extending zone of the felt, the zone being variable in transverse position and also in width. For example, movement of one of the members would position the zone, and movement of the other member would vary the width thereof. Alternatively, the vacuum box may be divided into separate sections each independently controlled by a valve, the valves being controlled according to the measurements of the moisture meter.

This aspect of the invention is applicable not only to the cleaning of the felt, but also to the control of moisture in the actual paper web. In this case, the vacuum box is replaced by a water supply system with adjustable means to enable water to be supplied to the web at a predetermined location across its width. The moisture meter is traversed as before, and the water supply system is controlled to add water if an overdry transverse portion is detected.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, of which:

FIG. 1 is a diagrammatic plan view of both aspects of the invention applied to felt cleaning in a paper making machine,

FIG. 2 is a side view of FIG. 1, but omitting various features for clarity,

FIG. 3 is a perspective view in more detail of the second aspect of the invention applied to felt cleaning,

FIGS. 4 a-4 f show a series of diagrammatic illustrations of the three movable members, and various relative positions thereof, and

FIG. 5 is a view similar to FIG. 3 showing how the second aspect of the invention can be applied to the control of moisture in a paper web.

Referring first to FIGS. 1 and 2, a paper making machine includes a felt 11 moving from right to left in the drawings. A first vacuum box 12 is secured beneath the felt 11, and extends tranversely thereof from one side to the other. The upper face of the vacuum box 12 has a transversely extending series of slots 13 which each extend in the general direction of travel of the felt 11, although they may be inclined thereto as shown. The vacuum box 12 is connected by a line 14 to a vacuum pump (not shown). In operation, the vacuum draws water and foreign particles from the felt 11 into the box 12.

Upstream of the vacuum box 12 is a high pressure water shower bar 15 which is secured above the felt 11 and extends transversely thereof from one side to the other. The bar 15 is connected by a line 16 to a high pressure water pump (not shown). The bar 15 is known per se, and includes a transversely extending series of jets or nozzles which in use direct high pressure jets of liquid at the felt 11. The bar 15 may be oscillated in known manner along it longitudinal axis.

An electrical vacuum switch 17 is secured to the vacuum box 12 so as to be responsive to the level of vacuum therein, and is connected by a signal line to the high pressure shower 15 to control its operation. The switch 17 is so constructed that when the vacuum in the box 12 rises to a predetermined high level the shower 15 is switched on, and is switched off when the vacuum falls to a predetermined low level.

As the felt becomes more clogged or plugged, the level of vacuum in the box 12 will rise since the slots 13 will be relatively more closed by the felt 11. When the amount of vacuum reaches the predetermined high level, the high pressure shower 15 will be switched on by the vacuum switch 17 to thereby effect an extra cleaning operation on the felt 11. As the felt becomes cleaner and therefore less clogged, the slots 13 will become less obstructed by the felt and the level of vacuum will fall. When the vacuum has fallen to the predetermined low level, the vacuum switch 17 operates to shut off the high pressure shower 15.

For example, if the level of vacuum with a new, clean felt 11 is in the range 8-10 inches of water, the vacuum level when the felt becomes dirty may rise to 20-24 inches. Therefore, the shower 15 could be switched on by the vacuum switch 17 when the vacuum reaches an undesirably high level of 15 inches, and switched off when the vacuum drops to 10-12 inches. The switch 17 may be adjustable so that the predetermined levels can be varied as desired by the operator.

Instead of being switched off when the vacuum has fallen to a predetermined low level, the switch 17 could be constructed to switch the shower 15 off after a predetermined length of time.

Some known high pressure showers 15 which oscillate, as previously mentioned, include a fail safe unit 19 which operates to switch the shower off if the oscillations slow down or stop, thereby preventing damage to the felt. In the present instance, the signal line 18 can be connected to the fail safe unit 19 to effect control of the shower 15.

Referring now to FIGS. 3 and 4 as well as to FIGS. 1 and 2, a second vacuum box 20 extends below and across the felt 11 immediately downstream of the first vacuum box 12. The vacuum box 20 has an upper surface with a transversely extending series of apertures 21, which may for example be in the form of slots or may be circular, the apertures 21 being shown as slots in FIG. 1 and as circular in FIGS. 3 and 4. The vacuum box 12 is connected by a line 22 to a vacuum pump (not shown). The vacuum box 20 has two relatively movable slide members 23, 24 below the upper surface containing the apertures 21. The slide members 23, 24 also each have a transversely extending series of apertures 25, 26 which will be described in more detail later.

Upstream of the high pressure shower 15 is a transversely extending rail 27 mounted below the felt 11. A moisture meter head 28 is slidably mounted on the rail 27 for to and fro movement across the width of the felt. The meter head 28 can be reciprocated along the rail 27 by any convenient means, for example by a chain drive with end of travel limit switches. The meter head 28 is connected by a signal line 29 to a moisture meter 30.

The moisture meter 30, in conjunction with its meter head 28, functions to provide a measure of the amount of water in the felt 11 at the transverse position at which the meter head 28 is located. A suitable moisture meter and head assembly is described in Canadian Pat. No. 874,046 issued June 22, 1971, and gives a voltage output proportional to the amount of water. The amount of water present is proportional to the amount of foreign particles plugging or clogging the felt 11. Thus the output of the meter 28 gives an indication of the condition of the felt 11. The moisture meter output is transmitted along a line 31 to a slide control 32, which has control lines 33, 34 connected to slide motors 35, 36 operable to move the respective slide members 23, 24.

This arrangement is useful when, as frequently happens, the foreign particles are collected unevenly across the width of the felt 11, and thus produce clogging or plugging of the felt unevenly across its width. Therefore if an even vacuum is applied across the felt, certain areas will not clean as well as others. This will result in an uneven water carrying capability of the felt. Such areas of the felt having an especially high amount of water are known as wet streaks. The present arrangement enables a cleaning operation to be effected at the transverse location on the felt at which a predetermined level of clogging is detected, thereby to at least partially remove wet streaks and produce a more evenly clean felt.

With reference particularly to FIG. 4, the apertures 21 in the upper surface of the box 20 are evenly spaced at a certain pitch, and the apertures 25 in slide member 23 are more closely spaced. There are thus slightly more apertures 25 in slide member 23 then there are apertures 21 in the upper surface of vacuum box 20. The spacing of apertures 26 in slide member 24 is the same as with slide member 23.

FIGS. 4 a and b show the apertures 21 in the upper surface of vacuum box 20 and the apertures 25 in slide member 23. FIG. 4 c shows the effect when slide member 23 is placed over the apertures 21 in upper surface 20. Some apertures are closed completely, and there is a zone Z1 of predetermined width where the apertures are aligned or partly aligned. In FIG. 4 c, the zone Z1 is near the left hand end of the figure. By moving the slide member 23 relative to the apertures 21, the zone Z1 can be moved along the upper surface 21, as shown in FIG. 4 d, where the zone Z1 is in an approximately central position.

FIG. 4 e shows slide member 24, and FIG. 4 f shows slide member 24 over slide member 23 and upper surface 20 when these are in the position shown in 4 d. By moving slide member 24 relative to slide member 23 and upper surface 20, the width of the zone of aligned apertures can be varied, and FIG. 4 f shows a narrower zone Z2.

Thus if slide members 23, 24 are moved simultaneously, the position of the zone across the width of the felt 11 is varied, and if slide member 24 is moved while slide member 23 is not the width of the zone is varied at the same transverse location.

The drive for traversing the meter head 28 also sends a signal along line 37 to the slide control 32 to indicate the tranverse position of the meter head 28. The slide control 32 also controls by a signal line 42, the vacuum pump which supplies the vacuum box 20. The slide control 32 is in fact a small computer which functions in the manner now to be described.

The meter head 28 traverses to and fro below the felt 11, and the voltage output along line 31 is stored in a memory in the slide control 32. The average voltage level on a transverse run is calcuated by the slide control 32, and is used as a reference on the next run. If the voltage rises by a predetermined amount, indicating the commencement of a wet streak, the slide control 32 operates to move slide member 23 to a position such that the apertured zone starts at the position where the voltage rises. Also, the vacuum pump supplying the vacuum box 20 is switched on. When the voltage drops below the preset value after further movement of the meter head 28, the slide control 32 moves slide member 24 to such a position that the apertured zone finishes at that position. If no wet streak is detected, the slide control then shuts off the vacuum pump supplying the vacuum box 20.

In this way, wet streaks on the felt 11 can be dealt with to remove the excessive amount of foreign particles present by applying vacuum from the box 20 in a zone of appropriate width and position, and thus produce a more even level of water across the width of the felt.

Instead of the three layers of apertures being provided as previously described to position and adjust the width of a vacuum zone applied to the felt, the vacuum belt may be divided into a transversely extending series of separate sections, each controlled by a solenoid valve, so that the control 32 controls the application or otherwise a vacuum to the felt from a section by appropriate operation of the relevant solenoid valve, rather than by positioning slide members. Such a vacuum box would be constructed in a similar manner to the shower box which will shortly be described with reference to FIG. 5. In a similar way, the slide system just described could be used instead of the sectioned shower box of FIG. 5.

The traversing moisture meter head which detects zones of greater (or less) wetness than average can also be used in paper manufacture to control the wetness of the paper web. Such an arrangement will now be described with reference to FIG. 5, and for simplicity the same reference numerals will be used where possible. The meter head 28 traverses below a paper web 38 and sends signals of wetness and position along lines 31, 37 to a control 32. Downstream of the meter head 28, a fine spray water shower 39 extends transversely below the web 38, and is divided into a transversely extending series of separate sections 40. The shower box 39 is connected to a water supply (not shown), and an outlet in the upper surface of each section 40 is controlled by a solenoid valve (not shown). A series of control lines 41 extend from the control 32 to the shower box 39, therebeing one line 41 to each solenoid valve.

The average voltage output of the meter head 28 on a transverse run is used as a reference for the next run. On this next run, the control 32 compares the moisture level at a respective section with the average, and opens, closes or leaves as is the solenoid valve of that section to apply moisture or not, as the case may be, to the felt 11 adjacent that section. Thus, the moisture level across the felt tends to be built up to a desired value.

The control 32 could alternatively be provided with a signal, for example by means of an adjustable dial, of a desired average moisture level, which would then form the reference. This would permit the operator to select the desired moisture level. This feature could also be applied to the previously described felt-cleaning arrangement.

Claims

I claim:

1. A method of cleaning an endless movable felt of a paper making machine including sensing variations in the amount of moisture in the felt across the width thereof, causing vacuum from a vacuum box adjacent and extending transversely of the felt to be applied to the felt in the zone extending across a portion of the width of the felt, and positioning said vacuum zone in alignment with a relatively high moisture zone of the felt, including transversely positioning said zone by relatively transversely-moving three members associated with the vacuum box, each member having a transversely-extending series of apertures cooperating to provide said zone.

2. A method according to claim 1 including positioning one movable member in response to the sensing of the commencement of a relatively high moisture zone in the felt and positioning another member in response to the sensing of the end of said felt zone.

3. A method of controlling the moisture content of a paper web in a paper making machine, including sensing variations in the amount of moisture in the web across the width thereof, causing a liquid shower from a liquid shower device adjacent and extending transversely of the web to be applied to the web in a zone extending across a portion of the width of the web by transversely positioning said shower zone by relatively transversely-moving three members associated with the vacuum box, each member having a transversely-extending series of apertures cooperating to provide said zone; and position the zone in alignment with a zone of relatively high moisture content in the web.

4. A method according to claim 3 including positioning one movable member in response to the sensing of the commencement of a relatively high moisture zone in the web and positioning another member in response to the sensing of the end of said web zone.

5. A paper making machine including an endless movable felt, a vacuum box adjacent and extending transversely of the felt, the vacuum box having adjustable means to cause vacuum to be applied to the felt in the zone extending across a portion of the width of the felt, comprising means including three relatively transversely movable members, each having a transversely-extending series of apertures cooperating with the apertures in the other members to provide said zone, means for sensing variations in the amount of moisture in the felt across the width thereof and means responsive to said sensing means to adjust said vacuum applying means so as to position said vacuum zone in alignment with a relatively high moisture zone of the felt.

6. A paper making machine according to claim 5 wherein the sensing means positions one of the movable members in response to the sensing of the commencement of a relatively high moisture zone of the felt, and positions another member in response to the sensing of the end of said felt zone.

7. A paper making machine including a liquid shower device adjacent and extending transversely of a paper web, the shower device having adjustable means to cause a liquid shower to be applied to the web in a zone extending across a portion of the width of the web comprising means including three relatively transversely-movable members, each with a transversely-extending series of apertures cooperating with the apertures of the other members to provide said zone; means for sensing variations in the amount of moisture in the web across the width thereof; means responsive to said sensing means to adjust said shower applying means so as to position said shower zone in alignment with a relatively high moisture zone of the web; said sensing means positioning one of the movable members in response to the sensing of the commencement of a relatively high moisture zone of the web and positioning another member in response to the sensing of the end of said web zone.