US2857823A

US2857823A - Suction roll silencer

Info

Publication number: US2857823A
Application number: US506763A
Authority: US
Inventors: George J Thiessen
Original assignee: National Research Council of Canada
Current assignee: National Research Council of Canada
Priority date: 1955-05-09
Filing date: 1955-05-09
Publication date: 1958-10-28
Anticipated expiration: 1975-10-28

Description

2 Sheets-Sheet 1 Filed May 9, 1955 Oct. 28, 1958 l G. J. THlr-:ssEN 2,857,823

SUCTION ROLL SILENCER Filed May 9, 1955 2 Sheets-Sheet 2 PRESSURE 3 PRESSURE P5555 uRE o TIME o r/ME PR'SS URE TME' o United States Patent() SUCTION ROLL SILENCER George J. Thiessen, Ottawa, Ontario, Canada, assignor to National Research Council, Ottawa, Ontario, Canada, a corporation of Canada Application May 9, 1955, Serial No. 506,763

7 Claims. (Cl. 9253) The present invention relates to a silencer device for suction rolls and in particular to asilencer device for the couc used in paper machines.

In the manufacture of paper one of the problems is the removal of the water in which the stock is carried to the machine. lt is customary to do this by the passage of the stock, supported on a screen, over vacuum or suction boxes. Some of these boxes are on the inside of rotating drums the low pressure being transmitted to the stock or paper by perforations in the drum surface. As these holes enter or leave the vacuum box air willv suddenly ow out of, or into, these holes in the drum surface. This action is similar to that in a siren and results in the high pitched scream which is so characteristic of paper machines and which is usually referred to as couch noise. The couch drum is, however, not the only one making this noise since any suction roll will behave in the same way.

Because of the large amount of air flowing and the length of the drum which is about 20 feet, the noise intensity is very high. Sound levels of 110 to 120 decibels are quite common (depending on the speed of the machine) in the areas near the machine commonly occupied by machine operators. Besides the extreme annoyance caused by such noise, communication is made very diicult and what is even more important damage is caused to the operators hearing.

Attempts have been made in the past to reduce the noise to a level and intensity not detrimental to the machine operators. One such attempt is disclosed in United States Patent No. 2,274,641 to E. J. Abbott and J. D. Krause which consists of a solid wedge attached to the leaving edge of the suction or vacuum box, the upper surface of the silencer device having a radius of curvature approximately equal to that of the inside surface of the couch roll but not concentric with it. The surface of the wedge is nearly in contact at the leaving edge of the sealing strip `of the vacuum box, the gap between the upper surface of the wedge and the surface of the couch roll increasing with the distance from the leaving edge.

In the operation of the silencer device above described,

it appears that the gap adjustment changes with the wear of the silencer. Since the size of the gap is critical, the silencer is out of commission after a relatively short period of use. A second noted disadvantage of the known silencer above described is that the gap is prone to become plugged with the pulp or paper being processed by the couch roll. Unless, therefore, arrangements are made periodically to clean the gap, the silencer ceases operating after a period of time of the order of days.

It is an object of the present invention to provide a silencer device for suction rolls, in particular couch rolls, in which the disadvantages above mentioned would Vbe minimized and which would be adapted to operate substantially without interruption or disturbance.

It is a further object of the invention to bring the noise emitted as a result of the air entering the holes in ,the couch roll or drum to a level not detrimental to rice the operators health and to the safe operation of the couch rolls.

It is a further object of the invention to control the stream of air entering the holes in the suction or couch roll as well as to control the oscillations in the holes of the couch or suction roll. It is another object of the invention to control both the stream of air and the oscillations in adjustment with the speed at which the roll rotates and the pressure used in the vacuum or suction box of the suction or couch roll.

Having regard to these and other objects, the present invention will be appreciated by a study of the following specification in conjunction with the accompanying drawings.

In the drawings:

Figure 1 is a cross-sectional view yof one embodiment of the silencer device of the present invention illustrating one size, shape and location of the silencer device.

Figure 2 is a cross-sectional view of another embodiment of the present invention illustrating the silencer device of different shape and construction than the embodiment illustrated in Figure 1. y

Figure 3 is a graph showing the variation in time of pressure inside the holes of the suction 0r couch roll after the evacuated hole has been suddenly exposed to atmospheric pressure.

Figure 4 shows three graphs (a), (b) and (c) showing other relationship of the pressure inside the openings of the suction or couch roll with time.

Referring in more details to the drawings, the silencer device of the invention comprises a chamber 1 extending substantially the length of the suction or couch roll 2 and arranged next to the leaving edge 3, of the vacuum or suction box 4. The suction or couch roll 2 has radial holes 5 arranged along the roll, the holes being spaced at desired intervals and extending across most of the surface of the roll 2. The suction or vacuum box is held against the underside of the suction or couch roll 2 and is provided with a wide opening from which suction is applied through the radial hole 5 to the material, such as paper, pulp or the like, travelling tangentially to the outer surface of the suction or couch roll 2. In Figure 1 the leaving edge 3 of the vacuum `or suction box 4 is brought in contact with the suction or couch roll 2 by means of a sealing strip 6. Any other suitable means of attachment of the vacuum or suction box to the suction or couch roll may be used. The silencer device comprises a chamber 1 with a narrow gap 7 cut in a strip 8 attached to the top edge of the chamber 1 adjacent the leaving edge of the suction box 4 as shown in Figure 1. The gap 7 extends like the chamber itself substantially the length of the suction roll. To permit the gap 7 to communicate with the chamber 1 the strip 8 is drilled with apertures 9b circumscribing an area of the strip 8 marked in Figure 1 as 9. The apertures 9b circumscribing the area 9 are as close together as is permitted by the strength requirements for the strip 8. The width of the strip 8 is at least twice as large as the diameter of the opening 5 of the couch or suction roll 2. The chamber 1 is provided in at least one of its side walls with at least one air inlet duct 10 which is adapted to supply air at a desired rate of flow to the inside of the chamber 1.

The embodiment of the present invention shown in Figure 2, comprises a gap 7 `adapted to be placed in communication with the hole 5 of the couch roll 2, as the latter rotates, the gap in this embodiment leading directly into the chamber 1, without the intermediary of a strip. As in the embodiment illustrated in Figure 1 the chamber 1 is arranged next to the leaving edge 3 of the vacuum or suction box 4. The enclosure 1 is provided in at least one of its walls with at least one air inlet duct 10v adapted to introduce air Vat a desired pressure .to `the enclosure 1 whereby to control and regulate the pressure inside the enclosure. i

Figure 3 shows the variation of pressure `inside the opening with the time elapsed after the opening 5 `which has been evacuated is suddenly exposed to the atmosphere. The rate of decay of the pressure, or in other words the rate at which the oscillations in theitube tend to die down and the pressure tends to approach atmospheric pressure, is determined by the rate of energy loss of the system. Frequency f of oscillation for a given length L of the opening closed at one end, and suddenly exposed at the open end to a pressure differentfrom the pressure inside the opening will be given approximately by theformula C fL in which c is the velocity of sound.

Figure 4 shows other forms which the relationship of pressure with time can take inside the opening 5 depend ing on the damping. When the damping is lowthe relationship will be that illustrated in Figure 4a, when the damping is high it will be that illustrated in Figure 4b and when the damping is greatly in excess of the critical value, the relationship will be that illustrated in Figure 4c.

The width of the gap 7 will be chosen for etiicient operation in relation to the average speed at which the suction or couch roll is expected to rotate, the effective length of the opening 5 in the suction or couch roll 2,

and the pressure in the vacuum box. In the practice of the invention, the width of the gap 7 chosen will be very small, e. g. about 0.020 to 0.030 inch but a width of up to about 0.220 inch may be used.

Since the opening 5 attains in its oscillations atmospheric pressure several times (the intersection points of the abscissa in Figure 3), it is, in principle, possible to close off the end at any one of these times. This ensures that the average pressure is atmospheric although the air is in general in a turbulent state and the opening therefore still radiates when exposed to the open air. However, in practice, the actual opening and closing of the opening 5 does not occur suddenly and involves a variation of the resistance to air ow. This resistance operates in practice to damp out the oscillations in the opening 5. Hence no appreciable radiation will occur when the opening 5 is exposed to the open air.

ln accordance withya preferred embodiment of the invention, `the chamber 1 is provided with at least one air inlet duct. The presence of the duct prevents the chamber from becoming scavenged of its air by the low pressure openings continually arriving in it. The size of the duct is preferably such that an air supply of the order of 2 cubic feet per second can be supplied to the enclosure when the suction or couch roll rotates at an average speed. The air inlet duct should preferably terminate in an acoustic filter or muier or in a chamber lined with absorbing material to prevent the radiation from the end of the duct to penetrate into the machine room. However, even without a lter or mui-lier arrangement adequate silencing takes place with the device of the present invention. The chief reason for this lies in the fact that a line source will radiate in aplane at right angles to the line. When forced to radiate in a direction parallel to the line the acoustic loading is greatly reduced and so is its acoustic eiciency. The air inlet duct or ducts is or are therefore preferably located at the ends of the chamber. Y

The silencer device of the present invention is well adapted to operate withsuction rolls of any type used in the industry, particularly couch rolls as used in a newsprint machine in-which the couch may be 20 feet long and about 4 feet in diameter. The shell of the .couch would be about `1 tto `11,/2 ,inchesfthickand the` diameter of `theopenings or holes `in the couch would generally be of the order of 5A6 of an inch. Itis a particular advantage of the silencer device of the present invention that the paper or pulp being processed need not stay in contact with the outer surface of the suction or couch roll much longer than usual. It is, of course, essential that the outer end of the opening 5 be closed when the opening is in contact with the gap of the silencer enclosure. However, in view of the very small width of the gap 7 which will preferably vhosen, the time of contact between the open area the gap 7 and the open area of the opening 5 would be extremely small and the outer end of the opening 5 need only be closed for that length of time.

There will of course be an optimum width for gap 7 and the following discussion will enable the most suitable width for any given operation to be chosen. By way of example, if the length of the opening 5 is approximately 'l1/2 inch, a frequency of oscillation of the order of 3000 cps. will be produced in the opening. ln this example, the time to reach atmospheric pressure for the rst time will be of the order of 0.1 milliseconds. Assuming a peripheral speed of the couch of 1800 feet per minute, the drum will move, during this interval, a distance of 0.030 inch. Hence this value of gap width would be approximately right. (Because of its own large diameter the hole remains in contact with the gap longer but this is approximately cancelled by the constriction of air flow caused by the narrow gap.) Experiments on this model gave maximum silencing for a gap width of 0.022 inch. When the pressure in the vacuum box was ll inches of mercury below atmospheric, the resistance of the gap is not a constant but increases with the increasing rate of flow. The width of the gap will therefore be increased with an increase in the difference in pressure between the vacuum box and the atmosphere.

Since the gap width can only be approximately calculated it is desirable to have some control during operation. The regulation of the pressure in the enclosure provides this control. Thus, if in the operation of the couch roll with the silencer device of the present invention the gap 7 were found to be wider than sufficient to bring the opening S to atmospheric pressure without overshooting, the enclosure would be kept at below atmospheric pressure (by simply constricting the air inlet duct). Conversely, the enclosure would be kept at above atmospheric pressure if the speed of rotation of the suction or couch roll 2 was higher than usual so that the gap was in contact with the holes for an unduly short interval of time. The latter condition is not a desirable one, however, since it requires extra pumping equipment. In general it is preferred therefore to operate in a region in which constriction of the inlet duct can compensate for either speed changes or design tolerances.

The enclosure box of the present invention may be made of any suitable material, care being taken to choose the material of sound attenuation sufficient to ensure that the sound energy penetrating is negligible.

The silencer device of the present invention permits effectively to suppress or substantially reduce the noise emitted by suction rolls or couch rolls, substantially without interruption or disturbance. It is thus of considerable advantage both to the health of the operators and to the efficient operation of the suction or couch rolls. The gap of the silencer enclosure does not appreciably Wear out in operation and this permits the use of the device without the necessity for adjustment. In view of the direction of the air flow, no appreciable clogging of the gap with shock or pump takes place. In view of the fact that the paper or pulp or the like being processed need only remain in contact with theouter surface of the roll for very short intervals of time beyond that spent over the suction box, the application of the silencer enclosure does not necessitate any change in the operating conditions of the machine.

.Itiisrintendcd thatitheipresent disclosure shouldnotbe construed in any limiting sense other than that indicated by the scope of the following claims.

What I claim as my invention is:

1. A silencer device for apparatus of the type including a rotated suction roll having radially extending holes, and a stationary suction box cooperating with the inner periphery of the roll as the roll is rotated, comprising means defining a chamber extending substantially the length of the roll and arranged next to the leaving edge of the suction box, said chamber having adjacent the inner periphery of the roll a gap extending substantially the length of the roll and adapted to place the chamber in communication with said holes in succession as the roll rotates, said gap being of a width not exceeding about 0.220 inch, and at least one air inlet duct in at least one of the walls of said chamber for regulating the pressure inside said chamber.

2. A silencer device for apparatus of the type including a rotated suction roll having radially extending holes, and a stationary suction box cooperating with the inner periphery of the roll as the roll is rotated, comprising means defining a chamber extending substantially the length of the roll and arranged next to the leaving edge of the suction box, said chamber having adjacent the inner periphery of the roll a gap extending substantially the length of the roll and adapted to place the chamber in communication with said holes in succession as the roll rotates, said gap being of a width not exceeding about 0.220 inch, and at least one air inlet duct in at least one of the walls of said chamber for regulating the pressure inside said chamber whereby to compensate for changes in the speed of the suction roll.

3. A silencer device for apparatus of the type including a rotated suction roll having radially extending holes, and a stationary suction box cooperating with the inner periphery of the roll as the roll is rotated, comprising means defining a chamber extending substantially the length of the roll and arranged next to the leaving edge of the suction box and having a sealing strip in its wall facing said hole whereby to cooperate with the inner periphery of said roll, said sealing strip being at least twice the diameter of said hole, said chamber having adjacent the inner periphery of said roll and arranged in said sealing strip a narrow gap extending substantially the length of the roll and adapted to place the chamber in communication with said holes in succession as the roll rotates, and at least one air inlet duct in at least one of the Walls of said chamber for regulating the pressure inside said chamber.

4. A silencer device for apparatus of the type including a rotated suction roll having radially extending holes, and

a stationary Suction box cooperating with the inner periphery of the roll as the roll is rotated, comprising means defining a chamber extending substantially the length of the roll and arranged next to the leaving edge of the suction box and having a sealing strip in its wall facing said hole whereby to cooperate with the inner periphery of said roll, said sealing strip being at least twice the diameter of said hole, said chamber having adjacent the inner periphery of said roll and arranged in said sealing strip a gap extending substantially the length of the roll and adapted to place the chamber in communication with said holes in succession as the roll 6 rotates, said gap being narrower than the width of any of said holes, and at least one air inlet duct in at least one of the walls of said chamber for regulating the pressure inside said chamber.

5. A silencer device for Iapparatus of the type including a rotated suction roll having radially extending holes, and a stationary suction box cooperating with the inner periphrey of the roll as the roll is rotated, comprising means defining a chamber extending substantially the length of the roll and arranged next to the leaving edge of the suction box and having a sealing strip in its wall facing said hole whereby to cooperate with the inner periphery of said roll, said sealing strip being at least twice the diameter of said hole, said chamber having adjacent the inner periphery of said roll and arranged in said sealing strip a gap extending substantially the length of the roll and adapted to place the chamber in communication with said holes in succession as the roll rotates, said gap being narrower than the width of any of said holes, and at least one air inlet duct in at least one of the walls of said chamber for regulating the pressure inside said chamber whereby to compensate for changes in the speed of the suction roll.

6. A silencer device for apparatus of the type including a rotated suction roll having radially extending holes,

and a stationary suction box cooperating with the inner periphery of the roll as the roll is rotated, comprising means defining a chamber extending substantially the length of the roll and arranged next to the leaving edge of the suction box, said chamber having adjacent the inner periphery of the roll a narrow gap extending substantially the length of the roll and adapted to place the chamber in communication with said holes in succession as the roll rotates, said gap being narrower than any of said radially extending holes of the suction roll, and at least one air inlet duct in at least one of the walls of said chamber for regulating the pressure inside said chamber.

7. A silencer device for apparatus of the type including a rotated suction roll having radially extending holes, and a stationary suction box cooperating with the inner periphery of the roll as the roll is rotated, comprising means defining a chamber extending substantially the length of the roll and arranged next to the leaving edge of the suction box, said chamber having adjacent the inner periphery of the roll a narrow gap extending substantially the length of the roll and adapted to place the chamber in communication with said holes in succession as the roll rotates, said gap being of a width between about 0.020 and 0.030 inch, and at least one air inlet duct in at least one of the walls of said chamber for regulating the pressure inside said chamber.

References Cited in the tile of this patent UNITED STATES PATENTS 1,091,941 Marx Mar. 31, 1914 1,581,656 Monaghan Apr. 20, 1926 2,107,812 Berry et al. Feb. 8, 1938 2,274,641 Abbott et al Mar. 3, 1942 2,290,777 Street July 21, 1942 FOREIGN PATENTS 677,526 Germany June 27, 1939