GB2062483A

GB2062483A - Moving band press

Info

Publication number: GB2062483A
Application number: GB8031701A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-10-03
Filing date: 1980-10-01
Publication date: 1981-05-28
Also published as: DE3037326A1

Abstract

A method and apparatus for dehydrating slurry 15a supplied onto an endless filter belt 10 involves pressing the slurry between cooperating rolls 1, 4 arranged above and below the endless belt. In order that the slurry passes through the gap at a rate as large as possible while being effectively dehydrated, the upper roll is positively driven at a peripheral speed which is at least equal to that of the lower roll but does not exceed a speed 30% higher than that of the lower roll. The upper roll 1 is advantageously provided on its peripheral surface with double oblique grooves which urge the slurry to the central area of the endless belt. Further, a plurality of rows of elastic soft endless belts 18 may be arranged between the endless filter belt and the lower roll to promote the discharge of the water squeezed out of the slurry, thereby improving the dehydration effect and increasing the throughput. <IMAGE>

Description

SPECIFICATION Method of an apparatus for dehydrating slurry The present invention relates to a dehydration technique and, more particularly, to a dehydration of slurry by an apparatus of a type having a pressure roll, a support roll and an endless belt adapted to run through the gap between these rolls.

Such a dehydration apparatus has been known as having at least one pair of dehydration rolls, i.e. a combination of a pressure roll and a support roll, and an endless belt adapted to run through the gap between these rolls, so that the slurry supplied to the endless belt is squeezed or pressed to decrease the water content. In this known apparatus, the driving power is transmitted only to the support roll, while the pressure roll is driven by the friction between itself and the slurry and endless belt carrying the later as the endless belt runs. Therefore, the slurry coming into the gap between the rolls acts as a driving medium for driving the pressure roll, so that the slurry is made to flow and be diffused due to a reactional force imparted by the pressure roll, resulting in a serious reduction of dehydration rate of the apparatus.

In addition, the rolls made of a metallic material or line with hard rubber for attaining an instantaneous high contact pressure impractically shortens the dehydration time because the contact is made only instantaneously, resulting in a lowered dehydration efficiency.

Various apparatus have been proposed heretofore through numerous Patents and Utility Models to overcome the above-described problems of the prior art.

For instance, the present inventor is aware of Japanese Patent Laid-open No. 109312/1976 which discloses an apparatus having fibrous rolls. Also, Japanese Patent Laid-open No. 112863/1977 discloses a dehydration apparatus in which the pressure roll is made to have a larger diameter than the support roll and means are provided for rinsing the filter cloth and dehydration of the filter cloth itself.

Japanese Patent Publication No.3494/1978 discloses a dehydration apparatus having heating rolls or rolls coated with plastic wire or rolls with circumferential groove. A dehydration apparatus shown in Japanese Utility Model Laid-open No. 99869/1976 suggests the use of a multiplicity of press rollers provided with a plurality of circumferential grooves. Japanese Utility Model Laid-open No. 61412/1980 discloses a dehyd- ration method in which the slurry is progressively compressed by a plurality of stages of pressure rollers to increase the pressure exerted by the final pressure roller. Finally, Japanese Patent Application No.96920/1978 of the same inventor as this application proposes to provide convexities and concavities or a multiplicity of circumferential grooves in the peripheral surface of the pressure rolls.Each of these proposals has its own advantage.

Under this circumstance, the present invention aims at providing an easy dehydration method and a simple apparatus for carrying out the method to attain a further improvement in the dehydration technique.

The present invention aims as its major object at increase the treating amount of slurry or decrease the water content and, furthermore, to simultaneously achieve both of increase the treating rate and decrease the water content, in the slurry dehydration apparatus of a type having an endless belt adapted to run through the gap between support roll and pressure roll arranged in a pair or pairs.

To these ends, according to the invention, the pressure roll is driven at a peripheral speed which is less than 30% higher than that of the support roll but not lower than that of the support roll, so as to increase the treating amount of the slurry by the dehydration apparatus.

An improvement in slurry intake efficiency, i.e. a further improvement of the treating amount, is achieved by providing the surface of the pressure roll with continuous double oblique groove.

At the same time, the nip width between the pressure roll and the support roll is increased by the provision of a plurality of endless belt made of a soft and elastic material between the endless belt and the support rolls disposed under the latter, to obtain a longer compression period and, hence, a higher rate of release of water content, thereby to assure a higher dehydration effect.

These features are suitably combined to provide further improvements in the slurry treating amount and dehydration power.

Fig. 1 is a side elevational view showing a basic arrangement of an apparatus to which this invention is applied; Fig. 2 is an explanatory side elevational view of an example of extendable arm for transmitting the torque of the support roll to the pressure roll; Fig. 3 is a front elevational explanatory illustration of the extendable arm shown in Fig. 2; Fig. 4 shows a capacity ratio curve representing the relationship between the overspeed rate of the pressure roll relative to the support roll and the slurry intake rate; Fig. 5 is an explanatory plan view of oblique groove of the pressure surface; Fig. 6 is an explanatory plan view of another form of oblique groove of the pressure roll surface; Fig. 7 is an explanatory plan view illustrating the action of the double oblique groove of the pressure roll surface;; Fig. 8 shows another embodiment in which an endless belt made of a soft and elastic material is interposed between the support rolls and the endless belt carrying the slurry; Fig. 9 is an enlarged illustration of the roll contact portion in the embodiment shown in Fig. 8; Fig. 10 shows in comparison the time change of the contact pressure in the direction of roll contacting angle A in the apparatus with and without the soft elastic endless belt; and Fig. 11 is an illustration of the dehydration apparatus equipped with the soft elastic endless belt.

Referring to Fig.1, support rolls 4 are carried by a plurality of shafts 5 and are driven at a predetermined rotation speed by a driving device which is not shown. An endless belt 10 made of a so-called filtration material having a water permeability but not permit solid matters to pass therethrough, e.g.

canvas, synthetic fiber cloth or the like is adapted to run while being guided by a plurality of guide rolls 11.

A pressure roller disposed above each support roller 4 receives, at its bearings 2, a pressure which is required for the dehySration of a slurry, hydraulically or by means of springs. In this ordinary dehydration apparatus, the pressure roll 1 is driven by the friction between itself and the support roll 4 through the medium of the endless belt 10, as the support roll 4 is driven. In consequence, the slurry 15a fed onto the belt 10 is taken into the gap between the rolls as a result of rotation of the pressure roll 1 and running of the belt 10, and is compressed by the pressure roll 1 to release a part of water contained therein downwardly through the endless belt 10. The slurry, now having low water content, attaches to the roll 1 and is separated from the latter by means of a scraper 12 and is taken out as a slurry cake 15b along a guide plate 13.

However, in the above described conventional dehydration apparatus, since the pressure roll 1 is driven through friction, the slurry is subjected to reactional forces of different direction at both sides of the thicknesswise neutral plane of the slurry, so that the thickness of slurry taken into the gap between rolls is inconveniently reduced to deteriorate the treating capacity of the dehydration apparatus. In addition, slip tends to occur between the rolls to cause the pressure roll to rotate at a peripheral speed lower than the linear running speed of the belt lotto obstruct the intaking ofthe slurry.

In consequence, a so-called flow diffusion of the slurry is caused, which can overcome solely by increasing the roll length and the belt width. At the same time, the rate of intaking of slurry is naturally decreased to uneconomically reduce the slurry treating rate per unit area of the filter cloth.

Particularly, the slip of the pressure roll is promoted when the dehydrated slurry attaching to the pressure roll is separated from the latter by a scraper, due to the friction between the scraper blade and the pressure roll surface and the resistance of the slurry against the separating force, so that the slurry intake rate is further decreased.

Under these circumstances, the present inventor has found, as a result of intense study for obviating the drawbacks of the prior art, that a remarkably high slurry intaking efficiency is obtainable by arranging such that, as shown in Fig. 4, both of the pressure roll and the support roll are positively driven and selecting the peripheral speed of the pressure roll to be at least equal to that of the support roll but does not exceed a speed 30% higher than that of the support roll. The inventor has confirmed also that the peripheral speed of the pressure roller higher than that of support roll in excess of 30% rather causes a smaller spread and attaching of the slurry.

The invention will be further described in more detail through a specific embodiments with referonce to Figs. 1,2 and 3.

A A pressure roll 1 receives a pressure required for the dehydration, hydraulically or through springs, and has a shaft 2 to which fixed is a driven gear 3.

A reference numeral 4 denotes a support roll disposed to opposite to the pressure roll 1, and is adapted to receive the pressure imparted by the pressurizing roll 1 as it is rotated in the direction of arrow. A gear 6 is affixed to the shaft 5 of the support roll 4.

Rotation of the gear 6 is transmitted to the gear 3 through gears 7a and 7b disposed in meshing condition between the gears 6 and 3, so as to make the pressure roll 1 and the support roll 4to be rotated in the opposite directions.

Reference numerals 8a and 8b denote shaft pins which fixed the gears 7a, 7b. The shaft pins 8a, 8b and the shaft 5 are pivotally secured to an arm 9a, and the shaft pin 8b and the shaft 2 are pivotally secured to an arm 9b. The arms 9a and 9b are extendable and shrinkable in accordance with the change of pressure applied to the upper pressure roll 1, so as to change the angle formed between these arms and, accordingly, the distance between the rolls 1 and 4.

The object of the invention can be achieved by arranging such that both rolls are driven independently by separate driving devices, instead of adopting the structure having the extendable arm. In such a case, the driving mechanism for the pressure roller preferably has a flexible construction to follow up the change in the pressure applied to the pressure roll.

A reference numeral 10 denotes a fibrous endless belt in the form of a so-called filter cloth permeable to water but does not permit solid matters to pass therethrough. The endless belt 10 is so mounted as to be able to run through the gap between the pressure roll 1 and the support roll 4 while being guided by guide rolls 11.

A reference numeral 12 designates a scraper for separating the slurry cake 15 from the pressure roll, while a guide plate for guiding the separated slurry cake 15b to suitable position is designated at a reference numeral 13. A reference numeral 14 designates a water collecting chamber for collecting and storing the water squeezed out of the slurry 1 spa, disposed beneath the support roll 4.

This dehydration apparatus operates in a manner explained hereinunder.

As the support roll 4 as the driving side roll is rotated in the direction of arrow, the torque is transmitted to the pressure roll 1 through the gear 6 of the support roll shaft, meshing gears 7a, 7b and then through the gear 3 of the pressure roll shaft. The gear 6 of the support roll shaft has gearteeth the number of which is 1 to 1.3 times as large as that of the gear 3 affixed to the pressure roll shaft, so that the pressure roll 1 is driven at a peripheral speed which is at least equal to that of the support roll 4 but does exceed a speed which is 30% higher than that of the support roll 4.

The endless belt 10 is made to run along the guide rolls 11 as a result of rotation of both rolls 1 and 4.

Then, slurry 15a is supplied onto the endless belt 10, and pressure is applied to the pressure roll 1 to press the slurry, so that the latter is efficiently taken into the gap between the rolls to be compressed to release the water content. The following table shows the slurry intake rate in the dehydration apparatus of the invention in comparison with that of the conventional apparatus.

Nature of raw slurry Rolled slurry Type of Water width (filter Intake apparatus content Amount cloth width) ratio Conventional method 84.7% 57.8 Kg/h 270mm 1 Method of invention 1 84.7 57.8 216 mm 1.25 Method of invention il 84.7 57.8 198 mm 1.38 Note) The ratio of rotation speed between the rolls used in this test is as follows

Speed ratio support roll: pressure roll Conventional method 1: friction drive (0.9) Method of invention I 1:1 Method of invention II 1:1.2 As has been described, according to the invention, the large slurry intake rate is obtained as compared with the conventional apparatus, because the pressure roll is positively driven at a speed equal to or higher than speed of the support roll, so that the required width of the filter cloth is reduced and the slip of rolls which is unavoidable in the prior art is completely eliminated to ensure a highly efficient and economical dehydration of slurry.

In addition, since the torque transmission is made through the extendable arms, the change in the pressure applied to the pressure roll 1 is well followed up.

The inventor has noticed that a slip is liable to take place between the surface of the pressure roll and the slurry, due to the smooth surface of the pressure roll. As a result of a study for overcoming this problem, the present inventor has found that the flowing diffusion of the slurry is effectively avoided to provide an extremely high slurry intake efficiency, by forming continuous double oblique grooves serving to gatherthe slurry to the central part ofthe endless belt, in the peripheral surface of the pressure roll and by driving the pressure roll at a speed higher than that of the endless belt.

Namely, according to the invention, there is provided a slurry dehydration method having the step of pressing the slurry on an endless belt between a pressure roll and a support roll, wherein the pressure roll is provided in its peripheral surface with a double oblique groove which converges upwardly from both axial ends toward the center of the pressure roll as viewed from the slurry inlet side, and the pressure roll is rotatively driven at a speed higher than that of the endless belt.

An embodiment carrying out this idea will be described hereinunder with reference to Figs. 5 to 7.

The pressure roll 1 is provided in its peripheral surface with double oblique grooves 16 which converge upwardly from both axial ends toward the center of the pressure roll 1 as viewed from the slurry inlet side. Although the left part 16a and right part 16b of the oblique groove are continuous in the example shown in Fig. 5, the groove 16 need not always be continuous. For instance, the left and right parts may be not continued to each other. In this case, each groove 16 forms a /\-like form. Alternatively, the left part 16a and right part 16b of the groove 16 may be arranged in a staggered manner as shown in Fig.

6.

For obtaining a uniform dehydration efficiency, it is preferred that the left and right parts 16a and 16b are arranged as multiplicity of oblique parallel lines.

The pressure applied to the pressure roll 1 is born by the support roll 4 while being positively driven in the direction of arrow X1 in Fig. 1.

In the dehydration apparatus of this embodiment, the pressure roll 1 is rotatively driven at a speed higher than that of the endless belt 10, so that a force P p is generated by the double oblique grooves 16 to gatherthe slurry 15a toward the central part of the endless belt to prevent the flowing diffusion of the slurry.

The driving of the pressure roll 1 at a higher speed than the endless belt may be made by an independent driving means or may be realized by transmitting the torque of the support roll 4 to the pressure roll by suitable transmission device such as a gear train.

The dehydrating operation with this apparatus is carried out in a manner explained hereinunder.

As the support roll 4 as a driving roll is rotated in the direction of arrow X1, the endless belt 10 is driven to run in the direction of arrow X2 along the guide rolls 11. Then, as the pressure roll 1 is driven at a higher speed than the endless belt 10 in the direction of arrow Y while the slurry is supplied to the endless belt 10, the slurry is efficiently taken into the gap between the rolls, because the lateral flowing diffusion of the slurry 15a is effectively prevented by the action of the pressing force P so that the dehydration is conducted at a high efficiency.The water squeezed out of the slurry 15a is collected by the water collector 14 through the endless belt 10, while the dehydrated slurry attaching to the surface of the pressure roll 1 is separated from the latter by means of a scraper 12 and guided by the guide plate 13 to a suitable place.

As has been described, in the dehydration apparatus of this embodiment, the slip of rolls and flowing diffusion of the slurry are completely eliminated to increase the intake amount of slurry so that the dehydration is performed at a distinguished economy and efficiency.

In the conventional dehydration apparatus, the rolls are made of a metal or are lined with a rubber of a a high hardness, so that the upper and lower roll exhibit only slight deformation when contacted by each other. Therefore, although a high contact pressure is obtained, such a contact pressure is exerted only instantaneously, i.e. only for a period of time which is too short to permit the water content in the slurry to pass through the filter cloth, and the high pressure is relieved so soon that the dehydration efficiency is lowered considerably.

In consequence, the aforementioned flowing diffusion of the slurry takes place to deteriorate the effi ciencyofthe dehydrating operation. The phenomenon of flowing diffusion of the slurry is serious particularly when the pressure of linear contact between the upper and lower rolls come to exceed 20 Kg/cm2.

Thus, it has been practically impossible to apply the pressure sufficiently high to effect the dehydration.

As a result of a further study, the present inventor has found that a superior effect is obtainable by arranging a plurality of endless belts of soft and elastic material between the filter cloth and the support rolls.

A practical embodiment carrying out this technical idea will be described hereinunder with specific reference to Fig. 11.

The pressure roll 1 may be provided with double oblique grooves as in the foregoing embodiment or may have a smooth rolling surface. A best effect is obtained when the pressure roll 1 is driven at a peripheral speed at least equal to that of the support roll 4 but never exceeds a speed 30% higher than that of the support roll. The endless belt 10 stretched over a plurality of guide rolls 11 is also a water permeable filter cloth. A plurality of rows of endless belts 18 are stretched between the support roll 4 and an auxiliary roll 19. The endless belt 18 is made of a soft and elastic material such as soft rubber, nonwoven fabric and the like. The endless belt is arranged in a plurality of rows as illustrated but not in the form of an integral web.If the endless belt 18 is formed as an integral web, it must have a large width comparing that of the endless belt 10 so that the attaching and detaching thereof is made extremely difficult to cause various troubles in the repair and maintenance works. In addition, it will be necessary to provide a specific means for preventing the endless belt 18 from winding. These inconveniences are overcome by arranging the endless belt 18 in the form of a plurality of rows or slits, because, by so doing, each endless belt 18 can run without winding simply by being guided by a guiding comb member.

In this embodiment, each endless belt 18 has a small width such as 10 to 20 mm, but can have various cross-section such as circular cross-section, rectangular cross-section and so forth. The endless belt 18 can be mounted in various ways. However, it is preferred to stretch the endless belts 18 between the support roll 4 and an auxiliary roll 19 disposed beneath the latter, because, by so doing, the frequency of pressing by the rolls per unit time is reduced to ensure a longer life of the endless belt 18 and because such a manner of mounting does not hinder the passage of the water. In such a case, the winding or lateral displacement of the endless belts 18 will be effectively prevented if the surfaces of the support roll 4 and the auxiliary roll 19 are provided with guiding combs for fitting the endless belts 18.

The dehydration apparatus of this embodiment operate in a manner explained hereinunder.

As the support roll 4 under driving is rotated in the direction of arrow, the endless belt 18 stretched between the support roll 4 and the auxiliary roll 19 are made to run in the direction of arrow. In consequence, the endless belt 10 is made to run along the guide rolls 11, due to the friction between the endless belt 10 and the endless belts 18.

Then, the slurry is poured onto the filter cloth, i.e.

the endless belt 10, and is pressed by the pressure roller 1 so as to release the water content thereof.

During the pressing, due to the presence of the soft resilient members between the rolls, a contact area formed between an angle p is formed on the surfaces of the rolls as illustrated in Fig. 9, in proportion to the pressure and the elasticity of the soft elastic material.

In the contacting region within the angle #a pres- sure distribution as shown in Fig. 10 is obtained so that the pressure application time is prolonged as compared with that obtained when there is no provision of the soft elastic members. As a result, the pressure is increased gradually over a longer period of time to facilitate the release of the water from the slurry. Since the volume of the slurry is decreased in proportion to the release of the water, the slurry intake rate is increased to diminish the flowing diffusion of the slurry. In addition, since the relief of the slurry 15 from the pressure is made also gradually, the reverse sucking of water from the endless belt is diminished to ensure a high degree of dehydration.

The water squeezed out of the slurry is discharged through the endless belt 10, while the dehydrated slurry attaching to the pressure roll 1 is scraped off by a scraper 12 and then suitably disposed.

In the described embodiment of the invention, the problems of the prior art is fairly avoided because it is possible to preserve a considerably large nip.

As has been described, according to the invention, there is provided a dehydration method and apparatus in which slurry carried by the water permeable endless belt running along a plurality of guide rolls is pressed between a support roll and a pressure roll which is biased into contact with the latter, wherein the pressure roll is driven at a peripheral speed which is at least equal to that of the support roll but does not exceed a speed 30% higher than that of the support roll. The pressure roll may be provided in its peripheral surface with double oblique grooves. The apparatus can have made of a soft elastic material and a plurality of rows of endless belts adapted to be pressed between the aforementioned endless belt and the support roll.

These features are suitably combined to offer a higher efficiency of dehydrating operation. The highest dehydration power and greatest slurry treating amount are obtained simultaneously when all of these features are combined.

Claims

1. A method of dehydrating slurry by a dehydration apparatus having a positively driven support roll, a pressure roll disposed above the support roll and pressed against the latter and an endless belt made of a water permeable filter cloth and stretched around a plurality of guide rolls so as to be clamped by said pressure roll and said support roll and run through the gap between said pressure and support rolls, characterized in that both of said pressure roll and said support rolls are driven positively and that the ratio of peripheral speed between said support roll and said pressure roll is selected to fall between 1:1 and 1:1.3.

2. A method of dehydrating slurry as claimed in claim 1, wherein said pressure roll is provided in its peripheral surface with a plurality of double oblique grooves which converge upwardly from both axial ends to central part of said pressure roll as viewed from the slurry inlet side.

3. A method of dehydrating slurry as claimed in claim 1, wherein a plurality of rows of endless belts made of a soft and elastic material are interposed between said endless belt and said support roll.

4. A method of dehydrating slurry as claimed in claim 3, wherein said pressure roll is provided in its peripheral surface with double oblique grooves which converge upwardly from both axial ends to the central part of said pressure roll as viewed from the slurry inlet side.

5. A slurry dehydration apparatus comprising a positively driven support roll, a pressure roll disposed above said pressure roll and adapted to be pressed against said support roll and an endless belt made of a water permeable filter cloth and adapted to run through the gap between said pressure roll and said support roll while being guided by a plurality of guide rolls, characterized in that said pressure roll and said support rolls are driven independently by separate driving devices.

6. A slurry dehydration apparatus comprising a positively driven support roll, a pressure roll disposed above said pressure roll and adapted to be pressed against said support roll and an endless belt made of a water permeable filter cloth and adapted to run through the gap between said pressure roll and said support roll while being guided by a plurality of guide rolls, characterized in that the torque of said support roll which is positively driven by a driving source is transmitted to said pressure roll by a transmission mechanism so as to rotatively drive said pressure roll in the direction opposite to that of said support roll.

7. A slurry dehydration apparatus comprising: two arms of an equal shape and size fitted to the opposite side of axis of a support roll to the driven side and mounted for free rotation; another two arms of an equal shape and size and attached to the axis of a pressure roll and connected at their ends to the ends of the first-mentioned two arms, two gears connected between respective two arms of said pressure roll and said support roll, small gears meshing with said gears and rotatably carried by shafts on the ends of said two sets of arms, and a small gear mounted on a shaft provided at an intermediate portion of said arm carried by said support roll and meshing with a gear affixed to the axis of said support roll and said small gears.

8. A slurry dehydration apparatus as claimed in claim 6, wherein the number of gear teeth of said gear affixed to said axis of said support roll is 1.0 to 1.3 times as large as the number of gearteeth of said gear attached to said axis of said pressure gear.

9. A method as claimed in claim 1, carried out substantially as described with reference to and illustrated by Figures 1 to 3, Figures 1 to 3 and 5, Figures 1 to 3 and 6, or Figures 8,9 and 11.

10. Apparatus as claimed in claim 6, substantially as described with reference to and illustrated by Figures 1 to 3, Figures 1 to 3 and 5, Figures 1 to 3 and 6, or Figures 8,9 and 11.

11. Any new or novel method as hereinbefore described.

12. Any new or novel apparatus as hereinbefore described.

New claims or amendments to claims filed on 30th December 1980.

Superseded claim 1 New or amended claim:~

1. A method of dehydrating slurry by a dehydration apparatus having a positively driven support roll, a pressure roll disposed above the support roll and pressed againstthe latter and an endless belt made of a water permeable filter cloth and stretched around a plurality of guide rolls so as to be clamped by said pressure roll and said support roll and run through the gap between said pressure and support rolls, characterized in that both of said pressure roll and said support rolls are driven positively and that the peripheral speed of the pressure roll is greater than that of the support roll, the ratio of the peripheral speeds of the pressure roll and the support roll being not more than 1.3:1.