FIELD OF THE INVENTION The present invention relates to the technical field of filter press, more particularly, to a method for attaching a filter element onto a filter plate of the filter press and a filter element produced therefrom.

BACKGROUND OF THE INVENTION A filter press is well-known to find a wide range of applications in chemistry, petroleum, mining, foods and pharmaceutical industries for separation of solids from liquids. Generally, the filter press comprises a plurality of filter plates arranged in parallel from one another, a frame on which the plurality of filter plates are supported, a pressure mechanism, for example a hydraulic or mechanical mechanism, for pressing the plurality filter plates together during the filtration cycle, and a cake discharge mechanism. Each of the filter plates is recessed on both sides and covered with filter elements such as filter cloth on both sides. Once pressed together, the plurality of filter plates form a series of chambers.

The filter plates have a feed port that passes through the entire length of the filter press so that all the chambers of the filter plates are connected together, and the slurry or the suspension is fed through the feed port into the chambers. Likewise, four corner ports connect all the plates and collect the filtrates that permeate the filter cloth towards outlets and then are drained away. The cakes are formed on the face of the filter cloth and fill the chambers. The cakes are compressed and dewatered during the filtration cycle and the cake thickness increases over time. Once the optimum combination of chamber filling and cake dryness is achieved, the filtration is stopped, the pressure is relieved and the cakes are discharged. A new filtration cycle starts.

The basic design to install the filter cloth on both sides of the filter plate is to sew the filter cloth into a sack into which the filter plate is inserted, or to stretch two pieces of filter cloth over two sides of the filter plate. The filter cloth has a hole positioned to correspond to the feed port of the filter plate, and the two pieces of the filter cloth are pressed against each other by a connecting means which is either sewn or bonded to the edges of the cloth holes and then is mounted on the feed port. To install the filter cloth on the filter plate, it is necessary to align the feed port and the cloth hole, and the connecting means are connected with the filter cloth and with the feed port in a leak-proof manner. If the feed port and the cloth hole are not aligned, the operation of the filter press would be less effective, and the leak may occur. Further, it is often that damage to the filter cloth may take place when the connecting means connects the filter cloth and the filter cloth is mounted on the feed port of the filter plate, which makes the cloth unusable. As can be seen, the current methods of installing the filter cloth on the filter plate is very labor intensive with a high risk of leakage and damage to the cloth.

CGR (Caulked, Gasketed, Recessed) filters are one type of the filter press. In addition to the difficulties discussed above, installing the filter cloth on the CGR filter plate further requires insertion of the perimeter edge of the cloth into a endless grove formed on the filter plate. In particular, a cord is sewn up around the perimeter edge of the cloth. To install the filter cloth, it is required to feed the cloth through the feed port of the CGR filter plate from one side so that each filter cloth is stretched over the surface of the filter plate, and the edge with the cord is forced (for example hammered) into the endless grove of the filter plate in order to effectively prevent a capillary seepage phenomenon. The manufacture, mounting and changing of the conventional CGR plate filter are involved with sewing and caulking the perimeter edge of the cloth, sewing up the cord and hammering it into the groove of the filter plate, feeding the filter cloth through the feed port of the filter plate and then stretching out and the like, all of which are time consuming and labor intensive, but also greatly increase the costs and prolong the production cycle.

Various efforts have been made in order to solve the problems associated with filter cloth installation and filter cloth leakage. For example, the co-pending PCT patent application no. PCT/CN2012/071506 of the applicant has proposed a connector assembly for fastening filter elements onto a filter plate of a press filter, the connector assembly comprising a first cylindrical core, a first flange extending circumferentially and vertically from one end of the first cylindrical core, a second cylindrical core, and a second flange extending circumferentially and vertically from one end of the second cylindrical core, wherein the first and second flanges are in firm connection with the filter elements, respectively. The first cylindrical core is shaped and dimensioned such that this cylindrical core snugly passes through a feed port of the filter plate, and the second cylindrical core is shaped and dimensioned such that this central core snugly passes through and is meshed with the first cylindrical core. Both the first cylindrical core and the first flange and both the second cylindrical core and the second flange are respectively molded as one piece from a non-woven fabric which is stiff enough to be self-sustaining, has the ability of shape maintenance, and is moldable. The disadvantage of this connector assembly is that it has to be made of a fabric material that is stiff enough to be self-sustaining, is also mouldable, and has the ability of shape maintenance. Another disadvantage is that the filter cloth and the connector assembly are preferably made of the same mouldable material so that they can be moulded together to define a unitary combination. However, it may not be so convenient and easy for the applications where flexible conventional filter cloth, which does not have the mouldability, is used.

Accordingly, there is a need for a new method which enables an easy installation of the filter element on the filter plate of a filter press and permits a reliable connection of the filter elements and the filter plate. There is also a need for a filter element that is able to be installed on the filter plate with tight fit.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for attaching a filter element onto a filter plate of a filter press at low cost, which permits an easy assembly and disassembly without causing damage to the filter element and also avoids the leakage of the filter element.

Another object of the present invention is to provide a method for attaching a filter element onto a filter plate of a filter press, which eliminates the process of feeding, connecting and stretching out the filter cloth and also eliminates the need for the caulking process by forming the filter elements to fit the shape of the plate and snapping the edges of the filter elements into the groove, thereby greatly reducing the labor intensity and costs for mounting and changing the filter cloth.

To attain the aforesaid objects, the invention provides a method for attaching a filter element onto a filter plate of a filter press using a curable material in fluid state or in softened state, said method comprising:

providing a mould which is shaped and sized to correspond to the filter plate, said mould being formed with one or more receiving areas positioned and sized to correspond to one or more attachment sites where the filter element is attached onto the filter plate;

- placing the curable material in fluid state or in softened state into the respective receiving areas of the mould;

stretching the filter element over the mould with one or more portions thereof held in the respective receiving areas of the mould;

press-moulding the curable material and the filter element, and allowing to cure the material together with said portions of the filter element in the respective receiving areas of the mould, thereby forming a cured filter element with rigid portions adapted for attachment onto the filter plate; and

attaching the cured filter element onto the filter plate by deploying the rigid portions of the cured filter element on the respective attachment sites of the filter plate.

According to the invention, the steps of placing the curable material and stretching the filter element over the mound may be interchangeable in the order of steps of the method.

In one specific embodiment of the invention, the mould is made of steel or aluminum and accurately reproduced in accordance with the filter plate.

Preferably, the curable material may be selected from the group consisting of polyurethane (PU), polyvinylchloride (PVC), polypropylene (PP), ethylene-vinyl acetate copolymer (EVA) and silicon in liquid form. In the case of curable liquid material, the curing of the liquid curable material together with the portions of the filter element may be carried out under heating conditions at a temperature not greater than a melting point of the filter element.

As an alternative, the curable material may be selected from a solid material which is curable after being thermally softened or molten. For example, the solid material may be selected from the group consisting of polyurethane (PU), polyvinylchloride (PVC), polypropylene (PP) and ethylene-vinyl acetate copolymer (EVA) in solid form and silicon.

In one embodiment of the invention, the solid material takes the form of sheet, and the solid sheet material is attached to the filter element at the attachment sites by stitching, the solid sheet material is heated together with the attached filter element at a temperature not greater than a softening point of the filter element to become softened, and then the softened material with the filter element is placed in the respective receiving areas of the mould to be press-moulded and to cure. In another embodiment of the invention, the solid material is heated to melt so that the solid material is provided in a fluid state, and in this case, the remaining steps to implement the method of the invention are same as the method using the curable liquid material.

It may be possible to put a release agent into the mould for facilitating releasing of the rigid portions of the cured filter element from the mould. It is also possible to add a thickening agent into the curable material to form a curable mixture. According to the method of the invention, a first cured filter element and a second cured filter element are respectively attached to two opposite sides of the filter plate of the filter press, wherein the rigid portion of the first filter elements adapted for attachment into a feed port of the filter plate is formed as a first canister shaped and dimensioned such that this first canister snugly passes through the feed hole of the filter plate, and the rigid portion of the second cured filter element is formed as a second canister shaped and dimensioned such that this second canister snugly passes through and is meshed with the first canister.

Advantageously, a plurality of first teeth and a plurality of first flutes may be provided on an inner wall surface of the first canister, and a plurality of second teeth and a plurality of second flutes may be provided on an outer wall surface of the second canister, such that the plurality of first teeth are received by the plurality of second flutes and the plurality of second teeth are received by the plurality of first flutes, while adjoining edges of the teeth engage each other to thereby form a lock therebetween. The teeth and the flutes may be either moulded in the mould or produced after the cured filter element is obtained.

A protrusion may be provided, which extends circumferentially and radially outward from a free end of the second canister to function as a stop for preventing displacement of the second canister relative to the first canister when they are meshed with each other. In a specific embodiment of the invention, the filter press is the type of CGR (caulked, gasketed, and recessed) filter press, the receiving area of the mould corresponding to an endless groove of the filter plate is provided as an endless groove for receiving the curable material and a perimeter edge of the filter element, such that, after the curing step, the cured filter element has a rigid perimeter edge adapted to be received in the endless groove of the filter plate. The receiving area of the mould corresponding to a feed port of the filter plate is provided as a cylindrical cavity for receiving the curable material and a portion of the filter element positioned correspondingly to the feed port, said cylindrical cavity and the feed port being of substantially same diameter, such that the cured filter element has a rigid canister adapted to snugly pass through the feed hole of the filter plate. In another specific embodiment of the invention, the filter press is the filter press is the type of recessed filter press, the receiving area formed along a perimeter of the mould is provided as a perimeter groove for receiving the curable material and at least three side flanges extending from a circumferential edge of the filter element, such that, after the curing step, the at least three side edges extend laterally and rigidly from the circumferential edge of the cured filter element and protrudes from a same side of the filter element. The rigid at least three side flanges are sized such that two of the cured elements used for attachment onto two opposite sides of the filter plate together are put together to surround the filter plate. The receiving area of the mould corresponding to a feed port of the filter plate is provided as a cylindrical cavity for receiving the curable material and a portion of the filter element positioned correspondingly to the feed port, said cylindrical cavity and the feed port being of substantially same diameter, such that the cured filter element has a rigid canister adapted to snugly pass through the feed hole of the filter plate. For the recessed filter press, the filter plate may be completely surrounded by the rigid four side flanges of the cured filter elements, or surrounded by the rigid three side flanges of the cured filter elements with an opened bottom side through which the filtrate flows out of the filter press.

The present invention also relates to a filter element produced by the method of the invention.

It is obvious that the method of the invention simplifies the installation and change of the filter element without the excessive labors. This not only reduces the operation costs for installing and changing the filter element, but also avoids the damage to the filter element and the leakage phenomenon. To have a better understanding of the invention reference is made to the following detailed description of the invention and embodiments thereof in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of the mould and the filter element for the CGR filter press according to a first embodiment of the invention.

Figure 2 is a font elevation view of an upper section of the mould shown in Figure 1 . Figure 3 is a cross-sectional view taken along line A-A of Figure 2.

Figure 4 is a font elevation view of a lower section of the mould shown in Figure 1 .

Figure 5 is a cross-sectional view taken along line B-B of Figure 4.

Figure 6 is a perspective view of the cured filter cloth taken out of the mould, which is ready for insertion into the CGR filter plate.

Figure 7 is a schematic diagram showing that the cured filter elements and a filter plate of the CGR filter press are ready to be assembled.

Figure 8 is a side view of the cured filter elements and a filter plate of the CGR filter press of Figure 7 in the assembled state. Figure 9 is a schematic view of the canisters of the filter elements formed with a plurality of teeth and a plurality of flutes.

Figure 10 is a cross-sectional view showing the engagement of the teeth with the flutes shown in Figure 9.

Figure 11 is a perspective view of the mould and the filter element for the recessed filter press according to a second embodiment of the invention.

Figure 12 is a flow diagram showing a process for moulding the filter element adapted for the recessed filter press.

Figure 13 is a perspective view of the cured filter cloth taken out of the mould shown in Figure 12, which is ready for insertion into the recessed type filter plate. Figure 14 is a schematic diagram showing that the cured filter elements and a filter plate of the recessed filter press are in the assembled state.

In the various figures of the drawings, like reference numbers are used to designate like parts.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to Fig. 1 , there is illustrated the mould and the filter element to be treated for the CGR filter press according to a first embodiment of the invention. In this embodiment, the filter element is a conventional filter cloth 30 which may be of any suitable material, for example a soft or flexible woven filter cloth or a needled punched felt fabric. The process of production of a cured filter element adapted for use in the filter plate of a filter press using a curable material will be described in details as follows.

First of all, a steel mould is prepared according to the size and configuration of the CGR filter plate. More particularly, the steel mould consists of a lower section 10 configured to reproduce the filter plate and an upper section 20 which is in cooperation with the lower section 10. In this embodiment, the lower section 10 is formed with an endless groove 12 in shape and size corresponding to the groove formed on the CGR filter plate. The lower section 10 is further formed with a receiving cavity 14 in a central region thereof. The inner diameter of the receiving cavity 14 is dimensioned such that it snugly passes through the central feed port of the CGR filter plate with tight fit. The depth of the receiving cavity 14 is dimensioned to cope with the feed port of the CGR filter plate, such that the two moulded filter cloth covered on the both sides of the CGR filter plate is ideally stretched over the plate. The upper section 20 comprises an annular neck 22 positioned to be inserted into the endless groove 12 of the lower section 10, and a barrel 24 positioned to be inserted into the receiving cavity 14 of the lower section 10.

Steel is used for making the mould in light of its high resistance to compression applied by a press machine when moulding the filter element. Replacement of steel by other materials such as aluminum for use in preparation of the mould is possible according to the actual needs and requirements. This would obvious to a person with ordinary skills in the art.

After making of the steel mold, the filter element with rigid portions is produced, for example, by using the following procedure. A piece of filter cloth 30 is cut to be adapted for the filter plate of the filter press. A circle hole of diameter smaller than that of the receiving cavity of the lower section 10 is cut at the center portion of the filter cloth 30 to avoid pulling and deformation formation of the cloth when the upper section 10 is held in the lower section 20, while maintaining the contact of the cloth with the curable material . Instead of formation of the circle hole, a cross-shaped pre-cut line 31 is created. A suitable amount of the curable liquid material is poured into the endless groove 12 and the receiving cavity 14 of the lower section 10, and subsequently the cut filter cloth 30 is stretched over the lower section 10 with a perimeter edge there of being received in the endless groove 12 and fully immersed in the curable liquid and the circumferential edge of the circle hole or the four quadrants arising from the cross-shaped pre-cut line 31 at the central portion thereof being received in the receiving cavity 14 and fully immersed in the curable liquid. It should be noted that it is possible to placing the filter cloth 30 followed by pouring the curable liquid material .

Now the curable liquid material and the filter cloth 30 come into contact and are housed together in the receiving areas of the mould. Then the upper section 20 is placed over and engaged with the lower section 10, allowing to cure the curable material and the filter cloth for a period of time. After the curing is completed, the perimeter edge of the filter cloth 30 is formed as a rigid perimeter flange 32, and the central portion of the filter cloth 30 is formed as a rigid canister 34 having one open end and one closed end. To allow the passage of the slurry to be filtered, the closed end of the canister 34 is cut away such that the canister 34 is open at both ends.

The term "curable material" herein refers to a material that can results in a harder, tougher or more rigid substance. For example, the curable material may harden or toughen when it is exposed to air. The curable material may be a curable liquid for example, polyurethane (PU), polyvinylchloride (PVC), polypropylene (PP) and ethylene-vinyl acetate copolymer (EVA). In the case of the curable liquid, the curing process may be carried out at room temperature or under heating conditions at a temperature not greater than a melting point of the filter element. For example, a hot water piping is arranged below the mould, which enables to quicken the curing process.

The curable material may also be a solid material having the ability of hardening or toughening after it is thermally soften or molten, for example, PU, PVC, PP and EVA in solid form as well as silicon and glass silicon. Preferably, the curable solid takes the form of sheet. The curable sheet is for example stitched onto the perimeter edge and the central portion of the filter cloth 30. It would be appreciated that other methods for attaching the curable sheet onto the filter cloth are possible. The curable sheet is then heated to soften at a temperature not greater than the softening point or melting point of the filter cloth. This temperature would not result in melting of the filter cloth, thus ensuring no damage is caused to the filter cloth. The softened material together with the filter cloth 30 are placed into the endless groove 12 and the receiving cavity 14 of the lower section 10 of the mould, respectively. The upper section 20 is put in place to allow the curing process to take place.

The curable solid may be of any shape other than the sheet. A machine that enables melting of the solid may be used to allow the solid to become molten or liquidized. The curable material is fluidic, and the subsequent process for producing the cured filter element would follow the procedure of using the curable liquid discussed above.

In order to provide ease of removing the rigid perimeter flange 32 and the rigid canister 34 from the mould, a releasing agent may be applied to the surface of the inner surface of the endless groove 12 and the receiving cavity 14 before pouring the curable material . Also, a thickening agent may be added into the curable material to form a curable mixture which is then use to come contact with the filter cloth to cure, if desired. This would be within the ability of a person skilled in the art. Referring now to Fig. 6, there is illustrated the cured filter cloth adapted for attachment onto the CGR filter plate. As illustrated, the cured filter cloth comprises a filter cloth body 33 which remains soft and flexible. The rigid perimeter flange 32 and the rigid open-ended canister 34 protrude outwardly from a same side of the body 33. Two cured filter cloths are required to cover both sides of the filter plate as shown in Figs. 7 and 8. The two cured filter cloths comprises a first cured filter cloth 301 and a second cured filter cloth 302. The open-ended canister 34 of the second filter cloth 302 has a diameter smaller slightly than a diameter of the open-ended canister 34 of the first filter cloth 301 , such that the open-ended canister 34 of the second filter cloth 302 snugly passes through and is meshed with the open-ended canister 34 of the first filter cloth 301 . The open-ended canister 34 of the first filter cloth 301 is shaped and dimensioned such that this canister snugly passes through the feed port 42 of the filter plate 40. The rigid perimeter flanges 32 of the first and second filter cloth 301 , 302 are pressed to be snugly received in and fixed within an annular groove 44 on both sides of the filter plate 40.

After the curing process is completed, the perimeter flanges 32 and the canisters 34 of the first and second filter cloth 301 , 302 exhibit excellent rigidity, hardness and dimension stability, thus can stably retain their respective shapes. To attach the cured filter cloths 301 , 302 onto the filter plate 40, it is only required to pass the open-ended canister 34 of the first filter cloth 301 from one side of the filter plate 40 through the feed port 42, and snap the perimeter flange 32 into and receive in the annular groove 44. Then, the open-ended canister 34 of the second filter cloth 302 is allowed to pass from the other side of the filter plate 40 through the feed port 42 and the canister 34 of the first filter cloth 301 in a manner that the canister 34 of the second filter cloth 302 is meshing inside the canister 34 of the first filter cloth 301 to form a barrel neck. Likewise, the perimeter flange 32 of the second filter cloth 302 is snapped into and received in the annular groove 44 on the other side of the filter plate 40. The whole assembly process of the filter cloth 301 , 302 onto the filter plate 40 may be made reference to Figs. 7 and 8.

As can be seen, the CGR filter press using the cured filter cloth eliminates the need for the caulking process by forming the filter cloth with the rigid perimeter flange, which has remarkable shape maintainability and is adapted to fit the groove of the plate, and snapping the rigid flange of the filter cloth into the groove of the filter plate which is held in place by tension. The CGR filter press also eliminates the process of fastening the filter cloth into the feed port of the filter plate because of the rigid canister which has remarkable shape maintainability. Therefore, the labor intensity and costs for implementing, assembling, repairing and changing the filter cloth is greatly reduced. Moreover, the first filter cloth and the second filter cloth are independent from each other, so either of the two piece of filter cloth can be changed or handled individually. Referring to Figs. 9 and 10, a plurality of first teeth 35 and a plurality of first flutes 36 are provided on an inner wall surface of the canister 34 of the filter cloth 301 , and a plurality of second teeth 37 and a plurality of second flutes 38 are provided on an outer wall surface of the canister 34 of the second cloth 302, such that the plurality of first teeth 35 are received by the plurality of second flutes 38 and the plurality of second teeth 37 are received by the plurality of first flutes 36, while adjoining edges of the teeth 35, 35 engage each other to thereby form a lock therebetween. This arrangement enhances the tightness of the connection of the two canisters. According to the invention, the teeth and the flutes may be moulded in the mould or produced after the cured filter element is obtained. Other methods may be used to provide a lock mechanism for the two canisters.

Turning back to Figs. 7 and 8, a protrusion 39 is provided, which extends circumferentially and radially outward from a free end of the canister 34 of the second filter cloth. The protrusion 39 may be forced to protrude beyond the canister 34 of the first filter cloth because of the elasticity of the curable material and serves as a stop for preventing displacement of the canister 34 of the second filter cloth relative to the canister 34 of the first filter cloth when they are meshed with each other. The provision of the protrusion 39 effectively prevents the displacement of one canister relative to the other when the pressure is applied to the filter plate of the CGR filter press in operation. Figs. 11 to 14 illustrate a filter cloth configured and adapted for a filter plate of the recessed type filter press. Like the first embodiment discussed above, the mould consists of a lower section 50 configured to reproduce the recessed filter plate and an upper section 60 which is in cooperation with the lower section 50. In this embodiment, the lower section 50 is formed with a cubic groove 52 consisting of four straight segments. The lower section 50 is further formed with a receiving cavity 54 in a central region thereof. The inner diameter of the receiving cavity 54 is dimensioned such that it snugly passes through the central feed port of the recessed type filter plate with tight fit. The depth of the receiving cavity 54 is dimensioned to cope with the feed port of the recessed type filter plate, such that the two moulded filter cloth covered on the both sides of the recessed filter plate is ideally stretched over the plate. The upper section 60 comprises four side walls 62 positioned to be inserted into the cubic groove 52 of the lower section 50, and a barrel 64 positioned to be inserted into the receiving cavity 54 of the lower section 50.

A piece of filter cloth 70 is cut such that it is sized to fit the filter plate of the recessed type filter press. In this embodiment, the filter cloth 70 is provided in cubic shape with four corner angles being cut out, in order to fit the cubic groove 52 of the mould. Like the first embodiment above, a circle hole or a cross-shaped pre-cut line 71 may be cut at the center portion of the filter cloth 70. After the curing process, the cured filter cloth is formed with four side flanges 72 laterally and rigidly extending from the circumferential edge of the filter cloth and with a rigid canister 74 extending from the center portion of the filter cloth. The four side flanges 72 and the open-ended canister 74 protrude outwardly from a same side of the filter cloth.

Referring to Fig. 14, two cured filter cloths are required to cover both sides of the recessed type filter plate 80. The two cured filter cloths comprises a first cured filter cloth 701 and a second cured filter cloth 702. The filter plate 80 is housed completely inside a space defined by the side flanges 72 of the first and second filter cloth 701 , 702 when they are arranged to face in opposite directions. As a variant, the cured filter cloth is formed to have three side flanges and an opened bottom side, whereby the filter plate 80 is surrounded by the three side flanges of the first and second cloth 701 , 702 when they are arranged to face in opposite directions, leaving the opened bottom through which the filtrate of the filter press is drained away.

The remaining procedures follow the first embodiment discussed above and would not be repeated herein.

The four side flanges 72 have the advantages of high rigidity, hardness, dimension stability and shape maintainability, hence two filter cloth may be put together facing in opposite directions to define a substantially closed space in which the filter plate 80 is completely disposed. The filter cloth eliminates the process of sewing the filter cloth into a sack and the process of fastening the filter cloth into the feed port of the filter plate. This not only reduces the operation costs for changing and repairing the filter cloth, but also simplifies the mounting of the filter cloth onto the recessed filter plate.

According to the invention, a wide range of curable materials are possible for use in curing the filter cloth and they are selected depending on customers' preferences or needs in various applications. Such materials have a common characteristic of hardening or toughening under some conditions, for example when being exposed to air. The materials may be a liquid or a solid which is capable of becoming cured after being thermally softened or molten.

While the embodiments described herein are intended as exemplary methods and exemplary filter press machines, it will be appreciated by those skilled in the art that the present invention is not limited to the embodiments illustrated. Numerous variations and modifications are easily obtainable by means of the skilled person's common knowledge without departing from the scope of the invention, however, such variations and modifications should fall into the scope of this invention.