Patent Application
20100236739
The present invention concerns dewatering blades for use in the forming and press sections of papermaking and similar machines, the blades comprising segments whose upper surfaces together comprise the fabric contacting surface of the blade, and in particular the bonding of one or more interlock members to the lower surface of the segments to interlock be secured within a channel within a base member.
Dewatering blades have been used for many years in the papermaking and similar industries to scrape or foil fluid from the undersides of fabrics so as to consolidate a mat or web, and to induce agitation in the stock carried by forming fabrics; many different designs are known and used. Although the present invention is described primarily in relation to the papermaking arts, the person skilled in the art will readily appreciate that the invention will find utility in all types of related continuous consolidation processes, such as sludge dewatering and filtration.
The fabric contact surfaces of these dewatering blades are typically comprised of carefully and precisely shaped segments of a ceramic or similar wear resistant material that are either bonded or mechanically attached in some manner to a base member. Typically the base member spans the full width of the machine and provides a firm base for the attachment of the ceramic segments; however, a sub-assembly system can be used, as described in our co-pending application U.S. Ser. No. 11/690,479. The fabric contacting surfaces of the segments are carefully shaped for engagement with the fabrics which pass over them in sliding contact. The machine side surfaces of the segments are typically shaped to fit a dovetail or other similar interlocking shape on the base member, as is well known in the art.
The prior art contains many examples of methods and apparatus to attach the segments to the base member; almost all rely on the basic dovetail and T-bar method disclosed by White et al. in U.S. Pat. No. 3,337,394. This patent teaches that drainage blades can be provided with a dovetail type recess adapted to fit over a T-shaped rail so as to mount them on the papermaking machine. The advantage of the method is that the blades are replaceable by sliding them off the rail and sliding a new one into position. The system also allows for accurate positioning of the blades in relation to the fabrics. Other examples are known.
Truxa in U.S. Pat. No. 3,520,775 and U.S. Pat. No. 3,647,620 teaches a means of adjusting the position of the blades relative to the papermaking fabric using a slot and pin type of arrangement. U.S. Pat. No. 3,743,574 to Walser et al. teaches a mounting system similar to White et al. U.S. Pat. No. 3,953,284 to Evalahti discloses a locking means for a T-bar type blade similar to that disclosed by White et al. Beauchemin in U.S. Pat. No. 4,004,969 discloses a removable wear resistant insert that is slidable into position to change foiling angles. U.S. Pat. No. 4,214,949 to Schiel et al. discloses a symmetrical blade adapted to be clamped to a support element by a leaf spring clip to provide interchangeable bearing surfaces. U.S. Pat. No. 4,544,449 to Arav discloses a mounting system for blades whereby the blades are secured to a “plank” by means of a series of pins which are welded to and project from the plank; the system is easy to manufacture and requires minimal machining.
U.S. Pat. No. 5,932,072 to Neun et al discloses mounting means in the form of “buttons” which hold the blades in position, replacing the traditional T-bar mounting means. Each blade includes a T slot on its lower side that is slid over the buttons; each button is comprised of a threaded cylindrical stem portion which engages with the machine frame and an upper cap.
U.S. Pat. No. 6,537,426 to Haunlieb discloses a connecting element or clamping means for releasably and adjustably securing a blade to the cover of a drainage device. Fasteners equipped with sleeves and located on the cover engage with angled slots in the underside of the blade mounting.
EP 1,127,186 to Jansson discloses a method of mounting a foil or blade whereby the blade is pushed into a stable operating position by means of springs which cause a locking member to engage clamping surfaces which hold the blade rigidly in position. An actuator is provided to allow the blade to be dismounted.
CA 1,235,010 to Fuchs discloses a blade comprised of ceramic segments which are comprised of upper and lower portions, the lower portions having projections which are arranged to be attached to a base member. The upper and lower portions are cemented together, but in an offset arrangement, such that each joint between adjacent lower portions is located partway between the joint between adjacent corresponding upper portions.
Currently, segments (typically ceramic) for use in papermaking dewatering blades are manufactured in one of three ways:
There are problems associated with all three of these current methods. In the first, the variation in the thickness of the ceramic (i.e. from the paper side surface to the bottom of the blade at its leading and trailing edges (T1 and T2) as compared to the interlocking portion at the base where the dovetail occurs and the ceramic increases in thickness as shown at T3 in
In the second method, there is a strong possibility due to variations in the bonding process, or as a result of machine operating conditions, that one or more of the bonded ceramic segments may come loose from the base structure during machine operation, causing significant damage to the papermaking fabric and possibly the machine components. In the method disclosed by Fuchs, in CA 1,235,010, a very high accuracy of alignment is required, which is difficult to achieve having regard to the typical small sizes of the ceramic segments, and such construction is extremely difficult to repair in the event of damage to any of the segments.
In the third instance, the cutouts made in the bottom of the ceramic to accept the clips can also result in stress cracks forming in the ceramic segments, or they may reduce the usability of the ceramic due to the chance of breaking through into the cutouts.
It is thus desirable to provide a more efficient and cost effective means whereby the ceramic segments could be reliably and efficiently bonded to the base without danger of their being disconnected and causing damage to either the papermaking machine or its components, in particular the papermaking fabrics. It would also be desirable if the ceramic segments could be produced in a more reliable and efficient manner, in particular without the significant differences in thickness, so that stress cracking in the segments could be reduced to a great extent, and one segment could serve a variety of purposes in a given blade configuration.
Thus, there is a need in the filtration process industry, and in particular the papermaking industry, for a more reliable and cost effective means of attaching the ceramic segments comprising the fabric contacting surfaces of dewatering blades and the like to the base members upon which they are mounted. The present invention provides a simple but effective means of overcoming these and other difficulties relating to the attachment of the ceramic segments to the base member.
The present invention provides a novel reliable and cost effective means for improving the attachment of segments, such as conventional ceramic segments, to the base member of dewatering blades for filtration. In the invention, one or more secondary interlock members are bonded to the machine side surfaces of the segments; the assembly consisting of the segment and at least one interlock member is then attached to the base member, by securing the interlock member within a channel in the base member, by means of an adhesive or a locking mechanism which is designed for use with or without an additional bonding agent.
For the purposes of this invention, the term “adhesive” is to be broadly construed as meaning any compound that adheres or bonds two or more items together, examples of which include thermoplastic adhesives, reactive adhesive systems, and LTV and light curable adhesives. Selection of a suitable adhesive for use in the practice of the present invention will be made by the practitioner based on the environmental conditions to which the adhesive will be exposed.
Thus in a first broad embodiment, the present invention seeks to provide a segment for a blade for dewatering a filtration fabric in a filtration process, the blade including a base carrier comprising a channel, the segment having a leading edge and a trailing edge and comprising
In a second broad embodiment, the present invention seeks to provide a dewatering blade for a filtration fabric, comprising
In a third broad embodiment, the present invention seeks to provide a method of making a dewatering blade for a filtration fabric, comprising the steps of
The interlock means comprise interlock members which can be individually bonded directly onto the lower surface of the segments, or alternatively can be mounted in a plurality on a strip which is then bonded onto the lower surface of the segments. The number of interlock members provided to each segment will depend on various factors, including the size of the segments, the configuration of the base carrier, the intended end use of the blade, and the selected configuration of the interlock members and their materials of construction.
Preferably, the interlock members have a varied cross-section along the direction from the bonded end to the free end, such that there is an indented intermediate portion, which facilitates securing within the channel.
Preferably, an adhesive material is included in the channel so as to solidify the attachment. Alternatively, the channel is provided with a snap/fit mechanism which engages the indented portions of the interlock members.
The invention will now be described with reference to the drawings, in which
As discussed above,
Referring to
In the present invention, the segments are produced in a substantially flat format without an integral channel or protrusion, thus allowing them to be manufactured at lower cost. By making the segments flat, the level of residual stress in the material is considerably reduced at their point of attachment to a base member in comparison to the more common shaped profiles of the prior art, making the segment less subject to cracking failures in operation and thus more reliable. The interlock means, for example interlock member 22 as shown in
A particular advantage of this method of construction is that the bonding of the interlock members 22 to the segments 20 can be completed in a highly controlled and clean environment, thus ensuring a much higher quality bond than has been previously available. By utilizing smaller parts in the assembly of the ceramic segments, it is now possible to optimize environmental cleanliness, adhesives and curing temperature to ensure the reliable adhesion of the segments with the interlock members to a much greater extent than has been possible with prior art assemblies. It is thus possible to utilize almost any suitable material for the interlock members because there are a wide range of adhesives that would be appropriate for use in such applications. Examples of suitable materials include high performance plastics, stainless steel, ceramics, aluminium, bronze, and so on.
After bonding of the selected interlock members 22 to the lower surface 21 of the segment 20, the interlock members are then pressed or slid, depending on the embodiment, into a channel (for example channel 35 shown in
A further advantage is that when the interlock members have been placed into the channel for securing by an adhesive, they can be aligned with great precision while the adhesive is hardening, with substantially increased accuracy and significant costs savings.
After the adhesive is cured, the assembly comprising the segments and the base can be installed by known means according to the intended end use for the blade. After completion of the installation, the upper surfaces of the segments can be finished to provide the desired profile with precision, again according to the intended end use.
In addition to the reliability and economic benefits provided by the segments, blades and methods of the invention, there is also an increase in the versatility of the segments that can now be utilized as compared to the conventional designs which include an integral dovetail or tee. The interlock members can be placed in any suitable location on the segment thus allowing fewer types of segment configurations to be required for a wider range of applications, while allowing segments of the same design to be mounted in different orientations, for example as shown in
The invention also provides the possibility of using different interlock members and arrangements thereof. For example, the interlocking with the base carrier can be done in the form of a snap-in or compression lock, for example by clip members 42 as shown in
Ceramic segments currently in use typically have a length in the machine direction of between ½ inch and 3 inches, and a width in the cross-machine direction of between ½ inch to 1½ inches, but larger and smaller sizes are known and used. The dimensions of the interlock members can thus be selected so as to be compatible with the selected size of the segments.
The interlock members, and the additional strip if used, can be made of any suitable materials that are compatible with the intended end use environment. High performance plastic or stainless steel would be typical but ceramic, aluminum, bronze could also advantageously be used. The configurations for the interlock means can include those shown in the exemplary figures, or any other suitable configuration appropriate for the intended end use.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US08/64214 | 5/20/2008 | WO | 00 | 11/11/2009 |
| Number | Date | Country | |
|---|---|---|---|
| 60939644 | May 2007 | US |
