Abstract:
Replacable refiner plates used for papermaking and refining of lignocellulosic and other natural and synthetic fibrous materials in the manufacture of paper, paperboard, and fiberboard products. The refiner plates include blade patterns and use corrosion resistant materials, as well as ceramic and ceramic composite materials. The blades and spacers overlap to define intercontacting surfaces with the blades and spacers metallurgically bonded throughout the intercontacting surfaces.

Description:
This application is a continuation-in-part of application Ser. No. 632,215 filed Apr. 15, 1996, now U.S. Pat. No. 5,740,972. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to papermaking and refining of lignocellulosic and other natural and synthetic fibrous materials in the manufacture of paper, paperboard, and fiberboard products. In particular, the invention relates to replacable refiner fillings used in the process of refining chip or pulp. 
     In nearly all production refining equipment in use today including beaters, jordans, conical refiners, multi-disc, and disc refiners, the refining working surfaces of the refiner fillings are comprised of closely spaced bars and grooves which work against each other through relative rotation while the fibrous material passes between them. The clearance between the opposed bar and groove working surfaces determines the power applied to the refiner, as well as the extent of refining of the fibrous material. 
     In each kind of refiner equipment, it is often desirable to make bars as narrow and as closely spaced from each other as possible in order to achieve maximum bar edge length for the refiner with resultant distribution of the refiner power over a greater number of bar contact or bar crossing points. This relative intensity, or specific edge load as it is called, is widely recognized as an important quality parameter for most paper and board products. 
     While the bars of any refiner type can be of any practical width and spacing, the actual width and spacing are limited by the materials and methods used to make them, or by the cost to make them, or both. In a typical disc refiner, the replacable working surfaces, or refiner plates as they are most commonly called, may be made by casting or machining. In some instances they may be made by fabricating wherein appropriately spaced bars are affixed by welding onto a base. 
     In the case of cast refiner plates, the width of the bar and the width of the groove are limited to no less than about 1/8&#34;. At normal groove depths of 1/4&#34; or so, cast bars narrower than this are prone to breakage due to internal flaws, and the need to have a draft angle of 3 deg. or so for the casting process, causes the groove volume (which provides for passage of fibrous material) to be greatly diminished at closer bar spacing than about 1/8&#34;. 
     In the case of machined refiner plates, the limiting factor is cost. The cost is more or less proportional to the number of grooves which must be milled to the required depth in a solid steel blank. 
     In the case of fabricated plates, cost is also a constraint because bars are individually welded. 
     Another important feature of replacement refiner plates is their useful life. During operation, the bars become worn down, until at some point, the depth of the groove between bars is so shallow that the refiner can no longer adequately transport fibrous material through the refiner plates. There are several causes of wear including abrasive nature of the fibrous materials and other particles in the medium, and the clashing of the refiner plates in the event of sudden interruption of the flow of process material. 
     The precise nature of the wearing of refiner plates is not fully understood. Hardness of the bar material has been shown to be an important factor. It has also been demonstrated that the rate of wear is very closely related to the corrosion resistance of the bar material. 
     In general, a compromise must be reached between the hardness, corrosion resistance, and toughness of the material that is chosen for a cast or machined refiner plate. Toughness is a required property because occasional tramp metal contamination occurs in the process medium. If the plates were to shatter when a piece of metal passed through the refiner, it would cause severe and costly operational problems for the paper or board mill. 
     There are several potential wear advantages to fabricated or machined refiner plates, however a serious limitation results from the necessity of producing refiner discs in a complete circle configuration. A full circle replacement plate for a 34&#34; or larger refiner will weigh several hundred pounds thus requiring lifting aids for installation into, and removal from, a refiner. Cast refiner plates can be, and usually are produced in segments, with each segment being 30, 45, or 60 degrees and with 12, 8, or 6 segments respectively being required to make up a complete replacement working surface for a single disc of a disc refiner. Each segment will weigh less than 35 pounds, and will usually be individually bolted into the place on the disc, such that an entire set of plates can be replaced by a person without the need for special lifting devices. For this and other reasons, most replacement disc refiner plates are castings, usually of special cast iron or stainless steel alloys. 
     As a practical matter, one of the reasons machined or fabricated plates are not produced as segments has to do with an operational requirement for non-parallel edge crossing of the refiner bars for processing fibrous material. If a stator plate and a rotor plate, whose working surfaces act against each other, contain bars whose leading edges pass each other in parallel or nearly parallel condition, there is a known tendency for excessive cutting of the fibrous material being processed. Thus it is often a process requirement that a refiner plate does not have any precisely radial bars, but rather that it have bars with at least a slight offset or oblique from a radial orientation, typically between 3 and 20 degrees. 
     Refiner disc plate segments have precisely radial side edges such that it is a somewhat costly complication to produce a disc working surface pattern having no precisely radial bar or groove at the segmental dividing lines. Therefore, the segment joint must cut across the pattern of bars and grooves at a shallow angle. This requirement is difficult and costly to accomplish in the case of machined and fabricated plates and which, even in the case of cast plates, leaves narrowly tapered bars likely to be very much weakened at their extremities. 
     Conical type refiners, known as jordans, have been in use for many decades. Many jordans are fitted with metal bars and wood or composite spacers (of lesser height) arranged more or less axially along the conical surfaces of both a plug and a shell so that as a rotating plug is moved into a stationary shell, the respective bars act against each other to cause the refining effect on the pulp slurry as it is pumped through the jordan. The bars are typically engaged in grooves or are otherwise restrained with circumferential tension bands. 
     The bars and spacers of a jordan filling are not structurally bonded to form a rigid one piece filling. As a result, the strength of this filling is severely limited, particularly when it is desirable to refine at low intensity and at high specific energy input (requiring a large number of narrow, closely spaced bars). To a large extent, jordans have been replaced by disc refiners which provide much greater operating efficiency. 
     In general, refiner disc fillings are produced either as cast segments, or are milled from solid annular castings or forgings. In either case, the filling is comprised of a single material throughout. 
     U.S. Pat. No. 4,023,737 to Pilao discloses the use of individual comminuting blades welded to respective surfaces of the comminutor members of the set. However, without intervening spacers, the strength of the blades to resist bending and breaking is severely limited. 
     U.S. Pat. No. 4,428,538 to Valdivia discloses the use of parallel grinding strips, each separated by an intermediate strip having a shorter height. While this does have the advantage that it allows the grinding and intermediate strips to rest against one another, it is still very limited in strength and rigidity since the alternating strips are not integrally attached and therefore cannot support the high shear forces that will exist at the interface when very high bar edge loads occur. 
     In the specific case of low consistency, low intensity refining, while high bar edge loads are not desirable in normal operation, the occasional tramp metal, or other hard contaminant, through the refiner introduces sudden and very high bar edge loads. In nearly all pulp and paper mill refining systems, such contaminants do occur, at least several times during the expected life of a refiner filling. 
     It is therefore necessary for a refiner filling to be capable of withstanding much higher loads than would be anticipated by the refining process specification. From a practical point of view, a refiner filling must be capable of withstanding at least some impact loading resulting from these occasional contaminants. The use of blades with or without spacers as described by Pilao and Valdivia would be very limited in any instance where the blade or bar thickness was less than about 5/32&#34;. 
     In sum, the utility of disc refiner plates is limited by the operational requirement for bars oriented obliquely to radial, by consequent manufacturing limitations, by the rate of working surface wear through corrosion and abrasion, and by limited ability to withstand impact loads caused by presence of occasional contaminants during refining operations. 
     SUMMARY OF THE INVENTION 
     The present invention provides improvements in replaceable refiner fillings and has as a primary objective the manufacture of refiner fillings with working surfaces using relatively narrow, closely spaced bars on the working surface of the plate. This is accomplished by using relatively thin blades of any suitable material, separated by shallower spacer bars having a thickness which determines the width of the grooves, and subsequently fusing or bonding the assembled blades and spacers into a solid piece by methods appropriate for the blade and spacer materials being used. 
     In another primary aspect of the invention, blade and spacer components are selected from metallic materials having different corrosion resistance. Cathodic protection for the refiner blade elements is achieved by using a metallic material for the spacer which is less noble, according to the Electromotive-Force Series of Metals, than the material used for the blade. In this way, the spacer, which is not subject to appreciable abrasion, will pit and corrode harmlessly, while the blade or bar wear is greatly reduced. This feature of galvanic, or cathodic, protection is also applied to cast or machined refiner plates by inserting or attaching sacrificial metal elements. 
     In a further primary objective of the invention, improved segmental replacement disc refiner plates are produced with segments having both non-circular edges (i.e., side edges) which are not precisely radial. Instead, the side edges are oblique to the precisely radial line by an angle between about 3 and 20 degrees such that the refiner plate segmental dividing line is parallel to the adjacent refiner blade. 
     A primary aspect of this invention is the use of a metal or other hard and durable material for the blades and spacers, which blades and spacers are then metallurgically bonded to each other along their entire intercontacting surfaces. A suitable metallurgical bond can be achieved through any of several known methods including welding, diffusion bonding, brazing, or any other method which results in a joint strength approaching that of the blade or spacer material. 
     In a preferred embodiment of the invention, stainless steel blades are metallurgically bonded to carbon steel spacers using a high temperature, vacuum furnace process. A suitable alloy is used to provide some dissolution of the parent metal of the blade and/or the spacer in the immediate region of the joint, such that at the conclusion of the high temperature process, the joint exhibits strength approaching the strength of the spacer material and greater than two-thirds the strength of the stainless steel blade. 
     Another aspect of the invention is the use of ceramic and metal composite materials as blade or spacer components in refiner fillings. A metal composite material which exhibits suitable strength and toughness characteristics for a particular refiner application could be used for the blades of the filling, while a much less costly material may be used for the spacers. Similarly, in the case of ceramic or ceramic coated blades, the use of a much lower cost, and more suitable material for the spacers represents a significant potential advantage over current refiner construction methods. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide improved refiner plates for use in papermaking refiners. 
     It is an object of the invention to provide improved refiner plates in which bars and spacers are assembled in proper order and are fused or bonded together. 
     It is a further object of the invention to provide improved refiner plates in which bars and spacers are selected for corrosion resistance. 
     It is a further object of the invention to provide improved refiner plates in which bars and spacers are selected from the Electromotive-Force Series of Metals with the spacers being a metal less noble than the metal selected for the bars. 
     It is a further object of the invention to provide improved refiner disc plate segments of a circle having side edges oblique to the radius of the circle and with at least a portion of the bars parallel to an oblique side edge. 
     It is a further object of the invention to provide improved refiner disc plate segments having side edges oblique to a radius of the disc with the bar pattern parallel to an oblique side edge and with the bar pattern repeating as necessary to have all bars on the working surface of the disc plate within a given range of obliquity to the radius. 
     Another object is to provide the use of a metal or other hard and durable material for the blades and spacers, which blades and spacers are then metallurgically bonded to each other. 
     Another object is to provide a blade/spacer joint which exhibits strength approaching the strength of the spacer material and greater than two-thirds the strength of the blade when the blade is stainless steel. 
     Another object is to provide metal composite materials which exhibit suitable strength and toughness characteristics for a particular refiner application for blade use in the filling, while a much less costly material may be used for the spacers. 
     Other and further objects of the invention will occur to one skilled in the art with an understanding of the following detailed description of the invention or upon employment of the invention in practice. 
    
    
     DESCRIPTION OF THE DRAWING 
     A preferred embodiment of the invention has been chosen for purposes of illustrating the construction and operation of the invention and is shown in the accompanying drawing in which: 
     FIG. 1 is a plan view of the working surface of a refiner disc plate showing an arrangement of bars according to the invention. 
     FIG. 2 is a section view taken along FIG. 2--2 of FIG. 1. 
     FIG. 3 is a section view of a modified form of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawing, a preferred embodiment of a refiner disc 10 according to the invention comprises a supporting plate 12 to which blades 14 and spacers 16 are affixed and wherein the blades and spacers define the disc working surface and intervening grooves 18. 
     As shown in FIG. 1, a preferred embodiment of the invention, the refiner disc 10 is defined by outer 20 and inner 22 concentric segments and side edges 24, 26 offset or oblique to the radius R of the outer circle. 
     Each segment may have a value for of 30, 45, or 60 degrees so that 12, 8, or 6 segments, respectively comprise a refiner disc. 
     The extent of offset of the side edges is indicated by the angle which is preferably between 3 and 20 degrees off the radial. Beginning at the right side edge 24 in FIG. 1, the segment bars 14 are positioned parallel to the right side edge and extend from the outer periphery 20 inwardly toward the inner periphery 22 of the segment. As shown in FIG. 1, the bars terminate short of the inner periphery thereby defining with the inner periphery a feeding zone 28 for pulp entry to the refiner blades and grooves. Feeder bars 30 aid in directing pulp flow into the refeiner grooves. Bores 32 accommodate fasteners (not shown) for securing the segments in place. 
     It will be apparent from FIG. 1 that blade obliqueness to the segment radial R increases with distance normal to right side edge 24. For example, the blade 14&#39; nearest the right side edge has an oblique angle equal to, while bar 14&#34; has a greater oblique angle, α&#39;. It is desirable with refiner plates to avoid shallow crossing angles (i.e., high degree of obliquity to radial) of stator and rotor blades and therefore desirable to maintain blade obliqueness in a range of 3 to 20 degrees. Hence, the blade pattern is begun anew at that location in the refiner segment where increasing obliqueness (as the case with blade 14&#34;) approaches 20 degrees. So, at this location the bar pattern is reset beginning with a low angle α, say 3 degrees, and continuing until the bar pattern reaches the left side edge of the segment 26. 
     Blade pattern repetition may be unnecessary in the case of narrower disc segments as in a refiner disc with 12 segments of 30 degrees each. 
     It will be seen that the disc refiner segment with non-radial side edges permits the blade of spacer immediately adjacent to one edge to be parallel to the edge while not being precisely radial in its orientation. Therefore, the bars on opposing rotor and stator plates never cross radially and thereby avoid refiner process disadvantages induced by radial crossing of bars. At the same time, the refiner plates according to the invention have the advantages of reduced cost and increased durability with having short blades bordering on one edge only of the disc segment. 
     The blades may be fabricated of any suitable durable material including metals such as aluminum and aluminum alloy, bronze, nickel and nickel alloys, stainless steels, carbon and alloy steels, titanium and titanium alloys, and ceramic or composite materials capable of forming a metallurgical bond to spacers. Similarly, the spacers are any suitable material preferably metallic that can be strongly bonded to the supporting plate. Materials for blades are selected for hardness and corrosion resistance. 
     As shown in FIG. 2, blades 14 and spacers 16 are placed in alternating relation, with the blades and spacers overlapping to define intercontacting surfaces 15. The intercontacting surfaces are also shown in FIG. 1 as extending the full length of blades and spacers. 
     It is a primary aspect of the invention to metallurgically bond blades and spacers entirely throughout the interconnecting surfaces of blades and spacers for the disc refiner filling. A metallurgical bond provides a joint of blade and spacer, with the joint having a strength of at least 50% of the yield strength of the spacer material. 
     In a preferred embodiment of the invention, the blades are fabricated of stainless steel, and the spacers of plain carbon steel, and the backing plate of either plain carbon steel or stainless steel. The entire assembly of blades, spacers and backing plate are metallurgically bonded to comprise a refiner disc by a process of copper brazing or high temperature diffusion welding. 
     In a preferred technique, stainless steel blades are bonded to carbon steel spacers using a high temperature, vacuum furnace process. A suitable alloy provides some dissolution of the parent metal of the blade and/or the spacer in the immediate region of the joint. The finished joint exhibits strength approaching the strength of the spacer material, and greater that two-thirds of the strength of the stainless steel blade. 
     During use, the topmost surface of the stainless steel blade is constantly exposed to abrasive removal of a protective oxide layer. The exposed surface is much more resistant to abrasive/corrosive wear because of the cathodic protection provided by the immediately adjacent and less noble carbon steel spacer. 
     As shown in FIG. 3, the invention provides the use of ceramic and metal composite materials as blade 40 or spacer 42 components in refiner fillings 44. The blades and spacers overlap to define intercontacting surfaces 45 extending the entire length of blades and spacers. Suitable commercially available ceramic materials include a wide variety of metal oxides, carbides, nitrites, and borides. Of particular interest in the fabrication of blades for refiner fillings are alumina (aluminum oxide-Al 2  O 3 ), zirconia (zirconium oxide-ZrO 2 ), silicon carbide (SiC), and silicon nitride (Si 3  N 4 ) which are readily available in powder form and for which fabrication methods and performance specifications are well known. The use of one of these structural ceramics for the manufacture of a blade or portion thereof greatly increases the abrasive wear resistence of a refiner filling as compared with metal materials. 
     Unsupported, pure ceramic materials have very limited application due to their lack of toughness. However by laminating a ceramic surface tape 40a to a metal blade 40b, the abrasion resistence of the edge is retained while the metal base 40b provides the necessary toughness. The combined metal and ceramic components of the blade are metallurgically joined at 46 in the same process in which the blades and spacers are joined. 
     A similar, though thinner supported ceramic edge is produced by applying one of the above materials using known commercial practices to the blades prior to assembly and subsequent joining of the blades and spacers. 
     Ceramic-metal composite materials (cermets) such as metal oxide, and metal carbide particles bonded with cobalt are also used for blade materials. The exceptional wear characteristics of ceramics are combined with the toughness of a metal (typically cobalt in the case of cutting tools) to provide a very durable blade for refiner fillings. 
     The bonded blade and spacer aspect of the invention permits the use of a wide variety of very highly engineered materials. It is only necessary that the material be capable of forming strong metallurgical bonds with the other blade and spacer components. As an example, copper brazing is commonly used to join ceramics and cermets to tool steel. 
     Various changes may be made to the structure embodying the principles of the invention. The principles of the invention, while described in preferred embodiment of refiner disc segments, are also applicable to other configurations of refiner fillings. For example, the invention also has application to working surfaces of refiners in conical configurations. 
     The foregoing embodiments are set forth in an illustrative and not in a limiting sense. The scope of the invention is defined by the claims appended hereto.