WEAR ELEMENT FOR SCREW PRESSES OR THE LIKE

Abstract: A wear element comprising a wear plate (2) of a hard, typically ceramic material, locked in a dovetail recess (20) of a bracket (1) made of steel. The bracket (1) consists of two initially separate parts (6', 6'') comprising a respective one of the two inclined dovetail wedge surfaces (5', 5'') of the dovetail recess (20). The two parts (6', 6'') are welded together when positioned with their respective wedge surfaces (5', 5'') tightly engaging a respective one of two complementary inclined wedge surfaces (4', 4'') formed on the wear plate (2).

Description: WEAR ELEMENT FOR SCREW PRESSES OR THE LIKE The invention relates to wear elements intended to be welded along the rim of the screw wing of screw presses or the like, comprising a wear plate of a hard, typically a ceramic, material locked in a dovetail recess formed in a steel bracket. In operation of screw presses, such as in the paper and cellulose industry, sugar production etc, the screw rim is subject to very high wear. In order to reduce this problem it has been proposed to arrange special wear ele¬ ments of the above described kind along the screw rim. SE 427 901 and DE 2 556 671 are examples of such proposals. These prior structures, in which the wear plate is mounted in its bracket by being pushed into a preformed dovetail slit, require accurate machining and adjustment of the parts in order to obtain a stable and rigid locking of the wear plate in the dovetail slit. Thus, a considerable amount of diamond grinding of the very hard ceramic materi- al will be necessary, with corresponding high costs of manufacture of the prior wear elements. As an alternative, the wear plates may be locked by through-going fasteners, but a such approach would reduce the functioning and life of the wear elements. The wear element according to the present invention is characterized in that the bracket is an assembly of two initially separate parts each comprising a respective one of the two inclined dovetail wedge surfaces of the dovetail recess, said parts welded together when positioned with their respective wedge surfaces tightly engaging a respec¬ tive one of two complementary inclined wedge surfaces formed on the wear plate. An important advantage resulting from this approach compared to the prior structures, is that in this case the ceramic wear plate can be used "raw" directly from the fur¬ nace, without necessity of any diamond grinding for dimen¬ sional adjustments, and without having to pierce its wear surface by fastening holes or the like. By welding the initially two-part steel bracket together around the cera¬ mic plate to form the dovetail recess, rather than pushing the wear plate into a preformed slit in the bracket, a rigid and very strong locking of the wear plate in the bracket is achieved, independently of any irregularities or inaccuracies in shape and dimensions of the ceramic wear plate. There are no fastening screws or the like that may loosen during operation, and the costs for producing this simple assembly are substantially lower than for that of the prior art. Advantageous embodiments of the invention are defined in the accompanying patent claims. The term "welding" as used in description and claims, is to be understood in a broad sense including bracing, for example. The invention will now be described with reference to the accompanying drawings in which: Figs. 1(a) - (d) are a side view, top plan view, end view and bottom plan view respectively of a wear element according to the invention, Figs. 2(a) - (c) are a side view, plan view and end view respectively of a wear plate to be used in the wear element according to the invention, Figs. 3(a) - (c) are a sectional view, plan view and end view respectively of a bracket for holding the wear plate of fig. 2, and Fig. 4 is a plan view of a slightly modified embodi¬ ment of the bracket of fig. 2. The wear element shown on fig. 1 consists of a wear plate 2 of a hard material such as ceramics, rigidly locked in a dovetail recess formed in a bracket 1 made of steel. As best shown in fig. 2 the wear plate 2 includes a trapezoidal body portion 9 with an unbroken wear surface 10 and a back portion 3 opposite the wear surface 10. The back portion 3 is shown as a rectangular, preferably sub¬ stantially square protrution of a smaller size than body portion 9 and formed with opposite, substantially parallel inclined wedge surfaces 4 ' , 4 ' ' for engaging complementary inclined wedge surfaces of the bracket recess, and parallel straight (i.e. substantially normal to the wear surface) side surfaces 12. The body portion 9 advantageously has a slightly curved front edge 13 of a curvature adapted to the screw rim to which the wear assembly is to be mounted, and slightly rearwardly converging side edges 14 for engaging a side edge of adjacent wear elements upon mounting onto the screw rim. In the example shown the one wedge surface 4' of the back portion and two side surfaces 12 thereof are offset relative to the front edge 13 and two side edges 14 respectively of the body portion 9, while the second wedge surface 4' ' of the back portion alignes with a correspon¬ dingly inclined rear edge 15 of the body portion 9. Preferably, the bracket 1 is made of stainless steel. As shown in fig. 3, according to an important feature of the invention, it is initially formed in two separate parts 6' and 6' ' , adapted to be welded together around the back portion 3 of the wear plate 2. In the example shown the bracket 1, like the wear plate 2 , is a substantially trape¬ zoidal plate having a curved front edge 16 and converging side edges 17 which, upon assembly, generally coincide with the front edge 13 and side edges 14 respectively of the wear plate. Each bracket part 6', 6'' is provided with a channel¬ like indentation 19', 19'' which, in the assembled (but yet not welded) state of the bracket parts shown in fig. 3, together form a substantially square recess or opening 20 formed as a dovetail slit having parallel inclined wedge surfaces 5', 5'' respectively corresponding to the wedge surfaces 4 ' , 4 ' ' of the wear plate back portion 3 and having straight end surfaces 18 corresponding to the straight side surfaces 12 of the back portion. Thus, the bottom surface of the indentations 19 ' , 19 ' ' of the bracket parts 6' , 6' ' respectively each form one of the parallel wedge surfaces 5', 5'' of the dovetail recess 20. The wear element according to the invention as shown in fig. 1 is implemented by positioning the two separate bracket parts 6' , 6' ' with their respective wedge surfaces 5' , 5' ' tightly pressed against a respective wedge surface 4 ' , 4 ' ' of the wear plate back portion 3, and then welding the two bracket parts 6' , 6' ' together along a welding groove 8 which, in the example shown in figs. 1 and 3 extends on either side of the recess 20 along a line paral¬ lel to and preferably substantially centrally between the wedge surfaces 5' , 5' ' . As a result the wear plate will be immovably locked between the wedge surfaces 5' , 5' ' and end surfaces 18 of the bracket parts. Preferably, to further strengthen the relative immobility of the wear plate and bracket, an adhesive 7 may be applied at least between the bottom surface of the wear plate body portion 9 and top surface of bracket 1. Advantageously, as shown in figs. 1 and 3, one of the brackets 6'' may have a thickened end portion 21 with a shoulder 22 aligned with the bracket wedge surface 5'' to engage a rear surface 15 of the wear plate body portion 4 aligned with the wedge surface 4 ' ' of the wear plate back portion 3, for providing additional support to the wear plate. Fig. 1(a) also illustrates how wear elements of the invention can be welded to the screw wing 23 of a screw 24 shown in phantom, by front weld 25 and rear weld 26. The bracket 101 shown in fig. 4 differs from bracket 1 of fig. 3, only by the welding grooves 108 formed by the assembled bracket parts 106', 106'' extending normal rather than parallel to the bracket top and bottom surfaces on each side thereof.

Claims: P A T E N T C L A I M S : 1. A wear element intended to be welded along the rim of the screw wing of screw presses or the like, comprising a wear plate (2) of a hard typically a ceramic, material locked in a dovetail recess (20) formed in a steel bracket (6), c h a r a c t e r i z e d in that the bracket (1) is an assembly of two initially separate parts (6', 6'') comprising a respective one of the two inclined dovetail wedge surfaces (5', 5'') of the dovetail recess (20), said parts welded together when positioned with their respective wedge surfaces (5', 5'') tightly engaging a respective one of two complementary inclined wedge surfaces (4', 4'') formed on the wear plate (2) . 2. Wear element according to claim 1, c h a r a c t e r i z e d in that each bracket parts (6', 6'') has a channellike indentation (19', 19'') the bottom of which each form one of the parallel wedge surfaces (5', 5'') of the dovetail recess (20), and that the wear plate (2) is formed with a back portion (3) engaging the dovetail recess (20) of the bracket (1), said back portion (3) having parallel wedge surfaces (4', 4'') complementary to the wedge surfaces (5', 5'') of the bracket parts (6', 6''), and side surfaces (12). 3. Wear element according to claim 2, c h a r a c t e r i z e d in that the wear plate (2) is formed with a substantially trapezoidal body portion (9) having an unbroken wear surface (2) opposite the back portion (3) , and that the side surfaces (12) of the body portion (3) and at least one wedge surface (4') thereof is staggered relative to the side (14) and front (13) edges respectively of the body portion (9) . 4. Wear element according to any one preceding claim, c h a r a c t e r i z e d in that the bracket parts (6', 6'') are welded together along a welding groove (8) exten¬ ding on each side of the recess (20) along a line parallel to and substantially centrally of the wedge surfaces (5', 5'') of the dovetail recess (20). 5. Wear element according to any one of claims 1 - 3, c h a r a c t e r i z e d in that the bracket parts (106', 106'') are welded together along welding grooves (108) extending across each side edge (17) of the bracket, normal to and preferably centrally relative to the bracket (101) wedge surfaces. 6. Wear element according to any one preceding claim, c h a r a c t e r i z e d in that one bracket part (6' ') is formed with a thickened end portion (21) with a shoulder (22) in alignment with the bracket wedge surface (5'') to engage a rear surface (15) of the wear plate body portion (4) aligned with the wedge surface (4'') of the wear plate back portion (3) .

Inventors: OMMUNDSEN DAG, OMMUNDSEN, DAG
Applicants: OMMUNDSEN DAG, OMMUNDSEN, DAG
Application year: 1995
Main classification: B04B1
IPC codes: B04B1, B30B9, B30B11