Wear protection for tables for centrifugal impact crushers

A table assembly for a vertical shaft impact crusher includes an impeller having rods embedded vertically in it next to its leading edge. The rods are made from a material which is harder than the material that the body of the impeller is made from. The rods are located where wear is most prevalent. In most situations this would be at both sides of the impeller, but it might be at the center as well. The top surface of the table between impellers is covered with bottom wear plates. The bottom wear plates have raised portions immediately adjacent to the leading edge of the impellers and sloped ramps between the raised portions and the rest of the wear plates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a system for protecting wear parts in a vertical shaft centrifugal impact crusher.

2. Description of the Related Art

Material is crushed in a vertical shaft centrifugal impact crusher by being thrown off of a rotating table against anvils which are located around the periphery of the table. The table has impellers on it at spaced-apart locations about its periphery which cause the material to leave the table in the direction which will maximize fracture of the material as it strikes the anvils. The material being crushed is often quite abrasive and it causes considerable wear of the table parts, particularly the impellers. In addition, because the table parts become caked with dust from the material being crushed it often is quite difficult to remove them for replacement when they become worn. Some vertical shaft impact crushers employ an open table design where the impellers are releasably attached to mounting brackets which are permanently attached to the top of a single horizontal table. Other vertical shaft impact crushers employ a closed table design where impellers are sandwiched between upper and lower table elements. Closed table crushers have impellers which are less subject to wear than open table crushers, but it is much more difficult to replace them. Thus, the increased labor costs and costs of down time when replacement is necessary offsets the longer wear of the impellers.

Attempts have been made to protect the wear parts in vertical shaft impact crushers in the past. Britzke, et al., U.S. Pat. No. 5,954,282 disclose a crusher impeller that has horizontal bores at selected locations on its face. Tungsten carbide rods are then placed in these bores. However, this provides very localized protection and the impeller body will still wear between and around the rods. In addition, the rods can become displaced in the harsh environment in which these devices operate.

Britzke, et al. also disclose wear plates which cover the table between adjacent impellers. These wear plates not only protect the top surface of the table, but they have ramps that are located immediately in front of the associated impeller to cause the material to be thrown up onto the center part of the impeller face. While this does somewhat solve the problem of wear being concentrated near the bottom of impeller it creates a dead space above the ramp and even wear is still not obtained.

SUMMARY OF THE INVENTION

In one aspect of the subject invention, increased life is provided for the wear parts of an open table vertical shaft impact crusher by embedding in each impeller one or more rods which are made from material which is harder and more wear-resistant than the material the impellers are made from. The rods are oriented vertically and are located near the leading edge of the impeller at locations where the most wear occurs. Typically this would be near each side of the impeller, but one might be placed at the center as well. In a preferred embodiment of the invention the rods are tungsten carbide.

In another aspect of the invention, a bottom wear plate covers the upper surface of the table between the leading edge of each impeller and the back of the mounting bracket of an adjacent impeller. The bottom wear plate has a raised portion which is immediately adjacent to the leading edge of the impeller. A sloped ramp extends between the raised portion and the rest of the bottom wear plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, a table assembly 10 is located within a cylindrical case (not shown) and rotated about a central axis A by a motor (not shown). Material to be crushed is deposited onto the table assembly through an opening 12 and falls onto a table 14 . Rotation of the table assembly creates a centrifugal force which throws the material off of the table where it impacts anvils (not shown) mounted on the inner wall of the case around the periphery of the table 14 . When the material strikes the anvils it is fractured into smaller pieces. The crushed material then drops to the bottom of the case where it is removed. In order to direct the material as it leaves the table so that it strikes the anvils at the correct angle to maximize the force of the impact, impellers 16 are mounted on the table at spaced-apart intervals.

In order to permit the impeller 16 to be easily replaced, a mounting bracket 18 is attached to the table at the location of each impeller. The mounting bracket includes a mounting plate 20 , which extends radially across the table, and two upright supports 22 which are attached to the back of a mounting plate 20 and the table 14 . The mounting plate has a rectangular opening 24 located in it and the impeller has a rectangular cross-sectioned tab 26 extending from its rear face which extends through the opening 24 . A pin (not shown) extends through a hole 28 in the tab to secure the impeller in place against the mounting plate 20 .

In order to reduce wear of the impeller, cavities 30 are located in its leading edge, which is where it engages the material being crushed. These cavities fill up with the material being crushed so that the material becomes a wear surface. To further reduce wear, elongate rods 32 , which are made from a material that is harder and more wear-resistant than the material the body of the impeller is made from, are embedded in the impellers. This is accomplished by casting the impellers around the rods. Impellers of this type are cast iron and to increase their hardness the iron has a high chrome content. The material often used for impellers is 28% chrome cast iron. A preferred material for the rods 32 is tungsten carbide. Grade 368 tungsten carbide has been found to work well. The rods are placed vertically in the impellers near their leading edge. Preferably the rods are located at the place on the impeller which experience the most wear. Typically this would be at both sides, but in many cases it may be helpful to have one located near the center of the impeller also. Located at the leading edge of each impeller, at its top and its bottom, are a series of semicircular cutouts 36 , the purpose of which will be explained later.

Bottom wear plates 34 protect the top surface of the table between the leading edge of one impeller 16 and the trailing edge of the mounting bracket of an adjacent impeller. In the embodiment illustrated, each bottom wear plate is divided into a first bottom section 34 a and a second bottom section 34 b . A portion of the first bottom section 34 a is located under the associated impeller 16 . The portion 38 of the first bottom section that is immediately adjacent to the leading edge of the impeller 16 is raised above the rest of the wear plate and a sloped ramp 40 extends between this raised portion 38 and the remainder of the wear plate. The edge of the raised portion 38 has a series of projecting semicircular tabs 42 which fit into the cutouts 36 at the lower leading edge of the impeller. Thus, the impeller holds the first bottom section down on the table and prevents the first bottom section from moving radially outwardly when the table is rotated, and no fasteners are required to keep it in place. The intersection 44 between the first bottom section 34 a and the second bottom section 34 b is angled with respect to a radial line on the table and is sloped with respect to the vertical so that the two bottom sections slightly overlap one another. In addition, the edge of the second bottom section 34 b fits behind the mounting bracket 18 . While the geometry of the first and second bottom sections index the section, the second section can be removed and replaced without removing the first section, and the second section needs to be fastened to the table with mechanical fasteners (not shown). The raised portion 38 and ramp 40 force the material being crushed up onto the face of the impeller to provide more uniform impeller wear.

A center liner 46 is located at the center of the table. The center liner is attached to the table by conventional means (not shown). The outer periphery 48 of the center liner overlaps the edges of the bottom wear plates 34 and its upper surface is co-planer with the raised portions 38 . The center liner has a raised center section 58 .

If desired, the table can be covered with a cover plate 60 which is located on top of the impellers 16 . The cover plate is attached to the table by conventional means, not shown. If a cover plate 60 is utilized, top wear plate 62 can be attached to its underside to protect it from wear. Like the bottom wear plates, the top wear plates are divided into a first top section 62 a and a second top section 62 b . A portion of the first top section 62 a is located under the associated impeller 16 . Both top sections are attached to the cover plate 60 by means of fasteners (not shown).