GB2118465A - Liner assembly for particle-throwing apparatus - Google Patents

Abstract

A wear liner assembly for lining front, rear, end and top walls of the guard housing of a blastant throwing wheel includes a plurality of liner plate members. The liner plate members have full-thickness edge portions which overlie or interfit with edge portions of adjacent ones of the liner plate members to define abrasive-tight labyrinth seals. A wrap-around corner joint connects end wall liner plate members with front and rear wall liner plate members, and facilitates replacement of broken or worn liner plate members. The liner plate members and the joint structures are configured such that selected ones of the liner plate members can be fabricated using either a relatively thin section of relatively brittle cast metal or a relatively thick section of relatively ductile cast metal. One embodiment of the invention includes plates having an edge configuration such that less expensive mounting structure can be used, as well as a more effective abrasive seal for the region of the wheel shaft. Lugs may be provided on the plate members adjacent the discharge opening of the housing to prevent abrasive particles entering the region between the liner members and housing. <IMAGE>

Description

SPECIFICATION Liner assembly for particle-throwing apparatus The present invention relates to a liner assembly for lining interior wall surfaces of a guard housing for a blastant throwing wheel of the type used to project particulate materials by centrifugal force from the ends of the blades of a rotating wheel onto an object or surface to be cleaned, abraded, peened or otherwise treated.

Reference is made to the following United States patents, the disclosures of which are incorporated herein by reference: "Particle-throwing apparatus", U.S.-A-3,160,990 issued 15th December 1964 to J.E. Bowling, Jr., et al, hereinafter called the '990 Patent'; "Blasting wheel construction", U.S.-A-3,191,346 issued 29th June 1965 to H.S. Chambers, hereinafter called the '346 Patent'; "Particle-throwing apparatus", U.S.-A-3,31 9,383 issued 16th May 1967 to J.E. Bowling, Jr. metal, hereinafter called the '383 Patent', and "Abrasive resistant articles and alloys", U.S.-A2,355,726 issued 15th August 1944 to Oscar E.

Harder et al, hereinafter called the 'Alloy Patent'.

The '383 and '990 Patents disclose particlethrowing apparatus of the type including a wheel which rotates inside a guard housing for forcefully projecting a stream of particles through an opening formed in the guard housing for impingement with objects or workpiece surfaces that are to be cleaned, abraded, peened or otherwise trnated. The guard housings each have a front wall, a rear wall, a pair of end walls, and a top wall closure. A liner assembly is provided for lining the front, rear, end and top closure walls. The wear liner assemblies disclosed in these patents each include a total of twenty-three parts. Some or all of the parts are made from very brittle cast iron of the type disclosed in the 'Alloy Patent'.

While brittle cast iron liner parts are very resistant to abrasion, they are highly susceptible to breakage, especially in corner regions and along edges where extremities of the liner parts have relatively thin cross-sections. The very hard material from which these liner parts are formed has an optimum thickness for providing the desired type of performance.

This optimum thickness is relatively thin; however, the material itself is difficult to cast in relatively thin cross-sections or in complex or convoluted shapes.

Moreover, the hardness of the material makes machining or grinding of the liner parts impractical due to cost. Accordingly, the liner parts are difficult and expensive to fabricate, and comprise relatively fragile, readily breakable structures which must be shipped, stored and handled with care.

While the very hard cast metal material from which the liner parts are formed ordinarily offers excellent resistance to abrasive impingement, occasions arise when particles of undesirably large size inadvertently are fed to the rotating blastant wheel which is housed inside the liner assembly. When this happens, the wheel vanes may be caused to break, and broken vane pieces may be hurled against the brittle liner parts causing liner breakage. In other situations, workpieces being treated may rebound into the wheel enclosure and cause liner breakage.

The occurrence of liner plate breakage is, in fact, quite common and the associated down-time for parts replacement poses a problem.

A drawback of the liner assemblies disclosed in the '383 and '990 Patents has been the relatively large number of liner components needed to provide a complete liner package, and the attendant difficulties and delays associated with removing and replacing such a large number of parts. Moreover, the effort involved in dealing with the large number of fastening bolts used to hold such a large complement of plates in place undesirably prolongs downtime.

Although the '346 Patent discloses a liner assembly having a relatively few number of liner components, that patent, and the patents referred to previously, fail to address certain considerations.

One of these considerations relates to expense. In certain markets, it is desired to provide a liner assembly having a smaller size and a less expensive technique for sealing a shaft of the wheel. A desirable liner assembly would employ the fewest number of liner components while, at the same time, providing an inexpensive shaft sealing system having an adequate abrasive seal.

The present invention addresses and overcomes the foregoing and other drawbacks of prior liner assembly proposals by providing a novel and improved liner assembly which (1) employs a small number of parts to fully line the guard housing of a particle-throwing apparatus, (2) simplifies replacement of broken and worn liner parts and thereby minimizes down-time associated with parts replacement, (3) provides highly effective, abrasive-tight labyrinth seals between adjacent liner parts and a wheel shaft, (4) allows an intermixing of relatively thin, relatively brittle liner parts with relatively thick, relatively ductile liner parts, whereby the hard, brittle cast iron material from which liner parts are customarily formed need not be utilized to the exclusion of more ductile cast steel material in providing the various parts of the liner assembly and (5) provides a seal adjacent the periphery of the liner assembly and the guard housing such that the need for a separate seal plate is eliminated.

An important feature of the invention lies in the provision of liner parts which form overlapping or interfitting joints that not only provide abrasive-tight labyrinth seals, but also permit selected one of the liner parts to be formed either from a relatively thin section of relatively brittle cast iron, or a relatively thick section of relatively ductile cast steel. By this arrangement, a liner assembly can comprise principally relatively thin, brittle cast iron liner plates, or an intermixed set of thin and thick plates of brittle and ductile materials, respectively.

By permitting a selection of thin and thick plates to be used together in a liner assembly, the present invention enables the user, for the first time, to independently determine whether selected ones of the liner plates are to take the form of thin, brittle structures, or thick, ductile structures. Thus thin, brittle plates can be used in high impingement areas where abrasion resistance must be maximized, and thick, ductile plates can be used where desired.

The joint system used to form abrasive-tight labyrinth seals between adjacent liner plate parts is unique in its provision of full-thickness plate edge portions which overlap or interfitwith edge formations of adjacent plates. The full-thickness construction of the overlapping or interfitting plate edge portions enhances plate strength and minimizes the likelihood of plate breakage.

The reduction in the number of liner parts required to provide a complete liner assembly minimizes the number and lengths ofjoints which are present in the assembled liner. By minimizing the number and length of joints, the likelihood of abrasive leakage through the joints is minimized, as is the problem of wear due to such leakage.

A liner assembly embodying the preferred practice of the present invention can be substituted for such liner assemblies as are disclosed in the '346, '383, and '990 Patents. Additionally, an embodiment of the invention is disclosed in which the need for a separate seal plate is eliminated, and an improved abrasive labyrinth seal is provided for the wheel shaft, thereby enabling a less expensive shaft sealing system to be provided.

Embodiments of the present invention will now be described by way of example, reference being made to the accompanying drawings, in which: Figure 1 is a partially exploded, perspective view of components of a liner assembly embodying the preferred practice of the present invention; Figure 2 is an exploded perspective view of the components thereof displayed as if supported on a planar surface; Figures 3 and 4 are sectional views on an enlarged scale, of liner assembly parts as seen essentially from planes indicated by lines 3-3 and 4-4 in Figures 1 and 3, respectively, with the liner assembly parts installed in a guard housing of a particle-throwing apparatus; Figure 5 is an enlargement of a portion of the sectional view of Figure 3, illustrating relatively thin, brittle, cast iron liner plates installed inside a guard housing;; Figures 6 and 7 are sectional views, as seen from planes indicated by lines 6-6 and 7-7 in Figure 5; Figure 8 is a sectional view similar to Figure 5, but illustrating relatively thick, ductile, cast steel liner plates installed inside a guard housing; Figures 9 and 10 are sectional views, as seen from planes indicated by lines 9-9 and 10-10 in Figure 8; Fiqure 11 is a sectional view similar to Figures 5 and 8, but illustrating a combination of relatively thick and thin cast metal liner plates installed inside a guard housing; Figures 12 and 13 are sectional views as seen from planes indicated by lines 12-12 and 13-13 in Figure 11;; Figures 14-17 are sectional views, as seen generalliy from a plane indicated by a liner A-A in Figure 1, of end liner plates which incorporate features of the present invention, with Figures 14 and 15 presenting a comparison of relatively thick and thin upper end liner plates, and with Figures 16 and 17 presenting a comparison of relatively thick and thin lower end liner plates; Figures 18 and 19 are sectional views, as seen generally from a plane indicated by a line B-B in Figure 1, of top closure liner plates which incorpo rate features of the present invention, with Figure 18 depicting a relatively thick liner plate, and with Figure 19 depicting an interchangeable, but relative liy thin liner plate; Figure 20 is a sectional view as seen from a plane indicated by a line 20-20 in Figure 3;; Figure 21 is a sectional view, similar to Figure 4, of a modified form of a liner assembly installed in a modified form of guard housing of a particlethrowing apparatus, and Figures 22 and 23 are sectional views taken along planes indicated by lines 22-22 and 23-23 in Figure 21.

Referring to Figures 1 and 2, components of a liner assembly for lining a guard housing of a blastant throwing wheel are indicated generally by the numeral 10. The liner assembly 10 includes a front wall liner structure 12, a rearwall liner structure 14, end wall liner structures 16, 18 and a top wall liner structure 20.

The front wall liner structure 12 includes left, right and central liner plates 22, 24,26. The rear wall liner structure 14 includes left, right and central liner plates 32, 34,36. The central plates 26,36 are identical. The left and right plates 22, 24 are mirror images of each other, as are the left and right plates 32, 34. The left and right plates 32,34 are shown as having ring-segment formations 38 cast integrally therewith, but these formations can be provided as one or more separate parts, if desired.

The wall liner structure 16 includes upper and lower liner plates 42,44. The end wall liner structure 18 includes upper and lower liner plates 52, 54. The upper plates 42, 52 are identical. The lower plates 44, 54 are identical.

The top wall liner structure 20 includes a single top wall liner plate 62. A receiving formation 64 is provided in the top wall liner plate 62 to receive upper edge portions of the front, rear and end wall plates 22, 24, 26, 32, 34, 36,42, 52 to establish a labyrinth seal therebetween.

The plates 22, 24, 26, 32,34, 36,42,44, 52, 54, 62 form an eleven member liner assembly but, in actuality, comprise only eight different plate configurations which need to be stocked as replacement parts.

A feature of the eleven-piece liner assembly 10 is that it may be substituted for the twenty-three-piece liner assemblies disclosed in the referenced '383 and '990 Patents, and may be installed in the guard housings disclosed in the referenced '383 and '990 Patents without the necessity of modifying these existing guard housings. Reference is made to the particle-throwing apparatti disclosed in the referenced '383 and '990 Patents which exemplify and illustrate typical environments within which liner systems embodying features of the present invention may be employed. Figures 3 and 4 hereof correspond to Figures 1 and 2 of the referenced '383 and '990 Patents and illustrate how liner components of the present invention may be substituted for liner components of the type disclosed in the referenced '383 and '990 Patents.

Referring briefly to Figures 3 and 4, a box-shaped guard housing of essentially trapezoidal crosssection is indicated generally by the numeral 100.

The housing 100 has a front wall 102, a rear wall 104, inclined end walls 106, 108, and a top wall closure 110. Threaded fasteners 112 secure the front wall liner structure 12 to the front wall 102. Threaded fasteners 114 secure the rear wall liner structure 14 to the rear wall 104. Threaded fasteners 116, 118 secure the end wall liner structures 16, 18 to the end walls 106, 108. Threaded fasteners 120 secure the top wall liner structure 20 to the top wall closure 110.

Several of the liner plate components 10 carry cast-in-situ nuts 122 which receive threaded fasteners 112,114,116,118, as is described in the referenced '383 and '990 Patents, to hold these liner plate components in place on the guard housing 100.

A separate seal plate 124 is disposed adjacent the lower periphery of the liner assembly 10 and the housing 100. The plate 124 keeps particulate matter away from the housing side of the liner assembly 10.

The liner plate components of the assembly 10 have overlying or interfitting edge portions which cooperate to define abrasive-tight, labyrinth seals between adjacent ones of the liner plates. The design of the liner assembly components 10 eliminates all line-of-sight openings through which blastans could otherwise travel in penetrating liner joints.

The left and right liner plates 22,24,32,34 define U-shaped grooves 140 into which opposed edge portions of the end plates 42,44,52,54 extend to define U-shaped, wrap-around labyrinth seals. Referring to Figure 6, the upper end liner plate 52 has an edge portion 150 which extends into a groove 140 formed along one side of the front wall liner plate 24.

The groove 140 has left, right and base surfaces 142, 144, 146. The edge portion 150 extends closely alongside the left surface 142 and abuttingly engages the base surface 146. The plates 24, 52 have inwardly-facing surfaces 152, 154 which extend in intersecting, substantially perpendicular planes.

When blastant is propelled toward the juncture between the plates 24, 52, it must execute a plurality of substantially right angle turns if it is to penetrate the U-shaped, wrap-around, labyrinth seal provided by this joint structure.

Similarly, referring to Figure 7, the lower end liner plate 54 has an edge portion 160 which extends into the groove 140 formed along one side of the front wall liner plate 24. The edge portion 160 extends closely alongside the right surface 144 and abuttingly engages the base surface 146. When blastant is propelled toward the juncture between the plates 24, 54, it must execute a plurality of substantially right angle turns if it is to penetrate the U-shaped, wrap-around, labyrinth seal provided by this joint structure.

The various liner plates which form each of the structures 12, 14,16, 18 have overlapping edge portions which define labyrinth seals between adjacent ones of these plates. By way of example, referring to Figure 5, the upper end plate 52 has an offset edge portion 170 which cooperates with an edge portion 172 of the lower end plate 54 to define a right angle labyrinth seal therebetween. The edge portion 170 is of L-shaped configuration and includes a downwardly facing surface 174 and an inwardly facing surface 176. The lower end liner plate 54 has an inwardly-facing surface 178 which contiguously joins the inwardly-facing surface 154 of the upper end liner plate 52, and has its upper end 180 extending in abutting engagement with the surface 174.When blastant is propelled toward the juncture between the plates 52, 54 it must execute substantially a right angle turn if it is to penetrate the L-shaped labyrinth joint formed between the plates 52, 54.

Similar L-shaped labyrinth joints are formed between others of the plates which form the structures 12,14,16,18. By way of example, referring to Figure 20, the front wall liner plates 22, 26 have overlapping edge formations 190, 192 which form a labyrinth seal therebetween. No line-of-sight openings are provided for blastant to penetrate through the liner assembly 10.

The liner plate components of the assembly 10, and the joints which are formed therebetween when the components are assembled, are configured in such away that selected ones of the liner plate components can be selectively formed from either relatively thin, brittle metal material, or relatively thick, ductile metal material. By way of example, Figure 5 illustrates the use of relatively thin upper and lower end plates 52, 54 lining the guard housing end wall 108, while Figure 8 illustrates the use of relatively thick upper and lower plates 52a, 54a lining the guard housing end wall 108, and Figure 11 illustrates the use of a combination of thick and thin plates 52a, 54 lining the guard housing end wall 108.

Thin liner plates have traditionally been employed in blastant wheel guard housings because the extremely hard, brittle alloy from which these plates have been made (the alloy disclosed in the referenced 'Alloy Patent') has an optimum performance thickness that is relatively thin. Making these plates thicker than the optimum thickness significantly diminishes their abrasion-resistant performance.

Where a more ductile alloy is to be used,-such as Hadfield's manganese steel, this material does not cast properly in thin cross-sections, and thicker liner plates are therefore required.

In accordance with one feature of the present invention, the overall thickness of the upper liner plates 52, 52a, as indicated in Figures 14 and 15 by the dimension "X", is maintained constant regardless of whether thin or thick plates 52, 52a are to be employed. Similarly, the overall thickness of the lower liner plates 54, 54a as indicated in Figures 16 and 17 by the dimension "Y", is maintained constant regardless of whether thin or thick plates 54, 54a are to be employed. Likewise, the overall thickness of the top liner plates 62, 62a, as indicated in Figures 18, 19 by dimension "Z", is maintained constant regardless of whether thin or thick plates 62, 62a are to be employed.By maintaining constant thickness dimensions, such as the overall dimensions X, Y and Z, thin and thick liner plates may be used inter changeably to line the end and top walls 106, 108, 110 of the guard housing 100.

While the plates of liner assembly 10 are preferably formed from cast metal material, as will be apparent to those skilled in the art, these members may also be formed from other materials such as wrought metal using welded constructions to form the described labyrinth seal formation parts and the like.

Referring to Figures 21-23, a modified form of the liner assembly 10 and the guard housing 100 are indicated by the reference numerals 210,300, respectively. In comparison with the liner assembly 10 and the guard housing 100, the liner assembly 210 and the guard housing 300 are less expensive to manufacture, are smaller in size, and have a less expensive shaft sealing system.

The liner assembly 210 includes a front wall liner structure 212, a rear wall liner structure 214, end wall liner structures 216, 218, and a top wall liner structure 220. The front wall liner structure 212 includes left, right and central liner plates 222,224, 226. The rear wall liner structure 214 includes left, right and central liner plates 232, 234, 236. The left and right plates 222, 224 are mirror images of each other, as are the left and right plates 232, 234. The left and right plates 232, 234 are shown as having ring-segment formations 238 cast integrally therewith, but these formations can be provided as one or more separate parts, if desired.

The central plate 236 includes an opening 239 through which the wheel shaft (not shown) extends.

In contrast to the embodiment disclosed in Figures 1-20, the opening 239 is not defined by interfitted plates. Additionally, horizontal ring protrusions 240, 241 extend laterally from the front and back of the plate 236. The protrusions 240, 241 essentially are annular flanges which establish labyrinth seals in cooperation with the wheel shaft. A feature of the embodiment disclosed in Figures 1-20 is that side liners 22,24 and 26 can be removed without removing the wheel runnerhead, and the other components of the wheel assembly. In Figures 21, 23, this feature is not available, but a better abrasive labyrinth seal for the wheel shaft is provided.

The end wall liner structure 216 includes upper and lower liner plates 242, 244; and the end wall liner structure 218 includes upper and lower liner plates 252, 254. The upper plates 242, 252 are identical. The lower plates 244, 254 are identical. The top wall liner structure 220 includes a single top wall liner plate 262. A receiving formation 264 is provided in top wall liner plate 262 to receive upper edge portions of the front, rear and end wall plates 222, 224, 226, 232, 234, 236, 242, 252 to establish a labyrinth seal therebetween. Labyrinth seals similar to the seals illustrated in Figures 1-20 are employed with the embodiment of Figures 21-23. The seal construction thus employed enables thick or thin plates to be used as desired, as described previously.

The box-shaped guard housing 300 is essentially trapezoidal in cross-section. The housing 300 includes a front wall 302, a rear wall 304, inclined end walls 306,308, and a top wall closure 310. The top wall closure 310 includes two, parallel plates 312, 314 extending across the top opening in the guard housing 300. The plate 312 includes openings alignable with openings in lugs316,318 projecting laterally from the walls 302,304,so each pair of aligned openings can receive a fastening means, such as a nut and bolt 320, for bolting the top wall closure 310 securely to the guard housing 300. This closure construction eliminates the knobs, channels and eyebolts illustrated at the top of Figures 3 and 4, is light in weight, and is relatively inexpensive to manufacture.In a manner similar to the embodiment of Figures 1-20, threaded fasteners 322 are provided to secure the plates 222, 224, 226, 232, 234, 236, 242, 244,252,254,262 to corresponding portions of the housing 300.

The guard housing 300 includes a discharge opening 323 through which its blastant wheel propels particulate material by centrifugal force. The lower end wall liner plates 244, 254 include laterally extending lugs 324, 326. The lugs 324, 326 are located adjacent wall members 328,330 to which the housing 300 is secured by outwardly extending flanges indicated at 332,334. The lugs 324,326 keep propelled particulate matter away from the intersection of the wall members 328,330, the flanges 332, 334, and the housing side of the plates 244,254.

In the embodiment illustrated in Figures 21-23, plates 222, 224, 226, 232, 234, 236, 242, 244, 252, 254 and 262 form an eleven-piece liner assembly 210, but in actuality, comprise only nine different plate configurations which need to be stocked as replacement parts. in Figures 22 and 23, central plates 226, 236 are not identical in configuration, as are central plates 226, 236 in Figure 2.

Afeature of the liner assembly 10 is that it may be substituted for the twenty-three-piece liner assem blies disclosed in referenced '383 and '990 Patents, and may be installed in the guard housings disclosed in the referenced '383 and '990 Patents without the necessity of modifying these existing guard housings. The liner assembly 210, and its guard housing 300, are smaller than the assembly 10 and the housing 100; the housing 300 and the assembly 210 are intended primarily for markets where smaller-sized, metrically dimensioned parts are in use.

While reference has been made herein to a downwardly-opening orientation of the guard housings 100,300, a particle-throwing apparatus of the type described herein may be oriented to project blastant particles in any desired direction. Accordingly, it will be understood that such terms as "top", "bottom", "front", "rear", "upward", "downward" and the like, as used herein, are intended simply to facilitate an understanding of the relative orientations of various components, and should not be interpreted as being limiting in scope.

Although the invention has been described in its preferred form with a certain degree of particularity, it will be understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the true spirit and scope of the invention as hereinaf

Claims (39)

ter claimed. CLAIMS

1. A plate-like liner member for lining a portion of a guard housing within which a blastant wheel is disposed, the wheel being supported for rotation to propel particulate material by centrifugal force through a discharge opening, the plate-like liner member comprising: a first surface exposed to particulate material propelled from the rotating blastant wheel, a second surface disposed on the other side of the liner member from the first surface, the second surface including means for securing the liner member to the housing, and a laterally extending lug positionable nearthe discharge opening for keeping particulate material from entering into the region of the second surface and the guard housing.

2. In a liner assembly for lining a portion of a guard housing within which a blastantwheel is disposed, the wheel being supported on a shaft for rotation to propel particulate material by centrifugal force through a discharge opening, the improvement comprising: a plate-like member for lining a portion of the interior of the housing, the member including an opening through which the shaft extends, the opening having a continuous periphery defined entirely by the plate-like member.

3. The liner assembly of claim 2, further comprising annular flanges surrounding the opening on each side of the plate-like member, the flanges extending laterally outwardly of the plate-like member.

4. In a liner assembly for lining a portion of the interior of a guard housing wherein a blastant wheel is supported for rotation to propel particulate material by centrifugal force through a discharge opening, the liner assembly including a first plate-like member engageable with a second plate-like mem berto define an end wall of the liner assembly, the plate-like members each having an inwardly-facing surface which is exposed to blastant propelled from th rotating blastant wheel, the second member having an edge portion extending along one edge of its inwardly-facing surface, the first plate-like member comprising:: a formation extending along one edige of its inwardly-facing surface and being engageable with the edge portion of the second member when the first and second plate-like members are assembled in abutting relationship to form a portion of a liner assembly, the formation being of a width sufficient to accommodate either a relatively thick second plate-like member or a relatively thin second platelike member while maintaining a substantially discontinuity-free surface exposed to blastant, the interfitting engagement provided between the edge portion and the formation also defining a blastanttight seal.

5. The liner assembly of claim 4, wherein the first plate-like member carries a cast-in-situ nut four receiving a threaded fastener for connnecting the first plate-like member to the guard housing.

6. The liner assembly of claim 4, wherein the second plate-like member carries a cast-in-situ nut for receiving a threaded fastener for connecting the second plate-like member to the guard housing.

7. In a liner assembly for a guard housing within which a blastantthrowing wheel is disposed and supported for rotation to propel particulate blastant material by centrifugal force through a discharge opening onto a workpiece surface to be treated, the improvement comprising: a first line plate formed from relatively thin metal; a second liner plate formed from relatively thick metal, the second plate engageable with the first plate to define an imperforate surface; and each of the plates having a face on one side thereof adapted to be impacted by blastant material, and a mounting face on the other side, each mounting face including means for securing the plate to the guard housing.

8. The liner assembly of claim 7, wherein the first liner plate is disposed further from the discharge opening than the second liner plate.

9. A top wall closure of a liner assembly for lining interior wall portions of a guard housing in cooperation with side wall and end wall closures, wherein a blastant wheel is supported for rotation to propel particulate material by centrifugal force through a discharge opening, the top wall closure comprising: a generally horizontally extending plate-like member, the member including a channel along at least a portion of its periphery, the channel being of a width sufficient to receive an edge portion of either a relatively thick or a relatively thin plate-like member such that an abrasive-tight labyrinth seal will be provided.

10. A method of providing a guard housing liner assembly with interchangeable first and second liner plate components wherein the first liner plate component is formed from relatively thin metal, and the second liner plate component is formed from relatively thick metal, comprising the steps of providing a first wall liner plate component formed from relatively thin metal, the first component having a wear-resistant face on one side thereof and having a mounting face on the other side thereof, the mounting face carrying a plurality of projections for engaging an inner wall portion of a guard housing;; providing a second wall liner plate component formed from a relatively thick metal, the second component having a wear-resistant face on one side thereof and having a mounting face on the other side thereof, the mounting face carrying a plurality of projections for engaging an inner wall portion of a guard housing; conforming the overall thickness dimension of the first component to a first predetermined dimension and conforming the overall thickness dimension of the second component to a second predetermined dimension, whereby when either of the first and second components is mounted in the guard housing with its projections abuttingly engaging the inner wall portion of the guard housing, the wear resistant surface of such mounted component is positioned at a set predetermined location spaced at a set predetermined distance from the inner wall of the guard housing.

11. The method of claim 10, further comprising the step of conforming the first predetermined dimension to be equal to the second predetermined dimension.

12. The method of claim 10, further comprising the steps of providing an additional liner plate means for abuttingly engaging one of said components when mounted on its inner wall portion of the guard housing, providing the additional liner plate means with a U-shaped groove of sufficient width to accommodate the thickness of an edge portion of the first or second liner plate component, and inserting an edge portion of said one component into the U-shaped groove in position to secure the additional liner plate means to the guard housing and to establish a blastant-tight, labyrinth seal therebetween.

13. A multi-piece guard housing liner assembly for lining the interior of a guard housing wherein a blastant wheel is supported for rotation to propel particulate material by centrifugal force through a discharge opening onto a workpiece surface to be treated, the guard housing having a box-like configuration with a front wall, a rear wall, a pair of end walls, and a top wall closure, the liner assembly comprising:: front wall liner means, including a plurality of front liner plates for lining the interior of the front wall; rear wall liner means, including a plurality of rear liner plates for lining the interior of the rear wall; a pair of end wall liner means, including end wall liner plates for lining the interiors of the end walls; top wall liner means, including a top wall plate for lining the interior of the top wall closure; the front wall liner means and the rear wall liner means defining U-shaped groove formations for interfittingly receiving front and rear edge portions of the end wall liner plates; the top wall liner means having a receiving formation for receiving upper edge portions of the front, rear and end wall liner means; and the front, rear, end and top wall plates having edge structures configured such that all joints between adjacent ones of said plates, when assembled, provide abrasive-tight, labyrinth seals to prevent blastant penetration through the joints of the liner assembly.

14. The guard housing liner assembly of claim 13 wherein selected ones of the liner plates each have a smooth, unbroken, imperforate inner face, and a generally flat body having at least one liner edge portion offset from the plane of the flat body, said edge portion being configured to underlie and cooperate with an edge portion of an adjacent one of said liner plates to define an abrasive-tight labyrinth seal therebetween.

15. The guard housing liner assembly of claim 13 wherein selected ones of said plates each having a housing face disposed toward a nearby portion of the guard housing and an interior face disposed toward a central part of the guard housing, the interior faces being smooth and imperforate, and the housing faces having spaced bosses carrying castin-situ nuts for receiving threaded fasteners to secure said plates to the guard housing.

16. The guard housing liner assembly of claim 13 wherein at least one of said plates is formed from an alloy claimed in the referenced 'Alloy Patent'.

17. The guard housing liner assembly of claim 16 wherein at least one other of said plates is formed from Hadfield's manganese steel.

18. The guard housing liner assembly of claim 13 wherein at least one of said plates is formed from Hadfield's manganese steel.

19. The guard housing liner assembly of claim 13, wherein the end wall liner plates disposed closest to the discharge opening include an outwardly-extending lug positioned near the discharge opening.

20. The guard housing liner assembly of claim 13, wherein a selected one of the rear liner plates includes an opening through which a support shaft for the wheel extends, the opening having a continuous periphery defined entirely by the liner plate.

21. The guard housing liner assembly of claim 20, further comprising annular flanges surrounding the opening on each side of the liner plate, the flanges extending laterally outwardly of the liner plate.

22. An eleven-piece guard housing liner assembly for lining the interior of a guard housing wherein a blastantwheel is supported for rotation to propel particulate material by centrifugal force through a discharge opening onto a workpiece surface to be treated, the guard housing having a box-like configuration with a front wall, a rear wall, a pair of end walls, and a top wall closure, the liner assembly comprising; a three-part front wall liner means, including a left front liner plate, a right front liner plate, and a central front liner plate for lining the interior of the front wall; a three-part rear wall liner means, including a left rear liner plate, a right rear liner plate, and a central rear liner plate for lining the interior of the rear wall; ; a pair of two-part end wall liner means, each including an upper end liner plate and a lower end liner plate for lining the interiors of the end walls; a one-part top wall liner means, including a top wall plate for lining the interior of the top wall closure; the front wall liner means and the rear wall liner means, each defining a pair of grooves for receiving, in interfitting relationships, front and rear edge portions of the end wall liner means; the top wall liner means defining a formation for receiving, in interfitting relationships, upper edge portions of the front, rear and end wall liner means; and adjacent ones of said plates, when assembled, having overlapping edge portions which, serving together with the interfitting relationships which are established between front, rear, end and top wall liner means, provide abrasive-tight, labyrinth seals at all junctures between adjacent ones of the eleven liner assembly plates.

23. The guard housing liner assembly of claim 22 wherein selected ones of the liner plates each have a smooth, unbroken, imperforate inner face, and a generally flat body having at least one linear edge portion offset from the plane of the flat body, said edge portion being configured to underlie and cooperate with an edge portion of an adjacent one of said liner plates to define an abrasive-tight, labyrinth seal therebetween.

24. The guard housing liner assembly of claim 22 wherein each of said plates has a housing face disposed toward a nearby portion of the guard housing, and an interior face disposed toward a central part of the guard housing, the interior faces being smooth and imperforate, and the housing faces having spaced bosses carrying cast-in-situ nuts for receiving threaded fasteners to secure said plates to the guard housing.

25. The guard housing liner assembly of claim 22 wherein at least one of said plates is formed from an alloy claimed in the referenced 'Alloy Patent'.

26. The guard housing liner assembly of claim 25 wherein at least one other of said plates is formed from Hadfield's manganese steel.

27. The guard housing liner assembly of claim 22 wherein at least one of said plates is formed from Hadfield's manganese steel.

28. The guard housing liner assembly of claim 22, wherein the lower end liner plates each include a laterally outwardly extending lug positioned near the discharge opening.

29. The guard housing liner assembly of claim 22, wherein the central rear liner plate includes an opening through which a wheel shaft extends, the opening having a continuous periphery defined entirely by the central rear liner plate.

30. The guard housing liner assembly of claim 29, further comprising annular flanges surrounding the opening on each side of the central rear liner plate, the flanges extending laterally outwardly of the central rear liner plate.

31. A plate-like liner member for lining a portion of a guard housing within which a blastant wheel is disposed, the wheel being supported for rotation to propel particulate material by centrifugal force through a discharge opening, the plate-like liner member comprising: a first surface exposed to particulate material propelled from the rotating blastant wheel, a second surface disposed on the other side of the liner member from the first surface, the second surface including means for securing the lining member to the housing, and a generally flat body having at least one linear edge portion offset from the plane of the flat body.

32. The plate-like liner member of claim 31, additionally comprising a laterally extending lug positionable near the discharge opening for keeping particulate material from entering into the region of the second surface and the guard housing.

33. The plate-like liner member of claim 31, wherein the liner member is formed from an alloy claimed in the referenced 'Alloy Patent'.

34. A plate-like liner member for lining a portion of a guard housing within which a blastant wheel is disposed, the wheel being supported for rotation to propel particulate material by centrifugal force through a discharge opening, the plate-like liner member comprising: a first surface exposed to particulate material propelled from the rotating blastant wheel, a second surface disposed on the other side of the liner member from the first surface, the second surface including means for securing the lining member to the housing, and a generally flat body having a channel along at least a portion of its periphery, the channel being of a width sufficient to receive an edge portion of either a relatively thick or a relatively thin plate-like member such that an abrasive-tight labyrinth seal will be provided.

35. The plate-like member of claim 34, wherein the channel is U-shaped in cross-section.

36. The plate-like liner member of claim 34, wherein the liner member aligns a portion of a substantially trapezoidal-shaped sidewall of the guard housing.

37. The plate-like liner member of claim 34, wherein the liner member is formed from an alloy claimed in the referenced 'Alloy Patent'.

38. A plate-like liner member constructed, arranged and adapted to operate substantially as herein described with reference to the accompanying drawings.

39. A liner assembly constructed, arranged and adapted to operate substantially as herein described with reference to the accompanying drawings.