CA1214041A - Liner assembly for particle-throwing apparatus - Google Patents

Abstract

LINER ASSEMBLY FOR
PARTICLE-THROWING APPARATUS

Abstract of the Disclosure 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 em-bodiment 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.

Description

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Background of the Invention 1 Field of the Invention 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 par-ticulate materials by centrifugal force from the ends of the blades of a rotating wheel onto an object or sur~ace to be cleaned, abraded, peened or otherwise treated.

2. Reference to Relevant Patents _ Reference is made to the following United States patents:

"Particle-Throwing Apparatus", U.S. Patent No.

3,160,990 issued December 15, 196~ to J.E. Bowling, Jr. et al, hereinafter called the '990 Patent;
"Blasting Wheel Construction", U.S. Patent No.
3,191,346 issued June 29, 1965 to H.S. Chambers, hereinafter called the '346 Patent;
"Particle-Throwing Apparatus", U.S. Patent No.
2C 3,319,383 issued May 16, 1967 to J.E. Bowling, Jr. et al, hereinafter called the '383 Patent;

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"Abrasive Resistant Articles and Alloys", U.S.
Patent No. 2,355,726 issued August 15, 1944 to Oscar E.
Harder e-t al, hereinafter called the Alloy Patent.
3. Description of the Prior Art The '383 and '990 Patents disclose particle-throwing 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 wi-th objec~s or workpiece surfaces that are to be cleaned, abraded, peened or otherwise treated.
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 suscepticle to break-age, especially in corner regions and along edges where extremi-ties of the liner parts have relatively thin cross-sections. The very hard ma-terial 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 par-ts impractical due to cost. Accordingly, the liner parts are difficult and expensive to fabricate, and comprise relatively fragile, !4~

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, khe wheel vanes may be caused to break, and broken vane pieces may be hurled against the brittle liner parts causing liner breakage. In o-ther situations, workpieces being treated may rebound into the wheel enclosure and cause liner breakage. The occurence 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 down-time.
Although the '346 Patent discloses a liner assembly having a relatively few number o~ liner componen-ts, 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 ~L2~L4(;1 ~

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.

Summary of the Invention 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) sim-plifies 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 uti-lized to the exclusion of more ductile cast steel material in providing the various parts o~ 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 elimina-ted.

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An important feature of the invention lies in the provision of liner parts which form overlapping or inter-fitting 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 rela-tively 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 inven-tion 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 pla-tes 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 interfi-t with edge formations of adjacent plates.
The full-thickness construction of -the overlapping or inter-fitting plate edge portions enhances plate strength and minimizes the likelihood of plate breakage.

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The reduction in the number of liner parts required to provide a complete liner assembly minimizes the number and lengths of joints which are present in the assembled liner. By minimizing the number and length of joints, the likelihood of abrasive leakage through the joints is mini-mized, 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.
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Brief Description of the Drawings The foregoing and other features and advantages of the invention will be better understood by referring to the following description of the preferred embodiment and the claims, taken in conjunction with the drawings, wherein:
FIGURE 1 is a partially exploded, perspective view of components of a liner assembly embodying the preferred practice of the present invention;
E'IGURE 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, o-f liner assembly parts as seen essentially from , . ~

40~1 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 llner 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 view, as seen from planes indicated by lines 9-9 and 10-10 in FIGURE 8;
FIG~RE 11 is a sectional view similar to FIGURES 5 and 8, hut 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 gen-erally 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 lS presenting a comparison of rela-tively 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 sec-tional views, as seen generally from a plane indicated by a line B-B in FIGURE 1, ~:. . I ;

~2~40~l of top closure liner plates which incorporate features of the present inven-tion, with FIGURE 18 depicting a relatively thick liner plate, and wlth FIGURE 19 depicting an inter-changeable, but relatively thin liner plate;
FIGURE 20 is a sectional view as seen from a plane indicated by a line 20~20 in FIGURE 3;
PIGURE 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 particle-throwing 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 15~ 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 rear wall liner structure 14, end wall liner struc-tures 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 skructure 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 25 ~ 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 forma-tions can be provided as one or more separate parts, if desired.

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The end 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 pro-vided 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 there-:~ betweenO
The plates 22, 24, 26, 32, 34, 36, 42, 44, 52, 5~, 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 substitu-ted 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 houslngs. 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 ~5 of the present inven-tion may be employed. FIGUR~S 3 and 4 hereof correspond to FIGURES 1 and 2 of the referenced '383 and '990 pa-tents, and illustrate how liner components of the present inven-tion may be subs-ti-tuted Eor liner componen-ts of the type disclosecl in -the referenced '383 and '990 patents.

Referring briefly to FIGURES 3 and 4, a box-shaped guard housing of essentially trapezoidal cross-section 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 fas-teners 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 fas-teners 120 secure the top wall liner structuxe 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 '3g3 and '990 Patents, to hold 15 ~ these liner plate components in place on the guard housing 100. A separate seal plate 124 is disposed adjacent th~
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 blastant could otherwise travel in penetrating liner joints.
The left and right liner pla-tes 22, 24, 32, 34 define U-shaped grooves 140 into which opposed edge portions of the end plates 42, 44, 52, 54 extend to defi.ne 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 ~p ~
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wall liner plate 24. T~e groove 140 has left, right and base surfaces 142, 144, 146. The edge portion 150 extends closely alongside the left surface 142 and abuttingly en-gages the base surface 146. The plates 24, 52 have in-wardly-facing surfaces 152, 154 which extend in intersect-ing, substantially perpendicular planes. When blastant is propelled toward the juncture between the plates 24, 52, it mus-t execute a plurality oE substantially right angle turns if it is to penetrate the U-shaped, wrap-around, labyrinth seal provided by this joint structure.
Similariy, 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 sur-face 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 pla-te 52 has an offset edge portion 170 which cooperates wi-th an edge portion 172 of the lower end plate 54 to define a right angle la~yrinth seal therebetween. The edge por-tion 170 is of L-shaped configuration and includes a downwardly facing surface 174 and an inwardly facing surface 176. The 4~4~

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 junc-ture be-tween the plates 52, 54 it must execute substan-tially a righ-t angle turn if it is to penetra-te -the L-shaped labyrinth joint formed between the plates 52, 54.
Similar L-shaped labyrinth joints are formed between others of the plates wh\i\ h form the structures 12, 14, 16, 18. By way of example, r\eferring to FIGURE 20, the front wall liner plates 22, 26 have overlapping edge forma-tions 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 a way that selected : ones of the liner plate components can be selectively formed from either relatively thin, bri-ttle metal material, or re-latively thick, duc-tile metal material. By way of example, FIGURE 5 illustrates the use oE relatively -thin upper and lower end plates 52, 54 lining the guard housing end wall 108, while E'IGU~E 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 combina-tion of thick and thin plates 52a, 5~ lining -the guard housing encl wall 108.
Thin liner plates have traditionally been employed in blastant wheel guard housi.ngs because the extremely hard, ~ '~

brittle alloy from which these plates have been made (the alloy disclc~sed in -the reEerenced Alloy Patent) has an optimum performance thickness that is relatively thin.
Making these plates thicker than the optimum thickness significantly diminishes their abrasion-resistant perfor-mance. Where a more ductile alloy is to be used, such as Hadfield's manganese s-teel, 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 in-vention, 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, l9 by dimension "Z," is maintained constan-t regardless of whether thin or thick plates 62, 62a are to be employed. By main-taining constant thickness dimensions, such as the overall dimensions X, Y ancl Z, thin and thick liner pla-te~s may be used interchangeably to line the end and top walls 106, 108, llO oE the guard housing lO0.
While the plates o:E liner assembly lO are pre-ferably 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 me-tal using welded construc-tions to Eorm -the described labyrinth seal formation parts and the like.

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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 com-parison 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 21~, end wall liner structures 216, 213, and a top wall liner s-tructure 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, righ-t and central liner plates 232, 234, 236. The left and right plates 222, 22~ are mirror images of each other, as are the left and right plates 232, 234. I'he 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 shaEt (not shown) extends. In contrast to the embodimen-t disclosed in FIGURES 1-20, the opening 239 is not defined by in-terfitted plates. Addi-tionally, hori~ontal ring protrusions 2~0, 2~1 extend la-terally from -the Eront 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 Eeature of the embodiment clisclosed in FIGURES 1-20 is that sicle l:iners 22, 2~ and 26 can be removed without removing the wheel runnerhead, and 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.

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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 pla-tes 244, 254 are identical. The top wall liner struc-ture 220 includes a single top wall linex 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 pla-tes 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 lugs 316, 313 projecting la-terally 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 secure:Ly to the guard housing 300. r~his closure construction elimina-tes the knobs, channels and eyebolts illustrated at the -top of FIGURES 3 and 4, is light :in weigh-t, and is relatively inexpensive to manufacture. In a manrler similar to the embodimen-t oE FIGURES 1-20, threaded fasteners 322 are provided -to secure the plates, 222, 22~, 226, 232, 234, 236, ~Z:~4~P4~

242, 244, 252, 254, 262 to corresponding por-tions of the housing 300.
The guard housing 300 includes a discharge opening 323 through which its blastant wheel propels particulate material by centrlfugal force. The lower end wall liner plates 244, 254 include laterally extending lugs 324, 326.
The lugs 324, 326 are loca-ted adjacent wall members 328, 330 to which the housing 300 is secured by outwardly extending flanges indicatecl at 332, 334. The lugs 32~, 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 actu-ality, comprise only nine different pla-te configurations which need to be stocked as replacement parts. In FIGURES
22 and 23, central pla-tes 226, 236 are not identical in configuration, as are central plates 226, 236 in FIGURE 2.
A feature of -the liner assembly 10 is that it may be substituted for the twenty-three-piece liner assemblies disclosed in referenced '383 and '390 Patents, and may be installed in the guard housings disclosed in -the referenced '383 and '990 Patents without the necessity of modifying these exist:ing guard housings. The liner assembly 210, and lts guard housing 300, are smaller then the assembly 10 and the housing 100; the housing 300 and -the assembly 210 are intended primarily for markets where smaller-sized, met-rically dimensioned parts are in use.

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While reference has been made herein to a down-wardly-opening orienta-tion 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 faci-litate an understanding of the relative orientations of various components, and should no-t 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 in-vention as hereinafter claimed.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 member to 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 the 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 edge 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 a relatively thick second plate-like member or a relatively thin second plate-like member while maintaining a substantially discontinuity-free surface and a blastant-tight seal; and mounting means for securing the first and second plate-like members to the guard housing, the mounting means permitting the second plate-like member to be removed and replaced without removing the first plate-like member.

2. The liner assembly of Claim 1, wherein the first plate-like member carries a cast-in-situ nut for receiving a threaded fastener for connecting the first plate-like member to the guard housing.

3. The liner assembly of Claim 1, 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.

4. In a liner assembly for a guard housing within which a blastant throwing 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 end liner plate formed from relatively thick metal;
a second end liner plate formed from relatively thin metal and disposed closer to the discharge opening than the first liner plate, 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, the means for securing the second plate enabling the second plate to be removed and replaced without removing the first plate.

5. The liner assembly of Claim 4, wherein the first liner plate is disposed further from the discharge opening than the second liner plate.

6. 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 being relatively thick for lining the inkerior 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 an upper end wall liner plate and a lower end wall liner plate having differing thicknesses;
the top wall liner means having a receiving formation for receiving upper edge portions of the front, rear and end wall liner means each havlng varying thicknesses;
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; and mounting means for securing the front, rear, end and top wall liner means to the guard housing, the mounting means for securing the lower end wall liner plates permitting the lower end wall liner plates to be removed and replaced without removing any of the other liner means.

7. The guard housing liner assembly of Claim 6 wherein the lower end wall 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 upper end wall liner plates to define an abrasive-tight labyrinth seal therebetween.

8. The guard housing liner assembly of Claim 6 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 hous.ing, 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.