US3708926A

US3708926A - Dust collector for use with vertically movable dust generators

Info

Publication number: US3708926A
Application number: US00094241A
Authority: US
Inventors: J Fogle
Original assignee: Wheelabrator Corp
Current assignee: Wheelabrator Corp
Priority date: 1970-12-02
Filing date: 1970-12-02
Publication date: 1973-01-09
Anticipated expiration: 1990-01-09

Abstract

A machine and method for treatment of vertically disposed surfaces of large dimension with dry particulate material comprising means for throwing the dry particulate material at high velocity in the direction toward said surface, a housing enclosing said throwing means having an opening through which the particulate material is thrown against said surface, means for establishing a sealing relationship about said opening between the housing and said surface to confine the particulate material, dirt and dusts within the sealed space, means for collecting the spent particulate material at the bottom portion of the housing and for introducing air into the housing for air washing the spent particulate material to remove dirt and dusts, recycling the washed particulate material for feed to the throwing means, a dust collector for receiving the dirt and dust from within the housing for separation thereof and means for maintaining subatmospheric conditions within the housing to guide the air flow through the housing and about said sealing means to minimize the exhaust of dirt and dust into the atmosphere and in which the support means for said housing includes means for movement of the housing in the vertical direction, means for movement of the housing in the horizontal direction and means for movement of the housing in the direction toward and away from the surface and means for mounting the housing for rocking movement about its pitch and yaw axes to adjust the housing with change in contour of the surface, and sensing means about the opening automatically to adjust the housing for change in contour about the pitch axis and/or the yaw axis and for movement of the housing in the direction towards and away from the surface and for abutting off the feed of particulate material in the absence of a sealing relationship between the housing and surface.

Description

United States Patent [1 1 Primary Examiner-Harold D. Whitehead Attorney-McDougall, Hersh, Scott & Ladd 'Fogle 1 Jan, 9, 1973 [5 DUST COLLECTOR FOR USE WITH S C VERTICALLY MOVABLE DUST A' machini'faia' method" for ireazme'm omrfieany GENERATORS disposed surfaces of large dimension with dry particui late material com risin means for throwin the dr [7'5] Inventorf James walkerton particulate materi l at l'iigh velocity in the directior l [73] Assignee: The Wheelab'rator Corporation, toward said surface, a housing enclosing said throwing Mishawaka, lnd. means having an opening through which the particulate material is thrown a ainst said surface, means for [22] Filed: 1970 establishing a sealing rel ationship about said opening [2]] Appl. No.: 94,241 between the housing and said surface to confine the particulate material, dirt and dusts within the sealed s ace, means for collectin the s ent articulate Related Apphcat'on Data n iaterial at the bottom portio n of the housillg and for [62] Division of Ser. No. 703,397, Feb. 6, 1968, Pat. No. intr ducing air into the housing for air washingthe 3,566,543. Y spent particulate material to remove dirt and dusts, I Y i recycling the washed particulate material for feed to [52] U.S. C1. ..51/273 the throwing s, a dust ll t r for r iving the [51] Int. Cl. .L ..B24b 55/06 dirt and dust from Within the housing for Separation 5811mm of Search ..285/61; 15/302;51/9,273 thereof and means for maintaining subatmospherict 1 conditions within the housing to guide the air flow through the housing and about said sealing means to [56] References Cited minimize the exhaust of dirt and dust into the at- Q mosphere and in which the support means for said UNITED STATES PATENTS housing includes means for movement of the housing 1 990,318 2 1935 Dabe ..s1 9 the vertical direction movement of the 3:034262 5/1962 Pawlson 51/9 housing ,in the horizontal direct on and means for 3,262,228 7/1966 Schenckm movement of the housing in the direction toward and 3,274,892 9/1966 cameww; "WM/273 x away from the surface and means for mounting the 2,634,560 4/1953 Ramm ..51 273 housing for rocking movement about its Pitch and y axes to adjust the housing with change in contour of the surface, and sensing means about the opening au- FOREIGN PATENTS 0R APPLICATIONS tomaticall to ad'ust the housin for change in contour aboul the pllch axls and/or the yaw axis and for 846,217 7/1949 Germany ..5l/9

movement of the housing in the direction towards and away from the surface and for abutting off the feed of particulate material in the absence of a sealing relationship between the housing and surface.

3 Claims, 11 Drawing Figures PAIENIEDJAN 9 ms SHEET 1 [IF 8 FIG.- 1

PATENTEDJAN 9l973 3; Y Y sum um 8 708826 DUST COLLECTOR Fonusr: WI'IH VERTICALLY I MOVABLE DUST GENERATORS This application is a division of my copending application Ser. No. 703,397, filed Feb. 6, 1968 and entitled Machine for Treatment of LargeVertical Surfaces, now U.S. Pat. No. 3,566,543, issued Mar. 2, 1971.

This invention relates to the treatment of surfaces of vertically disposed walls of large dimension, such as the outer side wallsof a ships hull, large conservation tanks for water, gas and the like fluid materials, or other paneled structures, and it relates more particularly to a method and means for cleaning such vertically disposed paneled structures or walls with dry particulate abrasive materials blasted onto the surface.

To the present such surfaces or walls are air blasted with crushed slag as the abrasive. Such abrasive particles breakdown so rapidly that no attempts are made for recovery and the abrasive is wasted after the single use. The described cleaning process is subject to a number of drawbacks including high cost by reason of the high cost of the compressed air that is required; the slow rate of cleaning; the need for three men for operation of a single cleaning head; the high cost for handling large amounts of abrasive; the labor and equipment required to remove the abrasive; and the need to dispose of the large amount of spent abrasive that is continuously being generated.

Aside from the above disadvantages, the process presently employed is characterized as a dirtyprocess which raises excessive amounts of dust and additional means are therefore required to protect personnel on the ship.

It is an object of this invention to provide a dust collector for usewith means for surface treatment of vertical panels'and walls of large dimension by blasting with dry particulate material. I These and other objects and advantages of this invention willhereinafter appear and, for purposesof illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawings in which FIG. 1 is a perspective view in elevation ofa machine embodying the features of this invention; I 1 FIG. 2 is a perspective view in side elevation of the blasting head alongsidea wall to be treated; I

FIG. 3 is an enlarged perspective view in rear elevation of the blasting head and supports;

FIG. 4 is a front elevational view of the blasting head and associated elements;

FIG. 5 is aside elevational view partially in section of the blasting chamber and abrasive handling parts;

FIG. 6. is a schematic elevated. view of the various frame members for support of the blasting chamber;

FIG. 7 is a view similar to that'of FIG. 6 showing the arrangement of elements for movement of the blasting head in theforward and rearward-direction relative the supporting frames;

7 FIG. '8 is aview schematically showingthe'arrangement of elements for angular adjustment of the blasting FIG. 9. is an elevationalview-partially in section of I the duct'communicating the blast chamber with the dust collector;

FIG. 10 is a sectional view taken alongline 10-10 of F IG. 9; and

' FIG. 11 is an electrical diagram for the machine;

Invention will hereinafter be described with reference to a machine for cleaning the outer surfaces of a shipshull with dry particulate material blasted onto the surface of the hull by a centrifugal wheel in an assembly which can be moved about the hull in'a manner to accommodate the various curvatures of the ships hull for substantially uniform complete coverage thereof It will be apparent from the description that the machine and method of this invention can be employed equally well for the cleaning or otherwise treating of the vertically disposed walls of outside storage or conservation tanks of large capacity or other vertically disposed walls of metal or the like paneled structures.

The machine of this invention makes use of a single blasting head 10 which includes a blast chamber 12 having an opening 14 at its forward end which may be of various configurations but which is preferably of oval or rectangular shape with the major length of the opening perpendicular to the. axis of the bladed centrifugal throwing wheel 16 mounted for rotational movement. within the base of the chamber 12 for-turning movementabout a vertical axis. Centrifugal blastingwheels of the type described are manufacturedand sold by The Wheelabrator Corporation of Mishawaka, Ind., under the trade name WHEELABRATOR" and are more specifically described inU. S.;Iats. Nos.

2,708,814 and 2,819,562. Suffice it'tosay that such throwing wheels comprise a plurality of radially extending blades arranged in circumferentially spaced apart relation between confining disc plates with means 'for feeding particulate treating material, such as steel shot, steel grit or the like-onto the innerends of theblades whereby such particulate material is thrown centrifu gally at high velocity from the outer ends of theblades as the wheel is rotated at highspeed about its axis by the driving motor 18. The particulate material is thrown forwardly from the ends of the blades through the open end of the blast housing into engagement with the'surface facing the blast housing.

For this purpose, a large flanged plate 20 is secured to the open edge of the blast chamber and inner and

outer sealing members

22 and 24, formed of resilient or rubber-like material such as polyurethane, and of frusto-conical shape, are secured to extend continuously about the blast opening 14 withthe rearward ends of the sealing members secured to the flanged plate 20 to provide a spacedrelationship therebetween. The resilient sealing members 22-'-and 24 areprotected from the abrasive thrown outwardly from the wheel by a baffle' plate 26- which is secured to the flanged plate 20 inwardly of the inner sealing member 22 and arranged to, project angularly outwardly between and sealing member. 'andthe interior. of the blast chamber for a distance to correspond with the in-- nermost reach of thesealingmembers. I 1 a The sealing members'22 and 24 are adapted to engage the surface to be treated immediately adjacent the blast area and means are providedforsealing engagement in a manner to deflect the forward edge portions of the sealing members when the blasting head is in proper position of use thereby to effect a sealing relation'ship between the blast chamber and the surface.

Air' inlet spaces 30 encircle the upper end portion of the blast chamber and communicate with the space between the inner and

outer sealing members

22 and 24 through openings 32 whereby air under pressure the slot 38 in the flanged plate at the base of the inner sealing member 22 or over the deflector plate 26 and the shed plates '40 at the bottom of the blast chamber. The blasting head is provided with an air inlet 42 immediately below the

shed plates

40, 44,46 and 48 for-theintrodu'ction of air which passes upwardly about the. inner ends v of the shed plates and through the descending curtain of spentiabrasive anddust to air wash the abrasive and remove dust and fines from the spent abrasive For this purpose,theshed plates 40, 44-,

46 and 48 comprise verticallyspaced apart downwardly angled plates having their inner edges in i overlapping .relations'hipto provide a cascade of the the wholeassembly. By the described arrangement of air flow, it becomes possible "to operate the blasting head continuously for hours with little, if any, heat build-up in the abrasive. v I v The side walls 50 of the blast housing below the blasting head converge angularly inwardly in the direction towardseach other to define a collecting chute through iwhich'the air washed abrasive and air separated particles fall gravitationally into a trough 52 at the bottom having a screw 54 rotatably mounted therein for'displacernent of the collected particulate material rearwardly'for'movement over a perforated.

plate or screen 56, which forms a part of the bottom wall of the conveyor and through which the reusable abrasive-particles pass while the larger particles of paint, rust, scaleand the-like are displaced over the surfaceyof the screen to a discharge chute 58'comminicating 'withthefar, end 'of the screen for discharge as waste. 1 I

'Theabrasiveparticles which pass" through the perforated plate or-screen 56 are returned as feed forthe v centrifugal throwing wheel. For this purpose, a trough 60 is providedbeneath the perforated'platefor collection of the abrasive particles passingfthrough the screen. A conveyor returns the abrasive particles collected in the 'trough to the feed'hopper62 abovethe blast chamber. Various conveyors or elevator means may be employed for lifting the abrasive particles to the feed hopper; In the preferred practice of this invention,

'blast chamberwith the-collector. i

it is desirable to make use of a means in which a substantial sealed relationship can be maintained in the conveyor means to minimize the flow of air there'thro'ugh in response to the suction generated in the blast chamber by the dust collector, which will hereinafter be described.

One such elevator means illustrated in the drawings comprises a tube elevator whichl ma'kes' use of a continuous length of rigid tubing 63 which encircles the blast assembly. A link'chain 64 extends continuously through the interior of the rigid tubing and spaced links are provided with disc members 66 which function in the manner of a piston head to sweep the abrasive particles in advance thereof through the tube. Such disc members are preferably formed of relatively rigid material, such as polyurethane discs, which are capable of sealing engagement with the surrounding wall of the tubing with minimum frictional resistance to permit linear displacement with the link chain without excessive work.

The portion of the tubing underlying the trough is cut away to provide an opening 68 through which the abrasive particles will fall from the trough into the tubular conveyor and into the path of the disc members.

Similarly, the portion of the tubing overlying the hopper 62 is also provided with an opening 70 toenable the raised abrasive particles to fall from the tubing into the hopper. Means for continuous displacement of the link chain is provided beyond the delivery opening in the form of an electrical motor 72 connected to a suitable speed reducer 74 having a sprocket on the end thereof fastened operatively to engage alternate links ofthe chain. v 5 I The-feed hopper 62 is mounted above the wheel .16 for feeding abrasive particles to the inner ends of the blades of the rotating wheel which throws the abrasive particles centrifugally from the ends of the blades in the direction toward the opening 14 in the blast head onto the facing surface to be processed. A valve 76, such as an electromagnetic valve, is interposed in the feed line 78 between the hopper and thewheel to control the flow rate of the shot, gritof otherabrasive particles to the wheel. The hopper is provided with a sensing means 80, such as a switchm'eans extending through the side wallinto a lower portion of the hopper to shut the valve when the level of abrasive falls below the sensing means in the hopper.

In operation with the sealing strips 22 and 24in seal ing engagement with the surface to effect a substantially sealed relationship between the blasting head and said surface, subatmospheric conditions can be maintained within the head to effect the described directional flow of air about the sealing strips and for air washing the spent abrasive aswell as to carry off the collector which communicates with the interior of the blasting head whereby suchsubatmospheric conditions are maintained simultaneously with the effective removal of dust entrained with the air traveling through the blastchamber thereby to prevent'the iss'uanceof suchdust and dirt into the atmosphere'. Use can be made of-a dust collector of the conventional type with ducts 82 connecting the outlets 84 at the top-of the Special means are interposed between the ducts and the dust collector to permit the various movementsof the blast chamber hereinafter to be described to enable the blast head to conform with the contour of the surface being cleaned and for movement of the blast chamber over the surface for coverage of the surface during the cleaning operation. Such special connection means for a movable head is believed to constitute a new and novel construction which may be described and claimed in a separate application but which will also hereinafter be described to complete the description of the machine.

Having described the basic elements of the blast head and the operation thereof, description will now be made with respect to the mounting of the head on suitable supports for movement of the head vertically to cover a-verticalsection of the surfaceand laterally for coverage of a width of surface as well as movement in the direction toward and away from the surface to achieve the desired sealing engagement with the surface during the operation. The blast head'will also be gimbal mounted for rocking movement about a vertical yaw axis as well as horizontal about a pitch axis to conform the head to change in surface'contour in the vertical direction as well as in the horizontal direction and with means operative automatically or manually-to effect such'movements in response to changes in contour or curvature and tomaintain the pressure contact between the head'and surface sufficient to deflect the ends of the sealing

members

22 and 24 to maintain the desired sealing relationship.

The described assembly, including the blast chamber, spent abrasive collector, hopper and elevator are mounted for movement together in the vertical, lateral, forward I and rearward directions on suitable frame and guide members including a tower 90 formed of four spaced masts or

columns

92, 94, 96 and 98. The tower is preferably adapted to be shiftable alongside the wall for positioning. the blast chamber operatively to engage additional increments of the wall surface for treatment. This semi-stationary tower would-normally be stationary during the time the blast head is in operation, but it would be capable of being moved intermittently to a newposition alongside the work surface by means of a barge, tracked vehicle'or otherwise. A main frame 100 in theform of a rectangularly shaped section formed of a pair of vertically disposed laterally spaced apart angle members. 102 and 104 and a pair of horizontally disposed vertically spaced apart

angle members

106 and 108, joined one to the other at their outer ends, is mounted for guided up and down move ment between the

fixed'masts

92, 94, 96 and 98. For thispurpose, the

side members

102 and 104 support vertically spaced apart guide rollers .110 extending laterally into'operative engagement inside tracks 112 providedon the inner surfaces of the masts to guide the main frame during movement verticallyrelative to the main frame. The rollers 110 are mounted for free rotamounted for free rotational movement on a spindle supported at its ends between the masts at a level above the upper limit of travel of the main frame. The chain is connected at one end to the center of the upper crosswise extending angle member 106 of the main frame while the other free end, which depends from the sprocket wheel 118, supports a counterbalance 120 for the main frame and the elements supported thereby. Motor means,not shown, are provided for movement of the chain to raise and lower the main frame. It will be apparent that other-means for elevating and lowering the main frame relative to the supporting masts may be employed and that the vertical travel of the main frame relative to the masts will depend somewhat upon the length ,of the masts. In a practical modification, the masts are dimensioned to enable vertical movementof the main frame for a distance within the range of 30 to feet. Means other than the tower and fixed masts can also be used to support and provide vertical movement of the main frame and assembly. For example, the main frame and assembly could be supported and moved vertically by means of overhead cables, cranes, telescoping supports or other means. An'inner frame 130 is adapted to be supported on the main frame for sidewise movement relative thereto. Such inner frame comprises a rectangular section formed of interconnected, laterally spaced apart, vertically disposed channel members 132 and 134 and horizontally spaced apart upper and lower crosswise extending

channel members

136 and 138. I v Laterally spaced apart rollers'140 mounted for rotational movement on the upper and lower, horizontally disposed main frame members are adapted to be received in guiderails 142 on the underside of the

channels

136 and 138 of the inner frame members to permit theinner frame member to move laterally relative to the main frame member 100 to the extentpermitted by the portions of the mainframe between the fixed masts. Thus the extent of lateral movement of the inner'frame will be somewhat less than'the amount of vertical movementof the main frame. In the illustratedmodification, a lateral travel of about 4 to 10 feet can be easily designed into theunit. Thus the inner frame 130 is capable of vertical and sidewise movement relative to the fixed m asts. I

Lateral movement of the inner frame 130 relative the main frame 100 is adapted to be effected by means of a pressure fluid'operated piston and cylinder assembly in which the end of the piston 144 is anchored to either the main frame 100 or the inner frame 130 while the base of the cylinder 146 is anchored to the other of the frame members with the piston and cylinder extending horizontally to effect lateral displacement of the inner frame relative the main frame. It will be apparent that the desired relative displacement between the frame members such as a horizontallydisposed rack secured to the inner frame in operative engagement with a motor operated pinion gear supported by theother frame with the pinion in engagement with the rack to .effect relative lateral movement of the inner frame to the main frame in response to motor operation of the gear in one'direction or'the other. a I

The inner frame 130'independently supports a head frame 150 in a manner to permit forward and backward movementrelative to the inner frame and the main H 7 frame and masts in the direction toward and away from the surface to be cleaned. As illustrated in FIG.- 6, the

130'are laterally spaced by an amount to receive the head frame supporting the blast therebetween. Secured to each of the inner edges of the laterally spaced apart vertical channel. members 132 and 134 are a pair of longitudinally disposed, inwardly platforms or rails 158 reside adjacent the-bottom side of thelower plat forms 1'53 toestablish a guided-support for the" head frame while permitting movementof the head frame horizontally in a direction perpendicular to the inner frarne. 1H Means are schematically illustrated in FIG. '7 of the drawingsfor actuation of the head frame for movement relative the. inner frame. As illustrated in the drawings,

chamber 7 side channel members 132 vand 134 of the inner frame 7 8 offset portion of the yoke, extends rearwardly for operation of a four-way valve 180 mounted on the head frame;

Change in surface contour will react through the rollers to cause the yoke to rock about its pivot'with cor? responding displacement of the arm 178 in one direction orthe other depending upon the change of angle of the yoke. Rocking movement of theyoke about its pivot in the clockwise direction will operate to 1 laterally spaced apart arms 192 and 194 which extend one suchi means comprises another pressure fluid operated piston andcylinder assembly in which the end of the piston 160 is pivotally attached to a-portion of the head frame 150 while the base of the cylinder 162 is pivotally attached to a rearward portion on the inner 7 frame 130. Pivotal means for attachment are employed to enable the gimbalrmounting of the blast chamber for rocking movement about its vertical and horiaontal axes relative the supporting'framesl T it will be understood that other conventional means matic'ally to' adjust the head in the'direction toward and away fromgthe surface being cleaned for equalizing pressure on the sea ls'in' amanner to maintain the desired scaling relation between the sealing members and the surface.

In the illustrated mbdificatiomthe means-for adjust-. ment of thehead about its pitch axis allows for change in the'con'tour of the'ships hull in the vertical direction.

In the illustrated. modification, such means comprises a yoke 170 on each side of the head pivoted at its center on pivot pins .172 rigid with the sidewall of the blast chamber for free rocking movement relativethe hous ing about the pitch axis. Casters 174, in the formof rubber rollers, are rotatably. mounted on the'vertically spaced, apart ends of the yoke in position to extend for .wardly of the face of the blast head into rolling engagement withvertically'spaced apart portions of the surface 116 being'treated, when the blast-head is in proper positionof use. An arm 178; pivoted at one end onto an the pitch axis'and about the-yaw'axis as well as autodescribed;

alongside the blast housing with pivot pins for trunnions.196 extending inwardly. into engagement with bearings on the sidewalls of the blast'housing pivotally to mount the blast housing for rocking movement; This the-blast housing of the blasting head is capable 'of rocking-movement about its horizontal axis relative the.

head frame. Rocking movement :of the blasting head relative the head frame is effected by a pressure fluid operated .piston and cylinder assembly with the cylinder 198 anchored at the far end to the yoke-190 while the piston 200 is pivotallysecured at its free end to a portion of the head vertically offset. from the pivotal axis. The piston and cylinder are controlled .by the four-way valve 180 for operation in one direction or the other for angular adjustment of the'head. .For pivotal support of the head for rocking move-. ment-about'the yaw'axis, the head andyoke are supported as a unit on a vertically disposed shaft 196 which extends through a vertically aligned opening through the center of-the yoke 19.0 thereby-to mount the yoke for-rocking movement aboutthe shaftasthe yaw axis. Angular adjustment of the yoke and head about the shaft is, effected by apressurc fluid operated piston and cylinder assembly 202 having the cylinder 204 pivotally secured .onto a bracket 206 rigid with the head frame 150' while the piston 208 is pivotally secured'to a portion of the yoke190 l aterally offset from the yaw axis 194. i

As-illustrated in FIG. 6, the entire head assembly which now includes theblasting head, thefyoke 190, in which the blasting 'head is mounted for rocking movement about the pitch axis, and the head frame 150 on which the yoke 190 is mountedifor rocking movement about the yaw axis, is supported on the rollers-140for relative movement injthc direction toward and away from the surface to be treated by the pressure fluid piston and cylinder assembly 1 60-162 as previously Rocking movement of the head'about its' yaw axis and endwise positioning of the head for sealing engagement with the surface is controlled by a pair of proximisensingmerhbers are capable of 210 as one or the other loses contact with the surface by reason of change in surface contour.

The laterally spaced apart sensing heads also operate switch means for actuation of the piston and cylinder assembly 160-2 between the inner frame 130 and the head frame 150 for adjustment of the head frame and blasting head in the direction toward and away from the surface in response to operative pressure between the surface and the sensing members therebyautomatically to adjust the head for the desired pressure contact with the surface.

The laterally spaced apart sensing members can also operate through suitable means to close the valve '76 and shut down the flow of abrasive to the throwing wheel responsive to loss of contact between both of the sensing members and the surface thereby to indicate complete separation between the surface and head and loss of the desired sealing relationship therebetween.

It will be understood that the controls achieved by the rollers 156 can be embodied in thesensing members thereby to enable elimination of the rollers and supporting structure. Under such circumstances,

. sensing members could be arranged in vertically spaced relation as well as in laterally spaced apart relation to detect changes in curvature or angle of the wall while at the same time sensing sealing engagement with the wall.

The main frame also supports a horizontally disposed platform 220 on which an operator may stand for vertical movement alongside the blasting head and a control panel 222 alongside the platform with control buttons for l the various operations under. the control of the operator. A 7

While the dust collector can be mounted on the main frame for vertical movement with the blasting head,it is preferred separately and stationarily to mount the dust collector as a unit separate and apart from the main frame, especially when the collector is of the dust tube type. When use is made of a separately supported stationary dust collector for use with a vertically movable dust generator, such as the described blast assembly, long expandable ductwork of the telescoping type is required in order to maintain proper communication between the dust collector and generator. Ductwork ofthis type is incorporated with a large number of problems as well as high cost. A new and novel concept for communication between a vertically movable dust generator and a stationary dust collector or separator has been developed nicating the longitudinally movable dust generator or iii blast housing with the stationary dust collector 230 comprises an elongate, vertically disposed rigid duct 232 of rectangular, triangular, or polygonal shape, having an open outer wall 234 which is covered throughout its length by a flat, flexible or rubberlike belt 236 dimensioned to have a length slightly greater than the length of the opening and a width slightly greater than the width of the opening so that the lateral edge portions of the belt will overlap flanged edge portions extending inwardly a short distance into the opening from the side edges of the adjacent side walls of the duct. The upper and lower end portions of the belt236 are fixed to the duct with the opening in the duct dimensioned to have a length corresponding to the vertical travel of the main frame. Box 240 having upper and

lower walls

242 and 246 converging to form a V-section therebetween and enclosed by

side walls

248 and 250, is mounted for vertical sliding movement with the main frame while in engagement with the open side of the duct in substantially sealing engagement therewith so that the open side of the V-shaped box faces the open side of the duct for complete communication therebetween. I

The box is dimensioned to'have a width corresponding to the width of'the open wall of the duct with the spaced relationship between the

side walls

248 and 250 corresponding to the width of the belt. I

Within the box an upper and a

lower roll

252 and 254 respectively are mounted for free rotational movement in the upper and lower ends of the box and a third roller 256 is mounted for free rotational movement at the apex of the V-shapedbo'x section. Betweenthe upper roller 254 and the roller 256 at the apex, there is provided a rigid guide plate 258, secured at its lateral edges to the side walls of the box. The guide plateextends from the upper roll 252 to the center roll 256 from a point spaced a short distance below the lower periphery of the upper roll 252 toa tangency with the upper periphery of the center roll 256 Another similar guide plate 260 extends from a tangency with the lower periphery of the center roll 256 to a point spaced upwardly a short distance from the upper periphery of the lower roll 254.

In its mounted relationship, the rubber-like belt 236 extends into the box about the lower periphery of the upper roll 252 over the upper guide plate 258 to the rear of the box over the center roller 256 and then under the lower guide plate 260 to the lower roll 254. Thus the belt is deflected from the duct throughout the length between the upper and

lower rollers

252 and 254 of the box to enable communication between the box and the duct while maintaining asealed relationship therebetween independently of the vertical position of the box relative the duct. Thus the flat rubber belt 236 coversthe open side of the duct throughout the entire length of the opening except the area the guide plates for guided support during travel through the box and about the rollers and to assist such guided support, it is desirable to form the ends'of the supporting

plates

258 and 260 with curvilinear lips 262.

An opening 264 is provided in a side wall of the box I and the flexible tubing 82connects the inlet opening 264 with theoutlet openings 84 in the upper wall of the blast chamber. Another opening is provided in one of the side walls. of the vertical duct and tubing or other means communicates the outlet opening of the duct with'the inlet opening to the dust collector 230.

Suction from the dust collector operates to hold the flat belt 236 in substantial sealing engagement at its lateral edges with the duct 232. The box is connected to the main frame for movement vertically relative the duct with the blast assembly. Thus as the assembly moves-up and'down the masts, the box 240 moves with the assembly relative the duct and the belt is displaced awayfrom the wall through the length covered by the box.

Various means may be provided for guiding the box 240 in sealing engagement between the lateral edges of the duct. One such means comprises spaced flanges of the lateral edges of the side walls of the box to define a recessed portion therebetween in which the flange portions extending inwardlyfrom the side walls of the duct are received in sliding engagement. It will be understood that the vertical duct'can be of triangular or other polygonal shapes and that other means, may be 12 and the surface becomes broken thereby to avoid loss of abrasive or the exhaust of dirt and dust intothe atmei'gjhere.

ile the sealed relationship is maintained between the head and the surface, spent abrasive is recovered for use and dirt and dusts are withdrawn from within the chamber for separation without being exhausted into the atmosphere. 1

Thus a continuous operation is achieved which permits efficient and economical use to be made of more expensive. and reusable abrasive, and vwithout loss of abrasive or exhaust of dust and dirt into the atmosphere. A much quieter operationis provided by reason of the seal that is maintained about the area being worked.

It will be understood that changes may be made in the details of construction, arrangement and operation without departing from the spirit of the invention, especially as defined in the following claims.

provided for sliding. engagement of the box relative the open side of the duct.

In operation, the main frame is raised to the desired level alongside the surface to be cleaned. The head frame-is then displaced forwardly until the desired sealvhag-engagement is established between the sealing members and the surface andthereafter the abrasive material is metered by the valve .76 for flow from the feed hopper 62 to the throwing wheel.

The wheel throws the abrasive forwardly at high velocity through the head opening onto the work surface and the spent abrasive falls gravitationally downwardly over the shed plates 40-48 to the bottom of the housing for'linear displacement bylthe screw 54 over the screen member 56. The reusable abrasive particles which pass through the screen are returned to the hopperby the tube elevator.

The suction from the dust collector causes air to be drawn into the blast housing for flow upwardly over the ends of the shed plates to air wash the abrasive falling from .theends of the plates whereby thedusts and dirt are removed from within the housing through the. outlets 84 to the dust collector.

While continuing to operate, the head can be moved up or down by the lift chain .116 to coververtical sec-. tionsof the surface and it can be moved laterallyfor covering an area ofthe surface without readjustment, of the entire assembly. After blast cleaning a vertical section, of the surface, ,the blasting operation can be stopped and the tower with the entire vassembly moved to a new location for blasting another vertical section.

The guiderollers and the sensing members operate automatically to adjust the head angularlyabout its horizontal or. vertical axis to conform the head to any change in contour of the surface. The sensing members lclaim: 1 1 1 1. In an assembly which makes usev of a dust generator having vertical movement and a stationary dust collector, means interconnecting the vertically movable dust generator withthe dust collector in amanner to establish a substantially scaling relationship therebetween comprising a vertically disposed duct having an'open side dimensioned to have a length cor responding to the length of vertical movement of the dust generating means, a belt of resilient material covering said open side without attachment thereto throughoutvthe length corresponding to the length of travel of the dust generating means, a head boxmovable .with said dust generating means in a vertical direction'and having an open side in facing relation with the open side of the duct and with sidewalls of said headbox being spaced to correspond with the open side'of the duct and to receive the belt therein, deflector means within the headbox over which the belt travels to deflect the belt in the direction away from the open side of the ductin' at least a portion of the area covered bythe head box to provide direct 'communicationbetween the interior of the head box and-the duct, conduit means communicating the interior of .the head box with the dust generator, other con duit means communicating the interior of the duct with the dust collector and ,means for generating subatm'ospheric conditions. within the duct constantly to urge the belt into sealing engagement with the portion of the duct not covered by the head box. r

2. 'A device as claimed in claim 1 in which rollers'are mountedwithin'the head box for free rotational movement about axes which definethe vertices of a triangle with two of the rollers adjacent the open side and in which the belt passes through' the head .box about the inner peripheral portions of the pair of rollers and about the outer peripheral portion of the roller in between to guide the b elt in a triangular path through th eheadbox'. I

3. Adevice as claimed in claim 2 which includes "a guide plate extending from the upperof the pair of rollers to the intermediate roller and from the intermediate roller to the lower of the pair of rollersto support the portions of the belt between the rollers.

Claims

1. In an assembly which makes use of a dust generator having vertical movement and a stationary dust collector, means interconnecting the vertically movable dust generator with the dust collector in a manner to establish a substantially scaling relationship therebetween comprising a vertically disposed duct having an open side dimensioned to have a length corresponding to the length of vertical movement of the dust generating means, a belt of resilient material covering said open side without attachment thereto throughout the length corresponding to the length of travel of the dust generating means, a head box movable with said dust generating means in a vertical direction and having an open side in facing relation with the open side of the duct and with side walls of said head box being spaced to correspond with the open side of the duct and to receive the belt therein, deflector means within the head box over which the belt travels to deflect the belt in the direction away from the open side of the duct in at least a portion of the area covered by the head box to provide direct communication between the interior of the head box and the duct, conduit means communicating the interior of the head box with the dust generator, other conduit means communicating the interior of the duct with the dust collector and means for generating subatmospheric conditions within the duct constantly to urge the belt into sealing engagement with the portion of the duct not covered by the head box.

2. A device as claimed in claim 1 in which rollers are mounted within the head box for free rotational movement about axes which define the vertices of a triangle with two of the rollers adjacent the open side and in which the belt passes through the head box about the inner peripheral portions of the pair of rollers and about the outer peripheral portion of the roller in between to guide the belt in a triangular path through the head box.

3. A device as claimed in claim 2 which includes a guide plate extending from the upper of the pair of rollers to the intermediate roller and from the intermediate roller to the lower of the pair of rollers to support the portions of the belt between the rollers.