US3026789A - Abrasive-blasting system - Google Patents

Description

March 27, 1962 Filed Dec. 3, 1959 w. H. MEAD 3,026,789

ABRASIVE-BLASTING SYSTEM 5 Sheets-Sheet l 5 INVENTOR. WILL/AM H. MEAD ii '"i liil 5 Sheets-Sheet 2 Filed Dec. 3, 1959 INVENTOR. WILL/AM H. MEAD A ATTORNEY March 27,, 1962 w. H. MEAD ABRASIVE-BLASTING SYSTEM 5 Sheets-$heet 3 Filed Dec. 3, 1959 INVENTOR. WILLIAM H- MEAD AT TOR/VEY 3,026,789 ABRASIVE-BLASTINE SYSTEM William H. Mead, 202 Camino Al Lago, Atherton, Calif. Filed Dec. 3, 1959, Ser. No. 857,042 15 Claims. (Cl. 98-415) This invention relates to an abrasive-blasting system. More particularly, it relates to an improved blast-room floor structure and an adjoining abrasive-separation unit which, together, provide for removal of the spent abrasive from the blast room and the separation thereof from the conveying airstream.

Abrasive-blasting Systems are well known in the art and comprise, in general, a blast room in which articles are subjected to surface treatment by abrasive particles plus means to recover and clean the spent abrasive so that it can be recirculated for use again in the blast hose. A blasting system which provides these operations is described in my Patent No. 2,912,918 to William H. Mead, wherein the abrasive used in the blast gun falls down through a floor comprising a plurality of hopper-like pockets and empties through apertures from the pockets into ducts which pass underneath.

In order to afi'ord the operator proper visibility in the blast room, ventilation is provided by the entry of air through the ceiling in a uniform distribution pattern, the air being drawn downward through the hopper apertures spaced substantially evenly over the entire floor area. The ventilation air also provides the necessary air currents that carry the used abrasive and waste out of the room through the aforementioned ducts.

A first major problem associated with the above type of closed-room blasting system was to provide a blastroom floor construction that was capable of trapping the spent abrasive and then guiding it into the path of a conveying airstrearn so that it could be removed from the floor. It was further essential that these two principal functions must be provided by a construction relatively simple yet sufficiently strong and rugged to support heavy loading. The early prior art in abrasive recovery systems relied on a single hopper, which required either a raised floor or excavation to accommodate the structure. The patent to Arnold, US. 2,839,338, eliminated the need for the single hopper by use of a plurality of small hoppers. However, floor constructions of the Arnold type heretofore relied on a complicated arrangement of parts to provide both the collecting hoppers and ducts. These priorart floor structures were thus relatively thick and bulky, in addition to being costly to construct and difficult to maintain.

Another problem which arose in connection with blasting systems having Arnold-type floor structures Was in removing the abrasive particles carried through the floor ducts, where the airstream was used both to ventilate the room and also to convey abrasive from. the blast room. Adequate ventilation for the blast room requires a large amount of air and a considerable excess over that needed for abrasive conveyance. The large flow of ventilating air created generally high air velocities in the conveying ducts and thus aggravated the problem of subsequently slowing down this air when it left the ducts, in order to remove the abrasive from the airstream when reclaiming it.

It is therefore an important object of the present invention to provide a greatly improved multi-hopper floor construction for a blast-room in combination with an adjoining abrasive concentrator-separatorso that the abrasive particles trapped by floor hoppers are easily carried from the blast-room floor for separation from the airstream by gravity, as the bulk of the air flows upward and out of the concentrator to the dust filter.

"2 26,789 EQQ w Another important object of the present invention is to provide a combined particle-collecting and air-conveying fioor construction, wherein the bottom of the collecting component is adjacent and substantially on the same plane as the conveying duct. The present invention thus provides an improved multi-hopper floor construction wherein the thickness of the floor need be no greater than the depth of the hopper. This novel duct-hopper construction provides either a thinner floor, having hoppers of the same size, or a larger size of hopper for a given floor thickness, since the floor thickness heretofore amounted to the sum of. the hopper depth and the duct depth.

Another object of my invention is to reduce the local wear problem caused by abrasive particles dropping from the hopper onto the bottom of the duct. This object is achieved by providing *a side exit for the abrasive near the bottom level of the hopper, whence it may be dispersed across the floor of the duct as it is picked up by the airstrearri.

Another object is to greatly reduce the fabrication complexity of prior multi-hopper floor constructions. The present invention, using the novel duct-hopper construction, reduces the amount of sheetmet-al-forming operations, in addition to the number of production-joints, required in fabrication. Yet my invention makes it possible to modify the original floor configuration to provide additional hopper and duct capacity and added airflow, with only minor structural changes, where such performance characteristics are desirable.

Another object is to provide a multi-hopper floor and concentrator combination, wherein the combined outlet area of the floor ducts is relatively small, as compared with the inlet area of the concentrator, thus providing a substantial expansion of the air as it enters the concentrator. This expansion acts to slow the air in the concentrator to aid abrasive separation and eflicient diversion of air and dust.

Another object is to prevent clogging of the duct walls and keep the blast-room floor free of debris, abrasive, etc., at all times. This object is achieved by providing a concentrator wherein the abrasive particles separated from the airstream are collected by a combined trough-and-duct construction with the bottom of the trough being substantially on the same plane as the duct.

Another object of the invention is to provide a multihopper floor construction for a blast-room having uniform downdraft ventilation, wherein orifices which connect the collecting-hopper and conveying-ducts are so varied in size from one side of the room to the other that the airflow through each hopper is the same. In my previously issued Patent No. 2,912,918, I discussed thor oughly the necessity for decreasing the size of the hopper orifices communicating with the conveying duct proceeding from the upstream end of the ducts toward their outlets, and of progressively increasing the cross-sectional area of the ducts toward their outlets, both of these measures serving to provide uniform downdraft ventilation across the floor. In the present invention, with the comppact duct and hopper construction, I have not only again provided for this feature but have presented improvements in this field.

It will be apparent from the following description that, although the invention is discussed in connection with blast-rooms, it can also apply to other types of rooms requiring uniform downdraft ventilation and removal of particles.

Other problems solved by the invention, as well as various objects and advantages, will appear from the following description. A preferred example is described in conformity with 35 USC 112, but is not intended to Patented Mar. 27, 1962 limit the invention to the specific details enumerated, because the invention is clearly defined in the appended claims.

In the drawings:

FIG. 1 is a plan view of an abrasive blasting system, showing the blast-room and an adjoining concentrator unit with portions broken away to show a floor construction embodying the principles of the invention.

FIG. 2 is a fragmentary plan view showing the floor of the blast-room in FIG. 1 in detail, with portions broken away to show the interior construction of the ducts.

FIG. 3 is a fragmentary view in perspective of a portion of the floor, taken from a rear corner of the blastroom with the sidewall removed to show in detail the construction of the troughs, ducts, and hoppers.

FIG. 4 is a plan view showing a diamond-shaped floor partition, and directly below it is a projection showing the partition in elevation.

FIG. 5 is an enlarged fragmentary view in section of a portion of the floor, taken along the line 5-5 of FIG. 2.

FIG. 6 is a view in elevation and in section, taken along the line 6-6 of FIG. 2, showing the internal duct structure.

FIG. 7 is a fragmentary view in elevation and in section showing the blast-room with its floor connected with the concentrator unit, showing also some details of the internal concentrator construction.

FIG. 8 is a fragmentary view in perspective of the floor and the concentrator unit shown in FIG. 7, with portions broken away to show the internal construction of the concentrator.

FIG. 9 is a fragmentary view in elevation and in section taken along the line 99 of FIG. 7, showing the lower portion of the concentrator and the duct inlets of the floor. The deflector plate and the collecting discharge duct are shown in phantom.

Broadly considered, my invention is directed to an improved abrasive blasting and reclaiming system 10 comprising a floor 18 of novel construction in combination with an adjoining abrasive concentrator-separator unit 22. These two basic components cooperate together within the system to trap the spent abrasive, separate it from the conveying airstrearn, and then collect it for reclamation and subsequent re-use in the blasting gun.

The total system 10 which incorporates my novel fioor 18 and concentrator 22 of the present invention is shown in plan view in FIG. 1 and comprises a blast-room 11 which is essentially a chamber enclosed by end walls 12 and 13 and side walls 14 and 15. Side walls 15 may be hinged to form doors for access to the room 11. The room 11, shown in greater detail in FIG. 7, may have a roof 16, or some form of air inlet maze which may or may not include a false ceiling.

The main floor 18 (FIG. 2) of the blast-room 11 comprises a plurality of the collecting hoppers 19 into which falls the spent abrasive and waste, and through which the downdraft of room-ventilating air passes. The hoppers 19 are uniquely arranged in series so as to communicate, by means of orifices 20, with longitudinal ducts 21 which are located alongside the hoppers 19 and which convey the abrasive and waste particles in the stream of ventilating air from the floor 18 to the adjoining concentrator 22. The concentrator 22 receives the large volume of ventilating air, separating out the reusable abrasive particles and concentrating them in a discharge duct 82 (FIG. 7) for conveyance to a cyclone reclaimer 23. During the separation process in the concentrator 22, the air, dust, and light waste which would otherwise contaminate the spent abrasive are carried away from an upper end 24 of the concentrator 22 to a dust separator 25, which may be a bag filter, wet precipitator, or other apparatus for separating dust from the air. The

dust is disposed of, while the clean air may either be exhausted into the exterior atmosphere or recycled to the room 11.

The forced draft of ventilating air may be drawn through the room 11, the conveying ducts 21, and the concentrator 22 by a suitable blower 26 (e.g., fan) in or adjacent the dust separator 25 (FIG. 1). The abrasive separated from the ventilating air in the concentrator 22 may be drawn, in turn, through a conduit 27 to the cyclone reclaimer 23 by means of a second, smaller fan, 28. The cyclone reclaimer 23, which may be of the well-known centrifugal type, removes all the remaining air from the abrasive and returns it by means of the conduit 29 to the top end 30 of the concentrator 22, leaving the reclaimed abrasive in the bottom of the cyclone 23 to be recycled and used again within the blast-room 11.

In blast-room systems of the type described, some form of air maze should be provided for adequate intake and distribution of air, preferably with sufficient back pressure to assure even, uniform distribution. A true roof 16 is not an essential feature of the blast-room 11, but where the room is out-of-doors, rather than in a building, the roof 16 gives protection from rain, wind, and snow. In FIG. 7 I have shown roof inlets in the form of shielded chimneys 31 which provide the necessary air flow pattern and yet protect the room interior from exposure to rain. A detailed description of the shielded chimney 31, along with other types of blast-room inlets and air-maze bafiie construction, may be found in my US. Patent Serial No. 2,912,918, to William H. Mead.

Referring to FIGS. 2-6, I will now describe in greater detail the novel improved floor 18 of the blast-room 11, which comprises an important feature of my invention. A supporting or perforate floor 17 generally rests on the main floor 18 and may comprise perforated steel plate or Wire mesh or other perforate structure strong enough to support an operator and the work-piece being surface treated. For example, A steel plate with holes about /2 in diameter, spaced to provide between about 45% to 55% of the open area, is satisfactory. The perforate fioor 17 is unnecessary, however, when the blasting is done remotely, without an operator present in the room, and the objects to be blasted can be adequately supported without a perforate screen. When heavy blasting work is to be done, the article being blasted may be supported by a dolly, wheeled into the room 11 on one or more railroad-type rails (not shown), or other type of conveying equipment may be used. As will be apparent from the following description, my novel floor 18 has unusually good strength characteristics, which enables it to support substantial loads without the perforated plate 17. How ever, it usually is an important element of the room, not only for convenience in walking and for support, but also as a scalping-plate to catch large flakes, etc., of waste and prevent them from plugging the hoppers.

The hoppers 19 are formed in part by a series of longitudinal members 35 which are V-shaped in cross-section, lying at a right-angle preferably, forming two sides 36 of equal width which are joined along an apex 37. A portion of the floor 18 in perspective is shown in FIG. 3. These V-shaped members 35 are inverted and arranged in parallel and attached by any well-known means, such as welding, to a rectangular baseplate 38, with their apexes 37 pointed upward and the edges of adjacent side-member 36 abutting. Thus, a series of troughs 39 are formed between the adjoining members 35 on their upper side, while conveying-ducts 21 of triangular cross-section are formed under each member 35. The base-plate 38 may be mounted on foundation blocks 42 and attached to the sidewalls 12 and 13 to form the basic supporting structure for the blast-room 11, as shown in FIG. 6.

To form the hoppers 19, diamond-shaped partitions 43 (FIG. 4) are placed within the troughs 39 and attached in some convenient manner, as by welding, to the sides 36 of each trough 39, in end-to-end sequence as shown in s eaves FIG. 3. The diamond partitions 43 are preferably bent at approximately a right angle, so that when they are placed in position within the troughs 39 the hoppers 19 are formed with an inverted pyramidal shape, having sides which slope at least 45 with respect to the baseplate 38. At the bottom of each hopper 19 is located an orifice .20, of predetermined size and shape, which provides a passage to the adjoining duct 21. In constructing my floor 18, I have found that the orifices may be formed conveniently by stamping slots in the edges of the metal blanks before they are bent to form the longitudinal V- shaped members to be used in ducts 21. The slots or orifices 20 are formed at predetermined intervals, so that when the floor is assembled they occur at the ends of the diamond-shaped partitions 43, thus providing an opening at the bottom of each hopper 19.

An important feature of my invention is that only some of the inverted V-members 35 of the floor 18 need be utilized as ducts 21. As shown in FIG. 2, every other inverted V-member 35 may be utilized as a conveying duct 21 while alternate V-members are kept as dummy ducts 40. Also, only the active duct members 21 have slots 20 at intervals along the edges of both sides 36 to provide communication with adjoining hoppers 19. The dummy ducts 46 are sealed at their upstream end against wall 12 of the blast-room and are sealed at their downstream end by a header-plate 41, shown also in FIG. 2. If increased airflow capacity from the blast-room 11 is desired, it requires only a simple modification to remove a dummy V-member 40, provide it with edge-slots 2t), and replace it on the base-plate 3% Normally, I have found that the alternate conveying ducts 21 are adequate to accommodate the removal of ventilating air from the blast-room 11. As shown in FIG. 9, another advantage of using alternate ducts in the novel floor and concentrator combination of the present invention is that the outlets 65 from these ducts 21 are then conveniently aligned with spaces 81 between the feeder troughs fit) just inside the concentrator inlet opening 66.

FIG. 5, a cross-sectional view, shows how the abrasive material trapped in a hopper 19 moves laterally into the adjoining duct 21 without having to be dropped to a duct below the hopper.

As disclosed in my recent Patent No. 2,912,918, it is necessary to maintain equal airflow through each hopper 19, in order to achieve uniform downdraft ventilation in the room 11 and effective conveyance of the entrained particles. The pressure within each duct 21 at the downstream end (nearest the concentrator 22) is substantially lower than at the upstream end (due to the pressure drop along the duct necessary for maintenance of a substantially constant conveying velocity). Therefore, to achieve equal flow through each hopper 19', the orifices or slots 20 opening from the hopper 19 into the downstream end of each duct 21 must be proportionately smaller than the orifices at the upstream end, and a proper balance of duct pressure and orifice size at each hopper must be determined.

The initial fiow through the ducts 21 is provided by openings 48 in the duct-walls 36 at the duct-end 51 (see FIG. 3). The openings 43 may be protected by a baffle 46, shown also in FIG. 7, that may extend inwardly from the side-wail 12. Air passes downwmd through the perforate-fioor 17 into each first hopper 19a, then travels laterally under the lower lip 45 of halide 46, upward again through perforate-floor 17, laterally over the end of hopper 1% adjacent the wall 12, downward again through the perforate-floor 17 to enter duct 21 through openings 48. The end-hopper 19a empties into the duct 21 through the first orifice 2% which is as large as, or larger than, the largest orifice 2% in the series, though it may be smaller than the opening 48.

As stated above, the orifice sizes are carefully calculated, as are the duct shapes and cross-sectional areas past each orifice. In my Patent No. 2,912,918, I presented a formula for defining the size of the circular orifices connecting hoppers and ducts as used on the floor structure described therein. However, in the unique floor construction of the present invention, which utilizes the aforementioned slot-type apertures 20, I discovered that the following equation can be used to best define the area of the apertures:

where A is the area of any particular slot, in square feet;

Q is the desired volume rate of air to pass through the slot in cubic feet per minute of free air;

C is the coefficien-t of entry of the air, a factor depending on the design of the hopper; and

P is the static vacuum in the duct adjacent the orifice, ex-

pressed in inches of water, relative to the pressure in the room.

In the design of the present invention, C has been determined experimentally to be about 0.80. It may vary somewhat if different shaped hoppers are used, but can be determined experimentally or can be derived from tables by those skilled in this art.

The static vacuum P is determined by the cross-sectional shape and area of the duct and, for a given air velocity and a given fioor, can be calculated from available tables. The volume flow rate Q of the air can be selected and governed, the size of the room and the horsepower of the blower for pumping the air being taken into account. Thus the proper area of each slot can be calculated. Each parallel duct wili have the same orifice pattern along its length.

The net result is that there will be the same fiow through each hopper 19. Thus, in a room 11 having a volume flow rate Q of cubic feet of free air per minute per square foot, and where the hoppers 6% are 6" square at their upper end, every hopper 6% in the room will have 20 cubic feet of air passing through its orifice each minute.

In some instaliations, due to manufacturing tolerances, installation tolerances, and other factors, the theoretical values may not be fully accurate. So, after installation, each orifice may be measured for P, the static pressure, by a manometer inserted therein from above. If corrections are necessary, the orifice opening may be reamed to widen it, or a washer may be inserted to narrow it.

Where the first orifice 20a empties into the duct 21, near its upstream end 51, the duct 21 has a minimum of cross-sectional conveying area, which then increases progressively downstream. To provide this variation in crosssectional area, a vertical V-shaped filler partition 50 (FIGS. 2 and 6) is attached within the upstream end 51 of each air-conveying duct 21 and fixed to the base-plate 33. The partition 54) is positioned with its open end 52 adjacent the wall 12 farthest from the concentrator 22 and has side-members 53 having short, straight sections 54 which are initially parallel and then converge to an apex 55 within the duct 21 at a point downstream. Attached to and covering the top of V-shaped partition 50 is a fiat filler-plate 56 which is rectangular in shape and extends from the upstream end 51 of the duct 21 to the end of the partition 56. Integral with the filler-plate 56 is a triangular section 57 (FIG. 2) which is bent upward within the duct 21 in a downstream direction and attached, as by welding, along the inner sides of the duct 21 with the point 58 of the triangular section 57 contacting the inner apex 37 of the duct 21 at a predetermined point downstream. As shown in FIG. 2, each orifice 2t adds air .to the expanding duct 21 as it proceeds downstream until at point 53 the percentage of air being added by each orifice is relatively small and the full cross-sectional area of the duct 21 now becomes available and is sufficient to carry the conveying airstream for all adjoining hoppers 19.

The through-passage of the duct 21 can be very narrow at the upstream end 51 because no substantial amount of abrasive can get into the passage 48. The introduction of a certain amount of substantially abrasive-free air through the passage '48 at the duct end assures a flow of air horizontally through the full length of the duct 21 and enhances movement of abrasive and waste from along the openings a, 20b, etc. This means that abrasive and waste will always be moved by air moving horizontally through the duct 21, as well as by the air that enters the duct 21 along with the abrasive through each hopper 19. Yet the opening 48 is not made so large as to divert any large proportion of air, for that would cancel the downdraft etfect. The proportions must be adjusted for the stated ends in view.

The variable shape of the ducts 21, as provided by the above-described structure, is important in order to get uniform downdraft ventilation, for the same amount of air should leave each square foot of floor. The increase in cross-sectional area of the duct corresponds to the amount of air added at each opening 20a, 20b, 20c, etc. The width is increased, first, by the partition 56, to prevent piling up of abrasive adjacent the opening and then, when a substantial flow of air is assured, the depth is increased by means of the slanted triangular section 57. In this way, the air flows straight down from the maze or room-ceiling to the ducts 21, without being diverted to some portions of the room more than others.

Of course, where blast-room operations do not require the uniform downdraft feature, the refinements such as the variable duct passage and orifice size can be eliminated and the novel floor construction of the present invention then can be simplified to an even greater degree.

A shown in FIGS. 7 and 8, the duct outlets 65 terminate along the lower side 13 of the blast-room 11 and open directly into the lower portion of the concentrator unit 22. The concentrator 22 is rectangular in shape, having side- walls 60 and 61 and end- walls 62 and 63 and a top section 64 which may be assembled according to well-known sheetrnetal construction practices. As the abrasive-laden air of relatively high velocity leaves the floor-duct outlets 65, it passes into a large inlet opening 66 of the concentrator 22. The concontrator 22 has a much larger area than the combined area of the duct outlets 65, thus causing the air leaving the ducts 21 to decrease rapidly in velocity as it enters the concentrator 22. This velocity reduction is essential in order to separate the abrasive particles and debris from the airstream. After entering the concentrator 22, the air-and-abrasive is deflected upward with decreasing velocity by a deflecting plate 67 which is supported by foundation frame 68. The deflecting-plate 67 is fixed lengthwise to the bottom 69 of the concentrator 22 near the inlet side 60 and slants upward at an angle of approximately to connect with the opposite sidewall 61. To prevent wear due to the constant impingement of the abrasive particles on the deflector-plate 67, I prefer to attach a layer 70 of rubber material on the upper face of the plate 67.

Above the deflector-plate 67, horizontal baflie-plates 71 and 72 are fixed by brackets 73, 74 or by welding to alternate sidewalls and 61. These baflles 71, 72 extend inwardly and downwardly at approximately 45 angles and provide a twisting path for the airflow which further retards its velocity, so that the abrasive particles and debris will more readily be removed from the airstream and precipitate downward before the air leaves the concentrator 22. Vertical bafile-plates 75 are installed in the concentrator 22 at intervals along its length and extend from the bottom 69 to a point near the top section 64. The vertical baflles 75 direct the main flow of air upwardly until it reaches the upper portion of the concentrator which forms in essence a plenum chamber 76. When the flow of air reaches the plenum chamber 76 it is then free from abrasive and any large particles of debris and contains only dust as it passes through the upper end 2 of the concentrator to the dust filter 25.

As shown in FIGS. 7 and 8 the falling abrasive is caught by a row of inclined V-shaped feeder troughs 89, which are attached each at their upper ends to the inner sidewall 60, from which point they slope downward at approximately 45 and are attached to the deflector-plate 67. The troughs are open-faced upwardly and are spaced at predetermined intervals along the inner sidewall 60. Vertical side-plates 78 are attached to each side of the troughs 80 and extend downwardly to the bottom section 69 forming spaces 81 between the troughs 80. These spaces 81 are aligned with the duct outlets 65 of the floor 18 so that the upwardly deflected airstream is directed easily by the side-plates 78 around the feeder-troughs 80.

Attached to the underside of the deflector-plate 67 and running lengthwise of the concentrator 22 is a collecting discharge-duct 82, which is positioned so that its bottom member 83 is on approximately the same level as the apex 85 of each inclined trough 80 on the opposite side of the deflector-plate 67. Apertures 86 through the deflector-plate 67 connect each inclined feeder-trough 80 with the collecting discharge-duct 82, so that abrasive which falls into the feeder troughs 89 is gravity-fed into the discharge-duct 82. The discharge-duct outlet 87 is located on the end-wall 62, Where it connects to conduit 27 which conveys the abrasive to the reclaimer 23. Above the discharge-duct outlet 87, a large door 88 is provided on end-wall 62 which can be opened conveniently to allow thorough inspection of the interior of the concentrator 22 and thus prevent the accumulation of large pockets of abrasive or debris which might otherwise get hung-up and reduce the efficiency of the system 10.

In operation, air enters from the exterior or the interior of a large building through an air maze or the shielded chimneys 31 of the blast-room roof 16 and is dispersed evenly downward to ventilate the room 11. The ventilating air passes directly down through the room 11 to the perforate-floor 17 and main-floor 18 into the hoppers 19 through the apertures 20 and into the conveying ducts 21. The quantity of air moving through the room 11 is kept at a uniform downdraft at all points within a short distance below the ceiling, by an even distribution of outlet-openings 20 from the many hoppers 19 and by the progressive increase in cross-sectional area of the ducts 21 between the walls 12 and 13, provided by the duct-filler members 50 and 54.

The spent abrasive and waste is carried away rapidly from the object being treated within the blast-room 11, by the downdraft of ventilating air, so that the operator has continuous visibility of his work piece. This abrasive and debris then falls through the perforate-floor 17 into the hoppers 19 and from there passes gradually through the slots 20 into the lower side-portions of the ducts 21, the force of the downdraft ventilation being sufiicient not only to keep the work clean, but also to carry the abrasive down the ducts 21 and into the concentrator 22.

The abrasive-laden air travels through the floor-ducts 21 at a relatively high velocity, typically of approximately 4500 ft./sec., to achieve adequate room ventilation. Upon reaching the concentrator inlet opening 66, the air expands and thus immediately slows down, while also hitting the deflector-plate 67 which turns the airflow upward. During its upward travel, the airflow, deflected by horizontal baflles 71, is further reduced in velocity to approximately 280 ft./min. The abrasive particles in the airstream strike the baflle-plates 71 and fall downward, Where they are ultimately caught by the feeder-troughs 8i) and fall into the collecting discharge-duct 82. The small fan 28 on top of the cyclone reclaimer 23 (FIG. 1) provides a suction force through conduit 27 connected to the collecting duct 82, which draws the separated abrasive into the reclaimer 23, Where it is processed for re-use. The main airflow through the concentrator 22 leaves at the outlet 23, from the concentrator plenum section 76 at the top, conveying this air to the dust-filter 25 where the dust is extracted by any of the Well-known means and the air is exhausted to atmosphere.

From the foregoing it is apparent that the present invention provides a greatly improved floor and concentrator construction for an abrasive blasting system. My device not only provides for the efficient separation and recovery of treating material from the ventilating and conveying airstream, but it also enables a simple and highly eflicient and economica1 construction, having several important advantages.

For example, my novel duct and hopper arrangement, when compared with previous multi-hopper floor devices, enables either reduction of the overall floor thickness of the blast-room 11, or larger and deeper hoppers to be made for any given thickness, since the conveying duct 21 is located on the same level as the bottom of the hopper 19, rather than being added on below the hopper. Thus, less material and labor are required in assembling the floor 18, and yet a more compact device is obtainable. Moreover, the arrangement of the inverted V-members 35 make it possible, by means of a simple modification, to vary the number of active ducts 21, either by blocking certain V-members 35 or by providing additional slots it where either a reduction or an increase in ventilation airflow is desired.

The movement of the abrasive and debris as shown in FIG. 5, in passing more or less laterally from the bottom of each hopper 19 through the orifice 2% into the duct 21, is another important feature of the present invention. 'It is not only effective in freely moving the abrasive into the path of the airstream, but serves to greatly reduce wear on the bottom of the ducts 21. Excessive duct-wear was heretofore a serious problem in multi-hopper floor devices and was caused by the abrasive dropping or being carried forcibly through the hopper directly into ducts located below the hoppers, causing the particles to bounce back and forth along the duct-walls as they were carried along by the airstream.

Another important feature of my device is that the large horizontal cross-section of the concentrator 22, when matched with the relatively small cross-sectional area of the adjoining duct-outlets 65, results in an immediate reduction in velocity of the air, which is an essential step in removing the abrasive from the airstream. This rapid velocity reduction, coupled with my unique internal concentrator structure, solves the problem of removing the abrasive from the air-ventilating stream, in a compact structure which cooperates with the improved floor 18 to perform this function. The simple construction of my blast unit also provides an arrangement which allows ease of inspection and accessibility of components for maintenance as well as the advantages of reduced initial cost.

To those skilled in the art to which this invention relates, many changes in construction and widely (littering embodiments and applications of the invention will suggest themselves Without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. In a blasting system for the surface treatment of materials providing for the recovery of the abrasive particles used in the blasting operation, the combination of a multi-hopper floor structure for the blast-room and an adjoining concentrator unit, said floor comprising a multiplicity of small hoppers arranged in rows, each said hopper being shallow and occupying only a small fraction of said floor area, the upper end of said hoppers occupying substantially the entire area of said floor; and a plurality of ducts having a triangular cross section and arranged in fixed spaced relation on said floor, each said duct lying adjacent one row of hoppers with its bottom located on the same plane as the bottom of said hoppers, said hoppers being open for passage thereto of ventilating air from said blast-room and the solid particles falling onto said floor; said duct-outlets being further attached to said concentrator unit having a relatively large expansion area which enables the air to slow down rapidly as it leaves said floor; and means in said concentrator to deflect the airstream upwardly; means to arrest the solid particles and separate them from the airstream, and means to trap the arrested particles so they can be drawn from the concentrator for re-use.

2. The blasting system of claim 1, wherein said means to trap said particles in the concentrator are inclined, V-shaped feeder-troughs arranged at predetermined intervals along the lower section of the concentrator.

3. The blasting system of claim 2, wherein said abrasive conveying ducts of said floor are spaced apart at their outlet ends with open spaces between, said spaces being aligned With said feeder-troughs so that the airstream can flow from said floor upwardly between said feeder-troughs in the concentrator.

4. In a blast-room having a perforate ceiling adapted to provide uniform downdraft ventilation, the combination of: a floor comprising a multiplicity of small hoppers having sloping sides converging at a depth substantially equal to the thickness of the floor with the upper end of said hoppers occupying substantially the entire area of said floor, said hoppers being arranged in rows, said rows being aligned adjacent conveyingducts whose floor level is substantially even with the bottom of the hoppers; an orifice on at least one side of each hopper and connecting each of said hopper rows with an adjoining duct, said orifices providing for the passage of the ventilating air from said blast-room through said hoppers to said ducts as well as spent abra sive and debris particles falling onto said floor and into said hoppers, said abrasive and debris particles flowing from said hoppers into said ducts, where they are carried from the floor by the ventilating airstream.

5. In a room employed for the surface treatment of materials and adapted to provide uniform downdraft ventilation, the combination of a floor comprising: a base plate; a plurality of longitudinally extending duct-members being ll-shaped in cross-section with side-members of substantially equal width, and apertures located at predetermined positions aiong the edges of at least some of said duct-members; said longitudinal V-shaped duct-members being fixed in inverted parallel arrangement on said base-plate so their edge-members are substantially abutting and engaged with said base-plate, forming thereby a series of open V-shaped troughs between said longitudinal duct-members; divided-members arranged transversely within said troughs forming a plurality of collecting hoppers within each trough of inverted pyramidal shape, said apertures along the edges of said sidemembers being located at the bottom of said hoppers, whereby the abrasive and debris from the surface-treating operation is collected in said hoppers and passes through said edge-apertures where it is conveyed through said long duct-members by the room-ventilating airstream to a separator.

6. The floor described in claim 5, wherein only alternate V-shaped duct-members are provided with apertures along the edges of both side-members, each of said apertures coinciding with the bottom of an adjoining hopper.

7. A floor for a blast-room, comprising: a base-plate, a plurality of troughs formed from structural members having the shape of an open triangle in cross-section with sides of substantially equal length and an open bottom, said structural members being arranged in fixed parallel relationship adjacent each other with the lower edges of the triangle-sides engaging said base-plate to form a passage under each said triangular member, and open troughs between said members; apertures located at predetermined intervals along the lower edges of a least some of said triangular structural-members; structural diamond-shaped filler-members fixed intermittently along said open troughs between said structural members, forming individual hoppers between each diamond-shaped filler-member along each of said troughs, said filler-members being positioned so that the bottom of each hopper formed thereby lies adjacent at least one of said apertures.

8. In a system for recovery of abrasive particles used in the surface-treatment of articles housed in a blastingroom, a floor to said blasting-room comprising: a baseplate; a series of parallel ducts and troughs on said baseplate, said ducts and troughs being formed by longitudinal inverted V-shaped members arranged in fixed relation on said base-plate; diamond-shaped partition means fixed in each said trough at predetermined spaced intervals, forming individual hoppers of pyramidal shape; slot means cut in the edges of at least some of said longitudinal members and located at predetermined intervals, coinciding with the bottom of each hopper, whereby each hopper passes through said slot and onto the floor of an adjoining triangular duct for conveyance therethrough.

9. The floor described in claim 8, wherein the slots in said longitudinal V-shaped members gradually decrease in size by predetermined increments and the cross-sectional area of the ducts is increased from the upstream of the floor toward its downstream, whereby the same amount of air passes through each hopper.

10. The floor described in claim 9, wherein the slots are formed according to the formula A .Q 4,005 GOV-15 where Q is the cubic feet per minute of free air to pass through each hopper, A the slot area for each hopper in square feet, C the coefiicient of entry for the air, and P the static vacuum in the duct adjacent the hopper, expressed in inches of water, relative to the pressure in the room.

11. The room of claim 8, wherein each duct has an exhaust outlet through which it conducts said air away from said room and wherein the cross-sectional area of said duct is greater at the outlet end than at the inlet end, to maintain a satisfactory conveying velocity therethrough, each said duct having a section of constant depth and increasing width, in no case extending more than the width of a hopper, followed by a second section of constant width and increasing depth.

12. A floor structure for a blast-room comprising: a

plurality of abrasive-collecting hopper arranged substantially in rows, each row of hoppers being adapted to communicate by means of an orifice in each hopper with an adjacent conveying-duct aligned to allow abrasive from the blast-room collected in each hopper to pass from said hopper to said duct, each orifice being located at the bottom of each said hopper, said hoppers having a uniform depth with the bottom of said hoppers being substantially on the same plane as the floor of said adjoining ducts.

13. In an abrasive-blasting system, a concentrator for separating abrasive and waste particles from the conveying air-stream, said concentrator comprising: a housing, defining generally an upper plenum section and a lower settling section; an inlet along one lower side of said housing adapted to receive abrasive-laden air flowing horizontally from a series of duct-outlets, said settling section being much larger in area than the combined area of said duct-outlets; an inclined deflector-plate just inside said concentrator inlet to deflect said abrasive-carrying airstream in an upward direction; a plurality of baflleplates within said concentrator arranged generally in the path of the upward-flowing airstream; a series of V-shaped feeder-troughs arranged in fixed spaced relation in the lower settling section of said concentrator, said troughs being open upwardly and fixed in a sloped position from the inside of one concentrator wall to said deflector-plate; a collecting-duct attached to said deflectorplate; and apertures in said deflector-plate providing a passage from each feeder-trough to said collecting-duct; whereby the airstream, upon entering said large inlet, is slowed in velocity and deflected upward, whereupon the abrasive particles carried by the airstream are arrested by said battle-plates and caused to fall into said feedertroughs and thence into said collecting-duct.

14. The concentrator described in claim 13, including an outlet in said upper plenum-section to remove the air and lighter dust particles which do not fall into the feeder troughs.

15. The concentrator described in claim l3, wherein said feeder-troughs are fixed within said concentrator with open spaces between each adjoining feeder-trough so the airstream can flow upward to the plenum section.

References Cited in the file of this patent UNITED STATES PATENTS 1,660,682 Stebbins Feb. 28, 1928 2,912,918 Mead Nov. 17, 1959 FOREIGN PATENTS 166,077 Australia Nov. 2], 1955

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