US2153590A - Disintegrator - Google Patents

Description

April 11, 1939. c. A. RIETZ 2,153,590

- DISINTEGRATOR Filed Sept. 21, 1955 5 Sheets-Sheet 1 INVENTOR. Car/ 14. 8/222;

ATTORNEY.

5 Sheets-Sheet 2 FIE E C. A. RIETZ DISINTEGRATOR Filed Sept. 21, 1935 34 INVENTOR. .-Ca/-/ 14/5/61 ATTORNEY.

April 11, 1939.

C. A RIETZ DISINTEGRATOR April 11, 1939,

Filed Sept. 21, 1935 5 Sheets-Sheet 3 INVENTOR. Car/ 4. fife/ ATTORNEY.

DISINTEGRATOR Filed Sept. 21, 1935 5 SheetsSheet 4 FIE E INVENTOR. Car/ 4. E/e/ ATTORNEY.

Patented Apr. 11, 1939 UNITED STATES iPATENT OFFICE DISINTEGRATOB Carl A. Rich, San Francisco, Calif.

Application September 21, 1935. Serial No. 41,517 10 Claims (01.83-11) This invention relates generally to machines and methods for the mechanical disintegration of various materials. More specifically it relates to machines of the hammer type wherein hammers carried by a rotor act upon the material to effect disintegration, with discharge of the disintegrated material through a screen.

It is a primary object of the invention to provide a machine and method of the above character which will aiford maximum capacity for a machine of a given size, with a minimum amount of power consumption.

Another object of the invention is to provide a disintegrating machine which can be used with materials where hammer mills of conventional character would be inoperative or relatively ineificient. For example the machine can be successfully employed where it is-desired to handle materials which disintegrate to form a slurry, or plastic or semi-plastic mass, which in ordinary disintegrators tend to plaster the inner walls of the machine. My machine can also be successfully employed in connection with fruits or food.- stuifs such as grapes, where seeds must not be crushed or disintegrated.

A further object of the invention is to provide a disintegrating machine which is capable of handling foreign objects such as tramp iron, without causing serious or permanent injury to the machine.

Another object of the invention is to provide a machine having a novel form of rotor assembly, whereby while the hammers of the rotor are securely held to the shaft, they can be readily removed for making repairs or renewal.

Additional objects of the invention will appear from the following description in which the preferred embodiments of the invention have been set forth in detail, in conjunction with the accompanying drawings.

Referring to the drawings:

Fig. 1 is a plan view, showing a machine incorporating the present invention.

Fig. 2 is a side elevational view, showing the same machine of Fig. 1.

Fig. 3 is an enlarged view of the machine shown in Fig. 2, with the parts in cross section.

Fig. 4 is a cross sectional detail taken along the line 4-4 Fig. 3. v

'Fig. 5 is a detailed plan view of a rotor, where the hammers are arranged to form a single helix.

Fig. 6 is a. cross sectional detail, taken along the line 6-6 of Fig. 3.

Fig. 7 is a cross sectional detail taken along the line 'l'l of Fig. 6.

Fig. 8 is a cross sectional view taken along the line H of Fig. 6;

Fig. 9 is a cross sectional view taken along the line 8-9 of Fig. 4.

Fig. 10 is a cross sectional view similar to F18. 9 showing a modification.

Fig. 11 is a cross sectional view taken along the line Il-ll of Fig. 10.

Referring first to Figs. 1 to 4 inclusive, my machine consists generally of a rotor it which is embraced by a screen II, with both the rotor and the screen being carried by a housing i2. Where a direct power drive is employed, as is generally the case, an electric motor l3 can be carried by the housing, with a direct coupling ll to the rotor shaft It. The hopper I1 is representative of suitable means for introduction of material to be disintegrated into the machine.

Before proceeding with a detailed description of the several parts, it should be noted by reference to Fig. 3 that the zone of operation to the hammers on rotor III, is of substantial vertical extent. Likewise, the screen ii substantially entirely embraces the zone of operation of the hammers, both circumferentially and longitudinally. Conventional hammer mills make use of a screen forming one wall of a surrounding stationary casing, and which extends for only a minor segmental portion of the circumferential distance about the rotor. This feature of my machine will be presently pointed out in greater detail.

In the design illustrated, the housing l2 includes a portion i8, which extends upwardly from the screen II, and which forms an inlet passageway or opening l9 through which material is admitted to the interior of the screen. The feed hopper ll communicates with passageway l9 through opening 2!, which, as shown in Fig. 3, is preferably ofiset with respect to the axis of shaft l6. An additional housing opening 22 is provided, which is shown being closed by plate 23. Where the material being handled or condition of operation is such that hopper ll cannot be employed for establishing a proper feed, plate 23 can be removed and a diilerent type of feeding device applied. For example, it is possible to use a device employing a feed screw, which will positively introduce the material into passageway iii. In this event it is of course evident that opening 2| is closed.

The lower end or base of housing I2 is formed by an annular ring 24, which is shown connected by webs 26 with an inner annular ring 21. Circumierentially spaced vertical struts 28 and 28 serve to connect webs 28 with a flange 30 formed on the upper housing part l8.

The annular space 3| surrounding the screen I is normally closed by the removable closure guard 32. This guard is removably clamped about the housing by suitable means such as clamping devices 33. The opening 34, between the rings 24 and 21, forms a substantially continuous annular outlet opening, which communicates with space 3|. It will be apparent that the disintegrated material passed by screen II is received in space 3|, and is then permitted to fall downwardly by gravity-through the outlet opening 34.

The hammers in the arrangement illustrated in Figs. 3 and 4, have been designated HI to HIS inclusive. Diametrically opposed pairs of hammers, which are in the same horizontal plane,

a zone directly below the zone of operation of hammers H9; the pair of hammers Hll sweep through a zone directly below the zone of operation of hammers HIO; etc. Likewise, it will be noted that the hammers HI to H8 inclusive, comprising the first group are of progressively increased length, so as to operate through a substantially conical shaped zone. The hammers H9 to H| inclusive, however, are all of substantially the same length, and have their outer ends in relatively close apposition to the inner peripheral surface of the screen I I. Such a predetermined apposition between the ends of the lower group of hammers and the screen II, is an impotant feature of the invention for many classes of material, and while the clearance afforded for different types of material may vary, in general the clearance between the ends of these hammers and the screen is not greater than the diameter of the apertures afforded by the screen.

With the grouping of hammers illustrated in Figs. 3 and 4, itis evident that a double helix or helicoid is formed, which has a definite pitch for the upper group of hammers HI to Ht inclusive,

and which has substantially one-half such pitch for the lower group of hammers H9 to Hi5 inclusive. Such a helicoidal arrangement tends to urge the material being acted upon by the upper part of the rotor downwardly and outwardly through the screen, while material which progresses into the zone of operation of the lower group of hammers H9 to H|5 inclusive, is more predominantly urged downwardly. Thus it may be said that the two groups of hammers establish two pressure zones within the screen H, in the upper zone of which the material acted upon is urged both outwardly and downwardly, and in the lower zone of which increased outward pressure is applied to the material. Disintegration of material therefore proceeds progressively, with an immediate discharge through screen H of particles which are reduced to proper size requirements upon impact of the material with the upper hammers, and with the lower hammers acting only on material which is not completely disintegrated by the upper hammers. Material is accordingly removed from the zone of operation of the hammers as rapidly as it is reduced to proper size requirements, thus reducing power consumption for a given amount of material handled,-

since the hammers perform no unnecessary work upon properly disintegrated material.

In operating upon certain materials it is desirable to employ hammers arranged to form a simple helix, in order to aflord lesser forces tending to urge the material being acted upon downwardly. The positioning of hammers for a single helix is illustrated in Fig. '5. It will be noted that in place of having two diametrically opposed hammers in the same plane, as in Figs. 3 and 4, no two hammers in Fig. 5 are in the same plane. With such a single helix, it is still possible to arrange the hammers whereby the path of sweeping movement of the individual hammers for the upper group are spaced, while the hammers of the lower group sweep completely through the space occupied by the same.

While in some instances the hammers can be pivotally secured to the shaft IS, in most instances it is preferable to employ a rigid connection, which will permit removal of the hammers for replacement or repair. The arrangement illustrated makes use of discs 36, which are each provided with spacing hubs 31, and which are locked to the shaft It by means of key 38. The uppermost disc 36 is engaged by a clip 39, which is releasably locked to the shaft l6. Tie rods 4| are shown extending downwardly through the discs to retain them in assembled relationship. Each of the hammers of the upper group have an integral arcuate portion 42, which can be disposed between these discs, and which are bored to receive two of the rods 4| (Fig. 4) Where a double helix is employed as in Figs. '3 and 4, it is therefore evident that successively lower hammers of the upper group have their arcuate portions 42 partially overlapped as viewed in plan, with connections to the tie rods 4|. For example, as shown in Fig. 4, the two hammers HI have their arcuate portions 42 between the uppermost disc 36 and the next lower disc 36, and are each attached to two tie rods 4|. The next lower hammers H2 have similar arcuate portions, which overlap in plan with the corresponding arcuate portions for the hammers HI, and which are attached to the same tie rods.

A somewhat different arrangement for attaching the hammers H9 to Hi5 inclusive is required, because of the vertical spacing of the same. Referring to Figs. 6 and 7, two diametrically opposed hammers, as for example the hammers Hi i, have portions M which extend between the discs 36, and which connect to diametrically opposed tie rods M. Adjacent diametrically opposed hammers, as for example hammers Hi2, have forked portions M, which span the corresponding disc 36, and which are attached to the other tie rods 4|. Likewise, all of the hammers of the lower group are provided with abutment portions it, which engage adjacent hammers, as illustrated in Fig. 6, and thus securely lock the hammers to the shaft.

As illustrated in Fig. 8, each of the hammers is preferably tapered rearwardly, with respect to lower end of rotor shaft I6. In the construction illustrated, structure 5| includes the inner and outer annular portions 52 and 53, which are connected by the webs 54. The outer periphery of the annular portion 53 is machined to-flt the inner periphery of the adjacent annular portion 21. Bolts 58 or like means can be employed for retaining the structure 5| inproper position with respect to the housing. The space 51, between the annular portions 52 and 58, which is occupied by webs 54, forms a chamber or wall extending below the zone of operation of the rotor hammers,

and which serves the purpose of receiving and trapping tramp iron and like foreign articles which may find their way into the machine together with the material being disintegrated. The lower end of this space 81 can be normally closed by plate 58. Note that the upper edges 58 of webs 54 are inclined downwardly and inwardly, so that if they are impacted with tramp iron, the tendency is to deflect the tramp iron downwardly into the space 51, rather than to deflect the same upwardly back in to the zone of operation of the hammers.

For journalling the lower end of the rotor shaft I8 to the structure 5|, there is shown a ball bearing assembly 8 I, the outer race of which is carried by an annular shell 82. This shell in turn is carried by the structure 5| by suitable means, such as bolts 83. To insure proper lubrication of the ball bearing 6|, the lower end of shaft I6 carries an impeller member 84, which operates in an,

annular groove 88. Oil duct 61serves to connect groove 66 with the ball bearing assembly GI, so that oil going down from the ball bearing assembly by gravity, is pumped back through the duct 81. v

To afford an oil seal about the rotor shaft immediately above the ball bearing assembly-8 I the rotor shaft carries a sleeve 88 which is fltted within the cylinder .88 formed by the shell 82. Piston rings 1| or like sealing means is provided on the periphery of sleeve 88, to afford a sealed contact with the cylinder 88, thus limiting flow of oil upwardly,and also preventing liquids from the material being operated upon, from flowing downwardly into the shaft bearing. Immediately above sleeve 68, there is a disc 12 which. forms a closure for the upper end of shell 62, and which is in relatively close proximity to the lowermost disc 38 of the rotor assembly.

Because of the relatively close apposition between the lower hammers H8-HI5, it is important to have the screen II fixed to a predetermined diameter. Suitable means for this purpose consists in providing a machined annular shoulder 16 on the structure 5|. At the upper end of the screen, there is also an annular ring 11 which is fixed to the housing, and which provides a machined annular shoulder 18 formed to the same diameter as the shoulder 16.

By reference to Fig. 4, it will be noted that the screen II is formed in two semi-cylindrical sections IIa, having outwardly turned flanges 18 on their vertical meeting edges. In mounting the screen sections Ila, the upper and lower edges are engaged with the machined shoulders 18 and 18, and their vertical flanged edges 18 are clamped together by clamping devices M and 82. Flat metal strips 88 may be interposed between the flanges 18, and the connection at this point can be somewhat strengthened by use of one or more rigid clamping bars 84; On one side of the screen the clamping device 8| is provided with a projecting portion 88, which is adapted to engage the strut 29, and thus prevent rotatlon'of the screen relative to the housing. The clamping device 82 is shown more clearly 1mm. 9. It extends substantially the length of the screen and is substantially 0 shaped, with clamping set screws 81 for engaging bar 84. In assembling the screen with respect to machine housing, the vertical flanges of the screen segments can be temporarily clamped together by bolts 88. Thereafter the clamps 8| and 82 are applied. ,Notches or slots 88 in the clamps, serve to accommodate the ends of bolts 88.

The bearingrillustrated at the upper end of shaft I8 can be described as follows: A casting 8| is mounted upon the upper end of housing portion I8, and serves to carry the motor support 82. The rotor shaft I8 carries a ball or roller bearing assembly 88, the outer face of which is flxed within the hollow casting 84. Below the ball bearing assembly 88, the rotor shaft carries an oil impeller 88-, which operates in an annular chamber 81. Oil from this chamber is caused to flow back to the ball bearing assembly 88, through duct 88. A suitable packing gland 88 surrounds shaft I8, and the body I8I of this gland is carried by the casting 84. Below the ball bearing assembly 83, there is also a sleeve I02 carried by the rotor shaft, which is provided with oil seal rings and which is fltted within a cylinder I88 formed as a part of the gland body IN. A journal of this character insures continuous and proper lubrication of the ball bearing assembly,

and at the same time entrance of foreign material into the ball bearing assembly is prevented. 1

through the inlet passage I8, and is impacted by the upper most hammers of the rotor. Upon impact with the hammers, together with impact upon the inner periphery of the screen, a preliminary shattering of the material occurs, with immediate discharge of material of proper fineness resulting from such an impact, through the perforations of screen II. Therefore, the only material proceeding downwardly through the zone of operation of the hammers, is material requiring further shattering to reduce it to proper fineness. As the material reaches the lower group of hammers, it is urged outwardly against the screen more intensively, and by virtue of further impact, the material is all reduced to proper fineness and passed through the screen I I. Material passed through the screen is received in the outer space 3| and from this space drops downwardly through the outlet opening 34. With certain materials being introduced into the machine, there is a tendency for the material to be deflected upwardly .upon contacting the hammers of the rotor. This tendency can be overcome by having the introduction opening offset from the axis of rotation of the rotor I8, whereby the material is introduced into the inlet passage I9 in a direction corresponding generally to the direction of rotation of the rotor.

It will be noted that the interior of housing portion i8 is of substantial depth. The space thus formed above the rotor functions as an accumulator, to retain material fed at a rate in exby the rotor.

cess of the rate at which the material is taken By maintaining a substantial amount of material in this space, operation at maximum capacity is assured, without however causing choking of the machine.

, It has been previously stated that my machine can be operated successfully upon many types of material, where conventional disintegrators would be inefficient or entirely inoperative. Particular reference has been made to materials of a plastic or semi-plastic consistency, or materials which when disintegrated form a pulp or plastic or semi-plastic mass, tending to plaster the inner walls of the machine. To illustrate this feature, reference can be made to the disintegration of grapes, to reduce the grapes to a pulp, without crushing of the seeds. In carrying out this operation, the clearance between the ends of the lower group of hammers, and the screen II, is slightly greater than the average diameter of the seeds, although less than the diameter of the openings in the screen. The grapes to be disintegrated can be fed to the machine at a relatively rapid rate, it being virtually impossible to choke the machine. Disintegration of the flesh of the grapes appears to occur practically instantaneously, to form a pulp of uniform consistency, and without causing crushing or disintegration of the seeds. As another example which will indicate usefulness of my.machine as compared to conventional machines, reference can be made to the disintegration of raw fish. In feeding such material to the machine, both the" flesh and the bones are disintegrated to form a substantially uniform disintegrated pulp, which is discharged from the machine, without plastering the walls of the screen, and without occasioning blocking or choking. Dehydrated fruit such as raisins can also be handled by the machine, as well as products of relatively high moisture content, such as tomatoes.

Aside from the handling of products of the type referred to above, the machine can be used on various chemical or metallurgical materials, either in wet or dry form, such as lime slurries or ore.

In disintegrating hot moist material, such as cooked fish press cake,- it is desirable to permit free venting of vapors from the machine. Thus if the material is being introduced through opening 22 by a suitablefeed device, vapors evolved in the disintegration operation are permitted to vent to the atmosphere through opening 2|. In this manner the moisture content of the material can be reduced to a substantial degree, to facilitate a subsequent drying operation. Where there is a tendency for the disintegrated material to plaster the inner walls of guard 32, and thus restrict proper discharge, this guard can be removed to permit direct lateral discharge. Also plate 58 can be removed to permit discharge downwardly as well as outwardly.

In applying the machine to relatively soft materials, such as tomatoes, grapes, fish, and the like, as compared to hard materials such as cement clinker, it is generally desirable to increase the length of the upper hammers, instead of em ploying a proportioning such as shown in Fig. 3. Thus as shown in Figs. and '11, the upper group of hammers H are of a length equal to the lower group, it being presumed in this figure that or breakage.

the hammers form a single helix, with the lower group of hammers sweeping completely through their zone of operation. When material tending to be of a stringy nature is being handled, such as scrap meat, it is also desirable to employ stationary combs which 'interlace with the upper hammers Thus in Figs. 9 and 10 one of the clamps 82a, for holding the sections of thescreen together, is shown provided with a central web Hi8 which extends between the screen flanges 19. This web carries the spaced combing elements II", which extend inwardly and which interlace with the upper hammers. In this instance clamp 82a is also provided with two sets of clamping set screws 81, and the sides of the clamp are notched, as at M8, to permit application of a temporary clamping bolt M9.

It will be noted that in general my machine utilizes a comparatively few number of hammers as compared to the large number of comparatively closely spaced hammers used in conventional hammer mills. By virtue of this feature of the machine, any tramp iron finding its way into the machine together with the material being disintegrated, will not become jammed between the hammers and the screen to cause serious injury hammers, and is entrapped in the lower tramp iron chamber 51. This feature is of great importance in the food industry, where in spite of precautions, tramp iron frequently finds its way in the material being handled.

I claim: 7

1. In a disintegrater, a rotor mounted upon a vertical axis and provided with a plurality of spaced hammers, whereby the zone of operation of the hammers is of substantially vertical extent, a substantially cylindrical shaped screen substantially entirely embracing said zone of operation, a housing serving to support the rotor and said screen, said housing being formed to provide an inlet opening at the upper end of the screen for feeding material to be disintegrated to the upper end of said zone of operation, said housing being also formed to provide an annular outlet opening at the lower end of the screen for delivering material passed by the screen, and an annular structure disposed below the rotor and surrounded by said outlet opening, 'said structure being formed to provide a tramp iron receiving chamber extending below said zone of operation.

2. In a disintegrator, a rotor provided with a plurality of spaced hammers, said hammers having an aggregate zone of operation which is of substantial extent in a direction longitudinally of the axis of rotation of the rotor, a substantially cylindrical shaped screen substantially entirely surrounding the zone of operation of the hammers, and housing means, serving as a support for the rotor and said screen, said housing means being formed to provide an inlet opening for delivering material to be disintegrated into one end of the screen, said housing means being also formed to provide-an outlet opening for discharging disintegrated material passed through the screen, one group of said hammers of the rotor to form a helicoid tending to urge 75 Instead thetramp iron or other stray metal quickly finds its way through the material into the interior of the screen from the inlet opening and outwardly through the screen, the pitch of the helicoid being substantially greater for the first group of hammers than for the second group.

3. In a disintegrator, a rotorcomprising a shaft, a plurality of members affording spaced annular flanges assembled on said shaft, a pluraiity of hammers arranged about said shaft, rods extending longitudinally of said shaft and through said flanges, and portions formed on each of said hammers which serve to embrace said flanges and which also engage at least two 4. In a disintegrator having a rotor provided with disintegrating hammers and means serving to support and journal the rotor, the combination of a substantially cylindrical shaped screen surrounding the hammers and formed of a plurality of segmental sections, supporting means for the screen forming annular shoulders for engagement by the end portions of the screen and including members disposed alongside the screen.

' of said members to prevent rotation of the screen relative to the same, all parts of the screen being out of direct engagement with said members.

5. In a disintegrator, a vertically disposed rotor provided with a plurality of spaced hammers, the hammers having an aggregate zone of operation whichis of substantial vertical extent and being disposed generally in the form of a helicoid, a substantially cylindrical shaped screen substantially entirely surrounding the zone of operation of the hammers, and housing means servingv to support both the rotor and said screen, said housing means being formed to afford an inlet opening for delivering material to be disintegrated into the upper end of the screen. and also being formed to aiford an outlet for discharging disintegrated material passing through the screen, the hammers of the rotor being positioned in at least two groups, one group of hammers extending downwardly from the upper end oi the screen and the other group of hammers extending upwardly from the lower end of the'soreen, the pitch of the helicoid formed by the upper group of hammers being substantially greater than the pitch for the lower group of hammers.

6. In a disintegrator, a rotor mounted upon a vertical axis and provided with a plurality of spaced hammers disposed generally in the form of a helicoid, whereby the entire zone of operation of the hammers is of substantial vertical extent, a substantially cylindrical shaped screen substantially entirely embracing said zone of operation, a housing serving to support the rotor and said screen, said housing being formed to provide an inlet opening at the upper end of the screen for feeding material to be disintegrated to the upper end of said zone of operation and also being formed to provide an outlet opening for material passed by the screen, a structure disposed below the rotor and formedto provide a tramp iron receiving chamber extending immediately below the zone of operation, the hammers of the rotor being disposed in at least two distinct vertically spaced groups, the pitch of the helicoid for the upper group of hammers being substantially greater than the pitch for the lower group of hammers.

7. In a disintegrator, a rotor mounted upon a vertical axis and provided with a plurality of spaced hammers, whereby the zone of operation of the hammers is of substantial vertical extent. a substantially cylindrical-shaped screen substantially entirely embracing said zone of operation, a housing serving to support the rotor and said screen, said housing being formed to provide an inlet opening at the upper end of the screen for feeding material to be disintegrated to the upper end of the zone of operation, the hammers of the rotor being positioned in the form of a helicoid tending generally to urge material introduced into the upper end of the screen towards the lower end of the screen, the hammers being in two vertically spaced groups with the pitch of the helicoid formed by the upper group of hammers beingsubstantially greater than the pitch for the lower group of hammers, said housing being formed to provide an outlet opening at the lower end of the'screen for delivering material passed by the screen, and an annular structure disposed below the rotor and surrounded by said outlet opening, said structure being formed to provide a tramp iron receiving chamber extending below said zone of operation.

8. In a disintegrator, a rotor provided with a plurality of groups of hammers arranged to rotate about-a'common axis, the hammers of one group only being spaced longitudinally of said axis, the zone of operation of said hammers being of substantial extent in a direction longitudinally of of operation are spaced in a direction longitudinally of the axis of the rotor, and the hammers of another group being mounted near the other end of the screen and having alternate hammers angularly disposed and each of such size as to sweep through substantially the entire space between its adjacent hammers whereby the hammers operate to sweep through the entire space occupied by the group.

9. In a disintegrator, a rotor provided with a plurality of groups of hammers arranged to r0- tate about a common axis, the hammers of one group only being spaced longitudinally of said axis, said hammers having an aggregate zone of operation which is of substantial extent in the direction of the axis of rotation, a substantially cylindrical shaped open-ended screen substantially entirely surrounding the zone of operation of the hammers, and housing means being formed to afford an inlet opening for delivering materials to be disintegrated into one end of the screen and being also formed to afford an outlet for discharging disintegrated material passingthrough the screen, the hammers of therotor being positioned to form a helicoid tending to urge material introduced into said one end of the screen towards the other end of the screen, said spaced group or hammers being mounted near the inlet opening and having a spacing such that their individual zones of operation are spaced in a direction longitudinally of the axis of the rotor, and the hammers of another group being mounted near the other end of the screen and having alternate hammers angularly disposed and each of such size as to sweep through substantially the entire space between its adjacent hammers so that their individual zones of operation sweep through the entire space occupied by the group.

10. In a disintegrator, a rotor mounted upon a vertical axis and provided with a plurality of spaced hammers, the hammers having an aggregate zone of operation which is oi substantial vertical extent and being disposed generally in the form of a helicoid, a cylindrically shaped screen surrounding the zone of operation of the rotor, and housing means serving to support the rotor and the screen, said housing means including upper and lower rigid parts, the upper housing part being formed to provide a chamber ex-

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