EP3042739B1 - Dry ice grinder and dry ice blasting device - Google Patents

Description

TECHNICAL AREA

The present disclosure relates generally and more particularly to a dry milling mill for a dry ice blasting apparatus having first and second media.

TECHNICAL BACKGROUND

It is generally known Trockencisstrahlvocrichtungen in which the properties of dry ice are used. Dry ice pellets, which consist of compressed CO2-Schnce, are accelerated with compressed air and in very cold condition (-78.5 ° C) are thrown against the surfaces to be cleaned.

The cleaning effect is based on three principles: on the one hand on the mechanical action of dry ice solids (similar to glass beads or sandblasting); continue to insist that the supercooled dry ice ejectors cause a cold shock on impact, causing the substrate to be removed from embrittlement and making it easier to remove; and finally that fine cracks and cracks form on cooling, into which fine particles of dry ice penetrate, where they sublime abruptly (ie change into the gaseous state), thereby greatly expanding in the cracks, thus enlarging the cracks and the particles to be removed thereby detach from the surface to be cleaned.

The actual blasting material, namely the dry ice, evaporates completely during this process and escapes into the atmosphere. Dry ice blasting therefore does not give rise to any residues except for the detached particles.

However, the dry ice pellets used with starting grain sizes of approx. 3 mm are not suitable for all cleaning tasks. There are cleaning tasks where smaller particle sizes are desired.

In order to obtain dry ice particles with smaller grain sizes, there are blast machines with roll grinders in which the pellets are comminuted in a crushing gap between opposing rolls and a crushing bar (see, for example DE 10 2009 027 974 B4 ). The crushed particles in the grinder are further conveyed after crushing, fed into a compressed air stream and fed to a jet nozzle. From the DE 10 2004 057 665 A1 a grinder is known in which dry ice pellets or other blasting material between two congruently shaped conical surface areas or between a cylindrical screw and a cylindrical tube surrounding it. Here provided relatively large effective grinding surfaces, which can cause high gas losses in the grinding of dry ice pellets.

When grinding in an open chamber, comparatively high blasting material (dry ice) losses can occur here, since during comminution a part of the dry ice is sublimated and lost. Also, in such roll mills, a plurality of sealed bearings (two per roll) are required to enable grinding also in a closed chamber when the blasting material is to be conveyed through the milling device by means of a conveying fluid (e.g., compressed air).

It is therefore the object to provide an improved dry ice mill, in which these disadvantages are at least partially eliminated. In particular, the object is to provide a dry ice blasting device in which the dry ice losses are as small as possible and the particle size and geometry as well as the blasting speed are optimally tuned to the cleaning task to be carried out.

This object is achieved by the dry ice mill according to claim 1 and the dry ice blasting apparatus according to claim 13.

SUMMARY

According to a first aspect, the present disclosure is a dry ice mill for a dry ice blasting device with a first and a second grinding media, wherein the first grinding body has a rotationally symmetric outer effective surface and the second grinding body has a rotationally symmetrical inner surface, each acting as Mahlflächen, the grinding media each with its outer effective surface and their inner active surface facing each other coaxially and mutually rotatable about an axis of rotation are arranged so that between outer active surface and inner active surface, an annular Mahlspalt is formed, in which when turning the grinding body against each other Trockeneismahlgut passes and is ground there. In this case, a contour profile of the outer active surface along the axis of rotation is defined by a first contour line and a contour profile of the inner active surface along the axis of rotation by a second contour line. In this case, the contour lines are designed so that at minimized ("minimized" means in this context that the width of the annular gap is zero, so inner effective surface and outer effective surface touching each other) annular gap the inner effective surface and the outer effective surface touching each other along an annular line - the annular gap so very narrow. In such an embodiment, it is ensured that the actual grinding process takes place decisively in the region of the minimized annular gap, ie only in the very narrow constriction. Thus, the material to be ground is crushed very gently and sublimation losses are minimized.

With such a grinder, the grinding process can be more easily implemented in a closed chamber and thus reduce the compressed air demand for conveying the blasting material, since the second grinding body with its inner active surface can form part of a closed grinding chamber. The liberated during grinding CO2 gas can thus form additional usable gas volume in the conveying gas flow, which can additionally increase the impact energy of the blasting material. The grinding media supply and the blasting material removal as well as the passage through the actual grinding mechanism and through the grinding gap can be made particularly streamlined by the grinding bodies arranged concentrically in one another. In this way, u.a. Flow and pressure losses are reduced in the promotion of grinding / blasting.

The material to be ground is guided in the conveying direction through the annular gap along the axis of rotation. The ground material is first pressed into the narrowing annular gap, where it is crushed. The comminuted particles then pass immediately from the (narrow and narrow) annular gap area into a widening area and continue there. The conveying effect takes place on the one hand by the gas flow along the rotation axis and by the movement of the grinding bodies relative to each other or by the relative movement of the inner active surface to the outer effective surface.

Other aspects and features will become apparent from the dependent claims, the accompanying drawings and the following description of embodiments.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1

eine schematische Darstellung eines Trockeneisstrahlgerätes

Fig. 2

eine Seitenansicht eines erfindungsgemäßen Trockeneismahlwerks mit einer Antriebseinheit;

Fig. 3

einen Längsschnitt durch das in Fig. 2 dargestellte Trockeneismahlwerk;

Fig. 4

einen Längsschnitt durch das in Fig. 2 dargestellte Mahlwerk in einer anderen Schnittebene;

Fig. 5A - 5E

schematische Darstellungen alternativer Mahlwerksgeometrien

Embodiments will now be described by way of example and with reference to the accompanying drawings. Showing:

Fig. 1

a schematic representation of a dry ice blasting device

Fig. 2

a side view of a Trockeneismahlwerks invention with a drive unit;

Fig. 3

a longitudinal section through the in Fig. 2 illustrated dry ice mill;

Fig. 4

a longitudinal section through the in Fig. 2 illustrated grinder in another sectional plane;

Fig. 5A - 5E

schematic representations of alternative grinder geometries

DESCRIPTION OF EMBODIMENTS

Before a detailed description of the embodiment with reference to Fig. 1 First, general explanations of the embodiments follow.

In one embodiment, the inner active surface frusto-conical (frusto-conical) is formed and the outer effective surface is provided in the region of the annular gap with a toroidal curved area (similar to the outer curvature in the belt area of a lifebuoy). This design has several advantages. Assuming a conveying direction through the second grinding body along its frusto-conical inner active surface, in which the grinding / blasting material is conveyed from the wide end of the truncated cone along the axis of rotation to the narrower end of the truncated cone, so initially the unbroken material is through the converging Surface areas of the inner active surface and the outer effective surface in the Mahlspalt (annular gap) into compressed. After passing through the grinding gap, the grinding stock comminuted there to the blasting material again exits into an area widening out of the annular gap, can expand there and does not clump together. Finally, the blasting material is then converged again in the direction of the narrow conical mouth together with a compressed air / Strahlgutstrahl and exits at an increased speed.

In another embodiment, the torically formed region merges into a conical region which forms one end of the first grinding body and projects into the frusto-conical cavity in the second grinding body. As a result, the nozzle effect described above is additionally enhanced.

In other embodiments, the thus formed particularly rotationally symmetrical Mahlgutabfuhrkammer opens into a discharge port, via which the grinding / blasting material can be fed directly into a hose assembly of the dry ice blasting device. This is possible without further deflections and thus loss.

In another embodiment, the first grinding element - which is optionally received with a grinding head rotatable within the second grinding body - provided with a Mahlgutzufuhrkammer passing through drive shaft which can be coupled to a drive unit and is mounted via a bearing assembly in a bearing sleeve connected to the drive unit , Thus, the first grinding body (or the grinding head) freely within the second grinding body - ie within the Mahlgutzufuhrkammer or the Strahlgutabfuhrkammer - are positioned. Drive, alignment and fixation via the bearing sleeve or the drive unit. By the bearing within the bearing sleeve ensures that the drive unit transmits only required for crushing the blasting rotary motion and remains free of transverse and axial forces.

In one embodiment, the bearing arrangement and / or the drive unit is sealed by way of a seal acting on the drive shaft (eg shaft seal, mechanical seal) towards the grinding material supply chamber. This reliably prevents grinding or grit and / or compressed air from getting into the bearing arrangement or into the drive unit. For sealing only a single seal is required. Compressed air and blasting material remain within the grinding material supply chamber.

In a further embodiment, the second grinding body is formed at the end of a holding piece, in which the Mahlgutzufuhrkammer is formed. Thus, the second grinding body can be exchangeable and formed of a different material as the Mahlgutzufuhrkammer.

In an embodiment in which the second grinding body and / or the bearing sleeve are designed to be axially adjustable along the axis of rotation towards the holding piece, this axial adjustment makes it possible to change the annular gap width. The first grinding body can be positioned in the axial direction relative to the second grinding body, so that the width of the annular gap is variable and so the grain size of the blasting material can be adjusted in the desired manner.

There are embodiments in which the width of the annular gap between 4 and 0.1 mm, in particular between 1 and 0.1 mm is set.

In one embodiment, a spindle assembly, via which the holding piece is coupled to the bearing sleeve, serves as an adjusting mechanism. Thus, by rotating the holding piece to the bearing sleeve, the axial position of the first grinding body can be adjusted to the second grinding body.

In another embodiment, the second grinding body is correspondingly arranged adjustable manner to the holding piece, for example via a spindle or a thread.

In one embodiment, the Mahlgutzufuhrkammer, which surrounds the first grinding body or its drive shaft coaxial, provided with a supply port which opens tangentially and inclined to the axis of rotation in the Mahlgutzufuhrkammer. Thus, the supplied millbase is cyclone-like guided together with the compressed air flow in the Mahlgutzufuhrkammer the annular gap. This design is aerodynamically advantageous and ensures a low-loss Mahlgutstrom in the annular gap.

There are embodiments in which the direction of rotation of the cyclone flow corresponds to the direction of rotation of the first grinding body in the second grinding body.

In other embodiments, the direction of rotation of the cyclone flow may also be opposite to the direction of rotation of the first grinding body in the second grinding body in order to obtain special comminution results, if appropriate.

In one embodiment, in which the second grinding body is interchangeably coupled to the holding piece via a thread, it can be exchanged particularly easily in the event of wear.

There are versions in which the thread is sealed by a special thread sealant to avoid gas losses through the thread gap. Such sealing compounds can be liquefied by heating, so that then the second grinding body can be unscrewed onto the retaining piece or from this.

In other embodiments, a sealing surface can also be provided as an alternative to the thread sealing means, via which the second grinding body can be sealed against the holding piece.

In order to set or change the grinding results as a function of the supplied millbase and the required blasting material according to the desired application situation, the outer active surface of the first grinding body and / or the inner active surface of the second grinding body can be provided with a surface structure. In particular, grooves, notches, nubs, teeth, serrations, depressions, and the like may be provided, which are arranged or formed in either lines, ring or spindle / thread structures.

There are also embodiments in which the surfaces of the outer active surface and / or the inner active surface are changed by special surface treatments or additional coatings in their properties in order to influence the grinding result itself or to improve the strength or the wear properties of the active surfaces.

There are embodiments in which the first and the second grinding body is made of an aluminum material, in particular of suitable wrought or cast alloys, and the active surfaces e.g. by anodizing or Hartanodisierbehandlung, changed, in particular hardened, were. Thus, a lighter and easy-to-work material can be used, which still has the required wear resistance on the active surfaces.

A dry ice blasting device, which is provided with such a dry ice mill, can be used particularly lossless, energy-saving and variable by the low weight and the adjustable blasting particle size (grit) for different tasks.

There are embodiments in which an additional fluid connection (eg for compressed air) is provided at the outlet end of the dry ice mill, via which the mixture emerging there can additionally be acted upon by conveying fluid in order to additionally accelerate this mixture of existing conveying fluid and dry ice, thus ensuring the jet properties continue to improve.

Coming back to Fig. 1 , This shows a schematic representation of a dry ice blasting device 100 with a hopper 101 with dry ice pellets serving as regrind 102, which have approximately the following dimensions (diameter about 3mm, longitudinal about 5 to 10mm) and are formed from compacted dry ice snow.

The feed container 101 opens at its lower end into a metering device 103 in which dry ice pellets 102 are transported via a rotating metering disk into a conveying air stream 104 which conveys the dry ice pellets 102 from the metering device via a feed line 106 into the dry ice mill 1. There, the dry ice pellets 102 (ground material) are crushed into blasting material 109 and directed together with the conveying air stream 104 from the dry ice mill 1 through a hose package 107 through a nozzle 108 as blasting material 109 (crushed dry ice pellets) against the surface 110 to be processed.

Optionally, a further conveying air flow 111 can be guided into the hose package 107 in order to additionally accelerate the blasting material 109 there.

This in Fig. 2 shown dry ice mill 1 comprises a drive unit 2, which is coupled via a bearing sleeve 3 with a holding piece 4, which carries at its end the second grinding body 22.

In operation, the regrind (dry ice pellets 102) passes through a supply port 6 into the interior of the holding piece 4, passes there the grinding surfaces (see below) and exits coaxially to a symmetry / rotation axis 7 via a discharge port 8 - possibly in the hose package 107th ,

Structure and function of the dry ice mill 1 are based on the in Fig. 3 and 4 illustrated sectional views explained. To the drive unit 2 (shown schematically without internal structure), the bearing sleeve 3 is flanged by screws 9. The drive unit 2 comprises an electric motor, not shown, whose shaft end 10 protrudes into a drive shaft 11 of a first grinding body 12, at the other end of a grinding head 33 is arranged with an outer effective surface 13. Shaft end 10, drive shaft 11, grinding body 12 and the outer effective surface 13 extend coaxially and rotationally symmetrically to the axis of rotation 7. The shaft end 10 is rotatably coupled via a suitable shaft-hub connection with the drive shaft 11.

In the region of the shaft end 10, the drive shaft 11 is rotatably and axially fixedly received via the bearing arrangement 14, which comprises two roller bearings (here: deep groove ball bearings) 15 and a spacer sleeve 16.

At its grinding-head end, the bearing sleeve 3 carries a sealing ring 17 serving as a seal, which rests with its sealing lip 18 on the drive shaft 11 of the first grinding body 12 and protects the bearing arrangement 14 and the drive unit 2 against the penetration of ground material and cold conveying fluid. The bearing sleeve 3 is inserted with one end in the retaining piece 4 and is sealed against the interior 19, which forms the Mahlgutzufuhrkammer, via a radially sealing O-ring 20. At the other end of the holding piece 4, the second grinding element 22 is connected via a thread 23 to the holding piece 4. The thread 23 is optionally sealed by means of a thread sealant (not shown) to the interior 19. In the interior of the second grinding body 22, the inner active surface 24 is formed, the frusto-conically tapering from the interior 19 of the outer active surface 13 facing the discharge port 8 extends out, which - for example, for connection of the hose package 107 - is provided with a thread 25.

Between the outer effective surface 13 on the grinding head 33 of the first grinding body 12 and the inner active surface 24 of the second grinding body 22 extends from the interior 19 ago and tapered in a Mahlgutabfuhrkammer 26 widening annular gap 27. The Mahlgutabfuhrkammer 26 is conically tapered.

The holding piece 4 is axially displaceably coupled to the bearing sleeve 3. In this way, the inner active surface 24 of the second grinding element 22 can be displaced away from or towards the first grinding body 12 together with the holding piece 4, so that the width of the annular gap 27 can be changed. For accurate adjustment is a spindle gear 28 in the bearing sleeve 3, in which a screwed into the retaining piece guide pin 29 (see Fig. 2 ) protrudes. Now, if the holding piece 4 is rotated relative to the bearing sleeve 3, so also changed its axial position to the bearing sleeve 3 in dependence on the rotation angle and the pitch of the spindle gear 28. Accordingly, the axial position of the grinding head 33 with its outer effective surface 13 to the second grinding body 22 with its conical inner active surface 24 and thus the width of the annular gap 27. In operation, the width of the annular gap is set between 4 and 0.2 mm, in particular between 1 and 0.2 mm.

The width of the annular gap 27 can be varied in a similar manner by screwing the second grinding body 22 to the holding piece 4. In the illustrated embodiment, however, this is not provided because the thread 23 is sealed here with a sealant and secured against loosening.

In operation, the first grinding body 12 is driven with its grinding head 33 via its drive shaft 11 from the shaft end 10 and rotates with its outer effective surface 13 about the axis of rotation. 7

The conveying air stream 104 enters together with the dry ice pellets 102 through the supply port 6, which leads inclined and tangential into the interior 19 (see Fig. 4 ), where it is cyclone-like guided around the first grinding body 12 into the annular gap 27. There takes the rotating in the same direction first grinding body 12, the dry ice pellets 102 and leads them through the rotational movement and the compressed air further through the annular gap 27. There, the dry ice pellets 102 between the outer effective surface 13 of the first grinding body 12 and the inner active surface 24 of the second grinding body 22 are crushed and occur as crushed blasting material 109 through the nozzle-shaped Strahlgutabfuhrkammer 26 additionally accelerated through the discharge port 8 in the hose package 107th

In order to improve the grinding action, the outer active surface 13 and the inner active surface 24 are provided with grinding / conveying grooves 30 (see Fig. 4 ).

To improve the sealing effect between the bearing assembly 14 and the interior 19 of the drive shaft 11 extends into the holding piece 4, wherein the inner surface of the holding piece 4 and the Drive shaft 11 initially form a very narrow gap, then the drive shaft 11 is tapered and then goes first conically widening in the toric outer active surface 13, which then merges conically tapered in the tip 31 of the first grinding body 12.

The tapered portion 32 of the drive shaft 11, improves the flow characteristics in the interior 19 (Mahlgutzufuhrkammer) and the tapered grinding head 33 improves the flow effect and the nozzle action in the Mahlgutabfuhrkammer 26th

Further possible designs of the active surfaces 13 and 24 on the grinding head 33 of the first grinding body 12 and in the second grinding body 22 are in the Fig. 5A to 5E shown.

Fig. 5A shows a grinding head 33A with a conical-convex outer surface 13, which sits in a conical inner active surface 24 and forms an annular gap 27 there.

Fig. 5B shows a frusto-conical grinding head 33B with a conical outer active surface 13 which sits in a toric-convexly curved inner active surface 24 and forms with this the annular gap 27.

Fig. 5C shows a cylindrical grinding head 33C with a tapered end, which has a cylindrical-conical outer effective surface 13 which sits in a conical inner active surface 24 and forms the annular gap 27 there.

Fig. 5D shows an embodiment in which a grinding head 33D sits with a toric-convex or even spherically curved outer effective surface 13 in a toric-concave or spherical-concavely curved inner active surface 24 and there forms the annular gap 27. In this case, the curvature / curvature of the outer effective surface 13 is greater (narrower curvature / curvature radius) than that of the inner active surface 24 (further curvature / curvature radius). This ensures that the annular gap 27 first tapers in the conveying direction and then expands again. For mounting of the grinding head within the component bearing the inner active surface (the second grinding body 22), this can be formed divisible.

Fig. 5E shows an embodiment with a conical grinding head 33E with a conical outer effective surface 13, which is disposed within the first in the conveying direction conically tapered inner active surface 24A and then again in the conveying direction expanding inner active surface 24B and at the transition edge 24C, the annular gap 27 defines.

In an alternative embodiment, the milling head 33E has a cylindrical outer-surface 13. In such an embodiment, then the width of the annular gap 27 by axial adjustment of the grinding head 33 is not possible. In a further alternative embodiment is in the Fig. 5E shown conically widening inner active surface 24 formed cylindrical with a constant diameter. In conjunction with a conically tapered outer active surface 13 also results in This embodiment is an initially tapered and widening after the constriction annular gap 27th

Further embodiments and variations of the invention will become apparent within the scope of the claims. LIST OF REFERENCE NUMBERS 100 Dry ice blasting device 12 first grinding media 101 hopper 13 Outside effective area 102 dry ice pellets 14 bearing arrangement 103 metering 15 Deep groove ball bearings 104 Conveying air stream 16 Stand Off 106 supply 17 circumferential seal 107 hosepack 18 sealing lip 108 jet 19 inner space 109 blasting 20 O-ring 110 surface 22 second grinding media 111 Conveying air stream 23 thread 24 Internal effective area 1 dry mill 25 thread 2 drive unit 26 Mahlgutabfuhrkammer 3 bearing sleeve 27 annular gap 4 holding piece 28 verge escapement 5 - free - 29 spigot 6 supply port 30 Grinding / conveyor groove 7 Symmetry / rotation axis 31 top 8th withdrawal connection 32 tapered shaft 9 screw 33 Grinding heads 10 shaft end 33A-E Grinding head (alternative shape) 11 drive shaft

Claims (14)

1. A dry ice grinder (1) for a dry ice blasting apparatus (100) comprising
   a first and a second grinding body (12, 22), wherein
   the first grinding body (12) has a rotationally symmetrical outer effective area (13) and the second grinding body (22) has a rotationally symmetrical inner effective area (24), which act as grinding areas,
   the grinding bodies (12, 22) are each arranged, with their outer effective area (13) and their inner effective area (24) facing one another, coaxially and in a manner rotatable relative to one another about an axis of rotation (7), so that
   an annular gap (27) is formed between the outer effective area (13) and the inner effective area (24), wherein, when the grinding bodies (12, 22) are rotated relative to one another, dry ice grinding material (102) gets into the annular gap where it is ground, characterized in that
   in each case a contour course of the outer effective area (13) along the axis of rotation (7) is defined by a first contour line and a contour course of the inner effective area (24) along the axis of rotation (7) is defined by a second contour line, the first and the second contour line being designed in such a way that, with a minimized annular gap (27), the inner effective area (24) and the outer effective area (13) touch one another along an annular line.
2. The dry ice grinder (1) according to claim 1, in which the inner effective area (24) is frusto-conical and the outer effective area (13) comprises a toric region in the region of the annular gap (27).
3. The dry ice grinder (1) according to claim 2, in which the toric region opens into a conical region which forms an end of the first grinding body (12) that projects into a frusto-conical cavity (26) in the second grinding body (22).
4. The dry ice grinder (1) according to claim 3, wherein the frusto-conical cavity (26) between annular gap (27) and an outlet end forms a, in particular rotationally symmetrical, grinding material discharge chamber which opens into a discharge connection (8).
5. The dry ice grinder (1) according to claim 1, 2, 3 or 4, wherein the first grinding body (12) is provided with a drive shaft (11), which passes through a grinding material supply chamber (19), can be coupled to a drive unit (2) and is mounted via a bearing arrangement (14) in a bearing sleeve (3) connected to the drive unit (2).
6. The dry ice grinder (1) according to claim 5, wherein the bearing arrangement (14) and/or the drive unit (2) is sealed towards the grinding material supply chamber (19) via a seal (17), in particular a shaft sealing ring, that acts on the drive shaft.
7. The dry ice grinder (1) according to claim 5 or 6, wherein the grinding material supply chamber (19) is formed in a holding piece (4) which, at one end, is connected to the second grinding body (22) and, at the other end, is coupled to the bearing sleeve (3).
8. The dry ice grinder (1) according to claim 6 or 7, wherein the second grinding body (22) and/or the bearing sleeve (3) are designed so as to be axially adjustable along the axis of rotation (7) with respect to the holding piece (4), so that a width of the annular gap (27) is adjustable.
9. The dry ice grinder (1) according to claim 8, wherein the holding piece (4) is coupled to the bearing sleeve (3) via a spindle arrangement (28, 29), so that, when the holding piece (4) is rotated relative to the bearing sleeve (3), the first grinding body (12) is adjusted axially relative to the second grinding body (22) and the width of the annular gap (27) is thus altered.
10. The dry ice grinder (1) according to any of claims 6 to 9, in which the grinding material supply chamber (19) coaxially surrounds the first grinding body (12) and is provided with a supply connection (6) which opens tangentially and inclined to the axis of rotation (7) into the grinding material supply chamber (19) in order to guide the supplied grinding material (102) into the annular gap (27) like a cyclone through the grinding material supply chamber (19).
11. The dry ice grinder (1) according to claim 8, 9 or 10, in which the second grinding body (22) is exchangeably coupled to the holding piece (4) via a thread (23).
12. The dry ice grinder (1) according to any of the preceding claims, in which the outer effective area (13) and/or the inner effective area (24) ate provided with a surface structure (30) that influences a grinding and/or a conveying effect, in particular with grooves, notches, knobs, teeth, serrations, depressions, spindle/thread structures.
13. The dry ice blasting apparatus (100) for blasting surfaces with a mixture of dry ice granulate (109) and conveying fluid (111), comprising a dry ice grinder (1) according to any of claims 1 to 12.
14. The dry ice blasting apparatus (100) according to claim 13, wherein an additional conveying fluid connection (111) is provided at an outlet end of the dry ice grinder (1), via which the escaping mixture can additionally be supplied with a conveying fluid in order to accelerate the mixture.

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