Rotary Foodstuff Mill

Technical Field

The invention relates to a rotary mill for milling particulate material such as grains and legumes.

Background Art

Rotary disintegrators in which particulate material is passed radially outward between interposed, widely spaced rows of pins or bars extending from opposed surfaces of a pair of rotors or a rotor-stator combination are described in US Patents Nos 901,217 and 3,497,144. These disintegra¬ tors operate at relatively low speeds and apparently grind the material between the pins or bars or break the material through impact with the bars or pins.

US Patent No 3,815,835 discloses a rotary disintegrator in which particulate material is disintegrated by passage between interposed rings of frustoconical teeth on a rotor and stator. The space between teeth in each ring is identical. The spaces between teeth also are inclined relative to the direction of rotation.

Disclosure of Invention

A principal object of the invention is to provide a mill and milling process that is adaptable for use in home kitchens to mill foodstuffs such as dried fruit, dried vegetables, grain, sugar, and legumes efficiently and cleanly to a uniform particle consistency.

Accordingly one aspect of the invention is a rotary mill that includes: a housing; a first wheel mounted within the housing and having concentric rows of circumfer- entially spaced tapered plane-sided blades extending from one of its faces; and a second wheel mounted within the housing in spaced, axial alignment with the first wheel and also having concentric rows of circumferentially

tapered plane-sided blades extending from one of its fac The blades of both wheels have a greater circumferential dimension than radial dimension. The first and second wheels are positioned with their respective rows of blades interposed in spaced, alternating relationship. spacing between blades in the innermost row of the inter posed rows must be at least equal to the maximum nominal particle size of the particles of material to be milled the spacing between the blades of the outermost row of t interposed rows must be less than the spacing between bl in the innermost row and be at least equal to the desire maximum nominal particle size of the milled material. T mill also includes an inlet in the housing for receiving the material to be milled that opens into the space betw the wheels radially inward of the innermost row of blade an outlet in the housing for discharging the milled mate located radially outward of the outermost row of the int posed rows of blades; and driving means connected to at least the wheel on which said innermost row is located f rotating that wheel such that the relative linear veloci between the innermost row of blades and the row next adj cent to the innermost row is sufficient to shear the material to be milled between the blades of the innermos row and the blades of said next adjacent row. The term "maximum nominal particle size" used herei means the largest dimension of the average particle of material to be milled or milled material, as the case ma be.

Another aspect of the invention is a process for milling a particulate material. The first step of the process is positioning a first wheel having concentric r of circumferentially spaced, tapered plane-sided blades extending from one of its faces in spaced axial alignmen with a second wheel that also has concentric rows of cir ferentially spaced, tapered plane-sided blades extending from one of its faces such that the rows of blades on th wheels are interposed between each other. The circumfer tial spacing between blades in the innermost row of the

interposed rows must be at least equal to the maximum nominal particle size of the material to be milled and the circumferential spacing between blades in the outermost row of the interposed rows must be less than the circumferential spacing between blades in the innermost row and be at least equal to the desired maximum nominal particle size of the milled material. The next step is feeding the material into the axial space between the wheels radially inward of said innermost row. The third step is rotating at least the wheel on which the innermost row is located at a speed sufficient to cause the material: to move through the spaces in the innermost row, to be sheared between the blades of the innermost row and the row next adjacent the innermost row, and to pass successively outwardly through the spaces between the blades of the interposed rows and be successively comminuted to a smaller particle size as it passes through each row. There is no significant recirculation of material inwardly. The last step of the process is to collect the material once it has passed through the spaces between the blades in the outermost row of the interposed rows.

Brief Description of Drawings

In the drawings:

Fig 1 is a perspective view of the preferred embodiment of the mill;

Fig 2 is an enlarged sectional view of a portion of the mill of Fig 1 taken along line 2-2 of Fig 1;

Fig 3 is an enlarged, exploded view of the milling assembly of the mill of Fig 1 with one of the milling elements rotated 90 relative to the other;

Fig 4 is an enlarged vertical sectional view of a portion of the assembly of Fig 3' showing the milling elements in operating position;

Fig 5 is an enlarged perspective view of a portion of one of the milling elements showing the structure of the element's blades;

Fig 6 is an enlarged plan view of a portion of one of the milling elements of Fig 3;

Fig 7 is an enlarged plan view of a portion of the other milling element of Fig 3;

Fig 8 is a top plan view of a portion of the mill o Fig 1; Fig 9 is a sectional view of the mill of Fig 1 take along line 9-9 of Fig 8;

Fig 10 is an enlarged, exploded view of a portion o the mill of Fig 1 showing the feed regulating means of t mill; and Fig 11 is an enlarged, partly sectional view of a portion of the mill of Fig 1 showing a cyclone separator assembly of the mill.

The front of the mill is toward the left in Figs 1 2. Like numerals refer to like parts in the drawings.

Best Mode for Carrying Out the Invention

Fig 1 depicts a rotary mill, generally designated 1 that is designed as a small kitchen appliance for millin raw, substantially dry, particulate foodstuffs such as d fruit, dried vegetables, wheat, rye, rice, sugar, and soybeans into cracked, powdered, or flour form. Mill 14 simple to operate and requires minimal cleaning. It als has no moving parts that are easily accessible to the us Furthermore, it is small enough to be stored easily. Mill 14 is presented to the user in two separable p a mill assembly, generally designated 15, and a milled product receiving pan 16. The outer configuration of assembly 15 and the inner configuration of pan 16 are su that assembly 15 may be turned upside down and placed in pan 16 for storage. The storage position of pan 16 is shown in phantom in Fig 2.

Referring to Figs 1 and 2, the major part of mill assembly 15 that is seen by the user is a housing 17 tha consists of a cover 18 and a base plate 19. Cover 18 prevents easy user access to the electrical and moving p of .assembly 15. Its top wall 22 has a generally L-shape recess 23 that extends along the front and one side of c 18 and serves as a hopper for the material to be milled.

shown in Fig 2 bottom wall 24 of hopper 23 slopes such that the material to be milled gravitates towards a feed orifice 25 at the bottom of inside, front wall 26 of hopper 23. (Material gravitation into orifice 25 is indicated by the solid arrow in Fig 2.)

Cover 18 also has a series of air vents 27 along the top edge of wall 26 that constitute part of the feed regulation means (described in detail below) of mill 14. It further has a shoulder 32 extending about its lower periphery into which a corresponding peripheral shoulder 29 of base plate 19 fits. Base plate 19 is affixed to cover 18 by screws, such as 32, that are received in threaded lugs, such as 33, projecting from the underside of cover 18 (Fig 2). Base plate 19 also prevents user access to the electrical and moving parts of mill assembly 15. It is also a mounting site for a motor-milling element subassembly, generally designated 34. Subassembly 34 basically comprises an electric motor 35, a rotor-stator housing 36, a rotor 37, and a stator 38. Rotor 37 and stator 38 are the milling elements of mill 14 and motor 35 is the drive means of the mill.

Motor 35 operates on 120 V ac and may be connected to line voltage by a conductor line 39 and a plug 42. Line 39 runs through a single pole, double throw switch 43 that has on, off, and pulse operation positions.

Motor 35 is a high speed motor that is capable of rotating its driving shaft 44 at speeds in the range of about 15,000 rpm to about 30,000 rpm. In lightweight embodiments of the invention, such as mill 14, the relative positions of motor 35 and hopper 23 are important in order to keep the motor torque ^' from flipping the mill over. When the hopper is to the right of the motor (as in Fig 1) , the rotor should rotate counterclockwise, and vice versa _a As shown in Fig 4 the journaling of shaft 44 is such that a slight axial movement of shaft 44 (indicated by the double- headed arrow in Fig 4) is permitted. Structure that permits such movement includes a reduced diameter forward end 45 of

shaft 44, a boss 46 on the rear side of rotor 37 that encircles end 45, a notch 47 in housing 36 that also encircles end 45, and a shaft bearing 48 that rides in t space between the rear end of boss 46 and the junction between end 45 and the remainder of shaft 44. As seen i Fig 4, the inner race of bearing 48 fits tightly between boss 46 and shaft 44, whereas the outer race of bearing is free to move axially. As discussed below, this axial movement permits the axial spacing between rotor 37 and to be varied. Shaft 44 has a threaded portion 49 at the tip of its forward end 45 for receiving rotor 37.

Rotor-stator housing 36 is mounted on the front sid of motor 35 by screws (not shown) or other suitable atta ment means. Housing 36 has a cylindrical recess 52 in i front side 53 for receiving rotor 37 and stator 38. A cylindrical orifice 54 extends axially through housing 3 at the center of recess 52. Shaft 44 extends freely thr orifice 54.

Figs 3 and 4 show the basic structures of rotor 37 stator 38 and their spatial relationship to each other. Rotor 37 has a disc-shaped body 55 with six concentric, spaced rings or rows 56 of circumferentially spaced blad 57 extending generally perpendicularly from its front fa 58. Body 55 has an axial bore 59 that receives shaft 44 A nut 50 affixes rotor 37 to end 45 of shaft 44 within recess 52.

Stator 38 also has a disc-shaped body 62. Six conc tric, spaced rings or rows 63 of circumferentially space blades 64 extend generally perpendicularly from the rear face 65 of body 62. Referring to Fig 4, rotor 37 and st 38 are positioned in spaced, axially aligned relationshi with their respective faces 58, 65 opposed and parallel rows 63 of stator 38 interposed in the valleys between t rows 56 of rotor 37. The radially innermost row of inte posed rows 56, 63 is on rotor 37 and is designated 66. radially outermost row of interposed rows 56, 63 is on stator 38 and is designated 67. Radially inward of row is a central space 68 into which unmilled particulate

material is fed from hopper 23 via feed inlet 25 which is defined by an orifice 69 in stator body 62 below the axis thereof.

As shown in Figs 2 and 3 recess 52 of housing 36 is open at the bottom edge of housing 36 to permit the bottom of the rotor-stator combination to extend slightly below the bottom of housing 36 and through a recessed product outlet opening 72 in base plate 19.

The circumferential spacing of blades 57 in row 66 of rotor 37 (represented by the letter "a" in Fig 7) , the radial spacing between rotor rows 56 and stator rows 63 (represented by the letter "b" in Fig 4) and the axial spac- ings between rotor 37 and stator 38 (represented by the letter "c" in Fig 4) are important features of the mill. Those spacings affect the particle size and uniformity of the milled product. The circumferential spaces between both rotor blades 57 and stator blades 64 are oriented substan¬ tially radially, that is they are generally perpendicular rather than inclined relative to the direction of rotation of rotor 37. For foodstuff milling, the minimum circum¬ ferential spacing between blades in row 66 is about 0.4 cm. Such spacing permits the unmilled feed to pass through the voids between blades in row 66. If the spacing was signifi¬ cantly less than 0.4 cm the feed would tend to remain within space 68 rather than passing through said voids. The radial spacing between rows 56, 63 should be between about 0.05 cm and about 0.09 cm. Radial spacing below 0.05 cm may not provide sufficient clearance tolerance to insure that the rows do not contact each other when the mill is operated. Radial spacing significantly greater than 0.09 cm may cause the milled product to be coarse. The axial spacing between

_* — rotor 37 and stator 38 may vary between about 0.05 cm and about 0.2 cm, with the particle size of the milled product varying accordingly from very fine flour to coarse consis- tence over the spacing range.

The circumferential spacing between blades 64 in outer¬ most row 67 of stator 38 (represented by the letter "d" in Fig 6) should be large enough to permit product of cracked

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particle size to pass through the voids between the blades in row 67. Therefore, that spacing should be at least 0.12 cm. Accordingly, the circumferential, spacing between blades 57 and 63 is not equal in each of rows 56, 63. Instead, as indicated, the blade spacing in outermost row 67 is less than the blade spacing in innermost row 66. The decrease in blade spacing may be progressive (spacing is less in each outwardly succeeding row) or stepped (two of more successive rows have identical spacing) . Circumferential spacing between blades in the rows 56, 63 intermediate rows 66, 67 should also be at least about 0.12 cm.

The shapes of the rotor blades 57 and the stator blades 64 are also important. As shown in Fig 5 blades 57 and 64 are plane-sided bodies that have two opposing radial sides, two opposed circumferential sides, and a top side. The blades are elongated circumferentially, that is their circum¬ ferential dimension is greater than their radial dimension. The circumferential and radial sides taper at least about 2 , causing the blades to have a trapezoidal "cross-section either circumferentially or radially (Figs 4 and 5) . Prefer¬ ably all sides taper to the same degree. Such taper enhances the strength of the blades and enables them to withstand the forces applied to them without breaking. The _. blade thickness at base and tip (represented by the letters "e" and "f", respectively, in Fig 5) also affects blade strength. Rotors and stators made from stainless steel or aluminum having blades with a base thickness of 0.18 cm and tip thick¬ ness of 0.08 cm have been used without breakage. The width- and length of the blades are believed to be of lesser importance. Both are desirably at least about 0.5 cm.

The rate at which unmilled feed enters milling element subassembly 34 via orifices 25, 69 is controlled pneumatic¬ ally by regulating the amount of air that mixes with the feed in space 68 between rotor 37 and stator 38. The less air, the greater the feed rate and vice versa. As discussed in detail below the feed rate in turn affects and controls . the particle size of the milled product,, The feed regulation means is shown in Figs 2 and 8-10. Air enters the means

through air vents 27 in wall 26 of hopper 23. Air flow is indicated by the dashed arrows in Fig 2 and the dashed and solid arrows in Fig 9. Air is drawn through vents 27 by the suction created by the rotation of rotor 37. The amount of air permitted to enter through vents 27 is regulated by a damper mechanism, generally indicated 73. Damper 73 consists basically of a discoid control knob 74 that functions as a cam and a horizontally slidable member 75 that acts as a follower. Control knob 74 has an upstand- ing finger grip 76 on its top side, an increased diameter mid-section 77, and an eccentrically positioned shaft 78 extending downwardly from its bottom side. Knob 74 is seated in a stepped circular opening 79 in wall 22 of cover 18 with mid-section 77 resting on the step and shaft 78 extending down through opening 79. Shaft 78 is received in an oblong opening 82 in member 75 and is held in place by a snap- fitting washer 83 that fits around the bottom end of shaft 78. Front end 84 of member 75 has a leading ridge 85 and a following furrow 86 (Figs 2 and 10) . Ridge 85 is slightly wider than the row of air vents 27 and its height (vertical dimension) is slightly greater than the height of vents 27. Accordingly, when member 75 is slid to its forwardmost position, front face 87 of ridge 85 is proximate to the inside of wall 26 behind vents 27, thereby substantially covering and blocking or closing vents 27. Top side 88 of ridge 85 rides against the interior side of wall 22 and the bottom side 89 of furrow 86 (Fig 2) rides against the top edge 92 of rotor-stator housing 36, thus inhibiting member 75 from moving vertically. The ends of ridge 85 and furrow 86 ride within a pair of parallel, lateral ways 93 (Fig 8) . Rear end 94 of member 75 has a slot 95 in which a stop member 96 extending downwardly from the interior side of wall 22 is received. When member 75 is slid rearwardly such that the closed (front) end of slot 95 engages stop 96, damper 73 is wide open and permits maximum air flow through vents 27.

As depicted in Figs 2 and 8 air entering vents 27 is drawn downwardly between face 87 and the inside of wall 26

into a channel 97 defined by the inside of wall 26, the front side of stator 38, ways 93, and a bottom wall 98. From channel 97 the air passes rearwardly through an elo gated opening 99 in stator 38 into space 68 to mix with incoming feed.

The rotation of rotor 37 creates substantial air fl and pressure in receiving pan 16 when mill 14 is operati It was thus found desirable to provide mill 14 with a cyclone-type inertial separator, generally designated 10 to collect the milled product of fine particle size that entrained in the air as a result of said air flow and pressure. The mill is also provided with an air filter assembly, generally designated 103, from which the air f the separator 102 is vented to the atmosphere. Without separator the entrained particles of milled product tend be blown out of receiving pan 16 around- the periphery thereof at the junction of shoulders 28 and 29. This oc notwithstanding the presence of a gasket 104 at the junc Cyclone separator 102 and air filter assembly 103 a illustrated in Figs 1 and 8-10. Separator 102.consists a two-segment telescoping cylindrical cup 105 whose uppe segment 106 is received partly in a generally cylindrica recess 107 formed in the bottom of base plate 19 near th front corner thereof. The lip 108 of cup 105 fits into groove within recess 107 to hold cup 105 in place. A vertically elongated air outlet passageway 109 is formed base plate 19 generally centrally within recess 107. Th lower end of passageway 109 extends below the lip of cup 105. Cup 105 has a flat, tapered handle 110 that extend outwardly from the exterior of segment 106 slightly belo the lip of the cup. Handle, 110 is thus in spaced, paral position relative to the bottom of base plate 19. Handl 110 together with base plate 19 and a vertical wall memb 112 extending downwardly from the bottom of base plate 1 the exterior of recess 107 define a tangential inlet 113 separator 102. As illustrated in Figs 9 and 11 a vortex mode of air flow is created within cup 105 as a result o tangential inlet 113.

Air filter assembly 103 is received tightly within the upper end of passageway 109 by means of a cylindrical connector 114 that is an integral part of housing 115 of assembly 103. Housing 115 has a rectangular opening 116 that registers with a like-shaped opening 117 in cover 18. The portion of housing 115 about opening 116 seats tightly against the inside of cover 18 at the periphery of opening 117. The tight fits between housing 115 and passageway 108 and cover 18 ensure that air flow from cup 105 to the atmosphere occurs via air filter assembly 103. An F-shaped filter element 118 is removably received within housing 115 through openings 116, 117. Filter element 118 traps entrained milled product particles that did not settle in separator 102. Element 118 may be made from porous or fibrous plastic or natural materials.

When mill 14 is stored, lower segment 119 of cup 105 may be retracted into upper segment 106 and the retracted cup placed into hopper 23.

Mill 14 is very easy to operate. Starting from their ' stored positions, mill assembly 15 and receiving pan 16 are first separated and segment 119 is telescoped out of segment 106 and cup 105 is inserted into recess 107. Assembly 15 is then placed on top of pan 16 as shown in Fig 1 and in solid line in Fig 2. Air damper mechanism 73 is then adjusted to the desired position by turning knob 74. As indicated previously when damper 73 is wide open a maximum amount of air mixes with the feed. Under these conditions the feed rate is minimized and a minimum load is placed on motor 35. Motor 35 thus runs at near top speed thus permitting mill 14 to mill the feed to a fine particle size. Vice versa, when mechanism 73 is closed a minimum quantity of air mixes with the feed. When this occurs, the feed rate is maximized and so is the load on motor 35. The greater load causes a decrease in the speed of rotor 37, which in turn results in a coarsely milled product. Damper settings intermediate full open and full close provide a product having particle sizes intermediate that of the full open product and the full close product. Markings indicating the

varying degree of particle size may be made about the periphery of opening 79 to guide the user in selecting t desired position for damper 73. After setting damper 73 foodstuff to be milled is dumped into hopper 23. Mill 1 is then plugged into line voltage via line 39 and plug 4 Motor 35 is then activated by moving switch 43 to its on position. Turning motor 35 on forces its driving shaft to its forwardmost position (axial spacing between rotor and stator 38 is about 0.05 cm) and rotates rotor 37. After motor 35 is turned on, the foodstuff gravitat from hopper 23 through orifices 25 and 69 into the centr space 68 between rotor 37 and stator 38. The foodstuff flung outwardly in space 68 (by the rotation of rotor 37) and into ^' the voids between blades 57 of row 66. There i is sheared between those blades and the blades 64 of the adjacent row 63 of stator 38. The linear velocity of bl 57 of row 66 is an important operating parameter of mill In order to mill foodstuff to a uniform, fine consistenc the linear velocity of blades 57 of row 66 must be at le about 45 meters/second, preferably in the range of 45 to

250 meters/second. The linear velocity will depend upon rotational velocity of rotor 37 and the distance of row from the axis of rotation. The above linear velocities must be maintained under load, that is during milling. The portions of the foodstuff that are sheared off between row 66 and the adjacent row 63 of stator 38 pass into the voids between the blades of said adjacent row 6 of stator 38. It then is comminuted by shearing by and/ impact with the next adjacent outward row of blades of rotor 37. In this manner the foodstuff passes successiv outwardly through the voids in the rotor and stator blad rows and is successively comminuted to a finer consisten at each row. There is no significant recirculation of foodstuff inwardly. Once it reaches outermost row 67 of stator 38 it passes through the voids thereof and drops of mill assembly 15 into pan 16 via outlet opening 72 in base plate 19. Any fines or light components (eg, bran) the product that became entrained in the air circulating

within pan 16 collect in cup 105 of separator 102 or are entrapped in filter element 118.

A milled product of cracked consistency may be made by closing damper 73 and moving switch 43 to its pulse opera- tion position. This causes the motor 35 to turn off and on which in turn causes shaft 44 to move rearward, thus increasing the axial spacing between rotor 37 and stator 38 (maximum 0.2 cm). This rearward motion of shaft 44 occurs automatically due to the relaxation of the magnetic field generated by motor 35.

After all the foodstuff has passed from hopper 23, the mill is permitted to run for a few seconds to allow all the foodstuff to clear from mill assembly 15. This clearance is evidenced by an increase in the speed of motor 35 as it transitions from load to free-running conditions. The mill is then turned off by moving switch 43 to its off position. Mill assembly 15 is then lifted from pan 16 to expose the milled product. If mill assembly 15 is inadvertently lifted from pan 16 without turning the mill off, row 67 of stator 38 acts as a guard to keep the user's hands out of contact with rotor 37. Cup 105 is removed from recess 107 and its contents are discarded or mixed with the rest of the product in pan 16, as desired.

In normal operation the foodstuff passes cleanly and completely through mill assembly 15 into pan 16. According¬ ly, the only clean up that is ^' required is to wipe the bottom of base plate 19, the interior of pan 16, and cup 105 once the milled product has been removed therefrom. Filter element 118 should be cleaned periodically. This may be done by withdrawing it from within housing 115 via opening 116 and washing it with air and/or water.

As indicated above mill 14 is designed as a home kitchen appliance. Other home kitchen embodiments or embodiments intended for other uses such as commercial or industrial milling of foodstuffs or other particulate material such as ores and crystalline chemicals may involve modifications of mill 14. Such modifications might include having more or fewer rows of blades on the rotor and stator,

^■ BU REA OMP

using a second rotor in place of the stator, employing a rotor/stator combination of larger diameter, increasing spacing between the innermost row of blades on the rotor accommodate larger material, or using other means such a a lever to move the motor shaft and vary the axial spaci between rotor and stator. In this regard home kitchen embodiments will usually have 4 to 12 rows of blades on their rotors and an equal number of rows of blades on th stators. Embodiments in which a second rotor is used in place of a stator will require two motors, since the rot will be rotated in opposite directions. Such embodiment will permit lower ^' blade velocities since the relative velocity between adjacent rows of blades will be greater when these rows are rotating in opposite directions. However, such embodiments are not preferred for home kitchens since the second motor makes the mill larger, heavier, and expensive.

These and other modifications that are within the ordinary skill of workers in the mechanical and milling are intended to be within the scope of the following cla

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