The present disclosure is directed to industrial centrifuges, in particular, to cylindrical centrifuge baskets for industrial centrifuges and methods of making the cylindrical centrifuge baskets.
Industrial centrifuges are regularly used to extract one or more chemical from a mixture of botanical (plant) matter. A common example is the extraction of sucrose sugar crystals from a processed mixture of sugarcane or sugarbeet biomass, called massecuite. In another botanical product extraction application, an industrial centrifuge can be used in a cold chemical extraction of CBD (cannabidiol) oil from biomass comprising industrial hemp or certain low-THC strains of marijuana. The extraction fluid carrying the CBD oil is forced out through the perforated holes in the basket sidewall of the spinning centrifuge basket by centrifugal forces that can be several hundred times the force of gravity.
Centrifuge baskets for industrial centrifuges can be made by roll forming a solid metal sheet into a metal cylinder, which is then coupled to a ring at one end and a baseplate at the other end to form a solid centrifuge basket. The cylindrical sidewall of the solid centrifuge basket is then perforated to produce the perforated centrifuge basket. However, forming perforations in a cylindrical sidewall is difficult and time consuming, which can increase the costs and cycle times needed to manufacture the centrifuge baskets. In another technique, the solid metal sheet can be pre-perforated when flat and then roll-formed to produce a perforated cylindrical sidewall of the centrifuge basket. However, the perforations in the solid sheet can produce localized weak spots in the perforated metal sheet. These localized week spots can buckle during roll forming to cause faceting and scalloping of the cylindrical sidewall of the centrifuge basket, which can impact the ability to rotationally balance the centrifuge basket. Improper balancing can cause premature wear and failure of the industrial centrifuge.
Accordingly, there is an ongoing need for methods for producing cylindrical centrifuge baskets for industrial centrifuges to improve the efficiency of manufacturing while maintaining the quality of the cylindrical centrifuge baskets. This disclosure relates to methods for the design and fabrication of a cylindrical centrifuge basket for an industrial centrifuge. In particular, the methods of the present disclosure include pre-perforating a solid metal sheet according to a skewed hole pattern in which the rows of perforations are aligned along a line forming a non-zero skew angle with a line of the surface of the solid metal sheet that would be parallel with the axis of rotation (center axis) of the cylindrical centrifuge basket once completed. The perforation pattern comprising a skewed hole pattern may reduce localized weak spots, which may reduce or prevent faceting or scalloping during roll-forming. Pre-perforating the metal sheet prior to roll-forming may increase the efficiency of producing the cylindrical centrifuge baskets. Other features and advantages of the methods of the present disclosure may become apparent through practice of the disclosed methods.
According to one or more aspects of the present disclosure, a method for manufacturing a cylindrical centrifuge basket may include perforating a metal sheet to form a perforated metal sheet having a plurality of perforations aligned along rows extending across a width of the perforated flat metal sheet. Each row may be skewed at a nonzero skew angle relative to a surface line on the perforated metal sheet, where the surface line is parallel to an axis of rotation of the cylindrical centrifuge basket. The method may further include, after perforating the metal sheet to form the perforated metal sheet, roller forming the perforated metal sheet to produce a perforated basket wall sheet, coupling a first edge of the perforated basket wall sheet to a second edge of the perforated basket wall sheet to form a cylindrical basket wall, and coupling a first end of the cylindrical basket wall to a ring, coupling a second end of the cylindrical basket wall to a baseplate, or both to form the cylindrical centrifuge basket.
According to one or more other aspects of the present disclosure, a method of forming a cylindrical basket wall for a cylindrical centrifuge basket may include forming a plurality of perforations in a metal sheet having a longitudinal dimension Y, a first longitudinal end, a second longitudinal end, and a transverse dimension X to produce a perforated metal sheet. The plurality of perforations may be arranged in a plurality of rows spaced apart along the longitudinal dimension Y, each row forming a perforation hole line. Each perforation hole line may form a non-zero skew angle relative to the transverse dimension X of the metal sheet. The method may further include, after forming the plurality of perforations, roller forming the perforated metal sheet to form a perforated basket wall sheet having a circular cross-sectional shape and a center axis wherein the center axis of the perforated basket wall sheet is parallel to the transverse dimension X of the metal sheet. The method may further include coupling the first longitudinal end to the second longitudinal end to form the cylindrical basket wall.
According to one or more other aspects of the present disclosure, a cylindrical basket wall for a cylindrical centrifuge basket made by any of the methods herein is disclosed. The cylindrical basket wall may comprise a plurality of perforations on the cylindrical basket wall, the cylindrical basket wall having on the cylinder surface a dimension X parallel to the cylindrical axis and an orthogonal circumference dimension U. The plurality of perforations may be arranged in a plurality of rows spaced apart along the orthogonal circumference dimension U, each row forming a perforation hole line having a non-zero skew angle Θ relative to a line on the surface the cylindrical basket wall parallel to the dimension X. The surface of the cylindrical basket wall may be divided into a plurality of N adjacent bands in the orthogonal circumference dimension U around the cylindrical basket wall, where N is an integer. Each of the plurality of adjacent bands may have a band length ΔU equal to or less than the maximum dimension of the perforations in the orthogonal circumference dimension U, a band width equal to the height H of the cylindrical basket wall in the dimension X, a total band surface area equal to H×ΔU, and a lost metal area B representing the area lost due to perforations present in the band. The Variance (B, Θ) in the lost metal area B over the N number of adjacent bands for the perforated cylinder having the non-zero skew angle Θ may be less than 20 percent of the Variance (B, 0°) in the lost metal area B over the N number of adjacent bands for a comparable perforated cylinder having a skew angle equal to 0°, where the Variance (B, Θ) function is the statistical variance function of B over the N bands on the surface of the cylinder.
The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:
Many industrial centrifuges use a perforated cylindrical separation basket, which can be formed by welding a roll-formed solid cylindrical basket wall sheet to the edges of a reinforcing ring at the top and disk-shaped baseplate at the bottom. The bottom disk-shaped baseplate comprises the basket floor and provides an attachment to the motor drive spindle. In conventional methods of producing a cylindrical centrifuge basket, the cylindrical basket wall is perforated after assembly of the cylindrical centrifuge basket, such as after roll-forming and attaching the reinforcing ring and disk-shaped baseplate. Conventional perforation designs place the lines of perforation holes in rows parallel to the rotational axis of the cylindrical centrifuge basket (e.g., the center axis of the cylindrical centrifuge basket). Pre-perforating a rectilinear hole pattern on the flat metal sheet prior to roll-forming can result in repetitive (regular and recurring) regions of sheet weakness which could cause a pre-perforated sheet to buckle and fold along these lines during roll-forming. The resulting output from the roll-forming process would be a perforated cylinder having a faceted polygon cross-sectional shape rather than a circular cross-sectional shape, which may make it more difficult to dynamically balance the cylindrical centrifuge basket.
The methods of the present disclosure are directed to methods of producing cylindrical centrifuge baskets by pre-perforating a metal sheet according to a hole pattern designed so that the perforation holes are in rows aligned along perforation hole lines that form non-zero skew angles with a line on the surface of the cylindrical basket wall parallel to the center axis of the cylindrical centrifuge basket. In particular, the methods of the present disclosure may include perforating a metal sheet to form a perforated metal sheet having a plurality of perforations aligned along rows extending across a width of the perforated flat metal sheet. Each row may be skewed at a nonzero skew angle relative to a surface line on the perforated metal sheet, where the surface line is parallel to an axis of rotation of the cylindrical centrifuge basket. The method may further include, after perforating the metal sheet to form the perforated metal sheet, roller forming the perforated metal sheet to produce a perforated basket wall sheet, coupling a first edge of the perforated basket wall sheet to a second edge of the perforated basket wall sheet to form a cylindrical basket wall, and coupling a first end of the cylindrical basket wall to a ring, coupling a second end of the cylindrical basket wall to a baseplate, or both to form the cylindrical centrifuge basket. The methods of the present disclosure may enable the metal sheet to be more efficiently pre-perforated and then roll-formed into a cylinder while avoiding faceting or scalloping. Thus, the methods of the present disclosure may improve the manufacturing time and cost of the cylindrical centrifuge baskets with little or no changes in cylindrical centrifuge basket quality or performance.
Referring now to
Referring again to
Referring again to
A cross-sectional view of the cylindrical centrifuge basket 100 is shown in
The cylindrical centrifuge basket 100 may spin at rotational speeds of approximately 1500 RPM or more, which may produce 900 G or more of centrifugal force. Therefore, dynamic balancing of the empty cylindrical centrifuge basket 100 and balancing of the entire industrial centrifuge 10 can reduce or prevent vibrations which could damage the industrial centrifuge 10.
Referring now to
For reference, coordinate axes X, Y, and Z are defined in
As shown in
A typical 3-roller sheet bending machine 300 is shown schematically in
Bottom anvil rollers 320 and 330 are coupled to the 3-roller sheet bending machine 300 in a manner that allows for variable spacing between the bottom anvil rollers 320 and 330. When bottom rollers 320 and 330 are coupled to simultaneously drive the intermediary sheet 220 in an anticlockwise direction, then the passive upper roller 350 rotates in a clockwise direction
Bending of the intermediary sheet 220 may be done by applying a controlled force 350 to the movable upper roller 310 in a downward direction toward the bottom anvil rollers 320, 330. This controlled force 350 acting on the intermediary sheet 220 through upper roller 310 may cause plastic deformation of the entering intermediary sheet 220 material so that a continuously curved sheet 360 emerges from the 3-roller sheet bending machine 300 with the desired radius of the cylindrical basket wall 110.
There are several methods of fabricating the finished cylindrical centrifuge basket 100 having perforations in the cylindrical basket wall 110. In a first fabrication method, since it is easier to roll a flat, unperforated sheet 200 into a continuous curve, the drilling of holes for the perforations can be done after the cylindrical basket wall 110 is fully formed and welded to the reinforcing ring 120 and the disk-shaped baseplate 130. In this method, the solid unperforated sheet is rolled and welded to produce a cylinder, attached to the reinforcing ring 120 and disk-shaped baseplate 130, and then perforated to form the perforation holes 112 in the cylindrical basket wall 110. The perforation holes may be radially drilled or end-milled on a 4-axis horizontal boring mill (3-axis horizontal boring machine plus a rotating table as a 4th axis). Alternatively, the perforation holes 112 may be water jet or laser cut.
In a second fabrication method, the sheet 200 for forming the cylindrical basket wall 110 can be pre-perforated while flat, prior to rolling the sheet 200 into the cylindrical basket wall 110. Hole-forming is much easier and faster on the flat sheet 200 compared to forming holes in a cylinder and may allow for production of a variety of hole shapes, such as polygonal or other non-round shapes, through water jet or laser cutting, die punching, or broaching.
However, in the second fabrication method, the pre-perforation of the sheet 200 before roll forming the sheet 200 into the cylindrical basket wall 110 may create problems in the sheet rolling process of
When any sheet 200 or intermediary sheet 220 of constant thickness t and width W is passed through the 3-roller sheet bending machine, there is a bending stress S proportional to the rolling force F (ref. 350 in
In the case of a line of perforations across the width W of the sheet 200, the cross-sectional area Axz is reduced by the material removed where the perforation holes 112 are, and thus the sheet 200 is weakened. As the XZ cross-sectional area Axz decreases, the bending stress S resulting from constant force F will increase. Along the centerline of the perforation holes 112, each hole reduces the XZ cross-sectional area Axz by an amount equal to t x D, where D is the diameter of the holes. In the case of a number (M) of holes of diameter (D) along that centerline, the centerline XZ cross-sectional area Axz can be expressed by the following Equation 1 (Eqn. [1]).
A
XZ
=tW−M(tD)=t(W−MD) Eqn. [1]
If the perforated sheet is significantly weakened and the bending stress S is elevated, this may cause the perforated sheet to start to fold or buckle along the along the weakened portion of the perforated sheet. Thus, the propensity of the sheet 200 to fold or buckle along a line parallel to the width W of the sheet 200 during roller forming may be proportional to the amount of material removed alone that line to create the perforation holes 112.
The propensity of regions of the sheet 200 for experiencing folding or buckling during roller forming may be modeled by dividing the sheet 200 into a series of narrow bands, each of which extends across the sheet width W so that each of the bands has a width equal to the sheet width W. Each successive band along the Y direction integrates the effect of the XZ cross-sectional area removed over a short length, such as a band having a length ΔY=D, where D is the hole diameter of the perforation holes 112. For a sheet 200 of constant unit thickness t, the total area represented by each band before forming perforations is ΔY×W=D×W. The amount that the sheet 200 has been weakened by forming the perforation holes 112 in the sheet 200 can be approximated by the % Material Remaining, which is the total area of the band (ΔY×W or D×W) minus the area of material removed after forming the perforation holes (M×D), which is denoted by the lost metal area B (where B=M×W). The % Material Remaining (% MR) can be determined by the following Equation 2 (Eqn. [2]).
If there are significant and cyclic differences in % MR between the bands along the sheet 200, then the sheet 200 entering the gap formed by rollers 310, 320 and 330 may tend to buckle and fold rather than to deform into a smooth continuous curve. The greater the cyclic variability in the % MR, the greater the probability that the sheet 200 will buckle and/or fold in the bands having lesser % MR. The result of the rolling process may be a rolled sheet having a cross-sectional shape that is faceted like a scalloped polygon with folds at the hole lines between the scalloped curved sections, rather than a smoothly curved cylinder having a circular cross-sectional shape.
Once assembled, the cylindrical centrifuge basket 100 with the perforation holes 112 then must be dynamically balanced. Faceting or scalloping can make the cylindrical centrifuge basket 100 much harder to dynamically balance. In addition, the high G-forces during centrifugation may cause biomass material to collect in the interior facet corners of the cylindrical basket wall 110, which can create or further exacerbate any dynamic balancing issues.
Referring now to
Rolling a flat sheet 200 with more uniformly distributed holes over the sheet 200 can reduce the tendency of the sheet 200 to fold or buckle, as the material strength is more consistent between bands. Referring now to
Forming the cylindrical basket wall 110 from a pre-perforated sheet 200 in which the perforation hole lines for a non-zero skew angle θ with a line on the surface parallel to the axis of rotation of the cylindrical basket wall 110 may produce the cylindrical basket wall 110 and cylindrical centrifuge basket 100 having a circular cross-sectional shape that is not faceted or polygonal. In embodiments, no portion of an inner surface 114 of the cylindrical basket wall 110 and/or the cylindrical centrifuge basket 100 is flat. In embodiments, no portion of an inner surface 114 of the cylindrical basket wall 110 and/or the cylindrical centrifuge basket 100 made therefrom has a radius of curvature that differs by more than 2% from the mean radius of curvature relative to the cylindrical axis of the cylindrical basket wall 110.
Applying the same banding model above, with a skewed perforation hole line 470, the band strength of the bands will vary along the sheet depending on what percentage of each band comprises partial and/or complete perforation holes 112. Since the impact of the skew angle θ of the perforation hole line 470 on the band strength is not obvious, a simple qualitative exemplary model was made using a square grid and is shown in
In the exemplary model of
For each of the three models of
The relative band strength in each band is presented in the graph in
In
In looking at Table 1, the characteristics of the Lost Metal Area B data column for each skew angle Θ vary substantially. Note that a total of 40 s2 hole area are lost in every cycle of 10 bands in each of
The standard statistical measure of variance of the band sample lost metal area B can be calculated over one 10 band cycle here using function VAR.P in Microsoft Excel on the bands 1-10 data in Table 1. Variance (B, Θ) is used to illustrate the differences from band to band in lost area B at different skew angles Θ and is summarized in Table 2:
When the perforation hole lines are parallel to the X direction at θ=0° skew, as in
The above exemplary model is illustrates how skewing of the perforation hole lines can improve the rolling properties of a pre-perforated sheet for making the cylindrical basket wall 110, and that improvement in sheet uniformity caused by introducing a non-zero skew angle θ can be quantitatively measured using the banding method and Variance (B, Θ).
Referring again to
For the cylindrical centrifuge basket 100 of
Note that mean lost metal area B is constant over all bands in a cycle: Skewing the perforation hole 112 lines only redistributes the hole area over different bands in the cycle, which changes the Variance (B, Θ) data. Looking at Variance (B, Θ) data as a percentage of the rectilinear unskewed case Variance (B, 0°) shows that even a small amount of skew (here 1.5°) can have a significant effect on the hole distribution uniformity of the perforated cylindrical centrifuge basket 100.
Referring now to
A small range in % MR along the sheet 200 can greatly reduce the effect of the perforation holes 112 on the consistency of the cylinder formation in roll-forming a pre-perforated sheet 200 to produce the cylindrical basket wall 110. Production of a uniformly curved cylindrical basket wall 110 may enable easier dynamic balancing of the basket 100 and predictable centrifuge performance.
Skewing of the perforation hole line 470 for the perforation holes 112 of the cylindrical centrifuge basket 100 also may enable the pre-perforation of the flat sheet prior to formation of the cylindrical basket wall 110 through roll forming. Use of skewed perforation hole lines on a flat sheet 200 which is pre-perforated prior to cylinder rolling thus may improve the cost and time of manufacturing of cylindrical centrifuge baskets 100 compared to the conventional post-assembly perforating method.
Many modifications and other embodiments of the present disclosure set forth herein will come to mind to one skilled in the art to which this subject matter pertains, once having the benefit of the teachings in the foregoing descriptions and associated drawings. Therefore, it is understood that the subject matter of the present disclosure is not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purpose of limitation.
This application claims the benefit of priority under 35 U.S.C. § 120 of U.S. Provisional Application No. 62/986,240, entitled “Method of Industrial Centrifuge Basket Perforation,” filed Mar. 6, 2020, the entire contents of which are incorporated by reference in this disclosure.
Number | Date | Country | |
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62986240 | Mar 2020 | US |