US3577649A - Device and method for controlling bulk density of dehydrated foodstuffs - Google Patents

Abstract

Bulk density of high-sugar-content dehydrated foodstuff is regulated by varying the thickness of the sheet of the said dehydrated foodstuff as it is being discharged from a drum dryer. The thickness of the said sheet is here varied upon varying the angle of attack of the doctor blade in respect to the drum surface of a drum dryer.

Description

United States Patent [72] Inventors James I. Wadsworth;

Alexander S. Gallo, Metairie; George M. Ziegler, .lr., llarahan; James J. Spadaro, New Orleans, La.

[21 1 Appl. No. 872,795

[22] Filed Aug. 29, 1969 Division of Ser. No. 690,536, Dec. 14, 1967,

Pat. No. 3,494,050

May 4, 1971 The United States of America, as

represented by the Secretary of Agriculture [45] Patented [73] Assignee [54] DEVICE AND METHOD FOR CONTROLLING BULK DENSITY F DEl-IYDRATED FOODSTUFFS 1 Claim, 6 Drawing Figs.

[52] U.S.C1 34/110, 1 256.5 1

[51] Int. Cl F26b 17/28 Field ofSearch 15/256.51, 256.53,256.5; /1 12, 174; /91; 241/166,

[56] References Cited UNITED STATES PATENTS 3,187,718 6/1965 Coghil] 15/256512 FOREIGN PATENTS 316,484 1 H1956 Switzerland 241/166 Primary Examiner-Walter A. Scheel Assistant Examiner-Leon G. Machlin Attorneys-R. Hofiman and W. Bier ABSTRACT: Bulk density of high-sugar-content dehydrated foodstuff is regulated by varying the thickness of the sheet of the said dehydrated foodstuff as it is being discharged from a drum dryer. The thickness of the said sheet is here varied upon varying the angle of attack of the doctor blade in respect to the drum surface of a drum dryer.

PATENTEU MAY 4 m.

sum '1 OF 4 INVENTORS JAMES I. WADSWORTH ALEXANDER S.GALLO GEORGE M. Z|EGLER,JR.

JAMES J. SPADARO [W ATTORNEY PATENTED'HAY 4mm 315577.649

VSHEEI 2 or 4 INVENTORS JAMES I.WADSWORTH ALEXANDER s. GALLO JAMES J. SPADARO Q ATTORNEY F|G.3 BY

GEORGE M. ZIEGLER,JR.

PATENTEU HAY 'j4l91l SHEET 3 BF 4 INVENTORS JAMES I. WADSWO'RTH ALEXANDER S.GALLO PATENIEDHAY 419? r r 1 75 saw u on I F 5 INVENTORS JAMES I. WADSWORTH v ALEXANDER s. GALLO GEORGE M. Z I EGLER,JR.

JAMES J.'SPADARO l DEVICE AND METHOD FOR CONTROLLING suuc DENSITY os-nsnvmwrsn soonsrurss This application is a division of Ser. No. 690,536, filed Dec. 14, 1967, now US. Pat. No. 3,494,050.

A nonexclusive, irrevocable, royalty free license in the invention herein described, throughout the world for all pur poses of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the The bulk density of processed food products varies not only with processing conditions but also with factors beyond the control of the processor, such as crop growing conditions, variety of the farm product being processed, soil conditions at the growing location, etc. This is especially a problem for drum drying foods containing a substantial amount of sugar. Even though the true density of the product remains fairly constant, large variations in bulk density result indirectly from 0 differences in the composition of the raw materials being processing through the modification of machinery used in processing the said foodstuffs. Still more specifically, this invention relates to an apparatus for controlling the bulk density of high sugar content foodstuffs during drum drying by incorporating means to regulate the angle of attack of the doctor blade relative to the surface of a dryer drum. This invention has been utilized successfully in the preparation of dehydrated foodstuffs, such as sweetpotato flakes, peach flakes, pumpkin 1 pie mix, and others, wherein the dehydrated foodstuffs have been produced with various selected bulk densities.

The principal object of this invention is to provide an improvement in food processing equipment which is used in drum drying of high sugar content foodstuffs such that the product bulk density can be controlled during drum drying.

A second object of this invention is to provide a device which allows variation of the angle of attack of the doctor blade to the dryer drum without disturbing the equilibrium of processing operations, wherein the line of contact between the .doctor blade and the drum does not change relative to the drum axis in a fixed coordinate system.

A third object of this invention is to provide a device for continuously controlling the bulk density of the foodstuff being processed while the machinery is in full operation.

A fourth object of this invention-is to provide a device.

which, while allowing the variation of angle of attack of the doctor blade in respect to the surface of the dryer drum, permits an indefinite number of settings for the pertinent angle of attack of the doctor blade. A fifth object of this invention is ,to provide a device which permits the plurality of adjustments of the doctor blade in respect to the surface of the dryer drum to be applicable to at least the single drum, double drum, and twin-drum dryer arrangements which are well known to those skilled in the art.

For purposes of describing invention the bulk density of a dehydrated food product may be defined as weight per unit volume of material in the aggregate." This difiers from true density in that the volume measured is occupied by both the discrete particles and the void spaces between them.

A continuing problem in the manufacture of dehydrated food products is the variation in product bulk density during processing which can result in undesirable variation in package fill. For example, when a processor is packaging his product on a volume basis, variation-in bulk density can result in either an overweight package, which will reduce the processors margin of profit, or an underweight package, which does not conform with label specifications. If a processor is packaging his product on a weight basis, a high bulk density will result in a package appearing to be underfilled, which is undesirable from the sales appeal point of view, and a low bulk density will result in the volume of the product being greater than that of the package thereby preventing the processor from filling his package. For a successful operation, the product bulk density must be maintained within suitable limits. Whenever there is a variation in bulk density which exceeds these limits it is necessary to revert to costly blending operations or other additional processing steps to obtain a product with an acceptable bulk density.

processed. This is due to a ruffling effect which occurs as the dry but hot thermoplastic material is scraped from the drum surface by the doctor blade resulting in a sheet of material discharging from the dryer which is many times thicker than the film of material adhering to the drum surface. The thickness of the sheet varies with the composition of the material being dried, and this variation in sheet thickness produces variation in bulk density.

For example, in the manufacture of dehydrated sweetpotato flakes a thin film of sweetpotato puree, which is applied to a steam heated drum dryer, is dehydrated to the desired moisture content in a partial-revolution of the drum. The dried material is then scraped from the drum surface by a doctor blade and discharged from the dryer in the form of a continuous sheet.

As the sweetpotato solids are scraped from the drum surface by the doctor blade a continuousruffled sheet, which is much thicker than the film of sweetpotato adhered to the drum surface, is formed. The ruffling effect is related to the sugar content of thesweetpotato which will vary for different varieties, different growing areas, different climatic conditions, different growing areas, different climatic conditions, different harvesting'times, and different curing processes. A higher sugar content causes more ruffling which results in a thicker sheet.

Bulk density varies with sheet thickness because the flaking equipment is designed to break the dry sheet into flakelike particles which have a nonvarying diameter size distribution. The only variation in particle size is in the flake thickness, therefore the variations in bulk density are due to variations in sheet thickness which result from differences in the raw materials. The bulk density of dehydrated sweetpotato flakes can range from 10 to 45 pounds per cubic foot, and this can be attributed to the variety, time of harvesting, and the time that the sweetpotato has been in storage (see Spadaro et al. paper bearing title lnstant Sweetpotato Flakes-Processing Modifications Necessitated by Varietal Differences," which appears bulk density of his product. This will result in an undesirable variation in the packaging operation especially where filling is done on a volume basis.

In the prior art we find that several methods are currently used for controlling bulk density of drum dried high sugar content products; however, all of these methods have serious drawbacks. A brief discussion of these methods follows.

One method of controlling the bulk density'is to. change the particle size by varying grinding or flaking conditions. There are several disadvantages to doing this. First, the appearance of a dehydrated flaked product varies with variation in particle size distribution. This is undesirable from the sales standpoint since a processor wants to provide his customers with a product having uniform appearance. Secondly, the particle size of a dehydrated product affects its reconstitution properties. 'Too largea particle would reduce the rate of water pickup, while too small a particle would either float to the top of the fluid or would tend to cake or form balled-up agglomerates. Excessive grinding, as would be required to obtain a substantial increase in bulk density, would cause an undesirable amount of fines which, after being packaged, tend to separate giving the impression of a nonuniform product.

Another method of controlling bulk density is to vary the thickness of the puree film adhered to the drum surface. This is one of the methods recommended by Lazar and Morgan Instant Applesauce," Food Technology, Vol. 20 (4), 531), but this has not proven successful. The production capacity of a drum dryer is closely related to the film thickness. Any variation in film thickness will result in variation of production rate which is extremely undesirable in continuous operation (see Wadsworth et al., Instant Sweetpotato Flakes-Factors Affecting Drying Rates on Double Drum Dryer," Food Technology, Vol. 20(6), June 1966).

A third method, one which is currently used commercially in the manufacture of dehydrated sweetpotato flakes to control bulk density, is to vary the composition of the material being fed to the drum dryer, such as adding sugar or enzymatically treating said material. There are two main disadvantages to this method. The first disadvantage is that there is a time lag (which is known cases has been timed at more than 60 minutes) between the corrective action of altering the composition of the material going to the dryer and the desired effects of changing the thickness of the sheet coming off the dryer. The second disadvantage here is that this is a trial-anderror procedure because, currently, there are no simple tests which can be used to predict exactly what modification in the composition of the feed material is required, thus making control of bulk density very erratic. In addition, it may not be possible to vary the composition of the feed material due to the restrictions placed upon such materials by the buyer. For example, in the production of sweetpotato flakes purchased by the US. Quartermaster Corps, specifications prohibit the addition of sugar and take that this is an adulteration of a natural product.

US. Pat. No. 3,009,8l5, granted to G. L. Lorant et al. in 1961 relates to the manufacture of strained food products which would have a relative high percentage of natural or added sugar. The novelty feature in this patent is a stretching of the hot plastic food sheet as it is being removed from the dryer thereby decreasing the sheet thickness. This method is also recommended by Lazar and Morgan for controlling bulk density of instant applesauce flakes. With Lorants method bulk density could be decreased within limits; however, it is not possible to increase the thickness of the sheet over that being discharged from the doctor blade.

The present invention consists of a device for controlling the bulk density of certain high sugar content foodstuffs during drum drying. A selected bulk density can be obtained by adjusting the angle of attack of the doctor blade to the drum surface.

To more fully describe the apparatus of this invention, reference is made to the accompanying drawings in which:

FIG. 1 is a schematic side elevation view to present the location of the various angles.

FIG. 2 is a side elevation view of the apparatus of the invention.

FIG. 3 is auxiliary top view of the doctor blade assembly adjustment mechanism.

FIG. 4 is a front elevation view, a schematic view of the assembled apparatus.

FIG. 5 is a schematic front view of the adjusting support member.

FIG. 6 is a schematic top view of the adjusting support member shown in FIG. 5.

A schematic illustration of the essential features of the invention is shown in FIG. 1. A more detailed account of the studies leading to this invention is disclosed in a paper entitled Controlling Bulk Density of High Sugar Products During Drum Drying, which appeared in Food Technology, Vol. 21, No. 7, pages 100 l03, in July of 1967. From these studies it was concluded that angle a (FIG. 1), which is the solid angle formed by the tangent to the drum surface and the beveled edge of the doctor blade, when held at a selected point about the periphery of the drum has an effect on the bulk density of the final product. Experience has provided those skilled in the art with the knowledge of the selected point at which the doctor blade contacts the drum. The selected point is 34, FIG. 2,

which is viewed as a line in FIG. 4. Viewed from a side elevation, the edge of the doctor blade becomes a point. The optimum location of the doctor blade relative to the point of applying feed material to the drum surface depends upon the design of the dryer and the characteristics of the feed material and is immaterial in the discussion of our invention.

Referring specifically to FIG. 1, this side elevation shows the periphery of the dryer drum 1 being touched by the doctor blade 2 at the point of contact 34, which is also the edge of the doctor blade 12. The fine line T is the edge of a surface tangent to the drum at line of contact, 34. Three angles are shown. These are referred to as a, 'y, and B, and as shown in FIG. I. The angle which affects the bulk density of drum dried high sugar content materials is the solid angle a, which is formed by the intersection of T, which is tangent to the surface of the drum at the line of contact 34 with surface B which is parallel to the beveled surface of the doctor blade. When the angle a (FIG. 1) is increased the bulk density of drum dried high sugar content products is decreased, and when angle a is decreased the bulk is increased. It should be noted that variation of angles [3 and 7 (FIG. 1) do not affect the bulk density when angle a is held constant.

An explanation for the variation of bulk density with angle a can be deduced from physical reasoning. The temperature of the material on the drum approaches the temperature of the drum surface by the time it reaches the doctor blade. Foodstuffs having a high sugar content tend to be thermoplastic and tacky at the operating temperatures of such machinery, even when the moisture content has been reduced to less than 4 percent. As the material is scraped from the drum surface by the doctor blade it ruffles to form a sheet discharging from the dryer which is much thicker than the film adhered to the drum surface. The bulk density, as stated previously, varies with the thickness of the sheet of food material.

The degree of ruffling (i.e., thickness) of the formed foodstuff sheet for a particular product depends upon the amount of impedance to the movement of the dry food material across the beveled surface of the doctor blade. For example, the degree of ruffling can be temporarily reduced (yielding a thinner sheet) by coating the doctor blade with a fluorocarbon spray thereby lowering the coefficient of friction between the material and the doctor blade which reduces the resistance to the movement of the sheet of foodstuff. The variation of the angle a has a similar effect. Reducing a has the effect of increasing the impedance to the movement of the high sugar content material and increasing a lowers the impedance. For physical reasoning a rough analogy can be drawn with fluid flow through a pipe bend where an increasing deflection results in an increasing friction loss.

In Table I, the effects of change of doctor blade angle with respect to the surface of the drum (angle a) on the bulk density of three drum dried high sugar content food materials are shown.

Table I.Efiect of contact angle between a doctor blade and the surfacg of the drum dryer on the bulk density of various selected drum dr high sugar content food products Bulk density (pounds per cubic foot) Angle (degrees), :1 Sweetpotato Peach Pumpkin flakes flakes pie mix Reference is now made to FIGS. 2, 3, and 4.

In FIG. 2, specifically, there is shown a dryer drum 1, wherein the rotation of the drum as viewed would be clockwise and the material adhered to the drum surface would be scraped off by doctor blade 2, and discharge from the dryer in the form of a continuous sheet 23, which is supported by roller 24, and deposited into a suitable container 25. The doctor blade 2 is held against the blade bar 26 by gib plate 27.

This, together with yoke 5, which is welded to the blade bar 26 constitutes the blade holder assembly 3.

The doctor blade holder assembly3, is pivotally held in place by holder adjusting support 4L in the bore 29L. Adjusting support 4L is pivotally held to dryer frame 13, which is resting on dryer bed 14, by fulcrum bolt 10, and it is secured in its desired position by securing bolt 9, which passes through support adjusting slot 19. The doctor blade holder assembly 3 is connected through yoke 5 to the tension adjusting rod 6 by yoke pin 11. Tension adjusting rod 6 passes through tension resisting bar 7 at tension bar slot (see FIG. 3), and this bar is attached to dryer frame 13 by bolt 22 through bolt slot 21. Blade angle and tension adjusting hand wheel 8 screws onto tension adjusting rod 6, which is threaded about three-fourths of the way. Lock nut 18 secures this arrangement in the selected position.

The numbered items thus far have had reference to the.

parts shown; however, there are left side and right side items involved. The left side shown in FIG. 2 must be complemented by a right side arrangement, parts of which must of necessity be the mirror image in design in order to provide the adequate support for the doctor blade assembly.

FIG. 5 shows the details of a holder adjusting support. This is a particularly significant part of the apparatus because it was designed such that the line of contact between the doctor blade and drum surface remains stationary, relative to a fixed coordinate system when angle a is varied. The particular part shown in FIG. 5 is a right hand holder adjusting support. There also is a left hand holder adjusting support; however, in fabricating these parts there would be no difference in machining these pieces other than the markings along the radial surface 33. The markings shown in FIG. 6, i.e., etc., are angles utilized in experimentation. In practice these could be replaced by any designation, such as letters or numbers, or simply fine lines. For the particular drum dryer used in this experimental work, the 30 through 90 FIGS. shown in FIG. 4A are equivalent to a angles of 148 through 88 respectively when a doctor blade with a 15 at angle is used.

For a satisfactory operation of the apparatus of the invention these three conditions must be taken into consideration (refer to FIG. 2 and 5): (l). The holder adjusting support pivoting axis 32 must coincide with the preselected line 34, which is the location at which the film of food product 30 is to be removed from the drum surface by the doctor blade; (2). the radial distance between holder adjusting support pivoting axis 32 and the doctor blade assembly pivoting axis 31 must be equal to the distance between the doctor blade assembly pivoting axis 31 and the doctor blade edge 12; and (3). centerline 35 of support adjusting slot 19 must be a circular arc with a center of curvature coinciding with holder adjusting support pivoting axis 32 and a radius of curvature equal to the distance between line 34 and the center of securing bolt 9. The length of the centerline of slot 19 will depend upon the desired adjusting span.

The design of the holder adjusting support 4 is a crucial one in respect to the dryer drum arrangement which we have.

chosen for illustrating the reduction to practice of the method of the invention. Modifications in design must be made to correspond to the dryer drum system in which 'the method of the instant invention is to be employed.

In the operation of the apparatus a change of angle a is accomplished as follows: Bolts 9 on both the left and right supports 4L and 4R are released and blade angle adjusting wheels 8 are then turned. Turning the hand wheels will exert a force on yoke 5 by means of the adjusting rod 6 through yoke pins 11, thus causing the supports 4L and 4R to rotate on bolts 10 which act as the fulcrum until the desired angle etched on the periphery of the supports coincides with an index point (arrived at experimentally and marked on the side frame 13). After this has been accomplished bolts 9 are secured and blade angle adjusting wheels 8 are further tightened clockwise to bring the doctor blade edge 12 to bear evenly on the drum surface and exert the necessary pressure for properly scraping the dehydrated material.

This invention provides to the food processing industry an apparatus forthe drum drying of high sugar content foodstuffs, such as sweetpotatoes, peaches, pumpkin pie mix, pears, apples, apricots, plums, oranges, and the like wherein bulk density in the preparation of the dehydrated foodstuffs is controllable. The ability to control bulk density is significantly functional in that the bulk density can be adjusted without interrupting the continuous operation and immediate response is obtained. Bulk density is adjusted simply by the turning of knobs or wheels which in turn alter the angle which the doctor blade makes with the tangent to the drum surface. With present available equipment, the angle a should be limitedto a range of about from 30 to 165, while the angle 7 should be between about 15 to 75. The limits of angle [3 would be dependent on the other two angles. This measurement is of no significance.

The preferred initial setting of the doctor blade is such that angle a would be between and It is also preferred to use a doctor blade having an angle y of about 15", which is a commercially acceptable angle in doctor blades. These initial settings allow an ample range of control to both increase or decrease angle a as the drying operation warrants.

To reiterate, the present invention is a device for regulating bulk density during drum drying of drum-dried foodstuffs of sugar content of at least about 25 percent by weight (dryweight basis), wherein varying the impedance to the movement of the dried foodstuff across the beveled surface of the doctor blade is accomplished by varying the angle of attach about from 30 to This angle is formed by the intersection of two planes, one parallel to the beveled surface of the doctor blade and the other tangent to the drum surface at the point where the doctor blade contacts the drum, wherein decreases or increases in bulk density of the drum-dried foodstuff are accomplished by increases or decreases in the magnitude of the pertinent angle. Furthermore, the invention is also a mechanical improvement which can be applied to existing equipment of the food processing industry becomes part of the operating equipment in a drum dryer system.

We claim:

1. In a drum-drying apparatus for drying foodstuffs of high sugar content,

said apparatus comprising, in combination, a rotatable elongated drying drum, associated stationary front and side supporting structure for said drum, said drum being mounted between said stationary opposing said support members for rotation about its longitudinal axis, and a doctor blade assembly for scraping dried foodstuffs from said drum,

an improved doctor blade assembly enabling control of the bulk density of dried foodstuff through variation of the angle of attack between the doctor blade and the surface of the drum, said assembly comprising:

a. a doctor blade having one side thereof beveled to provide a scraping edge, said doctor blade being disposed across the width of the rotatable drying drum with said beveled side in opposing attitude to the direction of rotation;

b. a pair of similar planar, pivotable support members, each of said planar support members having pivoting means locating a pivot axis, a circular arcuate slot in the planar surface having the pivot axis as its center, and a circular opening constituting a shaft support means, the center of said circular opening being radially spaced beyond the arcuate slot, the centerline of said arcuate slot being equidistant between the pivot axis and the center of said circular opening;

c. means for pivotably mounting said planar support members on each of the opposed stationary side support members of the drum, said planar members having a common pivot axis parallel to the axis of the drum and spaced from said drum axis to coincide with the peripheral surface of the drum;

. adjustable securing means extending through the arcuate slots of each of said planar support members and through said stationary side support members to secure said planar support members in any predetermined position;

. rotatable shaft means extending between and mounted in the circular openings of the planar support means;

. means for rigidly securing the doctor blade to the rotatable shaft so that the scraping edge of the doctor blade contacts the surface of the on the pivot axis of the planar support members;

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