US3138296A - Silo compartment for materials in powdery form - Google Patents

Description

United States Patent 3,138,296 SlLt) COMPARTMENT FOR MATEREALS 1N POl/VDERY FORM Karl Neidhardt, Qologne-Deutz, Germany, assignor to Gebriider Biihler, Uzwil, Switzerland, a firm Filed Jan. 31, 1961, Ser. No. 86,209 Claims priority, application Germany Feb. 3, H60 1 Claim. (Cl. 222-185) This invention relates to a silo compartment for loose or bulk materials in powdery or dust form which only flow with difiiculty, advantageously flour, and especially to the design of a discharge section of silo compartments for tall silos.

The discharge of the silo compartments for freely flowing bulk materials, for example, of coarse grain type, is generally formed by simple sloping discharge devices, since obstruction due to caking or the like scarcely occurs with such loose materials. The discharge of loose materials in powdery or dust form from silo compartments frequently presents difiiculties, because first the material tends to cake together because of a natural humidity and secondly the procedure has recently been adopted of employing silo compartments of considerable height, with which pressure causing strong compression of the material are set up because of the high silo filling.

Attempts have already been made to overcome these difliculties by various means, but it has not so far been possible to achieve a satisfactory solution. For example, oscillating rocker beams have been arranged both longitudinally and transversely of the outletfrom the compartment. Owing to the considerable height of the compartment which can reach 30 meters and higher, the pressure loading on such rocker beams is so high that disturbances occur. A displeasing feature in this case is also that material can be deposited beneath the rocker beams and this is undesirable on hygienic grounds where foodstulfs are concerned. Where sloping surfaces are arranged before the outlet of the compartment, these are disposed with a comparatively steep inclination, which is scarcely below approximately 75. Silo compartments equipped with stirrer devices are also not satisfactory. On account of the sloping surfaces, experience shows that they tend to set up disturbances in the discharge because of bridge formation flour. Furthermore, so-called crossbottom silos exist, in which each half of the discharge portion of the silo chamber is fitted with sloping surfaces which are inclined in diametrically opposed directions. In this case, on the one hand, the constructional costs are high due to the high base pressures, but on the other hand, with moist material, interruptions in the flow are set up on the side opposite the opening, since the material can become wedged between the sloping surfaces, which are likewise inclined at an angle of about 75. Consequently, silo compartments have also been used which have walls which remain vertical as far as the discharge end, that is to say, are without sloping surfaces, and chain discharge devices are arranged at the bottom of the silo compartment. However, these discharge chains are loaded by the pressure of all the contents of the compartment and they must be moved over the bottom under this load. The conveyor chains are consequently subjected to a comparatively high degree of wear and in addiiton there are possibilities of undesired deposition of material Within the chain casing.

In order to obviate the said difficulties, which are always recurring, discharge devices have also been developed by which the material is carried away by means of compressed air, with the use of filter bases and the like.

Such installations require special base constructions with special filter plates, compressed air installations, air-tight lock chambers, air-compensating installations and the like. The cost involved for the discharge device isconsiderable and in addition there is also the danger that, depending on the nature of the contents of the compartment, the pores of the filter plates become clogged in time, so that the efiiciency of the installation is considerably reduced.

The invention is concerned with a constructional form of a silo compartment discharge device, with which the disadvantages. set forth no longer occur. It is characterized in that the discharge section of the silo compartment comprises on the one hand a nose-like member projecting into the compartment space on the compartment wall above the discharge openingand spaced from the end of the compartment and a sloping discharge surface is provided on the opposite compartment wall at a lower level, and on the other hand that compartment wall which is opposite the nose-like member merges below the level of the end of the nose and by means of a troughshaped transition into the sloping surface directed towards the discharge opening. The sloping surface should have an angle relatively to the horizontal which is smaller than The design of the lower part of the outlet of the compartment as a space made trough-shaped on one side results in that a considerable widening of the discharge space becomes possible because of the rounding of the transition from the vertical compartment wall to the sloping discharge surface and also in view of the fact that the discharge opening is kept substantially free from the load of the material disposed in the compartment by the projecting nose. The wedge action which is produced immediately before the outlet and which otherwise leads to caking together of the fiourdike material is avoided. The widening effect resulting from the rounding permits the setting up of a strong thrust movement coming from above and changing into the sloping surface, whereby the column of flour, even under the most unfavorable conditions, is thrust by its own weight into the discharge space, where it can then flow out of the outlet in a loosened form. The combination of the projecting nose on the one side and the rounding at the transition from the vertical wall to the sloping surface produces the desired satisfactory result. Contrary to the opinion formerly held and also to current practice, this combination makes it possible for the first time to use sloping discharge surfaces which have an angle far below 70. On the contrary, the more the angular position of the sloping surface approaches 45, the better is the effect according to the invention, because the discharge space becomes larger as the angular position becomes smaller. The wedge effect of the sloping surface in relation to the oppositely disposed vertical wall is smaller with decreasing angular positions of the sloping surface than with a sloping surface at 70". It thus becomes possible by means of the design according to the invention to reach the extraordinary value of about 4050 for the sloping discharge surface. Any suitable device, such as a discharge gate or .even a conveyor belt, can be used as discharge means, the said device only regulating the outlet quantity. When using a discharge gate, the rotational movement of the latter is organically disposed in the stream of flowing material and the rotation thereof is assisted by this how.

One embodiment of the invention is shown by way of example in the accompanying drawing, in which:

FIG. 1 is a vertical section through the discharge portion of a silo compartment constructed according to the invention, and

FIG. 2 is a cross-section on the line 2-2 of FIG. 1.

The silo compartment 1 of square or rectangular crosssection is formed by the longitudinal walls 2 and 3 and the transverse walls 4 and 5. Provided on one longitudinal wall, for example on the wall 2, is a projecting nose 6 having a sloping surface 7 directed away from the wall 2 and projecting into the compartment space. At the end and as indicated at 8, this sloping surface, without any transition, abruptly extends rearwardly again to the compartment wall 2. Opposite the sloping surface 7, the compartment wall 3 extends vertically. Attached to the wall 3 is a sloping discharge surface 9, which extends as far as the outlet opening or discharge 10. The outlet opening is thus situated beneath the projecting nose 6 and is preferably kept somewhat smaller in its free width than the lower end of the projecting nose. Any suitable discharge member can be arranged beneath the outlet opening, and advantageously a rotatable discharge gate 11. The transition from the vertical wall 3 to the sloping surface 9 is preferably smoothly rounded as at 12. This rounding advantageously has a radius which corresponds at least to half the width of the compartment. A vibratory wall section 13 can be provided on the compartment wall 2 below the projecting nose 6 and the vibration can be initiated by means of a switch 14 mounted on the wall 6.

Due to the projecting nose 6 with the sloping surface 7 being at a predetermined distance above the outlet opening 10, the effect is achieved that the load of the contents of the compartment is to a substantial extent already taken up in the zone A. Since the vertical wall 3 in this zone A opposes the perpendicular pressure of the material of less resistance than the nose 6 serving to relieve the pressure on the space disposed beneath it, the material on the vertical Wall 3 is pressed downwardly owing to the pressure resulting from the weight. Due to the pressure loading, the material slides from the rounded transitional region 12 to the sloping discharge surface 9 in the zone B. When the compartment is full, a pressurefree zone C is formed below the nose 6, and this permits a corresponding loosening of the material leaving zone A. As soon as there is any withdrawal, it is the material from the zone D immediately above the outlet opening 10 which is extracted. The thrust force acting more strongly along the compartment wall 3, 12 and 9 than on the opposite wall 2, 7 displaces the material into those parts of zones B and D which become free and thereby causes the contents of the compartment to fiow.

The outlet opening 10 is freed from the load of the contents of the compartment by being covered by the projecting nose 6. At the sloping discharge surface 9, it is possible to operate with a substantially smaller slope than 75 namely, with a slope of 40".

If it should be desired to empty the zone D after a relatively long storage time, for example, with moist material without the material sliding down from the other zones, assistance for a short time with the vibratory plate 13 is sufficient. For this purpose, the diaphragm switch located at 14 is operated and switches on the vibratory plate 13 for a few seconds. The material immediately starts to flow, pressure is again applied to the diaphragm switch and switches off the vibration. It is only relatively seldom that this assistance is necessary and in practice is only required when the compartments have stood for a relatively long time with moist material under full pressure. For the actual discharge operation, no auxiliary means, for example in the form of conveyor chains, compressed air installations, stirrer mechanisms and the like, are required.

The sloping discharge surface 9 preferably starts substantially at the height of the lower part of the projecting nose disposed on the opposite compartment wall. The

smaller the inclination, the more advisable is it for the rounding to be provided at the transition from the vertical wall to the sloping surface. In the example illustrated, the radius of the rounding is about three-quarters of the width of the compartment. The depth of the projecting nose 6 can generally be one-third to one-quarter of the corresponding compartment width.

The satisfactory discharging of the material can also be assisted by the sliding surfaces in the discharge portion of the silo compartment being formed of a material which is porous and absorbent, at least on the smooth upper surface, while being hard and of high strength. The material is also to be free from grease and oil. In this way, it is possible to prevent the formation on the sliding surface of a film of condensate which would result in the separate flour particles sticking to the said surface and thereby causing a settlement of the loose material. Due to the fact that the material has a certain porosity, it also has a certain absorbent capacity, so that any condensate which is formed can be taken up by the material itself. The material should moreover have a low thermal conductivity. This circumstance also contributes to counteracting a formation of condensate.

The material of the sliding surfaces is preferably formed of a hard-wood plywood board with a high surface smoothness. Beechwood and especially red beech is extremely advantageous for this purpose. White beech is also to be considered, as well as maple or all woods with the said properties.

A high surface smoothness can be produced on the materials according to the invention, preferably by the following method: First, the surfaces are preferably saturated with hot water. As a result, all pressure zones which have for example been formed with plywoods or other boards by the pressing are removed. The rough surfaces formed in this way are thoroughly dried. The roughness is then carefully rubbed off with extremely fine-and sharp abrasives, as far as possible without using pressure and in the direction of the grain. This operation can be repeated until no roughness can be found after surface treatment with hot water. In this way, there are provided sliding surfaces having a smoothness which is fully maintained, even under the action of the humidity of the bulk material.

It is not absolutely necessary to use naturally grown materials for the purpose according to the invention. The sliding portion of the sloping discharge surface can also be formed by sheets or boards produced from sawdust, perhaps in combination with synthetic resin powder, by pressing. In this way, a porous and absorbent surface is obtained, which can be provided with a high surface smoothness.

What is claimed is:

In a silo for storing and gravity-discharging fluent, pulverulent material, said silo including a pair of opposed, parallel vertical walls connected by transverse side walls and defining a rectangular cross-sectional storage area for the pulverulent material; the improvement comprising means for maintaining free, gravity flow of material from said silo comprising a nose portion integral with and extending transversely of the inner surface of one of said vertical walls and including a planar, surface extending inwardly and downwardly at a shallow angle toward a lower portion of the silo and said other vertical wall and terminating in an abrupt, lateral shoulder extending beneath said nose portion at substantially a right angle to said one vertical wall, said one vertical wall terminating in a lower edge substantially in the plane of said one vertical wall, said other vertical wall extending parallel to said one Wall to a point near the height of said abrupt lateral shoulder and merging into an arcuate corner of a radius at least equal to one-half the distance between said vertical walls, said arcuate corner merging into an angular, bottom wall extending in a plane less than =23 with respect to the horizontal and terminating in a free edge spaced from an substantially coplanar with the lower edge of said one vertical wall and defining therewith between opposed transverse margins a downwardly opening discharge slot disposed beneath a downward projection of said abrupt shoulder of said nose portion, and discharge means disposed transversely beneath said discharge slot and exteriorly thereof for aiding to move gravity discharged pulverulent material away from said discharge seat.

References Cited in the file of this patent UNITED STATES PATENTS Ehmke Oct.,4,- 1898 Marsa Apr. 15, 1919 Snyder May 26, 1925 Sloan June 14, 1938 Prater Apr. 11, 1944 Smith Nov. 21, 1944 Dalmas Apr. 10, 1951 Hurter May 27, 1952

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