IE47133B1 - Tapered silo - Google Patents

Description

This invention relates to a silo having a tapered bottom end, which is particularly adapted, even if not exclusively, for small-sized plastics materials having a high degree of stickiness, humidity and electrostaticity.

It is known that the storage in silo of plastics materials having 5 the characteristics enumerated above involves considerable problems as regards the metered dispensing of the material once the storage period comes to an end.

By virtue of their characteristics, the individual small pieces of material tend to stick to each other, thus forming in the low section of the siTo a single agglomeration of solids which acts like a “bridge or aplug for the overlying stock.

This phenomenon creates, as it is universally recognised in the art the necessity of keeping the material continually stirred, especially in the lower section of the silos having a tapered bottom, wherein the occurrence of bridging is more likely.

The approaches as suggested heretofore in the conventional silos ar; not fully satisfactory under this particular respect, since they are unable to maintain the entire mass of material in the desirable status of stirri.ig, but - 2 47133 only portions of the material are influenced and, in addition, motors of high power are required in order that the stirrers may properly be actuated.

The principal object of the present invention is to provide a taperedbottom silo which is particularly, even if not quite exclusively, adapted to plastics materials of the characteristics enumerated above and in which the problem of stirring the material is brilliantly and thoroughly solved.

Another object of the present invention is, then,to provide a silo of the kind referred to above, which is also capable of ensuring a particularly accurate and constant metering of the material to be dispensed from time to time.

According to the invention, these objects are achieved by means of a tapered-bottom silo, particularly suitable for small sized plastics material having characteristics of low density and a high degree of stickiness, humidity and electrostaticity, characterised in that it comprises a helical screw stirring member coaxially located within the conical silo bottom, the diameter of said stirring member increasing progressively from its lower end to its upper end whereby its periphery traverses a conical path as the stirring member is rotated about said axis to produce an upward motion of the material engaged by its helical vane away from an outlet port located laterally relative to said stirring member at the lower end of the conical silo bottom, means being provided for ejecting and delivering the material received from said outlet port, said means extending laterally of the axis of said silo.

The use, as suggested herein, of a helical stirrer whose periphery lies in a conical surface solves the problem of stirring the material which is held in the tapered end of the silo. Such a stirrer, in fact, creates within the material concerned a continuous lifting motion, and an appropriate sizing of the conical peripheral surface of the helix relative to the silo bottom can extend such a motion laterally in such a way as to involve all the material contained in the tapered end of the silo, with the only exception of a narrow peripheral annulus along which the material, conversely, is enabled to fall by - 3 47133 the gravity pull only and thus to reach the outlet port and to pass therethrough in order that a constant output may be achieved and thereby a metering of the delivery which is also constant. No undesirable clogging or bridging phenomena are experienced so that the silo is constantly maintained under quite satisfactory working conditions. Inasmuch as, on the other hand, a comparatively slow motion of the material is sufficient, the use of a driving motor having a limited power is also appropriate, the result being that the silo becomes less expensive and the power demand is considerably reduced.

The characteristics of the present invention will become more clearly apparent from the ensuing detailed description of a practical embodiment thereof which is shown by way of example only in the accompanying drawings.

In the drdawings: FIGURE 1 is an axial cross-sectional view of the lower portion of a silo according to this invention.

FIGURE 2 shows the same lower portion of the silo in transversal cross-sectional view taken along the line II-II of FIGURE 1.

FIGURE 3 shows the outlet section of the silo in cross-sectional view, taken along the line ΠΙ-III of FIGURE 2.

The silo as depicted in the drawings essentially comprises a cylindrical wall 1, which is axially developed almost along the entire vertical extension of the silo, with the only exception of a bottom section 2, having a tapered wall 3 which is terminated at its end by a squared section 4 (FIGURES 1 and 2).

A plate 5, having a rectangular window 6 which is laterally offset towards the squared wall 4 closes at the bottom the tapered end 2 of the silo and supports in a central position, that is to say along the axis of the conical wall 3 and of the overlying cylindrical wall 1, a motor 7 intended to drive in rotation a heTical screw stirrer 8 located coaxially within the conical bottom 2.

The stirrer in question comprises a central shaft 9 borne by the motor 7 and maintained in a true axial position by three arms 10 (only two are - 4 47133 shown in FIGURE 1) angularly spaced apart through 120 degrees frora each other and fastened by plates 11 to the junction area between the walls 1 and 3.

Around the shaft 9 there is a helical vane 12 which is fastened to such a shaft by means of radial spokes 13.

To the top of shaft 9 are also fastened two paddles 14 and 15 having different radii, which provide stirring of the material above the arras 10. In such an area a level indicator 16 is additionally provided.

Beneath the plate 5 and in registry with the rectangular window 6, there is arranged, lastly, in a transversal direction, a dispensing screw 17 of cylindrical form, which is rotatably mounted within a cylindrical box 18: the latter has an inlet mouth 19 and an outlet port 20 and the screw 17 is driven by a motor 21 (FIGURES 2 and 3).

In operation, the motor 7 rotates, in the direction shown by the arrow F in FIGURE 1 the helical stirrer 8, which induces a slow upward motion of the material that stays in the inside of the conical enveloping surface of the vane 12. The material then falls by gravity along the conical sidewall 3 and creates an outlet stream with a constant rate of output through the outlet port 6. The constancy of the rate of flow is ensured by the noncompressed conditions to which the material is subjected in the conical section 2 due to the effects of the stir created by the screw 8 and the bearing action of the overlying material in the cylindrical section 1, as stirred by the paddles 14, 15.

It should be noticed that the movement created by the stirrer 8 also provides, if required, the admixture of possible different materials introduced in the silo together. The transversal screw 17, lastly, provides to deliver constant metered quantities of material to the dispensing port 20.

Claims (3)

1. A tapered-bottom silo, particularly suitable for small sized plastics material having characteristics of low density and a high degree of stickiness, humidity and electrostaticity, characterised in that it comprises 5 a helical screw stirring member coaxially located within the conical silo bottom, the diameter of said stirring member increasing progressively from its lower end to its upper end whereby its periphery traverses a conical path as the stirring member is rotated about said axis to produce an upward motion of the material engaged by its helical vane away from an outlet port located 10 laterally relative to said stirring member at the lower end of the conical silo bottom, means being provided for ejecting and delivering the material received from said outlet port, said means extending laterally of the axis of said silo.

2. A silo according to Claim 1, characterised in that said delivering means comprises a dispensing screw of cylindrical form arranged with 15 its axis transversely of the axis of said silo beneath said outlet port,

3. A silo according to Claims 1 and 2, substantially as hereinbefore described and illustrated in the accompanying drawings.