GB2039855A

GB2039855A - Apparatus for Constant Rate Feeding of Powdery Material

Info

Publication number: GB2039855A
Application number: GB7944610A
Authority: GB
Original assignee: Pennwalt Corp
Current assignee: Pennwalt Corp
Priority date: 1979-01-04
Filing date: 1979-12-31
Publication date: 1980-08-20
Also published as: IT1126861B; SE7910499L; DE2952777A1; FR2445813A1; BE880989A; DK3480A; IT8047518A0; NL8000027A; NO800013L

Abstract

Apparatus for feeding powdery material includes a hopper (12) with an outlet port (18) close to the hopper bottom, a rotatable open-centre helical screw (16), at least partially within the storage hopper and close to the bottom thereof, to advance powder within the hopper to the hopper outlet, a motor (20) for turning the helical screw and a stationary rod secured to the hopper outlet port and extending into the screw hollow interior. The rod prevents powdery material resident within the helical screw from rotating unitarily with the helical screw as the screw is rotated by the motor and feeds powdery material to the hopper outlet port. <IMAGE>

Description

SPECIFICATION Apparatus for Constant Rate Feeding of Powdery Material This invention relates to apparatus for feeding powdery material such as lime, flour, other foodstuffs, pharmaceutical materials, plastics and the like.

Various apparatus for feeding powdery material are known; typical of the known apparatus is that made by Vibra Screw, Incorporated, of Totowa, New Jersey, as shown in Vibra Screw's publication number 77VS-34C-5M, and that made by Acrison, Inc., of Carlstadt, New Jersey, as shown in Acrison's bulletin W718. The Vibra Screw approach provides a stationary hopper, with a vibrating baffle within the hopper, at an intermediate position above a vibrating rotatable feed screw at the hopper bottom. The Acrison approach provides two concentric open augers within a storage hopper with the smaller, inner auger extending axially beyond the larger, outer auger, into a close-fitting, concentric cylindrical discharge port.Also representing prior practice is the chemical feeder model A-690 made by Wallace 8 Tiernan Division, Pennwalt Corporation, as shown in Pennwalt Corporation's Wallace 8 Tiernan Division's catalog file 320.120. The Wallace Et Tiernan apparatus consists of a powder material storage hopper with a rotatable, double-ended helical screw in the bottom of the hopper. The screw is capable of both rotation and reciprocation simultaneously so that when the screw is moving axially in one direction, half the screw is collecting material and cleaning itself while the other half of the screw is feeding material. As the screw rotates and reciprocates, the powdery material is fed alternately from both ends of the screw to an outlet port at the storage hopper bottom.

A common problem in prior art devices is that feed rate of powdery material from the storage hoppers is not constant; complex mechanisms as exemplified by the apparatuses noted above have been developed in response to this problem. A simple rotating helical feed screw, whether of the opencenter type or of the closed-center type commonly referred to as an "auger", tends to become "caked" with the powder material as the screw attempts to feed the material to the outlet port. The caking produces an intermittent, erratic flow rate which is undesirable.

This invention provides apparatus for feeding powdery material at a substantially constant rate and includes a powdery material storage hopper which has an outlet port close to the hopper bottom, a rotatable helix in the form of an open center screw, formed of coiled wire, which is at least partially resident within the powder storage hopper and is proximate to the hopper bottom portion, for advancing powder within the hopper to the outlet port, a motor for rotating the helical screw and a stationary rod with one end secured to the hopper outlet port, which extends into the hollow interior of the helical screw and prevents powdery material resident within the screw from caking thereon.

Surprisingly, the apparatus feeds powdery material out of the feed hopper at substantially a constant rate, with feed rate varying by only a small percentage compared with feed rates of simple rotating helical feed screw apparatus known heretofore.

The invention is further described with reference to the accompanying drawings, in which: Figure 1 is a side elevation view, partially sectioned, of a preferred embodiment of apparatus for constant rate feeding of powdery material.

Figure 2 is a broken, partially sectioned, isometric view of an outlet port portion of the apparatus illustrated in Figure 1.

Figure 3 is a section view taken at arrows 3-3 in Figure 1.

Figure 4 is a view of the outlet port of an alternative embodiment of apparatus for constant rate feeding of powdery material, shown in a partially sectioned, broken isometric view.

Figure 5 is a sectional view taken at arrows 5-5 in Figure 4.

Referring to Figure 1 , apparatus for feeding powdery material is designated generally 10 and includes a storage hopper 12 into which powdery material, such as lime and indicated as 14, can be loaded through an open top. A motor 20, preferably secured to the side of hopper 12, has a motor drive shaft 21 extending into hopper 12. Suitable conventional seals, not shown, around drive shaft 21 prevent powdery material 14 from fouling motor 20. Motor 20 and hopper 12 are supported by and secured to a common base 28. Storage hopper 12 includes an outlet port 18 proximate the hopper bottom portion; outlet port 18 is preferably of generally cylindrical configuration and preferably has, at least partially resident therein, a rotatable helically coiled means 1 6, for advancing powder from within storage hopper 12 to outlet port 18.Rotatable helically coiled means 16 is secured to motor drive shaft 21; when motor 20 is energized, helically coiled means 16 rotates. Helically coiled means 16 is in the form of an open helix and serves as means for advancing powder within the hopper to and through the outlet port 18. Secured to an outlet end 30 of outlet port 18 is a rod 22 which preferably has a circular cross section. Rod 22 preferably extends through the entire length of outlet port 18 and at least partially into the interior of hopper 12; this characteristic of rod 22 whereby the substantially straight axially extending portion 31 of rod 22 is longer than the axial length of port 18, so that a portion of rod 22 resident within the open interior of helical means 16 is within hopper 12, is best viewed in Figure 2.

Rod 22 is secured to outlet port 18 in such fashion that the longitudinally extending preferably straight portion of rod 22 extends axially through the open interior of helical means 16, at a position radially displaced from the axis of rotation of means 16. The position of rod 22 where it is radially displaced from the axis of rotation of helical means 16 is best viewed in Figure 3. Rod 22 serves as means for preventing powdery material resident within helical means 16 from rotating unitarily with helical means 16 as helical means 16 is turned by motor 20. In this way, powdery material cannot "cake" in the interior of helical means 16. Hence free, uniform flow of powdery material out of outlet port 18, due to rotary motion of helical means 16, is assured.As helical means 1 6 rotates, powder is fed out of outlet port 18 in the direction shown by arrow A, until hopper 12 is substantially empty.

Referring now to Figures 4 and 5, there is shown an alternative embodiment of an outlet port portion of apparatus for constant rate feeding of powdery material, wherein the rod extending into the open interior of helical means 16 is of non-circular cross section. Rod 22A is preferably parallel to the axis of rotation of helically coiled means 16 which surrounds rod 22A, and rod 22A resides within the interior of helically coiled means 16. Preferably rod 22A extends the length of outlet port 1 8 and at least partially into the interior of hopper 12. The non-circular cross-section of rod 22A, as rod 22A is resident within helically coiled means 16, serves to prevent "caking" of powdery material within the center of helically coiled means 16; this assures relatively constant rate feeding of powdery material, out of outlet port 18, as helically coiled means 16 rotates.

Preferably helically coiled means 16 is formed of a wire rod, of circular cross-section, coiled so the pitch (distance between corresponding points points on adjacent coils) of the helix is somewhat greater than the wire rod diameter. Diameter of the wire rod forming helically coiled means 16 is indicated by dimension D in Figure 3; pitch of helically coiled means 16 is indicated by dimension P in Figure 1. Moreover, it is preferable that outer diameter of helically coiled means 16, as indicated by dimension E in Figure 3 be somewhat less than the inner diameter of outlet port 18, as shown in Figure 3, to avoid build-up of caked material between helical means 16 and the inner wall of port 18. It is necessary that at least a portion of helically coiled means 1 6 be resident within hopper 12 for feeding to be effective.The portion of helical means 16 which needs to extend into outlet port 18 is dependent on the relationship of the length of outlet port 18 to the interior diameter of outlet port 18. As the ratio of length to diameter increases, it is necessary to increase the extent to which helical means 16 protrudes into port 18, in order to prevent powdery material from clogging port 18. Preferably, helical means 16 extends through the entire axial length of outlet port 18.

Since many dry powdery materials tend to agglomerate while stationary and/or while being handled (which can lead to bridging above helical means 16) it is preferable that hopper 12 be equipped with conventional oscillating sides or side panels which move to agitate and thereby fluidize the powdery material so as to promote downward flow of the powdery material to the helical means 16 and thereby prevent bridging and cavitation. Such an oscillating side panel is shown schematically in Figure 1 and designated 50.

Surprisingly, when the present invention feeds powdery material such as lime, a substantial improvement in feed rate consistency is achieved over that obtained using representative prior conventional apparatus as exemplified by apparatus having only a simple rotating helically coiled open center screw-type feed means, without a rod member such as item 22.

Example 1 In one embodiment the invention was constructed with helically coiled means 16, formed of one quarter (1/4) inch diameter wire (0.635 cm), coiled to a one (1) and one-half (1/2) inch outer diameter circle (3.81 cm), with a three-quarter (3/4) inch (1.905 cm) pitch on the coil. Approximately one hundred (100) pounds (45 kg) of lime was loaded into the feed hopper for each trial. The helically coiled means was rotated at approximately ninety-seven (97) revolutions per minute. Test data was taken every two (2) minutes, with feed rate being sampled for a thirty (30) second interval each time data was taken.The following table contains the data measured with and without the rod 22 inserted into the interior of helically coiled means 16; during both trials oscillating side panels 50 were operative: ConventionalApparatus Apparatus of the Invention Lime Feed Rate Lime Feed Rate (Pounds ofLime/Hour) (Pounds ofLime/Hour) 66.5 (29.9 kg/hr) 53.3 (23.9 kg/hr) 48.6 (21.9 kg/hr) 50.4 (22.7 kg/hr) 50.2 (22.6 kg/hr) 52.3 (23.5 kg/hr) 41.5 (18.7 kg/hr) 51.0(23.0 kg/hr) 29.6 (13.3 kg/hr) 52.3 (23.5 kg/hr) 35.4 (15.9 kg/hr) 51.7(23.3 kg/hr) 35.9 (16.2 kg/hr) 51.5(23.2 kg/hr) 41.5 (18.7 kg/hr) 50.4 (22.7 kg/hr) 25.9 (26.4 kg/hr) 51.7 (23.3 kg/hr) 39.6 (17.8 kg/hr) 50.7 (22.8 kg/hr) 34.9 (15.7 kg/hr) 50.7 (22.8 kg/hr) 32.2 (14.5 kg/hr) 51.5(232 kg/hr) 45.5 (20.5 kg/hr) 51.5(23.2 kg/hr) 35.9(16.2 kg/hr) 49.1(22.1 kg/hr) 31.3(14.1 kg/hr) 48.0 (21.6 kg/hr) 40.16 (18.07 kg/hr) Average 51.29 (23.08 kg/hr) 10.01 (Standard Dev.)* 1.03 *N-1 weighting Example 2 In one embodiment the invention was constructed with helically coiled means 16 formed of three-sixteenth (3/16) inch diameter (0.48 cm) wire rod coiled to thirty-one/thirty-seconds (31/32) inch outer diameter (2.5 cm) circle with a five-eighths (5/8) inch (1.59 cm) pitch on the coil.

Approximately one hundred (100) pounds (45 kg) of lime was loaded into the feed hopper for each trial. The helically coiled rod was rotated at approximately ninety-seven (97) revolutions per minute.

Test data was taken every two (2) minutes, with feed rate being sampled for a sixty (60) second interval each time data was taken. The following table contains the data measured with and without the rod 22 inserted into the interior of helically coiled means 16; during both trials oscillating side panels 50 were operative.

ConventionalApparatus Apparatus of the Invention Lime Feed Rate Lime Feed Rate (Pounds of Lime/Hour) (Pounds of Lime/Hour) 31.2 (14.0 kg/hr) 19.0 (8.5 kg/hr) 29.8 (13.4 kg/hr) 18.7 (8.4 kg/hr) 28.3 (12.7 kg/hr) 19.2 (8.6 kg/hr) 27.3 (12.3 kg/hr) 19.0 (8.5 kg/hr) 26.1 (11.7 kg/hr) 19.0 (8.5 kg/hr) 24.2 (10.9 kg/hr) 18.7 (8.4 kg/hr) 20.5 (9.2 kg/hr) 19.0 (8.5 kg/hr) 16.8 (7.6 kg/hr) 18.4 (8.3 kg/hr) 18.0 (8.1 kg/hr) 18.4 (8.3 kg/hr) 21.9(9.9 kg/hr) 18.4 (8.3 kg/hr) 19.0 (8.5 kg/hr) 17.6 (7.9 kg/hr) 19.0 (8.5 kg/hr) 17.9 (8.1 kg/hr) 17.6 (7.9 kg/hr) 17.4 (7.8 kg/hr) 17.1 (7.7 kg/hr) 17.4 (7.8 kg/hr) 13.2 (5.9 kg/hr) 17.4 (7.8 kg/hr) 11.6 (5.2 kg/hr) 17.4 (7.8 kg/hr) 8.4 (3.8 kg/hr) 16.8 (7.6 kg/hr) 8.9 (4.0 kg/hr) 16.6 (7.5 kg/hr) 7.6 (3.4 kg/hr) 8.1(3.6 kg/hr) 18.73 (8.43 kg/hr) Average 18.14 (8.16 kg/hr) 7.51 (Standard Dev.)* 0.81 *N-1 weighting When the invention is utilized, variation in feed rate is reduced by approximately a factor of nine over that obtained with representative prior conventional apparatus having a simple open center rotating helical feed screw. Note in Example 1 above, standard deviation of feed rate data, when the invention was utilized, was 1.03 whereas standard deviation of feed rate data, when the aforementioned representative conventional apparatus was utilized, was 10.01. Also note in Example 2 above, standard deviation of feed rate data, when the invention was utilized, was 0.81 whereas standard deviation of feed rate data, when the aforementioned reprentative conventional apparatus was utilized, was 7.51.

Thus, the invention provides approximately a nine fold improvement in consistency of feed rate over that obtained when using representative prior conventional apparatus having a simple open-center rotating helical feed screw.

Claims

1. A powder feeding apparatus comprising a hopper having an outlet adjacent the bottom of the hopper and a screw conveyor positioned in the hopper for feeding powdered materials contained in the hopper to the outlet, wherein said screw conveyor comprises an open wound helical wire screw axially aligned with said outlet and a fixed rod extending into the open interior of said screw on or parallel to the axis thereof to prevent powder in the interior of the screw from rotating therewith.

2. Apparatus according to claim 1, wherein said helical wire screw extends from said hopper into said outlet.

3. Apparatus according to claim 2, wherein the external surface of the screw, within said outlet, is spaced from the inner wall defining said outlet.

4. Apparatus according to claim 1, 2 or 3, wherein said rod extends from said hopper into said outlet.

5. Apparatus according to claim 4, wherein said rod is fixed at the outlet end and extends into the interior of said open wound helical wire screw from the end thereof which is in or adjacent said outlet.

6. Apparatus according to any one of the preceding claims, wherein said rod extends substantially the whole length of said open wound screw.

7. Apparatus according to any one of the preceding claims, wherein the rod is spaced from the internal surfaces of the screw.

8. Apparatus according to claim 7, wherein the rod is of an elongate cross-section and lies on the axis of said screw.

9. Apparatus according to claim 7, wherein the rod is located to one side of the axis of said screw.

10. Apparatus according to claim 1, substantially as shown in the accompanying drawing.