GB2092998A - Handling materials of powder form - Google Patents

Abstract

Apparatus for handling powders comprises a hopper H having a base DC of which at least a portion is arranged to be vibrated in relation to the rest of the hopper in order to agitate the material and assist in its discharge, gas-injecting nozzles, e.g. GN being provided to blow gas over at least a part of the side walls and the base of the hopper. Provision may be made to inject gas through the nozzles in a predetermined sequence. Similarly vibration may be effected in accordance with a predetermined programme which may be related to the gas injection sequence. <IMAGE>

Description

SPECIFICATION Handling materials of powder form This invention relates to the handling of materials of powder form.

Materials of powder form can vary greatly in their physical properties and this variation can affect the ease with which they are handled. The particles of such materials can have a tendency to cling together and thus prevent easy flow of the material. These materials are often handled in large upright vessels such as hopper or silos. Handling can involve the filling and emptying of the silo or hopper in a controlled manner, for example to deliver a set quantity of material to a process or other use.

Handling can also involve the mixing or blending of two or more materials to produce a uniformly mingled product; the separation of materials and the short or long-term storage of a single material or blended materials for subsequent delivery. All such handling can be hindered by the adverse behaviour of the material, for example when particles cling together.

It is an object of the invention to provide material handling apparatus to overcome the adverse behaviour of the material.

According to the invention there is provided apparatus for handling materials of powder form including a base and side walls together with a material entrance and exit defining a vessel to contain the material, means including a plurality of nozzles being provided to inject gas over at least a part of the inner surfaces of the side walls and of the base of the vessel, means mounting at least a portion of the base for vibrational movement relative to the rest of the vessel and means for selectively controlling the injection of gas and the operation of drive means for effecting vibration of the said portion of the base whereby in use either or both the injected gas and the vibration act(s) on material in the vessel to disturb it in such a way that the material is caused to move freely within the vessel and, when reqired, through the exit.

The vessel may be a vertical hopper with abutting upper cylindrical and lower truncated conical side walls. The base may include a conical part pointing into the narrow end of the conical side wall and defining therewith a circumferential material exit.

The conical part of the base may support at least some of the plurality of gas nozzles spaced over the surface of the conical part. The gas supply means may be arranged to permit one or some of the nozzles to be supplied at a time, for example those in opposed or individual quadrants of the conical base.

The gas may be air or another suitable gas, e.g. an inert gas such as nitrogen. The gas supply means may include several gas supply sections each connected between a common gas supply conduit and respective gas nozzles for selective supply of gas to said nozzles, the common gas supply conduit being of "ring-main" form with a gas feed connection.

The control means may include an electrical or electronic timer/sequencer having control outputs and control devices responsive to the control outputs to start and stop pressurised gas supply and drive means power supply. The time/sequencer may be operable automatically to supply gas to selected gas nozzles in turn for distinct periods of time, which may overlap, in an overall sequence providing for supply to all nozzles in their turn. The timer/ sequencer may also be operable automatically to operate intermittently the vibration drive means. The timer/sequencer may be settable to a range of gas supply periods and overall sequence duration and nozzle turns with the sequence and to a range of intermittent power supply occurrences.

According to another aspect of the invention there is provided in or for a material handling apparatus having gas injection means effective to disturb material in the vessel, a gas supply and control arrangement including a gas feed connection to a gas flow conduit in ring-form, a plurality of gas supply means extending from respective connections on the conduit ring to respective said gas injection means and control means for said gas supply means.

The control means for said gas supply means may include means to regulate the pressure of gas in the conduit and means to start and stop the flow of gas in said conduit. The means to regulate and control the gas may be fluid pressure operated. The gas flow to the injection means may be a relatively high volume, low pressure flow, as from a blower, and the fluid to regulate and control the gas by said means may be at a relatively lower volume and higher pressure.

The gas supply means may be controllable by sequencer means to activate one or more parts of the gas injection means separately, sequentially or in combination as required or selected. The sequencer means may be an electronic timer to produce electric control outputs for respective gas supply means effective via electro-pneumatic valves.

There may be means to supply a high pressure clearing flow to said gas injection means and a non-return valve to isolate the gas supply means on the supply of said high clearing pressure.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is an outline of material handling apparatus embodying the invention, Figure 2 is a cross-sectional elevation of the lower part of a material handling vessel usable in the apparatus of Figure 1, Figure 3 is a plan view of this lower part of the vessel, Figure 4 is an outline of a control means usable in the apparatus of Figure land Figure 5 shows another form of the control means.

Referring firstly to Figure 1, an open topped hopper or silo has an upper cylindrical side wall S and a lower truncated conical sidewall C and is mounted on a suitable support frame not shown but indicated at F. A base B closes the truncated conical side wall C and provides a material exit E. Material can be loaded into the hopper H at the top I, which is normally closed by a lid (not shown).

The base B is of generally conical shape BC with an upstanding rim R at the outer edge. A rim RC of similar form is provided at the truncated end of conical wall C. A flexible coupling FC joins the base B to conical wall C to close the hopper in this region while permitting base B to move with respect to the rest hopper H. To support base B for such movement, resilient mountings RM are provided. These can be of any suitable form. In one embodiment the mountings are moulded rubber cores MC through which studs ST are passed and held by lock-nuts.

To put base B into vibrational movement, a vibrational drive means VDM is attached to one side of the base using a stiff mounting flange MF projecting from the base. Vibrational drive means VDM can be of any suitable form. In one embodiment a proprietary device, supplied by the Grantham Electricai Co. Ltd., of an electric motor rotating eccentrically mounted weights was used. A suitable flexible electrical power supply connection ESC is provided for the drive means.

The base B also includes a gas injection arrangement. In the illustrated embodiment a deflector cone DC is rigidly attached to cone BC to leave a small peripheral gap G for the passage of material. The gap G is only a small fraction of the diameter of cone DC. In one embodiment the cone DC is about 1 meter in diameter and the gap about 20 mm wide. The deflector cone supports a plurality of gas nozzles GN which are spaced over the cone DC as shown and described below. A flexible gas supply connection GSC permits the reliable supply of gas to the vibrating base. The supply of gas and electricity is controlled by a control means CM, shown in detail in Figure 4, which in turn receives a supply of electric power and compressed air, e.g. air at 80 psi.Gas nozzles are also provided on the conical wall C, as indicated by the reference GNF,the position and number being chosen to suit the material to be handled.

As further explained below the base B is vibrated and/or caused to inject gas into the hopper H in a controlled mannerto ensure the free movement and/or mixing of material in the hopper and free flow out of the exit E via the gap G.

The construction of base B is an important aspect of the apparatus to put the invention into effect as the apparatus must have a long reliable life under severe conditions of vibration in a dusty and generally harsh environment. In particular the gas supply path within the base must be reliable as access is difficult once the base is installed. To this end the base is stiffened by an internal framework of tubular hollow sections welded together. The hollow sections also provide ducts through which gas supply pipes can be passed. The ducts protect the pipes from damage and provide a stable support to which the pipes can be attached. The pipes within the base can thus all be rigid and the flexible portions to accommodate vibration can be outside the base for easy inspection and replacement. Flexible portions join the pipes to the gas nozzles.

Figures 2 and 3 show one form of the base in sectional elevation and plan respectively.

Figure 2 shows in cross-sectional elevation a re-inforcing frame RF, which is shown in plan in Figure 3, formed of rectangular hollow sections welded together and to base cone BC to stiffen the cone and support the mounting flange MF for the vibration drive means VDM, and gas supply pipes GS. The rigid gas supply pipes are secured to the frame RF and terminate in four manifold blocks MB (only one of which is shown) placed around the centre of the frame. Flexible pipes FP extend from the manifold blocks to individual gas nozzles GN.

The other ends of the rigid pipes GS extend beyond the frame RF and through the cone BC to a mounting position (not shown) at which the flexible connections GSC are made. In the illustrated embodiment there is an individual path from the control means to each gas nozzle. (Each gas nozzle may comprise a number, for example six orifices evenly spaced around a circular head and directed downwardly, typically at an angle of 10 ). Figure 2 also shows the position of exit gap G and the angle a of the conical side wall C. As is well-known in the art angle a can be chosen to suit the material to be handled in the hopper.

Figure 3, a plan view, shows one layout of the gas nozzles GN on cone DC. Twelve nozzles are provided and are spaced in circles of four and eight to be uniformly spread over the cone surface. The circles around the nozzles indicate the areas influenced by gas issuing therefrom, the spacing of the nozzle being such that there is as near a uniform distribution of gas as is possible.

The nozzles are conveniently grouped in threes, e.g as four groups GNA, GNB, GNC and GND, so that sequential or other selected gas activation can be applied over the surface of cone DC. (Gas connections and manifolds are omitted from Figure,3).

Figure 4 shows a control means for one embodiment of the invention and usable in conjunction with the apparatus described above. The control means controls the supply of gas from a source PN, typically air at 80 psi, and electricity from a source EL, typically 240 v a.c., 50 Hz.

The air supply from source PN is supplied to a main manifold M through a filter regulator unit, having a pressure indicating gauge 1. The manifold M is advantageously in the form of a "ring-main", that is a loop of conduit fed at one point by source PN and having draw-off tappings around the loop.

This "ring-main" improves the consistency of supply to each draw-off tapping as the amount and position of draw-off varies, as set out below, compared with a singie conduit with a sequence of draw-off points and a terminal draw-off, which would be subject to variable pressure-drops along its length unles of very large bore. The "ring-main" is also more economic of conduit than a specific feed to each draw-off. Air from source PN is also supplied directly as a power supply for four solenoid valves, 2. Four similar gas injection sections are supplied from the manifold M, the sections corresponding to nozzle groups GNA, GNB, GNC, GND. Each section includes a solenoid valve 2, a poppet valve 3 and a by-pass 4 for each poppet valve connected to control the supply of air from source PN to distribution manifold 6 (corresponding to the manifold MB of Figure 2) the outputs of which are connected via the flexible couplings to individual gas nozzles. Timer/sequencer TS is an electromechanical device which can be set to bring one or more groups of gas nozzles into use in turn, for example one pair of opposite groups alternating with and slightly overlapping the other pair approximately once a minute with a few, say 1 to 5, seconds overlap. The timer/sequencer also provides an intermittent output to the vibration drive means VDM, as shown. For example an output can be provided once in each use of a group of gas nozzles, that is one every half minute in the above example.The by-pass 4 provides a small supply of air to each nozzle at all times to prevent undue compacting of the material during lengthy storage.

This small supply also helps to keep the nozzles clear.

The provision of controlled excitation of gas jets in combination with the intermittent vibration or agitation greatly improves the ease with which the material in the hopper is handled e.g. moved out or mixed. Many of the more "difficult" powdered materials will "rat-hole", that is become static and develop vertical holes above the gas nozzles, despite the inclination and criss-crossing of gas directions. It has been found that a short period of vibration, applied while the gas jets are flowing, eliminates the "rat-holes" and causes the material to move freely.

Figure 5 shows a further control means which permits greater flexibility of control and better matching to material properties than a simple electromechanical timer/sequencer. In Figure 5 only one section of the gas circuit is shown, that feeding nozzles GND. A similar circuit section feeds each of the groups GNA, GNB, GNC, as indicated by the reference A.... GNA etc. These sections do not need description, given the description of the section shown.

An electrical supply EL is provided for an electro nictimer/sequencerTSE. This is an arrangement of integrated circuit elements to provide independent control of the duration and frequency of the energisation of each of outputs A, B, C, D corresponding to quadrants of the hopper. Controls K and DL are adjustable to control respectively the length of a cycle of gas injection and the dwell between, or overlap of portions within the cycle, as described above. Indicators, such as l.e.d.s. QL, indicate which quadrant or quadrants are injecting gas. Further controls, VT, enable the duration and timing of drive periods of vibrating drive means VDM to be controlled. In this way the operating cycle of the handling apparatus can be set up with a free choice of intervals and timings unconstrained by the limitations of an electromechanical device.The exact form of construction of device TSE is not described in detail as such devices are readily constructed by those skilled in the art from the wide range of integrated circuits now available, if necessary in conjunction with reference to the many suggested techniques now described in the literature. However, the provision of the two simple controls, duration and dwell, or overlap, eases use by operatives. The general requirements for materials handling are cycle times of about 20 seconds to a few minutes in sections appropriate to the number of gas nozzle groups and combinations with the ability to overlap or dwell between transitions by a few seconds, say one to twenty. The timing of the vibration is desirably adjustable throughout the cycle and its duration is again a few seconds, say one to twenty.

The facility for continuous operation of gas injection and/or vibration is desirable.

One procedure for setting up the apparatus for mixing a particular material using air will now be described. Clearly other procedures are within the scope of the invention, this being only an example.

First ensure that the vessel is clean and blow out all lines and nozzles with a high pressure (see AB in Figure 5 below) to remove blockages. Next place a small amount of material (say 5 kg in a 0.6 m vessel).

Adjust cycle time (knob K) to at least 20 seconds with dwell (knob DL) at or near zero. Adjust airflow from nozzles so that circles of influence from adjacent nozzles overlap by 25 mm. Ensure absence of dead spots, coronas etc. Note air rates and manifold and nozzle pressures. These are the minimum air conditions for mixing. Now add more material to cover the nozzles to a depth of 100 mm and adjust air conditions, dwell and cycle times without going below minimum air conditions already found. Look for a "boiling" action in the material with minimum air usage and avoid rat-holes, burping, excessive carryover of "fines" and dead spots while ensuring that the centre of the top surface is being renewed.

Having established these conditions, the apparatus can be filled to working height. Samples can now be taken at different heights and times to check progress of mixing.

The timer/sequencer TSE provides outputs to an electropneumatic valve EP for each gas nozzle group. Conveniently this valve is of the "Airmatic" type. Valve EP receives an air supply, e.g. at 80 psi, from source PN1 and provides an air output to slave valve SL to operate this when required. The slave valve SL is conveniently of the "AUDCO" V60 type.

The air output of valve SL is applied to a ball valve BV which itself controls the supply of injection gas, e.g. air, to the distribution manifold DM. Manifold DM has sealable tappings for a number of gas nozzle connections to the base B. The injection gas can be supplied to the various ball valves by a "ring-main" arrangement as shown in Figure 4. Conveniently a connection AB is provided by which a full pressure air blast, e.g. at 80 psi, can be applied directly to the nozzles to clear them. A non-return valve NRV prevents the air blast entering the control means.

The air actually injected is preferably regulated and filtered at REG before supply to ball valve BV. This air can be derived from a separate source PN2 or from source PN1. When a separate source PN2 is used this may be a low pressure, high volume supply, e.g. from a blower, rather than the high pressure, low volume supply of the typical 80 psi factory air supply. Advantageously the low pressure blower supply will be free of oil and other contaminents found in the factory air supplies. It may be convenient to use an air pressure controlled regulator REG operated by air supply PN1 through a manual regulator MR.

In operation of a typical apparatus the hopper is vertical and the depth to diameter ratio for material in the vessel should be 2:1 to 3:1 for good mixing action. When materials are to be mixed or blended the weighed components should be fed in together if possible, minor components particularly being fed continuously with the major.

The pressure actually supplied to the gas nozzles in the hopper is usually in the range 1 to 5 psi above atmospheric (i.e. psig). It has been found that light materials require 12 to 2- psig, heavier material 3 or more psig. The industry has various classifications for powder materials and consequent guide lines on relative size and shape of hoppers and outlets. The apparatus of the present invention is particularly appropriate for materials of between 100 mesh and 300 mesh and for finer cohesive or readily fluidised materials. Examples of the first type of materials are flour, resins and starch which do not readily flow by gravity alone and the second group includes pigments as cohesive material and talcum powder as fluidisable material.

In one particular application where a light material (density c.30lb/cu.ft., 450 kg/cu.m.) a resin, was to be held in store in a hopper for some hours or days before release at short notice, problems of compaction and clogging on de-aeration in store were overcome by the use of apparatus embodying the invention. After the material had been aerated on charging into the hopper it could be discharged, even a week later, by use of the vibrator alone.

Another improvement was when mixing materials which were liable to rat-holding e.g. a resin for binding foundry cores. Other materials which the apparatus will handle efficiently and reduce problems of clogging and rat-holing are ball-clays and pottery clays, plaster of paris, cement and Fuller's earth, both for storage and mixing.

The details of construction not described above will be readily apparent to those skilled respectively in the air-assisted and vibration-assisted materials handling arts while the problems and benefits of the combination of these arts in putting the invention into practice have been set forth. Nylon tubing has been found suitable for the flexible gas connections and steel tubing for the rigid gas feeds. It has been found necessary to operate the valve devices well within their ratings in view of the frequent actions required of them. Reliable operation under frequent action in dusty conditions and in the presence of vibration is most important. It is also possible to apply the gas supply and control techniques described above without use of vibration to provide a more effective gas injection arrangement than hitherto.

The techniques described will then produce a significant improvement in material handling with economy of air and electric power by precise control of the appropriate means for agitating the materials.

Claims (9)

1. Apparatus for handling materials of powder form including a base and side walls together with a material entrance and exit defining a vessel to contain the material, means including a plurality of nozzles being provided to inject gas over at least a part of the inner surfaces of the side walls and of the base of the vessel, means mounting at least a portion of the base for vibrational movement relative to the rest of the vessel and means for selectively controlling the injection of gas and the operation of drive means for effecting vibration of the said portion of the base whereby in use either or both the injected gas and the vibration act(s) on material in the vessel to disturb it in such a way that the material is caused to move freely within the vessel and when required through the exit.

2. Apparatus as claimed in Claim 1 in which the vessel is in the form of a vertical hopper having abutting upper cylindrical and lower truncated conical side walls and the base includes a conical part defining with the conical side wall a circumferential material exit, and at least some ofthe gas nozzles are mounted on the said conical part.

3. Apparatus as claimed in Claim 1 or 2 in which means are provided to permit selected one or groups of nozzles to be supplied at a time.

4. Apparatus as claimed in Claim 3 in which several gas supply sections are provided each connected between a common gas supply conduit and respective gas nozzles or groups of nozzles, the common gas supply conduit being in the form of a ring main.

5. Apparatus as claimed in any one of the preceding claims in which the control means comprise a timer/sequencer having control outputs and control devices responsive to the control outputs to start and stop the supply of gas to the nozzles and the supply of power to the vibration drive means.

6. Apparatus as claimed in Claim 5 in which the timer/sequencer is operable automatically to supply gas to selected gas nozzles in turn for distinct periods of time in an overall sequence providing for supply to all nozzles in turn.

7. Apparatus as claimed in Claim 6 in which the timer/sequencer is operable automatically to operate intermittently the vibration drive means in a predetermined relationship with the supply of gas to the nozzles.

8. Apparatus for handling materials of powder form constructed arranged and adapted to operate substantiaily as herein described with reference to Figures 1 to 3 of the accompanying drawings.

9. Apparatus for handling materials of powder form as claimed in any one of the preceding claims adapted to be operated substantially as described in relation to Figures 4 or 5 of the accompanying drawings.