CA1125143A - Process and mechanism for evolutive pulp flow regulation - Google Patents

Abstract

A B S T R A C T

The present invention is concerned with regulation of evolutive pulp. It offers a regulation process and mechanism, said mechanism including an elastic shape-changing pneumatic valve, valve opening control means, and modulating means causing a variation of said valve opening either way from an opening setting achieved through control means. The present invention can be applied to a continuous process for mixing plaster.

Description

llZ5143 Technical Field This invention is in the field of flow control.
Background of Prior Art The present invention is concerned with regulation of evolutive pulps. Evolutive pulps are liquids in which a certain reaction resulting in a physical or chemical transfor-mation takes place such as producing a solid phase or modi-fying the characteristics of the solid phase initially carried by said liquid. One example of evolutive pulp would be plaster powder mixed with water. This invention can be applied to the hydraulic binders industry, plaster industry and generally to any industry in which there is a need to control the flow rate of evolutive pulps carried through piping.
In order to cutoff, introduce variations, or regu-late a liquid flow rate to a given value, the use of elastic shape-changing valves is widespread. Such valves consist of a rigid tubular housing and a cylindrical inner cell, such as a sleeve, with enough elastic property to change shape. Valve closing is achieved through compression of the elastic sleeve by either the mechanical effect of a screw-nut-flywheel mechanism or by the effect of a pressurized fluid, such as water or air, sent between the housing and sleeve. When no mechanical or pneumatic action is exerted upon the sleeve, the valve allows direct passage of the product at full rate of flow; when the sleeve is subjected to a shape-changing action, the aperture of the sleeve opening is reduced and the valve allows only a reduced flow rate of the product. With a suf-ficiently strong mechanical or pneumatic action, the elastic walls of the sleeve eventually become joined, thus completely closing the valve.

Such manually controlled valves are recommended for viscous, pasty or abrasive liquids. But in the case of evolu-tive pulps, deposits form in the narrow channel created by the compressed sleeve, deposits which change the size of the sleeve aperture alter the valve setting and eventually create an obstruction.
It is also known to pulsate elastic shape-changing valves to keep material in a liquid state and to use large elastic sleeves to break up solids.
Brief Summary of the Invention The invention is aimed at preventing the deposit of evolutive pulps in a narrow channel created by a valve and is characterized by the fact that it comprises superimposing a pulsating signal on a regulation signal which is advantageous in maintaining a constant amount of ingredients in a mixing container continuously supplied with evolutive pulp ingredi-ents.
The invention offers as well a regulating mechanism for the rate of flow of evolutive pulps characterized by the fact that it includes a flow rate regulating valve, valve opening control means and modulating means causing a variation of the valve opening either way from an opening setting fixed by the control means which is advantageous in maintaining a constant amount of ingredients in a mixing container continu-ously supplied with evolutive pulp ingredients.
According to another characteristic, the invention'smechanism is characterized by the fact that the flow rate regulating valve is an elastic shape-changing pneumatic valve, consisting of a rigid housing, of a inner elastic sleeve, and of a valve opening control fluid intake between rigid housing and sleeve.

~12S~43 In accordance with the process and apparatus of the invention, the amount of material is maintained constant in a mixing tank, and the time of the material in the mixing tank is maintained constant, by supplying a regulating or sensing signal to a discharge control valve and superimposing a pulsating or vibrating or modulating signal on the sensing signal. This vibrating signal prevents deposit of material in the valve. Advantageously, the sensing signal is responsive to the weight of the mixing tank which preferably is free from upstream and downstream equipment. In accordance with the invention, the vibrating or pulsating signal may be caused by vibration of the mixing tank which is advantageous because it keeps the valve sleeve vibrating to prevent deposit of material on the interior surface of the sleeve. If necessary, a modulating piston may be used instead of, or to supplement, the pulsating signal supplied by the motor vibrations. The motor shaft is seldom exactly vertical, and therefore creates vibrations. Also, the irregular delivery of the gypsum powder to the mixing tank creates vibrations.
The pneumatic valve of the invention employs an inner elastic sleeve that is star-shaped in cross-section when subjected to pressure, which is advantageous because the star-shape makes deposit of the material more difficult.
Brief Description of the Drawings Figure 1 is a schematic view of a shape-changing elastic pneumatic valve;
Figure 2 is a schematic view of a setting mechanism for the rate of flow of evolutive pulps;
Figure 3 is a schematic section of the valve in Figure 1 illustrating its operation;
Figure 4 is a schematic view of a regulating ~lZ~i~43 mechanism for the rate of flow of evolutive pulps;
Figure 5 is a schematic view of apparatus in accordance with the invention for making a plasterboard building component;
Figure 6 is a perspective view of a receiving container in accordance with the invention;
Figure 7 is an enlarged view of the nozzle 18 and its associated parts; and Figure 8 is an enlarged view in section of the valve V.
Detailed Description of the Invention Figure 1 shows an elastic shape-changing valve V of the type used in our invention. It comprises a housing or rigid casing 1 of cylindrical shape with a lateral control fluid intake pipe 2, and an inner elastic sleeve 3, of for example rubber, also cylindrical and whose section is equal to that of the internal diameter of the rigid casing, or slightly stretched to contact the inner surface of the rigid casing.
The sleeve 3 assumes the star-shape cross-section of Figure 2 when a very low air pressure is applied to the outer surface of the sleeve 3. The ends of said sleeve 3 may be secured to casing 1 by being turned over the edge of casing 1 and tightened by securing rings. As shown in Figure 1, each end of sleeve 3 is held to casing 1 by a piece of tube 4 with the same shape as casing 1 but with slightly smaller dimension which is pushed in at each end of valve V. The tube 4 elements are connected by a threaded rod-nuts assembly 5 which is also used when securing rings are employed.
Advantageously, the sleeve 3 has a star configur-ation in cross-section as shown in Figure 2 when under pressure. This configuration keeps the sleeve 3 vibrating to llZS143 prevent deposit of mix on that surface. For example, the inscribed diameter of the sleeve varies from 21 mm to 15 mm when the air pressure varies from 100 to 300 mm of mercury.
~y way of example, in a typical sleeve of 0.8 mm thickness, its inscribed diameter varies from 21 mm to 15 mm when the controlling air pressure goes from 100 to 300 mm Hg where the initial at rest diameter is 32 mm and length is 82 mm. By inscribed diameter is meant the diameter of the inscribed circle 3a in the star-shaped sleeve 3b in Figure 3.
Figure 2 shows a mechanism for the setting of evolu-tive pulp flow rates which is in accordance with the invention.
A mixer 6 is provided in its lower part with a drainage open-ing on which is fitted a pipe 7 equipped with the flow rate regulating valve V of Figure 1.
Mixer 6 is continuously filled with an evolutive pulp product 8 whose flow rate regulation through pipe 7 is sought. This filling may be carried out using the apparatus disclosed in our copending Canadian patent applications Serial Nos. 321,011 and 321,012, respectively, entitled "Continuous Process Mixing of Pulverized Solids and Liquids and Mixing Apparatus" and "Plaster Board and Process and Device for Making Plaster Board" filed concurrently herewith. Lateral control fluid intake pipe 2 of control valve V is supplied witn com-pressed air, the pressure of this air being controlled by a pressure regulating assembly 9 set to a value corresponding to a set rate of flow of product 8 through valve V, therefore to a set change of shape of inner sleeve 3.
In accordance with the invention, a piston 10 actu-ated with a reciprocating motion and modulating the pressure of compressed air sent between housing 1 and elastic sleeve 3 of valve V is installed on control fluid intake pipe 2.

~lZ5143 Piston 10 may be reciprocated, for example, by a crank on a motor driven shaft (not shown) to create a modulation of the pressure in the valve V. The modulation frequency preferably may be about 2.4 Hz and may be in a width range on both sides of 2.4 Hz.
In other types of construction, piston 10 may be replaced by any other mechanism able to induce a modulation of valve V control fluid pressure.
The Figure 2 mechanism operates as follows : com-pressed air, whose pressure is set by pressure regulatingassembly 9 to a preset value Po, is sent through valve V to control pipe 2. This air pressurizes sleeve 3, which assumes a star-shape as represented in Figure 3, and the aperture of the channel in valve V for product 8 contained in container 6 becomes thus restricted. The selected flow rate to maintain the desired level of product 8 is obtained by the setting of pressure regulating assembly 9.
Alternating motion actuated piston 10 creates a modulation of the pressure in valve V above and below the value Po, which causes a periodic compression and release of sleeve 3. In this way, the sleeve is continuously in motion and this prevents any accumulation of product 8 when valve V
forms a narrow channel.
Figure 4 shows an evolutive pulp flow rate regu-lating mechanism in accordance with the invention.
Product 8 (or its separate constituents) is continu-ously introduced into mixer 6 at a constant rate by con-ventional mechanism (not shown). Mixer 6 is provided in its lower part with a drainage opening connected to pipe 7 equipped with valve V. The mixer 6 is supported by an arm llb of a force balance beam 11 in equilibrium on fulcrum 12, the llZ5143 equilibrium of beam 11 being achieved through a spring 14 and a counterweight 13 acting upon the other balance 11 beam arm.
The counterweight's position on beam arm 11 may be adjusted so that equilibrium is attained for any level of product 8 in the mixer 6. A damping piston 15 is connected to beam arm lla. The setting control of valve V is obtained through a pneumatic escape mechanism F. Such a mechanism F
has a fluid, generally air, under a pressure Po, and supplies the air to pipe 16, that is, connected to control fluid intake pipe 2. A pipe 17 also is connected with pipe 16 and vents the air through a nozzle 18 and directs the air against the bottom of beam arm lla. Two safety stops 19 and 20 are placed above and below the beam end lla, thus limiting movement of beam arm lla and the mixer's weight variations in relation with the selected weight adjusted with counterweight 13.
Pressure P is regulated through pressure regulator 9 and measured by a pressure gauge 21 represented as a mercury con-taining U-shaped tube.
Product 8 is stirred inside mixer 6 by a mixing impeller or agitator 22.
This evolutive pulp flow rate regulating mechanism operates as follows : the mixer 6 receives a supply of product 8 in continuous process. Said product 8 is stirred by agitator 22 and flows through discharge pipe 7 in a continuous process, the flow rate being regulated by valve V.
The pressure of air in pipe 16 is set using pressure regulating 9 at value Po in order to obtain, when escape flow through valve 18 is shut off (by moving manually the tip of beam arm lla onto nozzle 18), a position of valve V providing a product flow rate below the selected flow rate, and when escape flow through nozzle 18 is increased to its maximum (by ~S.Z~;143 having the beam tip of arm lla touching top safety stop 19), a position of valve V such that the product flow rate is higher than the one selected. Then the position of counterweight 13 on beam arm llb is adjusted so that beam 11 assumes a position intermediate its position completely blocking flow through nozzle 18 and its position against stop 19, in which position the selected flow rate of product 8 is achieved which is equal to the flow rate at which product 8 is introduced into mixer 6 in order to keep constantly a set amount of product 8 in mixer 6.
Any weight variation of product 8 in mixer 6 causes a deflection of balance beam ll. Thus, an overweight results in increasing the distance between beam arm lla and nozzle 18, therefore increasing the flow of air escaping from nozzle 18 and reducing the pressure of the air between sleeve 3 and housing 1 of valve V. Thus sleeve 3 expands to increase the size of the valve opening, to increase the flow of product through the valve V increases, so that mixer 6 empties more rapidly until the weight of product 8 is again at the desired point at which time beam 11 has returned to its original position, thus regaining equilibrium. In the opposite case, too small a weight of mixture in mixer 6 results in con-tracting sleeve 3 of valve V and therefore in greater holding back of product 8 in mixer 6, which results in regaining equi-librium at a predetermined weight of product 8 in mixer 6.
In the mechanism illustrated in Figure 2, a piston10 induces a modulation of the pressure of control air sent to valve V. In the case of the Figure 4 mechanism, which is preferred, vibrations in the pressure of control air are induced by vibrations from the mixer 6 including vibrations from agitator 22. These vibrations result in oscillations of 112~3 beam 11 and, consequently variations in the amount of air escaping through nozzle 18, causing pulsations in pressure of the air sent to valve V. Thus, sleeve 3 vibrates and contracts and expands rapidly. Under the effect of pressure it assumes a star-shape, and the vibrations from mixer 6 vibrates the valve sleeve 3 rapidly, thus preventing formation of deposits of product 8 on the interior surface of sleeve 3.
Sleeve 3 can be made with any leakproof elastic substance but it is necessary, before any setting of the mechanism, to determine the elastic characteristics of material used by establishing a diagram giving valve aperture size against pressure.
The elastic sleeve can be made with a very pliable inner tube material. This gives a light valve, reacting to a 15 low pressure of the order of .25 bar (7.38 in.Hg), total pressure in the escape pneumatic system being of the order of - 1 bar (29.52 in.Hg).
Damping device 15 is selected so that it allows preferred vibrations to be felt. A valve 23 is in the pneu-matic circuit downstream from the`pressure gauge before saidcircuit divides into pipes 16 and 17. Thus, once operating conditions of the installation are determined, it is easier to restart the installation after stoppage without any need to proceed with new settings. Valve 23 is closed and pressure is set at value Po already known. Safety stop may be connected with a valve that shuts off product 8 supply to mixer 6 when beam tip 11 makes contact with it.
A constant flow needle valve 24 is downstream of pressure regulating assembly 9 and acts to give constant flow and prevent back up from downstream.

Figure 5 shows apparatus in accordance with the l~ZS1~3 invention for making reinforced plasterboard building com-ponents. Pulverized plaster powder 200 contained in a hopper 202 is distributed on a constant weight weight-sensitive conveyor belt 204 set beforehand for a predetermined constant flow rate of plaster powder. Conveyor belt 204 discharges the plaster powder onto a vibrating pouring screened spout 206 which delivers it into mixer 6 having an agitator 22. A water reservoir 210 discharges into a line 212 having a valve 214 with line 212 being connected to a flow meter 216 discharging into a line 218 which in turn discharges into overflow trough 220 secured about the periphery of mixer 6 and adapted to overflow to supply mixer 6 with water adjacent the inner wall of mixer 6 to wash the inner wall. A line 217 branches off from line 218 and washes the upper portion of impeller shaft 222, and a line 219 branches off from line 218 and washes the lower portion of impeller shaft 222. In this manner plaster powder and water are supplied to mixer 6 at a constant rate to mix together.
The plaster powder-water mixture 8 (the evolutive pulp) discharges through the open lower end 224 of mixer 6 into pipe 226 controlled by valve V. Pipe 226 discharges into a receiving container 228 to permit the weighing of mixer 6 separately from the apparatus downstream of pipe 226. Con-tainer 228 is connected by a pipe 230 to a pump 232 that dis-charges into a pipe 234 supplying a distributing container 238.
Distributing container 238 discharges into a line 240 that supplies lines 242, 244 and 246 which discharge horizontally into a pouring head C having an upstream plate 248 and a downstream plate 250 connected to a guide plate 254. Pouring head C is mounted above a moving conveyor 256. A reinforce-ment sheet 258 of, for example, woven fiberglass is fed in llZ5143 between pouring head C and conveyor 256 to reinforce plaster poured onto conveyor 256 for the formation of a plasterboard building element.
With given rates of introduction of plaster powder and water, the mixing container filling level determines the mean time during which the plaster remains in the mixing container (at least 3 seconds and preferably for 15 to 30 seconds for plaster as well as other evolutive pulps). Here-tofore the filling level was attempted to be maintained by varying the rate of introduction of the ingredients while not changing their ratio which is very difficult. In the appa-ratus of Figure 5, it is accomplished by the invention by controlling flow through valve V that is made practical by the modulation of the control or sensing signal to valve V to keep the valve clear of any deposits, so that the relationship between the controlling signal and the flow rate of valve V is not changed by deposits in the valve that would partially block the flow through valve V.
As shown in Figure 6, receiving container 228 is fed by a pipe 226 that discharges into receiving container 228 having an open top 302 and a bottom 304. Discharge pipe 230 is tightly secured to bottom 304 and has a funnel 306 con-nected to its upper end for reception of material discharged from pipe 226, funnel 306 and pipe 226 being coaxial. A spray nozzle 310 is connected to a water line 312 to flush the bottom 304 in order to wash out any material not collected by funnel 306. A drain 314 in bottom 304 is connected to a dis-charge line 316. In addition to serving the function of dis-connecting mixer 6 from the apparatus downstream of pipe 226 for purposes of weighing mixer 6, receiving container 228 performs the function of preventing the hydrostatic pressure ~1;Z;5143 upstream of container 228 from affecting downstream pump 232.
Figure 7 is a partial view on an enlarged scale of the apparatus around nozzle 18 of Figure 4. Pipe 17 extends upwardly to feed the compressed air to nozzle 18 which is protected from being damaged from contact with plate 316 of beam arm lla by a sturdy nozzle head 318. Pipe 17 is sup-ported by a plate 320. The distance between beam plate 316 and nozzle 18 controls the amount of air vented from pipe 17, and controls the pressure of the air delivered in valve sleeve 3 through control pipe 2.
Figure 8 is an enlarged view in longitudinal section of valve V, which is diagrammatically shown in Figure 1, with control pipe 2, tubes 4 extending into both ends of pipe 1 and clamping the ends of sleeve 3 to the inner surface of pipe 1 except for middle portion 322 which is free to expand inwardly in a star-shape when actuated by the compressed air from control pipe 2, and clamps 324, 325 that clamp sleeve ends 326 and 328 to tubes 4. Pipe 1 may be 82 mm long and 33.5 mm in diameter, with the outside diameter of tubes 4 being 32 mm to fasten sleeve 3 between them. The initial length of sleeve 3 may be 140 mm, and 0.8 mm thick. In assembly, the bottom 328 of sleeve 3 may be rolled back and clamped to pipe 1 by clamp 325. Sleeve 3 is then stretched upwardly about 15 mm to keep sleeve 3 in tension, with half the perimeter of the sleeve 3 being about 46 mm and the average diameter of sleeve 3 being about 29 mm. Then upper sleeve end 326 is rolled back onto the upper end of tube 1 and clamped thereto by clamp 324.
The characteristics of the sleeve 3 material is such that a piece 10 cm long and 2 cm wide is stretched by 5 cm when held at the top and a weight of 1.2 kg is applied to its bottom. A very small variation in pressure varies the star-~Z5~3 shape of sleeve 3.
The invention deals with setting the flow rate ofevolutive pulp, but it also deals with the setting of evolu-tive pulps containing finely broken up inert loads, for instance, chopped fiberglass, also, the invention deals with setting the flow rate of non-evolutive liquids, whether loaded or non-loaded with finely divided inert loads such as chopped glass fibers.
Therefore, under the term of evolutive pulps, properly speaking, can be included evolutive pulps containing in addition inert loads, and loaded or non-loaded liquids.
Referring again to Figure 5, it is to be noted that the impeller 22 is driven by a motor 400 that drives a gear box 402 that in turn drives gear box 404 which drives shaft 222. Structural member 406 connects tank 6 and motor 400 so that they are mounted together and are carried by beam arm 410b. Spring 14 and modulating piston 15 are mounted on structural member 412 and are mounted on beam arm 41Oa. Knife edge 414 is positioned between motor 400 and mixing tank 6 so as to be in a position to maintain the motor and tank in equi-librium with a minimum amount of mixture in the tank.

Claims (18)

The embodiments of the invention in which an exclusive property of privilege is claimed are defined as follows:

1. A process for maintaining a constant amount of evolutive pulp in a mixing container comprising:
continuously supplying evolutive pulp ingredients to the mixing container, continuously withdrawing the evolutive pulp from the mixing container through a line having a valve controlled by a regulating signal, supplying a regulating signal to the valve to vary the setting of the valve to maintain a predetermi-ned amount of evolutive pulp in the mixing container, superimposing a pulsating signal on the regu-lating signal to prevent the deposit of pulp in the valve in order to maintain a constant relationship bet-ween the regulating signal and the rate of flow of pulp through the valve.

2. A process in accordance with Claim 1, cha-racterized in that the regulating signal is responsive to the weight of said evolutive pulp in the mixing container.

3. A process in accordance with Claim 1, cha-racterized in that the pulsating signal is responsive to vibration of the mixing container.

4. A process in accordance with Claim 1, 2 or 3, characterized in that the evolutive pulp is a mixture of plaster powder and water.

5. Evolutive pulp flow rate setting mechanism for continuously controlling the level of evolutive pulp in a mixer continuously receiving a supply of evolutive pulp ingredients comprising:
an elastic shape-changing pneumatic valve con-nected to said mixer;
control means supplying to said valve a regula-ting signal responsive to the weight of said evolutive pulp in said mixer; and modulating means further supplying to said valve a continuous rate of pulsating signals to prevent deposit of pulp in said valve.

6. A mechanism according to Claim 5, wherein said valve comprises a rigid housing, an inner elastic sleeve, and a valve opening control fluid intake between the housing and the sleeve.

7. A mechanism according to Claim 6, wherein the elastic sleeve at rest has a diameter not exceeding the inner diameter of the housing, and the sleeve is star-shaped in cross-section when subjected to pressure on the outside of the sleeve and varies in shape of the star when subjected to very little pressure before it varies in the size of the star when subjected to more pressure.

8. A mechanism according to Claim 7, wherein said sleeve is a flexible rubber adapted to react to pressure variations in the order of 0.25 bar.

9. A mechanism according to Claim 6, wherein said control means comprises a fluid supply under pressure equipped with a pressure regulator and a pressure gauge.

10. A mechanism according to Claim 7, wherein said control means includes a regulating air escape pneumatic mechanism associated with a force balance beam whose beam supports a container filled with evo-lutive pulp whose discharge flow rate setting is sought, and which controls the air escape pneumatic mechanism.

11. A mechanism according to Claim 9, cha-racterized in that said pressure modulator includes a piston actuated with a pulsating motion, said piston being connected with the valve control fluid intake.

12. A mechanism according to Claim 9 or 10 wherein said modulating means include a piston mounted in a cylinder and subjected to a periodic movement; said cylinder being connected to the fluid supply to said valve.

13. A mechanism according to Claim 10, further comprising a pressure modulator including mechanical means for inducing oscillations of the force balance beam.

14. A mechanism according to Claim 13, charac-terized in that the means for inducing vibrations com-prises an impeller acting in the evolutive pulp filled container.

15. A mechanism according to Claim 10, wherein said balance beam includes an arm opposite to an arm supporting said mixer, said balance beam arm being equi-librated by means of a spring and of an adjustable cali-bration counterweight.

16. A mechanism according to Claim 14, wherein said impeller and the driving means therefore are mounted to the mixer.

17. A mechanism according to Claim 7, wherein the elastic sleeve of said valve is made of a rubber material having characteristics such that a piece 10cm long and 2 cm wide is stretched by 5 cm when held at the top and a weight of 1.2kg is applied to the bottom thereof.

18. A mechanism according to Claim 7, wherein said sleeve has, at rest, a length of 140 mm, a thickness of 0.8 mm and a half-perimeter of 46 mm; said sleeve being mounted by being stretched 15 mm in length in a rigid housing 82 mm long and 33.5 mm in outer diameter, the exceeding length of the sleeve being rolled back onto the outer wall of the housing and clamped thereto.