METHOD AND APPARATUS FOR MEASURING THE BULK DENSITY OF A MATERIAL UNDER PRESSURE
United States Patent 3788125
The bulk density of a body of tobacco or similar material maintained under pressure is determined by loading a body of the material of known weight into a flexible bag having an open end, sealing the open end of the bag to the walls of a container of a known volume, expanding the bag into engagement with the walls of the container to reduce the volume of the space between the bag and the container to substantially zero and then introducing a fluid into the space between the bag and the container at a controlled and known rate of flow for a time sufficient to compress the body of material under a known measured pressure. The time that it takes to reach the known pressure, multiplied times the flow rate of the fluid, yields the volume of the space between the container and the compressed body of material. The volume of that space is subtracted from the known volume of the container and divided by the known weight of the compressed material to yield the bulk density of the material. An automatic control system and monitoring and computer devices are employed to control the sequence of the method and to produce a final result as a digital print-out or readout.
US Patent References:
Apparatus for measuring volumes of solid materials
Shea - February 1954 - 2667782
Apparatus and method for measuring the volume and density of solid material
Smith et al. - October 1962 - 3060724
Porosity data apparatus
Boland et al. - March 1967 - 3309912
Specimen mounting device for porosity determination apparatus
Orr et al. - October 1967 - 3348395
Apparatus for measuring volumes of solid materials
Shea - February 1954 - 2667782
Apparatus and method for measuring the volume and density of solid material
Smith et al. - October 1962 - 3060724
Porosity data apparatus
Boland et al. - March 1967 - 3309912
Specimen mounting device for porosity determination apparatus
Orr et al. - October 1967 - 3348395
Inventors:
Kirschstein, Werner P. (Greensboro, NC)
Wagner, John R. (Greensboro, NC)
Wagner, John R. (Greensboro, NC)
Application Number:
05/221689
Publication Date:
01/29/1974
Filing Date:
01/28/1972
View Patent Images:
Export Citation:
Assignee:
Loew's Theatres, Inc. (New York, NY)
Primary Class:
Other Classes:
131/904
International Classes:
G01N9/02; G01N9/00; G01N9/32
Field of Search:
73/32,433,37,434,38,94 131/21R,21A,22R
Primary Examiner:
Queisser, Richard C.
Assistant Examiner:
Kreitman, Stephen A.
Attorney, Agent or Firm:
Granville, Brumbaugh Et Al M.
Claims:
We claim
1. Apparatus for measuring the bulk density of a body of tobacco or similar material while under pressure comprising a container of known volume having a removable cover arranged to close the container and hold a fluid under pressure, a flexible and substantially fluid-impermeable bag contoured generally to match the internal surface of the container and having an open end, the bag being received within the container and having its open end connected to the container in sealing relationship to define within the bag a receptacle for the material and to define between the outside of the bag and the internal walls of the container a space having a volume varying from substantially zero to a value equal to the volume of the container minus the volume of the material, means for introducing a fluid under pressure into the bag to expand it into engagement with the internal surface of the container and reduce the volume of the space between the bag and the inside of the container to substantially zero, means for introducing a fluid under pressure into said space at a controlled and known rate of flow, and means for monitoring the time required to increase the volume of said space to dimensions established by the attainment of a given pressure within the space.
2. Apparatus according to claim 1 wherein the means for introducing fluid under pressure at a known rate of flow comprises a constant pressure source of fluid and a metering orifice.
3. Apparatus according to claim 1 wherein the internal surface of the container is defined by the internal face of a porous liner in the container.
4. Apparatus according to claim 1 and further comprising means for monitoring and converting into a usable signal the weight (W) of the material, means for monitoring and converting into a usable signal the time (T) required to attain a given pressure within the space between the flexible bag and the internal surface of the container, and computer means for receiving said signals, computing them with the known volume (V) of the container and the known rate of flow (Q) of the fluid under pressure according to the formula
5. Apparatus according to claim 4 and further comprising means for monitoring and converting into a usable signal the moisture content of the material and for applying said moisture content signal to the computer means and means wherein the computer applies a correction to the term (B) to provide a standard conditions result.
6. Apparatus according to claim 4 and further comprising means for monitoring and converting into a usable signal the temperature of the material and for applying the temperature signal to the computer means and wherein the computer means applies a correction to the term B to provide a standard conditions result.
7. Apparatus according to claim 4 and further comprising means for monitoring and converting into a usable signal the ambient barometric pressure in the environs of the container and for applying said pressure signal to the computer means and wherein the computer means applies a correction to the term B to provide a standard conditions result.
8. A method for determining the bulk density of tobacco or similar material comprising the steps of placing a sample of known weight (W) in a flexible and substantially fluid-impermeable open-ended bag enclosed in a container of known volume (V) and contoured generally to match the internal walls of the container, sealing the open end of the bag to the container, introducing a fluid under pressure into the bag to expand it into engagement with the internal surface of the container, introducing a fluid under pressure into the space between the bag and the internal surface of the container to equalize the pressures inside and outside the bag, opening the inside of the bag to the atmosphere, and introducing fluid under pressure at a controlled and known rate (Q) into the space mentioned above to raise the pressure in that space to a desired level while measuring the time (T) of said flow and computing the specific volume or inverse of density according to the formula
1. Apparatus for measuring the bulk density of a body of tobacco or similar material while under pressure comprising a container of known volume having a removable cover arranged to close the container and hold a fluid under pressure, a flexible and substantially fluid-impermeable bag contoured generally to match the internal surface of the container and having an open end, the bag being received within the container and having its open end connected to the container in sealing relationship to define within the bag a receptacle for the material and to define between the outside of the bag and the internal walls of the container a space having a volume varying from substantially zero to a value equal to the volume of the container minus the volume of the material, means for introducing a fluid under pressure into the bag to expand it into engagement with the internal surface of the container and reduce the volume of the space between the bag and the inside of the container to substantially zero, means for introducing a fluid under pressure into said space at a controlled and known rate of flow, and means for monitoring the time required to increase the volume of said space to dimensions established by the attainment of a given pressure within the space.
2. Apparatus according to claim 1 wherein the means for introducing fluid under pressure at a known rate of flow comprises a constant pressure source of fluid and a metering orifice.
3. Apparatus according to claim 1 wherein the internal surface of the container is defined by the internal face of a porous liner in the container.
4. Apparatus according to claim 1 and further comprising means for monitoring and converting into a usable signal the weight (W) of the material, means for monitoring and converting into a usable signal the time (T) required to attain a given pressure within the space between the flexible bag and the internal surface of the container, and computer means for receiving said signals, computing them with the known volume (V) of the container and the known rate of flow (Q) of the fluid under pressure according to the formula
5. Apparatus according to claim 4 and further comprising means for monitoring and converting into a usable signal the moisture content of the material and for applying said moisture content signal to the computer means and means wherein the computer applies a correction to the term (B) to provide a standard conditions result.
6. Apparatus according to claim 4 and further comprising means for monitoring and converting into a usable signal the temperature of the material and for applying the temperature signal to the computer means and wherein the computer means applies a correction to the term B to provide a standard conditions result.
7. Apparatus according to claim 4 and further comprising means for monitoring and converting into a usable signal the ambient barometric pressure in the environs of the container and for applying said pressure signal to the computer means and wherein the computer means applies a correction to the term B to provide a standard conditions result.
8. A method for determining the bulk density of tobacco or similar material comprising the steps of placing a sample of known weight (W) in a flexible and substantially fluid-impermeable open-ended bag enclosed in a container of known volume (V) and contoured generally to match the internal walls of the container, sealing the open end of the bag to the container, introducing a fluid under pressure into the bag to expand it into engagement with the internal surface of the container, introducing a fluid under pressure into the space between the bag and the internal surface of the container to equalize the pressures inside and outside the bag, opening the inside of the bag to the atmosphere, and introducing fluid under pressure at a controlled and known rate (Q) into the space mentioned above to raise the pressure in that space to a desired level while measuring the time (T) of said flow and computing the specific volume or inverse of density according to the formula
Description:
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for measuring the bulk density of a body of tobacco or similar material while the material is maintained under pressure.
In the tobacco industry, and for that matter in many other industries, it is frequently very important to measure the bulk density of a raw material that is maintained under pressure in a product. Prior knowledge of the volume occupied by the material enables optimum utilization of the material and provides an important factor in the quality control of the final product.
Using the manufacture of cigarettes as an example, by far the most significant factor in the cost of producing cigarettes is the cost of the tobacco. The tobacco in a cigarette is wrapped under pressure within the paper cigarette wrapper, and the amount of tobacco in the cigarette determines not only the major factor in the cost of the cigarette, but also the pressure drop, burning characteristics and other physical properties of the cigarette. Consequently, the tobacco-making machinery is closely controlled as to the amount of tobacco that goes into the cigarettes. Inasmuch as the bulk density of cut tobacco can vary considerably, depending upon the tobacco blend, the growing conditions of a particular lot of tobacco, the processing conditions and other factors, it is highly desirable to sample on a continuous basis the lots of tobacco that go into the cigarettes being produced.
A common way of determining the bulk density of a material under pressure is to load a known weight of material into a open-ended, cylindrical container of known volume, and then compress the material with a piston to apply a predetermined pressure. The position occupied by the piston in the container at the predetermined pressure is indicative of the final volume occupied by the material while under pressure. That volume, divided into the weight, yields a value for bulk density. However, the result of a relatively crude test of this sort is subject to considerable variation from sample to sample by reason of the degree to which pressure applied by the piston is distributed through the body of material, something which can vary appreciably from one sample to another. Moreover, the pressure applied is essentially linear in the axial direction of the test container, and in many instances does not simulate particularly well the pressure conditions on the material in the final product. For example, in a cigarette, the pressure applied by the wrapper on the body of tobacco is in substantially the radial direction with respect to the axis of the cigarette. A test based on a piston and cylindrical container form of apparatus represents basically a linear pressure. Inasmuch as a body of bulk material, such as tobacco, only partially resembles a true fluid in which any pressure applied is distributed equally in all directions, the result of a bulk density test involving an essentially linear pressure may, in many instances, yield a result that is not sufficiently precise to enable optimum control over the production.
SUMMARY OF THE INVENTION
There is provided, in accordance with the invention, a novel and improved apparatus, and a method, for determining the bulk density of a body of tobacco or similar material that is maintained under pressure. The apparatus and method of the invention involve a test sample to which a pressure is applied in a generally radial direction, thus providing close simulation of the pressure conditions that obtain in the final product, such as a cigarette. The apparatus is convenient to use, can be produced at relatively low cost and provides results that are highly reliable inasmuch as the test procedure is uniform for all samples and involves elimination of, or compensation for substantially all variables that might affect the result.
More particularly, the apparatus, in accordance with the invention, comprises a container of known volume having a removable cover and capable of holding a fluid under pressure. A flexible and substantially fluid impermeable bag contoured generally to match the internal surface of the container and having an open end is fitted within the container and its open end connected to the container walls in sealing relation to define within the bag a receptacle for the material and to define between the outside of the bag and the walls of the container a space having a volume varying from substantially zero to a value equal to the volume of the container minus the volume of the material in the bag.
Fluid under pressure is introduced into the interior of the bag to expand it into engagement with the internal surface of the container, and reduce the volume of the space between the outside of the bag and the inside of the container to substantially zero. A fluid under pressure is then introduced into the space between the bag and the container at a controlled and known rate of flow, and the time required to increase the volume of the space to dimensions established by the attainment of a pressure within the space and acting on the body of material is monitored. Inasmuch as the rate at which the fluid is introduced into the space between the container and the bag is known, the time required to attain a given pressure, when multiplied be the known flow rate of the fluid into the space, yields the volume in the container occupied by the fluid. The volume occupied by the fluid, subtracted from the known volume of the container, equals the volume of the compressed material in the bag. The volume occupied by the material under pressure is divided into the weight of the material to yield the bulk density of the material. The inverse of the bulk density is the specific volume and is indicative of the filling capacity of the test material when that material is under a given pressure.
In a preferred embodiment of the apparatus of the invention, an automated pressure supply and control system is provided to carry out the steps of the process of the invention in the appropriate sequence. It is also advantageous to provide a monitoring and computer system that includes components for monitoring the weight of the material and the time required to obtain a given pressure and computing the weight and time with the known volume and known rate of flow to produce a signal indicative of the specific volume of the material. That signal can be corrected by additional monitoring systems, such as a system for measuring the moisture content of the material, the environmental temperature and the environmental barometric pressure. The computer applies these variable factors to adjust the result and provide a standard conditions output. The output of the computer can be converted into a digital printout, a digital readout or any other desired form of output. Indeed, the method and apparatus of the invention may be used as an on-line part of the cigarette-making machine in which a sample of a tobacco lot that is about to be delivered to the machine is tested and the signal produced by the monitoring and computer system is applied directly to the control equipment of the cigarette-making machine to adjust the machine to produce a cigarette in accordance with the specific volume measured by the apparatus.
DESCRIPTION OF THE DRAWING
For a better understanding of the invention, reference may be made to the following description of an exemplary embodiment, taken in conjunction with the accompanying drawing, which is a generally schematic diagram of the embodiment.
DESCRIPTION OF AN EXEMPLARY EMBODIMENT
Referring to the drawing, the reference numeral 10 designates generally a container of known volume that constitutes the test vessel for the sample of material. As mentioned above, the apparatus and method of invention may be used for various bulk materials. For purposes of description, cut tobacco ready for manufacture into cigarettes is given as an example.
The vessel 10 comprises a cylindrical outer wall 12, a bottom 14 secured to the lower end of the cylindrical outer wall 12 and a removable top cover 16. The bottom 14 is fitted with a tubing connector 18 that communicates with a passage 20 leading into a cavity 22 defined between the bottom 14 and a screen or perforated plate 24. The plate 24 constitutes one electrode of a capacitance-type moisture sensor (to be described hereinafter). The top cover 16 of the vessel is also fitted with a tubing coupling 26 that communicates with a generally radial passage 28 and with an internal recess 30 formed on the interior of the cover and occupying substantially the total interior area of the cover. A screen or perforated plate 32 is mounted in the recess 30 a short distance from its base, and the cover also is provided with an appropriate form of seal 34 around its perimeter for engagement with the main body of the vessel 10.
The body of the vessel receives a liner 36 that is shaped and dimensioned closely to match the interior of the vessel, but with its outer surface spaced a short distance from the inner surface of the vessel. The liner 36 is constructed of a porous material that permits a fluid introduced into the bottom of the vessel through the coupling 18 to pass reasonably freely into the interior of the liner 36. Similarly, the porous material and the spacing of the liner from the wall of the vessel allows fluids within the liner 36 to pass outwardly and through the spaces and out through the coupling 18. The screen or perforated plate 32 in the top of the vessel permits fluid to be communicated into and out of the vessel by passing through the screen or plate and into or out of the recess 30 and the passage 28.
The sample of tobacco to be tested is loaded into a flexible bag 38 of impermeable material, such as a suitable flexible plastic film, which is open at its upper end and is shaped and dimensioned to conform substantially to the inner surface of the liner 36. The open end of the bag is sealed to the wall of the container by wrapping its open upper end 40 around a peripheral top flange 42 on the liner. The flange 42 and the upper edge of the bag that is wrapped around it fit in between the upper edge of the outer container wall 12 and the seal structure 34 of the cap or cover 16 of the vessel.
The volume of the vessel defined by the interior surface of the liner 36, the inner surface of the seal structure 34 and the surface of the plate 32 are known precisely. For convenience, this volume is designated hereinafter by the letter V. The weight of the body of tobacco loaded into the flexible bag 38 may, of course, be determined simply by weighing it on balance scales or, as described hereinafter, by weight monitoring equipment associated with the apparatus. The weight of the tobacco is designated by the letter W.
The apparatus includes a supply system that can be controlled to introduce a gas under pressure into the interior of the bag through the coupling 26. Inasmuch as the cover is sealed to the bag and the bag is sealed to the walls of the vessel, the interior of the bag constitutes a sealed compartment or chamber within the vessel that contains the body of tobacco. By forcing the bag outwardly with a gas under pressure into engagement with the inner wall of the liner 36, it is evident that the body of tobacco of a weight W occupies an initial volume V, that volume being known and being a constant in the test apparatus and method.
The volume that the body of tobacco material occupies under a given pressure may be determined by introducing a fluid, either a liquid or a gas under pressure, into the space defined between the outside of the bag 38 and the inside of the vessel body 12. For purposes of illustration an air system is depicted in the drawing and described herein.
More particularly, the equipment is used in conjunction with an appropriate source 44 of air under a pressure substantially above atmospheric pressure, say, 50 psig. The source 44 of air under pressure is connected by a main conduit 46 through a main shut-off valve 48 to a branch conduit, one branch 50 of which is connected to the coupling 26 in the top of the vessel and the other branch 52 to the coupling 18 in the bottom of the vessel. A valve 54 in the branch 50 permits the source of air under pressure to be connected selectively to the interior of the bag, and a valve 56 in the branch 52 permits the air under pressure to be connected selectively to the space between the exterior of the bag 38 and the interior of the vessel 10. Further details of the construction of the apparatus will be evident from a consideration of an operating cycle which follows immediately below. Inasmuch as the apparatus may be used without an automated system, which is present in the apparatus illustrated in the drawing, the following description of the procedure will assume a manual operation of the apparatus. A test sequence begins with a known weight W of the material loaded loosely into the interior of the bag 38. The cover is placed on the vessel 10 and held in sealed position on the vessel body by an appropriate device (not shown). When the bag is initially inserted into the vessel, it will be wrinkled and randomly spaced from the inner wall of the porous liner 36.
The valve 54 is open to admit air under pressure from the source 44 into the interior of the bag to force the bag out into engagement with the inner wall of the porous liner 36, so that the known weight of the body of tobacco within the bag occupies the volume V. At this stage an exhaust valve 58 connected to the coupling 26 is closed, the valve 56 in the conduit 52 is closed. An exhaust valve 60 connected to the conduit 52 and therefore to the coupling 18 is open. Accordingly, air under pressure from the source enters the bag and urges it out into engagement with the liner 36. Only a light pressure, say, something less than 0.5 psig is required firmly to engage the bag with the liner wall. The air that previously occupied the space between the bag and the liner freely passes out through the porous liner, along the passage afforded by the space between the outer wall of the liner and the inner wall of the vessel and out through the coupling 18 for exhaust through the valve 60. As soon as the desired pressure within the bag is reached, the valve 54 is closed to terminate the delivery of air into the bag.
At this point, it is desirable to establish a balance of pressure across the wall of the bag by opening the valve 56 to admit air under pressure into the space between the outer wall of the container and the inner wall of the porous liner and closing exhaust valve 60. As soon as the pressure in that space is equalized with the pressure within the bag, the exhaust valve 58 is opened so that air within the bag may be exhausted as the bag and the body of tobacco within the bag are compressed.
The conduit 52 from the source 44 of air to the space outside the bag includes a precision pressure controller 62 that may be set to deliver through the portion of the conduit 52 downstream of it air at a precisely controlled pressure, as measured by a gauge 64. Downstream from the pressure regulator is a precision flow rate orifice 66 that provides constant delivery of air through the conduit 52. If the delivery pressure is substantially above the ultimate pressure to be applied to the body of material within the container, the variation in flow rate through the orifice 66 as pressure builds up within the container is negligible. Accordingly, the volume of air introduced into the space between the bag and the inner wall of the vessel, which is referred to hereinafter by the letter S (for space), is determined by multiplying the known flow rate (volume of air/unit of time) times the time required to achieve a predetermined volume in the space S.
After a balanced condition has been reached between the interior of the bag and the space S, which at that point will be of substantially zero volume, the time during which air is introduced into the container space S is monitored and recorded. As soon as the desired pressure obtains within the space S, the valve 56 is closed, and the valve 60 may be opened to exhaust the pressure in the space S to the atmosphere. The specific volume of the body of tobacco within the bag is determined by multiplying the known flow rate through the flow rate orifice (a constant) times the time during which air was delivered through the metering orifice 66 to obtain the volume of the space S, subtracting it from the initial known volume V of the space within the vessel, thus obtaining the net volume occupied by the tobacco under the controlled pressure, and then dividing the net volume by the weight W.
As mentioned above, the measurements and calculations may be carried out manually. Inasmuch as the equipment is intended for continuous sampling of tobacco and accordingly will involve frequent repetition of the testing procedure, it is desirable to automate the test procedure and to provide a monitoring and computing system for providing a final, corrected, direct readout of a specific volume or another value representative of the filling capacity of the tobacco. The embodiment illustrated in the drawing and described hereinafter includes an automated system for carrying out the test sequence and monitoring and computer equipment for providing a direct readout of the results.
In particular, a pressure transducer 68 is connected to the conduit 50 and is set to produce a control signal for closing the valve 54 upon reaching the preset pressure appropriate to engage the bag 38 with the interior wall of the vessel liner 36. The system depicted in the drawings is illustrated generally schematically, and particular devices will be readily apparent to those skilled in the art. For example the control system may involve pneumatic or electrical signalling for operating pneumatic pilot valves that operate the main valves of the system or operate electrical solenoid valves. The control interconnections between the various elements are indicated by single solid lines in the drawings.
As soon as the pressure transducer 68 detects a desired pressure in the container within the bag 38, it supplies a control signal through line 70 to the valve 54 to shut the valve and a control signal through a line 72 to open the valve 56 and close the valve 60. At this point, air will begin to flow into the space S through the conduit 52. A pressure monitor 74 coupled to the conduit 52 monitors the pressure in the space S on a continuous basis. The pressure monitor 74 supplies a signal through line 76 to an analog computer 77. Other components of the pressure monitor 74 produce a control signal that is conducted through a line 78 to a timer 80 and starts the timer as soon as the pressure in the space S is substantially equal to the pressure within the bag 38. This signal is also supplied through a line 82 to the exhaust valve 58 to open the exhaust valve 58 and communicate the inside of the bag with the atmosphere. From this point, air is delivered at a known rate into the space S, and the timer 80 measures the time during which air flows through the conduit 52.
As soon as the pressure in the space S reaches the predetermined value under which a measurement is to be determined, the pressure monitor 74 responds by producing a signal that is conducted through a line 84 to a secondary timer 86. Tobacco, like many compacted bulk materials of a generally flexible nature, exhibits a property of creep. The secondary timer is provided to maintain a holding period at which a pressure of the predetermined value for the test is maintained so that as the body of tobacco is compacted further, additional quantities of air are supplied. Accordingly, the pressure monitor produces a signal indicative of the attainment of the desired pressure in the space S. That signal is conducted through a line 87 to the valve 56 and closes the valve and holds it closed until the pressure drops slightly below the desired pressure in the space. A typical value for the pressure in a tobacco test is 2.0 psig, a pressure that is close to the pressure of a rod of tobacco as wrapped in a cigarette. A signal indicative of the attainment of a 2.0 psig pressure is also conducted through the control line 78 of the main timer and shuts off the timer whenever the valve 56 is closed, so that only the time during which air is flowing through the conduit 52 into the space S is counted. The pressure monitor 74 will cycle the valve 56 on and off throughout the holding periods set into the timer 86. At the end of the holding time, the timer 86 produces a signal that is conducted through a line 88 to a digital printer 90 that prints out the final result of the test, as will be described in more detail below. A signal from the hold period timer 86 is also conducted through a line 92 and branches 94 and 96 to the valve 56 to close the valve 56 and to the exhaust valve 60 to exhaust the air pressure from the space S in the test vessel. A short delay time is built into the hold period timer 86 so that the printout, the opening of the valve 56 and the opening of the exhaust valve 60 occur in sequence, rather than simultaneously.
An appropriate master control system (not shown) is provided to reset the system for another test and to initiate the sequence of the automated control system described above.
The embodiment illustrated in the drawings also includes a monitoring and computer system that involves the generation of electrical signals indicative of the various factors involved in the final computation of bulk density under the test conditions. The principal unit of the monitoring and computer system is the analog computer 77. The details of the various components of this system, including the computer, are well within the state of the art and need not be described other than generally or illustrated other than schematically. As mentioned above, the pressure monitor 74 conducts a signal through the line 76 to the analog computer 77 indicative of the pressure in the space S. A unit 98 generates signals indicative of the air flow rate, which is a constant and is established by the metering orifice 66, and the volume of the container V, also a constant, and conducts them through a cable 99 to the analog computer. A weight monitor 100 produces a signal indicative of the net weight of the tobacco material in the test vessel and a line 101 conducts it to the computer. The timer 80 conducts a signal indicative of the total time during which air is delivered to the space S at the constant rate to the computer 77 through a line 102.
The information fed to the computer from the timer, the pressure monitor, weight monitor and the unit 98 are sufficient to provide a computer output of bulk density in accordance with the equation given above. However, it is advantageous to provide corrections to produce a standard conditions result. Accordingly, a moisture sensor 103 is connected by conductors 104 and 105 to the plate electrode 24 in the bottom of the vessel and a ring form of electrode 106 spaced somewhat above the bottom of the vessel and mounted on the exterior wall of the vessel. The moisture sensor is of a capacitance type and determines the moisture content of the tobacco by detecting the voltage drop between the capacitor plates 106 and 24 which is a function of the moisture content of the tobacco. The moisture sensor is connected by line 108 to a moisture compensator unit 110 that converts the signal from the moisture sensor into a correction value that is delivered through a line 112 to the computer. The correction value is applied in the computer to the computed value of bulk density to provide a standard conditions result. Additional corrections are made in the computed result by supplying information to the computer indicative of the environmental temperature and environmental barometric pressure, both of which affect the result under particular conditions where the test is being conducted. A temperature monitor 114 delivers a correction signal to the computer through a line 116 and a barometric pressure sensor 118 delivers a signal through a line 120 to the computer. As is the case with the moisture compensation signal, the computer applies the correction signals to the computed result of bulk density and produces a standard conditions output.
The computer output is fed to a digital printer 90 through a line 122 and to a digital readout device 124 through a branch line 126. The printer and digital readout are under the control of the timer 86. As soon as the holding time during which the predetermined pressure is maintained in the space S of the vessel has run out, the timer 86 conducts a signal to the printer through a line 88 that causes the test result from the computer to be printed out on a card or data sheet. The card or data sheet may also receive information from a clock 130 through a line 132 so that the card or sheet will record the date and time of the test. Additional information may be printed out, such as sample number, lot number or other identifying information concerning the tobacco material and so forth. The computed information can, as mentioned above, be used in other ways, such as automated control of the production equipment.
The above-described embodiment of the invention is intended to be merely exemplary, and numerous variations and modifications of it may be made by those skilled in the art without departing from the sphere and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as defined in the appended claims.
The present invention relates to a method and an apparatus for measuring the bulk density of a body of tobacco or similar material while the material is maintained under pressure.
In the tobacco industry, and for that matter in many other industries, it is frequently very important to measure the bulk density of a raw material that is maintained under pressure in a product. Prior knowledge of the volume occupied by the material enables optimum utilization of the material and provides an important factor in the quality control of the final product.
Using the manufacture of cigarettes as an example, by far the most significant factor in the cost of producing cigarettes is the cost of the tobacco. The tobacco in a cigarette is wrapped under pressure within the paper cigarette wrapper, and the amount of tobacco in the cigarette determines not only the major factor in the cost of the cigarette, but also the pressure drop, burning characteristics and other physical properties of the cigarette. Consequently, the tobacco-making machinery is closely controlled as to the amount of tobacco that goes into the cigarettes. Inasmuch as the bulk density of cut tobacco can vary considerably, depending upon the tobacco blend, the growing conditions of a particular lot of tobacco, the processing conditions and other factors, it is highly desirable to sample on a continuous basis the lots of tobacco that go into the cigarettes being produced.
A common way of determining the bulk density of a material under pressure is to load a known weight of material into a open-ended, cylindrical container of known volume, and then compress the material with a piston to apply a predetermined pressure. The position occupied by the piston in the container at the predetermined pressure is indicative of the final volume occupied by the material while under pressure. That volume, divided into the weight, yields a value for bulk density. However, the result of a relatively crude test of this sort is subject to considerable variation from sample to sample by reason of the degree to which pressure applied by the piston is distributed through the body of material, something which can vary appreciably from one sample to another. Moreover, the pressure applied is essentially linear in the axial direction of the test container, and in many instances does not simulate particularly well the pressure conditions on the material in the final product. For example, in a cigarette, the pressure applied by the wrapper on the body of tobacco is in substantially the radial direction with respect to the axis of the cigarette. A test based on a piston and cylindrical container form of apparatus represents basically a linear pressure. Inasmuch as a body of bulk material, such as tobacco, only partially resembles a true fluid in which any pressure applied is distributed equally in all directions, the result of a bulk density test involving an essentially linear pressure may, in many instances, yield a result that is not sufficiently precise to enable optimum control over the production.
SUMMARY OF THE INVENTION
There is provided, in accordance with the invention, a novel and improved apparatus, and a method, for determining the bulk density of a body of tobacco or similar material that is maintained under pressure. The apparatus and method of the invention involve a test sample to which a pressure is applied in a generally radial direction, thus providing close simulation of the pressure conditions that obtain in the final product, such as a cigarette. The apparatus is convenient to use, can be produced at relatively low cost and provides results that are highly reliable inasmuch as the test procedure is uniform for all samples and involves elimination of, or compensation for substantially all variables that might affect the result.
More particularly, the apparatus, in accordance with the invention, comprises a container of known volume having a removable cover and capable of holding a fluid under pressure. A flexible and substantially fluid impermeable bag contoured generally to match the internal surface of the container and having an open end is fitted within the container and its open end connected to the container walls in sealing relation to define within the bag a receptacle for the material and to define between the outside of the bag and the walls of the container a space having a volume varying from substantially zero to a value equal to the volume of the container minus the volume of the material in the bag.
Fluid under pressure is introduced into the interior of the bag to expand it into engagement with the internal surface of the container, and reduce the volume of the space between the outside of the bag and the inside of the container to substantially zero. A fluid under pressure is then introduced into the space between the bag and the container at a controlled and known rate of flow, and the time required to increase the volume of the space to dimensions established by the attainment of a pressure within the space and acting on the body of material is monitored. Inasmuch as the rate at which the fluid is introduced into the space between the container and the bag is known, the time required to attain a given pressure, when multiplied be the known flow rate of the fluid into the space, yields the volume in the container occupied by the fluid. The volume occupied by the fluid, subtracted from the known volume of the container, equals the volume of the compressed material in the bag. The volume occupied by the material under pressure is divided into the weight of the material to yield the bulk density of the material. The inverse of the bulk density is the specific volume and is indicative of the filling capacity of the test material when that material is under a given pressure.
In a preferred embodiment of the apparatus of the invention, an automated pressure supply and control system is provided to carry out the steps of the process of the invention in the appropriate sequence. It is also advantageous to provide a monitoring and computer system that includes components for monitoring the weight of the material and the time required to obtain a given pressure and computing the weight and time with the known volume and known rate of flow to produce a signal indicative of the specific volume of the material. That signal can be corrected by additional monitoring systems, such as a system for measuring the moisture content of the material, the environmental temperature and the environmental barometric pressure. The computer applies these variable factors to adjust the result and provide a standard conditions output. The output of the computer can be converted into a digital printout, a digital readout or any other desired form of output. Indeed, the method and apparatus of the invention may be used as an on-line part of the cigarette-making machine in which a sample of a tobacco lot that is about to be delivered to the machine is tested and the signal produced by the monitoring and computer system is applied directly to the control equipment of the cigarette-making machine to adjust the machine to produce a cigarette in accordance with the specific volume measured by the apparatus.
DESCRIPTION OF THE DRAWING
For a better understanding of the invention, reference may be made to the following description of an exemplary embodiment, taken in conjunction with the accompanying drawing, which is a generally schematic diagram of the embodiment.
DESCRIPTION OF AN EXEMPLARY EMBODIMENT
Referring to the drawing, the reference numeral 10 designates generally a container of known volume that constitutes the test vessel for the sample of material. As mentioned above, the apparatus and method of invention may be used for various bulk materials. For purposes of description, cut tobacco ready for manufacture into cigarettes is given as an example.
The vessel 10 comprises a cylindrical outer wall 12, a bottom 14 secured to the lower end of the cylindrical outer wall 12 and a removable top cover 16. The bottom 14 is fitted with a tubing connector 18 that communicates with a passage 20 leading into a cavity 22 defined between the bottom 14 and a screen or perforated plate 24. The plate 24 constitutes one electrode of a capacitance-type moisture sensor (to be described hereinafter). The top cover 16 of the vessel is also fitted with a tubing coupling 26 that communicates with a generally radial passage 28 and with an internal recess 30 formed on the interior of the cover and occupying substantially the total interior area of the cover. A screen or perforated plate 32 is mounted in the recess 30 a short distance from its base, and the cover also is provided with an appropriate form of seal 34 around its perimeter for engagement with the main body of the vessel 10.
The body of the vessel receives a liner 36 that is shaped and dimensioned closely to match the interior of the vessel, but with its outer surface spaced a short distance from the inner surface of the vessel. The liner 36 is constructed of a porous material that permits a fluid introduced into the bottom of the vessel through the coupling 18 to pass reasonably freely into the interior of the liner 36. Similarly, the porous material and the spacing of the liner from the wall of the vessel allows fluids within the liner 36 to pass outwardly and through the spaces and out through the coupling 18. The screen or perforated plate 32 in the top of the vessel permits fluid to be communicated into and out of the vessel by passing through the screen or plate and into or out of the recess 30 and the passage 28.
The sample of tobacco to be tested is loaded into a flexible bag 38 of impermeable material, such as a suitable flexible plastic film, which is open at its upper end and is shaped and dimensioned to conform substantially to the inner surface of the liner 36. The open end of the bag is sealed to the wall of the container by wrapping its open upper end 40 around a peripheral top flange 42 on the liner. The flange 42 and the upper edge of the bag that is wrapped around it fit in between the upper edge of the outer container wall 12 and the seal structure 34 of the cap or cover 16 of the vessel.
The volume of the vessel defined by the interior surface of the liner 36, the inner surface of the seal structure 34 and the surface of the plate 32 are known precisely. For convenience, this volume is designated hereinafter by the letter V. The weight of the body of tobacco loaded into the flexible bag 38 may, of course, be determined simply by weighing it on balance scales or, as described hereinafter, by weight monitoring equipment associated with the apparatus. The weight of the tobacco is designated by the letter W.
The apparatus includes a supply system that can be controlled to introduce a gas under pressure into the interior of the bag through the coupling 26. Inasmuch as the cover is sealed to the bag and the bag is sealed to the walls of the vessel, the interior of the bag constitutes a sealed compartment or chamber within the vessel that contains the body of tobacco. By forcing the bag outwardly with a gas under pressure into engagement with the inner wall of the liner 36, it is evident that the body of tobacco of a weight W occupies an initial volume V, that volume being known and being a constant in the test apparatus and method.
The volume that the body of tobacco material occupies under a given pressure may be determined by introducing a fluid, either a liquid or a gas under pressure, into the space defined between the outside of the bag 38 and the inside of the vessel body 12. For purposes of illustration an air system is depicted in the drawing and described herein.
More particularly, the equipment is used in conjunction with an appropriate source 44 of air under a pressure substantially above atmospheric pressure, say, 50 psig. The source 44 of air under pressure is connected by a main conduit 46 through a main shut-off valve 48 to a branch conduit, one branch 50 of which is connected to the coupling 26 in the top of the vessel and the other branch 52 to the coupling 18 in the bottom of the vessel. A valve 54 in the branch 50 permits the source of air under pressure to be connected selectively to the interior of the bag, and a valve 56 in the branch 52 permits the air under pressure to be connected selectively to the space between the exterior of the bag 38 and the interior of the vessel 10. Further details of the construction of the apparatus will be evident from a consideration of an operating cycle which follows immediately below. Inasmuch as the apparatus may be used without an automated system, which is present in the apparatus illustrated in the drawing, the following description of the procedure will assume a manual operation of the apparatus. A test sequence begins with a known weight W of the material loaded loosely into the interior of the bag 38. The cover is placed on the vessel 10 and held in sealed position on the vessel body by an appropriate device (not shown). When the bag is initially inserted into the vessel, it will be wrinkled and randomly spaced from the inner wall of the porous liner 36.
The valve 54 is open to admit air under pressure from the source 44 into the interior of the bag to force the bag out into engagement with the inner wall of the porous liner 36, so that the known weight of the body of tobacco within the bag occupies the volume V. At this stage an exhaust valve 58 connected to the coupling 26 is closed, the valve 56 in the conduit 52 is closed. An exhaust valve 60 connected to the conduit 52 and therefore to the coupling 18 is open. Accordingly, air under pressure from the source enters the bag and urges it out into engagement with the liner 36. Only a light pressure, say, something less than 0.5 psig is required firmly to engage the bag with the liner wall. The air that previously occupied the space between the bag and the liner freely passes out through the porous liner, along the passage afforded by the space between the outer wall of the liner and the inner wall of the vessel and out through the coupling 18 for exhaust through the valve 60. As soon as the desired pressure within the bag is reached, the valve 54 is closed to terminate the delivery of air into the bag.
At this point, it is desirable to establish a balance of pressure across the wall of the bag by opening the valve 56 to admit air under pressure into the space between the outer wall of the container and the inner wall of the porous liner and closing exhaust valve 60. As soon as the pressure in that space is equalized with the pressure within the bag, the exhaust valve 58 is opened so that air within the bag may be exhausted as the bag and the body of tobacco within the bag are compressed.
The conduit 52 from the source 44 of air to the space outside the bag includes a precision pressure controller 62 that may be set to deliver through the portion of the conduit 52 downstream of it air at a precisely controlled pressure, as measured by a gauge 64. Downstream from the pressure regulator is a precision flow rate orifice 66 that provides constant delivery of air through the conduit 52. If the delivery pressure is substantially above the ultimate pressure to be applied to the body of material within the container, the variation in flow rate through the orifice 66 as pressure builds up within the container is negligible. Accordingly, the volume of air introduced into the space between the bag and the inner wall of the vessel, which is referred to hereinafter by the letter S (for space), is determined by multiplying the known flow rate (volume of air/unit of time) times the time required to achieve a predetermined volume in the space S.
After a balanced condition has been reached between the interior of the bag and the space S, which at that point will be of substantially zero volume, the time during which air is introduced into the container space S is monitored and recorded. As soon as the desired pressure obtains within the space S, the valve 56 is closed, and the valve 60 may be opened to exhaust the pressure in the space S to the atmosphere. The specific volume of the body of tobacco within the bag is determined by multiplying the known flow rate through the flow rate orifice (a constant) times the time during which air was delivered through the metering orifice 66 to obtain the volume of the space S, subtracting it from the initial known volume V of the space within the vessel, thus obtaining the net volume occupied by the tobacco under the controlled pressure, and then dividing the net volume by the weight W.
As mentioned above, the measurements and calculations may be carried out manually. Inasmuch as the equipment is intended for continuous sampling of tobacco and accordingly will involve frequent repetition of the testing procedure, it is desirable to automate the test procedure and to provide a monitoring and computing system for providing a final, corrected, direct readout of a specific volume or another value representative of the filling capacity of the tobacco. The embodiment illustrated in the drawing and described hereinafter includes an automated system for carrying out the test sequence and monitoring and computer equipment for providing a direct readout of the results.
In particular, a pressure transducer 68 is connected to the conduit 50 and is set to produce a control signal for closing the valve 54 upon reaching the preset pressure appropriate to engage the bag 38 with the interior wall of the vessel liner 36. The system depicted in the drawings is illustrated generally schematically, and particular devices will be readily apparent to those skilled in the art. For example the control system may involve pneumatic or electrical signalling for operating pneumatic pilot valves that operate the main valves of the system or operate electrical solenoid valves. The control interconnections between the various elements are indicated by single solid lines in the drawings.
As soon as the pressure transducer 68 detects a desired pressure in the container within the bag 38, it supplies a control signal through line 70 to the valve 54 to shut the valve and a control signal through a line 72 to open the valve 56 and close the valve 60. At this point, air will begin to flow into the space S through the conduit 52. A pressure monitor 74 coupled to the conduit 52 monitors the pressure in the space S on a continuous basis. The pressure monitor 74 supplies a signal through line 76 to an analog computer 77. Other components of the pressure monitor 74 produce a control signal that is conducted through a line 78 to a timer 80 and starts the timer as soon as the pressure in the space S is substantially equal to the pressure within the bag 38. This signal is also supplied through a line 82 to the exhaust valve 58 to open the exhaust valve 58 and communicate the inside of the bag with the atmosphere. From this point, air is delivered at a known rate into the space S, and the timer 80 measures the time during which air flows through the conduit 52.
As soon as the pressure in the space S reaches the predetermined value under which a measurement is to be determined, the pressure monitor 74 responds by producing a signal that is conducted through a line 84 to a secondary timer 86. Tobacco, like many compacted bulk materials of a generally flexible nature, exhibits a property of creep. The secondary timer is provided to maintain a holding period at which a pressure of the predetermined value for the test is maintained so that as the body of tobacco is compacted further, additional quantities of air are supplied. Accordingly, the pressure monitor produces a signal indicative of the attainment of the desired pressure in the space S. That signal is conducted through a line 87 to the valve 56 and closes the valve and holds it closed until the pressure drops slightly below the desired pressure in the space. A typical value for the pressure in a tobacco test is 2.0 psig, a pressure that is close to the pressure of a rod of tobacco as wrapped in a cigarette. A signal indicative of the attainment of a 2.0 psig pressure is also conducted through the control line 78 of the main timer and shuts off the timer whenever the valve 56 is closed, so that only the time during which air is flowing through the conduit 52 into the space S is counted. The pressure monitor 74 will cycle the valve 56 on and off throughout the holding periods set into the timer 86. At the end of the holding time, the timer 86 produces a signal that is conducted through a line 88 to a digital printer 90 that prints out the final result of the test, as will be described in more detail below. A signal from the hold period timer 86 is also conducted through a line 92 and branches 94 and 96 to the valve 56 to close the valve 56 and to the exhaust valve 60 to exhaust the air pressure from the space S in the test vessel. A short delay time is built into the hold period timer 86 so that the printout, the opening of the valve 56 and the opening of the exhaust valve 60 occur in sequence, rather than simultaneously.
An appropriate master control system (not shown) is provided to reset the system for another test and to initiate the sequence of the automated control system described above.
The embodiment illustrated in the drawings also includes a monitoring and computer system that involves the generation of electrical signals indicative of the various factors involved in the final computation of bulk density under the test conditions. The principal unit of the monitoring and computer system is the analog computer 77. The details of the various components of this system, including the computer, are well within the state of the art and need not be described other than generally or illustrated other than schematically. As mentioned above, the pressure monitor 74 conducts a signal through the line 76 to the analog computer 77 indicative of the pressure in the space S. A unit 98 generates signals indicative of the air flow rate, which is a constant and is established by the metering orifice 66, and the volume of the container V, also a constant, and conducts them through a cable 99 to the analog computer. A weight monitor 100 produces a signal indicative of the net weight of the tobacco material in the test vessel and a line 101 conducts it to the computer. The timer 80 conducts a signal indicative of the total time during which air is delivered to the space S at the constant rate to the computer 77 through a line 102.
The information fed to the computer from the timer, the pressure monitor, weight monitor and the unit 98 are sufficient to provide a computer output of bulk density in accordance with the equation given above. However, it is advantageous to provide corrections to produce a standard conditions result. Accordingly, a moisture sensor 103 is connected by conductors 104 and 105 to the plate electrode 24 in the bottom of the vessel and a ring form of electrode 106 spaced somewhat above the bottom of the vessel and mounted on the exterior wall of the vessel. The moisture sensor is of a capacitance type and determines the moisture content of the tobacco by detecting the voltage drop between the capacitor plates 106 and 24 which is a function of the moisture content of the tobacco. The moisture sensor is connected by line 108 to a moisture compensator unit 110 that converts the signal from the moisture sensor into a correction value that is delivered through a line 112 to the computer. The correction value is applied in the computer to the computed value of bulk density to provide a standard conditions result. Additional corrections are made in the computed result by supplying information to the computer indicative of the environmental temperature and environmental barometric pressure, both of which affect the result under particular conditions where the test is being conducted. A temperature monitor 114 delivers a correction signal to the computer through a line 116 and a barometric pressure sensor 118 delivers a signal through a line 120 to the computer. As is the case with the moisture compensation signal, the computer applies the correction signals to the computed result of bulk density and produces a standard conditions output.
The computer output is fed to a digital printer 90 through a line 122 and to a digital readout device 124 through a branch line 126. The printer and digital readout are under the control of the timer 86. As soon as the holding time during which the predetermined pressure is maintained in the space S of the vessel has run out, the timer 86 conducts a signal to the printer through a line 88 that causes the test result from the computer to be printed out on a card or data sheet. The card or data sheet may also receive information from a clock 130 through a line 132 so that the card or sheet will record the date and time of the test. Additional information may be printed out, such as sample number, lot number or other identifying information concerning the tobacco material and so forth. The computed information can, as mentioned above, be used in other ways, such as automated control of the production equipment.
The above-described embodiment of the invention is intended to be merely exemplary, and numerous variations and modifications of it may be made by those skilled in the art without departing from the sphere and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as defined in the appended claims.