A METHOD FOR CONTROLLING MATERIAL AND MOISTURE CONTENTS

Abstract: The invention relates to a method of controlling the material and/or moisture content of an elongated object (4) which comprises, inter alia, fibrous material, in which a quantity of fibrous material containing a moist binder is compressed (7, 8) and the compressed quantity of fibrous material is dried by passing the material quantity between the electrodes (12, 13) of a drier (5) which is active at high frequencies. An increase or a decrease in the material content of the finished elongated object (4) is achieved by increasing or decreasing the proportion of fibre in respective quantities (via 6, 6a) and the moisture content is increased or decreased, either by decreasing or increasing the power output of the drier (5) and/or shortening or lengthening the stay time of respective quantities in the drier.

Description: TITLE OF THE INVENTION: A method for controlling material and moisture contents TECHNICAL FIELD The present invention relates to a method for controlling the material and/or moisture contents of an elongated object containing, inter alia, fibrous material. More specifically, but not exclusively, the present invention relates to a method of control which will enable the material and/or moisture content of a finished fibrous material and hardened or dried binder mixture to be held constant, where the star¬ ting material comprises a quantity of fibrous material incorporates a moist binder and which has been repeatedly compressed or compacted and the compressed quantities of fibrous material have been passed sequentially between the electrodes of a drier which is active at high frequencies and dries off the energy produced thereby. BACKGROUND PRIOR ART The Swedish Patent Specification published under number 415 547 teaches an arrangement for producing an elongated object or product by compressing a binder-containing fibrous material, such that a proportion of the total amount of fibrous material required for the whole object is supplied to a compression chamber equipped with compressing means, the said compressing means being activated to compress the material quantity and then displace said quantity into a matrix, whereafter the compressing means is withdrawn from the compressing chamber and returned to its original posi¬ tion, so as to enable the chamber to receive a further pro¬ portioned quantity of fibrous material, which is then com¬ pressed and displaced bv the compressing means. The matrix of the arrangement taught by the aforesaid Swedish specification comprises a plurality of wall parts, of which at least one can be moved relative to the object in the direction of the longitudinal extension thereof or in the production direction. The US Patent Specification 4,673,345 teaches a drier which is active at high frequencies and which is utilized as a heating device in an arrangement described in the afore¬ mentioned Swedish patent specification. SUMMARY OF THE PRESENT INVENTION TECHNICAL PROBLEMS When considering the present state of this art, as described in the aforegoing, and also those recommendations and propo¬ sals presented to one of normal skill in this art studying the prior art publications, in combination with his everyday technical expertise, it will be seen that in the case of an arrangement for producing fibrous elongated objects or pro¬ ducts a technical problem resides in providing conditions, in a simple manner which will enable the material and/or moisture content of the finished object to be controlled, while a particularly qualified technical problem resides in the ability to maintain the material and/or moisture content within pre-determined small margin limits. A more qualified problem is one of enabling the material content of the finished object or product to be readily con¬ trolled irrespective, or almost irrespective of the moisture content of said object. Another technical problem is one of providing conditions which will enable the material content and also the moisture content of the finished product to be held constant at vary¬ ing densities of the starting material. When considering the fact that the density of the produced elongated object constitutes a function of the prevailing material contents and also the prevailing moisture content, i.e. one and the same total density for a produced elongated object can be obtained at mutually different material and moisture contents, it will be seen that a pronounced techni¬ cal problem is one of providing, in a simple manner, condi¬ tions which will enable the material and moisture contents of the object to be controlled irrespective of one another and towards pre-determined values. A further qualified technical problem relating to a manufac¬ turing process of the aforesaid kind is one of realizing that the desired control in the case of simply maintaining a constant moisture content can be advantageously realized by solely varying the material content, so as to bring the finished product to a pre-determined density applicable to both a pre-determined material content and a pre-determined moisture content. It will also be seen that a technical problem in the case of the aforedescribed production process is one of creating conditions, in a simple manner, such that the moisture con¬ tent of the elongated object forming the finished product lies within pre-determined limits, and that an increase or decrease in density can therefore be achieved simply by increasing or decreasing the material content, this increase or decrease being advantageously effective by changing the fibre proportion in each measured quantity of material and by determining weight prior to introduction into the com¬ pression chamber. Another technical problem in this regard is one of realizing that the moisture content of the finished product can be increased or decreased not onlv by increasing and decreasing the moisture content of the material quantities but by increasing or decreasing the power output of the drier or by shortening or lengthening the stay time of the quantities in said drier. It will also be seen that a further qualified technical pro¬ blem is one of realizing that in the case of a drier which is active at high frequencies and in the case of a given application, the power supplied to the drier can be control¬ led solely by changing the capacitancce value of a further capacitance which is connected in parallel across the elec¬ trodes and which comprises plates which can be moved towards and away from one another so as to enable the power to be controlled by changing the distance between the two capaci¬ tor plates of the further capacitance. It will also be seen that a further qualified technical pro¬ blem in the case of a drier which is active at high frequen¬ cy and in the case of another application, is one of reali¬ zing that the power input to the drier can be controlled by lengthening or shortening an electrical conductor connected between the electrodes and therewith enable the voltage division and therewith also the drying effect per unit length to be moved along the electrodes. This will enable a greater drying effect to be obtained at the beginning of the drier than at the end thereof. As will be understood,^the power input to the drier can also be controlled by changing the value of the alternating vol¬ tage connected to the electrodes. SOLUTION The present invention relates to a method of controlling the material and/or moisture content of an elongated object which comprises, inter alia, fibrous material, in which a quantity of fibrous material containing a moist binder is compressed repeatedly and the compressed fibre-material • quantities are dried by passing said quantities between the electrodes of a high-frequency drier, in accordance with the teachings of the aforesaid US patent specification. The present invention enables the material content of the elongated object to be increased or decreased, therewith enabling an increase or decrease in density, by increasing or decreasing the fibre proportion in each fresh quantity of material supplied to the compression chamber. The invention also enables the moisture content of the fini¬ shed product to be increased or decreased, by decreasing or increasing the power output of the drier, which can be accomplished by decreasing or increasing the power input to the drier and/or by increasing or decreasing the through rate of the material quantity and therewith the stay time of the material quantity in the drier. In accordance with one alternative embodiment of the inven¬ tion, the power input to the drier is controlled by altering the capacitive value of a further capacitance connected in parallel over the electrodes, by changing the distance between two capacitor plates associated with the further capacitance. The power input to the drier can, of course, also 'be con¬ trolled exclusively by changing the value of the alternating voltage applied to the electrodes. The weight of each of the quantities of fibrous material containing moist binder is determined in a weighing device, and since the moisture content is more or less clearly determined it follows that the material content is clearly determined in relation to the measured weight. The fibrous material used may be wood chips, in the form of sawdust or cutter chips or shavings, and the binder may be a water-based glue product. It is also proposed that for the purpose of reducing the moisture content of the elongated object, a longer period of time is selected between mutually sequential compressed quantities of fibrous material. In an alternative embodiment, the power input to the drier is controlled by changing the length of an electric conduc¬ tor connected between the electrodes. This will also enable the drying power per unit length and the distribution of the drying power to be changed along the electrode. ADVANTAGES Those advantages primarily associated with a method accord¬ ing to the invention reside in the provision of conditions which will enable the material and/or moisture content of a finished elongated object comprising fibrous material in the form of wood material and provided with a dried and hardened binder to be controlled to pre-determined values, where separate control of material content and moisture content can be effected in a simple manner. The primary characteristic features of a method according " to the present invention are set forth in the characterizing clause of the following Claim 1. BRIEF DESCRIPTION OF THE DRAWINGS An exemplifying embodiment at present preferred of an arrangement which operates in accordance with the inventive method will now be described in more detail with reference to the accompanying drawings, in which Figure 1 is a highly simplified side view which illustrates the principle construction of an inventive arrangement intended for the manufacture of elongated objects, Figure 2 is a sectional view of a proposed drier which is active at high frequencies and utilized in the arrangement of Figure 1, Figure 3 is a simplified illustration of a coupling or cir¬ cuit arrangement for the electrodes incorporated in the high-frequency drier and operative in adjusting the power output, and Figure 4 is a simple illustration of a circuit for supplying electrical energy to an electrode-heating device. DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED Figure 1 is a highly simplified side view of an arrangement 1 for manufacturing an elongated object 4 in accordance with the present invention. The arrangement illustrated in Figure 1 includes a hydraulic piston-cylinder device 10, with associated piston and piston rod 9. The piston rod is reciprocatingly movable and co-acts with a compressing device 8, which has the form of a plunger and extends somewhat into a compression chamber 7 and forms a part of said chamber, namely a rear wall part thereof. In addition to said rear wall part, the compression chamber 7 is also defined by a bottom part and two side parts, and also by the latest compressed quantity of fibrous material. Arranged immediately above the compression chamber 7 is a device 6. The upper part of the device 6 may be configured with a space for receiving fibrous material and a space for receiving moist binding agent, the fibrous material and bin¬ ding agent being mixed into portions of pre-determined size and moisture content ' in a mixing station not shown, where¬ after the resultant proportions are fed to a lower space 6a of the device 6. A proportion, or quantity, of the total fibre material required for the whole of the object 4 is dispensed to the compression chamber 7 from the aforesaid lower space, with the aid of dispensing or portioning devi¬ ces not shown. A particularly suitable alternative, however, is to use a ready mixture of fibrous material and moist binder, and to supply this ready mix directly to the device 6, where said proportion or quantity is measured by a weighing device and a compression plunger or filling plunger presses a weighed quantity of said mix into the compression chamber 7 and forms therewith the upper part of the compression chamber 7. As will be understood, as an alternative to using a fibre suspension which is mixed with a binding agent, the elonga¬ ted object can be formed by spraying or moistening a fibrous material with binding agent, in which case, and particularly in the latter case, the material is fed directly to the com¬ pression chamber 7 and there subjected to pressure. The fibrous material may comprise cutter shavings, paper waste, plastics materials, sawdust and like materials. The compressing device 8, which has the form of a plunger, is moved reciprocatingly by the aforesaid hydraulic piston cylinder device 10, with associated piston and piston rod 9. In Figure 1 the compressing device 8 is shown in a side view, in a non-compressing position and therewith withdrawn from the compression chamber. When the compressing device occupies its illustrated position, the space located for- wardly of the compressing device is filled with fibre mate- rial from the device 6. This feed of material from said device can be effected by causing the compressing device 8 to expose an opening upon movement of said compressing devi¬ ce to the position shown in Figure 1 " , thereby ensuring that the space or compression chamber thus formed can be filled with the aid of a further plunger, not shown in the Figure. When the compressing device 8 is displaced linearly to the right in Figure 1, the fibre material or ibre-material quantity located in the compression chamber will be compres¬ sed against the preceding quantity of material, which has previously been compressed, so as to build-on a further quantity of material in the production of the complete object 4. During this described displacement of the compressing means 8, the filling or charging plunger is in its lower position. Thus, sequential proportions or quantities of material will be compressed in the compression chamber 7 and displaced in the form of an integral unit to a heating section, via a matrix. There is nothing to prevent this heating section from also including the compression chamber 7, particularly when the heating section utilizes a drier which is active at high frequency, since in this case it is only necessary for the electrodes to be allowed to pass the compression chamber 7 and to provide in the upper electrode an aperture which will accommodate the charging or filling plunger used to introduce a further, weighed quantity of fibre material into the compression chamber 7. The compressed fibre material, supplied with moist binder, is now introduced into the heating section and there treated with heat by means of a high-frequency heating device, whereafter the dried elongated object 4 can be discharged through a part 5b. The finished object is referenced 4. The object 4 may also conceivably be transferred directly to a treatment plant 3, i which the outer surfaces of the object are treated with an impregnating liquid, or coated with paint, varnish or the like. The arrangement illustrated in Figure 1 also includes a con¬ trol means 2 which controls the times at which reciprocating movement of the compressing device 8 is initiated. The con¬ trol means also controls material and binding agent and the device proportioning the volumes of individual quantities of material, and the device 6 containing the fibre material and pressing means associated with said device, together with other operational functions of the arrangement 1. The speci¬ fic electric circuitry of the control means 2 has not been illustrated, since the construction of said control means will be readily apparent from the following functional description. According to the present invention, the control means 2 also includes requisite electrical circuits for operating a dryer which is active at high frequencies. Figure 2 is a sectional view of a high-frequency dryer 5 constructed in accordance with the present invention. Figure 2 illustrates the orientation of the elongated binder-containing fibrous object 4 as it passes through a matrix, the upper surface of which is formed by the one electrode 12 of the high-frequency system, whereas the lower surface is formed by the second, the earthed electrode 13 of said high-frequency system. The two side surfaces of the matrix are formed by two rods 14, 15 which comprise a glass composite material and which are fitted in between the electrodes 12, 13. In accordance with the invention one electrode 12, although preferably both electrodes 12, 13, is arranged to co-act with one or more electrode-heating devices 16, the illustra¬ ted embodiment having four such devices 16 arranged to co-act with the upper electrode and four similar devices arranged to co-act with the lower electrode 13. These electrode-heating devices are intended to heat, prior to initiating the manufacturing process, not only the elec¬ trodes 12, 13 but also elements peripheral of said electro¬ des, such as the rods 14,15 and rods 17,18, and also other elements, such as a top cover plate, to a temperature such as to avoid condensation of the water vapour generated onto cold surfaces. It can be mentioned in this connection that water vapour is generated when drying the quantities of mixed fibre-binder materials at the very moment of starting up the drier. This water vapour normally rises and if it condenses on cold sur¬ faces it is liable to cause electric discharges. This is particularly applicable when the electrode and the electrode surroundings are not earthed in the system. It is also proposed that air laden with water vapour is removed through a pipe 19 from a space enclosed by the elec¬ trodes 12, 13 and the rods 14 and 15, and also from a„space 20 which surrounds the electrodes. The space 20 communicates with the pipe 19 via openings 21. The volume of air thus extracted is preferably adapted, with the aid of a fan means not shown, such that said air volume per unit of time is commensurate with or essentially commen¬ surate with the amount of water vapour generated in the drier. It should be noted in particular that if the volume of air withdrawn by suction is set to exceeds the volume of water vapour generated, only an insignificant amount of air will be able to pass in through the infeed side 5a, so that no wall portions will be cooled. Air which passes in through the outfeed side 5b will also have a cooling effect and should be avoided. In order to ensure that sufficient heat is obtained on the infeed side 5a, hot air may be directed onto the compression chamber 7 and elements located therein. In this case, the volume of air extracted by suction should be increased, so that the hot air will pass into the matrix and around said matrix and the electrodes. It is also proposed in accordance with the present invention that the lower system-earth electrode or the lower electrode 13 is firmly connected, via electrically insulating glass composite rods 18, to a bottom plate 22 which is joined to the plunger 8 and thus moves together with said plunger. The glass composite rod 14 is firmly connected to a plate 23 and the glass composite rod 15 is connected firmly to a plate 24, which are arranged to be displaced linearly by hydraulic piston-cylinder devices (not shown) corresponding to the piston-cylinder device 9, 10. The upper electrode 12 is connected firmly to a plate 25 via rods 17 which comprise a similar glass composite material. The plates 22, 23, 24 and 25 are made of an electrically conductive material. Located above the upper plate 25 is a heat insulating mate¬ rial 26, while located above said material 26 is a space 27 through which air laden with water vapour is conducted to a pipe or outlet 19 and from there away from the system. The inner surfaces of the plates or elements 22, 23, 24 and 25 are coated with a copper layer intended for screening the electromagnetic field. Since a given degree of relative movement will take place between the element 22 and the ele¬ ments 23 and 24, and between the elements 23 and 24 and the element 25, copper rails 30, 31 are arranged between said elements 22, 23 and 24 respectively, while copper rails 32, 33 are arranged between the element 25 and the elements 23 and 24. The aforesaid glass composite material comprises a material retailed under the trade mark "ARCLEX". Figure 3 illustrates a connection 36 for supplying energy to the high-frequency dryer. The connection 36 is connected to the upper electrode 12 which is connected through a connec¬ tion 37 to the bottom electrode 13, which in turn is connec¬ ted by an electrical conductor to system earth 38. The electrodes 12 and 13 are also connected electrically to a respective plate 34 and 35 of a capacitor, the capacitance of which can be varied by altering the distance "d_" between said plates. This variation in distance "d_" can best be effected by moun¬ ting the plate 3 for movement along a guide, towards and away from the plate 35. This possibility of adjusting the aforesaid distance "d_" enables the high-frequency circuit to be tuned to pre-selec- ted operating conditions. In the case of certain applications it may be necessary to adapt the system in a manner which is not contingent on the plate 34 and 35, but which requires the use of different lengths of the connection 37. It is possible with the aid of solely one, or with the aid of both adapting possibilities to change and move the volta¬ ge distribution, and therewith the drying effect along indi¬ vidual length sections of the electrodes 12 and 13. Figure 4 illustrates an exemplifying circuit for the supply of electrical energy to the heating device 16, said supply being effected over an inductance 40, 41 and with four capa¬ citances 42 and 42a, 43 and 43a connected to system earth 38 for the high-frequency system. This circuit, or coupling, is intended to reduce the generation of voltage occurring in the device 16 as a result of the high-frequency circuit and of the cable connections. The capacitances are intended to dampen induced voltage peaks. As will be seen from Figure 2, a plurality, four, heating devices 16 are arranged between electrically insulating, glass composite materials 17, each of said devices being supplied with energy through a Figure 4 circuit. The supply of electrical energy to the device 16 located adjacent the bottom electrode 13 can be effected directly to said electrode, without passing through the Figure 4 cir¬ cuit, since the electrode 13 is connected system earth 38. In the case of the illustrated embodiment, respective devi¬ ces are surrounded by a screening tube which extends out of the electromagnetic field. It should be noted, however, that in this case the device 16 shall be fully encompassed in a screening tube, a copper tube, which extends completely through the electromagnetic field. Although not shown in the drawings, the arrangement includes a temperature sensing thermostat which is connected to the upper surface of the electrode 12 and which senses through " an inductance and with the aid of a plurality of capacitan¬ ces, in the manner indicated in Figure 4. As previously mentioned, the bottom electrode 13 shall move together with the plunger 8, by means of which a quantity of fibrous material provided with a moist binder is compressed, while the two side walls, made of an electrically insulating material, are moved simultaneously through approximately half of said movement. The relative displacement between the stationary electrode 12 and the side walls 14, 15, and the relative displacement between the movable electrode 13 and the side walls is adap¬ ted so that there is generated thereby sufficient friction to join the separate fibre quantities together and to impart a smooth surface to said quantities. It will also be seen from Figure 2 that the first rods 14, 15 of glass composite material are arranged to abut the com¬ pressed quantities along two mutually opposite sides of the object 4, and that one or more second rods 17, 18 made of glass composite material are arranged to supportingly abut the electrodes 12, 13 along two mutually opposite sides. * The electrodes and rods extend from the compression chamber 7 to said end part 5b. plifying embodiment is located within the dryer 5, the upper electrode 12 being provided with an aperture through which the fibre-binder mixture can be passed, it also lies within the scope of the invention to provide a compression chamber which is separate to and spaced from the dryer. This latter alternative can be expected to afford somewhat simpler mea¬ sures in respect of the drier. The present invention relates primarily to a method of con¬ trolling the material and/or moisture content in an elonga¬ ted object 4 comprising, inter alia, fibrous material, in which a quantity of fibrous material containing a moist bin¬ der is pressed repeatedly in a compression chamber 7 and then dried by passing said material between the electrodes 12, 13 of a high-frequency drier 5. It is proposed in accordance with the invention that the material content of the elongated object 4 is increased or decreased by increasing or decreasing the proportion of fibre in each quantity supplied to the compression chamber 7. The moisture content of the object can be increas.ed or decreased by decreasing or increasing the power output of the drier. In accordance with one embodiment, the power input to the drier 5 is controlled by changing the capacitance of a further capacitor connected in parallel across the electro¬ des, by changing the distance "d_" between two capacitor pla¬ tes 34, 35 of said further capacitor. In accordance with another embodiment of the invention, this power control can be effected by lengthening or shortening the connecting conductor 37. This is carried out at constant voltage. As will be understood, the power input to the drier can also be controlled by changing the value of the high-frequency alternating voltage applied to the electrodes through the connection 36. The weight of each of the aforesaid quantities of fibrous material and binder to be supplied to the compression cham¬ ber 7 can be determined by means of a weighing device incor¬ porated in the aforesaid device 6, the moisture content of the fibre material and the supply of moisture through the glue products used being pre-determined. As an alternative to increasing or decreasing the moisture content of the produced product, the time lapse between mutually sequential compressed fibre-material quantities can be made shorter or longer, so that the material has a shor¬ ter or longer stay time in the drier 5. It is assumed that the time taken to feed a quantity of fibrous material to the compression chamber 7 and to com¬ press this fibre quantity therein is determined specifically by the control means 2 and that, as a result thereof, it is possible to control the time lapse between mutually sequent¬ ial, compressed fibre-material quantities in a simple fashion. It will be understood that the invention is not restricted to the illustrated and described embodiment, since modifica¬ tions can be carried out within the scope of the invention defined in the following claims.

Claims: CLAIMS 1. A method of controlling the material and/or moisture content of an elongated object comprising, inter alia, fibrous material, in which a quantity of fibrous material provided with a moisture-containing binder is compressed and the compressed material quantity is dried by passing said quantity between the electrodes of a drier which is active at high frequencies, characterized in that an increase or decrease in the material content of the finished elongated object is obtained by increasing or decreasing the propor¬ tion of fibre in said quantity; and in that the moisture content is increased or decreased by either increasing or decreasing the power output of the drier and/or shortening or lengthening the stay time of said quantity in the drier. 2. A method according to Claim 1, characterized in that the power input to the drier is controlled by changing the capa- citive value of a further capacitance connected in parallel across the electrodes. 3. A method according to Claim 2, characterized in that said control is effected by changing the distance between two capacitor plates associated with the further capacitance. 4. A method according to Claim 1, 2 or 3, characterized in that the power input to the drier is controlled by changing the value of the alternating voltage applied to the electro¬ des. 5. A method according to Claim 1, characterized by, with the aid of a weighing device, determining the weight of each of the quantities of fibrous material provided with binding agent. 6. A method according to Claim 1, characterized in that the fibrous material consists of wood chips, such as sawdust or cutter chips, and the binder consists of a water-based glue product. 7. A method according to Claim 1, characterized by lengthe¬ ning the time period between mutually sequential compressed quantities of fibrous material, in order to decrease the moisture content of the elongated object. 8. A method according to Claim 1, characterized in that the power input to the drier is controlled by changing the length of an electric conductor connected between the elec¬ trodes. 9. A method according to Claim 1 or 8, characterized by selecting the drying power per unit length and the distri¬ bution of the drying power along the electrode via the length of the conductor.

Inventors: ANDERSSON KURT, ANDERSSON, KURT
Applicants: ANDERSSON KURT, ANDERSSON, KURT
Application year: 1988
Main classification: B27N3
IPC codes: B27N3, B29C47, D21J3, F26B3, H05B6