MATERIAL COMPRESSING APPARATUS USED TO PRODUCE A RIGID ELONGATED MEMBER

Abstract: The invention relates to a material compressing arrangement used in a machine for producing a rigid, elongated member (4) from a binder-moistened loose material (2), comprising a compression section (7) in which binder-moistened loose material is compressed, a heating section (5) in which the compressed material batches are dried, and a conveyer means which causes each of the material batches (2b) compressed in the compression section to pass through the heating section (5). The compression section (7) is operative to compress a leading material batch (2a), as seen in the feed direction, during a short conveying distance to a greater extent than a following, pre-compressed material batch (2b) over a long conveying distance, by pre-compressing with the aid of a screw conveyer (10) and using compressed material batches (2a, 2a') located in the heating section (5) as a compression piston or ram, and to achieve final compression upon movement of these batches towards the compression section by the movable parts (15, 16) of the heating section (5).

Description: TITLE OF THE INVENTION; Material compressing appa¬ ratus used to produce a rigid elongated member TECHNICAL FIELP The present invention relates generally to a material- compressing arrangement, and more particularly, but not exclusively, to a material-compressing arrangement which can be used in machines for the manufacture of a rigid, elongated structural member. Such arrangements are used to compress starting material comprising a binder-moistened loose, fibrous material, such as cutter chips and sawdust, or corresponding material, whereafter the material is dried in a heating section to form said elongated member. The invention provides a simple material compressing arrangement which is well suited for use in a machine intended for the afore¬ said purpose and which includes a compression section or com¬ pression unit in which batches of binder-moistened, loose fibrous material are compressed. The machine also includes a heating section in which the compressed batches of material are dried, and conveying means operative to convey the material compressed in the compression unit through the heating section. In order to understand the present invention, it should be under¬ stood that the expression "material batches" as used in the pre¬ sent document does not refer to well defined batches, but rather to the fact that several such batches are required to form an elongated member or beam and that there is no clearly defined interface between mutually adjacent batches. The term "batch" is used to facilitate an understanding of the continuous manufacturing process that is afforded by the use of a compression section which can be filled with a material batch, and a heating section which comprises movable wall-parts and a bottom-part. BACKgRQVNP ART A machine of the aforesaid kind is known from the International Patent Application No. PCT/SE84/00303, which describes and il¬ lustrates an arrangement for producing an elongated member (a beam) , in which a compression device is mounted in a compression section such as to be able to displace and compress sequentially individual binder-moistened material batches, each clearly defined by weighing, so that the individual, compressed material batches can be passed sequentially through a high-frequency heating section. The aforesaid patent application describes a compression section in which a piston is reciprocatingly movable horizontally in the same direction as a central line assigned to said heating section and the outfeed direction of the finished member or beam, sub¬ sequent to having passed through the heating section. When the piston is located in a first position, a retracted posi¬ tion, a batch of binder-moistened loose material will fall down into a compression chamber, or alternatively is pressed into said chamber by means of a further piston, whereafter the chamber is closed and the horizontal piston is moved towards the heating section, wherewith the aforesaid batch of material is compressed in said compression chamber against the immediately preceding batch, and subsequent to having been compressed to a sufficiently high degree of compression all of the material batches located in the heating section are displaced together with the last com¬ pressed batch through a distance in the heating section equal to the axial extension of the compressed batch, wherewith the piston cam return to its retracted position and a fresh batch of binder- moistened, loose material can fall down in front of the piston. The subject matter of Swedish Patent Specification 415 547 (Swedi¬ sh Patent Application 7809708-4) also forms part of the known prior art. This publication teaches a heating section whose wall parts are reciprocatingly movable in a horizontal direction and function in part as means for guiding and conveying compressed material batches. Each of the aforesaid embodiments require the elongated member to be produced from separate, well defined batches of material which are well separated from one another by an interface or boundary region of different degrees of compression and also, to some extent, with fibre directions displaced in the vertical plane. SUMMARY OF THE PRESENT INVENTION TECHNICAL PROBLEMS When studying the present standpoint of techniques, as described above, it will be seen that a highly complicated technical problem resides in the provision of conditions, with the aid of simple means, whereby the movable parts or components of the heating section will not only function as means for conveying compressed material through the heating section, but will also function as a means for transmitting forces to the material in an opposite direction and therewith permit the material located in the heating section to function as a compression device or a compression piston for compression of the material(batches^located in the compression section. A further technical problem is one of realizing the possibilities of controlling the compression forces utilized solely by selecting and/or controlling the frictional forces acting between the com¬ pressed material in the heating section and the movable parts of said heating section, such as the wall parts and/or other parts thereof. It will also be seen that a technical problem is one of realizing that the desired possibility of controlling the compression forces can be achieved by controlling one or more control parameters of a plurality of available, further control parameters, at least nine such parameters, hereinafter explained in more detail. Another technical problem is one of realizing and of utilizing the fact that the frictiorial forces acting between compressed material in the heating section and the movable parts thereof will be very large, provided that there is no relative movement between said material and said movable parts, and that these forces will de¬ crease markedly when such relative movement occurs. Another technical problem is one of realizing and utilizing the fact that occurrent frictional forces are much larger than ex¬ pected, because compressed material, which has a high moisture content, tend to swell during the initial stage of the drying period. A further technical problem is one of realizing that with a com¬ pression arrangement, which provides a solution to one or more of the aforesaid technical problems, it is possible to increase production rate solely by increasing the relevant degree of pre- compression in the compression section, and to realize that this can be effected readily with the aid of a screw conveyer or like known conveyer means which is also permitted to function as a pre- compression means. It will also be seen that a technical problem is one of realizing and of utilizing the fact that there can be obtained with the aid of a screw conveyer, within said conveyer, a region of successive¬ ly .increasing compression, whereas at the end of the screw con¬ veyer there is obtained a binder-moistened material collection or agglomeration of circular cross-section and pre-compressed to a pre-determined degree, which is pressed into a right-angled (rectangular) space in which the shape of said material collection is changed at said given degree of pre-compression and thereafter obtains its final degree of pre-compression. It will be seen that a further technical problem is one of pro¬ viding conditions whereby material batches can be advanced without any noticeable boundary layer therebetween, despite realizing that the weight per unit volume of a finished elongated member requires the provision of a portioning and weighing device for individual batches of loose material, such that one batch cannot be discerned from adjacent batches, and therewith enable the provision of a piston-charged portioning device adjacent the compression section to be dispensed with. It will also be seen that a technical problem is one of realizing that with a compression section which solves each of the aforesaid technical problems and when the binding agent is glue and the loose material is cutter chips or sawdust, the final degree of compression must be achieved with a loose pre-compression and an immediately following locally-acted final compression in an axial direction, in order for the elongated member to exhibit pre-deter- mined mechanical strength properties, for instance fulfil the test results of accepted loading pallet members. It will also be seen that a technical problem is one of providing a principle solution to one or more of the aforesaid technical problems, by realizing that a screw conveyer can actually pre- compress the material batches to an extent satisfactory for the purpose intended, whereas the final compression can be effected by displacing one or more parts, such as wall parts or the bottom and/or upper part. • When using movable parts or sections in the heating section it will be seen that a technical problem is one of realizing that anticipated tendencies to rupture the material batch located in the compression section, or to vertical displacement of material in said batch, will not occur when the wall parts of said heating section are displaced towards the compression section and when a sufficiently high counterpressure is afforded (compression and/or force-application from the screw conveyer). When considering the present standpoint of techniques disclosed in the aforesaid Swedish Patent Application it will be seen that a technical problem resides in realizing the significance of allow¬ ing all, or at least a substantial part of the compression forces generated by the compressed material usually located in the heat¬ ing section to be taken-up within a well adapted, relatively long section located between a material conveyer and the entrance to the heating section. It will also be seen that a technical problem is one of realizing that earlier well-defined boundary layers which have a strength reducing effect and the material batches on either side of which have mutually different degrees of compression, can become less pronounced and reduced towards a more homogenous and stronger elongated member and that a major part of the requisite com¬ pression forces generated or all of said forces generated can be taken-up by and allowed to act within a well-defined section in which the degree of compression is changed by a constriction located within said section. In conjunction herewith, it will be seen that a technical problem resides in realizing the significance of configuring the constric¬ tion so that it converges slightly away from the heating section, and to adapt the configuration of said constriction and its length and breadth dimensions in relation to the cross-sectional shape of the elongated member, to the fibrous material used, to the length of the compressed material, usually in the form of batches^and to other parameters. Another technical problem is one of realizing the significance of adapting the length of the constriction to the nature and con¬ figuration of said constriction, to the cross-sectional shape of the elongated member, the desired compression forces, etc. Another technical problem is then one of realizing that in prac¬ tice said length should be at least half of the length of a com¬ pressed material batch entering the heating section. A further technical problem is one of realizing the significance of allowing the constriction to σoact with one of the sides which determine the cross-sectional shape of the elongated member, e.g. one side in the case of narrow cross-sectional shapes, two sides in the case of wider cross-sectional shapes and three or more sides when the cross-sectional shape is more square. It will also be seen that a technical problem is one of realizing that when the constriction used can be displaced between an active and an inactive position, the constriction should be given a U- shaped cross-section with three sides, or some similar cross- section, suitably when manufacturing an elongated member of right- angled cross-section, preferably rectangular cross-section (inclu¬ ding a square), and therewith realize that these three sides shall cooperate to form three mutually coacting, preferably movable constriction-defining parts. It is also a technical problem to realize the advantages afforded when material batches are compressed in accordance with the afore- given guidelines and the finally compressed material batches are rolled to desired cross-sectional shapes prior to passing into the heating section. Another technical problem is one of realizing the advantages afforded when the cross-sectional shape of the constriction has a final profiled cross-section (special cross-section) such that the material batches need only be rolled to a negligible extent, or need not be rolled at all prior to entering the heating section or be dimension-adapted downstream of the heating section, by giving the wall-parts of the heating section a form which corresponds to said special cross-section. Another technical problem is one of realizing the significance of selecting the configuration and angles of the constriction-defin¬ ing members such that the constriction will present the requisite counterpressure when compressing the collection of material pres¬ ent therein. Another technical problem is one of providing a stationary or a movable constriction while still enabling the compression section to be filled readily with loose fibrous material. Another technical problem is one of enabling the internal con¬ figuration of the constriction, normally its angular values, to be chosen so that the heat of compression generated can be dis¬ tributed over a sufficiently large surface area and therewith prevent the occurrence of local heat-concentrations liable to re¬ sult in local hardening of the material. Another technical problem is one of realizing the importance of selecting the length of the constriction in relation to the dis¬ tance through which a previously compressed material batch is advanced. Another technical problem is one of realizing the limits within which the decreasing cross-section of the constriction should lie in comparison with the selected cross-section of the heating section. One qualified technical consideration resides in the ability of providing for simple density control. With respect to density control, a technical problem is one of effectively utilizing and regulating the force produced by the static friction acting between movable sides of the heating sec¬ tion and the compressed material batches located in said section and accompanying said movable sides. A further technical problem is one of ensuring that the force deriving from said static friction will be greater than the force exerted by relative movement between compressed material batches and said sides during the compression stage, inter alia by ensur¬ ing that the static-friction surfaces are larger than the kinetic- friction surfaces. In this respect, a further technical problem is one of realizing the importance of allowing certain surfaces, preferably opposing surfaces, to compensate one another; a movable surface compensates a stationary surface. Another technical problem is one of realizing the importance of providing a particular movement pattern for one or more parts forming the constriction and relating this movement to the move¬ ments of the heat-section walls and to other factors, so as to obtain an extended compression depth or compression dimension for the boundary layer present between mutually adjacent material batches. SOLUTION The present invention relates to a material compressing arrange¬ ment which can be used in a machine intended for the manufacture of rigid, elongated members from binder-moistened loose material, said machine including a compression section operative to compress binder-moistened loose material, a heating section in which the compressed material is dried or hardened, and a conveyer arrange¬ ment operative to cause the material compressed in the compression section to pass through the heating section. The conveyer arrangement is based, inter alia, on the fact that parts of the heating section, normally the wall parts, but also the bottom parts, are reciprocatingly movable in the direction of movement of the material. For the purpose of solving one or more of the aforesaid technical problems, it is proposed in accordance with the invention that a If » material batch located in the compression section is compressed as a result of movement of earlier compressed material located in the heating section towards the compression section as a result of movement of one or more of said heating-section parts, these earlier compressed material therewith functioning as a compression piston or ram which is movable in the longitudinal extension of the elongated member. In accordance with the proposed, particularly suitable develop¬ ments of the invention, it is suggested that the material located in the heating section are displaceable towards the compression section and generate a large force which is unable to exceed the frictional force acting between the earlier compressed material and the heating-section parts movable towards the compression section. Compressed material located in the heating section can also be moved towards the compression section by a force which is deter¬ mined by the friction acting between compressed material and the wall-parts and/or bottom part of the heating section movable to¬ wards the compression section. Thus, the degree of compression to which the material located in the compression section is subjected is chosen in dependence on the force with which the material located in the heating section can be pressed towards the compression section, which force can be decreased in a controllable fashion by application of one or more of the following parameters or factors: a) reducing the number of movable parts or components of the heating section, such as solely the walls or therewith a bottom part and/or an upper part; b) increasing the release angle between parts or components of the heating section; c) reducing the speed at which the material pass through the heating section, with retained drying effect; d) increasing the drying effect with retained through- rate; e) choosing a chip- or dust-glue mixture which dries or hardens at a lower temperature; f) producing the mixture from different materials; g) increasing the proportion of glue used; h) changing the distribution of the drying effect along the heating section; i) increasing the input temperature of the glue mixture. A material batch located in the compression section can be pre- compressed to a greater or lesser extent, so that the production rate can be increased with increased pre-compression. The material batch or material batches located in the compression section will preferably be pre-compressed by a conveyer which functions to feed material batches to the compression section. The material batch located in the compression section is pre- compressed with the aid of a single screw conveyer. Furthermore, it is proposed that the relevant degree of compres¬ sion can be varied in correspondence with the desired density of the ultimate elongated member, and that when the binder is glue and the loose fibrous material consists of cutter chips or sawdust the final degree of compression will be at most 5:1. It is also proposed that the final degree of compression of the material batch located in the compression section is obtained through the force represented by the friction occurring between the material located in the heating section and said parts of said heating section and acting in a longitudinal direction of the elongated member. It is also proposed that a material batch compressed to a low degree of compression can be advanced in a cylindrical shape and given its final, non-cylindrical shape | in the final compression stage of the process. Furthermore, it is proposed that a pressure-absorbing surface located in the compression section and distal from the heating section is smaller than the cross-sectional area of the heating section adjacent said compression section. For the purpose of solving one or more of the aforesaid technical problems, it is proposed in accordance with the invention that the compression forces generated in the compression section by the compressed material in the heating section upon movement of said walls and said material is taken-up either totally or predomina¬ ntly within a constriction, normally in the form of a well-defined converging section located between said heating section and a conveyer intended for conveying loose fibrous material, in the absence of any influence from said conveyer, or with only a slight influence. In accordance with particularly advantageous developments, it is proposed that said section or constriction will have the form of a device whose smallest cross-sectional area is smaller than the cross-sectional area of the heating section. Preferably, the constriction will converge slightly in a direction away from the heating section and may comprise one or more reciprocatingly movable parts. r One of said parts may advantageously have a U-shaped cross-sec¬ tion, therewith forming three simultaneously movable wall-parts. Respective displaceable or movable parts have a wedge-shape, with the thin edge of the wedge facing towards the heating section and will have an angle smaller than 15°, preferably between 2° and 10°, and a length extension which exceeds 50% of a previously compressed material batch located in the heating section. The smallest cross-section of the constriction or section is reduced to less than 30%, with the height dimension of the heating section preferably between 10 and 20%. The aforesaid movable part or parts of the constriction device is or are located in a position facing the heating section during compression and is or are intended to move from the heating sec¬ tion when a further batch of loose material is charged to the arrangement, while moving the compressing material batches from the compression section. APVftNTA-gES Those advantages associated with the inventive arrangement reside in the provision of conditions in which final compression of material located in the compression section can be effected by causing previously compressed material located in the heating section to function as a compression piston when parts of the heating section, such as walls, floor and/or upper part are moved towards the compression section. The force with which the previously compressed material in the heating section is able to compress the material in the com¬ pression section is dependent on the frictional force prevailing between compressed material in the heating section and the movable parts of said section, provided that no relative movement occurs between said material and said heating-section parts, but that the material accompany the movement of said heating-section parts towards the compression section or compression arrangement. This frictional force can be controlled readily by application of one or more well defined parameters. The advantages primarily afforded by an arrangement in accordance with the present invention also reside in the provision of condi¬ tions wherewith final compression of a loosely packed material batch in the compression section is achieved by allowing the previously compressed material batches located in the heating section to function as a compression piston or plunger when the heating-section parts, such as walls, floor-parts and/or upper- part are moved towards the compression section without the loose- material conveyer means needing to function as a counter-pressure device or anvil device. In this way, compression is increased within a section that forms a boundary area between mutually adjacent compressing material batches, which reduces undesirable variations in compression on respective sides of a well-defined short boundary section. The primary characteristic features of arrangement constructed in accordance with the present invention are set forth in the charac- terizing clause of the following Claim 1. BRIEF DESCRIPTION OF THE DRAWINGS An exemplifying embodiment of a material-compressing arrangement at present preferred and included in a machine for producing an elongated member or beam and having the significant characteristic features of the present invention will now be described in more detail /with reference to the accompanying drawings, in which Figure 1 is a highly simplified side view of an earlier known machine for the manufacture of elongated members, Figure 2 is a side view, partly in section, of an inventive material compressing arrangement adapted for the use in the machine illustrated in Figure 1, Figure 3 is a function-time-diagram of the compression section and the parts or components of the heating section, Figure 4 is a perspective view of a device having a slightly converging form and positioned between the heating section and a loos-material conveyer; and Figure 5 illustrates compression "C" of the loos-material and remaining material "batches" between conveyer and heating sections. DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED Figure 1 illustrates a machine 1 intended for the manufacture of a rigid elongated member 4 from binder-moistened loose material 2, with the aid of a compression section 7 and a heating section 5. Thus, Figure 1 is a highly .simplified side view of a machine 1 for manufacturing an elongated member 4 or a beam. The machine illu¬ strated in Figure 1 includes a hydraulic piston-cylinder device 9a, having a piston and a piston rod 9. The piston rod is recipro- catingly movable and cόacts with a compressing device 8 in the form of a piston which extends slightly into the compression chamber 7' and which forms a part of said compression section 7, namely a rear wall-part of said section. Arranged immediately above the compression chamber 7 ' is a device 6, the upper part of which may be configured with a space for accommodating fibrous material and a space for accommodating binderr. The fibrous material and the binder (glue) are mixed together in predetermined proportions in a mixing station (not shown) and fed to a lower space. The material is metered from the lower space 6a in mutually sequential batches by a portioning and weighing device (not shown in Figure 1) such that the total amount of fibre material required to produce an entire elongated member is charged sequentially to the compression chamber 7- . Alternatively, a premix of fibre material and binder (glue) may also be charged to the device 6 directly. As an alternative to the use of a fibrous suspension mixed with binder, the elongated member can, of course, be formed by spraying or moistening a fibrous material with binder, and particularly in this latter case the material can be fed directly to the com¬ pression chamber 7 ' and there subjected to pressure. The material shall primarily be an electrically non-conductive fibrous material, such as cutter chips, waste paper, textiles, sawdust, wood chips and the like, or even such material admixed with plastic, bark and the like. The compression device 8, in the form of a piston, is caused to move backwards and forwards by means of a hydraulic piston-cylin¬ der device 9a having a piston and piston rod 9. The compression device 8 is shown in side view in Figure 1 and in a non-com¬ pressing position in which it exposes the compression chamber. When the compression device 8 is located in this position, the space located forwardly of said device is filled with a measured batch of fibrous material discharged from the device 6, preferably with the aid of a vertically extending plunger, not shown. This is effected in that when the compressing device 8 upon movement to the position illustrated in Figure 1 exposes an opening, it is ensured that the space or compression chamber defined therewith can be filled. When the compression device 8 is moved to the right in Figure 1, the fibre material or fibre batch located in the compression chamber is compressed against the preceding material batch, such as to build on one material batch after another and therewith produce the elongated member. Thus, each of the mutually sequential material batches will be compressed in the compression chamber 7' and the material batches are moved as a composite unit to a heating section 5. The binder- containing compressed fibrous material is introduced through the end part 5a of the heating section and there subjected to heat treatment via a known high-frequency machine (not shown), where¬ after the manufactured elongated member is discharged through the end part 5b of said heating section. The finished elongated member is referenced 4. If desired, the elongated member 4 can be transferred directly to a treatment machine 3, in which the outer surfaces of the elon¬ gated member can be coated with an impregnating liquid, paint, varnish, laquer or the like. The reference sign 1' in Figure 1 identifies a control means operative to activate the compression device 8, a material and binder mixing device, a volume proportioning device, a machine 6 containing fibrous material, press means and other functions of the arrangement 1. The specific circuitry of the control means 1' will not be described, since such circuitry can be readily devised on the basis of the following functional description. Figure 2 is a highly simplified illustration of the principle construction of a compression section and one part 5a (the forward part) of a heating section. Although the principles of the invention can be applied with one or more material batches in the compression section, with or without pre-compression, the first part of the following des¬ cription will be made with reference to a single material batch which has been pre-compressed to a given extent. The invention is based on the understanding that a conveyer means (displaceable wall parts) intended for conveying compressing material batches located in the heating section can also function as displacement means for a compressing plunger or piston in the form of previously compressed material batches located in the heating section as described in more detail hereinafter. Those who are conversant with this technical field will understand that the force which subsequently acts on the material batch in the compression section cannot exceed the prevailing frictional forces acting between the earlier compressed material batches and all parts of the heating section, such as the two wall parts, the bottom part and the upper part, when these move synchronously towards the compression section in the absence of relative move¬ ment between said material batches and said parts, and that said forces are therefore controlled by said prevailing frictional forces. The frictional forces prevailing with synchronous movement can be controlled in a manner described in more detail herebelow. » An explosive reduction in the effect of the frictional forces will occur when one or more parts (say the upper part) does not take part in said movement, but remains stationary. The side wall-parts 15 and the bottom part 16 of the proposed embodiment described hereinafter are synchronously movable. As will be understood, the prevailing frictional forces are, inter alia, dependent on the number of parts displaced, the size of the contact surface between said parts and the compressed material batches and also in dependence on whether said parts are displaced synchronously or asynchronously. It should be mentioned that the frictional forces attained and primarily utilized will prevail provided that the compressed material batches in the heating section accompany the movement of said movable part or components towards the compression section, and will decrease drastically immediately relative movement be¬ tween the compressing material batches and said parts occurs. The inventive compression section 7 illustrated in Figure 2 is also assumed to include a pre-compressing arrangement 10. This arrangement shall function to compress material batches 2b located in the space 11 to a constant or substantially constant degree of compression, when the parts of said heating section are located in a position furthest to the right, which also means that all ear¬ lier compressed material batches 2a, 2a' located in the heating section will be located in a position far to the right. In the following description, the arrangement 10 is described as having the form of a screw conveyer 18, 19. This arrangement 10 shall be such as to impart to density-determined batches a degree of pre-compression between 1.2:1 and 3:1, preferably 2:1, in a space 11 located at the end of the screw'conveyer. • It should be noted that this compression merely relates to a degree of pre-compression such as to enable a plurality of materi¬ al batches to form, in sequence, an elongated configuration in the absence of marked boundary or interface layers, with mutually different degrees of compression between mutually adjacent batch¬ es. It is true that the degree to which the batches are compressed will increase through the arrangement 10, which comprises a known screw conveyer, within the screw conveyer towards the space or section 11, but a constant degree of pre-compression shall prefer¬ ably prevail within the space 11. Any variation in pre-compression within the material batch in the compression section will probably be equalized during the final compression stage. The prevailing density of the glue-moistened fibrous material 2 can be evaluated with the aid of density determining means (not shown in the Figure) and when the density is beneath a standard value, the force exerted by or the speed of the screw conveyer can be increased with the aid of control means not shown. The section 7 also includes a final compression stage in which the binder-moistened pre-compressed material batch 2b is finally compressed in an axial direction, to form finally a compressed material batch, similar to that referenced 2a. Thus, Figure 2 illustrates an inventive material compressing arrangement used in a machine for producing a rigid elongated member or beam 4 from binder-moistened loose material 2, in which the heating section 5 comprises three movable parts, such as two wall-parts and one bottom-part, and where the direction of move¬ ment conforms with the direction of movement of said material. In the embodiment illustrated in Figure 2, two vertical wall-parts made of an electrically insulating material and of which only one, 15, is shown, can be moved reciprocatingly in the direction of the arrow 15a with the aid of means not shown, whereas a bottom part 16 can be moved in the direction of the arrow 16a synchronously with said wall-parts, with the aid of means not shown. The bottom part 16 is made of an electrically conductive material. It is assumed that the wall-parts 15 and the bottom-part 16 occupy their furthest position to the right in Figure 2. The upper part 20 is stationary. Pre-compression to a pre-determined degree of compression is effected by utilizing properties offered by a screw conveyer 10 utilizing a cylindrical tube 17 and a screw thread 18 mounted therein, rotatable by a shaft 19 and a drive means not shown in the Figure. The screw conveyer 10 functions in this case as a material feeding and pre-compressing device. The extent to which the material is pre-compressed can be con¬ trolled in dependence on the force acting on the screw threads, on the screw pitch, and on the diameter of the tube 17. A greater force and a smaller pitch of the screw thread results in greater compression. It is assumed that compression in the tube 17 takes place successively towards a desired degree of compression and against forwardly located compressed batches of material. The final degree of compression with respect to batch 2a should not exceed 5:1, but is dependent on the desired density of the ultimate elongated member. The cylindrical, pre-compressed material batches 2b are intended to be fed directly to the compression section for final compres¬ sion, wherein each subsequent material batch compressed to a lower degree will be advanced in the form of a cylindrical batch through the region 11, although said cylindrical batch is able to trans¬ form to a batch of right-angled cross-section within the region 11a of the final compression stage. Since the illustrated embodiment is based on the assumption that the wall-parts or side-parts 15 and the bottom-part 16 of the heating section 5 can be moved synchronously with one another, the intention is that when a material batch 2b is located in the compression section, the aforesaid parts 15 and 16 will be moved to the left simultaneously. When the wall-parts 15 and the bottom- part 16 are located in their positions furthest to the left in the drawing, the final compression of the material batch 2b will have taken place and the aforesaid parts will have been moved to the left through a further distance than that required to actually compress the material batch 2b so that when said parts are returned to their starting position they will move the com¬ pressed batch 2b to the position of the batch 2a. As a result of the arrangement illustrated in Figure 2, a batch of loose material 2b located in the compression section will be arranged for compression by movement of previously compressed material batches 2a, 2a 7 located in the heating section 5 towards said compression section, these previously compressed material batches thus functioning as compression pistons or rams and forc¬ ing the material batch 2b against a stop surface (the screw con¬ veyer). It will be seen that the degree of compression to which the mater¬ ial batch 2b in the compression section is subjected will depend on the force with which the material batches located in the heat¬ ing section are able to compact the material batch 2b located in the compression section. This force is dependent on the frictional effect and frictional force acting between the compressing mater¬ ial batches in the heating section and the aforesaid parts of the heating section, i.e. walls, bottom-part and/or upper part of said section. Reasons may be found for wishing to increase or decrease said frictional force and to regulate such force in a manner such that the compressing batch 2b will exhibit pre-determined properties. It is established that this frictional force can be reduced in a controlled manner, by adjusting one or more of the following parameters. A) RedHce the number of movable parts or components in the heating section The frictional force acting between the parts 15, 16, 20 of the heating section and the compressed material batches 2a, 2a ' is dependent on a number of circumstances, inter alia on the size of the contacting surface between the material batches 2a, 23' and one of said parts. If the part moved has a small contact surface, the frictional force will be smaller than when moving a part having a larger contact surface. In this respect, the cross-section of the elongated member can govern which of the parts will take part in the reciprocating movement. Thus, it will be obvious that when only the two vertical wall- parts 15 are moved backwards and forwards, so as to transport compressing material batches 2a, 2a' in the heating section throu¬ gh said section and for compressing a material batch 2b located in the compression section, the force acting during the compression phase will be smaller than when said two wall-parts 15 are also accompanied by the bottom-part 16 in synchronous movement towards the compression section. A,greater force would also be expected when the upper part 20 also took part in this synchronous movement. Furthermore, the degree of compression to which the batches are subjected and the aforesaid frictional force will also be changed when the wall-parts, the bottom-part and/or the upper-part are moved asynchronously. It will be noted here that reciprocating movement of the wall- parts 15 and the bottom-part 16 shall achieve, in a direction to the left in Figure 2, successive compression of the material batch 2b to Λ. finally compressed state, and thereafter move further to the left so that the last compressed batch will take the place of the next last compressed batch, whereafter movement of the said parts to the right convey the compressed material batch to the right in order to fulfil these two criteria. A small release angle increases the compression force but renders transportation of compressed material batches through the heating section difficult. B. Increased release angle It is known to permit certain parts, particularly the wall parts, to have a shape which diverges from the compression section and in the transport direction, and to increase the resultant release angle between said parts so that the compression force will decre¬ ase, since a smaller inner surface of said parts in the heating section are in coaction with compressed material batches located in the forward part 5a of the heating section. The release angle will primarily be the same between mutually opposite wall-parts as between the bottom-part and the upper-part, although different angles may be chosen, depending on the cross- sectional shape of the elongated member. IB some cases, the mutually opposing parts may be parallel. C t Decrease the speed It is also possible to decrease the speed at which the material batches are advanced through the heating section while retaining the drying effect, by decreasing the length of working stroke of the moving parts of the heating section and increasing the degree of precompression. This measure means that a region in which drying or hardening has been sufficient to form a solid material batch whose measurements are smaller than the cross-sectional size of the heating section will be displaced closer to the compression section. Displacement of this region towards said section results in less friction between the compressing material batches and said heating-section parts, the wall-parts or the bottom-part, when a non-hardened material batch generates a high frictional force in the absence of relative movement, whereas a hard or solid elongated member will result in less friction. The region in which non-hardened or dried compressed material batches are under expansion at the beginning of a drying or hardening phase is shortened in this way. D. Increase the drying effect Similar displacement of the aforesaid region towards the compres¬ sion section where drying or hardening occurs can also be obtained by increasing the drying effect while retaining the speed, and therewith afford a reduction in compression force. E. The choice of glue mixture Suitable selection of a chip-Jor sawdust-glue mixture which dries or hardens at a lower temperature will result in the same dis¬ placement of said region as in C and D above. It should be noted, however, that this method does not permit excessively large chan¬ ges. It is also possible to include a hardener, such as salmiac, in the mixture. Ammonia can be added in order to delay hardening up to a given temperature and a reduction in the amount of ammonia added will displace the region towards the compression section. These two measures result in a displacement of the region recited in M C" above with subsequent changes of the frictional force. F. Choice of material It can also be expected that an appropriate choice of chip materi¬ al and chip-glue-mixture will result in mutually different coeffi¬ cients^of friction against the heating-section parts, such as walls, bottom-part and upper-part. A material which exhibits a smaller coefficient of friction will, of course, result in a smaller compression force. G. increase the glue proportion An increase in the amount of glue used will not only result in a harder final product, but the friction between the compressed material batches and the heating-section parts will be reduced. H. Change the drying power distribution It is known that the distribution of drying power along the exten¬ sion of the heating section can be changed, by connecting the electroplates in the high-frequency machine with inductances, such as bands or straps, or by connecting-in separate capacitors, thereby also enabling the friction occurring between the compres¬ sed material batches in the heating section and the heating-sec¬ tion parts, such as walls, bottom-part and upper-part, to be changed. The arrangement of such bands or straps and the inclusion of capacitors is illustrated and described in the International Patent Applciation WO/8902353. • I. Increase the temperature of the glue mixture Displacement of the region towards the compression section as defined in "C" above can also be achieved by increasing the input temperature of the glue mixture or the temperature in the compres¬ sion section. Referring to Figure 2, the conveying device 10 has the form of a conical screw conveyer, the wall-parts of which are referenced 17 and 17' and the conical helix of which is referenced 18. When using a conical screw conveyer it is assumed that a first, small -pre-compression occurs within the region 30, whereas final pre-compression occurs within the region 31, so that a batch 2b pre-compressed to a given degree can be found located in the compression section. In this section the heating section 5 has a circular cross-sec¬ tional shape and is provided with electrodes 32, 33 and insulating blocks 34, 35, although the heating section may have any other cross-sectional shape, such as a right-angled cross-section. When the heating section 5 consists of a high-frequency machine, the wall-parts 15 (34, 35) of said section may be made of an electrically insulating material, whereas the bottom-part 16 (33) can be made of an electrically conductive material and earthed. The upper-part 20 is stationary and is connected to the high- frequency machine. Although Figure 2 shows only one sere;-/ conveyer for feeding bind¬ er-moistened fibrous material to the region 11, it will be under¬ stood that it lies within the scope of the present invention to use two or more such conveyers, for example one cylindrical con¬ veyer positioned in the extension of the heating section and a smaller screw conveyer positioned in the manner illustrated in Figure 2. Figure 3 illustrates a proposed embodiment of intermittently operating screw conveyers 18, 19, which are time related to the movements of the two wall-parts 15 and the bottom-part 16 and a stationary upper-part 20 of the heating section. The screw con¬ veyer 18, 19 is activated during the time interval t.,-t 2 and feeds a slightly pre-compressed batch 2b to the compression section 7. The two wall-parts 15 are then moved together with the bottom-part 16 to the left in Figure 2 whereby the material batch 2b is com¬ pressed successively by the previously compressed material batches 2a, 2a ' located in the heating section to an extent such that at time point t 5 , at maximum compression, relative movement occurs between said material batches 2a, 2a' and the walls 15 and the bottom-part 16, and therewith a smaller force. The movement of said parts is terminated at time point t_, at which time point the material batch 2b has been compressed to a pre-determined degree. During the time interval t_-t 4 , the wall- parts 15 and the bottom-part 16 are moved to a furthest position to the right, as seen in Figure 2, while dogging the recently compressed batch 2b somewhat into the heating section and leaving the compression section open. The screw conveyer 18, 19 are reac¬ tivated during this return movement, during the time interval t_ - V Figure 3 illustrates that a successively increasing compression force is obtained during the time interval t_ - t 5 , i.e. the previously compressed material batches 2a, 2a' accompany the heating-section parts 15, 16 in their movement towards the com¬ pression section 7. Relative movement between the parts 15, 16 and 20 and the previously compressed batches 2a, 2a' occurs during the time interval t 5 - t_, resulting in a smaller force. The force with which the material batches 2a, 2a' are moved into the heating section during the time interval t_ - t. is very small. The force diagram illustrated in Figure 3 is highly schematic and variations within wide limits can be expected. It will be seen from the force diagram, however, that a given initial force is required at time point t_ to overcome the static friction acting between compressed batches and the upper-part 20, and it is assumed that the sliding friction between the heating- chamber parts 15, 16 and 20 and the compressed material batches, the time interval t_ - t_, is slightly higher. Figure 4 is a perspective view of a device which has a converging form and which is positioned between a heating section 5 and a loose-material conveyer 18. This device, or restriction 40 has two vertical wall-parts 41, 42 which diverge towards the heating section, and a bottom-part 43 which slopes down towards said heating section. For the sake of clarity, the bottom-part 16 and the side-parts 15 of the heating section have not been shown in Figure 4. These heating-section parts, however, are intended to form support surfaces and slide surfaces for sliding coaction with the under- surface 43a of the bottom-part 43 and the outer surfaces 41a, 42a of the side-walls 41, 42 of said constriction device. The constriction 40 may be stationarily related to a frame which forms part of the arrangement, wherein the loose-material conveyer 18 and the constriction 40 have a fixed relationship with one another and the conveyer 18 is intended to feed loose, fibrous material through the constriction in a direction opposite to the compression direction. • It is proposed in accordance with the invention that the constric¬ tion 40, which is a gentle constriction, is positioned within the region 11. The loose material from which the loose material batch is comprised and which is to be compressed is conveyed by the conveyer 18 through the constriction 40 to the chamber of the compression section located downstream thereof. Although this chamber is located predominantly downstream of the constriction 40, the chamber also extends slightly into said constriction. When the walls 15, 16 of the heating section subsequently move towards the conveyer 18, the previously compressed material batch¬ es located in the heating section will move together with said walls and therewith function as a compression piston against the fresh material batch 2b. The material batch 2a is pressed back by the heating-section walls and the previously compressed material batches located in said heating section during the initial stage of said movement, there¬ with compacting the batch 2b and initiating congestions or agglomerations within the constriction, these material congestions forming an anvil surface or counter-pressure surface. It should be noted that the material congested region permits the degree of compression to decrease along the constriction 40 in a direction towards the conveyer 18, and consequently no pronounced, short or shallow boundary sections of wide variations in compres¬ sion will be formed between mutually adjacent material batches. It will be understood that a pronouncedly converging constriction will result in a shorter congestion region than a less pronounced or more gentle converging constriction. It will also be understood that when the constriction converges pronouncedly it is easier to press the whole or part of a com¬ pressed material batch from the constriction with the aid of a conveyer 18. In the case of a stationary constriction 40, it is suggested that the wedge angle is smaller than 25°, preferably between 15-10°. Alternatively, the constriction 40 may be movably mounted and arranged to take a position removed from the heating section 5 during the infeed of fresh, loose fibrous material to the com¬ pression section while the heating-section walls 15, 16 are moved to a position away from the constriction 40. r When this infeed of loose material is completed by the conveyer 18, said loose material can be subjected to a slight degree of pre-compression, by moving the constriction 40 to a position closer to the heating section. This pre-compression is most pronounced within the edge region and contributes effectively to forming a material aggregation or congestion of successively decreasing compression towards the conveyer 18 during the actual compression sequence, inter alia. Figure 5 illustrates the degree "C" to which the loose material is compressed between the conveyer 18 and the heating section 5 when the constriction is movable. More specifically, Figure 5 illustrates that compression ratio which is applicable when an immediately preceding compressed material batch 2a is moved by the walls of the heating section 5 from the conveyer 18 and the compression chamber has been filled with loose, fibrous material while the constriction 40 takes a position removed from the heating section 5 and where the con¬ striction 40 has been displaced to a position closer to the heat¬ ing section 5. The diagram shown in Figure 5 is based on the understanding that the conveyer 18 has only a significant influence on compression and that the degree of compression nevertheless increases slightly towards the constriction 40. Insertion of the constriction 40 into the compression chamber towards the heating section 5 will also have caused a slight increase in the compression of the material within the con¬ striction 40, so as to enhance the tendency of material congestion in a region adjacent the mouth 40a of the constriction 40. This is illustrated here by showing that the degree of compression is slightly higher within the narrower part 40b of the constriction 40 at the conveyer 18 than within the wider part 40a of said constriction. Also shown is the pronounced increase in compression of the prev¬ ious batch 2a within a broad area "ε", which now forms the boun¬ dary section of the next batch 2b in line. Movement of the batch 2a towards the constriction 40, as a result of wall-movement, results in compression of the batch 2b, the extent of said compression being shown by the broken line. Thus, the compression forces generated by static friction in the compression section by movement of the previously compressed batches 2a in the heating section towards the conveyer 18 will be taken-up, either completely or to an essential extent, within a longitudinally extending section (P) in the constriction 40 lo¬ cated between said heating section 5 and the loose-material con¬ veyer 18. In this case, the constriction 40 has a right-angled cross-sec¬ tion, which is slightly smaller than the cross-section of the mouth or entrance 40a of the heating section, and the constriction has a configuration which converges slightly in a direction away from the heating section 5,. The constriction may comprise a number of mutually separate, reσiprocatingly movable parts 41, 42, 43 which are moved reciprocatingly independently on one another by means not shown. Alternatively, these parts may be joined to form a single unit, as illustrated in Figure 4, with common movement therebetween. Although not shown in Figure 4, it can be advantageous to provide a conical upper-part of similar wedge shape. It is assumed in the illustrated embodiment that the upper-part is stationary. The constriction illustrated in Figure 4 has three right-angled parts positioned to form a U-shaped, square cross-section. It will be understood, however, that other cross-sectional shapes are possible within the scope of the invention. With regard to the σonicity or wedge-angle of said constriction parts it has been found in practice that in the case of the fibr¬ ous material concerned and the movably arranged constriction 40 said angle shall be smaller than 15° , preferably around 5-8° , thereby providing conditions in which material will be agglomerat¬ ed or congested over a relatively short distance of movement, while enabling requisite compression forces to be taken-up in the compression section, these forces being generated by the friction between movable parts of the heating section and the compressed material batches located in said heating section, and therewith afford the possibility of introducing a fresh batch of loose material readily into the compression section from the conveyer. With regard to the longitudinal extension of the constriction 40, it is proposed that said constriction shall have a length which exceeds 50% of the length of a previously compressed batch in the heating section. The smallest cross-section of the constriction shall be reduced to less than 30%. Possibly, different percentages will apply to the width dimension and height dimensions of the heating section, preferably between 10 and 20%. The invention also enables the density of the ultimately compress¬ ed material batch to be selected readily,and it is proposed that the compression force is chosen in dependence on adapted static friction between the movable parts of the heating section and com¬ pressed material batches in said heating section with compensation for losses. It also lies within the scope of the invention for said parts or wall-parts 41, 42 and 43 to be reciprocatingly movable and to normally take a position facing towards the heating section 5 during at least the final compression stage, while arranging said parts or wall-parts for movement away from the heatings section when a fresh batch of material is introduced at the same time as the last compressed material batch is moved from the compression section into the heating section. The sequentially compressed material batches are thus moved in sequence into the heating section while loose material is intro¬ duced into the arrangement, in a known manner, by means of the conveyer 18, at the same time as the constriction 40 is moved away from the heating section 5 to form a fully exposed compression chamber. The reference numeral 44 illustrates a possibility of allowing the upper part of the wall 40 to take a position of 45", for coaction with an upper cover of corresponding form. This cover may be wedge-shaped and stationary. Although in the case of the exemplifying embodiment all parts of the constriction have mutually the same wedge-angle it will be understood that this is not absolutely necessary and that dif¬ ferent parts may have different angles. Furthermore, said parts may have a different profile shape to that illustrated. It will be understood that the invention is not restricted to the aforedescribed and illustrated exemplifying embodiment, and that modifications can be made within the scope of the claims.

Claims: CLAIMS 1. A material compressing arrangement (1) used in a machine for producing a rigid, elongated member (4) from binder-moistened loose material, comprising a compression section (7) in which binder-moistened loose material is compressed, a heating section (5) in which the compressed material is dried, and a conveyer means /which functions to cause the material compressed in the compression section to pass through the heating section (5), inter alia by virture of the fact that one or more parts of the heating section is/are able to move in the movement direction of said material, c h a r a c t e r i z e d in that a material portion or batch located in the compression section is compressed as a result of movement of the material located in the heating section towards said compression section. 2. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that said material in said heating section is moved towards the compression section by movably arranged parts or components of the heating section. 3. An arrangement according to Claim 1 or 2, c h a r a c t e r i z e d in that the material in said heating section is moved towards the compression section by movably ar¬ ranged wall-parts and/or bottom-parts of the heating section. 4. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that the extent to which the material in the compression section is compressed is contingent on the pressing force exerted by the material batches located in the heating section, said force being reducable in a controlable manner by application of one or more of the following parameters: a) a reduction in the number of heating-section parts, such as two walls, which can be moved towards the compression section without displace ment of the bottom-part and/or the upper-part; b) an increase in the release angle between said parts; c) a reduction in the speed at which the material batches pass through the heating section, with retained drying effect; d) an increase in the drying effect with maintained speed; e) selection of a glue mixture which will dry or harden at a lower temperature; f) choice of material in the glue mixture; g) an increase in the amount of glue used; h) change the distribution of drying power along the heating section; i) temperature of the glue mixture. 5. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that material batch located in the compression section is pre-compressed. 6. An arrangement according to Claim 1 or 5, c h a r a c t e r i z e d in that the material batch located in the compression section is pre-compressed by a conveyer which functions to feed material to the compression section. 7. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that the material batch located in the compres¬ sion section is pre-compressed with the aid of a screw conveyer. 8. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that, when the binder is glue and the loose material is cutter chips or sawdust, the final degree of compres¬ sion is at most 5:1. 9. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that a batch located in the compression section is compressed to a final degree of compression with the aid of friction prevailing between the material located in the heating section and said heating-section parts, acting in a longitudinal direction of the elongated member. 10. An/-arrangement according to Claim 1 or 9, c h a r a c t e r i z e d in that the final degree of compression is selected in dependence on the desired density of the manufac¬ tured elongated member. 11. An arrangement according to Claim 1 or 9, c h a r a c t e r i z e d in that a material batch compressed to a low degree of compression can be advanced to the compression section in the form of a cylindrical batch and is given its final shape during a final compression stage. 12. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that a pressure-absorbing surface located in the compression section and distal from the heating section is smaller than the cross-sectional area of the heating section adjacent said compression section. 13. A material compressing arrangement according to Claim 1, c h a r a c t e r i z e d in that the compression forces generat¬ ed in the compression section by the compressed material in the heating section are taken-up, either completely or to a signi¬ ficant extent within a converging section located between said heating section and a loose-material conveyer. • 14. An arrangement according to Claim 1 or 13, c h a r a c t e r i z e d in that said section has arranged therein a device which has a smallest cross-section which is slightly smaller than the cross-section of the heating section. 15. An arrangement according to Claim 13 or 14, c h a r a c t e r i z e d in that arranged in said section is a device which converges slightly in a direction away from the heating section. 16. An arrangement according to Claim 15, c h a r a c- t e r ir-z e d in that said device comprises a number of recipro¬ catingly movable parts. 17. An arrangement according to Claim 1 or 16, c h a r a c¬ t e r i z e d in that one of said parts has a U-shaped cross- section. 18. An arrangement according to Claim 13 or 15, c h a r a c t e r i z e d in that respective parts are allotted an angle smaller than 25°, preferably between 5 and 15°. 19. An arrangement according to Claim 13 or 15, c h a r a c t e r i z e d in that the device has a length which exceeds by 50% the length of a previously compressed material batch, located in the heating section. 20. An arrangement according to Claim 14, c h a r a c t e r i z e d in that the smallest cross-section of said device is reduced to less than 30% of the heating section, preferably between 10 and 20%. 21. An arrangement according to Claim 1 or 13, c h a r a c t e r i z e d in that the density of a compressed material batch is adapted to static friction set in the heating section between movable wall-parts and compressed material batches. 22. An arrangement according to Claim 1 or 16, c h a r a c t e r i z e d in that said parts, in a position facing towards the heating section during compression, are ar¬ ranged to be moved from the heating section when refilling with a fresh batch of loose material.

Inventors: ANDERSSON CURT, NYBOM LARS-GOERAN, ANDERSSON, CURT, NYBOM, LARS-GOERAN
Applicants: ANDERSSON CURT, NYBOM LARS GOERAN, ANDERSSON, CURT, NYBOM, LARS-GOERAN
Application year: 1990
Main classification: B27N3
IPC codes: B27N3, B30B11