Abstract:
A porous hardenable drainage element is produced from a molding compound of expanded plastics granulate and a bonding agent by virtue of the fact that the molding compound is received in a ladle having a pouring opening closed off by a mold bottom, the molding compound is pressurized in the ladle, the element is molded from the molding compound in a mold formed by lowering of the mold bottom down into an opening cross section consistent with a cross section of the pouring opening, and the element is separated from the molding compound by mutual lateral displacement of the mold and the ladle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 13/576,643, filed Oct. 11, 2012, which is a U.S. National Stage patent application of PCT/SE2011/050130, filed on Feb. 4, 2011, which claims priority to Swedish Patent Application No. 1050117-9, filed on Feb. 5, 2010, each of which is hereby incorporated by reference in the present disclosure in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a method and a device for producing a porous hardenable drainage element from a molding compound of expanded plastics granulate and a bonding agent. The invention also relates to a drainage element produced by such a method and such a device. 
     BACKGROUND OF THE INVENTION 
     Drainage elements or slabs of this kind are often not only draining, but also heat-insulating and/or capillary-breaking. They are usually produced by the molding compound being pressurized and dispersed through a nozzle orifice down into passing open face molds, which move in a circulatory path. Once a mold is filled, an accompanying cover is pressed down into the mold to compress the molding compound, so that the spherical granulates adhere to one another to such an extent that the element attains the desired strength. During the compression, the mold and the cover are flowed through by warm air to harden the bonding agent, after which the cover is removed and the drainage element is forced out of the mold with the aid of ejectors in the mold. 
     One problem with this method is that the expanded pellets of the granulate do not get evenly distributed when the compound is dispersed in the mold, so that in some areas they become less tightly packed, resulting in the formation of cavities in the molding compound. When the elements are then compressed and hardened, the cavities can remain and impair the strength of the element, especially the compressive strength, as is indicated in the appended fig. 
     In addition, the molds have defined depths, so that only elements of a given thickness can be produced with one and the same device. 
     SUMMARY OF THE INVENTION 
     One object of the invention is to provide a method and a device which are capable of distributing the granulates more uniformly in the elements. 
     Another object is to provide a method and a device which can produce elements of different thickness in a simple manner. 
     According to one aspect of the invention, the molding compound is received and pressurized in a ladle having a pouring opening closed off by a mold bottom, and the molding compound is poured, by lowering of the mold bottom, down into a mold having an opening cross section consistent with the pouring opening, after which the element having a portion of the molding compound is separated from another portion of the molding compound remaining in the ladle by mutual lateral displacement of the mold and the ladle. 
     The fact that the molding compound is displaced in this way by lowering of the bottom end of the compound into the mold means that the molding compound does not need to be redistributed inside the mold during the molding, which is the case when a passing mold according to the prior art is filled successively by inflowing molding compound. In the prior art, the pressure of the molding compound reduces when it flows into the empty mold, so that the very light expanded pellets, which stick together by virtue of the sticky bonding agent, do not get a chance to be packed sufficiently tight in the mold due to the low pressure in the mold. By contrast, according to the invention, the whole pressure continues to act on the pouring end of the molding compound throughout the molding process. In other words, therefore, the molding compound has already managed to “settle” into a tightly packed state in the ladle before it is lowered into the mold. 
     By virtue of the even distribution, an optimal packing or fill factor is obtained, in which, broadly speaking, all granulate pellets have contact with and adhere to one another. As a result, granulate which is more difficult to pack and has more bulk density than earlier can also otherwise be used to obtain the desired or necessary compressive strength of the finished drainage element. In other words, granulate with a greater degree of expansion can then be used in the molding compound in order to economize on plastics raw material, without jeopardizing the strength. 
     Moreover, the fact that the mold bottom is lowered during the molding allows the thickness of the resulting drainage elements to be easily adjusted by variation of the degree of lowering of the mold bottom along the side walls of the mold. 
     Although, within the scope of the invention, it is conceivable to strip the mold from the pouring opening by displacement of the mold transversely to the pouring opening, the stripping, in one embodiment of the invention, comprises a lateral displacement of the ladle to a new raised mold bottom for molding of a new element. A plant according to the invention can hence have a plurality of fixed molding stations, situated side by side, between which the ladle can be laterally transferred after each molding operation. This amounts to an appreciable simplification in design terms compared with when the molds move in a circulatory path past the ladle. 
     In connection with the hardening of the binding agent in the mold, the element can be compressed by placement of a counterstay against the element on the top side of the mold and raising the mold bottom. It is thereby also possible, by varying the raising of the mold bottom, to produce slabs of different degrees of compression, and thus different desired compressive strengths, of the same molding compound. By making use of this variation in compression level, it is possible to save considerable storage and production costs, since granulate with just a few different degrees of expansion is needed for the molding compound. When, according to the prior art, it is wished to change the compressive strength, granulate with a new degree of expansion for each desired strength thus needs to be chosen. 
     In the compression process, it can also be possible to lower the counterstay to a varying extent in order to obtain a more double-sided compression. 
     The compression can further be realized by repeated raising and lowering of the mold bottom. Any remaining cavities in the molding compound can hence be removed by the temporary release of any built-up tensions which wedge the pellets in wrong positions, so that the pellets can be allowed to assume their tightly packed positions. Such repeated raising and lowering of the mold bottom can be carried out a necessary number of times in conjunction with successive raising of the mold bottom. It is also possible to make the raising and lowering of the mold bottom occur with high vibrating frequency, at least during a part, for example an initial part, of the compression phase. This can be easily achieved with appropriate control of, for example, hydraulic actuators. 
     The hardening can be realized with a flow of a heated fluid, such as warm air, through the element. The fluid can flow in a closed system and pass through the element through perforations in the mold bottom and the counterstay. Owing to the closed system, no energy is then leaked to the environment. 
     The ejection of the element from the mold can be effected by raising the mold bottom to a top surface in a plane coincident with the plane for the pouring opening. The fact that the ejection force thereby acts on the whole bottom face of the element minimizes the risk of the element breaking during the ejection process. 
     A device according to the invention for producing a porous hardenable drainage element from a molding compound of expanded plastics granulate and a bonding agent comprises a ladle having a pouring opening and displaceable along a plane for the pouring opening, and a mold comprising an opening cross section consistent with a cross section of the pouring opening and a raisable and lowerable mold bottom for lowering of the mold compound from the pouring opening and down into the opening cross section. 
     The device can have members for pressurizing the mold compound in the ladle, such as propellers. 
     The device can further have a counterstay for placement against the element at a top side of the mold as the element is compressed in the mold by raising of the mold bottom. 
     The counterstay and the mold bottom can further be breached by perforations in order to allow a flow of a heated fluid through the element. The element can hence be hardened in connection with the compression. 
     The device can further have a plurality of stationary molds, located side by side, and members for displacing the ladle between the molds. In such a reverse arrangement compared with the prior art, the molds with their raisable and lowerable mold bottoms are thus stationary and do not need to be transported round in the plant. 
     Other distinguishing features of the invention can emerge from the patent claims and the following description of illustrative embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic basic view illustrating a device and a method in different stages according to the invention; 
         FIG. 2  is a plan view of a device according to the invention; 
         FIG. 3  is a perspective view with broken-off parts of a device according to  FIG. 2 ; 
         FIGS. 4-8  are perspective views with broken-off parts, showing different stages in a production process of the device according to  FIGS. 2 and 3 ; 
         FIGS. 9A and 9B  are examples of cross-sectional areas with desired tight packing of expanded granulates of a drainage element according to the invention; and 
         FIG. 10  is a cross-sectional view of a part of a known drainage slab with expanded granulates which in some areas are insufficiently packed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the schematic representation in  FIG. 1 , different stages for molding of a drainage element  14  from a molding compound  10  consisting of expanded plastics granulate and a bonding agent are shown in basic view. In a first stage A, a molding compound  10  is accommodated in a ladle  30  and is pressurized, for example by one or more propellers (only one is shown in  FIG. 1 ), which can have different height positions in the ladle  30 . The ladle  30  has at its lower end a pouring opening  32  having a cross section corresponding to an opening cross section or an upper mold opening  42  of an underlying molding station  40 . In the molding station  40  there is a raisable and lowerable mold bottom  44 , which is maneuvered by one or more actuators  46  (only one is shown) in the form of, for example, hydraulic cylinders. 
     In the first stage A, the pouring opening  32  is thus closed off by the mold bottom  44 , which lies flush with a support surface  45  for the ladle  30 . 
     In the following stage B, the mold bottom  44  is lowered with the aid of the actuator  46  down into the mold opening  42  by a fraction substantially corresponding to the thickness, prior to the below-described compression, of the resulting drainage element. An end portion  12  of the molding compound  10  is jointly transported down into the mold opening, without being redistributed. 
     During the next stage C, the ladle  30  is laterally displaced on the support surface  45  for separation or shearing-off of the end portion  12 . 
     In the following step D, a drainage element  14  has been separated. The ladle  30  has then been transferred to a new molding station  40  for molding and separation of a further element in a manner corresponding to that which has been described above. 
     After this, the drainage element  14  is compressed and hardened in a manner which will later be described in greater detail. 
     In  FIGS. 2-8 , a plant  20  having a plurality of mutually adjacent molding stations  40 , each having a respective mold opening  42  with a raisable and lowerable mold bottom  44 , is shown. The ladle  30  is common to all stations  40  and is displaceable to these with the aid of actuating members in the form of a chain transmission  60  shown by way of example. 
     As shown in greater detail in  FIG. 3 , the chain transmission  60  comprises a pair of chains  62  connected to the ladle  30 , which chains, at opposite ends of the plant  20 , pass over chain sprockets  64  connected to shafts  66  driven by an electric motor  68 . The ladle  30  can be guided in a suitable manner (not shown) along the opposite outer sides of the stations  40 . 
     As can further be seen from  FIG. 2 , the ladle  30  can have an open top side, through which the molding compound is filled through an inlet tube  70 . The molding compound can be remixed and pressurized by abovementioned propellers  34  in the ladle  30 . As can be seen, in particular, from  FIGS. 4-8 , each molding station  40 , in other words, can be deemed to have the form of a closed space, which delimits a lower part of a mold channel whose upper part is delimited by the ladle  30 . In each station  40 , the raisable and lowerable mold bottom  44  is formed by a displaceable slide, piston or plate  44 , which can be actuated by the abovementioned one or more actuators (only one is shown in each station) in the form of hydraulic cylinders  46 . 
     As is indicated in greater detail in  FIG. 8 , apart from the above-described stages A-D, the elements  14  which have been molded in the plant  20  can also be compressed and hardened in each station  40 . For this purpose, each station  40  has a cover  50 , which in the shown example delimits an inner cavity and can be swung down about an axis  58  against a just molded element  14 . The cover  50  can then form a counterstay for compression of the element  14  with the aid of the actuator  46 . 
     The compression can be effected by repeated raising and lowering of the mold bottom, so any remaining dislocations in the tightly packed structure of expanded pellets can be largely eliminated. As previously mentioned, such repeated raising and lowering of the mold bottom is effected with reduced stroke length in conjunction with successive raising of the mold bottom. It is also possible to make the raising and lowering of the mold bottom occur with a high vibrating frequency, at least during a part, for example an initial part of the compression phase, with a view to vibrating the granulates so that they assume their tightly packed positions. This can be achieved with suitable known control members for the hydraulic cylinders  46 . 
     In  FIGS. 9A and 9B  are shown examples of sought-after tight packing of expanded granulates  100  in a cross-sectional area of a drainage slab  14 . Other configurations of a sought-after tight packing can also be found. A hardened bonding agent  102 , such as a water soluble thermosetting adhesive, encloses the granulates  100 , so that they become watertight. The hardened bonding agent  102 , moreover, bonds the granulates  100  at their contact points. The resulting drainage element  14  thereby acquires a coherent, draining, heat-insulating and capillary-breaking cavity structure in the spaces between the granulates  100 .  FIG. 10  shows by way of comparison a cross-sectional area of a sawn-through drainage element  14  according to the prior art. As can be seen from the darker portions inside the cross-sectional area, the element  14  has an undesirably large cavity structure as a result of imperfect packing of the granulates  100  during the molding and compression of the element  14 . A large cavity structure of this kind can give the drainage element  14  an altogether inadequate strength, in particular compressive strength. 
     As previously mentioned, it can be possible, in a manner which is not shown, also to arrange the cover  50  such that it can be raised and lowered, in order to possibly further improve the compression. 
     In  FIG. 8  it is shown that during the compression a heated fluid, such as warm air, is brought to flow through the element  14  via perforations  52  in the mold bottom  44  and in a cover bottom  54  of the cover  50 , in order to harden the bonding agent in the mold compound. For this purpose, the mold bottom  44  and the cover bottom  54  can also be formed of a grid structure (not shown). From a closed and expediently heat-insulated pipe system, the heated fluid can enter into each station  40  through inlet openings  48  and exit from each cover  50  through outlet openings  56 . In a manner which is not shown, the stations  40  can also be integrated as a coherent elongated unit, through which the heated fluid can flow freely to each station and exit through the respective cover  50 . 
     Once the bonding agent has hardened, the cover  50  can be swung back up into a vertical position indicated in  FIG. 2 . The axis  58  can be located at a distance somewhat above the stations  40 , so that a raking member  82  of a pusher  80  can pass under the cover  50  and push away the finished drainage elements  14  from the plant  20  to a conveyor  90 , such as a belt conveyor, for further handling, such as stacking and packaging of the elements  14 . 
     The above-detailed description is primarily intended to facilitate understanding, and no unnecessary limitations of the invention should be inferred from this. The modifications which become apparent to a person skilled in the art when examining the description can be made without deviating from the inventive concept or from the scope of the following patent claims.