Abstract:
The invention relates to a method for applying fluids, especially particle material, on a area that is to be coated, wherein the fluid is applied on the area to be coated in front of a blade when observed from the direction of forward movement of the blade and said blade is then displaced on the applied fluid. The method is characterized in that the blade performs an oscillation similar to a rotational movement.

Description:
CLAIM OF BENEFIT OF FILING DATE 
     The present application claims the benefit of the filing date of PCT Application Serial No. PCT/DE02/01103, (filed Mar. 26, 2002) (published as WO 02/083323) and DE 101 178175.1 (filed Apr. 10, 2001), the contents of which are hereby incorporated by reference in their entirety. 
     FIELD OF THE INVENTION 
     This invention concerns a procedure and a device for applying fluids in accordance with the general definitions of the independent claims. The invention also concerns the use of such a device. 
     BACKGROUND OF THE INVENTION 
     In many areas of technology, there is a need to apply fluids—especially those comprising particle material—in thin layers on to a carrier. In many such cases, it is also necessary for the applied layers to have the smoothest possible surface. 
     For example, a smooth application of particle material to be bonded plays an important role in rapid prototyping procedures. 
     A rapid prototyping procedure for creating casting patterns is known from DE 198 53 834.0, for instance. In this case, untreated particle material like quartz sand is applied in a thin layer to an assembly platform. A spraying device is then used to finely distribute bonding agent all over the particle material. After that, a hardener is applied over selected sections in order to strengthen corresponding areas of the particle material. This process is repeated several times to individually mould a body from the bonded particle material. This body is initially embedded in the surrounding, unbound particle material, from where it can be subsequently removed following completion of the assembly phase. 
     If this type of rapid prototyping procedure involves the use of quartz sand as the particle material and furan resin as the bonding agent, for example, a hardener comprising sulphuric acid can be used to produce a mould comprising a common substance familiar to experts. 
     Difficulties arising during these well-known procedures are often posed by the smoothest and thinnest possible application of particle material; this influences the layer thickness, i.e. the smallest unit and therefore also the accuracy at which the mould can be produced. 
     One procedure of applying a layer of powder on a surface is known from EP 0 538 244 B1; in this case, the surface is fed with powder and then travelled over by a roller which rotates slowly in a direction opposing its linear travel over the surface. The powder makes contact with the roller rotating in the opposite direction and is thus distributed in a layer on the surface as the roller travels over it. This coating technique prevents any significant shear stress from being exerted on previously applied layers and the mould from being damaged as a result. 
     U.S. Pat. No. 5,902,537 also describes the application of particle material by means of a roller rotating in a direction opposing its linear propagation. 
     However, if such coating techniques involve the use of powders with a strong tendency to form agglomerates, for instance, particle material possessing a very fine grain or a content of binder, it proves very difficult to apply the material in a thin and smooth layer. The particle material tends to form lumps which stick to the roller, thus preventing achievement of a smooth surface. 
     Given the use of particle material—especially with a tendency to form lumps—a counter-rotating roller also has the disadvantage of heavily soiling all components which make contact with the particle material, thus entailing more frequent maintenance and proving more expensive. 
     Similarly, the coating technique described in U.S. Pat. No. 5,730,925 is not capable of achieving smooth surfaces with powders tending to agglomerate, because the powders also form lumps and result in rough surfaces in this case. 
     U.S. Pat. No. 6,036,777 describes a device for applying powder to a surface. A distributor moving across the surface to be coated applies layers of powder on it. The distributor operates in conjunction with a vibrating mechanism for compacting the powder. 
     This vibrating mechanism also proves disadvantageous, the vertical exertion of force on the particle layer producing an undesirable compression effect which causes uneven compaction of the required mould or model. This results in uncontrolled displacements in the mould during its fabrication on the powder bed, thus impairing the production accuracy. 
     Under certain circumstances, particle material with a strong tendency toward agglomeration might even make it completely impossible to produce smooth layers. 
     However, it is precisely a generation of smooth powder layers which proves extremely important in many applications. In the case of the rapid prototyping procedure described in some detail earlier, it is essential to apply particle layers as thinly and evenly as possible in order to maximize the accuracy of component production. Layer thickness constitutes the smallest possible increment during step-by-step component build-up. The thicker and rougher the layers, the less accurate the shape of the final cast. 
     SUMMARY OF THE INVENTION 
     Accordingly, the purpose of this invention is to provide a device and procedure making it possible to distribute fluid in the most homogeneous manner on surfaces needing to be coated. 
     The invention solves this problem by providing a technique of applying fluids of the previously mentioned type by means of a blade vibrating in a circular motion. 
     In this type of technique, it turns out that the layer—comprising particle material, for instance—applied to the surface to be coated is fluidized by the blade&#39;s vibrating, rotary motion. This not only permits an extremely smooth and even application of particle material with a strong tendency toward agglomeration, but also makes it possible to influence fluid compression through the vibrations. 
     If the procedure forming part of the invention is embodied preferably so as to apply excess fluid to the surface to be coated, the blade&#39;s perpetual, rotary oscillation during its forward movement distributes the excess fluid/particle material evenly by forming it into a roll leading the blade&#39;s travel. This fills any cavities between small particle lumps and breaks up large lumps of particle material through the roll&#39;s motion. The particle material inside the roll is homogenized. A small proportion of the particle material leading the blade is drawn in through a gap below the blade, where it is compressed and applied as an even layer. 
     Application of the fluid or particle material to the area in front of the vibrating blade as it travels forward can take place in any manner familiar to experts. For instance, it is thinkable to feed the substance from a reservoir via a conveyor belt. 
     In particular, it is possible to realize the feed as described in DE 195 30 295, whose disclosure is referred in full measure. 
     It is also possible for a reservoir travelling with a recoater and containing particle material to continuously apply a certain amount of this material to the surface to be coated in front of the recoater and the moving blade. In this process, the reservoir&#39;s contents can be controlled via another, stationary vessel or supply source. 
     A vessel open at the bottom is included to maximize the precision of dosing particle material—which might be moist under certain circumstances—on a surface. The sand is compressed in a nearby vibrating channel to form an angle of repose. On actuation of the vibrating channel, the sand flows continuously out of the vessel. 
     A defined dosage of particle material could also be achieved with the help of a corrugated conveyor belt which seals off the reservoir at its open bottom and which—when actuated—spreads the sand lying in its recesses on the surface to be coated. This could be aided, for example, by a shaking motion. 
     For the procedure forming part of this invention, it proves advantageous if the blade rotates about an axis positioned above the surface to be coated, as viewed in the direction of fluid propagation. 
     The procedure forming part of this invention is able to achieve especially favourable results if the circular vibrations are executed in an angular range between 0.1 and 5°. 
     Also especially suitable for implementing the procedure forming part of the invention is a device for applying fluids—particularly those comprising particle material—on surfaces to be coated; this device consists of a blade with a leading dosage unit which applies fluid to the surface in front of the blade which then passes over the applied fluid. This blade is mounted so as to be able to vibrate in a circular motion. 
     In a preferred embodiment of this invention, the blade should be positioned so as to rotate about an axis positioned above the surface to be coated, as viewed in the direction of propagation of the fluid/particle material. 
     Furthermore, it proves advantageous to mount the blade such that it oscillates in an angular range between 0.1 and 5°. 
     If the blade extends over the entire width or length of the surface to be coated, the time taken by the layering procedure is minimized. End-to-end layering performed simultaneously in this manner also results in a smoother coat. 
     If, in a preferred embodiment of this invention, the blade is essentially aligned orthogonally with respect to the surface to be coated, the axis of rotation can be situated as far away as possible from this surface, thus maximizing the angular adjustment accuracy. 
     If the blade is aligned at an angle to the orthogonal axis of the surface to be coated, layer properties can be improved further through the use of certain fluids. 
     The device can be designed so as to drive the blade by means of at least one fast electric motor whose eccentric causes the blade to vibrate. 
     The blade should be shaped so as to allow the formation of a leading, intermediate reservoir of excess fluid in the direction of the blade&#39;s travel during operation of the device; this reservoir should preferably have the form of a roll. If the blade is also shaped to provide a sufficiently large inlet for particle material while moving, this allows a reliable and continuous intake of material. 
     Very favourable results are also obtained if the blade possesses rounded edges, the particle material inlet then being described by the radius defining the edge of the vibrating blade. 
     If, in another preferred embodiment, the vibrating blade consists of two parts—a moulded blade body and a fixture—it is possible to unscrew and replace the blade body in the event of damage due to wear, for instance. 
     As already mentioned on several occasions, the device according to the invention has proven especially suitable for applying particle material containing binder. 
     In this context, the device is particularly suitable for procedures involving a production of casting patterns. 
     Other advantageous aspects of this invention are indicated in the sub-claims and the general description. A more detailed explanation of the invention is provided with the help of the following, preferred sample embodiments with references to the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A device for applying particle material on a surface to be coated; 
         FIGS. 2   a ) and  b ) The geometry of a vibrating blade according to a first embodiment, perpendicular and inclined with respect to the surface to be coated; 
         FIG. 3  An additional vibrating blade with an improved geometry compared with the vibrating blade in  FIG. 2 ; 
         FIGS. 4   a ) and  b ) An additional vibrating blade with an improved geometry compared with the vibrating blade in  FIG. 2 , perpendicular and inclined with respect to the surface to be coated; 
         FIG. 5  Formation of a roll in front of the vibrating blade; 
         FIG. 6  Microscopic enlargement of the produced layer; 
         FIG. 7  Microscopic enlargement of the produced layer, flattened in parts; 
         FIG. 8  Action of a vibrating blade as defined by the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The procedure and device forming part of the invention are exemplified in a rapid prototyping procedure described in the following and involving a layer-by-layer production of casting patterns using particle material, bonding agent and hardener. 
     In particular, the employed mixture of particle material and bonding agent is assumed to exhibit a strong tendency to form lumps, as is usually the case in practice. 
     However, the use of such a particle material proves advantageous by eliminating the need for layering the material with binder—a step normally required by the rapid prototyping procedure—and thus making the coating technique faster and more cost-effective. 
     Use of the procedure and device forming part of this invention has proven especially beneficial in the case of particle materials possessing a tendency to agglomerate. 
     Particle materials with a small/medium grain size of less than 20 μm and wax powder also exhibit a strong tendency to agglomerate. 
     In a component moulding technique such as the one described in  FIG. 1  and involving a casting pattern, an assembly platform  10  serving as a base for configuring the mould is lowered by an interval corresponding to one layer thickness of the particle material  11 . After that, the particle material  11  comprising quartz sand, for instance, and mixed in a preferred embodiment with 2% binder (such as Albertus 0401 or Resifix by Huttenes) is applied in the specified layer thickness to the assembly platform  10 . This is followed by a selective application of hardener to areas requiring hardening. This can be done, for example, by means of a drop-on-demand dispenser operating similar to an ink-jet printer. These application steps are repeated to obtain the finished component, embedded in loose particle material  11 . 
     According to a preferred embodiment, a plastic blade  1  executing a rotary motion  12  about an axis  12 A is positioned above the assembly platform. The rotary motion  12  of this blade  1  is supplied by a fast electric motor whose eccentric causes the blade to vibrate. 
     The employed motor, for example, has a rated speed of 3000 rpm at 12 V, while the eccentric has an amplitude of 0.54 mm which results in an amplitude of 0.85 mm for the blade tip in the example described. A speed of 4050 rpm was measured at 15 V. This value corresponds to 67.5 Hz. Depending on the width of the blade  1 , it might be necessary to install several drive units. 
     The travel of the vibrating blade ( 1 ) over the surface to be coated—assembly platform  10  in this case—is regulated by laterally installed guides  13 . The drive power is supplied preferably by at least one motor with the following linkage, for instance: a cog belt routed via two idlers in parallel with the guide rail and fastened to the vibrating blade&#39;s fixture, one of the idlers being powered. 
     The volumetric tolerance of the coating system or recoater forming part of the invention makes it possible to deposit a substantial quantity of particle material  11  in front of the vibrating blade  1  at the beginning of the coating process, this quantity proving sufficient for the entire assembly platform  10 . In accordance with the represented, preferred embodiment, this is achieved through the use of a stationary vessel  14  which is emptied via a vibrating channel  15 . The vessel  14  accordingly has an open bottom facing the assembly platform  10 , the particle material  11  in the vessel  14  being compacted via the vibrating channel  15  located close to the outlet as well as the angle of repose forming in this process. On actuation of the vibrating channel  15 , the quartz sand  11  emerges continuously from the vessel  14 . 
     Experiments have shown that the procedure forming part of the invention benefits from a relatively high dosage of excess particle material  11  which ensures a sufficient availability of this material even at the end of the assembly platform. The fed quantity should exceed the required quantity preferably by at least 20%, excess proportions of up 100% proving advantageous in some cases. The excess quantity of particle material  11  is ultimately pushed by the vibrating blade  1  into a linear shaft  16  located at the rear of the assembly platform  10 . 
     To prevent a depletion of unused particle material  11  through excess dosage, the material is fed back to the reservoir  14 . For this purpose, the coating element  17  is furnished with an intermediate vessel  18  for storing the layer volume and excess volume of the particle material  11 . This intermediate vessel is filled from the reservoir  14  via the vibrating channel  15 , moves rapidly over the specially lowered assembly platform  10  to its other end, deposits its contents in front of the vibrating blade  1 , waits for the assembly platform to be returned to its correct height, and then commences coating while proceeding toward the reservoir  14 . Once there, excess particle material  11  is returned to the reservoir  14  by a lifting unit. This process is indicated by the arrow  19 . 
       FIG. 2  shows a vibrating blade  1  in an initial embodiment, positioned perpendicularly  FIG. 2   a ) and at an angle  FIG. 2   b ) with respect to the surface to be coated  2 . The forward motion of the vibrating blade  1  is indicated by the arrow  21 . 
     As shown in particular by  FIG. 2   b ), the geometry of the vibrating blade  1  represented in  FIG. 2  can result in a roughening of the previously produced, essentially smooth layer during reversal of the edge  3 . 
       FIG. 3  shows a vibrating blade  1  with an improved geometry compared with  FIG. 2 ;  FIGS. 4   a ) and  b ) show yet another vibrating blade  1  with an improved geometry compared with  FIG. 2 , positioned perpendicularly ( FIG. 4   a ) and at an angle ( FIG. 4   b ). 
     The blade  1  in  FIG. 4  differs from the one in  FIG. 2  by virtue of the fact that its edge  3  is slanted to allow particle material to be drawn in below the blade  1  even during reversal. This makes it possible to achieve smooth layers on the surface to be coated even during reversal of the blade  1 . 
     Especially favourable results are achieved if the speed of blade  1  is set to a value of up to 70 mm/s, preferably 60 mm/s. At excessively high speeds, quality of the surface coating can drop again. 
     A blade speed corresponding to 60 Hz and 50 mm/s proves particularly advantageous. 
     Extremely smooth layers entail a small, relative, reverse movement of the blade  1 , short of causing the blade to re-enter the surface area just coated. 
     This type of application does not produce any shear fissures in the material coating which otherwise always occur during layering by means of a counter-rotating roller. 
     Surprisingly, an excess of particle material  11  in front of the blade  1  turns out to provide favourable results. Even extremely large accumulations of particles in front of the blade  1  can be transported easily over the surface to be coated  2 . 
       FIG. 5  shows roll formation  4  in front of the vibrating blade  1  whose direction of forward motion is indicated by the arrow  21 . 
     Once the particle material  11  which has accumulated in front of the blade  1  no longer fits on the roll  4  formed in a curvature  5  of the blade  1 , it is simply transported in chunks above the roll  4 . As these chunks do not make any contact with the underlying layer, nor do they generate any shearing forces which could damage the newly created layers. 
     Even substantial soiling such as hard lumps of sand and broken bits of crust are thus easily transported together with the excess particle material to the end of the assembly area and pushed into the overflow line. 
       FIG. 6  shows a microscopic enlargement of a layer produced with particle material  11  containing binder. A hardening drop  6  with a diameter of roughly 4.5 mm has been applied to the layer. As opposed to dry sand, whose grains are drawn together by the capillary force of the liquid to form a type of wall on the outside of the moist area, the layer here remains completely even. 
       FIG. 7  shows that flattening does not necessarily improve the produced layers. The round indentation  7  in the lower, right-hand corner of the picture was produced by means of a spatula tip. However, it turns out that the action of a hardening drop  6  does not change notably if the drop is applied to this more densely compressed surface. A lower tendency to trickle at the edge of the drop  6  cannot be observed. 
       FIG. 8  provides a schematic representation of the action of the vibrating blade  1 . This edges of this particular blade are essentially aligned vertically with respect to each other, the edges facing the surface to be coated  2  rounded by radii of  20 A and  20 B. Radius  20 A describing the front of the blade  1  as viewed in its direction of forward motion is equal to 3 mm in the preferred embodiment represented here. 
     A roll  4  comprising excess particle material  11  is formed at the front  5  of the vibrating blade  1  and extends along its entire width. The continuous rolling motion homogenizes the material making up the roll  4 . Accordingly, the device forming part of the invention is able to make excellent use of an excess dosage of particle material. The excess quantity leads to the formation of a roll  4 . A failure of this roll to develop fully during the procedure forming part of this invention can result in flaws in the particle layer on the surface to be coated  2 . 
     A small proportion of the particle material  11  from roll  4  is drawn in through the gap formed by radius  20 A below the blade  1 , where it is compressed and applied evenly to the surface to be coated  2 . The geometry of the vibrating blade  1  should provide a sufficiently large inlet for the particle material  11  to ensure a reliable and continuous intake of material through this gap and prevent an impermissibly high compression of the fluid to be applied. 
     In  FIG. 8 , A designates the homogenization zone, B the compression zone, C the smoothing zone and D the compression zone on the return stroke. To avoid excessively high compression, the edge of the vibrating blade  1  facing its forward direction of travel  21  is also adequately rounded by a small radius  20 B. 
     If required during operation, it should also be possible to additionally smoothen the applied layer of particle material  11  during reversal of the blade  1  in the direction opposing the arrow  12 . For this reason, the rear edge has also been designed to permit material intake, even if only to a minor extent. 
     In general, the transitions between individual edges of the vibrating blade  1  should be well-rounded in order to achieve favourable results. This can be accomplished, for instance, by slightly chamfering the edges or furnishing them with curvatures as described previously. 
     In addition, conditions in the compression zone B can be adjusted easily and quickly by changing the inclination of the blade  1 . This would also make it possible to operate the blade  1  without any compression, potentially advantageous during coating with dry sand. 
     Best results are achieved if the blade  1  oscillates about its neutral position, defined here as the vertical alignment with respect to the surface to be coated. 
     The procedure forming part of this invention also permits an easy application of sand mixed with binder in a layer thickness of just 0.3 mm. 
     Indeed, layers less than 0.2 mm thick are achievable in some cases, even in the presence of relatively coarse material grain. This grain is either integrated into the pores of the layer last applied, given a compatible size, or prevented entirely from passing through the gap below the blade, instead being pushed ahead on the roll situated before the blade. 
     The packing density of the layer produced by this invention is relatively low, thus resulting in a relatively high porosity which, however, is nevertheless considerably lower than that obtained with dry sand applied by means of a slotted coating device.