A METHOD AND A SYSTEM FOR MANUFACTURING SHAPED OBJECTS OF WOOD DUST

Abstract: It is attractive to produce small wooden objects, e.g. pipe heads or furniture handles, by a moulding process based on an aqueous suspension of wood dust, but by the attempts made so far the process time has been so long that it has not been economical to produce objects with a required high quality by such a technique; one important thing is that the moulded objects should be dried out to a very low content of water. With the invention a very short process time is achieved by the use of injection mould parts (32), in which electrodes (34) are placed for subjecting the moulding cavities (8) to a HF-heating field such that both a rapid curing of a heat setting glue agent in the aqueous wood dust mass and a rapid driving out of the major part of the water will be obtained. The moulding cavities (8) have exhaust channels (24, 26) for the steam, and the means (6) for holding the mould parts (2 and 4) together are designed so as to be able to be effective by the very high steam pressure that is developed in the mould cavities.

Description: A method and a system for manufacturing shaped objects of wood dust. The present invention relates to a method of manu¬ facturing moulded bodies based on wood dust, e.g. smok¬ ing pipe heads. According to FR-547.636 it has already been proposed to manufacture pipe heads by a moulding process, by which the preferred pipe wood, viz. bruyere, can be used in dust form in a moulding mixture holding various binding and curing agents. In the conventional manufacturing of pipes of pure bruyere wood there is a large waste, and the wood can be utilized much better if it can be used in dust form as a significant constituent of a suitable moulding material for the production of the pipe heads. It is to be noted, however, that in the method according to FR-547.636 the moulding substance contains less than 50 % of wood, while the remaining components are not all too suitable from an environmen¬ tal point of view. Also US-A-2,352,201 deals with the moulding of pipe heads with the possible use of bruyere dust, but the product is mainly a plaster product, which is not too attractive. It is the purpose of the present invention to pro¬ vide a method, by which it is possible to produce moulded bodies such as pipe heads having a very high content of wood dust and being economically producible with a brief processing time, e.g. of the magnitude 30 sees., while in FR-547.636 a curing time of 60 hours is mentioned. The invention, however, goes a large step further in suggesting a moulding of many other small objects of wood than just pipe heads, or a moulding of larger ob¬ jects for that sake. The invention is based on the con¬ sideration that in the wood laminating technique there has been a remarkable development, which has made it possible, by means of special binding agents and curing methods, to obtain a rapid and very effective bonding between thin wooden plates in sandwich products, and according to the invention it should then be possible to achieve a correspondingly effective binding together of wood particles in a moulding compound, which is prepared with an absolute predominance of wood dust and only with the required minimum of binding and curing agents and is subjected to a similar curing treatment. It is essential that it is possible to hereby pro¬ duce the moulded bodies with a very high content of wood dust, such that the bodies will get the full character of real wooden products, which, by way of example, can be painted in quite the same manner as adjacent wooden parts, e.g. in case of moulded furniture handles. The same cheap wooden elements, when made by moulding, may even exhibit increased durability, as in the products there will be no weakening veins or stratifications. The modern binding agents as developed for binding together the plate elements in laminated wood products are both effective and friendly to the environment, and when it is pertinent in the present connection to bind together tiny wood particles in the form of wood flour or small chips it may be sufficient to use only a few percent of binding agent, such that the products may consist of e.g. 96 % wood, i.e. they will be practically purely wooden products. With the use of wooden chips the moulding will result in objects having a structured surface, which will not, of course, be similar to a natural wood sur¬ face with veins, but when unpainted it will still be more 'living' than e.g. a moulded plastic surface. The very brief processing time which can be ex¬ ploited with the invention is based on the use of high frequency heating. The modern, harmless binding agents are water based and are therefore easily heatable for curing by the influence of a high frequency field, which will be true not only when joining wooden plate ele¬ ments, but also when joining wooden particles in a moulding. For this reason, in connection with the inven¬ tion, it is possible to operate with such a brief pro¬ duction time that it will be highly economical to pro¬ duce 'wooden members' by moulding rather than by conven¬ tional shaping techniques such a copying cutting. This may apply to pronounced small wooden objects such as pipe heads or drawer handles, but also to larger objects such as clog soles, tortuous furniture legs or whole door blades. For the moulding mould parts can be used which are held together with a high pressure. This is required because a violent evaporation of water takes place during the desired rapid heating treatment for the curing of the binding substance, whereby the mould parts are affected away from each other. The water content should be as low as possible, though sufficient for the mixture of wood particles and binding agents to assume a character of a paste having a sufficiently low viscosity for being injectable into the mould cavity or cavities; this injectability, however, can be improved with the use of a minor amount of a gliding agent such as carboxy methyl cellulose or polyvinyl alcohol, whereby still less water can be used. The binding agent can suitably be a melamine glue, but more of the glues developed for the said production of laminated wood will be applic¬ able. It is important that the water content be kept as low as possible, because after the brief heating treat¬ ment the residual water content in the mouldings should be low, as these may otherwise tend to crackle. The mould parts in which the mouldings are made should be constructed from a very rigid material having good dielectric properties, and no metallic parts, even metal chips, should be present in the area where the high frequency field is applied. The field may suitably be applied between electrode plates built into the mould parts themselves, such that they can be situated rela¬ tively close to each other at the respective opposite sides of the moulding cavities. In the following the invention is described in more detail with reference to the drawing, in which:- Fig. 1 is a perspective view of a tool set for manufacturing objects according to the invention, Figs. 2 and 3 are lateral sectional views of these tools, shown in slightly open and fully closed position, respectively, Fig. 4 is a perspective view of a moulding, Fig. 5 is a similar view of a finished product, and Fig. 6 is a perspective X-ray view of a mould for the production of pipe heads. In Fig. 1 is shown a pair of mould parts 2 and 4, which can be arranged just as the mould parts in an ordinary injection moulding machine for plastic, i.e. with a fixed mould part 2 and a movable form part 4, the latter being carried on or by rearwardly projecting rods 6 connected to a mechanism for pushing forward and re¬ tracting the mould part 4 to and from a position in which it its pressed firmly against the mould part 2. In the interfacing front sides of both mould parts there are provided cooperating moulding cavities 8, and in the rear side of the mould part 2 there is provided a cen¬ tral inlet opening 10 for receiving an injector head 12 on a supply pipe 14, in which there is mounted, in a conventional manner, a feeder worm for conveying the moulding material from a non-illustrated supply con¬ tainer to the opening 10. The pipe 14,12 is displaceable in its axial direction, such that it can be moved be¬ tween a projecting position in engagement with the open- ing 10 and a retracted position spaced therefrom. As shown in Fig. 2 the opening 10 continues in a conical central channel 16 towards the front side of the mould part 2, where it merges into a depressed area 18, from which moulding passages 20 extend to the said moulding cavities 8; from these further passages 22 extend diagonally outwardly to the corners of the mould¬ ing part. The front side of the fixed mould part is shaped correspondingly.. At different places of the bottom areas of the cavities 8 air holes 24 are pro¬ vided, connected through channels 26 with outer connec¬ tor valves for pressurized air, for blowing out the mouldings from the moulding cavities 8 Each of the moulding parts 2 and 4 are made from two heavy plate portions 30 and 32 consisting of a very strong resin material with good dielectrical properties, the plate portions being tightened together about a metallic intermediate layer 34, which forms an electrode in an HF heating system, each of these metal plates being connected to a non-illustrated high frequency generator through a wire 36. Usually such electrode plates, i.e. anode and cathode, respectively, are made of aluminium, but with the invention it is relevant to transfer such high pressures through these intermediary plates that it is preferred to let them consist of medium hard brass. All edges on the plates should be rounded, also such hole edges which occur around the inlet opening 16 and around throughholes for spanner bolts 38 through the single mould parts. The electrode plates 34 should be kept free of metallic parts both in the space between them and in the respective rearward directions, at a minimum distance of some 10 cm. Since the movable mould part 4 is guided by metallic rods 6 the rear block plate portion 30 thereof should thus have a considerable thickness, while the electrode plates may be located quite close to the bot- torn areas of the moulding cavities 8. Correspondingly, as far as the fixed mould part 2 is concerned, the rear block plate 30 shall insulate the electrode plate 34 from metallic mounting means at the rear side of the mould part, but here there is the further circumstance that the supply pipe 14,12 for injecting the moulding material is located inside the opening 10, i.e. very close to the electrode plate 34. It is required, therefore, that this supply pipe after each injection be retracted from the rear side of the mould part 2 into a safe distance from the electrode plate 34 before the HF heating is initiated. If local concentrations of HF energy exist as a consequence of the presence of metallic parts in or near the field between the electrode plates 34, then burnings of the mould part material will easily occur. For effecting a moulding operation the mould parts 2 and 4 are pressed firmly together, and the worm pipe 14,12 is moved into engagement with the opening 10, whereafter the worn in the pipe 14 is actuated to dose in a suitable amount of moulding material into the joined mould. The injection pressure may be e.g. 900 kp/cm 2 , while the pipe nozzle 12 may engage the opening 10 with a pressure of some 5 tons. The closing pressure between the mould parts 2 and 4 has to be considerably higher, e.g. some 200 tons for a moulding volume of 300-400 cm 3 . A suitable material for the block plates 30 and 32 as well as for the bolts used for holding together these parts is G-Etronax EP 11 (Elektro-Isola, DK) . This mate¬ rial is a glass web/epoxy product, which has good di¬ electrical properties and is sufficiently pressure and heat resistant. After the injection of the moulding material the situation will be as shown in Fig. 3. Sufficient mould¬ ing material has been introduced for filling the cavi- ties 8 entirely, and preferably this is driven so far that the material, as indicated, comes out of the outer ends of the outer passages 22, whereby the total filling can be ensured by visual inspection from time to time. The injection can take place within a few seconds, whereafter the nozzle pipe 14,12 is retracted to a posi¬ tion in which its nozzle mouth has been removed e.g. 10 cm from the electrode plate 34 in the fixed mould part 2. Thereafter the HF generator is actuated for effect¬ ing a powerful heating of the moist moulding material in the moulding cavities, such that the water is driven out by a strong evaporation, viz. out through the outwardly open channels 10 and 22. The required heating time may depend of the thickness or volume of the moulding. In the example shown the moulding is a body for the making of eight furniture handles as shown in Fig. 5, and the total volume of this body can be e.g. 325 cm 3 . A suit¬ able heating time will be 15-20 seconds, this on the other hand being sufficient; it would be possible to make use of a still stronger HF field for driving out the water still more rapidly, but hereby the stability of the moulding system would be jeopardized, as a very high inner steam pressure is created. Preferably the heating should not be driven beyond some 95°, but gene¬ rally the temperature range 75-100° should be used, and the applied HF effect should be adjusted accordingly. By its injection into the mould the moulding material should not give rise to any considerable development of friction heat, since hereby a hardening of the glue agent may be initiated already prior to the mould being filled. This could speak for a rather high percentage of water, e.g. 20 %, but as already mentioned an alterna¬ tive is the use of a very small amount of a gliding agent, e.g. an amount of 0.1-2.0 % of the dry glue mate¬ rial. After the HF heating the mould parts are separated, whereby the entire, hardened moulding body will remain seated in one of the mould parts. The moulding, as indi¬ cated in Fig. 4, is blown out of the mould part by means of compressed air that is introduced through the chan¬ nels 26 and the valves 28, these being check valves in order to counteract an intrusion of moulding material into the channels. Upon its rejection from the mould part the moulding body is cut along the dotted lines s in Fig. 4, whereby a total of 4 x 2 handle members 40 as shown in Fig. 5 are formed; these members may be pro¬ vided with a drilled hole 42 in their respective end faces. By the said cutting these members will appear with overall unbroken moulding surfaces. The applied wood dust can range from flour over slip and sawdust to small chips. With the use of semi- large particles an attractive structuring of the surface of the members can be achieved, what may be desirable for members not to be painted. As the glue agent may be used a powder of urea formaldehyde which is mixed with water in the ratio 2:1, whereafter the mixture is left overnight and is then used for being mixed into the dry granular wood in a proportion of approximately 1:4. It is possible, how¬ ever, to use more advanced types of glue for lowering the glue consumption considerably, e.g. to only a few percent. As an example of such a glue can be mentioned a melamine glue "Melurit 100" (A/S F.Heimann & Co., DK) , which is prepared with a hardening agent. Also the said gliding agent can be incorporated therein. It has been found advantageous to use in the mix¬ ture of an amount of a puzzolane in the form of spherical flyash with small particle size. Presumably this material is actuated as a binder by the high pro¬ cess pressure. Fig. 6 schematically indicates a production tool 44 for pipe heads, provided with HF electrode plates 46 and a core body 48 of a dielectrical material for the shap¬ ing of the combustion chamber of the pipe head. It has previously been proposed to produce such heads by mould¬ ing, also with the use of bruyere wood dust, but not until the present invention it has been economically possible to establish such a production with the use of a moulding material ail-predominantly consisting of the bruyere dust, such that there is now provided a rea¬ listic basis for a much better exploitation of the ac¬ cessible bruyere material. In the foregoing, the material specified has been 'wood dust', but it should be noted that the invention is not limited to the use of just 'wood', as there are other vegetable materials which can be used, e.g. straw material.

Claims: C L A I M S : 1. A method of manufacturing moulded bodies based on wood dust, whereby a moulding material containing wood dust, glue agent and water is filled into a mould and is pressed therein, characterized in that the glue agent is of a heat actuated type, that the moulding is heated by high frequency heating, the moulding being placed in the mould in a space between opposed HF elec¬ trodes and being heated until the major parts of its water content has been exhausted by evaporation, and that the mould parts are held together with a high pres¬ sure for resisting the steam pressure created by said evaporation. 2. A method according to claim 1, characterized by the use of a melamine glue in admixture with a gliding agent and optionally with an amount of spherical flyash. 3. A method according to claim 1, characterized in that the process time of the moulding process is kept at approximately 30 seconds or less. 4. A system for carrying out the method claimed in claim 1, comprising opposed mould parts that can be held strongly against each other, characterized in that the mould parts are made as non-metallic parts with good dielectrical properties, and that they comprise or have at their rear sides respective electrode plates belong¬ ing to a HF heating system. 5. A system according to claim 4, characterized in that the electrode plates are tightened between mould part elements and consist of brass or a corresponding hard material of high conductivity. 6. A system according to claim 4, characterized in that the mould cavities in the mould parts are connected with channel means that are open to the surroundings.

Inventors: ANDERSEN ULRIK FLOTT, ANDERSEN, ULRIK, FLOTT
Applicants: ANDERSEN ULRIK FLOTT, ANDERSEN, ULRIK, FLOTT
Application year: 1990
Main classification: B27N5
IPC codes: A24F1, B27N5, B29C35, B29C43, B29C45, B29K103, D21J3