HK1062157B - Method and device for making door skin and hollow core door and for moulding wood fibre board - Google Patents

Description

Method and apparatus for manufacturing door panels, hollow doors and molded wood fiber slabs

The present invention relates to a method and apparatus that can be used in wood fibres, especially but not exclusively in complex shapes of widely differing height, so-called MDF (medium density fibreboard). The deformation of wood fibre boards that can be achieved with the invention is called extrusion, whereby a significant plastic deformation takes place with the flow and stretching of the material.

The deformation of wood fibre boards is known from international patent application WO 96/03262. With the method disclosed in this patent application, it is possible to bend wood fibre boards with a bending radius of a minimum of 2.5 times the thickness of the board.

It is known from other publications, such as european patent application 0420831, to provide wood fibre boards with a form by subjecting the wood fibre board to a pressing operation. The desired profile in this case is formed by locally varying the amount of compression of the material.

In view of the limited amount of deformation in the prior art fiberboard processing, it is an object of the present invention to provide a method of deforming a wood fiberboard to form thereon an area having a sufficiently large difference in height with respect to the fiberboard.

By the method according to the invention as indicated in claim 1, a wood fiberboard blank can be deformed to have a very complex profile with a bending radius smaller than the thickness of the board.

The invention also relates to a device for deforming a wood fiberboard blank. The device of the invention is indicated in claim 11. Further preferred features are indicated in the dependent claims.

The present invention is described in detail below with reference to the accompanying drawings.

Fig. 1 schematically illustrates an apparatus according to a preferred embodiment of the invention.

Figure 2 illustrates a door panel formed by the apparatus and method of the present invention.

Fig. 3 shows a portion indicated by an arrow III in fig. 2.

Figure 4 shows a cross-sectional view of the door panel along the line indicated by arrows IV-IV in figure 3 and the corresponding molded portion.

Fig. 5 shows a view corresponding to another embodiment.

Figure 6 illustrates a partial perspective view of another embodiment of a door panel.

Figure 7 shows an example of a press cycle with the method of the invention.

Figure 8 shows details of a press cycle.

Figure 9 illustrates a partial perspective view of the front side and corresponding back side of a door panel formed by the method of a preferred embodiment of the present invention.

Fig. 10 shows a partially broken perspective view of an embodiment of the die press of the apparatus of the invention, indicated by the arrow X in fig. 1.

Fig. 11 shows a perspective view of a portion indicated by an arrow XI in fig. 1.

Fig. 12 shows the die press of the apparatus of the present invention in a closed state prior to changing the die.

Fig. 13 shows a detailed view of the portion shown by arrow XIII in fig. 12.

Fig. 14 shows a view corresponding to fig. 13 during a further active phase of the changing device.

Fig. 15 shows a view corresponding to fig. 12 during a further operating phase of the changing device.

Fig. 16 shows a partially broken perspective view of an assembly line for use with the die press of fig. 15.

In general, the apparatus 1 shown in fig. 1 comprises a conveyor 4, on which wood fibre boards, in particular MDF boards, are conveyed. The transfer device 4 feeds the sheet 2 into a chamber 16 of a forming station 5. In this chamber 16 the plate 2 is heated in a manner described in detail below and treated with steam so that the material reaches its thermal softening point.

In this molten state the sheet passes from the forming station 5 into the forming zone 8 of a die press 7. This is done by a conveyor 6.

In the molding press 7 the forming zone 8 is bounded at the top and bottom by an upper die 9 and a lower die 10, respectively, the upper die 9 and the lower die 10 defining a specially formed mold cavity in the closed state of the molding press, as will be described in more detail below.

The lower die press 7 is activated as a result of the upper die 9 being moved in the direction of the lower die 10, in which the heat-softened wood fibre board is positioned.

Through a carefully defined course of movement of the upper moulds 9, which will be described in detail below, the wood fibre board will undergo a great plastic deformation due to the complex contours that can be provided therein. In the shown embodiment two wood fibre boards may be processed simultaneously, wherein a total of six door panels may be formed, i.e. three door panels per wood fibre board 2.

In the upper and lower moulds 9, 10, between the spaced apart door panels, a knife edge is formed at the edge, which knife edge can cut a slot 11 in the edge of the door panel, along which the fibreboard can be easily separated.

The lower and upper dies 10, 9 which may form six door panels placed one after the other in this embodiment as described above are preferably made of six separate upper and lower dies, one for each door panel to be formed. The particular embodiment of the door skin to be finished may vary from assembly to assembly so that the finishing may be tailored to the requirements of a particular model.

Before the plate 2 is moved by the conveyor 6 into the forming zone 8 of the moulding press, a piece of plastic can be provided on it, which will bond with the surface of the plate 2 during the pressing process. A very suitable material for this purpose is melamine paper. In which case the final product will obtain a synthetic surface, which is desirable for the particular application. No additional finishing is required for the finished product, such as door panel 3.

The method and apparatus of the present invention have been described in very general terms. The different parts will be explained in detail below.

An important aspect of the process of the invention is the choice of the base material. This relates to the wood fibre material and, if applicable, the melamine paper.

It is clear that the maximum heat softening that can be achieved, and the temperature achieved for this, is of crucial importance in connection with the selection of the wood fibre material. The heat softening point is a function of the chemical properties of the wood species and the board. But also the humidity of the honeycomb and the amount of heat applied are important. Softening at as low a temperature as possible is most desirable.

Satisfactory selection of the base material can be obtained experimentally by establishing the heat softening point for a test piece and the degree of heat softening at that point. It is clear that materials made from long-fiber wood fibers are satisfactory. Pine wood in particular is very suitable as a base material. Radiata pine is preferred because its thermal softening starts already at 95 c.

A slow reacting paper is used for the melamine used, unlike fast reactions which usually require lamination purposes etc. The treatment time should be longer than 10 seconds and preferably about 20 seconds. Such that the treatment with melamine only takes place after the wood fibre board has been maximally deformed.

In order to be able to perform the necessary large deformations, it is advantageous to use a material with a crepe support, i.e. crepe paper.

The treatment during which the sheet material assumes a softened state takes place in the forming station 5. The chamber 16 houses the plate 2 to be treated. The chamber 16 may be sealed. In the forming station 5 there is provided a vacuum pump, not shown, which creates a partial vacuum in the chamber 16 when the plate 2 enters the chamber 16 and the chamber 16 is closed. When a suitable low pressure is reached, steam from a boiler 15 is introduced into the chamber 16. The pressure in the steam chamber 16 will be raised again to about atmospheric pressure due to the provision and at the same time the steam will also penetrate into the pores of the wood fiberboard 2 very quickly.

The steam outlet means in the chamber 16 comprises a number of upwardly directed nozzles arranged in the bottom of the chamber, which nozzles spray steam supplied as a shower head onto the bottom surface of the plate 2. As a result and together with the adsorption effect due to the release of the depression, permeation of the vapour is achieved.

In the boiler 15 steam is generated at a low pressure of a few bar, preferably higher than 10 bar. Since the expanded steam temperature in chamber 16 will drop to just above 100 c and some of the steam will immediately condense in the plates. The plate is both heated and moistened.

In addition to heating due to direct contact with steam, the sheet 2 inside the forming station 5 is heated due to the heating of the walls of the chamber 16 itself and due to radiation giving off heat to the sheet 2 housed in the chamber 16. In the embodiment shown here, the cover 17 of the chamber 16, which may be a lid, is hollow and has been connected to a source of vapour. The cover of the chamber 16 will thus be able to take a high temperature corresponding to the steam in the boiler 15, which is thus higher than the temperature of the steam expanding in the chamber 16.

Due to the high temperature of the cover of the chamber 16, the plate 2 will be properly heated by radiation and also the condensation of the expanding steam on this cover will be prevented. It has been found that water droplets on the board 2 will cause serious defects in the final product. Condensation is prevented by heating the lid of the chamber 16 until it is substantially at the same temperature as the steam used for expansion.

The steam generated thus has two functions. In the high-pressure and high-temperature state, steam is used to heat the walls of the chamber 16 and particularly its cover, whereas in the expanded state inside the chamber 16, steam is used to wet and heat the plate 2 when the temperature and pressure are reduced due to the expansion.

The higher the low pressure in the pre-chamber 16 before steam supply, the shorter the treatment time of the plate. It has been found that at the above-mentioned pressure of 0.8 bar, the above-mentioned treatment time of the radiata-tion pine wood fibre board is 15 to 30 seconds. This is already much shorter than the pressing cycle time of the moulding press 7, so that the processing time in the forming station 5 is not critical to the production cycle.

For other types of wood a higher low pressure may be needed to first obtain the required short treatment time, so that the cycle time of the production is not affected. The treatment time of MDF of wood fibres of rubber trees is four times longer at a low pressure of 0.8 bar, because such a low pressure is not sufficient when using this material. The low pressure must be large to achieve a suitably short processing time.

By compensating for heat losses in the later transfer stage, the wood fibre material in the forming station 5 is heated as much as possible, but not too high or too thin and not easy to handle when it is in the moulding press.

In practice it has been found that a temperature of about 100 c is most suitable for MDF boards with a thickness of 3.8mm made of the above-mentioned radiata pine fibres.

After the wood fibre board 2 has been preheated in this way, it is subjected to a solid pressing treatment in a press 7.

In addition to the selection of the base material and softening, careful control of the pressing cycle and the particular design of the die cavity are important in order to achieve maximum deformation during the pressing process.

This last aspect will be described in detail with reference to an example of machining with the method and apparatus of the invention.

Figure 2 illustrates at 20, 21 and 22 the front side, back side and base material, respectively, of a door panel formed by the method and apparatus of the present invention. Such a door panel will be placed on a wooden frame and a similar or other door panel 3 similar thereto will be placed on the other side of the frame. The assembly thus formed forms a door having the appearance of a door made up of door columns 24, cross members 25 and door panels 26 mounted therebetween. This profile is obtained by extruding the profile 23 in a plate of the base material 22 in the manner shown.

It is apparent that the overall surface area of door facing 23 is greater than that of the sheet of base material 22. To form the profile 23, the sheet is moved into the profile from the adjacent portion.

Fig. 3 shows a detail of the part indicated by arrow II in fig. 2, wherein arrows 28, 27 indicate the movement of the material of the profile 23 in this direction during the extrusion process. It is clear that the stresses exerted on the sheet during extrusion, in particular in the cross direction indicated by the arrow 27, result in a particular critical state. The forced movement of the material may cause shearing or, in the case of a slight weight, detachment of the fibres from the surface.

With the method and the device according to the invention it is possible to subject the wood fibre material to such an extrusion process that the material is subjected to great stresses.

An important measure of the invention is to control the movement of the material during the extrusion process. With the die measures explained in detail below it is ensured that the direction of flow of material to the profile during extrusion can be controlled, which for example prevents material in the central area of the cross section shown in fig. 3 from flowing to the profile in the direction of the arrow 27, which would damage the material as described above.

Since the cavity die comprises a part structure in the closed state for gripping the fibre board material and holding it before the complete deformation has taken place, a controlled movement of the material during pressing is achieved. The flow of material through this narrowing is thus resisted. In figure 4 an upper mould 9 and a lower mould 10 are shown at a distance from each other with a just moulded door panel 3 in between. The shape of the door panel 3 corresponds to the shape of the cavity in the closed state of the upper and lower molds 9, 10. The part shown in fig. 4 relates to the area where the partial contour 23 is formed. The partial structure of the mold cavity is indicated by arrows 31, 32 and 33. For a modification of an MDF board, for example 3.8mm, the total height of the moulding space, indicated by the numeral 30, will be about 3.2 mm. This means that there will be a compression of the material in the areas that are not directly compressed here.

The mode height at the partial structures 31 and 32 is approximately 2.7 mm. The cavity height returns to 3.2mm again at 33.

It is clear that when the mould is first closed, a gradual stretching and flow of material in all directions will occur in the profile 23. With the last 1.1mm (3.8-2.7) of the die press stroke, the plates have been secured at the structures 31 and 32. During the last part of the stroke, no more material flows into the profile 23 from the right when forming the details of the profile and when locally experiencing the maximum strain on the material. But also the area between the arrows 31 and 32 is closed and there is no further material movement. The movement of material still required for deformation of the bottom of the profile will be from the left. Because the left side of the profile has less mass, the material strain will remain very limited during flow from that direction.

Due to these partial structures 31 and 32, it is possible to prevent the deformation of the profile in the final stage. The material from the right is pushed into the profile due to the large material strain that may be on the right side of the profile, resulting in tearing and detachment of the fibers formed at the surface of the plate 3.

Another important measure is to heat the upper and lower dies 9 and 10 so that the plate is heated further by contact with the plate 3. In the narrowing regions of the mold cavity, in this embodiment at arrows 31 and 32, first narrow contacts between the upper and lower molds 9 and 10 and the plates are formed, with the result that these regions are heated first and most. This is beneficial for the material flow required during the extrusion process due to the increased plastic of the temperature increasing plate.

Another effect of the structure in the mould cavity is that the detached fibres are pressed into the surface of the plate under great pressure. Suitable wood fibre boards, such as MDF boards, comprise a binder which is usually not fully hardened. This binder is further hardened by strong pressure and heat, so that the wood fiber is well bonded in a pressed state. The fibers which have already bonded to the surface after the material has moved are in this way bonded again firmly to the material.

In fig. 5, a portion of an upper die 35 and a lower die 36 are shown with a portion of a just-formed plate 37 therebetween. The profile 38 is somewhat simpler in the case of this embodiment than the profile 23 of fig. 4. As a result a narrowed area is sufficient, which is already indicated by arrow 39 on the right side of the profile, so that it is prevented that more material will flow from the right into the mould cavity in which the profile is formed after the initial deformation.

Although in the illustrated embodiment the shape of the mould cavity is substantially the same, in some cases the local structure of the mould cavity may vary along the length of the profile. It is clear that the movement of material is most critical at one corner of the profile. Control of the material movement therefore needs to be done properly. Less stringent controls may be employed at other locations along the profile.

As shown in the example of fig. 6, a portion of a pressed sheet 40 is shown, since there is no controlled movement of the material, due to excessive strain imposed on the material at the corner 42 between the profile 41 and the profile 43; so that the risk of material damage is greatest here. It is not certain that the movement of material near this corner 42 during extrusion will have to be controlled by local structures in the die cavity.

In this embodiment, the partial structures can be formed by providing the walls of the co-operating moulds with a suitably fixed shape. It is also possible, however, to control the movement of the material by means of movable elements accommodated in the die, which hold the plate to be pressed in a desired manner at a suitable distance between the upper and lower die, so that no further movement of the material takes place during the pressing in this position. The movable members may be formed by steel slides, but inserts made of a rubber-like material are also feasible.

The position of the local stopper or movable die obviously depends on the shape to be extruded. When designing this shape it should often already be possible to decide where the most critical part is and on the basis of this decide where the plate to be pressed must be fixed in order to control the flow of material. At the start of the trial extrusion, the mould can be adjusted accordingly when it is clear that an incorrect movement of the material occurs in a specific area. These adjustments will be apparent to one of skill in the art in view of the above.

In addition to the above, allowing the extrusion of wood fibre boards with very complex shapes, there may be good measures concerning the press cycle.

Figure 7 shows a suitable press cycle for the method of the invention. On the horizontal axis the time is indicated in seconds and on the vertical axis the pressure of the mould is indicated in kg/cm²Given, while the distance between the dies is mm. The dashed lines indicate the distance between the moulds and the continuous lines indicate the pressure.

The cycle starts when the softened wood fibre board has been placed in the mould. At which time the press is quickly closed until the two molds just come into contact with the plate. The mold is then closed very slowly until it is completely closed. The pressure is increased and maintained for a period of time when the mold is fully closed, after which the pressure is reduced to zero and increased again after a period of time. This is repeated once more for reasons explained below. When the pressure is reduced to zero for a third time, the mold opens and the product can be removed from the mold.

The mold is closed quickly during the first part of the closing cycle to achieve as short a cycle time as possible. But the second partial shut down cycle is critical to proper extrusion processing.

An example of the closing cycle process of this second part is shown in detail in fig. 8. In this case the first step is indicated by reference numeral 50. The mold is quickly closed during this step. At the end of this step the mould just comes into contact with the plate. The speed is then greatly reduced in step 51 to create a gradual movement of the material to form the general shape of the profile. The speed is then further reduced in step 52 and the movement is stopped in step 53. The strains formed in the material will be balanced and at the same time the deformation of the sheet material will increase due to the contact plate with the heated mould being heated. Next, the mold is closed still further in step 54, and the movement is stopped again in the following step 55. The material strain that has developed while still in this step can be re-balanced and the material can stretch and flow. The final portion of the shut down cycle is again gradually generated in step 56. The mold then closes and the pressure increases.

The graph shown here represents a process that depends on the profile being formed. Typically the closing speed is very low or even zero when the critical part of most profiles is being formed. Too high a closing speed during the moulding stage will cause damage to the final product, since visible material defects will form on the surface of the material. These material defects may be loose fibers or uneven surface portions. Depending on the end result the expert can determine whether the closing speed is too high or still somewhat high at a particular moulding stage. In this way it is possible to establish by experimental means a suitable closing curve, determining that the speed should be reduced or almost zero when the deformation caused by the actuated mould involves a large material strain. There should also always be sufficient time for heat to be transferred from the mould to a particular area of the material to be significantly deformed.

As described above and as can be seen from fig. 7, the pressure increases after this particular shut-down cycle. In FIG. 7 the maximum pressure exceeds 60kg/cm²But in some cases it may be similar to e.g. + -. 40kg/cm²The pressure of (2) is also sufficient. The amount of compression required for the material can then be achieved in the case of the above-mentioned example of a plate having an initial thickness of 3.8mm to 3.2 mm. In which case the entire plate is heated to a temperature at or above or below the temperature of the mold, e.g. 200 c. The pressure will decrease to almost zero after a period of time. It should be noted that the distance between the moulds does not change.

Water in the sheet that has accelerated beyond the atmospheric boiling point can suddenly change to steam due to the reduced pressure, and this steam can escape from the bypass between the dies. The pressure is then increased again to the maximum value used and held at this level for a while, so that the water still remaining heats up again. Most of this water escapes again when the pressure drops back to zero, after which the pressure finally increases to the maximum value used and remains at this level for a while. After the mold is opened, the moisture content of the wood fiber material drops to a very small value of about 5%.

The drying and venting cycle described above begins when the mold is held in intimate contact with both sides of the sheet. It is possible to prevent the wood fiber material from being pushed in half due to the expansion of water, which may cause surface defects of the product. Since the pressure does decrease but the moulds do not move relative to each other, the board remains supported over its entire surface area, as a result of which no movement of the wood fibres occurs due to the water vapour pressure.

Typically 2 to 3 drying-venting steps are required depending on the moisture content of the material, the temperature of the mold and other material properties. Depending on the material the mold temperature may be set at, for example, 160-200 deg.c.

The closing cycle described with reference to figure 8 lasts 20 to 30 seconds depending on other factors such as the complexity of the profile. The last 6 to 8mm of the closing distance in this 20 to 30 seconds is included in a plurality of steps.

It is clear that the moulding press will have to meet the most stringent requirements in view of the accuracy with which this movement is performed. These requirements relate both to the accuracy with which the closing speed of the moulding press can be controlled and to the accuracy with which the moulds can be kept parallel relative to each other.

It must be possible to control the closing speed of the press completely and also to vary the speed preferably between 0.1 and 50 mm/sec. High speed is required to limit the loss of time when starting to close to start opening the die press to commercialize the production.

The precision of the adjustment of the closing speed with a moulding press which is part of the apparatus according to the invention is 0.1 mm/sec.

The pressure can also be adjusted completely, preferably gradually from 0.5kg/cm for the above-described embodiment²To a maximum of, for example, 65kg/cm²。

In order to be able to process the above-mentioned product, i.e. the door panel, in a commercial manner, at the same time using a mould for manufacturing 6 door panels in one press cycle. The working surface area of the die press is thus 2.2 x 5.6 m. In this case, the relatively large area cannot be deformed by more than ± 0.1mm under a full compression molding, so that the required precise control of the closing speed with respect to the contour can be achieved in all mold sections.

And the parallelism of the upper die and the lower die must meet +/-0.1 mm.

The maximum operating temperature of the region of the molding press to which the mold is attached is about 200 c. The temperature variation over the working area of the molding press must be maintained within 2 c in order to be able to obtain the exact conditions required again in each part of the mold. Preferably those parts of the molding press that support the mold are heated by hot oil. In order to obtain the correct temperature, ducts are provided along the entire length of the platen, whereby the hot temperature flows in a parallel manner.

It is clear that the requirements that the moulding press needs to meet are not very strict when the extrusion process is not very complicated.

Fig. 9 shows a detail of the section indicated by the arrow IX in fig. 2. There is shown a front side 20 of a finished door facing 3 and a rear side 21 of the same door facing 3 adjacent thereto.

It can be seen that a wood grain pattern is provided on the front side 20. For this purpose, the upper mold is provided with a complementary relief. The relief can be formed in a suitable manner on the mould surface by photolithography. The embossments are transferred into the wood fiberboard by pressing the embossments into the wood fiberboard. The board is more compressed in certain sections, resulting in grooves corresponding to the lines of the wood grain pattern.

A pattern 60 is also formed on the rear side 21. This is also provided by applying a relief formed over the lower mold. The relief may also be formed by photo-etching and thus the back side 21 of the door panel obtains a certain roughness. Since the roughening glue adheres well to the rear side 21 of the door panel, a door made from the door panel 3 will have a longer life without the risk of the door panel becoming loose. The pattern 60 is preferably formed of small concave-convex portions having a size of about several tens of millimeters. In addition to better adhesion due to roughness, better adhesion is achieved due to the enlarged area.

Fig. 10 shows a detail view, partially broken away, of the die press 7 of a preferred embodiment of the invention. In this figure, it is clear that the upper and lower dies 9 and 10, as well as the fastening means to be described, with which the dies are mounted on the upper platen or the press platen and the lower platen, respectively, of the press 7.

Through the broken-away portion of the die press platen 59, a conduit 66 is visible, which has been described above and is used to convey the hot heating oil.

The loading and unloading of the plates and the extruded product are carried out by a supply carriage 62 and a discharge carriage 70, respectively, which can move along guide rails 61 extending a distance on both sides of the lower platen in front of and behind the die press 7. The guide rails 61 are mounted in a U-shaped configuration on the sides thereof, wherein wheels provided on the frame of the carriages 62, 70 are movable. Careful cross-positioning of the donor frame 62 is achieved by the vertical guides 63.

The supply carriage 62 itself is provided with a conveyor 64 which is movable along the carriage 62.

As previously mentioned, in this case two sheets 2 are placed from the forming station 5 on the belt 65 feeding the carriage 62 after the sheets have softened in the forming station 5. The feeding carriages 62 are positioned as far to the left as possible when leaving the forming station 5, i.e. in front of the moulding press. The sheet fed from the forming station 5 is carefully positioned on the belt 65. When this is done, the entire carriage 62 enters the molding press without moving the transfer device 64. When the carriage 62 reaches a position in which the plate 2 above its belt 65 has been brought into its correct relative position with respect to the mould, the carriage 62 moves backwards while driving the conveyor 64 at the same speed but in the opposite direction. The plate 2 thus maintains its relative position with respect to the mould and is correctly positioned with respect to the mould on the lower mould 10. The bracket 62 is pulled away as if it were coming from under the board.

After the panel has been positioned on the lower die and the supply carriage 62 has been moved back, the press cycle described above is performed to compress the door panel 3.

After the die press is opened again, the formed door panel 3 may be removed from the die press area by the discharge carriage 70 shown in fig. 11. As mentioned above, this carriage can also move along the rail 61. It can be seen that the carriage 70 has a U-shaped frame so that the legs of the frame can move along the rails 61. The frame 69 is provided with an arm support 71. They are elongated rods extending parallel to the legs of the frame 69 and movable in a vertical direction between a raised position and a lowered position by vertical guides 72. The movement of these arm supports 71 is generated by a cylinder 73.

Three arms 74 are arranged on the arm support 71 at a time. They can be rotated from the protruding position shown in fig. 11 to a position to the right in fig. 11, in which they extend substantially parallel to the rails 61. The movement of the arm 74 is controlled by a rod 79, and the rod 79 can be moved back and forth by a cylinder 80.

At its projecting end the arm lever 74 is arranged in an articulated manner on an elongated suction cup carrier 75, which suction cup carrier 75 supports a plurality of vacuum suction cups 76 on its underside. These vacuum chucks are connected to a vacuum device 78 by the hollow interior of the chuck body 75 and a flexible lead-through 77. The suction of the vacuum device 78 can be opened and closed by a valve 81.

To move the molded door panel from the compression zone, the discharge carriage 70 is moved between the molds and the arm 74 is rotated back until flush with the door panel 3. The cylinder 73 is then actuated by a suitable control device, as a result of which the arm support 71 is moved forward. The cylinders 80 are then actuated on both sides of the frame, as a result of which the arm levers 74 are rotated into their position as shown in fig. 11. Suction cups 76 are then brought into contact with the rear surface of the moulded door panel 3 by lowering cylinders 73 again. The vacuum is then created and as a result the suction cups firmly attach themselves to the door panel 3. In the following stage the cylinder 73 is reactivated to lift the arm support 71, with the result that the door panel 3 is lifted from the lower mould. Since the door panel is supported by suction cups, the discharge carriage 70 may be moved outwardly out of the pressing zone until it is positioned above a belt conveyor 82 provided therein.

After the belt conveyor 82 has been opened, the door panel 3 is then lowered onto the belt conveyor 82 and the suction cups are pivoted away, and the door panel can be removed. While the supply carriage can place the next board into the die press where the next press cycle can begin.

As mentioned above, the upper and lower dies of the preferred embodiment of the illustrated apparatus include six separate sets of dies, each for extruding one of the door facings. The six sets of dies are shown the same each time in these figures, but it will be apparent that different sets of dies may be used in an appropriate set depending on the desired mode of production.

In order to enable rapid changes from door panels produced with a first series of mold assemblies to door panels produced with a second series of mold assemblies, the apparatus of the present invention preferably includes a quick fastening device for the mold platens. This quick fastening means will be described below with reference to fig. 10-15.

Each die is individually set in the die press by a cylinder. Each of the upper die 87 and each of the lower die 86 is provided with a plurality of grooves at longitudinal ends thereof. Two of the grooves 90 are designed to mate with the cylinders 88, whereby the platen is secured to the die press. In addition to these cylinders 88, two auxiliary cylinders 92 are provided on the movable die press platen 59 for each set of lower and upper dies 86, 87 on each side. The top of which, as will be described below, may be fitted in the lower mold 86 with a recess 93.

The mold changeover device 85 operates as follows.

The starting point is the closed position of the die press as shown in fig. 12 and in detail in fig. 13. The molded door skins are contained between the molds so that the molds do not come into direct contact with each other and are not damaged.

To enable the mould to be switched, the auxiliary cylinder 92 is actuated so that its rotating crown 94 is turned a quarter turn first and then moved downwardly by the auxiliary cylinder 92 into the recess 93 of the lower mould. The rotating top 94 is then rotated a quarter turn to actuate the auxiliary cylinder 92 so that the rotating top 94 is pulled upward. When this occurs the swivel tops 94 engage their projections below the shoulder 95 of the recess 93 so that they engage the lower mold in this manner.

The cylinder 88 is then actuated and its rotating top 89 is turned a quarter turn, as a result of which they are released from the shoulder 91 of the groove 90.

The suction rod of cylinder 88 is then pulled in so that rotating top 89 no longer engages the mold.

The above situation is shown in fig. 14. Lower die 86 is being pulled against and held on upper die 87 by auxiliary cylinder 92, while upper die 87 is resting on movable die press platen 59 of die press 7.

The die press is then actuated so that the movable die press platen 59 moves upward. The completed upper and lower molds are moved and suspended from the mold press platen 59.

The next stage is shown in fig. 15. In this figure it can be seen that the carriage 62 is fed into the pressing zone, so that a support frame 97 is mounted on the carriage 62. When the carriage 62 is flush with the mold together with the supporting frame 97, the molding press 7 is actuated to gradually lower the molding press platen 59 until the lower mold 86 is located on the supporting bars 98 of the supporting frame 97. The auxiliary cylinders 92 are then actuated again to cause them to move the respective rotating tops downwards a few, to cause them to turn a quarter turn and to move them upwards. At which time the connection to the die press platen 59 is broken and the die press is actuated to move the die press platen 59 upward. The mold is now supported by the support frame 97 and can be removed while the carriage 62 is clear of the extrusion area.

A lifting device, not shown here, can lift the supporting frame 97 from the supply carriage 62 and replace it with another supporting frame 97 with another set of moulds, which other supporting frame 97 can be moved again into the pressing zone of the moulding press 7 and thereafter engage the auxiliary cylinder 92 after moving the moulding press platen 59 downwards. The die press platen 59 then lifts the die from the support frame 97 and this frame 97 is released from the extrusion zone with the carriage 62. The press platen 59 can then be moved downward again until the lower die is on the support of the press. After the cylinder 88 is actuated and the auxiliary cylinder is deactivated, the die press is ready for the next use.

Claims (68)

1. A method of manufacturing a hollow core door, the method comprising the steps of:

providing a wood composite flat blank;

wetting the slab to increase humidity;

preheating at least one surface of the slab to a temperature of no more than about 100 ℃;

after said preheating step is completed, positioning said flat blank between first and second platens within a die press, wherein at least one of said platens is heated;

deforming said flat blank into a formed door panel by a die press that closes said flat blank, including a plurality of door panels defined therein; and

at least one first formed door panel is secured to a first side of a door frame and one door panel is secured to an opposite second side of the door frame.

2. The method of claim 1, wherein preheating the slab comprises applying steam to the slab.

3. The method according to claim 2, characterized in that the preheating of the slab takes place in an enclosed space and the steam is introduced into said enclosed space in a free-flowing manner.

4. The method of claim 3, wherein the pressure in said space is reduced prior to the step of applying steam to said slab.

5. The method of claim 3, wherein the enclosed space includes walls and a roof, the method further comprising heating at least the roof within the space to a temperature greater than the temperature of the remainder of the space.

6. The method of claim 5, further comprising the step of heating the wall within the space.

7. The method according to claim 1, characterized in that the further heating of the slab takes place in the pressing step together with the heating of the platens or the dies.

8. The method of claim 1, wherein said pressing step comprises a pressure cycle comprising at least one pressure reduction between atmospheric pressure and a maximum pressure obtained in said pressure cycle.

9. The method of claim 1, wherein said pressing step comprises a pressure cycle comprising at least one pressure increase followed by a constant maintenance of pressure for a predetermined period of time.

10. The method of claim 1 wherein said pressing step comprises a pressure cycle comprising one or more pressure increases during said pressing cycle.

11. The method of claim 1 wherein said pressing step comprises a rapid closing of said platen, a relatively slow increase in said pressure, and a relatively slow decrease in said pressure.

12. The method of claim 1, further comprising the step of applying a coating to said slab after said preheating step.

13. The method of claim 1, further comprising building a relief on a surface of the sheet during the pressing step.

14. The method of claim 1, further comprising a pressure cycle wherein the temperature control of said platen during said pressing step is maintained within a narrow preselected range.

15. The method of claim 1, further comprising the step of maintaining a geometrically uniform gap between said platens during said pressing step.

16. The method of claim 1, further comprising the step of deforming said flat blank into a plurality of formed door panels.

17. The method of claim 16, further comprising forming corrugations (pinches) between adjacent formed door panels to facilitate separation of said adjacent door panels from one another.

18. The method of claim 1, further comprising the step of impressing a texture on said formed door skin during said pressing step.

19. The method according to claim 1 or 12, further comprising the step of supplying a material containing a thermosetting resin to the preheated slab.

20. A method of manufacturing a shaped door panel, the method comprising the steps of:

providing a wood composite flat blank;

placing said flat blank in a die press having first and second platens;

heating said first and second platens to thereby bring a temperature of one of said platens to at least about 140 ℃;

closing the die press at a predetermined closing rate to deform the flat blank into a door panel including a plurality of interior panels molded therein;

venting the die press in the deforming step; and

allowing curing of the resin within the deformed door panel to form a formed door panel.

21. The method of claim 20 including the additional step of preheating said plate with steam prior to said heating step.

22. The method of claim 21 wherein said preheating of said slab occurs in an enclosed space and steam is introduced into said enclosed space in a free-flowing manner.

23. The method of claim 22, wherein the pressure in said space is reduced prior to the step of applying steam to said slab.

24. The method of claim 21, further comprising the step of transporting the flat blank for preheating and further transporting said flat blank to a die press.

25. The method of claim 22, wherein the enclosed space includes walls and a roof, and further comprising heating at least the roof in the space to a temperature greater than the temperature of the remainder of the space.

26. The method of claim 25, further comprising the step of heating the wall of the space.

27. The method of claim 20, wherein further heating of said flat blank occurs in said pressing step in conjunction with heating of said platen or mold.

28. The method of claim 20 wherein said pressing step comprises a pressure cycle comprising at least one pressure reduction between atmospheric pressure and a maximum pressure attained during said pressure cycle.

29. The method of claim 20 wherein said pressing step comprises a pressure cycle comprising at least one pressure increase followed by a constant maintenance of pressure for a predetermined period of time.

30. The method of claim 20 wherein said pressing step comprises a pressure cycle comprising one or more pressure increases during said pressing cycle.

31. The method of claim 20 wherein said pressing step comprises a rapid closing of said platen, a relatively slow increase in said pressure, and a relatively slow decrease in said pressure.

32. The method of claim 20, further comprising the step of applying a coating to said slab after said preheating step.

33. The method of claim 20, further comprising building a relief on a surface of the sheet during the pressing step.

34. The method of claim 20, further comprising a pressure cycle wherein the temperature control of said platen during said pressing step is maintained within a narrow preselected range.

35. The method of claim 20, further comprising the step of maintaining a geometrically uniform gap between said platens during said pressing step.

36. The method of claim 20, further comprising the step of deforming said flat blank into a plurality of formed door panels.

37. The method of claim 36, further comprising forming corrugations between adjacent formed door facings to facilitate separation of said adjacent door facings from one another.

38. The method of claim 20, further comprising the step of impressing a texture on said formed door skin during said pressing step.

39. The method of claim 20 or 32, further comprising the step of providing a material comprising a thermosetting resin to said pre-heated slab.

40. Apparatus for deforming a wood fibre board blank into a finished shaped product having regions of substantially different height with respect to the original thickness of the wood fibre board, comprising:

a first station having means for heating and pre-wetting the mat;

a second station located after said first station for pressing said preheated and prewetted sheet into a desired shape, said second station comprising:

opposed platens, wherein each said platen has a mold attached thereto; and

means for controlling the opening and closing of the platens so as to apply pressure to the slab between the platens; the control means gradually increases the pressure on the mat to a predetermined pressure and maintains the predetermined pressure at a predetermined level for a predetermined time and gradually decreases the pressure to about zero during the press cycle.

41. An apparatus according to claim 40, including heating means on at least the roof of the forming station.

42. The apparatus of claim 40, further comprising a heating device inside the platen or mold.

43. The apparatus of claim 40, wherein the heating means comprises a guide channel for the preheated oil.

44. The apparatus of claim 40, wherein the second station further comprises a connecting device for engaging a selected mold.

45. The apparatus of claim 40, wherein the respective molds are energized independently of one another.

46. The apparatus of claim 40, further comprising a conveyor for conveying slabs to said first station, from said first station to said second station, and from said second station to said first station.

47. The apparatus of claim 40, wherein the die has means for preventing movement of the wood fiber material within the die at a location corresponding to an area of the mat that is subject to the most severe shear load during the pressing process.

48. The apparatus of claim 40, further comprising an automated device for converting molds on the apparatus to facilitate rapid processing of the slab.

49. A door panel, comprising:

a flat slab of medium density fiberboard molded into a three-dimensional slab through the steps of heating, pressurizing and venting, said fiber slab being vented while being molded into said three-dimensional slab, said three-dimensional slab including a first portion having a first preselected thickness and a second portion having a second preselected thickness, wherein said second preselected thickness is less than said first preselected thickness.

50. A hollow core door, comprising:

a door frame;

a first door facing and a second door facing attached to said door frame so as to define a hollow space therebetween, the first door facing comprising a flat slab of medium density fiberboard molded into a three-dimensional slab and having a plurality of door facings;

the molded door panel includes a first molded portion having a first preselected thickness, and a second molded portion having a second preselected thickness, wherein the second preselected thickness is less than the first preselected thickness.

51. A die press for door facings comprising:

first and second platens and heating each of said platens;

a plurality of openings are arranged in the side surface of at least one of the bedplate and used for exhausting air; and

an actuating device for moving at least one of said platens toward or away from the other of said platens to open and close said die press.

52. A method for forming a wood fiberboard blank into a formed product in a mold cavity of a molding press, wherein the molding press has at least one upper mold and one lower mold, at least one of which is movable from a first open position for receiving the blank toward the other to a second closed position defining the mold cavity, the method comprising:

heating the blank to a heat softening point to allow plastic deformation of the blank material;

providing the die cavity in the closed position with at least one restriction adapted to restrict lateral squeeze flow of the softened material of the slab, the restriction being positioned to prevent defects in the formed product;

heating at least one of the upper and lower molds; and

the slab is pressed in the mould cavity in a pressing cycle comprising at least one progressive deformation phase followed by at least one rest phase, while heating without opening the mould cavity.

53. The method of claim 52, wherein the heating of the plate comprises steam treatment of the plate.

54. The method of claim 53, comprising: heating a plate in an enclosed space; and before heating, further reducing the pressure in the space and introducing steam into this space in a free-flowing manner.

55. The method of claim 54, further comprising heating at least the top of the space to a higher temperature than the space.

56. The method of claim 54 or 55, further comprising additionally heating the walls of the space.

57. A method as claimed in claim 52, wherein pressing occurs with heating of the mould or holder during pressing.

58. The method of claim 52, wherein pressing comprises a press cycle having at least one state of reduced to about no pressure and a subsequent pressure increase to a die used in the pressing.

59. The method of claim 52, wherein pressing comprises rapidly closing a mold used therein and relatively slowly increasing and decreasing the pressure.

60. The method of claim 52, further comprising pressing a cover plate with the plate, the cover plate for covering the plate subjected to pressing.

61. A method according to claim 52, wherein a relief is provided in the visible surface of the board subjected to pressing during pressing.

62. An apparatus for deforming a wood fiberboard blank into a formed product, comprising:

a means for heating the mat to a heat softening point to plastically deform the mat material;

a die press having at least an upper die and a lower die, wherein at least one of the upper die and the lower die is movable from a first open position for receiving the slab toward the other to a second closed position defining a die cavity; and

in the closed condition, at least one restriction in the cavity, the restriction being suitable for limiting the lateral squeeze flow of the softened material of the slab, the restriction being positioned so as to prevent defects in the formed product;

characterised in that at least one of the upper and lower dies is adapted to be heated and the apparatus is adapted to press the slab in the die cavity in a press cycle comprising at least one progressive deformation phase followed by at least one rest phase, without heating opening the die cavity.

63. The apparatus of claim 62, including heating means at least at the top of the forming station.

64. The apparatus of claim 62 or 63, further comprising heating means inside the mould or holder for pressing.

65. The method of claim 64, wherein the heating device comprises a guide channel for the preheated oil.

66. The apparatus of claim 62, wherein the die press includes quick connect means for engaging the selected die.

67. An apparatus according to claim 62, wherein the mould is divided into at least two mould parts which can be supplied with energy separately from each other.

68. The apparatus of claim 62, further comprising a transfer device for transferring the plate from and to the die press.