The present invention relates to the field of processing structural slab-shaped elements, preferably but not limitedly made of wood or similar materials, and more specifically to a machine for finishing such elements. The invention relates in particular to an applicator for hot melt adhesives on the slab-shaped structural element or parts thereof.
The present invention relates to the field of processing structural slab-shaped elements, preferably but not limitedly made of wood or similar materials, and more specifically to a machine for finishing such elements. The invention relates in particular to an applicator for hot melt adhesives on the slab-shaped structural element or parts thereof.
Applicators for hot melt adhesives in the sector of reference are known in the current art, known more simply as glue applicators.
The glue applicator is a system for melting hot melt adhesives such as, and not limited to, EVA, PU, PP, provided in granulate form for their application on the edge of structural slab-shaped elements or on edging bands of such structural elements.
The structural slab-shaped element, hereafter simply referred to as 'panel', can be made of various materials (e.g. chipboard, MDF, solid wood, etc.) and have various regular (straight, rectilinear edges) or irregular (curved, undulated edges) shapes and colours. Similarly, the edging band can also be made of a variety of materials (e.g. and not only, polymers, wood, etc.), shapes and colours.
The gluing of the edging band takes place by applying a layer of adhesive of the desired type, colour and thickness, chosen on the basis of the type of panel and edge to be coated, to the edge of the panel to be coated.
Once the adhesive has been applied, the edge is pressed onto the panel by means of rollers that exert adequate pressure.
A known type of glue applicator comprises a non melted glue collection tank that is filled with the adhesive in granules.
Such adhesive is then brought into contact with melting means, such as resistors, which melt the granules as they heat up; the solution currently used to push the adhesive towards the melting means is one that employs a piston actuator, e.g. pneumatic or hydraulic.
The piston stroke represents one duty cycle, involves the entire quantity of adhesive contained in the tank and operates at a constant speed.
Therefore, once the entire quantity of adhesive has been melted, it must be collected in order to be used.
The melted adhesive is collected in a vat located downstream of the melting means.
From here, the adhesive in its molten state then goes to wet an applicator or coater roller, which comes into contact with the panel portion or the edging band and transfers the adhesive thereto.
A doctor blade placed tangent to the coater roller adjusts the thickness of adhesive in the front part of the roller and thus the quantity that is transferred to the panel.
A return channel from the coater roller to the vat allows the adhesive to recirculate, so that the excess flow of adhesive compensates for that which is consumed during the edge-banding.
Despite being widely used, the currently known glue applicators present various problems. A first issue is related to the handling of the glue in the two molten and non-molten states within the applicator itself. In fact, the quantity of glue in the tank must be correctly sized in order to complete a duty cycle with complete emptying of the tank.
If this were not the case, the glue inside the tank near the heating elements could melt or degrade and thus create blockages or solidifications within the tank that block the flow of granules.
However, the need to work in duty cycles, completely melting the glue in the tank in a single time, causes quite a few problems, as a large quantity of glue must be handled in the molten state.
The adhesive, kept molten at the desired application temperature, degrades rapidly over time and consequently loses its properties, therefore the dwell times in the vat must be designed to be as short as possible.
Again, it is sometimes required to make edge-banding sections of different colours, e.g. in the case of multi-coloured panels. In this case, the adhesive must also have different colours, and therefore the need arises to interrupt the edge-banding process and replace the adhesive in the glue tank with a different one. This implies long downtimes because it is necessary to wait for the system to cool down in order to extract the adhesive from the tank, and even in the case of tanks with rapid emptying systems, the amount of adhesive waste is still not negligible.
Another type of glue applicator includes an collection tank heated overall, where the adhesive granules are placed. Here, the granules melt and are brought to the roller application system by gravity with the help of a doctor blade, or by screw systems. This type of solution also presents the problems outlined above, because the glue is melted in its entirety in a single solution and therefore there is a large quantity of molten glue to be managed and stored pending use, with the risk of degradation explained above. Furthermore, to change glue types, the collection tank must be completely emptied of the molten glue, waiting for the cooling thereof before then starting a new duty cycle, with significant machine downtime.
In light of this state of the art, it is an aim of the present invention to provide a glue applicator that solves the problems described above. In particular, it is an aim of the glue applicator to ensure continuous, uninterrupted work, which consequently saves time and reduces working time.
It is further the aim of the glue applicator according to the invention to have a high durability performance of the glue properties, with low downtimes in the tank or collection vat.
A further aim is to reduce the number of machine downtimes for adhesive replacement and at the same time reduce the quantity of adhesive lost or wasted.
In general, it is the aim of the invention to provide a glue applicator adaptable to all edge-banding machines, both single-sided for straight panels and machines for curved panels.
In general, it is the aim of the glue applicator according to the invention to provide an alternative to known glue applicators.
This and other aims are achieved by the glue applicator according to the present invention, the essential features of which are defined by claim 1 annexed hereto. Other important additional features are the subject matter of the dependent claims.
The features and advantages of the glue applicator according to the present invention will become clearer from the following description of embodiments thereof, given by way of a non-limiting example with reference to the appended drawings wherein:
With reference to said figures, the glue applicator according to the invention comprises a supply and melting assembly 1 and a coater assembly 2 operatively placed one after the other. The function of the supply and melting assembly 1 is to feed the coater assembly 2 with adhesive in the molten state directly and instantaneously, in the desired quantity based on instantaneous adhesive consumption.
With particular reference to
The supply of the solid adhesive to the compartment 11 can take place by falling (gravity), in which case the feed port 10 will be located at the top of the compartment. Other positions of the port can still be envisaged, alternatively.
The supply and melting assembly 1 further comprises melting means 12 adapted to be heated to reach a temperature suitable for melting the adhesive in a solid state when in contact therewith.
The compartment 11 develops in the direction of a feed direction X of the adhesive. If the feed port 10 notionally represents the beginning of the adhesive path within the compartment, the melting means 12 are placed at the end of the compartment. The melting means 12 thus delimit the end section of the compartment 11 with respect to the feed direction X.
Further continuous supply means 13 of the adhesive to the melting means 12 are placed within the compartment 11. Such means 13 collect the adhesive granules in a solid state at the feed port 10 and push them in a continuous motion towards the melting means 12 along the feed direction X.
In a preferred embodiment, such continuous supply means 13 comprise a worm screw 13 arranged in axis with the feed direction X. The worm screw 13 develops within the compartment 11 between an inlet end 130 thereof at the port 10 and an outlet end 131 thereof at the melting means 12.
The worm screw 13 then collects at the inlet end 130 the granules entering from the port 10, to make them exit from the outlet end 131 near the melting means 12.
A thermal insulating block 14 is interposed between the melting means 12 and the outlet end 131 of the worm screw 13, which prevents the heat transmitted from the melting means 12 to also affect the outlet end 131 of the screw and thus prevents the granules in the screw from melting.
In an embodiment, the motion is transmitted to the worm screw by means of a chain transmission 15 but other alternative solutions are not excluded.
The compartment 11 further comprises a second port or outlet port 16 that allows, by reversing the motion of the screw 13, the discharge of the granules present inside the screw. For this purpose, the second port 16 is preferably arranged on the bottom of the compartment 11, but such positioning is not binding and alternative solutions can be implemented.
As shown in particular in
The perforated plate 120 has resistors 122 placed on the perimeter in a regular manner, so that the heat is correctly and evenly distributed. A thermocouple 123 measures the temperature in the centre of the plate 120, allowing it to be adjusted and controlled.
The perforated plate 120 further defines a first face 120a facing the compartment 11 towards the outlet end 131 of the worm screw 13 and a second face 120b opposite the first facing the coater element 2.
With particular reference to
The rotating roller 20 is supplying a collection chamber 21 of the molten adhesive that exits from the perforated plate 120. Given the high viscosity of the adhesive in its molten state, it is arranged on the rotating roller 20 and is drawn by it in rotation towards a scraper element 22, which is placed tangentially on the rotating roller. The accumulation of adhesive on the scraper element 22 thus spreads over the entire height of the roller 20, wetting it completely.
In a preferred embodiment, the scraper element 22 has an axial development along an axis Y' thereof which is parallel to the rotation axis Y of the coater roller 20. The scraper element 22 can have, for example, a roller or cylinder configuration.
On the periphery thereof, the scraper element 22 then has an edge 220 that runs vertically along the entire height of the coater roller 20, which scrapes and adjusts the thickness of adhesive on the front part of the roller 20, i.e. the quantity of adhesive that will be transferred to the panel.
The scraper 22 also has a through hole 221, arranged axially to Y'. The through hole is in fluid communication with the collection chamber by means of an access (223) located at the periphery of the scraper tangent to the coater roller 20. Therefore, part of the molten glue contained in the collection chamber also penetrates inside the hole 221 (
A lower end 221a of the hole 221 is intercepted by a spigot 222 which, when open, allows the molten glue in the collection chamber 21 of the applicator to be discharged.
An upper end 221b of the through hole 221 is instead open on the outside of the collection chamber.
Sensor means 23 are provided to monitor the adhesive level in the hole 221. The sensor means 23 comprise, but are not limited to, a laser sensor 23 placed at the upper end 221b of the hole 221 so as to 'see' the inside of the hole 221 itself and monitor the level of the adhesive therein.
The sensor means are connected to an electronic control unit that controls at least the supply of glue through the feed port 10, the motion of the worm screw 13 and the switching on/off of the melting means 12.
If the glue level seen by the laser sensor 23 falls below a desired, pre-set level, the laser sensor 23 sends a signal to the control unit, which activates the worm screw and the resistors of the perforated plate to produce new molten adhesive.
This is possible due to the fact that the worm screw 13 can be adjusted in activation and rotational speed, unlike the previously described known systems with pneumatic actuator, which have an intrinsic irregularity in operation, as there is always a need for a compartment loading step and thus a downtime where no molten adhesive can be produced.
In addition, cooling systems such as, but not limited to, a ducted compressed air recirculation system in the compartment can be provided to prevent the adhesive granules from melting in the compartment of the worm screw. Channels of such a recirculation system are shown in
The glue applicator according to the invention achieves several advantages.
Firstly, the applicator achieves the advantage of having a continuous and direct supply of molten glue to the coater roller. This is made possible by the use of the worm screw 13, which provides a continuous feed of molten adhesive from the melting means, limiting the molten glue fed instantly to the coater roller to the required quantity. Instantaneously, therefore, the percentage of molten adhesive in the chamber 21 is reduced to the bare minimum necessary for the instantaneous application of adhesive to the edging band. This makes it possible, first of all, to have a collection chamber 21 that is much smaller than the vats of traditional applicators; in fact, the collection chamber 21 in this case serves only as a simple vessel for the accumulation of excess glue scraped from the periphery of the coater roller and not, as in the case of traditional applicators, as a deposit of molten glue produced beyond the instantaneous working needs of the melting means.
At the same time, the adhesive degradation problems described above (which occur when the molten adhesive sits for a long time in the collection chamber downstream of the melting means) are practically eliminated.
The glue applicator according to the invention also solves the need for adhesive changes, e.g. for colour or type changes. In fact, thanks to the outlet port 16, the adhesive granules still present in the compartment of the worm screw can be pushed out and recovered. The quantity of adhesive lost will therefore only be that at the coater roller, which is minimal.
The present invention has been described hereto with reference to preferred embodiments thereof. It is intended that other embodiments may exist which relate to the same inventive core, all falling within the scope of protection of the claims indicated below.