EP2310173B1

EP2310173B1 - Process for edge finishing of mdf boards

Info

Publication number: EP2310173B1
Application number: EP09776218.1A
Authority: EP
Inventors: Søren Wienke IVERSEN
Original assignee: SI Holding Aulum APS
Current assignee: SI Holding Aulum APS
Priority date: 2008-07-10
Filing date: 2009-05-12
Publication date: 2013-11-27
Anticipated expiration: 2029-05-12
Also published as: DK200800968A; DK177227B1; EP2310173A1; CN102149522A; WO2010003418A1; CN102149522B

Description

Field of the Invention

The present invention concerns a method according to the preamble of claim 1 used for preparing an item made of MDF (medium density fibreboard) material before final treatment of the item, which e.g. may be a coating.
It is a known problem that in order to achieve high quality on coated edge surfaces of items made of MDF, extensive sanding and finally careful coating are required. The total manufacturing price of an item based on MDF is strongly influenced by this edge treatment.

Background of the Invention

JP 60220704 A describes a method for edge finishing of fibre boards where a roller is heated with a burner and pressed against the edge of the board. It is very inexpedient to have open fire in a wood item production, and by the indicated method it is very difficult to control the temperature and thereby achieve a uniform quality of the treated items. In many countries there is an outright ban on having open fire in production premises where the working of wood items occurs due to the impending fire hazard.
A further process is disclosed in DE19653317 wherein the edge section of MDF plates is exposed to a tool under the influence of ultrasound. The high frequency of the sound makes the tool oscillate very quickly, whereby a treatment of the edge is achieved.
A still further device and process is disclosed in DE19945346 and DE19810148 (by incorporation) wherein a process for finishing edges of MDF material is disclosed. A rotating tool is brought into contact with the MDF to be treated. The temperature is maintained up to the melting temperature of the adhesive used in the MDF, whereby a smoothening of the edges is achieved. Various means for achieving and maintaining the temperature in the working tool is disclosed. A preferred working temperature is 230°C.
At such high temperatures unwanted working environmental hazards and dangers becomes present, due to increased risk of ignition, fire and even explosions.
From DE20310596 is a further finishing process disclosed. The applicant being the German Institut für Holztechnologie, proposes necessary parameters in order to achieve a satisfying smoothening effect on MDF materials. The temperature is suggested to be maintained in the interval from 200° to 450°C.
As is the case with the previous technology, such high temperatures creates undesirable working conditions, and furthermore discoloration of the MDF material in the heated zone.

Object of the Invention

The purpose of the present invention is to seal the edges of an MDF plate so that the edge coating is easier to perform, i.e. with less preparation, and simplified and in that a uniform quality for all treated items is achieved, the process being mechanical. Furthermore prior art problems relating to high temperature treatment with derived deterioration in working conditions and increased hazards are also addressed and solved by the present invention.
The invention will strongly reduce the time consumption and the costs associated with the use of prior art.
In summary, the invention will thus imply:

A simplified process for finishing treatment of MDF items.
The process can be automated to a wide extent.
Reduced use of time and thereby fewer costs (using less varnish and no abrasive materials).
Uniform quality from one series to another.

The invention finds application in all products where MDF is used, e.g. but not limited to:

Furniture
Kitchen and bath equipment
Shop equipment
Display equipment
Partitionings
Boards, strips and panels

The MDF material is widely used in the wood industry for making furniture, cabinets and fixtures, among others. MDF is made of fine wooden fibres with glue as binder.
The material is relatively easy to work, and by cutting a stable structure is left which can be finished into an acceptable product quality. A very used finishing treatment is sanding and filling, ended by coating.
However, the prior art method is inexpedient to integrate in an automated production facility. In the polishing stage, wax-containing components are used which are frequently deposited on various tool elements as an inadvertent side effect. Besides, the process typically requires manual handling in shifting between the different stages of production.
Due to the structure in the MDF materials having glue as binder, a heating process will be a usable treatment of item edges in order to reactivate the glue, smooth the edge and thereby achieve a hardened, homogenous and tight surface which is ready for coating. In this connection it is important to note that when heating the adhesive in order to reactivate it, the present invention only heats until reactivation is achieved. More heating, i.e. to a higher temperature will cause most adhesives used in MDF to crystallize, which will require more smoothening action, and thereby longer and more costly working time.
It is the object of the invention to automate the edge treatment most possible such that the edge of the item can be hardened by heat and made ready for coating, this without having to use tools in which fire form a part.

Description of the Invention

A first aspect of the invention is a process for finishing edges of items (10) made of MDF material, the process being characterised by:

a tool mounted in means that cause the tool to rotate;
an edge of the item being subjected to a pressure action by a machining surface on the rotating tool;
the rotating tool being imparted a movement at a feeding speed along the edge of the item and in contact with the latter while acting on the edge of the item.

The moving of the tool relative to the item may be by moving the item forward/back relative to the tool, or by moving the tool forward/back in relation to the item; this is termed the relative feeding speed of the tool.
The friction between the edge of the item and the rotating tool causes a brief local heating which acts as a kind of reactivation of the glue component in the fibre structure of the MDF item. By reheating, the glue in the MDF board is reactivated such that the mechanical action by the tool partly melts, extracts and redistributes the glue in the outermost material layer where the items is worked. Hereby is achieved a smooth, even and very uniform edge surface which largely do not need any treatment afterwards before varnishing or painting.
According to the invention, the temperature of contact surface of the tool against the item is determined by:

the relative feeding speed of the rotating tool;
the pressure action of the rotating tool;
the material and surface structure of the tool; and
the rotational speed of the tool;
means for heating the contact surface of the tool.

As the process is effected mainly by friction between the edge of the item and the tool, it will be possible to regulate the process itself by adjusting either the relative feeding speed between tool and board, i.e. the higher the speed, the higher temperature, as the frictional heat produced between the MDF material and the tool will increase due to an increased speed. Similarly, an increased pressure, i.e. also an increase of the friction between the item and the rotating tool will cause a rise in temperature. Correspondingly, reducing the speed or the pressure will reduce the friction, thereby lowering the temperature. The material and surface structure of the tool also influence the temperature, as well as MDF boards may be made with different densities, and in some cases it may be desirable to modify the surface structure of the tool such that the most optimal friction between the item and the tool is achieved with regard to reactivating the glue. Also, it would obviously be possible to change the rotational speed of the tool whereby the same advantages as mentioned above are achieved in connection with the feeding speed and the pressure, as an increased rotational speed entails increased friction and thereby increased temperature, and a lower rotational speed will lower the friction between the items and thereby the temperature.
According to the invention, the process is controlled such that the range of the temperature of the tool surface in contact with the item is from 45°C to 90°C. In this temperature range, the glue may be reactivated in such a way that it becomes partially fluid and is smoothed whereby a smooth and relatively dense edge structure is achieved. At substantially higher temperatures, the temperature begins to have influence on the MDF material, and therefore it is desirable to keep the friction at a level such that the temperature is kept in the indicated interval.
It is surprising that it is possible to achieve this effect at such low temperatures, as the prior art unanimously suggests temperatures of at least 200° C or more.
In a further preferred embodiment of the process, the pressure action by the rotating tool is angled 0 -> 90° relative to the X - Y plane of the item.
The items treated will typically be plate items where the length and the width of the plate are presently referred to as X- and Y-axes, respectively, and the thickness of the plate will typically be termed the Z-axis. The X-Y plane is thus the larger part of the plate. It is important to control the angle of attack of the tool against the item, as there may be applied different bevellings on the edges according to the particular construction in which the MDF item is to form part; for example, it will often be natural in kitchen designs that the MDF boards are cut perpendicularly to the plane of the board, whereas in furniture production, there will often be a need for a sloping bevelling or even a rounding. By thus providing in the process that pressure action of the rotating tool can be angled relative to the X-Y plane of the board, it is thus possible to configure the tool to largely all tasks.
In a further preferred embodiment of the process, the MDF item can be moved relative to the rotating tool, or the rotating tool can be moved relative to the MDF item.
In some embodiments where the tool forms part of a large processing facility, it will be more expedient to move the MDF items past the tool as there is probably other processing stations before or after the edge machining process, and in that way a relatively rational MDF machining facility may be built up.
By also having the option of moving the tool relative to the item, handheld or small apparatuses that may be moved along the side of MDF panels may therefore be used for small or special production series.
In yet a further embodiment of the process according to the invention, electronic means are used for an automatic control and optimisation based on the parameters and process data for tool pressure against item, tool temperature and/or temperature of the point of attack by the tool on the item, rotational speed of the tool and feeding speed of the tool.
By applying electronic means is achieved that the entire process, in particular in a large plant, can be controlled via a central computer such that the process parameters can be optimised all the time and be kept within the given intervals, either by regulating the pressure, the feeding speed, the positional speed of the tool, etc.
This also provides possibility of further embodiments of the invention where calculations are made for accumulated active time consumption per tool, and/or performing calculations of the accumulated length of the edge machining.
Typically, the edges of the MDF items will, after being treated by a process as mentioned above, be prepared to a painting or varnishing process which thus finishes the treatment of the item.

Description of the Drawing

Preferred applications of the invention are explained in the following with reference to the Figures, wherein:

Fig. 1: shows an example of how an MDF board is processed by a tool;
Fig. 2: shows another example of how an MDF board is processed by a tool;
Fig. 3, 4, 5: show various examples of edge formation that can be processed;
Fig. 6: shows schematically the control means used for controlling the process;
Fig. 7: shows an example of a production line of which the invention forms a part.

The invention finds application in a fully automated production unit in which the processed MDF items are finished such that they are ready for coating.
An important aspect of the invention is the use of a rotating tool which is fed under pressure along the edge of the MDF item in a continuously progressing movement. The friction arising between the rotating tool and the MDF item develops heat that reactivates, redistributes and re-hardens the glue in the MDF material.
The effect of the process is a combination of:

Structure and composition of the MDF material.
The rotational speed of the rotating tool.
The feeding speed of the rotating tool.
The pressure of the rotating tool against the MDF item.
The action of temperature on the edge of the item.
The geometric shape and material of the rotating tool.

Preliminary tests display good results by using:

MDF board with plate thickness in the range 5 mm -> 25 mm; typically 12 mm.
Rotational speed of tool in the range 1100 rpm -> 1300 rpm; typically 1200 rpm.
Feeding speed of tool/item, even and continuous at 6 -> 10 m/min; typically 8 m/min.
Pressure of tool against item 1 -> 4 bar, typically 3 bar by a 12 mm item if there is an adjacent rabbet or groove parallel with and close to the edge.
Pressure of tool against item 1 -> 8 bar, typically 6 bar by a 12 mm item without an adjacent rabbet parallel with and close to the edge.
The geometric shape and material of the tool: Circular tool and size will depend on the capacity of the machine, 10-20 cm in diameter, made of hardened tool steel, Cr-Va-steel, steel K340 or similar; diameter typically 17 cm.
The steel item may be chromium-plated.
Alternatively may be used a ceramic tool or a combined steel and ceramic tool.
Temperature range of the contact surface of the tool is 45°C to 90°C, typically 60°C.

All geometric edge profiles can be processed and the shape of the machining tool in question can be adapted correspondingly, for example but not limited to: ellipse, circle, triangle and rounded square.
In the above example, the rotational speed of the tool varied between 1100 and 1300 rpm, but nice results has also been achieved at substantially higher speeds, up to 6000 rpm.
Another aspect of the invention is that the tool contact against the edge of the item may vary, depending on the desired edge profile:

a process wherein the pressure action (13) by the rotating tool is parallel with the X - Y plane of the item;
a process wherein the pressure action (13) by the rotating tool is angled 0-> 90° relative to the X - Y plane of the item.

The decisive element in the process is that the rotating tool is moved forward or backward in relation to the item. This means irrespectively of the item being moved or the tool being moved, the result is the same.
A process wherein:

the MDF item (10) is moved in relation to the rotating tool (11); or
the rotating tool (11) is moved in relation to the MDF item (10).

Fig. 1 shows an example of how the edge (12) of an MDF board (10) is processed by a rotating tool.
The rotating tool has a bevelling that fits the edge profile by a tolerance of typically 1/10 mm.
The rotating tool is not a cutting tool but rather bevelled in such a way that a homogenous pressure is exerted across the entire edge. The tool is advanced along the edge and bears physically on the edge with a constant pressure/temperature.
By too high temperature, the pressure against the item is alleviated or the rotational speed of the tool is reduced, and by too low temperature, the pressure or the rotational speed of the tool is increased. The rotating tool has a rotary axis (15) which is perpendicular to the surface of the board.
In the indicated example, the pressure (13) is directed inwards against the edge of the board in parallel with the X, Y plane of the board, i.e. in parallel with the surface of the board.
Standard means (5) for producing the rotation of the tool can be a motor with fixed rotational speed or a motor where the rotational speed can be varied up/down. Alternatively, the rotating means can be controlled by pneumatics or hydraulics.
Standard means (16) for performing the required pressing (13) by the tool against the item can be implemented by hydraulics, by pneumatics or as a controllable spring arrangement, e.g. torsion mechanics and a piston.
Fig. 2 shows another example of how the edge (12) of an MDF board (10) is processed by a rotating tool (11). The rotating tool has no bevelling.
The rotating tool is not a cutting tool but bevelled in such a way that a homogenous pressure is exerted across the entire edge. The tool is fed along the edge and bears physically on the edge with a constant pressure/temperature. The rotating tool has an axis of rotation (15) which is angled about 45° relative to the surface of the board.
In the indicated example, the pressure (13) is directed inwards against the edge of the board perpendicularly to the surface of the edge, thus angled relative to the X, Y plane of the board, i.e. angled relative the surface of the board.
Figs. 3, 4 and 5 show various examples of edge shapes that may be processed. The edge of the item may have arbitrary geometric shape, e.g. but not limited to: rectangle, ellipse, circle, triangle and rounded square.
The shape of the tool is designed such that it fits the given task, and may be formed with a cutout like the tool (11) indicated in Fig. 1, or without cutout like the tool (11) indicated in Fig. 2.
Fig. 6 shows a preferred process setup. The rotating tool (11) is driven by a motor including means for controlling rotation of the tool (17) at a stable rotational speed. The tool is fed (14) along the item (10) via means, e.g. a motor and a spindle, including means (18) that ensure stable and continuous feeding speed.
As alternative to feeding the tool (11, 18), the board (10) may be advanced (26) in contact with the tool (11) via a standard conveyor system (22, 23) simultaneously holding the board. The direction of rotation of the tool (11) may advantageously be following in relation to the feeding direction (26) of the item.
In order to improve the quality of finishing and to achieve a continuous and uniform feeding of the tool, means (16) which can influence the acting pressure of the tool on item (10) are used. During the machining there will compensated in this way for inhomogenities in the hardness of the item. These means can be a simple spring load or a controlled hydraulic device.
The temperature of the attack surface of the tool (11) against the item (10) is an important and decisive factor in order to achieve high finish on the machined edge. The temperature can be measured via standard means, e.g. by means of an optical/thermographic external measuring apparatus (20), or alternatively via a built-in thermometer in the metal part of the tool.
Means (6) for stabilising the temperature of the tool, i.e. keeping the temperature constant when the tool is not actively processing a board edge may advantageously be implemented, e.g. in the time between the end of processing a board until the next board is brought to engage the tool.
Standard means in the form of a heating element (6) in which fire does not form part is usable, e.g. based on electric/magnetic induction. A practical arrangement may be that the tool is rotated in a gap between two heating elements.
In a variant of this function, i.e. for maintaining the operating temperature of the tool when no items are processed, an MDF board piece with same edge profile may temporarily be introduced. By holding the board piece against the tool, the temperature can be maintained in the tool without necessitating incorporation of other, more expensive means. The board piece may e.g. be mounted at the end of a cylinder rod which is activated when no items for machining pass by.
Typically, the surface temperature of the tool is registered by means of a temperature sensor including a laser.
As an element in administrative functions, advantageously there may be implemented standard means for detecting when a new board is machined. For example, a simple infrared sensor (21) may sense whether a board is processed or not. The feeding speed of the conveyor belt is accessible, and the speed in possibly measurable and controllable via standard control means (22).
Relevant functions that may be calculated and used are e.g.:

Board consumption which is a sum of the machined edge length.
o Detect time (time-object) for object/no object.
○ Feeding speed (speed-object) of conveyor belt and thereby of the object.
o Edge length of a board machined in one cell;
length = 2 x t-object [s] x speed-object [m/s]
Time consumption for the rotating tool, i.e. how many minutes the tool has been actively operating.

Depending on the requirements to production quantities and degree of automation, the invention can be used as element in large/small cell concept, wherein:

One cell has means for processing an item on one edge at a time; or
one cell has means for processing an item on two edges at a time, where in this setup typically parallel edges are machined simultaneously and pressure is exerted on the tool simultaneously on both edges;
two cells may support machining of all four item edges.

In a more advanced process setup, further electronic means (19) may be used for an automatic control and optimisation based on the parameters and process data for tool pressure against item, tool temperature, rotational speed and feeding speed of the tool.
In an automated configuration, a control may be achieved in several alternative ways where the primary goal is to keep the temperature in the point of attack of the tool constant and at operational value or in a permissible operational range.

In a production, it will normally be advantageous that feeding of items is performed with constant speed, and control parameters primarily become:

Rotational speed of rotating tool	Pressure of rotating tool against the item	Feeding speed of item versus tool
Constant	Variable	Constant
Variable	Variable	Constant
Variable	Constant	Constant

Standard equipment can be used for the necessary control (19), as an example but not limited to: pneumatics, springs, rubber rollers, PC's, microprocessors and PLL controls. The control unit may include a stand-alone unit containing computer, screen, operating means, memory and storage medium, and/or it may be a component in an integrated automated production facility which comprises network based client/server technology with access to intranet and to Internet.
Fig. 7 shows a preferred implementation of the invention in a production setup of which several cells coupled together via conveyor belts (23) are part.
Items in the form of MDF boards (10) are introduced on the conveyor belt at inlet (30). The item (10) is automatically advanced to the first processing cell (31) where two parallel edges are machined by the rotating tool (11) which is subjected to pressure by the pressure exerted on the tool (13).
Items are automatically moved on to a shifting position (32) from where the item is fed on along the conveyor belt to the second cell (33) where two parallel edges are machined by the rotating tool (11) which is subjected to pressure by the pressure exerted on the tool (13).
The edges of the item are hence ready for coating and may quality assessed in a possible final inspection (34).
A fully automatic processing system may have an integrated coating cell (24) which is part of finishing the item; in that case items may automatically be moved to a position (35) where coating of the edges is effected via nozzles/rollers (25) disposed in the coating cell. The nozzles may e.g. be movable and controllable.
A more simple coating process in which no movable nozzles are required can be effected with two coating cells provided in the course of the process (24.1 and 24.2). In each of these cells, two edges are coated at a time, while items are conveyed via the conveyor belt (23).
In a fully automated setup, extensions can be made with standard means for an automatic control of board feeding (30) and disposition of items (10) on the conveyor belt (23).
The invention may find application in production of objects which are made of MDF material and where high quality of the visible edges is demanded. The list of items is long, and the following are just examples: racks, shelves, cabinets, boxes, strips, panels, partitionings, frames etc.

Claims

A process for finishing edges of items (10) made of MDF material, comprizing
• a tool mounted in means that cause the tool to rotate;

• an edge (12) of the item being subjected to a pressure action by a machining surface on the rotating tool (11);

• the rotating tool (11) being imparted a movement at a feeding speed along the edge of the item and in contact with the latter while acting on the edge (12) of the item;
wherein the temperature of contact surface of the tool against the item is determined by:

• the relative feeding speed of the rotating tool;

• the pressure action of the rotating tool;

• the material and surface structure of the tool; and

• the rotational speed of the tool;

• means for heating the contact surface of the tool,
characterised in that the temperature range of the contact surface of the tool with the item is from 45°C to 90°C.
A process according to claim 1, wherein the pressure action (13) by the rotating tool is angled 0 -> 90° relative to the X - Y plane of the item.
A process according to one or more of claims 1 to 2 above, characterised in that
• the MDF item (10) is moved in relation to the rotating tool (11); or

• the rotating tool (11) is moved in relation to the MDF item (10).
A process according to claim 1, characterised in that electronic means (19) are used for an automatic control and optimisation based on the parameters and process data for tool pressure against item, tool temperature and/or temperature of the point of attack by the tool on the item, rotational speed of the tool and feeding speed of the tool.
A process according to claim 1, characterised in that calculation of the accumulated length of the edge finishing is performed.
A process according to claim 1, characterised in that calculation of the accumulated active use of time per tool is performed.
A process according to claim 1, characterised in that a painting process ends the edge fmishing.