GB1590487A

GB1590487A - Apparatus continuously manufacturing chipboard or fibreboard panels

Info

Publication number: GB1590487A
Application number: GB8337/78A
Authority: GB
Original assignee: Hermann Berstorff Maschinenbau GmbH
Current assignee: KraussMaffei Extrusion GmbH
Priority date: 1977-03-08
Filing date: 1978-03-02
Publication date: 1981-06-03
Also published as: JPS53110654A; DE2710000A1; SE7802599L; FR2383007A1; FI780534A

Description

(54) APPARATUS CONTINUOUSLY MANUFACTURING CHIPBOARD OR FIBREBOARD PANELS (71) We, HERMANN BERSTORFF MASCHINENBAU GmbH, a body corporate organised and existing under the laws of the Federal Republic of Germany of 3 Hannover Kleefeld, An der Breiten Wiese 3/5, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to apparatus for continuously manufacturing chipboard or fibreboard panels.

In such apparatus chips or fibres are pressed against a revolving heated press drum by a taut endless belt, an upper horizontal pass of which forms a spreading surface for the material to be compressed upstream of the place where the belt runs onto the drum. The material lying on the spreading surface may be pre-pressed in one or more nips between heated rolls and pre-heated by heaters arranged above and below the endless belt. After leaving the press drum the fully pressed strip of chipboard or fibreboard is fed to a machine for further processing.

In previously proposed apparatus for this purpose the heated press drum has had a diameter of 4,000 mm and the direction changing rollers generally have a diameter of 1500 mm. Since the endless belt loops round the press drum and associated direction changing rollers and also forms the surface onto which the chips or fibres are spread, an endless belt approximately 60 metres long is required. The roller which is last as seen in the working direction subjects the belt to high tensile stress, in order to ensure that the belt will exert high pressure on the material to be compressed while looping round the large-diameter press drum. The pressure per unit area which can be obtained in this way is 5 kp/cm2 at the maximum.

The endless belt has to be made of a special steel if it is to withstand the tensile stresses arising from the required pressures per unit area. Strip steel is an ultra high strength material. Merely increasing the thickness of the endless belt so that it can be subjected to higher tensile stresses is not feasible since as the thickness of the endless belt increases the constant changes in bending very rapidly cause fatigue, leading to damage to the belt within a very short time. For this reason the thickness of belt which can be used is very limited.

The endless belt is a costly and expensive part of the machine.

According to the invention there is provided apparatus continuously manufacturing chipboard or fibreboard panels comprising a first endless belt guided around at least two direction changing rollers, said first belt having an upper pass extending in a substantially horizontal plane and positioned below apparatus for spreading onto the belt a layer of chips or fibres to be pressed, rollers defining one or more pre-pressing nips for the layer, at least one heater for pre-heating the layer and disposed above and/or below the upper pass of the belt, a rotatable heated press drum and a further endless press belt guided by further rollers, pressed by said further rollers against a portion of the periphery of the press drum and positioned so that the pre-pressed and pre-heated layer of chips or fibres passes from said first endless belt onto said further endless press belt and is subsequently pressed by said further endless press belt against the press drum and heated as it passes around the press drum to form a chipboard or a fibreboard panel.

The provision of said first belt as a separate preliminary endless belt and forming the spreading surface for the material to be compressed, saves about 30 metres on the length of the further endless belt which co-operates with the press drum. Thus 30 m of a high strength or ultra high strength belt of special steel can be dispensed with, thereby making the machine itself appreciably cheaper.

The first belt acting as a preliminary endless belt forming the spreading surface and disposed upstream of the press drum, need be subjected only to negligible tensile stress, in order to fulfil its function which is purely that of a conveyor belt. The tensile stress is reduced to as little as 1/60th of that applied to the further endless belt co-operating with the press drum. For this reason alone the first belt may be one of lower quality. Since the first belt is subjected only to relatively few changes in bending around its direction changing rollers, it can be expected to have a long life.

The diameters of the direction changing rollers for the further endless steel belt cooperating with the press drum cannot be reduced below a certain level to keep the stresses due to bending of the further endless belt as small as possible. The minimum diameter of the direction changing rollers for the further endless belt is about 1400 mm. Since the tensile stress on the first belt is reduced to as little as 1/60th, it is possible not only to employ a different material for the first belt but also to reduce the cross sectional area of this cheaper quality first belt, i.e. to reduce the belt thickness. This in turn means that the associated direction changing rollers can have a smaller diameter, since the bending stress is reduced linearly with the belt thickness, so that the life of the first belt is not unduly shortened despite use of small diameter direction changing rollers.The use of a separate first, spreading belt thus also makes it possible to use direction changing rollers of considerably smaller diameter for the first, spreading belt.

The invention is diagrammatically illustrated by way of example in the accompanying drawing which is a side elevation of apparatus according to the invention.

Referring to the drawing, a layer of chips or fibres is spread onto an endless belt 2 by a spreading machine 1. The layer of chips or fibres undergoes its first pre-pressing in a first pre-pressing nip between rollers 3, which rollers 3 may be heated. The layer is further heated by preliminary heaters 4 and re-pressed in a second pre-pressing nip between rollers 5. The endless belt 2 on which the layer is spread is guided by direction changing rollers 6 and 7 and conveys the pre-pressed layer over a stationary guide member 8 onto a feed roller 9. The feed roller 9, with an endless press belt 16 running over it, receives the pre-pressed chip or fibre layer and draws it into a continuous press 15.While looping round a press drum 10, the layer of chips or fibres is pressed between the endless press belt 16 and the press drum 10 to form a web of board, and in the process is subjected to very high pressure by rollers 11 and 12 in order to improve the pressing operation. The fully pressed web or board 17 is fed to apparatus (not shown) which cuts it into lengths. After looping round the press drum 10, the endless press belt 16 is guided back onto the press drum 10 by direction changing rollersl4 and 13 and the rollers 11, 9, and effects a further pressing process as it is again looped round the press drum 10. The roller 13 is adjustable in position to adjust the tension in the endless press belt 16 so that a high pressure per unit area can be obtained during the looping of the layer of chips or fibres around the drum 10.

One practical example of the dimensions of the machine is given below: Diameter of press drum 10: 4,000 mm Diameter of pressing and direction changing rollers 9, 11, 13 and 14: 1,550 mm Length of endless press belt 16: approx. 32 m Diameter of direction changing rollers 6, 7 for endless spreading belt 2: 1,000 mm Diameter of the rollers 3 for the first pre-pressing nip. 800 mm Diameter of the rollers 5 for the second pre-pressing nip: 800 mm Length of spreading belt 2: about 33 metres Thickness of spreading belt 2: 1.2 mm Thickness of endless press belt 16 in continuous press 15: 1.8 mm As already mentioned the relatively large diameter rollers 9, 11, 13 and 14 minimise the reversed bending stressses on the endless press belt 16, thereby considerably extending its life.

Since the spreading belt 2 is subject only to negligible tensile stresses, it can be far weaker in design, in respect of both its thickness and its quality without its life being reduced.

What should be specially emphasised is that it is possible to make the diameters of the direction changing rollers 6 and 7 for the spreading belt 2 appreciably smaller than those of the direction changing rollers 9, 11, 13 and 14 for the endless press belt 16, since the reduction in diameter has no effect on the durability of the very expensive endless press belt 16. In prior art machines for continuously manufacturing chipboard or fibreboard panels only one endless belt has been provided, and must be guided below the spreading machine 1 by large diameter direction changing rollers.

The use of a separate spreading belt also has the following very important advantage. In prior art machines with only one endless belt onto which the chips or fibres are spread, the endless belt has to be considerably cooled before the layer of chips or fibres can be spread over it. The belt comes from the heated press drum at a temperature of about 1500C and has to be cooled to about 80 C by a first direction changing roller, corresponding to the roller 7, in the spreading area, which must therefore be provided with a very high power cooler.

Cooling of the endless belt is necessary in order to avoid premature curing of the binder in the very fine lower surface layer of the chips or fibres which contacts the belt. Premature cooling causes scaling of the surface layer, i.e. the bond between the surface layer and an intermediate layer of coarser chips is inadequate.

If a separate spreading belt 2 is used according to the invention, then the endless press belt 16 no longer needs to be cooled. One can therefore save not only the cost of a very expensive cooler for the return roller 7 but also the large amount of heat which such a cooler dissipates. There is also a saving in heating energy for re-heating the endless press belt before it loops against around the press drum 10. During the looping round movement the endless press belt 16 is heated by heaters 18 and by the press drum 10 but less heat is required in the apparatus of the invention since the press belt 16 has not been previously cooled to a significant extent.

A further advantage is that slight deformations which appear in the endless steel belt of prior art apparatus, and which form air cushions between the cooling roller and the belt when the belt is re-cooled, prevent effective re-cooling at these positions. When the chip or fibre layer is spread onto the belt, the binder in the surface layer is prematurely cured, giving the pressed board an uneven surface. If a separate spreading belt 2 is used according to the invention, slight deformations in the endless press belt 16 have no detrimental effect on the surface of the pressed board.

Instead of having a spreading belt 2 made of steel, a wire gauze belt or a coated conveyor belt can be used. In fibreboard production a belt of wire gauze is particularly advatageous if a vacuum is provided under the belt to assist deposition of the chips or fibres.

WHAT WE CLAIM IS: 1. Apparatus continuously manufacturing chipboard or fibreboard panels comprising a first endless belt guided around at least two direction changing rollers, said first belt, having an upper pass extending in a substantially horizontal plane and positioned below apparatus for spreading onto the belt a layer of chips or fibres to be pressed, rollers defining one or more pre-pressing nips for the layer, at least one heater for pre-heating the layer and disposed above and/or below the upper pass of the belt, a rotatable heated press drum and a further endless press belt guided by further rollers, pressed by said further rollers against a portion of the periphery of the press drum and positioned so that the pre-pressed and pre-heated layer of chips or fibres passes from said first endless belt onto said further endless belt and is subsequently pressed by said further endless press belt against the press drum and heated as it passes around the press drum to form a chipboard or a fibreboard panel.

2. Apparatus according to claim 1, including a stationary guide member positioned between the first endless belt and the further endless press belt.

3. Apparatus continuously manufacturing chipboard or fibreboard panels substantially as hereinfore described and illustrated with reference to the accompany drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

As already mentioned the relatively large diameter rollers 9, 11, 13 and 14 minimise the reversed bending stressses on the endless press belt 16, thereby considerably extending its life.

Since the spreading belt 2 is subject only to negligible tensile stresses, it can be far weaker in design, in respect of both its thickness and its quality without its life being reduced.

What should be specially emphasised is that it is possible to make the diameters of the direction changing rollers 6 and 7 for the spreading belt 2 appreciably smaller than those of the direction changing rollers 9, 11, 13 and 14 for the endless press belt 16, since the reduction in diameter has no effect on the durability of the very expensive endless press belt 16. In prior art machines for continuously manufacturing chipboard or fibreboard panels only one endless belt has been provided, and must be guided below the spreading machine 1 by large diameter direction changing rollers.

The use of a separate spreading belt also has the following very important advantage. In prior art machines with only one endless belt onto which the chips or fibres are spread, the endless belt has to be considerably cooled before the layer of chips or fibres can be spread over it. The belt comes from the heated press drum at a temperature of about 1500C and has to be cooled to about 80 C by a first direction changing roller, corresponding to the roller 7, in the spreading area, which must therefore be provided with a very high power cooler.

Cooling of the endless belt is necessary in order to avoid premature curing of the binder in the very fine lower surface layer of the chips or fibres which contacts the belt. Premature cooling causes scaling of the surface layer, i.e. the bond between the surface layer and an intermediate layer of coarser chips is inadequate.

If a separate spreading belt 2 is used according to the invention, then the endless press belt 16 no longer needs to be cooled. One can therefore save not only the cost of a very expensive cooler for the return roller 7 but also the large amount of heat which such a cooler dissipates. There is also a saving in heating energy for re-heating the endless press belt before it loops against around the press drum 10. During the looping round movement the endless press belt 16 is heated by heaters 18 and by the press drum 10 but less heat is required in the apparatus of the invention since the press belt 16 has not been previously cooled to a significant extent.

A further advantage is that slight deformations which appear in the endless steel belt of prior art apparatus, and which form air cushions between the cooling roller and the belt when the belt is re-cooled, prevent effective re-cooling at these positions. When the chip or fibre layer is spread onto the belt, the binder in the surface layer is prematurely cured, giving the pressed board an uneven surface. If a separate spreading belt 2 is used according to the invention, slight deformations in the endless press belt 16 have no detrimental effect on the surface of the pressed board.

Instead of having a spreading belt 2 made of steel, a wire gauze belt or a coated conveyor belt can be used. In fibreboard production a belt of wire gauze is particularly advatageous if a vacuum is provided under the belt to assist deposition of the chips or fibres.

WHAT WE CLAIM IS: 1. Apparatus continuously manufacturing chipboard or fibreboard panels comprising a first endless belt guided around at least two direction changing rollers, said first belt, having an upper pass extending in a substantially horizontal plane and positioned below apparatus for spreading onto the belt a layer of chips or fibres to be pressed, rollers defining one or more pre-pressing nips for the layer, at least one heater for pre-heating the layer and disposed above and/or below the upper pass of the belt, a rotatable heated press drum and a further endless press belt guided by further rollers, pressed by said further rollers against a portion of the periphery of the press drum and positioned so that the pre-pressed and pre-heated layer of chips or fibres passes from said first endless belt onto said further endless belt and is subsequently pressed by said further endless press belt against the press drum and heated as it passes around the press drum to form a chipboard or a fibreboard panel.
2. Apparatus according to claim 1, including a stationary guide member positioned between the first endless belt and the further endless press belt.
3. Apparatus continuously manufacturing chipboard or fibreboard panels substantially as hereinfore described and illustrated with reference to the accompany drawing.