Method and arrangement for manufacturing a mineral fibre web

Description

[0001] The invention relates to a method and an arrangement for manufacturing a mineral fibre web according to the preambles of the independent claims presented further below.

[0002] Mineral fibres are manufactured by melting suitable mineral-containing raw materials, such as diabase, limestone or slag in a melting furnace. The obtained melt is led to a fiberising apparatus, where it is formed into mineral fibres. A cascade-type fiberiser may typically be used as a fiberising apparatus, the cascade-type fiberiser typically comprising four fiberising rotors which rotate around a horizontal or nearly horizontal axis. The axes of the fiberising rotors are typically arranged on different heights. Melt is fed to the mantle surface of the first fiberising rotor, where a part of it adheres. Other part of the melt is thrown towards the mantle surface of the second fiberising rotor. Again a part of the melt gets a hold of the mantle surface and the rest of the melt is thrown towards the mantle surface of the third rotor. A part of the melt again adheres to the third mantle surface and the rest is thrown to the fourth mantle surface, of which preferably the entire remaining melt mass gets a hold. The melt, which has got a hold of respective rotors' mantle surface, is by means of centrifugal force formed into fibres, which detach from the melt rings on the fiberising rotors. Mineral fibres may also be manufactured by feeding mineral melt into a rotating cup-like centrifuge. On the outer circumference of the centrifuge cup have been arranged holes through which mineral melt is thrown, forming at the same time mineral fibres.

[0003] The detachment of the fibres, their trajectory after detachment, and also their qualitative properties may be assisted by arranging air blows near or around the fiberising apparatus, the force and the direction of which air blows may be used to influence also the properties of the forming fibres. The fibres are directed from the fiberising apparatus to a moving collecting member, for example to an inclined conveyor or a rotating drum, arranged in front of the fiberising apparatus, in the second end of the collecting chamber. Binder is also generally added to the fibres before their collection. A continuous primary mineral fibre web, i.e. a primary fibre web, is thus formed on the collecting member, which web is transferred with the aid of conveyors from the collecting member to be processed further.

[0004] Generally the aim is to collect the primary fibre web as thin and light as possible onto the collecting member. It is possible to collect a primary fibre web, the surface weight of which corresponds to the surface weight of the final product, but then an uneven result is often obtained, and the orientation of the fibres cannot be controlled to a sufficient extent. In practise a light primary fibre web is therefore collected, from which a secondary fibre web having a desired weight is formed later in the process, for example by folding.

[0005] One problem in the manufacturing of a secondary fibre web formed by folding has been that certain normal variation occurs in the surface weight of the primary fibre web during the manufacturing process, whereby also the surface weight of the folded secondary fibre web varies. Variation in the surface weight of the secondary fibre web also occurs if the conditions during the folding stage of the primary fibre web do not remain constant in a desired manner.

[0006] Publication EP 1997944 discloses a method for manufacturing mineral wool. In the method surface weight of the mineral fibre web is measured in several locations with a method based on the attenuation of x-rays before the web is cured. The results are used to control at least one process parameter. In the method the process parameter is controlled based on a measurement result obtained from the process. This may lead to "swaying" of the process and to complicated adjustment procedures.

[0007] One object of the present invention is to reduce or even eliminate the above-mentioned problems, which appear in the prior art.

[0008] One object of the present invention is to provide a method, with which variations occurring in the surface weight of the secondary fibre web can be minimised.

[0009] The above-mentioned disadvantages are eliminated or reduced, and the above-mentioned objects are attained with the present invention, which is characterised in what is defined in the characterising part of the independent claims presented further below.

[0010] Some preferred embodiments according to the invention are disclosed in the dependent claims presented further below.

[0011] A typical method according to the invention for manufacturing a mineral fibre web and for improving the homogeneity of the manufactured fibre web comprises

• producing mineral fibres with a fiberising apparatus,
• collecting the produced mineral fibres onto a moving collecting member and forming a continuous primary fibre web, which primary fibre web has edges and which defines a first longitudinal direction, which is unidirectional, i.e. parallel, with the edges, the primary fibre web mainly comprising fibres arranged in the first longitudinal direction,
• transferring the primary fibre web in the first longitudinal direction,
• arranging by folding the primary fibre web into partly overlapping layers transversally to the first longitudinal direction in order to form a secondary fibre web, whereby the secondary fibre web defines a second longitudinal direction and a first transverse direction, the secondary fibre web thus mainly comprising fibres arranged transversally to the second longitudinal direction, and which secondary fibre web has a first and a second parallel large surface, which large surfaces comprise the edges of the primary fibre web and the distance between which surfaces defines the height direction of the secondary fibre web, which height direction is perpendicular to the second longitudinal direction and the first transverse direction, the folds in the primary fibre web forming the side edges of the secondary fibre web,
• selecting a target surface weight of the secondary fibre web and one of the following selection variables:
  i) a whole number representing the number of folds in the vertical direction of the secondary fibre web, or

  ii) surface weight of the primary fibre web to be collected,
  whereby the production value of the unselected selection variable is determined with the aid of the target surface weight of the secondary fibre web and the selected selection variable, and the manufacturing process is adjusted to obtain the production value.

[0012] A typical arrangement according to the invention for manufacturing a mineral fibre web comprises

• at least one fiberising apparatus for producing mineral fibres,
• blowing means for blowing the mineral fibres off the fiberising apparatus,
• a moving collecting member arranged in front of the fiberising apparatus, on which the blown mineral fibres are collected as a continuous primary fibre web, which has edges and which web defines a first longitudinal direction, which is unidirectional, i.e. parallel, with the edges,
• transfer means for transferring the primary fibre web away from the collecting member,
• folding means for folding the primary fibre web into partly overlapping layers transversally to the first longitudinal direction in order to form a continuous secondary fibre web, whereby the secondary fibre web defines the second longitudinal direction and the first transverse direction, the secondary fibre web thus mainly comprising fibres arranged transversally to the second longitudinal direction, and which secondary fibre web has a first and a second parallel large surface, which surfaces comprise edges of the primary fibre web and the distance between which surfaces defines the height direction of the secondary fibre web, which is perpendicular to the second longitudinal direction and the first transverse direction, the folds in the primary fibre web forming the side edges of the secondary fibre web,
• weighing means for determining the surface weight of the secondary fibre web, whereby the arrangement further comprises
• optimising means into which a target surface weight of the secondary fibre web and one of the numeral values representing the following selection variables is fed and/or stored:
  i) a whole number representing the number of folds in the vertical direction of the secondary fibre web, or

  ii) surface weight of the primary fibre web to be collected,

  • weighing means for determining the surface weight of the primary fibre web,
  • calculation means, with which a production value of the unselected selection variable is determined with the aid of the target surface weight of the secondary fibre web and the numeral value of the selected selection variable fed and/or stored into the optimising means, and
  • adjustment means for adjusting the manufacturing process and for obtaining the determined production value.

[0013] Now it has surprisingly been found out that by adjusting the manufacturing process of the mineral fibre web by using the target surface weight of the secondary fibre web together with either a) a whole number representing the number of folds in the vertical direction of the secondary web, or b) surface weight of the primary fibre web to be collected, or possibly all three variables together, it is possible to produce a homogeneous secondary fibre web and/or to control the conditions of the fiberising process substantially better than before. Highly preferably in this manner it is possible to produce a secondary fibre web, which surface weight may be kept constant substantially better than before. In the method according to the present invention the essential variables have thus been found and determined, with the aid of which variables the manufacturing process may be easily controlled and guided in the right direction. In the method according to the invention the aim is thus not to adjust the manufacturing process with the aid of information obtained directly from the process, but the aim is to guide it based on pre-selected values of the production variables.

[0014] The folding of the primary fibre web may be performed normally by using folding means, such as for example a pendulum conveyor, which may comprise for example two vertical conveyor elements placed against each other, between which the primary fibre web is guided. The upper end of the pendulum conveyor is attached to a supporting point and its lower part is allowed to perform a pendulum motion in the lateral direction of a receiving conveyor. The primary web is discharged from the lower part of the pendulum conveyor, from the space between the conveyor elements placed against each other to the moving receiving conveyor, where it is arranged into partially overlapping layers. The primary web forms a fold at the edges of the receiving conveyor, where the pendulum conveyor changes its direction of motion during the folding process. The folded primary web forms the secondary web.

[0015] The whole number representing the number of folds of the fibre web in the vertical direction of the secondary fibre web may be determined by observing the secondary fibre web from the side and by counting the folds of the fibre web located on the perpendicular vertical line drawn from its first large surface to its second large surface. The observation direction is thus at a 90 degree angle in relation to the advancing direction of the secondary fibre web. The observation direction is at a 90 degree angle also in relation to the lateral direction of the secondary fibre web, which is at a 90 degree angle in relation to the advancing direction of the secondary fibre web. The whole number representing the number of folds is typically between 1-50, more typically between 2-40, most typically between 3-30. The whole number may also preferably be between 5-15, sometimes preferably between 6-12.

[0016] According to one embodiment of the invention, a production value for the surface weight of the primary fibre web to be formed is determined with the aid of the target surface weight of the secondary fibre web and the whole number representing the number of folds in the vertical direction of the secondary fibre web. This means that the surface weight of the primary fibre web to be formed is selected based on the target surface weight of the secondary fibre web and the number of folds to be produced. Typically the surface weight of the primary fibre web varies between 200-375 g/m², more typically between 250-350 g/m². When the process operator thus has defined a whole number representing the desired number of folds in the secondary fibre web and the target surface weight of the secondary fibre web, a surface weight for the primary fibre web is defined on the basis of these values, which surface weight is within the variation interval allowed by the process and with which the target values of the predetermined variables may be obtained.

[0017] The selected surface weight of the primary fibre web to be collected may be obtained by adjusting other suitable process parameters, for example by altering the speed of the collecting member. Thus the speed of the collecting member is altered to be suitable for the production process, i.e. the speed of the collecting member is not too slow, whereby the collected primary fibre web would become too heavy to be processed in the subsequent process devices, and neither too fast, which would cause problems in coordinating the speeds of the subsequent process devices. Typically the speed of the collecting member is selected to vary between 40-250 m/s, more typically 50-200 m/s. It is possible to influence the surface weight of the primary fibre web also by adjusting the amount of mineral fibres to be formed, i.e. by increasing or decreasing the amount of formed fibres.

[0018] According to one preferred embodiment of the invention, the number of folds in the vertical direction of the secondary fibre web is essentially the same in two different locations of the secondary fibre web, which are situated at a distance from each other in the longitudinal direction, i.e. travel direction, of the secondary web. The number of folds in the vertical direction of the secondary fibre web is most preferably essentially the same in every location of the secondary fibre web, i.e. the whole number representing the number of folds of the fibre web in the vertical direction of the secondary fibre web is thus preferably constant in every location of the secondary fibre web in the travel direction of the web. With a fold amount, which is as uniform as possible in different locations of the secondary fibre web, a surface weight which is as uniform as possible and thus also a homogeneous density of the secondary fibre web may be ensured.

[0019] According to one embodiment of the invention the first end of the first fold of the primary fibre web on the first large surface of the secondary fibre web is in the vertical direction essentially at the same perpendicular line with the second end of the second fold of the primary fibre web on the second large surface of the secondary fibre web. Between the first and second fold there may be an optional number of folds, having first and second ends which are arranged at the same vertical line with the ends of the other folds in a corresponding manner.

[0020] The folds of the primary fibre web and their number may be observed with observation and/or viewing means, for example with a camera, which may have been operationally connected to a picture recognition unit. With the aid of the picture recognition unit or picture recognition system, the number of folds of the primary fibre web, which form the edge of the formed secondary fibre web, and their position in relation to each other, may automatically be determined. If a deviation is noticed in the number of folds, the folding process may be corrected, for example by altering the speed of the receiving conveyor.

[0021] In one embodiment of the invention the true surface weight of the secondary fibre web is measured at predetermined intervals, even continuously, and with the aid of the measured surface weight and the selected selection variable, the production value of the unselected selection variable is redetermined at predetermined intervals, and the manufacturing process is adjusted to obtain the production value. The redetermination of the production value of the unselected selection variable may be performed automatically or the process operator may perform the redetermination of the production values by manually adjusting.

[0022] In one embodiment of the invention the weight of the primary and/or secondary fibre web may be measured with the aid of a weighing conveyor.

[0023] In the following, the invention will be described in more detail with reference to the appended schematic drawing, in which

[0024] Figure 1 shows an exemplary arrangement according to the invention.

[0025] In Figure 1 is shown an exemplary arrangement according to the present invention. A primary fibre web 1 is folded with folding means 2, which move as a pendulum from one side to the other perpendicularly out from the level of the paper. Thus the primary fibre web is arranged into folds 3, 3', 3", 3"', which are arranged partly overlapping each other, and which form a secondary fibre web 4, which has a first large surface 4' and a second large surface 4". The first edge 1' of the primary fibre web 1 forms an essential part of the first large surface 4' of the secondary fibre web 4 and correspondingly the second edge 1" of the primary fibre web 1 forms an essential part of the second large surface 4" of the secondary fibre web 4. The primary fibre web 1 comprises mineral fibres, which are generally mainly arranged in the advancing direction of the primary fibre web, which in Figure 1 has been shown with an arrow A. The primary fibre web generally also comprises one or several binders, possibly also other additives, such as fire retardants. Additives and/or binders may be added to the web in connection with the folding or just before the folding.

[0026] The secondary fibre web formed of the folded primary fibre web 1 is formed on the receiving conveyor 5, by adjusting the advancing speed of which the angle and number of the folds 3, 3', 3", 3"', and thus also the thickness and surface weight of the secondary fibre web may be adjusted. From the receiving conveyor 5 the secondary fibre web is transferred to a further conveyor 6, which may for example be a weighing conveyor, with which the surface weight of the formed secondary fibre web may be measured.

[0027] The secondary fibre web is thus formed of folds 3, 3', 3", 3", the first ends 31, 31' of which are located on the first large surface 4' of the secondary fibre web 4 and the second ends 32, 32' on the second large surface 4" of the secondary fibre web 4. Preferably the folds 3", 3"' are arranged so that the first end 31 of the fold 3" on the first large surface 4' is in the vertical direction on the same line as the second end 32' of the fold 3"' on the second large surface 4". The location of the ends 31, 32' on the same imaginary line is illustrated in Figure 1 with dotted lines.

[0028] When the ends of the folds are aligned, the variation occurring in the surface weight of the secondary fibre web may be minimised and a web may be obtained, the surface weight of which remains within the limits of a very small variation interval. The folding may be monitored with viewing means (not shown), which may have been connected to the process monitoring and controlling system.

[0029] One embodiment of the invention has been described in the following non-limiting example.

EXAMPLE

[0030] The target surface weight of the secondary fibre web m_sek to be manufactured is selected as 3 kg/m². The number of folds n, is selected as the selected selection variable, which is given the value 10. Thus the surface weight of the primary fibre web m_prim may easily be calculated by m/n, whereby the value 0,3 kg/m² is obtained.

[0031] It is apparent to a person skilled in the art that the invention is not limited exclusively to the examples presented above, but that the invention may vary within the scope of the claims presented below.

Claims

1. A method for manufacturing a mineral fibre web, which comprises

- producing mineral fibres with a fiberising apparatus,

- collecting the produced mineral fibres onto a moving collecting member and forming a continuous primary fibre web, which primary fibre web has edges and which defines a first longitudinal direction, which is parallel with the edges, the primary fibre web mainly comprising fibres arranged in the first longitudinal direction,

- transferring the primary fibre web in the first longitudinal direction,

- arranging by folding the primary fibre web into partly overlapping layers transversally to the first longitudinal direction in order to form a secondary fibre web, whereby the secondary fibre web defines a second longitudinal direction and a first transverse direction, the secondary fibre web thus mainly comprising fibres arranged transversally to the second longitudinal direction, and which secondary fibre web has a first and a second parallel large surface, which large surfaces comprise the edges of the primary fibre web and the distance between which surfaces defines the height direction of the secondary fibre web, which height direction is perpendicular to the second longitudinal direction and the first transverse direction, the folds in the primary fibre web forming the side edges of the secondary fibre web,
characterised in

- selecting a target surface weight of the secondary fibre web and one of the following selection variables:

i) a whole number representing the number of folds in the vertical direction of the secondary fibre web, or

ii) surface weight of the primary fibre web to be collected,
whereby the production value of the unselected selection variable is determined with the aid of the target surface weight of the secondary fibre web and the selected selection variable, and the manufacturing process is adjusted to obtain the production value.

2. The method according to claim 1, characterised in determining the production value for the surface weight of the primary fibre web to be collected with the aid of the target surface weight of the secondary fibre web and the whole number representing the number of folds in the vertical direction of the secondary fibre web.

3. The method according to claim 1 or 2, characterised in that the selected or determined target surface weight of the primary fibre web to be collected is obtained by altering the speed of the collecting member.

4. The method according to any of the claims 1-3, characterised in that the number of folds in the vertical direction of the secondary fibre web is essentially the same in two locations of the secondary fibre web, which locations are at a distance from each other in the longitudinal direction.

5. The method according to claim 4, characterised in that the first end of the first fold of the primary fibre web on the first large surface of the secondary fibre web is in the vertical direction essentially at the same perpendicular line with the second end of the second fold of the primary fibre web on the second large surface.

6. The method according to any of the preceding claims 1-5, characterised in that the true surface weight of the secondary fibre web is measured at predetermined time intervals, and with the aid of the measured surface weight and the selected selection variable, the production value of the unselected selection variable is redetermined at predetermined time intervals, and the manufacturing process is adjusted to obtain the production value.

7. An arrangement for manufacturing a mineral fibre web, which comprises

- at least one fiberising apparatus for producing mineral fibres,

- blowing means for blowing the mineral fibres off the fiberising apparatus,

- a moving collecting member arranged in front of the fiberising apparatus, on which the blown mineral fibres are collected as a continuous primary fibre web, which has edges and which web defines a first longitudinal direction, which is parallel with the edges,

- transfer means for transferring the primary fibre web away from the collecting member,

- folding means for folding the primary fibre web into partly overlapping layers transversally to the first longitudinal direction in order to form a continuous secondary fibre web, whereby the secondary fibre web defines the second longitudinal direction and the first transverse direction, the secondary fibre web thus mainly comprising fibres arranged transversally to the second longitudinal direction, and which secondary fibre web has a first and a second parallel large surface, which surfaces comprise edges of the primary fibre web and the distance between which surfaces defines the height direction of the secondary fibre web, which is perpendicular to the second longitudinal direction and the first transverse direction, the folds in the primary fibre web forming the side edges of the secondary fibre web,

- weighing means for determining the surface weight of the secondary fibre web, characterised in that
the arrangement further comprises

- optimising means into which a target surface weight of the secondary fibre web and one of the numeral values representing the following selection variables is fed and/or stored:

i) a whole number representing the number of folds in the vertical direction of the secondary fibre web, or

ii) surface weight of the primary fibre web to be collected,

- weighing means for determining the surface weight of the primary fibre web,

- calculation means, with which a production value of the unselected selection variable is determined with the aid of the target surface weight of the secondary fibre web and the numeral value of the selected selection variable fed and/or stored into the optimising means, and

- adjustment means for adjusting the manufacturing process and for obtaining the determined production value.

8. The arrangement according to claim 7, characterised in that the arrangement comprises viewing means for determining the number of folds in the vertical direction of the secondary fibre web.

9. The arrangement according to claim 8, characterised in that it comprises an automatic picture recognition unit, which is arranged in connection with the viewing means.

10. The arrangement according to any of the claims 7-9, characterised in that the weighing means comprise a weighing conveyor.