SE454337B - SET FOR MANUFACTURING MULTI-LAYER FIBER MATERIAL - Google Patents

Description

10 l5 20 25 30 454 357 heating device e.g. a steam battery for heating drying air, a long drying tube and a cyclone and for driving drying air through these three components in the aforementioned order a fan. The blow line is connected to the drying tube at its end facing the heating device and the fibers are separated after the passage through the drying tube from the cooled and humidified air in the cyclone. From this, the drying air is normally released into the open air.

In some cases it is instead led to a second drying tube and from this to a second cyclone. This arrangement is called a two-stage dryer and is used to save heat energy in such a way that the blow line from the refiner is connected to the inlet end of the second drying tube, that dried fibers are separated from the drying air, which is then released into the second cyclone, that the dried fibers is led to the inlet end of the first drying tube and that after passage through this tube they are separated from the drying air in the first cyclone in a completely dried state, ie that between the two drying tubes. i There is a physical connection between, on the one hand, the lowest moisture content to which the fibers can be dried, and, on the other hand, the condition of the drying air during the separation of the fibers. High temperature and low relative humidity of the air promote drying to a low fiber moisture ratio.

In order to achieve the same fiber moisture ratio, the air from a dryer with one step from the cyclone must correspond to the state of the air in a two-stage dryer, when it passes from the first cyclone to the second drying tube. As the fibers are pre-dried in the second drying tube, the required water evaporation in the first drying tube is reduced and consequently the air flow can be kept lower than in a single-stage dryer.

Urea formaldehyde glue is usually added dissolved in water at 50% concentration. The addition can take place after the fiber drying in special glue mixers. Known ones give an uneven distribution of the binder on the fibers, which leads to over-glued fibers forming tufts. If the fibers for the surface layers are treated in this way, the tufts appear on the surfaces of the finished boards in the form of dark spots. which reduce the value of the discs.

The addition can alternatively take place before the fibers dry, for example by pumping into the blow line. Surface stains can be avoided in this way, but the binder is affected when the fibers are transported in the hot air in the dryer. so that in order to achieve the desired strength values of the boards, the amount of binder must be increased by about 20% at normal drying temperatures. This increases the total manufacturing cost by about 5%.

It is known to produce three-layer carpets, where the fibers for the surface layers are applied with binder before drying and the fibers for the middle layer after drying. Since the amount of fibers of each type is approximately equal, the additional cost of avoiding surface stains in this way can be halved.

For the implementation, one has used equipment for grinding, drying and adding binders for fibers intended for the middle layer and another for fibers intended for the surface layers. The refiners with associated auxiliary equipment _ constitute a large part of the plant's total investment cost.

To limit this, most medium-sized and small plants are constructed with only one refiner and a dryer and binders are added before drying, thereby avoiding stained surfaces, but there is no possibility of differentiating the amount or variety of binder or moisture. quotient of the thickness of the molded mats. In order to achieve the desired strength properties of the finished boards, a minimum amount of binder is required, which is usually different for the outer and inner parts of the board. For homogeneous mats, the higher addition level must be chosen for the entire fiber feed.

If in the case of three-layer mats binders and fibers for a certain case for surface and middle layer fibers must amount to 0.080 and 0.090, respectively, when added after drying, then the ratios may need to be increased to 0.100 and 0.110, respectively, when added before drying. The corresponding ratios when adding the middle layer fibers after drying are consequently 0.100 dry matter ratio between to the surface layer fibers before drying and to 0.090, respectively, or if both fiber feeds are equal on average 0.095. In the case of homogeneous mats, on the other hand, a dry matter ratio of the size 0.110 is required. The increase in the size of the additive required for the addition of binder before drying could be considerably reduced by lowering the temperature of the drying air at the inlet of the drying tube. In order for the condition of the drying air at the separation of the fibers to give the desired fiber moisture ratio, the drying air flow must then be increased. and more expensive drying and more fan energy, This requires a larger but above all more heat energy is needed for the drying. It is therefore preferable to keep the inlet temperature as high as possible in view of the risk of self-ignition of the fibers.

Methods are known in which fibers produced in a pressurized refiner suspended in steam through two or more blow lines are each fed to a dryer.

After the fibers have been dried and additives added, they are usually collected in bunkers, one for surface and one for middle layer fibers, from which they are discharged and fed to a mat forming station, where they are spread in layers on top of each other. From the bunker for surface layer fibers, two flows are discharged, one of which is used to form the lower and the other of the upper surface layer.

The present invention relates to methods of saving binders and heat energy when producing multilayer carpets of fibers mixed with a thermosetting binder and having a certain moisture ratio with for at least one of the layers deviating from the other composition.

An extension of the invention can also reduce investment costs.

The object of the invention is achieved primarily by using a two-stage dryer, in the first stage of which a fiber stream is dried at a high temperature and then a binder is added and in the second stage a second fiber stream containing binder is dried at a low temperature.

The object of the extension of the invention is achieved by using a. refiner, from which one fiber stream is blown to the first stage of the dryer and another with the addition of binder is blown to the second stage of the dryer.

The invention will be described in more detail in the following with reference to Figures 1 and 2. Since for the practice of the invention only devices well known to the person skilled in the art are required, these are shown only schematically for the sake of clarity.

Figure 1 shows a flow chart with two refiners 1, 2 connected to each blow line 3, 4. Figure 1 also shows, connected to each other in said order, a heating device 5 for air, a fan 6, a first drying pipe 7, a cyclone 8, a second drying tube 9, and a second cyclone 10. The cyclones 8, 10 are provided with fiber dispensers 11, 12. The blow lines 3, 4 are each connected to a drying tube 7, 9 at the pipe end, as shown in figure 1. The fiber dispenser 12 at the cyclone 8 is connected to an adhesive mixer 13, to which also a dosing device 14 for adding binder is connected. The glue mixer 13 is connected to a bunker 15 for intermediate storage of fibers intended for the middle layer of the mats.

A second dosing device 16 for binder is connected to the blow line 3, which opens into the second drying tube 9. The fiber dispenser 11 at the second cyclone 10 is connected to a bunker 17 for intermediate storage of fibers intended for the surface layers of the mats. Figure 2 shows a variant: of the diagram shown in Figure 1 with a refiner 18 connected to two blow lines 3, 4, identical to those shown in Figure 1 and opening in the same way in separate drying tubes 7¿ 9. In the same In this way, a dosing device for binder is also connected to the blowing line 3, which opens into the second drying tube 9. In other respects, what is shown in Figure 2 corresponds. the flow chart completely with that shown in Figure 1.

The discharge of fibers from the bunkers 15, 17 to the forming station and their spreading there in three layers on top of each other is a technique well known to the person skilled in the art and does not require further description.

The function of the invention will be explained in the following in Example 1, and a comparison will be made with two commonly known methods in Examples 2 and 3.

Example 1 Fresh air is sucked in by the fan 6 through the heating device 5, where it is heated to 160 ° C, and after passage through the drying pipes 7, 9 and the cyclones 8, 10 is blown out into the open. Two approximately equal fiber flows with a moisture ratio of 0.87 are blown through lines 3, 4, suspended in about 0.55 kg of steam per kg of dry fiber, to each drying tube ~ 9, 7. In one line, 0.085 kg is fed. .._.....: ......._ .. 1 _... _ \ .... \. Binder dissolved in an equal amount of water per kg of dry fiber by means of: the dosing device 16 and the mixture is introduced into the second drying tube 9, where it accompanies the drying air to the second cyclone 10. The other half of the fibers is blown as they are in the 160 ° C hot air in the first drying tube 7 and accompanies the air to the first cyclone 8, where the fibers are separated and the glue mixer 13 is supplied through the fiber feeder 12.

Under normal conditions of fresh air and if the drying tube is of sufficient length, the air leaving Cyclone 8 has cooled to 10 ° C and the relative humidity is below 5%. With this final state of the air in the first drying step, the moisture content of the fibers is reduced to below 0.01, ie they are practically completely dry when they are fed to the mixer 13.

The air leaving the cyclone 8 is passed through the second drying tube 9 and the second cyclone 10 and is thereby cooled by the accompanying mixture of fibers and binder to 67 ° C and the relative humidity is set at 40%, which is the state of the departing drying air. ten. At the same time, the drying stops at the moisture ratio 0.13 before the fibers of the fiber feeder 11 are fed to the bunker 17 for surface fibers by means of the fiber feeder 11.

The above applies to 19 kg dry air per kg dry fiber in total. In the glue mixer, the hard-dried fibers are added by means of the binder 14 by means of the dosing device, after which the mixture is transferred to the middle fiber bunker. The binder is added in an amount of 0.090 kg dissolved in the same amount of water per kg of dry fiber. The moisture ratio then increases to 0.090-0.100. The achieved moisture ratios promote a rapid heating of the mats during hot pressing. A fast curing binder can be used without inconvenience for the middle layer fibers, as it does not participate in the drying, which further shortens the pressing time, which determines how large and expensive press is required. By adding the binder for the surface layer fibers before drying, stained disc surfaces are avoided.

The far-reaching drying of the middle layer fibers, which is desirable, cannot be achieved without the air leaving the cyclone 8 being hot and dry. The invention therefore leads to the surface layer fibers being dried at no cost for heating drying air.

The fact that the drying air at the entrance to the second drying tube 9 is cooled in combination with the use of a slow-curing binder for the surface layer fibers. causes the binder to be slightly affected during the passage through the dryer. The relationship between binder and fibers can therefore be kept at a low level.

In the extension of the invention illustrated in Figure 2, the two fiber streams are ground in a common refiner with associated auxiliary equipment and then divided for individual treatment. The refiner must then in principle have twice as large per unit, however, increases only slightly with capacity, capacity. The acquisition cost why such an arrangement cheapens the facility.

At the same time, maintenance costs are reduced and larger refiners are given better fibers with the same use of grinding energy.

Example 2 In most fibreboard plants, the desired production capacities can be achieved with the input of a single refiner.

With regard to what has been said, therefore, such a solution is generally chosen and homogeneous discs are produced.

When stained surfaces reduce the value of the sheets, the binder is added before drying and accompanies the fibers through the dryer. With regard to the drying costs, the drying air is heated to 160 ° C. The binder is thereby affected in that in order to achieve the desired strength in the inner parts of the board, the dry content ratio between binder and fibers must be poured at 0.105 - 0.110 and this throughout the entire carpet thickness. The binder supply will thus be significantly higher than that in Example 1. In order to reach a desired moisture ratio, more drying air is also needed. such degree, Example 3 At very-large capacities, the fiber requirement must be covered by the input of two refiners, each connected to a dryer. If both fiber streams are added with binder after drying, it is required that the dry matter ratios in the surface layers and the middle layer are 0.080 resp. 0.090. To avoid stains, add before drying. The dry matter ratio for the surface layers must then be increased. Applied in Example 1, the ratio of the surface layers to the surface layer fibers binder must be raised, thereby low temperature drying as 0.085 and the binder inlet being the same as in Example 1. However, the heat consumption in the low temperature dryer becomes so large that it is preferable to increase the incoming air temperature to 160 ° C. then the dry matter ratio must increase to 0.095 - 0.100. This procedure is thus inferior to that in Example 1 both in terms of costs for binders and for drying heat energy.

The invention is not limited in terms of the number of mat layers, drying steps, inserted refiners or blasting lines from one and the same refiner, but can be varied within the scope of the Patent Language. The invention is not limited to drying each stream in a single drying step, but can e.g. one stream is pre-dried in one drying step and finally dried in another, and any binder may be added between the drying steps.

The invention may also be varied so that when using a multi-component binder, one or more components or other substances are added separately and in a manner other than that described.

Claims (4)

454 337 H 'Patent claim 1. Methods of making multilayer carpets of fibers with the addition of thermosetting adhesives by grinding lignocellulosic materials in an atmosphere of steam under pressure, drying the fibers in partial flows separately and forming carpets in layers on top of each other with the layers between them different composition in terms of either binder or * moisture ratio or both characterized in that at least two partial streams are dried separately in each or each step in a multi-stage dryer. 2. A method according to claim 1, characterized in that at least one partial flow is added binder before drying and at least another binder is added after drying. Method according to claim 1, characterized in that at least the partial flow is dried in more than one step and that binder is added between any of the steps. 4. A method according to claims 1f - 3, characterized in that at least two of the substreams are formed by grinding in a refiner common to them as a result of division into substreams.