FI74749B - FOERFARANDE OCH ANORDNING FOER REGLERING AV EN TRAESLIPMASKIN. - Google Patents

Description

1 74749

Method and apparatus for adjusting a wood chipper

The invention relates to a method and a device for adjusting a wood grinding machine according to the preamble of claim 1. Such grinders are often formed as continuous grinders in which the chains rotate continuously and thus continuously press the wood against the stone. Compression grinders have the advantage of high volume capacity compared to continuous grinders. However, the quality of the grind is not quite as good as in continuous grinders.

Numerous measures have been taken to further improve the quality of grinding in compression and continuous grinders. Thus, it has long been known that the temperature of the pulp in the basin of a grinder, i.e. the so-called basin mass, has a certain effect on the quality of the grind. Thus, it is known that the temperature of this pool mass must be as high as possible, i.e. in any case it must be above a certain limit value.

Although the hot sanding method brings about a certain improvement in the quality of wood chips, the quality has not hitherto been uniform, but has been subjected again and again to temporal, more or less sudden variations. There are several possible explanations for this, such as the following: differences in wood structure; differences in opening size between individual owls, i. at the interface between the wood and the grindstone; differences in stone structure; differences in the quality of the stone mantle surface; and so on.

Despite numerous attempts to make these variables uniform, so far no uniformly good, stable quality of wood chips has been achieved.

74749

The object of the invention is to find measures that the grinding process takes place in a wood grinding machine of the type mentioned at the beginning as stable as possible and that the quality of the ground sand produced is kept at a high, stable level.

This object is solved by the features of the characterizing part of claim 1.

The following has been observed: instability (which is known as a variation in specific power demand) is always associated with variations in the temperature of the pool mass. Experiments have then shown that the temperature of the pool mass has a very decisive effect on the instability, and thus also on the quality of the groundwood. It is clear that the temperature of the pool mass varies due to all possible disturbance quantities. By stabilizing within very narrow limits, quality is also kept at a high and stable level.

As mentioned at the beginning, it is already known to keep the temperature of the pool mass above a certain minimum value ("hot ground").

It has also been found that a strong rise in the temperature of the pool mass is determined by e.g. too little wood supply or poor, e.g. worn stone surface and thus attempting to prevent such an increase possibly by increasing the wood supply, which is usually accompanied by a corresponding increase in spray water, often by lowering the pool mass level or increasing the pool mass consistency and finally stopping the wood grinding machine to sharpen the stone; .

Thus, it has not been found that direct interference with the pool mass temperature could stabilize the conditions in the grinding area, especially when the pool mass temperature is already at the upper limit value.

Of course, additional measures can also be used, such as spraying hot water to clean the stone to improve the grinding process or, in principle, the quality of the wood chips. Of course, stone sharpening periods must also be preserved.

Il 3 74749

In the following, the device according to the invention will be described with the aid of the control diagram shown in Fig. 1a in a preferred variant. Figure Ib also shows the corresponding operating diagrams of the control components and Figure 2 shows in principle a grinder with its control devices.

Figure 2 shows a substantially continuous grinding machine in which wooden logs are fed through a conveyor belt 31 into a feed shaft bounded on the side by conveyor chains 30.

The conveyor chains 30 press the wooden logs against the grindstone 2, which treats them as spray water is added to the grinder basin 8 as a collected wood grinding suspension. The height of the wood grinding suspension in the grinder basin 8 is adjusted by means of a pressure sensor 11 through a controller 22 which controls a valve 10 in the grinder basin outlet pipe 9 via a setting motor 12. To grind the sticks, a chip grinder 24 is mounted in front of the outlet pipe 9. Dilution water is fed into the grinder basin via pipe 3 and sprayed by nozzles 7. The temperature of the dilution water, which is generally the warm return water of the manufacturing plant, can be controlled by cold water supply through pipe 4 and by valve 5 controlled by regulator 1. The temperature of the grinder basin is then passed via the sensor 6 to the controller 1. The controller 1 thus keeps the temperature of this wood grinding suspension in the grinder basin substantially constant, e.g. at about 85 ° C. It has been found that a very high temperature of the wood grinding suspension in the grinder basin (grinding basin temperature) is very advantageous for a good grinding process. It can be said that the higher the temperature in the grinder pool, the higher the temperature in the grinding area against the grindstone. Thus, the quality of wood chips also becomes better. However, the temperature must not be selected or resisted, it must not rise so high that excessive evaporation occurs in the grinding zone, which is then known to be formed mainly in part.

In this case, due to the coarse tearing of the fibers 74749 4, the stone produces fibrous pieces or short fibers from the wood joint, while the aim is to produce a wood grinding suspension consisting of relatively long fibers by uniform grinding. However, the temperature in this open-ground grinder, which can therefore only be operated at atmospheric pressure, must in no case exceed the range of about 90 to about 95 ° C. The temperature sensor 6 and the controller 1 are now used to ensure that the temperature does not rise too much in the grinder basin.

Namely, it has now been proved that the irregularities occurring in the grinding process are observed in the rise of the pool temperature. Thus, by accurately measuring the pool temperature, these irregularities can be avoided or corrected very quickly, so that the pool temperature is kept in the range of about 4 to 8 K, e.g. 92 ° C below the limit. Despite this proposed measure, there are now operating conditions in which it is certainly not possible to keep the bottom temperature of the grinder constant. Such operating conditions arise especially when, for example, the moisture content of the wood varies very much and suddenly very dry wood has to be sanded. Likewise, the electoral list is when the wooden owls become oblique layers in the shaft of the grinder, or when the wooden owls are even substantially sanded on the end side. Then the specific working power of the wood grinder becomes very strongly too high, where the quality of the wood chips decreases very sharply. In such cases, if the matter is not addressed in time, the grinding efficiency often has to be reduced very much, in particular for a fairly long time, which, of course, severely impairs the production efficiency. Of course, these operating modes are also associated with an increase in the temperature of the grinder basin. However, in this case, often or not enough, the adjustment shown is usually sufficient to stabilize it. Therefore, in such cases, the following adjustment method is used, with reference to Figs. 1a and Ib.

For this, the specific work power is measured. It consists of the quotient of the working power of the grinding stone engine and the amount of wood ground,

II

74749 5 which amount is best measured at 100 kg wood / hour. The limit value for specific work would then be about 120 to 130 when the electrical power of the motor is measured in kilowatts. The amount of wood sanded can then be determined by measuring the feed 30 of the grinder chains. The specific power signals are processed in a low-pass filter to give a diagram B showing the specific power over time. From this curve, a period of pulses is formed by a limit value sensor 13 with a differentiation input, which is summed in an integrator 14, which may be, for example, part of an electronic calculator. Here, it is calculated upwards at a frequency, proportional to the constant, incidentally, the height of the exceedance during the period in which the limit values are exceeded, and downwards at a frequency approximately four to five times lower at other times, as shown in Scheme D. If, for example, at time t1 the limit value is reached in the integrator 14, then this gives a pulse to the interference magnifier 15. This then preferably gives, e.g. via a digital-to-analog converter 16, e.g. a constant 5 ° C error signal to the controller 1 Correspondingly, of course, the nominal value of the pool mass temperature could also be restored. The analog structure of this severity control is, of course, also possible, but it is likely to be more difficult to perform if it requires equivalent accuracy. The disturbance quantity is then decoupled in zero steps over a predetermined phase, e.g. 10 or 20 minutes, if no new disturbance pulse is received from the integrator 14, which is the case when the corresponding counter position is reached again as a result of exceeding the limit values due to specific operating power. in the integrator, as is the case in diagram D at time t2- In this case, the interference quantity had already been almost completely discharged. In any case, however, the interference quantity is in each case connected to the controller 1, e.g. up to the maximum value of the constant error signal of 5 °. This interference quantity is expediently transmitted to the input of the actual value of the controller 1.

Thus, this is given a misconception about the practically too high temperature of the grinding machine basin, so that it tries to cope with this 74749 6 temperature increase by adding cold water through the valve 5. By correspondingly lowering the pool temperature of the grinder, in most cases it is possible to quickly overcome an undesired operating condition. Long-term production losses are thus largely avoided.

If, in this mode of operation, the electrical power taken from the drive motor of the grindstone becomes too high, then the wood supply is reduced accordingly, so that in any case unauthorized operating conditions are avoided. In addition to this, the quality of the wood produced is also very good and corresponds almost to the quality of so-called pressure ground, in which the wood is ground in a closed grinder chamber at pressures of about 1.5 bar at a correspondingly high temperature, e.g. 115 ° C. In any case, the device according to the invention allows a substantially simpler and cheaper structure of a wood sander compared to pressure sanders.

In case the immersion depth of the grindstone in the pool mass is too small, it can also be arranged that the temperature of the dilution water of the pool mass is not affected, i.e. it is not cooled, but that e.g. the shaft water next to the grindstone in the wood log receiving shaft 26 is adjusted accordingly. lowering its temperature. If such shaft water is not provided, the temperature of the spray water, which is sprayed via the spray pipes 25 directly onto the grindstone, can also be adjusted, i.e. it is reduced in this case. This is best done through a heat exchanger or by adding cold water to the spray water. The shaft-water temperature control could also be performed in addition to the pool mass temperature control.

Instead of controlling the temperature of the pool mass or shaft water, it could in principle be advantageous to operate alone with the above-mentioned control of the temperature of the spray water, which is sprayed on a certain area of the grindstone before it enters the actual grinding area. In both this and other cases, the temperature of the pool mass could then be measured, namely preferably in such a way that the basic II.

7 7474 9 is used to determine the average. The determination of such an average is also possible when measuring the temperature of the wood grinding suspension to be sprayed out on the discharge side of the grinding stone with a plurality of temperature sensors 6 '. In contrast, measuring the temperature of the shaft water is not appropriate because it is not possible because the measuring sensors cannot be placed between the wooden sticks.

When measuring the temperature of wood chips sprayed away from the grindstone, the above-mentioned temperature limit value can be further increased. The upper limit value can even be the measured temperature of the wood particle suspension to be sprayed out at 100 ° C. This is especially the case when there is a sufficient shaft water height in the grinder shaft above the grinding area, which slightly raises the boiling point of the water.

If it is desired to use an even greater equipment input to determine the irregularities of the specific working power of the grinder, then in principle it is possible to disregard the determination of its limit value and to find out any variation, i. especially increases in specific work efficiency. In this case, the different steepnesses can be estimated correspondingly more strongly, e.g. calculated in a calculator in the case of a higher steepness at a higher frequency. At a certain limit position of the calculator, an error signal or a correction signal for calculating the nominal temperature of the pool mass or the shaft water or spray water is then transmitted, as in the method described above. Otherwise, the course of the method is exactly as shown in Figures D and E in Figure Ib.

However, it has been found that the first method presented is fully sufficient for the requirements and that the operation of the grinding machine is thus controlled.

Claims (7)

8 74749 A method for controlling a wood grinder, in which wood powders are ground in a feed channel or shaft, preferably at atmospheric pressure, preferably by means of a sandstone floating in the pulp, optionally by adding spray water, the process to the pool mass temperature, characterized in that when the specific working power of the grinder exceeds the limit value for a longer or more frequent time, taking into account the time intervals between the time periods during which the grinder falls below the specific working power limit, a signal is given to reduce the pool mass temperature or shaft water temperature or Method according to Claim 1, characterized in that the times of the non-fitting time of the specific working power of the grinder are taken into account relatively less than the time periods in which the limit value of the specific working power of the grinder is exceeded. A method according to claim 2, characterized in that depending on the determined limit value of the total amount of the time limit for exceeding the specific working power limit of the grinder, taking into account the corresponding non-crossing times, a signal is generated to lower the pool mass temperature or shaft water temperature or spray water temperature. A method according to claim 3, characterized in that the signal is decomposed to zero starting shortly after its administration and until a new corresponding signal occurs in order to lower the temperature evenly or in steady steps. Il 9 74749 Method according to Claim 1, characterized in that the large variations in the specific working power of the grinder are determined according to the slope of the specific working power in question by means of a corresponding estimate of this slope, and that the slope estimates are calculated up to one limit value from which the slopes are recalculated to lower the temperature of the pool mass or the temperature of the shaft water or the temperature of the spray water, or a corresponding upward correction of the actual value of the corresponding temperature is carried out, whereby this signal is again reset to zero evenly or at regular intervals starting shortly after its delivery. Device for controlling a wood grinder, in particular operating at atmospheric pressure, characterized in that it has a limit value sensor (13) and a device (14, integrator) for determining both the crossing time and the non-crossing time of the specific working power of the grinder and giving an error signal to the pool mass. the artificial temperature disturbance occurs for temperature control (1) or for lowering the nominal value of the pool mass temperature when the overshoot time is prevalent or too general. Device according to Claim 6, characterized in that it has an integrator (calculator 14) for summing or reducing non-crossing times for the specific operating power of the grinder in a wooden manner and for providing a constant disturbance or lowering the pool mass temperature setpoint, respectively, depending on the calculation. 10 74749