EP0429820A2 - Process and apparatus for controlling the manufacturing process in the continuous production of elements having a plaster binder - Google Patents

Abstract

The invention relates to a method for controlling the production process in the continuous production of gypsum-bound workpieces, in which the fresh mass with a belt press or the like, consisting of a plurality of successively arranged press segments, is compressed to the end of hydration, which is characterized in that the at Hydration arising source pressure is measured and used to control the production process. The invention further relates to an associated device, in which each individual press segment is equipped with a distance measuring device and a target / actual value comparator. <IMAGE>

Description

The invention relates to a method according to the preamble of claim 1 and an apparatus for performing the method.

A control device for a compression unit of a belt press is already known from DE PS 33 16 946. This invention takes advantage of the fact that the reaction of the binder with water to form the dihydrate is an exothermic process, i. H. it releases heat. It is therefore possible to determine the end of hydration by evaluating the hydration temperature-time curve, namely as the time from the start of the litter to the maximum of the temperature curve. In laboratory examinations, this measurement is usually carried out under quasi-adiabatic conditions in order to avoid heat flow and thus a falsification of the temperature-time curve. For technical processes, it is usually sufficient to determine the temperature profile under the given conditions.

In the method to be carried out with this control device, the temperature development becomes exothermic hardening gypsum binder mass used as a control variable. By definition, the end of hydration is reached when the temperature development exceeds a maximum. To carry out this method, however, a measuring device is required which continuously determines the temperature development, so that an additional device is required in addition to the already existing pressure measurement. In addition to the outlay on equipment, a temperature measurement is also fraught with uncertainty factors which do not guarantee exact measurement value acquisition. In particular, temperature compensation processes between the material, the compression unit and the environment are to be mentioned as disturbance variables, which cannot be compensated from an economic point of view. Under practical conditions, it is doubtful whether temperature fluctuations in the materials are not considered incorrect measurements.

In principle, both a continuous and a batch process can be used for the compression. The most important continuous process in common is that the belt press consists of a large number of individual press segments arranged one after the other (Fig. 1). Such a press describes e.g. B. H. Soiné in wood as raw material 42 (1984), pages 63-66. The invention is based on belt presses of this type with press segments arranged one after the other.

The object of the invention is to provide a simpler and cheaper method for controlling the production process and to provide a corresponding device.

This object is achieved by the method according to claim 1 or the device according to claim 6.

For a better understanding of the invention, the principles of the setting mechanism of exothermic hardening binders will now be discussed using the example of gypsum: The production of products based on gypsum is based on the processes of dehydration and rehydration. When burning gypsum dihydrate (

CaSO ₄ ^` 2 H ₂ O

) arises from dehydration with corresponding burning conditions sulfatic binders, which essentially consist of hemihydrate

CaSO ₄ ^` 1/2 H ₂ O

) consist.

When the binder is mixed with water, the hemihydrate goes into solution up to the saturation concentration, and dihydrate forms again through hydration, the solubility of which is only about the fourth part of that of the hemihydrate, so that dihydrate is deposited in crystalline form from the solution which is supersaturated with dihydrate . This process continues until the hemihydrate is completely converted into dihydrate, and a polycrystalline, space-stable solid is formed in this way.

The timing of the hydration process is characterized in technology by the parameters stiffening start, stiffening end and end of hydration. The start of stiffening and the end of stiffening indicate a certain consistency of the gypsum mixture, the end of hydration denotes the end of the conversion of hemihydrate to the dihydrate. These time parameters are counted from the "start of the litter", ie from the time when the binder and water meet.

A compression process is now used in the production of certain plate-shaped workpieces based on gypsum, for example in the production of fiber-reinforced gypsum boards or gypsum-bonded particle boards in a semi-dry process. According to the prior art, the rule applies that the compression process may begin at the latest when the stiffening begins and may be ended at the earliest after the end of the stiffening, better still after the end of hydration; this is the only way to ensure the maximum strength of the material.

As already mentioned, continuous systems can be used for the production processes mentioned, which enable higher production capacities compared to discontinuous ones and in which a continuous mixing and shaping which is advantageous in terms of production technology can be achieved. A section of such a system is shown in Fig. 1.

On a belt press of this type, the fresh mass is then compacted to the end of hydration after being sprinkled in. The increase in volume of the hardened binder is hindered according to the previous manufacturing technique. This creates a measurable source pressure.

According to the invention, this source pressure is now used to control the production process.

The end of hydration is always reached when no increase in the swelling pressure can be determined. Fig. 2 shows a temperature-time curve versus the pressure-time curve. It follows that the measurement of the source pressure gives the same results as that of the temperature. However, the invention has decisive advantages over the prior art. First, no additional devices such as. B. a temperature measuring device is necessary, and secondly, the measurement of the source pressure is not dependent on environmental influences.

und ${\text{P}}_{\text{(n+1)}}\underline{{\text{}}^{\text{<}}}{\text{P}}_{\text{n}}$

erfüllt ist.However, the invention has further advantages. It is possible according to the invention if the maximum swelling pressure and so that the end of hydration is reached, the following press segments are set to zero. A decisive energy saving is thereby achieved. This is important because the setting behavior can be influenced within limits by adding adjusting agents (retarders / accelerators). Thus, e.g. B. with the addition of an accelerator, the end of hydration can be reached earlier, so that a "shorter" belt press would in itself be sufficient. In the method according to the invention, however, the press segments which follow are then set to zero after the end of the hydration, so that they no longer perform any work and energy savings are thereby achieved. Such a differentiated control is not possible with all methods of the prior art. In all these cases, the belt press has to do work until the end of its overall length. The process according to the invention can thus save the work which the press segments would have to do after the end of hydration has been reached. The subsequent press segment is reset when the condition regarding the pressure P.

and ${\text{P}}_{\text{(n + 1)}}\underline{{}^{\text{<}}}{\text{P}}_{\text{n}}$

is satisfied.

According to the invention, it is of course exactly as possible to cancel the compression at a desired swelling pressure. This can e.g. B. may be of interest for research purposes about the setting mechanism. Another embodiment of the invention also makes it possible to use the differential quotient of pressure per unit of time instead of the absolute pressure to control the production process.

The device according to the invention for performing this method is explained in more detail with reference to the figures. Fig. 1 shows a section of the construction of a continuous belt press 1 with press segments 4 arranged one after the other. Fig. 1 also shows a fleece transfer device device 2 and a plate removal device 3. Fig. 3 shows the pressure measurement and the control device.

The device consists for each individual press segment of a target / actual value comparator 5, a distance measuring device 6 and a pump 7. Each individual press segment 4 is then connected to a comparator 8.

An advantage of the invention is that the distance measuring device is present in the already known belt presses from the prior art. As an additional device, only a comparator 8 is now provided, which compares the individual pressures of the individual press segments 4.

und ${\text{P}}_{\text{(n+1)}}\underline{{\text{}}^{\text{<}}}{\text{P}}_{\text{n}}$

erfüllt, so wird mittels der Steuerung das nachfolgende Pressensegment auf Null geschaltet. Dies ist in Abb. 4 an zwei Meßpunkten veranschaulicht.If a mixture is now fed to the press via the nonwoven transfer device 2, it is compressed by the belt press 1 in accordance with the specification (for example, predetermined plate thickness). The necessary pressure is applied by the individual press segments 4 (corresponds to the cylinders). If the distance measuring device 6 now detects a deviation from the target value, the pump 7 adjusts so that the predetermined thickness can always be maintained. According to the invention, these pressure measurements are now passed on to the comparator 8. Now is the condition ${\text{P}}_{\text{(n-1)}}{\text{<P}}_{\text{n}}$

and ${\text{P}}_{\text{(n + 1)}}\underline{{}^{\text{<}}}{\text{P}}_{\text{n}}$

fulfilled, the following press segment is switched to zero by the control. This is illustrated in Fig. 4 at two measuring points.

nicht erfüllt ist. In diesem Fall wird also demnach das nachfolgende Pressensegment nicht auf Null gestellt. Beispiel 2 zeigt einen Fall, bei dem die Bedingung

und ${\text{P}}_{\text{(n+1)}}\underline{{\text{}}^{\text{<}}}{\text{P}}_{\text{n}}$

erfüllt ist. In diesem Fall wird also das nachfolgende Pressensegment auf Null gestellt. Die restlichen Pressensegmente müssen demnach keine Arbeit mehr verrichten. Das ganze System ist damit exakt steuerbar und kommt mit einer minimalen Energie aus.Fig. 4 shows the characteristic course of the swelling pressure over time. Here example 1 shows that the condition ${\text{P}}_{\text{(n-1)}}{\text{<P}}_{\text{n}}$

is not fulfilled. In this case, the subsequent press segment does not become zero posed. Example 2 shows a case where the condition

and ${\text{P}}_{\text{(n + 1)}}\underline{{}^{\text{<}}}{\text{P}}_{\text{n}}$

is satisfied. In this case, the subsequent press segment is set to zero. The remaining press segments therefore no longer have to do any work. The entire system can thus be controlled precisely and manages with minimal energy.

Accordingly, for the first time, the invention provides a way of optimally controlling a continuous belt press 1 with little outlay on equipment. Another advantage is that device parts can be used for this method, which are already available on conventional belt presses of the prior art. According to the invention, the fact is taken advantage of that the source pressure is used for control, and a device is specified for this purpose.

Claims (8)

Process for controlling the production process in the continuous production of gypsum-bound workpieces, in which the fresh mass is compressed to the end of hydration with a belt press or the like, consisting of a plurality of press segments arranged in succession, characterized in that the swelling pressure which arises during the hydration is measured and used Control of the production process is used. Method according to claim 1, characterized in that the required pressure P in the individual press segments arranged one after the other is regulated with the aid of the swelling pressure and that when the condition is fulfilled ${\text{P}}_{\text{(n-1)}}{\text{<P}}_{\text{n}}$

and ${\text{P}}_{\text{(n + 1)}}\underline{{}^{\text{<}}}{\text{P}}_{\text{n}}$

the pressure ${\text{P}}_{\text{(n + 2)}}$

is set to zero in the subsequent press segment. Method according to claim 1 or 2, characterized in that the pressing process is stopped when a predetermined pressure is reached. Method according to one of the preceding claims, characterized in that the differential quotient is determined from the source pressure per unit of time and this differential quotient is used to control the production process. A method according to claim 4, characterized in that the pressing process is terminated at a certain predetermined differential quotient. Device for carrying out the method according to one of claims 1 to 5, characterized in that each individual press segment (4) of the plate press has a distance measuring device (6), a target / actual value comparator (5) and a pump (7) for the pressure medium for actuating the press segments (4). Apparatus according to claim 6, characterized in that the individual press segments (4) are connected to a comparator (8) which compares the pressures of the individual press segments (4). Apparatus according to claim 7, characterized in that the comparator (8) is additionally connected to the individual press segments (4) and can control them.

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