EP0814924B1 - Method of ensuring sand-mould quality by measuring the rate of flow of oil to the head of a press - Google Patents

Abstract

The invention relates a control or regulation of a multipiston squeeze head or block squeeze head of a molding machine for clay-bonded molding sand (molding material). In an active pressing process with a squeeze head moving in downward direction, e. g. consisting of multislides or multipistons, the displacement of individual multislides has so far been detected through by end switches (approach switches) or through inductive stroke transducer. Thus, reached positions are registered and processed in a control means. Subject matter of the invention is an adaptation of influenceable parameters to obtain a sand mold of good quality on a long-term basis. Surprisingly, the measurement of the flown oil (Q;qt(t)) provides a basis for the improvement of the sand mold. If models of different sizes are molded subsequently, the quantity of sand required is different. According to the control signal of the invention (Q;qt(t)), more or less sand is filled into the bunker.

Description

The invention relates to a method according to claim 1, in particular the control or regulation of a Multi-stamp press head or block press head of a molding machine for clay-bound molding material (e.g. molding sand).

With active pressing from above with a press head e.g. out The path of individual multi-stamps has so far been widely stamped Limit switches (proximity initiators) or inductive rod measurement detected. Reached positions are registered and in the Control processed. Likewise, this type of Distance measurement for the press head - with or without multiple stamps - as Whole thing possible.

From US-A 5,409,052 (Kaneto), corresponding to DE-A 43 40 401, a device and a method are accessible to the person skilled in the art, with which the upper and lower mold halves of a sand mold can be produced at the same time. The device works horizontally in order to compress the molding material in the horizontal direction in relation to a two-sided model. In order to record the thickness of the mold halves in the manufacturing process, the end positions of the press plates are measured with linear displacement sensors (there 6.6A) and fed to a control device which derives the thicknesses of the mold halves from them. An electrode 7 is arranged with two poles on a press plate in order to detect the resistance of a finished pressed mold and also to send a corresponding signal to the control device. The same control device calculates the water content of the mold half from the thicknesses and the resistance in order to directly check the properties of the molding sand during the manufacture of the upper and lower mold halves (cf. column 2, lines 15 to 25, 48 to 68 and column 1, Lines 27 to 31).

The aforementioned document relates to pressing with press plates, while the person skilled in the art also has access to a compacting device with multiple punches, cf. JP-A 57-142 743 (Komatsu) or JP-A 55-16 786 (Sintokogio). The latter document relates to the production of sand molds with the same molding material hardness, even when using a complicated model. For this purpose, it is proposed there to measure the oil pressures in each divided cylinder and to activate a relief valve (there 16) when the respective oil pressure reaches a value which is greater than a predetermined value. The relief valve drains oil into a tank (there 12) to keep the specified pressure constant.

The problem of the invention is to adapt the parameters that can be influenced in a molding machine in order to maintain a good long-term shape. Constant height of the bale of form should be made possible as well as uniformity of compaction. The time for compression should be adjusted so that a minimum time per mold is achieved.

The parameters are to be obtained directly on the molding machine (measured), including a measurement of the volume, the mass or changing their hydraulic fluid to the press head will (claim 1). The measurement of the fluid is surprising a good starting point for the controlled or regulated Improvement of the sand shape.

Four options for regulation or control concern the Regulation of the amount of molding material in the molding box (claim 2, Old. a), the measurement of the stamp position without the stamp arranged sensors (claim 2, alt. b), the detection, Acquisition or optimization of the stamp end position or the desired end position of the stamp before its physical End position (claim 2, alt. C) for a specific model form ("Pressing end") or measuring and changing the Compressibility of the molding material (claim 2, Alt. D).

The variants can be used individually or cumulatively, up to all four "alternatives" at the same time.

If models of different sizes are molded in succession, so the amount of sand required as a "molding material" is different. After the model change, registered in the state of the art a mechanical height detection device over the mold boxes current fill level of the boxes after pressing. With over or Undershoot is the amount of sand that is in the hopper for the following pressing process is made available accordingly corrected. This ensures that after Model change again filled an optimal amount of sand and can be compressed (according to the control signal more / less Molding material filled into the machine bunker).

The method used according to the invention simplifies the apparatus expenditure considerably.

Technical aids for dynamic mass (flow) measurement (e.g. oil flow as hydraulic fluid) work e.g. after this Coriolis principle. With this dynamic mass measurement, a Measuring signal supplied, which is proportional to the mass flow (kg / h). Affect conductivity, density, temperature and viscosity the measurement is not.

The measuring principle can be used for the detection of volume flows e.g. Hydraulic oil can be used. The principle is based on the controlled generation of Coriolis forces. These powers occur in a system whenever there is a translational (rectilinear) and rotatory (rotating) Movement overlap.

In the practical implementation of this functional principle an oscillation is set instead of the rotary movement. Two from Straight tubes flow through the product and vibrate (Resonance) offset and form a kind of "tuning fork". By the Mass flow will phase in and out of vibration on the outlet side changed differently, what about optical Sensors is detected. The phase difference is proportional to Mass flow and is available as a linear standardized output signal to disposal. The resonance frequency of the measuring tubes is dependent of the vibrating mass and thus of the product density. A Control circuit ensures that the system is always in resonance is operated. The resonance frequency then becomes Product density calculated.

For the computational compensation of temperature effects, the Temperature of the measuring tubes detected. This signal corresponds to the Product temperature and is also available for external purposes Available.

Another method for recording volume flows (= volume per unit of time) is possible with a screw volumeter. This work on the principle of displacement. The pouring Hydraulic fluid causes the spindles to rotate inside the tapped rotary movement by inductive proximity switches a frequency signal is generated. This gives you the measure of the volume delivered per unit of time.

What type of measurement "volume flow" and "mass per Unit of time "is a matter of application (Coriolis, Volumeter, piston accumulator ...). If a low pressure surge, contactless, low-wear measuring principle is used, the best results are obtained.

The compressibility correction or the corresponding optimization works long-term, by adding or blocking sludge or about the change in moisture content of the molding sand before it is filled into the Molding box (claim 3, claim 4). With every press (Forming) is available via the hydraulic fluid gradient measurement new measured value for the compressibility available, the one desired change of the sand causes. So far from the If this regulation is still desired, it is based on a setpoint-actual value comparison (claim 5, claim 8).

The electronic device is also disclosed here Regulation and control technology that the specialist for Carrying out the method based on the measurements of the Uses fluid stream or its derivatives.

Figur 1

repräsentiert ein Ausführungsbeispiel für das Regelverfahren 1, bei dem die Sandmenge nach einem Modellwechsel geändert wird, um gleiche Sandballen-Höhen zu erreichen.

Figur 2

repräsentiert ein Ausführungsbeispiel, mit dem ein nach Preßende ausgerissener Stempel anhand einer Ölmengenmessung erkannt werden kann.

Figur 3

betrifft ein Beispiel, wie der Zeitbedarf zur Herstellung einer Sandform aufgrund einer Messung des geflossenen Ölvolumens minimiert werden kann, wodurch auch der Energieverbrauch gesenkt wird.

Figur 4

repräsentiert ein Ausführungsbeispiel für eine Korrektur der Verdichtbarkeit des Sandes durch Messung von Ölfluß-Änderung pro Zeitintervall.

Six examples of the invention are described using control methods 1 to 6. Figures 1 to 4 represent Examples 1 to 4 thereof.

Figure 1

represents an exemplary embodiment for the control method 1, in which the amount of sand is changed after a model change in order to achieve the same sand bale heights.

Figure 2

represents an exemplary embodiment with which a stamp torn out after the end of the pressing can be recognized on the basis of an oil quantity measurement.

Figure 3

relates to an example of how the time required to produce a sand mold can be minimized based on a measurement of the flow of oil, which also reduces energy consumption.

Figure 4

represents an embodiment for a correction of the compressibility of the sand by measuring oil flow change per time interval.

Figure 1 shows schematically in the left half press rams which are connected to a common oil well Q and which penetrate into a sand ridge R with different depths (deep, normal, high). A model M can be seen on the bottom of the schematically indicated molding box F.

The stamps in the left image are too deep in the back of the form penetrated, the stamps in the right drawing are too high. The Stamps in the middle part of the picture have the normal position on the The upper edge of the molding box lies. The one to the right of the three Curves drawn in diagrams show the mean "normal", the 30 liter oil volume between the retracted position Stamp and end position "normal" in the diagram shows. 45 liters Oil represent the deep penetration of the left stamp in the Diagram and 16 liter oil volume represent that too high lying stamp. The respective remaining height of the Sand bales can be seen in the lower right part diagram. The stamps are 40mm too high for 16 liters of oil; for 30 liters flowed oil is the specified and set setpoint ± reached zero, and when 45 liters of oil flowed, they penetrate Stamp 30mm too deep in the mold box F.

Depending on the measured amount of oil q (t), which is between The start and end of the press have flowed, the amount of sand is according to upper part diagram (b) changed, especially increased or degraded. With 30 liters of oil it remains unchanged, with 45 liters Oil is greatly increased and with only 16 liters of oil flowing it is greatly lowered.

The sand quantity change represented in FIG. 1 when changing the model to obtain the same stamp depth works with curves (a) and (b) according to the two sub-diagrams.

A model change is the change from one model volume to another. When the model volume is changed, the amount of molding material that can be arranged in the molding box changes, ie if the model is changed from a deep model to a high model M, it is no longer possible to fill the box with as much molding material in order to achieve the same final height after compression.

The movement of the multi-stamps is as a whole about the oil volume measured. This measurement is carried out using a previously described measuring device (Coriolis, Volumeter, Piston measurement). At the end of the press, the actual oil flow registered. If a lot of oil has flowed, the stamps H stand the stamps are deep, little oil has flowed at the end of the press high.

In a box F after a model change is a changed model filled with the appropriate amount of molding material. The Position of the multiple stamps or the block press head H is at Compression recorded by the amount of oil flowed (= oil volume) is registered. Via a calibration curve (a) in the control the height of the ram at the end of the press from the amount of oil flowed determined. The deviation from the level of the ram before Model changes are counteracted by changing the amount of molding material. Another calibration curve is used for this. The second calibration curve (b) results from the manufacturing operation for the previously used models or is a permanently installed curve (e.g. from a model database).

For example, if the stamps were set too low, the next impression more sand filled. The stamps were due high, the next impression will be less sand filled.

FIG. 2 represents the reproducibility of the stamp position and shows the start of the multi-stamp press head H in the left part. After an oil quantity q (t) of 30 liters (for example) has flowed, the stamps have moved into their end position after 1 second. If the oil is withdrawn from the plunger, the oil flowing back is compared with the amount of oil that has flowed until the end of the press. A small tolerance range T _B is opened to compensate for inaccuracies. If the amount of oil flowing in and the amount of oil flowing back are not the same, an error message is output.

The stamps are specifically moved back and forth by positive / negative oil pressures.

After a specific ancestor of the multiple stamps, they are supposed to be around an equal or partial amount thereof can be reduced. Around to check whether this movement is carried out completely has been completed, the amount of oil flowed or the driven height difference registered. The full or partial amount is recorded. If the vehicle is not driven back correctly triggered an error or correction message.

At the end of the press, for example, a stamp is torn out. The Return flow does not correspond to the amount in the ancestor. The The machine must be stopped and a repair carried out.

The end position reached after the end of the press is also via this Reproducibility measurement compared. Conclusions about leaks in the Hydraulic system or machine errors are possible.

Figure 3 represents an energy consumption and time requirement minimization.

The time requirement minimization and the minimization of the energy consumption by measuring the oil flow per same time period T _{0 are shown} . If the oil flow reaches a predetermined (low) value or becomes zero for the same period of time, it is determined from the measurement that an end of the press is near or imminent. The next step in the sequence control can be started immediately; Dead times or holding patterns are not necessary. Figure 3 illustrates schematically the end of the press at about 1 second and shows that the amount of oil flowed there is only small in the same 10 ms interval (T ₀ ). The pressing process can already be stopped here.

The flow of hydraulic oil per unit of time is determined by monitors the measuring system built into the hydraulic circuit. The Situation "pressing end" is when the volume per unit time strives towards zero. Via curves stored in the control the course of the press can be detected during the movement of the multi-punch.

For the information
End of pressing = "switching off the pressure"
the corresponding signal from the actual value
Volume / time unit compared to a target value or the value zero and the baling pressure switched off.

This means that "about" zero can be switched off immediately at a defined point in time or with volume flow per unit of time and the following movement step can be triggered. The machine cycle time is shortened, energy consumption is optimized and reduced. FIG. 4 represents a compressibility correction (VD) and shows two gradients x, y for sand with high compressibility (normal α, α _y ) and for low compressibility of the sand (large α, α _x ), where α _x > α _y . Both diagrams therefore show the change in the oil volume per time, with the start of the respective slope characterizing the point in time at which the punches hit the molding sand.

For sand with low compressibility (with high bulk density) this impact is comparatively late because of the sand is filled comparatively deep. Hit the stamp accordingly, only late for resistance, but then for stronger ones Resistance, which is shown by the high gradient. Different the sand with high compressibility, here is only a weak one To detect a decrease in the oil volume per unit of time, accordingly but a comparatively earlier start to this change. Both Gradients meet at the end of a press in the same Point, especially at zero oil flow.

In Figure 4, the beginning of the gradient x, y is for clarification relocated to the same point, with a different slope of the q '(t) function.

Due to the different gradients, a measured value for change the compressibility by adding more Water or less water in the mixer that contains the molding sand provides, take place and so a compressibility correction justified, which always enables the same compressibility, without the compressibility being measured itself, instead only the gradient of the oil flow to the individual Stamp.

Assumption is that the same model is molded and the same Sand volume is filled. Due to differences in the The preparation of molding materials becomes more different from the compressibility Delivered molding material.

Slightly compactable sand is actually relatively deep filled, highly compactable sand is actually relatively filled up in the molded box.

If comparatively highly compactable sand is available, the time period T ₁ until the multiple stamp encounters resistance (dead time, dead stroke) is relatively short; with low compressible sand (high bulk density), it is comparatively long.

The function "volume per unit time" over time in FIG. 4 runs steeply with low compressible sand, with high compressible sand (VD ↑) runs the function "volume flow per Unit of time "comparatively flat. The functions of the courses "Volume per unit of time" over time is recorded. The triggered control according to this speed function an adjustment of the amount of sand filled in or a readjustment the moisture / compressibility in the sand preparation in long term (multiple blends spacing).

Too steep drop means "volume per unit of time" for example too low compressibility. There will be more sand filled (short-term), the amount of moisture (compressibility) over the water control in the mixer increased (long-term) by the Increase compressibility. The same applies vice versa to weak waste per time (less water in the mixer).

To control the physical property of the molding material also an addition change in the slurry or a Serve slurry composition.

For the sake of information, it is pointed out that the punches H do not hit the molding sand at the same time as the ancestor (dead stroke and dead time) and then move into the molding sand at different speeds. The simplification according to the figure 4 shown is that an equal pouring height has been assumed so that with low and high compressibility (VD) both gradients begin to fall at the same time T ₁ ; or to put it the other way round, the two functions x and y are shown shifted towards each other in the direction of "dead stroke" and dead time, in order to be able to compare the functions running curved (1 / x, e ^-x ) better graphically. In practice, differently compactable sands (with different bulk density) are also filled in at different heights, solely due to the movement into the mold box F and the filling frame, despite the same mass. In general: Bulk density large low Compactibility VD small large Flowability strong small possible pressing paths low large Filling level deep high

The integral over the functions x or y (integral over x · dt from 0 to end of pressing) results in the functions not shifted total oil flow Q for the pressing, which at x and y is different.

An aggregate control in a molding plant is without a figure described

The pressurized units in the molding plant are so regulated that oil consumption is always the same as possible becomes. The storage volumes decrease. The aggregates are smaller. The oil consumption is minimized. Tips in consumption are avoided and no longer need to be buffered.

Several consumptions are measured by a measuring device in the Hydraulic cylinder monitored. As part of the control engineering If necessary, their control commands are triggered so that the Oil pressure / time unit for the entire system is approximately constant.

Claims (10)

1. Process for influencing the quality of moulding material moulds made from moulding material compressing devices using a compressing unit which can be controlled via hydraulic fluid, wherein

   (a) the hydraulic fluid volume (q(t)) flowing to the compressing unit or its mass is measured and the measured value is used directly and/or as a variation value (q'(t), q"(t)) in control or regulating;

   (b) the volume, the mass or its variation according to group (a) are used to alter parameters of the moulding material or shaping of the moulding material, in particular the sand or sand shaping, in controlling or regulating manner.
2. Process according to claim 1, in which

   (a) the quantity of moulding material is altered, which is placed in a filling frame or mould box, before the pressing process starts; or/and

   (b) the compressing unit is switched off or an error warning is emitted when during return motion of presses of the compressing unit to a reference position, the same approximate hydraulic fluid volume or the same hydraulic fluid mass is not recorded by the measurement, which has flowed to the presses during pressing; or/and

   (c) the measured or calculated value fluid volume per unit of time or fluid mass per unit of time is compared with zero or a small reference value to record the end of a pressing process; or/and

   (d) the compressibility (VD) of the moulding material conveyed to the compressing unit, in particular moulding sand, is altered depending of the gradient of the hydraulic fluid volume or its mass.
3. Process according to claim 1 or 2, in which the alteration in hydraulic fluid mass or the hydraulic fluid volume, in particular the oil volume (q(t)) or its at least first derivative with time (dq(t)/_dt), is used to alter the compressibility of the moulding material conveyed to the compressing unit, in particular moulding sand.
4. Process according to claim 3, in which the alteration takes place long term as the adjusting variable effect to control the moulding material conveyed for shaping.
5. Process according to one of claims 2 to 4, in which the reference value is selected so that the moulding material shape has sufficient hardness with at the same time as short as possible pressing action.
6. Process according to one of claims 2 to 5, in which a or the alteration in compressibility is effected by altering the addition of water or/and by changing the addition of washing material, additives or a composition thereof.
7. Process according to one of the above claims, in which the hydraulic fluid measurement is integrated in the compressing device, in particular the moulding machine, or is associated with it.
8. Process according to claim 2, in which the alteration in quantity of moulding material supplied is activated only for a preceding change of mould.
9. Process according to one of the above claims, in which the compressing unit has presses (H) and calibration curves (a, b) are used to alter the quantity of moulding material, which indicate the dependency of the press position on the hydraulic fluid volume (q) and the dependency of the quantity of moulding material on a measured hydraulic fluid volume or it derivative.
10. Process according to one of the above claims, in which the compressing unit has presses (H) and all presses are coupled to a common hydraulic fluid source and a volume-per-unit time transducer is arranged in the supply line to the presses (H).

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