US3727894A

US3727894A - Apparatus for moistening mixable materials

Info

Publication number: US3727894A
Application number: US00876461A
Authority: US
Inventors: K Ahrenberg
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-11-15
Filing date: 1969-11-13
Publication date: 1973-04-17
Anticipated expiration: 1990-04-17
Also published as: DE1808998B2; DE1808998C3; BE741734A; NL6916738A; FR2023425A1; GB1255426A; DE1808998A1; CH517541A; CA934751A

Abstract

The invention relates to methods of controlling the moistening of mixable materials and to apparatus for carrying out the methods. The invention is particularly applicable to the moistening of foundry casting sand with water. In one method of high-speed low-inertia auxiliary mixing tool is rotated in the sand and the quantity of water added is determined in dependence on the resistance of the sand to rotation of the tool as measured by the power consumption of an electric motor driving the tool. Also disclosed is apparatus for carrying out the method automatically.

Description

United States Patent 1 Ahrenberg 1 APPARATUS FOR MOISTENING MIXABLE MATERIALS [76] lnventor: Kurt Ahrenberg, l-Iuettenweg 5, l-lerborn, Germany [22] Filed: Nov. 13, 1969 [21] Appl. No.: 876,461

[30] Foreign Application Priority/Data Nov. 15, 1968 Germany ..P 18 08 998.0

[52] US. Cl. ,.259/154, 259/168, 259/174, 259/177 R [51] Int. Cl ..B28c 7/04 [58] Field of Search ..259/l49, 154, 161,

[56] References Cited UNITED STATES PATENTS 3,359,766 12/1967 Haas ..68/l2 R X 3,497,884 3/1970 Tichy et a]. ....68/12 R X Eirich et a1 Warmkessel 4/1968 Eirich etal ..259/85 3 ,249,970 5/1966 3,109,632 11/1963 2,904,401 9/1959 Booth ..23/188 FOREIGN PATENTS OR APPLICATIONS 49,771 8/1966 Germany ..259/179 Primary Examiner-Robert W. Jenkins Assistant Examiner-Philip R. Coe Attorney-McGlew and Toren [57] ABSTRACT The invention relates to methods of controlling the moistening of mixable materials and to apparatus for carrying out the methods. The invention is particularly applicable to the moistening of foundry casting sand with water. In vone method of high-speed low-inertia auxiliary mixing tool is rotated in the sand and the quantity of water added is determined in dependence on the resistance of the sand to rotation of the tool as measured by the power consumption of an electric motor driving the tool. Also disclosed is apparatus for carrying out the method automatically.

14 Claims, 5 Drawing Figures COMPUTER /52 PATENTED APR 1 7 7 WW 1 0F 5 IN VE N TOR KurtAI-RENBERG PATENTED APR 1 71975 SHEEI 2 OF 5 m VEN TOR KqrtAHRENBERG b awn im Hnnvsys PATENTED APR 1 71973 SHEET 3 [IF 5 Ell-.2.

h I I I I I L 1A a1: Q27 v I N VENTOR KMAHRENBERG BACKGROUND OF THE INVENTION For the purpose of determining the moisture content of moulding sands for casting, it is known to use measuring capacitors, or to pass a test amount of the sand over a plate provided with slots of difierent widths, the moisture content being determined in dependence on the amount of sand which falls through the slots, relative to the amount remaining on the plate. Finally, it is known to determine the moisture content of the sand by a cone test.

The above-mentioned known methods suffer either from the disadvantage that it is not possible to impart a predetermined consistency to the sand, or that test samples must frequently be taken from the sand, which interrupts the treatment.

SUMMARY OF THE INVENTION One object of the present invention is to provide an improved apparatus for controlling the moistening of mixable materials such as foundry moulding sand.

Another object is to provide such an apparatus in which the quantity of moistening liquid added is determined in dependence on the resistance of the material to an auxiliary mixing tool.

Another object is to provide such an apparatus in which the auxiliary mixing tool is a high-speed low-inertia rotary mixing tool.

According to the present invention apparatus for moistening a mixable material, comprises a container for the material, a main mixing tool for mixing the material, a high-speed low-inertia auxiliary mixing tool, driving means to rotate the auxiliary tool in the material, and means to add a quantity of moistening liquid to the material determined in dependence on the power consumption of said driving means.

Preferably the auxiliary mixing tool rotates at a speed which is higher by a multiple than the main mixing tool, for example at a peripheral speed of from to 70 metres per second.

With the apparatus of the invention the following advantages may be obtained.

Because the resistance of the material to a tool which rotates at high speed is comparatively large, the power consumption of the driving means for the auxiliary mixing tool is large, thus permitting an accurate comparison between the actual and required values, that is, between the actual and required consistency of the material.

Controlling the consistency of the material by automatic moistening of the material may be carried out with greater precision, and the apparatus required for that purpose is simplified.

The temperature of the material may if desired be taken into consideration at the same time.

Depending on the consistency of the material, which can for example comprise moulding sand, ceramic material, concrete, lime sandstone materials, granulated materials, and pressing and ramming materials, the resistance to mixing and the power consumption may be in widely different ranges. It is therefore advantageous for the driving means for the auxiliary mixing tool to be a variable speed electric motor, preferably a pole-changing motor. In this way, depending on the consistency of the material or the nature of individual components of the material, the most favourable treatment for each particular case can be achieved.

Finally, care should be taken that the moisture introduced into the mixing material to achieve a predetermined consistency does not exceed its desired value unless additional apparatus is provided for O removing moisture. It is therefore important that the moisture be distributed rapidly in the material; as otherwise, under certain circumstances, an excessively low power consumption may momentarily be indicated and an incorrect control order be transmitted to the regulating apparatus, resulting in the further excessive addition of moisture. A regulating signal corresponding to the power consumption of the motor must preferably therefore be derived when almost unvarying conditions are obtaining in the apparatus, that is, in particular, when the tool is rotating at a speed which is uniform and therefore free from acceleration, and the material is sufficiently homogenised for continuation of the mixing operation not to vary the power consumption of the motor.

In order to ensure that the further addition of moisture is only derived from the power consumption signal after a substantially unvarying condition of the above-mentioned nature has been achieved, the apparatus for carrying out a two-stage method in which a given amount of moisture is firstly introduced into the material and, subsequently, further moistening is controlled in dependence on the power consumption of the motor, can with advantage be embodied with a regulating. apparatus which has an adjustable time delay operable after the first supply of moisture. This time delay can be made correspondingly larger when the time constants in the control circuit affect the measurement, so that the measured values of the power consumption are in fact taken as consistency values measured in the substantially unvarying condition of the material, and are transmitted to the regulating apparatus for the purposes of further controlling the moistening operation.

BRIEF DESCRHIPTION OF THE DRAWINGS Two embodiments in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. ll shows the first embodiment in diagrammatic form,

H6. 2 shows the second embodiment in block form, and

FIGS. 3 to 5 show the electric circuit of the second embodiment, the circuit being completed by placing FIG. 41 to the right of FIG. 3, and FIG. 5 to the right of FIG. 4i.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. l, a counter-flow mixer comprises a clockwise-rotating mixing container 2 in which operates a relatively low-speed anti-clockwise-rotating main mixing tool A having a plurality of mixing blades, and a high-speed low-inertia auxiliary mixing tool B. The container 2 is rotated by a gear motor 29 which drives a ring gear 212 secured to the container. The axes of rotation of both tools A and B are eccentric relative to the axis of rotation of the container 2, and the tool B lies outside the working area of the tool A.

In operation, a known amount 1 of material to be mixed and moistened is put into the container 2 and treated with an amount 3 of fluid. Hereinafter the material will be assumed to be casting sand and the fluid water. In a first mixing stage, which is not necessarily regulated, the amount of water is metered by a meter 14 controlling a valve in such a way that, together with the usual initial water content of the sand, the sand is still definitely below the desired final water content necessary to achieve the desired consistency or plasticity. This first stage prepares for the subsequent stage of finely regulating the water content, and also brings the water content to a value at which the electric current or power used by an electric motor 4 driving the tool B can be satisfactorily measured.

The sand is then homogenised by the tools A and B, during which step many materials have a tendency to increase in volume up to an expansion level 6. For clarity, the levels 3 and 6 are shown in exaggerated form. Further high-speed tools, combined with stationary tool systems, can also be used instead of the tools A and B. The uniform distribution of the water can be achieved in a short period of, for example, 10 to seconds, after which time a magnetic valve 7 controlled by a time relay 13 opens, so that valves 8a to 8d are acted upon by water pressure.

The power used by the motor 4 in driving the tool B is then measured by a power measuring means having contacts 10a to 10d. There is normally connected between the motor 4 and the power measuring means a measured value treatment unit 11 by means of which the measured value is transformed and smoothed. When the sand is homogenous the power used by the motor 4 is a direct, generally non-linear, function of the consistency of the sand. As the motor 4 is driven by a constant network voltage, the reading of the power measuring means is proportional to the current used and causes one or more of the contacts 10a to 10d to be tripped so that the measured value which is obtained in analog form is quantised in four steps. Depending on the number of contacts 10a to 10d tripped, a control unit 12 acts on the magnetic valves 80 to 8d in such a way that any of the contacts 10a to 10d tripped cause the corresponding valves 8a to 8d to be opened.

The amount of water allowed into the sand during this second stage depends on the condition of the valves 80 to 8d, the common supply pipe 16 to which is throttled after a predetermined period by the magnetic valve 7. In this way, the amount of water added depends on the number of valves 8a to 8dopen, and this is determined by the consistency of the sand following the first stage. Following the addition of the water in the second stage the sand is again homogenised and subsequently discharged. All the control and regulating elements are then returned to their initial conditions.

The above described method and the apparatus can be modified in various ways without going outside the scope of the invention. Thus the valves 8a to 8d could be closed by flow measuring means instead of the time relay 13. Depending on the specific use to which the apparatus is put, the valves 8a to 8d can also be formed as regulating valves, regulating cocks, snap valves or restrictor valves with a large flow cross-section if thick or viscous fluids are used for moistening. The valve control can be effected by potentiometers which fully open the valves initially and then successively close them in dependence on the power used by the motor 4.

If the motor 4 is a three-phase motor, the abovementioned power measuring means will desirably be used, while with a direct-current motor a contact ammeter is preferable. When hydraulic motors are used to drive the tools A and B, they are combined with known regulating and measuring devices.

The invention permits reliable control of the moistening operation and rapid homogenisation of the sand. By using a constant weight of sand a high degree of measuring precision can be achieved because of the possibility of reproducing the values of power used relative to a given water content, and hence calibrating the power measuring means. Also, a high-speed low-inertia auxiliary tool has a sensitive reaction to variations in water content of the sand, so that the range of power used is extended and differentiation between different water contents increased. The sensitivity and precision of the regulation is still further increased if the motor 4 is connected directly, that is without the interpolation of gears, to the tool B/Additionally, it has been found advantageous if the motor 4 maintains its speed of rotation substantially constant within the measuring range. As different measuring ranges are found desirable for different materials, it is of advantage for the motor 4 to be pole-changing.

It has been found preferable for the tool B to be in the form of a H-shaped spinner 5, the bars of which diverge upwardly in a V-shape. However other tools suited to the specific properties of the material can also be used.

in the apparatus shown in FIGS. 2 to 5, two limit contacts are associated with the power measuring means W coupled to the motor 4 for the auxiliary tool B. With the two limit contacts in this embodiment, a four-stage mode of operation is achieved by means of a suitable circuit connected to the power measuring means W and in this way the required water content can be approached in steps.

In order to make the cycle time of the mixer as short as possible, the apparatus should be set very rapidly and automatically to the water content which is still missing from the material. The amount of water in the old sand which is found for example in foundries, can however vary within wide limits. If for example the water content in the sand which has not yet been treated is in the vicinity of the required value, the first stage, which generally adds a large amount of water, and possibly even the second stage, are omitted so that then only the third and fourth stages are operative, with correspondingly smaller amounts of water added. The

sequence in time of the additions of water and the amounts of water to be added can therefore be adjusted as desired as will now be described.

in H6. 2, the container 2 is shown diagrammatically with a main mixing tool A and a spinner or auxiliary tool B, the motor 4 of which is coupled to the power measuring means W. The power measuring means W transmits a signal to a pulse transmitter U1 which actuates the counting circuit Z. The counting circuit Z is connected to a transmitter U3 which actuates a magnetic valve V for the required water supply periods and intervals The magnetic valve V can be actuated in four modes by the transmitter U3 in the embodiment shown, the variation in the supply periods and intervals in each mode resulting in a variation in the amount of water added. With the shortest supply period and the longest interval, the throughput is 0.25 litres per minute, whilst with the longest supply period and the shortest interval, the throughput is 60 litres per minute.

The mode of operation of the metering control cir' cuit with four-stage automatic operation will now be described with reference to FIGS. 3 to 5. The metering operation is initiated when a switch B1 in the current path 12 is temporarily closed. This results in the relay 11A being energised, whereby the contacts DlA in the current path 39 are closed. This results in the control voltage for the metering apparatus being connected.

The relay d3 in the counting circuit Z is energised by way of the rest contacts D2/0 in the current path 18 The relay d3 closes inter alia the contact D3 in the currentpath 24 which'supplies voltage to two potentiometers (not shown) of the transmitter U3, which serve to adjust the water-supply period and interval of the first mixing stage. These two potentiometers are built into the transmitter U3 together with the interval potentiometers of the second, third and fourth mixing stages. Therefore, for each stage there is provided a potentiometer for adjusting the supply period of the valve V and a potentiometer for adjusting the interval. The transmitter U3 therefore acts as a pulse transmitter with variable supply periods and intervals. The intervals must be selected in such a way that the water which is added during the firstsupply period of the magnetic valve'V mixes thoroughly with the sand. Only then does the power measuring means W indicate a rise in power consumption by the motor 4, and only after the power rise has terminated should the second addition of water take place.

Owing to the relay d3 being energised, the contact D3 in the current path 35 is also closed, energising the relay dl2. As a result, the rest contact D12 in the current path 43 is opened, which opens the circuit of the voltage path for the power measuring means W, which path includes the resistor R1. At the same time the working contact D12 in the current path 43 is closed, which closes the voltage path by way of the variable resistor R3 and the resistor R2. A voltage varied for example by 20 percent can be delivered to the power measuring means W by the resistor R3. By means of such an increase in voltage in the voltage path, the indication of the indicator (not shown) of the power measuring means W can be made to exceed the actual power consumption of the motor 4.

Asfalready mentioned, the closed contact D3 in the current path 24 passes voltage to the two potentiometers for the first stage and by the contact 143 of the transmitter U3, the valve relay d9 in the current path 28 is energised and de-energised according to the supply periods and intervals set in the two potentiometers. Accordingly, the supply of water to the sand is effected by the valve V. For this pu'rpose, the valve relay d9 switches the contacts D9 in the current path 11 which includes the valve V.

consumption by the motor 4 and the indicator of the power measuring means W leaves the minimum mark,

whereupon the relay d14 in the current path 41 is energised. The contact D14 in the currentpath 31, which is supplied with voltage by way of the closed contact D15 of the relay d15, energises the relay d1 1 in by way of the contact D3 which is also closed by the relay d1 1. The rest contact D11 in the current path 28 then opens and de-energises the valve relay 9. The working contact D11 in the current path 16 is closed at the same time by the relay d1 1 and transmits voltage to the terminal 5 of the transmitter U1.

The transmitter U1 is also a pulse transmitter with variable working periods and interval. The working period of the pulse transmitter U1 is set to be very short as it acts to restrict the transmission of pulses, while the interval period acts as a response delay, so that the indicator of the power measuring means W is generally not quite at rest in operation of the metering apparatus, and so that its first maximum deflection should not initiate any stepping of the counting circuit Z. In other words, the supply of water to the sand should be stopped at that moment, but the pulse transmitter U1 should not yet step the counting circuit Z on to the next I stage.

When the indicator of the power measuring means W has finally moved off the minimum mark, the contact ul of the transmitter U1, which contact ul lies in the current path 14, closes temporarily, and the coil 42 of the counting circuit Z which also lies in the current path 14 is energised. As a result, the counting circuit Z is stepped on by one step. The result of this is that the rest contact D2/0 opens and the working contact D2/1 in the current path 19 closes. The contact D2/1 energises the relay d4 in the current path 19, of which the working contact D4 which is in the current path 25 then closes and transmits voltage to the-two potentiometers for the supply periods and intervals of the second stage. The transmitter U3 energises and deenergises the valve relay d9 according to the valves set by way of the contact 143, and the water supply of the second stage takes place.

Owing to the relay d3 becoming deenergised, the relay dl2 is also de-energised by way of the contact D3", the contacts D12 and D12 of the relay d12, which lie in the current path 43, switching the voltage path of the power measuring means W to normal voltage. As a result of this switch to normal voltage, the indicator of the power measuring means W returns to the minimum mark and the relay d14 becomes de-ener-.

gised, the contact D14 opening. At the same time the contact D3 in the current path 31 opens and de-energises the relay dll. The rest contact D11 of the relay dll which lies in the current path 28 prepares for the energising of the valve relay d9. The working contact D1 1 of the relay d3 simultaneously interrupts the control voltage for the transmitter U1 so that further stepping on of the counting circuit Z is prevented.

At this moment, the power measuring means W is operating without increased voltage. If now the power consumption of the motor 4 is again increased by the supply-of water in the second stage, the indicator of the power measuring means W again moves off the minimum mark. The relay dl4 is again energised and its working contact D14, which is in the current path 31, energises the relay d1 1 by way of the contact D4 in the current path 32, which contact has already been closed by the relay d4. The rest contact D11 of the relay dll de-energises the valve relay d9. The working contact D11 is closed at the same time and transmits control voltage to the transmitter U1. The transmitter U1 steps the counting circuit Z by a further step, as already described above.

In that case, the relay d4 becomes de-energised and the relay d of the counting circuit Z is energised by way of the closed contact D2/2. The contact D4 in the current path 32 opens owing to the relay d4 becoming de-energised and de-energises the relay dll. The working contact D5 is closed by the relay d5 and transmits voltage to the two potentiometers in the transmitter U3 for the supply periods and intervals of the third stage. At the same time, the working contact D5 in the current path 36 is closed and transmits voltage to the relay d13 in the same current path. The relay dl3 actuates the switching contact D13 and D13 in the current path 44, which interrupts the voltage path of the power measuring means W by way of the resistor R1 and switches the latter to the variable resistor R5. Depending on the particular setting of the latter, an increased voltage is then again transmitted to the voltage path of the power measuring means W, which results in an increased power consumption indication. From this it is apparent that the voltage increase in the first and the third stages can be adjusted separately.

The valve relay d9 which actuates the valve V is energised and de-energised, as already mentioned, by the transmitter U3. When the indicator of the power measuring means W finally reaches the maximum mark, the relay 1115 in the current path 42 becomes deenergised. The rest contact D of the relay dl5, which lies in the current path 33, closes and energises the relay dll by way of the working contact D5 which is already closed. The relay dll de-energises the valve relay d9 by way of the contact D1 1 and supplies voltage to the transmitter U1 by way of the contact D1 1 as already described above. As a result, the counting circuit Z is stepped on by one step. The relay d5 of the counting circuit becomes de-energised and the relay d6 becomes energised by virtue of the contact D2/3 being closed. Owing to the de-energisation of the relay d5, the relay 13 in the current path 36 is de-energised by way of the contact D5. Also, the switching contact D13, D13 which lies in the current path 44 and which is actuated by the relay d13 switches the voltage path of the power measuring means W back to normal voltage. This condition is shown in FIG. 5. The result of this is that the indicator of thepower measuring means W again moves off the maximum mark so that the relay 1115 is again energised.

The two potentiometers in the transmitter U3 for the supply periods and intervals of the fourth and last stage are energised by the relay d6. The transmitter U3 again accordingly actuates the valve relay :19. This results in a further supply of water to the sand and the indicator of the power measuring means W again returns to the maximum mark, owing to the rising power consumption of the motor 4. As a result, the relay d15 is again deenergised and its rest contact D15 which is in the voltage path 33 energises the relay dll by way of the working contact D6 in the current path 34, which contact is already closed by the relay d6. The relay d1 1 deenergises the valve relay d9 and transmits voltage to the transmitter U1 by way of the contact D11. The transmitter U1 thereupon steps the counting circuit Z by a further step. The working contact D2/4 of the counting circuit Z, which contact lies in the current path 22, transmits control voltage to the terminal 5 of the reset circuit U2 for resetting the counting circuit Z. The working contact u2 of the circuit U2 which lies in the current path 13, energises the coil dlZ, whereby the control voltage for the entire apparatus is interrupted by way of the contact DlZ in current path 37. The working contact 142 of the reset circuit U2, which contact lies in the current path 15, transmits a halfwave rectified voltage by way of the zero-position contact D2 to the coil 42 which thereupon returns the counting circuit Z to its zero position. The pulse transmission of the reset circuit U2 last for about 1 second.

After the above switching operation has taken place, the supply of water is concluded and the apparatus is ready for a new metering operation.

If, by virtue of the power measurement, it turns out that there is initially a relatively large amount of water in the sand, the various stages are omitted until the power measuring means W indicates a value which shows that the addition of water is necessary. Manual release of the valve relay d9 for corresponding switching of the magnetic valve V is also possible by way of the manual switches B3 and B4 in the current path 30.

Instead of the above described circuit with a power measuring means W, the principle upon which the invention is based can also be embodied by a control circuit having for example a current measuring means with an electronic coefficient forming means, or any other measuring device for supplying the necessary measured values. If materials with widely varying starting temperatures are to be processed, additional temperature sensing means 50 which operate in combination with a computer 32 are used, in order to correct the influence of temperature on the amount of water contained in the material.

Various other modifications can be made without departing from the invention as defined by the appended claims. In particular it is to be noted that the references to sand and water in the specific description are only examples of the materials and liquids with which the invention can be used.

lclaim:

1. Apparatus for moistening a mixable material by the multi-stage addition of a moistening liquid, comprising a container rotatable about a substantially vertical axis and arranged to hold the material to be mixed and moistened, a vertically arranged relatively lowspeed rotatable main mixing tool located within said container for mixing the material, a vertically arranged high-speed low-inertia auxiliary mixing tool located within said container and spaced laterally from said main mixing toolso that its path of rotation is outside the path of rottion of said main mixing tool, driving means for rotating the auxiliary tool in the material, means for a step-wise addition of moistening liquid to the material to bring its moisture content to a predetermined level, and control means for regulating said means for a step-wise addition of moistening liquid to the material determined in dependence on the power consumption of said driving means for said auxiliary mixing tool, and said control means includes a means for affording an interval in which the moistening liquid thoroughly mixes with the material before the power consumption of said driving means is determined.

2. Apparatus according to claim 1 wherein the driving means is an electric motor.

3. Apparatus according to claim 2 wherein the auxiliary mixing tool is connected directly to the electric motor.

4. Apparatus according to claim 3 wherein the rotational speed of the electric motor is substantially independent of the load thereon.

5. Apparatus according to claim 3 wherein the elec tric motor is a variable speed motor.

6. Apparatus according to claim 3 wherein the electric motor is a pole-changing motor.

7. Apparatus according to claim 1 wherein the auxiliary mixing tool is approximately H-shaped.

8. Apparatus according to claim 1 wherein said control means comprises means operative after the addition of moistening liquid to the material to prevent the addition of further moistening liquid for a predetermined time.

9. Apparatus, as set forth in claim 1, wherein said auxiliary mixing tool is approximately H-shaped and.

the upwardly extending sides of said auxiliary mixing tool converge in the downward direction.

10. Apparatus for moistening a mixing material, comprising a container for the material, a main mixing tool for mixing the material, a high-speed low-inertia auxiliary mixing tool, driving means for rotating the auxiliary tool in the material, control means for adding a quantity of moistening liquid to the material determined in dependence on a power consumption of said driving means for said auxiliary mixing tool, said control means comprising means for measuring the power consumption of said driving means, said means for measuring the power consumption including devices for sensing the limiting values of the power consumed in each stage of the moistening of the mixable material between a minimum value and a maximum value, an indicator of the power consumed, and means for increasing the power consumed as shown on said indicator by a predetermined amount relative to the actual power consumption of said driving means, a first pulse generator to which in operation said measuring means supplies a signal, a counting circuit controlled by said first pulse generator and including a plurality of counting stages, a second pulse generator including means to determine the supply periods and intervals for the supply of moistening liquid to the material, and a magnetic valve by way of which the moistening liquid is supplied to the material, in operation the counting stages supplying signals to said second pulse transmitter to determine the time during which said magnetic valve is operated for supplying moistening liquid and said second pulse transmitter determining the supply periods and intervals within each stage of the addition of the moistening liquid.

ll. Apparatus according to claim 10 wherein said means in the second pulse transmitter to determine the supply periods and intervals comprises potentiometers.

12. Apparatus according to claim 10 wherein the counting circuit has four stages and the second pulse transmitter has four stages whereby the moistening liquid can be added in four separately controllable stages.

13. Apparatus, according to claim 10, wherein said first pulse transmitter is adjustable for variable working periods and intervals.

14. Apparatus, according to claim 10, wherein a reset circuit is arranged for returning said counting circuit to zero, and said reset circuit being controlled by said counting circuit.

Claims

1. Apparatus for moistening a mixable material by the multistage addition of a moistening liquid, comprising a container rotatable about a substAntially vertical axis and arranged to hold the material to be mixed and moistened, a vertically arranged relatively low-speed rotatable main mixing tool located within said container for mixing the material, a vertically arranged high-speed low-inertia auxiliary mixing tool located within said container and spaced laterally from said main mixing tool so that its path of rotation is outside the path of rotation of said main mixing tool, driving means for rotating the auxiliary tool in the material, means for a step-wise addition of moistening liquid to the material to bring its moisture content to a predetermined level, and control means for regulating said means for a step-wise addition of moistening liquid to the material determined in dependence on the power consumption of said driving means for said auxiliary mixing tool, and said control means includes a means for affording an interval in which the moistening liquid thoroughly mixes with the material before the power consumption of said driving means is determined.

5. Apparatus according to claim 3 wherein the electric motor is a variable speed motor.

9. Apparatus, as set forth in claim 1, wherein said auxiliary mixing tool is approximately H-shaped and the upwardly extending sides of said auxiliary mixing tool converge in the downward direction.

11. Apparatus according to claim 10 wherein said means in the second pulse transmitter to determine the supply periods and intervals comprises potentiometers.