GB1593074A - Method of and apparatus for controlling the operation of a straight-through screw mixer - Google Patents

Description

(54) METHOD OF AND APPARATUS FOR CONTROLLING THE OPERATION OF A STRAIGHT-THROUGH SCREW MIXER (71) We, VEB GISAG, of Gerhard Ellrodt-Strasse 24, 7034 Leipzig, German Democratic Republic, a Corporation organised under the laws of the German Democratic Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to a method of and an apparatus for controlling the operation of a continuously operating straight-through screw mixer by monitoring the supply thereto of at least one liquid component, such as binders, catalysts, degradation promoters, more particularly in the production of rapid cold hardening foundry casting materials.

Straight-through screw mixers are known which operate without monitoring the supply of the liquid components. In such mixers there is no warranty that the moulding material discharged at the end of the final mixing screw of the straight-through screw mixer and passed directly into a mould box or core box contains all the liquid components, and quite especially those which are dosed in only small proportions.

A straight-through screw mixer with a liquid component feed monitoring device is known, which is characterised by the fact that contacts are arranged at the admixing stations of the liquid components, said contacts being wetted by the respective components and are connected in such a way that they maintain the mixer drive in the switched on state during the feed of the liquid and stop it when the liquid feed is interrupted (DT-AS 1 938 685). This apparatus has the disadvantage that, although it stops the installation when one of the liquid components is lacking, it does not become operative when the delivery stream diminishes so that a satisfactory mixing is no longer ensured. It also has the disadvantage that its capacity to function is ensured only when the liquids to be monitored are sufficiently electric conductive.

The invention aims at providing a method and an apparatus, whereby it is achieved that even for very small proportions of components, or electrically nonconductive liquid components, a failure of the feed, which may be imperceptible to the operator owing to the feed quantities which are frequently very small, is detected reliably. By this means it is possible to avoid wastage in the production of moulds and cores which frequently is only detected when the first unserviceable moulds and cores are removed from the mould box or core box after expiry of the curing time.

The invention seeks to produce a controlling system which, in contradistinction to the known devices, not only becomes operative when the liquid component supply stream fails completely, but as soon as the supply stream diminishes so that the mixture is no longer fit for use. It should also be useful for all liquid media, irrespective of their electrical conductivity.

To this end, the present invention consists in a method of controlling the operation of a continuously operating straight-through screw mixer, wherein liquid components to be supplied to the mixer are respectively fed, before their entry into the mixing and conveying screw, each to an intermediate vessel provided with a discharge outlet which is reached only after the liquid accumulates in the vessel to a pre-determined degree, the height of the liquid in the vessel being monitored by a float arranged for actuating means for stopping the mixer if the liquid level falls below the level of the discharge outlet.

The invention also consists in an apparatus apparatus for controlling the operation of a straight-through screw mixer having at least one mixing and conveying screw, and requiring the supply of at least one liquid component, comprising for each liquid component, a vessel having an inlet for connection to a supply of the liquid and an outlet disposed above the level of the inlet, the outlet issuing into the mixing and conveying screw, a float in said vessel, a guide pin on said float slidingly guided in a guide tube provided on said vessel, a contactless switch operated by the float and arranged for changing from one switching condition to another when the level of the liquid in the vessel drops below the level of said outlet, the contactless switch being connected to a switching amplifier, there being signal devices and switch means controlling the screw-mixer, the arrangement of the contactless switch being such that if the liquid delivery falls below a predetermined rate or ceases, the float causes the contactless switch to be triggered, the resulting switch pulse being fed to the amplifier to operate the signal devices and the switch means to stop the mixer.

The functional cycle of the apparatus according to the invention is as follows: The liquid component coming from a delivery pump or dosing pump, passes, immediately upstream of the discharge into the screw mixer, through a cylindrical, vertically arranged vessel. The liquid level in the vessel then rises to the level of a horizontally arranged discharge pipe, bent through 90 degrees at the end. If the supply of the liquid component is interrupted, the liquid level in the vessel falls until the liquid level is at the same level as the lowest point of the internal cross-section of the discharge pipe.

When supply of the liquid component commences, the liquid level rises and with it the float, which, like the vessel, consists of nonconductive and acid-resistant, preferably plastics material, by a predetermined distance depending upon the quantity of liquid supplied, whilst the float advantageously provided with conductive material at its upper end approaches the contactless switch adjusted to a quite specific distance in the vertical direction until a switching pulse is triggered. If the supply of the liquid component remains below the prescribed value or fails completely, then the liquid level and hence the float sinks back to a lower level or returns to the initial level, whereby once again a switching impulse is triggered which can be used to stop the mixer.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example one embodiment thereof, and in which: Fig. 1 shows a straight-through screw mixer with liquid supply monitoring means; and Fig. 2 is a diagram of the liquid supply monitoring means.

The liquid supply monitoring system 1 is arranged at the transfer point between the two mixing and conveyor screws 4, 4' which are driven by electric motors 2 and connected together by a swivel joint 3. The pivotable mixing and conveyor screws rest upon a stand 5 which is provided with a vertically arranged pivot axis 6 to accommodate them. The stand 5 serves simultaneously to accommodate the feeding and dosing pump 7 for the liquid component. The supply tank for the liquid component is not shown in the drawing. For dosing the solid components into the first mixing and conveyor screw 4, there is arranged above the pivot axis 6, a dosing device 8 which is fed from a tank or hopper 9 arranged above it.

The solid components passing from the tank 9 through the dosing device 8 into the mixing and conveyor screw 4 are wetted at the transfer point between the two mixing and conveyor screws 4, 4' by the liquid component, which travels through the liquid supply monitoring system 1 from the liquid feed line 10. Referring to Fig. 2, the liquid component passes through an inlet pipe 11 into an intermediate tank 12 and flows through a discharge pipe 13 onto the dry components in the second mixer 4'.

Floating on the liquid in the intermediate tank 12 is a float 15 having a guide pin 18 guided in guide tube 19 provided on the tank. The tank 12, guide tube 19, float 15 and guide pin 18 are made of non-conductive, preferably acidresistant material, such as plastics material. On the upper end of the guide pin there is a layer or member 17 of conductive material e.g.

metal. 14 indicates the liquid level in the tank which in the drawing is in the position of rest.

16 is a contactless switch or proximity sensor in which, as the level of liquid in the tank 12 rises during delivery of the liquid, a pulse is triggered by the metal member 17. The pulse on contact or interruption is transmitted through leads 20 to a switching amplifier 21 to cause operation of an acoustic signal device 22 or optical signal device 23, or it may be used to interrupt the drive motor 24 of the screw mixer.

The distance between the contactless switch or proximity sensor 16 and the guide tube 19 of the intermediate tank 12 is variable by adjusting the vertical position of the contactless switch or proximity sensor 16 above the tube 19, so that in conjunection with different heights of the liquid level due to varying delivery quantity, an interruption of the circuit occurs not only when the delivery stream fails completely, but also when the delivery stream diminishes by a pre-determined amount.

WHAT WE CLAIM IS: 1. A method of controlling the operation of a continuously operating straight-through screw mixer, wherein liquid components to be supplied to the mixer are respectively fed, before their entry into the mixing and conveying screw, each to an intermediate vessel provided with a discharge outlet which is reached only after the liquid accumulates in the vessel to a pre-determined degree, the height of the liquid in the vessel being monitored by a float arranged for actuating means for stopping the mixer if the liquid level falls below the level of the discharge outlet.

2. A method of controlling the operating of a continuously operating straight-through screw mixer substantially as herein described.

3. An apparatus for controlling the operation of a straight-through screw mixer having at least one mixing and conveying screw, and requiring the supply of at least one liquid component, comprising for each liquid component, a vessel having an inlet for connection to a supply of the liquid and an outlet disposed above the level of the inlet, the outlet issuing

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   the arrangement of the contactless switch being such that if the liquid delivery falls below a predetermined rate or ceases, the float causes the contactless switch to be triggered, the resulting switch pulse being fed to the amplifier to operate the signal devices and the switch means to stop the mixer.

   The functional cycle of the apparatus according to the invention is as follows: The liquid component coming from a delivery pump or dosing pump, passes, immediately upstream of the discharge into the screw mixer, through a cylindrical, vertically arranged vessel. The liquid level in the vessel then rises to the level of a horizontally arranged discharge pipe, bent through 90 degrees at the end. If the supply of the liquid component is interrupted, the liquid level in the vessel falls until the liquid level is at the same level as the lowest point of the internal cross-section of the discharge pipe.

   When supply of the liquid component commences, the liquid level rises and with it the float, which, like the vessel, consists of nonconductive and acid-resistant, preferably plastics material, by a predetermined distance depending upon the quantity of liquid supplied, whilst the float advantageously provided with conductive material at its upper end approaches the contactless switch adjusted to a quite specific distance in the vertical direction until a switching pulse is triggered. If the supply of the liquid component remains below the prescribed value or fails completely, then the liquid level and hence the float sinks back to a lower level or returns to the initial level, whereby once again a switching impulse is triggered which can be used to stop the mixer.

   In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example one embodiment thereof, and in which: Fig. 1 shows a straight-through screw mixer with liquid supply monitoring means; and Fig. 2 is a diagram of the liquid supply monitoring means.

   The liquid supply monitoring system 1 is arranged at the transfer point between the two mixing and conveyor screws 4, 4' which are driven by electric motors 2 and connected together by a swivel joint 3. The pivotable mixing and conveyor screws rest upon a stand 5 which is provided with a vertically arranged pivot axis 6 to accommodate them. The stand 5 serves simultaneously to accommodate the feeding and dosing pump 7 for the liquid component. The supply tank for the liquid component is not shown in the drawing. For dosing the solid components into the first mixing and conveyor screw 4, there is arranged above the pivot axis 6, a dosing device 8 which is fed from a tank or hopper 9 arranged above it.

   The solid components passing from the tank 9 through the dosing device 8 into the mixing and conveyor screw 4 are wetted at the transfer point between the two mixing and conveyor screws 4, 4' by the liquid component, which travels through the liquid supply monitoring system 1 from the liquid feed line 10. Referring to Fig. 2, the liquid component passes through an inlet pipe 11 into an intermediate tank 12 and flows through a discharge pipe 13 onto the dry components in the second mixer 4'.

   Floating on the liquid in the intermediate tank 12 is a float 15 having a guide pin 18 guided in guide tube 19 provided on the tank. The tank 12, guide tube 19, float 15 and guide pin 18 are made of non-conductive, preferably acidresistant material, such as plastics material. On the upper end of the guide pin there is a layer or member 17 of conductive material e.g.

   metal. 14 indicates the liquid level in the tank which in the drawing is in the position of rest.

   16 is a contactless switch or proximity sensor in which, as the level of liquid in the tank 12 rises during delivery of the liquid, a pulse is triggered by the metal member 17. The pulse on contact or interruption is transmitted through leads 20 to a switching amplifier 21 to cause operation of an acoustic signal device 22 or optical signal device 23, or it may be used to interrupt the drive motor 24 of the screw mixer.

   The distance between the contactless switch or proximity sensor 16 and the guide tube 19 of the intermediate tank 12 is variable by adjusting the vertical position of the contactless switch or proximity sensor 16 above the tube 19, so that in conjunection with different heights of the liquid level due to varying delivery quantity, an interruption of the circuit occurs not only when the delivery stream fails completely, but also when the delivery stream diminishes by a pre-determined amount.

   WHAT WE CLAIM IS: 1. A method of controlling the operation of a continuously operating straight-through screw mixer, wherein liquid components to be supplied to the mixer are respectively fed, before their entry into the mixing and conveying screw, each to an intermediate vessel provided with a discharge outlet which is reached only after the liquid accumulates in the vessel to a pre-determined degree, the height of the liquid in the vessel being monitored by a float arranged for actuating means for stopping the mixer if the liquid level falls below the level of the discharge outlet.
2. 2. A method of controlling the operating of a continuously operating straight-through screw mixer substantially as herein described.
3. 3. An apparatus for controlling the operation of a straight-through screw mixer having at least one mixing and conveying screw, and requiring the supply of at least one liquid component, comprising for each liquid component, a vessel having an inlet for connection to a supply of the liquid and an outlet disposed above the level of the inlet, the outlet issuing

   into the mixing and conveying screw, a float in said vessel, a guide pin on said float slidingly guided in a guide tube provided on said vessel, a contactless switch operated by the float and arranged for changing from one switching condition to another when the level of the liquid in the vessel drops below the level of said outlet, the contactless switch being connected to a switching amplifier, there being signal devices and switch means controlling the screwmixer, the arrangement of the contactless switch being such that if the liquid delivery falls below a pre-determined rate or ceases, the float causes the contactless switch to be triggered, the resulting switch pulse being fed to the amplifier to operate the signal devices and the switch means to stop the mixer.
4. 4. An apparatus as claimed in claim 3, wherein the vessel and the float are made of a nonconductive and acid-resistant material, preferably plastics material.
5. 5. An apparatus as claimed in claim 3 or 4, wherein the guide pin of the float carries at its end adjacent the contactless switch a metal member operatively associated with the contactless switch.
6. 6. An apparatus for controlling the operation of a straight-through screw mixer, substantially as herein described with reference to and as shown in the accompanying drawings.
7. 7. A straight-through screw mixer having a controlling device as claimed in any one of claims 3 to 6.