GB2459929A

GB2459929A - Method and Apparatus for Preparing Dry Mortar

Info

Publication number: GB2459929A
Application number: GB0808725A
Authority: GB
Inventors: Campbell Brown; Conor Mcalinden
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-05-14
Filing date: 2008-05-14
Publication date: 2009-11-18
Also published as: GB0808725D0

Abstract

An apparatus for the continuous preparation of dry mortar consists of metering means for metering the constituent materials of the mortar, such as sand, cement and one or more additives, and supplying the metered materials to a conveying means 20, which may be in the form of a screw conveyor. The conveying means 20 conveys the metered materials to a mixing means 30, which may be in the form of a mixing chamber, wherein the materials are blended to form a homogeneous dry mortar. Further disclosed is a method for the continuous preparation of dry mortar comprising metering the constituent materials of the mortar, such as sand, cement and one or more additives and conveying the metered materials through a mixing means 30 wherein the metered materials are blended to form a homogeneous dry mortar at an outlet of the mixing means. The metering means may comprise a metering screw conveyor 9, 10. The sand may be provided in a dry sand hopper 2 with a level sensor. Within the mixing chamber 30 an agitator 40 may be located. The agitator 40 may comprise a shaft and a plurality of radially extending mixing blades (see fig 3).

Description

Method and Apparatus for Preparing Dry Mortar This invention relates to a method and apparatus for preparing dry mortar and in particular to a method and apparatus for preparing dry mortar for use in dry mortar silos.

Typically mortar for construction purposes is prepared off site, by mixing of sand, cement and water. Subsequently the wet mix is conveyed to a construction site in specially adapted vehicles having a rotating drum for mixing the mortar. However, a significant drawback with this process is that the mortar begins to set as soon as the binder (cement) comes into contact with moisture, therefore the mixed wet mortar must be used quickly and, due to the difficulty in delivering exactly the required amount of mortar, considerable wastage may occur.

More recently, attempts have been made to overcome the abovementioned disadvantages by delivering a dry mixture of sand and cement to the construction site, known as dry mortar, and feeding metered quantities of the dry mortar to a mixing chamber wherein the dry mortar is mixed with water. Such dry mortar is typically conveyed to a construction site in a silo mountable on the back of a lorry, the silo being mounted on a support frame whereby the silo can be mounted in an upright position once removed from the lorry. A conveying and mixing device is provided at a lower end of the silo comprising a horizontally arranged passage having a rotatable shaft mounted therein driven by an electric motor, a first part of the passage defining a screw conveyor for conveying dry mortar from the silo to a second part of the passage defining a coaxial mixing chamber wherein a second part of the shaft is provided with mixing blades, water being supplied into the mixing chamber for producing wet mortar at an outlet of the mixing chamber. An example of such alTangement is shown in US 4,855,960.

Dry mortar for placing in such silos is typically prepared by a batch process comprising a sand drying stage, a weighing stage for weighing the required separate amounts of sand, cement and other additives (such as plasticisers), and a mixing stage for mixing the weighed materials together to create a homogeneous batch dry mortar which is subsequently stored in a storage vessel before loading into silos for conveying to construction sites for use. Such known batch process is very time consuming and the apparatus required to carry out each stage of the batch process is expensive, requiring large amounts of space and large and heavy duty conveying mechanisms, such as bucket conveyors, for conveying the materials between the various stages.

According to a first aspect, the present invention provides an apparatus for the continuous preparation of dry mortar comprising metering means for metering the constituent materials of the mortar, such as sand, cement and one or more additives, and supplying the metered materials to a conveying means, said conveying means conveying the metered materials to a mixing means, wherein the materials are blended to form a homogeneous dry mortar.

Preferably the metering means controls the respective flow rate of each of the constituent materials into the conveying means.

Preferably a control means is provided for controlling the metering, conveying and mixing means.

Preferably the metering means comprises a plurality independently controllable metering devices for metering the flow rate of respective components of the mortar passing into the conveying means. Preferably each metering device comprises a metering screw conveyor having a spiral feed screw, the speed of rotation of each feed screw being controlled by the control means to meter the respective components of the mortar into the conveying means in the required proportions.

Preferably said conveying means comprises a primary screw conveyor containing a rotatable feed screw drivable by a motor. Preferably said metering devices communicate with the primary screw conveyor at spaced locations along the length of the primary screw conveyor.

Preferably said metering devices are arranged to deliver material into the primary screw conveyor from above whereby such material is delivered into the primary screw conveyor under gravity.

In a prefened embodiment, the metering devices comprise a first metering screw conveyor for metering and conveying dry sand into the primary screw conveyor at a first location along the length of the primary screw conveyor, a second metering screw conveyor for metering and conveying cement into the primary screw conveyor at a second location along the length of the primary screw conveyor, downstream of said first location, and at least one further metering screw conveyor for metering and conveying one or more additives into the primary screw conveyor at one or more locations downstream of said second location.

In one embodiment, said first metering screw conveyor conveys dry sand from a dry sand hopper, said dry sand hopper receiving sand from a sand drying apparatus upstream of said dry sand hopper, conveying means, such as a screw conveyor, being provided for conveying dry sand from said sand drying apparatus to said dry sand hopper.

The dry sand hopper may be provided with one or more sand level sensors for controlling the operation of the metering, conveying and mixing means of the apparatus. A low sand level sensor may be provided for sensing when the dry sand hopper is becoming empty, whereby said control means may interrupt the operation of the metering, conveying and mixing means when the low sand level sensor indicates that the dry sand hopper is empty or nearly empty. A high sand level sensor may be provided for sensing when the dry sand hopper is becoming full, whereby said control means may initiate operation of the metering, conveying and mixing means when the high sand level sensor indicates that the dry sand hopper is full or nearly full. Such arrangement may be required where the sand drying apparatus cannot produce dry sand at a rate sufficient to meet the demand of the metering, conveying and mixing means.

Preferably the mixing means comprises a mixing chamber having an inlet end, adapted to receive dry material from an outlet end of said primary screw conveyor, and outlet end for delivering homogeneous mixed dry mortar, an agitator being rotatably mounted within said mixing chamber for mixing the dry mortar and for controlling the passage of material from said inlet to said outlet end of the mixing chamber. Preferably said outlet end of the mixing chamber is arranged below the inlet end of the mixing chamber such that material can pass through the mixing chamber under the action of gravity.

Preferably the feed screw of the primary screw conveyor is rotatable by means of a first motor, said agitator of said mixing chamber being rotatable by means of a second motor, said first and second motors being controllable independently. In one embodiment said first and second motors comprise electric motors. Said motors may be connected to the respective shafts of the screw conveyor and mixing means by suitable reduction gears. A further electric motor may be provided for driving each of said metering devices, such as metering screw conveyors, for controlling the metering of material into the primary screw conveyor.

Preferably said mixing chamber comprises a cylindrical chamber, said agitator being rotatably mounted within said chamber for rotation about a rotational axis coaxial with the axis of said cylindrical chamber. In a prefelTed embodiment, said mixing chamber is arranged in an inclined, vertica' or substantially vertical orientation with said in'et end at an upper end and said outlet end at a lower end, said agitator being arranged to control the passage of material through the mixing chamber. By arranging the mixing chamber vertically, any back torque on the mixing means is minimised because the material effectively passes through the mixing chamber under the action of gravity.

Preferably said agitator comprises a shaft mounted coaxially within said cylindrical mixing chamber and having a plurality of radially extending mixing blades. Preferably each of said blades has a leading edge and a trailing edge with respect to the direction of rotation of the shaft of the mixing means, each blade being mounted at an angle or pitch such that the leading edge of each blade is lower than the trailing edge thereof whereby the blades mix and convey material through the mixing chamber during rotation of the blades. Preferably each blade has a pitch of between 20° and 30°, more preferably between 20° and 25°.

Preferably said blades are provided in axially spaced groups, the blades in each group being arranged at equally circumferential spacing in a respective horizontal plane. Alternatively said blades may be arranged in a spiral configuration.

Preferably, each group of blades comprise at least two, more preferably at least three equally spaced blades. In one embodiment, each group of blades comprises four equally spaced blades. Preferably respective blades of each group are axially aligned with respective blades of each adjacent group.

In a prefened embodiment, elongate rods are joined to and extend between respective axially aligned blades of each group. Preferably each elongate rod extends substantially parallel to the rotational axis of said shaft of the mixing means. Preferably at least one or more of said elongate rods are joined to the blades at or adjacent an outer end of the blades.

In one embodiment, an elongate rod is joined to and extends between the trailing edges of respective axially aligned blades of each group, preferably at an outer end of each blade.

Preferably one or more further elongate rods are provided extending between leading edges of respective axially aligned blades, preferably joined to said blades at a location between inner and outer ends of each blade.

According to a second aspect, the present invention provides a method for the continuous preparation of dry mortar comprising metering the constituent materials of the mortar, such as sand, cement and one or more additives and conveying the metered materials through a mixing means wherein the metered materials are blended to form a homogeneous dry mortar at an outlet of the mixing means. Preferably the method comprises metering the flow rate of the constituent materials of the mortar supplied to the mixing means.

Preferably the method comprises conveying the constituent materials to the mixing means by means of a screw conveyor. Preferably the consitiuent materials are metered into the screw conveyor at respective spaced locations along the length of the screw conveyor.

Preferably the method comprises the further step of drying the sand prior to metering.

Preferably the material is conveyed through the mixing means in a downwards, preferably vertical, direction whereby the material passes through the mixing means under the action of gravity. Preferably the method includes the step of rotating a rotatable agitator within the mixing chamber to mix the materials while at the same time controlling the flow of material through the mixing chamber.

According to a further aspect of the present invention there is provided an apparatus for the continuous preparation of dry mortar comprising a primary feed screw having means for metering two or more dry materials, such as sand, cement and one or more additives, into the feed screw in predetermined quantities and/or at a predetermined flow rate, a mixing chamber being provided at a downstream end of said feed screw, said mixing chamber comprising a vertically or substantially vertically arranged tube having an rotatable agitator coaxially within said cylindrical mixing chamber for mixing said materials and for controlling the flow of said materials through said mixing chamber in a downwards direction towards a lower outlet thereof such that the material passes through the mixing chamber under gravity.

Preferably each of said two or more dry materials is fed into said primary feed screw at a predetermined flow rate, for example by means of a metering screw conveyor.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-Fig. 1 is a schematic view of an apparatus for preparing dry mortar according to an embodiment of the present invention; Fig. 2 is a side view of the agitator of the mixing means of Fig. 1; and Fig. 3 is an end view of the agitator of Fig. 2 As illustrated in the drawing, an apparatus for preparing dry mortar according to the present invention comprises a dry sand hopper 2 receiving dry sand from a sand drying apparatus 3 via an inclined screw conveyor 4. The dry sand hopper 2 is provided with upper and lower sand level sensors 5,6 for synchronising the operation of a mixing apparatus with the dry drying apparatus as will be described in more detail below.

The dry mortar mixing apparatus comprises a horizontally aligned primary screw conveyor 20 having a feed screw 21 for feeding material into a vertically arranged mixing chamber 30. A feed screw is rotatable by means of a first electric motor 22.

Sand is fed from the dry sand hopper 2 into the primary screw conveyor 20 at a first location adjacent an inlet end of the primary screw conveyor 20 by means of a first metering screw conveyor 7 driven by an electric motor 8 for controlling the flow rate of dry sand into the primary screw conveyor 20.

Cement is fed into the primary screw conveyor 20 at a second location, downstream of said first location, by means of a second metering screw conveyor 9 driven by a further electric motor (not shown) for controlling the flow rate of cement into the primary screw conveyor 20.

One or more additives, such as a plasticiser, is fed into the primary screw conveyor at a third location, downstream of said second location, by means of a third metering feed screw 10 driven by a further electric motor for controlling the flow rate of said one or more additives into the primary screw conveyor 20.

A control means controls the operation of the various electric motors to control the rotation of the first 7, second 9 and third 10 metering feed screws and the primary feed screw 20 to provide a continuous flow of dry mortar at an outlet end of the primary screw conveyor 20 having a mixture of sand, cement and additives in the desired proportions. The mixture is fed into a side region of a mixing chamber 30 wherein the mixture is mixed to form a homogenous dry mortar.

The mixing chamber 30 comprises a vertically oriented cylinder 32 having an upper inlet end 35, adapted to receive material from an outlet end of the primary screw conveyor 20, and an open lower outlet end 36. A rotatable agitator 40 is coaxially mounted within the tube 32 to be rotatable by an electric motor 38 connected to an upper end of the agitator 40 via a reduction gearbox.

Dry material is delivered from an outlet end of the screw conveyor 20 into a side region of the mixing chamber 30 adjacent the upper end 35. The rotatable agitator 40 within the mixing chamber 30 mixes the sand, cement and additives to provide a homogeneous dry mortar and controls the passage of the mortar through the mixing chamber 30 into a hopper 50, from where the mortar is conveyed by a further screw conveyor 52 to the lower end of a bucket elevator 54 for transfer to a storage silo.

As shown in Figs. 2 and 3, the agitator 40 comprises a shaft 41 mounted coaxially within said cylindrical mixing chamber 30 and having a plurality of radially extending mixing blades 42. Each of said blades 42 has a leading edge 43 and a trailing edge 44 with respect to the direction of rotation of the shaft 41, each blade 42 being mounted at an angle or pitch such that the leading edge 43 of each blade 42 is lower than the trailing edge44 thereof whereby the blades 42 convey material through the mixing chamber 40 during rotation of the blades 42 and act to retain the material within the mixing chamber 40 due to the width of the blades 42. In a preferred embodiment each blade is arranged at a pitch angle of 23° to the horizontal, although other angles may be required to suit different materials.

As shown in Figs. 3 and 4, the blades 42 are arranged in axially spaced groups, each group comprising four equally spaced blades. In the embodiment illustrated, eight groups of blades are provided, each group comprising four equally spaced blades. However, more or less groups may be provided, each group having more or less blades, depending upon the size of the mixing chamber and the consistency of the mortar to be produced. Respective blades of each group are axially aligned with respective blades of each adjacent group.

To provide enhanced mixing and control of the movement of the mortar through the mixing chamber, elongate rods 45 are joined to and extend between respective axially aligned blades 42 of each group, each elongate rod 45 preferably extends substantially parallel to the rotational axis of said shaft 41 of the agitator. Elongate rods 45 are joined to and extend between the trailing edges 44 of the axially aligned blades 42, preferably joined to the blades 42 adjacent an outer edge thereof. Preferably one or more further elongate rods 46 are provided extending between leading edges 43 of respective axially aligned blades 42, preferably joined to said blades 42 at a location between inner and outer ends of each blade 42.

In use, dry sand is conveyed from the sand drying apparatus 3 into the dry sand hopper 2 via the screw conveyor 4. Once the upper sand level indicator 5 indicates that the dry sand hopper 2 is full, the control means will initiate operation of the electric motors 22,7,3 8 to begin metering of the sand, cement and additives into the primary screw conveyor 20 and from the primary screw conveyor 20 into the mixing chamber 30, wherein the material will be mixed and conveyed into the hopper 50 by rotation of the agitator 40. If the supply of dry sand from the sand dryer is insufficient to match the demand of the first metering screw conveyor 7, the level of sand in the dry sand hopper 2 will fall until the low sand level sensor 6 indicates that the dry sand hopper is almost empty, whereupon the control means will shut off the motors to stop the screw conveyors 7,9,10 and 20 and the agitator 30 until the dry sand hopper is replenished, as indicated by the upper sand level indicator 5.

The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention.

Claims

Claims 1. An apparatus for the continuous preparation of dry mortar comprising metering means for metering the constituent materials of the mortar, such as sand, cement and one or more additives, and supplying the metered materials to a conveying means, said conveying means conveying the metered materials to a mixing means, wherein the materials are blended to form a homogeneous dry mortar.
2. An apparatus as claimed in claim 1, wherein the metering means controls the respective flow rate of each of the constituent materials into the conveying means.
3. An apparatus as claimed in any preceding claim, wherein a control means is provided for controlling the metering, conveying and mixing means.
4. An apparatus as claimed in claim 3, wherein the metering means comprises a O plurality of independently controllable metering devices for metering the flow rate of LI) respective components of the mortar passing into the conveying means.
5. An apparatus as claimed in claim 4, wherein each metering device comprises a metering screw conveyor having a spiral feed screw, the speed of rotation of each feed screw being controlled by the control means to meter the respective components of the mortar into the conveying means in the required proportions.
6. An apparatus as claimed in claim 4 or claim 5, wherein said conveying means comprises a primary screw conveyor containing a rotatable feed screw drivable by a motor.
7. An apparatus as claimed in claim 6, wherein said metering devices communicate with the primary screw conveyor at spaced locations along the length of the primary screw conveyor.
8. An apparatus as claimed in claim 7, wherein said metering devices are arranged to deliver material into the primary screw conveyor from above whereby such material is delivered into the primary screw conveyor under gravity.
9. An apparatus as claimed in claim 8, wherein the metering devices comprise a first metering screw conveyor for metering and conveying dry sand into the primary screw conveyor at a first location along the length of the primary screw conveyor, a second metering screw conveyor for metering and conveying cement into the primary screw conveyor at a second location along the length of the primary screw conveyor, downstream of said first location, and at least one further metering screw conveyor for metering and conveying one or more additives into the primary screw conveyor at one or more locations downstream of said second location.
10. An apparatus as claimed in claimed 9, wherein said first metering screw conveyor conveys dry sand from a dry sand hopper, said dry sand hopper receiving sand from a sand drying apparatus upstream of said dry sand hopper, conveying means, such as a screw conveyor, being provided for conveying dry sand from said sand drying apparatus to said dry sand hopper.

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11. An apparatus as claimed in claim 10, wherein the dry sand hopper is provided with L.() one or more sand level sensors for controlling the operation of the metering, conveying and Q mixing means of the apparatus. (\J
12. An apparatus as claimed in claim 11, wherein a low sand level sensor is provided for sensing when the dry sand hopper is becoming empty, whereby said control means is adapted to interrupt the operation of the metering, conveying and mixing means when the low sand level sensor indicates that the dry sand hopper is empty or nearly empty.
13. An apparatus as claimed in claim 11 or claim 12, wherein a high sand level sensor is provided for sensing when the dry sand hopper is becoming full, whereby said control means is adapted to initiate operation of the metering, conveying and mixing means when the high sand level sensor indicates that the dry sand hopper is full or nearly full.
14. An apparatus as claimed in any of claims 6 to 13, wherein the mixing means comprises a mixing chamber having an inlet end, adapted to receive dry material from an outlet end of said primary screw conveyor, and outlet end for delivering homogeneous mixed dry mortar, an agitator being rotatably mounted within said mixing chamber for mixing the dry mortar and for controlling the passage of material from said inlet to said outlet end of the mixing chamber.
15. An apparatus as claimed in claim 14, wherein said outlet end of the mixing chamber is arranged below the inlet end of the mixing chamber such that material can pass through the mixing chamber under the action of gravity.
16. An apparatus as claimed in claim 15, wherein the feed screw of the primary screw conveyor is rotatable by means of a first motor, said agitator of said mixing chamber being rotatable by means of a second motor, said first and second motors being controllable independently.
17. An apparatus as claimed in claim 16, wherein said first and second motors comprise electric motors.

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18. An apparatus as claimed in claim 17, wheein said motors may be connected to the Lt) respective shafts of the screw conveyor and mixing means by suitable reduction gears.

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19. An apparatus as claimed in claim 17, wherein a further electric motor is provided for driving each of said metering devices, such as metering screw conveyors, for controlling the metering of material into the primary screw conveyor.
20. An apparatus as claimed in any oc laims 14 to 19, wherein said mixing chamber comprises a cylindrical chamber, said agitator being rotatably mounted within said chamber for rotation about a rotational axis coaxial with the axis of said cylindrical chamber.
21. An apparatus as claimed in claim 20, wherein said mixing chamber is arranged in an inclined, vertical or substantially vertical orientation with said inlet end at an upper end and said outlet end at a lower end, said agitator being arranged to control the passage of material through the mixing chamber.
22. An apparatus as claimed in claim 20 or claim 21, wherein said agitator comprises a shaft mounted coaxially within said cylindrical mixing chamber and having a plurality of radially extending mixing blades.
23. An apparatus as claimed in claim 22, wherein each of said blades has a leading edge and a trailing edge with respect to the direction of rotation of the shaft of the mixing means, each blade being mounted at an angle or pitch such that the leading edge of each blade is lower than the trailing edge thereof whereby the blades mix and convey material through the mixing chamber during rotation of the blades.
24. An apparatus as claimed in claim 23, wherein each blade has a pitch of between 20° and 30°, more preferably between 20° and 25°.
25. An apparatus as claimed in any of claims 22 to 24, wherein said blades are provided in axially spaced groups, the blades in each group being arranged at equally circumferential spacing in a respective horizontal plane.
26. An apparatus as claimed in any of claims 22 to 24, wherein said blades are arranged C in a spiral configuration.LU0
27. An apparatus as claimed in claim 25, wherein each group of blades comprise at least sJ two, more preferably at least three equally spaced blades.
28. An apparatus as claimed in dim 25, wherein each group of blades comprises four equally spaced blades.
29. An apparatus as claimed in claim 27 or claim 28, wherein respective blades of each group are axially aligned with respective blades of each adjacent group.
30. An apparatus as claimed in claim 29, wherein elongate rods are joined to and extend between respective axially aligned blades of each group.
31. An apparatus as claimed in claim 30, wherein each elongate rod extends substantially parallel to the rotational axis of said shaft of the mixing means.
32. An apparatus as claimed in claim 30 or 31, wherein at least one or more of said elongate rods are joined to the blades at or adjacent an outer end of the blades.
33. An apparatus as claimed in any of claims 30 to 32, wherein an elongate rod is joined to and extends between the trailing edges of respective axially aligned blades of each group.
34. An apparatus as claimed in claim 33, wherein one or more further elongate rods are provided extending between leading edges of respective axially aligned blades, preferably joined to said blades at a location between inner and outer ends of each blade.
35. A method for the continuous preparation of dry mortar comprising metering the constituent materials of the mortar, such as sand, cement and one or more additives and conveying the metered materials through a mixing means wherein the metered materials are blended to form a homogeneous dry mortar at an outlet of the mixing means.
36. A method as claimed in claim 35, further comprising the step of metering the flow rate of the constituent materials of the mortar supplied to the mixing means.If)
37. A method as claimed in claim 35 or claim 36, comprising conveying the constituent 0 materials to the mixing means by means of a screw conveyor. c'J38. A method as claimed in claim 37, wherein the consitiuent materials are metered into the screw conveyor at respective spaced locations along the length of the screw conveyor.39. A method as claimed in any of claims 35 to 38, comprising the further step of drying the sand prior to metering.40. A method as claimed in any of claims 35 to 39, wherein the material is conveyed through the mixing means in a downwards, preferably vertical, direction whereby the material passes through the mixing means under the action of gravity.41. A method as claimed in any of claims 35 to 40, comprising the step of rotating a rotatable agitator within a mixing chamber of the mixing means to mix the materials while at the same time controlling the flow of material through the mixing chamber.42. An apparatus for the continuous preparation of dry mortar comprising a primary feed screw having means for metering two or more dry materials, such as sand, cement and one or more additives, into the feed screw in predetermined quantities and/or at a predetermined flow rate, a mixing chamber being provided at a downstream end of said feed screw, said mixing chamber comprising a vertically or substantially vertically arranged tube having an rotatable agitator coaxially within said cylindrical mixing chamber for mixing said materials and for controlling the flow of said materials through said mixing chamber in a downwards direction towards a lower outlet thereof such that the material passes through the mixing chamber under gravity.43. An apparatus as claimed in claim 42, wherein each of said two or more dry materials is fed into said primary feed screw at a predetermined flow rate, for example by means of a metering screw conveyor. 0)15 L() (\J