GB2263072A

GB2263072A - Concrete mixers

Info

Publication number: GB2263072A
Application number: GB9300390A
Authority: GB
Inventors: Anthony Michael Humpish
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-01-10
Filing date: 1993-01-11
Publication date: 1993-07-14
Anticipated expiration: 2013-01-11
Also published as: GB2263072B; GB9300390D0

Abstract

A concrete mixer comprises a drum (20) having a helical internal blade formation (7 and 8) adapted to expel the contents of the drum when the drum is rotated in an appropriate direction. In order to avoid sticky mix material being carried up with a blade portion and then falling off the blade portion behind the blade which carried it up an obstructing member (21) is provided towards the mouth of the drum. The obstructing member may take the form of a cylindrical tube (21) extending between at least two adjacent blade portions. The obstructing member 21 prevents mix material from falling behind a blade which carries it upwards. The obstructing member may include a spiral slot (31 Fig. 4, not shown) or a triangular aperture (Figs 5, 6, not shown) <IMAGE>

Description

CONCRETE MIXERS AND THE LIKE This invention relates to concrete mixers and the like, and to a method of mixing.

The drum of an inclined axis concrete mixing vessel is normally made of a number of cylindrical and/or concial sections joined to one another so that they share the same axis. One end of the drum is closed with a permanently attached disc, and the other end of the drum is permanently open. The drum conventionally has a number of blades which are attached to the inside surface of the drum so as to form one or more helices which run the length of the drum.

In operation the axis of the drum is inclined, for example at 13 degrees to the horizontal, and the drum is rotated so that the helix propels the contents of the drum towards the closed end of the drum. It is this action which agitates and/or mixes the contents of the drum. The contents of the drum are introduced into it through the open end, the mouth, by means of a loading hopper. The contents of the drum are discharged by reversing the direction of the drum and the helix thereby driving'the contents upwards, up the incline, towards and out of the mouth of the drum.

This way of mixing ingredients together is widely used, especially in the concrete mixing industry, and is regarded as a satisfactory method of production of many mixtures. However, there can be problems when dealing with certain combinations of ingredients. For example, mixtures of concrete which have a low water content (so called "dry mix" concrete, and mixtures having a sticky or viscous nature). These mixtures can be produced satisfactorily, but in the conventional drum arrangement referred to above there is sometimes great difficulty in discharging sticky mixtures at an acceptable rate. For example, it might take around five minutes or so to discharge a wet-mix concrete mixture from a drum, but if the mixture is a dry-mix concrete it can take up to thirty minutes or so.

It is an aim of the present invention to alleviate the problem discussed above.

According to a first aspect of the invention I provide a mixer drum for concrete or the like having a curved blade or blades, for example helical blades, which in use urge mix material out of the drum when the drum is rotated in a first angular direction about its axis, the drum having a blocking member extending between at least two adjacent axially spaced blade portions so as to prevent, or substantially hinder, mix material from passing, in a radial direction, between said blade portions in the region of the blocking member.

Thus mix material does not fall back on itself into a region of the mixer drum from which it has just come.

Preferably the blocking member is mounted at or towards the inner radial edge of the blades.

Preferably the blocking member has a cylindrical configuration. Preferably the axis of the blocking member is coaxial with the axis of rotation of the drum.

Preferably the blocking member comprises only part of a cylinder. Preferably the blocking member has a circular cross-section when sectioned on a first diametral plane, or a cross-section which is not a complete circle. Preferably the blocking member has a circular cross-section when sectioned along a first diametral plane and a cross-section which is not a complete circular cross-section when sectioned along a second diametral plane.

In one preferred arrangement the blocking member extends between two adjacent blades only, and does not extend to a third. Preferably said two blades are the two nearest the mounth of the drum.

The blocking member may have one or more apertures provided in it. These assist in preventing blockages.

The blocking member may have a relatively large hole in it.

The blocking member preferably has a charging aperture adapted to receive a charge to be mixed and allow the charge passage to the interior of the drum.

The drum preferably discharges its contents via a different route.

According to a second aspect of the invention I provide a concrete mixer vehicle having a mixer drum in accordance with the first aspect of the invention.

According to a third aspect of the invention I provide a method of preventing or hindering mix material in a concete mixer drum, or the like, during expulsion of the mix material from the drum from falling back over mixing blades into a region of the drum from which the material has previously been moved, the method comprising physically obstructing the path of falling of mix material by having an obstructing, or blocking, member which prevents or hinders mix material from moving radially inwards further than the obstructing member.

Preferably the obstructing member is provided at or near the radially inner edge of the blades.

We also claim protection for concrete mixed using our mixer or method, and articles made from such concrete.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings of which: Figure 1 schemetically shows the prior art; Figure 2 schemetically shows a drum in accordance with the invention; Figure 3 shows features of detail of the drum of Figure 2; Figure 4 shows a second drum; Figure 5 sHows part of a third drum; Figure 6 is a fragmentary perspective view from the rear of the drum of Figure 5.

Figure 1 shows a conventional mixing drum such as may be mounted on a vehicle (the vehicle is not shown) inclined at an angle to the horizontal. The drum 1 comprises a cylindrical shell portion 2 having conical shell portions 3 and 4 welded at each end. A closure plate 5 closes the lower end of the drum. The upper end of the drum has an open aperture 6. A helical blade 7 is attached to the interior wall of the drum and extends radially inwards. A second helical blade 8, similar to the first helical blade 7, is provided at half a pitch spaced away from the first helical blade 7. The helical blades carry a flange 9a and 9b respectively, at their radially inner ends.

In the prior art mix material enters and leaves the drum via the aperture 6. As mix material is driven upwards towards the aperture 6 so as to discharge it there can be problems if the mixture is sticky. If the mix material sticks to the blades 7 and 8 it can be carried upwards with them and can then fall off the blade after it has reached a height. Mix material which falls off the blade, after having been carried upwards, can fall down behind the blade so as to be between a first and third blade portion, instead of being between the first and a second blade portion, as it was previously. The phenomenon is illustrated in Figure 1.

A sticky glob of mix material 10 clings to a first blade portion 7 and is originally between the first blade portion 7 and the second blade portion 8. As the drum rotates in a clockwise sense (so that the bottom of the drum as seen in Figure 1 moves towards the viewer and the' top of the drum moves away from the viewer) the blade portion where the glob is moves (with the drum) axially backwards and when it reaches a point, say, point 11 at about 90 degrees away from the view shown in Figure 1 it falls off the blade 7, falling vertically downwards. It falls behind the blade portion to which it previously clung, between the first blade portion and the third blade portion of the blade 8 (illustrated as dotted fall-line 12). Thus instead of being moved forwards the sticky glob 10 is actually further back than when it started.Of course, mix material which does not get carried up with the blades is driven forwards. A combined effect of some of the material being driven forward and some of the material being carried up with the blades and falling backwards can result in the mixer simply churning the mix material when it is supposed to be discharging it.

There can be a continual back flow of material substantially balancing the forward flow so that the net result is only a small forward flow, or even hardly any forward flow at all. At the moment drivers of concrete mixer vehicles resort to hitting the sides of the drum with a sledgehammer to encourage the globs of material to fall off the blades quicker, so that they are not carried backwards any further than can be helped.

It will be appreciated that the above discussion of the mechanism of the backs low process is the result of my considerations and contributes at least in some small part towards the invention.

Figure 2 shows a modified drum 20 having a blocking, or obstructing, member 21. Since the structure of the drum 20 is very much the same as that of the drum 1 the same reference numbers have been given to the same components.

The blocking member is a cylindrical tube, or open ended cylinder, which extends axially inwards from the open aperture 6, beyond a first blade portion 22 of blade 8, beyond a second blade portion 23 of blade 7, and up to a third blade portion 24 (which is part of the blade 8). The axially inner end of the blocking member 21 is at the start of a fourth bade portion 25 (of the blade 7).

One way of looking at the blocking member 21 is that it might be considered to be an extension of the flanges 9 of the first, second and third blade portions so that their flanges join together. Alternatively, their structure could be considered to be the omission of the flanges 9a from the rearmost blade portions and their replacement by a cylindrical tube.

Mix material is loaded into the drum via the centre of the blocking member 21. Mix material is discharged from the drum between the wall of the conical shell 4 and the outside surface of the blocking member 21, as shown by arrow 26. The discharge material is trapped between the blade portions 22 to 24, the outside surface of the blocking member 21, and the inside surface of the conical shell 4.

When a glob of sticky mix material is carried upon a blade portion, say blade portion 23, and it reaches a height it cannot now fall back behind the blade portion which carries it up because the blocking member 21 prevents it from doing so. It is either carried round still stuck to the blade portion, or it can slide back down the blade portion towards the region from which it was carried - but it cannot fall back behind the blade portion. This clearly reduces the backflow of mix material.

I have found that in one prototype the present invention increases the speed of delivery of sticky mix material from previously being around 30 minutes to around 4 or 5 minutes. This is merely mentioned as an example, and is in no way a promise of performance since the delivery rate depends upon the size of the drum, the nature of the material being mixed, the configuration of the blades, the tilt angle of the drum, the angle of the ground upon which the vehicle is standing, and several other factors.

Figure 4 illustrates another blocking member, referenced 30, which also basically comprises an open ended tube mounted at the open mouth of the drum and sharing the axis about which the drum rotates and mounted at the radially inner edges of the blades.

However, the blocking member 30 of Figure 4 has grooves or slots 31 extending through its walls. The slots 31 comprise a spiral slot.

The slots 31 comprise blockage release means and prevent the space between adjacent blade portions from being completely blocked by mix material, The slots give the mix material somewhere to go, even if it is falling into the centre of the blocking member and then moving axially rearwards of the drum.

Figures 5 and 6 show another drum 40 having another obstructing member 41.

The first blade portion 22 in this embodiment does not extend right to the edge of the drum (and indeed in many of the others may not extend right to the edge of the drum). The obstructing member 41 effectively extends from the inner radial edge of the last two blade portions 22 and 23 to the end of the drum. It has a full circumference from the last blade portion 22 to the end of the drum, but extends only part of the way around (possibly half way around) at the axial region of the drum between the blade portion 22 and the blade portion 23. The aperture between the flange 9a on the second blade portion 23 and the continuous portion, referenced 42, of the obstructing member has a generally triangular shape if it is unrolled and flattened out. The apex of the triangular aperture is about 90 degrees out of the page, towards the viewer, when seen in Figure 5.

I have found that even having an obstructing member between the last two blade portions has a significant effect upon the rate of delivery of the mix.

It will be appreciated that in any of the embodiments described the obstructing member may be of any axial length, but is not normally more than one third of the length of the drum. The diameter of the obstructing member is decided in accordance with the combined geometry of the helical blades and the loading mechanism (not shown).

The obstructing member may, of course, have a form other than cylindrical, for example it could be a conical tube. It may be provided with holes or slots, or with a spiral slot as in Figure 4. The obstructing member is preferably coaxial with the axis of rotation of the drum, but not necessarily so.

Claims

1. A mixer drum for concrete or the like having a blade or blades which in use urge mix material out of the drum when the drum is rotated in a first angular direction about its axis, the drum having a blocking member extending between at least two adjacent axially spaced blade portions so as to prevent, or substantially hinder, mix material from passing, in a radial direction, between said blade portions in the region of the blocking member.

2. A mixer drum according to claim 1 in which the blocking member is mounted at or towards the inner radial edge of the blades.

3. A mixer drum according to claim 1 or claim 2 in which the blocking member has a cylindrical configuration.

4. A mixer drum according to any preceding claim in which the blocking member has a portion which comprises part only of a cylinder.

5. A mixer dr-tm according to any preceding claim in which the blocking member has a circular cross-section when sectioned on a first diametral plane.

6. A mixer drum according to any preceding claim in which the blocking member has a circular cross-section when sectioned along a first diametral plane and a cross-section which is not a complete circular cross-section when sectioned along a second diametral plane.

7. A mixer drum according to any preceding claim in which the blocking member extends between two adjacent blades only, and does not extend to a third.

8. A mixer drum according to any preceding claim in which the blocking member has one or more apertures provided in it.

9. A mixer drum substantially as described herein with reference to Figures 2 and 3; or with reference to Figure 4; or with reference to Figure 5 and 6 of the accompanying drawings.

10. A concrete mixer vehicle having a mixer drum in accordance with any one of claims 1 to 9.

11. A method of preventing or hindering mix material in a concrete mixer drum, or the like, during expulsion of the mix material from the drum from falling back over mixing blades into a region of the drum from which the material has previously been moved, the method comprising physically obstructing the path of falling of mix material by having an obstructing, or blocking, member which prevents or hinders mix material from moving radially' inwards further than the obstructing member.

12. A method according to claim 11 in which the obstructing member is provided at or near the radially inner edge of the blades.

13. A method of preventing or hindering mix material in a concrete mixer drum, or the like, during expulsion of the mix material from the drum from falling back over mixing blades substantially as described herein.