AU678656B2 - Centre discharge concrete mixer - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPE C IFI CATION FOR A STANDARD PATENT

ORIGINAL

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Name of Applicant: Actual Inventor: Address for Service: Invention Title: MAX GEORGE HOOD Max George HOOD SHELSTON WATERS Margaret Street SYDNEY NSW 2000 "CENTRE DISCHARGE CONCRETE MIXER" Details of Associated Provisional Application No: PM3504 dated 24th January, 1994 The following statement is a full description of this invention, including the best method of performing it known to me:i -I -2- The present invention relates to concrete mixers.

Two types of concrete mixer are currently in widespread use. The first type, generally referred to as a truck or "transit" mixer, typically comprises a drum mounted to the chassis of a suitable prime mover.

The drum is supported for rotation about an inclined axis, and incorporates internal helical blades adapted to mix the concrete upon rotation of the drum. The second type of mixer is known as a "central" mixer.

This is essentially a large heavy duty mixer adapted to mix concrete in a stationary position. The present invention relates more specifically to central mixers.

In the past, dry batching into truck mounted g mixers has normally been done due to the generally greater mixing efficiency of this type of mixer.

However, central mixers have nevertheless commonly been used on projects such as concrete freeways or airports, where the plant can be located on the construction site. In such situations, non-agitating transporters 20 such as open tipping trucks may be used since the concrete is normally carried no more than a few kilometres before being deposited in front of large spreaders. The spreaders also perform a re-mixing function before the concrete is finally levelled and finished.

Central mixers cannot necessarily mix concrete more thoroughly than truck or transit mixers. However, they can mix a comparable volume in between one third -3and one half of the time, and as such are considerably more efficient with respect to production output. It is also easier with central mixers to monitor slump, consistency, uniformity, and other relevant parameters of the concrete at a central point on site, rather than relying on individual truck drivers to monitor and control uniformity of the mixed load. This provides obvious additional advantages in terms of quality and consistency.

.ic Recently, lightweight transit mixers and trucks have been introduced and these are able to transport between 0.5 m 3 and 1.0 m 3 more concrete than conventional heavyweight mixing trucks, whilst remaining within the axle load limitations stipulated by the 15 relevant statutory regulations. However, due to the *o thinner lightweight steel used in the mixing drums these lightweight mixers are prone to wear faster in the drum and blade areas when mixing dry materials.

Consequently, in order to minimise such wear, central 20 mixers are now also being used increasingly to pre-mix concrete in "readymix" applications.

For these readymix applications, the central mixer is normally used to pre-mix the concrete and then to discharge the mixed concrete into lightweight Zfuek mixers for delivery to site. As such, the truck mixers under these conditions are not required to mix the dry ingredients. They merely serve to agitate the pre-mixed concrete mass on route at about 1 to 2 rpm, thereby 4 preventing undesirable segregation of the mix which normally occurs in tipping trucks and other forms of non-agitating transporter over long distances. Of course, the truck mixers in this context also provide a convenient means for discharging the concrete on location by reverse rotation of the drum in the usual manner. Most significantly however, the wear to which the lightweight truck mixers would otherwise be subject is substantially reduced when used in conjunction with central mixers.

For these reasons, the demand for central mixers and central discharge mixers in particular is expected to increase dramatically as the number of lightweight ses: truck mixers in service increases, in order to take advantage of the larger loads that can be transported.

Numerous types of central mixers are known, 9. 9 including tilting mixers, pan or turbine mixers, twin S"paddle mixers and split drum mixers. The split drum mixer is one of the most production efficient types, and 20 it is such mixers with which the present invention is more particularly concerned due to the preference for this type of mixer in readymix concrete applications.

Such applications include large dams and civil works where aggregates of up to 200 mm diameter are often used.

Split drum mixers generally comprise a generally spherical drum formed from two substantially hemispherical half shells supported for conjoined rotation on a common shaft about a horizontal axis. One 5 half shell is attached to the end of the shaft by an internal spoked wheel or spider. The other half shell is able to slide axially on the shaft. Discharge is achieved by retracting the sliding half shell with the drum rotating. This opens an annular vertically orientated gap between the half shells, thereby permitting rapid central discharge of the contents of the drum under gravity without significant segregation, even with high discharge heights.

Whilst this design does provide efficient mixing and high discharge rates, because of the complexity of the internal sealing arrangement of the shaft and the discharge mechanism, the capital cost of the equipment is excessive and the mixers are prone to reliability problems. Furthermore, the internal seals in particular, due to being immersed in concrete, are subject to frequent failure and rapid abrasive wear.

Moreover, their relative inaccessibility complicates the repair and replacement of seals and bearings on the 20 internal shaft. These factors combine to produce *oop S"excessively high maintenance costs in addition to the high initial cost of the capital equipment.

Additionally, the large internal spoked wheel or spider supporting the fixed shell interferes with the flow of concrete within the drum, requires considerable maintenance, and also necessitates the use of an excessively complex configuration of internal mixing blades. This aspect of the design also adversely -6affects capital cost, maintenance cost, reliability and mixing efficiency.

It is an object of the present invention to provide an improved concrete mixer which overcomes or substantially ameliorates at least some of these disadvantages of the prior art.

Accordingly, the invention provides a concrete mixer comprising a mixing drum supported for rotation about a substantially horizontal axis, a plurality of discharge ports spaced around the periphery of the drum, and closure means adapted for movement between a closed position covering the ports to substantially seal the drum and an open position wherein the ports are exposed, said ports being disposed to permit discharge of the contents of the drum under gravity with the closure S. means in the open position irrespective of the rotational position of the drum.

In one preferred embodiment, the closure means takes the form of an axially slidable closure sleeve :i 20 surrounding the drum and disposed to cover the ports in the closed position.

Preferably, the total area of the discharge ports corresponds approximately to the total discharge area of a comparable split drum mixer in the open or discharge configuration.

Preferably also, the drum is defined by a substantially cylindrical central region with tapered ends. The discharge ports preferably take the form of a I 7 series of rectangular apertures spaced uniformly around the periphery of the drum, approximately midway between its ends. In this embodiment, the closure sleeve preferably comprises a substantially cylindrical sliding door coaxial with the drum. Preferably, the door is internally machined to ensure accurate concentricity with the drum.

A removable guide chute is preferably supported immediately below the drum in the vicinity of the discharge ports to channel the discharging concrete and permit direct charging of truck mixers or tipping trucks.

The sliding closure sleeve or door is preferably connected by means of peripheral support arms to an 15 external bearing on a main support shaft of the drum. A pair of hydraulic actuators are preferably operable on the respective support arms via a suitable thrust

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S•bearing to permit accurate control over the axial position of the sliding sleeve relative to the drum and 20 hence the discharge flow rate. This arrangement also ensures positive closure.

Annular seals and an assembly of rollers or slides are preferably disposed intermediate the door and the drum to retain relative concentricity and to seal the joints around Lhe discharge ports In another preferred embodiment, the closure means is in the form of a plurality of discrete gates associated with the respective ports. Preferably, the 8 gates are supported for axial sliding movement between the open and closed positions. However, pivotal movement of the gates is also contemplated.

The gates are preferably rectangular and are provided with individual hydraulic actuators.

Preferably also, an hydraulic control circuit is configured to move the actuators and hence the sliding gates in unison.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:- Figure 1 is a side elevation showing a concrete mixer according to a first embodiment of the invention, which utilizes an axially sliding sleeve to open and close the discharge ports; *Figure 2 is an end elevation showing the mixer of Figure 1; o Figure 3 is an enlarged diagrammatic cross-sectional view showing a first preferred 20 configuration of door seals for the embodiment of Figure 1; Figure 4 is a cross-sectional view similar to Figure 3 but showing an alternative arrangement of door seals and hydraulic actuators; Figure 5 is a cross-sectional view similar to Figures 3 and 4 showing another alternative form of actuator for the sliding door; Figure 6 is a diagrammatic internal projected

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9 view showing the relationship between the internal mixing blades and the peripheral discharge ports; Figure 7 is a cross sectional view showing the internal mixing blades on one side extending partially over the discharge ports with the sliding door in a corresponding half open position in a slow discharge mode; Figure 8 is a side elevation showing a concrete mixer according to a second embodiment of the invention which utilizes a plurality of discrete axially sliding gates to individually open and close the respective discharge ports; Figure 9 is an end elevation of the mixer of figure 8; Figure 10 is a partially sectioned side elevation of the drive shaft used in conjunction with the mixer of figure 8; Figure 11 is an enlarged cross-sectional side view showing the sealing arrangement for one of the 20 gates of the mixer of Figure 8; and .o Figure 12 is a partial cross-sectional end view of the gate seal shown in Figure 11.

Referring firstly to Figures 1 and 2, wherein corresponding features are denoted by corresponding reference numerals, the first embodiment of the invention provides a concrete mixer 1 of the "central" type. The mixer comprises a drum 2 defined by a generally cylindrical central section 3 and tapered end 10 portions 4 and 5. The drum is supported for rotation about a horizontal longitudinal axis 8 and is connected to a suitable drive motor (not shown) via reduction gearbox 9 and main drive shaft 3.0. The end of tne drum remote from the drive shaft is suppor' ide rollers 11 mounted to a structural frame Ai input chute 13.3 feeds material axially into the end 5 of the drum remote from the drive shaft.

The drum incorporates a series of internal mixing blades 14 (see Figure 6) which are disposed to direct material within the drum towards a series of discharge ports in the form of substantially rectangular apertures 15 spaced uniformly around the periphery of the drum, approximately midway between its ends. A cylindrical closure sleeve 20 is disposed for axial sliding movement around the drum to form a sliding door. The sleeve and drum are substantially coaxial.

,eee S"The cylindrical sleeve is connected to an external bearing 21 mounted on the main drive shaft 20 via support arms 22 which extend around the corresponding end 4 of the drum. A series of annular seals, rollers or slides are disposed intermediate the sleeve and the drum to retain relative concentricity and to seal the joints around the discharge ports, as described in more detail below. The cylindrical sleeve is supported for axial displacement between a closed position wherein the sleeve covers the discharge ports to substantially seal the drum and an open position 11 wherein the ports are exposed.

The ports extend around the entire periphery of the drum to permit discharge of the contents of the drum under gravity with the sleeve in the open position, irrespective of the rotational position of the drum. As best seen in Figure 6, the internal mixing blades 14 are disposed in a criss-cross configuration to direct cement toward the discharge ports and thereby facilitate rapid discharge upon rotation of the drum. The blades also generate a criss-cross mixing action which provides fast mixing and excellent uniformity of the concrete load.

a The blades on one side (in this case the top blades when viewing Figure 6 and the left hand blades in Figure 7) extend half way across the apertures to provide a slow discharge mode with the sliding door 20 half open if required. This is shown in more detail in Figure 7.

The axial displacement of the sleeve is effected S"by a pair of hydraulic actuators (not shown) which operate on the support arms 22 and thrust bearing 21 via 20 suitable linkages, bushes and bearings. The S°corresponding displacement of the support arms is accommodated by the clearance space A provided on the drive shaft between the adjacent end 4 of the drum and the associated shaft bearing 25. A removable discharge chute 26 collects and channels material discharged through the ports.

Figure 3 is an enlarged cross-sectional detail showing a first embodiment of a sealing mechanism for -I 12 the sliding sleeve or door. In this embodiment, a first annular sealing ring 30 is mounted to a corresponding annular flange 31 formed on the drum by means of a peripheral array of bolts 32. The remote edge 35 of the sealing ring 30 sealingly and slidingly abuts the adjacent inner surface of the cylindrical sliding door.

The opposite edge of the sleeve or door incorporates a second sealing ring 36 adapted for abutting engagement with a corresponding annular flange 37 formed from circumferential plates 38 welded to the periphery of the drum. In the closed position, as shown in the drawing, the sleeve in conjunction with the first and second sealing rings and flanges 31 and 37 effectively seals the discharge ports 15. The sleeve 20 is thus moved axially to the right, as shown y the arrow, to open the ports. Sealing is also assisted by the weight of the concrete itself exerting pressure on the sealing rings.

The seal 30 is preferably formed from a polymer sold in Australia under the trade name "ERAPOL E95A", by Era 20 Polymers Pty. Limited. ERAPOL E95A is a liquid isocyanate terminated pre-polymer based on PTMEG ,)olyether polyol. Such polymers have been found to exhibit excellent abrasion, impact and chemical resistance, in combination with a high load bearing capacity.

Figure 4 shows an alternative sealing arrangement wherein again, the first sealing ring 30 slidingly abuts the corresponding inner surface of the sleeve. In this 13 case, however, the second sealing ring 36 is mounted to the corresponding end of the sleeve by means of circumferential retaining plate 41. In this configuration, the second sealing ring directly abuts the adjacent annular flange 42 which extends radially from the outer surface of the drum. In this case, an hydraulic actuator 45 is shown operating directly on the sleeve 20 to move the sleeve axially to the right, as shown by the arrow, to open the ports and to the left to close them. It will be appreciated that various other .P configurations of seals, flanges, spacing elements and actuators may also be used.

Figure 5 shows another sealing and actuating arrangement wherein an arnular ring 50 extends radially outwardly from the sliding sleeve or door 20. The ring 50 is engaged by a pair of spaced apart rollers 52, the axes of which are substantially perpendicular to the axis of the drum. One such set of rollers is preferably disposed on each side of the drum and connected to 20 respective hydraulic actuators by suitable intermediate S"linkage mechanisms. In this way, it will be appreciated that simultaneous horizontal displacement of the roller assemblies effects a corresponding axial movement of the sliding cylindrical door or sleeve between the open and closed positions.

A second embodiment of the invention incorporating a different form of closure mechanism is shown in Figures 8 and 9, wherein corresponding features 14 are denoted by corresponding reference numerals. In this embodiment, the discharge ports 15 are individually sealed by a series of discrete axially slidable gates 54. The gates 54 are each moved separately between the open and closed positions by respective hydraulic actuators 56. An hydraulic control circuit (not shown) is configured so that all of the gates move substantially in unison.

The hydraulic fluid for the actuators 56 is fed through the central drive shaft 10 as best shown in figure 10. This drive shaft includes a rotary sealing

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mechanism 60 at its proximal end. The outer annular

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o portion 61 of the rotary sealing mechanism is anchored to the mixer chassis by flange 63 to prevent rotation, as shown more clearly in Figure 9, whilst the inner portion rotates with the drive shaft. This allows the hydraulic lines to be fixedly connected to stationary inlet ports 62 and 64.

Inlet port 62 is in fluid communication, via a first transfer port in the form of annular channel 66, e* with axial bore 68 which extends through drive shaft from the sealing mechanism to the mixing drum. A similar inlet port 64 is in fluid communication, via a second transfer port in the form of annular channel with bore 72 which also extends longitudinally through the drive shaft. The outlets of bores 68 and 72 are thus disposed for conjoined rotation with the mixing drum. In this way, hydraulic lines extending from a I 15 power pack 73 to the inlet ports 62 and 64 transfer fluid through the rotary seal, and into the rotating drive shaft. The outlets of this shaft are then fed via ports 68 and 72 to pressure and volume equalising manifolds (not shown) attached to the mixer body.

Further hydraulic lines (also not shown) connect the manifolds to the individual hydraulic actuators 56 associated with each port. Hydraulic pressure can then be applied at either inlet port 62 or 64 respectively to extend or retract the hydraulic actuators 56, so as to .'.open or close the discharge ports 15 as required. As with the annular sleeve 20, the gates 54 can be partially opened to provide a slow discharge mode.

Figure .1 shows a side view of a sealing arrangement for one of the sliding gates 54. This sealing mechanism includes a first radial seal 74 which slidingly abuts the adjacent inner surface of the gate *oooo 54. A second seal 76 is provided at the opposite end of the discharge port 15, remote from the actuator. This 20 second seal 76 mates with sealing member 78 which is S"attached to the leading edge of the gate by a series of bolts 80. Thus, when closed the gate 54 in combination with seals 74, 76 and 78 effectively seals the corresponding discharge port 15. Seals 74, 76 and 84 are moulded from a single piece of polyurethane in a rectangular configuration, corresponding to the shape of the discharge ports. This eliminates the risk of leaks which can occur when individual sealing strips having

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16 joins are used. A flange 82 is provided on the sliding gate 54 for connection to a clevis dispose,' on the end of the piston rod associated with the corresponding hydraulic actuator 56.

Figure 12 shows the end view of the seal assembly of Figure 11. From this perspective, it will be seen that the side edges of the sliding gate 54 travel between radially spaced seals 82 and 84 in a direction normal to the plane of the page when moving between the open and closed positions. All seals used in this arrangement are made from Polyurethane of around 90 Duro hardness.

:The polyurethane seals wear due to friction between sliding gates 54 and the corresponding upper 15 surfaces of the seals. To compensate for this wear, a series of four spacer bars 88 are provided in a rectangular configuration underneath the respective "edges of each seal. Cams 90 located under each end of each spacer bar can be periodically rotated via shafts 20 92 to force the associated spacer bar and the accompanying seal edge upwardly and hence maintain a tight seal against gate 54. The cams are locked in the required position by lock nuts 94.

In the preferred embodiment, the volume of the drum is approximately 21m 3 which gives a capacity for approximately 6m 3 of concrete. The preferred drum speed is approximately 10 rpm which produces an effective mixing time of approximately 60 seconds. The

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17 discharge time is approximately 20 seconds. The drum is provided with 9 discharge ports equispaced around its periphery. All edges of the discharge ports are provided with a gate liner 86 which resists abrasion of the ports whilst concrete is discharging therethrough.

The present invention has been found to provide all the advantages of central type mixers as compared with truck mixers, and yet ameliorates the significant disadvantages of known split drum mixers in terms of excessive mechanical complexity, capital and maintenance .cost, and poor reliability. Maintenance is particularly enhanced because many of the working parts are .o accessible externally. The internal configuration of a mixing blades is also substantially simplified because the present invention obviates the need for the internal spider assembly necessary to support the fixed half-shell of the drum in previous designs. The eooo invention also obviates the need for an inner seal to protect the sliding bearing supporting half the drum 20 from the ingress of concrete, as required in known designs. Thus, the invention represents a commercially significant improvement over the prior art.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims (30)

1. A concrete mixer comprising a mixing drum supported for rotation about a substantially horizontal axis, a plurality of discharge ports spaced around the periphery of the drum, and closure means adapted for movement between a closed position covering the ports to substantially seal the drum and an open position wherein the ports are exposed, said ports being disposed to permit discharge of the contents of the drum under gravity with the closure means in the open position irrespective of the rotational position of the drum.

2. A concrete mixer as claimed in claim i, wherein the drum is defined by a substantially cylindrical central region with tapered ends, and is supported for rotation about a longitudinal axis.

3. A concrete mixer as claimed in claim 1 or claim 2, wherein the discharge ports are a series of apertures S"spaced around the periphery of the drum.

4. A concrete mixer as claimed in claim 3, wherein 20 the apertures are disposed substantially midway between the ends of the drum.

A concrete mixer as claimed in any one of the preceding claims, wherein the drum is rotated by a drive motor via a reduction gearbox and a main drive shaft.

6. A concrete mixer as claimed in claim 5, wherein the end of the drum remote from said drive shaft is supported by guide rollers mounted to a structural frame.

7. A concrete mixer as claimed in claim 6, further 19 comprising an input chute disposed to feed material axially into the end of the drum remote from said drive shaft.

8. A concrete mixer as claimed in any one of the preceding claims, wherein said drum includes a series of internal mixing blades.

9. A concrete mixer as claimed in claim 8, wherein said internal mixing blades are disposed to direct concrete towards said ports to facilitate rapid discharge upon rotation of the drum.

10. A concrete mixer as claimed in claim 9, wherein said internal mixing blades are disposed in a criss-crossed configuration.

11. A concrete mixer as claimed in any one '.aims 15 8 to 10, wherein the mixing blades to one side jA said discharge ports extend part way across the discharge 00 5 ports to provide a slow discharge mode with said closure means in a partially opened configuration.

12. A concrete mixer as claimed in any one of the 20 preceding claims, wherein the closure means includes a S"closure sleeve disposed for longitudinal sliding movement around the drum.

13. A concrete mixer as claimed in claim 12, wherein the sleeve comprises a substantially cylindrical sliding door coaxial with the drum.

14. A concrete mixer as claimed in claim 13, wherein the closure sleeve is internally machined to ensure accurate concentricity with :he drum.

I 20 A concrete mixer as claimed in any one of claims 12 to 14, wherein a removable guide chute is supported immediately below the closure sleeve in the vicinity of the discharge ports to channel the discharging concrete.

16. A concrete mixer as claimed in any one of claims 12 to 15, wherein the closure sleeve is connected by peripheral support arms external to the drum to an external bearing disposed for axial sliding movement on the main drive shaft, to accommodate axial movement of the sleeve between the open and closed positions.

17. A concrete mixer as claimed in claim 16, wherein is". a pair of hydraulic actuators are operable on the support arms via a thrust bearing to control the position of the closure sleeve relative to the drum and 15 hence to control the flow rate of the discharging eeo. concrete. OS

18. A concrete mixer as claimed in any one of claims 12 to 17, wherein an assembly of rollers or slides are disposed intermediate the sleeve and the drum to retain 20 relative concentricity. S"

19. A concrete mixer as claimed in any one of claims 12 to 18, further including sealing means to seal the discharge ports with the sleeve in the closed position.

A concrete mixer as claimed in claim 19, wherein said sealing means comprises of a first annular sealing ring mounted to an annular flange formed on said drum, wherein a remote edge of said sealing rim sealingly and slidingly abuts an adjacent inner surface of said I 21 sleeve, wherein an opposite edge of said sleeve incorporates a second sealing ring adapted for abutting engagement with an annular flange formed on the periphery of the drum, such that in the closed position the sleeve in conjunction with the first and second sealing rings and flanges seals the discharge ports.

21. A concrete mixer as claimed in claim 19, wherein said sealing means comprises a first sealing ring slidingly abutting a corresponding inner surface of the sleeve and a second sealing ring mounted to the corresponding end of the sleeve by means of a circumferential retaining plate, such that the second sealing ring directly abuts an adjacent annular flange extending radially from the outer surface of the drum in the closed position to seal the ports.

22. A concrete mixer as claimed in claim 19, wherein said sealing means comprises an annular ring extending radially outwardly from the sleeve, said ring being engaged by at least two pairs of spaced apart rollers, the axes of said spaced apart rollers being substantially perpendicular to the longitudinal axis of the drum, one pair of rollers being disposed on each side of the drum and connected to hydraulic actuators, whereby simultaneous horizontal displacement of the rollers by the actuators effects a corresponding movement of the sleeve between the open and closed positions.

23. A concrete mixer as claimed in any one of claims 22 1 to 11, wherein said closure means includes a plurality of discrete gates associated with the ibpective discharge ports.

24. A concrete mixer as claimed in claim 23 further including control means configured to move the gates substantially in unison between the open and closed positions.

A concrete mixer as claimed in claim 23 or claim 24, further including drive means in the form of a plurality of hydraulic actuators respectively disposed to move the gates individually between the opened and closed positions.

26. A concrete mixer as claimed in claim 25, wherein hydraulic fluid for said actuators is fed through a central drive shaft of the mixing drum.

27. A concrete mixer as claimed in claim 26, wherein said drive shaft includes a rotary sealing mechanism comprising an outer portion fixed with respect to a oee oI support frame of the mixer to prevent rotation, an inner portion adapted for rotation with the drive shaft, and transfer ports adapted sealingly to transmit hydraulic fluid between the outer portion and the inner portion.

28. A concrete mixer as claimed in claim 27, wherein said drive shaft incorporates a first longitudinal bore adapted to transfer hydraulic fluid to said hydraulic actuators via an intermediate manifold to effect substantially simultaneous movement of the gates into 23 the closed position, and a second longitudinal bore adapted to transfer hydraulic fluid to said hydraulic actuators via an intermediate manifold to effect substantially simultaneous movement of the gates into the open position.

29. A concrete mixer as claimed in claim 28, further including first and second fixed inlet ports disposed on the outer portion of the rotary sealing mechanism, and in fluid communication respectively with the first and second bores in the drive shaft via respective annular transfer ports configured to permit transfer of hydraulic fluid irrespective of the rotational position oeee of the drive shaft.

30. A concrete mixer substantially as hereinbefore 15 described with reference to Figures 1 to 7 or Figures 8 to 12 of the accompanying drawings. DATED this 24th Day of January, 1995 MAX GEORGE HOOD Attorney: STUART M. SMITH Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS 1 I ABSTRACT A concrete mixer comprises a mixing drum (2) supported for rotation about a substantially horizontal longitudinal axis A plurality of discharge ports are spaced around the periphery of the drum Closure means (20,54) are adapted for movement between a closed position covering tha ports to substantially seal the drum and an open position wherein the ports are exposed. The ports are disposed to permit discharge of the contents of the drum under gravity with the closure means in the open position, irrespective of the rotational position of the drum.