GB2134434A

GB2134434A - Centrifugally moulded concrete products

Info

Publication number: GB2134434A
Application number: GB08236563A
Authority: GB
Inventors: Kaito Eimatsu
Original assignee: SHEKISAN KOGYO CO Ltd
Current assignee: SHEKISAN KOGYO CO Ltd
Priority date: 1982-12-23
Filing date: 1982-12-23
Publication date: 1984-08-15
Also published as: GB2134434B

Abstract

A core (7) is insertable into a rotary mould (15), and fresh concrete is charged into the rotary mould to fill the annular gap (S) between the wall of the rotary mould and the surface of the core. After filling the annular gap, the core is withdrawn leaving a layer of fresh concrete of a uniform thickness on the inner peripheral surface of the rotary mould. The latter is then rotated at a predetermined speed to apply a centrifugal force to the fresh concrete to form the desired hollow concrete product, such as a pile or post. The insertion and withdrawal of the core into and out of the rotary mould is conducted by moving a truck (16), (Figure 5, not shown) carrying the rotary mould linearly towards and away from the core which is held stationary. <IMAGE>

Description

SPECIFICATION Method of and apparatus for producing centrifugally formed concrete products The present invention relates to a method of and apparatus for producing centrifugally formed concrete products such as, for example, concrete piles or posts or pipes, using a rotary mould.

Hitherto, a split type rotary mould consisting of an upper half part and a lower half part has been used in the centrifugal forming of elongate concrete products such as concrete piles or concrete poles. In the production of such concrete products, the lower half of the rotary mould is charged with a predetermined amount of concrete by means of the upper half part of the mould. The upper half part of the mould is then turned to close the rotary mould which is then rotated to form a concrete layer of a predetermined thickness on the inner peripheral surface of the rotary mould, thereby to form a cylindrical concrete product such as concrete pile.

According to another known method, fresh concrete is fed into a rotary mould which is kept closed.

In such a case, a concrete charging pipe is inserted into the rotary mould and is moved gradually in the axial direction of the mould while discharging the concrete to charge the concrete over the entire length of the mould.

The first mentioned method employing the split type rotary mould suffers from the following disadvantages. Since the rotary mould is rotated after the upper half part of the mould is brought to the closing position subsequent to the charging of the concrete, the concrete is locally concentrated particularly in the begining of the operation so that inevitably the power transmission to the rotary mould is rendered unsmooth. In addition, it is necessary to add a large amount of water in order to maintain sufficient fluidity of the fresh concrete. In consequence, the efficiency of the operation is lowered impractically.

Also, the second-mentioned method employing a concrete charging pipe has also encountered problems. It is necessary to employ a long concrete charging pipe in accordance with the increase in the length of the concrete product. Since the concrete charging pipe is cantilevered, it is necessary to make the concrete charging pipe of small diameter at its free end and of large diameter at its base end, in order to minimize the bending of the pipe during the operation. This shape of the concrete charging pipe inevitably increases the resistance to flow of concrete in the concrete charging pipe. To reduce the resistance, it is necessary to increase the fluidity of the concrete by adding a large amount of water.

Furthermore, considerable power is required to charge the concrete, resulting in equipment breakdown or rapid wear of the concrete charging pipe.

According to one aspect of the invention, there is provided a method of forming concrete product by centrifugal force comprising the steps of inserting a core mould into the central portion of a rotary mould for centrifugal forming; charging fresh concrete into an annular gap between the inner surface of said rotary mould and the outer surface of said core mould; and rotating said rotary mould thereby to form a hollow cylindrical concrete product.

According to another aspect of the invention, there is provided apparatus for forming a concrete product by centrifugal force comprising a concrete charging pipe for charging fresh concrete into a rotary mould; a connecting pipe connected at its one end to the end of said concrete charging pipe; a core mould connected at its one end to the inside of said connecting pipe and projecting therefrom for insertion into said rotary mould and a truck for carrying said rotary mould and movable in a direction parallel to the axis of said core mould.

Hence, the annular space between the outer surface of the core mould and the inner surface of the rotary mould is used as the concrete feeding pipe.

Moreover, fresh concrete can be charged even when it has a comparatively low fluidity so that both of the slump value and charging pressure can be decreased advantageously.

Also, the fresh concrete can be charged at a uniform thickness on the inner peripheral surface of the rotary mould before the centrifugal force is applied.

Unlike the conventional concrete charging pipe through which the concrete is charged, the core mould used need not have so large a difference of diameter between the free end and its base end, because the core mould is required only to bear the weight of itself, although it is cantilevered as in the case of the conventional concrete charging pipe.

After inserting a core mould of a suitable diameter into the rotary mould, fresh concrete is charged into the annular space between the outer surface of the core mould and the inner surface of the rotary mould. This can be done with a comparatively small force because the loss of power due to friction between flowing concrete and stationary walls is comparatively small. In consequence, the risk of trouble with the apparatus is reduced advantageously. For instance, the conventional method and apparatus necessitate a slump value of more than 15cm and a pump pressure in excess of 100kg/cm2. A high pressure inevitably increases the risk of trouble with the equipment such as a pump, and requires a large water content in the concrete.In contrast, according to the invention, the slump value can be reduced down to 1 Ocm and the concrete can be charged at a relatively low pump pressure of less than 50kg/cm2.

Consequently, the risk of breakdown and other trouble is reduced significantly.

When the core mould has a large length, it may be supported by a suitable supporting bar or bars. The portion of the long core mould received by the rotary mould may be supported by a suitable supporting member.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a front elevational view of one embodiment of apparatus according to the present invention in a state of use, with a truck omitted and showing a rotary mould in section; Figure 2 is a plan view of the concrete charging assembly of the apparatus of Figure 1 with a power supply and the hopper omitted; Figure 3 is an enlarged sectional view taken along the line A---A in Figure 1; Figure 4 is an enlarged sectional view taken along the line B-B of Figure 1; Figure 5 is a front elevational view of an example of the support of core mould, showing the state in which the mould is mounted on a truck; Figure 6 is an enlarged sectional view of another example of the core mould; Figure 7 is a front elevational view of an example of the.connection between a connecting pipe and the mould; Figure 8 is a sectional view showing another example of the hopper; and Figure 9 is a sectional view of a hopper having no stirring bar.

Referring to the drawings, the apparatus shown therein has a hopper 1 provided therein with a stirring device. Extrusion cylinders, 3 having pistons 2,2 are connected to the lower side of the hopper 1 through chutes 29,29. The ends of the extrusion cylinders 3;3 are connected to one end of a single charging pipe 5 through branch pipes 4,4. The other end of the charging pipe 5 is joined to one end of a connecting pipe 6. The above-mentioned components down to the charging pipe 5 are materially identical to those of known apparatus. A core mould 7 has a support pipe 8 which is extended into the connecting pipe 6 and fixed securely to the inner surface of the connecting pipe 6 by a plurality of support plates 9 extending radially at a constant circumferential pitch.The core mould 7 having an outside diameter matching the bore diameter of the concrete product is fixed to the portion of the supporting pipe 8 extending outwardly from the connecting pipe 6. The core mould 7 has a hollow tubular structure as will be seen from Figure 4 and is connected to the supporting pipe 8 by a plurality of supporting plates 10,10which are arranged radially at a predetermined circumferential pitch. The diameter of the core mould 7 is reduced gradually at its two ends to provide conical or frusto-conical portions 7a, 7b which facilitate the insertion and withdrawal ofthe core mould 7.Before insertion into a rotary mould 15, the core mould 7 is supported by, for example, supporting posts 11,11 which are pivotably connected by pins 12, 12to brackets 13,13 on the floor and urged towards an upstanding position by means of springs 14,14. Therefore, as a truck 16 carrying the rotary mould 15 is moved in the direction of the arrow 17 in Figure 5to bring the end 16a ofthetruck 16 into contact with successive supporting posts 11, the supporting posts 11 tilt sideways in the direction of arrow 18 against the force of the springs 14,14, so that the core mould 7 is inserted into the rotary mould without substantial difficulty.Then after the core mould 7 is perfectly received by the mould 15 as shown in Figure 1, the pistons 2, 2 are alternatingly driven reciprocatably in the directions of arrows 19, 20, so that fresh concrete in the hopper 1 is charged through the branch pipes 4,4 as indicated by arrows 21, 22. Concrete charged through the two branch pipes 4,4 merges so that the concrete is continuously charged as indicated by an arrow 23 through the connecting pipe 6 and to fill the gap S between the rotary mould 15 and the core mould 7 as indicated by an arrow 24. As the gap S is completely filled, the truck 16 is moved in the direction of arrow 25 together with the rotary mould 15, so that the core mould 7 is withdrawn from the rotary mould 15.The withdrawal of the core mould 7 will be facilitated by slightly rotating the rotary mould 15 because, by so doing, the concrete is displaced towards the inner surface of the rotary mould to reduce its affinity to the core mould. After withdrawal of the core mould the rotary mould is rotated at a predetermined speed to apply a centrifugal force to the fresh concrete thereby to form the desired hollow concrete product.

It is also possible to provide the core mould 7 with a retractabie supporting projection 26 which is adapted to be projected to provide a supportforthe core mould during insertion of the core mould but is retracted during the withdrawal of the core mould 7 to reduce the resistance.

In the apparatus described above, some friction takes place between the outer surface of the core mould and the concrete because the core does not rotate even when the rotary mould is rotated. It is, however, possible to construct the apparatus to permit the rotation of the core mould 7 during rotation of the rotary mould 15. Figure 6 shows an arrangement for permitting rotation of the core mould 7. In this arrangement, the supporting plates forthe core mould 7 are fixed to a ring 27 which in turn is rotatably mounted on the supporting pipe 8, so that the core mould 7 is allowed to rotate following up the rotation of the rotary mould 15.

In the described embodiment, the core mould 7 before insertion into the rotary mould is supported by supporting posts 11 which are adapted so as to be pivoted automatically upon impact with the truck 16 as the latter moves. This arrangement, however, is not exclusive and various other arrangements may be adopted for supporting the core mould before insertion into the rotary mould.

Figure 7 shows a different embodiment in which the connection between the rotary mould 15 and the connecting pipe 6 is achieved by tightening together a flange 6a of the connecting pipe 6 and a flange 15a of the rotary mould 15 by means of butterfly bolts 28.

This arrangement, however, is only illustrative and can be modified in various forms.

An example of the hopper used in the apparatus of the invention will now be explained with specific reference to Figures 8 and 9. This hopper is intended for ensuring a substantially constant rate of charge of concrete even when the fresh concrete has a comparatively small fluidity. Referring to Figure 8, a rotary shaft 30 having a pointed end is arranged coaxially in a frusto-conical hopper. A feeder blade 31 consisting of a resilient wire helicallywoundto define a frusto-cone is attached to the lower end portion of the rotary shaft 30 by arms 32. The lower end 31 a of the feeder blade 31 is exposed to the inside of the lower end of the hopper 33.In Figure 8, reference numeral 34 denotes a plurality of stirring bars fixed to the upper portions of the rotary shaft 30 so as to extend radially therefrom, while reference numeral 35 designates a bearing for supporting the rotary shaft 30. The bearing 35 is fixed to the inner surface of the hopper 33 by means of three to four arms 36.

Figure 9 shows another example of the hopper in which the stirring bars 34 are omitted. In this example, the feeder blade 31 preferably has such a height as to reach a portion near the bearing 35.

When either one of the hoppers shown in Figures 8 and 9 is used, the fresh concrete in the hopper 33 is gradually lowered and fed downwardly through the action of the feeder blade 31 and/or the stirring bars 34 as the shaft 30 is rotated by a suitable power source, and is smoothly and continuously supplied into the cylinder 3 from the lower end of the hopper 33 through the chute 29.

As has been described, the fresh concrete is charged into the annular gap between the outer surface of the core mould and the inner surface of the rotary mould, so that the length of the concrete charging pipe can be reduced sufficiently even in the production of concrete products having large lengths. Since the charging of concrete is made in a bit-by-bit fashion, there is no fear of separation of aggregates. In addition, it is possible to lower the charging pressure of the fresh concrete and to lower the slump value because it is possible to obtain a sufficiently large cross-sectional area of the passage for the fresh concrete in the rotary mould as compared with the conventional apparatus employing a hollow insertable concrete charging pipe.

It is, therefore, possible to attain higher strength of the concrete products, while avoiding troubles and wear of equipment such as of the pump and charging pipe.

In addition, since the core mould is fixed to the supporting pipe which is concentrically supported in the connecting pipe, it is possible to hold the core mould rigidly and concentrically with the rotary mould. It is, therefore, possible to easily insert and set the core mould at the central portion of the rotary frame.

Furthermore, the core mould as a unit with the connecting pipe can be replaced easily to permit free design of the cross-sectional area of passage for the concrete in the connecting pipe, so that any increase of resistance against the flow of fresh concrete due to the fixing of the supporting pipe is avoided advantageously.

Although the invention has been described through specific terms, it is to be noted here that the described embodiments are only illustrative but not exclusive.

For instance, it is possible to use a solid rod having, for example, a cross-shaped cross-sectional shape in place of the tubular supporting shaft for supporting the core mould.

Also, the core mould need not be withdrawn until after rotation of the rotary mould.

Other changes and modifications may be made thereto without departing from the scope of the invention which is limited solely by the appended

Claims

claims. CLAIMS

1. A method of forming a concrete product by centrifugal force, comprising the steps of inserting a core mould into the central portion of a rotary mould for centrifugal forming; charging fresh concrete into an annular gap between the inner surface of said rotary mould and the outer surface of said core mould; and rotating said rotary mould thereby to form a hollow cylindrical concrete product.

2. The method of claim 1, wherein said concrete product is a pile or a pole.

3. The method of claim 1,wherein the core mould is withdrawn from the rotary mould before or after rotation of said rotary mould.

4. Apparatusforforming a concrete product by centrifugal force, comprising a concrete charging pipe for charging fresh concrete into a rotary mould; a connecting pipe connected at its one end to the end of said concrete charging pipe; a core mould connected at its one end to the inside of said connecting pipe and projecting therefrom for insertion into said rotary mould; and a truck for carrying said rotary mould and movable in a direction parallel to the axis of said core mould.

5. The apparatus of claim 4, wherein said core mould is supported for rotation.

6. The apparatus of claim 4 or claim 5, wherein said core mould is cantilevered and is provided on the lower side at or adjacent to the other end with a supporting projection.

7. The apparatus of any one of claims 4 - 6, including pivotable posts for supporting the core mould before insertion.

8. A method of forming a concrete product by centrifugal force, substantially as herein before described with reference to the accompanying drawings.

9. Apparatus for forming a concrete product by centrifugal force, substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings.