GB2137924A - Moulding concrete articles - Google Patents

Abstract

A process of forming a concrete moulded article from wet concrete of relatively high slump consistency is disclosed including the steps of constructing at least one mould corresponding to the shape of said article, said mould including a continuous membrane 7 contactable with the surface of said article, pouring concrete into said mould to form said article, compressing said concrete by forcing said membrane 7 against the surface of the concrete whereby surplus liquid is drained through the membrane out of the concrete such that the concrete exhibits partially cured characteristics, releasing said compression and separating said article from said mould. <IMAGE>

Description

SPECIFICATION Improvements Relating to Concrete Pipe and Pole Manufacture The present invention relates to method and apparatus for making concrete pipes and particularly but not exclusively reinforced concrete pipes.

The commercial manufacture of concrete pipes and particularly steel reinforced concrete pipes can be divided into two main categories-those cast in rotating moulds and those cast in stationary moulds.

Processes using rotating moulds generally use either the so-called roller suspension process or the centrifugal process.

The roller suspension process uses a concrete of stiff low slump consistency. The wet concrete is placed in position and compacted by a rotating suspending roller. No effort is made in this process to remove any excess water. By low slump is meant high viscosity and high slump is meant low viscosity concrete when wet.

The centrifugal process also uses concrete of a stiff low slump consistency. Here the wet concrete is placed in position and compacted by centripetal force. The mould is rotated at considerably higher speeds than in the roller suspension process. Excess water is squeezed to the inside surface of the pipe and removed with trowels.

In each of the above methods a concrete of high density and strength is obtained while each product also has a very low permeability once the concrete has cured. However, such processes require expensive machinery and equipment for performance.

In each case the length of the pipe that can be cast is limited by the severe rotational effects on either the moulds or suspending rollers in each process respectively, or the difficulty of achieving even filling of the pipe mould in the case of the centrifugal process. Pipes of up te 15' have been produced commercially in this way; however, a limit of 8' is generally used.

Processes using stationary moulds can also be divided into two main categories-those using high slump concrete which is then allowed to set in the mould and those using a low slump concrete where the mould is removed or stripped substantially after casting is complete.

In the process using the low slump concrete, the concrete is compacted by vibration and pressure. However, unlike the rotational processes mentioned above a low permeability concrete is not achievable and further, to achieve satisfactory pipe strengths (as a result of low concrete strength because of low permeability) the wall thickness of the pipe has to be greatly increased in this latter process. The use of high slump concrete in stationary moulds is time consuming and requires a large number of moulds.

The process according to the present invention has as its main objective to combine the ease and convenience of a stationary vertical mould using wet concrete of a high slump consistency, to obtain at least an equivalent product to those obtained by the rotational processes and which, further, the mould can be stripped substantially immediately casting is completed.

According to the present invention there is provided a process for forming a pipe of mouldable settable material such as concrete comprising the steps of constructing an inner and outer mould forming a substantially annular cavity, pouring said material into said cavity to form said pipe, compressing said material by decreasing the gap between said inner and outer mould to remove surplus liquid from said material such that said material has the characteristics of being at least partially cured, releasing said compression and separating said pipe from said annular cavity.

According to a further aspect of the present invention there is provided a process for forming an elongate plain sided article of mouldable settable material such as concrete comprising the steps of constructing at least one mould corresponding to the shape of said article pouring said material into said mould to form said article, radially moving said mould relative to said article to compress said material forming said article to remove surplus liquid from said material such that said material has the characteristics of being at least partially cured releasing said compression and separating said article from said mould.

In a more specific aspect there is provided a process for forming a cylindrical elongate article from concrete preferably of high slump consistency compressing the steps of constructing at least one mould corresponding to the shape of said article, said mould including a continuous membrane contactabie with the surface of said article, pouring concrete into said mould to form said article, compressing said concrete by forcing said membrane against the surface of the concrete whereby surplus liquid is drained through the membrane out of the concrete such that the concrete exhibits partially cured characteristics, releasing said compression and separating said article from said mould.

Specifically the invention is preferably adapted to the production of concrete pipes particularly but not exclusively reinforced pipe and solid or hollow poles where the slump consistency of the concrete pipes is high yet allows almost immediate removal of the mould upon completion of the process thereby freeing the mould for further use.

Some advantages of this process over the rotational processes previously described are: 1. No limitation on pipe length as a result of the dynamic forces in the moulds or their supports.

2. Concrete does not need to be supported by the mould during curing or while it takes its initial set.

3. Casting time of the concrete is greatly reduced.

Further, this process has advantages over the stationary vertical substantially immediate strip process. Some of these are: 1. Greater density is obtained which leads to lower permeability.

2. Higher strength concrete provides for considerable reduction in pipe wall thickness irrespective of whether reinforcing is used.

Finally, the process of the present invention combines the quality of the rotational processes with the speed of the substantially immediate strip vertical process.

The invention will now be described with reference to the accompanying drawings in which: Figure 1 is a partial sectional view of a mould suitable for forming a pipe with or without reinforcing mesh.

Figure 2 is a detailed sectional view showing mould filling apparatus.

Figure 3 is a schematic flow diagram illustrating steps 3a to 3f of the moulding process for a reinforced concrete pipe.

Referring to Figure 1 the mould includes an inner former 3 of rubber or polyurethane moulded on a steel or like stationary support 1 8. The inner former 3 is mounted within mould ends 8 and 9.

The outer former includes a compressing membrane 2 of rubber or polyurethane and a permeable membrane of preferably of closely woven nylon or cotton material. The membranes are adapted to be clamped into the mould ends 8 and 9 at 20 and 21 by a support tube 6 preferably of resilient stiff material such as polyurethane.

The outer mould is encased in a steel casing 4 adapted to apply pressure to the ends 20 and 21 of the membranes 8 and 9.

Procedure 1. The removable mould end 9 is placed over the upper end of extendable inner mandrel 11 so that the inner diameter of mould end 9 is in slidable contact with the outer surface of mandrel 11.

2. The reinforcement cage 1 2 is placed coaxiallyon mould end 9 and lower filling tube 13 is lowered so that the filling tube enters upper end of reinforcement cage 12. The outside diameter of filling tube 1 3 is preferably only slightly less in diameter than the inside diameter of the cage 12 so that the cage 1 2 is accurately located in cavity 10.

3. Vacuum is applied to cavity 1 through tube 5 to draw cylindrical plastic compressing membrane 2 and permeable membrane 7 radially outwards against cylindrical plastic support tube 6. Filling tube 13 is lowered into the outer mould so that lower end 24 of filling tube 1 3 engages upper end of piston 1 7 and lower end of support tube 6 is adjacent to lower mould end 9.

4. The outer mould case 4 is tightened using screw 25 to force cylindrical plastic support tube 6 radially inwards so that the upper and lower ends of support tube 6 contact upper mould end 8 and lower mould end 9 respectively to-form moulding cavity 10. The mould case 4 supports plastic support tube 6 during casting, thus ensuring that pipe wall is of uniform thickness.

5. Concrete is then placed in filling tube 13 and filling tube and extendable inner mandrel 11 are simultaneously raised through mould end 9 and cavity 1 0. Concrete passes through gap 14 into cavity 1 0. Concrete is preferably vibrated by fingers 23 while filling is being carried out.

Concrete thus comes into contact with permeable membrane 7 which immediately allows water to drain from concrete.

6. When cavity 10 is completely filled, cap 1 5 is fitted to upper mould end 8 so that it contacts inner former 3 to form a seal to prevent concrete escaping when pressure is applied to cavity 1.

7. Vacuum is then released from cavity 1 allowing the compressing membrane 2 to apply a radially inward force to the concrete in cavity 10.

The relaxed diameter of compressing membrane 2 is always less than the diameter of freshly placed concrete so that the outer mould face is maintained in contact with the surface of the concrete when vacuum is released from cavity 1 and before pressure is applied. Therefore there are no circumferential compressive forces generated in membrane 2 when the pressure is applied.

The radially inward force naturally occurring in the membrane is increased by the application of pressure, preferably hydraulic, through tube 5.

Pressures of up to 50 P.S.I. have been applied with satisfactory results. When pressure is applied to compressing membrane 2 permeable membrane 7 is forced against the fresh concrete; this force squeezes the water from the concrete.

This excess water passes through the permeable membrane 7 downwards through permeable mesh 1 9 and out through drainage holes 1 6 which are open to atmosphere. Vibration can be applied to the mould during this process to assist with compaction and removal of water. During this process the effective thickness of the concrete wall of the pipe will be reduced by approximately 10% depending on the amount of free water available for removal. Pressure applications in excess of atmospheric are workable, however the delay in stripping because of slower drainage may become a factor.

8. When compressing process is complete the pressure is removed from cavity 1 and a vacuum is reapplied to this cavity. This draws the compressing membrane 2 and permeable membrane 7 which are attached to each other radially outwards away from the concrete.

Preferably simultaneously, mould case 4 is released allowing cylindrical plastic support tube 6 to resume its original diameter thus increasing the space between the concrete and permeable membrane 7. Gap 1 5 is also removed.

9. Either before or after the components forming the outside diameter of the pipe are removed the extendable inner mandrel 11 is activated to form gap between inside diameter of the concrete pipe and mandrel 11. An advantage of carrying out this step before removal of the outer mould components, is that concrete is not stretched or broken as a result of the shear forces between the inner former 3 and the concrete.

Rubber or plastic is used on the inner mandrel 11 because with relatively low forces, its thickness is reduced as it stretches, thus providing the necessary clearance to remove the pipe. The inner former 3 is stretched by means of piston 1 7 which is inside cylinder 1 8. Hydraulic pressure is applied to cylinder 18 and as rubber inner former 3 is attached to cylinder 18 at its lower end and piston 1 7 at its upper end, the rubber can be stretched approximately 60%.

The friction that exists between the contacting surfaces of cylinder 1 8 and rubber former 3 is such that during application of stretching forces to the rubber, progressive reduction of rubber thickness takes place along the length of the mould from top down to the bottom of the mould thereby creating a peeling effect of the rubber from the surface of the wet concrete avoiding cracking of the concrete and damage to its surface.

1 0. After inner former 3 has been stretched, it is lowered through pipe. The components that form the outside and ends of the pipe can also then be removed from the machine.

Satisfactory results have been achieved in tests using a membrane of woven nylon material through which water, but very little cement will pass. As some cement does find its way through this membrane it has been necessary to fix thins membrane 7 to a plastic or similar ring 21. This ring is not fixed to compressing membrane 2 and therefore allows for cement particles to be flushed out from between the permeable mesh 1 9 and the compressing membrane 2. Both the permeable membrane 7 and the permeable mesh 19 are readily available. Spacers 20 and 22 have been added to give a more uniform thickness of concrete along the length of the pipe. It is important that the supporting tube 6 is stronger than compressing membrane 2 otherwise the compressing membrane 2 will not be drawn radially outwards when the vacuum is introduced into cavity 1. Drainage holes 16 are drilled axially in ring 21.

Claims (4)

1. A process for forming a pipe of mouldable settable material such as concrete comprising the steps of constructing an inner and outer mould forming a substantially annular cavity, pouring said material- into said cavity to form said pipe, compressing said material by decreasing the gap between said inner and outer mould to remove surplus liquid from said material such that said material has the characteristics of being at least partially cured, releasing said compression and separating said pipe from said annular cavity.

2. A process for forming an elongate plain sided article of mouldable settable material such as concrete comprising the steps of constructing at least one mould corresponding to the shape of said article pouring said material into said mould to form said article; radially moving said mould relative to said article to compress said material forming said article to remove surplus liquid from said material such that said material has the characteristics of being at least partially cured releasing said compression and separating said article from said mould.

3. A process for forming a cylindrical elongate article from concrete preferably of high slump consistency compressing the steps of constructing at least one mould corresponding to the shape of said article, said mould including a continuous membrane contactable with the surface of said article, compressing said concrete by forcing said membrane against the surface of the concrete whereby surplus liquid is drained through the membrane out of the concrete such that the concrete exhibits partially cured characteristics, releasing said compression and separating said article from said mould.

4. A process for forming a concrete article substantially as herein described with reference to the accompanying drawings.