The invention relates to a method for producing a concrete tube in a mould and removing the tube from said mould. In particular, the method relates to producing concrete sewer tubes.

A known method for producing a concrete tube, which method is used for decades, is by providing a vertical mould having a shell out of one piece and an elongate core arranged within the shell. The mould is filled with an almost set concrete mixture. The concrete is compressed in the mould and directly afterwards, the mould is slid of the compacted almost set concrete mixture, which will more or less maintain the shape of the mould.

In order to ensure some reasonable tolerances on the diameter of the concrete tube, steel rings are arranged on both ends of the concrete tube.

Then the tube is moved to a drying chamber, in which the concrete is allowed to set and cure. Finally, the steel rings are removed and the concrete tube is ready for use.

Besides the difficulties of maintaining reasonable tolerances in diameter, the resulting concrete tube also has a rough surface. Furthermore, the energy consumption of the drying chamber is substantial.

Another method for producing a concrete tube is for example known from WO 2014048648.

In this method, a vertical mould is provided having a partitioned shell and an elongate core arranged in the shell. The elongate core can be shrunk in diameter.

The vertical mould is filled with liquid concrete. The liquid concrete is then allowed to set and cure inside of the mould. When the concrete is sufficiently cured, the partitioned shell is taken apart and the core is shrunk in diameter, such that the core can be taken out of the cured concrete tube.

The shrinkable elongate core has a complex mechanism to allow for the reduction in diameter. This complex mechanism is prone to malfunctioning as the cured concrete typically adheres to the outer surface of the core and prevents the reduction in diameter.

It is an object of the invention to reduce or even remove the above mentioned disadvantages.

This object is achieved with the method according to the invention, which method comprises the steps of:

- providing a mould comprising an elongate core and a partitioned shell arranged around the core;

- filling the mould with liquid concrete;

- allowing the concrete to set and cure in the mould;

- after the concrete has set and cured, applying a force between the core and the shell in longitudinal direction of the elongate core, such that the elongate core is pulled out of the set concrete;

- opening the partitioned shell by taking apart at least two shell parts;

- removing the set and cured concrete tube. With the method according to the invention, the elongate core is pulled, in longitudinal direction, out of the set and cured concrete tube. By applying a force between the core and the shell, a sufficient large force can be generated by which the adhering force of the concrete on the elongate core can be overcome. As the concrete tube is still housed in the shell, the concrete is only subjected to a compression force, which cured concrete typically can withstand

excellently . The advantage of the method according to the

invention is that no complex, shrinkable core is required. A simple one piece elongate core, having a fixed shape can suffice for this method.

Preferably, the mould is positioned with the

elongate core in vertical, gravitational direction when to be filled with liquid concrete and wherein the shell with set and cured concrete is rotated in horizontal position, after the elongate core has been pulled out.

Although, the mould can be filed by pumping concrete in the mould when in a horizontal position, having the mould in vertical direction will facilitate the expulsion of air out of the mould and ensure a more homogeneous cured concrete.

In an embodiment of the method according to the invention the concrete tube is lifted from the mould after the partitioned shell is opened. Because the shell part, on which the tube is supported, is in horizontal position, sufficient space will be available around and above the concrete tube, to safely lift the tube out of the mould and transport it away.

In a preferred embodiment of the method according to the invention the outer surface of the elongate core is a steel surface and wherein the outer surface is polished.

The steel surface provides sufficient strength for the pull forces when removing the core from the concrete tube. Furthermore, the polished surface minimizes the adhesion forces and at the same time provides for an excellent smooth finish of the inner surface of the tube. This smooth inner surface ensures that, when in use, dirt will not easily adhere on the inside, keeping the concrete tube clean for a longer period of time, than concrete tubes produced with a rougher surface .

In a further preferred embodiment of the method according to the invention the elongate core is tapering in longitudinal direction providing a releasing shape. Due to the releasing shape, the core has to be shifted out of the

concrete tube for only a small distance in order for the core to have sufficient play relative to the tube, such that is can be pulled out further without any resistance.

In yet a further preferred embodiment of the method according to the invention, the partitioned shell has in assembled state a non releasing mould shape. The non releasing mould shape will provide a better grip of the shell on the outer surface of the concrete tube, when the pull force is generated between the shell and elongate core.

The invention also relates to a mould for use with the method according to the invention, wherein the mould comprises :

- a base frame;

- an elongate core arranged on the base frame;

- a partitioned shell arranged around the core and releasable coupled to the base frame; and

- lifting means arranged to the base frame for lifting the partitioned shell from the base frame.

With the mould according to the invention, the partitioned shell and elongate core are coupled to the base frame to provide a rigid mould, when the liquid concrete is poured in. However, when the pressure force is to be generated between the core and the shell, the shell is decoupled from the base frame, such that a relative movement is possible between the core and the shell.

In a preferred embodiment of the mould according to the invention at least one flexible joint is arranged between the elongate core and the base frame to allow tilting and shifting of the elongate core relative to the partitioned shell .

Providing a flexible joint allows the elongate core to tilt and shift relative to the partitioned shell to compensate for any misalignment during pulling the elongate core out of the shell.

In another preferred embodiment of the mould

according to the invention the lifting means comprise a plurality of hydraulic cylinders arranged to engage on the circumference of the partitioned shell.

Hydraulic cylinders can typically provide large forces, which are required to overcome the adhesive forces of the cured concrete on the elongate core.

In a further preferred embodiment of the mould according to the invention the elongate core comprises a mould frame releasable coupled to the base frame and wherein the partitioned shell is releasable coupled to the mould frame.

With the mould frame, it is possible to move the attached elongate core and partitioned shell independent of the base frame, which could comprise the lifting means. This allows for a number of mould frames with elongate core and partitioned shell to use a single base frame with lifting means.

In yet a further embodiment of the mould according to the invention the plurality of hydraulic cylinders is controlled dependening on the mould frame coupled to the base frame. This allows for different sizes of mould frames to be coupled to the base frame. Only the hydraulic cylinders are controlled, which will engage with the partitioned shell at the optimal positions.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a cross sectional view of a first step of the method according to the invention.

Figure 2 shows a second step of the method according to the invention. Figure 3 shows a third step of the method according to the invention.

Figure 4A and 4B show cross sectional views of an embodiment of a mould according to the invention.

Figure 5 shows the mould of figure 4 in a releasing position .

In figure 1 a mould 1 is provided. This mould 1 has a base frame 2 on which an elongate core 3 and a partitioned shell 4 is arranged. In the first step of the method according to the invention, the space 5 between the core 3 and the shell 4 is filled with liquid concrete C and the concrete is allowed to set and cure.

Figure 2 shows a second step of the method according to the invention. The concrete has set and cured, resulting in a concrete tube 6. Hydraulic cylinders 7 arranged in the base frame 2 are controlled to push the partitioned shell 4

upwards, while the elongate core 3 is arranged to the base frame 2. The hydraulic cylinders 7 provide a push force between the elongate core 3 and the shell 4, which overcomes the adhesion of the concrete tube 6 on the elongate core 3.

Figure 3 shows a third step of the method according to the invention. Now the elongate core 3 is pulled out of the concrete tube 6, the partitioned shell 4, together with the concrete tube 6 is lifted further and rotated to a horizontal position.

The partitioned shell 4 is disassembled in to two shell parts 8, 9, after which the concrete tube 6 is lifted out of the shell part 8 and transported further.

Figure 4A and 4B show cross sectional views of an embodiment of a mould 20 according to the invention. The mould 20 has a base frame 21 with a number of hooks 22, 23 with which a mould frame 24 can be engaged.

Three elongate cores 25, 26, 27 are arranged perpendicular to the mould frame 24. These elongate cores 25, 26, 27 are enclosed by a partitioned shell 28, 29.

The partitioned shell 28, 29 is releasable coupled by couplings 30.

The base frame 21 is furthermore provided with hydraulic rods 31, which can be operated independently. When some of these rods 31 are operated (as shown in figure 5) , while the mould frame 24 is coupled by the hooks 22, 23 and the partitioned shell 28, 29 is released from the mould frame 24 by releasing the couplings 30, the partitioned shell 28, 29 is pushed up from the mould frame 24. As a result the elongate cores 25, 26, 27 are pulled out of the mould 20 and thus out of the set concrete tubes 32, 33, 34.