The present method concerns a procedure for the manufacture of a product of sulphur concrete.

A method whereby a product is formed by casting sulphur concrete in a mould with a suitable form is already known.

Sulphur concrete is a heterogeneous mixture of granulates as in classic concrete, being a mixture of fine filler substances, sand and fine and coarse stones.

As distinct from traditional cement concrete, water and cement as binding agents are replaced by sulphur or by a sulphur compound.

The granulates provide a stone carcass, while the sulphur forms the binding agent throughout this stone carcass.

When mixing sulphur concrete the sulphur or sulphur compound is heated to above the melting or solidification temperature of the sulphur or the sulphur compound so it becomes liquid. After mixing with the other raw materials the liquid is poured into a mould.

After cooling the sulphur solidifies. As soon as the sulphur concrete has cooled sufficiently to below the abovementioned melting temperature, the product formed will have hardened and the product can be removed from the mould.

In the rest of the description the tt rm sulphur equally refers to a sulphur compound that can be made liquid by heating above a certain melting or solidification temperature and that can solidify again by being cooled to below this temperatu

It is known that contraction cavities can form in products of sulphur concrete during solidification as a result of the phase transition from liquid to solid. During this physical reaction the crystal structure in sulphur changes giving it a higher density with contraction as a consequence .

A disadvantage is that this contraction causes contraction cavities in the heterogeneous sulphur concrete.

Another disadvantage is that the stone carcass can impede the contraction of sulphur and result in increased internal stress .

The contraction of sulphur then results in the origination of either undesired contraction cavities or undesired internal stress.

Such a method is known from WO 2014/041.658 for forming pipes of sulphur concrete by means of rotational casting. This document describes that the contraction phenomenon in sulphur unavoidably occurs in the sulphur concrete, and more specifically causes an unsmooth surface on the inside wall of the pipes. This document offers a solution to this phenomenon whereby a spatula is used to smooth the abovementioned inside wall that presses against the sulphur concrete at a temperature of 110 to 115 °C, so at a sulphur concrete temperature below the solidification temperature of sulphur. With this method, however, the contraction problems are not prevented through the entire thickness of the pipe formed.

From EP 0.778.088 a technique is known for the manufacture of synthetic pipes starting with a resin that is made liquid then cast in a rotating mould. In this case one starts with a liquid homogeneous resin without the addition of granulates, so one is not confronted with the same problems as when casting a heterogeneous mixture such as liquid sulphur concrete.

CN 1.318.669 describes a method for the manufacture of cross beams in traditional cement concrete that is poured into a mould, with the mould rotated around its own longitudinal axis. It is the intention here that an open channel forms in the middle of the cross beam around the axis of rotation, along which the excess of water and cement slurry can be collected and removed during rotation. This technique is not applicable for sulphur concrete because no water and slurry is applied in sulphur concrete.

KS 2006.0066446 describes a method for the manufacture of pipes of sulphur concrete, whereby liquid sulphur concrete is poured into a mould that is then made to rotate before being raised by hooks, and without further rotating the mould is taken to a cold space to allow the sulphur concrete to solidify. During these consecutive stages one has no active control whatsoever of the temperature of the sulphur concrete so also not of the course of solidification and imperfections unavoidably originate in the material of the formed pipe.

Consequently, the purpose of the present invention is to provide a method whereby one or more of the abovementioned or other disadvantages are resolved without the advantages of the use of sulphur concrete being compromised.

To this end, the invention concerns a method for the manufacture of a product in sulphur concrete comprising the following steps:

- the provision of a heterogeneous mixture of sulphur concrete consisting of at least sulphur or a sulphur compound and fine and coarse granulates;

- the mixing and heating of this sulphur concrete to a temperature that is higher than the melting or solidification temperature of the sulphur or sulphur compound in the sulphur concrete;

- the provision of a mould in the form of a drum that is driven around its axis and of which the inside has the form of the outside of the product to be manufactured;

- the heating of the rotating mould to obtain and retain a mould temperature that is higher than the solidification temperature of the sulphur or sulphur compound present in the sulphur concrete; during or after the heating of the mould, the simultaneous addition of the heated liquid sulphur concrete that spreads as a liquid layer on the inside of the mould by the rotation of the mould and the centrifugal force;

when the layer of liquid sulphur concrete has reached a certain thickness, corresponding to the quantity of sulphur concrete needed to form the product or otherwise, stopping the heating of the mould and starting to cool from the outside of the rotating mould to cool the liquid sulphur concrete in the mould from outside and allow solidification;

keeping the inside space of the drum at a temperature that is higher than the solidification temperature of the sulphur or sulphur compound in the sulphur concrete; if required, the gradual further supply of heated liquid sulphur concrete in the mould during the further cooling of the rotating mould from the outside until the necessary quantity of sulphur concrete to form the product has been reached;

when the sulphur concrete has sufficiently hardened in the mould, stopping the mould's drive means and removal of the formed product from the mould.

In this way the liquid sulphur concrete is first cooled on the wall of the mould and solidified. The cooling and solidification front that originates then evolves in the radial direction from outside to inside, whereby the centrifugal force continues to press liquid sulphur and the fine filler substances against the solidification front, filling contraction cavities and avoiding internal stress. With the correct dosage of freshly added liquid sulphur concrete one ensures that this fresh sulphur concrete follows the progression of the solidification front, so the granulates of the freshly additional sulphur concrete are prevented from migrating outside through the already formed solidification front by the centrifugal force, so an undesired concentration of granulates on the outside of the formed pipe is prevented as well as a concentration of solidified sulphur on the inside of the hardened pipe.

Account must be taken of a well-balanced grain construction of the fine and coarse granulates in the sulphur concrete to avoid separation during the rotation of the mould, otherwise the risk exists that a concentration of solidified sulphur and fine filler substances will form mainly on the inside of the hardened product.

The coarse stone carcass sets very quickly after the formation of the required wall thickness. With correct dosage, the liquid sulphur and the fine granulates in the liquid sulphur concrete can still move radially from outside to inside in the direction of the cooling and solidification front.

The already formed solidification front prevents the heavier granulates from moving more towards the outside of the mould due to the centrifugal force during the further course of rotation. As a result, an undesired concentration of granulates on the outside of the element is prevented. An important advantage of the method is that such a product manufactured from sulphur concrete is resistant to acids, being a significant advantage in many applications such as sewer pipes or suchlike. The drum of the mould is preferably applied rotatably around a horizontal rotary axis, so an even dispersion of the liquid sulphur concrete is obtained over the axial length of the length of the drum.

The mould is preferably made of a heat-conducting material such as steel to assist heat transfer during the heating and cooling of the mould and the sulphur concrete present therein .

The method is highly suitable for forming sewer pipes or cross beams for rail applications, whereby in the latter case the mould can be provided to form a number of cross beams in the same mould at the same time.

The invention also relates to a device for the manufacture of pipes according to the method of the invention, whereby the device is made up of a mould with a drum; drive means to be able to rotate the drum around its axis; a reservoir for the mixing of a composition of sulphur concrete with sulphur or a sulphur compound and fine and coarse granulates; means to be able to heat the sulphur concrete to a temperature above the melting temperature of the sulphur or sulphur compound; means to be able to gradually add the heated sulphur concrete during the rotation of the mould to the mould; means to be able to heat the rotating mould to a temperature that is higher than the solidification temperature of the sulphur or sulphur compound; means to be able to cool the rotating mould from outside and means to keep the inside space of the mould at a temperature that is higher than the solidi ication temperature of the sulphur or sulphur compound.

With the intention of better showing the characteristics of the invention, a preferred embodiment of the method according to the invention is described hereinafter, by way of an example without any limiting nature, with reference to the accompanying drawings, wherein: figure 1 shows a longitudinal section of a product in the form of a pipe that is manufactured according to a method according to the invention;

figure 2 shows a cross-section according to line II-II in figure 1;

figure 3 schematically shows a cross-section device according to the invention for the manufacture of a pipe as in figure 1;

figure 4 shows a cross-section according to line IV-IV in figure

figures 5 to 7 are an illustration of the steps of the method according to the invention;

figure 8 shows a cross-section of a device according to the invention for the manufacture of cross beams; figure 9 shows a cross-section according to line IX—IX in figure 8; Figure 1 shows an example of a product 1 in the form of a sewer pipe 1 in sulphur concrete manufactured according to a method of the invention. The product 1 has an outer surface 2 and an inner surface 3 and two ends, being a female end 4 and a male end 5 respectively, such that a multiple of products 1 fit in each other with these ends 4 and 5 with a seal to be able to construct sewers.

The product 1 is in this case mainly cylindrical and has an outside diameter D of for example 250 to 400 mm and a thickness d of for example 40 to 55 mm. Use can be made of a device 6 as shown in figures 3 to 7 for the manufacture of these products 1.

This device 6 comprises: - a ventilation chamber 7 with fans 8 to be able to blow through ambient air or cooled air;

- a mould 9 fitted in the ventilation chamber 7 in the form of a smooth drum 10 made of steel or another heat- conducting rigid material of which the form of the inside 11 mainly has the negative form of the outside 2 of the product 1 to be formed, so an inside diameter D corresponding to the outside diameter D of the pipe 1 to be formed;

- drive means 12 to be able to rotate the drum 10 around its horizontal X-X' axis, whereby the drive means 12 in this case are formed by rollers 13 that are rotatably bearing-mounted in a frame 14 and on which the drum rests, whereby the rollers 13 are mechanically connected to a drive motor 15;

- covers 16 and 17 to be able to at least partly close off the open ends of the drum 10 and that also partly determine the form of the mould for the short ends 4 and 5 to be formed of the product 1 to form in the form of a pipe;

- means 18 to heat the drum 10 by means of heating appliances 19, for example in the form of radiators, blowers of hot air or suchlike mounted on the outer circumference of the drum 10 or at least along a part of this circumference;

- a reservoir 20 for a mixture of sulphur, sand and granulates;

- means 22 to be able to heat the mixture in the reservoir 20 to a temperature above the melting temperature of sulphur to create a liquid sulphur concrete 21;

- means 23 to be able to gradually add the heated liquid sulphur concrete 21 from the reservoir 20 to the mould

9, whereby the means in this case are formed by a supply pipe 24 that leaves the reservoir 20 and that arrives with a certain length centrally in the mould 9 and that is provided with outlets 25 for the sulphur concrete 21, and whereby the means 23 also have a screw 26 that extends through the supply pipe and that can be driven rotationally by means of a motor 27.

The method according to the invention uses the device 6 as explained below based on figures 5 to 7. The liquid sulphur concrete 21 in the reservoir 20 is kept at a temperature whereby the sulphur is in the molten state in the sulphur concrete, so the mixture of sand, granulates and sulphur and any other components is liquid.

Starting with an empty mould 9 as shown in figures 3 and 4 the drum 10 of the mould 9 is driven rotationally around its axis X-X' and the drum 10 is simultaneously heated by means of heating appliances 19 to a temperature above the melting temperature of sulphur.

When the temperature of the drum 10 is sufficiently high, the screw 26 is driven to gradually transport the liquid sulphur concrete 21 from the reservoir 20 to inside the mould 9.

The centrifugal force evenly disperses the liquid sulphur concrete 21 over the inside 11 of the drum 10 to form a first liquid layer 28 as shown in figure 5.

When the liquid layer 28 has a certain thickness A or has reached the maximum thickness, the heating appliances 19 are switched off and the fans 8 are started, as shown in figures 6 and 7, to allow cool ambient air to flow along the drum 10 through the ventilation chamber 7 to cool the drum 10.

The abovementioned thickness A can correspond to a situation in which the whole quantity of sulphur concrete 21 needed to form the product 1 is not yet used, but the thickness can also be reached when this whole required quantity is supplied.

The liquid layer 28 will as a result start to cool from the inside of the drum 10 so a cylindrical solidification front will also be formed between the already solidified sulphur concrete 21 on the outside and the still liquid sulphur concrete on the inside, whereby this solidification front moves in the radial direction and gradually assists the further cooling of the drum 10 and the layer 28 of sulphur concrete 21 therein.

If the final required quantity of sulphur concrete 21 has not yet been reached, fresh liquid sulphur concrete 21 is supplied on top of the layer 28 in the mould 9, while the mould 9 is still rotationally driven and the fans 8 continue to blow cool air over the drum 10.

In this case the granulates arrive on an already hardened or partly hardened layer of sulphur concrete so they cannot migrate to the outside and stay in place, while on the one hand fresh liquid sulphur concrete is added from inside and on the outside the solidification front 29 moves further inwards, whereby cavities with the tendency to originate along the solidification front are immediately filled by the centrifugal force on the rotating sulphur concrete 21 with liquid sulphur concrete 21.

The supply of liquid sulphur concrete 21 from the reservoir 20 is for example stopped when a measured quantity of sulphur concrete 21 is poured into the mould to after solidification obtain a product 1 with the required thickness d.

After the cast product 1 has sufficiently cooled and hardened, it can be removed from the mould and stored for delivery.

The device 6 preferably has means to retain, during the pouring of the liquid sulphur concrete 21, a temperature in the empty inside space 30 of the mould 9 that is higher than the melting temperature of sulphur.

These means can for example consist of active heating or can also be formed by passive means such as covers 16 and 17 that ensure that during the addition of the fresh liquid sulphur concrete 21 in the inside space 30 the heat in this inside space 30 cannot escape along the open ends of the drum 10 to keep the liquid sulphur concrete 21 inwards of the already solidified sulphur concrete 21 liquid and to prevent a second solidification front from originating that moves from inside to outside, in other words in the opposite direction of the centrifugal force, whereby any contraction cavities at this second solidification front would not automatically be filled and remain as cavities in the cast pipe 1.

In this way; with the method and the device according to the invention, pipes are made of sulphur concrete without inclusions or cavities and this despite the inherent heterogeneous composition of the sulphur concrete started with, and with a uniform distribution of the constituent heavier and lighter parts of the sulphur concrete.

Figures 8 and 9 show a variant of two side by side devices according to the invention that in this case are each intended to simultaneously manufacture a number of cross beams as these are known in the railway world as a support for the track rails.

In this case the mould 9 is a drum 10 that is made up of a series of constituent moulds 9' applied in the peripheral direction of the drum 10 side by side, whereby the constituent moulds 9' have the negative form of the cross beams to be formed and whereby these constituent moulds 9' are oriented with their longitudinal direction Y-Y' parallel to the rotary axis X-X' and with their pouring opening 31 radially inwards and with their bottom 32 radially outwards.

At the short ends of the drum 10 in this case further means 33 are provided to be able to insert the reinforcement bars in the constituent moulds 9' that are not shown in the figures and that are kept stressed during casting.

Otherwise the method is identical to that described above for the manufacture of a pipe. In this case the centrifugal force will evenly spread liquid sulphur concrete 21 with the turning of the drum 9 to gradually fill the constituent moulds 9' . It is clear that the invention is not limited to sewer pipes or cross beams, but it can equally be used for other supporting or non-supporting products whereby, depending on the required application, the possibility exists prior to the pouring of the sulphur concrete to apply reinforcement in the mould that, for example, can be held between the covers 16 and 17 during casting.

The present invention is by no means limited to the embodiment as described as an example and shown in the drawings, but such a method and device according to the invention can be realized in all kinds of variants, without departing from the scope of the invention.