PROCEDURE AND EQUIPMENT FOR APPLYING A PLASTIC

LAYER ON THE INTERNAL SURFACE OF CLOSED-SECTION

PREFABRICATED CONCRETE UNITS, ESPECIALLY PIPES

The invention relates to a procedure for applying a plastic layer on the internal surface of prefabricated closed-section concrete or reinforced concrete units, especially pipes. The invention also relates to equipment for the realisation of the procedure.

In the field of hydraulic engineering, especially in sewerage systems, a large amount of prefabricated reinforced concrete pipes and also pipes made of plastic or steel are used for pipeline construction. One of the most important advantages of reinforced concrete pipes, especially in the case of gravitation and low- pressure pipelines constructed from such pipes, is that their static stability can be ensured practically under any construction circumstances, and the necessary and sufficient static - load- bearing - requirements with respect to these pipes can be fulfilled accurately and completely. While pipelines constructed from reinforced concrete pipes are put down as rigid structures below the ground surface, pipelines made of plastic pipes, due to their high elasticity, can be made to comply with stability requirements by exploiting active lateral earth pressure, which requires an extremely precise pipe-laying technology. The advantage of plastic pipelines, especially the ones constructed from fibreglass reinforced polyester pipes, is that their resistance to corrosion and abrasion and their hydraulic characteristics are extremely good, at the same time their disadvantage is that they are rather expensive. Such characteristics of reinforced concrete pipes and other products are less favourable than the same characteristics of

plastic structures, but their price is more favourable, as a result of which reinforced concrete pipes are widely used.

As a result of this the improvement of the above characteristics of reinforced concrete and concrete pipes, especially their resistance to abrasion and corrosion, is gaining increasing experience.

Different forms of plastic coating ("relining" technologies) have been used for a long time for the reconstruction of damaged or spoilt concrete or/ and reinforced concrete pipelines, for example by spraying different liquid plastic compositions or applying a foil cover on their surface, or even by making an independent plastic pipe out of plastic pipe units inside the existing pipelines, but often the efficiency of sprayed coatings produced using the presently known technologies - in the course of which spray nozzles moved inside a fixed pipe are used - is not satisfactory either from technical or economical aspects, composite action between the independent and rather thick plastic pipe with the already existing pipe cannot be regarded as solved, the static function is filled - at least mainly - by the plastic pipe, so the realisation of such pipeline reconstruction is generally extremely expensive.

In the case of concrete and reinforced concrete structures with a plastic coating it is often a problem - depending on the circumstances of use - that the thermal expansion coefficients of the two different types of materials are rather different, which makes their permanent joint construction even more difficult.

Consequently the task to be solved with the invention is to provide a solution for applying a plastic coating on the internal surface of closed- section prefabricated concrete or reinforced concrete units, especially pipes, which makes it possible to use a quick and economical production method on the one part and

- satisfactory — composite action, a solid and secure connection

between the surface of the prefabricated concrete and the applied plastic layer on the other part.

The invention is based on the recognition that if the spraying of the liquid artificial resin is performed while the prefabricated concrete or reinforced concrete pipe piece is rotated around its own longitudinal geometrical axis on the one part, and at the same time the spray nozzle is moved forwards and backwards inside the pipe along its longitudinal axis on the other part, the artificial resin can be applied at an optimal rate and in the planned width providing a layer of excellent quality. We also realised that a layer in excellent composite action with the concrete material can be produced from fibreglass-reinforced thermosetting artificial resin, especially fibreglass-reinforced polyester resin, if short spikes or/ and couplers made of metal, practically steel, concreted in the course of prefabrication protrude from the surface of the concrete material, which set into the cross-linked plastic layer anchoring it, as it were, to the concrete surface; or if - in a given case combined with such spikes-couplers - the internal surface of the pipe is roughened with sand granules spread on the concrete material and setting in it.

On the basis of the above recognition, in accordance with the invention the set task was solved using a procedure for applying a plastic layer on the internal surface of closed-section prefabricated concrete or reinforced concrete units, especially pipes, in the course of which fibreglass-reinforced thermosetting artificial resin is applied onto the internal surface by spraying it with a spray nozzle, which procedure is based on that bonding elements, especially couplers and/ or spikes and /or hooks made of metal are embedded in the internal surface of the prefabricated concrete or reinforced concrete unit in a protruding way, or/ and the internal

^sHT-face-is- roughened; "and then ^" firjfeglass-feinforced artificial resin

is sprayed on the surface while it is being rotated continuously around its own longitudinal geometrical axis and the spray nozzle is being moved inside the unit along a straight track.

A favourable realisation of the procedure is characterised by that the internal surface of the unit, especially pipe, is roughened in a way that in the last phase of prefabricating the unit its internal surface layer is pulped and sand, favourably washed, dried and screened silica sand with a grain diameter of 0.8-1.2 mm is spread on the surface of the pulped layer, in a given case the spread sand material is rolled into the pulped layer, and fibreglass- reinforced artificial resin is sprayed on the surface after the pulped layer has set. According to another method of realisation while applying the fibreglass-reinforced artificial resin the unit is rotate at such a speed that its centrifugal acceleration is 1.0-1.6 g; and the spray nozzle is moved along its straight track - forwards and backwards several times in a given case - at a speed of 0.4-2.0 m/sec. It may also be favourable, if a 2-3 mm wide fibreglass- reinforced artificial resin layer is applied onto the internal surface of the unit, where it is left to cross-link.

Another favourable realisation method of the procedure is characterised by that the layer is made from basalt fibre, carbon fibre, aramid fibre, kevlar fibre, glass fibre or a combination of two or more of the above fibres and from vinylester or epoxy or furan or bakelite or melamine or polyester water based polyurethane resin. It may also be favourable, if the layer is made from fibreglass- reinforced polyester resin; and if the artificial resin components are sprayed from the spray nozzle with compressed air favourably at a pressure of 3.0-5.0 bar together with the fibre material cut into 10- 50 mm pieces using compressed air and - in a given case - sand, and in this way the mixture is sprayed on the internal surface of

:d^eon ^~ c ^' rete ^~ andTeirlforced ^" concrete unit.

The equipment for the realisation of the procedure has a spray nozzle suitable for spraying fibre-reinforced artificial resin; and this equipment is based on the idea that it has a rotary unit suitable for rotating the concrete or reinforced concrete unit, especially pipe, around its own longitudinal geometrical axis (X); and a motion structure suitable for moving the spray nozzle inside the unit, especially pipe, along a straight track practically parallel to its longitudinal geometrical central axis.

A favourable construction of the equipment is characterised by that the motion structure is formed for example by a car that can be driven forwards and backwards along a track and an element, especially a pipe-shaped casing, connecting the spray nozzle with the car. It may also be practical, if the components, especially artificial resin components connected to the spray nozzle and the technological pipes for feeding compressed air are placed inside the casing.

Below the invention is described in detail on the basis of the attached drawing containing a favourable construction of the equipment. In the drawings figure 1 shows the complete equipment in diagrammatic side view, partly in section; figure 2 shows the top view of a possible construction of the spray nozzle; figure 3 shows the side view of the spray nozzle as in figure 2.

As it can be seen in figure 1, the equipment has a car 2 that can be driven on wheels 2a forwards and backwards on a track 1, which car 2 is constructed in a way suitable for accommodating containers 3 for storing chemicals on the one part, and on the other part it has a spray device - situated on top according to the

^presenφ^exaτnple=^~exteή^ing ^{~^} foTward ^" s rnarKecT with reference

number 4 as a whole, at the end of which spray device 4 that is a combined spray nozzle 5 for spraying liquid artificial resin components. The spray device 4 itself consists of an external casing 4a and an internal bundle of technological pipes 4b - shown as a broken line in figure 1 -, which are connected to the spray nozzle 5. The h length of the spray device must exceed the H length of the prefabricated reinforced concrete pipe 6 to be provided with an internal plastic layer, but in theory it must be at least of the same length. The longitudinal geometrical central axis of the pipe 6 is marked with reference letter X in figure 1. The following pipes are placed in the casing 4: pipes for forwarding resin and catalytic agent, pipe forwarding compressed air needed for spraying resin, which pipes are connected to the combined pump unit (not shown here) and are also connected to the chemical containers 3. The combined spray nozzle 5 also contains a fibreglass-cutting unit, in a way already known in itself. Inside the casing 4 there are yarn guide ceramic rings to take fibreglass roving to the spray nozzle 5. There are separate compressed air pipes to support fibreglass- cutting, the yarn-cutting unit is suitable for cutting glass fibres of a length of 10-50 mm. The spray nozzle 5 may also be combined with a sand spraying unit, to which the compressed air is fed through a separate pipe, which is also situated in the casing 4. In figures 2 and 3 a spray nozzle 5 - known in itself - is shown in detail as an example, also showing its operation, which may be remote controlled. In figure 2 the technological pipes can be seen in top view: pipe 13 is for feeding resin mixed with accelerator, pipe 14 is for feeding catalytic agent, and pipe 15 is for feeding solvent (acetone) needed for washing the spray nozzle 5 after finishing spraying. Pipe 16 is for feeding compressed air needed for spraying and pipe 17 is for feeding compressed air needed for fibreglass

^euMtøg _f ^a^d^threPCompresse ^' d'air gefs into the yarn-cutting unit 18

through a branch-pipe 17. The cut and expelled yarns are marked with reference number 19, and the mixture flow is marked with reference number 20.

A plastic layer is applied on the internal surface of a prefabricated concrete or reinforced concrete pipe using the equipment as in figure 1 according to the following:

The prefabricated reinforced concrete pipe 6 the internal surface of which is to be provided with a plastic layer - which pipe 6 was made with ROCLA technology in a way that in the last phase the internal surface of the pipe was pulped and washed silica sand was spread on the pulped surface or/ and short spikes or couplers protruding inside the pipe wall were concreted in the course of prefabrication in an amount determined by planning with respect to a specific surface, e.g.: with a 100x100 mm raster - is heated to a temperature of about 70 ⁰ C, then it is placed on the rollers 8, 9 of the rotary unit 7 in a way that the opening of the pipe 6 faces the car 2; in this position the geometrical axis of rotation y_ of the rollers 8, 9, the longitudinal geometrical central axis x of the pipe 6 and the casing 4 are parallel to each other. By starting the drive motor 12 of the rotary unit 7 the rollers 8, 9 and the pipe 6 are rotated slowly and continuously as shown by arrow ω, and at the same time the spray nozzle 5 connected to the casing 4 is moved forwards and backwards with the car 2, in synchrony with driving the car 2 as shown by double arrow a _^ along a straight track inside the pipe 6 and along its full length H, while thermosetting artificial resin mixed with fibrous material and - in a given case - silica sand is sprayed on the internal surface of the pipe with the spray nozzle 5. The slow rotation of the pipe 6 and the slow moving of the spray nozzle, 5 forwards and backwards is continued until a fibre- reinforced artificial resin layer of the desired even thickness is

-ereated^on-the— internacTsufface of ^~ the pipe 6, which layer sets

perfectly along the spikes/ couplers or/ and the pipe surface roughened with sand spreading and is in composite action with it. The airtight seal and required smoothness of the external surface of the plastic layer is ensured by the slow rotation, which can be regulated with the drive motor 12 with a continuously adjustable revolution number in the same way as the speed at which the car 2 is driven forwards and backwards as shown by double arrow a.

Below the invention is described in detail on the basis of an example.

Example

A prefabricated reinforced concrete pipe with an internal diameter of 60 cm is made with "Rocla" technology known in itself, in the last phase of which the internal pipe surface is pulped, and washed, dried and screened silica sand with a grain diameter of 0.8-1.2 mm is spread on the surface of the pulped layer, and the spread sand layer is rolled into the pulped concrete material. As an alternative solution couplers made from 10.8-1.5 mm thick untreated steel wire with a 100 x 100 mm raster are built into the concrete material of the pipe in a way that they extend 1-2 mm from the surface.

After the reinforced concrete pipe has set, it is heated to a temperature of about 70 °C and it is placed on a rotary unit - as shown for example in figure 1 - and rotate it continuously along its longitudinal geometrical central axis. At the same time a spray nozzle, practically a spray gun, is started inside the pipe and moved slowly and continuously in a longitudinal direction, and with the spray nozzle fibreglass-reinforced polyester resin and - in a given case - sand is sprayed on the surface roughened with silica sand or provided with protruding coupler/ spikes as described above.

Spraying is performed with 4.5 bar compressed air in a way that polyester resin mixed with pre-mixed accelerator, such as CO- naphthenate or dimethyl-aniline is pumped into the spray nozzle through a pipe, and catalytic agent, favourably peroxide determined exactly for this mixture is fed to the same place through another pipe. Practically this operation is performed with a combined pump unit. The two components expelled from the spray nozzle are mixed with 4.5 bar compressed air blown here impregnating the cur fibreglass material fed here at the same time. With the yarn-cutting part-unit forming a part or accessory of the spray nozzle the fibreglass is cut up to 10-50 mm long pieces using compressed air - in a way already known in itself - led to the spray nozzle through a pipe separate from the pipe in which compressed air for spraying is carried. Apart from cut fibreglass the plastic layer to be formed may also contain sand, which - washed, dried and screened silica sand with a grain diameter of 0.8-1.2 mm -, together with the mixture of fibreglass and artificial resin is fed with compressed air carried here through a separate pipe and sprayed on the internal pipe surface. The fibreglass roving is taken to the yarn-cutting part unit with the help of fibreglass guiding ceramic rings.

The mixture impregnated glass fibres and artificial resin composition produced as above hits the pipe surface roughened with silica sand or containing coupler and sets on it.

The pipe is rotated and the spray nozzle is moved forwards and backwards inside the pipe, that is spraying is continued, until the desired 2-3 mm thick plastic layer is formed, the airtight seal, even, perfectly smooth surface of which is ensured by slow rotation. Both the speed of rotating the pipe and moving the spray nozzle along a straight track are continuously adjustable, as a

result of which the layer thickness can be ensured with high precision.

After the cross-linking - setting - of the artificial resin, which is also facilitated by heating the pipe to 70 ⁰ C as mentioned above, the procedure of applying a plastic layer on the internal surface of the prefabricated reinforced concrete pipe is concluded, and the product can be used as required.

The advantage of the invention is that with a simple and economical technology, using ordinary materials, in a plant, that is under clear, controlled circumstances a wear and abrasion resistant layer of a minimum thickness with excellent hydraulic characteristics can be formed on the internal surface of prefabricated concrete and reinforced concrete pipes, which is integrated with the material of the pipe and is in composite action with it. In this way a product is created having the positive characteristic features of the two types of material - (reinforced) concrete and plastic - in the most economical way possible, representing a service value higher than even before.

Obviously the invention is not restricted to the construction example described in detail above, or to the shown and described construction of the equipment, but it can be realised in several different ways within the scope of protection defined in the claims.