GB2024051A - Coating the interior walls of pipes - Google Patents

Abstract

Apparatus for coating the interior walls of pipes with a material which comprises two or more constituents to be mixed in correct proportions within the pipe to be coated, the constituents being fed to a mixing and distributing device within the pipe to be coated by respective positive displacement pumps, is modified in that the operation of said two pumps is controlled by pre-set adjustment elements usable selectively according to the diameter of pipe to be coated and the thickness of coating required. The adjustment elements take the form of screws 86 mounted on indexable heads 76, 77, the selected screw abutting the ends of piston rods 56, 57 so as to cause reversal of the pneumatic rams 54, 55 upon actuation of switches 62, 63 associated with changeover valves. <IMAGE>

Description

SPECIFICATION Apparatus for coating the interior walls of pipes The invention relates to apparatus for coating the interior walls of pipes with liquid cold setting resin materials mixed with a liquid curing agent or initiator.

By the coating of underground pipes, for example by a suitable plastics coating medium, such pipes can be proofed against leakage and can also be protected against deterioration, or against further deterioration (and in this connection it may be mentioned that an existing pipe may first require to be scoured free of rust of other deposits before the coating is applied). However, the invention is not only applicable to the coating of pipes underground but may be used for coating pipes at or above ground level.

Various kinds of cold setting resin materials have been used for coating the interior walls of pipes, notably the epoxy cold setting resins and the polyester cold setting resins but one disadvantage of using these materials is that the proportions in which they must be mixed with a liquid curing agent or initiator is critical. This is particularly so when using an epoxy cold setting resin where the proportion in which it is mixed with a curing agent or initiator must be maintained preferably within 1% and certainly with 5% of the correct proportion.The proportions are not easy to control since the epoxy resin and curing agent cannot be mixed in for example a tank for subsequent application in the correct proportions to the interior walls of pipes because, if it was passed through a single delivery tube to the member which applies it to the pipe wall, premature curing or setting would occur and any resin still remaining in the tube after the process had been completed would also set. It has therefore been proposed to deliver the resin and curing agent or initiator through separate delivery pipes to a member within the pipe to be coated, the materials being intimately mixed together within said member and then applied to the interior wall of said pipe.It is also necessary to be able to vary the quantity of material flowing through the two delivery pipes, whilst still maintaining the proper quantitative relation between the two, so that the thickness of the applied coating can be varied and so that an appropriate adjustment can be made when a different size of pipe is to be coated.

It has previously been proposed to use a pumping device for feeding the cold setting resin material and the curing agent or initiator to respective delivery pipes in the required proportions, said pumping device including two positive displacement pumps for the respective liquids, the swept volume of the two pumps being in the same proportions as the proportions in which the liquids are required to be mixed, means being provided for driving the pumps at the same rate. However, it has been found that this is not a satisfactory solution to the problem when the materials concerned are highly viscous, thixotropic substances.This is thought to result from the fact that such substances do not flow readily into the pressure chambers of the pumps concerned so that pumping in the theoretical proportions, that is to say in the proportions according to the swept volumes of the respective pumps, is not possible. Even if, by trial and experiment, it has been found possible to pump the separate substances to a particular size of pipe to be coated in the required proportions, the pumping of the same two substances to a pipe of twice that diameter has not simply involved the doubling of the pump strokes as one would imagine. On the contrary it has been found that this has resulted in the separate substances being wrongly proportioned and this again is thought to result largely from the flow characteristics of the substances concerned.A further complication is that the resin material has a different temperature/viscosity gradient to that of the curing agent or initiator so that variations in the ambient temperature as the coating process has taken place has resulted in wide variations in the proportions of the liquids being fed to the delivery pipes.

According to the invention, there is provided apparatus for use in coating the interior walls of pipes, the apparatus including a rotatable drum upon which at least two flexible pipes are to be coiled to traverse said two pipes through a pipe the interior walls of which are to be coated, a first pump for feeding a liquid or plastics coating medium through one of said two flexible pipes and a second pump for feeding a liquid curing agent or initiator through the other of said two flexible pipes, a distributing device connected to the ends of said two flexible pipes for mixing together the liquid or plastics coating medium and the liquid curing agent or initiator and for distributing the mixed substance upon the walls of the pipe to be coated, and respective control means for controlling the operation of the two pumps, and thus for controlling the delivery of the coating medium and of the liquid curing agent or initiator, directly in accordance with the rate at which the flexible pipes are traversed through the pipe to be coated, whereby variations in the rate of rotation of the drum, and thus in the rate of traverse of said flexible pipes, are simultaneously matched by appropriate variations in the rate of delivery of the mixed substance to the walls of the pipe to be coated so that the coating is of substantially uniform thickness, the control means each including a plurality of pre-set adjustment elements usable selectively according to the diameter of pipe to be coated and the thickness of coating required.The respective control means for controlling the operation of the two pumps will preferably be coupled together for simultaneous selection of the pre-set adjustment elements whereby in preparing the apparatus for the coating of a particular diameter of pipe the proportions in which the coating medium and the liquid curing agent or initiator are mixed together in the distributor device are accurately maintained.The respective control means for controlling the operation of the two pumps may be constituted by respective indexable heads each of which carries a plurality of screws, constituting the pre-set adjustment elements, capable of being brought into line with an extension of an associated ram piston rod so as to reverse the associated ram piston when the abutment of the extension of said associated ram piston rod against the selected screw operates a valve or switch. The indexable heads may be geared together or connected together for simultaneous rotation by means of an endless chain.

A further flexible pipe may be coiled upon the rotatable drum and connected to the distributing device for the purpose of conveying air under pressure to a compressed air motor forming part of said device, the compressed air motor being drivably connected to means, also forming part of said device, for intimately mixing together the liquid or plastics coating medium and the liquid curing agent or initiator and for distributing the mixed substance upon the interior walls of the pipe to be coated. Drive means will preferably be provided for rotating the drum at a substantially constant speed to draw the flexible pipes, and with them the distributing device, along the pipe to be coated.The control means for con4rslling the operation of the two pumps will preferably include respective change-over valves for reversing the pneumatic rams at opposite ends of their working strokes said change-over valves being operated by respective switches actuated when the ram pistons reach predetermined positions in their travel in one direction and by a further switch associated with the drive means to be actuated in timed relation to the rotation of the drum, whereby there is a period of dwell between successive ram strokes, any speeding up or slowing down of the pumping strokes due to temperature variations taking place during a coating operation being automatically compensated for by variations in the periods of dwell between successive ram strokes. The apparatus may include means for heating the coating medium and the liquid curing agent or initiator.

In order that the invention may be fully understod and readily carried into effect, a preferred embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a diagrammatic view of a part of apparatus embodying the invention, coupled to a spraying or distributing device shown to be disposed within an underground pipe, Figure 2 is a partly schematic perspective view of the part of the apparatus illustrated in Fig. 1, Figure 3 is a perspective view of another part of the apparatus, Figure 4 is a detail view of a part of the apparatus which will presently be referred to, and Figure 5 is a diagrammatic view illustrating a pneumatic circuit which will presently be referred to.

Referring now to the drawings, apparatus for use in coating the internal walls of pipes by the method referred to includes a drum 10 mounted for rotation about a horizontal axis in a stand 1 2 including a pair of opposed mounting brackets 14. The stand is mounted on wheels 1 6 so that it may readily be moved from place to place.

Flexible pipes 1 8 and 1 9 are coiled upon the drum 10, and are provided for the purpose of conveying, respectively, a liquid or plastics coating medium and a liquid curing agent or initiator to a spraying or distributing device 20 being traversed along an underground pipe 22 by a pull applied to said flexible pipes. The ends of said flexible pipes remote from the spraying or distributing device are connected to a shaft 24 at the axis of the drum, the connection being shown diagrammatically in Fig. 2.The liquid or plastics coating medium, and the liquid curing agent or initiator, are conveyed to the respective pipes 1 8 and 1 9 along passageways extending through the shaft 24, connectors 26 and 1 7 being provided at one end of said shaft for the connection thereto of non-rotatable conduits 28 and 29 for conveying the coating medium under pressure from respective pumps (not shown) housed in pump units generally indicated 30 and 31.

A further flexible pipe 32 is also coiled upon the drum 10 and is provided for the purpose of conveying air under pressure to a compressed air motor (not shown) forming part of the device 20, the latter being a device for intimately mixing together the liquid or plastics coating medium and the liquid curing agent or initiator and for distributing the mixed substance upon the wall of the pipe 22. (The device 20 which is illustrated in Fig.

1 is shown to include a plurality of flails 34 which are driven by the compressed air motor so as to make repeated impacts or rapid wiping actions upon the coated wall of the pipe 22 in the wake of a distributing member 36 also driven by the compressed air motor).

The end of the pipe 32 remote from the spraying or distributing device is also con nected to the shaft 24 and air under pressure is delivered thereto along the axis of the shaft from the end remote from the connectors 26 and 27. A connector (not shown) is provided for the connection of a non-rotatable conduit 38 to the shaft 24, said conduit communicating with a source of compressed air.

Means are provided for rotating the drum 10 at a substantially constant speed to draw the pipes 18, 19 and 32, and with them the spraying or distributing device 20, along the pipe 22. Said means include a compressed air motor 40, a reduction gear unit 42 and respective chain drives 44 and 46 between the motor and gear unit and between the gear unit and the drum.

The pump units generally indicated 30 and 31 are disposed side by side and include respective reservoirs 48 and 49 for the liquid or plastics coating medium and for the liquid curing agent or initiator. They are mounted on wheels 50 so that they can readily be moved from place to place. Respective covers 52 and 53 on the respective reservoirs are removable to disclose filling orfices.

Respective pneumatic rams 54 and 55 are mounted vertically on the reservoirs 48 and 49 and respective piston rods 56 and 57 extend from said rams into the reservoirs and are connected to piston pumps (not shown) within the reservoirs. (The rams and certain other items of the apparatus are shielded from view by a cover 58 but the latter is shown in ghosted outline for clarity).

Respective spool-type change-over valves 60 and 61 are mounted on the sides of the pneumatic rams for reversing the latter, and each valve is operated by switches which open at the appropriate times to subject one end or the other of the spool of the valve to a pressure of compressed air. As shown in Fig.

4, respective switches 62 and 63 are located above the rams 54 and 55 and are actuated, when the ram piston concerned (not shown) reaches a predetermined position in its upward travel, to put an air line 64 in communication with one end of the respective spool valve by way of an air line 66 or 67 as the case may be. (Means are provided and will presently be described for varying the limit of upward travel of each ram piston). A further switch 68 is located on the side of the reduction gear unit 42 and is actuated, by a member (not shown) built into said gear unit and rotatable at a much reduced speed relative to the speed of rotation of the compressed air motor 40, but of course at a speed directly proportional to the speed of rotation of the drum 10, to put an air line 70 briefly into communication with the other end of each change-over valve by way of an air line 72.An air line 74 is connected to each change-over valve to feed compressed air to one end or the other end of the double acting ram concerned depending upon the setting of the change-over valve.

The means provided for varying the limit of upward travel of each ram piston include respective indexable heads generally indicated 76 and 77 which are rotatably mounted about vertical axes above the rams 54 and 55. Each indexable head can be adjusted, as indicated by the arrows in Fig. 3, into any one of six positions, but a length of endless chain 100 encircles respective chain wheel portions of the indexable heads so that they are adjustable together.

Referring more particularly to Fig. 4, the indexable heads are provided with respective pairs of discs 78 and 80 spaced apart upon respective rotatable shafts 82. The discs 78 are each provided with six holes 84 equally spaced apart on a common pitch circle diameter whilst the associated discs 80 each carry six screws 86 in line with said holes. The arrangement is such that on upward strokes of the rams the piston rods 56 and 57 can pass through respective holes 84 in the discs 78 and abut against the lower ends of whichever screws 86 have been positioned in line with said rods. The indexable heads are axially movable to cause the discs 80 to act against the switches 62 and 63. The screws 86 are adjusted to project from the discs 80 by varying distances and locking means (not shown) are provided to secure them in their axially adjusted positions.Indexing means (not shown) are provided so that the heads can be rotated and a particular one of the screws 86 of each head brought quickly into operative position.

The pressure of compressed air which actuates the pneumatic rams is such that a period of dwell is rquired between each working stroke of each ram to limit the delivery of coating medium to the flexible pipe 1 8 and of the liquid curing agent or initiator to the flexible pipe 1 9 to what is required, having regard to the rate of travel of the spraying or distributing device through the pipe 22, the diameter of the pipe being coated and the thickness of coating required.The diameter of the pipe being known, and the thickness of coating required also being known, the quantity of coating medium required and the quantity of the liquid curing agent or initiator required per unit length of pipe being coated are constants and can in fact be determined solely by the selection of appropriate screws 86 of the indexable heads to act as the stops controlling the lengths of stroke of the respective pneumtic rams (because it will be understood that the number of working strokes of each pneumatic ram per unit length of pipe being coated is a constant by virtue of the fact that the switch 68 is actuated at a frequency of time directly proportional to the rate of rotation of the drum, and the drum is of such a diameter that the build up of coils of pipe upon it throughout a coating operation does not effect that rate of travel of the device 20 along the pipe being coated to any significant extend). The screws are therefore each adjusted according to the delivery of coating medium and of the liquid curing agent or initiator required for a particular pipe diameter, and the screws are numbered as shown in Fig. 4 according to the diameters of pipes for which they are intended to be used. The period of dwell in each case is of course after the ram piston concerned has reached the limit of its downward travel and before the switch 68 is again actuated to trigger a further working stroke of each piston.The pistons commence their working strokes in unison but of course take different periods of time to complete their strokes by virtue of the different viscosities of the materials being pumped. It will be understood therefore that changes in viscosity of the coating medium and of the liquid curing agent or initiator as work proceeds (brought about for example by changes in atmospheric temperature) can only affect to a very limited extent the quantities of the substances being fed through the flexible pipes per unit length of distance traversed by the spraying or distributing device since any slowing down in the operative pumping speed of the ram piston caused by increasing viscosity is immediately compensated for by a corresponding decrease in the subsequent period of dwell.A speeding up in the operative pumping speeds of the ram pistons is of course immediately compensated for by a corresponding increase in the periods of dwell.

Similarly, variations in the rate at which the device 20 is traversed through the pipe to be coated, provided it is traversed at a reasonably steady rate, cannot affect the thickness of the applied coating medium since, provided there is a period of dwell between successive reciprocations of the ram pistons, the length of stroke of each ram piston is fixed and the number of pumping strokes per minute is directly proportional to the rate of traverse of the device 20 through the pipe to be coated.

The present invention renders it unnecessary for a responsible person to remain in attendance throughout a coating operation and in fact once the apparatus is correctly adjusted it can be left in the charge of unskilled workers since, as previously explained, further adjustments as a resulty of changing viscosity of the coating medium are unnecessay and the precise rate at which the flexible pipe is traversed is not critical (although in fact the workman operating the apparatus will be instructed to commence a coating operation with the compressed air motor running at a certain nominal speed and said motor is provided with a tachometer for this purpose).

It has been found that by the use of apparatus embodying the invention the coating of pipes with material such as referred to has been greatly facilitated. It is now possible to formulate the material exactly as required, for example according to the condition of the pipe which is to be coated and according to the nature of the liquid, substance or gas, as the case may be, which the coated pipe is to convey. The apparatus can then be adjusted to suit the resultant formulation, i.e. to suit the viscosity of the formulated substances and the required proportions in which the coating medium is to be mixed with the liquid curing agent or initiator, for use in any one of several different diameters of pipe and/or for the application of different thicknesses of applied coating.That is to say for example, the illustrated apparatus can be adjusted for use in coating any one of six diameters of pipe, each pipe diameter being coated to a particular thickness. Alternatively, for example, the apparatus could be adjusted for use in coating any one of three diameters of pipe, each pipe diameter being capable of being coated with alternative thicknesses of coating. The indexable heads are shown in Fig. 4 to be marked with an indication of the pipe diameters for which the screws 86 have been adjusted.

These markings can be observed through respective apertures (not shown) in the cover 58. (It will be understood that in checking the proportions of the substances delivered at any particular setting this can be done either by measuring the volume or weight of the substances simultaneously flowing into separate receptacles from the delivery ends of the flexible pipes in the same short period of time).

However, it will be understood that the adjustments referred to above only hold good at a particular ambient temperature because as previously mentioned the resinous coating medium always has a different temperature/ viscosity gradient to that of the curing agent or initiator. Temperature variations along the flexible pipes matter very little because once the materials are in the pump chambers there is ample power to force them along the flexible pipes and any very slight speeding up or slowing down of the pumping strokes is taken care of by variations in the periods of dwell as previously explained. On the other hand, the flow of the materials into the pump chambers can be seriously affected by any substantial change of ambient temperature and can consequently upset the proportions in which they are delivered to the flexible pipes. Consequently, as illustrated in Fig. 5, in a modification of the apparatus described above, the reservoirs 48 and 49 are provided with an electrical heating element 102 to being the temperature of the coating medium and of the liquid curing agent or initiator to a temperature slightly greater than normal ambient temperatures. The electric current is supplied by a generator 104 driven by a compressed air driven motor 106. The motor is supplied with air under pressure, from a source not shown, by way of an air line 108. A further air line 110 from which the other supplies of air are taken, that is to say in the air lines 64, 70 and 74, is adapted to be closed by a solenoid operated valve 11 2 under the control of a heat sensor 11 4 which monitors the temperatures of the coating medium and liquid curing agent or initiator.The arrangement is such that the apparatus cannot be used to coat the walls of a pipe until the materials in the reservoirs have been raised to the required temperature (at which the apparatus has previously been adjusted). In this way the apparatus can be left in the hands of unskilled workers in the knowledge that they cannot commence a coating operation before the materials have been brought to substantially the required working temperatures. In this way, not only will the apparatus commence working with the materials at the viscosities which they had when the apparatus was adjusted, but the effects of changes in ambient temperatures will be minimised if not entirely eleiminated.The only adjustments which the unskilled workers can make are the simultaneous adjustments of the indexable heads to suit the size of the pipe which is to be coated and/or the thickness of the required coating if this is one of the indexable variables.

Various other modifications may be made without departing from the scope of the invention. For example, the change-over valves 60 and 61 could be solenoid operated in which the case the switches 62, 63 and 68 would be electric switches. The switch 68 could of course be associated with any other moving part rotating at a speed proportional to the rate at which the flexible pipes are traversed through a pipe to be coated, provided of course that it can be caused to trigger a convenient number of reciprocations of each pump per unit distance of pipe traversed by the device 20 (which can be determined by trial and experiment but which a skilled person will be able to decide upon, possibly by pure calculation, without the need for experiment). The compressed air motor could if desired be replaced by an electric motor. The drum 10 and the pump units 30 and 31 could be, and indeed preferably will be, mounted on a common wheeled frame. The indexable heads could be geared together instead of being connected together by a length of endless chain. In this case the screws 86 would still be adjusted in pairs but of course, by virtue of the contra-rotation of the heads, would be arranged oppositely one set to the other.

Claims (9)

1. Apparatus for use in coating the interior walls of pipes, the apparatus including a rotatable drum upon which at least two flexible pipes are to be coiled to traverse said two pipes through a pipe the interior walls of which are to be coated, a first pump for feeding a liquid or plastics coating medium through one of said two flexible pipes and a second pump for feeding a liquid curing agent or initiator through the other of said two flexible pipes, a distributing device connected to the ends of said two flexible pipes for mixing together the liquid or plastics coating medium and the liquid curing agent or initiator and for distributing the mixed substance upon the walls of the pipe to be coated, and respective control means for controlling the operation of the two pumps, and thus for controlling the delivery of the coating medium and of the liquid curing agent or initiator, directly in accordance with the rate at which the flexible pipes are traversed through the pipe to be coated, whereby variations in the rate of rotation of the drum, and thus in the rate of traverse of said flexible pipes, are simultaneously matched by appropriate variations in the rate of delivery of the mixed substance to the walls of the pipe to be coated so that the coating is of substantially uniform thickness, the control means each including a plurality of pre-set adjustment elements usable selectively according to the diameter of the pipe to be coated and the thickness of coating required.

2. Apparatus according to claim 1, in which the respective control means for controlling the operation of the two pumps are coupled together for simultaneous selection of the pre-set adjustment elements whereby in preparing the apparatus for the coating of a particular diameter of pipe the proportions in which the coating medium and the liquid curing agent or initiator are mixed together in the distributor device are accurately maintained.

3. Apparatus according to either one of the preceding claims, in which the respective control means for controlling the operation of the two pumps are constituted by respective indexable heads each of which carries a plurality of screws, constituting the pre-set adjustment elements, capable of being brought into line with an extension of an associated ram piston rod so as to reverse the associated ram piston when the abutment of the extension of said associated ram piston rod against the selected screw operates a valve or switch.

4. Apparatus according to claim 3, in which the indexable heads are geared together or are connected together for simultaneous rotation by means of an endless chain.

5. Apparatus according to any one of the preceding claims, in which a further flexible pipe is coiled upon the rotatable drum and is connected to the distributing device for the purpose of conveying air under pressure to a compressed air motor forming part of said device, the compressed air motor being drivably connected to means also forming part of said device, for intimately mixing together the liquid or plastics coating medium and the liquid curing agent or initiator and for distributing the mixed substance upon the interior walls of the pipe to be coated.

6. Apparatus according to any one of the preceding claims, in which drive means are provided for rotating the drum at a substantially constant speed to draw the flexible pipes, and with them the distributing device, along the pipe to be coated.

7. Apparatus according to any one of the preceding claims, in which the control means for controlling the operation of the two pumps include respective change-over valves for reversing the pneumatic rams at opposite ends of the working strokes and operated by respective switches actuated when the ram pistons reach predetermined positions in their travel in one direction and by a further switch associated with the drive means to be actuated in timed relation to the rotation of the drum, whereby there is a period of dwell between successive ram strokes, any speeding up or slowing down of the pumping strokes due to temperature variations taking place during a coating operation being automatically compensated for by variations in the periods of dwell between successive ram strokes.

8. Apparatus according to any one of the preceding claims, including means for heating the coating medium and the liquid curing agent or initiator.

9. Apparatus for use in coating the interior walls of pipes, the apparatus being arranged and adapted to be used substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.