GB2301786A

GB2301786A - Applying two-part mixtures of materials

Info

Publication number: GB2301786A
Application number: GB9611630A
Authority: GB
Inventors: David Mark Needham
Original assignee: MERCOL PROD Ltd; NEEDHAM SPECIALISED MACHINES L
Current assignee: MERCOL PROD Ltd; NEEDHAM SPECIALISED MACHINES L
Priority date: 1995-06-07
Filing date: 1996-06-04
Publication date: 1996-12-18
Anticipated expiration: 2016-06-04
Also published as: GB2301786B; GB9511522D0; GB9611630D0

Abstract

Two materials, especially ones which react together, are applied by means of a spraying device 26. Each material is supplied from its own tank 48, 50 via a three-way valve 25, 26 to a mixer upstream of the sprayer. To avoid wastage when the spray-gun trigger is released, the valves 25, 26 are automatically switched to positions where each material is recirculated to its respective reservoir. The returned materials flow through back-pressure valves 47, 49 which may be adjusted so that the pressure drop in each fluid line is the same during recirculation as it is when spraying. This gives "steady-state" conditions throughout spraying.

Description

Apparatus for Applying Paint and the Like The invention relates to apparatus for applying paint and the like, in particular to apparatus for spraying two-part or multipart mixtures of materials, for example cold setting resin materials mixed with a liquid curing agent or initiator, where it is important to ensure that these are mixed in precisely the correct proportions.

Various designs of pumping apparatus have been proposed for pumping the separate components of such two-part mixtures in the required proportions through respective flexible pipes, the resin material and the curing agent or initiator generally being mixed together in a mixing device adjacent to or forming part of a distributing device, this possibly being at some considerable distance from the pumping apparatus. Consequently, it is a particular problem that, because the resin material and the curing agent or initiator have different viscosities, the proper proportions are very difficult to maintain.However, it has been found that when used on a continuous or semi-continuous basis, for example when coating the interior surfaces of long lengths of underground pipes, a steady state situation becomes established where temperatures and pumping pressures vary very little throughout the coating operation so that the proper proportions are more easily maintained.

To achieve such steady state conditions, it may be necessary to waste a quantity of the mixed material as the resin material and the curing agent or initiator are pumped through their respective pipes and through the mixing device and distributing device before a spray coating run is actually commenced. However, it will be understood that if a continuous or semi-continuous coating operation is to be carried out, the wasted quantity of mixed material as a percentage of the material to be used may be very small indeed, whereas if intermittent operation is to be carried out, such a quantity of waste before each relatively short coating operation would be totally unacceptable because it would represent the loss of a very much greater percentage of the material.Furthermore, if the apparatus is being used intermittently and the materials are therefore liable to cool down to some variable extent between periods of use, the problem of maintaining the proper proportions of the two-part coating mixture is exacerbated, this being due to a number of reasons; for example, the two components may tend to cool down at different rates so that the difference in their viscosities may vary to an indeterminate extent. Indeed, resin materials have a different temperature/viscosity gradient to that of the curing agent or initiator so that, particularly when using such two-part mixtures, changes of temperature as a coating operation proceeds can result in wide variations in the proportions of the two components of the coating material being pumped to the distributing device.The invention has for its object to provide apparatus in which these problems will be at least alleviated.

According to one aspect of the invention, there is provided a method of spray or otherwise coating, intermittently, using a two-part mixture of materials, the method including the steps of feeding by means of a first pump one of the materials from a first holding tank through a flexible pipe connected to a distributing device, feeding by means of a second pump the other of the materials from a second holding tank through another flexible pipe connected to said distributing device, controlling the operation of said first and second pumps so that the two materials are delivered to the distributing device in the required proportions, and, during periods when said distributing device is inoperative, re-circulating the two materials through respective return pipes back to their respective holding tanks so that steady state conditions tend to be maintained.The method may include the step of controlling the pressures in the respective return pipes whereby each pressure drop as the materials are returned to their holding tanks is substantially the same as the pressure drop occurring when the mixed materials issue from the distributing device.

According to another aspect of the invention, there is provided apparatus for use in spray or otherwise coating with two-part mixtures of materials, the apparatus including a first pump for feeding one of the materials from a first holding tank through a first flexible pipe and a second pump for feeding the other of the materials from a second holding tank through a second flexible pipe; a distributing device connected to the ends of the two flexible pipes for mixing together the two materials and for distributing the mixed substance over a work surface; control means for controlling the operation of the two pumps in step with each other and thus for controlling the delivery of the two materials to the distributing device in the required proportions; and respective return pipes for returning the two materials back to their respective holding tanks whenever the distributing device is inoperative, so that steady state conditions tend to be maintained throughout the operation of the apparatus. The return pipes may be provided with respective back pressure valves which will be adjustable to produce substantially the pressure drops which occur when the distributing device is operable.

In the drawings, which illustrate, by way of example only, a particular embodiment of the invention Figure 1 is a diagrammatic view of apparatus embodying the invention, Figure 2 is a partly schematic perspective view of a part of the apparatus, Figure 3 is schematic perspective view of another part of the apparatus, and Figure 4 is a hydraulic circuit diagram.

Referring now to Figure 1 of the drawings, the apparatus there illustrated has been built as a mobile unit, generally indicated 10, which is mounted on wheels 12 and provided with a drawbar 14.

At the rear of the unit is a rotatable drum 16 mounted for rotation about a horizontal axis between mounting brackets 18.

Flexible pipes 20,21 and 22,23 are coiled upon the drum 16, the pipes 20 and 22 being flow pipes provided for conveying, respectively, a liquid or plastics coating medium and a liquid curing agent or initiator through a mixing device 24 and then to a distributing device constituted by a spray gun 27. (The purpose of pipes 21 and 23 will be described presently). As shown in Figure 2, the ends of the flexible pipes 20,22 remote from the distributing device are connected to a shaft 28 at the axis of the drum, the connection being shown diagrammatically in the drawing.The liquid or plastics coating medium, and the liquid curing agent or initiator, are conveyed to the respective pipes 20 and 22 along passageways extending longitudinally part way through the shaft 28, connectors 30 and 32 being provided at one end of said shaft for the connection thereto of non-rotatable conduits 34 and 36 for conveying the coating medium and liquid curing agent or initiator under pressure from respective pumps 38 and 40 (see Figure 4). Meters 51 and 53 are provided at the output sides of the respective pumps.

Referring now in particular to Figure 4, the pumps 38 and 40 are driven by respective double acting hydraulic rams 39 and 41 which are fed with oil under pressure from respective hydraulic pumps 35 and 37. The pumps 38 and 40 draw the substances concerned from respective holding tanks 48 and 50 mounted back to back on the unit 10 (see Figures 1 and 2).

A power unit 52 (which can either be an internal combustion engine, as illustrated in Figure 1, or an electric motor) is provided for powering the apparatus, that is to say for driving the pumps 35 and 37 which provide oil under pressure for powering the respective hydraulic rams 39 and 41. In the hydraulic circuit illustrated in Figure 4 there are two main sub-circuits, generally indicated 56 and 58, in which the hydraulic rams 39 and 41 are respectively contained.As shown, the sub-circuits also include respective pressure relief valves 64 and 66, respective flow control valves 68 and 70, and respective spool valves 72 and 74 which are operable to reverse the flow of hydraulic fluid to the respective hydraulic rams 39 and 41. (Proximity switches, not shown, are provided to detect the arrival of the respective pistons of the hydraulic rams 39 and 41 at the ends of their strokes and to cause the reversal of their associated spool valves 72 and 74 so that the pumps 38 and 40 can operate continuously).

The rate of operation of each hydraulic ram 39 and 41 is dependent on the setting of the respective flow control valve, and the arrangement is such that, at the commencement of a spray coating operation, a particular head of pressure can be caused to act in the flexible pipe 20 conveying the liquid or plastics coating medium, this being the safe maximum pressure which the pipe can withstand, and the coating medium is therefore forced through the pipe at a rate which is dependent on the viscosity of the substance.Control means for controlling the delivery of the coating medium and of the liquid curing agent or initiator to the mixing device 24 in the required proportions are not illustrated but include means for counting the number of reciprocations of the respective meters 51 and 53, and a computer (not shown) to which this information is continuously fed, the computer being arranged to adjust the setting of the flow control valves 68 and 70 by means of respective actuators (not shown).

Referring now in particular to Figure 3, it will be seen that during operation of the apparatus, that is to say when the mixed substances are being sprayed from the spray gun, the liquid or plastics coating medium and the liquid curing agent or initiator flow through respective 3-way valves 25 and 26 located adjacent the mixing device 24. However, means are provided whereby, as the trigger of the spray gun is released, said 3-way valves are switched automatically so that the flow of coating medium and of the curing agent or initiator from the flexible pipes 20 and 22 is diverted, through the respective flexible pipes 21 and 23, back to the holding tanks 48 and 50 by way of respective manually adjustable back pressure valves 47 and 49.The flexible pipes 21 and 23, being return pipes for returning liquid or plastics coating medium and the liquid curing agent or initiator back to their respective holding tanks, are connected at their ends remote from the mixing device and spray gun to the shaft 28 at the axis of the drum 16 by means identical to those illustrated for connecting the pipes 20 and 22 thereto, that is to say by means of respective passageways (not shown) extending longitudinally of that part of the shaft not illustrated in Figure 2, and respective connectors (not shown) at that end of said shaft. Respective pairs of pressure gauges 76,78 and 80,82 are provided in the flow and return pipes for the coating medium and curing agent or initiator, that is to say at the mixing device end of each flow pipe and at the holding tank end of each return pipe.During the operation of the apparatus, the back pressure valves 47 and 49 can be manually adjusted from time to time to ensure that each pressure drop as the materials are returned to their holding tanks is substantially the same as the pressure drop occurring when the mixed materials issue from the spray gun. Thus it will be understood that, regardless of whether the apparatus is used in a continuous or intermittent manner, a steady state condition will tend to come about so that the proper proportions of the coating medium and curing agent or initiator will be maintained.Indeed, it will be understood that before the apparatus is put to use, the materials can be circulated for some time to bring about such steady state conditions so that only the material in the mixing device and in the distributing device (which will be the curing agent or initiator previously used to flush out the distributing device after use) will ever be wasted.

Thus there is provided apparatus for applying paint and the like which has been found to be particularly useful for spraying mixed materials in an intermittent manner, for example by means of a spray gun. Two-part and multi-part mixtures of materials, for example cold setting resin materials mixed with a liquid curing agent or initiator, can be sprayed in an intermittent manner by the apparatus despite the fact that such materials require to be mixed in precisely the correct proportions and that intermittent operation in the past has been found to upset correct proportioning. The apparatus also makes possible the use of the proportioning apparatus described above, including the meters 51 and 53 which need to operate continuously in order to meter the materials correctly, despite the fact that the actual discharge of mixed material may be taking place intermittently.

Various modifications may be made. For example, the apparatus need not necessarily be built as a mobile device; furthermore, whether or not it is built as a mobile device, the apparatus need not necessarily be provided with a rotatable drum on which the flexible pipes can be wound. However, if intended for the lining of the interior walls of pipes for example (in which case the rotatable drum would be an essential part of the apparatus) the manually operable spray gun would be replaced by a distributing device of the kind described in UK Patent No. 2237351 (where the application of the coating is not effected by spraying but by a flinging radially outwards of the material followed by repeated impacts or rapid wiping actions by a set of rotating flails mounted on the distributing device) and means would be provided for feeding the distributing device along the interior of the pipe to be lined. Although in the foregoing description the back pressure valves 47 and 49 have been said to be manually adjustable, it would be quite possible to arrange for them to be adjustable automatically whereby each pressure drop as the materials are returned to their respective holding tanks is substantially the same as the pressure drop occurring when the mixed materials issue from the distributing device.Means other than those described above could be devised for ensuring that the materials are pumped along their respective pipes at the required relative rates to ensure them being mixed together in the correct proportions.

Although the invention is mainly of use with apparatus for applying a coating of a cold setting resin material mixed with a liquid curing agent or initiator, it may well be of use with apparatus for applying other two-part or multi-part mixtures of materials where the proportions of the mixed materials are difficult to maintain if steady state conditions cannot be maintained.

It will be understood that the various parts of the apparatus illustrated in Figure 3 are completely out of scale with each other and that the 3-way valves 25 and 26, and the mixing device 24, may well be incorporated in the handle of the spray gun 27.

However, it would on the other hand be quite possible for several spray guns to be connected to the output side of the mixing device by way of respective flexible pipes for several operatives to be supplied with mixed material under pressure from the same source.

Claims

1. A method of spray or otherwise coating, intermittently, using a two-part mixture of materials, the method including the steps of feeding by means of a first pump one of the materials from a first holding tank through a flexible pipe connected to a distributing device, feeding by means of a second pump the other of the materials from a second holding tank through another flexible pipe connected to said distributing device, controlling the operation of said first and second pumps so that the two materials are delivered to the distributing device in the required proportions, and, during periods when said distributing device is inoperative, re-circulating the two materials through respective return pipes back to their respective holding tanks so that steady state conditions tend to be maintained.

2. The method according to claim 1, including the step of controlling the pressures in the respective return pipes whereby each pressure drop as the materials are returned to their holding tanks is substantially the same as the pressure drop occurring when the mixed materials issue from the distributing device.

3. Apparatus for use in spray or otherwise coating with twopart mixtures of materials, the apparatus including a first pump for feeding one of the materials from a first holding tank through a first flexible pipe and a second pump for feeding the other of the materials from a second holding tank through a second flexible pipe; a distributing device connected to the ends of the two flexible pipes for mixing together the two materials and for distributing the mixed substance over a work surface; control means for controlling the operation of the two pumps in step with each other and thus for controlling the delivery of the two materials to the distributing device in the required proportions; and respective return pipes for returning the two materials back to their respective holding tanks whenever the distributing device is inoperative, so that steady state conditions tend to be maintained throughout the operation of the apparatus.

4. Apparatus according to claim 3, in which the return pipes are provided with respective back pressure valves which are adjustable to produce substantially the pressure drops which occur when the distributing device is operable.

5. Apparatus according to either one of claims 3 and 4, in which the first and second pumps are driven by respective double acting hydraulic rams.

6. Apparatus according to claim 5, in which the first and second pumps are associated with respective reciprocating type meters which control the delivery of the two materials in the required proportions, said meters operating continuously throughout the operation of the apparatus despite the operation of the distributing device being intermittent.

7. Apparatus according to claim 6, in which control means for controlling the delivery of the two materials to the distributing device in the required proportions include means for counting the number of reciprocations of the respective meters and a computer to which this information is continuously fed throughout the operation of the apparatus, the computer being arranged to adjust the setting of respective flow control valves when required by means of respective actuators.

8. A method of spray or otherwise coating, intermittently, using a two-part mixture of materials, substantially as hereinbefore described.

9. Apparatus for use in spray or otherwise coating using a twopart mixture of materials, the apparatus being constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.