Apparatus and method for producing and dispensing a reaction mixture

Apparatuses for producing and dispensing a reaction mixture include a mixing head for mixing the reaction components that are fed via two supply lines. The apparatuses also include a decompression system to relieve pressure from the supply lines to avoid the reaction components seeping into the mixing head. The decompression system includes two pressure vessels each with two sides, separated by a membrane. One of these sides forms an expansion chamber for the reaction component while the other side is connected to a pneumatic system. With this pneumatic system, the expansion chamber can be pressurized before the production of the reaction mixture is started. After the production of the reaction mixture, the pressure can be relieved.

The present invention relates to an apparatus for producing and dispensing a reaction mixture, in particular a foaming reaction mixture for producing a foam. The reaction mixture is produced in the apparatus starting from at least a first and second reaction component, which are kept under pressure in a first and a second container respectively. The apparatus comprises a mixing head for mutually mixing the first and second reaction component, which mixing head is provided with an outlet for the mixture of both reaction components. The apparatus also comprises a first supply line for feeding the first reaction component from the first container under the pressure prevailing therein to the mixing head, a second supply line for feeding the second reaction component from the second container under the pressure prevailing therein to the mixing head, a first shut-off valve in the first supply line and a second shut-off valve in the second supply line, the first and the second shut-off valves both having an open and closed position, a third shut-off valve for closing the first supply line in the mixing head and a fourth shut-off valve for closing the second supply line in the mixing head, the third and the fourth shut-off valve comprising a common plunger which is configured to slide, in particular in its longitudinal direction, for opening and closing the third and the fourth shut-off valve simultaneously, a first expansion chamber connected to the first supply line between the first and the third shut-off valve, a second expansion chamber connected to the second supply line between the second and fourth shut-off valve, a pneumatic system for the pressurisation of and pressure relief from the first and second expansion chambers and from the first supply line as from the first to the third shut-off valve and from the second supply line as from the second to the fourth shut-off valve, and a control system for operating the pneumatic system as well as the first, second, third and fourth shut-off valves for starting and stopping the production and dispensing said reaction mixture.

Such an apparatus is known from EP 0 757 618. This known apparatus is used to mix a polyol component and an isocyanate component. The mixing head is located in a spray gun that can be used to spray the foaming reaction mixture. Both reaction components are kept under a pressure of 6 to 12 bars in a container, more particularly in a bottle that is pressurised by means of a bottle filled with nitrogen gas. The reaction components are fed under this pressure into the mixing head where they are mixed. A problem with the shut-off valves in the spray gun is that they are unable to form a perfect seal for the first and second supply lines, as a result of which the reaction components may still seep into the mixing head after the spraying has stopped, where they can react with one another and consequently pollute the mixing head, and possibly even block the spray gun. Although the supply lines are not only shut off in the spray gun but also closer to the containers, the reaction components in the supply lines remain under pressure due to the elastic expansion of the supply lines. The invention described in EP 0 757 618 therefore consists of relieving the pressure in the supply lines after having closed the shut-off valves in the spray gun and in the supply lines on the side of the containers, in order for the reaction components to be no longer under pressure at the level of the shut-off valves in the spray gun, thus making it impossible for them to seep into the mixing head.

The pressure-relief system described in EP 0 757 618 consists of a cylinder housing containing a piston that is pneumatically pressurized at the start of the spraying process to push the respective reaction component out of the expansion chamber. When the spraying stops, the pneumatic pressure of the piston is removed, enabling the expansion chamber to expand again, which allows the reaction component to flow from the supply line into the expansion chamber through the pressure prevailing in the supply line, in such a way that the pressure in the supply line is removed.

A problem with the pressure-relief system according to EP 0 757 618 is that the isocyanate reaction component reacts with water to form solid urea compounds. Since compressed air always contains water vapour, the isocyanate component will react when it comes into contact with the compressed air, i.e. with the water in the compressed air. If the compressed air contains too much moisture, it is even possible that the water will condense inside the pneumatic system, due to the increase in the dew point temperature when the air is compressed. Despite the fact that the pistons of the pressure-relief system have rubber sealing rings, it is necessary pursuant to EP 0 757 618 to provide a double piston in the pressure-relief system, with a solvent being provided in between the two pistons, more particularly Mesamoll®. The solvent ensures that the small residue of reaction component left on the cylinder wall with every movement of the piston is dissolved in the solvent and is thus no longer able to react with the moisture in the compressed air. In this way, the pressure-relief system can thus continue to work autonomously for a considerable period of time.

A disadvantage of such a pressure-relief system, however, is that it is a relatively complex and expensive system. The cylinder wall has to be perfectly smooth because otherwise too much residue of the reaction component could remain on the cylinder wall with every movement of the piston and thus contaminate the solvent too quickly, despite the presence of rubber gaskets around the piston. In practice, the known pressure-relief system also requires regular and relatively cumbersome maintenance. After all, the solvent and the gaskets on the pistons usually have to be replaced every year. This work takes a number of hours and must be carried out by specialised personnel. The decompression system thus makes the apparatus relatively expensive to buy and also to maintain.

An object of the invention is therefore to provide a new apparatus for producing and dispensing a reaction mixture, the decompression system of which is less complex and also requires less maintenance.

To this end, the apparatus according to the invention is characterised in that said first and second expansion chamber are formed respectively by a first and a second pressure vessel, each having two sides separated from each other by a membrane, of which the first side forms the first and second expansion chamber, respectively, which are arranged to be filled with said first and respectively said second reaction component, and of which the second side is connected to said pneumatic system to be filled with a gas, which gas is in contact with the reaction component on the first side of the pressure vessel via said membrane, said first and said second pressure vessels being detachably connected to said pneumatic system and to the first and second supply lines respectively.

Since the reaction components are separated in the first and ub the second pressure vessel by a membrane from the gas, in particular from the compressed air, the reaction component cannot possibly come into contact with the gas, more particularly with the moisture present in it. In contrast to the prior art pressure-relief system with the cylinder-piston mechanism, no double separation with a solvent in between thus needs to be provided in the pressure-relief system with the pressure vessels, according to the invention. Nor is a solvent change therefore required during the maintenance of the apparatus.

During maintenance, the two pressure vessels do not have to be dismantled and cleaned, as they can easily be replaced by new pressure vessels. After all, the construction of such pressure vessels is so simple that the cost price can be kept low. If the pressure vessels can be opened to replace the membrane in them, they can also be reused if required. The used pressure vessels can therefore by recycled on a larger scale and thus in a more efficient and safe manner then if this had to be done on site by the maintenance technician on each occasion.

The use of a pressure vessel containing a membrane as a membrane pump for mixing reaction components is already known from DE 39 18 027 and NL 6610193. However, an important disadvantage of such apparatus is that the pressure on the reaction components fluctuates during the production of the reaction mixture because each time the membrane pump is squeezed empty, it has to be refilled with the reaction component. This can only be avoided by making the membrane pump sufficiently large, and by refilling it each time, so that there is always enough reaction component in the membrane pump itself. Naturally, voluminous membrane pumps will be required for dispensing larger volumes of reaction mixture. These require a sufficiently powerful actuator. Furthermore, it is not easy to keep the reaction components at the right pressure at all times with such pumps. A final disadvantage is that either an extra pump is required to fill the membrane pump, or that the reaction components must also be under pressure in the containers, whereby that pressure ensures that the reaction components remain under pressure at the level of the mixing head and can thus seep into the mixing head.

In a particular embodiment of the apparatus according to the invention, said control is provided with a manual or automatic actuator for starting and stopping the production and dispensing of the reaction mixture.

The manual actuator is for example formed by a trigger or push button on the spray gun, operating as a switch. With a manual actuator, the production of the reaction mixture can easily be started and stopped by the person operating the spray gun containing the mixing head. In an automatic installation, for example in an automatic filling system, an automatic actuator can be applied that is preferably linked to a sensor. With the automatic actuator, the production and dispensing of the reaction mixture can be started and stopped automatically in this manner, as soon as the spray gun and the article to which the reaction mixture is to be applied are thus positioned correctly in relation to each other.

In a particular embodiment of the apparatus according to the invention, the pneumatic system is configured to bring the first expansion chamber under a pressure which is higher than the pressure in the first container and to bring the second expansion chamber under a pressure which is higher than the pressure in the second container.

This embodiment allows the reaction component present in the first and second expansion chambers to be squeezed out of the expansion chamber before the production and dispensing of the reaction mixture commences. When the first and second expansion chambers have been emptied in this way, the production and dispensing of the reaction mixture will thus immediately occur under the pressure existing in the first and second containers. Both reaction components will thus be mixed in the right proportions from the start.

In a particular embodiment of the apparatus according to the invention, the aforementioned control is configured to pressurise said first and second expansion chambers by means of said pneumatic system before the first and second shut-off valves referred to above are opened.

Since both expansion chambers are pressurized in this way before the first and the second shut-off valves are opened, it will be impossible for the reaction components to be squeezed into these expansion chambers under the influence of the pressure exerted on them in the containers. The membranes in the pressure vessels will thus not be pushed further towards the second side of the pressure vessels. The movement and thus the deformation of these membranes is hence kept to a minimum, resulting in minimal wear and tear of the membranes.

Said control is preferably configured to only open the aforementioned third and fourth shut-off valve after having opened the first and second shut-off valve.

Since a larger pressure is exerted in the pressure vessels than in the containers, the expansion chambers will first be emptied via the first and second shut-off valve. By only opening the third and fourth shut-off valve afterwards, the reaction components are fed to the mixing head under the pressure existing in the containers right from the start of the production of the reaction mixture. Furthermore, it is avoided that when starting and stopping the production of the reaction mixture in rapid succession, the amount of reaction component in the expansion chambers can accumulate, which would cause greater deformation of the bladders or membranes in the pressure vessels and thus subject them to greater wear and tear.

In a particular embodiment of the apparatus according to the invention, said control is configured to relieve the pressure from said first and said second expansion chamber after the third and fourth shut-off valve have been closed.

In this way, the pressure of the respective reaction component on the third and fourth shut-off valve is automatically removed after the production of the reaction mixture is stopped, which thus automatically avoids the reaction components seeping further into the mixing head.

Said control is preferably further configured to relieve the pressure from said first and said second expansion chamber only after a predetermined period of time after having closed the third and fourth shut-off valve, more particularly after a predetermined period of time of at least 5 seconds, preferably after a predetermined period of time of at least 10 seconds.

Since the expansion chambers remain empty during this period of time, and since the pressure on the two reaction components in the respective supply lines remains equal to the pressure of the reaction component in its container, the production of the reaction mixture can be immediately restarted during this period of time. Due to the relatively short period, no reaction component will be able to seep further into the mixing chamber under the pressure exerted on the reaction components.

Said control is preferably furthermore configured to close said first and said second shut-off valve before the pressure is relieved from said first and second expansion chamber.

Since the first and second shut-off valve are closed before the pressure is relieved from the expansion chambers, no reaction component will be able to flow from its container to the expansion chamber, and the expansion chamber will thus only need to take in the minimal amount of reaction component required to relieve the pressure from the supply line. This way, only minimal movement and deformation will be required of the bladders or membranes in the pressure vessels, resulting in only minimal wear and tear.

In a particular embodiment of the apparatus according to the invention, said pneumatic system is provided to bring the pressure of the gas in the second side of the first and the second pressure vessel substantially to atmospheric pressure when releasing the pressure from the first and the second expansion chamber.

Since the pressure in the supply lines will also be substantially the same as the atmospheric pressure, there will no longer be a pressure difference over the third and the fourth shut-off valve and no reaction component will be able to seep through these shut-off valves.

In a particular embodiment of the apparatus according to the invention, the first and the second pressure vessels is provided with a support surface for limiting the movement of said membrane in the direction of the first and the second expansion chamber respectively, the support surface being preferably provided for substantially completely supporting the membrane.

In this embodiment, the membranes do not have to absorb the pressure difference between the gas pressure on the second side of the membranes and the pressure of the reaction component on the first side of the membranes themselves, as a result of which these membranes can be made lighter and as a result of which the pressure of the gas can be considerably higher than the pressure of the reaction components, in such a way that the expansion chambers can be emptied relatively quickly by the two pneumatic systems. The production of the reaction mixture can therefore begin relatively quickly after the apparatus is activated, in particular after the actuator is actuated.

Said control is preferably configured to open said third and said fourth shut-off valve only after the membrane of the first and second pressure vessel has been pressed against said supporting surface by the first and the second pneumatic system.

The production of the reaction mixture therefore only starts after the pressure on the reaction components has become equal to the pressure in the containers.

In a particular embodiment of the apparatus according to the invention, said membrane is convex, with the convex side of the membrane being directed towards the first and the second expansion chamber respectively.

The shape of the membrane must be considered in an unloaded condition in this respect, i.e. when both sides of the membrane are in contact with the atmosphere. Due to the convex shape of the membrane, it does not have to be stretched or only to a minimal extent to empty the expansion chamber so that the membrane is only subjected to minimal wear and tear.

The membrane preferably remains convex when the pressure is relieved from the first and the second expansion chamber.

In a particular embodiment of the apparatus according to the invention, instead of being a diaphragm, said membrane is bladder-shaped, with the first and the second expansion chamber being located outside the bladder shape.

The shape of the membrane must be considered in an unloaded condition in this respect, i.e. when both sides of the membrane are in contact with the atmosphere. When the bladder has a sufficiently large size, the membrane doesn't have to be stretched or only minimally due to the bladder-shape to empty the expansion chamber so that the membrane is only subjected to minimal wear and tear.

In other words, the volume of the pressure vessel on the first side of the membrane is so great that it can absorb the volume of reaction component flowing into the expansion chamber when the pressure is relieved from the supply line, without a need for the membrane to flip, i.e. turn from convex into concave. Since the deformation of the membrane remains limited, it will be subject to less wear and tear.

In a particular embodiment of the apparatus according to the invention, said membrane is manufactured from a fluoropolymer elastomeric material.

It has been found that such a material is chemically resistant to the reaction components, in particular to isocyanate and polyol reaction components. Tests have demonstrated that such a membrane is still fully intact even after more than 300,000 spray cycles.

In a particular embodiment of the apparatus according to the invention, in said first supply line between said first shut-off valve and said first container, and in said second supply line, between said second shut-off valve and said second container, a first and a second float chamber is provided, containing a first and a second float respectively for the detection of the level of respectively the first and the second reaction component in the first and the second float chamber, said first and said second float chamber preferably have an internal volume which is larger than 2 litres, preferably larger than 3 litres and more preferably larger than 4 litres.

The floats in these float chambers facilitate detection of the reaction component's container being empty. When the latter is empty, the gas used to pressurise the reaction component will after all enter the float chamber via the supply line, thereby lowering the liquid level in the float chamber. In this case, the control is preferably configured to limit the amount of reaction component that can be fed out of the float chamber after the float has reached its lowest limit, in order to prevent gas from the float chamber getting into the supply line behind the float chamber.

Due to the relatively large volume that the float chamber preferably has, it is possible to connect a new container with a reaction component to the supply line without a need to degas the float chamber. The new container is after all connected at atmospheric pressure, which allows the gas in the float chamber to expand. When the pressure in the container is increased, fresh reaction component will be squeezed into the line and into the float chamber, as a result of which the gas in the float chamber will be compressed under the pressure prevailing in the container in such a manner that the float will once again have risen above its minimum level. The gas that was present in the supply line between the float chamber and the container can also be squeezed into the float chamber. Since the outlet of the float chamber is located in the lower part of the float chamber, no gas will end up in the supply line behind the float chamber.

In a particular embodiment of the apparatus accordance to the invention, a first and a second filter respectively are provided respectively in said first supply line, between said first shut-off valve and said first container, and in said second supply line, between said second shut-off valve and said second container, which filters are located in a first and a second housing respectively.

The filters ensure that solid impurities are filtered from the liquid reaction components so as to prevent these causing blockages. For example, solid impurities may have formed in the isocyanate component if it has come into contact with moisture from the air.

The first and second housing, i.e. the housings of the filters, form preferably also the first and second float chamber.

The advantage of this embodiment is that it enables a more compact design and that the filter housings do not need to be vented.

As an alternative with separate filter housings and float chambers, said first float chamber is preferably located in the first supply line between the first filter and the first container, and the second float chamber is located in the second supply line between the second filter and the second container, the first and the second filter being preferably provided with a venting system.

In this alternative embodiment, there is again no need to vent the two float chambers since the compressed gas contained therein only occupies a limited space at the top of the float chambers. The housings of the filters located behind the float chambers in the supply lines are preferably vented in order to keep the filters and their housings compact. The venting only needs to take place at the time the filters are replaced provided the control referred to above is configured not to allow any gas from the float chambers to the rest of the supply line.

The housing of the first filter and the housing of the second filter are preferably provided with heating elements to heat the first and second reaction component respectively in these housings. If separate float chambers are present, they are preferably also provided with heating elements.

By providing these heating elements, it is possible to always feed the reaction components at the same temperature, and thus with the same viscosity, via the supply lines in such a way that the reaction components can always be mixed correctly and in the right proportion in the mixing head.

Preferably, a heating element is provided in the first supply line and in the second supply line to heat the reaction component which is present in the supply line.

In a particular embodiment of the apparatus according to the invention, said first and said second container are configured to be brought under a pressure of 5 to 10 bars, preferably under a pressure of 6 to 8 bars.

The reaction components can be adequately mixed in the mixing chamber under this pressure. The advantage of such relatively low pressures is that the pressure in the pneumatic system can also be limited so that the usual compressed air systems can be used, either through a central compressed air system or through a separate air compressor.

In a particular embodiment of the apparatus according to the invention, said pneumatic system comprises a first pneumatic system for the pressurisation of and for the pressure relief from the first expansion chamber and from said first supply line as from said first to said third shut-off valve, and a second pneumatic system for the pressurisation of and the pressure relief from the second expansion chamber and from said second supply line as from said second to said fourth shut-off valve.

In an alternative embodiment of the apparatus according to the invention, said pneumatic system comprises a common pneumatic system for the pressurisation of and the pressure relief from the first and the second expansion chamber and said first supply line as from said first to said third shut-off valve, and said second supply line as from said second to said fourth shut-off valve.

In a particular embodiment of the apparatus according to the invention, it comprises said first container which is filled with the first reaction component and said second container that is filled with said second reaction component, said first supply line being connected to the first container, and said second supply line being connected to the second container.

The invention also relates to a method for producing and dispensing a reaction mixture with an apparatus according to the invention, in which method said first supply line is connected to said first container, which is filled with the first reaction component, and said second supply line is connected to said second container which is filled with the second reaction component, after which the first and the second container are pressurised.

In a particular embodiment of the method according to the invention, when the first container is empty it is replaced by a filled first container and when said second container is empty it is replaced by a filled second container.

Lastly, the invention also relates to the use of a first container and a second container for carrying out a process according to the invention, the reaction mixture being a polyurethane reaction mixture containing no or insufficient physical blowing agents, preferably less than 4% by weight and more preferably less than 2% by weight, to be dispensed in the form of a froth and the first and the second container being arranged to be pressurised, in particular under a pressure of at least 5 bars.

An advantage of such containers is that they can not only be pressurized for dispensing the reaction mixture, but since the reaction mixture is not dispersed in the form of a froth, and both reaction components thus contain no or only a relatively small amount of physical blowing agent, the pressure can be removed from both reaction components, in particular from the supply lines to the mixing head, without causing them to expand.

In a particular embodiment of the use according to the invention, the first container contains an isocyanate reaction component and the second container a polyol reaction component, which polyol reaction component mainly contains water as blowing agent for the production of a polyurethane foam. The polyol reaction component is preferably free of physical blowing agents.

Physical blowing agents are, in particular, liquids with a low boiling point such that they evaporate during the polyurethane reaction to form a gas as blowing agent. In this embodiment, the absence of physical blowing agents ensures that no pressure can be generated in the apparatus if certain parts of it, such as part of the supply lines, are in hot conditions.

The apparatus according to the invention is intended for producing and dispensing a reaction mixture. The reaction mixture is a mixture of at least two reaction components, each of which is contained in a pressure container. The first container1contains the first reaction component, while the second container2contains the second reaction component. For example, the reaction mixture may be a polyurethane reaction mixture, which may in particular contain a blowing agent, such as water, for producing a polyurethane foam. Such a reaction mixture is usually produced by mixing an isocyanate component as the first reaction component with a polyol component as the second reaction component. Both reaction components themselves consist of a mixture of different products, which may for example include catalysts, stabilisers, chain extenders, cross-linking agents, blowing agents, pigments, dyes and the like, in addition to the polyol compound and the isocyanate compound. The reaction mixture may also comprise a polyisocyanurate reaction mixture, for example.

The reaction mixture preferably contains water as a chemical blowing agent. The reaction mixture is preferably free from physical blowing agents or contains such a small quantity thereof that the reaction mixture is not dispensed in the form of a froth. After mixing both reaction components, the reaction mixture preferably contains less than 4% by weight physical blowing agents, and more preferably less than 2% by weight. The foam system is therefore not a froth system that needs to be kept under pressure and that would produce additional pressure when the pressure is relieved. Furthermore, the absence of physical blowing agents, or the limited quantity of these, ensures that no pressure can be generated in the apparatus if certain parts of it, such as part of the supply lines, are in excessively hot conditions.

The reaction components are pressurised in the first1and the second container2, with a riser duct48being provided in order to remove the reaction component from the bottom of the container1,2. To pressurise the containers, both containers1,2are connected to a gas bottle3with a liquid gas. This gas bottle3preferably contains liquid nitrogen. Such nitrogen is substantially free of water, which means that no reaction will occur in the containers with the reaction component. This is especially important for the isocyanate component as it can react quickly with water to form urea compounds. As shown inFIG.1, both containers1,2can be pressurised with a single gas bottle3but, if necessary, each container1,2can be connected to a separate gas bottle3. The latter makes it possible to set a separate pressure for the two reaction components, taking into account the fact that the viscosity of the two reaction components will normally be different. Preferably one of the containers, more particularly container2for the polyol component, is connected to compressed air via a line47. This variant embodiment is depicted inFIG.4. The advantage of this embodiment is that less nitrogen gas will be required for dispensing the reaction mixture.

FIG.1shows a pressure control valve4on the gas bottle3, which can be used to set the pressure in the containers1,2. In the variant embodiment ofFIG.4, a pressure control valve49is also fitted on compressed air line47. With these pressure control valves4,47, the pressure in the containers is for example set to 6 bars.

At the end, the apparatus comprises a mixing head5in which the reaction components are mixed. The mixing head5is provided with an outlet6for dispensing the reaction mixture. In the apparatus according to the invention, both reaction components are fed to the mixing head5under the pressure prevailing in the containers1,2. The first reaction component is fed via a first supply line7to the mixing head5, while the second reaction component is led via a second supply line8to the mixing head5. The pressure on the reaction component at the level of the mixing head5may be smaller than the pressure in the container1,2due to possible pressure losses in the supply lines. Since the pressure loss will be greater for more viscous liquids, it may be appropriate to put the container for the more viscous reaction component, in particular of the polyol component, under greater pressure than the container for the less viscous reaction component.

The mixing head5can form part of a mixing gun equipped with a trigger9. The trigger9forms a manual actuator for starting and stopping the production and dispensing of the reaction mixture, and to that effect, it is preferably connected to a switch connected to the control system20. For example, when the apparatus is incorporated in an automated filling installation, the trigger9can nevertheless be replaced by an automatic actuator.

In the first supply line7, between the first container1and the mixing head5, there is successively a first manual shut-off valve10, a first filter11, a first automatic shut-off valve12and a first pressure vessel13. In the second supply line8, between the second container2and the mixing head5, there is successively a second manual shut-off valve14, a second filter15, a second automatic shut-off valve16and a second pressure vessel17. In the mixing head5, the first supply line7ends in a third automatic shut-off valve18and the second supply line8ends in a fourth automatic shut-off valve19. The third and the fourth automatic shut-off valve18,19preferably contain a common plunger that is moved in its longitudinal direction to open and close both shut-off valves simultaneously, as disclosed for example in U.S. Pat. No. 5,375,743. The various automatic shut-off valves are operated through a control. This control is made up, for example, of a PLC control20, i.e. a programmable control, which is connected by electrical wiring21to the automatic shut-off valves12,16and by electrical wiring34to the shut-off valves18,19. The automatic shut-off valves can be either operated directly electrically, but they are preferably pressure-controlled shut-off valves that are operated by compressed air and controlled by an electrically operated control element.

Both manual shut-off valves10,14are used to close the supply lines7,8when the apparatus is no longer in use. The third and fourth shut-off valves18,19serve to start and stop the production and dispensing of the reaction mixture. The first and second automatic shut-off valve12,16are used to relieve the pressure of the last part of the first and second supply lines7,8by means of the pressure vessels13,17when the third and fourth shut-off valve18,19have been closed. As a result, the pressure is relieved from this third and fourth shut-off valve18,19, so that no more reaction component can seep into the mixing head5if the third and fourth shut-off valves18,19do not provide a 100% sealing.

The spray gun used in the apparatus may be for example a spray gun as described and shown in U.S. Pat. No. 5,375,743. Such a spray gun makes it possible to mix the two reaction components efficiently at relatively low pressures. For more details on this spray gun, reference is made to U.S. Pat. No. 5,375,743, which is included herein by way of reference.

FIGS.5and6correspond toFIGS.5and6of this US patent and show the main parts of the spray gun according to the second embodiment disclosed therein. The spray gun comprises a grip52which carries the trigger9. The mixing head5of the spray gun is fixed to the grip52and comprises a metal barrel53which has a cylindrical longitudinal boring54. The boring54comprises two parts, namely a first part55, at one side of the barrel53, and a second part56, at the other side of the barrel53. The first part55of the boring54has a smaller diameter than the second part56thereof.

A cylindrical core57, made of a synthetic material, in particular of PTFE, is pressed in the first part55of the boring54. With one of its extremities, which is provided with a conical washer piece67, it engages a collar58in the first part55of the boring54and is pressed against this collar58by means of a screw cap59, a metal sleeve60and Belleville washers61. The cylindrical core57is provided with a longitudinal boring which forms the mixing chamber62of the mixing head5.

The mixing chamber62is provided at one extremity with the outlet6for the reaction mixture and, at it other extremity, with a first inlet63, for the first reaction component, and with a second inlet64, for the second reaction component. The first inlet63is connected via a first screw connector65to the first supply line7whilst the second inlet64is connected via a second screw connector66to the second supply line8. Both reaction components are injected under pressure into the mixing chamber62and impinge onto each other so as to be mixed instantaneously.

The mixing head5further comprises a plunger68which fits into the mixing chamber62and which can slide therein in its longitudinal direction. In one of its two extreme positions, namely in the open position of the mixing head5illustrated inFIG.5, the plunger68is retracted from the mixing chamber62whilst in its other extreme position, namely in the closed position of the mixing head5illustrated inFIG.6, it extends entirely through the mixing chamber62and through the outlet6thereof. In the open position, illustrated inFIG.5, the reaction components are injected through the inlets63and63into the mixing chamber62and the reaction mixture is ejected out of the mixing chamber62through the outlet6thereof. In the closed position, illustrated inFIG.6, the inlets63and64are closed-off by means of the plunger68and any reaction mixture produced in the mixing chamber62has been push-out thereof by means of the plunger68. Due to the axial pressure exerted by the Belleville washers61onto the cylindrical core57, the synthetic material of this core57is compressed somewhat and is pressed against the lateral side of the plunger68to achieve an optimum sealing effect. In the mixing head5illustrated inFIGS.5and6, the third shut-off valve12is comprised of the first inlet63which co-operates with the plunger68to be opened or closed whilst the fourth shut-off valve19is comprised of the second inlet64which co-operates with the same, common plunger68to be simultaneously opened or closed.

To be able to move the plunger68between its two extreme positions, it is connected to a piston69which slides within the second part56of the cylindrical boring54of the barrel53. The piston69is urged by means of a compression spring70in the direction wherein the inlets63and64, or in other words the third18and the fourth shut-off valves19are closed. To open these valves18and19, a hydraulic fluid can be pumped by means of a pump71in the second part56of the cylindrical boring54, on the other side of the piston69.

In the embodiment illustrated inFIGS.5and6the pump71circulates the hydraulic fluid through the mixing head5over a filter with heat exchanger72to be able to heat the mixing head5. An electro-hydraulic valve73in the hydraulic circuit enables to produce the required hydraulic pressure in the mixing head5to open the third18and the fourth shut-off valves19upon electrical actuation of the electro-hydraulic valve73. The hydraulic fluid comprises preferably a solvent, for example Mesamoll® to rinse the plunger68in its retracted position.

Alternatively, in case no heating of the mixing head5is required, the actuation of the plunger68can be simplified by using a pneumatic system to actuate the plunger68. The second part56of the cylindrical boring54of the barrel53can for example be connected to a source of compressed air over a solenoid valve, for example to the pneumatic system described hereinafter for controlling the operation of the different shut-off valves.

Especially when both supply lines7,8comprise a flexible hose, these supply lines7,8will expand elastically under the pressure of the reaction component present in them when they are connected to containers1,2. To relieve the pressure from these lines7,8, part of the reaction component present in them must be able to flow from the lines, in such a way that the lines can shrink again and no longer exert further pressure on the reaction component. For the first supply line7, the excess of the first reaction component can flow into the first pressure vessel13after the first and third shut-off valves12,18have been closed, while the excess of the second reaction component, after the closure of the second and fourth shut-off valves13,19, can flow into the second pressure vessel17.

The structure of both pressure vessels13,17is depicted inFIG.2. The pressure vessel consists of a metal casing22with a detachable coupling23at the top, in particular a screw coupling, for connecting the pressure vessel to a compressed air line and a detachable coupling24at the bottom, in particular a screw coupling, for connecting the pressure vessel to the first or second supply line7,8. Within casing22, a first, respectively a second expansion chamber25,26is formed for the reaction component by a flexible membrane (diaphragm)27that divides the space inside the pressure vessel in two. The free edge of membrane27is clamped to the inside of casing22by means of a plastic ring28.

The first or second chamber29,30respectively on the other side of membrane27is connected to a compressor44for compressed air with a compressed air line45,46. For the first pressure vessel13, this compressed air line45is part of a first pneumatic system for the pressurisation of and pressure relief from the first expansion chamber25, while for the second pressure vessel, the compressed air line46forms part of a second pneumatic system for the pressurisation of and pressure relief from the second expansion chamber26. Since the first expansion chamber25is connected to the first supply line7and the second expansion chamber26to the second supply line8, these supply lines7,8will be pressurized or depressurised together with the expansion chambers25,26.

The first pneumatic system comprises, in addition to the compressor44and the compressed air line45, a first solenoid valve31in the compressed air line45, which is connected to the control20via electrical wiring32. When the solenoid valve31is electrically energized, the first chamber29of the pressure vessel13is connected to the compressed air in such a way that it comes under pressure. Via membrane27, the first expansion chamber25also comes under pressure. The pressure exerted on the expansion chamber25is preferably greater than the pressure that prevails in the first container1, for example a pressure of 9 bars, such that the first reaction component will be squeezed out of the expansion chamber25. If the first automatic shut-off valve12has not yet been opened, the part of the first supply line located between the first12and the third shut-off valve18will be pressurized again. As soon as the first shut-off valve12is opened, any excess of the first reaction component can be squeezed back into the first container1. When the first12and the third shut-off valve18are closed, the electrical power can be removed from the solenoid valve31, as a result of which the first chamber29of the pressure vessel13is connected to the free atmosphere. The first reaction component can thus flow freely into the first expansion chamber25, thus relieving the pressure in the first supply line7, as from the first12to the third shut-off valve18, i.e. pressure is relieved from the entire part of the first supply line7which extends between the first12and the third shut-off valve18.

The second pneumatic system works in the same way as the first. It comprises, in addition to the compressor44and the compressed air line46, a second solenoid valve33in the compressed air line46, which is connected to the control20via electrical wiring32. When the solenoid valve33is electrically energized, the second chamber30of the pressure vessel17is connected to the compressed air in such a way that it comes under pressure. Via membrane27, the second expansion chamber26also comes under pressure. The pressure exerted on the expansion chamber26is preferably greater than the pressure which prevails in the second container2, for example a pressure of 9 bars, such that the second reaction component will be squeezed out of the expansion chamber26. If the first automatic shut-off valve16has not yet been opened, the part of the second supply line located between the second and the fourth shut-off valve16,19will be pressurized again. As soon as the second shut-off valve16is opened, any excess of the second reaction component can be squeezed back to the second container2. When the second and the fourth shut-off valves16,19are closed, the electrical power can be removed from the solenoid valve33, as a result of which the second chamber30of the pressure vessel17is connected to the free atmosphere. The second reaction component can thus flow freely into the second expansion chamber26, thus relieving the pressure in the second supply line8, as from the second to the fourth shut-off valves16,19, i.e. pressure is relieved from the entire part of the second supply line8which extends between the second16and the fourth shut-off valve19.

In the alternative embodiment depicted inFIG.4, there is only one common pneumatic system. This system is formed by the valve31which is connected to the compressor44via the compressed air line45. A branch line is provided on the compressed air line to the first pressure vessel13, which simultaneously leads the compressed air to the second pressure vessel17via the compressed air line50. In this embodiment, the pressure vessels13,17are thus simultaneously pressurised or depressurised.

Membrane27, located in both pressure vessels13,17, has a convex shape, with the convex side of membrane27facing the expansion chamber25,26. Membrane27remains preferably convex towards the expansion chamber25,26also when the pressure of the supply line7,8has been relieved and when the excess reaction component has thus ended up in the expansion chamber25,26. Since the membrane27is thus minimally deformed, it will also be subject to limited wear and tear. Furthermore, due to its convex design, the membrane27will be pressed laterally against the casing22under the influence of the compressed air, whereby the sealing between the membrane27and this casing22improves as more pressure is applied to the membrane27. When the membrane27is put under pressure, substantially all of the reaction component will have been squeezed from the pressure vessel13,17, and the membrane will be pressed against a support surface35provided by the internal surface of the casing22. Since the membrane does not need to stretch or only to a limited extent, it will be subject to little wear and tear as a result.

The membrane27itself is preferably made of a fluoropolymer elastomeric material. It has after all been found that such a material can withstand the chemical influence of the reaction components for a considerable period of time, even if the reaction component is allowed to flow in and out of the expansion chamber more than three hundred thousand times.

The control is connected via the wiring34also with the third and fourth shut-off valves18,19and moreover with a sensor on the trigger9. When both supply lines7,8are pressurised, i.e. when both the first and the second automatic shut-off valves12,16are open, the control system20will open the third and the fourth shut-off valves18,19when the trigger9is operated, as a result of which the reaction mixture is produced and dispensed through the outlet.

The structure of both filters11,15of the embodiment inFIG.1is shown in more detail inFIG.3. Filters11,15contain a housing36with an inlet37at the top and an outlet38at the bottom for the reaction component. The outlet38is fitted with a filter element39, arranged to filter the reaction component.

To enable detection of an empty container1,2, in the first supply line7, between the first shut-off valve12and the first container1, a float chamber40is provided containing a float41, arranged to detect the level of the reaction component in the float chamber40. A same float chamber40with float41is also provided in the second supply line8, between the second shut-off valve12and the second container2. Since the reaction components are squeezed into the supply lines7,8at the bottom of the containers1,2under the pressure of the gas in the containers, gas will flow through the supply lines from as soon as the respective container is empty. The gas will then end up in the float chamber40where the liquid level will drop, which can be detected by means of the float. The float41is preferably arranged to detect an empty container when the float chamber40still contains a quantity of reaction component. Control20is then preferably configured to continue dispensing the reaction mixture until it is stopped by the actuator, unless this is preceded by the float chamber being empty.

If the float system40,41is independent from the filter11,15, as shown inFIG.4, the float system is preferably located in the supply line7,8between the container1,2and the filter11,15. The filters11,15are preferably fitted with a venting system42in that case. Since the control20ensures that the float chambers40will never be empty, the filter11,15only has to be vented once, namely only when the filter elements39are replaced.

The float chambers40have preferably each an internal volume in excess of 2 litres, preferably in excess of 3 litres and more preferably in excess of 4 litres. When connecting a new container1,2, the manual shut-off valves10,14must be open or opened before the containers1,2are pressurised. This will place the gas in the float chamber40under atmospheric pressure. When the containers1,2are then placed under pressure, the reaction component will flow through the first part of the supply line into the float chamber, where it will compress the gas present in the float chamber40. Due to the relatively large volume of the float chamber40, the compressed gas only takes up a limited proportion of this volume in such a way that the float41can continue to operate effectively without the need to vent the float chamber40. In other words, the float41will indicate again shortly after the container is placed under pressure that the container is filled.

However, the float chambers40are preferably also equipped with a venting system51, in particular the float chamber for the isocyanate component. For the isocyanate component, the float chamber40should preferably be vented at start-up so that no moisture remains in it. When reconnecting a full container1, it is no longer necessary to vent the float chamber as only dry nitrogen gas is present in the float chamber40.

In the embodiment illustrated inFIG.3, the float chamber40and the float41are arranged in the housing36of the filter11,15. The internal volume of the housing36, which overall forms the float chamber40, must be sufficiently large to accommodate both the filter element39and the float41. The float41can be installed above the filter element39, as indicated inFIG.3, but it is also possible to install the float41next to the filter element39. The advantage of placing the float41above the filter element39is that when the float41indicates that the container1,2is empty, there is still a considerable amount of reaction component in the filter/float chamber in order to be able to still produce a relatively large amount of reaction mixture. A further advantage of this arrangement is that the housing36can be made more elongated for the same internal volume, so that the housing36has a larger surface area. This is advantageous when heating elements39are provided in or on the housing, which in the embodiment according toFIG.3, are formed by a heating jacket43applied around the housing36. Since the housing36is elongated and since it has an internal height that in particular amounts to more than three times or even more than five times the average internal diameter of the housing, it has a relatively large surface area and thus a greater capacity for transferring the heat of the heating elements43to the reaction component in the housing36. If the float chamber40is not located in the housing36of the filter, both the float chamber40and the housing40can be fitted with heating elements43.

Instead of, or in addition to the heating elements43, heating elements are also applied preferably in the supply lines7,8themselves. These heating elements are in particular wire-shaped and located in the supply lines7,8so that the reaction component will flow around them. Efficient heat transfer can be obtained in this manner, so that the heating elements on the float chamber or on the filter may optionally be omitted.

Also, in the preferred embodiment, in which the housing36of the filter also forms the float chamber40, this float chamber has preferably an internal volume in excess of 2 litres, preferably in excess of 3 litres and more preferably in excess of 4 litres. For example, the internal volume of the float chamber40is approximately 7 litres. The advantage of this embodiment is that even when replacing the filter element, the housing36of the filter does not need to be vented. The internal volume of this housing36is indeed so large that when the gas contained in the housing36and in the first part of the supply line7,8when the container1,2is replaced, it only occupies a limited proportion of the internal volume of the housing36when it is pressurised, which means that the float41can continue to operate effectively. It is of course recommended that the outlet of the float chamber40is located at the bottom, more in particular at a level where reaction component will always remain present, managed by control system20, in order to prevent gas ending up in the mixing head5through the supply lines where it would disrupt the mixing process.

The various phases of operation of the apparatus under the control of control system20and the transitions between these phases are indicated in table1below.

In phase a the pressure vessels13,17are in connection with the atmosphere via the solenoid valves31,33and the expansion chambers25,26are therefore under atmospheric pressure. Upon squeezing the trigger9, the solenoid valves31,33, or only the solenoid valve31in the embodiment according toFIG.4, connect the pressure vessels13,17with the compressed air, as a result of which the expansion chambers25,26are pressurised (phase b). In a next step, the first and the second shut-off valves12,16are opened, as a result of which the supply lines7,8come under pressure from the containers1,2(phase c). This only happens after 0.5 sec to ensure that the expansion chambers25,26are pressurised, which prevents expansion chambers25,26from being filled with reaction component under pressure from the containers1,2, which would cause membrane27to deform too much and which could potentially even cause reaction component to seep between membrane27and the wall of the pressure vessel. After 1 sec, the third and fourth shut-off valves18,19are opened, thus starting the production of the reaction mixture in the mixing head5under the pressure exerted in the containers1,2on the reaction components (phase d). This phase d of the production and dispensing of the reaction mixture continues for as long as the trigger9remains squeezed. Upon the release of the trigger9, the third and fourth shut-off valves18,19will close, thereby stopping the production and dispensing of the reaction mixture (phase e).

Phase e, in which the supply lines7,8remain under the pressure prevailing in containers1,2, is maintained for 15 seconds. The apparatus is thus in standby mode, during which squeezing trigger9again will immediately restart the production and dispensing of the reaction mixture, through a transition to phase d. If the trigger9is not pressed again during the standby phase, the first and second shut-off valves12,16will also close in phase f and then immediately switch to phase a again by reconnecting the pressure vessels13,17to the atmospheric pressure by means of the solenoid valves31,33.

If the trigger9is only pressed for a short time, and for example already released in phase b or c, the apparatus follows the same cycle, nevertheless skipping phase d. This ensures that the two expansion chambers25,26are always emptied before the first and the second shut-off valve12,16are closed in such a way that the two expansion chambers25,26are always fully available for depressurising the supply lines7,8.