Systems and methods for vacuum impregnation

Abstract

To provide vacuum impregnation systems and processes used to seal pores and small gaps in articles such as single parts or assembled parts.SOLUTION: A vacuum impregnation system 100 includes a vacuum tank formed by a receptacle 102 and a lid 104. A part is subjected to a vacuum, immersed in a polymer impregnating liquid, and subjected to positive pressure to introduce the polymer impregnating liquid into porosities of the part. Then, the pressure is released to atmospheric pressure, and the polymer impregnating liquid is solidified, preferably without an active polymerization step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates generally to the field of vacuum impregnation systems and processes in which a part is subjected to a vacuum, the part is immersed in an impregnating liquid, and a positive pressure is applied to the part to force the impregnating liquid into the pores of the part where it solidifies. [Background technology]

[0002] Vacuum impregnation systems are used to seal pores and small gaps in articles, such as single components or assemblies. Such sealing is useful, for example, to reduce or prevent the intrusion of water, oil, soil, and other contaminants into the component or assembly, and helps prevent corrosion of the article. Articles can include cast metals and other materials, including combinations of metal and plastic materials. Generally, vacuum impregnation is performed by subjecting the article to a vacuum, contacting the article with an impregnating liquid, and then optionally applying a positive pressure to promote the migration of the impregnating liquid into the pores and gaps. Vacuum impregnation processes can be classified into two groups: dry vacuum and wet vacuum.

[0003] Dry vacuum impregnation involves placing a part in a sealed chamber containing a gaseous environment, such as ambient air, and applying a vacuum to remove the gaseous environment from the chamber (including from pores and gaps within the part). While the vacuum is maintained, sealant is transferred from a reservoir into the sealed chamber, and upon release of the vacuum, the sealant is drawn into the pores and any unused sealant is returned to the reservoir. Dry vacuum impregnation can include applying a positive pressure, typically about 4-7 bar (400-700 kPa), and holding that pressure for a selected period of time to allow the sealant to penetrate the pores.

[0004] Wet vacuum involves immersing the part in the impregnating liquid in a vacuum chamber and holding it under vacuum until all air is removed from the container and sealant. The challenge with wet vacuum is overcoming the head pressure of the sealant in the vacuum chamber and minimizing the negative pressure on the pores and gaps. This has the drawback of trapping a finite amount of air in the pores, which can ultimately lead to a decrease in the quality of the seal. In a second step, the vacuum is released, leaving the part in the sealant at atmospheric pressure, allowing the sealant to penetrate into the pores and gaps within the part.

[0005] Most commonly, the impregnating liquid is a low-viscosity monomer solution that is easily removed from the exterior of the part by spinning or similar mechanical means after impregnation, leaving the liquid in the pores and interstices. The low-viscosity monomer solution is then polymerized in situ in a post-processing step. Low-viscosity monomer materials have been commercially successful, at least in part, due to their ease of delivery into the pores and interstices of the part. Common monomer materials include, for example, methacrylate monomers, which typically have viscosities of about 5 MPa·s to about 65 MPa·s (5 to 65 centipoise) at 23°C. These are thermosetting materials that polymerize and crosslink to form hard polyacrylate solids. For various reasons, these in-situ polymerized seals have been found to be prone to failure in simulated life-cycle durability tests to seal gaps between adjacent metal and plastic components on certain electronic assemblies, such as mobile phone assemblies.

[0006] To overcome the drawbacks of in-situ polymerization encapsulation, in-situ polymerized monomer solutions can be replaced with polymer impregnating solutions that do not require polymerization or crosslinking after impregnation and only require drying to form encapsulation. The polymer can be dissolved or dispersed in a solvent such as water. One drawback of polymer / solvent impregnating solutions made to a viscosity similar to that of a monomer solution by adding a large amount of solvent is the energy and time required to dry them. Another potential drawback is that the impregnating solution may lack sufficient polymer solids, causing the polymer sealant to shrink upon drying, resulting in ineffective pore and gap sealing.

[0007] To solve this problem, applicants have opted for thicker (i.e., more viscous) polymer materials containing more polymer solids and less solvent, with viscosities ranging from approximately 50 Pa·s to 3000 MPa·s and greater, depending on the polymer's non-Newtonian behavior (50 to 3000 centipoise). While thicker polymer solutions or dispersions have been shown to provide improved sealing performance and do not require crosslinking, they present other disadvantages. For example, thicker polymer solutions are less suitable for use in wet vacuum processes because the head pressure of the liquid solution limits the amount of air that can be removed from pores and gaps, particularly below the liquid surface, where the positive pressure of the liquid and the vapor pressure of any solvent act against the drawn vacuum. This, combined with the higher viscosity of the polymer impregnant, leads to poor sealing performance. Although the problems caused by the liquid head pressure can be reduced by carrying out the vacuum impregnation process in shallow tanks, commercial production volumes of small parts require many relatively large diameter pressure-rated tanks, which can be cost-prohibitive, especially when stainless steel is required to resist corrosion by some polymer impregnation fluids.

[0008] The problems associated with using the wet vacuum process can be addressed to some extent by using a dry vacuum process. With a dry vacuum process, fewer, deeper, smaller-diameter tanks can be used for the same production volume because there is no hydraulic head pressure to overcome and the vessel height does not affect sealing quality. However, the dry vacuum process also has drawbacks. For example, intense foaming is likely to occur when the thick impregnating liquid first enters the vacuum environment of an empty tank. This foaming has been observed to cover large areas of the vacuum impregnation system and dry into a hard film. Furthermore, unlike dilute monomers, the thick impregnating liquid does not fully drain from the tank sidewalls at the end of a cycle. As a result, the foamed impregnating liquid and other impregnating liquids that come into contact with the tank walls during the process form thick, difficult-to-remove deposits on the tank sidewalls after just a few operating cycles. This problem is exacerbated by the fact that the impregnating liquid is highly viscous and highly solvent-resistant. Therefore, cleaning the tank interior almost always requires an operator to enter the vessel, which leads to operational complications such as the need to schedule downtime and stricter requirements for operator safety.

[0009] Therefore, prior art vacuum impregnation systems can be further improved. Summary of the Invention [Means for solving the problem]

[0010] Applicant's invention is directed to overcoming one or more of the above drawbacks with a dry vacuum impregnation system and dry impregnation process as disclosed herein.

[0011] According to one aspect (Aspect 1) of the present invention, a vacuum tank having a container and a removable lid, the container and lid collectively forming a sealed vacuum chamber when the lid is on the container; a rack fixedly or removably supported within the vacuum chamber and configured to hold one or more items; an inner tank movably mounted to the container and configured to hold a predetermined amount of impregnating liquid therein, the inner tank being vertically movable between a first position in which the one or more articles are not immersed in the impregnating liquid and a second position in which the one or more articles are at least partially immersed in the impregnating liquid; a vacuum and pressure control system comprising one or more gas control circuits in fluid communication with the vacuum chamber when the lid is on the container; A vacuum impregnation system is provided that consists of, consists essentially of, or consists of:

[0012] Aspect 2. The vacuum impregnation system of Aspect 1, wherein the rack is removably supported within the vacuum chamber by at least one attachment.

[0013] Aspect 3. The vacuum impregnation system according to any of the above aspects, wherein the rack is fixed to the lid or container.

[0014] Aspect 4. The vacuum impregnation system of any of the above aspects, wherein the inner tank is attached to a shaft that extends through a seal at the bottom of the vessel.

[0015] Aspect 5. The vacuum impregnation system of any of the above aspects, wherein the inner tank is removably attached to the shaft.

[0016] Aspect 6. The vacuum impregnation system of any of the above aspects, wherein the shaft comprises a linear slider.

[0017] Embodiment 7. The vacuum impregnation system of any of the above embodiments, further comprising an actuator attached to the shaft and configured to move the inner tank between the first position and the second position.

[0018] Embodiment 8. The vacuum impregnation system of any of the above embodiments, further comprising a fluid control circuit extending from the inner tank to a source of impregnation liquid.

[0019] Aspect 9. The vacuum impregnation system of any of the above aspects, wherein the fluid control circuit comprises a flexible tube extending from the inner tank to a fluid port in the vessel.

[0020] Aspect 10. The vacuum impregnation system of any of the above aspects, wherein the fluid control circuit comprises a passageway extending through the shaft.

[0021] Aspect 11. The vacuum impregnation system of any of the above aspects, wherein the vacuum control system includes one or more of a first gas control circuit in communication with a vacuum pump, a second gas control circuit in communication with a pressurized gas source, and a selectively openable vent.

[0022] Aspect 12. The vacuum impregnation system of any of the above aspects, wherein the inner tank is coated with a non-stick coating.

[0023] Aspect 13. The vacuum impregnation system of any of the above aspects, wherein the inner tank includes a removable inner liner.

[0024] Aspect 14. The vacuum impregnation system of any of the above aspects, wherein the liner is a reusable or disposable liner made of a metal or plastic material.

[0025] Aspect 15. The vacuum impregnation system of any of the above aspects, wherein the inner tank includes a removable inner circumferential band disposed within the inner tank.

[0026] Embodiment 16. The vacuum impregnation system of any of the above embodiments, wherein the band includes a flat ring pressed against the inner surface of the inner tank and isolates the inner tank from the impregnation liquid at the air / impregnating agent interface.

[0027] According to another aspect (Aspect 17) of the present invention, there is provided a method of operating a vacuum impregnation system, comprising the steps of: (a) placing one or more articles in a vacuum tank at ambient pressure; (b) after step (a), sealing the vacuum tank; (c) providing a predetermined amount of impregnating liquid into the vacuum tank and into an inner tank positioned below the article or articles; (d) after steps (a) and (b), reducing the internal pressure in the vacuum tank to below ambient pressure; (e) after steps (c) and (d), raising the inner tank to at least partially immerse the one or more articles in the impregnation liquid; (f) after step (e), increasing the internal pressure in the vacuum tank above ambient pressure; (g) after step (f), lowering the inner tank to a position where the one or more articles are not immersed in the impregnation liquid in the inner tank; (h) after step (g), reducing the internal pressure in the vacuum tank to ambient pressure; (i) after step (h), opening the vacuum tank and removing the one or more articles from the vacuum tank; A method is provided that comprises, consists essentially of, or consists of:

[0028] Embodiment 18. The method of any of the above embodiments, wherein step (c) occurs before and / or simultaneously with step (a) or step (b).

[0029] Embodiment 19. The method of any of the above embodiments, wherein step (c) occurs after step (b).

[0030] Embodiment 20. The method of any of the above embodiments, wherein step (d) is performed after completing step (c).

[0031] Aspect 21. The method of any of the above aspects, wherein the vacuum tank comprises a container and a removable lid, and step (a) comprises attaching a rack to the container that holds one or more articles.

[0032] Embodiment 22. The method of any of the above embodiments, wherein the vacuum tank comprises a container and a removable lid, and step (a) comprises attaching a rack to the lid that holds one or more articles.

[0033] Embodiment 23. The method of any of the above embodiments, wherein step (c) comprises pumping a predetermined amount of impregnation liquid from outside the vacuum tank into the inner tank through a flexible tube.

[0034] Embodiment 24. The method of any of the above embodiments, wherein the inner tank is attached to a shaft that extends through a seal at the bottom of the vacuum tank, and step (e) includes raising the shaft, and step (g) includes lowering the shaft.

[0035] Embodiment 25. The method of any of the above embodiments, wherein step (c) includes pumping a predetermined amount of impregnating liquid into the inner tank from outside the vacuum tank through a passageway extending through the shaft.

[0036] Embodiment 26. The method of any of the above embodiments, further comprising (j) after step (i), drying the one or more articles from the vacuum tank if there is no crosslinking.

[0037] Embodiment 27. The method of any of the above embodiments, wherein step (j) comprises air drying or heating to transform the impregnating liquid into a solid.

[0038] In one embodiment, the dry vacuum impregnation system includes a tank-within-tank configuration in which the impregnating polymer is contained in an open-top inner tank located within a pressure-resistant outer tank having a lower section with no outlet and an upper section terminating in a sealable opening. The inner tank is positioned below the upper section of the outer tank, and the part to be impregnated is introduced into the inner tank through the sealable opening. Instead of moving the impregnating polymer from container to container, the inner tank containing the polymer is movably positioned within the outer tank and is moved upward during use to surround the part to be coated until it is immersed in the impregnating polymer. This significantly reduces foaming of the impregnating polymer caused by turbulent flow of the polymer between the storage tank and the vacuum impregnation tank, as well as excessive foaming caused by introducing the polymer into the tank under vacuum.

[0039] With the inner tank containing the polymer solution at the bottom of the traverse, the parts to be sealed are lowered into the outer tank, preferably by a hoist or the like, and the parts are usually suspended above the polymer liquid on a rack or other support. The top of the outer tank is then closed, the pressure-resistant outer tank is sealed, and a vacuum is applied to evacuate air from within the pressure-resistant outer tank of the vacuum impregnation system, including the pores / gaps of the parts. The inner tank is then raised, thereby immersing the parts in the polymer solution, and the vacuum is released to help move the polymer liquid into the gaps and pores. The outer tank is then pressurized to a pressure above atmospheric pressure, thereby forcing additional thick polymer into the pores / gaps of the parts. After a selected time, approximately 30 to 300 seconds, the pressure is released to return to atmospheric pressure, and the inner tank is lowered, allowing excess polymer to drip from the outer surfaces of the parts and the rack back into the inner tank. The rack is raised, and optionally a catch tray for excess polymer is placed below the rack, and then the rack is removed and transported to a cleaning station where excess polymer is removed from the surface of the part, and from there to a drying station where the polymer is dried, converting the viscous polymer liquid into a solid, optionally with elastomeric properties, thereby sealing pores and gaps in the article.

[0040] In particular, when a dry vacuum is used, the vacuum impregnation vessel does not need to have the large footprint of multiple shallow tanks to accommodate the head pressure issues of a wet vacuum process, and therefore, deeper tanks with smaller diameters can be used without adversely affecting sealing quality. [Brief explanation of the drawings]

[0041] [Figure 1] FIG. 1 is a schematic diagram of an exemplary vacuum impregnation system. [Figure 2] 2 shows the embodiment of FIG. 1 in a first operating state; [Figure 3] FIG. 1 illustrates an alternative embodiment of an exemplary impregnation system in a first operating state. [Figure 4] 2 shows the embodiment of FIG. 1 in a second operating state. [Figure 5] FIG. 2 shows the embodiment of FIG. 1 in a third operating state. [Figure 6] FIG. 1 illustrates an exemplary method for operating a vacuum impregnation system. DETAILED DESCRIPTION OF THE INVENTION

[0042] In the figures, like reference numbers indicate like features.

[0043] The embodiments described herein relate to a vacuum impregnation system and a method of operating a vacuum impregnation system. It will be understood that the embodiments described herein are exemplary and that other embodiments may incorporate various different aspects or combinations of the features described herein.

[0044] FIG. 1 illustrates a first exemplary embodiment of a vacuum impregnation system 100. The system 100 includes a vacuum tank formed by a container 102 and a lid 104. The container 102 is configured as the lower portion of the vacuum tank and is generally liquid-tight. The lid 104 is configured as the upper portion of the vacuum tank and is also generally liquid-tight. The container 102 terminates at its upper end with an upwardly facing opening 106, and the lid 104 has a similarly shaped downwardly facing opening 108. The lid 104 is securable to the container 102 to form a generally liquid-tight and air-tight vacuum chamber 112. One or both of the openings 106, 108 may be surrounded by or include an O-ring 110 or other seal, which may be provided on a radially extending flange to help form the generally liquid-tight enclosure. As used herein, "substantially liquid-tight" means that when all working passages and openings are closed, no gas or liquid can pass through the structure, or only a nominal amount of gas or liquid that does not affect the operation of the system can pass through the structure.

[0045] The vessel 102 and lid 104 are preferably formed in the shape of a conventional pressure vessel, having a cylindrical sidewall terminating in a domed, hemispherical, trispherical, or semi-ellipsoidal head. However, the vessel 102 and lid 104 may be generally spherical or other shapes. The vacuum tank may be configured to contain the desired operating pressure and vacuum and to withstand the expected operating temperatures. For example, the vacuum tank may be rated to operate at internal pressures ranging from 10 mmHg to 20 atmospheres of positive pressure, more preferably from 20 mmHg to 10 atmospheres of positive pressure. The vacuum tank may also be rated to operate at temperatures ranging from 5°C to 200°C, more preferably from 15°C to 100°C.

[0046] The system 100 also includes a rack 114 (or multiple racks) configured to be positioned inside the vacuum chamber 112 within the vacuum tank, either fixedly attached within the vacuum chamber or removably supported within the vacuum chamber. The rack 114 or multiple racks may be fixed to one or both of the container 102 and the lid 104. The rack 114 is preferably removably supported and / or fixed within the vacuum tank. For example, the container 102 may include an inner lip 116 extending radially inward from the container's inner wall surface 114, and the rack 114 may include an outer lip 120 extending radially outward from the rack 116 to engage the inner lip 116 and hold the rack 114 in a predetermined vertical position within the vacuum chamber 112. Other embodiments may use other mechanisms, such as hooks, to secure the rack 114 to the container 102 or the lid 104.

[0047] The connection mechanism may be configured for automated installation and removal of the rack 114 from the vacuum chamber 112. For example, the inner and outer lips 116, 120 may be configured to support the rack 114 vertically, but allow some radial and rotational movement to account for imprecision in the operation of the loading device (e.g., a crane or overhead hoist). If desired, mechanisms may be provided to secure the position of the rack 114 in all directions, such as bolts or clamps to prevent movement of the rack once it is in place. Other alternatives and modifications will be apparent to those skilled in the art in view of this disclosure.

[0048] In other embodiments, the rack 114 may be permanently secured to the container 102 or lid 104. For example, the rack 114 may be welded in place or secured by fasteners that are not intended to allow removal of the rack during normal operation and cleaning procedures. In this case, as described further below, removable holders, supports, baskets, etc. may be used to position parts within the rack for impregnation and, optionally, transport.

[0049] The rack 114 is also configured to hold one or more articles to be vacuum-impregnated and allow the impregnating liquid to contact the articles. For example, the rack 114 can include a mesh basket or a series of nested mesh baskets that support the articles from the bottom, or one or more hooks that can hold corresponding openings in the articles. The rack 114 can also be configured to suspend one or more articles without the rack 114 being immersed in the impregnating liquid. For example, each article can be suspended from the rack 114 by an intermediate disposable connector, such as a strand or loop made of plastic material. Other alternatives and variations will be apparent to those skilled in the art in view of this disclosure.

[0050] The system 100 further includes an inner tank 122 that is typically closed at its lower end so as to hold a predetermined amount of impregnating liquid, but has an open top 124 sized and shaped to receive the rack 114 and / or articles held on or suspended from the rack. For example, the inner tank 122 may comprise a cylindrical chamber having a diameter slightly smaller than the adjacent portion of the inner wall surface 118 of the container. The inner tank 122 may have a coating of a so-called non-stick material, such as polytetrafluoroethylene (PTFE), and / or may include a removable inner liner 122', such as a reusable or disposable liner made of metal or plastic material, which is expected to facilitate periodic cleaning of the inner tank 122 and allow the selection of less expensive materials for manufacturing the inner tank 122 and the container 102. For example, for surfaces that are not directly contacted by the potentially corrosive polymer impregnation liquid, stainless steel may be replaced with a lower-quality steel, such as carbon steel, aluminum, or other suitable metals without interfering with the objectives of the present invention.

[0051] The inner tank 122 is movably mounted to the vessel 102 so that it can move vertically between a first position, in which the articles held on the racks are not submerged in the impregnating liquid in the tank, and a second position, in which the articles are at least partially (preferably completely) submerged in the impregnating liquid. The operation of the inner tank 122 is described in more detail below.

[0052] The inner tank 122 may be movably mounted to the vessel 102 using any suitable mechanism. In the illustrated example, the inner tank 122 is mounted on a shaft 126 that extends through a seal 128 in the bottom of the vessel 102. The shaft 126 and seal 128 may have any suitable configuration for forming an airtight or pressure-resistant seal. For example, the shaft 126 may comprise a polished stainless steel cylinder that extends through an opening in the bottom of the vessel 102, with one or more mechanical or gland seals mounted within the opening extending radially and contacting the shaft 126 to form the sliding seal 128. The seal 128 may include any suitable arrangement, such as wipers, sealing lips, compression rings, O-rings, V-rings, wedges, packing material, etc., as known in the art of hydraulic seals. In this case, the shaft 126 is a linear slider that moves axially along the length of the shaft 126 and does not necessarily rotate about its axis. In other cases, the shaft 126 may include a lead screw that engages with internal threads in the bottom of the container 102 or have other configurations.

[0053] The actuator 130 is attached to the shaft 126 and is configured to move the inner tank 122 between a first (lowered) position and a second (raised) position. In the illustrated example, the actuator 130 comprises a hydraulic or pneumatic piston 132 and cylinder 134 assembly, which generates power by pressurizing a cylinder chamber, as is well known. In this case, the piston 132 is attached to the shaft 126 by a rigid connector 136. Thus, actuation of the actuator 130 moves the piston 132 upward, thereby moving the inner tank 122 from the first position to the second position. It will be readily appreciated that this configuration can be modified in a variety of ways. For example, the piston 132 can be fixed in place and the cylinder 134 can be coupled to the shaft 126. Alternatively, the shaft 126 can be formed as a piston that fits directly into a corresponding hydraulic or pneumatic cylinder. As another example, connector 136 may comprise one or more mechanisms, such as a chain and sprocket, a belt and pulley, gears, a transmission, levers, linkages, etc., for converting motion of piston 132 into motion of shaft 126. It will also be appreciated that actuator 130 may alternatively comprise an electric motor or other source of motion. The particular function of actuator 130 and its connection to shaft 126 is not critical to the present invention, and many variations will be appreciated in light of this disclosure.

[0054] The vacuum impregnation system 100 also includes a fluid control circuit 138 configured to supply the impregnating liquid to the inner tank 122. The fluid control circuit 138 includes any suitable arrangement of valves, passages, and / or pumps for transporting the impregnating liquid to (and optionally from) the inner tank 122. For example, the fluid control circuit 138 may include a pump 140 and an impregnating liquid valve 142, which are in turn fluidly connected to an impregnating liquid source 144 (e.g., a tank or supply passage).

[0055] The fluid control circuitry 138 may be connected to the inner tank 122 by various fluid passageway arrangements. In the example of FIG. 1 , a flexible tube 146 extends from the inner tank 122 to a fluid port 148 that penetrates the vessel 102. The fluid port 148 may be any suitable fitting arrangement (e.g., a pipe with or without a threaded connector, etc.) known in the art of pressure vessel design. The flexible tube 146 may comprise a flexible hose or the like, sized to allow the inner tank 122 to move between the first and second positions without impeding movement of the inner tank 122 or blocking the hose, and preferably is abrasion-resistant to prevent damage from repeated contact with other components. A steel-braided, pressure-rated hose or other suitable hose may be used for this purpose, although other alternatives will be apparent to those skilled in the art in light of this disclosure.

[0056] 1, the fluid control circuit 138 may be connected to the inner tank 122 by a passageway 150 extending through the shaft 126. This eliminates the need for flexible tubing 146 inside the tank environment, although flexible tubing 152 may be required to connect the shaft passageway 150 to other portions of the fluid control circuit 138.

[0057] Both embodiments using the flexible tube 146 or the shaft 150 to supply the impregnating liquid to the inner tank 122 provide the option of selectively removing the impregnating liquid from the inner tank 122 by draining or pumping it in a countercurrent direction. This can be advantageous to return the impregnating liquid to a reservoir for later use, to prepare the inner tank 122 for cleaning, or to provide other benefits.

[0058] Notwithstanding the above, in other embodiments, the fluid control circuit 138 may be configured to supply only the impregnating liquid to the inner tank 122. For example, the fluid control circuit 138 may be configured to supply the impregnating liquid through the open top 124 of the inner tank 122. In one such embodiment, the fluid control circuit 138 may include an outlet nozzle attached to the inner wall surface 118 of the container 102 at a position above the open top 124 when the inner tank 122 is in the first position. In this case, the impregnating liquid may be pumped through the nozzle and injected or sprayed into the inner tank 122, but cannot be removed by backflow. The fluid control circuit 138 may also be configured to inject the impregnating liquid into the inner tank 122 through the top end 106 of the container 102 before the lid 104 is attached. Other alternatives and variations will be apparent to those skilled in the art in view of the present disclosure.

[0059] It is also envisioned that multiple inner tanks 122 may be used in some embodiments. Such multiple tanks 122 may be useful for vacuum impregnation of several articles using different impregnation liquids or for vacuum impregnation of smaller batches of articles without having to fill the entire volume of a single inner tank 122. The multiple inner tanks 122 may be movable together (e.g., mounted on the same shaft 126 or provided as separate parts of a single, unified structure) or may be independently movable (e.g., mounted on separate shafts and with separate actuators).

[0060] The inner tank 122 may also be removable, for example, to clean the inner tank without personnel entering the vessel to facilitate successive processing of parts using a replacement tank. The inner tank 122 may also be interchangeable with tanks having different dimensions or may be filled to different heights to vacuum impregnate various articles or combinations of articles.

[0061] The inner tank 122 may be fitted with a removable inner peripheral band positioned near the surface of the impregnation liquid in the inner tank, e.g., near the air / impregnation interface. This band forms a flat ring pressed against the inner surface of the inner tank 122 and may be, for example, a spring-loaded metal ring. This band isolates the inner tank from the impregnation liquid at the air / impregnation interface and allows polymer deposits generated during processing to collect on the band surface, thereby facilitating easy removal of the deposits. This feature may be used instead of or in combination with the liner 122′.

[0062] The vacuum impregnation system 100 may also include a vacuum control system that operates to control the gas pressure within the vacuum chamber 112. For example, the vacuum control system may include a first gas control circuit 154 that reduces the gas pressure within the vacuum chamber 112 below the ambient pressure outside the vacuum tank, a second gas control circuit 156 that increases the gas pressure within the vacuum chamber 112 above the ambient pressure outside the vacuum tank, and a third gas control circuit 158 ​​that equalizes the pressure within the vacuum chamber 112 to the ambient pressure outside the vacuum tank.

[0063] The gas control circuits 154, 156, and 158 can incorporate any suitable arrangement of equipment that provides the desired functionality. For example, in the illustrated embodiment, the first gas control circuit 154 may include a first valve 160 connecting a vacuum tank to a vacuum pump 162, the second gas control circuit 156 may include a second valve 164 connecting the vacuum tank to a compressor 166, and the third gas control circuit may include a third valve 168 connecting the vacuum tank to ambient air. The vacuum control system components may also include other devices such as filters, liquid traps, gauges, and the like. Any automated or manually operated control system may be used to operate the vacuum control system components. Other alternatives and modifications will be apparent to those skilled in the art in view of this disclosure.

[0064] The vacuum impregnation system 100 also preferably includes a liquid drain circuit 170, such as a liquid drain valve 172, configured to drain the impregnation liquid, condensate, and other liquids from the bottom of the vacuum tank.

[0065] The selection and use of valves, vacuum pumps, compressors, etc. are well known in the art of vacuum impregnation systems and need not be described in further detail herein.

[0066] An exemplary method for operating the vacuum impregnation system 100 and other embodiments is shown in FIGS. 2 through 6. The exemplary process begins by placing the articles 200 to be sealed on the rack 114 (step 600), placing the rack 114 on the container 102 or lid 104 (step 602), and sealing the vacuum tank by securing the lid 104 to the container 102 (step 604). Steps 600 and 602 can be performed in any order (i.e., the articles 200 can be placed on the rack 114 before or after the rack 114 is secured to the container 102 or lid 104). FIG. 2 shows the articles secured to the rack 114 before the rack 114 is secured to the container 102. FIG. 3 shows the rack 114 secured to the lid 104 in an alternative embodiment. If the rack 114 is permanently secured to the vacuum tank, step 602 is performed by default. FIG. 4 shows that the rack 114 is secured to the vacuum tank and the lid 104 is secured to the container 102 to form a sealed vacuum chamber 112 .

[0067] In step 606, the inner tank 122 is filled to a desired level with the impregnating liquid 202. Step 606 can be performed before or after the lid 104 is sealed to the vessel 102. For example, FIG. 2 shows the impregnating liquid 202 at a low level (or even completely absent) while the rack 114 is being loaded, and the impregnating liquid 202 may be maintained at this level until the lid 104 is sealed to the vessel 102. In contrast, FIG. 3 shows the impregnating liquid 202 being filled to a working level before sealing the lid 104 to the vessel 102.

[0068] Step 608 is performed after sealing the lid 104 to the container 102. In step 608, a vacuum is created in the vacuum chamber 112, for example, by activating the first gas control circuit 154 to pump ambient air out of the vacuum chamber 112. Optionally, one or more purging steps may be performed before step 608 to help remove gases in the ambient air that may interfere with the process. For example, nitrogen may be pumped into the vacuum chamber 112 to displace the ambient air before performing step 608.

[0069] Step 608 is preferably performed after the inner tank 122 is filled with the impregnating liquid in step 606. This helps prevent foaming of the impregnating liquid 202, which can occur when the liquid is introduced into a vacuum atmosphere, and provides a significant improvement by facilitating easier, safer, and / or less frequent cleaning of the vacuum tank. However, it is believed that introducing the impregnating liquid 202 within the confines of the inner tank 122 can at least partially isolate foaming-related problems for the inner tank 122. In this case, the majority of the cleaning process is directed toward cleaning the inner tank 122, which can be facilitated by making the inner tank 122 removable (e.g., attaching the inner tank to the shaft 126 with nuts 174 or other fasteners) or by providing the inner tank 122 with a removable liner 122′. Thus, embodiments may optionally perform the vacuum generation step 608 before or simultaneously with introducing the impregnating liquid in step 606.

[0070] Next, in step 610, the inner tank 122 is raised by actuating the actuator 130 until the article 200 to be vacuum impregnated is submerged in the impregnating liquid 202. The article 200 may be fully submerged, or only to a desired extent if it is not necessary to completely impregnate the article 200. Once submerged, the impregnating liquid surrounds the article and the pores and gaps to be filled and can penetrate to some extent into such pores and gaps.

[0071] Performing step 610 after step 608 results in a dry vacuum impregnation process (i.e., the vacuum is generated before immersing the article 200), which is expected to reduce or eliminate uneven impregnation of the article at different locations within the vacuum chamber 112, since the generation of the vacuum in the holes does not compete with the head pressure generated by the immersion liquid. This allows the vacuum tank to be relatively large vertically, resulting in higher throughput for a given capital investment in the processing equipment.

[0072] While the article 200 is immersed, the process continues to step 612, where the second gas control circuit 156 is activated to increase the pressure in the vacuum chamber 112 above atmospheric pressure level. Increasing the pressure in the sealed container forces the impregnating liquid into the evacuated pores and gaps, improving the seal.

[0073] Next, in step 614, the articles 200 are removed from the impregnating liquid by actuating the actuator 130 to lower the inner tank 122 until the impregnating liquid is below the lowest article 200 on the rack 114. During and after this step, any residual impregnating liquid 202 on the articles 200 is drained from the articles 200 into the inner tank 122 to be reused or recycled.

[0074] Finally, in steps 616 and 618, the vacuum chamber 112 is vented to atmosphere by activating the third gas control circuit 158, and the article 200 is removed.

[0075] It will be appreciated that some or all of the foregoing process steps may be performed according to various operating parameters. Examples of such parameters include the magnitude of the vacuum created in step 608, the magnitude of the pressure created in step 912, the soak time in step 610, the wait time before venting the tank to the atmosphere in step 616, etc. Additionally, the temperature of the article 200, the air pressure within the vacuum chamber 112, and the impregnating liquid 202 can all be adjusted. The exact desired values ​​or ranges of such variables can be determined by routine experimentation.

[0076] Embodiments are expected to be particularly useful when used with relatively viscous impregnating liquids, which can be selected to be more or less viscous depending on whether the article is an assembly that may require disassembly for maintenance. Preferably, the impregnating liquid is selected to form a uniform, homogeneous seal, providing a robust seal between the sealing material and a wide variety of materials, including metals and plastics, that make up the assembly. The impregnating liquid is also preferably provided as an inert polymer dissolved or dispersed in a solvent, preferably water, which does not require a separate curing step to complete the seal; only evaporation of any remaining carrier or solvent, most preferably water, is required. Those skilled in the polymer art will understand that an inert polymer refers to a polymer lacking sufficient functional groups to impart a particular chemical reactivity to the polymer. Suitable inert polymers may include, by way of non-limiting example, polyacrylates, polyvinyl alcohols, polyurethanes, polyvinyl acetates, and the like. The impregnating liquid may optionally contain additives known to be used in formulating adhesives and sealants, such as rheological aids, wetting agents, anti-aging agents, stabilizers, biostats, and / or color pigments. Generally, thick impregnating polymer materials have viscosities ranging from about 50 Pa·s to 5000 mPa·s and greater, depending on the non-Newtonian behavior of the polymer (50-5000 centipoise) solution.

[0077] Embodiments can be configured to seal holes and gaps in a variety of articles, including articles having both metal and plastic components. Exemplary articles include, but are not limited to, telecommunications equipment (e.g., radios, cell phones, etc.), audio equipment (e.g., headphones, speakers, microphones), and other electronic devices such as computers, processing units, electronic control devices, wiring harnesses, electrical connectors, etc.

[0078] As noted above, although the invention has been illustrated and described with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various changes in the details may be made within the scope and range of equivalents of the claims without departing from the invention.

[0079] Although embodiments have been described herein in a manner that enables a clear and concise specification to be written, it is intended and will be understood that the embodiments may be combined or separated in various ways without departing from the invention. For example, it will be understood that all preferred features described herein are applicable to all aspects of the invention described herein.

[0080] While preferred embodiments of the present invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will occur to those skilled in the art without departing from the spirit of the invention. It is therefore intended by the appended claims to cover all such modifications which fall within the spirit and scope of the invention.

Claims

1. a vacuum tank comprising a container and a removable lid, the container and the lid collectively forming a sealed vacuum chamber when the lid is on the container; a rack fixedly or removably supported within the vacuum chamber and configured to hold one or more items; an inner tank movably mounted to the container and configured to hold a predetermined amount of impregnating liquid therein, the inner tank being vertically movable between a first position in which the one or more articles are not immersed in the impregnating liquid and a second position in which the one or more articles are at least partially immersed in the impregnating liquid; a vacuum and pressure control system comprising one or more gas control circuits in fluid communication with the vacuum chamber when the lid is on the container; A vacuum impregnation system comprising:

2. The vacuum impregnation system of claim 1 , wherein the rack is removably supported within the vacuum chamber by at least one attachment.

3. The vacuum impregnation system of claim 1 , wherein the rack is fixed to the lid or the container.

4. 10. The vacuum impregnation system of claim 1, wherein the inner tank is attached to a shaft that extends through a seal at the bottom of the vessel.

5. The vacuum impregnation system of claim 4 , wherein the inner tank is removably attached to the shaft.

6. The vacuum impregnation system of claim 4 , wherein the shaft comprises a linear slider.

7. 7. The vacuum impregnation system of claim 6, further comprising an actuator attached to the shaft and configured to move the inner tank between the first position and the second position.

8. 8. The vacuum impregnation system of claim 7, further comprising a fluid control circuit extending from the inner tank to a source of impregnation liquid.

9. 9. The vacuum impregnation system of claim 8, wherein the fluid control circuit comprises a flexible tube extending from the inner tank to a fluid port in the vessel.

10. The vacuum impregnation system of claim 8 , wherein the fluid control circuit comprises a passageway extending through the shaft.

11. 10. The vacuum impregnation system of claim 1, wherein the vacuum control system comprises one or more of a first gas control circuit in communication with a vacuum pump, a second gas control circuit in communication with a source of pressurized gas, and a selectively openable vent.

12. The vacuum impregnation system of claim 1 , wherein the inner tank is coated with a non-stick coating.

13. The vacuum impregnation system of claim 1 , wherein the inner tank includes a removable inner liner.

14. The vacuum impregnation system of claim 1 , wherein the liner is a reusable or disposable liner made of metal or plastic material.

15. The inner tank includes a removable inner circumferential band disposed within the inner tank. The vacuum impregnation system of claim 1 .

16. 10. The vacuum impregnation system of claim 1, wherein the band comprises a flat ring pressed against the inner surface of the inner tank and isolating the inner tank from the impregnating liquid at an air / impregnating agent interface.

17. 1. A method of operating a vacuum impregnation system, comprising: (a) placing one or more articles in a vacuum tank at ambient pressure; (b) after step (a), sealing the vacuum tank; (c) providing a predetermined amount of impregnating liquid into the vacuum tank and into an inner tank positioned below the one or more articles; (d) after steps (a) and (b), reducing the internal pressure in the vacuum tank to below ambient pressure; (e) after steps (c) and (d), raising the inner tank to at least partially immerse the one or more articles in the impregnation liquid; (f) after step (e), increasing the internal pressure in the vacuum tank above ambient pressure; (g) after step (f), lowering the inner tank to a position where the one or more articles are not immersed in the impregnation liquid in the inner tank; (h) after step (g), reducing the internal pressure in the vacuum tank to ambient pressure; (i) after step (h), opening the vacuum tank and removing the one or more articles from the vacuum tank; A method comprising:

18. 18. The method of claim 17, wherein step (c) is carried out before and / or simultaneously with step (a) or step (b).

19. 18. The method of claim 17, wherein step (c) occurs after step (b).

20. 18. The method of claim 17, wherein step (d) is performed after completing step (c).

21. 20. The method of claim 17, wherein the vacuum tank comprises a container and a removable lid, and step (a) comprises attaching a rack to the container that holds the one or more articles.

22. 20. The method of claim 17, wherein the vacuum tank comprises a container and a removable lid, and step (a) comprises attaching a rack to the lid that holds the one or more items.

23. 18. The method of claim 17, wherein step (c) comprises pumping the predetermined amount of impregnating liquid from outside the vacuum tank into the inner tank through a flexible tube.

24. 18. The method of claim 17, wherein the inner tank is attached to a shaft that extends through a seal in the bottom of the vacuum tank, and step (e) includes raising the shaft and step (g) includes lowering the shaft.

25. 25. The method of claim 24, wherein step (c) comprises pumping the quantity of impregnating liquid into the inner tank from outside the vacuum tank through a passageway extending through the shaft.

26. 20. The method of claim 17, further comprising the step of: (j) after step (i), drying the one or more articles from the vacuum tank in the absence of crosslinking.

27. 27. The method of claim 26, wherein step (j) comprises air drying or heating to transform the impregnating liquid into a solid.

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