Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Reexamination Certificate
1999-02-26
2001-09-18
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
C174S11000P, C174S036000
Reexamination Certificate
active
06291773
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to precluding fluid wicking and, in particular, to precluding fluid wicking within an interior of a cable.
BACKGROUND OF THE INVENTION
A wide variety of applications in the industry of monitoring the characteristics of rotating machinery require at least one transducer or sensor to be internally mounted within a machine case. A mounting bracket may be used to strategically mount the transducer and a cable associated with the transducer is routed out of the machine case. The routing of the cable through the machine case is usually through an adapter which includes some type of rubber grommet. The rubber grommet prevents leakage of fluid through the case via an outer surface of the cable.
Typically, a junction box is mounted on or near the exterior of the machine case and encloses the connections between the transducer cable and an extension cable that is used to route the output of the transducer to a processing unit.
As noted, the rubber grommet adequately prevents fluid from exiting through the machine case via the outer surface of the cable. However, a long felt problem in the industry still exists in that the fluid permeates through cuts and cracks in the outer jacket of the cable and is wicked up by the interior and particularly the braiding of the cable and is thus allowed to flow directly to the junction box or onto a shop floor. This not only causes a safety hazard, but an environmental hazard as well. As a result, the junction box must be periodically drained of fluid and/or the shop floor cleaned.
In addition, fluid may penetrate to the interior of the cable by way of a transition area between the transducer and one end of the cable. Furthermore, the tip of the transducer itself may become damaged and allow an entry for fluid to be wicked up by the interior and particularly the braiding of the cable.
SUMMARY OF THE INVENTION
The present invention solves the problem of fluid wicking within the interior of a cable such that the fluid is drawn from within a machine case to an outside environment. This is achieved through a process of impregnating the cable with a special sealing composition such as that sold by Loctite under the name “Flexseal XT”. This material is a liquid and is designed to cure when it reacts with an activator-type of material such as copper. If the cable being used does not include an activator-type of material, an additional problem arises in how this liquid composition is to be cured once it has been impregnated into the cable. Impregnating the cable with the sealing composition and then curing the sealing composition within the cable are some of the problems the present invention addresses.
A triaxial cable will be employed in describing the method used for successfully impregnating the cable with the sealing composition and curing this composition so that it precludes fluid wicking therethrough.
A typical triaxial cable includes an ultimate strata, a penultimate strata and a central strata concentrically disposed. The central strata includes a central signal transmission medium separated from the penultimate strata by a central insulator or dielectric. The penultimate strata includes a braided sheath circumscribing a braided conductor and an insulator interposed therebetween. The ultimate strata surrounds the interior or the penultimate strata and central strata of the cable.
The first step in impregnating the cable with the sealing composition is to provide a leakage path for the sealing composition to pervade within the interior of the cable. This is accomplished by cutting the cable to a desired length and then removing any crimping of the cable due to the cutting action. In addition, if the ends of the braided conductor and/or sheath are soldered, one must be careful that the wicking of the solder paste and flux do not completely seal off the ends of the cable.
At this time it is preferred that both ends of the cable are stripped in a step-like fashion in order to expose a desired length of the braided conductor, the braided sheath and the central signal transmission medium. As will be delineated below, this allows the ends of the cable to retain their original flexibility after the process of curing the sealing composition is completed.
Once the cable is provided with ample leakage paths, it is placed within a basket. The ends of the cable are coupled to the basket in an elevated position such that when the liquid composition has been impregnated into the cable it does not flow back out.
Now that the cable has been properly coupled to the basket, the basket is placed within a chamber of a machine. The chamber of the machine is sealed and a pressure differential, i.e., a vacuum, is applied thereby providing a pull system for exhausting gas from the interior of the cable and from the substantially moisture free chamber. The liquid composition is then added in order to submerge the cable or at least come in contact with one or more leakage paths provided at one or both ends of the cable. The pressure differential (vacuum) is continuously applied during the process of adding the sealing composition. This pressure differential pulls out any air bubbles which have formed within the solution itself or within the cable.
Once this step of the process is completed, the pressure differential (vacuum) is removed and the chamber is bled back to room pressure. Then, the fluid is applied under pressure. The added pressure in the chamber forces the sealing composition within the interior of the cable. This is the actual impregnation step of the process.
The next step is to bleed off the pressure of the chamber so that it is brought back down to room pressure. The chamber is then opened and the basket is removed from the bath of sealing composition. The basket is then spun in order to remove any of the excess sealing composition from the exterior of the exposed cable. This is done in a manner that allows the uncured sealing composition to be retained within an intermediate portion of the cable.
Next, the cable is washed by agitating the basket up and down in a warm bath of water and mild detergent. After the first warm bath, the basket is placed into a second bath of clean water and then into an activator solution.
The washing cycle completely cleans the liquid composition out of the ends of the cable which have been exposed by the stripping process and also off the exposed cable. Even though the exposed ends of the cable have been rinsed clean of the sealing composition the rest of the cable remains completely impregnated.
The temperature of the solutions used in the washing cycle are elevated in order to partially cure the sealing composition impregnated into the cable.
Finally, the basket having the ends of the cable still coupled thereto is put into an oven and baked. The cable becomes semi-rigid after the sealing composition is completely cured in the oven. However, the length of cable which runs from the very ends of the cable to where the ultimate strata begins retains its original flexibility as a result of the sealing composition being washed out.
The need for flexibility at one end of the cable is particularly important because it is required to make several very sharp angle bends when operatively coupled to a transducer. In addition, the ends of the cable may be required to make an additional sharp angle bend at an area where they exist at a back end of the transducer or a connector.
OBJECTS OF THE INVENTION
A primary object of the present invention is to provide a new and novel method of precluding fluid wicking within the interior of a cable.
A further object of the present invention is to provide a cable as characterized above which is impregnated with a sealing composition.
Another further object of the present invention is to provide a cable as characterized above wherein the sealing composition which is impregnated into the cable has been properly cured.
Another further object of the present invention is to provide a cable as characterized above which allows a length at one or b
Berg Dave Van Den
Nikkels Robert
Bently Nevada Corporation
DeBoo Dennis
Mayo III William H.
Reichard Dean A.
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