Vacuum Impregnation Process Solves Leaking Cable Problem for Machinery Monitoring Manufacturer

By David Gaines
For Wiring Harness News

Braided metal covers on coaxial or triaxial cables are an essential medium that protects the interior wiring from signal interference. For electronic OEM's, another challenge is to produce a braided cable that is environmentally sound, one that will withstand harsh chemicals and industrial fluids.

Occasionally, an even more demanding challenge requires that the cable does not act as a conduit for unwanted contaminants and liquids that can compromise the integrity of the connection. One forward-looking electronic OEM recently found a unique solution for avoiding this problem.

Bently-Nevada Corporation's manufacturing plant in Minden, Nevada makes vibration sensor equipment for rotating machinery in large plants — oil refineries, power generation facilities, and petrochemical plants. The company also produces machinery management software, vibration monitors and vibration transducers. Bently has been in the machinery monitoring business since 1969, with additional manufacturing plants in Houston, Texas and Manchester, England for a total of 1,200 employees worldwide.

Bently-Nevada specializes in proximity probes that mount inside the casings of turbines and monitor shaft vibrations that, if left unmonitored, could eventually damage the shaft bearings. Normally, the probes are located near the bearings and are in contact with oil. From this location, the sensor's signal travels through a braided coaxial or triaxial cable to a Proximitor® (Proximitor® is a trademark of Bently Nevada Corporation) outside the machine. From the Proximitor®, the signal is fed through a conduit to a control room where it is monitored by a computerized system.

However, a problem began to surface in controlling oil seeping through their transducer cables at some of their clients' industrial plants. The cable would act like a candlewick, picking up oil and delivering it to the Proximitor® enclosure. Additionally, when the Teflon® (Teflon® is a trademark of Dupont Corporation) jacket on the cable was cut or had an abrasion, it allowed the oil to drip out at that point. Maintenance crews would then have to go in to drain the oil from the enclosure and clean it up off the floor.

Since environmental laws mandate that all leaking fluids be accounted for, processing plants must remain vigilant for fluid leaks of any kind. An oil leak is not only an environmental problem, but the work involved to clean up the facility and equipment and then document it, is a time and money waster for these high intensity operations.

Bently's first solution to the leaking oil problem consisted of cutting the cable and then inserting a hard epoxy plug, one to two inches long, in the middle of the cable and then splicing the cable back together. This would allow the oil to migrate down the cable to the plug, which would dam up the oil. If a client's cable had to be routed through a tight bend radius where the plug was located, the plug would constrict the cable from bending, making it difficult to route. The process was labor-intensive, costly, and cumbersome.

It became imperative for Bently to find a workable solution that would offer their clients maintenance free operation, and eliminate the need to rework the cables.

While talking to a supplier of industrial resins, Bently-Nevada learned of a company called Magna-Tech/TechnaSeal that helps companies engineer sealing solutions. Located in Muncie, Indiana, Magna-Tech offers vacuum impregnation sealing with applications custom-tailored to meet unique demands.

"Magna-Tech proved very willing to assist us with a solution," emphasized Dave Van Den Berg, a Project Engineer at Bently. "Since this was a very different application for them, we went through many prototypes with which they willingly helped us."

After a thorough investigation and many prototype runs, Magna-Tech devised a special process for the braided cable that was found to stop oil from flowing through it. Their recommendation was to seal the cable with vacuum impregnation.

Vacuum impregnation is effective because the seal is made with an anaerobic resin composed of methacrylate monomers, which are formulated differently than those found in metal sealants. The resin is purposely designed to seal at the interface between two dissimilar materials—such as plastic and metal—and endure the differing coefficients of expansion of these materials. The chemical is non-hazardous and presents no residue, so it carries no adverse effects on solderability or electrical conductivity. The resin is formulated to withstand a wide range of temperatures from -40°C to +150°C.

Research demonstrates that vacuum impregnation permanently seals parts in a way that cannot crack or degrade, with better quality control and higher production rates than most other sealing methods. There is no shrinkage, it stops corrosion, and it meets thermal shock requirements.

To assure quality control, Magna-Tech/TechnaSeal's process is ISO 9002 and QS 9000 certified. Manufacturers stand to profit from this because the proper seal on a part can prevent the failure of a larger component. Since "First Time Capability" is the standard by which most manufacturers measure success, total sealing means they can warrant that their product will perform flawlessly right from the start. All this adds up to financial savings for OEMs by reducing replacement costs and service hours.

"Once all of the porosities and voids in the cable were completely filled in with vacuum impregnation process, the oil no longer has a path to migrate down the cable," Van Den Berg pointed out. "The cured resin they call Flex-Seal remains flexible, so our cable now bends around corners without cracking or breaking the seal."

Vacuum impregnation sealing stopped the migrating oil, and totally eliminated the need for cleaning up oil messes and documenting oil loss at their customer's sites.

"When we started using vacuum sealing, about three years ago, we estimated a saving of about $14 per cable on the time and materials needed to rework the cables," Van Den Berg stated. "The sealing has not only saved us a lot of time and effort, but it has saved our clients a great deal of time and money too."

"I found that Magna-Tech was very willing to help us with the prototyping," Van Den Berg commented. "There are very few companies that do this kind of work at a competitive price, while still delivering consistent quality, I could recommend them to other engineers needing this type of solution."

For more information on vacuum impregnation sealing for electronic cables and connectors contact MagnaTech/TechnaSeal at 3416 South Hoyt Avenue, Muncie, IN 47302. Phone (284) 5050 or Fax (765) 286-0557; E-mail: info@magnatechmfg.com or visit Internet: http://www.technaseal.com or http://www.magnatechmfg.com.