Crislip Processes Custom-Made Rubber Linings for Chemical Tanks
Feb 1, 1998 12:00 PM, Foss Farrar
THE CRISLIP CORPORATION found a niche market installing rubber linings in tank trailers afterthree decades in the industrial rubber relining business. During those years, the company developed a rubber manufacturing process.
Crislip is based in Creston, Ohio, about 25 miles west of Akron. Incorporated in 1951, the company started out as a job shop for a major rubber manufacturer, removing rubber from worn tank treads of military tanks. Crislip later did tank lining work for another major rubber manufacturer.
In the early 1960s, Denver Crislip Sr, the company founder, began working independently of major rubber suppliers. This was a tough period of growth for the company because it had to "stretch and strain" to find rubber and adhesives for manufacturing, says the founder's son and company president, Denver "Sonny" Crislip Jr. Major suppliers stopped providing materials, and Crislip started producing its own brand of rubber lining materials.
"We floundered for awhile," Crislip says. "We specialized in refurbishing cell components for manufacturers of chlorine. We were removing failed linings from chlorine cells, repairing steel and cast iron cell parts, and relining the parts with rubber."
In the early 1980s, the chemical manufacturers serviced by Crislip closed down. That was when Crislip changed the focus of its business to installing linings in tank trailers.
Tanks Become Priority "We had been lining tanks through the years - maybe one or two a year - but they were never a big part of the business," Crislip says. "Now they are a priority."
Crislip installs rubber linings in about 40 to 45 tank trailers per year. These tanks haul hazardous wastes and chemicals, mostly acids and caustics. New tanks represent 80% of the total installation business. The other 20% are tank lining repair and reline projects. Old linings are stripped out and the tanks are sandblasted before Crislip installs new linings.
Though well-established with tank truck customers in the United States and Canada, Crislip is not pursuing new markets. The company prefers to stay small.
"We don't plan to expand," Crislip says. "When we were lining 35-ft chlorine cells, we had 20 employees. Now we have eight. The chlorine cell work was dirty and required moving very heavy parts. Tank work is cleaner and more agreeable."
Customers Demand More The Crislip Corporation has a good reputation in the industry, Crislip adds. The company offers a standard one-year guarantee for workmanship and materials on lining jobs. "We may not always be right," he says. "But if we're not, we always make it right." Producing effective tanker linings is trickier these days than in the past, Crislip says.
In the past, tank trucks hauling clean acid went from Point A to Point B, then returned to their home terminals empty, Crislip says. But much of the acid hauled today is "left-over slop" being transported for disposal.
"These days acid often is not clean. It's a byproduct of another process," he says. "So you get acid with undesirable traces of other chemicals. Also, truckers need to run loaded in both directions. Linings take a beating."
Newly installed rubber tank linings for waste haulers should last seven to 10 years, Crislip says. But there is no simple way to predict real-world performance.
"We have installed some linings that have lasted 19 years," he says. "On the short end, one brand-new lining failed after one load. In that instance, the carrier put the wrong chemical in the tank. It was a solvent, and the lining had no resistance."
The Department of Transportation requires that tank trailer linings be inspected visually and electrically spark- tested once a year. The Crislip Corporation does the federally mandated inspections for customers, but that isn't a big part of the company's business. Custom-formulated rubber linings are the focus.
Selecting Lining Formulas Each tanker lining installed by the Crislip Corporation is made of custom-mixed materials. The company makes a careful determination of what ingredients to use and in what quantity.
"A single formula that works for all applications doesn't exist," Crislip says. "We choose materials based on the products a tank will transport. We also need to know the concentrations, temperatures, and impurity levels of these products. With that information, an evaluation is made of the chemical resistance properties of the materials we offer, and any reactions that may take place between the lining materials and the products hauled in the tank."
The three types of linings typically produced by the Crislip Corporation are natural rubber, chlorobutyl, and hypalon. For natural rubber linings, the company produces three variations - soft, semi-hard, and hard.
"Soft rubber may not handle something that is hot, Crislip says. "However, chlorobutyl may take temperatures up to 200 degrees F. Hypalon has the advantage of heat resistance, increased chemical resistance to some products, and some amount of resistance to solvents and oils."
The Crislip Corporation has developed tank lining recipes that have a proven track record, Crislip says. Materials are custom-mixed for Crislip by a rubber company in suburban Akron, Ohio.
Processing Rubber Sheets "Our mixer gives us the basic polymer material in slabs," Crislip explains. "We take the slabs and process them into rubber sheet that is usable as linings."
Crislip's first step in producing sheet for linings is to place the raw slabs in a warm-up mill. The mill consists of two large rollers and has the appearance of an oversized wringer for a washing machine. As the material is processed through the mill, it becomes hot and putty-like and sticks to the front roll. A worker cuts the material free and moves it to a rack of rollers called a calender. In the calender, the rubber material is rolled into thin continuous lengths.
"The warm-up mill produces slabs about a half inch thick," Crislip says. "Slabs processed through the calender are less than 1/32 inch thick. We throw the hot half-inch slabs into the top nip of the calender, and it spreads out and bands up on the middle roll. This thin layer then is stripped from the calender roll and applied to a polyethylene film liner. The plastic liner supports the rubber and prevents it from sticking together when it is rolled."
The plastic-lined rubber layer is run to a length of 180 feet. It is cut, removed from the take-up roll, and fed through the machine again, adding another layer of lining material. "By adding layers, we get the material to the thickness we want," Crislip says. "Most of our linings are one-quarter inch thick."
The quarter-inch sheet is rolled on a core awaiting installation. The plastic liner is not removed from the base of the sheet until it is ready to be installed in a tank.
An Art Form Installing tank linings is largely an art, Crislip says. Newly hired company employees train through observation and, finally, by doing the work themselves. On average, it takes a worker about three years to become proficient in all lining application procedures.
In preparation for lining, the tank interior surface and openings are sandblasted. A metal primer that also serves as an adhesive then is applied to the freshly blasted metal. A second coat of rubber-to-metal adhesive is applied to the primer. Finally, a tacky third adhesive is applied.
Meanwhile, rubber sheet is cut to proper shape, the plastic is removed, and a sticky rubber tack cement is applied to the lining. The cemented rubber lining is rolled in a cloth liner and passed to a crew inside (typically two people). These workers carefully position the lining, remove the cloth, then roll and "stitch" the rubber. Stitching is the process of pressing the sticky cement-coated side of the rubber sheet to a sticky cement-covered section of the tank. A narrow hand roller is run briskly over the entire surface to push out any trapped air bubbles.
Rubber panel edges are beveled at 30-degree angles. This is necessary for the superior, more labor intensive stive-butt cap-strip form of installation that Crislip uses. Accurate work usually results in a close, firm fit. "If the panels are installed properly, it's difficult to tell where a seam is," says Duaine "Buzz" Crislip, company vice-president and Sonny's brother.
After installation, the lining is visually inspected and electrically spark-tested. Any flaws are corrected. The lining then is cured by injecting steam under pressure into the tank. Curing takes four to 24 hours. The tank interior then is cooled and dried. The entire lining is again spark-tested to expose any flaws.
The Crislip brothers say that their company does not save much by producing their own rolls of rubber for tank linings as opposed to purchasing the rolls from an outside supplier. But the in-house production operation provides cost economies through recycling of trimmed remnants, referred to as scrap.
"We can't make the initial roll of lining materials much cheaper, but we save a lot using the scraps," Sonny Crislip says. "We use every piece of scrap rubber because it can be reprocessed." Scrap rubber is valued at about $1.50 per pound, he adds.
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