In the spirit of transferring technology between industries, a ceramic-over-metal coating process used in offshore oil drilling applications has migrated to injection molding in the form of ceramic-coated barrels. One of the first beneficiaries of this transfer was injection molder Plasticraft, based in Albertville, AL. The company operates more than 50 horizontal and vertical presses, molding, among other products, insert molded levelers and knobs on a 200-ton rotary table Trueblood machine.

This particular press runs about 80 hours a week, molding nylon 6/6. Tim Miller, maintenance supervisor at Plasticraft, says the 1.75-inch barrel was the victim of chronic chemical wear and surface damage. Also, abrasive damage and wear was caused by metal particles in regrind material from insert molded parts that were recycled. “Every now and then they’d grind up bolts and inserts and that would really eat up barrels,” says Miller.

Such wear necessitated barrel replacement once every 12 months. Miller says he had two barrels that he rotated on a tag-team basis, repairing one while the other ran in the press. Plasticraft was not only spending money to repair worn barrels, but the company was also losing money to downtime during each replacement.

With the hope of getting more for its barrel buck, Plasticraft, at the behest of barrel supplier General Plastex, tried a new ceramic-coated barrel. The barrel was produced by General Plastex using a 4140-HT steel with a D-2 steel liner. It was then treated with a composite ceramic material that thermochemically bonds to the interior of the barrel. This water-based film of ceramic is applied and heated, producing a thickness on the barrel wall of .002 to .003 inch. An interphase between the ceramic material and the metal barrel surface creates a bond with the substrate that reportedly produces a bond strength in excess of 10,000 psi. After bonding, General Plastex reports, the surface density is 98 percent, which minimizes porosity and helps the lining resist chemical corrosion.

Although Miller admits he didn’t know what to expect from the barrel, at Plasticraft the results proved more tangible. The barrel was installed on the Trueblood press in 1995 and then used almost continuously until August 1998, when it was removed for evaluation. After almost three years of use and more than 12 million cycles the barrel showed a minimum of wear and was returned to the press, where it continues to run today. “We have already experienced three times the normal barrel life,” Miller says. “I don’t think that barrel was off by more than half a thousandth when we pulled it. The screw, on the other hand, was pretty much torn up.”

Dave Mantyla, sales and general manager at General Plastex, says the ceramic coating is designed for molders who need a technological advance to address corrosion problems. “It’s not for everyone, but if you’re running a corrosive material, it will do the job,” he says. “If you’ve addressed your wear problem with a metallic barrel, then this would be the next step up. It’s for people who’ve pushed the envelope on abrasion and corrosion.” He says molders who run PVC, glass-filled nylon, PBT, and fluorocarbon-based materials would be good potential candidates for the ceramic-coated barrel.

Mantyla emphasizes that the ceramic does not act as a liner in the barrel; it’s a coating that fills voids in the steel matrix of the barrel. In lab tests, the ceramic demonstrated a hardness range of 1000 to 1850 Vickers. In chemical testing the material withstood hot 30 percent calcium chloride and hot sulfuric acid; the calcium chloride test produced no wear after more than 560 hours.

General Plastex reports that there are no known steels with which the ceramic will not bond except for solid carbide, which is not used in barrels in solid form. For price, Mantyla says the ceramic-coated barrel compares with its premium metallic counterparts and generally runs about 30 percent more than a standard barrel.