CPVC is not for everyone but new pipe equipment makes it easier.

Vinyl extruders have hesitated to tackle CPVC pipe, which is trickier to process. But new screw and die designs can help them along the learning curve.

If you're a PVC pipe processor, odds are you've at least looked at the chlorinated PVC (CPVC) business as a potential way to expand your operation. CPVC pipe is used primarily in chemical/industrial markets and to service fire sprinklers. Two years ago, it looked like dozens of vinyl extruders were poised to pounce on a new opportunity for CPVC in residential hot-water piping that was created by the demise of polybutylene in this application.

In residential hot-water delivery, CPVC pipe is made in copper-tube sizes, from 0.5 to 2-in. diam. PVC pipe makers figured that since they already made water pipe for the residential market, adding CPVC pipe would be a natural extension to their product lines.

As it turned out, far more processors looked than leaped into CPVC. A lot of things held them back, but one of their major concerns was processing. "I've been running PVC for more than 20 years, and there's quite a bit of difference in running CPVC," says Mark Porter, president of Coastline Plastics in Yulee, Fla., who sold his PVC pipe business about three years ago to focus exclusively on CPVC.

"Simply put, running CPVC can be like running concrete if you don't know what you're doing," Porter warns. "It took us five months to climb the learning curve before we started making product."

Processing concerns weren't the only reason PVC pipe makers got cold feet about CPVC. For one thing, the pipe market has been relatively flat for the past year, which is hardly the type of business climate that encourages processors to make significant equipment upgrades. For another, CPVC competes not only against brass, but also against crosslinked PE, a flexible material that most would agree is easier to extrude.

CPVC has fought some environmental battles as well. Recently, for example, California banned its use in homes. With that estimated 8-million-lb/yr market gone for now, some processors have been left with more pipe than they could sell, which has created overcapacity and falling prices.

Compared with PVC, there are also limitations on material supply for CPVC. BFGoodrich is far and away the major domestic supplier, followed by Georgia Gulf and Kaneka Texas. While BFGoodrich does offer two "over-the-counter" grades of CPVC for water distribution, its FlowGuard Gold line of pipe materials is available on a select basis as part of a licensing package.

At press time, about a half-dozen processors were licensed to make and sell pipe under the FlowGuard Gold trademark. This arrangement entitles processors to BFG's marketing and promotional services aimed at pipe specifiers in the building/construction industry.

These and other hurdles notwithstanding, indications are that established PVC processors are starting to take another look at CPVC. "It is true there was more activity a while ago, but there has also been some activity over the last few months," says Roger Griffen, product manager for Georgia Gulf. Compared with the PVC pipe business, Griffen notes that a CPVC pipe maker has a smaller field of players to compete against and therefore has the potential to achieve better profit margins.

New twists in twin screws

The starting raw material for CPVC is, in fact, PVC. However, the additional chlorine atom has a significant impact on the way the material is processed. "It's not black magic," notes one processor interviewed for this story, but CPVC compounds are far more sensitive to heat and shear than their PVC cousins. Unlike PVC formulations, which by and large are tweaked by the processors themselves, CPVC compounds are generally run right out of the bag.

Machine builders say that while CPVC can probably be run on existing twin-screw vinyl lines, they don't recommend it. Suppliers recommend more "robust" extruders powered by a motor of at least 60 hp on a machine sized in the 60-mm range. And don't expect to see typical PVC outputs. Porter of Coastline Plastics says his Krauss-Maffei KMD-90 parallel twin-screws run CPVC at about half the rate he would expect to get with PVC.

Machine builders have spent the last few years developing new screw designs specifically for CPVC. While the particulars are proprietary, CPVC screws generally have a different compression rate and lower shear factor than PVC screws, notes Horst Eigruber, president of American Maplan. CPVC screws, he explains, must provide mixing without overworking or overshearing the material.

Chris Weinrich, who is product manager for extrusion systems at Cincinnati Milacron, agrees: "We recommend a medium- or low-shear screw. Conventional PVC pipe screws generate too much shearing."

"There are a number of ways to generate more mixing without compressing or overshearing CPVC," adds Dave Murdoch, product manager for pipe, profile, and tubing at Davis-Standard. "For instance, use a three-start precompression section instead of a two-start. That way, you're increasing residence time to promote mixing without compressing or shearing the material."

Get the die right

Although screw design is important, the experts say the real trick is in the die. Once again, this hardware must be designed specifically for CPVC. Some processors have had to learn that lesson the hard way. One who was relatively new to CPVC ran through three sets of conventional PVC tooling before finally going with a design specially tailored for CPVC.

Although die makers won't divulge the materials they use to build their tools, resin makers say both 420 and 450 stainless steels have provided excellent results, as have PTFE-filled, anodized aluminum and chrome-plated steel. All surfaces that come in contact with the melt should be chrome plated, notes Jim Murphy, Davis-Standard's business area manager for pipe, profile, and tubing. "The material is more corrosive and more prone to decompose than PVC."

Because the pipe itself is so small in diameter, most processors can extrude two of them at a time through dual-head dies. In this type of arrangement, extruder flow is divided by a Y-shaped block to create separate melt streams that feed independent heads. Milacron, Davis-Standard, Krauss-Maffei, and American Maplan each offers its own version of a dual-strand block.

These tools may differ a bit from supplier to supplier, but they are similar in one fundamental respect: The entire tool must have a streamlined, low-inventory design, owing to CPVC's propensity to degrade. "You need short, small-diameter flow channels and a streamlined pipe head." says Murdoch of Davis-Standard. Hans-Jurgen Matthesius, extrusion sales manager for Krauss-Maffei, notes that while PVC processors can generally run a variety of pipe sizes from a single head, CPVC processors should have a different head for each size they run.

Coil or cut?

Downstream of the die, vinyl processors will find themselves in familiar territory. Machine builders recommend using brass sleeves for their vacuum sizing tanks. Some processors interviewed for this story say they have gotten by with conventional cutoff devices.

According to Chris Weinrich of Cincinnati Milacron, flying-knife or rotary blades work best when producing small-diameter piping. Lately, however, more and more PVC processors have been coiling their product anyway, making cutting less of an issue.