By 1989, fences were 25% of Bufftech's sales, and by 1991, Bufftech was out

of pipe altogether. Kroy Building Products in York, Neb., was also

exclusively a pipe maker until 1990, when it started making PVC fences. By '

96, Kroy had split its pipe and fence making into two companies, of which

fencing was much larger.
Nebraska Plastics Inc. in Cozad, Neb., is considered to have made the first

PVC fencing in 1976. "That fence such as temporary fence,portable fence,wire

mesh fence still stands on a farm east of Cozad, Neb.," notes company

president Rex German. Other small PVC pipe makers began to follow suit in the

early to mid-'80s, like Triple Crown Fence (now part of Royal Group) in

Milford, Ind., and Bufftech (now part of Certainteed) in Buffalo, N.Y. They

were drawn by the double-digit profit margins in fencing, as compared with

less than 1% margins in pipe.
Makers of window and siding profiles also got into fences as a profitable way

to reuse scrap that they could less readily put back into windows and siding.

Lumber and building-products companies have also gotten into PVC fences. An

example is lumber maker Irwin Industries in Peachtree City, Ga., which began

making PVC fence profiles five years ago. "Now other profile companies are

looking at fences as an additional product line," says Tom Brown, sales

manager at ExtrusionTek Milacron in Batavia, Ohio.
Pipe and siding companies initially approached fence manufacturing quite

differently. Pipe makers extruded monolayer products very fast, often with

dual-strand dies, and without worrying much about surface cosmetics. They

applied high-output pipe cooling techniques such as vacuum sizing, flooded

cooling, and high-intensity spray. On the other hand, window-profile makers

were used to extruding far more slowly than pipe, with close attention to

cosmetics and dimensional tolerances. They used dual-strand lines primarily

on smaller profiles, and they typically relied on dry-sizing calibrators. In

addition, window-profile makers put uv-resistant cap layers on exposed

surfaces of their fence products to reduce their overall use of stabilizers

and titanium dioxide.
Now the two approaches are meeting somewhere in the middle: Profile makers

are speeding up their fencing lines with use of high-speed pipe cooling and

dual-strand lines of all sizes. Coextrusion of uv cap layers is also growing

in popularity.
However, there are dissenters. Royal Crown and Nebraska Plastics, for example,

are committed to monolayer extrusion, believing it makes a superior fence

product. Nebraska Plastics' German warned about coextrusion at the fence

convention in Fla. this year: "Unfortunately, many producers have begun using

PVC fence as a dumping ground for inferior materials. While coextrusion

itself isn't the culprit, it gives opportunistic producers the chance to mask

inappropriate materials with a capstock."
"The latest change in the fence business is getting higher capacity machines

and running them faster, without the dimensional constraints of window

profiles," says Lawrence of Outdoor Advantage. His firm runs conical twin at

over 1200 lb/hr, thanks in part to a very long, 14-ft puller.
As an example of how fast things are changing, just a year ago, standard

cooling tanks for PVC fencing pumped 60-100 gal/min of water from 100-150

nozzles, or else used turbulent immersion cooling. But in the past year

Conair has delivered several high-intensity spray-cooling tanks for fences

that deliver 200-340 gal/min through up to 370 spray nozzles in a 24-ft tank.
"Evaporative cooling, used properly in the initial stage of cooling, can

increase cooling 20-30% over immersion," says Conair product manager Robert

Bessemer. Such intensive cooling-combined with a system for air/water

separation, vacuum, and water recirculation-has been used on high-output pipe

lines for 15 years but is relatively new to fences, he says.
Cooling lines are also getting longer to keep up with higher production rates.

Calibrators have gone from 24 to 48 in. long, and flood tanks from 20 to 30

ft, plus in some cases another 10 ft of spray tank. Recently installed fence

lines typically use 40 ft of cooling. "In the past year, we've probably

raised our output 50% by improving the streamlining in dies and adding to the

length of dry calibration and wet cooling tanks," says Kansas American's

Doering.
For extruding fences at 1200-2000 lb/hr, ExtrusionTek Milacron recommends its

80- or 92-mm conical twin-screw for the substrate and a 55-mm conical twin

for the cap layer. A standard 1.5 x 5.5 in. fence plank typically runs at up

to 16 ft/min, whereas a high-output parallel twin-screw reportedly can push

speeds to 30 ft/min while running dual strands.
Davis-Standard expanded its Gemini series of parallel twin-screws last year

with a larger 140-mm model that puts out up to 2800 lb/hr of pipe. But so far

the biggest Gemini extruder used in fencing is the 114-mm, good for 1600 lb/

hr.

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David ZHENG is the CEO of http://www.temporary-fence.com.au .A company specialized in selling all kinds of fence products such as temporary fence,portable fence,wire mesh fence etc.