Pipe makers extruded new market

By 1989, fences were 25 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 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.

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.