MATERIALS AND ASSEMBLY. (cover story)

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Author: Brown., Alan S.1

It costs about $250,000 a day to lease an offshore oil platform, so oil companies are justifiably hesitant about embracing new technologies that might fail. Yet plastics continue to work their way into demanding downhole drilling applications, thanks to attractive properties and the use of finite element analysis to reduce risk during implementation.

An example is the resin umbilical clamp developed by PolyOil Ltd. of Westhill, Scotland, for BP pic's Schiehallion oilfield in the North Sea. About as thick as a man's forearm, umbilical cables contain the electrical and fiber optic wires used to control undersea well equipment. They are typically clamped onto steel pipes, which are then threaded together and lowered down a larger steel casing (called a riser) to the wellbore on the seabed.

Plastic umbilical protector is installed on a section of steel pipe, which is being lowered down a riser tube to the sea floor.

The wellbore may he thousands of feet below the surface. The lower the wellbore, the greater the water pressure on the riser and everything in it.

The clamps must handle the pressure while supporting the weight of thousands of feet of heavy cable. They must also stand up to constant buffeting against the sides of the moving riser as it sways with ocean currents, storms, and the constant bobbing of the offshore rig above it.

PolyOil's plastic clamps are designed to take punishment. Cast from a high-molecular-weight resin, they are tough enough to withstand the constant jostling. Equally important, their inherent lubricity brings their coefficient of friction down to 0.03, compared with 0.09 for steel and 0.14 for zinc. That makes plastic clamps easier to ram down thousands of feet of riser.

Resin clamps offer other advantages as well. Because they weigh about half as much as steel, operators find them easier and safer to clamp over the umbilical. They are also impervious to corrosion, and easy to customize by molding in additional features.

Offshore drillers rarely use standardized products. So when BP ordered a customized PolyOil umbilical clamp, it also requested finite element analysis of the design. "They were looking for design verification, but they also wanted to know how far a driller could push the equipment," said PolyOil's engineering director, Calum Whitelaw. "Offshore oil rigs are hazardous places to work, and equipment limits have to be explicitly written into the operational procedures."

PolyOil tapped consulting engineers AMEC-NNC of Cheshire, U.K., to run the analysis. It used Abaqus simulation software from Abaqus Inc. in Providence, R.I., to model how the clamp withstood stress when bolted onto the umbilical and when subjected to lateral impacts and bending forces inside the riser. FEA showed that lateral forces might overs tress the hinge side of the clamshell-style clamp, a problem easily remedied by adding some thickness to a nearby rib. "We were able to make a straightforward change that increased our confidence in the product," Whitelaw said. The ability of FEA to provide that extra certainty makes it easier for even conservative industries such as offshore oil to embrace plastic drilling components and other new technologies.

Meshed FEA model of umbilical protector in red and blue clamped to green steel pipe in riser.

Cotter pins or their antecedents ft have probably been around since someone first hammered a wooden peg through an axle to keep a wheel from tailing off. So what could possibly be new about cotter pins?

Plenty, it turns out. In fact, Pivot Point Inc. of Hustisford, Wis., has introduced several cotter pin innovations over the past 20 years. They began in the early 1980s, when the father of the company's current owner, Rue Leitzke, challenged him to try to invent a better cotter pin.

The result, after many disfigured paper clips, was the Rue Ring. Its straight wire slipped through the clevis pinhole, while the ring part of the pin spiraled around the clevis to hold the cotter in place. Sliding the end of the spiraled wire under the straight wire coming out of the clevis hole created a secondary lock that tensioned the Rue Ring and dampened vibration.

Unfortunately, the Rue Ring had one great disadvantage: It looked like one of those elaborate knots practiced by Boy Scouts. "We sold millions, but it was not real intuitive," said Pivot Point's vice president of operations, David Zimmermann. "If a consumer had to put it on or take it off, he might get confused."

Soon enough, other companies began selling positive locking cotter pins. Pivot Point scurried back to the drawing board (and its supply of paper clips). The result was the bowtie cotter pin, a far more intuitive design.

At first glance, the bowtie cotter looks like a standard hairpin cotter, which has a loop on one end to tension the curved wire that fits around the clevis pin shaft. Unlike the hairpin, though, the bowtie pin doesn't end after going over the shaft. Instead, it forms a second loop (which makes it look like a bowtie) and doubles back to butt up against the shaft. This locks the bowtie cotter into place so it won't pop out if someone hits it. The result, Zimmermann said, is a positive locking cotter pin that users can easily understand how to insert and remove.

The company continues to innovate. It revised its Ring Ring design to make it easier to lock and unlock on a regular basis. It also invented a selflocking implanted cotter (SLIC), which has a pop-up wedge on its end. Pushing it through a hole depresses the wedge. Once in the open, the wedge jumps up and locks the cotter into place. "It's great in blind hole applications where you can't get to the back to put nut on bolt," said Zimmermann. "It's much easier than tumbling around trying to put a pin in the back of a cotter."

Pivot Point continues to develop new nonthreaded fasteners, including a SLIC that will be easier to remove from blind holes and tubes. Which shows that even after centuries of use, there's still room for innovation in cotter pins.

Collisions between robots are â€" not common, but they can happen when the machines cross paths with unplanned obstructions or even with other robots during line setup. Such crashes can damage tooling. They may also twist and turn the robot so that, like a large lever attached to a wound-up spring, it carries enough energy to pose a threat to anyone who has to manually disengage it.

The SR-61 from ATI Industrial Automation in Apex, N.C., is the latest in a series of sensors intended to make it easier to untangle robots after a crash.

Robots usually move too fast for sensors to prevent crashes. Instead, ATI seeks to reduce damage and improve safety. As soon as its sensor detects a collision, it signals the controller to perform an emergency stop. It also releases the robot's rigidity so that it complies with the collision. This makes it safer to extricate. If the robot is able to extricate itself and torsional rotation does not exceed 20 to 25 degrees, the SR-61 automatically resets.

Workbenches usually merit no more than an afterthought in assembly line design. Yet when contract electronic manufacturer Cirtronics Corp. of Milford, N.H., decided to move to lean manufacturing, it spent up to eight months evaluating four different workbenches.

Why the fuss? Cirtronics is 20 percent owned by its employees. "We wanted our employees to have a comfortable place to work," said team leader Irene Lemay, who helped evaluate the ergonomic effectiveness of workbenches. "If they're comfortable, they'll have fewer health problems and higher productivity."

This goal was complicated by Cirtronics' team-oriented assembly approach. While most teams work in assigned areas, members often move to other teams to smooth out spikes in workload. As a result, employees switch workbenches on a regular basis. That made bench height an important consideration. One bench was a set height. "You had to adjust your chair or put a wood block underneath so you could put your foot up," Lemay said. That didn't prove as comfortable over a full shift as the benches with crank or motorized height adjustments.

The company's decision to move to lean manufacturing involved setting up kanban-style part bins that visibly signal the need for restocking. In the past, those bins either took up valuable workbench real estate or went on stacked trays on the side. That left workers either cramped for space or reaching for parts. Lemay's team wanted workbenches with shelves to keep parts within easy reach without expropriating valuable work space.

Cirtronics also wanted an aesthetically pleasing color that reflected its high-tech image.

Ultimately, Lemay's team opted for the Align workbench from Lista International Corp. in Holliston, Mass. Its motorized system adjusted work surface height between 25.5 and 41.5 inches, moving the kanban-ready shelves with the bench so they retained their relationship to the work surface. The unit also featured a switch that stored three height adjustments and leveling guides for uneven floors.

The workbench chosen by Cirtronics has motorized adjustment, foot pads, and shelves and bins for parts supply, alone with a clear, well-lit surface.

The units came with adjustable, glare-free lighting, adjustable footrests, and privacy panels that also served as bulletin boards. "They even created a special gray color for us, Cirtronics gray, so the benches would look the way we wanted," Lemay said.

Personal armor may stop bullets and bombs, but its protection comes at a cost. Today's bulletproof vests are made of Kevlar aramid or other high-strength fabrics. Adequate protection takes multiple layers of fabric, which makes armor bulky and uncomfortable to wear.

One potential solution involves a little-known class of materials called colloidal shear-thickening fluids. During normal use, they flow as easily as conventional liquids. When subjected to sudden stresses that make them flow at higher shear rates, they instantly turn rigid and act like a solid material.

Impregnating conventional aramid fibers with shear-thickening fluid creates a more effective barrier, says armor developer Norman Wagner, a professor of chemical engineering at the University of Delaware's Center for Composite Materials. When he plunges an ice pick through four layers of Kevlar fabric wrapped around a foam block, it goes right through. Four layers of fluid-impregnated Kevlar fabric stop the ice pick cold.

Wagner's demonstration is especially interesting because conventional Kevlar vests usually fail to stop ice picks and knives, although they resist penetration by high-velocity bullets. Wagner's fluid-impregnated fabrics defeat bullets, too, and do so with fewer layers. This leads Wagner to believe that switching to fluid-impregnated fabrics will enable designers to create thinner, more flexible armor.

Wagner began unraveling the secrets of shear-thickening fluids more than 10 years ago. The syrupy colloids consist of submicrometer-size silica particles suspended in polyethylene glycol liquid. Wagner found that shear forces created "jamming clusters" of silica particles that freeze the fluid into a solid. The effect is similar to cement, which grows harder to mix the faster it is stirred.

Wagner originally intended to use his knowledge to improve the manufacture of coated and photographic papers. Instead, he began collaborating on armor with Eric Wetzel of the U.S. Army Research Laboratory's Weapons and Materials Research Directorate.

The University of Delaware recently licensed the technology to Armor Holdings Inc., a leading manufacturer of personal and vehicle armor systems. Wagner sees other non-armor applications as well, ranging from aircraft engines, car doors, tires, and sporting apparel to bomb blankets and paratrooper boots that stiffen on impact to protect a jumper's ankles.

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By Alan S. Brown., Associate Editor