Solid modeling helps engineers douse fires

The firefighter faces a predicament. His success in saving lives is measured in minutes, as he sprints inside each burning house. But to be safe inside, he must carry hoses and oxygen tanks, while wearing a helmet and heavy boots. Modern materials have helped lighten his load, but even technology can't change some things, like the tremendous kick-back force generated by water gushing through the thick fire hoses.

So when Stewart McMillan set out to redesign the Crossfire, his company's firefighting hose nozzle, he had several demands. He had to keep the equipment lightweight, low cost, and high performance. And oh, yes-he also faced a time challenge, since his team began the project in October 1999, with the goal of displaying a working model at the industry's biggest trade show, just five months away.

To solve all these challenges, McMillan's company-Task Force Tips (TFT, Valparaiso, IN)-designed a nozzle with about 60 components in what McMillan calls "the most complex product we've ever made." They also designed a patent-pending accelerometer for a shut-off switch, making it safe enough to be used in the dangerous firefighting environment.



From its squat, stable tripod base, the Blitzfire can spray water at an angle as low as 9 degrees. And an accelerometer cut-off switch keeps the firefighter safe if the enormous pressure makes it slip.

By designing the product in 3D CAD and using rapid prototypes to get real-time design feedback from focus groups, TFT was able to complete the job and display the new Blitzfire monitor at FDIC, the Fire Department Instructors Conference.

Safety first. Details like weight and price are important, but with emergency equipment, safety is the primary concern. And the TFT engineers knew exactly what they wanted to do-prevent the 23-lb nozzle from whipping around if firefighters lost their grip on the powerful stream.

"The trickiest thing about the whole design is that devices like this are inherently dangerous," says Dave Kolaz, design engineer. "Most of the reaction is going straight back, and if it's on a hard, smooth surface like concrete, the piece can pick up and start to flail around. People have literally been killed."

Before designing a single part, they had a solution in mind.

"The idea for it had been rolling around inside our heads-the idea of a trip mechanism which would allow it to shut off when it moves," says TFT President McMillan.

Designing the cut-off switch

. "Once the flow is above a certain amount, a person can't hold it standing up," Kolaz says. In fact, a hose spraying 500 gpm pushes back with 250 lbs of reaction force-enough to lift a 200-lb man off his feet.

To control these enormous forces, the Blitzfire detects lifting or sliding-a 1-g acceleration will trip it, and it will stop the water within 0.3 sec. But conventional accelerometers couldn't do the trick. The designers had to experiment with techniques of their own.

The patent-pending design consists of two stainless-steel rods resting in a groove, lined up like train cars. If the nozzle moves suddenly, the rods slip out of the groove.



The Blitzfire accelerometer 'functions very much like a moustrap,' McMillan says. 'There's a ratchet held by a lever with an inertial sensing weight on a spring.

With this safety mechanism in place, firefighters can use the Blitzfire to extinguish fires in whole new ways. A conventional "deluge gun" generates so much kickback (like a shotgun) that it demands two firefighters to spray 150-200 gallons per minute, aimed up at a steep angle. But the Blitzfire can shoot up to 500 gpm at a nearly flat angle, and still be controlled by a single firefighter.

To handle this great flow, TFT designed the Blitzfire to sit on a squat tripod, integrated into the frame. The handle is positioned just 10 inches above the ground, and when a firefighter needs to move it, the carbide-tipped legs fold quickly.

"Before, you could deploy it no lower than 35 degrees-you had to lob the water in, like laying siege to a castle," McMillan says. "Now you can use it down to 9 degrees, so you can get right in the front door of the house and sweep the room all the way to the back."

"It's the M60 machine gun of the fire service-in World War II, that was the first machine gun you could pick up and move, so it wasn't merely defensive."

And none of this would be possible without the new accelerometer.

3D CAD enables fast RP. For its design software, TFT used five seats of SolidWorks 1998, running on 600 MHz Dell computers with 256 MB RAM. (The company is now transitioning to SolidWorks 2001.)

"The whole thing is having a solid model you can do different things with-that's the single biggest savings of time," McMillan says. Modeling in 3D allowed TFT to save time in creating rapid prototype models, production molds, and even the graphics in the user manual.

He also saved time in training his engineers. In fact, one TFT employee taught himself to use SolidWorks, simply by using the software for his job designing fixtures and clearances for machine tools.

Once they had a fairly complete CAD model, rapid prototyping was the key to getting this product out the door. To get feedback on the design, TFT convened a 14-person focus group of salesmen, engineers, and firemen.

"We've been too close to the vest in the past; we were worried about secrecy and the patent issue. Now we can try to prevent problems before we make the products. And we haven't been able to detect any [information] leaks," McMillan says.

"We cast functional prototypes within a month and had a meeting where the focus group really slammed it; they turned it completely inside out. But as it turned out, they were good changes."

McMillan didn't just take notes-he quickly made changes to the CAD model. In fact, TFT was able to hand physical models of the revised product to the focus group by the end of the three-day meeting.

Aside from using solid model files to create rapid prototypes, TFT also saved time in production casting. It took them only three days to be ready for casting, compared to 12-16 weeks before.

"We ran production on the first run-we did no prototypes," McMillan says. "We could have found some problems and not have to throw out some parts, but we still got to market faster than if we had [prototyped]."

Overall, TFT shaved about nine months off its typical design cycle. Adding this much speed to the process actually changes the nature of the design cycle, he said: "It allows you to make a lot more mistakes, but you can call them experiments. Also, now you're testing the strengths and materials of actual parts, instead of calculating them."

"Five months was the design cycle time to where we had six units at the trade show," Kolaz says. "I can still barely believe it."

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