Fighting fire with castings: firefighting is a high stress occupation for both the men and women in uniform and the castings that support them. This article profiles how castings are used to help protect people and aid those working toward fire prevention.

Firefighters exist to help people in times of crisis, whether that is to topple a five story building or to rescue a cat from a tree.

"Fire fighting is a very rewarding career, but it can take its toll on a person. We try not to get emotionally involved when we answer a call, but it's rough when there are people who are seriously hurt," said Tom Farinella, fire chief flit the city of Des Plaines, Illinois.

While these men and women work to aid others in need, it's important to notice that firefighters can't do their job alone. They require the aid of state-of-the art technology to help their super-human efforts. This is where castings come in.

Castings are an integral component to fire prevention, doing everything possible to improve the performance of critical fire fighting tools, including fire trucks and pumps.

Standing on Durability

According to Farinella, fire equipment must operate dependably for a lengthy time period due to a limited number of funds. "Every piece of equipment is supplied through a city lurid for public works, but that also includes equipment for police and city vehicles and equipment," Farinella said. "We are on schedule to replace every fire engine after 15 years. The equipment needs to stand up for that period of time."

In order to produce high strength, durable components at a low cost. fire fighting equipment manufacturers turn to castings. "From the very beginning, we design our track's components, whenever possible, with castings as our intent," said Rich Demski, project manager for new product development at Pierce Manufacturing, a manufacturer of fire trucks and accessories located in Appleton, Wisconsin. "Durability is critical. A normal vehicle travels 10 miles per call and answers 1000 calls per year. All the components must stand up to that heavy level of use."

Nearly all of Pierce's fire trucks are custom-built for either municipalities. career firefighters, chemical plants, oil refineries or government facilities such as air force and marine bases that require onsite fire prevention. Because each truck Pierce designs is unique, the majority of their castings are designed in-house.

During the initial metal component design phase, Pierce starts with a fabrication and then works its way up to the final casting. "We start with a fabrication and then use that to test and optimize the geometry of the design," Demski said. "We run it through durability and fatigue testing, and then re-optimize the component lot casting. This way we can make quicker changes without having to retool the entire casting."

According to Demski, whenever redesigning a component for a custom fire truck, the firm always looks for areas of improvement. "Were constantly looking to see if we can integrate a few castings, such as braketry and attachment points, into (me continuous component. We also go over the design with the foundry involved to see if there are any other changes that can be made to save weight or to reduce costs."

Building a Fire Truck

Driving a fire truck is nothing like driving a car. The horsepower on an engine can range anywhere from 325-500. "Every one of our drivers has to go through an extensive training program to become certified to drive the fire truck," said Farinella, who also stressed the complexities of having to drive a vehicle of that size quickly to the site of an emergency. "We place a large emphasis on defensive driving, and that comes with learning as much as possible about the vehicle."

The trucks built at Pierce are expected to drive up to 55-65 mph with quick acceleration. They are also expected to remain running for periods beyond 24 hr in emergency cases. "Due to the longer periods of operation, there are a lot of stringent cooling requirements that need to be met." said Demski.

One of the key systems used in Pierce fire tracks is an independent front suspension system developed by it's parent company, Oshkosh Track Corp., Oshkosh, Wisconsin. The independent front suspension, which allows a wider steering angle so that the trucks can have greater agility of movement, also allows for independent wheel movement, reduced spring rate and improved ride and mobility.

The independent suspension system utilizes three castings: the upper control arm, lower control arm and steering knuckle. "These three castings are highly-optimized for high tolerance levels due to the great deal of stress that is placed on them," said Vadim Pikhovich, materials/process engineer at Oshkosh Truck Corp.

Upper Control Arm--The upper control arm is a low alloy steel cast via green sand. It weighs 88 lb and is 24 in. by 17 in. "We chose to go with steel for this casting due to the presence of extremely high stresses along the ribs of each arm," Pikhovich said. "Since the part is highly optimized to maximize the use of material in each cross section and keep the overall weight of the casting down, low alloy steel was chosen because of its higher ductility and toughness compared to austempered ductile iron."

Unfortunately, the selection of steel led to the need for tight quality control, as steel has poor fluidity and a high tendency to form slag due to oxidation. "'We kept a much tighter control of the chemistry of the melt to assure desired mechanical properties. Any deviation from the proper chemistry could lead to quench cracking problems during heat treatment and poor machinability."

Lower Control Arm--The lower control arm (Fig. 1a) is sand cast using ductile iron. It weighs approximately 61 lb and is 27 in. by 21 in. In the design of this component, Oshkosh was able to produce a 10-12% weight saving simply by converting from steel to ductile iron. "The density in ductile iron is lower than that of steel due to the presence of graphite nodes in the microstructure of ductile iron," said Pikhovich.

[FIGURE 1 OMITTED]

The casting designers also had to enforce several areas of the casting near the ball joint well and along the ribs of each arm where it was experiencing heavy stress levels. "These areas are specified on the casting drawing as areas of higher quality in terms of radiographic acceptance criteria," Pikhovich said. "This way, we can ensure the highest quality possible."

Steering Knuckle--The steering knuckle (Fig. 1b) is sand cast in a low alloy steel. It is 91 lb and 7.6 in. x 8.5 in. Oshkosh implemented the same quality parameters as seen in the upper control arm due to high stress areas in the ball joint regions. "The center part of die casting also is machined to provide attachment for a spindle, therefore the integrity of this region is critical to the performance of the casting," Pikhovich said.

Extended Cab

Another casting application featured on Pierre's custom trucks is a cab extension, which is a C-channel shaped casting (Fig. 2) mounted on the end of the frame rail, right under the cab of the truck. The extension, which has ribs reinforcing the side of the channel, provides support for the cab and other componentry. It also has features designed to support mounts for towing the track by raising the front off of the ground

[FIGURE 2 OMITTED]

The cab extension shown was initially designed as a fabrication. However, concern was expressed due to the large number of weldments featured. "After analyzing the manufacturability of the weldment, it was concluded that it would be quite difficult to produce this part with dimensional consistency," Pikhovich said, citing that the labor cost to produce the part also was estimated to be high.

"By converting this part to a casting, the engineers were able to eliminate weld joints which led to a considerable improvement in the fatigue life of the part," Pikhovich said. "We were also able to incorporate additional symmetrical features, allowing the casting to fir both the left and right hand side of the cab." Finally, by converting the part to a casting, the design engineers were able to vary cross sections of the casting in order to reduce the overall weight to 138 lb.

Pierce also was able to reduce the possibility of porosity and slag inclusions through casting geometry, "Castability of the geometry was kept in mind from the outset of the project," Pikhovich said. "The casting was designed to obtain a geometry that had relatively even feeding modulus across the casting. This allowed us to re duce common casting defects."

A Foundry's Perspective

While Pierce designs nearly all of their own castings, they still need someone to actually pour the castings. That's where Neenah Brass & Aluminum Foundry, Neenah, Wisconsin, comes in. Neenah is one of Pierce's major suppliers of castings, producing several components for its custom-built fire trucks.

"While we do not directly recommend a material or design, we work with the engineers to make parts casting friendly and cost efficient," said Bruce Cherek, president of Neenah Brass & Aluminum Foundry. "We have assisted Pierce with design and material changes for new parts and material changes to solve problems that they were experiencing."

One casting that Neenah produces for Pierce is the cab pivot block (Fig. 3). The part is a section of Pierce's newly designed chassis cabs, which allow for the cabs to tilt forward for access to the engine and transmission. The part is located in the cab and is attached to the floor structure.

[FIGURE 3 OMITTED]

The cab pivot block was redesigned when Pierce did an overhaul of its engine programs. 'This is one part where we assisted their engineering department in making it a casting," said Cherek, "We cast it in an aluminum alloy A356-T6 for its light weight and strength." Neenah also provided Pierce with a fully machined casting. The part was designed to handle the required load capability for raising the cab while utilizing only a single part.

Under Pressure

One of the most important parts of the firefighting process is the water pump. These pumps need to always provide a consistent water flow at a specified pressure for firefighters to subdue the fire. For that, engineers once again turn to castings.

"The types of castings we produce for firefighters are typically hidden from the eye, but are very important," said Dave Bumbar, president of Aurora Metals Division L.L.C., Aurora, Illinois, a subsidiary of Hiler Industries, Inc. Aurora produces impellers (Fig. 4) for centrifugal pumps, which moves water in various degrees of volume and pressure through the fire hoses. "The impellers are a critical component to ensuring that water will always reach its desired location at its desired pressure and volume."

[FIGURE 4 OMITTED]

The centrifugal pumps can be used as either portable units, they can be mounted within an emergency vehicle or they can be permanently mounted inside a commercial building to ensure that the fire system is frilly pressurized from the bottom floor to the top, A wide range of water volume and pressures can he achieved depending on the type of pump required. A non-specialized pump can provide water in volumes ranging from 50 5000 gpm at pressures ranging from 40-650 psi.

Manufacturers often choose a bronze impeller casting for its combination of strength and corrosion resistance. Aurora produces these castings using its vacuum casting permanent mold technology, which allows for consistent and clean waterway surfaces with crisp detail within thin blade sections. "Because of the unique and challenging geometry of an impeller, our vacuum casting technique is able to cleanly fill blade edges down to 0.09 in. thick," said Bumbar.

"Consistency, dependability and reliability are critical to any fire-related product," said Bumbar. "You can imagine the quality cost of the hydraulic testing of each pump and the useless indirect cost of having to disassemble and retest a pump when it does not meet the performance criteria because of poor quality."

Casting from the Heart

Not all castings made for the firefighting industry help to prevent fires. Others are lot the commemoration of those that have past in the line of duty.

"As a public service to our local firefighters, we cast and provide them at no cost a bronze flag holder for the graves of all deceased members of the department," said Cherek. "I was privileged to be invited to the memorial service of a young fireman who died from complications of exposure to a toxic substance while fighting a fire, and was present when the Captain presented his family with the marker.

"Those are probably the most important castings we make for the firefighting industry."

For More Information

"Metalcasting Engineering Systems; Harnessing the Benefits of Metalcasting," J. Tirpak, V. Olmstead and R. Farrara. Paper No. 99-120, Transactions of the American Foundry Society, Des Plaines, Illinois.