Advice For Specifying The Right Mixer Dallas TX

Cement mixers are specialized pieces of equipment, customized to meet the needs of particular applications.

To ensure that a mixer delivers maximum performance and life in a particular application, it's important that buyers specify the features that meet their unique requirements.

Two key considerations are local regulations governing vehicle lengths and weights, since these will dictate the axle spacing needed to maximize mixer payload.

Some states require compliance with the Federal Bridge Formula; others don't. This significantly affects axle spacing and setup.

"A truck designed to meet the bridge formula tends to be longer, in order to spread the weight. That defines where the steering axle goes, and also has an impact on frame dimensions," said Brian Lindgren, vocational sales director at Kenworth Truck Company. "In most cases, you would spec a booster axle at the rear to increase the allowable weight. You need at least 427 inches from the centerline of the front steering axle to the centerline of the booster axle to be sure you meet the distribution requirements for a 36-foot bridge," he said.

"At the same time you need to stay within the 40-foot overall vehicle length limit, so the steer axle needs to be as far forward as possible. A 427-inch bridge length in a 480-inch overall length leaves only 53 inches for front and rear overhang. The rear mudflap is usually 25 inches from the center of the booster axle, so the steer axle needs to be within 28 inches of the front bumper," Lindgren said. "Also, be careful not to specify a permanently mounted tow hook that extends out the vehicle front. It could make your truck over the legal length."

In states where you don't need to comply with the bridge formula, you can specify trucks shorter, making them more maneuverable on job sites. But you may need to specify lift axles to carry the extra weight.

Depending on the weight carried by the steering axle and the laws in your state, you may also need to specify wide-based front tires. "In the states where tire footprint is regulated, it's typically 600 pounds per inch of tire width," said Lindgren. "That will require a wide tire such as a 425/65R22.5 to get to 20,000 pounds on the two front tires."

Location Issues

Where you expect to be delivering concrete will also influence your mixer specifications. The heavier the load and the rougher the terrain, the more you need a beefed-up chassis and suspension.

"Most mixers need to get into pretty rough job sites," said Lindgren, "so be sure to specify suspension that offers plenty of articulation."

The frame-rail specifications are influenced by the type of mixer barrel used. "If the barrel has a sub-frame welded to the chassis rails that is approved by the OEM, a single 11-5/8-inch frame is fine," said Lindgren. "You'll want a transition plate bolted to the frame at the back of the cab, which goes as far as forward as possible. This reduces stress on the rails.

"But if the mixer pedestals are mounted directly to the frame rails, you'll need an inserted frame of at least 10-3/4 inches," he said. "Remember, it's not just strength you're looking for, but stiffness, too. And, if you have more than one pusher axle, you should have an inserted rail to withstand the higher side loads."

Mixer manufacturers often request cross members in specific locations. It's a good idea to check with them before the truck is built.

The type of construction sites you typically visit will affect the amount of traction you require. "I always recommend side-to-side differential locks in both rear axles for traction off the pavement. In areas with sandy soil, such as Florida, all-wheel drive - also known as six-by-six - has been more commonly specified so mixers don't get stuck on job sites," Lindgren said. "More recently, we've seen operators specifying a six-by-four configuration with active tire-pressure control systems. These allow the driver to reduce tire pressure to get the traction needed to travel off road in the sand."

The Drive Train

Big horsepower is not a requirement for mixer applications. "You should get just enough horsepower to do the job," said Lindgren. "Generally, 320 horsepower to 350 horsepower is plenty for most applications. Extra horsepower just uses more fuel, puts more strain on the rest of the drive train and adds to initial purchase cost."

The transmission you put behind the engine must provide a wide range of ratios. You need a low enough gear to inch along at a job site, and a high enough gear to attain decent highway speeds. Lindgren said, "The Eaton Fuller-9ALL is a common transmission specified for mixers. It has a really low ratio for crawling while pouring curbs or other continuous pours. But there's also a high enough top end for traveling at highway speeds," he said.

"We're seeing more automatic transmissions being specified," he noted. "With the electronic controls on the newer automatics, shifting is smooth and responsive. They're easier on drivers and reduce stress on the drive train, and enable the truck to keep up in traffic more easily. The only downsides are higher initial cost, and a slight decrease in fuel mileage."

The power take-off (PTO) must come directly from the engine in order to provide enough power for the mixer system. Whether you use front engine or rear engine PTO depends on the chassis configuration. Lindgren recom-mends a rear-engine PTO anytime there's room for it.

"Front engine PTOs can reduce the size of the radiator," Lindgren said. "With 2007 engines rejecting more heat, you need a larger radiator to cool the same horsepower, not to mention the added heat load of transmission coolers, power steering coolers, air conditioner, and so on. Also, the pump for a front engine PTO sits out front in a vulnerable spot. The hydraulic lines have to snake past the engine, and often close to the exhaust, to get back to the mixer drive motor. Rear engine PTOs make a cleaner installation."

But in those areas where the front pedestal must be mounted immediately back of cab, front engine PTO is the only alternative. "A front-mounted PTO makes sense in Florida where the weight laws give you an incentive to get more load on the steering axle," he said.

If you spec an automatic transmission, you definitely want a rear engine PTO because it will provide 30-percent higher output speed due to the gearing at the flywheel. This allows much less slip in the torque converter when you are crawling along and want to keep the drum speed up to pour concrete. Too much slip in the torque converter can lead to overheating the transmission or the engine's cooling system.

According to Lindgren, the rear axle ratios should be evenly matched with the transmission so engine runs at approximately 1,600 rpm at highway speeds. "You should also be able to go as slow as 1.5 mph at 1,400 or more rpm," he said. "A 4.30-to-1 ratio with 11R22.5 tires and the -9ALL transmission works well. With a six-speed automatic transmission, use a 4.88-to-1 or slower ratio."

Another thing to remember is air filtration. Lindgren recommends using a pre-cleaner on under-hood air cleaners to filter out large particles, supplemented by plenty of element area on the main filter. Dual external air cleaners are better, and many customers like the look. "A little money spent up front on a better air cleaner is cheap compared to a dusted engine," he said. And better filtration will usually mean longer life for the filter elements.

Weight Watching

Weight is an issue with mixers, but you have to reduce vehicle weight by a lot to be able to haul an extra half yard of concrete. So you must carefully consider the amount of extra concrete you'll have to deliver to recoup the higher cost of lighter vehicle components.

You can slim down by specifying components - such as wheels, air tanks and clutch housings - in aluminum rather than steel. "Use the smallest fuel tank you can get away with," Lindgren added. "Most mixer applications burn about 4 to 4-1/2 gallons per hour. So a 55-gallon to 60-gallon tank is usually plenty of fuel for one shift."

Lindgren suggests engines such as the Cummins ISL or Caterpillar C9 to save up to 800 pounds compared with a 12-liter block. "With 350 horsepower and 1,250 pound-feet of torque, these 9-liter engines have all the power most operators need,"he said.

Lindgren also advises selecting an aluminum cab for its light weight and corrosion resistance.

You can save as much as 400 pounds by choosing the right suspension, Lindgren said. "You can also leave shock absorbers off the rear because the weight of the mixer means you will never be running light."

Using wide-base "super single" tires instead of duals on the rear can save hundreds of pounds in wheel and tire weight. "The trade-off is that you get a narrower track if you stick with standard track axles," said Lindgren. "You can go with a wider track, but then you may not have the option to go back to duals later."

Driver Performance Items

Finally, let's look at a few driver performance-related items. To get the best turn performance and road feel from steering, Lindgren recommends dual small steering gears rather than a large single gear with an assist ram. The dual system usually requires less maintenance than a single system with assist.

Lindgren recommends specifying as many windows as possible and mounting the exhaust behind the cab rather than at the side to keep out of the way of the corner windows.

While we're talking windows, Lindgren suggests picking low-replacement-cost windshields when they are available. "Most mixer fleets replace at least one windshield side per truck per year. Two-piece flat-glass windshields with roped-in seals can be replaced in half an hour for a total cost of under a hundred dollars. This can save thousands of dollars over the life of the truck."

With lift axles, it's smart to get a six-channel ABS system. "Lift axles, especially steerable ones, are normally over-braked for the load," Lindgren says. "By including them in the ABS system, it's much easier for the driver to avoid locking them up and flat-spotting the tires."

Two last driver performance items that Lindgren recommends: "For a small price in cost and weight, treat your drivers to Kenworth's Extended Day Cab and Kenworth QuietCab® package. The Extended Day Cab gives the driver 6 inches more room fore and aft, and 5 inches more headroom. The QuietCab option reduces in-cab noise by 2 decibels, meaning it cuts perceived noise by almost 50 percent. These options can dramatically reduce driver fatigue, and that helps them be more productive."