November/December 2014
In the market for a new truck scale? Scrapyard layout and capacity needs will guide some purchasing decisions, but for others you’ll need to weigh the options.
By Diana Mota
What’s the most important piece of equipment in a scrapyard? You could easily make the case for the truck scale. It’s an inventory control measure, says the principal of a Southeastern company that sells scales from various manufacturers. It collects data that are a crucial part of doing business, adds a manager for a central Ohio-based scale maker: “An accurate and dependable truck scale is essential to the success of your operation. Your truck scale is your cash register.” It’s also a safety device, ensuring vehicles don’t leave the yard with overweight loads, notes a vice president for a Wisconsin-based company.
The purchasing decisions scale customers make can benefit or burden them for years, the manager says. It’s a long-term, major investment, so it’s important to do your homework and match a system to your yard’s current and expected future needs, these experts say. “It only takes one severely overloaded truck to cause permanent damage to a scale not properly suited for the application,” the vice president warns.
Scale Dimensions
What length, width, and capacity truck scale does your facility require? Ideally, the weighbridge, or scale deck—the structure trucks drive onto for weighing—will accommodate the longest and widest vehicle that will access the system, the Wisconsin vice president says. If you’re replacing a scale on an existing foundation, however, the deck will need to fit the foundation’s dimensions, points out the vice president of engineering services at a Missouri-based scale maker.
Most weighbridges come in modular sections. You can add modules to lengthen a scale, but not to widen it. A common size for a full-length truck scale in a scrapyard is 70 feet by 11 feet, but as trucks get longer, “we’re starting to see more 75- or 80-foot” installations, the Wisconsin vice president says. Eighty-foot-long scales already are the most common length in Canada, the central Ohio manager says. The vice president of engineering services agrees that scales purchased today are larger than those purchased in the past. “Scales 80 feet long by 12 to 14 feet wide are common, but bigger is not always better,” he warns. “The scale must be large enough to handle your largest anticipated trucks. Anything greater is a waste.” For each additional 10 feet in length, “expect the cost to increase by an average of 13 percent,” he adds. Further, the bigger the scale, the more land it requires for scale traffic and ramps, the central Ohio manager says.
A wider scale can make it easier to maneuver the truck onto the scale, one company says, but others point out that with too much width, there’s a chance the driver will not evenly distribute the truck load across the load cells. Manufacturers also offer custom sizes and shapes. “The proper scale size ultimately depends on the type of vehicles that the scale buyer expects to weigh over the next 25 years,” the Wisconsin vice president says.
You can measure truck scales’ capacity in several ways. Gross capacity is the total weight that can be evenly distributed over the entire surface of the weighbridge. The gross capacity should exceed the total weight of the heaviest loaded trucks that you’ll weigh, the central Ohio firm says. While companies can make scales with gross capacities of 200,000 pounds or more, “a lot of operations won’t need that capacity,” says the general manager of a northeastern Ohio-based scale maker. Most scrapyard truck scales will weigh trucks, including loads, up to 80,000 pounds, the Wisconsin vice president says. “That’s the legal highway limit, but everybody builds a scale that will support heavier loads than that.” Some states have adopted higher total load limits and require more axles to support the vehicle, the Wisconsin firm says, which would require scales with greater capacities. That said, “most scale manufacturers list product capacity between 120,000 and 200,000 [pounds] so all state regulations are covered.”
Concentrated load capacity is a scale’s ability to handle a load in a limited footprint, which for a truck scale is the maximum weight of the load applied by a dual-tandem axle. A standard scale has a 100,000-pound CLC, the central Ohio firm says; it makes scales with up to a 140,000-pound CLC.
The sources disagree whether gross capacity or CLC—or deflection, a measure of the scale’s rigidity—correspond with overall strength and durability. The central Ohio scale maker asserts that a higher gross capacity or CLC does not correspond with greater strength, quality, or durability because those ratings don’t measure deflection—the amount the weighbridge flexes or bends. The Wisconsin firm agrees that deflection is important, though for a different reason: The load cells, the scale’s load-sensing devices, require that the load be applied straight, plum, and level for an accurate weight reading. Maintaining a rigid weighbridge free from deflection ensures that the load will be applied properly, it says. Scales that deflect under a load are generally not as accurate as scales that provide minimal deflection, it says.
At least two other manufacturers take a different view. “In our opinion, greater CLC does indeed equal [greater] strength,” the Missouri scale maker says. Further, a lack of deflection does not necessarily equate to greater strength and durability, he says—it depends on the design. The central Ohio manager agrees. As long as the manufacturer designed the scale to deflect, it’s not a problem, he says. Too-rigid designs are susceptible to stress cracks in the tread plate, he cautions.
Volume of traffic is the number of trucks per day the manufacturer designs the scale to handle. Up to 50 trucks a day is light volume; 51 to 200, average; and 201 to 800, high, the Wisconsin vice president says. Another manufacturer calls up to 100 trucks a day light volume, but it also uses 200 trucks a day as the dividing line between average and heavy volume.
Also consider what types of vehicles will use the scale. Will it weigh heavy off-road vehicles such as forklifts, cranes, or front-end loaders? The central Ohio manager points out that “the tire patterns of these vehicles can develop very heavy point loads that exceed the kind of point load that a [highway-legal] truck would ever place on a scale. Those high point loads can damage a scale.”
“Just make sure that any vehicle traveling across the scale does not exceed legal highway loads,” the Wisconsin vice president says. “If one piece of equipment does, let the manufacturer know ahead of time so the scale design can be modified to accept the heavier vehicle.”
The sources also disagree on how best to determine a scale’s ability to withstand high traffic volume and heavy truckloads. “Steel content is one of the best ways to judge,” the Wisconsin vice president says. “Weighbridges with more steel will last longer, and that means more transactions over the life of the scale.” Shipping weight is one indication of how much steel a deck has, he says: “The higher the shipping weight, the more steel.” Manufacturers say they can increase the thickness or amount of metal in the weighbridge to accommodate a heavy-duty cycle. A scale with less steel will cost less, the vice president says, but it doesn’t last as long. “It really depends on what the end user can afford.”
The Ohio manager disagrees with using steel content as the measure of sturdiness, however. “More steel weight does not necessarily correlate with longer life cycles,” he says. “It’s not about how much steel you have; it’s about how the steel you have is used.” The only way to judge a scale’s ability to stand high traffic or heavy loads, he says, is to review test results that show the scale was tested to stand up to 1 million or 2 million trips of a dual-tandem-axle vehicle across the scale carrying 100 or 150 percent of load capacity. Such real-world tests are more reliable than engineering software simulations, he says.
Determining the right scale capacity for your operation is important because a weighbridge’s structural integrity is critical, the Wisconsin vice president says. Over time, cutting corners on a system by not buying something durable enough for your needs could result in a bridge that bows or dimples, creating weight inaccuracies, scale downtime, and, eventually, complete failure, he adds.
Installation Options
Whether a customer installs a scale aboveground or in a pit often depends on site conditions and preference, the manufacturers say. Each has its pros and cons. Aboveground scales cost less to install because they require less foundation work than pit scales, these sellers say. They also are easier and less costly to service or repair because components such as load cells are easier to access. Users can clean around the scale components using a water hose or air compressor from the side and inspect them by walking around the scale’s perimeter, the Wisconsin vice president says.
Aboveground scales need more yard space, however, because they require ramps. A typical installation requires a 140-foot-long space: 70 feet for the scale, 25 feet for each ramp, and 10 feet for each approach, the vice president says. Some states specify a minimum ground clearance depth beneath a scale, the Southeastern scale seller says.
Overhead obstructions, height restrictions, or limited yard space could make a pit-style scale a better choice for certain facilities, the manufacturers say. These scales sit flush with the surrounding ground, making ramps unnecessary. The Missouri-based company says it sells fewer pit scales than aboveground scales because they’re more expensive, both initially and over time. The higher installation costs are for additional foundation work, such as excavation and reinforcing steel and concrete, the Wisconsin company says. Because scale inspections, service, and maintenance occur inside the pit, work in those spaces must follow the confined-space regulations of the Washington, D.C.-based Occupational Safety and Health Administration, which include use of a harness, cable lifts, and air-quality monitors. This can increase the cost and time such work requires. Pits also can collect debris, spilled product, mud, and water, and they can become homes for pests such as rodents, the manufacturers say.
Driving Surface
Weighbridge modules have either steel or concrete-filled decks. Factory-built steel decks usually come welded to an internal system of beams or structural components, the central Ohio company says. “Closed” steel designs can trap condensation and cause the scale to rust from the inside out, the Wisconsin company’s vice president says, which can reduce a weighbridge’s life span to 10 years. More open designs that allow moisture to escape or evaporate can last 25 or 30 years, he says, and an automotive-quality finish such as urethane, epoxy, or powder coating also will help prolong scale life.
The central Ohio manager disagrees about open designs being superior, however, particularly “if the manufacturer of the closed steel design purges the closed steel structures of oxygen so that rust cannot develop and provides a 100-percent continuous weld.” He suggests that the best way to evaluate the typical life span of a particular scale design is to check references: Ask scale sellers for the names of longtime customers who can attest to how long their scale has lasted.
Diamond-checkered tread plates provide traction. Three-sixteenths of an inch of tread depth is common in scrap applications, the central Ohio manufacturer says, but other applications can have tread depths of up to 1 inch.
Concrete decks have steel structures into which the concrete is poured during installation to create the driving surface. Concrete decks can offer advantages, especially for small truck scales, the central Ohio company says. They have four times the mass of steel decks, therefore they can better resist the longitudinal forces the truck’s wheels create during acceleration, it says. Some users prefer the traction of concrete in wet or snowy environments, it adds, even though it considers the vehicle traction of a patterned steel tread plate comparable to that of a concrete deck. A concrete deck might provide better traction for pedestrians, however. Concrete decks resist rust and corrosion better than steel decks and generally require less maintenance, the Wisconsin vice president says.
A concrete deck can cost less than a steel deck, but “you need time for that concrete deck to cure,” says the Southeastern scale seller. “If you’re building a new plant, that’s not a problem, but if it’s a replacement, that’s not a good option if you need to be operational tomorrow.” The central Ohio company manager explains that once the foundation is ready, a steel-decked scale can be operational in about six hours; a concrete deck can take an additional 30 days. Further, the price of a concrete deck does not include the cost of the concrete, pouring services, or additional foundation reinforcement requirements. “All things considered, prices between concrete deck scales and steel deck scales can be comparable,” the central Ohio company says.
Some manufacturers offer factory-poured concrete decks. While they eliminate the on-site curing time, they can cost more to transport and could be damaged during transport, it points out.
The Brains of the Scale
Load-cell systems consist of the cells, cables, connections, and junction box, if any. A standard-size truck scale will have up to 12 cells measuring the vehicle’s weight. A junction box, typically at the scale, combines the load-cell signals and communicates the weight to the terminal with a single cable. Some newer systems don’t require a junction box, however. Instead, the load cells independently communicate with the terminal. “Load cells are the brains of any truck scale,” the northeastern Ohio general manager says. The predominant designs are analog, hydraulic, digital, and analog/digital hybrid. Most analog cells convert the mechanical force they measure to an electrical signal at the junction box, whereas digital cells do it at the cell. Scale-management systems monitor the load cells and work with most analog load cells. “If one [cell] acts up, they will identify it before the scale goes out of operation,” explains the vice president of engineering services.
These sources recommend closely considering the type of load cell you buy. “Choosing the right load-cell system can prevent profit loss, limit downtime, and save money on repairs,” the central Ohio manager says. Their recommendations differ, however. Analog cells have been around for decades, tend to cost less, and are available from multiple sources, while digital or hydraulic load cells are less common. The Missouri vice president says only one or two sources sell them currently. “Digital load cells require that you use a weight indicator that is compatible with the load cells, and that can severely limit your choices,” he adds. He advocates purchasing a widely used load-cell design. “Some manufacturers have unique designs that, 10 years from now, could be obsolete.”
The central Ohio manager disagrees that the most common technology is the best. “Take into consideration the size and reputation of the supplier,” he says. Otherwise, you could choose a more established technology that experiences more problems and incurs higher costs over time. Instead, he advocates picking the load-cell technology that has the fewest components and failures, is easiest to diagnose in the event of a failure, can be easily and quickly repaired, and, ideally, can be diagnosed remotely.
All but one analog load-cell design require a junction box, he points out, which “is often a source for service breakdowns” due to water infiltration that can damage the connections or cause inaccurate weighing. Junction boxes require significant troubleshooting time and money, he adds. “There are no cons to not having a junction box.” The Missouri scale maker agrees that “a poorly designed junction box can be a source of trouble when water leaks into it,” though “junction boxes can provide a convenient location for checking load cells.” He says there’s no difference in accuracy, reliability, or durability between digital and analog load cells, and “every major manufacturer either already offers or will soon offer both technologies.”
Load cells are designed to resist heat, cold, and precipitation to various degrees, but they are vulnerable to lightning strikes, the northeastern Ohio general manager points out. The scales often come with grounding features, but grounding alone might not protect the system from a high-intensity strike, the central Ohio company says. Some companies offer additional protection, such as gas-filled discharge tubes in the junction box or transient voltage suppressors, which are circuit breakers that react based on the voltage and frequency levels power surges produce. The central Ohio company recommends asking about what warranty coverage each manufacturer offers for lightning damage. Often it’s prorated based on the age of the scale, it notes.
Control Units and Options
Most scale systems come with a terminal—also called an indicator, interface, or control unit—to compute and display a vehicle’s weight. Most of the manufacturers make scales that display weight in 20-pound increments up to 200,000 pounds. The increment size on legal-for-trade scales relates to the maximum scale capacity, the central Ohio manager explains: The smaller the increment, the lower the gross capacity of the scale. Control units range from simple to elaborate. Advanced and/or customized software can control multiple scales, offer industry-specific modules, keep track of multiple users on a network, remotely calculate transactions via Web browser, or synchronize data among multiple networked sites, the central Ohio company says.
About 90 percent of transactions require drivers to weigh their vehicles full and then empty, or vice versa, for the scale to compute gross, tare, and net weight. Some scale management systems store tare weights for vehicles so they only need to cross the scale loaded. “You can do a complete ticket on one pass,” the Wisconsin vice president says. Customers and drivers “love it because it saves time, and time is money.”
The control units also can operate a multitude of peripherals and options, including printers, traffic controls such as gates or lights, video monitors, intercoms, and radiation sensors. Automated and self-service systems, which use features such as card readers to identify drivers or vehicles, can streamline operations and keep drivers in their vehicles, manufacturers say. The systems have a display that prompts drivers to enter data using a keypad, keyboard, or touch screen; some come with a ticket printer. They work well for operations with high repeatability or limited variables, or where the weighmaster is not present, the Wisconsin vice president says.
Add-ons that don’t connect to the control unit include guardrails to guide drivers onto the scale, nonslip surfaces, and a walkway or mezzanine for drivers who must exit their truck while on the scale.
Bottom-Line Considerations
A standard truck scale installation can cost $50,000 to $100,000, the manufacturers say, but half of that could be concrete work and site preparation, the northeastern Ohio general manager says. The central Ohio company estimates that of the total cost, 35 percent is the weighbridge, 20 percent is the load-cell system, another 20 percent is the foundation, 15 percent is delivery and installation, and 10 percent is the terminal and software, though the amounts can vary significantly depending on the project, the complexity of the construction work required on site, or the level of sophistication of the software package, that company’s manager says. Consider the total cost of ownership by factoring in downtime as well as repair and service costs, these manufacturers caution.
The environment, application, and composition of a truck scale can affect its life span, but with due diligence and reasonable care, a scale should provide 25 or more years of service, the Wisconsin vice president says.
Diana Mota is associate editor of Scrap.
In the market for a new truck scale? Scrapyard layout and capacity needs will guide some purchasing decisions, but for others you’ll need to weigh the options.