Built to withstand the highly corrosive solid waste environment, where a seemingly endless stream of garbage trucks tests its mettle, a truck scale that is in use in Lewis County, Washington, is an augmented version of a Survivor OTR from Rice Lake Weighing Systems, Rice Lake, Wisconsin. The entire truck scale, including cover plates and load cell stands, are made from hot-dipped galvanized steel.
Galvanization is a process that bonds molten zinc to steel, forming layers of armored alloy that shield the steel from corrosion. Invented in India in the fourth century, galvanization was first used in the construction of the Iron Pillar of Delhi, which still stands today—nearly 1,700 years later. The process has evolved dramatically over the centuries.
Rudimentary galvanic paint traditionally was used to fortify metal until hot-dip galvanization was invented in 1742, revolutionizing the process by immersing metal in molten zinc to create a uniform coating. In 1772, Luigi Galvani made another technological leap forward. While performing scientific experiments on frog cadavers, he discovered that electricity creates unusual results. First observing a simple muscle twitch in frog legs when electricity was applied, Galvani broadened his experiments to ultimately discover the electrochemical process that occurs between metals. In 1836, modern hot-dip galvanization was patented and named after Galvani.
First, metal is cleaned with sulfuric acid and fluxed with ammonium chloride before being coated in liquid zinc at a temperature of 840 F. This creates a strong, long-lasting bond between the metal and zinc and completely insulates the metal from contact with the surrounding environment.
Out with the old
Before the galvanized truck scale was installed, the Lewis County Solid Waste Utility was using a 20-year-old steel deck truck scale that finally had succumbed to the slow, steady march of time. Solid waste is a difficult material to handle, and Lewis County's equipment is expected to endure the test.
Collecting from residential and commercial customers, the county has no way of knowing the contents of each garbage can or dumpster—and people throw away some pretty strange things. Usually, they’re completely harmless; however, processing miscellaneous objects, such as propane tanks, concrete highway dividers or objects containing chemicals, can cause tremendous wear and tear on equipment. Heavy items create damaging collisions when loaded and transferred; combustible objects can explode; and chemicals from batteries, almost-empty household cleaning containers and everything in-between mix together to attack equipment.
With no protective coating, the old scale was consumed by rust. Erratic readings and component lockups were becoming more frequent. It was time for an upgrade. To better serve the county, a scale designed for this environment and to fit the existing foundation was needed. Lewis County called Scales Northwest, a company with locations in Oregon, Washington and Idaho.
Bill Norwood, solid waste operations supervisor for Lewis County, says, “I’ve worked with other scale companies in the past, and Scales Northwest really knows the business inside and out. They were very professional and took care of all the measurements to make sure the scale fit our foundation. Ultimately, when the scale was installed, it fit perfectly.”
Before installation, however, another integral component to extend the scale’s life span was put in place: a gantry system to move the scale platform for routine cleanout.
Tracks running along each side of the foundation were put in place. This allows a gantry crane to be positioned on each corner of the truck scale. Chain is attached to custom pick-hooks built into the truck scale’s load cell pockets, and the entire scale deck is lifted and moved out of position for foundation cleanout. Every three months, the procedure takes place, and Lewis County has it down to a science.
“It only takes us two hours from start to finish,” Norwood says. “Because of the scale’s self-centering load cells, the procedure is pretty fast. When we’re done cleaning the pit, we can drop the scale back into position, and it’s ready to go. There is no checking system we have to fiddle with. It just works.”
Each Survivor truck scale features Rice Lake’s G-Force self-checking mounting system, which the company says uses gravity to return the scale to center without check rods or bumper bolts. “Our old scale used canister-type load cells,” Norwood says. “We had to hold each load cell in place with a little pin while we tried to align everything.”
The shining armor adorning the scales is a visual indicator of the durability that lies within. This durability is exercised on each load.
Because of the transfer process, the scales are subjected to more weight than dead load would indicate. When a truck dumps its contents on the tipping floor, located approximately 12 feet above the scales, a front-end loader pushes the solid waste to an opening in the floor. Beneath this opening, a container sitting atop the scale receives the payload. Those 12 feet might seem nominal, but the drop can create an impressive amount of velocity when it comes to heavy objects contained in the material. When these objects hit the bottom of the container, a force far exceeding the weight (called shock load) is exerted on the scale. Then, an excavator compacts the material, creating an aftershock.
Not everything from the trucks makes its way to the scale, however. Masters of repurposing, Lewis County salvages items that can be reused—from concrete blocks to decorative items. The blocks are used to build traffic lanes around the facility. Empty soda and water bottles create a greenhouse elsewhere on the property. Tin sculptures decorate the site and great visitors. One man’s trash is another’s treasure, indeed.
To some, galvanizing a truck scale might seem like an extreme measure. However, Lewis County needed an exceptional solution for its environment. From leachate to shock loading, any scale would be put to the test. “The amount of steel that’s in that scale is incredible,” Norwood says. “We joke that it would last 30 years without galvanization, so we estimate it’ll last exponentially longer with it. That scale will still be here after I’m long retired.”
This article was supplied by Rice Lake Weighing Systems, Rice Lake, Wisconsin.