Scale Maintenance Savvy

November/December 2014

An inaccurate scale can cause your recycling company to lose money on every transaction. Prevent such losses by following these scale maintenance practices.

By Russ Desilets

When you installed your truck scale, your state office of weights and measures certified that it met the necessary regulatory requirements, and the manufacturer promised it would hold to accurate tolerances. Unfortunately, external variables and real-world issues can knock your scale out of calibration and cost you a lot of money. How much? Let’s say your scale overweighs by 20 pounds on each incoming load. If you weigh 100 truckloads a day, you’re overweighing—and overpaying—by 2,000 pounds. If the incoming scrap is 10 cents a pound, you’re losing $200 a day. If the material is more valuable—say, $3 a pound—you’d lose $6,000 a day. Multiply that by 300 working days a year, and you could be out $1.8 million a year. The losses would be even more dramatic if your scale is off by more than 20 pounds. Such weight-related losses are a persuasive argument for undertaking preventive maintenance steps in your scale operations such as the following.

Implement a calibration and inspection agreement. A calibration and inspection agreement with your scale service provider can cost as little as $500 a year depending on your type of weighing device, the frequency of inspections, and other factors.

Two inspections a year is adequate for most scales, but the heavy traffic in scrap recycling operations can justify more frequent attention. Talk with your scale service vendor to map out a schedule that works best for your company.

How long should you expect a normal inspection and calibration service call to take? That depends on several factors, including whether the load cells are analog or digital. Let’s say a typical scale has eight to 10 load cells. If the load cells are analog, it could take four to six hours to calibrate them correctly. With a digital scale, the calibration could take less than 30 minutes.

Keep the scale foundation clean. Recycling operations generate a lot of dirt and debris, so it’s important to regularly remove the buildup to prevent scale inaccuracies. A pressure sprayer is a fast and easy way to clear debris and keep the scale and foundation in prime operating condition. Make sure, however, that your scale’s junction boxes, electronics, and load cells are rated to withstand pressure washing, or you could damage them during the cleaning process.

Perform your own inspection. A scale can function properly only when all of its components are in good order and working together. That’s why it’s prudent to conduct your own internal inspections of the entire scale system. How often you conduct these inspections depends on factors such as the cost of your scale system, its use, and the operating environment. Your scale vendor can assess the conditions in your facility and make a recommendation. A typical internal inspection might include these checks:

• Examine the weighbridge for damage or signs of wear and corrosion.
• Review the junction boxes inside and out, looking for signs of damage, corrosion, or moisture entry.
• Check that the module connection hardware—the steel components that connect two or more adjoining weigh modules to make the weighbridge one continuous bridge—is intact and not damaged.
• Examine the load cells for damage, corrosion, and signs of moisture entry into the enclosure and the cable entry gland, a seal designed to keep moisture from entering the load-cell enclosure and prevent the cable from being pulled out. Liquid is a good conductor and can easily short out your electronics if it enters the sensing element area.
• If your scale has load-cell cables with a quick-disconnect feature, check the connections frequently, as they are responsible for a significant number of avoidable failures.
• Inspect all wiring for damage. Exposed conductors cause communication errors when wet and are usually the cause of erratic performance.
• Determine if your scale needs to be repainted. Your scale’s paint isn’t just for good looks; it’s a critical barrier that protects against corrosion of the weighbridge steel.
• If your scale has cover plates, inspect the connection hardware and make sure it’s there, functional, and not packed with mud and debris.
• Grease the load cell cups at recommended intervals. A load cell cup is a hardened steel component that sits on top of a load cell, forcing it to remain centered during weighing yet allowing some movement. Some manufacturers incorporate zerk-type fittings that allow you to apply grease without physically separating the load cell components.
• Inspect the concrete under and around your scale for signs of failure, and address any issues as soon as possible. Left unchecked, concrete-related problems will only get worse and could cause larger—and more costly—problems.

Adjust the checking system. It’s natural for your weighbridge to expand and contract slightly at different times of the year. This thermal expansion requires you to readjust your scale’s checking system, which keeps the weighbridge in place as it naturally rocks and moves from traffic. Too small a gap in the checking can cause binding and weighing errors. Too large a gap allows excessive movement, which adds unnecessary wear to components and could even result in a scale tipping. So be sure the checking is properly secure.

Keep your scale grounded. Today’s truck scales use sophisticated electronics to communicate weight data to the scale readout instrument, so it’s critical to have a securely grounded scale as a basic defense against lightning and power surges. Ensure that the scale is connected to the manufacturer’s specified grounding system and that there are no interruptions in this system. Transient voltage seeks the easiest path to ground. If your scale isn’t grounded through a ground rod connection, it surely is grounded through other components. Disrupting the ground connection shunts power surges to other places, such as your load cells or electronics, which could cost you thousands in repairs.

Monitor your scale’s use. Your scale is designed to move slightly as vehicles pass over it, but abusive and aggressive traffic movements accelerate wear—which means more money spent on repairs. You might not be able to monitor how fast traffic passes over your scale, but many scale manufacturers offer accessories such as traffic signals and guidepost kits for the scale’s entrance and exit to help you manage traffic flow, limit truck speed, and promote traffic discipline at your scale.

Install scale accessories where necessary. If you have a low-profile scale, it’s closer to the ground than a higher-profile scale, which means it takes less debris accumulation to affect its operation and it’s more difficult to clean under the scale. In such cases, you might want to consider installing riser plates to elevate your weighbridge, reducing the risk of debris accumulation and providing clearance for cleaning and inspection.

In terms of other accessories, don’t forget that your scale’s load cells operate in the worst environment possible, with exposure to dirt, moisture, scrap, and other challenges. It’s prudent, therefore, to consider covering them with boots, which act like a protective glove and prevent debris from interfering with their proper operation. Also, at each end of your scale, there is a small gap between the scale and foundation. This gap is a great place for dirt, debris, and scrap to fall under the scale and accumulate. Installing T-shaped belting in and along this gap is a smart way to prevent this accumulation.

Neglecting your scale will cost you money. Whether you implement the above best practices alone or partner with a scale service provider, you’ll reap the benefits in less downtime, greater scale life, and more accurate weighing.

Selecting a Scale Service Provider

When searching for a scale service provider, consider a variety of factors. Start with longevity and experience in the scrap industry. How long has the vendor been in business? Has it worked with other recycling companies? Does it know the challenges of operating a scale in a scrap recycling environment?

Also compare vendors based on the services they provide. One priority in a calibration and inspection program is to make sure the vendor tests your scale with certified weights that are traceable to a federal standard. The service provider should be able to provide documentation of the test weights’ traceability. As part of the vendor’s inspection process, does it review the electronic and mechanical components to look for wear or looming issues that could result in inaccuracies or unexpected downtime? Finally, after the inspection, be sure the service company provides a written evaluation of the inspection results and reviews the scale’s condition with you.