Solid Waste Technologies
Truck Scales: Re-Weighing Your Options
New truck scale technologies can resolve old nuisances and even mean the difference between profit and loss in a solid waste transfer or disposal facility. Periodic reviews of what new options are available can make your decision making more fruitful.
In the technologically advancing solid waste business, billing by weight is becoming far more common, and the scale becomes the company cash register. If the scale is inaccurate or unreliable, customers will be overcharged or undercharged, either of which can be bad for business. A scale that is frequently being repaired also comes under suspicion by customers, as well as local weights and measures officials. Bad news travels fast, and if your customers don't trust you, they will go elsewhere for their hauling needs.
Most scale systems today incorporate all the advancements the electronic age has to offer, such as digital readouts and ticket printers, and the system usually can be interfaced with a computer for extensive record keeping. Beyond the new computer-age functions, there are several other components to review while evaluating your next scale purchase. These include the size and capacity needed, the type of load cell and whether the scale should be above-ground or pit-mounted. In addition, a solid waste facility is one of the toughest applications for a truck scale, because of the exposure to lightning, rain, flooding, accumulation of debris, rodents and even corrosion. Some of the most important aspects of buying a scale relate to selecting one that will handle this harsh environment.
Today's most common truck scale has a platform 10-feet wide and 70-feet long, a capacity of 100 tons and eight or more load cells under the platform. The platforms can be steel or concrete and are engineered to last for 20 or more years. Selecting a shorter platform could adversely affect your operations in the future as well as its resale value. Many truck models are getting longer, so if you buy one that's "just tight" today, in five or 10 years, you may find your platform too short for most of the businesses you serve. Having a 70-foot scale can also broaden your options by allowing you to let nearby businesses in other industries (with varying truck lengths) use your scale to weigh.
The durability of the platform is also important. Soil reclamation operations that receive frequent and heavy loads, for instance, should purchase a heavy duty deck that will last longer under the extra high axle loads. In any case, don't assume that a 100-ton scale can handle all loads up to 100 tons. Decks have been known to crack over time, and some have actually collapsed. Overall scale capacity ratings do not reflect how a scale is loaded and a Concentrated Load Capacity rating does not indicate a unit's strength.
The true indication of strength is how heavy an axle the scale is designed to carry. The "dual axle capacity" of a scale is probably the best indication of its strength, because it reflects how the scale is loaded (heavy dualaxle trucks traveling over the scale). A dual axle capacity of 40 tons or more is appropriate for most solid waste handling facilities.
Side rails are worthwhile to consider as an addition to platforms. With dozens of trucks a day passing over the scales, some wheels could slip off the edge, leading to serious damage of the truck and scale.
One of the basic decisions to be made is choosing between an above-ground (low profile) design and a pit-mounted scale. A truck pit should only be considered if there is no room for a low profile model, since the pit is nothing more than a hole waiting to get filled with water, trash, mud and vermin. Accumulated debris can affect scale performance, while water, corrosion and rodents are well known to cause failures of load cells (even in above-ground scales). If you must use a pit, the load cell selection should be narrowed to those that are stainless steel and are immune to water damage.
Above ground (low profile) scales are usually about 16 inches high, with four to six inches of clearance under the scale. It is very important to keep the area under the scale free of debris, and you will be well advised to find a scale with six inches of clearance instead of four. It is surprising to some how the extra two inches of room eases cleaning under the platform. A disadvantage for above-ground scales is that they need ramps and approaches - as much as 30 to 35 feet at each end. Weights and Measures department personnel in your area can provide the exact requirements for your station.
There are two primary types of load cells available, electronic and hydrostatic. (Digital load cells are a version of electronic cell with extra circuitry that helps identify when a load cell is damaged.) Electronic load cells are by far the most common throughout the trucking industry. They can provide reliable service in areas that are not exposed to water, lightning, corrosion or rodents.
Lightning is the number one enemy of a truck scale, and a strike - or even a nearby strike - can destroy one or all of the scale's load cells in a heartbeat. With eight or 10 cells in a scale, that can mean wiping out an investment of more than $20,000. Lightning only needs to strike in the vicinity of your operation to cause damage, and surge protectors can't do much. Grounding systems to prevent damage can be expensive and may actually add to the problems. It is a shock for some to realize that after you have replaced cells damaged by lightning, the scale is still just as vulnerable to the next lightning strike.
Water is the next big danger to load cells because it wicks into the cable connections, and damages the delicate circuitry inside. Junction boxes are also areas where moisture and condensation can cause big problems. Commonly attempted solutions are silicone and caulking - but they usually have little success.
With hydrostatic load cells, all sensitive electronic components of the scale are located in the scale house or control room, not under the scale platform. They are impervious to water and electrical damage, including lightning. Hydrostatic load cells operate on a thin film of fluid (only 0.030 of an inch thick) and send a pressure signal to a summing totalizer and digital display in the scale house. Copper or stainless steel capillary tubing (1/8 inch in diameter) is used to transfer this signal, eliminating electronic cables from the scale platform. A typical 70-foot hydrostatic truck scale uses only about one pint of fluid, and there are no pumps or reservoirs because there is no movement of the fluid. It is simply used as a medium to transfer the pressure signal away from the platform.
Generally, hydrostatic truck scales are priced about 10 percent higher than good quality electronic scales. The life cycle operating costs (total cost of ownership), however can be exceptionally low. The scales can maintain their calibration for years without needing adjustment. If a hydrostatic load cell is physically damaged and does need replacement, it often can be done without affecting the scale calibration and without breaking the seal on the digital indicator.
Electronic scales commonly have to replace three or more cells a year. With load cells priced between $1,000 and $1,500, and labor and calibration costs reaching $1,000, annual maintenance costs for a truck scale easily can be $5,000 and can reach $20,000. It won't take too many failures to come close to the cost of a whole scale.
The materials from which a load cell is fabricated is critical. A solid waste facility should insist on materials that provide the best available corrosion protection from salts, oils and other chemicals. For electronic load cell scales, the selection of materials is usually steel or 17-4PH stainless steel. The 17-4PH is the best material available for electronic load cells, but more protection is available from grade 304 stainless steel, used to construct hydrostatic load cells.
Buyers should also be aware of load cells that claim to be grade 304, but in reality have only a housing or mount assembly made of 304. In those instances, the load cell itself is often a lower grade of stainless (such as 174PH) and is not as resistant to salts and oils. It is also a good idea to cover all load cell cables with stainless steel braiding. This will offer some protection from rodents who like to snack on electronic cables.
The load cell capacity is also a key element in purchasing a durable scale. Don't settle for low capacity cells. The most common capacity is 50,000 pounds, and this may be insufficient in many instances. Some 60,000-pound capacity units are available, and hydrostatic cells have a 75,000 pound capacity.
The higher capacity cells can better handle the shock loading and reaction forces of a solid waste operation. Using more cells under a platform (10 instead of eight for instances), only increases the number of components vulnerable to damage; it does not reduce the stress on individual load cells.
Sanitary Waste Disposal Company, South Windsor, CT, is a family owned business, steadily growing in the greater Hartford area for the past 35 years. Fred Defeo, and his son Ron, have built a loyal customer base by providing customer satisfaction. A few years ago, Ron realized further growth was partly dependent on the company adding a truck scale. Then began a surprisingly long period -- two years -- investigating scale suppliers. During the process, Ron found that most salespeople spent little time talking about their scales. "They seemed more interested in selling me a service contract and an extended warranty. I began to wonder, why do I need so much service on a brand new truck scale?"
Ron called friends and colleagues that already had truck scales. "Almost everyone I talked to was having load cell failures," Ron said. The two biggest culprits were water and electrical damage, things they get plenty of in South Windsor, especially during the summer. "Some of my friends had load cells knocked out repeatedly and were paying big dollars for repairs."
When Ron questioned salespeople about water and lightning, they again brought up service contacts and extended warranties. Ron's personal investigation soon showed that warranties don't prevent failures; they don't pay for down-time and they don't pay the full repair bill. "The warranties I was seeing were not worth much, yet I was expected to pay up to $1,500 per year to keep them going!" He found that most warranties cover defects in material and workmanship, and usually only a year. They also typically cover only the load cells, not labor or re-calibration costs that come with any repair. And, Ron found they don't usually cover damage from water or lightning, except at additional cost.
The search for Ron ended satisfactorily, when he discovered a friend who was using hydrostatic load cells (available from Emery Winslow). This cell seemed to solve most of the problems his friends were experiencing. And the clincher was finding that Emery Winslow offered a lifetime warranty on the load cells against water and electrical damage.
The rest is history. Sanitary Waste bought a hydrostatic scale one year ago and has not incurred any maintenance costs during that time. "The scale hasn't given us a day of trouble," says Ron. "It calibrated in a flash, and most important, it has prevented failures and down-time."
This is a reprint of an article that appeared in Solid Waste Technologies
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