Industrial Truck Scales Repair and Custom Weighing Systems Service

Preventive Maintenance Is Key To Truck Scale Performance
Ensuring you follow a thorough preventive maintenance plan can mean the difference between a five year old scale life or a generation long scale life.

Customers who purchase a truck scale demand the most return on their investment. Naturally, their level of satisfaction will depend largely on the scale’s accuracy, durability, and reliability over time.

Installing a scale known for its structural integrity is the first step to ensuring dependable performance, but even a quality scale’s performance can slip if not maintained properly.

Rice Lake Weighing Systems Heavy Capacity Scales Group has developed a basic preventive maintenance (PM) plan for examining components that are vulnerable to conditions that can cause accuracy errors and lost calibration. Derived from more than 50 years of experience selling, installing and servicing heavy capacity scales, these guidelines serve as a practical reference. Because all scales—particularly those installed outdoors—are subject to unique circumstances, it’s impossible to cover every cause of trouble. However, regular checks similar to those described in the following paragraphs can help ensure a quality truck scale lasts for decades.

Scheduling Maintenance Checks
We suggest checking truck scales every six months at a minimum. A convenient time to run your PM inspection is during the scale’s regularly scheduled calibration check. You’ll also want to consider the location and circumstances of the application. It’s a good idea to inspect a scale just prior to peak usage times, such as harvest season in agricultural operations.

Visual Inspection
The only tool you’ll need for much of the inspection is a good pair of eyes. A scale is only as good as its foundation, so that should be the first element you examine. If the operator has indicated the occurrence of errors, it may be due to significant foundation settling caused by poor site preparation or shoddy concrete work. Regardless, take note of any cracks in the foundation. Cracks that lead to movement or settling will cause chronic calibration errors. For the scale to once again read accurately, the foundation will need to be repaired, which may require removing part or all of the foundation and pouring a new one.

Next, take a look at the deck. Rust or crumbling concrete can weaken the scale’s structure and cause problems if not addressed. You may want to clean and paint rusted steel, and repair or replace concrete as needed to maintain the scale’s structural integrity. After examining the surface, look for debris such as gravel or crumbled concrete caught between the foundation and scale deck. Binding is a common cause of inaccuracies and can result from something as small as a single rock. Installing T-Strip molding between the deck and foundation can help keep debris from getting caught or falling down into the scale. In addition, some manufacturers of above ground scales offer the option of end cleanout plates that can be removed, allowing access to remove material that builds up on the foundation’s surface closest to the scale’s end.

Once you’ve cleaned out debris, be sure that the clearance between the walls and deck is even and consistent with manufacturers’ specifications. Bowing and other irregularities caused by pit wall cracks, frost heaving, or poor concrete work on the deck or wall could result in future binding. Some scales utilize suspension systems that don’t require checking devices, eliminating a time-consuming step in your PM protocol. First inspect check rods to determine if the attachment points are solid, and then check for binding. It may not be possible to visually determine if a problem such as binding exists. If there is a problem, weight readings will not be consistent from section to section. Inspect hardware to be sure that jam nuts are tight, rods are level and free of foreign material, and washers are not rusted or distorted. Even if they are working properly, you should replace corroded hardware components so they don’t fail in the future.

Unlike check rod binding, bumper bolt displacement will be easy to see. Bumper bolts need to be tight so they don’t move on their own, yet maintain clearance when the scale is both empty and loaded. Seasonal temperature and weather changes can cause concrete and steel to expand and the bumper bolts can bind tight against the contact area. If binding occurs, adjust bumper bolts to maintain the proper amount of clearance for all conditions.

Next, examine the load cells and the area surrounding them. The load cell area may contain a rodent nest, dirt or other debris that’s built up since the scale’s last check. Load cells must have clearance to deflect through their capacity range. The same type of foreign materials that can bind the scale deck can also keep the load cells and suspension components from moving freely.

The performance of a load cell is often dependent on the condition of the attached cable, which should be the next stop on your inspection. Inspect the load cell cable for rodent damage. If rodent damage is present, you can bet the seal is degraded as well. To combat this occurrence, some manufacturers offer rigid or flexible metal conduit to run the cable through, providing a layer of protection that’s nearly impervious to damage from rodents. Steel overbraid cable provides more protection from rodent damage than cable sheathed with polyurethane or plastic, but is still vulnerable and will need to be checked more frequently. Weather is another enemy of load cell cable. A damaged seal around the gland where the cable enters the cell can cause water infiltration. When exposed to moisture, cables can also serve as wicks. Water can move along the cable’s length by capillary action until it enters the load cell or junction box. Once inside, it can not only damage these components but seep into the inner layer of the cable. Wet cables may not cause signal distortion immediately, but may slowly corrode the copper wires or shield beneath the insulation, setting the stage for future problems.

Now move on to the junction box (j-box). Internal condensation is the most common moisture problem. This condition occurs from normal air exchanges from heating and cooling cycles, and over-aggressive washing that damages sealing components that haven’t been properly maintained. If left unchecked, wiring terminals and other components in the enclosure will corrode. Due to its material properties, a stainless steel j-box promotes internal condensation and are therefore more vulnerable to this problem. If stainless steel is not required, the best practice is to install a new Tuff Seal j-box.

Quality Counts
Whether you own a pit-type, above ground, siderail or portable vehicle scale, a portion of your preventive maintenance plan rests in the hands of the manufacturer. It’s not uncommon for scales that are functioning correctly to collapse without warning. The culprit? Rust. Many scale understructures are left untreated and vulnerable to corrosion. Steel deck scales that have a welded bottom plate also promote corrosion because water that seeps into the scale cannot run into the ground and is less likely to evaporate. In these cases you can and should protect the scale components mentioned earlier; however, there isn’t a solution for protecting the understructure. If you are considering a truck scale purchase, you may want to look at a scale that includes a corrosion-resistant undercoating or does not include a bottom plate. Depending upon the scale’s location, special features, and the material it is weighing, your scale inspection may or may not require all of the steps mentioned above. However, these guidelines should give you a good start for developing a preventive maintenance plan for your truck scales.

Portions of this article courtesy of Mark Johnson, Jr. is the Business Unit Manager for heavy capacity scales at Rice Lake Weighing Systems.

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