What harsh environments must your load cells withstand?
This article explains how to select a load cell that will perform reliably in harsh environments and harsh operating conditions.
Load cells are critical components in any weighing system, they sense the weight of material in a weighing hopper, other container or processing equipment. In some applications, load cells may be exposed to harsh environments with corrosive chemicals, heavy dust, high temperatures, or excessive moisture from flushing equipment with large volumes of liquids. Or the load cell may be exposed to high vibration, unequal loads, or other harsh operating conditions. These conditions can lead to weighing errors and, if incorrectly selected, even damage the load cell. To select the appropriate load cell for a demanding application, you need to fully understand your environmental and operating conditions, and which load cell features are best suited to handle them.
What makes the application difficult?
Please carefully observe the environment around the weighing system and under which operating conditions the system must work.
Will the area be dusty?
Will the weighing system be exposed to temperatures above 150°F?
What is the chemical nature of the material being weighed?
Will the system be flushed with water or another cleaning solution? If cleaning chemicals are to be used to flush equipment, what are their characteristics?
Is your flushing method exposing the load cell to too much moisture? Will the liquid be sprayed at high pressure? Will the load cell be submerged in the liquid during the flushing process?
Could the load cells be loaded unequal due to material buildup or other conditions?
Will the system be subjected to shock loads (sudden large loads)?
Is the dead load (container or equipment containing material) of the weighing system proportionally larger than the live load (material)?
Will the system be subject to high vibrations from passing vehicles or nearby processing or handling equipment?
If the weighing system is used in process equipment, will the system be subject to high torque forces from the equipment motors?
Once you understand the conditions your weighing system will face, you can select a load cell with the correct features that will not only withstand those conditions, but will perform reliably over time. The following information explains which load cell features are available to handle your demanding application.
Building materials
For help selecting the right load cell for your demanding requirements, consult an experienced load cell supplier or an independent bulk solids handling consultant. Expect to provide detailed information about the material the weighing system will be handling, the operating environment, and what conditions will affect the operation of the load cell.
A load cell is essentially a metallic element that bends in response to an applied load. This element includes the strain gauges in the circuit and can be made of tool steel, aluminum or stainless steel. Tool steel is the most common material for load cells in dry applications because it offers good performance at a relatively low cost and offers a large capacity range. Tool steel load cells are available for both single point and multipoint load cell (known as single point and multipoint) applications. It works best in dry conditions, as moisture can rust tool steels. The most popular tool steel alloy for these load cells is type 4340 because it is easy to machine and allows for proper heat treatment. It also springs back to its exact starting position after the applied load is removed, limiting creep (gradual increase in load cell weight readings when the same load is applied) and hysteresis (two weights of the same applied load The difference between the readings, one obtained by increasing the load from zero and the other by reducing the load to the maximum rated capacity of the load cell). Aluminum is the least expensive load cell material and is typically used for load cells in single point, low volume applications. This material is not suitable for use in wet or chemical environments. Type 2023 aluminum is the most popular because, like type 4340 tool steel, it returns to its exact starting position after being weighed, limiting creep and hysteresis. The strength and corrosion resistance of 17-4 PH (prescription hardened) stainless steel (also known as grade 630 stainless steel) give it the best overall performance of any stainless steel derivative for load cells. This alloy is more expensive than tool steel or aluminum, but offers the best performance of any material in wet applications (i.e. those requiring extensive washdown) and chemically aggressive applications. However, some chemicals will attack Type 17-4 PH alloys. In these applications, one option is to apply a thin layer of epoxy paint (from 1.5 to 3 mm thick) to the stainless steel load cell. Another way is to choose a load cell made of alloy steel, which can better resist corrosion. For assistance in selecting the appropriate load cell material for a chemical application, refer to chemical resistance charts (many are available on the Internet) and work closely with your load cell supplier.
Post time: Aug-15-2023
