Aluminum or Stainless Steel Electronic Loadcells?
We get this question from time to time especially when we come up against repair requests from food processing customers with stringent hygienic requirements.
With food processing applications in particular we get into very wet and moist environments, slight electrical currents inherent in scales and dissimilar metal situations will cause electrolysis and accelerated corrosion of subcomponents in your scale base.
When does it matter?
The short answer is you should always spend the few extra dollars for a high quality stainless steel load sensor in your application if you have regular washdown procedures in your facility or the scale is expected to be operating in damp or wet environment for its life cycle. I would say 8 times out of 10 an aluminum load cell will need to be replaced several years sooner than the same cell made of stainless steel.
Why choose aluminum in the first place then...
Of course it comes back to initial costs of the device being higher for the stainless steel upgrade. We try to urge customers to consider their devices total cost of ownership when making these purchasing decisions.
- As the scale fails before our staff notices it, how much product we will give away?
- Or worse, a large shipment goes out weighing light which causes a rejection at your customers dock?
- The cost of the first service call for travel time, labor, overnight shipping, and replacement parts is typically much higher than the incremental cost to upgrade to a stainless steel loadcell when buying a new device
- Lost productivity with staff struggling to decide if their package weights are correct, leaving the production line to swap a scale out
- Tying up your maintenance manager with diagnostic time, scheduling vendors when they should be keeping the other machines in your facility going and not tinkering with scales
What factors should I consider?
This particular scale was used extensively for cutting vegetables like onions, carrots, peppers and was brought into our shop with the customer reporting that the scale was drifting and not repeating measurements. Many times the chemical makeup of the liquids on the cell will affect the speed at which the load cells will corrode.
As the cell corrodes it degrades the adhesion on the surface of the metal between the potting compound that keeps the electronics in the cell safe and dry. This eventually lets moisture into the sensitive strain gauge area of the loadcell ultimately leading to pre-mature failure of the device.
Do all cells have potting compound?
To some degree yes, but some cells have what we call "Hermetically sealed" internal areas. This is typically done using some form of stainless steel "bellows" or flexible structure that is welded to each end of the cell to keep it sealed from the environment.
This allows the loadcell to still properly deflect to function properly but eliminates the issue of the potting compound delaminating. This type of additional sealing is only found on stainless steel load sensors typically in higher capacities (floor scales, hoppers, silos) as the flexible steel covering would still affect small capacity loadcells too much for it to be functional.
Are all loadcells electronic?
Seems silly to have all of these sensitive electronics down where they can get wet and cause issues anyways, right? Well you would be correct, unfortunately the core technology in nearly all loadcells industry wide comes down to the "strain gauge" and that is really all we have at the moment.
But there are loadcells that use a hydraulic pressure down where they are most susceptible to moisture. You can see this loadcell uses a rubber diaphragm that holds a temperature stable glycol solution. There is a top section not shown here that mounts to the underside of the floor scale that pushes down onto this diaphragm that creates the pressure in the system. The pressure signal is run with stainless steel tubing up the wall to a safe location where it is then converted into an electronic signal using a single electronic loadcell.
But even you can see that the body of this cell is made using stainless steel to ensure that there aren't any issues with corrosion long term.
If you got this far, thanks for taking the time to learn some of the nuances in why we quote more expensive equipment up front for some of our customers... We know it will put your business in a better position in the long run to be successful!