Stainless steel scales for wet and hygienic areas: 304 or 316, cleaning and verification
A scale in a cold store, an abattoir, a fish processor or a car wash has different requirements from a scale on a desk. The material must withstand water, salt and cleaning agents, the sealing must suit the way it is cleaned, and the verification must survive the wet work. Below you will find when to choose stainless steel, which grade, which scales go with it and how to keep them clean.
Stainless steel: 304 or 316, and exactly what is made of stainless steel
Stainless steel does not rust because the chromium in the steel forms a thin oxide layer that repairs itself. Two grades are used in scales:
- Stainless steel 304 (1.4301, 18 per cent chromium, 8 per cent nickel) is the standard. It withstands water, moisture, grease and most cleaning agents.
- Stainless steel 316 (1.4401 or 1.4404, with 2 to 3 per cent molybdenum) additionally withstands chlorides: brine, salt water, sea air and chlorine-based cleaners. That is the choice for fish processing, cheese making, salt baths and the chemical industry. On 304 stainless steel, chlorides leave pits, and rust still starts in those pits.
More important than the grade is what is made of stainless steel. Many scales have a stainless steel platform on a painted steel base. That is fine in a dry room, but with daily hosing down the base rusts from the inside. For wet areas choose a scale made entirely of stainless steel: no painted part that can still start to rust, with rounded edges and preferably a platform you can lift or unscrew to clean underneath. That is why an OHAUS Defender 3000 stainless steel, an Adam W series or a KERN BXC - all three fully stainless steel and waterproof - costs more than a painted scale with the same range.
Stainless steel is not automatically better. A painted scale in a dry warehouse lasts just as long, and aluminium is lighter for a scale that is moved often. You choose stainless steel for the cleaning and for what goes on the platform.
Scales by type of wet work
- Dry warehouse or workshop: IP54 is sufficient; a higher rating costs money and delivers nothing.
- Cold store, greenhouse, damp production: IP65. Condensation and a wet cloth are no problem.
- Food processing with hosing down: IP67 or IP68 for the platform, and pay separate attention to the indicator. See the floor scales rated IP65 or higher and the pallet scales rated IP65 or higher; among the bench scales, the KERN SXC, the KERN FOB, the Adam Gladiator and the Baxtran TOPGi are among those built for wet work.
- High-pressure cleaning with hot water: IP69K for the platform, as on the Baxtran PTB and the Baxtran BGI; note that with the BGI the supplied GI400i indicator is itself IP65 and therefore needs separate care with the high-pressure cleaner.
- Outdoors: at least IP65, and bear the temperature in mind; an LCD screen becomes sluggish below zero and a battery delivers less.
- Load cells in a pit or a silo: IP68, and a cable that can withstand rodents and moisture.
If you are torn between two ratings, only choose the higher one if the cleaning calls for it. The difference is in the sealing, not in the accuracy.
The sealing: the weakest link determines how you clean
Stainless steel says nothing about water resistance; for that you look at the IP rating. What the digits mean and which rating suits which environment is explained in which IP rating does my scale need. Here we are concerned with cleaning in practice.
A scale consists of a platform with load cell, a cable and an indicator. Each of the three has its own rating, and the manufacturer usually quotes the highest. So read the data sheet: a platform with an IP68 load cell can have an IP65 indicator, and then the indicator determines how you clean. The battery compartment, the cable gland and the connections at the back are the weak spots. A USB port with a rubber cap is only sealed when the cap is on.
A load cell rated IP65 or higher also needs a junction box with the same rating; the junction box is more often the cause of a moisture fault than the cell itself. And after immersion an IP67 scale must dry out. The rating promises that no water will get in temporarily, not that it can remain standing in water.
Verified and still wet
An IP rating and verification go together. A verified scale in an abattoir or a fishmonger's is quite normal: the Adam Gladiator and many Baxtran and KERN models are IP67 or IP68 and can also be supplied verified. Do pay attention to the seals: they cover the housing screws and the calibration access, and they must not be damaged during cleaning. See what is a verified scale. We calibrate on site, so the scale does not need to leave the wet area; re-verification is arranged through the manufacturer. See verification, calibration and repair.
Cleaning without damage
Most moisture faults are caused not by water but by cleaning agents and the way of spraying. Chlorine-based cleaners attack 304 stainless steel, strongly alkaline agents attack aluminium. A high-pressure jet held close to a cable gland or a keypad forces water inside, even at IP67. So rinse from top to bottom, keep your distance, do not aim at seams and connections, and let the scale dry before it goes on the charger. If water does get in, acting quickly pays off: take the battery out, let it dry, and if the indicator behaves strangely call repair and maintenance before the circuit board corrodes. The daily check and a maintenance checklist are in maintaining and cleaning your scale.
More on choosing by workplace in which industrial scale suits your application; the IP ratings side by side are in which IP rating does my scale need.
And if there is also a risk of explosion?
Flour, sugar, milk powder and solvents are found precisely in wet and hygienic businesses, and can form an explosive atmosphere. A stainless steel scale with a high IP rating is not thereby suitable for a hazardous area; that is a separate certification. The zones, the equipment categories and the choice of a scale are explained in what is an ATEX scale.
Frequently asked questions
Is stainless steel always better than painted steel?
No. In a dry room a painted scale lasts just as long and costs less. You choose stainless steel if it is hosed down, if salt or acid gets on the platform, or if food safety requires it. Then check whether only the platform is stainless steel or the whole scale.
When do I need 316 stainless steel instead of 304?
With chlorides: brine, salt water, sea air and chlorine-based cleaning agents. Think of fish processing, cheese, salt baths and the chemical industry. In most other food businesses 304 stainless steel is sufficient.
Can a verified scale be hosed down?
Yes, if the IP rating allows it. Pay attention to the seals over the screws and the calibration access: they must not come loose or be damaged, otherwise the verification is no longer valid.
My platform is IP68, so why is the indicator only IP65?
Because an indicator has keys, a screen and connections that are harder to seal than a welded load cell. The lowest rating in the system determines how you clean. If you also want to hose down the indicator, choose a stainless steel indicator rated IP68 or IP69K.