Surface Finish And Material Construction Options

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Some of the most important features of the equipment AZO offers are our high-quality welds, coatings, surface finishes (the preparation of the surface) and materials (the type of steel used). While finish options are more limited for our Bulk Bag Unloaders, various combinations of finishes and surface roughness choices are completely at your plant’s disposal when selecting AZO equipment such as our Receivers, Screw Feeders, Screeners and Bag Dumps.

There are six main metal finishes to choose from, and AZO sales associates are ready to work with you to decide what specifically your plant and processes require. Let’s take a look at a few key relevant topics and then dive into the differences between our six famous finishes.

Materials of construction

The first step in customizing equipment to fit your needs is choosing between two distinctive materials of construction — carbon steel and stainless steel. The versions of AZO stainless steel available include 304, 304L, 316 and 316L.

AZO Stainless Steel Passivation

All of our stainless equipment is “passivated,” a process that removes unwanted oil and debris. Passivation washes a metal to its original corrosion specifications and removes contaminants that may be previously embedded during the fabrication process. It is required in passivation to remove these contaminants down to the structure of the stainless steel’s surface.

What the AZO finish/material titles represent

AZO has a distinct labeling system in place for the combinations of our finishes and material constructions. Each character in these titles represents different information. For example, with the A22 combination, the “A” and the first “2” represent whether the material offered is carbon or stainless steel (with other options these first two characters can also represent the grade of stainless steel). The second “2” in “A22” specifies the surface finish grade. As this number increases, so does the quality of the surface finish.  

Our six different finish/material combinations:

While food and pharmaceutical companies generally choose higher grade finishes to minimize cross-contamination and to expedite cleaning, we offer different material/finish combinations that can be used in any system depending on your plant’s requirements and processes. Here is a breakdown of the different surface finish/material options AZO offers from our highly automated factories that can be custom-designed to fit your needs:


A21_AZO A21_AZO2


A21 is considered to contain the basic surface finish. The outside of the A21 component is welded, and both the inside and outside surfaces are brush cleaned. Spot welds (where brackets are not fully welded continuously) are present on the outside of the tank in the A21 option. This is the biggest difference between A21 and A22. Still, on the inside of the A21 option there are no spot welds.


AZO big bag unloader AZO bulk bag unloader


Like A21, both the inside and outside of the A22 vessel are brush cleaned. Everything on the inside of A22 is welded continuously.




A22R features an easy-to-clean design that meets higher requirements with regard to sanitation. The outside of A22R is brush cleaned. The inside welds are continuously welded and ground flush. The inside surface roughness has a micron rating of Rz < 20 microns, and the outside has a micron rating of Rz < 35 microns.

Mechanical polishing and arithmetic formulas

When a surface is made smoother using abrasives and mechanical tools, it is referred to as mechanical polishing. Increasingly finer abrasives are used to polish the material until it reaches the specified level of smoothness.

So how do we take a glance at the completed conditions of our metals? The answer is Ra and Rz — arithmetic formulas that are used to measure the final result of the polishing.

While Ra specifically measures roughness, Rz measures the maximum height of the metal microscopically as it is polished. Both formulas are used together so that measurements are accurate.    


A23_AZO A23_AZO1


The interior welds of A23 are polished and they are easier to clean than A22R. The welds are brushed smooth. A23 is optimal for certain plant requirements and the design meets higher sanitation requirements. The inside surface roughness has a micron rating of Rz < 8 microns, and the outside has a micron rating of Rz < 20 microns.




A23R features a design that meets higher sanitation requirements. However, it is more suited for some specific plant requirements than A23 because of the quality of both its inside and outside polish. The inside of A23 and A23R have seams that are continuously welded and ground smooth, but the outside polish of A23R distinguishes the two finishes. Both the inside and outside surface roughness of A23R has a micron rating of Rz < 8 microns.


A24_AZO1 A24_AZO


A24 is electro polished making it the best option for some specific plant requirements. The inside and outside are both continuously welded and ground smooth. The surface roughness of A24 has a micron rating of Rz < 5 microns. A24 is the ultimate stainless steel finish and optimized for the highest level of sanitation.

If you would like to customize AZO equipment to fit your needs and processes, contact our sales team to discuss the right material construction and surface finishes that will help your plant and processes run smoothly in the long term. AZO GmbH has always been a leader in the ingredient automation industry, and for more than 40 years AZO Inc. has brought robust German engineering to North American shores.
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