The stainless steel finish of a fabrication project is no less important than the steel’s grade or form, because the stainless steel finish is most likely to impact aesthetics, performance and safety.Whatever the intended use, choosing the right finish option is essential.
Each finish leaves a unique look, and some also help the steel stay clean and hold up to environmental factors. Brushed stainless steel finishes are more resistant to corrosion and are easier to sanitize, while matte finishes cost less but are more susceptible to moisture, salt and other sources of corrosion.
According to ASTM International Standards, there are eight stainless steel finishes. Numbers 1 and 2 are called “mill finishes” and can be used as-is or may be a preliminary step to polishing. Finishes 3 through 8 are achieved mechanically by polishing the metal with fine abrasive belts. The three most popular stainless steel finishes are No. 2B – Matte finish,No. 4 – Brushed finish,No.8 – Mirror finish
No. 2B – Matte finish
No. 2B matte is the most broadly-used finish in stainless steel fabrication and forms the foundation for smoother finishes. Achieved through a cold-roll process, the finish resembles a hazy mirror with limited reflectivity. No. 2B finishes are frequently the most cost-effective option available and used in applications where aesthetics are less critical or additional finishing is planned.
To produce a No. 2B finish, the stainless steel is cold rolled through special rolls or dies to smooth out the pits of the metal’s surface. The steel is then annealed, and its surface is softened and descaled through pickling. Additional smoothness is achieved through a final, light cold rolling pass.
Common applications include:
Chemical plant equipment
Pharmaceutical equipment
Paper mill equipment
Laundry and dry cleaning
Refrigeration
Sewage equipment
No. 4 – Brushed finish
The No. 4 Brushed finish can vary with different suppliers and even from batch to batch from the same supplier. The variations arise from differing manufacturing conditions, such as wearing of the abrasive belts used in these finishes. Some level of variation should be expected when ordering No. 4 Brushed finish. It can be helpful to request a sample of a few square inches to ensure the finish achieves the desired effect.
Brushing the stainless steel produces a distinctive look with a muted luster and a pattern of fine parallel lines. It has strong decorative appeal without being too reflective, as too much reflectiveness can be undesirable. For example, overly reflective stainless steel accents on a building could be blinding in bright sunlight. The drawbacks to this finish include reduced corrosion resistance, because the grooves of the finish are susceptible to rust.
The stainless steel finish is created by sanding the stainless steel in one direction with a 120-180 grit belt, followed by softening with a 80-120 grit medium non-woven belt.
Common applications include:
Jewelry and watches
Home appliances
Air conditioners
Water heaters
Architecture
Automotive design
No.8 – Mirror finish
No. 4 brushed finish is achieved by mechanically polishing the metal with increasingly-finer abrasives. Hallmarks of the finish are a distinctive subdued luster and a pattern of uniform parallel polishing lines.
Depending on the project’s requirements, the grit abrasive can be anywhere within the range of 120 and 320. Higher grit numbers indicate a finer polish and lead to a more reflective surface. At the higher end of No. 4 finish, the stainless steel is considered food grade.
The appearance of stainless steel with a No. 4 finish will differ between metal fabricators due to different working conditions, equipment, operating techniques and sanding belts. For this reason, it’s advisable for a customer to request a sample from the fabrication company to ensure the look of their No. 4 finish is acceptable for the project.
Common applications include:
Mirrors
Ornamental trim
Clean rooms
Column covers
Wall panels
Reflectors
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