Question

The surface finish generally adopted in milk storage tanks inner surface is

• A. 150 grit
• B. 300 grit
• C. 1.2 grit
• D. 0.5 grit

Hint:

Sanitary Surface Finishing: Milk Storage Tank Interiors = 150 GRIT (No. 4 Finish, $Ra \le 0.8\;\mu\text{m}$) for sanitary cleanability.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Sanitary surface finish standards in dairy equipment fabrication: 3-A Sanitary Standards and BIS mandate that product-contact surfaces of milk storage tanks and processing vessels be mechanically polished to a No. 4 finish using 150 grit (or 150--180 grit, equivalent to surface roughness $Ra \le 0.8\ \mu ext{m}$).
Key Formula or Approach:
\[ \text{3-A Sanitary Standard No. 4 Finish} \equiv \mathbf{150 \text{ Grit Polish}} \quad (R_a \le 0.8\;\mu\text{m} / 32\;\mu\text{in}) \]

Step 2: Detailed Explanation:
In sanitary dairy equipment design, fabrication, and cleanability standards (3-A Sanitary Standards BIS: 2494):
- The inner product-contact surface of milk storage tanks, pasteurizers, and silos must be smooth, non-porous, and free of microscopic crevices or pits that could trap bacteria and milk residue:
1. No. 4 Sanitary Finish (A): The standard industrial surface finish generally adopted for the inner surface of milk storage tanks.
2. Produced by progressive mechanical abrasive polishing finishing with 150 grit (or 150 to 180 grit abrasive belts).
3. This produces a surface roughness average of $Ra \le 0.8\ \mu ext{m$ ($32\ \mu ext{inch}$)}, ensuring rapid, complete self-draining cleanability during automated Clean-In-Place (CIP) cycles.

Step 3: Final Answer:
Therefore, the surface finish generally adopted is 150 grit, corresponding to option (A).