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　　 Pressure-resistant manhole Surface treatment not only affects the aesthetic appearance of manholes but also directly impacts their manufacturing and operational performance; therefore, it is an essential component of the production process. Next, let’s examine the surface‑treatment methods used for pressure‑rated manholes.

　　The hot-rolled surface undergoes heat treatment and pickling. It is typically used for cold-rolled materials, industrial tanks, chemical‑processing equipment, and similar applications, with thicknesses ranging from 2.0 mm to 8.0 mm.

　　Bright finish: After cold rolling to No. 2D, the material undergoes heat treatment and acid pickling, resulting in a relatively soft texture and a silvery-white luster. It is used for deep drawing applications, such as automotive components and water pipes.

　　Matte finish: NO.2B is produced through cold rolling, heat treatment, and pickling, followed by final rolling to achieve a moderately bright surface. Its smooth surface facilitates subsequent grinding, further enhancing its luster, and it finds wide application in areas such as tableware and building materials. With an improved surface treatment that enhances mechanical properties, it is suitable for virtually all applications.

　　Coarse Sand No. 3: Polished using a 100–120 grit abrasive belt. It delivers superior luster and features discontinuous coarse grain patterns. Suitable for interior and exterior architectural finishes, electrical appliances, and kitchen equipment.

　　No. 4 fine sand: Produced by grinding with 150–180 grit abrasive belts. It exhibits good luster and features discontinuous coarse lines; the grain pattern is finer than that of No. 3. Used for bathrooms, interior and exterior architectural finishes, electrical appliances, kitchen equipment, food-processing machinery, and more. #320: Ground‑finished products using #320 grit. They have good luster and display discontinuous coarse lines, with a grain pattern finer than No. 4. Suitable for bathrooms, interior and exterior architectural finishes, electrical appliances, kitchen equipment, food-processing machinery, and other applications. HL No. 4: A brushed finish achieved by continuous polishing with appropriately graded abrasive belts (finely graded from 150 to 320). Primarily used for architectural decoration, elevators, building door panels, and panel surfaces. Bright surface: BA—bright annealed after cold rolling, followed by leveling. Pressure-resistant manhole Common Surface Polishing Methods

　　1. Magnetic Abrasive Polishing of Manholes: Magnetic abrasive polishing utilizes magnetic abrasives that, under the influence of a magnetic field, form an abrasive brush to grind the workpiece. This method offers high machining efficiency, excellent surface quality, easy control of processing conditions, and favorable working conditions. With the selection of appropriate abrasives, the surface roughness can reach Ra 0.1 μm.

　　2. Fluid‑polished manhole: Fluid polishing achieves surface finishing by utilizing a high‑velocity liquid flow that carries abrasive particles to the workpiece surface. Hydraulic‑driven grinding employs hydraulic power to induce rapid reciprocating motion of a liquid medium loaded with abrasive particles across the workpiece surface. The working medium is primarily composed of a specially formulated compound—typically a polymer—that exhibits excellent fluidity under low pressure, mixed with abrasive particles. This abrasive tool can be manufactured from silicon carbide powder.

　　Pressure‑rated manholes are typically installed on storage tanks, vent and breathing valves, tank cleaning equipment, manhole access points, and for fire‑safety purposes. They serve as safety devices to protect storage tanks and are especially suitable for material storage and nitrogen‑blanketed atmospheres.