What are the core processing techniques for stainless steel strips?

Processing stainless steel strips refers to a series of processes such as cutting, forming, surface treatment, and performance optimization on coiled stainless steel strips (with a thickness typically ranging from 0.01 to 3mm and a width from 10 to 2000mm), to meet the demands of "high precision, specific shapes, and customized performance" in fields such as electronics, automobiles, kitchenware, and medical devices.

Processing stainless steel strips

Its core features are continuous production, high dimensional accuracy and strong surface consistency. The appropriate process should be selected in combination with the material properties of the stainless steel strip (such as corrosion resistance and hardness).

The processing of stainless steel strips usually follows the process of "pretreatment → forming processing → finishing → surface treatment → performance optimization". Different processes correspond to different product requirements. The core processes are as follows:

1. Pretreatment process: Laying a foundation for subsequent processing

The purpose is to remove impurities from the surface of the strip material and adjust its flatness to avoid affecting the subsequent forming accuracy.

Degreasing and cleaning

Function: Remove residual rolling oil and dust during the rolling process (if oil stains remain, bubbles will occur during subsequent welding/coating).

Process: Soak in alkaline cleaning agent (such as sodium hydroxide solution) + spray, then rinse with pure water and dry with hot air.

The water film on the surface after cleaning should be continuous (without any breaks), and the oil residue should be ≤5mg/m².

Leveling (straightening)

Function: Eliminate the "wave shape" (such as edge waves and middle waves) of the strip after rolling to ensure flatness (usually required to be ≤0.1mm/m);

Equipment: Multi-roll straightening machine (12 to 24 rolls, with more rolls for thin strips), which "smooths out" deformation through the pressure difference between the upper and lower rolls.

Note: For hard stainless steel strips (such as 430 hard), the rolling speed should be reduced to avoid cracking.

2. Finishing process: Enhance dimensional accuracy and surface quality

Make "fine-tuning" on the formed products to ensure they meet the final assembly requirements.

Deburring/chamfering

Reason: Burrs are prone to occur on the edges after shearing and stamping (usually ≤0.05mm, which can scratch the assembly parts).

Process: For thin strips, use "passivation polishing wheels" (flexible grinding), for thick strips, use "abrasive belt grinding", or chemical deburring (corrosion by acidic solutions);

The burr height should be no more than 0.01mm, and the edges should have no sharp corners.

Fixed-length straightening

Function: For sheet materials after cross-cutting, correct minor bends (such as "warping") to ensure flatness;

Equipment: Straightening machine (with suction cup positioning), with an accuracy of ±0.02mm/m.

Cleaning and drying

Function: To remove residual metal shavings and polishing powder during the finishing process;

Process: Ultrasonic cleaning (suitable for complex structures) + hot air drying (temperature 60~80℃, avoiding oxidation).

3. Surface treatment process: Optimize appearance and functionality

Adjust the surface condition according to product requirements, which is divided into "decorative treatment" and "functional treatment" :

Decorative treatment

Brushing (HL) : Use a abrasive belt to sand in one direction to form uniform stripes (common patterns: 120#, 240#, 400#, the larger the number, the finer it is), used for kitchenware and elevator panels.

Mirror polishing: Through rough grinding (grinding wheel) → fine grinding (polishing wheel + polishing paste), the surface roughness Ra is made ≤0.02μm (reflecting like a mirror), and it is used for medical devices and high-end decorative parts.

Colored coating: A colored film layer (such as gold or black) is formed on the surface through vacuum coating (such as PVD), which is both decorative and corrosion-resistant, and is used for mobile phone frames and jewelry.

Functional treatment

Passivation treatment: Immerse the strip in chromate solution to form an oxide film (2 to 5μm thick), enhancing corrosion resistance (for example, the salt spray test of 304 strip after passivation can reach over 500 hours), and it is used for outdoor equipment.

Coating treatment: Apply Teflon (PTFE) or epoxy resin to form a heat-resistant/wear-resistant coating, which is used for non-stick pans and bearing gaskets.

Electrolytic polishing: By electrolytic action, it removes tiny protrusions on the surface, reduces roughness (Ra≤0.1μm), and simultaneously enhances corrosion resistance. It is used for food contact parts (such as straws and tableware).

4. Performance optimization process: Adjust mechanical or chemical properties

For products that require specific strength and elasticity, performance is optimized through heat treatment or mechanical processing:

Annealing treatment

Function: Eliminate work hardening (such as the increase in hardness and decrease in toughness of the strip after stamping), and restore the soft state;

Process: 300 series stainless steel is heated at 1050 to 1100℃ (held for 30 to 60 minutes), followed by rapid cooling (water quenching), and its hardness can be reduced from HV250 to below HV150.

Application: It is used for parts that require secondary bending (such as stainless steel hoses).

Tempering treatment

Function: Enhance elasticity (such as in spring parts), stabilize dimensions;

Process: 400 series stainless steel is heated at 300 to 500℃ (held for 1 to 2 hours), then cooled slowly to maintain the hardness at HV200 to 250 while keeping its elasticity.

Application: Stainless steel spring pieces, clips.

Surface alloying

Function: Enhance surface hardness (such as anti-scratch);

Process: A nitrided layer (5 to 10μm thick) is formed on the surface through nitriding (500 to 550℃), and the hardness can reach above HV800.

Application: Mobile phone keys, precision gears.