Bending process specification for African rural lighting ready board body (suitable for outdoor, salt spray, long-distance transportation,stress cracking prevention, available for Eskom Africa project

1、 The bending process of the box follows the core principles

Considering the working conditions in rural Africa: outdoor/semi outdoor installation, large temperature difference between day and night, humid salt spray, and long-distance transportation with bumpy roads, the bending of lighting ready boards in rural Africa should not only prevent instantaneous cracking during molding, but also avoid fatigue microcracks and corrosion propagation in the later stage. The following principles should be followed:

1. The principle of stress homogenization (primary) prohibits sharp and dead corners. Continuous rounded corners must be set on the inner side of the bend to eliminate stress concentration points; The tensile strain on the outer side of the bend should be controlled within the allowable range of the material to prevent visible microcracks at the bend angle. Microcracks will rapidly corrode and expand in the humid and hot salt spray environment of Africa, causing perforation and fracture of the box.

2. The principle of matching the direction of rolling fibers is to ensure that the bending curve of the plate is parallel to the rolling texture of the steel plate as much as possible during cutting (bending along the grain); Try to avoid bending curves perpendicular to the rolling direction (horizontal bending), as the risk of cracking in horizontal bending increases by more than twice. If the structure cannot be avoided, it is necessary to increase the bending radius.

3. Unified R angle standardization principle: Try to unify the radius of all bending angles within the same box to reduce mold replacement; The drawing clearly indicates the inner radius (inner rounded corner), and the industry default bending radius refers to the inner radius to avoid processing errors caused by confusion between the inner and outer radii.

4. The principle of structural avoidance is to maintain a sufficient safe distance between the opening, cutting, and welding seams and the bending line: the distance between the center of the hole and the bending line is ≥ 2.5 times the thickness of the plate; It is prohibited to directly open holes or punch notches in the bending area. The sharp corners of notches must be rounded to prevent bending and tearing.

5. The principle of controllable rebound forming is to reasonably match the width of the V-groove of the upper and lower molds (usually using 6T~10T groove), and set the bending angle compensation; Prohibit one-time overpressure forced bending to avoid hidden internal damage caused by excessive stretching of the board fibers.

6. Taking into account both anti-corrosion and strength principles, no peeling, wrinkling, or indentation is allowed at the bending point; The coating on the angled surface is prone to damage, and the better the molding quality, the higher the adhesion of the spray coating, and the delay of salt spray corrosion.

2、 Recommended corner radius for bending of rural lighting ready boards in Africa (cold-rolled steel plate Q235/SPCC, mainstream plate for lighting ready boards in Africa)

T=thickness of the board; R=Bend inner corner radius

Design recommendation value (production stability, consideration of anti cracking and appearance, priority adoption)

Plate thickness 1.0 mm: R ≥ 1.0 mm (1T)

Plate thickness 1.2 mm: R ≥ 1.2 mm (1T)

Plate thickness of 1.5 mm: R ≥ 1.5 mm (1T)

Plate thickness 2.0 mm: R ≥ 2.0 mm (1T)

Extreme minimum value (only for emergency trial production, not recommended for bulk export to Africa)

The minimum shall not be less than 0.8T; it is strictly prohibited for the sharp blade die to be bent when R<0.5T.

⚠️ Key reminder: For products intended for long-term outdoor use in Africa, it is not recommended to use the 0.8T limit value, and R=1T should be prioritized. Extreme radius bending is prone to producing invisible microcracks, which will gradually fail under the long-term effects of transportation vibration and damp heat salt spray.

If galvanized sheet/stainless steel box is used

Galvanized steel plate: minimum R ≥ 1.0T

304 stainless steel: R ≥ 1.2T~1.5T (poorer plasticity, prone to cracking)

3、 Supporting process measures for rural lighting ready boards in Africa to comprehensively prevent stress cracking

1. Raw material control: The surface of the steel plate should be free of scratches, rust, and heavy hardening creases;

2. Cutting: Laser/cutting to remove burrs from the cutting surface, and sharp edges are prone to tearing when bent;

3. Mold: The rounded corners of the upper mold blade are consistent with the design R, and the V-mouth of the lower mold is matched according to the plate thickness. The working surface of the mold is smooth and free of chipping;

4. Bending process: Set the holding time, form slowly, and avoid impact bending;

5. Post processing: Forced tapping and correction are prohibited in the bending area, as tapping may induce microcracks;

6. Drawing annotation specifications: Clearly indicate the inner bending radius R, and the technical requirements state that no cracks, wrinkles, or peeling are allowed during bending.