Why Low MOQ Electro-Galvanized Coil Suits Trial and Short-Run Production
Electro-galvanized (EG) coil is made by depositing zinc onto cold-rolled substrate in an electrolytic cell at close to ambient temperature. Because the zinc is plated rather than dipped, the strip never passes through a molten zinc pot, so the original yield strength, elongation and surface finish of the substrate are retained while the surface gains a uniform, tightly adherent zinc layer. Coating mass is even on both faces, and the line can be run coil by coil, which is what makes low minimum order quantities realistic instead of forcing a buyer into a full pot-sized campaign.
That flexibility matters for trial lots on a new appliance housing, replacement coils for a line that has run short, or a mixed-grade shipment that combines commercial and deep-drawing material in one delivery. Buyers can validate formability, weldability and paint adhesion on production-intent material before committing to volume.
At a glance
Substrate: cold-reduced carbon steel sheet per JIS G3141, grades SPCC, SPCD and SPCE
Coated product: electrolytically zinc coated sheet and strip per JIS G3313, grades SECC, SECD and SECE
Typical zinc coating: 10-50 g/m2 per side, equal on both faces
Thickness 0.12-3.5 mm, width 600-1500 mm, coil inner diameter 508 mm or 610 mm
Grade Mapping: SPCC, SPCD and SPCE to SECC, SECD and SECE
The galvanized grade name is built systematically from the base metal grade plus the letter E for the electrolytic coating, so SPCC becomes SECC, SPCD becomes SECD and SPCE becomes SECE. Choosing the correct line in the table below is the most important decision in a drawing or stamping operation, because formability, not coating mass, decides whether a panel tears at the die radius.
| Base grade (JIS G3141) | Quality | Coated grade (JIS G3313) | Typical use |
|---|---|---|---|
| SPCC | Commercial quality | SECC | Flat and lightly formed parts, enclosures, cable trays |
| SPCD | Drawing quality | SECD | Moderate drawing, appliance side panels, housings |
| SPCE | Deep drawing quality | SECE | Deep drawn parts, oil pans, complex covers |
| SPCF | Drawing quality, improved | SECF | Severe drawing with tight radii |
| SPCG | Extra deep drawing quality | SECG | Very severe forming, multi-stage draws |
Dimensions, Coating Weight and Standard Specifications
| Item | Range |
|---|---|
| Thickness | 0.12-3.5 mm |
| Width | 600-1500 mm as rolled; slit widths from 90 mm |
| Coil inner diameter | 508 mm or 610 mm |
| Coil weight | 3-8 t per coil |
| Zinc coating, per side | 10-50 g/m2; 20/20 and 30/30 g/m2 are the most common pairings |
| Surface treatment | Chromate passivation, oiled or anti-finger print |
| Appearance | Uniform matte grey finish, no visible spangle, which is characteristic of electrolytic plating |
| Standards | JIS G3141 for the substrate, JIS G3313, ASTM A879 / A879M and GB/T 15675 for the coated product |
Coating mass converts to coating thickness at the density of zinc, 7.14 g/cm3, so 20 g/m2 per side equals roughly 2.8 micrometres of zinc and 50 g/m2 equals about 7 micrometres. Uniformity is a strong point of the electrolytic route: because the cell controls current density across the strip, side-to-side and edge-to-centre variation stays small, which keeps spot welds consistent and lets tight-radius forming proceed without coating flaking.
Process Route and Coating Selection by Environment
The full cold galvanizing sequence runs as follows:
Chemical degreasing followed by hot water wash
Water rinse and electrolytic degreasing
Water rinse, then acid pickling and rust removal
Water rinse into the electrogalvanizing cell
Water rinse, passivation and hot water rinse
Drying, quality inspection and packaging
| Service environment | Zinc per side | Typical parts |
|---|---|---|
| Indoor, dry and heated (C1) | 10-15 g/m2 | Electrical enclosures, furniture frames, internal brackets |
| Indoor with occasional condensation (C2) | 20-25 g/m2 | Appliance panels and liners, air-conditioner casings |
| Sheltered outdoor, suburban (C3) | 30-35 g/m2 | Gutters, fencing, light structural trim |
| Urban, industrial or coastal (C4-C5) | 40-50 g/m2 plus paint | Underbody guards, coastal cladding, exhaust shields |
Where the part is painted, the zinc layer acts as a sacrificial primer: it protects exposed cut edges and scratches long after the paint film is breached. Where the part is left bare, coating mass is the primary determinant of time to first white rust, so specification should always follow the corrosivity category of the end location rather than a default coating.
Quality Control and Small-Batch Delivery
Coating mass verified per side by weighing strip samples before and after chemical stripping
Adhesion checked with bend and impact tests after forming
Thickness gauged across the width at head, middle and tail of every coil
Surface inspected for scratches, roll marks and passivation streaks before wrapping
Coils wrapped in moisture-barrier film and protected with inner and outer ring pads for transport
Small lots are normally shipped as single coils with the mill test certificate quoting heat number, grade, coating mass and mechanical properties, so incoming inspection can be completed against the same document the line was released to.
Frequently Asked Questions
Q: What is the difference between SPCC and SECC?
SPCC is the cold-reduced carbon steel sheet grade; SECC is the same steel after continuous electrolytic zinc coating. Mechanical properties come from the substrate, corrosion resistance from the coating.
Q: Is electro-galvanized coil the same as hot-dip galvanized coil?
No. Electro-galvanized zinc is plated in an electrolytic cell and gives a thin, very uniform matte coating of roughly 10-50 g/m2 per side, while hot-dip coating is thicker, commonly 60-275 g/m2, and shows a visible spangle.
Q: What minimum order quantity applies to a low MOQ coil?
Trial quantities can be quoted from a single coil, typically 3-8 t, and grades can be combined within one shipment where width and coating specification allow.
Q: Can SECC be deep drawn?
Only lightly. For drawing operations choose SECD or SECE, whose SPCD and SPCE substrates supply the elongation the die needs.
Q: How should electro-galvanized coil be stored?
Keep it dry, wrapped and clear of the floor, and consume it within the recommended shelf life. Chromate passivation and oiling delay white rust but do not replace dry storage.
Q: Is the coating identical on both faces?
Yes. Electrolytic plating deposits an equal coating mass on each face unless a differential specification is ordered.