1.What are the core indicators of oil coating uniformity for cold-rolled coils? What oil coating method is typically used?
The purpose of oiling cold-rolled coils is to form a uniform and continuous anti-rust oil film on the surface of the strip steel to prevent rust during storage and transportation, without affecting subsequent processing (such as stamping, welding, and painting).
Key Indicators:
Oil Film Thickness Uniformity: The deviation of the oil film thickness along the width of the entire strip is typically required to be controlled within ±0.2 g/m² (or ±0.2 mg/square foot).
Target Oil Film Range: Ordinary anti-rust oiling typically uses 0.5 ~ 2.0 g/m²; if subsequent stamping is required, it may be reduced to 0.3 ~ 0.8 g/m² to avoid slippage or oil accumulation during stamping.
Mainstream Oiling Methods: Currently, electrostatic oilers are commonly used in continuous cold-rolling production lines. The principle is that the oil is atomized into charged microparticles through a high voltage (usually 40~80 kV), which are then uniformly adsorbed onto the grounded strip steel surface under the action of an electrostatic field. This method achieves high uniformity, low oil volume, and non-contact oiling, making it the preferred equipment for ensuring uniformity.
2.What are the key process parameters that affect the uniformity of oil coating? How can they be controlled?
The oiling voltage determines the degree of oil atomization and electrostatic adsorption. Too low a voltage results in large oil droplets and poor adhesion; too high a voltage results in a fine oil mist that is easily dispersed. It is generally controlled between 40 and 80 kV, and adjusted according to the type of oil and the width of the strip.
Oil temperature: Affects oil viscosity and atomization effect. Too low an oil temperature leads to excessively high viscosity and uneven atomization; too high an oil temperature leads to oil aging and increased volatility. It is usually controlled at 30~50℃ and equipped with a constant temperature heating system.
Oil application amount setting: directly determines the oil film thickness, and achieves closed-loop control by adjusting the oil pump flow or injection pressure, and is linked to the production line speed - automatically adjusts the oil application amount when the speed changes, and keeps the oil amount per unit area constant.
3.What quality problems can result from poor oil coating evenness?
Thin oil film or localized missed areas:
Rust risk: Missed areas are highly susceptible to rust during storage and transportation, forming "yellow spots" or "pitting," leading to product failure.
Abnormal stamping: Uncoated areas may develop scratches or roughening during stamping.
Excessive oil film thickness or localized accumulation:
Oil spot contamination: When the oil volume is too large, the oil is squeezed out after winding, forming "oil spots," affecting the appearance and adhesion of subsequent coatings.
Stamping slippage: An excessively thick oil film can cause material slippage and inaccurate positioning during stamping, affecting processing accuracy.
Poor welding: Excessive oil at welding points can cause defects such as porosity and spatter.
Uneven lateral distribution (thicker in the middle/thinner at the edges or vice versa):
Edge corrosion: Insufficient oil film at the edges will cause the strip edges to rust first, affecting the yield.
Coil edge collapse: Abnormal oil content at the edges may affect interlayer friction during coiling, leading to poor coil shape.
4.How to test and verify the uniformity of oil application?
Online oil film thickness gauge: Installed after the oiling machine, it uses infrared absorption or X-ray fluorescence principles to measure the oil film distribution in the width and length directions of the strip in real time. Data is displayed and recorded in real time, and an automatic alarm is triggered when limits are exceeded.
Key indicators: Monitors the average, maximum, minimum, and standard deviation to ensure that the overall strip width deviation is within the control range.
5.What are the differences in the control strategies for coating uniformity for different product types?
For applications requiring long rust prevention periods (e.g., export by sea): the oil film thickness needs to be appropriately increased to 1.5~2.5 g/m², while strengthening edge coverage inspection.
For no-clean stamping: the oil film must simultaneously meet the requirements for rust prevention and stamping lubrication, with the highest uniformity requirement; deviations are typically controlled within ±0.1 g/m².