1.What is the core mechanism by which dust causes mold sticking?
Acting as an abrasive, directly damaging the surface:
Scratching the sheet metal: Hard dust particles (such as iron oxide powder and silicate particles) are pressed into the relatively soft steel sheet surface under high pressure, causing continuous, directional scratches, affecting the product's appearance and subsequent coating.
Damaging the mold: These particles can scratch fine grooves on the working surfaces of molds (especially dies, blank holders, etc.). Once the mold's smoothness is damaged, its surface becomes rough, making it easier to trap metal particles, providing "anchor points" for mold sticking.
Disrupting the lubricating film, causing localized high-temperature melting:
Isolation effect: Dust particles act like a "sand blanket" between the sheet metal and the mold, preventing stamping oil or lubricant from forming a complete and uniform lubricating film.
Absorbing lubricant: Some fine dust particles can absorb oil, causing localized areas to experience dry friction or boundary friction.
Vicious cycle: In areas of lubrication failure, friction increases sharply, generating localized instantaneous high temperatures. When the temperature reaches a certain level, the microscopic protrusions on the sheet metal surface will undergo "cold welding" (microscopic welding) with the mold surface, forming an initial adhesion point. This point will snowball, continuously adhering to more material, eventually forming a visible "tumor-like" adhesion. This tumor will then scratch all subsequent stamping parts.
2.What are the main sources of dust?
Rolling process residue: Extremely fine iron powder may be generated during the final rolling processes of cold-rolled coils.
Rust-preventive oil/oil contamination: If rust-preventive oil is not clean enough or is improperly stored, it may become contaminated with environmental particulate matter.
Storage and transportation contamination: When exposed to the factory environment, it can absorb dust, fiber debris, etc. from the air.
Secondary contamination within the workshop: Poor cleanliness of the workshop environment during uncoiling, leveling, and feeding processes can cause contamination.
3.What are some quick on-site assessment methods?
Observe the characteristics of sticking/scratching: Defects caused by dust are usually random and discontinuous. The scratches are in the same direction as the feed direction and may appear in any area of the sheet material.
Inspect the raw materials: Use a clean white cloth or tape (adhesive side down) to firmly wipe the surface of unused rolls of material and check for obvious black or gray stains.
Comparative experiment: For a batch of problematic material, perform a thorough local cleaning (e.g., wiping with solvent) before stamping. If the defects disappear or are significantly reduced, dust can be identified as the main cause.
4.How can we control it at the source?
Specify clear surface cleanliness requirements to suppliers (refer to industry standards).
For high-requirement products (such as outer coverings), add a pre-treatment cleaning process using a degreasing cleaning machine (including brushing, spraying, rinsing, and drying).
5.How to control the process?
Improve the workshop environment, especially in material storage areas and feeding line areas, and control dust.
After uncoiling and before entering the mold, install online cleaning devices such as:
- Adhesive rollers/felt rollers: Physically remove dust.
- High-pressure air blowing: Used in conjunction with a dust collection device.
- Electrostatic precipitator: Even better results.
Use high-quality, clean, specialized stamping lubricating oil and ensure even application.