1.What are the internal sources in the production process?
Annealing Furnace Pollution:
Furnace Dust: The refractory materials inside the annealing furnace may produce fine particles due to aging or airflow. If the protective atmosphere inside the furnace is impure or the furnace pressure is improperly controlled, these particles may deposit on the strip surface.
Furnace Roller Scaling: Contaminants such as iron oxide scale may accumulate on the surfaces of the furnace rollers. As the strip passes through, these contaminants may be scraped off and adhere to the strip surface.
Zinc Pot Area:
Zinc dross: The iron-zinc reaction in the zinc pot produces bottom dross and floating dross. If the strip vibrates during galvanizing, or if the air knife pressure or angle is unstable, tiny dross particles can be blown up or carried away, attaching to the surface of the unsolidified zinc layer and forming dot-like or granular defects.
Zinc ash: The liquid zinc on the zinc pot surface oxidizes when exposed to air, forming zinc ash. If ash removal is not timely or standardized, zinc ash can also be drawn into the strip.
Air Knife Area:
The air knife uses a high-speed airflow to remove excess zinc from the strip surface. If the compressed air contains oil, water, or solid particles, or if there is buildup on the air knife lip, these contaminants may be sprayed onto the strip surface.
2.Will powder be generated in the production environment?
If the air quality of the factory is poor (such as near roads, construction sites, or other heavy industrial plants), the air will be filled with a large amount of silicate particles, carbon particles, clay minerals, etc. These particles will settle on the surface of the running strip with the air flow, especially in the cooling and coiling areas.
3.What are the external sources?
Dust accumulated on factory ceilings and steel structures can be blown away by traffic, equipment vibration, or air convection.
Dust generated by other factory operations (such as grinding, welding, and handling) can also cause cross-contamination.
4.What are the sources in coiling and subsequent processes?
The "intake" effect during coiling:
This is a significant and common source of dust. When steel strip is coiled, air is drawn in between the layers. If the surrounding air contains dust, this dusty air is "entrained" into the coil. As the coil cools, vibrates, and deforms during storage and transportation, this dust is trapped between the layers and becomes visible during subsequent uncoiling.
Contamination during storage and transportation:
Transportation: During transportation by truck or ship, dust and contaminants can enter from the ends of the coil without proper protection.
Storage: Unclean warehouse environments, dusty floors, or prolonged stacking can all lead to dust accumulation.
5.What are the specific components of dust?
Zinc and zinc oxides: From zinc pots and zinc ash.
Iron oxides: From substrates or furnace rollers before annealing.
Silicon, aluminum, and calcium compounds: Primarily from dirt and sand in the ambient air.
Carbon particles: From incomplete combustion or diesel exhaust.
Salt crystals: If passivation solution remains, chromates and other substances may be detected.