1.What is the paper sleeve in the middle of a cold-rolled coil? What is its most basic function?
The paper sleeve in the middle of a cold-rolled coil, officially called a high-strength multi-layer paper tube or fiber sleeve, is a cylindrical support inserted into the inner ring (core) of the steel coil.
Its most basic function is to support and protect the inner diameter of the steel coil. Cold-rolled coils typically weigh tens to over twenty tons. Without this sleeve support, the inner ring of the steel coil would collapse, deform, or slip between layers under its own enormous weight. The sleeve acts like a "skeleton," maintaining the shape and size of the inner hole of the steel coil.
2.How do paper sleeves protect steel coils during transportation and hoisting?
Preventing Indentations/Markings: When steel strips or chains are used for securing and hoisting steel coils through their inner bore, the immense securing force concentrates at a single point on the inner coil. The thickness and rigidity of the paper sleeve evenly distribute this concentrated force across the entire inner coil surface, preventing the steel strip from creating deep "V"-shaped indentations at the inner edge of the coil. Such indentations would render the steel strip unusable in that area.
Impact Resistance: During transport, when bumps or shaking occur, the paper sleeve absorbs some of the impact energy, preventing the inner coils of the steel coil from colliding and causing curling or wrinkling.
3.How do paper sleeves help downstream users with unwinding?
Ensuring Uncoiling Accuracy: Modern stamping and slitting lines typically use expansion-shrink uncoilers. When the cone or expansion shaft is inserted into the inner hole of the steel coil and tightens, the smooth and even inner wall of the paper sleeve ensures perfect alignment between the cone and the coil. If the inner hole is deformed, the steel coil will swing violently during uncoiling, causing strip misalignment, strip breakage, and even equipment damage.
Protecting Equipment: The paper sleeve acts as insulation and cushioning, preventing hard friction caused by direct contact between the inner coil of the steel coil and the metal drum. This protects the uncoiler cone and prevents the generation of iron filings and rust that contaminate the production line.
4.Does the paper sleeve itself affect the quality of the cold-rolled coil? For example, does it cause rust?
Rust Risk: Ordinary paper contains moisture when damp. If the paper sleeve has excessive moisture content, it will adhere tightly to the inner ring of the steel coil, creating a sealed, humid environment that leads to severe corrosion of the inner ring. Therefore, paper sleeves used for cold-rolled coils must be moisture-proofed, and their moisture content must meet strict standards.
Surface Indentation: If hard particulate impurities adhere to the surface of the paper sleeve, or if the paper tube itself is not rigid enough and is flattened, these defects will be imprinted on the surface of the innermost coils of steel under the enormous winding tension of the steel coil, causing paper tube imprint defects and resulting in downgrading or scrapping of this portion of the product.
5.Why choose paper as the material for the sleeve? What are its advantages?
High cost-effectiveness and sufficient strength: Through multi-layer composite construction, its radial compressive strength is extremely high, sufficient to support steel coils weighing tens of tons, while its cost is far lower than that of steel sleeves.
Lightweight and easy to handle: Compared to steel sleeves, paper sleeves are very light, making them easy for on-site workers to handle and install. After use, they can be recycled as waste paper, aligning with environmental protection and the circular economy concept.
Customizable cushioning: Paper sleeves have a certain degree of elasticity, providing slight elastic deformation during bundling, which better absorbs vibrations, while pure steel sleeves transmit vibrations entirely to the steel coil itself.