In the aerospace, chemical, medical, and high-end equipment manufacturing sectors, cold-rolled pure titanium sheets and strips have become an indispensable core substrate due to their exceptional properties, including light weight, high strength, and corrosion resistance. However, in the actual production of thin-gauge titanium strips, the persistent quality defect known as "ribbing" has long plagued major manufacturers. This issue not only compromises product quality but also leads to waste of raw materials and loss of production capacity, making it a technical bottleneck that the industry urgently needs to overcome.
What is ribbing in titanium strip? After cold-rolled titanium sheets and strips are coiled, localized circumferential bulges appear on the surface of the coil; this phenomenon is referred to as "ribbing" in the industry.
For pure titanium strips, ribbing is highly specific to certain specifications. It mostly occurs in thin-gauge products with a thickness of less than 0.8 mm, primarily manifesting as single raised ribs that are clearly visible to the naked eye and difficult to eliminate naturally during subsequent processing.
The Multiple Hazards of Ribbing Defects Ribbing is by no means a simple surface flaw; rather, it is a production hazard with far-reaching consequences:
1. Compromises sheet flatness and surface quality: It causes additional waviness in the strip, resulting in composite defects where bulges and waviness intertwine, directly leading to product downgrading;
2. Increases production waste: In severe cases, defects require shearing and rewinding, resulting in significant waste of titanium raw materials;
3. Reduces production efficiency: Rework and the sorting of defective products consume production line hours and disrupt production rhythms;
4. Harms corporate profitability: Rising defect rates and declining yield rates directly squeeze profit margins and damage the company's reputation for supply reliability in high-end markets.
An In-Depth Analysis of the Two Key Causes of Rib Formation
1. The quality of hot-rolled raw material is a critical factor. Extensive rolling tests have confirmed that hot-rolled coils of the same specifications but from different batches exhibit significant differences in the probability and extent of rib formation after cold rolling; the quality of the incoming hot-rolled material directly determines the risk of rib formation during cold rolling.
Hot-rolled raw materials commonly exhibit defects such as scratches, sickle bends, cracks, and local high spots, with local high spots having the most pronounced impact. Even if the area of a high spot is extremely small, for ultra-thin titanium strips below 0.8 mm, it is sufficient to induce localized bulging and ribbing, leading to more complex sheet shape defects.
2. The cold-rolling process is the dominant factor. Currently, the industry predominantly uses six-high, ten-high, and twenty-high multi-high rolling mills to produce titanium strip and sheet. Even advanced Japanese twenty-high rolling mills can achieve efficient rolling of 0.3–3 mm titanium strip with excellent dimensional accuracy and surface quality; it remains difficult to avoid ribbing and waviness issues when producing heavy-coil, wide-width thin strips.
Under fixed width-to-thickness ratio production conditions, defects can be precisely controlled through simple process adjustments without the need for major equipment modifications: 1. Optimize tension parameters: Appropriately reduce pre-tension to prevent buckling instability caused by excessive axial force; 2. Upgrade process lubrication: Replace rolling lubricants with those suitable for pure titanium, optimize lubrication uniformity, and improve stress distribution; 3. Increase winding friction: Place backing paper at the winding end to raise the coefficient of friction and suppress localized slippage and bulging of the strip; 4. Strictly control incoming hot-rolled material: Screen and reject hot-rolled coils with localized high spots, cracks, or sickle-shaped bends in advance to reduce the risk of ridge formation at the source; 5. Customize flatness control curves: Discard stainless steel rolling parameters and establish dedicated flatness control curves tailored specifically for pure titanium strip.
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