Laser Texturing Technology Laser texturing(Laser Beam Texturing, abbreviated asLBT orLT) uses a pulsed laser beam with high energy density (104~106W/cm2) and high repetition frequency (103~104 pulses/second), focused to irradiate the surface of a rotating roll, forming numerous tiny molten pools. Simultaneously, auxiliary gas is blown at a certain angle to shape the molten metal in the pools. When the light pulse stops, the metal in the micro-pit molten pool rapidly cools under the roll's own heat conduction, forming micro-pits and ring-shaped raised edges around the pits, creating phase-strengthened points. Meanwhile, the laser moves axially relative to the roll to complete the roll texturing. By adjusting laser texturing process parameters, such as laser power, pulse frequency, pulse waveform, auxiliary gas type, direction and flow rate, as well as roll rotation speed, the shape and distribution of textured pits on the roll surface can be precisely controlled.
Characteristics of laser texturing:
(1)Texturing parameters are controllable. By using point-by-point texturing, the size and spacing of pits can be controlled, thereby enabling control over parameters such as surface roughnessRa and peak countPc values.
(2)Simple structure. Laser texturing equipment can adopt a "lathe-type" mode where the roll rotates and the optical system translates along the roll axis, making the equipment simple and reliable, with a small footprint and space, and no dust or noise pollution, thereby reducing equipment investment costs. Additionally, depending on user conditions, a laser system can be added to the lathe after the grinder to further reduce equipment investment costs.
(3)High texturing efficiency. In the past, acousto-optic boxes or chopping disks were used to generate laser pulse signals, limiting the laser output power. With technological advancements, the advent of multi-head optical path control systems has multiplied texturing efficiency, making texturing time shorter than that of shot blasting equipment.
4 Application of laser texturing process
Due to the unique nature of laser texturing technology, it has a positive impact on rolls, cold rolling production, and cold-rolled products that cannot be replaced by other texturing methods.
4.1 The laser texturing process can significantly improve the service life of rolls. By analyzing the texturing principle and rolling process, it is easy to understand that the improvement in the service life of laser-textured rolls is mainly achieved through the following three approaches.
(1) Surface modification and fine-grain strengthening effect. During laser texturing, the material in the roll surface action zone undergoes extremely fast melting and solidification (heating rate can reach 10^6 to 10^9 °C/s, cooling rate ≥ 10^5 °C/s, far higher than water quenching), forming ultra-fine grain (deep submicron to nanometer scale) or even amorphous structures. Its hardness can exceed HV900 (HRC67), far higher than what conventional quenching can achieve. The high-hardness surface structure helps improve the wear resistance of the roll surface.
(2) Wear-resistant effect of textured morphology. After laser texturing, the roll surface morphology changes, with micro-pits and bumps uniformly distributed on the roll surface. This surface morphology is beneficial for improving the friction state between the roll and the strip during rolling, as well as maintaining good lubrication conditions. The uniformly distributed micro-pits can also collect wear particles, preventing them from wearing the roll and scratching the strip surface.
(3) Toughening effect of surface stress relaxation. To improve service life, cold work rolls are usually subjected to surface quenching treatment. The higher the required hardness, the more severe the volume expansion effect caused by martensitic transformation, and the greater the residual compressive stress. Excessive compressive stress can easily lead to roll surface bursting, which is harmful to roll usage. Laser texturing of such rolls generates residual tensile stress in the laser-irradiated area of the surface layer due to thermal expansion and contraction during melting and solidification. X-ray stress measurement results show that when the density of laser-irradiated areas (micro-pits) reaches a certain level, this uniformly distributed tensile stress can effectively relax the strong residual compressive stress originally present in the roll surface layer, thereby toughening the roll surface.
The variation of the surface roughness Ra of the steel strip rolled by laser-textured rolls is as follows: in the initial rolling stage (approximately 15% of the rolling volume), the surface roughness decreases rapidly, and then slows down. This is mainly related to the surface morphology of the laser-textured rolls. During the initial use of the laser-textured rolls, the peaks of the raised parts become blunt quickly. After a period of use, the raised parts become relatively blunt, and the wear of the laser-textured rolls correspondingly decreases. The height of the peaks and the shape of the pits can be controlled by changing the texturing process. Therefore, when using laser-textured rolls, the rolling conditions will not change significantly due to excessive variation in roughness values. The service life of laser-textured rolls varies depending on the cold rolling reduction rate, the material of the cold strip, and its hardness. Compared with shot-blasting texturing equipment, the shot-blasting texturing equipment produced by Qingdao Hongxu United Equipment has a strengthening effect, improving the surface hardness of the rolls and extending their service life.