###### Abstract  
In a hot rolling process, excessive friction between rollers and steel plates may lead to the formation of scratches on the steel plate. To reduce scratch formation in the finishing mill of the hot rolling process, two techniques are proposed in this work: flying touch and velocity synchronization. The proposed flying touch method can reduce the impact of the generated force when the upper roller collides with the steel plate. In addition, the proposed velocity synchronization method can decrease the frictional force resulting from the velocity difference between the rollers and steel plate. The effectiveness of the proposed methods was demonstrated through simulations and experiments using a \(1/40\) downscaled hot rolling simulator. The simulations and experimental results demonstrate that the proposed methods can reduce the magnitudes of friction and impact forces that lead to scratch formation on the steel plates in the hot rolling process. hot rolling; scratch; flying touch; velocity synchronization; downscaled simulator +
Footnote †: _Applied_  
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Footnote †: thus mitigating the undesirable effects of friction during continuous plastic film printing processes [6]. The study demonstrated that a friction-isolated rotary system can reduce the root-mean-square tracking error by up to 61% compared with the error when using a conventional roll-to-roll system without a frictional isolator. In particular, studies on scratch defects caused by the intense friction between the rollers and steel plates during the rolling process have been conducted [7; 8]. [PERSON] and [PERSON] investigated the control methods for reducing scratch formation during the cold rolling process [7]. They reported that the generation of coil scratches can be reduced by adjusting parameters such as oil film thickness and temperature. [PERSON] studied the scratch resistance of steel during the hot rolling process based on the material properties of the roller [8]. The study confirmed that the microstructure of rollers can also affect scratch formation. The foregoing techniques can aid in diminishing the generation of scratches during hot rolling. However, to achieve better scratch formation reduction, it is necessary to develop designs involving mechanical and control methods that are capable of directly reducing the impact force. In this study, the flying touch and velocity synchronization methods are proposed to achieve the following goals during the hot rolling process. * Flying touch method  
In the general hot rolling system, the steel plate passes between the fixed upper and lower rollers to process the plate into coils. In the proposed flying touch hot rolling method, the upper roller only lightly touches the steel plate upon contact, thus reducing the generated impact force. Accordingly, the roller design must enable the upper roller to move up and down. * Velocity synchronization method  
When the steel plate passes through the gap between the upper and lower rollers, plate scratching can occur because of the frictional force caused by the velocity difference between the rollers and steel plate. In the finishing mill, if the velocity of the steel plate is synchronized with the rotational velocity of the roller, then the frictional force during processing is diminished; consequently, reducing the probability of generating scratches. The proposed velocity synchronization and flying touch methods for reducing the impact of friction between the rollers and steel plate during the hot rolling process are introduced in Section 2. To evaluate these two methods experimentally, the hot rolling system should be designed such that the upper rolling roller is moved vertically while the upper and lower rolling rollers are rotated. This proposed hot rolling system is built as a 1/40 downscaled model of an actual system operating in the Pohang Iron and Steel Company (POSCO, Pohang-si, Korea).