In terms of maintenance and management of high-speed steel rolls, the following three issues should be paid attention to
1. Correctly determine the number of uses
The number of times a high-speed steel roll is used between two grindings depends on the maintenance of the oxide film and roughness on the roll surface after each removal. Under normal circumstances, the front rack can be used 3 to 7 times, the rear rack can be used 2 to 4 times, and the CPC high-speed steel roller can even be used more than 10 times.
2. Use roll surface flaw detection to avoid roll failure accidents
High-speed steel rolls must be water-cooled or air-cooled immediately after being removed from the machine to ensure that thermal expansion is eliminated before the next use. High-speed steel rolls are prone to thermal cracks. If rolling stops abnormally, the high-speed steel rolls must be replaced immediately. In order to avoid failure accidents such as roll peeling, ultrasonic flaw detectors should be used to detect roll surface cracks after the rolls are cooled.
3. Use professional tools to enhance the grinding effect
Due to the high hardness of high-speed steel rollers, grinding is difficult, so special grinding wheels and automatic grinders must be used. After the grinding is completed, the eddy current flaw detector and ultrasonic flaw detector are used to conduct composite flaw detection on the roll surface. High-speed steel rolls that are normally removed from the machine may have slight thermal cracks left after grinding and are put into use on the machine. The high-speed steel rolls that were taken off the machine due to rolling accidents must be ground to remove cracks on the roll surface and a certain amount of grinding must be added.
Problems that often occur in the use of high-speed steel rolls can be summarized into the following three major symptoms:
1. The surface of the roll is prone to defects such as oxidation, cracks, and peeling.
Rolls with different chemical compositions and metallographic structures should be selected for different rolling mill runs and rolling environments. The cooling conditions of high-speed steel rolls are stronger than those of high-chromium cast iron rolls. The amount of cooling water should be as sufficient as possible. It is advisable to use a flat nozzle instead of the original conical nozzle and use 3/4 of the cooling water for cooling the tappet side of the roll to control the surface temperature of the roll below 50°C.
In addition, the amount of cooling water in the middle of the roll body should be multiplied by the amount of cooling water in the middle of the roll body. Otherwise, not only will the roll cracks be easily caused, but also the “three-point difference” or “ribboning” phenomenon of the strip will easily occur when the amount of steel passing is not too much. Some steel rolling manufacturers even need to increase the cooling water by 40% to 60%. Therefore, steel rolling manufacturers should consider the amount of cooling water before using high-speed steel rolls.
2. The friction coefficient between the roller and the rolled material increases.
The friction coefficient between the high-speed steel roller and the rolled material is large, the rolling load increases, and slipping is prone to occur. This can be reduced by appropriately controlling the reduction of each stand, using oil lubrication, strip surface cooling, and reducing the billet temperature. Small friction coefficient. Lowering the billet temperature may result in a lower strip edge temperature, and the cooling of the strip edge can be controlled by an induction heater. In addition, optimizing the composition of high-speed steel rolls is also an effective means to reduce the friction coefficient.
3. Roller damage due to steel rolling accident
High-speed steel materials have low impact toughness, high brittleness, and weak accident resistance. Therefore, management must be strengthened to ensure normal operation of the rolling mill and reduce damage to the rolls caused by rolling accidents.