How to improve the efficiency of HSS roll processing?

With the development of CNC machining technology, CNC roll lathes have gradually become popular and used in roll manufacturers and steel mills due to their high processing accuracy, stable quality, and strong processing capabilities. However, due to factors such as CNC programming technology, tool material, and worker operating level, the processing efficiency of profile steel roll passes is relatively low. It is understood that the processing efficiency of rolls with the same specifications in various types of steel mills is relatively high. The difference is more than 30%.


HSS rolls processing


1. High-speed steel roll


High-carbon high-speed steel composite rolls (referred to as HSS rolls) are the fastest-growing hot-roller materials with the broadest application prospects in recent years. Its composition is relatively complex alloy steel. After quenching in the heat treatment process, it will remain hardened even if cooled in the air. The working layer material is high-carbon steel, and the core material of the roll is ductile iron, graphite steel or forged steel. The two different materials are compounded by centrifugal casting or CPC process. The matrix structure is generally tempered martensite. + Bainite + carbide, carbide is distributed in the matrix in a highly dispersed form, so it has high wear resistance and strong toughness, making turning difficult.

High-speed steel rolls are characterized by good thermal stability, good hardenability, high carbide hardness, easy-to-form oxide films, good thermal crack resistance and wear resistance, and the requirements for cooling water are far lower than those of cemented carbide. Its single groove rolling capacity can reach 4-5 times that of cast iron rolls. It is beneficial to the negative tolerance control of rolled materials and improves the surface quality of rolled materials. HSS roll is a new material roll developed mainly for use in online bar finished products and finished product front racks, as well as slit rolling pre-cutting and slitting pass shapes. The hardness can reach HSD78~90, has high wear resistance, and also has good impact resistance and thermal fatigue resistance.

With the popularity of high-speed steel roll, online bar rolling mills, R&D and manufacturing manufacturers have spread rapidly. However, the alloy elements added by each manufacturer during the casting process of high-speed steel rolls are different. Therefore, in terms of processing and use, cutting is difficult and easy. The degree and online use effect are not completely consistent. Overall, it mainly contains carbide-forming elements such as tungsten, molybdenum, chromium, vanadium, and niobium.


2. Roller performance requirements


As mentioned in the above content, the selection of different materials has different use values for the rolls. In addition, in the actual production and use process, we also have some special requirements for the performance of the rolls:


(1) Hardness


Cast iron rolls have relatively high requirements for hardness. Cold rolls have the highest hardness requirements among the materials I know, with the highest hardness reaching 105HS. The hardness is relatively easy to measure, in actual use, because the roll is very easy to wear, and the wear mechanism is very troublesome and complicated, but wear is an indicator to evaluate the wear resistance of the roll, so the hardness is used to measure it, and materials with lower hardness will have weaker wear resistance. Therefore, the hardness can generally be used to reflect the wear resistance of the roll.


(2) Impact resistance


Because the main use of the roll must be taken into consideration, the impact resistance of the roll needs to be considered during the process of processing the roll. When it accepts objects with relatively high pressure, it will not be damaged by external substances and can be guaranteed at all times during use. Its own sturdiness can avoid unnecessary dangerous situations and potential threats to the safety of people and property.


(3) Smoothness


As an important part of the steel rolling machine, the roller also has certain requirements for the smoothness of the surface of the roller when making products with relatively thin specifications. If there are impurities or unevenness on the surface of the roller, it will also have a certain negative impact during the use process on the machine, so we also need to consider this during the actual processing process to ensure the good performance and usability of the roll.


3. Design of CNC machine tool holder support system


The company’s steel products have large specifications, deep roll grooves, long protrusion length of the toolbar during processing (100-150mm), and insufficient tool rigidity. Only a small cutting amount can be selected during processing, which seriously affects the processing efficiency and product processing. Quality cannot be guaranteed either.

In order to improve this situation, the toolbar support tooling is designed: a support plate is welded with bolts in front of the tool holder. The support plate is designed with guide keys. The screw rod adjusts the front and rear support positions through the guide keys and adjusts the support height through the spiral support. In this way, the front and rear support positions and heights can be adjusted according to actual production needs, effectively preventing the front end of the tool from hanging in the air and enhancing the tool’s rigidity. The effect of this tooling is good after use. The cutting depth on one side is increased from 2mm to 5mm. At the same time, vibration marks on the hole surface are reduced, which effectively ensures product quality and improves processing efficiency.

4. High hardness roll processing method


(1) After inspection before processing, the rolls must be assembled and calibrated. After the rolls are clamped on the lathe and calibrated, the initial requirements should be met. The specific requirements need to be formulated according to the specific situation.

(2) Carry out rough turning of the outer circle

When rough turning the outer circle, it should be considered that the machining direction of the outer circle and the chamfering position are exactly opposite, so the chamfering is not easy to be too large during processing. When the outer circle reaches the size requirements, the chamfering should also be done at this time. can be processed well; in addition, we must also pay attention to the cutting parameters when machining the outer circle. Different tool materials have different suitable parameters, but the cutting parameters cannot be too fast, otherwise, the turning tool will not be able to bear it and will affect the surface quality of processing.

(3) Carry out rough turning hole processing

Mark the line according to the required size, and then turn. Check at any time during turning. It is best to use manual feed because the roller is relatively hard. Manual feed is easier to control and has less deviation and alignment effects on rolling steel.

(4) Fine turning outer circle

The difference between the fine-tuning of the outer circle and the rough turning of the outer circle is that the cutting amount of the fine-tuning of the outer circle is relatively small, but the required accuracy is better. You need to be careful during the operation. Before turning, you should pay attention to the entire roll. Measure to ensure the original requirements are met after turning.

(5) Precision turning hole pattern

At the stage of finishing the hole pattern, the cutting speed needs to be slowed down. The speed needs to be adjusted to the slowest speed. Manual cutting must still be used and grinding bit by bit until the requirements are finally met. Pursuing speed too much is not appropriate, and you should also be careful when operating.

High-speed steel rolls have high hardness and wear resistance. Under the same rolling conditions, compared with chilled cast iron rolls and high-nickel-chromium composite cast iron rolls, the wear amount is smaller, the single-groove rolling volume is doubled, and the surface quality of steel can be greatly improved. It can effectively control negative dimensional accuracy and the advantages of online bar units are becoming increasingly prominent.

However, the tool material for processing high-speed steel rolls is a major bottleneck restricting its development. With the continuous upgrading of CBN tool materials, through reasonable processing technology, and when the rigidity of the machine tool meets the processing conditions, the processing difficulty will gradually decrease, and the processing efficiency will be improved. With further improvement, the cooling method of high-speed steel rolls will also be improved.

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