How to reduce rolling costs in the steel rolling industry?

The roll is the main component of the rolling mill and the most important consumable spare part in the steel rolling production process. It is not only related to the rolling cost and rolling mill operation rate but also directly affects the dimensional accuracy and surface quality of the rolled material.

How can we effectively reduce rolling costs and get out of the predicament? This is the common expectation of the current steel rolling industry!

 

In today’s fierce competition in the steel market and the sluggish steel industry, whoever can reduce production costs will control the space for survival. Although low-priced inferior rolls will reduce the purchase cost, due to the impact on the operating rate of the rolling mill, the rolling cost per ton of steel rolled products will not only not be reduced, but will be greatly increased. When other fixed costs cannot be changed, only by improving the operating rate of the rolling mill and increasing the production volume will the rolling costs be significantly reduced; only by ensuring the stability of the negative rate can the output of rolled products be directly increased and the efficiency of the enterprise improved. The use of high-quality high-speed steel rolls is exactly the way to reduce the rolling cost. The most effective measure to reduce costs and increase rolled product output.

 

high-speed steel rolls in strip mills

 

1. Selection of wire rod mill rolls

 

With the rapid development of modern rolling mill equipment, such as the completion and commissioning of Morgan and Danieli wire and bar continuous rolling production lines, the selection of rolls has undergone great changes compared with the traditional ones. Since the entire rolling mill uses full short stress For continuous rolling of alternating linear and vertical lines and non-twisted passes, except for the roughing stand rolls, the strength of the rolls is not the main performance index to be evaluated. The wear resistance and toughness of the rolls should be fully considered, as well as the impact on the rolling mill operation rate. and improvement of surface quality of rolled products.

1) Roughing stand rolls of bar and wire rod mills

First of all, due to the high rolling pressure, deep roll grooves, and high cutting force caused by large reduction, the roll must have high strength and continuous rolling; on the other hand, due to the slow rolling speed of the stand and the hot roll It takes a long time, so it is necessary to ensure that the roll has good thermal crack resistance and spalling resistance; at the same time, the roll must also have good wear resistance, impact resistance and bite resistance.

It’s clear that some of these properties are contradictory. Steel rollers have better bite properties and higher strength than ductile iron rollers, but their wear resistance and heat crack resistance are not as good as ductile iron rollers. Some manufacturers use semi-steel rolls for rough rolling stands. Although they can meet the requirements of the rolling mill in terms of strength and wear resistance, the thermal cracks of the rolls are very serious. Therefore, it is ideal to use pearlite ductile iron roll I with a hardness of 45-50HSD for the first stand of the roughing rolling mill, which contains ferrite in the matrix structure and a hardness of 45-50HSD, and for other stands.

2) Intermediate rolling mill frame rolls

On the one hand, the rolls of the intermediate rolling mill stand have deeper pass shapes and greater rolling pressure, so the strength of the rolls cannot be ignored; on the other hand, due to the large pass size of the rolls, the cooling of the groove bottom cannot be fully carried out, so, the roll’s thermal crack resistance and impact toughness must be sufficient. At the same time, the wear resistance of the rolls of this stand puts forward higher requirements than the rough rolling stand. In particular, the hardness of the bottom of the groove should be similar to the hardness of the top of the groove. Therefore, the matrix structure of the intermediate rolling stand should be pearlite. The roller surface hardness is 60-68HSD. Pearlite ductile iron roller II or III is ideal and very economical. Moreover, the roller surface wear and hot cracks are less after use. Although acicular bainite ductile iron is wear-resistant It has good thermal crack resistance, but its thermal crack resistance is slightly worse than that of pearlitic ductile iron. At the same time, the price of real “acicular bainite ductile iron” material is higher, making it uneconomical to use in this frame.

3) High-speed wire rod mill finishing rolling unit roll ring

The roll rings of the finishing rolling unit of high-speed wire rod rolling mills all use tungsten carbide roll rings without exception. There is currently no substitute product. Pre-finishing rolling can either use tungsten carbide roll rings or high-speed Steel roller rings or roller, the latter has relatively low wear resistance but has good crack resistance, low price and high cost performance.

4) Finishing stand rolls of bar rolling mill

The rolls of the finishing rolling stand of the bar rolling mill must not only ensure the normal operating rate of the rolling mill, reduce the number of roll changes, and increase the output of rolled materials, but also ensure the surface quality of the rolled materials, that is, more steel can be produced and good steel can be produced. Therefore, the wear resistance of the roll’s performance is the most critical performance indicator. At the same time, due to the rolling of the rebar, the toughness and spalling resistance of the roll are still crucial. Therefore, most of the frames used use bainitic ductile iron with a matrix structure of bainite and a roll surface hardness of 70-78HSD. Roller.

However, with the development of rolling technology and the increasing requirements for rolling mill operation rates, bainitic ductile iron rolls can no longer meet the requirements of rolling mills. Nowadays, K1, K2, K4, and even K5 of the finishing rolling stands all use high-speed steel rolls with a matrix structure of tempered martensite and a roll surface hardness of 80-90HSD. The K3 stand with split rolling uses high-toughness high-speed steel rolls with a surface hardness of 70-80HSD, which is the most popular. Welcome, not only the roll wear resistance is good, and the rolling mill operation rate is high, but also the surface quality of the rolled material is good, and the product market competitiveness is strong, especially since it is conducive to the control of product negative stability.

 

2. Development of roll materials for modern rolling mills

 

The development of modern rolling processes and rolling technology has had a huge impact on the design of rolling mills and the selection of rolls. On the one hand, advanced low-cost continuous casting machines are widely used to reduce or eliminate expensive rolling mill equipment; on the other hand, rolling mill production efficiency is maximized.

Therefore, new generation roll materials such as high-speed steel rolls, tungsten carbide carbide composite rolls, steel-based tungsten carbide composite rolls, and high boron steel rolls are increasingly used in modern continuous rolling mills. The application of the new generation of roll materials in bar and wire rod mills not only breaks the traditional roll production pattern but also significantly improves the operating rate of the rolling mill.

 

Choosing high-quality high-speed steel rolls is the most effective measure to reduce rolling costs.

 

1. High-speed steel rolls are known as the most cost-effective rolls at this stage

 

In recent years, high-speed steel rolls have been widely loved by the steel rolling industry for their good wear resistance and high product dimensional accuracy and stability in more than 100 sets of bar rolling mills at home and abroad, breaking the gap in roll varieties that has been maintained for decades. pattern. Through the improvement of roll varieties and quality, it is ensured that the rolling mill operation rate is improved; it is ensured that the rolling process is continuously improved and improved.

Because high-speed steel has high wear resistance and hardenability, especially red hardness at high temperatures, high-speed steel is more suitable for use as a manufacturing material for rolls. When high-speed steel rollers are used in bar rolling mills, not only the rolling volume per single groove can be increased by 3-5 times compared with needle-structured ductile iron rollers, but the wear of the rollers is small, and the service life is doubled, but also the high-speed steel rollers per ton price are only one-quarter of the price of tungsten carbide combined rolls, so it is cost-effective.

 

2. Professional serial production of high-speed steel rolls

 

In order to continuously improve the product quality of high-speed steel rolls, and make the product varieties and application fields more serialized, the roll production and delivery cycle time is reasonable, and the technical guidance during the use of the product on the machine is more appropriate. Depending on the characteristics of the rolling line and the user’s requirements, professional serial production of high-speed steel rolls can be used.

Produces high-speed steel rolls for rebar rolling, high-toughness high-speed steel rolls for rebar rolling slitting racks, high-speed steel rolls for round steel rolling, high-speed steel rolls for strip rolling, High-speed steel rolls for spring flat steel rolling, high-speed steel rolls for pre-finishing stands of high-speed wire rod mills, and semi-high-speed steel rolls, etc.

Integrating the development and production of rolls, we have successfully developed high-toughness high-speed steel rolls (YLS alloy rolls) for the K3 frame of split rolling. Its use effect is more than 4-5 times that of bainite rolls.

Firstly, the high-speed steel rolls should be serialized according to the characteristics of the rolling material and the use characteristics of the rolling mill; secondly, the composition of the high-speed steel rolls should be optimized to avoid the problem of component segregation in centrifugal production. At the same time, the heat treatment process of the high-speed steel rolls should be improved to enhance the hardness of the rolls. Evenness. For example, for the high-speed steel rolls produced in our factory, through the optimization of components and the improvement of the heat treatment process, the surface hardness uniformity of the roll body is not greater than 2HSD, and the cutting performance of the roll is significantly improved; the hardness difference of the working layer is not greater than 1HSD, and the stability of the use of the roll is Greatly increased, the comprehensive service life of the roll can be increased by about 20% compared with previous similar products, but the sales price of the roll does not increase, and it is deeply loved by the majority of users.

 

3. Only high-quality high-speed steel rolls can reduce rolling costs

Once any product is widely recognized by society, it is often accompanied by the phenomenon of fakes passing off as genuine and bad as good, and rollers are no exception. Nowadays, most steel rolling companies that make good use of high-speed steel rolls can be said to be uncomfortable without high-speed steel rolls. However, there are also steel rolling companies that shake their heads when talking about high-speed steel rolls. Because these companies once used high-speed steel rolls produced by a certain roll company, the rolling volume was not as good as ordinary cast iron rolls, so they no longer want to use them; some roll companies even use improved infinitely chilled rolls to pass off as semi-high-speed steel rolls to users; Some roll companies even seize the market at very low prices when users purchase them. However, the products they provide to users have insufficient total alloy additions, so the rolls have low performance indicators and poor wear resistance, and cannot be used on multiple rolling lines. Failure to achieve the ideal indicators agreed upon by both parties not only caused certain economic losses to both supply and demand parties but also directly affected the expectations of roll users for a high-speed steel roll.

For steel rolling mills, under the current market conditions, the best way out of the predicament is: on the one hand, to reduce production costs and increase corporate benefits; on the other hand, to maximize the surface quality of rolled products and enhance the market competitiveness for rolled products. High-quality high-speed steel rollers have the characteristics of high hardness, good wear resistance, and stable overall performance of the rollers. Not only can the surface quality of the rolled material be significantly improved, which enhances the market competitiveness of the product, but also the rolls have a long service life, fewer roll changes, high rolling mill operation rate and daily output. Usually, the daily output can be increased by more than 10%, that is to say For 12mm rebar during rolling, each set of rolling lines can increase the output by more than 400 tons per day. Therefore, it reduces the ton cost of rolled materials, the consumption of rolls and the waste of resources, especially the dimensional accuracy and stability of rolled materials. The improvement benefit is greater. Under normal circumstances, the control rate of negative difference stability can be increased by 2% than before, which directly and effectively increases the benefits of the enterprise. Therefore, using high-quality high-speed steel rolls is the most effective measure to reduce rolling costs and increase corporate benefits.

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