The Structure Of Rolling Mill

The Structure Of Rolling Mill 

A rolling mill has a common construction independent of the specific type of rolling being performed:

· Work rolls

· Backup rolls - are intended to provide rigid support required by the working rolls to prevent bending under the rolling load

· Rolling balance system - to ensure that the upper work and backup rolls are maintained in proper position relative to lower rolls

· Roll changing devices - use of an overhead crane and a unit designed to attach to the neck of the roll to be removed from or inserted into the mill.

· Mill protection devices - to ensure that forces applied to the backup roll chocks are not of such a magnitude to fracture the roll necks or damage the mill housing

· Roll cooling and lubrication systems

· Pinions - gears to divide power between the two spindles, rotating them at the same speed but in different directions

· Gearing - to establish desired rolling speed     

· Drive motors - rolling narrow foil product to thousands of horsepower

· Electrical controls - constant and variable voltages applied to the motors

· Coilers and uncoilers - to unroll and roll up coils of metal

Slabs are the feed material for hot strip mills or plate mills and blooms are rolled to billets in a billet mill or large sections in a structural mill. The output from a strip mill is coiled and, subsequently, used as the feed for a cold rolling mill or used directly by fabricators. Billets, for re-rolling, are subsequently rolled in either a merchant, bar, or rod mill. Merchant or bar mills produce a variety of shaped products such as angles, channels, beams, rounds (long or coiled), and hexagons.

The Usage And Features Of Ladle Refining Furnace

The Usage And Features Of Ladle Refining Furnace

LF refining furnace was successfully developed in 1971 by Japanese technical staff. And the furnace hasn’t had vacuum equipment, so the heating arc processing occurs on the steel surface of the slag in which LF refining furnaces the so-called submerged arc refining.

When adding the synthetic slag, stirring the molten steel with argon is necessary, and the refining occurs under a non-vacuum-reducing atmosphere. Afterward, the LF Furnace was improved, it can refining in the vacuum and heated under the non-vacuum circumstance when the vacuum extraction equipment is installed.

The main use of an LF refining furnace is for primary melting furnace (electric arc furnace, Converter, intermediate frequency furnace) refining of molten steel. It’s crucial metallurgical equipment for producing high-quality carbon steel, alloy structural steel, bearing steel, tool steel, stainless steel, etc, and meets the needs of Continuous Casting and Continuous Ligation.

This kind of LF refining Furnace has functions electric are heating, argon stirring, wire feeding, measuring temperature and sampling, alloying, etc. And in the terms of purchasing the LF refining furnace, the users can make choice by the steel grade and smelting technology.

The Usage And Types Of Straightener

The Usage And Types Of Straightener

The Usage of the Straightener

During the heating, rolling, finishing, and transportation process of the rolling piece, the external force, temperature changes, internal force changes, or some other factors, very easily lead to curve, deform, and some other variations, for solving these problems, we need to use a straightener to eliminate the stress from both inside or outside, then we can get straight final steel, the straightener is essential equipment in a rolling mill workshop, and is widely used for other workshops like cars and ships.

The Types of the Straightener

According to the requirement of the final product specification requirement, the straightener style would be the difference, divided by working theory, and application purpose can be divided as the following:

Press straightener

Parallel straightener

Cross rolls straightener

Stretch straightener

Bending straightener

Reverse straightener

Except for the above straightener, there are still a lot of special straighteners, basically, with the development of technology, the straightener will be promoted very quickly, for different requirements of the application.

The Usage Of Water In Rolling Mill Machines

The Usage Of Water In Rolling Mill Machines

With the development of the steel industry, more attention is paid to the protection of mechanical machines, such as roughing machines, reversible rolling mills, pre-finishing rolling mills, finishing rolling mills, and wire-rod mills. Therefore, most of the water used in the iron and steel industry is used for cooling, protecting equipment, and improving the working conditions of the employees. The Health and safety of the employee require dust control, which is commonly accomplished by sprinkling water on floors and machines.

Water use in all types of hot rolling mills is mainly for scale removal and temperature control. When steel is heated to the high temperature desired for hot rolling, its surface is oxidized and a hard scale is formed. If not removed before rolling, this scale would be rolled into the steel and would cause surface defects.  A common method of scale removal is to spray water under a pressure of as much as 2,000 psi (pounds per square inch) against the steel immediately before it enters the rolls.

Cooling water is sprayed on the rolls during hot rolling to prevent distortion and reduce erosion of the roll surfaces. Because considerable heat is produced by the rolling processes, water also serves to keep the steel at its proper rolling processes. Upon emergence from rolling mills, steel may be sprayed with water to hasten cooling. This spray prevents excessive scale formation. Roll bearings also require cooling. Spent cooling water flows to the scale pit along with that used for scale removal and may be reused after clarification and cooling.

The Use And Maintenance Of Roller

The Use And Maintenance Of Roller

The roller is the biggest wearing part, expensive so for reducing the cost, we should carefully maintain it.

1. Full quality test before entering the workshop

The roller is a high technology, high value-added product, should apply quality tests according to the quality standard, test the roller surface, and end’s hardness, the hardness deviation should be below ±（2-3）HS, apply ultrasonic to test the inside flaws, surface wave for testing surface quality, visual inspection for outside flaws.

2. Regular refacing

We should change the roller regularly for better protection even if the surface is flawless, roller working hours should be 50-100H, and the supportive roller should reface after 2000-3000h, for removing the working layer, the remover layer should be thicker than the working layer.

3. Use the roller in the right way.

Use the roller according to the guidance, should adjust the temperature to 70-80℃ when switching rollers, the cold roller should be at 30-50℃, should cold down in the water, and the roller neck should be lubricated, keep clean, avoid rusting and grinding damage iron sheet, prevent misoperation and accident.

4. Avoid roller break accident

Breaking down of  roller is a destructive accident, there are normally two reasons, one is because of the quality of the roller, normally we can find flows in the breaking point, the other reason is from the outside and causes the roller's power and torque is overweight, we should avoid this circumstance.

The Characteristics Of Horizontal Rolling Mill And Tandem Rolling Mill

The Characteristics Of Horizontal Rolling Mill And Tandem Rolling Mill

The horizontal rolling mill is mainly used for the production of various sections of steel, narrow hot strips, and small billets. The following are the main features of the horizontal rolling mill :

(1) A row of rolling mills is driven by a motor. The rolling speed of each rolling mill is the same, and the rolling speed cannot be increased as the length of the rolling stock increases, so the output is low and the labor productivity is low;

(2) The structure of the rolling mill is generally three-roller or two-roller alternate;

(3) The rolling mill operation mode is mostly shuttle rolling or loop rolling. With flexible deformation and strong adaptability, each rolling mill can roll several times. The product range is wide and the operation is relatively easy;

(4) The rolling mill equipment is simple, with less investment and quick construction.

The tandem rolling mills are arranged in a row according to the rolling direction of the rolling stock. The rolling stock is only rolled once on each rolling mill. Each rolling mill is driven separately. Each rolling mill has different rolling speeds, that is, the rolling speed of the rolling rolls can be related to the rolling stock. The reduction in the section or the increase in the length of the rolled piece increases. Therefore, compared with the horizontal rolling mill, the rolling mill has the advantages of short gap time, high production efficiency, and less auxiliary equipment.

However, when this kind of rolling mill works, the rolling stock sequentially enters each rolling mill without forming a continuous rolling relationship, and the rolling stock is lengthened as the number of rolling passes increases, and the distance between the racks increases as the length of the rolling stock increases, so Longitudinal mills occupy a longer plant. This type of rolling mill is only suitable for large and medium-sized steel production. In order to overcome this shortcoming, the tandem mill was further developed into an off-road and a chess mill.

In cross-country rolling mills and staggered rolling mills, the head and tail of the rolling stock are alternated in different passes, which means the upper head becomes the tail of the track, and the tail of this track becomes the next head again. The rolling stock has lateral movement during the rolling process. The arrangement of the cross-country rolling mills and staggered rolling mills is more concentrated, which overcomes the shortcomings of the long mill. These mills also have a fast rolling speed and are suitable for the production of large, medium, and small complex sections of steel such as I-beam, channel steel, and H-beam.

The Work Theory Of Film Bearing

The Work Theory Of Film Bearing

Film bearing is a radial running bearing that uses lubricant as a media, the basic working theory is, during the rolling process, the bearing journal moves because of the rolling power, and the bearing center and the bearing journal have skewing, making two zones in the gap of film bearing and journal, one is called amplification area, the gap is getting bigger and bigger according to the rotating direction, one is called constriction area, the gap is getting smaller according to the rotating direction. When the rotating journal brings the lubricant from the amplification area to the constriction area, the gap becomes smaller and smaller, forming a lubricant wedge, creating pressure on the lubricant oil pressure, the pressure from every point in the film altogether is bearing capacity of film bearing, when the rolling power is bigger than the bearing capacity, the journal center and the bearing center eccentric distance enlarges, in the constriction area, the gap between bearings changing fast in the direction of journal rotating, the thickness of film get to the thinnest, the pressure of film getting bigger, carry capacity getting bigger, until balance the rolling power of the journal will not deviation, the bearing and journal completely separated by the film, become all liquid lubricant in theory.

From the film bearing theory, we can sense that the most important specification is film thickness, if the thickness is too thin, and the impurity in the lubricant is too big, which is just like metal touching directly, can lead to burning inside, meanwhile, if the thickness of the film is too thin, if steel pushing accident happens, it is very easy to course direct contact which leads to burning, the smallest thickness of the film is related to bearing structure material, related parts’ accuracy, and film bearing system assemble accuracy, lubricant, and rolling power.