Hot Rolling - Productivity Science and Quality Science

The quality of the rolled product is decided by the rolling stands inside the finishing mill. The dimensional exactness depends on numerous components counting the beginning stock measurements, roll pass arrangement, temperature, microstructure, roll surface quality, roll and stand firmness and the stock/roll contact condition. The material characteristics which are important are the geometric shape and resilience. Mechanical properties include  abdicate and extreme malleable qualities, % decrease in zone (ductility) and hardness. Microstructure characteristics include grain estimate, grain conveyance, stage composition and stage dissemination.

The ultimate shape of the stock is basically subordinate on these parameters. These parameters are exceptionally vital to a roll pass originator when planning a specific rolling pass for particular shape and estimate necessities. Precision in calculating these parameters are basic when fulfilling such geometric necessities as roundness (in case of bars and bars) and resistance. The mean effective plastic strain is greatly imperative for foreseeing and controlling the mechanical properties of the rolled item after rolling. 

There are essentially three problems, present during the rolling.   They are –

(i) Resistance of material to distortion, as a work of strain, strain rate and temperature,

(ii) The capacity to calculate the dispersions of the strains, strain rates, push and temperature within the distortion zone, and

(iii) The conditions at the roll metal interface, i.e., the coefficients of grinding and heat exchange.

B. The parameter that affects the quality of the rolled products are- 

 Work roll profile

 Work roll geometry

 Chemical composition of material.

 Geometry of the material

 Rolling schedule  

 Gear ratio

 Proper control of coolant and lubricants

 Bearing temperature in the gear boxes

 Gap between the rolls

 Standing time of work roll

 Material hardness and temperature

 Velocity of in and out material (slabs)

 Thickness percentage reduction

 Roll forces

 Power applied to rolling mills

 Static and rolling torque

 Number of passes

 Time span between passes

 Vibration

C. Problems and defects in roll products

 Defects from cast ingots before rolling.

 Variation in thickness.

 Improper flatness.

 Fractional errors due to roll gap profile.

 Edging.

 Surface defects due to high surface to volume ratio.

 Laps due to misplace of rolls can cause undesired shapes.

 Flakes or cooling cracks along the edge.

 Scratches.

Reference of the research paper to be given.

Important News

2021

JFE Steel Deploys Data Science-Based Equipment Anomaly Detection System

at All Hot-Rolling Mills

—Designed to improve productivity by preventing equipment faults

https://www.jfe-steel.co.jp/en/release/2021/210929.html

THE DEVELOPMENT OF THE THEORY OF METAL

ROLLING AND ITS APPLICATION TO ROLLING MILL CONTROL

by

JOHN HUNT SLOANE

A THESIS

submitted to

OREGON STATE UNIVERSITY

in partial fulfillment of

the requirements for the

degree of

MASTER OF SCIENCE

Summer 1964

Rolling theory can be divided into two broad and general categories, that which applies to hot - rolling and that which applies to cold rolling. 

In hot - rolling the yield stress characteristic of the metal is strain -rate dependent and frictional force between the roll and stock is high. 

In cold - rolling the yield stress characteristic of the metal is essentially independent on the rate of deformation and the frictional force between roll and stock is low.

Of primary influence upon the rolling process are the following parameters: the work roll diameter, the reduction in one pass, the initial thickness of the work piece, the speed of rolling (rate of strain), the front and backtensions, the nature of friction between the rolls and the material being rolled, the temperature field in the material, the physical properties of the material being rolled, the shape of the roll contour and the mill behavior under load. Most of these are properties or characteristics of the process under consideration rather than the machine (mill) doing the work. 

In addition to the above considerations are such things as the memory of the material, or the effect of previous treatment; the elastic deformation of the rolls under load; and, the state of waistropy. 

The most complete and theoretically correct work in this field was done by Orowan (1943) (7). His work was based upon the assumptions set down by Von Karman (1925) (14) in his pioneer paper on rolling mill theory. Bland and Ford (1948) (1), further assumed away some of the problems involved in Orowan's theory, and it is upon the former that the bulk of the following is based. 

This thesis shall be limited to the cold - rolling of strip.