Roll Pass Design
Roll pass design is based on the characteristics of initial input (weight of billet/bloom, steel grade, and steel temperature before and during the course of rolling), characteristics of finished rolled product (dimension of section, tolerances and specification concerning to mechanical properties, and surface finish of rolled product), and characteristics of the rolling mill (number of stand, roll diameter, strength of rolls, rolling speed, available power of the drive motor, and available mill equipment). Other factors which are of important considerations for good roll pass design are rolling load, draft, strain, and rate of heat transfer which do affect the condition of plastic flow of steel material. Further shape of a section in a particular pass must ensure a free flow of steel in the roll gap/groove. Selection of appropriate taper/groove angle in the pass is necessary in order to avoid jamming of steel material in the rolls.
Roll Pass design is a set of methods for determining the dimensions, shape, number and type of arrangement of rolling mill passes.
Roll pass designing also includes the calculation of pressing forces and their distribution on the roll passes. Only section iron is rolled between the shaped rolls. Sheets and wide strips are pressed between roller switch a smooth cylindrical or barrel-shaped surface.
Several passes are made for each section; a square or round billet acquires a specified form on each successive passage.
The roll passes are designed to avoid excessive stresses in the metal being rolled, since such stresses could lead to the formation of cracks and other flaws.
Roll pass design is an essential part of long product rolling process, since the long products are rolled between the shaped rolls in the long product rolling mills. Roll pass design generally means the cutting of grooves in the roll body through which steel to be rolled is made to pass sequentially to get the desired contour and size.
The primary objective of the roll pass design is to ensure production of a product of correct profile within the tolerance limits, free of defects, with good surface quality and the required mechanical properties. In addition, economic condition must be achieved while rolling the product, for example, maximum productivity at the lowest cost, optimum energy utilization, easy working conditions for the rolling crew and minimum roll wear.
OBJECTIVE OF ROLL PASS DESIGN
· Steel sections are generally rolled in several passes, whose number is Determined by the ratio of initial input material and final cross section
Of finished product.
· The cross section area is reduced in each pass and form and size of the stock gradually approach to the desired profile.
· Production of correct profile within tolerance limits with good surface finish (free from surface defects).
· Maximum productivity at lowest cost.
· Minimum roll wear.
· Easy working.
· Optimum energy utilization.
Basic Requirement for Correct Roll Pass Mill
· The number and arrangement of passes in particular roll stand should assure the most uniform possible exploitation of all the passes in each stand.
· Uniform draught in last passes & different draught in early forming passes of profile, where the section is large & metal is hot.
· Draught should be distributed so as to ensure as far as possible
Uniform wear and to avoid overloading of drive installations and
Rolls.