CC BY
754S. Spuzic
The University of South Australia BASIC CONCEPTS IN ROLL PASS DESIGN
The idea of roll pass design (RPD) is to design a series of grooves [1] within which the rolled
[2] material will be deformed in order to achieve the desired morphometry [3] (geometry and dimensions) and mechanical attributes [4] of the finished product. The objective of RPD is to ensure that the product meets the desired quality [5] within constrains of the mill [6] and at minimum cost. The first approximation to RPD problem is to ensure practical manufacture of a long product with specified morphometric envelope and mechanical attributes [7].
A prerequisite for RPD analysis is to review the rolling mill layout and manufacturing parameters. Roll pass design can be viewed as a technique that results in producing the following documentation.
1. Product specification, that is, nominal features and tolerances for morphometry and the surface topography, as well as for the mechanical, chemical, microstructural [8] and other attributes of the product material [4]. The relevant information is usually available already (by means of international or national standards [9]), however, sometimes this is a matter for negotiation with the customers, resulting in the manufacturing norms for the agreed quality.
2. Specification of the above aspects for a series of transition objects - intermediate solids, including the initial feed. Manufacturing by rolling includes a number of discrete stages (sometimes over 50). The initial feed (usually a cuboid [10]) is deformed gradually, thus undergoing a decrease in cross-sectional area and an increase in the overall length during each stage (rolling pass). While the chemical composition does not change, the mechanical, surface and microstructure aspects will be substantially affected by the specifications of:
- temperature gradient and its rate within and between each rolling pass;
- deformation extent, gradient and rate within and between each pass.
The relevant information (cross-sectional areas, elongations, rolling speeds, etc.) is usually summarized in so called 'rolling schedules' and complemented by means of technological instructions (documentation).
3. Deformation zone morphometry for each pass, by means of defining each in the sequence of roll grooves. This information complements the aspects in the point (2), with the 'working' diameters of the rolls the body of which is cut to create these grooves. The relevant information is summarized by means of groove drawings, including the positions of each groove relative to each other.
4. Tools (rolls) specification, that is, nominal features and tolerances for morphometry and surface topography, as well as for the mechanical, chemical, microstructural and other attributes of the tool material. This information includes the location of each roll in rolling mill, as well as the maximum and the minimum roll diameters, bearing in mind that each roll is redressed several times during its life to re-generate the initial groove morphometry. This is usually done after several rolling campaigns. Additional information includes the method of roll cooling, and in some cases, lubrication.
5. Complementary documentation, describing the feed preparation and heating techniques, as well as the finishing operations, after the rolling process itself is accomplished (such as the product cooling, straightening and cutting to the delivery lengths). This documentation includes information about the auxiliary equipment such as rolling tackle (guides and guards) which are necessary for guiding the rolled solid into each deformation zone.
Task (1) is straightforward, and the RPD engineers do not have much, if any, manoeuvring space in deciding the cutting lengths either. The major design analyses are related to the stages (2) to (5).
The diversity of combinations used by roll pass designers worldwide to define aspects in (2),
(3) and (4) is mind provoking. It is understandable that differing rolling mills [11] use different
RPD systems for manufacturing similar products. This normally is a consequence of differences in mill layouts [12], stand configurations and other technical aspects. However, quite often the similar mills use very different RPD for rolling identical products. Useful RPD knowledge can be extracted [13] by analysing [14] this variety.
Additional important documentation consists of mill operation and maintenance records such as productivity, yield, tool life, maintenance indicators and the resource consumption.
Optimisation of RPD, providing that process is void of catastrophic interruptions (such as appearance of cracks and tool fracture), can be evaluated on the basis of the following norms: 1 - yield; 2 - productivity; 3 - reliability; 4 - costs.
RPD in hot rolling mills is a principal factor that delimits all four listed norms.
Ideally, hot rolled material should plastically flow through a sequence of passes in such way to maintain an optimal level in all four above norms (indicators). More detailed analysis leads to the recognition of factors such as rolling pressure, friction, temperature, rolling and sliding velocity and tool life. All these variables are significantly affected by the phenomena embodied within the deformation zone which, in turn, is substantially influenced by the roll pass design.
There are number of different methodologies used in RPD, and the following algorithm presents a generic framework for accomplishing an RPD task.
REFERENCES
1. https://www.dropbox.com/s/6aaukdb4xeqqag7/Calibre.pdf?dl=0
2. http://www.doitpoms.ac.uk/tlplib/metal-forming-2/rolling.php
3. http://thelibraryofmanufacturing.com/imagesforming/metalrolling2a.jpg
4. https://dl.dropboxusercontent.com/u/14617698/050a.pdf
5. http://spuzic.yolasite.com/quality.php
6. http://s274.photobucket.com/user/sethmcs/media/degarmo_18-1.jpg.html
7. https://en.wikipedia.org/wiki/List of materials properties#Mechanical properties
8. http://www.msm.cam.ac.uk/phase-trans/abstracts/CP1b.html
9. http://www.passdesign.ru/index.php?option=com content&view=article&id=84&Itemid=106
10. http://www.amathsdictionaryforkids.com/qr/cimages/cuboid.gif
11. http://www.pertengineering.com/innovation/img/it03.jpg
12. http://www.rmttools.com/wp-content/gallery/sample-layout/sample-layout-of-Rolling-Mill-2.jpg
13. https://db.tt/NuNv9UM7
14. https://en.wikipedia.org/wiki/Multivariate analysis
