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ABSTRACTPurpose: The purpose of this paper is to evaluate the influence of technological parameters of flattening in the ball rolling mill on spread and geometrical properties of strips made of stainless steel of 1.4310 type and to obtain mathematical models of flattening process.Design/methodology/approach: Flattening was performed in ball rolling mill in which cylindrical rollers have been replaced with balls of ~ 15mm diameter. Due to small dimensions to be measured we suggested the method of vector measurement of digital image. In order to evaluate the influence of technological parameters of flattening process, experimental planning method was used. The adoption of fractional experiment plan of 35-1 type enabled to reduce the number of experiments to 81, despite 5 variables.Findings: The results of performed tests have shown that strip spread is dependent on ball roughness, used draft, relation of wire diameter to ball diameter, back tension stress. The influence of tension stress has not been proved. 41554
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Strip flatness depends on used draft. Observations have proved good quality of strip edges. No fractures have been detected, even in the case of flattening by means of big draft. Strip surface was of good quality.Research limitations/implications: Test results we have obtained indicate usefulness of research method that has been used as far as determination of influence of flattening process technological parameters on spread and strip geometrical properties are concerned. It has also been proved that it is purposeful to replace cylindrical rollers with balls in rolling mills.Practical implications: Flattening process mathematical models enable to assess rational procedure of flattening process parameters selection in a ball rolling mill, that determines obtaining of the required geometrical characteristics of strips.
The results can be used directly when manufacturing strips for springs made of stainless steel 1.4310.Originality/value: Uniform thickness throughout strip width, parallel flat surfaces, narrow dimension tolerance, good surface quality and naturally rounded side edges make it presumable that flattening method by means of ball-shaped tools is likely to become an accepted method of metal strips with required flatness manufacturing.Keywords: Plastic forming; Ball rolling mill; Stainless steel; Experimental planning 1. Introduction The development of precision industry is responsible for constant increase of demand for narrow and thin steel strips with small dimension tolerance and functional characteristics fit for respective usage. New solutions are being sought both in the area of equipment for strip production and technologies of strip production. Selection of the best technology of narrow and thin strip production depends among other things on type of material the strip is to be made of, its final dimensions and properties, requirements concerning surface and edge quality. An efficient method of strip manufacturing is their flattening in ball rolling mill. In this unique and prototypical machine
1. I ntroduction cylindrical rollers have been replaced with balls of ~ 15mm diameter. The roller is used for flattening wires with diameter below 0,5 mm. Proper selection technological parameters of wire flattening process determines obtaining of strips with required functional characteristics and geometrical properties. The paper presents evaluation of the influence of technological parameters of flattening process in the ball rolling mill on spread and flatness of rolled strips made of hardened stainless steel of 1.4310 type. Experimental planning method enabled to obtain flattening process mathematical models thanks to which it is possible to design and control production process in such a way to obtain strips of required dimensions, with required geometrical properties.Stainless steel of austenitic structure, selected for tests, is very plastic when in softened state, but its strength properties are low. Their increase can be obtained thanks to cold working, for example by drawing and flattening. Wire and strips are used among other things for production of elastic and joined elements. They also serve for production of strings, medical equipment, devices for chemical and food industries [1-7].