Experimental study of horizontal impact forces acting on equipment of thick sheet rolling stands during rolling

Technical aspects, methods and results of experimental studies of reversing rolling stands details horizontal accelerations of thick sheet rolling mills 3000 and 3600 are shown. Sequence of horizontal movements of bottom work roll with chocks in windows of housings during normal metal-in, steady rolling and metal-out is given. Usage of obtained experimental data and calculation of horizontal forces of work rolls chocks impacts against housings provided execution of stress calculations of technical solutions for increase of rolling stands durability.


Introduction
Horizontal impact forces acting on equipment of thick sheet rolling stands during rolling influence quality of rolled metal and durability of rolling equipment [1]. High values of contact stresses and deformations arise in details of thick sheet rolling stands [2,3]. Stabilization of work of main drive lines of thick sheet rolling mills during increase of their productivity is important task [4][5][6]. Theoretical data of dynamic loading of rolling stands (that was proved experimentally) was used to make stress calculations of technical solutions for reduction of impact loads [7][8][9][10][11][12]].

Formulation of task
Experimental studies of accelerations of thick sheet rolling stands details require usage of expensive equipment that is why more popular solution is direct measurement of forces of horizontal impacts of rolls chocks against housings and control of their displacements (movements). Machining of rolling stands details usually must be done to install sensors for direct measurements of forces of horizontal impacts but it can reduce durability of details. Therefore accelerations measurements of details are popular because sensors are installed on details prepared surfaces without their significant machining. Analysis of measured horizontal accelerations and displacements during unsteady and steady rolling helps to visualize dynamics of rolling stands.
Objectives of this paper:  explain technical aspects and methods of experimental measurements of horizontal accelerations and displacements of work rolls (WRs) chocks of rolling stands of thick sheet rolling mills 3000 and 3600 [13][14][15];  detailed analysis of obtained experimental measurements of horizontal accelerations and displacements of details of the thick sheet rolling mills;  describe usage of the experimental measurements for increase of rolling equipment durability.

Materials and Methods
Specialists from Pryazovskyi State Technical University (PSTU, Ukraine) and Peter the Great St. Petersburg Polytechnic University (SPbPU, Russian Federation) fulfilled:  experimental measurements of horizontal accelerations and displacements of details of rolling stands of thick sheet rolling mills 3000 and 3600 (Ukraine);  detailed analysis of obtained experimental measurements;  projects of technical solutions for increase of rolling equipment durability. Analog-to-digital converter (ADC) Е14-440, computer, inertial sensors, displacement sensors, etc. were used during the experiments ( fig. 1). Inertial sensors FLXL 150 AQC (mass is around 12 grams, measurement limits are from 0m/s 2 to 50×9.81m/s 2 , sensitivity is equal to 38mВ/g) were used to measure accelerations during displacements of WRs chocks in housing windows.
Displacement sensors are beams of equal resistance with glued on them strain gauges (resistance of each is 200 ohms) switched in bridge circuit. Signals from sensors via ADC were recorded into computer database.   Analysis of movements of BWR with chocks in windows of housings during normal metal-in shows below given sequence that happens in 90% of normal metal-in cases:  stage #1 is when BWR chock is in the middle of housing window or pressed to any column of housing before rolling ( fig.3, а);  stage #2 is when BWR chock moves against rolling direction during metal-in (start of rolling, unsteady rolling), hits column of housing and then there are numerous fading impacts of BWR chock against columns of housing on entry side and delivery side ( fig.4, b);  stage #3 is when BWR chock is pressed to housing on entry side during steady rolling ( fig.4, c);  stage #4 is when BWR chock hits column of housing on entry side during metalout ( fig.3, d).
1 is BWR; 2 is BWR chock; 3 is column of housing on entry side; 4 is column of housing on delivery side  table 1 where shown values of forces of horizontal impacts of BWR chock against housing were calculated by usage of below given method (formulas from 1 to 6, method is developed by authors of this paper). Sign minus of accelerations means that BWR chocks are moved towards entry side of the thick sheet rolling stand. To define horizontal forces of rolls chocks impacts against housings (refer to table 1) of strip and thick sheet rolling stands when accelerations, movements and masses are known below given method based on BWR chocks is proposed. Force of horizontal impact of BWR chock against housing (as per Newton's second law): where m is reduced active mass of BWR assembly with chocks, bearings, etc., kg; а is horizontal acceleration of BWR chock, m/s 2 . Reduced active mass m of part of BWR assembly means that BWR assembly is considered as assembly with mass Σm (sum of masses of all elements in the assembly). Impacts of BWR assembly against housings happen only by its chocks on DS and OS. Difference of horizontal accelerations of BWR chocks shows necessity to consider BWR assembly as element that consists of two parts where each part can hit housing. BWR assembly consists of two reduced active masses, namely mDS from DS and mOS from OS.

Results
Horizontal accelerations and displacements of WRs chocks define values of impact loads acting on housings (facing strips). Their biggest values act during metal-in and metal-out. 2. Detailed analysis of obtained experimental measurements of horizontal accelerations and displacements of details of the thick sheet rolling mills is done. It helped to calculate horizontal forces of BWR chocks impacts against housings which maximum value is around 1.58·10 6 N.
3. Sequence of horizontal movements of BWR with chocks in windows of housings during normal metal-in, steady rolling and metal-out is given. 4. It is recommended to use proposed method of horizontal forces calculation of BWR chocks impacts against housings to define ones of top WR chocks impacts against housings. 5. Usage of obtained experimental data and calculation of horizontal forces of WRs chocks impacts against housings provided execution of stress calculations of technical solutions for increase of rolling stands durability [3,16,17].