Pilot Mill Research Articles

The Deformation Microstructure and Recrystallization Behavior of Warm Rolled Steels.

The deformation microstructure of various warm (ferritic) rolled steels was characterized and its influence upon the subsequent annealing behavior determined. The materials investigated included three interstitialfree (IF) steels (stabilized with either titanium or niobium), an extra low carbon (ELC) steel, and four experimental low carbon chromium steels with varying levels of boron, nitrogen and phosphorus. Single pass rolling experiments were conducted in a pilot mill at temperatures between 440 and 850°C and the asrolled microstructures were examined using optical microscopy. Particular attention was paid to the nature and intensity of the in-grain shear bands produced. Partial annealing was conducted to examine the nucleation of recrystallization in the deformed microstructure. Shear bands of moderate intensity were usually formed in the IF steels, which tended to be insensitive to rolling temperature. For the ELC steel, intense shear bands were formed at low rolling temperatures, but at higher temperatures this intensity was found to be drastically reduced. The development of shear bands at the higher rolling temperatures was significantly enhanced by alloying with chromium. The differences in shear band frequency and intensity are explained in terms of the dynamic strain aging behaviors of the various materials. Recrystallized grains were found to nucleate preferentially on the shear bands during annealing, regardless of their morphology or intensity.

Determination of Bran Contamination in Wheat Flours Using Ash Content, Color, and Bran Speck Counts

ABSTRACTA fast new method based on image analysis, ScanPro Speck Expert (SPX), to determine the bran contamination in wheat flour was studied and compared with existing methods (air‐oven, ash, and color measurements) using an Agtron color meter and a Minolta chromameter. Twenty‐one hard red winter wheat flour samples with ash contents of 0.30–0.58% were collected from the Kansas State University pilot mill and used for this study. Intrinsic variability in the flour sample because of randomness of bran speck orientation and distribution in the sample holder could result in variation in the speck count. Simple and multiple linear regression analyses showed that estimation of flour ash content from the SPX results (R2 = 0.91) would be more accurate than the results from color measurements (R2 = 0.66 [Agtron color meter] and 0.74 [L*]). The added capability of SPX image analyzer to not only count the number of bran specks but also to measure their areas probably increases the accuracy of determining the bran contamination in wheat flour by image processing.

Hold-up studies in a pilot scale continuous ball mill: dynamic variations due to changes in operating variables

In the past experimental studies on mill hold-up were done using tracers and residence time distribution analysis (RTD). In one or two studies the entire content of the mill was weighed after the experimental run. Either as a result of inflexible experimental setup or difficulties in measuring hold-up in closed-circuit industrial mills via the RTD approach, the published correlation between hold-up measurements and mill feed rate disagree with each other. In this study a carefully constructed pilot mill enabled hold-up measurements in real time while the mill was operating. Therefore, extremely accurate hold-up data and transient hold-up data were obtained. In light of this data the correct trends in hold-up as a function of operating conditions are established. Explanations for the observed trends are provided throwing much light on anomalies on previously published data.

Fate of Dwarf Bunt Fungus Teliospores During Milling of Wheat into Flour

ABSTRACTWheat contaminated with teliospores of Tilletia controversa Kühn (TCK) was mixed with uncontaminated wheat and processed through the Kansas State University pilot mill. Two 50‐bu lots of the contaminated mixture were cleaned, tempered, and milled. Approximately 500 samples of wheat, cleanings, and mill fractions were collected and examined for the presence of intact and broken TCK teliospores. Whole wheat samples (50 g) were washed, sieved through a 60‐μm nylon sieve, and pelleted by centrifugation. Contents of the pellet were examined microscopically for the presence of TCK spores. The procedure was modified as needed to accommodate cleanings and mill fractions. Levels of spore contamination in whole wheat samples decreased at each step during the handling process, and large numbers of spores were found in materials that were sieved or aspirated from the grain. Very few spores were found in bran, germ, and shorts; none were detected in red dog or straight‐grade flour. The results showed that a high percentage of spores can be removed from wheat by mechanical cleaning but that it is not feasible to remove all of them.

Effects of Break‐Roll Speed Differential on Product Yield and Semolina Granulation in a Durum Pilot Mill System

ABSTRACTChanges in break‐roll speed differential in a 25‐quintal (55‐cwt) durum pilot mill system (136 kg/hr feed rate capacity) affected total yield of semolina, flour, and bran; semolina yield from different purifiers; and semolina granulation (150‐ to 841‐μm particle size range). By adjusting the speed differential of the break and chunk roll pairs from 1.5:1 to 2.5:1 to 3.5:1, semolina yield increased significantly from 55 to 67 to 72%, respectively, and bran yield decreased significantly from 24 to 15 to 11%, respectively. Shorts yield was not affected by speed differential. At 1.5:1, semolina contained 9% flour, compared with 5% flour at 2.5:1 and 3.5:1.

Breakage of coals in ring-roller mills Part 2. An unsteady-state simulation model

A mathematical model has been developed for predicting unsteady behavior of a ring-roller mill. The model is based on specific rates of breakage, primary breakage distributions, classification actions of particles in the mill and mass transport relation of mill hold-up and flow rates through the mill. The validity of the model was verified by pilot mill testing. Transient behavior of the mills during rapid changes of load, feed and operating conditions were then demonstrated.

Application of the Single‐Kernel Characterization System to Wheat Receiving Testing and Quality Prediction

ABSTRACTSingle‐kernel characterization system (SKCS) 4100 measurements on wheat were reproducible and stable and gave good correlations with relevant reference data, e.g., kernel weight vs. 1,000 kernel weight, kernel hardness vs. particle size index, and kernel moisture vs. oven moisture. Under field conditions at a receiving station in Coleambally (NSW, Australia), the SKCS 4100 operated faultlessly and the reproducibility of the results was as good as in the laboratory. The measurements were completed within the time taken for the normal testing sequence, and the histograms were shown to provide valuable information about the samples that would not otherwise be available. For example, the distribution of moisture contents of individual kernels provides additional information about the samples' potential storage stability. Data on the uniformity of hardness could be interpreted in terms of the potential of the wheat to provide a consistent milling performance. An imprecise (r2 = 0.44) but potentially useful calibration was obtained for the prediction of flour yield under test milling conditions using SKCS 4100 measurements on wheat. A much stronger correlation (r2 = 0.83) was obtained between SKCS data on wheat and the starch damage contents of flours produced on a pilot mill. Thus, the SKCS 4100 has the potential for early generation screening of wheat lines for flour yield and starch damage.

Progress in measuring and modelling load behaviour in pilot and industrial mills

The need for an accurate and comprehensive understanding of load behaviour in industrial mills is outlined, and the implications of the availability of techniques for measuring load behaviour in these mills for both design and control is explored. Some research performed on a pilot mill used to investigate the effect of grid liners on autogenous milling is described. Considerable slip between liners and load occurred, with the result that a simple torque model (taking into account the orientation of the load and the slurry pool as measured by conductivity probes passing through the mill shell) was adequate for describing mill power at high mill speeds. The different behaviour of overflow and discharge mills as affected by slurry and load volume was explored. Some work involving the measurement of the axially distributed behaviour of the load in an industrial mill is then described. Liner movement, load orientation (measured with conductivity probes) and load temperature were measured as a function of axial position. The load orientation was found (surprisingly) to be almost independent of axial position but was a strong function of load volume. The axial temperature profile correlated in a logical fashion with other operating conditions. The relevance of these measurements for mill control is explored.

Computer-integrated ball burnishing of a plastic-injection-mould cavity insert

This paper describes an attempt to burnish a plastic-injection-mould cavity insert made of pre-hardened AISI P20 alloy steel. A CAD model of the cavity insert was first created and the associated NC tool path down-loaded to a CNC vertical machining centre, in which the milling and burnishing were undertaken. The procedure for creating a solid model of the mould cavity insert is presented. In the absence of published data on the machinability of the alloy steel, pilot milling and burnishing operations were performed on flat specimens, in order to ascertain suitable speeds, feeds and depths of cut. The best surface finish of 0.30 μm R tm was achieved by a depth of penetration of 10 μm and a feed of 0.1 mm. The variation of surface roughness with depths of penetration, as well as the merits of single- and double-pass burnishing, are discussed. The average surface roughness of the burnished cavity insert was 0.91 μm R tm, which was a 70.4% improvement over the surface quality of the as-milled condition.

Characterization of mill products by analysis of in-flow digitalized images

A sensor has been designed and tested in a pilot mill to characterize granular products in the food industry. It consists of: • • a mechanical system which takes a representative part of the product, • • a CCD camera to capture images, • • a software package for image analysis and data processing. The method consists of comparing a sample with a predetermined ‘quality class’. The decision system is built on example learning: real cases fed into the system allow its configuration. Three quality classes have been defined, they correspond to the rolls gap (0.30, 0.40, 0.50 mm) of the first break rolls of a semolina pilot mill. In these conditions, the classification accuracy rate achieved by the system is higher than 80%.

Aleurone and Pericarp Fluorescence as Estimators of Mill Stream Refinement for Various Canadian Wheat Classes

Mill streams from laboratory-scale and pilot-scale millings of seven Canadian wheat classes were used to extend previous evaluations of fluorescence imaging as a flour refinement estimator. Flour streams and diverse mill streams derived from throughout the Grain Research Laboratory (GRL) Pilot Mill during the milling of Canada Western Red Spring (CWRS) wheat were subjected to fluorescence measurement of pericarp and aleurone tissue. Both techniques showed clear differentiation among the mill streams. Strong linear relationships of pericarp fluorescence to ash content, grade colour and L* (brightness) were found. Relationships of aleurone fluorescence to the same refinement indices, although still statistically significant (P<0·05), were weaker because of the previously established tendency for break flours to exhibit lower aleurone fluorescence than reduction flours of comparable refinement. Extending the GRL Pilot Mill break system to broaden the refinement range within CWRS break flours confirmed a strong linear relationship between break flour refinement and aleurone fluorescence. The robustness of fluorescence as a flour refinement indicator under different milling conditions was examined for commercially grown wheats from seven Canadian wheat classes using three different mills. For every wheat class and every milling process both fluorescence techniques showed clear differentiation among flour streams. Pericarp fluorescence was strongly related to flour refinement for all wheat classes, aleurone fluorescence was less strongly related because of anomalous low fluorescence of break flours. The relationships of pericarp fluorescence to the flour refinement indices were heterogeneous among wheat classes. It is well established that flour ash content and flour colour have limitations for estimating the refinement of flours from wheats of diverse origin. Therefore, the heterogeneity of pericarp flourescence relations among wheats provides evidence that pericarp fluorescence is a more objective flour refinement estimator. The regression equations of pericarp fluorescence to flour refinement indices when a single wheat was milled by different mills were clustered closely, although heterogeneity was evident for several wheats.

Experimental validation of a rolling stand elastic deformation model

Predicting strip profile due to roll deformation is a major concern in the rolling industry. We are developing a numerical model coupling iteratively a semi-analytical elastic rolling stand deformation calculation with a three-dimensional Finite Element Method for the strip deformation and rolling force distribution predictions. The present paper describes a comparison with experiments on a 4-high pilot mill, consisting in cold rolling various rake-shaped assemblies of aluminum rods. Under such conditions we may assume the rolling force to be equally distributed among the rods. Therefore, off-line measurements of rod exit thicknesses yield the loaded roll profile as elastic recoveries of rods are identical. Measured and predicted rolling forces of a single rod are also compared.

Fundamental phenomena governing heat transfer during rolling

To quantify the effect of roll chilling on the thermal history of a slab during hot rolling, tests were conducted at the Canada Center for Mineral and Energy Technology (CANMET) and at the University of British Columbia (UBC). In these tests, the surface and the interior temperatures of specimens were recorded during rolling using a data acquisition system. The corresponding heat-transfer coefficients in the roll bite were back-calculated by a trial-and-error method using a heat-transfer model. The heat-transfer coefficient was found to increase along the arc of contact and reach a maximum, followed by a decrease, until the exit of the roll bite. Its value was influenced by rolling parameters, such as percent reduction, rolling speed, rolling temperature, material type,etc. It was shown that the heat-transfer coefficient in the roll gap was strongly dependent on the roll pressure, and the effect of different variables on the interfacial heat-transfer coefficient can be related to their influence on pressure. At low mean roll pressure, such as in the case of rolling plain carbon steels at elevated temperature, the maximum heat-transfer coefficient in the roll bite was in the 25 to 35 kW/m2 °C range. As the roll pressure increased with lower rolling temperature and higher deformation resistance of stainless steel and microalloyed grades, the maximum heat-transfer coefficient reached a value of 620 kW/m2 °C. Obviously, the high pressure improved the contact between the roll and the slab surface, thereby reducing the resistance to heat flow. The mean roll-gap heat-transfer coefficient at the interface was shown to be linearly related to mean roll pressure. This finding is important because it permitted a determination of heat-transfer coefficients applicable to industrial rolling from pilot mill data. Thus, the thermal history of a slab during rough rolling was computed using a model in which the mean heat-transfer coefficient between the roll and the slab was determined from an estimate of the rolling load. It was found that the heat loss of a slab to the roll was 33 pet of the total, which emphasizes the importance of accurately characterizing the heat-transfer coefficient in the roll bite during hot rolling.

The thermal and metallurgical state of steel strip during hot rolling: Part II. Factors influencing rolling loads

Traditional models for computing roll forces during hot rolling generally ignore the steep thermal gradients set up in the through-thickness direction due to roll chilling and deformation heat. In this paper, Alexander’s model has been modified to account for the effect of thermal gradients on roll forces. Flow stress data have been obtained by conducting tests on a cam plastometer and a Gleeble 1500 for a 0.05 pct carbon, a 0.34 pct carbon, and a 0.07 pct carbon with 0.024 pct niobium steel for temperatures and strain rates attained in each of the stands on Stelco’s Lake Erie Works (LEW) hot-strip mill. The hyperbolic sine equation has been shown to fit the data and is capable of predicting flow stress over a range of temperatures and strain rates. Simulations of the industrial operation have been conducted on the pilot mill at CANMET, and it has been shown by comparing predicted and measured roll forces that the friction coefficient is reduced from 0.3 to ∼R 0.35 to 0.25 in the presence of a lubricant. It has also been shown that incorporating the steep thermal gradients in the roll-bite zone increases predicted roll forces by 6 to ∼R 10 pct over the values computed based on centerline temperatures. The model has been validated also by comparing predictions with roll forces measured on the industrial mill.

The thermal and metallurgical state of steel strip during hot rolling: Part III. Microstructural evolution

A mathematical model has been developed to compute the changes in the austenite grain size during rolling in a hot-strip mill. The heat-transfer model described in the first of this series of papers has been employed to calculate the temperature distribution through the thickness which serves as a basis for the microstructure model. Single-and double-hit compression tests have been conducted at temperatures of 900 °C, 850°C, 950 °C, and 875 °C on 0.34 and 0.05 pct carbon steels to determine the degree of recrystallization by metallographic evaluation of quenched samples and by measuring the magnitude of fractional softening. The Institut de Recherches de la Siderurgie Francaise, (IRSID) Saint Germain-en-Laye, France equation has been found to yield the best characterization of the observed recrystallization kinetics. The equations representing static recrystallization kinetics, recrystallized grain size, and grain growth kinetics have been incorporated in the model. The principle of additivity has been invoked to permit application of the isothermal recrystallization data to the nonisothermal cooling conditions. The model has been validated by comparing predicted austenite grain sizes with measurements made on samples quenched after one to four passes of rolling on the CANMET pilot mill. The austenite grain size evolution during rolling of a 0.34 pct carbon steel on Stelco’s Lake Erie Works (LEW) hot-strip mill has been computed with the aid of the model. The grain size decreased from an initial value of 180μm to 35μm in the first pass due to the high reduction of 46 pct. The changes in austenite grain size in subsequent passes were found to be small in comparison because of the lower per pass reductions. It has been shown that the equation employed to represent grain growth kinetics in the interstand region has a significant influence on the computed final grain size. Altering the rolling schedule had a negligible influence on the final grain size for a given finished gage. A 200°C increase in entry temperature to the mill resulted in a 20μm increase in final grain size, which is significant. This can be attributed to increased grain growth at the higher temperature.

The thermal and metallurgical state of steel strip during hot rolling: Part I. Characterization of heat transfer

A technique using intrinsic thermocouples was developed to monitor the thermal response of steel samples during hot rolling. A series of hot-rolling tests was conducted with the thermocoupleinstrumented samples on CANME’s pilot mill to simulate individual stands of Stelco’s Lake Erie Works hot-strip mill. A mathematical model of heat transfer in the roll bite has been employed to back calculate the roll/strip interface heat-transfer coefficients for lubricated and unlubricated conditions. The influence of reduction, rolling speed, and prerolling on roll-strip heat transfer has also been examined. For unlubricated rolling tests, the heat-transfer coefficient in the roll bite increased with time, reaching a steady-state value of 57 kW/m2 °C. The corresponding number for the lubricated tests was 31 kW/m2 °C. The observed variation in the interface heat-transfer coefficient with increasing strain and interface pressure points to a strong dependence on the real area of contact between the strip and rolls. Therefore, it appears that heat transfer between the two surfaces occurs primarily by conduction across asperity contacts. The high heat-transfer coefficients attained at the roll/strip interface promote chilling of the strip to a depth of approximately one-eighth of the thickness. To validate the overall heattransfer model, predicted surface temperatures of the strip have been compared with interstand temperature measurements obtained on the industrial mill using pyrometers.

MODELING THE MILLING OF HARD RED WINTER WHEAT: ESTIMATION OF CUMULATIVE ASH AND PROTEIN RECOVERY

ABSTRACT A nonlinear model consisting of segmented cubic and linear functions was used to describe cumulative ash as a function of wheat's physical characteristics (wheat size, 1,000 kernel weight, protein content, whole wheat ash, pearling value, and Zeleny sedimentation). The protein content of the flour (i.e., protein recovery of the mill) was studied as a function of the whole wheat protein content. The empirical models were developed using data from 54 samples of hard red winter wheat milled in the pilot mill of the Department of Grain Science and Industry at Kansas State University, Manhattan, Kansas. The empirical models developed were implemented into an electronic spreadsheet capable of estimating milling yields, ash content, and protein content of straight grade, patent, and remaining clear flours from the ash curve.

Validity and reliability of a method for retrospective evaluation of chlorophenate exposure in the lumber industry.

This paper describes the validity and reliability of a method to retrospectively assess exposure to antisapstain agents used in sawmills (chlorophenates). The method is based on experienced workers' estimates of exposure for each job title at the sawmill where they work. At a pilot mill, 10 randomly selected workers estimated the frequency and duration of exposures to chlorophenates for all 59 job titles. The reliability of their mean exposure estimates was very high, with an intraclass correlation coefficient for all raters of 0.91 (based on a calculated index of exposure). To assess validity, urinary chlorophenate levels were measured for 86% of the workers at the mill during the summer and/or fall, and compared to experienced workers' estimates of exposure. The correlation between workers' exposure estimates and the urinary chlorophenate levels for each job title were consistently above 0.65 for all analyses and greater than 0.72 when summer and fall urine sample results were averaged. The evidence indicates that the validity and reliability of worker exposure estimates are high enough to justify investigation of the method's generalizability to other sawmills.

Milling and Baking Qualities of Some Canadian Wheat Classes Alone and in Blends with Brazilian Wheat Under Brazilian Processing Conditions

A mill flow was developed for the GRL pilot mill to produce flour comparable in quality and extraction rate to that produced by Brazilian mills. Canadian wheat classes were compared for milling and baking quality, alone and in blends with Brazilian wheat. When milled as mixed grists with Brazilian wheat all the Canadian wheats extended flour extraction rate; the soft Brazilian wheat gave an extraction rate of 76% compared to means of 79% and 78% for mixed grists containing either 50% or 30% Canadian wheat, respectively. No. 1 Canada Western Red Winter wheat gave the best milling performance of all the Canadian wheats tested. Because of its relatively soft texture, HY 320 was the least effective of the Canadian wheats in improving milling performance when blended with Brazilian wheat. No. 3 Canada Western Red Spring wheat and No. 1 Canada Utility (CU) wheat were most effective in improving dough strength in blends with the weak Brazilian wheat. Remix bread quality of flours produced from mixed grists of Canadian wheat with Brazilian wheat all were superior to the Brazilian wheat flour, particularly in the case of CU wheat blends. RésuméOn a développé une coulée de meunerie pour le moulin pilote GRL pour produire une farine comparable en qualité et en taux d'extraction à celle produite par des moulins brésiliens. Des classes de blé canadien furent comparées au blé brésilien au point de vue mouture et aptitude à la cuisson, seuls ou en mélanges. Tous les blés canadiens ont augmenté les taux d'extraction de la farine lorsque moulus en mélange avec du blé brésilien; le thé non brésilien a donné un taux d'extraction de 76% par rapport à 79% et 78% pour des grains mélangés contenant respectivement 50% et 30% de blé cana-dien. De tous les blés canadiens étudiés, c'est le blé roux d'hiver de l'ouest canadien No. 1 qui a donné la meilleure performance de mouture. A cause de sa texture relativement molle, le HY320 fut le moins efficace de tous les blés canadiens pour l'amélioration de la performance de mouture quand mélangé à du blé brésilien. Le blé roux du printemps de l'ouest canadien no. 3 et le blé Utilité du Canada (CU) no. 1 furent les plus efficaces pour améliorer la force de la pâte dans les mélanges avec le blé brésilien faible. L'aptitude à la panification des farines obtenues de mélanges de blés canadien et brésilien, particulièrement dans le cas des mélanges au blé CU.

The effect of grate design on the behaviour of grate-discharge grinding mills

A model for the effect of flowrate and viscosity of slurry on the hold-up of slurry in a grate-discharge grinding mill has been developed. Given detailed specifications of the grate design (such as the area in the grate within which the holes are situated, the number of holes per m 2 and the hole size) and the flowrate and viscosity of the slurry flowing through the mill, the model provides estimates of the volume of slurry held up in the mill and the distribution of this slurry down the length of the mill. The model has been assessed using data obtained from milling tests performed on a 2.5-kW pilot mill in which grate design, slurry flowrate and slurry viscosity were varied. It was shown that only three parameters need to be determined by regression on the experimental data to ensure that the model is able to predict the holdup in the mill to within 8%. The application of this model to grate design and circuit optimisation is briefly discussed. The grinding rate G (t/h of new −75 μm material) and power consumption E (kWh/t of new −75 μm material) were also measured in the above-mentioned tests. Using multilinear regression it was shown that G was not affected by grate design in the region of operation covered by the experiments, while E was only a weak function of grate design.