STUDY ON ROUGH RICE FISSURING DURING INTERMITTENT DRYING

The Assuring of rough rice during intermittent drying was studied through experimental and numerical methods. The moisture distribution inside the rice kernel during drying and tempering was obtained by diffusion model. The moisture gradients were used to analyze the hydro stresses in the rice kernel during intermittent drying.

Discontinuing the drying process with tempering can decrease the hydro stresses in the rice kernel. Decreased unit drying time or increased intermittent ratio caused decrease of the stresses in the rice kernel during intermittent drying. Less fissured rice was also observed by discontinuing the drying process in the experiments. Higher intermittent ratio or lower unit drying time caused lower percentage of fissured rice in the experiments.     

Stress and Structural Relaxation in Tempering Glass

Temper stresses are brought about, primarily, by a partial relaxation of transient stresses generated by rapid cooling of the glass. Stress relaxation under nonisothermal conditions is competently handled by a mathematical tempering model, in which glass is treated as a simple viscoelastic material. However, this model proved inadequate in some respects since the properties of glass depend not only on its instantaneous temperature but also on its prior thermal history. A tempering model was therefore developed that incorporates both stress and structural relaxation. Predictions of this structural model are compared with experimental data on tempering and contrasted with predictions of the viscoelastic model. Such comparisons revealed that, typically, structural relaxation accounts for approximately 24% of the total residual temper stresses.     

STUDY ON ROUGH RICE FISSURING DURING INTERMITTENT DRYING

Abstract

The Assuring of rough rice during intermittent drying was studied through experimental and numerical methods. The moisture distribution inside the rice kernel during drying and tempering was obtained by diffusion model. The moisture gradients were used to analyze the hydro stresses in the rice kernel during intermittent drying.

Discontinuing the drying process with tempering can decrease the hydro stresses in the rice kernel. Decreased unit drying time or increased intermittent ratio caused decrease of the stresses in the rice kernel during intermittent drying. Less fissured rice was also observed by discontinuing the drying process in the experiments. Higher intermittent ratio or lower unit drying time caused lower percentage of fissured rice in the experiments.     

Application of a New Method for Radiative Heat Transfer to Flat Glass Tempering

Temperature distributions within semi-transparent materials like glass strongly determine their behavior. It is fundamental to take radiation into account to determine exact temperature distributions. The Rosseland Approximation for radiation is usually an appropriate method, but is only valid with an optically thick glass. In the present paper, we propose an improved approximation that is both efficient and sufficiently accurate even for the semi-transparent region. This new radiation model is used to determine the temperature along the flat glass thickness during tempering. The impact of temperature evaluation on residual stresses is discussed.     

Compressive Surface Strengthening of Brittle Materials by a Residual Stress Distribution

A theoretical approach is presented for predicting the strengthening of brittle materials subjected to a residual stress distribution represented by a polynomial series. In the approach, the stress intensity factor for a surface crack is derived incorporating the effect of crack closure. The crack-closure distance is then calculated using an approximate approach which allows the strengthening due to the residual stresses to be estimated. Illustrating the approach using residual stresses typical of tempering, it was found the approach agreed well with previous work. The influence of partial crack closure was found to give higher values of the stress intensity factor than would be calculated if the crack were assumed to be open. This effect decreases the amount of strengthening predicted and gives a wide range of conditions for which subcritical crack-growth processes can occur. For the example of tempering it was also found that these are conditions when weakening or spontaneous failure of the body can occur.     

Approximation of temperature dependence of the modulus of elasticity of glass

A refined nonlinear value of the main parameter of a material, i.e., the elongation modulus versus the instant temperature value, was suggested for introduction into the computational algorithm of tempering stresses.     

Stress and Failure Prediction for the Drying, Tempering, and Cooling of Extruded Durum Semolina

This work presents a method to predict the stress and breakage that is caused by the drying of hygros-copic materials. Stresses were predicted for a viscoclasic cylinder with the properties of extruded durum semolina, or pasta noodles. The stresses were calculated as functions of the transient moisture and tem-perature gradients in the material which were predicted for the combined processes of drying, tempering,and cooling. The time and radial position of failure were predicted based on failure data for extruded semolina.

Isotherm data for extruded durum semolina were obtained for temperatures from 40 to 60°C and for relative humidities from 75 to 95%. The results were fit with a modified form of Henderson's equation.Thermal conductivities were measured for temperatures from 30 to 50°C and a moisture range of 12 to 27% (dry basis).

A drying model based on the principles of irreversible thermodynamics; (Fortes, 1978; Fortes and Okos, 1981a, 1981b) was used to successfully predict drying curves for a range of experimental conditions. Transient moisture and temperature profiles were calculated numerically, and a receding evapora-tion front was predicted to exist. Drying was predicted to be a coupled liquid, vapor, and heat transport phenomena.

The drying data were used in a stress analysis of a Maxwell viscoelastic cylinder to predict trends in stress development under various contiitions of combined drying, tempering, and cooling. High temperature-high humidity drying, HTHH, (lOO°C, 65% RH) was compared with low temperature-low humidity drying, LTLH, (53°C, 13% RH). The HTHH drying offered definite advantages in terms of reduced product breakage susceptibility. The reasons for those advantages were increased failure strength and a decreased moisture gradient at the end of drying. In a five-stage drying process, the cooling stage was shown to have a significant impact on the predicted levels of stress and on the strength of the extruded material. Analysis of the model suggested that gradual temperature and humidity transitions from stage to stage in multistage processes were important to product quality.     

Strengthening of Glasses by Partial Leaching

A technique for strengthening certain alkali borosilicate glasses is described. Porous surface layers of a desired thickness are created on an article, taking advantage of the phase separation and leaching phenomena in such glasses. The semiporous composite is then heated to sinter the high-silica clad about the borosilicate core. On cooling, residual compressive stresses develop within the cladding. The mechanical properties of cylindrical specimens prestressed by this method were characterized by photoelastic measurements and moduius-of-rupture tests. Residual stresses as high as —410 MPa were observed and found to be in reasonable agreement with the form of a previously developed thermal-stress model. The roles played by thermal tempering and stress-relaxation effects are also discussed.     

Chemical tempering of porcelain tiles

This work presents an innovative approach for strengthening porcelain tiles via chemical tempering, which consists in replacing cations with smaller ionic radius by similar cations with larger ionic radius. Na-containing porcelain tiles were immersed into molten KNO₃ bath. A concentration profile of Na and K in the cross section of porcelain tiles to a depth of 200 µm from the surface confirmed the ion exchange. Compressive stresses on the material surface were produced, leading to flexural strength of up to 54.5 MPa (~74% increase) after chemical tempering at 360 °C during 5.5 h.     

淬火、回火温度对35CrMoA钢的力学性能及低温冲击的影响

阐述了淬火温度、回火温度对 35CrMoA钢力学性能及低温冲击 (- 60℃ )的影响。     

Calculation of Residual Stresses in Glass

Lee, Rogers, and Woo presented a theory for calculating the stresses produced in glass by tempering. Unlike earlier treatments, theirs takes account of the viscoelastic properties of glass. The purpose of this paper is to evaluate this theory by comparison with experimental data. Discrepancies were found to exist between calculated and observed stress distributions. For cases in which glass is quenched from initial temperatures well above the strain point, these discrepancies result from the numerical formulation of the theory, not from any shortcomings of the theory itself. A modification of this formulation brought calculated and observed stresses into good agreement. For quenching from lower initial temperatures , the present theory could not be brought into agreement with experimental data. The reasons for this are briefly considered in the context of the structural heterogeneity of tempered glass and its possible effects on residual stresses.     

A method for calculating the impact strength of sheet glass

Theoretical bases for calculating the dynamic strength of tempered sheet glass under the test conditions envisaged by GOST 5727-88 are considered. Methods for calculating the minimum height of a falling ball, the dynamic stresses appearing in specimens of tempered glass, and the minimum degree of tempering required for providing a specified dynamic strength of the glass are considered.     

Impact strength of polymers 2: The effect of cold working and residual stress in polycarbonates

The influence of cold working on the toughness improvement in glassy amorphous polycarbonates was studied. Cold working processes, namely rolling and. Steckel rolling were used to produce thickness reductions up to 40 percent in flat-strip specimens. The notched Izod impact strength and tensile properties were measured as a function of strip thickness reduction. It was shown that the toughness enhancement in polycarbonates cold worked to low thickness reductions was due to the residual stress state present as opposed to molecular orientation which becomes significant at higher degrees of cold work. Residual stress measurements were made by using the layer removal technique. Residual tensile stresses as high as 2100 psi were present in 1/4-in. cold-rolled polycarbonate at the surface. The maximum stress in the center of the specimen was 1100 psi in compression. The residual stresses at the surface decreased with increasing thickness reduction. The residual stress state for Steckel rolled. 1/2-in. polycarbonate was also measured and found to be more complex than for the thinner samples, The results demonstrated that surface tensile stresses and interior compressive stresses can produce large values of impact strength if the notch is to be machined after cold working. Thus, the values of impact strength measured from the notch Izod specimen are sensitive to the residual stress state in the polymer. This behavior is in contrast to earlier studies on thermally quenched material in which the material was quenched after notching. The thermal quenching produced surface compressive stresses which were also present at the notch tip. The presence of compressive residual stresses at the center of the notch suppressed the formation of a craze leading to toughness enhancement in cold worked polycarbonate strips. It is shown that by control of residual stresses in polycarbonate, strips at least 1/2 in. in thickness can be made to exhibit ductile failure in the notched Izod impact test.     

Variation of Densities and Refractive Indices in Tempered Glass

A knowledge of density distributions in tempered glass is helpful in better understanding the tempering process. Since the densities and refractive indices of a glass are uniquely related, density distributions were determined by a schlieren technique which gives a direct measure of index gradients. The advantages of this nondestructive approach are that it yields the location of each density fraction within the glass and that it is equally applicable to fragments and whole pieces of tempered glass. Thus, it also allows observation of changes in local densities which accompany fracture and the release of internal stresses.     

Impact strength of polymers: 1. The effect of thermal treatment and residual stress

The effect of thermal annealing and quenching on the notched Izod impact strength of several polymers has been studied. Primary emphasis was placed on polycarbonate, but ABS, PVC, polysulfone, and polymethylmethacrylate were also studied. It was determined that residual stresses created by thermal quenching from above the glass transition temperature can have a great effect on impact strength for the polycarbonate, PVC, and polysulfone polymers studied. In fact, it is shown that the thickness transition observed in impact strength for polycarbonates is governed by the residual stresses and not by thickness. In polycarbonates, quenched sheets up to 3/8 in. in thickness have shown impact strengths of 18 ft-lb/in. whereas sheets 1/8 in. in thickness can be embrittled by annealing, showing an impact strength of 2 ft-lb/in. However, it has been shown that this embrittlement results from the absence of residual stress. Residual stresses having maximum values up to 3000 psi (in Compression) have been determined at the polycarbonate sheet surface using birefringence measurement techniques. The existence of these compressive stresses is postulated to restrict the extent of craze growth at the notch tip, and the impact specimen can yield rather than fail in a brittle manner if the stress state is sufficient.     

Influence of different tempering conditions on the adhesion properties of thermoplastic/liquid silicone rubber combinations

The application field of thermoplastic/liquid silicone rubber (LSR) combinations is remarkably wide, ranging from household consumers to the automotive sector. For the application of these combinations, the adhesion is the deciding factor. The adhesion is not only influenced by the applied polymers, but also by a tempering step. In the case of LSR, the industry already uses tempering for improving its mechanical properties. To date, there is no profound knowledge in annealing the combinations thus making the influence on adhesion unclear. Therefore, the influence of different tempering temperatures (80°C, 100°C, and 120°C) and times (1, 3, 6, and 9 h) on adhesion between the thermoplastic (PBT and PA 12) and LSR was examined. The results clearly showed that post‐tempering influences the single components. In the case of PBT, postcrystallization already occurs at 80°C, which is reflected for instance by increasing the degree of crystallinity by about 22%. LSR showed post‐cross‐linking and the release of volatile components. Analyzing the tempering impact on adhesion the peel resistance of LSR and PBT decreased around 23% at 80°C. The covalent bonds at the boundary layer are weakened due to the postcrystallization and the release of volatile components. POLYM. ENG. SCI., 56:849–855, 2016. © 2016 Society of Plastics Engineers     

Multi-stage intermittent drying of rough rice in terms of tempering and stress cracking indices and moisture gradients interpretation

In this study, multi-stage intermittent drying (MSID) of rough rice is considered based on stress cracking index (SCI), tempering index (TI), and total drying/tempering duration for Hashemi and Koohsar varieties experimentally and theoretically. The samples were dried at 60°C for 20, 40, and 60?min and tempered at 60°C for 40, 80, 120, 160, 200, and 240?min after each drying stage. Afterward, the completion of the tempering process was assessed using the TI along with analysis of moisture content kinetics by a simplified drying model. For both varieties, the SCI decreased significantly until continuing the tempering operation to certain durations and increased for longer drying durations in each drying stage. Considering the SCI and the total drying/tempering duration, the tempering durations of 200 and 160?min after 40?min drying in each stage were determined as the best performed conditions for MSID of Hashemi and Koohsar varieties, respectively. The results achieved by the TI were in conformity with those obtained by the mathematical model. It was concluded that the TI and simulation of surface moisture content on a kernel could be applied for estimating the time required for supplementation of the tempering process to eliminate moisture content gradients created inside the kernels during the drying process.     

Effects of cultivar and tempering procedures on crude soybean oil volatiles

The effects of soybean cultivar and tempering procedures on crude soybean oil volatiles were investigated by gas chromatography/mass spectrometry (GC/MS). Varietal differences in volatiles were not obvious. Trends in volatile contents due to tempering were noted primarily when comparing mean peak areas of these compounds in oils stored 16 days at 60°C. Differences in volatiles in response to tempering were not apparent in oils that had not been stored. Equilibration of beans with water resulted in oils with higher volatile contents than those from untempered beans. Steaming lowered volatiles from equilibrated values, and pressure steaming had an even more dramatic lowering effect.     

Effect of tempering approach following cross-flow drying on rice milling yields

Abstract

Three tempering approaches were followed after drying rough rice at 16.3% and 20.5% initial moisture contents (IMCs) using 57?°C/13% RH air at an airflow of 0.56 (m³/s)/m² for 30, 60, and 90?min in an experimentally simulated cross-flow drying column. For the longer drying durations, post-tempering head rice yields were consistently less when the interstitial air from rice from different cross sections of the drying column was allowed to “interact” during tempering than when the rice from these different cross sections was tempered separately; this effect was more prominent at the greater rice IMC. RH of the interstitial air during tempering was measured and used to estimate the minimum tempering durations required for the different tempering approaches.     

玻璃喷雾钢化工艺研究

喷雾钢化工艺理论上比气冷钢化工艺更节能,为了探究喷雾钢化工艺的实际节能效果,本文采用尺寸为40 mm×40 mm×5 mm的平板玻璃进行了气冷钢化和喷雾钢化试验。结果表明:与气冷钢化工艺相比,喷雾钢化工艺在冷却过程中至少节能25.06%;喷雾钢化工艺可以提高玻璃的钢化程度,即破碎后的颗粒数增加了至少8.91%,表面压应力提高了至少12.12%;随着雾载分数的增加,冷却时间减少,节能效果和钢化程度提高。