EFFECTS OF SCREW RESTRICTIONS ON THE PERFORMANCE OF AN AUTOGENOUS EXTRUDER

The Brady Crop Cooker is a low-cost autogenous extruder capable of manufacturing products suitable for human consumption in less developed countries (LDC). Versatility is achieved by the design of the extruder which directly affects its operation. One such design aspect is the inclusion of internal screw channel restrictions. The effects of location and number of restrictions on operation and product quality were studied. Results indicated that restrictions affected the location of the mechanical energy input and therefore temperature profiles along the screw. Increasing the number of restrictions also promoted cleavage of starch molecules due to the resulting higher shear in the screw channel.     

MODELING A TWIN SCREW CO-ROTATING EXTRUDER1

This work desribes the simulation of a twin screw co-rotating extruder. Based on a uni-directional analysis, the temperature and pressure profiles within the extruder are predicted from knowledge of feed and extruder characteristics. A non-Newtonian, non-isothermal viscosity model is used to describe the materials rheology. the analysis covers an evaluation of conditions within the solid conveying zone, the melt pumping zone and a melt shearing zone achieved by reverse screw elements. the total energy input (both mechanical and through the barrel) is also evaluated. the simulation work has proved satisfactory in the design and optimization of extruder operation.     

变频器在纺丝螺杆调速中的应用

介绍在纺丝螺杆挤压机的调速方法中 ,用交流变频调速代替直流调速。改进后的调速系统性能良好 ,故障率低 ,且可节电 33%。     

卧式高速自动滚丝机的设计

综合滚丝和搓丝的优点采用轮弧滚丝法，用圆柱滚轮和圆弧搓丝板的组合，基于无切屑滚压成型加工工艺方法，设计了卧式高速自动滚丝机．该机可连续加工，生产率高，自动化程度高，可广泛应用于中、小型制钉企业和包装、木制品加工等行业     

可转位式转子槽粗铣刀的廓形设计探讨

本文讨论了可转位式阴转子槽粗铣刀的廓形拟合问题。这种铣刀是将圆柱形硬质合金刀片按切向倾斜安装在盘形刀体上,切削时圆弧刀刃在选定点的基面内的运动轨迹为椭圆,利用电子计算机可求出刀片的最佳安装位置,使椭圆曲线逼近理论廓形,误差在允许范围之内。     

TWIN SCREW EXTRUSION OF PINK SALMON MUSCLE: EFFECT OF MIXING ELEMENTS AND FEED COMPOSITION

The effects of type of mixing element in the screw configuration and feed composition on specific mechanical energy input and product attributes during twin-screw extrusion were investigated. The mixing elements studied were kneading, reverse screw and combination of kneading and reverse screw elements. The feed composition was changed by altering the ratio of rice flour to pink salmon muscle. Incorporation of mixing elements increased the specific mechanical energy, and water solubility index; but decreased apparent density and Warner-Bratzler shear stress. Expansion ratio was maximum with kneading elements. However, reverse screw and combination produced extrudates with lesser expansion than that obtained using conveying screws with no mixing element. Increasing the fish solids content in the feed decreased specific mechanical energy, expansion ratio, and water solubility index; but increased the shear stress and apparent density. The shear stress for 0% and 30% fish solids blends were not affected in the expansion ratio range of 3 to 10. Water solubility index and shear stress were linearly related to specific mechanical energy and apparent density respectively.     

NEW MELT CONVEYING MODELS FOR A SINGLE SCREW EXTRUDER1

The flow theory in an extruder is fundamental to the study of extrusion technology. Present analytical solutions of the flow theory used in many studies give significant overpredictions of the volumetric flow rate due to erroneous boundary conditions used. Modified flat plate models with and without considering side wall effect and a coaxial cylinder model for Newtonian fluids were derived in this study using new boundary conditions confirmed by Choo et al. (1980). Using experimental data from published literature, it was found that the volumetric flow rates in the extruder were better predicted by these models than the numerical solutions or the original analytical solutions.     

双螺杆挤出机生产PP荧光增白母粒

介绍了双螺杆挤出机的工作原理、优点。对荧光增白母粒的生产工艺进行了探索、研究。     

MODELING the AVERAGE SHEAR RATE IN A CO-ROTATING TWIN SCREW EXTRUDER

A procedure similar to the one commonly used with mixers has been utilized to develop a model for estimating the shear rate in co-rotating twin screw extruders. Newtonian and non-Newtonian fluids were used to estimate the average shear rate for three screw configurations of a Baker Perkins (MPF-50D) twin screw extruder. As would be expected, the shear rate was highly correlated to the screw speed. At a given screw speed, 30 forwarding paddles generate the highest rate of shear, followed by feed screws and single lead screws. No data was found in the published literature to provide comparison with the results of this work. However, the model has performed well in heat transfer analysis of twin screw processes. The procedure is sensitive to screw configuration, accounts for the shearing effects in the different regions within the extruder barrel, and covers a range of screw speeds (100–400 RPM) typical of what is encountered in industrial pilot plants. Even though much more work remains to be done before the shear rate can be confidently characterized for composite screw configurations, this technique provides a sound foundation.     

PROPERTIES of CROSS-LINKED STARCH PRODUCED IN A SINGLE SCREW EXTRUDER WITH and WITHOUT A MIXING ELEMENT

Starch was extruded with sodium hydroxide and sodium trimetaphosphate in order to cross‐link it in a single‐screw extruder with and without a mixing element at constant screw speed of 90 rpm in the first set of experiments and at similar mean residence time controlled by screw speed in the second set of experiments. For the screw without mixing element in the second set of experiments, screw speed was adjusted to give the similar residence time as the single‐screw extruder with mixing element at 220 rpm. Phosphorus content and pasting curves of extrudates showed that starch was cross‐linked during extrusion. Replacing the screw without mixing element by the screw with mixing     

PHYSICOCHEMICAL PROPERTIES OF TEXTURIZED MEAT ANALOG MADE FROM PEANUT FLOUR AND SOY PROTEIN ISOLATE WITH A SINGLE‐SCREW EXTRUDER 1

The objective of this study was to establish conditions for the texturization of soy protein isolate and peanut flour mixture using a single‐screw extruder. The effects of feed moisture, screw‐speed, and barrel temperature on the characteristics of the texturized products were studied. Feed moisture was the most important factor affecting the texture. Feeding ingredients with 22% moisture had the highest water absorption and expansion indices, and Hunter L value (P < 0.05). When the screw speed was above 180 RPM, the meat analog had a 12% decrease in the expansion index and a 5% decrease in moisture content (P < 0.05). When the barrel temperature was increased to 165C, there was a 12% decrease in the water absorption index, and a 23% decrease in the expansion index of the meat analogs (P < 0.05). Overall, an acceptable meat analog could be successfully produced with 22% moisture in the raw ingredient, screw speed at 140 RPM, and barrel temperatures at 150, 155, and 160C for the three temperature zones respectively.     

SCREW CONFIGURATION EFFECTS ON RESIDENCE TIME DISTRIBUTION AND MIXING IN TWIN-SCREW EXTRUDERS DURING EXTRUSION OF RICE FLOUR

Screw configuration effects on residence time distribution and mixing were investigated during twin-screw extrusion of rice flour. The type, length, and position of mixing elements, and spacing between two elements significantly affected residence time distribution and mixing. Mean residence time (t_mean) and extent of mixing were lower for screw profiles with KB than those with RSE. A systematic increase in t_mean was observed as the mixing elements were moved farther away from the die, with longer elements, and with increased spacing between two elements.     

ANALYSIS of the HELICAL SCREW RHEOMETER FOR FLUID FOOD

The Helical Screw Rheometer (HSR) is being evaluated for rheological measurements of fluid food suspensions. the HSR consists of a helical screw enclosed in a tight fitting cylinder. With a closed system the inner screw is rotated creating a linearly increasing pressure differential along the axis of the screw, which is proportional to the viscosity of the fluid. This paper presents theoretical one- and two-dimensional flow analyses for Newtonian fluids using both rectangular and cylindrical coordinates. For non-Newtonian fluids a one-dimensional rectangular analysis was developed using the power law model.     

差动螺杆加料称Q-2调速系统的改造

本文对直流调速系统存在的问题作了阐述,对交、直流调速系统,作了简明对比。根据变频调速的优越性,对现有的直流调速进行了改造,解决了生产中存在的问题。文章还简要介绍了改造过程的设计及调试。     

APPLICATION of LASER DOPPLER ANEMOMETRY to MEASURE VELOCITY DISTRIBUTION INSIDE the SCREW CHANNEL of A TWIN-SCREW EXTRUDER

Velocity measurements inside the screw channels of a co-rotating, self-wiping twin-screw extruder (ZSK-30) have been carried out using the noninvasive technique of Laser Doppler Anemometry. A two-dimensional Argon-ion laser Doppler system was used to measure tangential and axial velocity components in one of the screws, away from the intermeshing zone. Heavy corn syrup with naturally occurring particles was used in the extrusion experiments. the measured tangential velocity distribution agreed with the expected distribution for a Newtonian fluid. Measurements also indicated that near the screw root and away from the flights, shear rates were substantially lower as compared to the shear rates near the barrel. the results indicated that this technique is suitable for making velocity measurements in a twin-screw extruder using model fluids.     

SCREW CONFIGURATION EFFECTS ON STARCH BREAKDOWN DURING TWIN-SCREW EXTRUSION of RICE FLOUR

Screw configuration effects on starch breakdown and ext rudate porosity were investigated during twin-screw extrusion of rice flour. the type, length, position, of mixing elements and spacing between two elements significantly affected molecular breakdown of starch in rice flour and extrudate porosity. Generally, screw profiles with reverse screw element produced more starch breakdown and porous extrudates than those with kneading block. A systematic increase of starch breakdown was observed as the mixing elements were moved fart her from the die, with longer elements, and with increased spacing between elements. Extent of starch breakdown affected porosity of extrudates. Extrudate porosity decreased systematically with increasing distance between die and mixing element, with larger spacing between the elements, and by moving two elements (with same spacing) farther from the die, irrespective of the element type and length. Porosity increased with increasing die temperature.     

BARLEY β-AMYLASE HYDROLYSIS of STARCH DURING TWIN SCREW EXTRUSION

Effect of moisture content, screw rpm and β-amylase dose on the rate of maltose production in a Baker-Perkins twin screw food extruder has been studied. Fifteen experiments were conducted using a fixed screw configuration at a fixed mass flow rate of 15 kg/h, under isothermal conditions (t=57°C) and a pH of 5.5. Each of the three variables was found to have a significant effect (P<. 05) on maltose production. Using response surface regression analysis on the experimental data, a quadratic objective function was derived. the function was optimized, subjecting it to three explicit boundary conditions, using the adaptive complex method. the optimization process yielded a maximum maltose production of 34% at 54% moisture content, 30 rpm screw speed and 157 units of enzyme/g of starch. the extent of saccharification was about 30%.     

EFFECT of SCREW CONFIGURATION and SPEED ON RTD and EXPANSION of RICE EXTRUDATE

The influence of screw configuration and screw speed on the residence time distribution and product expansion was determined for rice meal processed in a corotating twin screw extruder. Screw speed had strong effect on the E(t)- and F(t)-diagrams, with the mean residence time varying inversely with screw speed from 206 s to 256 s. the F-diagram was modeled by the combination of perfect mixing and plug flow. the P estimates, which express the fraction of material in plug flow, varied inversely with screw speed from 0.41 to 0.55 for the operating conditions in this study. Both screw configuration and screw speed were statistically significant to the expansion ratios of rice extrudate, with the expansion in the height ranging from 2.98 to 4.13.