碾米机碾白理论的研究应用和机型（二）

5　碾白机理[5]碾白运动是由米粒的碰撞和翻滚运动组成的 ,这是碾白的基本因素。5 1　碰撞运动分 3类 :第 1类是米粒和碾白辊接触获得速度和压力时的碰撞 ;第 2类是具有速度的米粒在一定的碾白压力下相互碰撞 ;第 3类是具有速度的米粒在一定的碾白压力下和碾白室内壁、碾白室中其他构件的碰撞。第 1类碰撞是碾白工作的基础。5 1 1　擦离碾白的碰撞 (工作图略 )第 1类碰撞 :米粒和铁辊筋前向面碰撞时产生的冲击力 ,作用于米粒的皮层和胚乳结合处。筋对米粒施加压力 ,在米粒皮层面和筋之间产生摩擦力。冲击力和摩擦力形成力偶 ,力矩为皮层厚…     

基于离散元法的糙米碾白过程仿真初探

碾白是谷物加工中重要的加工工序,为了研究该过程中糙米的破碎率,基于离散元方法,以EDEM软件为平台,对糙米碾白进行离散元仿真。仿真糙米颗粒破碎,通过离散单元法的Hertz-Mindlin黏结模型,用"黏结键"将更小的球形颗粒黏结在一起,当颗粒受力达到其破碎强度时,"黏结键"断裂,从而可以有效模拟糙米的破碎。通过对糙米碾白仿真,得出糙米的动力属性和破碎率都较符合实际情况。     

多场因素对糙米破碎影响实验研究

运用MNSW型碾米机对糙米进行碾白实验,探究碾辊转速、碾白温度与糙米碾白时间对糙米破碎率的影响。根据预实验结果确定碾辊转速与碾白时间梯度,标定各参数,保证数据准确后进行实验。对实验结果进行统计,通过Origin软件绘制破碎曲线,并对实验进行评估。结果表明在低温碾米时,碾辊转速在1 200～1 400r/min范围内,糙米破碎率较低,碾白效果好;碾白时间在30～40S时成品米白度已符合国家粮食色泽鉴定标准,碾白时间越长糙米破碎率越高。     

碾米机自动停止装置

专利说明本发明为有关工作负荷减轻时,电动机能够自动停止的碾米机控制电路。原有的一机出白碾米机,其结构简单,价格便宜,使用也很方便。但在碾白过程中,若糙米流量减小时,碾白室内的压力则降低,碾白辊处于空转状态而使米粒移送困难,长时间停留在碾白室内。由于米粒受到过碾作用,使碎米量增加。     

碾米机碾白运动速度的理论计算

碾米机的碾白过程由于受到多种因素的影响,因此,碾米机的碾白理论是十分复杂的。但是从长期的生产实践和理论研究工作中证实,米粒在碾白室内的运动速度和受压状态,是影响碾米机碾白效果的主要因素,也是研究碾米理论问题的本质。许多研究者围绕米粒在碾米机碾白室内的运动速度和压力,从各个角度对碾白理论进行了许多有益的研究和论述,以求碾米机最佳的工作参数。本文将就有关碾米机碾白运动的速度理论计算进行探讨,以响当前对碾米机碾白理论的讨论。     

橡胶籽冲击特性研究

用碰撞的原理破碎橡胶籽是一种重要的方式,为了研究橡胶籽在碰撞过程中的破碎力学规律,采用RFP数据采集系统对橡胶籽所受的瞬时碰撞力进行动态测量试验,分析高度、角度、初速度对橡胶籽所受碰撞力的影响。试验结果表明:高度从0.5m提高到2.0m,碰撞力从1.712N增加到3.461N;角度从30~°增加到90~°,碰撞力从0.831 N增加到2.401N;初速度从0.5m/s增加到5.0m/s,碰撞力从1.781N增加到3.311N;通过SPSS软件进行单因素曲线估计,并拟合出各因素与碰撞力的最优曲线关系图,经分析得出高度、角度和初速度均与碰撞力呈较强正线性相关关系,在此基础上进行多因素线性回归分析,根据试验数据推出具有显著性的公式,并用插入法验证了公式的准确性;研究结果可结合不同情况下的橡胶籽破碎力,设计合理的破壳机结构,使得橡胶籽进入破壳机后能够更有效地完成脱壳工作。     

粒型和含水率对籼糙米力学特性的影响

大米加工过程中会产生破碎籽粒,降低整精米率和影响大米食用品质。研究3种籼糙米的力学特性影响因素(含水率、糙米粒型)与籼糙米碾白品质之间的关系,结果表明,籼糙米含水量增加会逐渐降低压缩力、剪切力、三点弯曲力的破碎力值,含水率从12.88%增加到16.46%时,压缩破碎力值、剪切破碎力值和三点弯曲破碎力值分别降低了22.17、6.92 N和2.38 N。沙软粘、美香粘和天龙一号的厚度平均值为1.59、1.67 mm和1.65 mm,三点弯曲破碎力平均值分别为17.20、18.28 N和20.18 N。沙软粘糙米有31%的籽粒厚度为1.60 mm,美香粘糙米有30%的籽粒厚度为1.70 mm,天龙一号种糙米有46%的籽粒厚度为1.65 mm。达到加工精度即碾减率为10%时,沙软粘、美香粘和天龙一号的碎米率分别为18.50%、16.30%和16.60%。因此厚度均匀性高的糙米碾白产生的碎米少。     

经溜槽装入筒仓的玉米减损效果试验

不同含水率(11.64%、13.54%、15.43%、16.43%w.b.)的玉米从仓顶入仓,一种工况是玉米经直溜槽与螺旋溜槽流入筒仓与仓底碰撞;另一种工况是玉米从仓顶自由下落与仓底碰撞。测定2种工况下落碰撞的玉米籽粒破碎率,并使用质构仪测定2种碰撞后的玉米籽粒及未碰撞的玉米籽粒的破坏力和破坏能。结果表明:玉米的含水率越大,经过碰撞后破碎率越小;不同含水率的玉米,经过溜槽下落碰撞的平均破碎率是3.84%,自然下落碰撞的平均破碎率是7.65%;不同含水率的玉米,经过溜槽下落碰撞的玉米籽粒的破坏力平均值是234.96 N,破坏能平均值是49.71 m J,自由下落碰撞的玉米籽粒的破坏力平均值是219.09 N,破坏能平均值是42.43 m J;说明溜槽起到了缓冲碰撞的作用。     

上吸风环形风道碾米机设计与试验

针对卧式碾米机收集到的米糠混有碎米的缺陷,设计一种具有环形风道的上吸风式碾米机,可直接对米糠和碎米进行分离收集.运用Fluent对该新型碾米机流场进行分析,采用多孔介质模型模拟碾白室内糙米对气流的阻碍作用,并搭建样机利用PIVlab软件进行观测,结果表明:当上吸风口与喷风机风速分别为6 m/s和10 m/s时,环形风道内形成环形绕流,流速分布均匀、流场稳定,平均风速为4.1～4.6 m/s,垂直方向分速度为2.0～6.5 m/s,介于米糠与碎米悬浮速度之间;气压隔板形成狭管效应,上升气流从1.4 m/s加速至3～4 m/s;喷风槽附近米筛网内外压差最大约5550 Pa;试验证明碎米与米糠的分离效果良好.     

基于离散元法砂辊碾米机碾白室内物料运动仿真

以立式砂辊碾米机为例,运用离散元法分析软件EDEM对碾白室内物料运动过程进行仿真计算。建立碾白室和糙米籽粒的离散模型,设置相应的参数,对砂辊碾米机碾白室内物料流进行离散元模拟。得出碾白过程中糙米籽粒运动轨迹曲线、受力大小,将这些数据以图表形式显示便于分析仿真结果,研究成果为研究碎米产生机理提供了参考依据。     

不同脱皮设备对青稞米加工碎米率的影响研究

本实验采用青稞为原料,对比了青稞米加工中柔性脱皮机和碾米机对碎米率的影响。分析了两种脱皮设备对青稞麸皮中淀粉含量的变化趋势和原因,探讨了入机水分、脱皮率、灭酶、筛分工序等对青稞米加工过程中碎米率的影响。研究结果显示,青稞米加工最佳的入机水分为16%;碎米率随着脱皮率升高而升高,碾米机的碎米增长率高于柔性脱皮机;脱皮率＜10%时,灭酶对碎米率无显著性影响,脱皮率＞10%时,灭酶处理使碎米率显著上升;脱皮率＞10%时,筛分工序能够降低碎米率和提高青稞米粉的亮度;柔性脱皮机能缓解青稞制米时碾米机过碾的问题,降低了富葡聚糖相中淀粉的含量。     

储粮横向通风多尺度热湿耦合传递研究

温湿度是影响粮食安全储存的重要因素,为保证储粮安全,采用机械通风,使粮堆和粮粒的温度和水分含量可以得到有效控制。该文基于多孔介质的传热传质理论,建立了仓储稻谷通风过程中粮堆内部流动和热湿耦合传递的数学模型以及粮粒的热量传递和水分输运模型。采用计算流体力学的方法,从粮堆尺度和粮粒尺度,分析了机械通风过程中仓储粮堆和粮粒内部的温度、水分分布规律。研究发现,通风过程阶段,粮堆内部温度降温显著,粮堆整体平均水分呈降低趋势,且粮堆内部温湿度受外界环境温湿度的影响很大;研究还发现粮粒水分扩散速度远小于温度扩散速度。研究结果可以为储粮横向通风保水降温的工作以及粮堆局部霉变、发热和害虫的发育的预防提供参考。     

干法、半干法和湿法磨粉工艺制备的糙米米线品质研究

采用干法、半干法和湿法3种方式将糙米磨粉制备糙米米线,干法粉碎强度10～40 Hz,半干法调节含水量为20%～35%及湿法料液比为1∶1、1∶2、1∶3、1∶4,研究了3种磨粉方式对糙米米线蒸煮品质和质构性质的影响,并分析了糙米磨粉颗粒细度及损伤淀粉含量与糙米米线蒸煮品质的相关性。结果表明,磨粉方式及磨粉工艺条件显著影响糙米米线的蒸煮、质构和感官品质,糙米磨粉颗粒细度与糙米米线最佳蒸煮时间显著正相关,与糙米米线断条率显著负相关。糙米磨粉损伤淀粉含量与糙米米线最佳蒸煮时间、硬度显著负相关,损伤淀粉含量与糙米米线断条率显著正相关。干法粉碎强度10、半干法水分调节含量20%、30%和35%、湿法粉碎料液比1∶3～1∶4时,糙米米线的品质较好。     

Effects of Combine Harvesting on Head Rice Yield and Chaff Content of Long and Short Grain Paddy Harvest in Sri Lanka

Paddy harvesting is the process of collecting the mature rice crop from the field which consists of activities such as cutting, handling, threshing and cleaning. Cutting, threshing and cleaning plays an important role to reduce postharvest losses. Lower performance of traditional harvesting process, labour shortage, reduced turn-around time and use of high yielding varieties have inevitably forced farmers to shift into mechanical grain harvesting in Sri Lanka. Rice milling is carried out to produce an edible polished or white rice product from harvested rough rice. Head rice yield is considered for marketing purposes because broken rice has low price in the market. Field survey was conducted in Polonnaruwa, Ampara and Hambanthota districts to identify most popular types of combine harvesters operating in the above districts. Paddy samples were collected from harvest of two most popular models of combine harvester in triplicate. Paddy sample of 1m² area from every paddy field were harvested separately by manual harvesting followed by manual threshing and cleaning in laboratory as control sample of relevant paddy field. Moisture content of the paddy grains were measured in the paddy field using digital moisture meter before harvesting. Paddy samples were subjected to sun drying until the moisture content come down to 14±1% before the quality analysis in the laboratory. Each paddy sample was analyzed for moisture content, chaff percentage and head rice yield percentage (HRY). Paddy was milled using laboratory scale rubber roll sheller and abrasive polisher. Chaff content percentage was measured by adding 100 ml of paddy to water and volume of chaff was measured using graduated cylinder. HRY was calculated dividing the weight of grain partials, which are larger than the ³/₄ of the grain, by weight of paddy sample. HRY between the two combine harvesting machine models evaluated were not significantly different at p<0.05 and also it was not significantly dependent on the harvesting methods such as combine harvesting and manual harvesting. The chaff content was significantly higher in model-2 in comparison to control sample for long grain paddy while model-1 was not significantly different with control sample for short grain paddy.     

优质籼米地下仓储藏过程中品质变化

为探索成品粮绿色、安全的储藏方法,在南方高温高湿地区,利用地下仓储藏黄花粘和籼优998两种优质籼米,定期检测水分、碎米总量、小碎米率、垩白粒率、黄粒米、直链淀粉、品尝评分值、色泽气味、不完善率、害虫虫口密度等指标。实验结果显示,实验期间,大米水分呈小幅下降;2种大米不生虫时间长达13个月;小碎米率、色泽气味等指标无显著性变化;碎米总量、黄粒米、不完善粒含量小幅增加,直链淀粉含量逐渐增加,但均未导致大米质量等级下降;垩白粒率显著增加,品尝评分值显著下降,且均造成大米质量定等下降。根据国家标准《大米》的规定,籼优998于储藏3个月后,质量定等由二级降为三级,储藏6个月后,已不属于优质籼米,黄花粘于实验结束后仍为优质籼米三级。说明地下仓具有良好的保湿、保鲜和害虫抑制效果,优质籼米耐储性能与储藏条件和品种均相关。     

Incidence of open crack formation in short-grain polished rice during soaking in water at different temperatures

The incidence of open crack formation in short-grain polished rice during soaking in water at different temperatures was investigated. Rice with a moisture content of 10.4% (wet basis) was soaked in distilled water for 90 min at 15 °C, 25 °C or 35 °C, and the rate of open crack formation and the moisture content of the rice during soaking were measured. Results show that the rate of open crack formation increased with decreasing the soaking temperature. A model based on the relationship between the tensile stress calculated from the moisture gradient in a rice grain and the tensile strength calculated from the average moisture content of a rice grain provided a reliable qualitative estimate of the difference in the rate of open crack formation at different temperatures. It can be concluded that water diffusion into rice grains should be accelerated to prevent the formation of open cracks.     

Physicochemical, mechanical and thermal properties of brown rice grain with various moisture contents

The effects of moisture content on the mechanical and thermal properties of either a short‐grain variety (Akitakomachi) or two long‐grain varieties (Delta and L201) of brown rice were studied. Total starch contents of the three varieties were comparable, but the amylose content of L201 was significantly higher than that of the other two varieties. The maximum compressive strength of brown rice grain was much higher than the maximum tensile strength. L201 showed the highest maximum compressive and tensile strengths. The phase transition temperatures (glass transition temperature T_g and melting temperature T_m) were examined by differential scanning calorimetry. The T_g and T_m for L201 were higher than those for Delta and Akitakomachi. The maximum compressive strength, maximum tensile strength, T_g and T_m for the three varieties of brown rice grains decreased with increasing moisture content. The T_g of individual brown rice kernels decreased from 53 to 22 °C as moisture content increased from 12 to 25% wet basis. A statistical model was calculated by using linear regression to describe the change in T_g in terms of moisture content.     

Modeling of mass transfer and initiation of hygroscopically induced cracks in rice grains in a thermally controlled soaking condition: With dependency of diffusion coefficient to moisture content and temperature – A 3D finite element approach

Rice grains develop cracks and eventually break during soaking. Since published simulation studies on hygroscopic swelling induced cracking were scarce, the present study attempts to model the mass transfer of moisture and hygroscopic swelling of rice grains using principles of finite element analysis performed in three dimensions (3D). Ultimately, to understand the crack formation in response to the existence of tensile and compressive stresses caused by moisture gradient in the grain during soaking. An empirical equation was developed to establish dependency of the diffusion coefficient of rice to both moisture content and temperature. Using a 3D replica of short grain japonica rice, the modeling was carried out using existing laws of diffusion and was validated using experimental data. Results showed that the rate of moisture diffusion and hygroscopic swelling were found to increase with increase in soaking temperature. The internal stress, however, was found to decrease with increase in soaking temperature. The simulated moisture content and increase in volume of rice grain were favorably in agreement with experimental results. Highly stressed sites that are prone to breakage have been clearly identified.     

基于原位观测的糙米籽粒力学特性研究

采用原位观测结合质构仪手段,研究稻谷加工过程中糙米籽粒受挤压力时的力学-结构特性,分析了压距等因素下糙米籽粒的挤压作用过程。结果表明：糙米所受的挤压力随压距的增大而增大,在外力冲击下,籽粒内部产生抗压应力,随之产生裂纹。粳米籽粒存在脆性,先产生裂纹,在挤压力增大之后,裂纹扩展,最后籽粒断裂;籼米和连糯籽粒脆性更明显,在产生裂纹后,短时间裂纹扩展,籽粒迅速断裂;速率对粳米所受挤压峰值力无明显影响;粳米所受的挤压峰值力随籽粒含水率的上升而减小,随温度的上升而减小,裂纹数量随浸泡时间的上升而增加,籽粒破坏程度随温度的上升而增大;3种米型在相同压距和压缩速度下的受挤压峰值力为：籼米>粳米>连糯。     

Effect of radio frequency heating on the mortality of Rhizopertha dominica (F.) and its impact on grain quality

The use of radio frequency (RF) heating to reach temperatures lethal to stored product pests has significant potential. We examined the lethal effects of RF on the stored grain pest, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), under four different RFs, three types of grain, and different moisture contents of rice. The quality of two rice cultivars, after RF heating, was also tested. When heated to 58 °C by RF, R. dominica adult mortality reached 100%. The mortality of R. dominica adults reached 100%. The fastest mortality rate occurred at 50–52 °C. With an increase in RF, the time needed to attain a lethal temperature decreased. The heating time to reach 100% mortality differed among the three types of grain; for example, the heating time of wheat was faster than corn or rice. Kernel size and chemical composition was the main factor influencing the RF lethal rate in the different types of grain under the same experimental conditions. There was a significant linear relationship between moisture content (m.c.) and heating time (Y = −38.05 X + 15.501, R = 0.9803) in rice. RF heating of rice to 58 °C did not significantly affect milling quality, storage quality, or seed quality. Thus, heating time, types of grain, and the m.c. of the grains are three important factors that should be considered in RF heating to control stored product pests. These results indicate that RF heating could be an effective physical method for killing stored grain pests.