Surface Hardening Technology Of Tartary Buckwheat And Improvement Test On Hulling Machine

The food and medicinal value of tartary buckwheat is very high,which makes tartary buckwheat has broad market prospects.China is rich in tartary buckwheat resources.However,the existing tartary buckwheat hulling equipment and hulling process are developed based on the experience on hulling buckwheat or other grains.Therefore,there are the problems of low rate of the whole kernel and serious loss of nutrient activity.In order to improve the hulling efficiency of tartary buckwheat,the following researches were carried out in this study.Firstly,based on analyzing physical and mechanical properties of tartary buckwheat related to hulling,a hulling method by hardening tartary buckwheat kernel was proposed.In addition,a set of hulling process was developed.Finally,the first generation hulling prototype was improved,and the hulling performance of the prototype was tested and verified.The main works and conclusions of this study are as follows:(1)The physical and mechanical properties related to hulling characteristics of tartary buckwheat were measured.The results are as follows: when the moisture content of tartary buckwheat samples was 13.32 ± 0.07%,the length of tartary buckwheat kernel was 4.652 ± 0.125 mm,the width was 3.200 ± 0.045 mm,the thickness was 2.982 ± 0.065 mm;the thickness of tartary buckwheat shell was 0.20±0.01 mm.The total number of buckwheat between Ф3.0 ~ Ф3.3 mm was 41.4%.The mass fraction of tartary buckwheat kernel in buckwheat was 75.43 ± 0.48%.The volume expansion coefficient of grain was 1.72.The maximum destructive power of grain was 77.26 ± 5.89 N,and the maximum destructive power of the wheat kernel benevolence was 9.385 ± 0.83 N.(2)By comparing the hardened layer thickness of tartary buckwheat kernel and the gap between the shell and the kernel in different heat treatment methods,a kind of surface hardening technique and hulling process were proposed.By comparing the thickness of the hardened layer and the size of the gap between the shell and the kernel at the maximum cross section of tartary buckwheat with the three kinds of heat treatment,microwave,boiling water short dip and atmospheric steaming,it was found that atmospheric pressure steaming can’t only improve the hardness of tartary buckwheat kernel surface,but also increase the gap between shell and kernel.Then tartary buckwheat processing technology was determined before hulling.Firstly,tartary buckwheat was dipped in warm water at 30 ± 2 ℃ for 40 minutes until the infiltration depth of tartary buckwheat kernel was 0.43 ± 0.19 mm.Secondly,the tartary buckwheat was steamed at atmospheric pressure for 20 minutes,followed by draining the surface moisture so that the surface hardening thickness of tartary buckwheat kernel reached to 0.53 ± 0.14 mm.Finally,the water content of tartary buckwheat was reduced to between 15% and 22% after drying at 65 ℃ for 90 min.(3)To solve the problem of leakage and low grinding ability of the first generation of tartary buckwheat hulling machine,some improvements were made on the first generation prototype.They were: changing the connection between grinding pieces and rubbing pieces to chute connection,increasing the working radius of brushes to promote tartary buckwheat outflow,adding vacuum structure,and adding a filter screen to the feed device to filter hard impurities.(4)The main factors affecting the hulling machine were analyzed,and the optimum hulling parameters were determined.The experimental factors were grinding airbag pressure(15.0 ~ 55.0 kPa),grinding chamber gap(3.2 ~ 6.4 mm),rubbing airbag pressure(15.0 ~ 35.0 kPa),rubbing room gap(3.0 ~ 7.0 mm)and spindle speed 750 r / min).Taking the hulling rate and the whole kernel rate as the experimental index,the single factor test was carried out and then orthogonal test was carried out.Based on the analysis of the test results,the regression equation between the hulling rate and the experimental factors,the whole kernel rate and the experimental factors were established.Then the optimal parameters of the regression equation was optimized and validated.The results show that the hulling effect was the best when the grinding airbag pressure was 15.0 kPa,the grinding chamber gap was 6.4 mm,the kneading airbag pressure was 15.0 kPa,the kneading chamber gap was 3.3 mm and the spindle speed was 729 r / min.At this time,the hulling rate was 84.44 ± 1.04%,and the whole kernel rate was 80.83 ± 0.87%.Compared with the first generation of hulling machine,hulling rate was decreased by 5.67%,but the whole kernel rate was increased by 48.99%.