The Statistical Mixture Design of Rice Polishing Cylinder Surapong Bangphan, Sukangkana Lee and Sermkiat Jomjunyong  Abstract—This study presents the application of the mixture design technique in generating the optimal mixture for the rice mill cylinder when using the new materials. The three new materials; Quartz were chosen from three different regions of Thailand in order to compare with the imported materials; Emery. Quartz used in this study are natural stone and found in Thoen district (Lampang province) , Bophloi district (Kanchanaburi province) and from Wiang Pa Pao district (Chiangrai province) respectively. Design of Experiment (DOE) was used as a tool in order to generate the suitable mixture. All 10 mixtures were generated by the Simplex Centroid Design technique with Special Cubic type. ANOVA and Regression was used for analysis. In this model, three control factors: x 1 , x 2 and x 3 represent Quartz no.16, no.18 and Reused Silicon carbide no.18, respectively. The process variables were the temperature (z 1 ) and the paddy moisture content (z 2 ). The rice milling tests were conducted on kow dauk mali 105 rice. After milling, the percentage of good rice and the wear rate of polishing cylinder were calculated and analyzed using Regression analysis and Analysis of Variance (ANOVA). The response optimization was quartz from Thoen district. At a significant level  = 0.05, the values of Regression coefficient, R 2 (adj) were 78.62 % And R 2 (adj) were 70.67 %. The Optimal mixture gave 92.136% good rice and the wear rate of 1.887 g/hr. Keywords—Abrasive Materials, Rice Polishing Cylinder, Mixture Design, Design of Experiment I. INTRODUCTION The quality of milled rice are depends on many factors such as rice strain, the rate of feeding, clearance between a rubber and abrasive cylinder, paddy moisture content which usually are controlled not to be exceed 14% ect. But the most important factor is the type of the abrasives [1]-[2]. Furthermore, one of the major problems encountered is the wear of the polishing stone i.e. stones come off or chip from the cylinder and mix in the milled rice. This seems to be the Surapong Bangphan is Ph.D. Candidate Department of Industrial Engineering, Faculty of Engineering, Ubon Ratchathani University 85 Satholamark Road, Warin chamrap District, Ubon Ratchathani, Thailand, 34190 (corresponding author to provide phone:(+66)0-4535-3300; fax:(+66)0- 4535-3333 ;e-mail : pong_pang49@yahoo.com). Sukangkana Lee ASST. PROF. Ph.D. Department of Industrial Engineering, Faculty of Engineering, Ubon Ratchathani University, 85 Satholamark Road, Warin chamrap District, Ubon Ratchathani, Thailand, 34190 (e-mail: Sukangkana.lee@gmail.com). Sermkiat Jomjunyong ASSCO .PROF. Ph.D. Dean of Engineering Faculty, Chiang Mai University, Chiang Mai , Thailand. 50300 (e-mail:sermkiat@chiangmai.ac.th). common problem but for the farmer, wear of stone reduces the cylinder life and can increase milling cost. Also, the polishing cylinders are locally made and the qualities of the cylinder are often not consistent. Furthermore, the mixture of the abrasive cylinder is varied [2]. The major rice polishing technique in Thailand is the abrasive type. The major mixture of polishing cylinder consists of Emery grain, Silicon carbide, Calcined Magnesite and Magnesium chloride solution. The Emery stone is a major abrasive medium containing about 50 wt%. The Emery stones used in Thailand are imported from Europe are dark brown to black in color and have high hardness. However, it was found that the quality of this imported product is descending i.e. hardness values up on the pureness. In addition, good quality Emery stone is becoming rare resulting in progressively cost increasing. It was reported that the imported emery stone were more than 1.25 million US dollar per annual [3]. Therefore, there is an attempt in replacing Emery stone with other materials available in Thailand. Recently, Bangphan and Lee., reported that the Quartz has appropriate abrasive characteristics such as sharp edge, hardness, natural substance ect., therefore, it has a potential for rice polishing cylinder compared with the Emery grain [2]-[3]. The mixture design and analysis is an important methodology for development and optimization of food products [4]-[6]. Mixture designs are also among the most widely used tools for product formulation [7]-[11]. Therefore the purpose of this paper is to generate the suitable mixture from alternative domestic composite materials using Design of Experiment (DOE). This would lead to cost reduction and create more alternative choices for abrasive medium. II. EXPERIMENTAL PROCEDURE A. Materials Preparation Quartz is a natural mineral found in many areas in the Western and the Northern region of Thailand. The chemical formula of Quartz is SiO 2 . Quartz contains 46.7 wt %Si and 53.6 wt %O. The Mohr scale hardness of quartz is equal to 7. Quartz used in this experiment has white color. Samples were collected from Bo Phloi district in Kanchanaburi province, Thoen district in Lampang province and from Wiang Pa Pao district in Chiangrai province. Imported silicon carbide was replaced by reused silicon carbide obtained from the Alumina- Silicon carbide plate. Reused silicon carbide contains 50.0 wt %Si and 21.0 wt% C. All replaced materials were mechanically crushed and meshed to sizes. The binder paste or Proceedings of the World Congress on Engineering 2008 Vol II WCE 2008, July 2 - 4, 2008, London, U.K. ISBN:978-988-17012-3-7 WCE 2008