Design and Development of a Low Cost Grain Flour Blender

One of the major solutions to reduce the consumption of wheat flour in the country is to introduce flour mixtures blended with rice flour and other locally produced grain flour to the market and flour based food processors, since it has a great demand even now. Blending equipment are essential to produce flour mixtures with uniformly distributed particles. Flour blending machines are available in the international market, but they are very expensive and those are not at an affordable price to purchase even for medium scale flour producers. Therefore, a low cost grain flour blender was designed and developed to introduce for flour producers. Developed grain flour blender was tested by blending rice flour with wheat flour to the ratio of 3:7 which is generally used for preparing bread. It was found that the minimum blending time required for giving a uniform mixture was 3 minutes when the equipment was operated at 51 rpm. Capacity of the blender was 50 kg per batch and it was operated by a 3 hp electric motor. When the developed flour blender is compared with the available blending machines in the international market with same capacity, it was found that the developed flour blender reduces the blending time and the initial cost of the machine is reduced by 5 times while the flour blending cost is reduced by 25%.


Introduction
Increasing the availability of rice flour and other locally produced grain flour by developing flour processing industry in the country and popularizing food prepared with theses flour among the people, consumption of wheat flour could be reduced to a remarkable level. One of the major solutions to reduce consumption of wheat flour further is introducing flour mixtures blended with rice flour and other locally produced grain flour to the market and flour based food processors, since it has a great demand even now. According to the research findings, any wheat flour based food item can be prepared adding 20% rice flour by following the same manufacturing methods. Therefore blended rice flour can be introduced to bakeries and other flour based food industries and also to the wheat flour consuming people in the upcountry to make their favourite food item called roti. Some bakery owners have now started to prepare bakery products such as bread, biscuits and cake with rice flour or wheat flour blended rice flour. In this regard, the problem faced by the bakery owners and other flour based food manufactures is finding suitable flour mixtures. However, a few flour processors in the country have introduced blended flour (ex: rice flour with wheat flour, rice flour with finger millet flour etc.) to the market and there is a good demand for their products. Blending of flours is basically done by these processors manually with the help of spoons and plastic vessels. This method being time consuming, laborious and inefficient, the final product is not uniform in composition. Flour blending machines are available in the international market, but they are very expensive and those are not affordable even for medium scale flour producers. Therefore, a low cost grain flour blender was designed and developed under this project to introduce for flour producers. Performance of the developed equipment was evaluated.
ENGINEER ingredients throughout each other, in an effort to produce a uniform distribution of each component throughout the mix [1].
Mixing is defined as a shuffling type unit operation process involving both large and small particle groups and even individual particles. Mixing is an energy consuming process which produces a random distribution of particles. It is dependent on the probability that an event happens in a given time and once the desired mixing has been attained, it is essential that the particles in the mix cease movement so that the system may exist in a state of static equilibrium without segregation. Some of the parameters affecting efficient mixing are: a) Particle parameters like particle size, particle shape, size distribution, particle density, cohesively, hygroscopicity and hardness. An ideal mixer should be capable of producing a complete blend in reasonable time without damaging the product. Additionally, it should be dust-tight, require less maintenance and low energy, capable of easy discharge, and cleaned easily. All these properties cannot be found in a single mixer. However, a logical selection of a mixer can be done based on powder characteristics of the constituents of the mixture, quality requirements of the product and process requirements & limitations. And also, the points needed to be considered, to ensure overall success of a mixing process, are flexibility to cope with a variable batch size, transportation of mixing vessel between operations (like loading, mixing, packaging), easy access for sampling, separation of processed materials, requirement of frequent cleaning and nature of the mixing surface. The effectiveness of a mixer depends on the powders to be mixed, the time of mixing, number of rotations of the mixer etc [4].
The cost of the flour blender of with a capacity of 50 kg/batch available in the international is Rs.550,000. Blending time is about 10-15 min.
Flour blending cost is about Rs. 1.29 per kg.  A hollow shaft was fixed at the centre axis of the cylindrical drum and three SS-304 flat blades having a cross section of 50 mm x 5 mm and 575 mm length were bolted to the arms welded to the hollow shaft. Blades were fixed with an angular distance of 120 0 between each. The position of the blades can be changed. Another set of three blades having same dimensions as described above were bolted to the arms welded to the inner periphery of the cylindrical drum. Each blade was bolted to three arms. The cylindrical mixing drum containing blades, hopper and closing door was fixed to rigid frame by using a 25 mm diameter mild steel shaft running through the hollow centre axis shaft and two pillow block bearings fixed at the ends of the shaft. Two 6 mm diameter SS rods were attached to the closing door as the controller for the door opening. Closing door can be kept at a place by fixing the rods by a locking mechanism fixed to the cylindrical drum. Discharging plate was fabricated using 18 BWG (1.5 mm) SS-304 sheets and fixed at the bottom of the cylindrical drum. Discharging plate has an angle of 40° to the horizontal. The equipment is mounted on the rigid frame made of mild steel angles. The rigid frame was fabricated using 37.5 mm x 37.5 mm angles having 5.5 mm thickness. The Frame has overall dimensions of 600 mm x 725 mm x 1100 mm. Power required to rotate the mixer was given by a 3hp, three phase electrical motor fixed to the frame. Rotational speed of the motor is 1440 rpm. A rotational speed of 51 rpm was given to the cylindrical mixing drum by reducing the motor speed with two belt drive systems having speed reduction ratios of In operation, mixing drum was held in an upright position and flour to be mixed were put to the machine. Then the door was closed and locked. Power supply was switched on and mixing was done for a few minutes. Then power was switched off. The speed of the machine was gradually reduced before coming to the stationary position.

Design
By turning the mixing drum to a position that the hopper comes to the bottom and then the door was unlocked and opened slowly and fixed at a position with the help of door controlling devices. Then flour mixture was discharged from the machine.

Design Description:
Considering the maximum space required for a batch size of grain flour under design conditions, dimensions of casing and hopper were selected. Size of the blades were selected according to the inside dimension of the cylindrical mixing drum. Materials were selected for a hygienic design. Various components of the equipment were designed with the help of the standard relations in a Text Book of Machine Design [2]. Power requirement for blender was calculated by using the relevant formula [3]. Considering nearest available values of the material and also the available facilities for fabrication, the dimension of the components were selected. And also, one sheet of 8'x4' SS-18 BWG (1.5 mm) was used totally for fabrication to reduce the cost of the machine while satisfying the design requirements.

Power
Power requirement for the operation of the developed equipment was calculated by using the following expression [3].  The operating capacity of the machine was 50 kg per batch. However in the designing process, it was assumed that the maximum food capacity was 1.5 times the operating capacity and power requirement was calculated. Preliminary tests were conducted to find the required rotational speed (rpm) for mixing and it was found that the required rotational speed for mixing was about 50 rpm. Hence the pulleys were selected to achieve this rotational speed (rpm) for the mixing machine.

Cross sectional dimensions of the blade
arm [2] The cross section of the arm is obtained by considering the arm as cantilever i.e., fixed at the shaft end and carrying a concentrated load at the blade end. The length of the cantilever is taken equal to the distance from shaft to the centre of the blades. It is further assumed that at any given time, power is transmitted from shaft to the flour load of the blender through only 2 blades. Since one blade has 3 arms, total number of arms under consideration is 6. Tangential load per arm is given by the following equation [2] n R Considering the availability tA was taken as 5mm Therefore, BA =50mm.

Frame
The equipment is mounted on a rigid frame made of mild steel angles. The rectangular dimensions of the frame are selected according to the dimensions of the cylindrical drum and considering easy operation of the equipment. The thickness of the frame materials was calculated according to the load acting on frame, such as weight of the equipment itself, weight of the grain flour and forces acting on the frame. The equipment has a frame of overall dimensions 600 mm x 725 mm x 1100 mm, fabricated from mild steel angles of 37.5 mm x 37.5 mm x 5.5 mm.

Materials and Methods
Preliminary tests were conducted to find the required rotational speed (rpm) to mix flour in the blender and it was found that the required rotational speed of the blender was 51 rpm. Pulleys were selected accordingly to obtain the above rpm for the blender by considering the rpm of the motor. Blender was operated with a 3hp motor. The blender was tested by blending rice flour and wheat flour to the ratio of 3:7, which is generally used as a mixture for preparing bread. The capacity of the blender was 50 kg per batch. 35 kg of wheat flour and 15 kg of rice flour were put into the blender and blending was done with different time periods (1 min, 2 min, 3 min and 4 min) and three replicates with each batch.
The performance of the blending equipment was evaluated with regard to the time required for blending to give a uniform mixture. The uniformity of the blended mixture was evaluated with gluten content and particle size distributions. Four samples were taken from four different places in the blender to find the uniformity in each trial. Determination of Gluten [5] was done by following SLS method. Particle size distributions were measured by using the impact laboratory test sieve shaker (Model: YGM15418). 150μm, 125μm, 106μm, 90μm and 75μm sieves were fixed to the sieve shaker. A sample of 200g was put to the sieve shaker and it was operated for 20 minutes. Particle size distribution was calculated by measuring weight of the materials retained in each sieves.
Data obtained for gluten content and particles size distributions were subjected to analysis of variance (ANOVA) using AgRes statistical package for windows version 3.01. Completely randomized design (CRD) was used to evaluate the data and mean comparisons were done by using least significant difference test. Table 1 shows the gluten content at different places of flour mixture with mixing time. Data were statistically analyzed and the analysis has shown that the gluten content is significantly different when mixing times are 1 and 2 minutes and it is not significantly different when mixing time is 3 minutes and above. These gluten contents results indicate that the minimum mixing time required to give a uniform flour mixture is 3 minutes. Table 2 shows the percentage particle size distribution at different places of flour mixture with mixing time. Data were statistically analyzed and the analysis has shown that the percentage particle size distribution is significantly different when mixing times are 1 and 2 minutes and it is not significantly different when mixing time is 3 minutes and above. These results indicate that the minimum mixing time required to give a uniform flour mixture is 3 minutes. Above results for gluten contents and percentage particle size distributions at different places of flour mixture indicate that the minimum blending time required to give a uniform flour mixture is 3 minutes.  Fabrication cost for the developed flour blender was about 100,000 SLR and flour blending cost was 0.97 SLR per kg. When the developed flour blender is compared with the available blending machines in the international market with same capacity, developed flour blender has reduced the blending time and the initial cost of the machine by 5 times while the flour blending cost is reduced by 25%.

Conclusion
Based on the results of gluten content and percentage particle size distribution at different places of flour mixture, it can be concluded that the minimum mixing time required to give a uniform flour mixture is 3 minutes.