Read more: Description of Cassava Chips Machine
In this article I will explain how to design of cassava chips machine. Design process begins by calculating the power requirement for cassava cutting process. The power will be a reference in choosing an electric motor. Having chosen the type of electric motor, the next process is to calculate the strength of the machine parts according the machine construction. In this post, the calculation of the strength and dimensions of the machine parts are limited only to the calculation of cutting blade strength.
Power requirement for cassava cutting process
The electric motor is a power supply to drive the entire system dynamic of cassava chips machine. Advantages of electric motors compared to other types of resources for electrical energy easily available and practical for small-capacity machine. Selection of the electric motor based on the calculation of the cutting load.
The cutting process occurs when the cutting force is greater than the cutting load requirement. Cutting load derived from the cassava ruptures strength. Cassava ruptures strength is ability of cassava to withstand the cutting forces provided by the cutting blades. The greater ruptures strength of cassava, the cutting load will be even greater. So that the force required by the cutting blade becomes larger in order to cut the cassava.
F = Cassava cutting load (Kg)
σ = Cassava ruptures strength (mN/mm2)
i = Blade number
d = Cassava diameter (mm)
g = Gravity (m/s2)
The total forces requirement in the cutting process consists of cutting forces and frictional forces. The cutting forces which received cassava force of blade movement during cutting process. The frictional force is the force that inhibits the movement of the blade when the cutting process due to the thrust of cassava to feed. Friction is occurs between cassava with blades spinning disc.
Cutting force is influenced by the angle blade and the cutting load. Angle blade will also affect the sharpness of blade, the sharp cutting blades will cut the smaller force is needed, but the life time blade becomes lower. Therefore, it is necessary to design the right angle of blade so that the required cutting force as small as possible with a higher life time.
Based on many references of the blade, blade angle ideal range is 20 degree. If the cutting load already known on the previous formula, then the blade cutting forces can be calculated with the formula;
FC = Blade Cutting Force (Kg)
F = Cutting Load (Kg)
α = Blade Angle (20 degree)
Frictional force caused by the thrust that form the normal force perpendicular to the friction area of cassava. The driving force comes from pressure given to cassava in order to move towards a spinning cutter blade. On cassava chips machine, the pressure cassava assigned manually by hand, so the pressure tend to be constant. The pressure must not be less than the blade axial force, because it will cause unstable slice thickness. The pressure must not be greater than the cassava ruptures strength, because it will cause a rupture.
If the coefficient of kinetic friction between the cassava with a disc blade is µ, the friction forces that occur are:
FF = Friction force (Kg)
P = Cassava driving force (Kg)
µ = coefficient of kinetic friction
The total force requirement to the cassava cutting process is a tangential force consisting of a cutting forces and friction forces, formulated as follows:
FT = Total force requirement (Kg)
FC = Blade Cutting Force (Kg)
FF = Friction force (Kg)
Having in mind the total force required for the cutting process of cassava, the force requirement can be converted into units of power because the force is the tangential force generated from the electric motor rotation. In general, the power requirement for the cutting process of cassava chips machine can be calculated using the formula:
P = Power Requirement (Kw)
T = Torque (kgmm)
n = Blade speed (rpm)
The torque on the blades can be calculated using the formula:
Note:
T = Torque (kgmm)
FT = Total force requirement (Kg)
R = Radius of blade position (mm)
Design of the cutting blade strength
The cutting blade strength of the cassava chips machine is located at the tip of blade, so that the blade tip must always be sharp in order to retain the ability to cut cassava well. Cutting ability will decrease if the blade tip experiencing torpor due to frictional forces and cutting forces. Bluntness caused the blade tip isn’t able to withstand the frictional forces and cutting forces. So that the blade does not experience the bluntness, the tip of blade should be made radius.
Frictional forces and the cutting forces are working continuously on the cutting blade will cause the stress at the blade tip. Cutting blade strength is the ability of cutting blades to withstand the stress so as not to cause wear and tear. Cutting blade has a good strength if the allowed stress for the blade material is greater than the maximum stress. The maximum stress of cutting blades can be calculated using the formula:
σ = Maximum stress (Kg/mm2)
FC = Blade Cutting Force (Kg)
FF = Friction force (Kg)
A = Area of the blade tip (mm2)
Area of the blade tip can be calculated using the formula:
A=2.r.l
Note:
A = Area of the blade tip (mm2)
r = Radius of the blade tip (mm)
l = Length of the blade tip (mm)
Cutting blades on the disc is clamped by the clamp fastened with two screws. Disc and clamp gets a load in the direction of the x-axis and y-axis of the cutting forces and frictional forces. The load was detained by two bolts. Force on the x-axis direction resulting tensile force on the bolt. Force on the x-axis direction is equal to the normal force of blade.
Fx = N
Force on the y-axis direction resulting in shear forces on the bolt. Force on the y-axis direction of the same with a blade cutting forces and frictional forces together.
Fy = FC + FF
Once known force on the x-axis direction and forces on the y-axis direction, then we can calculate the strength of bolt which binds cutter knife.
That is a description about the Design of Cassava Chips Machine. If you find misconceptions in this post, please provide the correction in the comment box. If you want to know more details about cassava chips machine can be seen in a previous article titled Cassava Chips Machine by Planer Cutting System.
very nice
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