Design of Paper Shredder Machine

Design of Paper Shredder Machine - This machine is used to crush pieces of paper, especially A4 paper HVS document type, maximum paper weight of 80 gms and a maximum of 10 sheets per cycle. This machine uses a knife crusher is a kind of zigzag blades capable of cutting the longitudinal and transverse directions simultaneously. A more complete description of this machine can be seen in a previous article entitled paper shredder machine by zigzag cutting system and more detail of specification can be seen in an article specification of paper shredder machine. (Read more: description of paper shredder machine) (Read more: Specification of paper shredder machine)

In this article I will explain how to design of the paper shredder machine. The design process begins by calculating the power required for the cutting process. The power will be a reference in choosing the electric motor. After determining the electric motor, the following design process is the calculation of machine parts according to the concept and construction design. Base on description of the paper shredding machine, we can determine what parts of machine must be calculate dimension and strength.  Therefore, part design of paper shredder machine is spur gear transmission, helical gear transmission and main shaft.

Shredder Blade Calculation

The cutting process will occur if cutting forces on each shredder blade exceeds the tear strength of the paper. Cutting forces required on each shredder blade are:

Note:
Fi    = Cutting Force per Blade (Kg)
KS   = Tear Strength of Paper (mN)
S     = Max Paper Load (Sheet)
g     = Gravity (m/s2)

Tear strength of paper can be seen in the paper specification for HVS document type of paper.

The cutting force required to crush a paper is influenced by the number of blade and the number of blade cutting edge. So the cutting forces for vertical and horizontal direction can be formulated as follows:

Note:
F1   = Cutting Force for Vertical Direction (Kg)
F2   = Cutting Force for Horizontal Direction (Kg)
Fi    = Cutting Force per Blade (Kg)
i      = Number of Blade
k     = Number of Blade Cutting Edge

Power Requirement for Paper Shredder Design

The power required to crush a paper is influenced by torque and speed of blade. Power Requirement for cutting process can be calculated by formula:

Note:
P   =  Power Requirement (Kw)
T    =  Torque (kgmm)
n    = Blade speed (rpm)

Torque in the blade occurs due to cutting force in the vertical cutting direction (F1) and the the horizontal cutting direction (F2), so the total torque in the blade can be calculated by formula,

Note:
T     =   Torque (Kgmm)
F1   =   Cutting Force for Vertical Direction (Kg)
F2   =   Cutting Force for Horizontal Direction (Kg)
R1   =   Radius of blade on F1 point (mm)
R2   =   Radius of blade on F2 point (mm)

Machine Part Calculation for Paper Shredder Design

Based on the machine construction is described in the article paper shredder machine, there are some critical part must be calculated its dimensions and strength. The machine parts are main shaft, spur gear and helical gear.

Main Shaft Design

Main shaft is the supporting shaft for shredder blade. On the shaft, there is a cutting force on each shredder blade whose value according to the results of previous calculations (cutting force for each blade = Fi). The cutting forces will cause the bending load on the shaft. Main shaft also receives a torque that is distributed by the gear transmission. Therefore the main shaft receives a bending load and torque loads simultaneously. Main shaft calculation as it can use the existing formula in the article torque and bending load of shaft together. (Read more: shaft design)

Spur Gear Design

Paper shredder machine uses two pairs spur gear. The first of spur gear is used as a gear drive for the shredder blade. The spur gear serves to make the shredder blade right and left rotating at the same speed but in opposite directions.  The second of spur gear is used as gear reducer which serves to reduce a rotation by gear ratio is 1/8. Its ratio is too high, so spur gear transmission system is divided into two parts, namely the first stage spur gear by gear ratio is 1/4 and the second stage spur gear by gear ratio is 1/4. Spur gear calculation for determined spur gear dimension and strength can use the existing formula in the article calculation of spur gear dimension and strength with reference to the power requirement and the speed of standard motors. (Read more: spur gear design)

Helical Gear Design

Paper shredder machine uses a helical gear as a gear reducer of the electric motor. Helical gears have the ability to withstand the radial and axial force so it is good if connected directly to the high speed motor. This machine is fitted helical gear using a ratio of 1/5. Helical gear calculation for determined helical gear dimension and strength can use the existing formula in the article calculation of helical gear dimension and strength with reference to the power requirement and the speed of standard motors. (Read more: helical gear design)

That is a description about the Design of Paper Shredder Machine. If you find misconceptions in this post, please provide the correction in the comment box.

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Heat Treatment Furnace Design

Heat Treatment Furnace Design - Heat treatment furnace is a type of furnace that is used to provide a heat treatment at a work piece such as normalizing, tempering, annealing, hardening, hot forming, stress relieving, etc. The heat required for the heat treatment process varies depending on the type of material and heat treatment processes that need. In general, heat treatment furnace has a temperature between 400 to 1200‘C.

Generally, the design of the heat treatment furnace includes the calculation of power requirement, wall furnace design, heater design, determined of thermocouple and thermocontrol, design of boogie system and door system. But in this post is only described about estimated energy and power requirement.

If you want to design a heat treatment furnace, you must be know about user requirement are:

• Maximum Temperature, the temperature is very influential in the design of furnace because it will be based on calculation of power requirement, heater design, wall furnace design, and determined of thermocouple and thermo control.
• Work piece material and heat treatment process, if the maximum temperature unknown, you can see the charts or the tables of material temperature. An example of a table for the material temperature in VCN-150, VCL-140 and EMS-45 (standard Bohler) is displayed below.

• Furnace capacity includes the volume of the furnace chamber and the weight of material to be processed. As well as the temperature, furnace capacity will also be based on calculation of power requirement and wall furnace design.
• Heating time target and the available power. Time and electric power have a relationship of mutual influence. The goal faster heating time, it takes more power, and otherwise.

Estimated energy requirement for the heat treatment furnace

If the data is known, you can calculate the energy needed to heat the furnace. At the time of furnace work, the heater element will heat the air in the furnace chamber. The hot air will be absorbed by the furnace walls and work piece in the furnace chamber. Therefore, the total energy required to heat the furnace is:

Note:
Q_R   = Energy Requirement (Joule)

Q_m   = Energy for Work piece Heating (Joule)

Q_a   = Energy for Air Heating (Joule)

Q_w   = Energy for Heat Storage (Joule)

The energy to heat the workpiece is calculated on the basis of the heat capacity that can be received by the workpiece on a specific temperature change. Each material has a different specific heat capacity. Here is a table of the specific heat capacity of certain specified materials.

If the initial temperature of workpiece is T1 and heated to a temperature T2, the energy required for heating the workpiece can be calculated by the following equation:

Note:
Q_m   = Energy for work piece heating (Joule)

m     = Mass of work piece (kg)

c_m    = Specific heat capacity of work piece (Joule/kg ^oC)

T₁    = Initial temperature (^oC)

T₂    = Final temperature (^oC)

Energy for air heating is the energy used to heat the air in the furnace chamber. If the initial air temperature is T1 and heated to a temperature T2, the energy required for heating air can be calculated by the following equation:

Note:
Q_a   = Energy for air heating (Joule)

V_a    = Air volume (m³)

C_a   = Air heat capacity is 1200 Joule/m^{3 o}C

T₁    = Initial temperature (^oC)

T₂    = Final temperature (^oC)

Heat storage is heated air that is absorbed by the furnace wall. The furnace wall function is resist the heat in the chamber. Therefore, the furnace wall is made of a material having a thermal conductivity which is very low such as firebrick, insulating bricks, ceramic fiber, calcium silicate and rockwool. Although able to withstanding the heat, the furnace wall can still absorb heat depending on the material heat capacity used for the furnace wall. Then, the value of the heat capacity of the furnace wall for some materials indicated.

Energy required to replace the heat absorbed by the furnace wall is by the following equation:

Note:
Q_w   = Energy for heat storage (Joule)

V_w   = Volume of wall furnace (m³)

C_w   = Heat capacity of wall material (Joule/m^{3 o}C)

T₁    = Initial temperature (^oC)

T₂    = Final temperature (^oC)

If ‘L’ is the furnace length, ‘W’ is the furnace width and ‘H’ is the furnace height, so volume of the furnace wall is:

 

Estimated power requirement for the heat treatment furnace

The power required to heating process in the furnace chamber for on the time is by following equation:

Note:
P_R     = Power requirement (Watt)

Q_R     = Energy requirement (joule)

t         = Time heating (sec)

Determining the electric power to be greater than the power requirement or divided by the efficiency of the furnace so that the heat generated on time. Furnace efficiency is regarding the heat loss that occurs in the furnace chamber.

That is a description about Heat Treatment Furnace Design on the topic of energy and power requirement estimated. Other topics related to Heat Treatment Furnace Design  will be described in other post like the wall furnace design, heater design, determined of thermocouple and thermocontrol, design of boogie system and door system.

Furnace calculation formula and table are reference to the handbook of Heat Transfer by Holman and Technical Bulletin by Applied research services.

If you find misconceptions in the furnace calculation, please provide the correction in the comment box.

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