Research, design and implementation of a coconut shell shredder and dehydrator machine for organic fertilizer production

INTRODUCTION

Introduction

1.1.1 A brief overview about coconut fruit

As the above- mentioned, coconut plays a vital role in Vietnam's agriculture With more than

Coconut cultivation spans 175,000 hectares in Vietnam, making it the fourth most important perennial crop in the country The Mekong Delta accounts for nearly 80% of the nation's total coconut production, with Ben Tre province contributing approximately 72,000 hectares and Tra Vinh province covering around 20,000 hectares.

The coconut tree has enormous potential for both the economy and the environment

Coconut trees are remarkably versatile, with nearly all parts being useful; their trunks and leaves serve as effective construction materials, while coconut water and flesh are prized ingredients in cooking and oil production Additionally, these trees thrive in challenging environments, demonstrating resilience against drought, waterlogging, and nutrient-deficient soil.

In addition to the edible parts of the coconut, the often-overlooked coconut shell has valuable components The coconut husk contains two primary elements: coco peat and coco fiber, both of which are extensively utilized in various industries and agriculture Notably, coco peat serves as an essential ingredient for organic fertilization, highlighting its significance in sustainable farming practices.

Coco peat is a lightweight, non-fibrous substance derived from the Coconut Fiber Extraction process, effectively holding together coconut fiber and shell This 100% organic ingredient is essential for agriculture, particularly in enhancing fertile production due to its remarkable moisture retention capabilities, holding up to 800% of moisture when dry By serving as a primary component in organic fertilization, coco peat improves soil aeration and buffering, facilitating better airflow to plant roots Additionally, its spongy nature allows for efficient nutrient storage and release As a renewable and completely natural material, coco peat meets the growing demand for chemical-free fertilization, aligning with current trends in sustainable agriculture.

1.1.2 Structure and general mechanical properties of coconut fruit

The image depicts the cross-sectional structure of a coconut fruit, highlighting that the nutrient-rich white flesh and coconut milk are often utilized for various purposes Consequently, it is essential to concentrate on the components that yield coconut coir and coco peat The accompanying table presents the percentage distribution of each part of the coconut fruit.

Fig 1.2 Structure of coconut fruit

Table 1.1 Distribution of coconut fruit

This project focuses on the extraction of coco peat and coconut coir from coconut husk To achieve this, it is essential to gather input data regarding the mechanical properties of these layers The following table presents key properties of coconut husk, derived from previous research conducted at Tra Vinh University.

Table 1.2 Mechanical properties of coconut husk [5]

Bonding force of coconut coir

Statics friction coefficient of coconut husk contact with steel by inner smooth surface

Statics friction coefficient of coconut after proceeded with steel shredding machine and water

Maximum shear stress For fresh coconut: 189.5 N

For gray husk: 201.7 N For dry husk: 263.3 N

Fig 1.3 Mechanical properties of coconut shell [24]

1.1.3 Investigate the market of coconut shredder machine

The coconut shredder machine market is currently diverse, with significant popularity in Vietnam; however, many manufacturers prioritize products other than coconut husk processing.

About Vietnamese manufacturer, there are two company participate in this field are Moc Kim Son (MKS) [8] company and 3A Agriculture Machinery [9] These machine and specification are showed as a table below

Table 1.3 Specification of MKS and 3A machine Specification Unit Moc Kim Som company 3A Agriculture Machinery

Main material Plate steel, I beam V5 steel, 2mm sheet metal

Input material Fresh/dry husk Fresh/dry husk

Fig 1.4 Coconut shredder machine from MKS and 3A

With all the information we have as summarized above, we have some analyze about the advantages and disadvantages of both machines from Vietnamese manufacturers

The coconut shredder machine from MKS stands out as a superior option compared to the 3A model, thanks to its dual mechanisms designed for efficient crushing and shredding of coconut husk Additionally, it features a belt conveyor that seamlessly transfers the output material to various types of containers, enhancing compatibility with different machines, such as screw drives.

The 3A machine, priced at 12,500,000 VND, is significantly more affordable than the MKS machine, costing less than 12 times as much While the 3A machine features a simple rotating blade mechanism for shredding coconut husk, its frame may appear less rigid and lacks safety features However, it offers a broader range of applications, capable of processing not only coconut husk but also various products like grass and boughs, making it an excellent choice for small-scale businesses.

To summarize both machines, we listed they pros and cons to the table below

Table 1.4 Pros and Cons about MKS and 3A machine MKS shredder machine 3A shredder machine

Pros 2 separate mechanism for better output material quality

Simple mechanism, low maintaining cost

High productivity High productivity Rigid machine frame Inexpensive price

Cons High cost for purchasing and maintaining

Bad frame machine design, make output material fly out of machine

Too heavy, hard to transportation

Not suitable for small business

In terms of international manufacturers, although India and Sri Lanka both have the highest coconut production among other countries, their machine seems slightly outdated and lacks safety and aesthetics

There are two notable companies from China and Brazil that have all-around performance coconut shredder machines They are Xtmachinery [11] and JF company

[12], and their machine specification will be listed in the table below Table

Specification of Xtmachinery and JF machines

Table 1.5 Specification of Xtmachinery and JF80 machine Specification Unit Xtmachinery XT65*27 JF 80

Main material Plate steel, I beam V5 steel, 2mm sheet metal

Input material Fresh/dry husk Fresh/dry husk

Fig 1.5 Coconut shredder machine from XTmachinery and JF Brazil

In the same process with Vietnam manufacturing, we will analyze both their advantages and disadvantages

The coconut shredder machine from China features a hammer mill equipped with a full circle screen and dual rotor shredder mechanisms, enhancing its efficiency The dual rotors allow for increased coconut shredding capacity, while the full circle screen significantly speeds up the operating cycle by facilitating quicker removal of coco peat However, the design may pose challenges for screen replacement during maintenance.

JF Brazil offers a compact product that matches the performance of its Chinese counterpart, utilizing a hammer mill mechanism with a single rotor and half-circle screen This design enhances mobility, making it ideal for small-scale businesses While it is compatible with tractors, it requires double the power of an electric motor.

Overall, both machines have extremely high productivity The pros and cons are listed in the table below

Table 1.6 Pros and Cons about Xtmachinery and JF Brazil Xtmachinery machine JF 80

Pros Double rotor shredder mechanism

Full circle screen Compatible with both electric motor and tractor High productivity High productivity Cons High cost for purchasing High cost for purchasing

Not mobility , too much heavy ( 1000 kg)

Hard to maintenance due to full circle screen

In conclusion, the coconut shredding machine market is thriving both nationally and globally, driven by the increasing demand for recycling coconut husks for economic and environmental benefits Despite advancements in this sector, manufacturers primarily cater to large-scale industries, leaving small-scale businesses underserved Additionally, the high cost of three out of four machines, exceeding 100,000,000 VND, poses a significant barrier for individual buyers.

The urgency of the topic

Nowadays, the need for coconut in Vietnam and other countries seems to keep high demand This led to the promotion of coconut production on both a small and large scale

In the mass production of coconut harvesting and processing, advanced technologies are utilized to maximize the potential of coconut trees, transforming coconut milk extraction, grinding coconut flesh, and repurposing byproducts into coco peat and coconut coir However, the significant investment required for such extensive systems poses a risk for small-scale businesses.

To address the concerning trend of coconut husk waste, a two-step processing machine is essential This machine should efficiently shred coconut husks into smaller pieces and extract remaining water from the processed material It is crucial that this equipment is affordably priced to support small-scale businesses By implementing this solution, we can significantly mitigate the issues associated with coconut husk disposal.

This is why we choose the topic: Research, design, and implementation of a

Objection of the project

The coconut shredder machines available on the market, both domestically and internationally, offer varying advantages and disadvantages, particularly in terms of productivity However, three out of four models are priced over 100,000,000, making them unaffordable for small-scale businesses Additionally, many of these machines, including those from XTmachinery, lack an effective dewatering mechanism and can be complicated to maintain.

So that, our project will focus on these following aim:

- Easy to maintain shredding mechanism

Research method

- Experimental analysis for gathering input data and testing machine after manufactured

- Theoretical calculation for design and calculating machine component

Aim, mission and scope of the project

- Aim of the project: Coconut shell shredder and dehydrator machine, calculation report, technical drawings

- Mission of the project: Design and implement fully functional prototype of coconut shell shredder and dehydrator machine with reasonable price for small scale business

+ Appling theatrical knowledge about mechanical design and machine manufacturing to solve

+ Time for designing and manufacturing is 5 months

Input data

- Input material: fresh or dry coconut husks

1.6.2 Define input data about coconut husk:

To effectively investigate the properties of coconut husk, we require not only the minimum force needed to break it but also two additional key data points: its weight and overall dimensions This study will utilize experimental methods to gather and analyze these essential characteristics.

Weigh of the coconut husk:

About weigh of the coconut husk, we considering these data by recording 5 coconut husk samples for fresh and dry in total of 10 samples

Table 1.7 Overall weigh of fresh and dry coconut husk Experiment No Fresh coconut husk (gram) Dry coconut husk (gram)

Fig 1.6 Fresh and dry coconut weigh

Fresh coconuts weigh significantly more than dry coconuts due to the loss of water and the outer shell This makes shredding dry coconuts easier, as they do not require a dehydrator In contrast, fresh coconuts, which have a high water content and a sticky texture, necessitate shredding followed by a dewatering process to remove excess moisture.

Size of the coconut husk:

We measured the size of coconut husks by analyzing a total of 10 samples, consisting of 5 fresh and 5 dry specimens Using tape measurement, we recorded the overall height, width, and diameter of each sample, with the results detailed in the table below.

Table 1.8 Overall dimensions of fresh and dry coconut husk Experiment No Fresh coconut husk (cm) Dry coconut husk (cm)

Height Width Diameter Height Width Diameter

Fig 1.7 Overall size of fresh and dry coconut husks

The experiment reveals that fresh coconuts are significantly larger than dry coconuts, indicating that the feed hopper should have a minimum dimension of 17 cm to accommodate this size difference.

Table 1.9 Input data about coconut husk

INPUT DATA ABOUT COCONUT HUSK

Condition of coconut husk type Fresh and dry

Average weight of fresh coconut husk kg 1220

Average weight of dry coconut husk kg 278

Destroy stress of coconut husk N/mm2 1.25 × 10 6

- The output material much pass through 16mm screen hole diameters

- The fresh coco peat as considerable dry condition after processing

- After processed, fresh material including coco peat and coconut coir

Table 1.10 Output material for organic fertilizer

OUTPUT DATA ABOUT COCONUT COIR AND PEAT

Type of output material type Cocopeat, coir and powder

LITERATURE REVIEW

Shredding mechanism

Shaft shredding machines utilize one or more shafts to effectively reduce material size, making them essential in various agricultural applications, including corn powder production, fodder manufacturing, yeast production, and lipid processing.

The shaft shredding mechanism operates by grinding large particles into smaller sizes as they pass through the narrow gap between the shafts The shredding time varies depending on the hardness of the input material and the desired output size For sticky and durable materials, mechanisms such as shaft 2 type VII or shaft 2,3,4 type IX should be utilized In contrast, for smaller grains or beans, a 2 or 4 shaft shredding mechanism is recommended.

Most of these shafts are casted with special cast iron like (C 3.2% ~ 3.7%; Si 0.4

The material composition includes approximately 0.7% carbon, 0.2% to 0.8% manganese, 0.5% phosphorus, 0.14% sulfur, and 0.25% nitrogen, resulting in a high surface hardness ranging from HB 370 to 450 For shafts requiring greater hardness, around 500 HB, the structure is designed with a core made of cast iron, which is then encased in a chromium-nickel alloy.

Fig 2.1 Mechanism of shaft shredder [3] Fig.2.2 Double shafts shredder machine [12]

This mechanism employs a rotating blade system within a confined chamber to effectively cut materials using the sheer force of the blades The blade configuration can consist of three or four blades designed with a specific angled slope, facilitating the downward flow of material Additionally, the machine features a screen at the bottom to sort the materials into the desired size.

Fig 2.3 Rotary blade mechanism by 3A machinery [9]

Most machines utilizing this mechanism operate through direct transmission or belt drive transmission The blade must rotate at a minimum of 1400 rpm to function effectively While the machine's structure is straightforward, this mechanism is only appropriate for cutting grass or softer materials It is not suitable for processing coconut husk, which can be either hard when dry or ductile when fresh.

Fig 2.4 Rotary blade mechanism in food industry

The hammer mill operates on the principle of shredding materials through the impact of hammers, which strike the materials, as well as the collision of the materials against the machine's sides and the friction generated between them.

General speaking, the process of hammer mill mechanism consists of 4 steps: Step Description

1 Material go into the machine by gravity

2 These material will be shredder by hanged hammer that fixed or freely rotated onto the shaft with high rotation speed

3 The material is crushed or shattered by repeated hammer impacts, collisions with the walls of the grinding chamber, and particle on particle impacts

4 Small grains or material then go through the screen with designated holes

2.1.4 Comparison and choose shredder mechanism

Table 2.1 Advantages and disadvantages of shredder mechanisms

Mechanism Shaft shredding Rotary blade Hammer mill

- Adjustable size of output material

- Easy to maintaining and cleaning

- Varies type of input material

Disadvantages - Too complex to build

- Require high power motor to properly run

- Cannot achieve very fine output material

- Hard to maintaining the screen

Shaft shredding Rotary blade Hammer mill

After thorough analysis of various shredder mechanisms, our team selected the hammer mill mechanism due to its superior suitability for our needs and its numerous advantages over other options.

Transmission system for shredder mechanism

Gear drives, also known as gear transmission trains, are essential mechanisms that transfer rotary motion and torque between shafts and machine components Commonly utilized in speed gearboxes, engines, and turbines, they are valued for their ability to transmit high torque with minimal backlash Various types of gears, including external, internal, spur, helical, bevel, and spiral bevel gears, contribute to their versatility and efficiency in mechanical applications.

This project involves utilizing an external gear transmission system, where the drive gear is connected to the motor's shaft and the driven gear is fixed to the hammer mill mechanism While this setup offers several advantages, it is crucial to evaluate the potential risks, as a jammed shredder mechanism could prevent the driven shaft from rotating, leading to motor overload Additionally, manually machining gear drives on a milling machine is often seen as a complex task.

To prevent damage to the surface of both gears, it is essential to properly cover the area during operation, as the small particles of coco peat can fall into the drive Additionally, increasing the shaft distance in accordance with the matching principle is not feasible unless an intermediate gear is utilized.

A chain drive is a transmission system that conveys rotary motion and torque between shafts, typically comprising two or more sprockets and interconnected links This mechanism ensures zero slip, similar to gear drives, allowing for consistent velocity during operation Additionally, the use of chain links enables flexibility in adjusting shaft distances to meet user specifications.

In this project, we propose using two chain sprockets—one attached to the motor's shaft and the other to the shredding mechanism However, employing a chain drive for the hammer mill mechanism poses risks due to potential motor overload from zero slip, as well as excessive noise at high speeds Additionally, the chain link and sprocket are difficult to machine and can wear quickly without proper lubrication The requirement for clean operating conditions further complicates the use of chain drive near the hammer mill shredder Conversely, the chain drive can be effectively utilized in our dehydration mechanism, benefiting from the zero slip feature.

The belt drive operates on the principle of friction to transmit motion and torque, utilizing a structure similar to chain drives, featuring two or more pulleys connected by a belt Various types of belt drives exist, including round belts, flat belts, V belts, toothed belts, and link belts While belt drives are more cost-effective than chain or gear drives, they still effectively fulfill the role of power transmission.

The belt drive is an ideal transmission system for the hammer mill mechanism due to its frictional motion principle, which allows the belt to slip on the pulley if the output shaft encounters issues, preventing motor overload and potential damage This feature alerts operators to stop the machine before any burning smell occurs Additionally, the belt drive offers design flexibility by allowing adjustments in the distance between shafts, similar to a chain drive Furthermore, it operates more quietly at high speeds compared to chain drives, making it suitable for the dusty environments typical of hammer mill operations.

2.2.4 Comparison and choose transmission drives for shredder mechanism

Table 2.3 Advantages and disadvantages of transmission drives

Mechanism Gear drive Chain drive Belt dive

- Slip belt to protect motor from overload

- Can work in dusty environment

- Hard to maintaining, require clean environment

- Cannot protect motor from overload

- Very noisy at high speed

- Hard to maintenance, require clean environment

- Losing speed due to slip belt

- Transmission ratio is not stable

Gear drive Chain drive Belt drive

After careful consideration, it is evident that belt drives offer greater compatibility and affordability compared to chain and gear drives Therefore, our team has opted to select a belt drive as the transmission mechanism for the hammer mill shredding process.

Motor type selection for hammer mill shredder mechanisms

3-phase motor is the most popular electric motor used around the world It responsibility is to transferring electrical energy into mechanical energy (in this cases are rotating motion)

A 3-phase motor comprises two primary components: the stator and the rotor Its operation is based on the principle that when alternating current (AC) flows through the stator, it generates a rotating magnetic field (RMF) This magnetic field rotates around the stator at synchronous speed, enabling the motor to function effectively.

The rotating magnetic field (RMF) travels through the air gap between the stator and rotor, cutting through the rotor conductors This interaction between the moving RMF and the rotor generates a short circuit, inducing flux that leads to rotational motion.

Fig 2.9 3-phases motor working principle [17]

Although 3-phases motor is a good mechanical power for this project Our aim is to create the machine for small scale business that can work in 220V electrical system or 1- phase electric If we wish to use this type of motor, we need to add inverter to transfer 1- phase electric onto 3-phase electric which can significantly boosting the cost

A single-phase motor, also known as a 1-phase motor, shares a similar structure with a squirrel cage three-phase motor, consisting of two primary components: the stator, which remains stationary, and the rotor, which rotates.

A single-phase motor comprises two windings: the main winding and the auxiliary winding When power is supplied to the main winding, a capacitor is connected in series with the auxiliary winding, creating a phase shift in the current between the two windings.

Unlike 3-phase motor which can self-starting, 1- phase motor need to use the capacitor to start and increase the cost factor

Fig 2.10 Wire diagram of 1-phase motor [18]

Fig 2.11 1-phase induction motor structure [19]

Utilizing a 1-phase motor addresses the electrical system challenges faced by small businesses that primarily rely on single-phase electricity Our focus is on developing machinery tailored for small-scale enterprises, which is why we have selected a 1-phase induction motor as the primary power source for our hammer mill shredder mechanism.

Dehydrator mechanism

The screw press dehydrator consists of a fixed cylinder with a rotating screw inside, designed to efficiently dehydrate materials such as coco peat As the input material is conveyed by the screw, it undergoes continuous compression due to the decreasing pitch of the screw This compression generates pressure that forces water out of the material, allowing it to pass through a screen and resulting in a drier output.

The screw press system in industrial applications features a sludge inlet for material input, consisting of two primary zones: the thickening zone and the dewatering zone, each occupying half of the screw.

Fig 2.12 General structure of a screw press mechanism [20]

The screw press mechanism offers advantages such as high efficiency, capacity, and ease of operation; however, its application in our project is limited due to the low water content in coco peat compared to sludge This makes the screw press inefficient for our needs Additionally, the complexity of machining and maintaining the screw presents challenges that do not align with our goal of implementing a machine suitable for small-scale business operations.

A belt press, also known as a belt filter press, is an effective mechanism for water removal from various materials, operating on the same compression principle as a screw press This device consists of two belts that encase the material, which then passes through one or more pairs of press rollers The tension of the belts and the narrow gap between them facilitate the expulsion of water, necessitating the use of specialized materials for the belts to ensure optimal performance.

Fig 2.13 Belt press mechanism applied in industry [21]

In our project, we aim to optimize the industrial belt press by implementing a simplified design that incorporates a belt conveyor to transfer material from the shredder to the dehydrator The dehydrator features two rollers that allow the belt and material to pass through a narrow gap, providing an efficient solution for processing coco peat This straightforward mechanism ensures both simplicity and acceptable efficiency for our application.

In conclusion, our group has chosen the simple belt press for the dehydrator mechanism due to its ease of maintenance and operation compared to the screw press The belt press's straightforward design keeps machining costs reasonable, making it suitable for small-scale businesses Additionally, we have opted for a chain drive for this simple belt press to enhance its functionality.

MECHANICAL DESIGN

Block diagram

POWER SUPLLY Providing 1-phase 220V electrical energy for the machine which suitable for small-scale business

ELECTRICAL BOX Receiving electrical power from POWER SUPPLY then distributing this energy and signal to actuators of this machine

MOTOR 4KW Receiving electrical power and signal form ELECTRICAL

BOX This motor transferring the electrical into mechanical power which powering the belt drive

BELT DRIVE Transferring mechanical power (moment) from MOTOR

4KW to HAMMER MILL MECHANISM

The main component of our shredder mechanism They receiving rotational energy from MOTOR 4WK through

BELT DRIVE to shred our coconut husk

SCREEN SCREEN received the material processed though

HAMMER MILL MECHANISM Only material with desirable size can pass though this SCREEN

MOTOR 0.75 KW Receiving electrical power and signal form ELECTRICAL

BOX This motor transferring the electrical into mechanical power which powering the chain drive

CHAIN DRIVE Transferring mechanical power (moment) from MOTOR

0.75KW to BELT CONVEYOR and PRESS PULLEY MECHANISM

BELT CONVEYOR Transferring the shredded material to PRESS PULLEY

Squeeze out the water from the shredded mechanism

MACHINE FRAME Fixing and holding the whole machine

INPUT MATERIAL The material we want to preceded: Coconut husk

Our desired material after processed by the machine: coco peat and coco coir with less water

Leftover water or dehydration process

Fig 3.1 Block diagram of coconut husk shredder and dehydrator machine

The coconut husk shredder and dehydrator machine using two separate mechanisms:

The hammer mill and press belt mechanisms work together to process input materials efficiently A 4kW single-phase motor converts electrical energy into rotational energy, powering the hammer mill to shred materials to the desired size, which are then sorted by a screen The shredded mixture is conveyed via a belt conveyor to the press pulley mechanism, where water is extracted, resulting in a dehydrated output of coco peat and coco coir The belt conveyor and press pulley are driven by a 0.75kW single-phase motor through a chain drive All components are securely mounted on a robust machine frame made from welded steel bars, ensuring stability and durability.

The machine delivers a 1-phase electric power supply at 220V, making it ideal for small-scale businesses The electrical power and signals are efficiently distributed through an electrical box, utilizing buttons, signal lights, and various electrical equipment.

Design and calculate the hammer mill mechanism

Fig 3.2 Mechanism diagram of hammer mill

To select the appropriate motor for a hammer mill mechanism, it is essential to analyze various input data The initial step involves calculating the velocity of the hammer mill.

Based on [3], the velocity of hammer mill determined by this formula:

By formula (3.1), in order to destroy the material after each crush, the necessary velocity must be 1.5 or 2 times the destroy velocity

So, the velocity when smashing multiple time according to [3]

V vđ = V fv = √k cl [0.81 + 2.31 log(λ)] (3.2) With:

- V fv : Destroy velocity when smashing multiple time

- k cl : Mechanical properties of material

To determine the shredding coefficient for our small-scale business machine, we found that the time required to shred coconut husk is relatively long Therefore, we opted for a smashing time of six cycles to optimize the shredding process.

So we have the shredding coefficient:

In case of 1-time smashing, the required velocity is:

- a: the length of material (mm) choose a = 167 mm average size [5]

- x 1 : the non-deform size of material (our desired output material) (mm) Choose x 1 = 0.75 𝑚𝑚 ( varies from 0.5~1).

- ρ: specific weight of material (kg/m 3 ) ρ = 390 kg m 3 [5]

- σ fv : destroy stress (N/m 2 ) Choose σ fv = 1.25 × 10 6 N m 2 [5]

To effectively shred material in a single impact, a high velocity is necessary; however, this approach is often inefficient in terms of machining and energy consumption Consequently, it is more economical and energy-efficient to process the material multiple times Therefore, when using a hammer mill, it is crucial to consider the velocity to optimize both cost and energy usage during the shredding process.

Then, the rotational speed of hammer mill: n = ω 2π (rpm) (3.5)

𝜋 = 2515 (𝑟𝑝𝑚) With: r: The diameter of drum (mm)

3.2.2 Choosing motor for hammer mill mechanism

60 (𝑊) (3.6) With: n: Rotational speed of hammer mill n = 2515 rpm

A: Work required for shredding material Based on this formula:

- Z: Number of hammer mill on machine Z= 32

Required power for hammer mill mechanism:

- 𝜂 đ : efficient coefficient of belt drive 𝜂 đ = 0.92

0.92 × 0.995 = 3800(𝑊) Choose motor with 4 Kw in power and 1450 rpm in rotational speed

3.2.3 Calculating belt drive for hammer mill mechanism

Since the driving shaft of the belt transmission are mounted on the motor shaft, the input parameters are taken on the motor shaft

- Power on the driving shaft: P = 4 Kw

- Rotational speed of driving shaft: n = 1450 rpm

Selection belt and cross section:

- We have power Pd = 4,3 (Kw), rotating speed nd = 1425 (rpm) According to figure 4.1 page 59 in [1]

- => Choosing type A belt (GOST) or type A belt (TCVN) based on [1]

Select diameter of belt drive:

- We determine the diameter of the belt wheel according to the table 4.13 [1]

- Selecting d 1 = 200 mm based on the standardize: 63 , 71 , 80 , 90 , 100 , 112 ,125 ,140 , 160 , 180 , 200 , 224 , …

Calculating the velocity of driving pulley:

Calculating the diameter of driven pulley:

- Choosing the diameter of driving pulley 𝑑 2 = 112 based on [1]

So, the real transmission ratio is:

200= 0.56 Check for error of belt transmission ratio:

The real rotational speed of belt drive:

3.2.3.3 Calculating center distance of belt drive:

- The shaft distance must satisfy this formula:

= 1737.2 (𝑚𝑚) Choosing l = 1800 mm based on standard on 14.3 in[TC]

Calculating the exact length of shaft distance

- Based on formula 4.6 in [TC]

- Based on formula 4.7 in [TC]

3.2.3.4 Calculating the number of belt:

- According to formula 4.6 in [TC]

- P1 = Pd = 4 (kW): Power of driving pulley

- Kđ = 1.5: coefficients of dynamic load (work 2 shifts) (table 4.7) [1]

- C α = 0,98: coefficient of angle wrap’s effect (table 4.15) [1]

- Cl = 1: coefficient of length’s effect (table 4.16) [1]

- Cu= 1,135: Coefficient of ratio’s effect (table 4.17 [1])

- Cz =0.95 Coefficient of load’s effect (table 4.18 [1])

3.2.3.5 Calculating the width of and outer diameter belt pulley

- Based on formula 4.17 and table 4.21 in [TC], the width of belt pulley

- Outer diameter of belt drive calculated by formula 4.17 in [TC]

3.2.3.6 Calculate the initial tension and the force acting on shaft

- Calculating 𝐹 0 based on formula 4.19 in [TC]

Table 3.3 Parameter of belt drive

Power on driving shaft P 4 kW

Rotation speed of driving shaft n 1450 Rpm

Diameter of driving pulley d1 200 mm

Diameter of driven pulley d2 112 mm

Width of the belt B 50 Mm

Force exerting of shaft Fr 772.7 N

3.2.4 Calculating the shaft for hammer mill mechanism:

- Chose the shaft’s material is C45 Steel (quenching), strength stress σb = 650 MPa

- The torque stress allowance [τ] = 15÷30 (MPa)

- Power on hammer mill shaft:

- By the working diagram, we need to calculate the load diameter at three position: Hammer mill fixing, bearing, and belt pulley

- Position for each machine component:

Fig 3.3 Force diagram on hammer mill shaft

Fig 3.4 Free body diagram of hammer mill shaft

- Determine the forces and moments acting on shaft:

Fig 3.5 Force and moment diagram of hammer mill shaft on yOz plane

Fig 3.6 Force and moment diagram of hammer mill shaft on xOz plane

- Equivalent moment at each cross section

- [𝜎]: allowable stress of shaft material = 63 (MPa) based on table 10.5 [1]

- We only considering the diameter at dangerous cross section In this case this is at A, belt pulley cross section, hammer mill cross section

At belt pulley cross section:

At hammer mill cross section:

Finally, we have the diameter for the shaft:

Table 3.4: Diameter at each cross section of shaft

Cross section Diameter value (mm)

At belt pulley cross section 35

3.2.4.3 Verify the strength condition for shaft

- At dangerous cross section: bearing assembly cross section σ −1 = 0.436σ b = 0.436 × 600 = 261.6 (MPa) τ −1 = 0.58σ −1 = 0.58 × 261,6 = 151.7 (𝑀𝑝𝑎)

- Calculating σ aj and σ mj based on 10.22 in [1] σ mj = 0 σ aj = σ maxj = M j

- Calculating τ mj and τ aj based on 10.23 in [1] τ mj = τ aj = τ maxj

- Calculating K σdj and K τdj based on 10.26 in [1]

- Calculating s σj and s τj based on 10.21 in [1] s σj = σ −1

- Finally, calculating s j based on formula 10.19 in [1]

3.2.4.4 Verify the strength condition for key

- Based on table 9.1a on [1] we choosing keyway with this diameter:

3.2.4.5 Choosing bearings and verifying the bearing condition

- Total forces acting on bearing:

- We verify the strength at the bearing that bear bigger load: 𝐹 𝐴 = 1084.38 (N)

- Choosing the ball bearing SKF 6270 with pillow housing and the diameter:

Table 3.6 Ball bearing SKF 6270 specification:

Notation d (mm) D (mm) C (kN) C o (kN)

- Verify the bearing based on dynamics load:

- 𝑉 = 1 coefficient about the number of rotation

- Verify the stress based on static load

In order to prevent the residual deformation, the ball bearing need to satisfy the condition:

Design and calculate the press pulley dehydrator mechanism

Fig 3.7 Mechanism diagram of press pulley

3.3.1 Choosing motor for press pulley mechanism

- The power of belt conveyor motors calculated based on

- 𝑃 1 : required power for the belt conveyor working without load (kW)

- 𝑃 2 : required power for the belt conveyor working with horizontal load (kW)

- 𝑃 3 : required power for the belt conveyor working with vertical load (kW)

- f: friction coefficient of ball bearing

- W: weigh of moving component in conveyor

- 𝑊 𝑚 : weigh of product in length unit (kg/m)

- V: velocity of belt conveyor (rpm)

- 𝑙: Length of belt conveyor by horizontal (m)

- 𝑙 𝑜 : Length of belt conveyor by adjusting length (m)

- 𝑊 𝑙 : distribution weigh of belt conveyor

- 𝑊 𝑐 : weight of rotating component (kg)

- 𝑊 𝑡 : weigh of rotating component in return direction (kg)

- Productivity of belt conveyor based on [1]

- A: area of cross section of material flow (m 2 )

- V: velocity of belt conveyor (rpm)

- 𝛾: specific weight of material (tones/m 3 )

- 𝑠 : coefficient depend on the slope

- Calculating weigh of moving component:

0.84+ 0 + 2 × 4.5 = 25.9 (𝑘𝑔) Our belt conveyor is less than 1m so we don’t use branch => 𝑊 𝑟

- 𝜂 𝑥 : efficient coefficient of chain drive

- 𝜂 ổ : efficient coefficient of ball bearing

- Choosing motor with power is 0.75 kW, number of revolution is 50 rpm (with reducing gearbox)

- Belt tension force on shaft:

23.6 = 53.94 (𝑁) With V is belt conveyor speed

2 ) = 107.84 (𝑁) With 𝜃 is the wrap angle of belt conveyor on shaft

Table 3.7 Transmission distribution ratio of dehydrator mechanism

Because the load and velocity is low, so we using roller chain

- With u=1, choosing 𝑧 1 = 24, so that the number of teeth on the rest is z$

𝑘 𝑜 = 1 (Center line and sprocket have the angle < 60 𝑜 )

𝑃 𝑡 = 𝑃𝑘𝑘 𝑧 𝑘 𝑛 = 0.208 × 1.43 × 1.042 × 1 = 0.310 (𝑘𝑊) Based on table 5.5 in [1], with 𝑛 01 = 50 (𝑟𝑝𝑚), choosing 1 line chains with 𝑝 12.7 𝑚𝑚 satisfy the fatigue condition:

Using Inventor to calculate the perimeter of chains is 2359.71 mm

3.3.2.2 Verify the strength of chain drive

According to the KANA model 40-1X10FT, the fatigue load is Q100 N Weight of 1m of chain drive is q=0.61 kg

1.2 × 529.26 + 7.56 + 0.09 = 28.16 According to table 5.10 in [1] with n = 50 rpm, [s]=7 So s > [s]: Satisfy the fatigue condition

According to the formula 5.17 and table 13.4 in [1]:

- Pitch circle diameter of chain sprocket

- With: 𝑟 = 0.5025𝑑 𝑙 + 0.05 = 0.5025 × 7.75 + 0.05 = 3.94 (mm) và 𝑑 𝑙 = 7.75 (based on table 5.2 [1])

- Using C45 steel, quenching to reach the hardness HB210 will reach allowable stress [𝜎 𝐻 ] = 600 MPa Satisfy the condition

- Calculating forces acting on shaft based on formula 5.20 in [1]

- Chose the shaft’s material is C45 Steel (quenching), strength stress σb = 650 MPa

- The torque stress allowance [τ] = 15÷30 (MPa)

- Torsional moment at working shaft:

- Initial diameter of working shaft

Fig 3.8 Force diagram on press pulley

Fig 3.9 Free body diagram of press pulley

- Total force based on direction y= 0:

- Total force based on direction x = 0:

Fig 3.10 Force and moment diagram of press shaft on xOz plane

Fig 3.11 Force and moment diagram of press shaft on yOz plane

At belt pulley cross section:

At hammer mill cross section:

- At dangerous cross section: d = 45 cross section σ −1 = 0.436σ b = 0.436 × 600 = 261.6 (MPa) τ −1 = 0.58σ −1 = 0.58 × 261,6 = 151.7 (𝑀𝑝𝑎)

- Calculating σ aj and σ mj based on 10.22 in [1] σ mj = 0 σ aj = σ maxj =M j

- Calculating τ mj and τ aj based on 10.23 in [1] τ mj = τ aj = τ maxj

- Calculating s σj and s τj based on 10.21 in [trinh chat] s σj = σ −1

- Finally, calculating s j based on formula 10.19 in [trinh chat]

- Based on table 9.1a on [1], we choosing keyway with this diameter:

- We verify the strength at the bearing that bear bigger load: 𝐹 𝐵 = 1964.4 (N)

Fig 3.12 Force diagram of belt conveyor shaft

- Total force based on direction y= 0:

- Total force based on direction x = 0:

Fig 3.14 Force and moment diagram of belt conveyor shaft

- At dangerous cross section: d = 30 cross section σ −1 = 0.436σ b = 0.436 × 600 = 261.6 (MPa) τ −1 = 0.58σ −1 = 0.58 × 261,6 = 151.7 (𝑀𝑝𝑎)

- Calculating σ aj and σ mj based on 10.22 in [1] σ mj = 0 σ aj = σ maxj =M j

- Calculating τ mj and τ aj based on 10.23 in [1] τ mj = τ aj =τ maxj

- Calculating s σj and s τj based on 10.21 in [1] s σj = σ −1

- Finally, calculating s j based on formula 10.19 in [trinh chat]

- Based on table 9.1a on [1], we choosing keyway with this diameter:

- We verify the strength at the bearing that bear bigger load: 𝐹 𝐵 = 673.42(N)

MANUFACTURING PROCESS

Hammer mill mechanism machining process

The hammer mill mechanism serves as the primary mechanical actuator of our machine, comprising nine distinct components: the main shaft, hammer mill shafts, bushes, hammers, screws, washer, side plate, core plate, and key Our team machined three core components—the main shaft, hammer mill shafts, and bushes—utilizing the equipment available at Viet-Duc Center, while the remaining components were sourced from various suppliers This section will first discuss the elements we manufactured in-house, followed by those acquired from external vendors.

The main shaft serves as the core of our hammer mill mechanism, receiving rotational motion and energy from the motor via a belt drive This motion is then transferred to the hammer, generating the powerful smashing force essential for effective material processing.

+ Tolerances for assembly: At the step diameter we need to assembly bearing

In this case we use clearances fit then fixed it by the screws of bearing

+ Keyway: This shaft will be assembled with pulley of belt drive, so that it will have the keyway

4 Material removal allowances and machining methods

+ Material removal allowances: the largest diameter is 40mm and the leght of

56 shaft is 510 mm So we choosing the C45 cylindrical structure steel with diameter and length are 45mm and 530mm respectively

+ Machining method: Turning on engine lathe and milling on milling machine for keyway

Table 4.1 Machining routes for main shaft

No Route Steps Machine Cutting tool

Drilling center Center drill bit

2 Face turning to reach 510 mm parameter

Face turning Carbide insert tool

3 Rough turning Rough turning to 41 mm Rough turning to 37 mm for the step diameter

4 Rough turning Rough turning to 37 mm for the remain step diameter

3 jaw chuck and driving center tip

Fig 4.2 Technical drawing of main shaft

- Cutting condition for each routes:

- Deep of cut: choose t= 5mm

- Feed rate: According to [2] page 8, choose S = 1.5 mm

- Cutting speed: According to formula in [2] page 9

Follow the table 1.1 in [2], we have:

Table 4.2 Parameter for face turning

Follow the table 9.1 we have:

Route 2: Face turning: Same condition with route 1 until reach 510 mm

Route 3: Rough turning to 41 mm and 37 mm for the step diameter:

- Deep of cut: choose t= 4 mm

- Feed rate: According to [2] page 8, choose S = 1 mm

In this route, the only parameter that change is 𝐾 𝑜𝑣 = 1 based on table 10.1 in

Route 4: Rough turning to 37 mm for the step diameter: same cutting condition with route 3

Route 5: Finishing turning to 40mm diameter

- Deep of cut: choose t= 0.5 mm with 2 steps

- Cutting speed: According to table 5.19 in [3], we have 𝑉 = 200 𝑚𝑚/𝑚𝑖𝑛

Route 6 and 7: Finishing turning to 35mm diameter

Deep of cut: choose t= 0.5 mm with 4 steps

Feed rate: According to [2] page 8, choose S = 0.1 mm

Cutting speed: According to table 5.19 in [4], we have 𝑉 = 200 𝑚𝑚/𝑚𝑖𝑛

- Deep of cut: 2.5 mm for 2 steps

𝑇 𝑚 × 𝑡 𝑥 𝑣 × 𝑆 𝑦 𝑣 × 𝐵 𝑢 𝑣 × 𝑍 𝑝 𝑣 × 𝐾 𝑣 (4.1) Follow the table 1.1 in [2], we have:

Table 4.3 Parameter for milling keyway

Fig 4.3 Main shaft machining on lathe machine at Vietnamese-German Center

60 Fig 4.4 Main shaft machining on milling machine at Vietnamese-German Center

4.1.2 Hammer mill shaft machining process

Fig 4.6 Technical drawing of hammer mill rod

The hammer mill shaft plays a vital role in this mechanism It secure hammer and let them rotating freely on shaft

+ Tolerances for assembly: We want the hammer freely rotating on shaft so we need to use clearance fit

- Material removal allowances and machining methods

For our project, we are utilizing C45 cylindrical structure steel with a diameter of 22mm and a length of 300mm, accommodating material removal allowances of up to 20mm in diameter and a shaft length of 250mm.

+ Machining method: Turning on engine lathe

3 Rough turning Rough turning to 20.5 mm Semi-finishing turning to 20 mm

5 Cutting condition for each routes:

- Deep of cut: choose t= 5mm

Step 1: Rough turning to 20.5mm

- Deep of cut: choose t= 1.5 mm

- Feed rate: According to [2] page 8, choose S = 1 mm

In this route, the only parameter that change is 𝐾 𝑜𝑣 = 1 based on table 10.1 in

Step 2: Semi-finishing turning to 20mm

- Deep of cut: choose t= 0.5 mm

- Cutting speed: According to table 5.19 in [4], we have 𝑉 = 200 𝑚𝑚/𝑚𝑖𝑛

Fig 4.7 Hammer mill shaft machining at Vietnamese-German Center

Fig 4.8 Technical drawing of bushes

The bushes function is to constraint the movement of hammers on hammer mill shaft

+ Tolerances for assembly: These bushes assembly onto hammer mill shaft easily and freely rotate So that we choose clearance fit

- Material removal allowances and machining methods

For our project, we require material removal allowances for a bush with a maximum diameter of 40 mm and a length of 20 mm Therefore, we have selected C45 cylindrical structure steel, featuring a diameter of 40 mm and a length of 23 mm, to meet these specifications effectively.

+ Machining method: Cutting work piece on band saw machine Turning and drilling on engine lathe

Cutting work piece in to 23mm

Deep of cut: choose t= 0.5mm

Feed rate: According to [2] page 8, choose S = 1.5 mm

Cutting speed: According to formula in [2] page 9

66 Fig 4.9 Cutting work piece and drilling bushes at Vietnamese-German Center

Fig 4.10 Final product of bushes

4.1.4 Side plate and center plate:

Fig 4.11 Technical drawing of side plate

Fig 4.12 Technical drawing of center plate

The side plate and center plate are the parts that connecting and fixing main shaft and hammer mill shaft together

+ Tolerances for assembly: 4 holes in each plate must have clearance fit for easy assembly

When it comes to machining sheet metal parts, the process can be challenging due to inadequate equipment As a result, we choose to outsource this task to HONG DAT for expert handling.

Technical Co Ltd., They used laser cutting machine to cut this part

Fig 4.13 Center and Side plates

Fig 4.14 Technical drawing of hammer mill

These hammers mill will be hanged on hammer mill shaft and rotating freely When the machine working, these hammers will contact with material to crush it up

+ Tolerances for assembly: 2 holes in each plate must have clearance fit for easy assembly

Outsourcing the machining of our sheet metal parts to HONG DAT Technical Co Ltd has proven effective due to our limited equipment They utilize advanced laser cutting machines, ensuring precision and quality in the fabrication process.

4.2 Hammer mill cover manufacturing process

The hammer mill cover is a crucial component that houses the hammer mill mechanism, ensuring its efficient operation while protecting operators from potential hazards caused by material ejection This structure consists of four interconnected parts: the upper cover, middle cover, lower cover, and screen, all designed to work seamlessly together.

The upper cover is use to guide the material onto the hammer mill mechanism and protect the operator from the flying particle in shredder process

+ Material: 5mm SPC sheet steel and 10mm SPC sheet steel for rib

- Machining method: This is sheet metal part which include 2 machining methods: laser cut, welding

- Bill of materials (BOM): Because these part we outsource to Hong Dat Technical

Co Ltd so we need to made the BOM to get the quote

Table 4.8 Bill of materials for upper cover

No Name of part Quantity Material Images

Table 4.8 Bill of materials for upper cover (cont.)

After we have BOM, we export all the related sheets and component into technical drawing, as well as assembly drawing to vendor

Fig 4.18 Upper cover assembly drawing

Fig 4.19 Upper cover final product

Fig 4.20 Middle cover technical drawing

The middle cover is use to fix the hammer mill They also have auxiliary side ledges for better shredding efficiency

Table 4.9 Bill of materials for middle cover

- The middle sheet 5 is hard to machining It consists of bending metal sheet with

5 iron bars welded onto it

- Same with the upper cover, we need 6 holes with 13mm diameter to joint these together by M12 screws

- The middle covers also have 22.5mm radius haft circle for the main shaft can go through and connected with ball bearing

- The ribs in the sheet 4 are to increase the sturdiness of machine

75 Fig 4.21 Middle cover technical drawing

Fig 4.23 Lower cover technical drawing

The middle cover is use to fix the hammer mill They also have auxiliary side ledges for better shredding efficiency

Table 4.10 Bill of materials for lower cover

Table 4.10 Bill of materials for lower cover (cont)

78 Fig 4.24 Lower cover assembly drawing

Fig 4.27 Screen cover technical drawing

The primary function of the machine component is to sort materials into the desired size, ensuring efficient processing The screen is designed for easy sliding onto the lower cover and includes a protective cover for enhanced functionality.

+ Material: 4mm SPC sheet steel

- Machining method: This is sheet metal part which include 3 machining methods: laser cut, welding and bending

Fig 4.30 Machine frame technical drawing

The machine frame is the most crucial component of our machine, as it supports the entire load from the mechanism, motor, spare parts, and electrical boxes Therefore, precise calculations and careful manufacturing of the frame are essential to ensure optimal performance and durability.

+ Material: Various type of profile steel which will listed in the section below + Feature: 4 wheels and take-up mechanism to make the machine moving freely

- Machining method: This frames mostly implemented by steel cutter and welded

Table 4.11 Bill of materials for machine frame

84 Fig 4.31 Welding drawing of machine frame

Fig 4.34 Machine frame wheel and take-up mechanism assembled and painted

The dehydrator operates using a system of four rollers linked by a textile belt, powered and driven by a motor through a chain mechanism Due to their large size and complexity in machining, these rollers were outsourced to a local mechanical shop, as the Vietnamese-German Center faced challenges in producing them.

Fig 4.35 Driving shaft technical drawing

Fig 4.36 Driven shaft technical drawing

Roller fixture plate: Outsourced at HongDat Technical Company

Fig 4.37 Roller support plate technical drawing

Fig 4.38 Support plate welded onto machine frame

88 Fig 4.39 Assembled rollers on machine

MACHINE ASSEMBLY PROCEDURES

Hammer mill mechanism assembly

The hammer mill mechanism comprises nine essential components, with the main shaft securely welded to three plates: two side plates and one center plate The remaining parts are assembled using tolerances and temporary joints, such as screw-nut connections.

In order to make it easier for precise welding, 3 plates, hammer mill shaft, bushes and hammer mills will be assembled first to create the frame

Then we assembled the shaft onto the assembly above with 2 UCF ball bearing Finally, we fixed it onto machine frames and weld 3 plates onto main shaft

After that, we assembly lower cover, hammer mill mechanism, middle cover and upper cover onto machine frames based on this procedure:

Fig 5.2 Hammer mill mechanism assembly

90 Fig 5.3 Assembly hammer mills and bushes onto hammer mill shaft and plates

Fig 5.4 Assembly last side plate onto the mechanism by screws and washes

91 Fig 5.5 Assembly the lower cover onto machine frame

Fig 5.6 Finished assembly of hammer mill mechanism

Hammer mill mechanical drive: belt drive

According to the calculation, we need belt drive with 3 lines of belt, the type of belt is V-belt A-60

First, we need to assembly two pulley onto mechanism shaft and motor shaft

Then fixed the motor onto machine frame so that it linear with the pulley of hammer mill shaft

Finally, we attach 3 lines of belt on to the drive and have some final adjustment

Fig 5.7 Belt drive assembly process

Fig 5.8 Belt drive assembly in practice

Press belt mechanism assembly

The press belt mechanism consists of 3 main parts: support plates, pulleys and belt

The system of 4 pulleys will be assembled onto the machine frame by the support plates welded onto machine frame

To begin the assembly process, it's essential to weld support plates onto the machine frames in the correct position Next, we will attach the top and bottom pulleys along with the UCF and take-up housing, followed by fitting the belt onto these pulleys.

Next, we assembly the couple of pulleys for dehydrator mechanism with UCF and take-up housing

Finally, we need some last adjustment with the position of each pulley the belt itself,

Fig 5.9 Dehydrator mechanism assembly procedure

Fig 5.12 Assembly front pulley, belt and under pulley

Press belt mechanism drive: chain drive

According to the calculation, we use roller chain with complex structure The motor transferring the power to driving sprocket, then transferring it again into 3 driven sprockets by chain links

Electrical box wiring and assembly

To effectively manage two single-phase motors, we aim to control their operation both individually and simultaneously This need for separate and combined functionality is the driving force behind our design of the wiring diagram.

Choosing the right contactor for a 4kW motor is essential; improper selection can lead to the contactor and thermal relay being unable to handle the motor's current requirements.

In this case, the power of motor is 4kw = 4000 w, the 1 phase grid in our country is 220V and 𝑐𝑜𝑠𝜑 = 0.8 So that the electric quota of this motor:

√3 × 220 × 0.8= 13.12 𝐴𝑚𝑝𝑒 The starting current of 1-phase motor is around 5~7 time the Idm, so that we need the bigger contactor Following the experiment for fast choosing contactor, we have:

For the thermal relay, according to the figure below, we have 1-phase 4kw motor

So that we choose 24A thermal relay

When selecting a circuit breaker (CB) for a 1-phase motor, it is crucial to consider that the starting current can be significantly higher than the motor's nominal current, typically ranging from 3 to 5 times the nominal value.

So we choose 40A CB for this machine

When selecting electrical wire for a motor, it is crucial to choose the appropriate diameter; too small a wire may result in insufficient current to start the motor, while too large a diameter can significantly increase costs.

According to [23], with the power 4kw, we should choose 10mm diameter wire

Fig 5.18 Exterior electrical box Fig 5.19 Interior electrical box

After putting all major and small parts together, with some adjustment, our group successfully assembled the machine

Fig 5.21 Frond and back views of finished machine

Fig 5.22 side views of finished machine

EXPERIMENT AND ANALYSIS

IMPROVEMENT, RESULT AND CONCLUSION

Tiêu đề	Research, design and implementation of a coconut shell shredder and dehydrator machine for organic fertilizer production
Tác giả	Chu Huy Hoang, Dang Ngoc Thien, Hoang Huu Nghia
Người hướng dẫn	Phan Thanh Vu, ME
Trường học	Ho Chi Minh City University of Technology and Education
Chuyên ngành	Machine Manufacturing Technology
Thể loại	Graduation project
Năm xuất bản	2022
Thành phố	Ho Chi Minh City

Định dạng
Số trang	133
Dung lượng	10,45 MB