However, because energy consumption is calculated by the multiple product of the shear force and shear velocity, in several cases if the chopping process has a small shear force with hig
Trang 1THAI NGUYEN UNIVERSITY THAI NGUYEN UNIVERSITY OF TECHNOLOGY
THAI NGUYEN – 2020
Trang 2698 million tons, 1730 million tons and 417 million tons, respectively
Corn is the third most important food crop after rice and wheat [27], widely grown around the world [45, 97] Corn stalks account for one-third of the annual production compared to other agricultural residues [41] In Vietnam, maize is not only an important cereal and food, but also recently plays a role as a raw material plant for the production of environmentally friendly ethanol - E5 [10] In particular, a new trend is being developed that direct cultivation of biomass maize will also increase the demand for post-harvest processing
Chopping of harvested corn stalks is an important preliminary step in the processing of animal feed, biomass pellet production as well as in other processing processes For example, the corn stalk should be chopped into 6.4 mm lengths for gasification [95], 1 mm long for chemical conversion [102], 2-10 mm for composting yeast forage, or 5-6 mm long for briquetting [76] On the industrial scale, chopping can be done by specialized chopping components, which are combined at the rear of harvesters
In developing countries such as Vietnam, farmers often burn all kinds of agricultural residues on fields This is not only a waste but also a negative impact on the environment, such as air pollution or causing forest fires One of the reasons is that the cost of chopping is
Trang 3still high Because agricultural residues are often very cheap, depreciation, labor and especially energy consumption will account for a large proportion of the cost of semi-finished products Therefore, finding solutions to reduce the amount of energy consumed when chopping has been carried out by many international studies [24, 34, 37, 43, 78, 87, 107] In Vietnam, scientific publications were found to mainly focus on design techniques based
on productivity, durability, etc for harvesting machines combined with chopping of some agricultural products such as maize [ 3, 4, 6, 17], straw after harvesting rice [19] or banana stalks [1], processing pineapples [9], cutting fibers from coconuts [13] These designs focus on solving the chopping function according to the principles of cutting discs, cutting drums, designed to achieve the chopping productivity However, the issue of energy saving has hardly been mentioned by previous studies
Many international studies have been done to reduce cutting force and cutting power by improving the tool design and selecting a reasonable cutting mode Reducing shear force is considered as one
of the optimal solutions to reduce energy consumption Moreover, reducing the cutting force will also contribute to reducing the size of the machine's parts and thus reducing the size of the machine However, because energy consumption is calculated by the multiple product of the shear force and shear velocity, in several cases if the chopping process has a small shear force with high velocity, it may required a large power consumption In some studies, empirical models using a pendulum have been developed to measure the shear force and shear power required when chopping agricultural residues [32, 39, 66, 71, 85, 100] Factors assessed include the effects of the type of cutting blade, the different cutting angles [24, 27, 44, 96] Several other studies have evaluated the influence of the straight blade sharp angle, the rotation speed of the disc-type knives to the cutting ability of corn stalks [32, 78, 85, 90, 103] A new approach of
is applying biomechanics to design and manufacture of knife profiles based on the tooth profile of insects such as mantis, corn-eating worms, grasshoppers, hair trimmers [64] , 65, 71, 72, 100] Finite element method and experimental simulation results show numerous benefits in terms of shear force and power consumption reductions However, this type of blade profile would be difficult in
Trang 4manufacturing, sharpening and thus would be difficult to apply in commercial machines There have been many studies to find solutions to save energy consumption [27, 28, 38, 44, 49, 66, 68, 69] However, the solution to the multi-objective optimization problem for both shear forces and energy consumption, especially for chopping machines using counter edge [24, 34, 37, 43, 78, 87, 107]
is still a remained knowledge gap
Another research direction to save energy in the process of chopping agricultural residues is to identify proper working parameters [28,
31, 33, 49, 50, 58, 59, 61, 78, 88, 89]
To date, the problem of concurrently reducing the force and cutting power directly on chopping machines, using counter edge has not been solved No studies have been found to evaluate the simultaneous effects of working parameters and structural parameters on cutting force and power on such machines For the above reasons, the topic: "The study identifies some reasonable parameters of the process of cutting corn stalks after harvest" with urgency and practical significance
2 Aims, objectives and scopes of the present research
2.1 Research aims
The main aims of this study is to determine important structural parameters and proper operational parameters of the chopping process of havested corn stalks in order to concurrently minimize the cutting force and cutting power
Research subjects:
The study subjects are some main parameters affecting shear force and energy consumption of corn stalk choppers
2.2 Research objectives
Objectives of this study are as following:
+ Designing and manufacturing an experimental device that can control the input parameters, obtain all output parameters of the chopping process, meeting the requirements of the experimental study;
+ Identify parameters that have strong effects on the force and cutting power when chopping corn stalks after harvesting;
Trang 5+ Identify a set of design and operation parameters of chopping machines to minimize cutting force and cutting capacity;
+ Develop a profile model of chopping blade to ensure design parameters
2.3 Scopes
The scope of the study is to conduct experiments of chopping single corn stalks in order to determine the specific cutting force and cutting power, providing a basis for calculating the problem of cutting process Experiments are carried out in laboratories
Parameters to be evaluated include: feed angle, approach angle and cutting speed The harvested corn stalks used as experiments were stored under the same conditions It is assumed that mechanical properties and moisture content of experimental samples are the same
The research methods used in this study include design of experiments, applied statistical analysis and mathematical regression techniques
3 Application-oriented significances
+ The results can be applied to design and manufacture of agricultural chopping machines Although only experimented with corn stalks, the significant effects of the feed angle and the approach angle were due to the grain texture of the stem Most other stalks and agricultural residues also have such grain structure Therefore, the trend of influence of the above angles can be applied when chopping other plants
+ The research results of the thesis can be used in design calculations and selection of working parameters for disk chopping machines, contributing to the exploitation and processing of agricultural residues for production and life, reduce energy costs, thereby contribute to reduce the environmental pollution
4 The new contributions of the study
+ Studied the cutting force and cutting power in chopping of corn stalks for an intermediate cutting speed (Ranged from 1 to 10 m/s) This is a new contribution to this research trend in the world
Trang 6+ Evaluated the simultaneous effects of approach angle, feeding angle and cutting velocity to the cutting force and cutting power in chopping process of corn stalks This is a new contribution compared
to previous scientific publications
+ Carried out a couple of conflict objective functions, including the cutting force and cutting power Thereby, the multi-objective optimization problem for both cutting force and cutting power of corn stalks has been solved Compared to a typical case of practical use of chopping machines, applying the optimal parameters not only reduced the cutting force by 2.3 times, but also dropped down the power consumption by 4 times Identified a set of working parameters, which serves as a basis for designing and manufacturing chopping machines of agricultural residues, applied in production practices
+ Proposed a blade profile using logarithm spiral and evaluated its advantages compared to blades using straight and curved edges Using the proposed profile allows to keep the approach angle as constant along the blade edge Consequently, the optimum value of the approach angle can be maintained belong the cutting edge of the blade
+ Developed an algorithm to automatically calculate and draw the blade shape with different sizes The embedded software module
in AutoCAD environment allows to create technical drawings and to export the data sets for tool machining on CNC machines
6 Thesis structure
Chapter 1 Literature review
Chapter 2 Theoretical basis of chopping process of agricultural residues
Chapter 3 Design, manufacture and evaluate the experimental system
Chapter 4 Experimental study and development of the blade profile
CHAPTER 1 LITERATURE REVIEW
1.1 Introduction
Trang 71.2 State-of-the-art of corn production in the world and in the country
1.2.1 Corn production in the world
1.2.2 Maize production in the country
1.3 Some characteristics of the maize after harvested
1.4.1 Processing animal feed
1.4.2 Processing commercial products
1.5 Agricultural residues chopping machines
1.5.1 Drum chopper
1.5.2 Disc chopper
1.5.3 Chopping machine using tooth knives
1.6 Experimental studies
1.6.1 Assignments of angle parameters
1.6.2 Pendulum-impact for experimental device
1.6.3 Vertical rotational disk device
1.6.4 Universal testing machine
1.7 Some results in saving energy consumption
Trang 8The specific parameters of corn stalks that affect the chopping process have been confirmed in previous studies Important parameters include: the moisture content, elastic modulus, friction coefficient between corn stalks and some materials
Experimental models for harvesting machines would not be fully applied to practical chopping machines, due to the inconvenience to implement fedding angle The experimental model used inconvenient impact pendulum to measure shear force, which is difficult to vary the cutting speed Some other types of experimental devices using univeral testing machines are not convenient to vary the cutting speed and feed angle Therefore, this study uses a real chopping machine with rotational disk to implement experimental study
CHAPTER 2 THEORETICAL BASIS OF CHOPPING PROCESS OF AGRICULTURAL RESIDUES
2.1 Introduction
2.2 The chopping principle
2.3 Basis of chopping process dynamics
2.4 Multi-objective optimization
Chapter conclusions
Chapter 2 presented a summary of the theoretical basis and the cutting principles of the chopping process The contents of this chapter provided a basis for the study of dynamics and energy consumption of corn stalk chopping Some important contents are summarized as follows:
There are two basic principles of the process of cutting agricultural stalks, including: 1) impact cutting, the relative movement between
Trang 9the knife and the material tree (cutting motion) performed in the normal direction; 2) shear cutting, cutting motion combines both normal and tangent directions Compared to impact cutting, the shear-cutting process significantly reduces the cutting force In order
to keep the stalks in the wedge-shaped clearance of the cutter and the counter edge, the velocity of the slide should be set based on the friction coefficient between the stem and the tool material
Cutting force and power consumption are two objective functions that have a conflict of interest Therefore, it is necessary to solve the optimal problem simultaneously for both above mentioned criteria The multi-objective problem identifies each criterion in accordance with cutting technology steps: applying two expected functions (2.8) and (2.9); Implementing experimental study on a real chopping machine (cutting) to concurrently optimize the two objective functions
In order to clarify the research question, it is necessary to develop an experimental device similar to commercial chopping machines, having capable of varying the cutting speed and the correlation angles between the knife and the stalks These contents will be
presented in the next chapter
CHAPTER 3 DESIGN, CREATION AND EVALUATION OF
TESTING EQUIPMENT SYSTEM 3.1 Introduction
3.2 Design of experimental system
Trang 10Fig 3.2 Relative position of the stalk in the cutting process: 1) cutting tool, 2) hinge joints, 3) force sensor, 4) maize stalk, 5) counter shear, 6) spring
3.2.2 Structural design
Some of the structural design are presented in Fig 3.3 and 3.4
(a) (b)
Fig 3.3 Diagram of the drive principle of a chopping machine a) Structure
of a commercial machine, b) Proposed structure: 1) electric motor; 2) Belt transmission; 3) drive shaft; 4) flat knife disc; 5) Coupling; 6) Torque sensor; 7) Load cell; 8) counter shear
Fig 3.3 A 3D model of the
experimental setup 1) belt wheel,
2) spindle shaft, 3) knife, 4) screw,
5) clamp, 6) maize stalk, 7) counter
shear
Fig 3.4 Relative position of the stalk in the cutting process
3.3 Selecting measuring and data collection equipment
3.3.1 Cutting force sensor
The cutting force sensor Kistler 9712A500 (Figure 3.6) was used to measure the impact force
Trang 11(a) (b)
Fig 3.5 (a) Force sensor Kistler 9712A500 và (b) Force sensor holder
3.3.2 Measure the friction force
The friction force was used by a mini load cell with a capacity of 100
N (Figure 3.7)
3.3.3 Torque sensor
A torque sensor RTT-200 (Figure 3.8) was used to measure torque transferred via the spindle
Fig 3.6 Load cell FSSM-100 Fig 3.7 Torque sensor RTT-200
3.3.4 Equipment for collecting and processing data
A DAQ model NI USB-6008 was used to collect data
3.3.5 Software for designing and analyzing experimental data
The Minitab software was used to design of experiments and analyze the results OriginLab software was used to analyze the data
3.4 Manufacture and installation of experimental systems
The experimental device was implemented as shown in Figure 3.9
Fig 3.8 Practical Experimental Setup
3.5 Operation and some results of the system survey
3.5.1 Operating experimental systems
Trang 123.5.2 Measure cutting force and torque
Fig 3.10 Friction measurement experiment
Bảng 3.1 Experimental results of sliding friction measurement
Mass (kg) Normal force
(N)
Friction force (N)
Friction coefficient
Angle friction (0)
arctan (3.3)
Trang 133.6 Chapter conclusions
In this chapter, input parameters were determined including: feed angle, approach angle, cutting speed and the gap between the cutting edge and the counter edge The experimental device has been developed to allow for infinite control of these parameters, meeting well the data requirements according to theory of design of experiments The system of measuring and data collection equipments allows to measure output parameters simultaneously including cutting force and cutting torque to ensure reliability An experimental model was developed to determine the coefficient of sliding friction between corn stalks and cutter material Experimental studies, carried out on the above mentioned experimental system will be presented in the next chapter
CHAPTER 4 EXPERIMENTAL RESULTS AND
DEVELOPMENT OF CUTTING NETWORK MODELS 4.1 Introduction
4.2 Experimental description
Three sets of experiments were performed including: screening test; optimization of single objective, and multi-objective optimization experiments
4.3 Screening experiment
Table 4.1 Experimental Factors in Screening Experiments