2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 1 An ASABE – CSBE/ASABE Joint Meeting Presentation Paper Number: 141902781 The… [616746]

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 1
An ASABE – CSBE/ASABE Joint
Meeting Presentation

Paper Number: 141902781
The Analysis of the Ring Die Hole of Pellet Mill Based on Finite
Element
Fei Peng, Ph.D. Student: [anonimizat], China Agricu ltural University. P.O. Box 154 ，No.17 Qinghua East road,
Haidian District, Beijing, Ch ina, 100083, [anonimizat]
Hongying Wang*, Professor
College of Engineering, China Agricu ltural University. P.O. Box 154 ，No.17 Qinghua East road,
Haidian District, Beijing, Ch ina, 100083, [anonimizat]
Jie Yang, Ph.D. Student: [anonimizat], China Agricu ltural University. P.O. Box 154 ，No.17 Qinghua East road,
Haidian District, Beijing, Chi na, 100083, [anonimizat]
Dandan Kong, Master student: [anonimizat], China Agricu ltural University. P.O. Box 154 ，No.17 Qinghua East road,
Haidian District, Beijing, China, [anonimizat]
(*Corresponding author: Hongying Wang)

Written for presentation at the
2014 ASABE and CSBE/SCGAB Annual International Meeting
Sponsored by ASABE
Montreal, Quebec Canada
July 13 – 16, 2014
Abstract . The granulation process needs to be accomplished in conjunction with ring die and roller, so the ring

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 2die and roller need to have good mechanical properties and service life. Based on full study of domestic and
international pellet mill, a kind of small pellet mill will be designed and its 3D model also will be established with
3D design software PROE. After that, the gradual pr ocess of pellets during ex truding will be simulated and
analyzed based on Finite Element, the internal stress and displacement fields in the extrusion will be gotten, the deformation trends and friction during the extrusion stress distribution were analyzed. The results can
provide a reliable scientific basis for correct design of pellet mill. The resu lts can provide theoretical basis for
the optimization design of pellet mill, improve it’s serv ice life, reduce the develo pment cost and provide the
basis for high efficiency and low energy consumption production of feed manufacturers and enterprises.
Keywords. Pellet mill; Extrusion and pelleting; Finite element; Simulation analysis

Introduction
Pellet mill is one of four main machines of the f eed processing machinery, which occupies an important
position in the feed granulation processing. As import ant part of pellet mill, ring die and roller are the key
structure of granulation molding, but th ey still have a lot of disadvantages su ch as unreasonable structure, the
wear failure and low service life, so the design and rese arch of roll and die have important significance for feed
manufacturers and enterprises. Many researches (Vervaet et al., 1994; Mani et al., 2006; Nielsen et al., 2009)
on compacting and pelleting. Vervaet et al. (1994) Determined the parameters influencing granule quality using a continuous granulator in an experimental design. Rolfe et al. (2001) determined how particle size, moisture
content and screw speed affected the pellet durability, wate r stability index, and buoyancy. Arshadi et al. (2008)
Studied some factors effect pelletizing of sawdust, and found out that the some parameters which was helpful to design the pelletizing process for moderate energy consumption and high pellet quality.
There are a lot of studies have been researched on the me chanism of extruding and pelleting. Tabil et al. (1996)
researched the relationship between the physical qua lity of alfalfa pellets and process conditions, and
developed a correlation between energy consumption and pellet durability. A rational model to give a
theoretical explanation of how the biomass specific param eters, such as the friction coefficient and Poisson’s
ratio, influenced the pelletizing pressure was establ ished and verified (Holm et al.,2006; Holm et al.,2007).
Jingfeng et al. (2007) carried out an experiment based on different granularity of alfalfa powder, and
established the mathematical model to obtain the relations hip of the extruding force, granularity and density as
basic parameter. Nielsen et al. (2009) investigated the effect of fibre orientation in the raw material particles of
sawdusts on their pelletizing properties, however, the studies focused primarily on pelleting formulations and
processing technology.
The objectives of this work were: (1) to establish the models of extrusion by mechanical analysis, and the finite

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 3element analysis on the surface of t he ring die were done by ANSYS; (2) to simulate and analysis the internal
stress and displacement fields during the gradual proc ess of pellets. The sudy c an provide a scientific method
and theoretical basis for the structure design of ri ng die and the improvement of pelleting technology.
The model of forming process
Based on the effect of comprehensive factors which are te mperature, the frictional force, the pressing force and
others, the gap of the powder is narr owed during the pelleting process. Then it forms into pellets that have a
certain strength and density. As showed in figure 1, the materials between the ring die and roller result into
three areas: material supplying area, extruding defo rmation area, and extruding formation area (XIE,. 2002).
The materials between the ring die and roller result in to three areas: material supplying area, extruding
deformation area, and extruding formation area. (1) Material supplying area. In this area, the materials flatten
against the inner surface of the ring die tightly effected by the centrifugal force generated by the rotational die.
There is not significantly affected by mechanical which affects on the materials. The density of the material is
0.4-0.7 g/cm3 ; (2) Deformation area. Effected by the rotation of the ring die and the roller, the materials
gradually come into the area in which the materials are gradually compressed under the action of the extruding
force, forming the relative displacement among the materi als. With the increase of the extruding force, the gap
of the material particles decreases rapidly. Elastic deformation and plastic deforma tion occur simultaneously.
The density of the material in this area is 0.9-1.0 g/cm3 ; (3) Formation area. In this area, the clearance of the
material particles reduces further. Wi th the increase of the extruding force, the contact area of the material
particles increases rapidly. The density of the material in this area can reach 1.2-1.4 g/cm3.

Figure 1. The sketch of pelleting mechanism
In the deformation area, CAO and JIN (2003) figured out β is the necessary conditions of pelleting processing.

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 4According to figure 2, it can be calculated as the following equation:

212 1
1tanffff
 (1)
) 2( cos cos2 2 2rRr r rRh     (2)
Where: β is the critical angle (°), f 1 is the friction coefficient between the materials and the ring die, f 2 is the
friction coefficient between the materials and the roller; h is the extruding height of the materials, R is the radius
of the ring die, r is the radius of the roller.
The production rate of pelleting can be given as follows:





  2
2 2
02
0 cos sin ) 1 12 n RNrZQ (3)
Where: Q is productivity (t/h), Z is the number of the roller, r 0 is the hole diameter of t he ring die, N is the hole
number of the ring die, ρ0 is the initial density of the materials. n is the rotation rate of the ring die. λ is the ratio
between the diameter of the ring die and roller.

Figure 2. The sketch of pelleting mechanism

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 5

Figure 3. The force sketch of material in the die hole
The following derivation gives an expression for the pelle tizing pressure-variation changes in the entrance of
the hole (Figure 3). The equation derived above holds very useful information related to the pelletizing of
different raw materials. The equation 4 ( Holm et al., 2006) can be given as follows:

LRN rxfv
LRN
XVPeVPPh LR 0 / 2 0  (4)
Where: PX is the extruding pressure intensity in the limit of X; PN0 is the pretightening pressure intensity
(N/mm2); VLR is the materials’ Poisson Ratio; f is the fric tion coefficient between the materials and the hole of
ring die; X is the distance between the cross section and outlet.
Model Building
Modeling the three-dimensional of the ring die
The three-dimensional model was established wi th 3D design software PROE. Elastic modulus E and Poisson
ratio of the ring die’s materials were 2.1 GPa and 0.25, respectively. As Figure 4 showed, the three-dimensional were: 220mm for the external diameter, 180 mm for the internal diameter, and 30mm for the width,
respectively. The hole diameter of the ring di e had three size: 1.0mm, 1.5mm, and 2.0mm.

Figure 4. The 3D design based on the software PROE
After that, the gradual 3D design was imported in to ANSYS, Solid45 elements was chosen to define the

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 6element type. Then material model was simplified to re move the hole, the parameters was set, and the model
was meshed as the following Figure 5. Assuming the pr ocess affected on two-dimensional plan, the 3D model
was simplified further to 2D (Figure 6).

Figure 5. The meshing of the model based on the software ANSYS
Then the contact was established, it belonged to surface to surface contact problems of rigid-flexible body.
After that, the constraint, load, and drive were impose d. Afterwards, the deformation trends and friction during
the extrusion stress distribution were analyzed.
The finite element model for the ring die hole
Due to the extrusion pressing from the roller, the loos e materials bonded together in the extruding formation
area. For the convenience of research, the materials can be considered as a continuum compressible and
studied based on the continuum elastic-plastic mechanic s theory. The sketch of extruding process was Figure
6. According to the symmetry of die hole and materials, half of them was considered as the model of simulation
(Figure 7). The material properties were shown in Table 1.

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 7

Figure 6. The sketch of extruding model

Figure 7. The model and it’s FEM grid
Table1 Material properties
Type Attributes parameters
density ρ/ kg/m3 1200
angle of internal friction /° 32
1. materials cohesion /kPa 10
modulus of elasticity E/MPa 2
Poisson's ratio μ 0.4
2. the ring die modulus of elasticity E/GPa 210

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 8 Poisson's ratio μ 0.25
3. the roller friction coefficient μS 0.2

Results and Discussion
As can be seen from Figure 8 (a, b, c), in the process of extrusion, the material subjected to the combined
effects from the above pressure and squeeze of the mold hole wall friction, the stress of material showed some
regularity: with the continuous extr usion press, the bottom stress of materials was larger and the dense was
bigger; the materials closer to the ring hole suffer ed bigger extruding force and displacement; the materials
closer to the center suffered smaller extruding force and displacement.

(a). The contour chart of radial stress (b) . The contour chart of axial stress

(c). The contour chart of radial strain (d). The contour chart of equivalent stress
Figure 8. The stress and st rain analysis based on ANSYS
As can be seen from Figure 8 (d), after the material got into the die hole, it suffered the friction force which
comes from the extrude force of the roller and the friction force of the ring hole. In the place of the chamfer of

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 9ring hole, the materials suffered uniform force; in t he contact place between die hol e chamfer and the straight
hole, the material suffered the maximum friction force. The material suffered frictional resistance after getting
into the straight hole and led to the phenom enon that the fluidity of the exter nal part was worse than the interior.
Therefore the pellet feed faced the result of elastic exp ansion and hysteresis, which caused some internal force.
This will be part of the reason for causing for tr ansverse cracks on the surface of pellet feed.
Conclusions
The simplified extruding and pelleting model was built in ANSYS, and FEM meshing, constraints, and load
were also imposed.
Combining the main characteristics of extrusion and pe lleting process and the stress condition of the materials
getting into the ring die hole, the process was simula ted and analyzed based on Finite Element. The results
showed that: both the structure displacement and stress we re within permissible range, so the material will not
cause damage to the ring mold hole.
In the processing of extruding, the st ress and strain of the material closer to wall of the die hole increased,
having certain administrative levels. As the materials got into the chamfer area, the equivalent stress increased
gradual; after the materials got into the straight hol e, the equivalent stress incr eased slowly. Because the
influence by frictional resistance, t he fluidity of the external materials was worse than the interior, which was
part of the reason for causing for transver se cracks on the surface of pellet feed.
The simulation result showed that: ANSYS can reveal the forming mechanism of extrusion feed very well,
which provided a scientific method and theoretical basis for the structure de sign of die and the improvement of
pelleting technology.
Acknowledge
This research was supported by the Science and Tec hnology Support Project of China (No.2011BAD26A0401)
and Special Fund for Agro-scientific Research in the Public Interest (No.201203015).
References
Arshadi M, Gref R, Geladi P, et al 2008. The influence of raw mate rial characteristics on the
industrial pelletizing process and pellet quality. F uel Processing Technology. 89(12): 1442-1447.
de Blank H, Hendrix E, Litjens M, et al. 1997. On ‐Line Control and Optimization of the Pelleting Process of
Animal Feed. Journal of the Science of Food and Agriculture. 74(1): 13-19.
Holm J K, Garc ía-Maraver A, Popov V, Zamorano M. 2011. A revi ew of European standards for pellet quality.
Renewable energy. 36(12): 3537-3540.
Henriksen U B, Hustad J E, et al. 2006. Toward an understanding of controlling parameters in softwood and
hardwood pellets production. Energy & fuels. 20(6): 2686-2694.
Holm J K, Henriksen U B, Wand K, et al. 2007. Experim ental verification of novel pellet model using a single
pelleter unit. Energy & fuels. 21(4): 2446-2449.
Jingfeng W, Jianlong H, Weiguo Z. 2007. Simulated ex periment and model of pelletizing density and extruding
force for alfalfa powder. Transactions of the Chines e Society for Agricultural Machinery. 38(1): 68-71.
Jun X Z, De W B, Wei L Y, et al. 2002. The new technology of feed pelleti ng. Feed Industry, 23(3), 7-11.

2014 ASABE – CSBE/SCGAB Annual International Meeting Paper Page 1 0Mani S, Tabil L G, Sokhansanj S. 2006. Specific ener gy requirement for compacting corn stover. Bioresource
Technology. 97(12): 1420-1426.
Nielsen N P K, Holm J K, Felby C. 2009. Effect of fibe r orientation on compression and frictional properties of
sawdust particles in fuel pellet productio n. Energy & Fuels. 23(6): 3211-3216.
Rolfe L A, Huff H E, Hsieh F. 2001. E ffects of particle size and processi ng variables on the properties of an
extruded catfish feed. Journal of aquatic f ood product technology. 10(3): 21-34.
Tabil Jr L, Sokhansanj S. 1996. Process conditions a ffecting the physical quality of alfalfa pellets. Applied
Engineering in Agriculture, 12.
Vervaet C, Vermeersch H, Khotz M S, et al. 1994. Parameters influencing granule quality using a
continuous granulator. International jour nal of pharmaceutics. 106(2): 157-160.