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Comparison of wear characteristics of diamond segments under different sawing modes in sawing hard stone
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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International Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM
Comparison of wear characteristics of diamond segments under different sawing modes in sawing hard stone
T
⁎
Shuo Wanga,b,c, Jinsheng Zhanga,b,c, , Peiyu Donga,b,c a
School of Mechanical Engineering, Shandong University, China Key Laboratory of High-Efficiency and Clean Mechanical Manufacture (Ministry of Education), School of Mechanical Engineering, Shandong University, Jinan 250061, China c Research Centre for Stone Engineering, Shandong Province, Jinan 250061, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Diamond segment Diamond particles Wear characteristics Motion Sawing modes
In this study, the wear characteristics of two kinds of diamond segments with different composition of matrix were compared and investigated under two sawing modes through an experiment. Diamond particles were studied through scanning electron microscopy and three dimensional imaging system. Then, the remaining height of diamond segments was measured by digital vernier caliper. The wear characteristics of diamond segments were analyzed from wear morphology, protrusion height of diamond particles and the remaining height of diamond segments. The motion of two sawing modes and their effects on trajectories were analyzed which presented that the rocking reciprocating sawing mode can reduce sawing length and sawing time compared with horizontal reciprocating sawing mode used daily in industry. The results of experiment demonstrated that the main wear mechanism attributed to diamond segments wear is the fracture and falling of diamond particles caused by heavy loads especially in rocking reciprocating sawing mode. The average protrusion height of diamond particles is related with loads and the bonding strength of matrix. However, diamond segments wear can be effectively reduced in rocking reciprocating sawing mode while cobalt-based segments were adopted because a higher bonding strength to diamond particles can be provided compared with iron-based segments. The matrix of segments can be abrased slower while sawing length and sawing time were reduced.
1. Introduction
force and energy, models to estimate sawing force and sawing power and energy were established respectively. Luo [4] studied the formation reasons of different states of diamond particles; Ucun et al. [5] tested the effect of cooling condition on diamond segment consumption during sawing. Tonshoff et al. [6] described the formation process of swarf and the contact characteristics between stone and diamond particles, and divided diamond segment wear into matrix wear and diamond wear; Y Özçelik et al. [7] developed models for predicting diamond bead wear on the basis of experiments on different rock types. Huang and Xu [8] proved that brazed diamond wire was superior to sintered diamond wire according to their sawing performance. Aydin et al. [9] discussed the influence of process parameters on segment wear, and revealed that peripheral speed and the properties of stone are main factors related to diamond segment wear. Carrino et al. [10] proposed a protocol to evaluate diamond tools wear during sawing, and their results are reliable and replicable. A.J. Gant et al. [11] investigated the wear mechanisms of WC-Co-diamond composites in drilling, concluded that the major wear reason was the predominate
Diamond segments have been accepted and used widely in stone sawing for a long time [1]. They are mainly manufactured from diamond particles and metal powders, and are usually welded or embedded in metal tools and played an important role in stone sawing. Most of the sawing was performed by diamond particles on its surface. When diamond particles fracture or fail, the matrix of segments will be abrased to expose more diamond particles to continue sawing. Although its application has become mature, its consumption and cost are still concerning. In order to study the wear mechanism of diamond segment and related diamond tools, scholars have conducted extensive studies in many aspects and established various models. Ersoy et al. [2] studied the impact of stone properties and process parameters on wear characteristics through a series of comparative experiments and concluded that the main wear mechanism was abrasive wear. Turchetta [3] systematically analyzed the relationship between diamond segment wear,
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Corresponding author at: School of Mechanical Engineering, Shandong University, Jinan 250061, China. E-mail address: [email protected] (J. Zhang).
https://doi.org/10.1016/j.ijrmhm.2019.105149 Received 25 October 2019; Received in revised form 4 November 2019; Accepted 11 November 2019 Available online 11 November 2019 0263-4368/ © 2019 Elsevier Ltd. All rights reserved.
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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the sawblades and diamond segments are respectively represented by lines and points. Its horizontal displacement could be expressed as [29]:
wear of WC-Co matrix which left diamond particles unsupported. Yan et al. [12] compared ultrahard polycrystalline diamond (UHPCD) and polycrystalline diamond (PCD) through a grinding against granite, found that the wear resistance of UHPCD is about two times than that of PCD. Duan et al. [13] developed a new type of diamond-enhanced tungsten carbide composite button bit which is used in percussion drilling and the wear resistance of the button bit is 100 times more than conventional cemented tungsten carbide. Konstanty and Tyrala [14] compared circular saws with frame saws and found that the increasing of exposed diamond particles can effectively protect the matrix from abrasion, tail formed on matrix can enhance diamond retention. Other researchers have conducted extensively studies on the influence of physical and mechanical properties of stone on sawing performance [15,16], sawability [17–19] and wear characteristics [20,21] on diamond segment. According to previous studies, the main factors affecting diamond segments wear can be summarized as: (1) properties of matrix composition (2) diamond concentration and particle size (3) cooling condition (4) processing parameters (5) sawing modes (6) properties of stone [14,22]. Unfortunately, limited literatures focused on the wear characteristics of diamond segments in different sawing modes till now. Buyuksagis [23,24] have conducted a research on the effects of diamond segments composition on sawing performance through a disc sawing experiment, confirmed differences between cutting modes in circular sawing, found that up-cutting mode can save more energy and the wear rate was lower compared with down-cutting mode. W.I. Clark et al. [25] introduced a diamond wire machine that added rocking motion on its tension wheel. After that, Huang et al. [26] established its kinematic model, revealed that the length of the contact between the wire and the workpiece can be reduced effectively and varied periodically compared with diamond wire machines without rocking motion. Zhang et al. [22] designed a special frame saw with eccentric hinge as its guiding mechanism, aiming to replace reciprocating motion with unidirectional sawing. The state of diamond particles was more superior, and the wear rate was lower in that frame saw because of the build-up of tail on segment matrix. Sawing modes were proved vital for sawing performance and diamond segment wear. In this study, the wear characteristics of diamond segments under different sawing modes were investigated by an experiment. Two kinds of sawing modes were analyzed and compared based on their effects on trajectories and diamond segment wear. The wear mechanism of diamond segments is studied from microscopic and macroscopic perspectives.
L (1‐cosα ) 2
x=
α = ωt
(1) (2)
Where x is the horizontal displacement of sawblades and diamond segments; L is the length of stroke, equal to twice the length of crank; α is the angular of flywheel and crank rotated; ω is the angular velocity of the flywheel and crank; t is the running time of the frame saw. The trajectories of diamond segments in frame saws can be deduced as followings: 1) With the feeding of stone, the vertical motion of both ends of the sawblade can be expressed as:
yt1 = k × x ‐vf t
(3)
yt2 = (L‐x ) × k ‐vf t
(4)
Where yt1 is the vertical displacement of the front end of sawblades; yt2 is the vertical displacement of rear end of sawblades; k is the coefficient of horizontal displacement and vertical displacement which is determined by the guiding mechanism; vf is the feed speed of the frame saw. 2) Therefore, the vertical displacement of each segment could be expressed as:
y=
yt2 ‐yt1 × x n + yt1 ‐vf × t LT
(5)
Where LT is the length of the sawblade; y is the vertical displacement of segments; xn stands for the position of segments with front end of the sawblade as the origin. The difference between the rocking reciprocating sawing mode and horizontal reciprocating sawing mode lies in the vertical motion. In horizontal reciprocating sawing mode, k is 0 or negligible, so its vertical displacement can be simplified to:
y = ‐vf t
(6)
Detailed differences were reflected in Fig. 2. 2.2. Trajectories of diamond segments Trajectories of diamond segments on the sawblade in a cycle of reciprocating stroke were obtained and displayed by Matlab, as shown in Fig. 3. The lines in different colors in Fig. 3 are the trajectories of different segments on a sawblade. Because of the scale of the images, the vertical displacement of segments is actually not obvious. Compared with horizontal reciprocating sawing mode, the effect of feeding on trajectories in rocking reciprocating sawing mode is so small but non-negligible. As shown in Fig. 3(a), the slopes of trajectories of segments approximately vary with their position on the sawblade, and some trajectories in the middle intersect with others. With the intersection, some segments will move to the upper part of the trajectories that was sawn in the previous stroke by adjacent segments, so they will break away from sawing for a while until they return to the bottom of trajectories, as shown in Fig. 4 [26]. As shown in Fig. 4, different from continuous sawing, the sawing length in rocking reciprocating sawing mode in one stroke was determined by adjacent segments, which is much shorter than that in horizontal reciprocating sawing mode. In addition, the sawing depth in rocking reciprocating sawing mode was decided by the trajectory of this segment in the previous stroke, which is depended on the feed speed, not restricted by adjacent segments. Therefore, the sawing depth in rocking sawing motion is much greater than that in horizontal
2. Sawing modes of diamond frame saws Two different sawing modes are used on two frame saws, one is rocking reciprocating sawing mode, the other is horizontal reciprocating sawing mode. The frame saw realizes stone processing by a set of sawblades installed and tensioned on the saw frame. In the sawing process, the sawblades is driven by the crank and connecting rod mechanism to realize reciprocating motion, and the stone is driven by the lifting mechanism to realize uniform upward feeding. As shown in Fig. 1. Problems restricting its development are unstable sawing process and severe wear of diamond segments [27]. Generally, diamond segments wear in frame saw is severe because of its continuous reciprocating sawing [14]. On the other hand, the sawblades will become unstable and deviate from the original sawing path by excessive load applied to the sawblades, which will have an adverse impact on the quality of the sawing [28]. 2.1. Establishment of sawblades motion model The prototype of motion in frame saw was described in Fig. 1, and 2
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
S. Wang, et al.
Fig. 1. The schematic diagram of conventional frame saw.
were used in the experiment. Their compositions were designed on the basis of daily used diamond segments composition in industry, as shown in following Table 2. Diamond segments were weld on sawblades which is made of 75Cr1 and each sawblade was welded with 25 segments with spacing of 120 mm. The size of the sawblade is 4100 mm (length) × 150 mm (height) × 3.5 mm (thickness). A total of 80 sawblades were used in the experiment. The workpiece used in the experiment was trimmed by single wire sawing machine into the designing size of 2600 mm (length) × 1500 mm (width) × 2000 mm (height). Its physical properties were shown in Table 3.
reciprocating sawing mode. This has raised concerning problems that the heavy load caused by sawing depth in the rocking reciprocating sawing mode may have a negative impact on segment wear. 3. Experiment procedure 3.1. Experiment set up The experiment was carried out on two frame saws mentioned above: the specific frame saw with rocking reciprocating sawing mode and a conventional frame saw with horizontal reciprocating sawing mode which is widely used, as shown in Fig. 1. The structure parameters of frame saws were listed in Table 1.
3.3. The designing of post-test detection The morphologies of worn segments were observed by a scanning electron microscopy (ZEISS EVO 18) to obtain detailed information of diamond particles. And three dimensional imaging system was introduced into the detection to obtain the protrusion height of diamond
3.2. Details in experiment In order to further study the wear mechanism of diamond segments, two groups of diamond segments with different matrix compositions
Fig. 2. Differences between rocking reciprocating sawing mode and horizontal reciprocating sawing mode. (a) States of the sawblade at different moment in the rocking reciprocating sawing mode. (b) State of sawblade in the horizontal reciprocating sawing mode. 3
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
S. Wang, et al.
Fig. 3. Trajectories of segments in two kinds of sawing modes. (a) Trajectories of diamond segments in rocking reciprocating sawing mode. (b) Trajectories of diamond segments in horizontal reciprocating sawing mode.
the proportion of different diamond particles can reflect and explain segment wear in a convincing way. The proportions of different diamond particles on selected segments obtained in the detection were shown in Fig. 6. The results show that the wear characteristics of the two groups of diamond segments are completely different under the two sawing modes. In group (a) (iron-based), a surprising proportion is pulled-out which reached 22% in rocking reciprocating sawing mode, higher than that in horizontal reciprocating sawing mode, which is only 16%. Similarly, the proportion of macro-fracture diamond particles accounted for 23%, 21% respectively in rocking reciprocating sawing mode and horizontal reciprocating sawing mode. This phenomenon is concerning, because when the proportion of macro-fracture and pulledout diamond particles exceeds one-third, the sawing will become less efficient [4]. Well-state diamond particles (fresh, whole and microfractured) of group (a) (iron-based) reached 9.5%, 24%, and 16.5% respectively in rocking reciprocating sawing mode, generally lower than horizontal reciprocating sawing mode (14%, 30%, 13.5%). These particles are main undertaker of sawing, and their proportion decided the wear rate and sharpness of diamond segments. As comparison, the proportion of pulled-out particles in group (b) (cobalt-based) segments is significantly less, reached 11% in rocking reciprocating sawing mode and only 9% in horizontal reciprocating sawing mode. As expected, except for blunt diamond particles, all the other kinds of diamond particles increased in different amplitude. Well-
particles on diamond segments. Then, a digital vernier caliper with an accuracy of 0.001 mm was used to measure the remaining height of diamond segments before and after the experiment. Total 180 segments from two groups under different sawing modes were observed and measured. The counting and measurement were repeated three times, and the average value was taken to ensure the accuracy of the statistical results.
4. Results and discussions 4.1. Wear characteristics of diamond particles 4.1.1. Wear morphologies of diamond particles Based on the existing studies, the types of worn diamond particles can be divided as: (1) Fresh, (2) Whole, (3) Micro-fractured, (4) Macrofractured, (5) Blunt, (6) Pulled-out [22]. The corresponding images were listed in Fig. 5. Among them, fresh and whole diamond particles are generated by the consuming of segment matrix; micro-fractured and some of macro-fractured diamond particles are mainly caused by fatigue abrasion, heavy loads and impact; blunt diamond particles were formed by insufficient sawing depths; and pulled-out can be developed by macro-fractured particles or caused by the heavy loads, which is the main reason of segment consumption. Proper processing parameters and stronger bonding strength to diamond particles can reduce the proportion of pulled-out. In existing literature, it is widely believed that 4
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
S. Wang, et al.
Fig. 4. Comparison of diamond segments trajectories. (a) Explanation of diamond segments trajectories in rocking reciprocating sawing mode. (b) Explanation of diamond segments trajectories in horizontal reciprocating sawing mode.
sawing mode (14%, 34%, 19%). More obviously, macro-fracture diamond particles reached 28% in rocking reciprocating sawing mode and 20% in horizontal reciprocating sawing mode. Compared with industrial production, the proportion of pulled-out particles in the experiment indicated that the load is heavy and the bonding strength of matrix is insufficient. Group (a) (iron-based) is often used in sawing marble in industry because of its lower cost, but load imposed on particles in this experiment is much heavier because of the higher hardness of stone. At the same time, the effect of increased sawing depth also contributed to the enlargement of loads, which can be reflected by the proportion of pulled-out particles in group (a) (ironbased) segments under rocking reciprocating sawing mode. Heavy load is also proved by high proportion of macro-fracture diamond particles regardless of matrix composition in rocking reciprocating sawing mode although some of them developed into pulled-out particles. Obviously, the bonding strength to diamond particles of group (a) (iron-based) segment matrix is not able to meet the requirement in this experiment. As comparison, group (b) (cobalt-based) performed much better than group (a) (iron-based) under same working condition with a lower proportion of pulled-out particles. Except for the superior performance of cobalt-based matrix and mature application of cobalt, the addition of tungsten can also enhance the bonding strength to diamond particles, prevent more well-state diamond particles from falling and ensure the sharpness of segments, as described in existing literature [14,30,31]. Although the falling of well-state diamond particles reduced in group (b) (cobalt-based), the proportion of macro-fracture diamond particles increased either, which is harmful to segment wear resistance
Table 1 Parameters of frame saws used in experiment. Frame saws
Parameters
Dominate power(kw) Stroke (mm) Maximum feeding speed (mm/h) Feeding speed used in experiment (mm/h) Feed motor (kw) Maximum flywheel speed (r/min) Flywheel speed used in experiment (r/min) Cool liquid (L/min)
110 800 300 70 15 100 70 10
Table 2 Information of segments used in the experiment. Diamond segments
Group (a) (iron-based)
Main composition of matrix
Cobalt 87.08% Iron 41.8% Silicon 6.27% Copper 28.17% Tungsten 3.8% Cobalt 14.58% Silicon 10.37% 20 (length) × 13 (height) × 5 (width) 30% 40/50 mesh
Size (mm) Concentration (%) Particle size (mesh)
Group(b) (cobalt-based)
state diamond particles (fresh, whole and micro-fractured) of group (a) (iron-based) reached 10%, 27.5%, and 19% respectively in rocking reciprocating sawing mode, still lower than horizontal reciprocating
5
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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Table 3 Properties of the workpiece. Main mineral composition Quartz
Orthoclase
Plagioclase
16% ±
44% ±
27% ±
Shore hardness
Compressive strength(MPa)
Bending strength(MPa)
Density (kg/m3)
97
122.6
17.4
2.97
experiment because they can expose to outside of the stone and are generally higher, as shown in Fig. 8. Detailed average remaining height of diamond segments was shown in Fig. 9. In group (a) (iron-based), average remaining height of diamond segments in horizontal sawing mode is generally higher than that in the rocking reciprocating sawing mode. In addition, the remaining height of diamond segments in rocking reciprocating sawing mode is not uniform as that in horizontal reciprocating sawing mode, diamond segments in the middle of sawblade is higher than others. The remaining height of diamond segments in horizontal reciprocating sawing mode didn't vary significantly. In group (b) (cobalt-based), the differences of segments height on one sawblade is similar to that in group (a) (iron-based). Average remaining height of diamond segments is much higher compared with than that in group (a) (iron-based) regardless of sawing modes. What is more noteworthy is that the average remaining height of diamond segments in rocking reciprocating sawing mode is higher than that in the horizontal reciprocating sawing mode, which is contrary to the results in group (a) (iron-based). The consumption of diamond segments is accord with the proportion of pulled-out diamond particles in group (a) (iron-based) segments. When the proportion of functional diamond particles (fresh, whole and micro-fractured) reduced, the matrix will be abrased by hard-wearing particles (e.g. the stone debris and diamond fragments) to expose more diamond particles to continue sawing. The remaining height of diamond segments in group (b) (cobaltbased) showed different wear characteristics. The analysis should be combined with wear morphologies of diamond particles on the segments. The state of diamond particles is better in both of sawing modes. While diamond particles were bonded tightly, the characteristic of the
and sharpness. Diamond morphology in the experiment are still worse than conventional industrial sawing, the bonding strength and the quality of diamond particles need to be further reinforced to ensure the wear resistance and sharpness of diamond segments in sawing hard stone. 4.1.2. Protrusion height of diamond particles The protrusion height of diamond particles is related with matrix properties and loads. Diamond particles with a higher protrusion height have to bear a heavier moment which may lead to its falling. Generally, the protrusion height of diamond particles cannot exceed the 1/2 of the grain size [32]. As shown in Fig. 7, the protrusion height of diamond particles in the experiment is correspondence with the proportion of pulled-out. A lower protrusion height was observed in rocking reciprocating sawing mode because of heavier loads compared with horizontal reciprocating sawing mode. The mean protrusion heights of diamond particles in group (a) (iron-based) and group (b) (cobalt-based) under two sawing modes reached 66.3 μm, 78.3 μm, 99.3 μm and 104.3 μm respectively. The differences between two groups of segments demonstrated the stronger bonding strength of cobalt-based segments, a higher protrusion height can be achieved, which is accord with the states of diamond particles. 4.2. The remaining height of diamond segments The remaining height of diamond segments was divided into three categories according to their position on sawblades: front (NO.6–10), middle (NO.11–15) and rear (NO.16–20). The state of diamond segments near two ends (NO.1–5 and NO.21–25) was not considered in this
Fig. 5. Different states of diamonds observed with SEM: (a) fresh; (b) whole; (c) micro-fractured; (d) macro-fractured; (e) blunt; (f) pulled-out. 6
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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Fig. 6. Proportion of different diamonds particles. (a) Group (a) (iron-based) (b) Group (b) (cobalt-based).
5. Conclusions Analysis and an experiment were conducted and the corresponding wear was obtained in order to investigate wear characteristics of diamond segments in different sawing mode. Two groups of segments with different composition were compared and the results of the experiment were interpreted and analyzed from the microscopic and macroscopic perspectives respectively. Based on the above research, the conclusions can be drawn as follows: 1) The rocking reciprocating sawing mode which provided a variable vertical motion to the sawblades can reduce sawing length and sawing time. 2) Falling and fracture of diamond particles are main reasons of diamond segment, especially in rocking reciprocating sawing mode because of its effects on sawing depth compared with horizontal reciprocating sawing mode. And the protrusion height of diamond particles was lower in rocking reciprocating sawing mode. 3) The effects of rocking reciprocating sawing mode on segment wear can be reflected while adopting cobalt-based segment, because diamond particles were bonded more tightly compared with ironbased segment which is widely used in industrial sawing. The time required for single diamond particle to develop from whole to macro-fractured and pulled-out is much longer and the matrix can abrase slower while well-state particles can work longer.
Fig. 7. The protrusion height of diamond particles in the experiment.
rocking reciprocating sawing mode can show up. The time required for single diamond particle to develop from whole to macro-fractured and pulled-out is much longer with the steeply reduction of sawing length and sawing time as mentioned in above analysis. The matrix can abrasion slower while well-state particles can work longer. On the other hand, the nonuniform remaining height on one sawblade in rocking reciprocating sawing mode was cause by the combination of feeding and rocking motion. As shown in Fig. 10 which ignored horizontal displacement. The variation of segments sawing depth at both ends is greater in reciprocating stroke than segments in the middle. Thus the loads on the diamond segments in the middle will be more stable and smaller.
Declaration of Competing Interest We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.
Fig. 8. Position of segments outside the stone.(a) Remaining height of group (a) (iron-based) (b) Remaining height of group (b) (cobalt-based). 7
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
S. Wang, et al.
Fig. 9. Average remaining height of segments after sawing.
[12]
[13] [14] [15]
[16] [17]
Fig. 10. Differences of sawing depth in rocking reciprocating sawing mode.
[18]
Acknowledgement
[19]
This work was supported by the Taishan Industrial Leading Talent project of Shandong Province, China [No.tscy20150228] and Shandong Key Research and Development Project [NO.2019GGX104022]. The authors are most grateful to Shandong Rizhao Hein Saw Co., Ltd. for supporting this work by providing the diamond tools and frame sawing machines.
[20]
[21]
[22]
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International Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM
Comparison of wear characteristics of diamond segments under different sawing modes in sawing hard stone
T
⁎
Shuo Wanga,b,c, Jinsheng Zhanga,b,c, , Peiyu Donga,b,c a
School of Mechanical Engineering, Shandong University, China Key Laboratory of High-Efficiency and Clean Mechanical Manufacture (Ministry of Education), School of Mechanical Engineering, Shandong University, Jinan 250061, China c Research Centre for Stone Engineering, Shandong Province, Jinan 250061, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Diamond segment Diamond particles Wear characteristics Motion Sawing modes
In this study, the wear characteristics of two kinds of diamond segments with different composition of matrix were compared and investigated under two sawing modes through an experiment. Diamond particles were studied through scanning electron microscopy and three dimensional imaging system. Then, the remaining height of diamond segments was measured by digital vernier caliper. The wear characteristics of diamond segments were analyzed from wear morphology, protrusion height of diamond particles and the remaining height of diamond segments. The motion of two sawing modes and their effects on trajectories were analyzed which presented that the rocking reciprocating sawing mode can reduce sawing length and sawing time compared with horizontal reciprocating sawing mode used daily in industry. The results of experiment demonstrated that the main wear mechanism attributed to diamond segments wear is the fracture and falling of diamond particles caused by heavy loads especially in rocking reciprocating sawing mode. The average protrusion height of diamond particles is related with loads and the bonding strength of matrix. However, diamond segments wear can be effectively reduced in rocking reciprocating sawing mode while cobalt-based segments were adopted because a higher bonding strength to diamond particles can be provided compared with iron-based segments. The matrix of segments can be abrased slower while sawing length and sawing time were reduced.
1. Introduction
force and energy, models to estimate sawing force and sawing power and energy were established respectively. Luo [4] studied the formation reasons of different states of diamond particles; Ucun et al. [5] tested the effect of cooling condition on diamond segment consumption during sawing. Tonshoff et al. [6] described the formation process of swarf and the contact characteristics between stone and diamond particles, and divided diamond segment wear into matrix wear and diamond wear; Y Özçelik et al. [7] developed models for predicting diamond bead wear on the basis of experiments on different rock types. Huang and Xu [8] proved that brazed diamond wire was superior to sintered diamond wire according to their sawing performance. Aydin et al. [9] discussed the influence of process parameters on segment wear, and revealed that peripheral speed and the properties of stone are main factors related to diamond segment wear. Carrino et al. [10] proposed a protocol to evaluate diamond tools wear during sawing, and their results are reliable and replicable. A.J. Gant et al. [11] investigated the wear mechanisms of WC-Co-diamond composites in drilling, concluded that the major wear reason was the predominate
Diamond segments have been accepted and used widely in stone sawing for a long time [1]. They are mainly manufactured from diamond particles and metal powders, and are usually welded or embedded in metal tools and played an important role in stone sawing. Most of the sawing was performed by diamond particles on its surface. When diamond particles fracture or fail, the matrix of segments will be abrased to expose more diamond particles to continue sawing. Although its application has become mature, its consumption and cost are still concerning. In order to study the wear mechanism of diamond segment and related diamond tools, scholars have conducted extensive studies in many aspects and established various models. Ersoy et al. [2] studied the impact of stone properties and process parameters on wear characteristics through a series of comparative experiments and concluded that the main wear mechanism was abrasive wear. Turchetta [3] systematically analyzed the relationship between diamond segment wear,
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Corresponding author at: School of Mechanical Engineering, Shandong University, Jinan 250061, China. E-mail address: [email protected] (J. Zhang).
https://doi.org/10.1016/j.ijrmhm.2019.105149 Received 25 October 2019; Received in revised form 4 November 2019; Accepted 11 November 2019 Available online 11 November 2019 0263-4368/ © 2019 Elsevier Ltd. All rights reserved.
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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the sawblades and diamond segments are respectively represented by lines and points. Its horizontal displacement could be expressed as [29]:
wear of WC-Co matrix which left diamond particles unsupported. Yan et al. [12] compared ultrahard polycrystalline diamond (UHPCD) and polycrystalline diamond (PCD) through a grinding against granite, found that the wear resistance of UHPCD is about two times than that of PCD. Duan et al. [13] developed a new type of diamond-enhanced tungsten carbide composite button bit which is used in percussion drilling and the wear resistance of the button bit is 100 times more than conventional cemented tungsten carbide. Konstanty and Tyrala [14] compared circular saws with frame saws and found that the increasing of exposed diamond particles can effectively protect the matrix from abrasion, tail formed on matrix can enhance diamond retention. Other researchers have conducted extensively studies on the influence of physical and mechanical properties of stone on sawing performance [15,16], sawability [17–19] and wear characteristics [20,21] on diamond segment. According to previous studies, the main factors affecting diamond segments wear can be summarized as: (1) properties of matrix composition (2) diamond concentration and particle size (3) cooling condition (4) processing parameters (5) sawing modes (6) properties of stone [14,22]. Unfortunately, limited literatures focused on the wear characteristics of diamond segments in different sawing modes till now. Buyuksagis [23,24] have conducted a research on the effects of diamond segments composition on sawing performance through a disc sawing experiment, confirmed differences between cutting modes in circular sawing, found that up-cutting mode can save more energy and the wear rate was lower compared with down-cutting mode. W.I. Clark et al. [25] introduced a diamond wire machine that added rocking motion on its tension wheel. After that, Huang et al. [26] established its kinematic model, revealed that the length of the contact between the wire and the workpiece can be reduced effectively and varied periodically compared with diamond wire machines without rocking motion. Zhang et al. [22] designed a special frame saw with eccentric hinge as its guiding mechanism, aiming to replace reciprocating motion with unidirectional sawing. The state of diamond particles was more superior, and the wear rate was lower in that frame saw because of the build-up of tail on segment matrix. Sawing modes were proved vital for sawing performance and diamond segment wear. In this study, the wear characteristics of diamond segments under different sawing modes were investigated by an experiment. Two kinds of sawing modes were analyzed and compared based on their effects on trajectories and diamond segment wear. The wear mechanism of diamond segments is studied from microscopic and macroscopic perspectives.
L (1‐cosα ) 2
x=
α = ωt
(1) (2)
Where x is the horizontal displacement of sawblades and diamond segments; L is the length of stroke, equal to twice the length of crank; α is the angular of flywheel and crank rotated; ω is the angular velocity of the flywheel and crank; t is the running time of the frame saw. The trajectories of diamond segments in frame saws can be deduced as followings: 1) With the feeding of stone, the vertical motion of both ends of the sawblade can be expressed as:
yt1 = k × x ‐vf t
(3)
yt2 = (L‐x ) × k ‐vf t
(4)
Where yt1 is the vertical displacement of the front end of sawblades; yt2 is the vertical displacement of rear end of sawblades; k is the coefficient of horizontal displacement and vertical displacement which is determined by the guiding mechanism; vf is the feed speed of the frame saw. 2) Therefore, the vertical displacement of each segment could be expressed as:
y=
yt2 ‐yt1 × x n + yt1 ‐vf × t LT
(5)
Where LT is the length of the sawblade; y is the vertical displacement of segments; xn stands for the position of segments with front end of the sawblade as the origin. The difference between the rocking reciprocating sawing mode and horizontal reciprocating sawing mode lies in the vertical motion. In horizontal reciprocating sawing mode, k is 0 or negligible, so its vertical displacement can be simplified to:
y = ‐vf t
(6)
Detailed differences were reflected in Fig. 2. 2.2. Trajectories of diamond segments Trajectories of diamond segments on the sawblade in a cycle of reciprocating stroke were obtained and displayed by Matlab, as shown in Fig. 3. The lines in different colors in Fig. 3 are the trajectories of different segments on a sawblade. Because of the scale of the images, the vertical displacement of segments is actually not obvious. Compared with horizontal reciprocating sawing mode, the effect of feeding on trajectories in rocking reciprocating sawing mode is so small but non-negligible. As shown in Fig. 3(a), the slopes of trajectories of segments approximately vary with their position on the sawblade, and some trajectories in the middle intersect with others. With the intersection, some segments will move to the upper part of the trajectories that was sawn in the previous stroke by adjacent segments, so they will break away from sawing for a while until they return to the bottom of trajectories, as shown in Fig. 4 [26]. As shown in Fig. 4, different from continuous sawing, the sawing length in rocking reciprocating sawing mode in one stroke was determined by adjacent segments, which is much shorter than that in horizontal reciprocating sawing mode. In addition, the sawing depth in rocking reciprocating sawing mode was decided by the trajectory of this segment in the previous stroke, which is depended on the feed speed, not restricted by adjacent segments. Therefore, the sawing depth in rocking sawing motion is much greater than that in horizontal
2. Sawing modes of diamond frame saws Two different sawing modes are used on two frame saws, one is rocking reciprocating sawing mode, the other is horizontal reciprocating sawing mode. The frame saw realizes stone processing by a set of sawblades installed and tensioned on the saw frame. In the sawing process, the sawblades is driven by the crank and connecting rod mechanism to realize reciprocating motion, and the stone is driven by the lifting mechanism to realize uniform upward feeding. As shown in Fig. 1. Problems restricting its development are unstable sawing process and severe wear of diamond segments [27]. Generally, diamond segments wear in frame saw is severe because of its continuous reciprocating sawing [14]. On the other hand, the sawblades will become unstable and deviate from the original sawing path by excessive load applied to the sawblades, which will have an adverse impact on the quality of the sawing [28]. 2.1. Establishment of sawblades motion model The prototype of motion in frame saw was described in Fig. 1, and 2
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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Fig. 1. The schematic diagram of conventional frame saw.
were used in the experiment. Their compositions were designed on the basis of daily used diamond segments composition in industry, as shown in following Table 2. Diamond segments were weld on sawblades which is made of 75Cr1 and each sawblade was welded with 25 segments with spacing of 120 mm. The size of the sawblade is 4100 mm (length) × 150 mm (height) × 3.5 mm (thickness). A total of 80 sawblades were used in the experiment. The workpiece used in the experiment was trimmed by single wire sawing machine into the designing size of 2600 mm (length) × 1500 mm (width) × 2000 mm (height). Its physical properties were shown in Table 3.
reciprocating sawing mode. This has raised concerning problems that the heavy load caused by sawing depth in the rocking reciprocating sawing mode may have a negative impact on segment wear. 3. Experiment procedure 3.1. Experiment set up The experiment was carried out on two frame saws mentioned above: the specific frame saw with rocking reciprocating sawing mode and a conventional frame saw with horizontal reciprocating sawing mode which is widely used, as shown in Fig. 1. The structure parameters of frame saws were listed in Table 1.
3.3. The designing of post-test detection The morphologies of worn segments were observed by a scanning electron microscopy (ZEISS EVO 18) to obtain detailed information of diamond particles. And three dimensional imaging system was introduced into the detection to obtain the protrusion height of diamond
3.2. Details in experiment In order to further study the wear mechanism of diamond segments, two groups of diamond segments with different matrix compositions
Fig. 2. Differences between rocking reciprocating sawing mode and horizontal reciprocating sawing mode. (a) States of the sawblade at different moment in the rocking reciprocating sawing mode. (b) State of sawblade in the horizontal reciprocating sawing mode. 3
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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Fig. 3. Trajectories of segments in two kinds of sawing modes. (a) Trajectories of diamond segments in rocking reciprocating sawing mode. (b) Trajectories of diamond segments in horizontal reciprocating sawing mode.
the proportion of different diamond particles can reflect and explain segment wear in a convincing way. The proportions of different diamond particles on selected segments obtained in the detection were shown in Fig. 6. The results show that the wear characteristics of the two groups of diamond segments are completely different under the two sawing modes. In group (a) (iron-based), a surprising proportion is pulled-out which reached 22% in rocking reciprocating sawing mode, higher than that in horizontal reciprocating sawing mode, which is only 16%. Similarly, the proportion of macro-fracture diamond particles accounted for 23%, 21% respectively in rocking reciprocating sawing mode and horizontal reciprocating sawing mode. This phenomenon is concerning, because when the proportion of macro-fracture and pulledout diamond particles exceeds one-third, the sawing will become less efficient [4]. Well-state diamond particles (fresh, whole and microfractured) of group (a) (iron-based) reached 9.5%, 24%, and 16.5% respectively in rocking reciprocating sawing mode, generally lower than horizontal reciprocating sawing mode (14%, 30%, 13.5%). These particles are main undertaker of sawing, and their proportion decided the wear rate and sharpness of diamond segments. As comparison, the proportion of pulled-out particles in group (b) (cobalt-based) segments is significantly less, reached 11% in rocking reciprocating sawing mode and only 9% in horizontal reciprocating sawing mode. As expected, except for blunt diamond particles, all the other kinds of diamond particles increased in different amplitude. Well-
particles on diamond segments. Then, a digital vernier caliper with an accuracy of 0.001 mm was used to measure the remaining height of diamond segments before and after the experiment. Total 180 segments from two groups under different sawing modes were observed and measured. The counting and measurement were repeated three times, and the average value was taken to ensure the accuracy of the statistical results.
4. Results and discussions 4.1. Wear characteristics of diamond particles 4.1.1. Wear morphologies of diamond particles Based on the existing studies, the types of worn diamond particles can be divided as: (1) Fresh, (2) Whole, (3) Micro-fractured, (4) Macrofractured, (5) Blunt, (6) Pulled-out [22]. The corresponding images were listed in Fig. 5. Among them, fresh and whole diamond particles are generated by the consuming of segment matrix; micro-fractured and some of macro-fractured diamond particles are mainly caused by fatigue abrasion, heavy loads and impact; blunt diamond particles were formed by insufficient sawing depths; and pulled-out can be developed by macro-fractured particles or caused by the heavy loads, which is the main reason of segment consumption. Proper processing parameters and stronger bonding strength to diamond particles can reduce the proportion of pulled-out. In existing literature, it is widely believed that 4
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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Fig. 4. Comparison of diamond segments trajectories. (a) Explanation of diamond segments trajectories in rocking reciprocating sawing mode. (b) Explanation of diamond segments trajectories in horizontal reciprocating sawing mode.
sawing mode (14%, 34%, 19%). More obviously, macro-fracture diamond particles reached 28% in rocking reciprocating sawing mode and 20% in horizontal reciprocating sawing mode. Compared with industrial production, the proportion of pulled-out particles in the experiment indicated that the load is heavy and the bonding strength of matrix is insufficient. Group (a) (iron-based) is often used in sawing marble in industry because of its lower cost, but load imposed on particles in this experiment is much heavier because of the higher hardness of stone. At the same time, the effect of increased sawing depth also contributed to the enlargement of loads, which can be reflected by the proportion of pulled-out particles in group (a) (ironbased) segments under rocking reciprocating sawing mode. Heavy load is also proved by high proportion of macro-fracture diamond particles regardless of matrix composition in rocking reciprocating sawing mode although some of them developed into pulled-out particles. Obviously, the bonding strength to diamond particles of group (a) (iron-based) segment matrix is not able to meet the requirement in this experiment. As comparison, group (b) (cobalt-based) performed much better than group (a) (iron-based) under same working condition with a lower proportion of pulled-out particles. Except for the superior performance of cobalt-based matrix and mature application of cobalt, the addition of tungsten can also enhance the bonding strength to diamond particles, prevent more well-state diamond particles from falling and ensure the sharpness of segments, as described in existing literature [14,30,31]. Although the falling of well-state diamond particles reduced in group (b) (cobalt-based), the proportion of macro-fracture diamond particles increased either, which is harmful to segment wear resistance
Table 1 Parameters of frame saws used in experiment. Frame saws
Parameters
Dominate power(kw) Stroke (mm) Maximum feeding speed (mm/h) Feeding speed used in experiment (mm/h) Feed motor (kw) Maximum flywheel speed (r/min) Flywheel speed used in experiment (r/min) Cool liquid (L/min)
110 800 300 70 15 100 70 10
Table 2 Information of segments used in the experiment. Diamond segments
Group (a) (iron-based)
Main composition of matrix
Cobalt 87.08% Iron 41.8% Silicon 6.27% Copper 28.17% Tungsten 3.8% Cobalt 14.58% Silicon 10.37% 20 (length) × 13 (height) × 5 (width) 30% 40/50 mesh
Size (mm) Concentration (%) Particle size (mesh)
Group(b) (cobalt-based)
state diamond particles (fresh, whole and micro-fractured) of group (a) (iron-based) reached 10%, 27.5%, and 19% respectively in rocking reciprocating sawing mode, still lower than horizontal reciprocating
5
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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Table 3 Properties of the workpiece. Main mineral composition Quartz
Orthoclase
Plagioclase
16% ±
44% ±
27% ±
Shore hardness
Compressive strength(MPa)
Bending strength(MPa)
Density (kg/m3)
97
122.6
17.4
2.97
experiment because they can expose to outside of the stone and are generally higher, as shown in Fig. 8. Detailed average remaining height of diamond segments was shown in Fig. 9. In group (a) (iron-based), average remaining height of diamond segments in horizontal sawing mode is generally higher than that in the rocking reciprocating sawing mode. In addition, the remaining height of diamond segments in rocking reciprocating sawing mode is not uniform as that in horizontal reciprocating sawing mode, diamond segments in the middle of sawblade is higher than others. The remaining height of diamond segments in horizontal reciprocating sawing mode didn't vary significantly. In group (b) (cobalt-based), the differences of segments height on one sawblade is similar to that in group (a) (iron-based). Average remaining height of diamond segments is much higher compared with than that in group (a) (iron-based) regardless of sawing modes. What is more noteworthy is that the average remaining height of diamond segments in rocking reciprocating sawing mode is higher than that in the horizontal reciprocating sawing mode, which is contrary to the results in group (a) (iron-based). The consumption of diamond segments is accord with the proportion of pulled-out diamond particles in group (a) (iron-based) segments. When the proportion of functional diamond particles (fresh, whole and micro-fractured) reduced, the matrix will be abrased by hard-wearing particles (e.g. the stone debris and diamond fragments) to expose more diamond particles to continue sawing. The remaining height of diamond segments in group (b) (cobaltbased) showed different wear characteristics. The analysis should be combined with wear morphologies of diamond particles on the segments. The state of diamond particles is better in both of sawing modes. While diamond particles were bonded tightly, the characteristic of the
and sharpness. Diamond morphology in the experiment are still worse than conventional industrial sawing, the bonding strength and the quality of diamond particles need to be further reinforced to ensure the wear resistance and sharpness of diamond segments in sawing hard stone. 4.1.2. Protrusion height of diamond particles The protrusion height of diamond particles is related with matrix properties and loads. Diamond particles with a higher protrusion height have to bear a heavier moment which may lead to its falling. Generally, the protrusion height of diamond particles cannot exceed the 1/2 of the grain size [32]. As shown in Fig. 7, the protrusion height of diamond particles in the experiment is correspondence with the proportion of pulled-out. A lower protrusion height was observed in rocking reciprocating sawing mode because of heavier loads compared with horizontal reciprocating sawing mode. The mean protrusion heights of diamond particles in group (a) (iron-based) and group (b) (cobalt-based) under two sawing modes reached 66.3 μm, 78.3 μm, 99.3 μm and 104.3 μm respectively. The differences between two groups of segments demonstrated the stronger bonding strength of cobalt-based segments, a higher protrusion height can be achieved, which is accord with the states of diamond particles. 4.2. The remaining height of diamond segments The remaining height of diamond segments was divided into three categories according to their position on sawblades: front (NO.6–10), middle (NO.11–15) and rear (NO.16–20). The state of diamond segments near two ends (NO.1–5 and NO.21–25) was not considered in this
Fig. 5. Different states of diamonds observed with SEM: (a) fresh; (b) whole; (c) micro-fractured; (d) macro-fractured; (e) blunt; (f) pulled-out. 6
International Journal of Refractory Metals & Hard Materials 87 (2020) 105149
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Fig. 6. Proportion of different diamonds particles. (a) Group (a) (iron-based) (b) Group (b) (cobalt-based).
5. Conclusions Analysis and an experiment were conducted and the corresponding wear was obtained in order to investigate wear characteristics of diamond segments in different sawing mode. Two groups of segments with different composition were compared and the results of the experiment were interpreted and analyzed from the microscopic and macroscopic perspectives respectively. Based on the above research, the conclusions can be drawn as follows: 1) The rocking reciprocating sawing mode which provided a variable vertical motion to the sawblades can reduce sawing length and sawing time. 2) Falling and fracture of diamond particles are main reasons of diamond segment, especially in rocking reciprocating sawing mode because of its effects on sawing depth compared with horizontal reciprocating sawing mode. And the protrusion height of diamond particles was lower in rocking reciprocating sawing mode. 3) The effects of rocking reciprocating sawing mode on segment wear can be reflected while adopting cobalt-based segment, because diamond particles were bonded more tightly compared with ironbased segment which is widely used in industrial sawing. The time required for single diamond particle to develop from whole to macro-fractured and pulled-out is much longer and the matrix can abrase slower while well-state particles can work longer.
Fig. 7. The protrusion height of diamond particles in the experiment.
rocking reciprocating sawing mode can show up. The time required for single diamond particle to develop from whole to macro-fractured and pulled-out is much longer with the steeply reduction of sawing length and sawing time as mentioned in above analysis. The matrix can abrasion slower while well-state particles can work longer. On the other hand, the nonuniform remaining height on one sawblade in rocking reciprocating sawing mode was cause by the combination of feeding and rocking motion. As shown in Fig. 10 which ignored horizontal displacement. The variation of segments sawing depth at both ends is greater in reciprocating stroke than segments in the middle. Thus the loads on the diamond segments in the middle will be more stable and smaller.
Declaration of Competing Interest We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.
Fig. 8. Position of segments outside the stone.(a) Remaining height of group (a) (iron-based) (b) Remaining height of group (b) (cobalt-based). 7
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Fig. 9. Average remaining height of segments after sawing.
[12]
[13] [14] [15]
[16] [17]
Fig. 10. Differences of sawing depth in rocking reciprocating sawing mode.
[18]
Acknowledgement
[19]
This work was supported by the Taishan Industrial Leading Talent project of Shandong Province, China [No.tscy20150228] and Shandong Key Research and Development Project [NO.2019GGX104022]. The authors are most grateful to Shandong Rizhao Hein Saw Co., Ltd. for supporting this work by providing the diamond tools and frame sawing machines.
[20]
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[22]
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