阅读说明：本技术 一种原位生成ZrB2-SiC增韧PcBN刀具及其制备方法 (ZrB is generated to normal position2-SiC toughened PcBN cutter and preparation method thereof ) 是由 王海龙 张凯 张珂皓 赵鹏博 邵刚 宋博 王海亮 范冰冰 许红亮 卢红霞 张锐 于 2020-12-08 设计创作，主要内容包括：本发明提出了一种原位生成ZrB_2-SiC增韧PcBN刀具的制备方法,本发明采用ZrSi_2粉、B_4C粉和活性炭粉为结合剂原料,原位反应生成ZrB_2-SiC复合PcBN,与传统直接采用陶瓷结合剂原料与cBN粉料混合的方法相比,原位反应生成的ZrB_2和SiC相的晶粒更加细小,分布更加均匀,其与cBN主晶粒的界面结合更加紧密,所生成的ZrB_2和SiC的晶粒易长成棒状或者板条状结构,能够提升PcBN的强韧性。(The invention provides an in-situ generated ZrB 2 The invention relates to a preparation method of a-SiC toughened PcBN cutter, which adopts ZrSi 2 Powder, B 4 The C powder and the activated carbon powder are used as raw materials of a bonding agent and are subjected to in-situ reaction to generate ZrB 2 The ZrB generated by the in-situ reaction of the-SiC composite PcBN is compared with the traditional method of directly mixing the ceramic bond raw material and the cBN powder 2 The crystal grains of the SiC phase are finer and more uniformly distributed, the interface bonding with the cBN main crystal grains is more compact, and the generated ZrB 2 And SiC crystal grains are easy to grow into a rod-shaped or strip-shaped structure, so that the toughness of the PcBN can be improved.)

1. ZrB is generated to normal position₂the-SiC toughened PcBN cutter is characterized by comprising the following raw materials in percentage by weight: 70-90% of cBN powder and 10-30% of mixed powder bonding agent;the mixed powder binder comprises zirconium silicide powder, boron carbide powder and activated carbon powder which are mixed according to the molar ratio of 2:1: 3.

2. An in-situ generated ZrB as defined in claim 1₂the-SiC toughened PcBN cutter is characterized in that the mixed powder bonding agent is prepared by mixing zirconium silicide powder, boron carbide powder and active carbon according to the molar ratio of 2:1:3, wherein ZrO is used as the active carbon₂The ball is a ball milling ball, the absolute ethyl alcohol is a ball milling medium, the materials are mixed through ball milling, dried and sieved by a 60-mesh sieve.

3. An in-situ generated ZrB as defined in claim 2₂-SiC-toughened PcBN tool, characterized in that the ZrO 2₂Equal to the mixed powder binder.

4. An in-situ generated ZrB as defined in claim 2₂the-SiC toughened PcBN cutter is characterized in that ball milling and mixing are carried out for 4-8 hours at a rotating speed of 100-200 r/min.

5. A method of manufacturing the PcBN tool of claim 1, comprising the steps of:

(1) 70-90% of cBN powder and 10-30% of mixed powder bonding agent are mixed with ZrO₂Mixing the balls for 2-4 h;

(2) mixing the mixed material with ZrO₂Sieving and separating the balls, and performing vacuum drying;

(3) sintering at the temperature of 1400-1600 ℃ under the pressure of 4-6 GPa, and carrying out furnace cooling after heat preservation for 5-10 min.

6. The method of making a PcBN cutter as claimed in claim 5, wherein the cBN powder grain size is 3-6 microns.

7. The method of producing a PcBN cutter according to claim 5, wherein ZrO in step (1)₂The amount of balls added and the total amount of the mixed powder binder and the cBN powderEqual amounts.

8. The method for preparing a PcBN tool according to claim 5, wherein in step (2), the PcBN tool is sieved by a 60-mesh sieve and vacuum dried at 200-400 ℃ for 30 minutes.

9. The method for manufacturing a PcBN tool according to claim 5, wherein the sintering temperature in step (3) is 1500 ℃, the pressure is 5GPa, and the holding time is 5 min.

Technical Field

The invention belongs to the technical field of cutter manufacturing, and particularly relates to in-situ generation of ZrB₂a-SiC toughened PcBN cutter and a preparation method thereof.

Background

Compared with common ceramic cutters and hard alloy cutters, the PcBN cutter has the advantages of high hardness, good thermal conductivity, long service life, high cutting speed and the like, and shows good application prospects in the aspects of cutting hardened steel, wear-resistant cast iron, high-temperature alloy and the like in recent years. However, the defects of difficult sintering, low toughness and the like limit the application development of the alloy. At present, the common bonding agent for preparing the PcBN cutter is metal Al, Ti, Co and other powder and a small amount of TiC or Si₃N₄Mixing, using the liquid phase of the high temperature metal, promotes densification of the PcBN, but the hardness and high temperature strength of the product are reduced due to softening of the metal, which typically occurs at 700 c to 800 c. The pure ceramic bonding agent can overcome the defects of the metal bonding agent, but the pure ceramic bonding agent has poor sintering performance, so that a completely compact PcBN cutter material is difficult to prepare, and the toughness of the PcBN cutter material is also poor. The pure ceramic bonding agent composite PcBN cutter material is generated through the in-situ reaction, the sintering can be promoted by utilizing the heat release of the original text reaction, and meanwhile, the in-situ reaction generated phase has good compatibility with the cBN, so that the toughness of the PcBN cutter material can be improved.

CN109456062A discloses a PcBN cutter and a preparation method thereof, which are mainly prepared by taking cubic boron nitride single crystal, silicon carbide, organic polysilazane and a heat curing auxiliary agent as raw materials, wherein PSN generates SiC and Si on the surface of cBN crystal grains in the sintering process₃N₄The nanocrystalline is directly used as a bonding agent to participate in the sintering process and is sinteredSiC nanocrystalline generated in the process grows on the raw material silicon carbide crystal grains to form a rod-shaped structure, so that the fracture toughness and the bending strength of the PcBN cutter can be improved; however, the PcBN material produced by the sintering process has a relatively low hardness, and the phase produced in the PcBN tool produced by the sintering process is mainly SiC and Si in addition to the main phase cBN₃N₄Phase, there is also a problem of a small amount of simple substance of Si.

Therefore, in order to overcome the defects of the prior art, a preparation method of the PcBN cutter is provided, so that the obtained PcBN cutter is more compact, the toughness of the PcBN cutter can be improved, and no simple substance or impurity phase is generated in the prepared PcBN cutter, which is a problem to be solved by the technical personnel in the field.

Disclosure of Invention

Based on at least one of the technical problems, the preparation method of the PcBN cutter enables the obtained PcBN cutter to be more compact, can improve the toughness of the PcBN cutter, and does not generate simple substances and impurity phases in the prepared PcBN cutter.

In view of this, the present invention provides an in-situ ZrB₂the-SiC toughened PcBN cutter consists of the following raw materials in percentage by weight: 70-90% of cBN powder and 10-30% of mixed powder bonding agent; the mixed powder binder comprises zirconium silicide powder, boron carbide powder and activated carbon powder which are mixed according to the molar ratio of 2:1: 3.

Further, the preparation step of the mixed powder bonding agent is that zirconium silicide powder, boron carbide powder and active carbon which are mixed according to the molar ratio of 2:1:3 are mixed with ZrO₂The ball is a ball milling ball, the absolute ethyl alcohol is a ball milling medium, the materials are mixed through ball milling, dried and sieved by a 60-mesh sieve.

Further, ZrO₂Equal to the mixed powder binder.

Further, the ball milling and mixing time is 4-8 hours, and the rotating speed is 100-200 r/min.

According to a second aspect of the present invention, there is provided a method of manufacturing the PcBN tool of claim 1, comprising the steps of:

(1) 70-90% of cBN powder and 10-30% of mixed powder bonding agent are mixed with ZrO₂Mixing the balls for 2-4 h;

(2) mixing the mixed material with ZrO₂Sieving and separating the balls, and performing vacuum drying;

(3) sintering at the temperature of 1400-1600 ℃ under the pressure of 4-6 GPa, and carrying out furnace cooling after heat preservation for 5-10 min.

ZrSi is selected from the mixed powder bonding agent₂、B₄C and C are taken as raw materials, a bonding agent is prepared according to the molar ratio of 2:1:3, and the in-situ reaction is ensured to generate the target toughening phase ZrB₂And SiC, the reaction formula is as follows:

2ZrSi₂+B₄C+3C=2ZrB₂+4SiC （1）

further, the cBN powder has a grain size of 3 to 6 μm.

Further, ZrO in step (1)₂The amount of balls added was the same as the total amount of mixed powder binder and cBN powder.

Further, in the step (2), the mixture is sieved by a 60-mesh sieve and is dried in vacuum for 30 minutes under the conditions of 200 ℃ and 400 ℃.

Further, in the step (3), the sintering temperature is 1500 ℃, the pressure is 5Gpa, and the heat preservation time is 5 min.

Through the technical scheme, the invention provides a preparation method of the PcBN cutter, which has the following advantages:

the invention adopts ZrSi₂Powder, B₄The C powder and the activated carbon powder are used as raw materials of a bonding agent and are subjected to in-situ reaction to generate ZrB₂The ZrB generated by the in-situ reaction of the-SiC composite PcBN is compared with the traditional method of directly mixing the ceramic bond raw material and the cBN powder₂The crystal grains of the SiC phase are finer and more uniformly distributed, the interface bonding with the cBN main crystal grains is more compact, and the generated ZrB₂And SiC crystal grains are easy to grow into a rod-shaped or strip-shaped structure, so that the toughness of the PcBN can be improved. PcBN-ZrB prepared by the invention₂The bending strength of the-SiC cutter composite material can reach 380-420MPa, the hardness can reach 41-52GPa, and the fracture toughness can reach 4-5.2 MPa^1/2。

Drawings

FIG. 1 is an XRD pattern of a PcBN tool made by the method of making example 1 of the invention.

FIG. 2 is an SEM photograph of a cross section of a PcBN tool made by the manufacturing method of example 1 of the invention.

Detailed Description

In order that the above objects, features and advantages of the present invention can be more clearly understood, the present invention will be described in further detail with reference to specific embodiments. It should be noted that the embodiments of the present invention and features of the embodiments may be combined with each other without conflict.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those specifically described herein, and therefore the scope of the present invention is not limited by the specific embodiments disclosed below.

The invention provides an in-situ generated ZrB₂the-SiC toughened PcBN cutter consists of the following raw materials in percentage by weight: 70-90% of cBN powder and 10-30% of mixed powder bonding agent; the mixed powder binder comprises zirconium silicide powder, boron carbide powder and activated carbon powder which are mixed according to the molar ratio of 2:1: 3.

In some embodiments of the PcBN cutter manufacturing method, the mixed powder bonding agent is prepared by mixing zirconium silicide powder, boron carbide powder and activated carbon in a molar ratio of 2:1:3 and ZrO₂The ball is a ball milling ball, the absolute ethyl alcohol is a ball milling medium, the materials are mixed through ball milling, dried and sieved by a 60-mesh sieve.

In some embodiments of the PcBN tool manufacturing method of the invention, ZrO₂The quantity of the mixed powder is equal to that of the mixed powder binder; anhydrous ethanol.

In some embodiments of the preparation method of the PcBN cutter, the ball milling and mixing time is 4-8 hours, and the rotating speed is 100-200 r/min.

The present invention proposes a method of making the PcBN tool of claim 1, comprising the steps of:

(1) 70-90% of cBN powder and 10-30% of mixed powder bonding agent are mixed with ZrO₂Mixing the balls for 2-4 h;

(2) mixing the mixed material with ZrO₂Sieving and separating the balls, and performing vacuum drying;

(3) sintering at the temperature of 1400-1600 ℃ under the pressure of 4-6 GPa, and carrying out furnace cooling after heat preservation for 5-10 min.

ZrSi is selected from the mixed powder bonding agent₂、B₄C and C are taken as raw materials, a bonding agent is prepared according to the molar ratio of 2:1:3, and the in-situ reaction is ensured to generate the target toughening phase ZrB₂And SiC, the reaction formula is as follows:

2ZrSi₂+B₄C+3C=2ZrB₂+4SiC（1）

in some embodiments of the methods of the present invention for making a PcBN tool, the cBN powder grain size is 3-6 microns.

In some embodiments of the method for producing a PcBN tool of the invention, ZrO in step (1)₂The amount of balls added was the same as the total amount of mixed powder binder and cBN powder.

In some embodiments of the method for preparing the PcBN tool of the invention, the PcBN tool is sieved by a 60-mesh sieve in the step (2), and is dried for 30 minutes in vacuum at the temperature of 200-400 ℃.

In some embodiments of the method for manufacturing the PcBN tool, the sintering temperature in the step (3) is 1500 ℃, the pressure is 5Gpa, and the heat preservation time is 5 min.

Example 1

Preparing a mixed powder bonding agent: selecting ZrSi₂Powder, B₄Weighing and proportioning C powder and activated carbon powder serving as raw materials according to a molar ratio of 2:1:3, putting the prepared mixed powder into a polytetrafluoroethylene ball milling tank, and selecting ZrO with the same amount as that of a mixed powder binder₂The ball is a ball milling ball, absolute ethyl alcohol is a ball milling medium, a planetary ball mill is adopted for mixing materials, the mixing time is 4 hours, and the rotating speed is 100 r/min; after ball milling and mixing, the mixture is dried by adopting a rotary evaporator, and the dried mixed powder is sieved by a 60-mesh sieve for later use.

The PcBN cutter material comprises the following raw materials in percentage by weight: 90% of cubic boron nitride powder and 10% of mixed powder bonding agent.

The preparation method of the PcBN cutter material comprises the following steps: weighing cBN micropowder (with the granularity of 3-6 microns) and mixed powder binder according to the formula, and using ZrO₂The balls being ball-milled, ZrO₂The addition of the balls is as followsThe total amount of the mixed powder bonding agent and the cBN powder is equal, and a three-dimensional mixer is adopted for mixing, wherein the mixing time is 4 hours; mixing the mixed material with ZrO₂Sieving the balls with a 60-mesh sieve for separation, then pouring the mixed material into a pyrophyllite mould, and then carrying out vacuum drying for 30 minutes at the temperature of 200 ℃; putting the pyrophyllite mould into a cubic press, synthesizing for 5min under the conditions that the temperature is 1500 ℃ and the pressure is 5GPa, cooling along with a furnace after sintering, taking out the mould, and separating the sintered body from the mould to obtain the PcBN-ZrB₂-SiC tool composite material.

PcBN-ZrB prepared in this example₂The hardness of the-SiC cutter composite material is 48.9GPa, the bending strength is 385MPa, and the fracture toughness is 4 MPa.m^1/2。

The PcBN tool manufactured in this example was subjected to XRD testing, and the results are shown in fig. 1. As is clear from FIG. 1, the phase formed in the PcBN tool produced mainly formed SiC and ZrB in addition to the main phase cBN₂The phase, without the generation of simple substance and impurity phase, achieves the expected target.

The PcBN tool manufactured in this example was subjected to SEM testing, and the test results are shown in fig. 2. It can be seen from FIG. 2 that the PcBN tool made by sintering is relatively dense.

Example 2

Preparing a mixed powder bonding agent: selecting ZrSi₂Powder, B₄Weighing and proportioning C powder and activated carbon powder serving as raw materials according to a molar ratio of 2:1:3, putting the prepared mixed powder into a polytetrafluoroethylene ball milling tank, and selecting ZrO with the same amount as that of a mixed powder binder₂The ball is a ball milling ball, absolute ethyl alcohol is a ball milling medium, a planetary ball mill is adopted for mixing materials, the mixing time is 4 hours, and the rotating speed is 100 r/min; after ball milling and mixing, the mixture is dried by adopting a rotary evaporator, and the dried mixed powder is sieved by a 60-mesh sieve for later use.

The PcBN cutter material comprises the following raw materials in percentage by weight: 80% of cubic boron nitride powder and 20% of mixed powder bonding agent.

The preparation method of the PcBN cutter material comprises the following steps: weighing cBN micro powder (the granularity is 3-6 microns) and the mixed powder bonding agent according to the formula,with ZrO₂The balls being ball-milled, ZrO₂The adding amount of the balls is equal to the total amount of the mixed powder bonding agent and the cBN powder, and a three-dimensional mixer is adopted for mixing, wherein the mixing time is 4 hours; mixing the mixed material with ZrO₂Sieving the balls with a 60-mesh sieve for separation; then pouring the mixed material into a pyrophyllite mould, and then carrying out vacuum drying for 30 minutes at the temperature of 200 ℃; putting the pyrophyllite mould into a cubic press, synthesizing for 5min under the conditions that the temperature is 1500 ℃ and the pressure is 5GPa, cooling along with a furnace after sintering, taking out the mould, and separating the sintered body from the mould to obtain the PcBN-ZrB₂-SiC tool composite material.

PcBN-ZrB prepared in this example₂The hardness of the-SiC cutter composite material is 51GPa, the bending strength is 420MPa, and the fracture toughness is 5.2 MPa.m^1/2。

Example 3

Preparing a mixed powder bonding agent: selecting ZrSi₂Powder, B₄Weighing and proportioning C powder and activated carbon powder serving as raw materials according to a molar ratio of 2:1:3, putting the prepared mixed powder into a polytetrafluoroethylene ball milling tank, and selecting ZrO with the same amount as that of a mixed powder binder₂The ball is a ball milling ball, absolute ethyl alcohol is a ball milling medium, a planetary ball mill is adopted for mixing materials, the mixing time is 4 hours, and the rotating speed is 100 r/min; after ball milling and mixing, the mixture is dried by adopting a rotary evaporator, and the dried mixed powder is sieved by a 60-mesh sieve for later use.

The PcBN cutter material comprises the following raw materials in percentage by weight: 70% of cubic boron nitride powder and 30% of mixed powder bonding agent.

The preparation method of the PcBN cutter material comprises the following steps: weighing cBN micropowder (with the granularity of 3-6 microns) and mixed powder binder according to the formula, and using ZrO₂The balls being ball-milled, ZrO₂The adding amount of the balls is equal to the total amount of the mixed powder bonding agent and the cBN powder, and a three-dimensional mixer is adopted for mixing, wherein the mixing time is 4 hours; mixing the mixed material with ZrO₂Sieving the balls with a 60-mesh sieve for separation; then pouring the mixed material into a pyrophyllite mould, and then carrying out vacuum drying for 30 minutes at the temperature of 200 ℃; putting pyrophyllite mould into a cubic press at a certain temperatureSynthesizing for 5min under the conditions of 1500 ℃ and 5GPa, cooling along with a furnace after sintering, taking out a mold, and separating a sintered body from the mold to obtain the PcBN-ZrB₂-SiC tool composite material.

PcBN-ZrB prepared in this example₂The hardness of the-SiC cutter composite material is 42GPa, the bending strength is 390MPa, and the fracture toughness is 4.8 MPa.m^1/2。

Example 4

Preparing a mixed powder bonding agent: selecting ZrSi₂Powder, B₄Weighing and proportioning C powder and activated carbon powder serving as raw materials according to a molar ratio of 2:1:3, putting the prepared mixed powder into a polytetrafluoroethylene ball milling tank, and selecting ZrO with the same amount as that of a mixed powder binder₂The ball is a ball milling ball, absolute ethyl alcohol is a ball milling medium, a planetary ball mill is adopted for mixing materials, the mixing time is 4 hours, and the rotating speed is 100 r/min; after ball milling and mixing, the mixture is dried by adopting a rotary evaporator, and the dried mixed powder is sieved by a 60-mesh sieve for later use.

The PcBN cutter material comprises the following raw materials in percentage by weight: 80% of cubic boron nitride powder and 20% of mixed powder bonding agent.

The preparation method of the PcBN cutter material comprises the following steps: weighing cBN micropowder (with the granularity of 3-6 microns) and mixed powder binder according to the formula, and using ZrO₂The balls being ball-milled, ZrO₂The adding amount of the balls is equal to the total amount of the mixed powder bonding agent and the cBN powder, and a three-dimensional mixer is adopted for mixing, wherein the mixing time is 4 hours; mixing the mixed material with ZrO₂Sieving the balls with a 60-mesh sieve for separation; then pouring the mixed material into a pyrophyllite mold, and then carrying out vacuum drying for 30 minutes at the temperature of 300 ℃; putting the pyrophyllite mould into a cubic press, synthesizing for 5min under the conditions that the temperature is 1400 ℃ and the pressure is 6GPa, cooling along with a furnace after sintering, taking out the mould, and separating the sintered body from the mould to obtain the PcBN-ZrB₂-SiC tool composite material.

PcBN-ZrB prepared in this example₂The hardness of the-SiC cutter composite material is 45GPa, the bending strength is 385MPa, and the fracture toughness is 4 MPa.m^1/2。

Example 5

Preparing a mixed powder bonding agent: selecting ZrSi₂Powder, B₄Weighing and proportioning C powder and activated carbon powder serving as raw materials according to a molar ratio of 2:1:3, putting the prepared mixed powder into a polytetrafluoroethylene ball milling tank, and selecting ZrO with the same amount as that of a mixed powder binder₂The ball is a ball milling ball, absolute ethyl alcohol is a ball milling medium, a planetary ball mill is adopted for mixing materials, the mixing time is 4 hours, and the rotating speed is 100 r/min; after ball milling and mixing, the mixture is dried by adopting a rotary evaporator, and the dried mixed powder is sieved by a 60-mesh sieve for later use.

The PcBN cutter material comprises the following raw materials in percentage by weight: 80% of cubic boron nitride powder and 20% of mixed powder bonding agent.

The preparation method of the PcBN cutter material comprises the following steps: weighing cBN micropowder (with the granularity of 3-6 microns) and mixed powder binder according to the formula, and using ZrO₂The balls being ball-milled, ZrO₂The adding amount of the balls is equal to the total amount of the mixed powder bonding agent and the cBN powder, and a three-dimensional mixer is adopted for mixing, wherein the mixing time is 4 hours; mixing the mixed material with ZrO₂Sieving the balls with a 60-mesh sieve for separation; then pouring the mixed material into a pyrophyllite mould, and then carrying out vacuum drying for 30 minutes at the temperature of 200 ℃; putting the pyrophyllite mould into a cubic press, synthesizing for 5min under the conditions that the temperature is 1600 ℃ and the pressure is 4GPa, cooling along with a furnace after sintering, taking out the mould, and separating the sintered body from the mould to obtain the PcBN-ZrB₂-SiC tool composite material.

PcBN-ZrB prepared in this example₂The hardness of the-SiC cutter composite material is 42GPa, the bending strength is 405MPa, and the fracture toughness is 4.7 MPa.m^1/2。

Example 6

Preparing a mixed powder bonding agent: selecting ZrSi₂Powder, B₄Taking C powder and activated carbon powder as raw materials, weighing and proportioning the raw materials according to the molar ratio of 2:1:3, putting the prepared mixed powder into a polytetrafluoroethylene ball-milling tank, and selecting ZrO equivalent to the mixed powder binder₂The ball is a ball milling ball, absolute ethyl alcohol is a ball milling medium, and a planetary ball mill is adopted for feedingMixing materials, wherein the mixing time is 6 hours, and the rotating speed is 200 revolutions per minute; after ball milling and mixing, the mixture is dried by adopting a rotary evaporator, and the dried mixed powder is sieved by a 60-mesh sieve for later use.

The PcBN cutter material comprises the following raw materials in percentage by weight: 80% of cubic boron nitride powder and 20% of mixed powder bonding agent.

The preparation method of the PcBN cutter material comprises the following steps: weighing cBN micropowder (with the granularity of 3-6 microns) and mixed powder binder according to the formula, and using ZrO₂The balls being ball-milled, ZrO₂The adding amount of the balls is equal to the total amount of the mixed powder bonding agent and the cBN powder, and a three-dimensional mixer is adopted for mixing, wherein the mixing time is 8 hours; mixing the mixed material with ZrO₂Sieving the balls with a 60-mesh sieve for separation; then pouring the mixed material into a pyrophyllite mould, and then carrying out vacuum drying for 30 minutes at the temperature of 200 ℃; putting the pyrophyllite mould into a cubic press, synthesizing for 10min under the conditions that the temperature is 1550 ℃ and the pressure is 5GPa, cooling along with a furnace after sintering is finished, taking out the mould, and separating a sintered body from the mould to obtain the PcBN-ZrB₂-SiC tool composite material.

PcBN-ZrB prepared in this example₂The hardness of the-SiC tool composite material is 45GPa, the bending strength is 412MPa, and the fracture toughness is 4.9 MPa.m^1/2。

PcBN tool embodiments

The PcBN tool of the present embodiment is manufactured by the manufacturing method in the embodiment of the manufacturing method described above, and will not be described here again.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.