阅读说明：本技术 一种高强韧多晶硬质合金挤压圆棒的制作方法 (Manufacturing method of high-toughness polycrystalline hard alloy extruded round rod ) 是由 王忠平 王恺 黄志平 廖志娟 郭光富 金江 于 2021-08-20 设计创作，主要内容包括：本发明公开了一种高强韧多晶硬质合金挤压圆棒的制作方法,具体包括以下步骤：S1、制粉：将WC、Co、Cr、晶粒抑制剂、强化相研磨制粉；S2、取料：按照质量分数计,称取70-80％的WC粉、1-7％的Co粉、1-7％的Cr粉、2-4％的晶粒抑制剂粉、5-20％的强化相粉,得到混合粉料；S3、混料；S4、挤压圆棒；S5、烧结：将制得的圆棒坯体放置于烧结炉内进行烧结,以1-2℃/S的速度升温至1100-1350℃,在此温度下进行烧结60-100min,烧结完成后进行冷却,得到半成品圆棒；S6、热处理；通过添加晶粒抑制剂,可从内部抑制WC晶粒的长大,能够有效的抑制WC的连续或者非连续长大,对WC晶粒长大的抑制效果明显,使得值得的高强韧多晶硬质合金挤压圆棒内部结构更均匀,强度和韧性更好。(The invention discloses a manufacturing method of a high-toughness polycrystalline hard alloy extruded round rod, which specifically comprises the following steps: s1, milling: grinding WC, Co, Cr, a grain inhibitor and a strengthening phase into powder; s2, taking materials: weighing 70-80% of WC powder, 1-7% of Co powder, 1-7% of Cr powder, 2-4% of grain inhibitor powder and 5-20% of strengthening phase powder according to mass fraction to obtain mixed powder; s3, mixing materials; s4, extruding a round rod; s5, sintering: placing the prepared round rod blank into a sintering furnace for sintering, heating to 1100-1350 ℃ at the speed of 1-2 ℃/S, sintering for 60-100min at the temperature, and cooling after sintering to obtain a semi-finished round rod; s6, heat treatment; by adding the grain inhibitor, the growth of WC grains can be inhibited from the inside, the continuous or discontinuous growth of WC grains can be effectively inhibited, the inhibition effect on the growth of the WC grains is obvious, and the high-strength and high-toughness polycrystalline hard alloy extrusion round bar has the advantages of more uniform internal structure and better strength and toughness.)

1. The manufacturing method of the high-toughness polycrystalline hard alloy extruded round rod is characterized by comprising the following steps:

s1, milling: grinding WC, Co, Cr, a grain inhibitor and a strengthening phase into powder, filtering the powder by a 300-mesh screen, and taking the undersize as the prepared powdery raw material;

s2, taking materials: weighing 70-80% of WC powder, 1-7% of Co powder, 1-7% of Cr powder, 2-4% of grain inhibitor powder and 5-20% of strengthening phase powder according to mass fraction to obtain mixed powder;

s3, mixing materials: adding the weighed mixed powder into a mixer for mixing, adding a grinding medium, a dispersing agent and a forming agent, and uniformly mixing to obtain a prepared raw material;

s4, extruding a round bar: putting the prepared raw materials into a charging barrel of an extruder, and pressing the raw materials into a round bar blank under the pressure of 100-200 MPa;

s5, sintering: placing the prepared round rod blank into a sintering furnace for sintering, heating to 1100-1350 ℃ at the speed of 1-2 ℃/S, sintering for 60-100min at the temperature, and cooling after sintering to obtain a semi-finished round rod;

s6, heat treatment: quenching the prepared semi-finished round bar at the temperature of 900-1100 ℃ and tempering at the temperature of 300-400 ℃ in a vacuum environment to obtain a primary round bar;

s7, grinding: and (3) polishing the outer surface of the primary finished round bar, carrying out size detection after polishing, smearing anti-rust oil after the size of the round bar meets the requirement, packaging and warehousing.

2. The method for manufacturing the high-toughness polycrystalline hard alloy extruded round rod according to claim 1, wherein the grain inhibitor is one or two of ZrC and VC.

3. The method for manufacturing the high-toughness polycrystalline hard alloy extruded round rod according to claim 2, wherein the strengthening phase is any one or more of TiC, TiN and TaC.

4. The method for manufacturing the high-toughness polycrystalline hard alloy extruded round rod according to the claim 1, wherein in the step S3, the grinding medium is hexane or absolute ethyl alcohol, and the mass fraction of the grinding medium in the total amount of the mixed powder is 0.5-1.5%.

5. The method for manufacturing the high-toughness polycrystalline hard alloy extruded round rod according to claim 4, wherein in the step S3, the dispersing agent is dodecylbenzene sulfonic acid, stearic acid or ethofenamine, and the mass fraction of the dispersing agent in the total amount of the mixed powder is 0.5-1%.

6. The method for manufacturing the high-toughness polycrystalline hard alloy extruded round rod according to claim 5, wherein in the step S3, the forming agent is one or more of rubber, paraffin, ethylene glycol and SBS, and the forming agent accounts for 1-2% of the total mass of the mixed powder.

7. The method for manufacturing the high-toughness polycrystalline hard alloy extruded round rod according to the claim 6, wherein in the step S3, in order to ensure that the components in the prepared raw materials are mixed uniformly, the mixture is not only stirred continuously, but also the powder at the bottom is conveyed to the upper part continuously, after the mixture is mixed for 40-60 minutes, sampling and testing are carried out at least three different positions, the mass ratio of the components in each sample is within 3% of the standard mass ratio, otherwise, the mixture is carried out for 10-20 minutes, then the sampling and testing are carried out again according to the process, and the process is circulated until the mass ratio of the components in each sample is within 3% of the standard mass ratio.

8. The method for manufacturing the high-toughness polycrystalline hard alloy extruded round rod according to any one of claims 1 to 7, wherein in the step S4, when the extrusion pressure reaches the maximum pressure value, the pressure is maintained for 15 to 20 minutes.

9. The method as claimed in any one of claims 1 to 7, wherein in step S5, when the temperature in the sintering furnace is increased to 1100-1350 ℃, Ar gas is introduced into the sintering furnace, and the pressure of Ar gas in the sintering furnace is 3-4 MPa.

Technical Field

The invention relates to the technical field of production of hard alloy extruded round bars, in particular to a manufacturing method of a high-toughness polycrystalline hard alloy extruded round bar.

Background

Cemented carbide is an alloy material made from a hard compound of refractory metals and a binder metal by a powder metallurgy process. The alloy has a series of excellent performances of high hardness, wear resistance, good strength and toughness, heat resistance, corrosion resistance and the like, is basically kept unchanged at the temperature of 500 ℃, and still has very high hardness at the temperature of 1000 ℃. The hard alloy round bar, namely the tungsten steel round bar, has stable mechanical property, is easy to weld, has high wear resistance and high impact resistance, and is mainly used for manufacturing tools such as drills, end mills, reamers and the like. The main raw materials of the existing hard alloy round bar during production are a hard phase and a bonding phase, wherein the hard phase is mainly WC, and the bonding phase is mainly Co or Cr. In order to inhibit the growth of WC grains, techniques such as hot isostatic pressing, hot-pressing sintering, microwave sintering, etc. are generally used to inhibit the growth of WC grains through the combined action of temperature and pressure. However, this external suppression method is not effective enough. Therefore, the applicant provides a manufacturing method of a high-toughness polycrystalline hard alloy extrusion round bar, by adding a grain inhibitor, the growth of WC grains can be inhibited from the inside, the continuous or discontinuous growth of WC can be effectively inhibited, and the inhibition effect on the growth of WC grains is obvious.

Disclosure of Invention

The invention aims to provide a method for manufacturing a high-toughness polycrystalline hard alloy extrusion round bar, which can inhibit the growth of WC grains from the inside by adding a grain inhibitor, can effectively inhibit the continuous or discontinuous growth of WC, and has obvious inhibition effect on the growth of WC grains.

The invention is realized by the following steps: a manufacturing method of a high-toughness polycrystalline hard alloy extrusion round rod specifically comprises the following steps:

s1, milling: grinding WC, Co, Cr, a grain inhibitor and a strengthening phase into powder, filtering the powder by a 300-mesh screen, and taking the undersize as the prepared powdery raw material;

s2, taking materials: weighing 70-80% of WC powder, 1-7% of Co powder, 1-7% of Cr powder, 2-4% of grain inhibitor powder and 5-20% of strengthening phase powder according to mass fraction to obtain mixed powder;

s3, mixing materials: adding the weighed mixed powder into a mixer for mixing, adding a grinding medium, a dispersing agent and a forming agent, and uniformly mixing to obtain a prepared raw material;

s4, extruding a round bar: putting the prepared raw materials into a charging barrel of an extruder, and pressing the raw materials into a round bar blank under the pressure of 100-200 MPa;

s5, sintering: placing the prepared round rod blank into a sintering furnace for sintering, heating to 1100-1350 ℃ at the speed of 1-2 ℃/S, sintering for 60-100min at the temperature, and cooling after sintering to obtain a semi-finished round rod;

s6, heat treatment: quenching the prepared semi-finished round bar at the temperature of 900-1100 ℃ and tempering at the temperature of 300-400 ℃ in a vacuum environment to obtain a primary round bar;

s7, grinding: and (3) polishing the outer surface of the primary finished round bar, carrying out size detection after polishing, smearing anti-rust oil after the size of the round bar meets the requirement, packaging and warehousing.

Further, the grain inhibitor selects any one or two of ZrC and VC.

Further, the strengthening phase is any one or more of TiC, TiN and TaC.

Further, in the step S3, the grinding medium is hexane or absolute ethyl alcohol, and the mass fraction of the grinding medium in the total amount of the mixed powder is 0.5 to 1.5%.

Further, in the step S3, the dispersing agent is dodecylbenzene sulfonic acid, stearic acid or ethoprofen, and the mass fraction of the dispersing agent in the total amount of the mixed powder is 0.5-1%.

Further, in the step S3, the forming agent is one or more of rubber, paraffin, ethylene glycol and SBS, and accounts for 1-2% of the total amount of the mixed powder.

Further, in step S3, in order to ensure that the components in the preparation raw material are uniformly mixed, the mixing is performed while continuously stirring, and the powder at the bottom is continuously conveyed to the upper part, so that after the mixing is performed for 40 to 60 minutes, sampling and testing are performed from at least three different positions, the mass ratio of the components in each sample is within 3% of the standard mass ratio, otherwise, the mixing is performed for 10 to 20 minutes, and then sampling and testing are performed again according to the above process, and the process is repeated until the mass ratio of the components in each sample is within 3% of the standard mass ratio.

Further, in the step S4, when the extrusion pressure reaches the maximum pressure value, the pressure is maintained for 15 to 20 minutes.

Further, in the step S5, when the temperature in the sintering furnace rises to 1100-1350 ℃, Ar gas is filled into the sintering furnace, and the pressure of the Ar gas in the sintering furnace is 3-4 MPa.

Compared with the prior art, the invention has the beneficial effects that:

1. by adding the grain inhibitor, the growth of WC grains can be inhibited from the inside, the continuous or discontinuous growth of WC grains can be effectively inhibited, the inhibition effect on the growth of the WC grains is obvious, and the high-strength and high-toughness polycrystalline hard alloy extrusion round bar has the advantages of more uniform internal structure and better strength and toughness.

2. By adding the strengthening phase powder, under the action of the strengthening phase, the matrix grains of the hard alloy extrusion round bar are refined, the hardenability of the matrix is increased, and the strength of the alloy is further improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a flow chart of a method for manufacturing a high-toughness polycrystalline hard alloy extruded round rod.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

The first embodiment is as follows:

referring to fig. 1, a method for manufacturing a high-toughness polycrystalline cemented carbide extruded round bar specifically includes the following steps:

s1, milling: WC, Co, Cr, ZrC and TiC are ground into powder, the powder is filtered by a 300-mesh screen, and the undersize is the prepared powdery raw material. Wherein ZrC is a grain inhibitor and has the function of inhibiting WC grains from growing, TiC is a strengthening phase, and the TiC has the advantages of refining matrix grains and increasing matrix hardenability and has the function of further improving the alloy strength.

S2, taking materials: weighing 7kg of WC powder, 0.1kg of Co powder, 0.7kg of Cr powder, 0.2kg of ZrC powder and 2kg of TiC powder, wherein the total weight is 10kg, and obtaining mixed powder.

S3, mixing materials: and adding the weighed mixed powder into a mixer for mixing, adding a grinding medium, a dispersing agent and a forming agent, and uniformly mixing to obtain a prepared raw material. Wherein the grinding medium is hexane in an amount of 50 g. The dispersant is dodecyl benzene sulfonic acid, and the dosage is 50 g. The forming agent is made of rubber, and is used after being ground into powder, and the using amount is 100 g. In order to ensure that all components in the prepared raw materials are uniformly mixed, the materials are not only continuously stirred during mixing, but also the powder at the bottom is continuously conveyed to the upper part, after the materials are mixed for 40 minutes, sampling and testing are carried out from at least three different positions, the mass ratio of all the components in all the samples is within 3 percent of the standard mass ratio, otherwise, the materials are continuously mixed for 10 minutes, then the sampling and testing are carried out again according to the process, and the process is circulated until the mass ratio of all the components in all the samples is within 3 percent of the standard mass ratio.

S4, extruding a round bar: and (3) putting the prepared raw materials into a charging barrel of an extruder, pressing the raw materials into a round bar blank under the pressure of 100MPa, and keeping the pressure for 15 minutes when the extrusion pressure reaches 100 MPa.

S5, sintering: and placing the prepared round rod blank into a sintering furnace for sintering, heating to 1100-1350 ℃ at the speed of 1 ℃/S, sintering for 60min at the temperature, and filling Ar gas into the sintering furnace when the temperature in the sintering furnace is increased to 1100-1350 ℃, wherein the pressure of the Ar gas in the sintering furnace is 3 MPa. And cooling after sintering to obtain the semi-finished round bar.

S6, heat treatment: and quenching the prepared semi-finished round bar at the temperature of 900-1100 ℃ and tempering at the temperature of 300-400 ℃ in a vacuum environment to obtain the initially-finished round bar.

S7, grinding: and (3) polishing the outer surface of the primary finished round bar, carrying out size detection after polishing is finished, obtaining the finished round bar after the size of the round bar meets the requirement, and then smearing anti-rust oil, packaging and warehousing.

Therefore, when the high-strength and high-toughness polycrystalline hard alloy extrusion round bar is manufactured by the method, the grain inhibitor is added, so that the growth of WC grains can be inhibited from the inside, the continuous or discontinuous growth of WC can be effectively inhibited, the inhibition effect on the growth of the WC grains is obvious, the internal structure of the high-strength and high-toughness polycrystalline hard alloy extrusion round bar is more uniform, and the strength and the toughness are better.

In addition, when the high-strength and high-toughness polycrystalline hard alloy extrusion round bar is manufactured, strengthening phase powder is added, and under the action of the strengthening phase, the matrix grains of the hard alloy extrusion round bar are refined, the hardenability of the matrix is increased, and the strength of the alloy is further improved.

Example two:

referring to fig. 1, a method for manufacturing a high-toughness polycrystalline cemented carbide extruded round bar specifically includes the following steps:

s1, milling: WC, Co, Cr, VC and TiN are ground into powder, the powder is filtered by a 300-mesh screen, and the undersize is the prepared powdery raw material. Wherein VC is a grain inhibitor and has the function of inhibiting WC grains from growing, TiN is a strengthening phase and has the advantages of refining matrix grains and increasing matrix hardenability, and the VC-based strengthening phase has the function of further improving the alloy strength.

S2, taking materials: according to the mass fraction, 7.5kg of WC powder, 0.5kg of Co powder, 0.5kg of Cr powder, 0.3kg of ZrC powder and 1.2kg of TiN powder are weighed, and the total weight is 10kg, so that mixed powder is obtained.

S3, mixing materials: and adding the weighed mixed powder into a mixer for mixing, adding a grinding medium, a dispersing agent and a forming agent, and uniformly mixing to obtain a prepared raw material. Wherein, the grinding medium is anhydrous ethanol, and the dosage is 150 g. The dispersant is stearic acid, and the dosage is 100 g. 100g of paraffin and ethylene glycol are used as the forming agent. In order to ensure that all components in the prepared raw materials are uniformly mixed, the materials are not only continuously stirred during mixing, but also the powder at the bottom is continuously conveyed to the upper part, after the materials are mixed for 60 minutes, sampling and testing are carried out from at least three different positions, the mass ratio of all the components in all the samples is within 3 percent of the standard mass ratio, otherwise, the materials are continuously mixed for 20 minutes, then the sampling and testing are carried out again according to the process, and the process is circulated until the mass ratio of all the components in all the samples is within 3 percent of the standard mass ratio.

S4, extruding a round bar: and (3) putting the prepared raw materials into a charging barrel of an extruder, pressing the raw materials into a round bar blank under the pressure of 150MPa, and keeping the pressure for 18 minutes when the extrusion pressure reaches 150 MPa.

S5, sintering: and placing the prepared round rod blank into a sintering furnace for sintering, heating to 1100-1350 ℃ at the speed of 1.5 ℃/S, sintering for 80min at the temperature, and filling Ar gas into the sintering furnace when the temperature in the sintering furnace is increased to 1100-1350 ℃, wherein the pressure of the Ar gas in the sintering furnace is 3.5 MPa. And cooling after sintering to obtain the semi-finished round bar.

S6, heat treatment: and quenching the prepared semi-finished round bar at the temperature of 900-1100 ℃ and tempering at the temperature of 300-400 ℃ in a vacuum environment to obtain the initially-finished round bar.

S7, grinding: and (3) polishing the outer surface of the primary finished round bar, carrying out size detection after polishing is finished, obtaining the finished round bar after the size of the round bar meets the requirement, and then smearing anti-rust oil, packaging and warehousing.

Example three:

referring to fig. 1, a method for manufacturing a high-toughness polycrystalline cemented carbide extruded round bar specifically includes the following steps:

s1, milling: WC, Co, Cr, ZrC, VC and TaC are ground into powder, the powder is filtered by a 300-mesh screen, and the undersize is the prepared powdery raw material. Wherein ZrC and VC are grain inhibitors and have the function of inhibiting WC grains from growing, and TaC is a strengthening phase and has the advantages of refining matrix grains and increasing matrix hardenability, and the ZrC and VC alloy has the function of further improving alloy strength.

S2, taking materials: weighing 8kg of WC powder, 0.7kg of Co powder, 0.1kg of Cr powder, 0.2kg of ZrC powder, 0.2kg of VC powder and 0.8kg of TaC powder according to the mass fraction, and obtaining 10kg of mixed powder.

S3, mixing materials: and adding the weighed mixed powder into a mixer for mixing, adding a grinding medium, a dispersing agent and a forming agent, and uniformly mixing to obtain a prepared raw material. Wherein the grinding medium is anhydrous ethanol, and the dosage is 100 g. The dispersant is ethionamide, and the dosage is 100 g. The forming agent used was ethylene glycol and SBS, 75g each. In order to ensure that all components in the prepared raw materials are uniformly mixed, the materials are not only continuously stirred during mixing, but also the powder at the bottom is continuously conveyed to the upper part, after the materials are mixed for 50 minutes, sampling and testing are carried out at least three different positions, the mass ratio of all the components in all the samples is within 3 percent of the standard mass ratio, otherwise, the materials are continuously mixed for 15 minutes, then the sampling and testing are carried out again according to the process, and the process is circulated until the mass ratio of all the components in all the samples is within 3 percent of the standard mass ratio.

S4, extruding a round bar: and (3) putting the prepared raw materials into a charging barrel of an extruder, pressing the raw materials into a round bar blank under the pressure of 200MPa, and keeping the pressure for 20 minutes when the extrusion pressure reaches 200 MPa.

S5, sintering: and placing the prepared round rod blank into a sintering furnace for sintering, heating to 1100-1350 ℃ at the speed of 2 ℃/S, sintering for 100min at the temperature, and filling Ar gas into the sintering furnace when the temperature in the sintering furnace is increased to 1100-1350 ℃, wherein the pressure of the Ar gas in the sintering furnace is 4 MPa. And cooling after sintering to obtain the semi-finished round bar.

S6, heat treatment: and quenching the prepared semi-finished round bar at the temperature of 900-1100 ℃ and tempering at the temperature of 300-400 ℃ in a vacuum environment to obtain the initially-finished round bar.

S7, grinding: and (3) polishing the outer surface of the primary finished round bar, carrying out size detection after polishing is finished, obtaining the finished round bar after the size of the round bar meets the requirement, and then smearing anti-rust oil, packaging and warehousing.

Example four:

referring to fig. 1, a method for manufacturing a high-toughness polycrystalline cemented carbide extruded round bar specifically includes the following steps:

s1, milling: WC, Co, Cr, ZrC, VC, TiC, TiN and TaC are ground into powder, the powder is filtered by a 300-mesh screen, and the undersize is the prepared powdery raw material. Wherein ZrC and VC are grain inhibitors and have the function of inhibiting WC grains from growing, TiC, TiN and TaC are strengthening phases and have the advantages of refining matrix grains and increasing matrix hardenability and have the function of further improving alloy strength.

S2, taking materials: according to the mass fraction, 10kg of WC powder 8kg, Co powder 0.7kg, Cr powder 0.4kg, ZrC powder 0.2kg, VC powder 0.2kg, TaC powder 0.2kg, TiC powder 0.2kg and TiN powder 0.1kg are weighed, and mixed powder is obtained.

S3, mixing materials: and adding the weighed mixed powder into a mixer for mixing, adding a grinding medium, a dispersing agent and a forming agent, and uniformly mixing to obtain a prepared raw material. Wherein the grinding medium is anhydrous ethanol, and the dosage is 100 g. The dispersant is ethionamide, and the dosage is 100 g. The molding agent used was 100g of rubber and paraffin each. In order to ensure that all components in the prepared raw materials are uniformly mixed, the materials are not only continuously stirred during mixing, but also the powder at the bottom is continuously conveyed to the upper part, after the materials are mixed for 60 minutes, sampling and testing are carried out from at least three different positions, the mass ratio of all the components in all the samples is within 3 percent of the standard mass ratio, otherwise, the materials are continuously mixed for 20 minutes, then the sampling and testing are carried out again according to the process, and the process is circulated until the mass ratio of all the components in all the samples is within 3 percent of the standard mass ratio.

S4, extruding a round bar: and (3) putting the prepared raw materials into a charging barrel of an extruder, pressing the raw materials into a round bar blank under the pressure of 200MPa, and keeping the pressure for 20 minutes when the extrusion pressure reaches 200 MPa.

S5, sintering: and placing the prepared round rod blank into a sintering furnace for sintering, heating to 1100-1350 ℃ at the speed of 2 ℃/S, sintering for 100min at the temperature, and filling Ar gas into the sintering furnace when the temperature in the sintering furnace is increased to 1100-1350 ℃, wherein the pressure of the Ar gas in the sintering furnace is 4 MPa. And cooling after sintering to obtain the semi-finished round bar.

S6, heat treatment: and quenching the prepared semi-finished round bar at the temperature of 900-1100 ℃ and tempering at the temperature of 300-400 ℃ in a vacuum environment to obtain the initially-finished round bar.

S7, grinding: and (3) polishing the outer surface of the primary finished round bar, carrying out size detection after polishing is finished, obtaining the finished round bar after the size of the round bar meets the requirement, and then smearing anti-rust oil, packaging and warehousing.

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 may be made to the present invention by 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.