阅读说明：本技术 一种超大规格环锻件的制造方法 (Manufacturing method of super-large-specification ring forging ) 是由 陶志勇 聂徐庆 梁剑雄 董凯 任国柱 王长军 雷雪 刘振宝 王太江 杨志勇 张智 于 2020-12-11 设计创作，主要内容包括：本发明提供了一种超大规格环锻件的制造方法,属于金属热加工技术领域。本发明通过在坯体的内圈和外圈之间设置分圈,并以分圈为界线,对坯体进行两次锻造,使第一阶段锻造所得锻件出现外低内高的台阶差,形成外圆环状带箍,有效阻止内圆金属向外侧流动,避免了坯体在锻造过程中壁厚方向的扭曲失稳,不需要修扭后再进行扩孔,缩短了制备周期；且能够精确控制环锻件的尺寸。本发明提供的制造方法能够制造外径在3000mm以上的超大规格环锻件。(The invention provides a manufacturing method of an oversized ring forging, and belongs to the technical field of metal hot working. According to the invention, the split ring is arranged between the inner ring and the outer ring of the blank body, and the blank body is forged twice by taking the split ring as a boundary line, so that the forged piece obtained by forging in the first stage has a step difference of low outside and high inside to form the outer circular band hoop, the metal of the inner circle is effectively prevented from flowing outwards, the distortion and instability of the blank body in the wall thickness direction in the forging process are avoided, and the reaming is carried out after the torque correction is not needed, so that the preparation period is shortened; and the size of the ring forging can be accurately controlled. The manufacturing method provided by the invention can manufacture the ultra-large-scale ring forging with the outer diameter of more than 3000 mm.)

1. The manufacturing method of the ultra-large-scale ring forging is characterized by comprising the following steps of:

calculating to obtain the size of the required blank according to the size of the ring forging by using formulas I, II and III;

(D_{outer 0}×D_{Outer 0}-D_{Inner 0}×D_{Inner 0})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Inner 1}×D_{Inner 1})×H₁Formula I;

D_{outer 0}-D_{Inner 0}＝2H₀Formula II;

(H₀-H₁)/H₀formula III, ═ n;

wherein D is_{Outer 0}The outer diameter of the blank is mm; d_{Inner 0}The inner diameter of the blank is mm; h₀The height of the blank is mm; d_{Outer 1}The outer diameter of the ring forging is mm; d_{Inner 1}Is the inner diameter of the ring forging, mm; h₁The height of the ring forging is mm; n is the height pressing amount, and n is more than or equal to 20 percent;

primarily forging the steel ingot according to the calculated size of the blank to obtain the blank;

forging after ring division is arranged between the outer ring and the inner ring of the blank to obtain the ultra-large-specification ring forging; the outer diameter of the super-large-specification ring forging is more than or equal to 3000 mm;

the diameter of the blank is calculated according to a formula IV:

(D_{outer 0}×D_{Outer 0}-D_{Is divided into}×D_{Is divided into})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Is divided into}×D_{Is divided into})×H₁Formula IV;

wherein D is_{Is divided into}The diameter of the blank is mm; d_{Outer 0}The outer diameter of the blank is mm; d_{Outer 1}The outer diameter of the ring forging is mm;

the forging comprises a first-stage forging and a second-stage forging which are sequentially carried out; the forging object of the first-stage forging is an annular blank formed by the outer ring and the split ring of the blank; and the forging object of the second-stage forging is an annular blank formed by the inner ring and the split ring of the blank.

2. The method according to claim 1, wherein n is 25 to 35%.

3. The manufacturing method according to claim 1, wherein the temperature of the primary forging is 850-1240 ℃, and the primary forging comprises one or more of upsetting, drawing and punching.

4. The manufacturing method according to claim 1, wherein the initial temperature of the first-stage forging and the second-stage forging is 1180 to 1240 ℃ independently, and the finish forging temperature of the first-stage forging and the second-stage forging is 800 to 850 ℃ independently.

Technical Field

The invention relates to the technical field of forging, in particular to a method for manufacturing an ultra-large-specification ring forging.

Background

The shape characteristics of thick-wall ring forging: the wall thickness is greater than the height, and when this type of shape tradition reaming was forged, pressure was exerted to the wall thickness direction, caused wall thickness direction distortion unstability, need increase the direction of height and levels, repaired and turned round the back and carry out the reaming again, continuous repeated reaming + level and smooth process moreover, the forging cycle length, the size is looked the on-the-spot shaping condition and is carried out on-the-spot judgement, and the technical maturity is lower, unable accurate control process size.

Disclosure of Invention

In view of this, the present invention provides a method for manufacturing an oversized ring forging. The ring forging obtained by the manufacturing method provided by the invention avoids the distortion instability in the wall thickness direction, does not need torsion repair, and shortens the preparation period; and the size of the ring forging can be accurately controlled.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a method for manufacturing an oversized ring forging, which comprises the following steps:

calculating to obtain the size of the required blank according to the size of the ring forging by using formulas I, II and III;

(D_{outer 0}×D_{Outer 0}-D_{Inner 0}×D_{Inner 0})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Inner 1}×D_{Inner 1})×H₁Formula I;

D_{outer 0}-D_{Inner 0}＝2H₀Formula II;

(H₀-H₁)/H₀formula III, ═ n;

wherein D is_{Outer 0}The outer diameter of the blank is mm; d_{Inner 0}The inner diameter of the blank is mm; h₀The height of the blank is mm; d_{Outer 1}The outer diameter of the ring forging is mm; d_{Inner 1}Is the inner diameter of the ring forging, mm; h₁The height of the ring forging is mm; n is the height pressing amount, and n is more than or equal to 20 percent;

primarily forging the steel ingot according to the calculated size of the blank to obtain the blank;

forging after ring division is arranged between the outer ring and the inner ring of the blank to obtain the ultra-large-specification ring forging; the outer diameter of the super-large-specification ring forging is more than or equal to 3000 mm;

the diameter of the blank is calculated according to a formula IV:

(D_{outer 0}×D_{Outer 0}-D_{Is divided into}×D_{Is divided into})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Is divided into}×D_{Is divided into})×H₁Formula IV;

wherein D is_{Is divided into}The diameter of the blank is mm; d_{Outer 0}The outer diameter of the blank is mm; d_{Outer 1}The outer diameter of the ring forging is mm;

the forging comprises a first-stage forging and a second-stage forging which are sequentially carried out; the forging object of the first-stage forging is an annular blank formed by the outer ring and the split ring of the blank; and the forging object of the second-stage forging is an annular blank formed by the inner ring and the split ring of the blank.

Preferably, n is 25-35%.

Preferably, the temperature of the primary forging is 850-1240 ℃, and the primary forging mode comprises one or more of upsetting, stretching and punching.

Preferably, the initial temperature of the first stage forging and the second stage forging is 1180 to 1240 ℃ independently, and the finish forging temperature of the first stage forging and the second stage forging is 800 to 850 ℃ independently.

The invention provides a method for manufacturing an oversized ring forging, which comprises the following steps:

calculating to obtain the size of the required blank according to the size of the ring forging by using formulas I, II and III;

(D_{outer 0}×D_{Outer 0}-D_{Inner 0}×D_{Inner 0})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Inner 1}×D_{Inner 1})×H₁Formula I;

D_{outer 0}-D_{Inner 0}＝2H₀Formula II;

(H₀-H₁)/H₀formula III, ═ n;

wherein D is_{Outer 0}The outer diameter of the blank is mm; d_{Inner 0}The inner diameter of the blank is mm; h₀The height of the blank is mm; d_{Outer 1}The outer diameter of the ring forging is mm; d_{Inner 1}The inner diameter of the ring forging is mm; h₁The height of the ring forging is mm; n is the height pressing amount, and n is more than or equal to 20 percent;

primarily forging the steel ingot according to the calculated size of the blank to obtain the blank;

forging after ring division is arranged between the outer ring and the inner ring of the blank to obtain the ultra-large-specification ring forging; the outer diameter of the super-large-specification ring forging is more than or equal to 3000 mm;

the diameter of the blank is calculated according to a formula IV:

(D_{outer 0}×D_{Outer 0}-D_{Is divided into}×D_{Is divided into})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Is divided into}×D_{Is divided into})×H₁Formula IV;

wherein D is_{Is divided into}The diameter of the blank is mm; d_{Outer 0}The outer diameter of the blank is mm; d_{Outer 1}The outer diameter of the ring forging is mm;

the forging comprises a first-stage forging and a second-stage forging which are sequentially carried out; the forging object of the first-stage forging is an annular blank formed by the outer ring and the split ring of the blank; and the forging object of the second-stage forging is an annular blank formed by the inner ring and the split ring of the blank.

According to the invention, the split ring is arranged between the inner ring and the outer ring of the blank body, and the blank body is forged twice by taking the split ring as a boundary line, so that the forged piece obtained by forging in the first stage has a step difference of low outside and high inside to form the outer circular band hoop, the metal of the inner circle is effectively prevented from flowing outwards, the distortion and instability of the blank body in the wall thickness direction in the forging process are avoided, and the reaming is carried out after the torque correction is not needed, so that the preparation period is shortened; and the size of the ring forging can be accurately controlled.

Drawings

FIG. 1 is a schematic cross-sectional structure view of a ring forging;

FIG. 2 is a schematic structural view of a blank;

FIG. 3 is a schematic structural diagram of a forged part obtained after the first-stage forging;

FIG. 4 is a schematic structural view of a forging obtained after the second stage forging;

FIG. 5 is a photograph of the oversized ring forging obtained in example 1;

FIG. 6 is a photograph of the oversized ring forging obtained in example 2.

Detailed Description

The method for manufacturing the oversized ring forging provided by the invention is described in detail below according to figures 1-4.

The invention provides a method for manufacturing an oversized ring forging, which comprises the following steps:

calculating to obtain the size of the required blank according to the size of the ring forging by using formulas I, II and III;

(D_{outer 0}×D_{Outer 0}-D_{Inner 0}×D_{Inner 0})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Inner 1}×D_{Inner 1})×H₁Formula I;

D_{outer 0}-D_{Inner 0}＝2H₀Formula II;

(H₀-H₁)/H₀formula III, ═ n;

wherein D is_{Outer 0}The outer diameter of the blank is mm; d_{Inner 0}The inner diameter of the blank is mm; h₀The height of the blank is mm; d_{Outer 1}The outer diameter of the ring forging is mm; d_{Inner 1}Is the inner diameter of the ring forging, mm; h₁The height of the ring forging is mm; n is the height pressing amount, and n is more than or equal to 20 percent;

primarily forging the steel ingot according to the calculated size of the blank to obtain the blank;

forging after ring division is arranged between the outer ring and the inner ring of the blank to obtain the ultra-large-specification ring forging; the outer diameter of the super-large-specification ring forging is more than or equal to 3000 mm;

the diameter of the blank is calculated according to a formula IV:

(D_{outer 0}×D_{Outer 0}-D_{Is divided into}×D_{Is divided into})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Is divided into}×D_{Is divided into})×H₁Formula IV;

wherein H_{Is divided into}The diameter of the blank is mm; d_{Outer 0}The outer diameter of the blank is mm; d_{Outer 1}The outer diameter of the ring forging is mm; d_{Is divided into}The diameter of the blank is mm;

the forging comprises a first-stage forging and a second-stage forging which are sequentially carried out; the forging object of the first-stage forging is an annular blank formed by the outer ring and the split ring of the blank; and the forging object of the second-stage forging is an annular blank formed by the inner ring and the split ring of the blank.

According to the size of the ring forging, the size of a required blank is calculated by using formulas I, II and III.

(D_{Outer 0}×D_{Outer 0}-D_{Inner 0}×D_{Inner 0})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Inner 1}×D_{Inner 1})×H₁Formula I;

D_{outer 0}-D_{Inner 0}＝2H₀Formula II;

(H₀-H₁)/H₀formula III, ═ n;

wherein D is_{Outer 0}The outer diameter of the blank is mm; d_{Inner 0}The inner diameter of the blank is mm; h₀The height of the blank is mm; d_{Outer 1}The outer diameter of the ring forging is mm; d_{Inner 1}The inner diameter of the ring forging is mm; h₁The height of the ring forging is mm; n is the height depression amount, and n is more than or equal to 20 percent.

FIG. 1 is a schematic sectional structure view of a ring forging, namely a schematic sectional structure view of a ring forging to be finally obtained, wherein H₁Height of ring forging, D_{Outer 1}The outer diameter of the ring forging, namely the diameter of the outer ring of the ring forging; d_{Inner 1}The inner diameter of the ring forging, namely the diameter of the inner ring of the ring forging; FIG. 2 is a schematic view of the structure of the blank, i.e. the blank which needs to be formed in the early stage, wherein D_{Outer 0}Is the outer diameter of the billet, i.e. the outer ring diameter of the billet, D_{Inner 0}Is the inner diameter of the blank, i.e. the inner circle diameter of the blank, H₀The height of the blank.

In the invention, the design of the formula I is based on the principle that the volume of the forged blank is consistent with that of the obtained super-large-scale ring forging.

In the invention, n in the formula III is more than or equal to 20%, and more preferably 25-35%, and in a specific embodiment of the invention, n in the formula III is 28.6%.

According to the invention, through formulas I-III, the size of the blank is designed according to the final ultra-large-specification ring forging, and the compaction effect during forging forming is ensured.

After the size of the blank is calculated, the steel ingot is initially forged according to the calculated size of the blank to obtain the blank.

The invention is not particularly limited to the obtaining of the steel ingot.

In the invention, the temperature of the primary forging is preferably 850-1240 ℃; the initial forging mode preferably comprises one or more of upsetting, drawing and punching, and the parameters of upsetting, drawing and punching are not particularly limited as long as a blank with a corresponding size can be obtained.

After a blank is obtained, forging after ring division is arranged between an outer ring and an inner ring of the blank to obtain the ultra-large-specification ring forging; the outer diameter of the super-large-specification ring forging is larger than or equal to 3000 mm.

In the invention, the diameter of the blank is calculated by a formula IV:

(D_{outer 0}×D_{Outer 0}-D_{Is divided into}×D_{Is divided into})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Is divided into}×D_{Is divided into})×H₁Formula IV;

wherein D is_{Is divided into}The diameter of the blank is mm; d_{Outer 0}The outer diameter of the blank is mm; d_{Outer 1}Is the outer diameter of the ring forging, mm.

In the present invention, the forging includes a first-stage forging and a second-stage forging which are performed in this order; the forging object of the first-stage forging is an annular blank formed by the outer ring and the split ring of the blank; and the forging object of the second-stage forging is an annular blank formed by the inner ring and the split ring of the blank.

The invention is characterized in that a sub-ring is arranged between the outer ring and the inner ring of the green body, and the green body is divided into two parts based on the sub-ring, namely the part between the outer ring and the sub-ring of the green body and the part between the inner ring and the sub-ring of the green body. During forging, the part between the outer ring and the split ring of the blank is forged firstly, namely, the forging is performed in the first stage, after the forging is performed in the first stage, the diameter of the outer ring of the forged piece obtained by the forging in the first stage is consistent with that of the outer ring of the final ring forged piece, and the structure of the forged piece is shown in fig. 3. And then, performing second-stage forging on the forged piece obtained by the first-stage forging, wherein the target object of the second-stage forging is the part between the inner ring of the blank and the split ring, and after the second-stage forging is finished, the diameter of the inner ring of the forged piece obtained by the second-stage forging is directly consistent with that of the inner ring of the final ring forged piece, and the structural schematic diagram is shown in fig. 4.

In the invention, the initial temperature of the first-stage forging and the second-stage forging is preferably 1180-1220 ℃ independently, and the finish forging temperature of the first-stage forging and the second-stage forging is preferably 800-850 ℃ independently.

According to the invention, the split ring is arranged between the inner ring and the outer ring of the blank, and the blank is forged twice by taking the split ring as a boundary line, so that the forged piece obtained by forging in the first stage has a step difference of low outside and high inside to form the outer annular band hoop, thereby effectively preventing the metal of the inner circle from flowing outwards and avoiding the distortion instability of the blank in the wall thickness direction in the forging process.

The following will explain the method for manufacturing an oversized ring forging provided by the invention in detail with reference to the examples, but they should not be construed as limiting the scope of the invention.

Example 1

The size of the super-large-specification ring forging is the diameter D of the outer ring_{Outer 1}Is 3000mm, the diameter of the inner ring_{D inner 1}Is 1000mm, height H₁Is 500 mm;

calculating the size of the blank according to formulas I, II and III;

(D_{outer 0}×D_{Outer 0}-D_{Inner 0}×D_{Inner 0})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Inner 1}×D_{Inner 1})×H₁Formula I;

D_{outer 0}-D_{Inner 0}＝2H₀Formula II;

(H₀-H₁)/H₀28.6% formula III;

height H of the obtained blank₀700mm, outer ring diameter D of the blank_{Outer 0}2740.8mm, the diameter of the inner ring is D_{Inner 0}1340.8 mm;

calculating the diameter D of the split ring of the blank by using the formula IV_{Is divided into}：

(D_{Outer 0}×D_{Outer 0}-D_{Is divided into}×D_{Is divided into})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Is divided into}×D_{Is divided into})×H₁Formula IV;

the diameter D of the split ring of the blank is obtained_{Is divided into}1947.3 mm.

Rounding the size of the blank in the actual forging execution, namely the actual blank size is as follows: the diameter of the outer ring is 2745mm, the diameter of the inner ring is 1340mm, the height is 700mm, and the diameter of each partial ring is 1950 mm.

Primarily forging the steel ingot to obtain a blank; and under the conditions that the initial temperature of the initial forging is 1190 ℃ and the final forging temperature is 850 ℃, a blank with the dimensions of 2745mm of the outer ring diameter, 1340mm of the inner ring diameter and 700mm of height is obtained through upsetting, drawing and punching.

Forging the blank to obtain the ultra-large-specification ring forging;

the forging comprises a first-stage forging and a second-stage forging which are sequentially carried out; the forged product of the first stage forging is a blank which is formed by forging the outer ring of the blank and a ring-divided blank into a blank with the outer ring diameter of 3000mm, the ring-divided diameter of 1950mm and the height of 500 mm; the forged object of the second-stage forging is an annular forged piece formed by forging the inner ring of the blank and the annular blank formed by ring division, wherein the diameter of the component ring is 1950mm, the diameter of the inner ring is 1000mm, and the height of the component ring is 500 mm; the initial temperature of the first stage forging and the second stage forging is independently 1190 ℃ and the finish forging temperature is independently 850 ℃.

FIG. 5 is a diagram of an object of the oversized ring forging obtained in the embodiment. The shape distortion condition of the ultra-large-specification ring forging is tested by adopting a field observation method, and the result is displayed: the oversized ring forging piece is regular in shape and free of distortion and instability.

Example 2

The size of the super-large-specification ring forging is the diameter D of the outer ring_{Outer 1}Is 3500mm, inner circle diameter_{D inner 1}1200mm, height H₁Is 550 mm;

calculating the size of the blank according to formulas I, II and III;

(D_{outer 0}×D_{Outer 0}-D_{Inner 0}×D_{Inner 0})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Inner 1}×D_{Inner 1})×H₁Formula I;

D_{outer 0}-D_{Inner 0}＝2H₀Formula II;

(H₀-H₁)/H₀28.6% formula III;

height H of the obtained blank₀770.3mm, the outer ring diameter D of the blank_{Outer 0}3275.3mm, the diameter of the inner ring is D_{Inner 0}1734.7 mm;

calculating the diameter D of the split ring of the blank by using the formula IV_{Is divided into}：

(D_{Outer 0}×D_{Outer 0}-D_{Is divided into}×D_{Is divided into})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Is divided into}×D_{Is divided into})×H₁Formula IV;

the diameter D of the split ring of the blank is obtained_{Is divided into}2631.8 mm.

Rounding the size of the blank in the actual forging execution, namely the actual blank size is as follows: the diameter of the outer ring is 3280mm, the diameter of the inner ring is 1740mm, the height is 775mm, and the diameter of the divided ring is 2635 mm.

Primarily forging the steel ingot to obtain a blank; and under the conditions that the initial forging temperature of the initial forging is 1200 ℃ and the final forging temperature is 820 ℃, a blank with the dimensions of 3280mm in outer ring diameter, 1740mm in inner ring diameter and 775mm in height is obtained through the working procedures of upsetting, drawing and punching.

Forging the blank to obtain the ultra-large-specification ring forging;

the forging comprises a first-stage forging and a second-stage forging which are sequentially carried out; the forged product of the first-stage forging is a blank which is formed by forging the outer ring of the blank and a ring-divided blank into a blank with the outer ring diameter of 3280mm, the ring-divided diameter of 2635mm and the height of 775 mm; the forged article of the second-stage forging is a ring forging piece formed by forging the inner ring of the blank and a ring-divided annular blank, wherein the diameter of the ring-divided annular blank is 2635mm, the diameter of the inner ring is 1740mm, and the height of the inner ring is 775 mm; the initial temperature of the first stage forging and the second stage forging is independently 1200 ℃ and the finish forging temperature is independently 820 ℃.

FIG. 6 is a diagram of an object of the oversized ring forging obtained in the embodiment. The shape distortion condition of the ring forging is tested by adopting a field observation method, and the result shows that: the forging piece is regular in shape and has no distortion and instability.

Example 3

The size of the super-large-specification ring forging is the diameter D of the outer ring_{Outer 1}4000mm, inner diameter_{D inner 1}1900mm, height H₁Is 530 mm;

calculating the size of the blank according to formulas I, II and III;

(D_{outer 0}×D_{Outer 0}-D_{Inner 0}×D_{Inner 0})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Inner 1}×D_{Inner 1})×H₁Formula I;

D_{outer 0}-D_{Inner 0}＝2H₀Formula II;

(H₀-H₁)/H₀28.6% formula III;

height H of the obtained blank₀742.3mm, outer ring diameter D of the blank_{Outer 0}3721.7mm, the diameter of the inner ring is D_{Inner 0}2237.1 mm;

calculating the diameter D of the split ring of the blank by using the formula IV_{Is divided into}：

(D_{Outer 0}×D_{Outer 0}-D_{Is divided into}×D_{Is divided into})×H₀＝(D_{Outer 1}×D_{Outer 1}-D_{Is divided into}×D_{Is divided into})×H₁Formula IV;

the diameter D of the split ring of the blank is obtained_{Is divided into}2913.1 mm.

Rounding the size of the blank in the actual forging execution, namely the actual blank size is as follows: the diameter of the outer ring is 3725mm, the diameter of the inner ring is 2240mm, the height is 745mm, and the diameter of each partial ring is 2915 mm.

Primarily forging the steel ingot to obtain a blank; the initial forging temperature of the initial forging is 1220 ℃, and the final forging temperature is 800 ℃, and a blank with the size of 3725mm in outer ring diameter, 2240mm in inner ring diameter and 745mm in height is obtained through the working procedures of upsetting, drawing and punching.

Forging the blank to obtain the ultra-large-specification ring forging;

the forging comprises a first-stage forging and a second-stage forging which are sequentially carried out; the forged product of the first stage forging is a blank which is forged into a blank with the outer ring diameter of 3725mm, the split ring diameter of 2915mm and the height of 745mm by the outer ring of the blank and a split ring formed annular blank; the forged object of the second-stage forging is a ring forged piece formed by forging the inner ring of the blank and a ring-divided blank into 2915mm in diameter, 2240mm in diameter and 745mm in height; the initial temperature of the first stage forging and the second stage forging is independently 1220 ℃ and the finish forging temperature is independently 800 ℃.

The shape distortion condition of the ring forging is tested by adopting a field observation method, and the result shows that: the forging piece is regular in shape and has no distortion and instability.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.