CA1067583A - Dual-gas shielding method - Google Patents
Dual-gas shielding methodInfo
- Publication number
- CA1067583A CA1067583A CA266,406A CA266406A CA1067583A CA 1067583 A CA1067583 A CA 1067583A CA 266406 A CA266406 A CA 266406A CA 1067583 A CA1067583 A CA 1067583A
- Authority
- CA
- Canada
- Prior art keywords
- shield
- gas
- velocity
- welding
- cup
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Arc Welding In General (AREA)
Abstract
Abstract of the Disclosure The disclosure of the present applicatîon relates to an improved method of open-arc welding. According to the present method, the outer shield of a double-shield welding system consists of a stream of gas formed in a shield concentric with the inner shield. This method is distinguished by the fact that atmospheric air may be used as the outer shield gas because the outer-shield velocity is so regulated as to prevent the air from being drawn into the weld area.
In an alternate embodiment of the same method, the outer-shield gas flow is in a direction opposite that of the inner shield. In this alter-nate embodiment, in which air is drawn into the welding cup, the velocity at the outer cup is in a range predominantly above the velocity at the inner cup. In the embodiment in which the gas in the outer shield flows in the same direction as that in the inner shield, the outer-shield gas velocity is in a range more nearly approximating the inner-shield gas velocity.
In an alternate embodiment of the same method, the outer-shield gas flow is in a direction opposite that of the inner shield. In this alter-nate embodiment, in which air is drawn into the welding cup, the velocity at the outer cup is in a range predominantly above the velocity at the inner cup. In the embodiment in which the gas in the outer shield flows in the same direction as that in the inner shield, the outer-shield gas velocity is in a range more nearly approximating the inner-shield gas velocity.
Description
~Q67583 Background of the Invention In the art of arc welding it has been found to be necessary to take steps to prevent the inclusion of contaminants such as water vapor in the weld~ In particular, it has been observed that water vapor has a tendency to cause porosity in the weld area. A popular method of prevention has been to sur-round the welding tip with a shield of inert gas. In certain environments, however, it was found that the width of shield required resulted in a high volume rate of flow of the costly inert gas, so various other schemes for increasing the isolation of the weld from contaminants have been investigated. Among these have been several double-shield systems, such as Wempe, United States Patent No. 2,903,559, which employs shielding gases other than air.
Summary of the Invention The invention relates to the method of arc welding that includes shielding the plasma "bell" formed between a weld-ing cup and a workpiece by forming at least two concentric gas shields by emitting from the welding cup gas streams which are physically separated until they leave the welding cup, the inner gas shield thereof comprising an inert gas. In a broad aspect, the invention resides in forming an outer gas shield with a gas stream in which at least half the gas is air separating the outer gas shield from the inner gas shield at the exit of the welding ' cup, such that the outer gas shield is kept beyond the outside of the plasma "bell" formed between the welding cup and the work-piece during welding and causing the outer gas shield gas stream , to exit the welding cup at a velocity approximately equal to the '' inner gas shield gas stream velocity at the welding cup exit.
, 30 . .
` ' ~ -2- ~ ~ , ' -- . , , ~067583 Bri'ef Des'criptio'n'of''the~ Dr'awings Figure 1 is a sectional view of an apparatus for use with the method of this invention;
Figure 2 is a diagram of the gas flow from a single-shield welding ~ystem:
:
~ ' .
, .~, .
., .
,' -2a-.~
' ~:
.. . .
~067583 Figure 3 is a diagram of the gas ~low from a double-shield system used according to the method of the present invention;
Figure 4 is a diagram of the gas flow from a double-shield system used in accordance with an alternate embodiment of the method of the present invention.
Detailed Description of the Preferred Embodiment In Eigure 1, inner chamber 12 is formed by the inside surface of - cylindrical wall 10. In a typical apparatus, the cross section of chamber 12 may have a radius of 5/16". An outer chamber 18 is formed by the outer c~lindrical wP~l 20 and the outer surface of c~lindrical wall 10, and this chamber is filled with a material 16 suitable for acting as a diffuser, such as stainless steel wool. Outer wall 20 is penetrated by gas passage 26.
A typical radius of the cross section of chamber 18 would be 5/8". Cylin-drical wall 10 terminates in separating member 22, which serves to separate the outer shield from the inner shield and keep the outer shield beyond the outside of the plasma "bell" that forms between welding tip 24 and the work-piece during welding. A typical separating member could have a radius of 9/16".
During operation, the inner-shield gas, typically argon or another inert gas, is introduced into inner chamber 12 by a method familiar to the art. The gas travels down inner chamber 12 and out its exit, welding cup 25, shielding the welding tip 2l~, which might have a 3/16" radius. ~he outer-shleld gas, which is claimed as being at least half a mixture of nitrogen and oxygen and can therefore be ordinary air, is introduced from a suitable source into gas passage 26, thr~ugh which it passes to outer chamber 18. The gas entering chamber 18 has a horizontal bulk velocity because of its travel along gas passage 26. ~his horizontal flow is broken up b~ stainless-steel-wool diffuser 16, increasing the static air pressure in outer chamber 18, which in turn causes a bulk velocity at exit 23 of chamber 18 due to the dif-fusion which results from the static-pressure difference between chamber 18 and the ambient atmosphere. An equilibrium is established between the volume of ; :
.:
- . . . .
~ 1067583 gas entering through gas passage 26 and that leaving exit 23, so the velocity of the gas leaving exit 23 can be regulated by controlling the volume rate of the gas entering outer chamber 18. With a welding-tip-to-workpiece dis-tance of 1/2", the volume rate at which gas is supplied to inner chamber 12 is between 11 ft.3/hr. and 13 ft.3/hr. Between 15 ft.3/hr. and 20 ft.3/hr.
of gas is supplied to outer chamber 18. Taking into account the sizes of exits 23 and 25, this gives a range of ratios of outer-shield gas velocity to inner-shield gas velocity of 0.8 to 1.5, which is the range that produces the best results. While the method of the present specification can be prac- -ticed with outer-shield velocities which give velocity ratios outside this range, significant deterioration in results can be expected outside a ratio range of approximately 0.5 to 2.0, which translates to velocities in the outer shield in the range of 100 ft./min. to 250 ft./~in.
With a wider separating member 22, the velocity ratios become less critical. This, of course, alters the required velocity ratio somewhat from that quoted above. Nevertheless, optimum results will still be found in the range quoted. In addition, those skilled in the art will appreciate that increased velocities are required when the tip-to-workpiece spacing increases.
The mechanism by which the method of the present invention works has not been conclusively determined, but the following possible explanation is offered. In a single-shield welding cup as shown in Figure 2, gas leaving exit 25 is thought to flow in a path similar to that depicted by curved arrow 28. In the area indicated by arrow 30, air from the surrounding atmosphere is drawn into the shield-gas flow with the result that ambient air is drawn into plasma "bell" 32 if the shield diameter is not relatively large. In such a situation it has been found that porosity occurs when the humidity in the air reaching plasma bell 32 is at least at a -10C dew-point level.
;` According to the present invention, gas leaves inner chamber 18 of Figure 3 in the same manner as it leaves the single-shield welding cup of Figure 2. As a result, there exists a tendency for a flow pattern to result which is similar to that shown in Figure 2. However, the presence of ".
C750270 ~4~
: , . . . , - . . .
an outer shield ha~ , ~ ~i~ i~ ~e ~n~ ~a~e~ ~y c~ p~esen~
invention is thought to have the effect of breaking up this pattern without disturbine the plasma bell. Thus, since the tendency of the inner-shield stream to draw air into the plasma bell is overcome by the outer stream, the choice of gas for the outer stream is relatively unimportant, so even ordinary air can be used in the outer stream. As will be appreciated by those skilled in the art, the inner-shield gas velocity in area 34 must be aa~usted for factors such as the area of the shield and the distance between the welding tip and the workpiece; the precise optimum velocity relationship for any welding setup can therefore only be achieved by ad~usting the outer-shield velocity within a range dictated by the method of the present inven-tion until the best results are observed.
The present invention may also be practiced by drawing air into, rather than forcing air out of, outer chamber 18. Results have shown that a greater velocity is required at entrance 23 when air is being drawn into, rather than forced out of, chamber 18. Best results are obtained from the apparatus shown when the velocity ratio is between 1.0 and 2.2 with an inert-gas supply of between 15 and 20 ft.3/hr. Again, this supply rate may be in-creased when tip-to-workpiece distance is increased, and the apparatus may be operated outside this ratio range. Without increasing the spacing between the inner and outer shields, however, a deterioration in results is encountered outside the ra~io range o~ 0.7 to 2.8, which transl~tes to a velocity range ; o~ 150 ft./min. to 360 ft./min.
It i9 thought that the drawing of air into the welding cup works for the same reason that forcing air out of the welding cup works. That is, it overcomes the tendency of the inner-shield flow to cause air to be drawn into the welding arc. In this case, as Figure 4 suggests, the circular flow is diverted from its ordinary course by the ~low of air into the entrance 23 ; corresponding to exit 23 in the previous embodiment.
The results of the present method with an inward-flowing outer shield are not as good as those which result from an outward-flowing shield, ~ ':
C750270 ~5~
~067583 but it is suggested that the inward-flowing shield may be preferred in applications in which smoke is to be removed from the welding area.
While the invention has been described in con~unction with speci~ic embodiments thereof, it is evident that many P~ternatives, modi-~ications, and variations will be apparent to those skilled in the art in light of the ~oregoing description. Accordingly, the invention is intended to embrace all such alternatives, modi~ications, and variations as fall within the broad scope o~ the appended claims.
What is claimed is:
. .
. . .
.~ , . ..
.. . .
.,~ ''- : ' . . ,. : ,. . .
Summary of the Invention The invention relates to the method of arc welding that includes shielding the plasma "bell" formed between a weld-ing cup and a workpiece by forming at least two concentric gas shields by emitting from the welding cup gas streams which are physically separated until they leave the welding cup, the inner gas shield thereof comprising an inert gas. In a broad aspect, the invention resides in forming an outer gas shield with a gas stream in which at least half the gas is air separating the outer gas shield from the inner gas shield at the exit of the welding ' cup, such that the outer gas shield is kept beyond the outside of the plasma "bell" formed between the welding cup and the work-piece during welding and causing the outer gas shield gas stream , to exit the welding cup at a velocity approximately equal to the '' inner gas shield gas stream velocity at the welding cup exit.
, 30 . .
` ' ~ -2- ~ ~ , ' -- . , , ~067583 Bri'ef Des'criptio'n'of''the~ Dr'awings Figure 1 is a sectional view of an apparatus for use with the method of this invention;
Figure 2 is a diagram of the gas flow from a single-shield welding ~ystem:
:
~ ' .
, .~, .
., .
,' -2a-.~
' ~:
.. . .
~067583 Figure 3 is a diagram of the gas ~low from a double-shield system used according to the method of the present invention;
Figure 4 is a diagram of the gas flow from a double-shield system used in accordance with an alternate embodiment of the method of the present invention.
Detailed Description of the Preferred Embodiment In Eigure 1, inner chamber 12 is formed by the inside surface of - cylindrical wall 10. In a typical apparatus, the cross section of chamber 12 may have a radius of 5/16". An outer chamber 18 is formed by the outer c~lindrical wP~l 20 and the outer surface of c~lindrical wall 10, and this chamber is filled with a material 16 suitable for acting as a diffuser, such as stainless steel wool. Outer wall 20 is penetrated by gas passage 26.
A typical radius of the cross section of chamber 18 would be 5/8". Cylin-drical wall 10 terminates in separating member 22, which serves to separate the outer shield from the inner shield and keep the outer shield beyond the outside of the plasma "bell" that forms between welding tip 24 and the work-piece during welding. A typical separating member could have a radius of 9/16".
During operation, the inner-shield gas, typically argon or another inert gas, is introduced into inner chamber 12 by a method familiar to the art. The gas travels down inner chamber 12 and out its exit, welding cup 25, shielding the welding tip 2l~, which might have a 3/16" radius. ~he outer-shleld gas, which is claimed as being at least half a mixture of nitrogen and oxygen and can therefore be ordinary air, is introduced from a suitable source into gas passage 26, thr~ugh which it passes to outer chamber 18. The gas entering chamber 18 has a horizontal bulk velocity because of its travel along gas passage 26. ~his horizontal flow is broken up b~ stainless-steel-wool diffuser 16, increasing the static air pressure in outer chamber 18, which in turn causes a bulk velocity at exit 23 of chamber 18 due to the dif-fusion which results from the static-pressure difference between chamber 18 and the ambient atmosphere. An equilibrium is established between the volume of ; :
.:
- . . . .
~ 1067583 gas entering through gas passage 26 and that leaving exit 23, so the velocity of the gas leaving exit 23 can be regulated by controlling the volume rate of the gas entering outer chamber 18. With a welding-tip-to-workpiece dis-tance of 1/2", the volume rate at which gas is supplied to inner chamber 12 is between 11 ft.3/hr. and 13 ft.3/hr. Between 15 ft.3/hr. and 20 ft.3/hr.
of gas is supplied to outer chamber 18. Taking into account the sizes of exits 23 and 25, this gives a range of ratios of outer-shield gas velocity to inner-shield gas velocity of 0.8 to 1.5, which is the range that produces the best results. While the method of the present specification can be prac- -ticed with outer-shield velocities which give velocity ratios outside this range, significant deterioration in results can be expected outside a ratio range of approximately 0.5 to 2.0, which translates to velocities in the outer shield in the range of 100 ft./min. to 250 ft./~in.
With a wider separating member 22, the velocity ratios become less critical. This, of course, alters the required velocity ratio somewhat from that quoted above. Nevertheless, optimum results will still be found in the range quoted. In addition, those skilled in the art will appreciate that increased velocities are required when the tip-to-workpiece spacing increases.
The mechanism by which the method of the present invention works has not been conclusively determined, but the following possible explanation is offered. In a single-shield welding cup as shown in Figure 2, gas leaving exit 25 is thought to flow in a path similar to that depicted by curved arrow 28. In the area indicated by arrow 30, air from the surrounding atmosphere is drawn into the shield-gas flow with the result that ambient air is drawn into plasma "bell" 32 if the shield diameter is not relatively large. In such a situation it has been found that porosity occurs when the humidity in the air reaching plasma bell 32 is at least at a -10C dew-point level.
;` According to the present invention, gas leaves inner chamber 18 of Figure 3 in the same manner as it leaves the single-shield welding cup of Figure 2. As a result, there exists a tendency for a flow pattern to result which is similar to that shown in Figure 2. However, the presence of ".
C750270 ~4~
: , . . . , - . . .
an outer shield ha~ , ~ ~i~ i~ ~e ~n~ ~a~e~ ~y c~ p~esen~
invention is thought to have the effect of breaking up this pattern without disturbine the plasma bell. Thus, since the tendency of the inner-shield stream to draw air into the plasma bell is overcome by the outer stream, the choice of gas for the outer stream is relatively unimportant, so even ordinary air can be used in the outer stream. As will be appreciated by those skilled in the art, the inner-shield gas velocity in area 34 must be aa~usted for factors such as the area of the shield and the distance between the welding tip and the workpiece; the precise optimum velocity relationship for any welding setup can therefore only be achieved by ad~usting the outer-shield velocity within a range dictated by the method of the present inven-tion until the best results are observed.
The present invention may also be practiced by drawing air into, rather than forcing air out of, outer chamber 18. Results have shown that a greater velocity is required at entrance 23 when air is being drawn into, rather than forced out of, chamber 18. Best results are obtained from the apparatus shown when the velocity ratio is between 1.0 and 2.2 with an inert-gas supply of between 15 and 20 ft.3/hr. Again, this supply rate may be in-creased when tip-to-workpiece distance is increased, and the apparatus may be operated outside this ratio range. Without increasing the spacing between the inner and outer shields, however, a deterioration in results is encountered outside the ra~io range o~ 0.7 to 2.8, which transl~tes to a velocity range ; o~ 150 ft./min. to 360 ft./min.
It i9 thought that the drawing of air into the welding cup works for the same reason that forcing air out of the welding cup works. That is, it overcomes the tendency of the inner-shield flow to cause air to be drawn into the welding arc. In this case, as Figure 4 suggests, the circular flow is diverted from its ordinary course by the ~low of air into the entrance 23 ; corresponding to exit 23 in the previous embodiment.
The results of the present method with an inward-flowing outer shield are not as good as those which result from an outward-flowing shield, ~ ':
C750270 ~5~
~067583 but it is suggested that the inward-flowing shield may be preferred in applications in which smoke is to be removed from the welding area.
While the invention has been described in con~unction with speci~ic embodiments thereof, it is evident that many P~ternatives, modi-~ications, and variations will be apparent to those skilled in the art in light of the ~oregoing description. Accordingly, the invention is intended to embrace all such alternatives, modi~ications, and variations as fall within the broad scope o~ the appended claims.
What is claimed is:
. .
. . .
.~ , . ..
.. . .
.,~ ''- : ' . . ,. : ,. . .
Claims (2)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In the method of arc welding that includes shield-ing the plasma "bell" formed between a welding cup and a work-piece by forming at least two concentric gas shields by emitting from the welding cup gas streams which are physically separated until they leave the welding cup, the inner gas shield thereof comprising an inert gas, the improvement comprising: a. form-ing an outer gas shield with a gas stream in which at least half the gas is air; b. separating the outer gas shield from the inner gas shield at the exit of the welding cup such that the outer gas shield is kept beyond the outside of the plasma "bell"
formed between the welding cup and the workpiece during welding;
and c. causing the outer gas shield gas stream to exit the welding cup at a velocity approximately equal to the inner gas shield gas stream velocity at the welding cup exit.
formed between the welding cup and the workpiece during welding;
and c. causing the outer gas shield gas stream to exit the welding cup at a velocity approximately equal to the inner gas shield gas stream velocity at the welding cup exit.
2. The method as recited in claim 1 wherein causing the outer gas shield gas stream to exit the welding cup at a velocity nearly approximating the inner gas shield gas stream velocity at the welding cup exit comprises: causing the outer gas shield gas stream to exit the welding cup at a velocity of 100 ft./min. to 250 ft./min.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US67092876A | 1976-03-26 | 1976-03-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1067583A true CA1067583A (en) | 1979-12-04 |
Family
ID=24692463
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA266,406A Expired CA1067583A (en) | 1976-03-26 | 1976-11-23 | Dual-gas shielding method |
Country Status (3)
| Country | Link |
|---|---|
| BR (1) | BR7701861A (en) |
| CA (1) | CA1067583A (en) |
| IN (1) | IN145790B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11179795B2 (en) | 2018-10-11 | 2021-11-23 | Arthur Wu | Welding cup systems and methods |
-
1976
- 1976-11-23 CA CA266,406A patent/CA1067583A/en not_active Expired
- 1976-11-26 IN IN2116/CAL/76A patent/IN145790B/en unknown
-
1977
- 1977-03-25 BR BR7701861A patent/BR7701861A/en unknown
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11179795B2 (en) | 2018-10-11 | 2021-11-23 | Arthur Wu | Welding cup systems and methods |
Also Published As
| Publication number | Publication date |
|---|---|
| IN145790B (en) | 1978-12-23 |
| BR7701861A (en) | 1978-01-24 |
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