DE1815386A1 - Method for shielding a gas leak - Google Patents

Description

18153;

PATENT Pending © IPL.-ΙΝφ. QERHAÄD SCHWAN B MUNICH f ". QOtKZSS, STSASSE 15

H-7146-C

UNION CARBIDE CORPORATION 270 Park Avenue, Neui York, NY'10017, W ₀ St ₀ A.

Method for shielding a gas leak

The invention relates to a method for shielding a gas = outflow against the surroundings of the gas outflow, and in particular a method in which the gas outflow is an arc outflow isto

Gas flowing out of a nozzle, hereinafter referred to as gas outflow = - mung, is used in numerous processes, in particular in metal production, forging and in coating processes »For example, oxygen-fuel-gas escapes, who may carry a powder with them, used for cutting and treating metals. Gases are also used to shield electric arcs, Gases were also introduced into electric arcs, so that at least a certain amount of gas was introduced into part of the Arcing and forming an arc discharge., In many In some cases it is desirable to prevent gas or electric arc flow from contamination by the natural environment

ftSNSfOtCHiS 0 »ll> 40qO! B · KABEl: ff IfCTBIC PATE NT

to protect gas or arc leakage.

The invention is generally concerned with a novel method of preventing contamination of a sow flow through the natural environment of this gas leak. The invention is therefore applicable to all of the above Baiapiale processes represented applicable »although the invention is in the following for the sake of simplicity and illustration a preferred embodiment is described in connection with "it arc deposition processes in which arcs" outflows are used «

In a particularly advantageous type of arc build-up welding, an arc is maintained between two electrodes, a gas is introduced into the arc and the arc plasma obtained is passed through a constricting nozzle opening. The material to be applied as a coating is introduced into the arc, generally in the form of a powder, and added to the arc by means of the arc _. workpiece to be coated »This method is described in detail in US Pat. No. 3,016,447.

Although this method has worked extremely well, it nevertheless has a number of shortcomings. So it can with Arc cladding leads to contamination of the arc discharge by the surrounding air, as a result is the coating material oxidized and does it become acidic?

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Coating containing nitrogen «Are coatings made from pure metal? If the metallic coatings are porous, they have a low ductility and it is difficult to process them with tight tolerances while achieving a satisfactory surface quality «. In addition, the chemical changes that the hot coating UJB r keto ff performed in the presence of the impurities, undesirably affect the desired physical properties of the coating material. M.

The invention is based on the object of creating a method in which the contamination of a gas outflow by the environment is kept to a minimum. It should be prevented that the surrounding eina Lichtbogeneusströmumg Ges is sucked into the Liehtbogeneysatrömung ^v. When the process is applied to arc deposition welding, the oxydation of the material carried along in a Liehtbogenausstrümung should be kept as small as possible an arc = outflow of powdered material carried along should be prevented «,

According to the invention, the gas outflow to be protected against contamination from the environment is provided with an annular Protective gas stream enveloped, the width of which in mm between the

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1.25 and 20 times the value of the square root of what is measured in mm Diameter of the nozzle opening through which the gas flow passes through to that in the annular protective gas flow The flowing gas is coaxial with the gas outflow, and the square root (τ)? of momentum flow (Pulse / time unit) of the annular gas flow has a

4-4-

U / ert v / on at least 2.44 kg ^ / s m, where Q is the flow rate of the ring-shaped gas flow in m / s, A is the ring area in m and? is the gas density in kg / m.

The invention is based on the finding that an annular flow of inert gas, one width and one longitudinal Has momentum flow within the specified limits and which is designed as a uniform turbulent flow, shields a gas outflow in an excellent manner, so that the oxygen concentration of the gas effluent is essentially is equal to that of the annular protective gas flow ,, If the width of the ring-shaped shielding gas flow in mm between 1.25 and 20 times the square root of the in mm measured diameter of the opening of the nozzle, from which the gas flow emerges, and if the square root (τ)? of the longitudinal momentum flow of the gas flow is greater than

4- 4.

2.44 kg ^z / sm is, the Reynolds number (Re) of the gas flow is generally above 2000. Carrying out the method according to the invention with a Reynolds number below 2000 is possible, but the effectiveness of the edge distance is

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shielding improved, if the Reynolds number is increased,

4-

ujährend the ratio Ui / D within the limits indicated uiird held _o

Further features, advantages and possible uses of the Invention emerge from the subclaims and from following description of preferred embodiments in Connection with the accompanying drawings »They show:

Figure 1

a schematic representation of the subject matter of the invention,

Figure 1A

a partial cross-section of the front end of a for performing the method according to burner suitable for the invention,

Figure 2

a family of curves showing the influence of the flow rate of the annular protective gas flow on the oxygen concentration of the shielded gas outflow for different Reveals ring surfaces and protective gases,

Figure 3

a curve showing the influence of the parameters of the annular protective gas flow on the Oxygen concentration illustrated, and

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Figures 4 and 5 sets of curves that show the influence of the

4-

holdniases Ul / D on the oxygen concentration at different burner distances to show »

The invention is ideally suited for shielding an arc discharge in which a powdery over « Zugswerkstoff carried along and in a heated state to one Workpiece is brought that is to be coated with such a material »With arc deposition welding, the generally an arc is formed between first and second electrodes located within an arc torch. An arc gas is introduced into the arc to create an arc discharge »Der Coating material is introduced into the arc and the arc outflow and from these to the workpiece " transported. Previously, the coatings produced by such a process were generally oxidized the invention is used in the described arc deposition welding process, the oxygen contamination in the substantially eliminated, so that coatings are obtained that have essentially the same degree of purity as the starting material used to produce the coating. The following table clearly shows the advantages of the inventive method.

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Oxygen content dee applied by means of an arc torch Shit good

Table I.

Applied
Weld metal Oxygen content (%) Initial
powder Conventional
coating with coaxial beam
shielding manufactured
the coating copper
nickel
tungsten
titanium
molybdenum 0.126
0.172
0.027
0.655
0.419 0.302
0.456
0.274
> 2.0
0.710 0.092
0.151
0.030
0.730
0.160

Ulis is apparent from the table that the oxygen content of coatings that are provided by the inventive method fro _~%, substantially lower than in conventional coatings, that is, without Koaxialstrahlabschirmung, obtained; in most cases it is equal to or even less than the oxygen content of the starting powder.

A schematic representation of a typical device for carrying out the method according to the invention can be found In FIG. 1, “on a conventional arc torch 1 of the type known from U.S. Patent 3,016,447 is one Koaxialstrahlabschirmeinrichtung 3 attached so that the

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Arc outflow from the nozzle opening 5 having the diameter D in the torch 1 through the middle part of the Device 3 runs through. The coaxial beam shielding device 3 is selected so that the width measured in mm of the annular protective gas flow 1.25 to 20 times UJert is the square root of the diameter D measured in mm, In this case, the width U1 of the device 3 is equal to the width of the annular protective gas flow.

In Figure 1A, the diameter D of the device 3A is selected and matched to the diameter D of the nozzle opening 5A that the width of the annular gas flow, which in

D - D in this case is equal to a, in the specified Ulertebe-

rich falls. In this embodiment of the invention laces the inner surface 7A of the device 3A does not enter the jet emerging from the nozzle opening 5A, but only forms one Channel through which the arc discharge exits from device 3A. On the other hand, the area 7A would be so small made that a substantial constriction of the exiting jet would be achieved, then the inside diameter of this Neck to the opening diameter used in calculating the width parameter.

Figure 4 shows that with a torch distance, that is to say the distance between the arc torch and the workpiece, of 25.4 mm Effectiveness of the ring-shaped protective gas flow at a given flow rate up to a maximum or preferred

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4-

V ratio of about 6 mm * ■ increases and then decreases

4r begins until a ratio of approximately 20 mm is reached, (UO the effectiveness is just acceptable, ”Figure 5 shows a family of curves similar to FIG. 4, which shows that the relationships shown in FIG. 4 are even more pronounced when the burner distance is 12.7 mm found that the present invention is advantageous in processes in which the distance between the end of the device and the workpiece is up to about 40 to 50 times the nozzle opening diameter is ,,

From the family of curves according to FIG. 2 it follows that the molecular weight of the gas used has an influence on the resulting oxygen contamination of the arc outflow «, Es it can be seen that argon is more effective than helium and that with the same flow rate it is more appropriate to use a to work smaller ring, which leads to higher speeds »

The effectiveness of the shielding in the method according to the invention does not only depend on the width of the ring-shaped protection = gas flow, but also from a size that is referred to here as the square root of the momentum flow and the. is defined by the expression (j)? »The expression (S-) <? is derived as follows:

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- ίο -

If the expression (j) ^Q > ^{Z is written} as (^ $) or as (Q9) (§) (- ^), the result is the square root of the momentum flow, since (Q?) Is the weight flow rate, (~) the speed and ( -r) is the reciprocal of the area.

In FIG. 1, area A is the cross-sectional area of the ring through which the inert gas flow passes. In FIG. 1A, the area results from the equation % (θ -Dj.

FIG. 3 shows that in order to achieve a substantial reduction in the oxygen content in the arc outflow

Λ 4-

the value of (£) 9 ^ ~ should be greater than j.

8 m ~ i ~

The composition of the gas will of course affect the momentum flow. Figure 2 shows that, for example, argon as Shielding gas for the purposes of the invention is more suitable than helium.

In a preferred embodiment of the invention, a Arc torch with a UJoIfram electrode and a nozzle designed with an opening diameter of 3.2 mm so that there are it can accommodate a coaxial shielding device of the type illustrated in FIG. 1A with a diameter D of 25 mm.

te. The ring of the shielding device is preferably covered with a porous metal, with a grid or with another Appropriate material covered to ensure a uniform

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Ensure flow over the full cross-section and a non-uniform velocity distribution due to the gas = to avoid introductions, the method according to the invention works best if not a smooth, laminar flow, but a uniformly turbulent flow is achieved. An arc is formed between the aluminum frame electrode and a second electrode within the arc burner. A powdery material is inserted into the arc guided and in the arc outflow to a workpiece transported »A protective gas, preferably argon, is fed into the Coaxial beam shielding device 3 or 3A introduced in a flow rate that allows the required pulse flow to be achieved.

If the coaxial beam shielding device is too wide Ring, very high flow rates are required to » to achieve the desired pulse flow, so that the method economically less interesting «On the other hand, the I If the ring is too narrow, the ring-shaped shielding gas flow becomes too thin and unstable and does not fulfill its function, the crowd of the gas entrained by the central gas outlet, It has been found that the arc conditions, for example the amperage of the arc and the The flow rate of the arc gas, a negligible one Have an influence on the effectiveness of the annular protective gas flow. For example, a change in the flow rate resulted

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3 3

The arc gap in the range from 5.7 m / h to 17.0 m / h only a very slight change in the oxygen content the electric arc flow.

Uleitere details of the invention and their application can be found in the following examples,

Example I.

An arc torch with a Wolfran electrode surrounded by a nozzle 3.2 mm in diameter and 4.8 mm in length was used to produce a coating. Argon was introduced into the arc torch as an arc gas at a rate of 12.7 m / h. The arc current was 125 A at 78 V. The distance between the torches was 12.7 mn. Nickel powder with an oxygen content of 0.172 % was introduced into the arc torch in an amount of 24 g / min. The application rate of the powder on the carrier was 15 g / fflin. A coaxial beam shielding device similar to that illustrated in Figure 1A was attached to the arc torch. The annular coaxial gas flow enveloping the external arc flow had a width of 7.9 mm. Argon gas was introduced into the facility at a flow rate of 56.6 m / h, giving a value for the square root of the momentum flux of

73 2 ko "^

- - was received. The oxygen content of the

s m ~ z ~

formed coating was 0.150 % _t, which is a reduction

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corresponds to 0.022 %. The coating was very clean and could be worked on very well.

Example II

The apparatus used in this experiment corresponded to that of Example I with the exception that the nozzle 3.2 mm long _and argon was introduced into the arc torch at a flow rate of 12.7 m / h. The arc current was 100 A at 80 U. The distance between the torches was 12.7 mm. Titanium powder with an oxygen content of 0.651 % was used in an amount of 20 g / lllin. initiated into the arc burner. The application rate of powder on the carrier was 13 g / fflin. The coaxial jet had a width of 7.9 mm. Argon was introduced into the coaxial stream at a flow rate of 56.6 m / h. This gave a value for

73 2 k is the square root of the momentum flux of - ■. The sour »

sm "*" material content of the formed coating was 0.730% _o Machinability and the possibility of surface finishing were excellent.

Example III

The apparatus used ear the same as in Example II. The DüeenlMnge was 4.0 mm ₀ The arc conditions were the same as in Example II was fllolybdänpulver. With an oxygen content of 0.419% in an amount of 33 g / lflin.

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inserted into the arc torch. The order rate was 20 g / min. The coaxial beam was 7.9 mm wide, Argon was introduced into the coaxial jet at a flow rate of 56.6 m / h introduced; this resulted in a value for the square

73 2 ko * ^ root of momentum flux from -. The oxygen content

8 m "a
of the coating was 0.155 %

considerably reduced by 0.264 %.

Example IV

The conditions were the same as in Example III. The arc current was 150 A at 80 V. Tungsten powder with an oxygen content of 0.027 % was used in an amount of 68 g / fllin. introduced into the arc torch. The order = output was 51 g / fflin. The width of the coaxial beam was

73 2 ko ~ ^ 7.9 mm; the square root of the momentum flux was ¹ J

β m ^ "

The coating had an oxygen content of 0.030 %. The coating thus had practically the same low oxygen content as the original UJoIfram powder; As a result, it is better suited for applications that require high strength at room temperature and high temperatures.

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Claims (1)

■ ■ - 15 claims Method of preventing the contamination of one from Rapid gas outflow emerging from a nozzle through the vicinity of the gas outflow, characterized in that the rapid gas flow is enveloped with an annular, coaxial gas flow, the width of which in mm between 1.25 and 20 times the UIert of the square root of In mm measured diameter of the nozzle opening, and that in the annular, coaxial gas stream with a gas initiated such a flow rate that the annular, coaxial gas flow a value for the square ' 4r root (j) 9 of the longitudinal momentum flow that is at least equal, where Q is the flow rate β m "^" ₃ ge of the ring-shaped gas flow in m / s, A is the ring area 2 3 in j and ·? the gas density in kg / m is » Z ₀ A method according to claim 1, characterized in that the width of the annular coaxial gas stream has the in mm measured diameter of the nozzle opening in ram about six times the square root UIart ₀ 3ο Method according to claim 1 or 2, characterized in that the Reynolds number of the coaxial gas flow is greater than 2000 ₀ 9 0 9 8 31/0878 Method according to one of the preceding claims, characterized in that the gas for the ring-shaped coaxial gas flow argon used uiirdo Application of the method according to one of the preceding claims for the production of an essentially acidic « substance-free coating on a carrier by plasma » ^v Overlay welding, in which an arc is drawn between two Electrodes maintain a light in the arc arc gas flow introduced and the obtained arc " plasma through a constricting nozzle opening which conducts a rapid, high-energy arc » A current is generated which carries the excess catalyst with it and mean of the annular coaxial gas flow around = is wrapped «, BATH ORIGINAL 909831/0878