RU2570253C1 - Device for cooling of cap electrode of resistance spot welding - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: holder is made with axial cavity. The pipe supplying cooling medium is installed in axial cavity of the holder with clearance relatively its wall. On side surface of the cap electrode a cylindrical groove is made. The cap electrode is located on the cone surface of the holder with creation of the axial clearance between the bottom of the cap electrode cavity and face end of the holder, and ring clearance between the side surface of the face part of the holder and groove surface. The said ring clearance is opened to the axial clearance, and is connected with transverse openings in the holder wall with clearance in its cavity. The clearance is sealed at the face end of the pipe.

EFFECT: increased cooled surface of the cap electrode, thus decreasing its heating and resistance.

1 dwg

Description

The invention relates to welding production and is suitable in KTS electrodes used for welding sheet blanks, parts, etc.

A device is known for cooling a KTS electrode having a hollow and conical outside shank located in the front inner conical part of the hollow holder, in which a tube is installed with a gap connected by a rear end to a small cavity of the cap, where its transverse window for refrigerant is open, and the second window is also under the refrigerant - into a large cavity made from its front end, in which the tube is placed with a gap, and the cap itself is attached to the back of the holder or may be absent (see patent RU No. 2420378 C2, 02.03.2009).

Its disadvantages: significant length, mass and labor intensity of the electrode due to its conical surfaces and the shank with the cavity; effective cooling of only the central part of the electrode located in the zone of this cavity, etc.

Another device of the cap electrode is known, which has a conical cavity at the rear end, in which the front part of the holder (extension) with a cavity under the tube, the rear part in the cap socket indicated above, with refrigerant inlet and outlet windows is placed with an axial clearance (see GOST 25444-90 p. 2), and its front does not protrude beyond the front end of the holder.

This electrode is simpler, more technologically advanced, shorter and several times cheaper than the previous one, but its internal cooling is not efficient enough due to the washing of not the entire bottom area of the cavity with the refrigerant, but only a part of it equal to the transverse area of the holder (extension) cavity. As a result, a stagnant zone with a refrigerant is formed in the peripheral zone of the bottom of this cavity, where it does not circulate and therefore boils in a film mode, which leads to a heat exchange crisis of the first kind — overheating of not only this zone, but also the front of the electrode, accelerating wear of the latter at work.

The aim of the invention is to eliminate these disadvantages of this device, i.e. improving the cooling efficiency of the electrode-cap by increasing the cooled area of its cavity and eliminating the stagnant zone with the refrigerant.

It is achieved by the fact that in the device for cooling the electrode-cap of spot welding, placed by a conical rear cavity on the conical front of the hollow holder with an axial clearance between its bottom and the front end of the latter, in which a tube is connected with a gap connected by a rear end to the small cavity cap, where its transverse window under the refrigerant is open, and its second window under the refrigerant - into a large cavity made from its front end, in which the tube is placed with a gap, and the cap itself is attached to the back of the holder, between the holder and the electrode-cap at the bottom of its cavity, an annular gap is formed, open in the axial clearance of their connection and connected by the transverse windows of the first with a gap between it and the tube, sealed at its front end.

A comparative analysis of the known device with the proposed one indicates the following: at the bottom of the conical cavity of the electrode-cap form the mating surfaces of it and the holder an annular gap, which is open in the axial clearance formed by the bottom of the cavity of the electrode-cap and the front end of the holder. An annular gap is connected by the transverse windows of the holder with a gap between it and the tube, and the last gap is sealed from its front end.

From the above it follows that the proposed device has novelty, has significant differences from known solutions, is industrially applicable and therefore meets the criterion of "invention".

The formation of an annular gap at the bottom of the cap cavity increases its internal cooled surface several times. By performing transverse windows near the holder in the zone of this gap, the refrigerant circulates along the axial and annular gaps between the front of the holder, the bottom and the inner side surface of the cap, which significantly increases its cooling efficiency.

To ensure this condition, a sealing device is placed in the annular gap between the tube and the holder between these windows and its front end, which provides refrigerant circulation along the axial and annular gap between the cap and the holder, and then the heat-heated cap of the refrigerant is discharged through these windows into the gap between the tube and the cavity of the holder, from which it is removed beyond its limits.

It is illustrated by the drawing, which shows the electrode cap 1 with a conical or radial front part, located with its conical rear cavity on the front conical part of the holder 2 (extension cord), the rear part of which with the cap attached to it with transverse windows, is not represented here.

Between the bottom 3 of this electrode and the front end 4 of the holder there is an axial clearance 5, and a tube 7 is placed in the cavity of the holder with a gap 6, which does not contact its front end with the bottom 3 of the electrode-cap 1.

At the front end of the holder 2 there are transverse windows 8, perpendicular or inclined relative to its longitudinal axis and open with the outer side in the annular gap formed by the lateral surfaces of the cavity of this electrode and the front of the holder 2 (a cylindrical groove is made at the bottom of this cavity or from the front end outer cylindrical or conical surface or a combination of the surfaces of these elements). The inner sides of the window 8 open into the gap 6 between the holder 2 and the tube 7, which is sealed with a ring 9 placed between its front end and the inner sides of the windows 8.

The electrode-cap 1 is cooled as follows: a refrigerant is supplied through the cavity of the tube 7 — water, which rushes into the axial clearance 5 between the front end of the holder 2 and the bottom 3 of the cavity of the electrode-cap 1, heated by the heat of the welding point of the connected workpieces or parts to each other, which rushes mainly in the axial direction from its front end to this cooled bottom. The refrigerant washes the entire bottom 3, removing heat from the welding heat received in the electrode cap and heats up at the same time. The heated refrigerant rushes further from the axial clearance 5 into the annular gap between the surfaces of the cavity of the electrode 1 and the front of the holder 2, cooling and its side surface adjacent to the bottom 3 of the cavity of the electrode, further heating up. Next, the heated refrigerant is discharged through the transverse windows 8 into the gap 6 between the tube 7 and the holder 2 and is removed from the device.

The opposite scheme of circulation of the refrigerant is not excluded, when it is led through the gap 6 to the cooling zone of the electrode-cap and removed from there along the cavity of the tube 7.

Such a circulation scheme eliminates the stagnant zone (without refrigerant circulation) that the prototype had from the edge of the hole of the holder 2 to the edge of the bottom of the conical cavity of the electrode-cap 3. In it, the heat from this bottom to the refrigerant was transferred not by convection, but by conduction (its thermal conductivity), which much less efficiently and led to overheating of the cooled surface in this zone with the formation of film boiling it, which reduces several times the heat sink from this surface to the cooling medium and, therefore, its overheating and local overheating roar of the front end of the electrode-cap, leading to an acceleration of its wear.

Due to the formation of an annular gap at the bottom 3 of the conical cavity of the electrode-cap with the corresponding surfaces of the holder and the holder, the cooled area of the bottom 3 increased, and the presence of transverse windows 8 in the front of the holder 2 eliminated the stagnant zone with refrigerant at the bottom of the cavity and also increased the internal side cooled surface of this cavities. This solution increased the efficiency of liquid cooling of the electrode-cap several times in comparison with the prototype.

To confirm this, we consider the Newton-Richmann equation

$$Q=\alpha \Delta T\cdot F\cdot \Delta \tau ,\left(\mathrm{one}\right)$$

which determines the amount of heat Q removed from the refrigerant from the cooled surface of the electrode-cap with area F over a time interval Δτ equal to the cycle of the welding machine for our device.

Here, α is the heat transfer coefficient from the heated bottom and side surface of the electrode-cap cavity to the refrigerant, ΔT is the temperature difference between these surfaces and the refrigerant circulating there.

In turn, during flow cooling of the electrode cap α is determined by the criterion equation of Nusselt-Mikheev

$$Nu=\mathrm{0,023}{\mathrm{Re}}^{0.8}{\mathrm{Pr}}^{0.43},\left(2\right)$$

- критерий Прандтля, $$\mathrm{Re}=\frac{V\cdot d}{\vartheta }\left(4\right)$$

- критерий Рейнольдса, в котором v - скорость циркуляции хладагента; d - эквивалентный гидравлический диаметр одного или нескольких каналов, по которым циркулирует хладагент; ϑ - кинематическая вязкость хладагента - воды; а - ее коэффициент температуропроводности.Where $$\mathrm{Pr}=\frac{\vartheta }{a}\left(3\right)$$

- Prandtl criterion, $$\mathrm{Re}=\frac{V\cdot d}{\vartheta }\left(\mathrm{four}\right)$$

- Reynolds criterion, in which v is the refrigerant circulation rate; d is the equivalent hydraulic diameter of one or more channels through which the refrigerant circulates; ϑ - kinematic viscosity of the refrigerant - water; and - its coefficient of thermal diffusivity.

When v = 0, Re = 0 and Nu = 0, when there is a stagnant zone with a refrigerant, as in the prototype, then heat is transferred from the peripheral part of the heated bottom of the cavity to the existing refrigerant therein, which is much less efficient than convection in the proposed device.

In its turn

$$\alpha =\frac{Nu\cdot \lambda }{d},\left(5\right)$$

where λ is the coefficient of thermal conductivity of the refrigerant - water.

Let us numerically evaluate the cooling efficiency of the electrode-cap by the proposed device and the prototype device, asking for the same cycle duration Δτ, heat transfer coefficient a and temperature difference ΔT. We accept the diameter of the holder hole 2 d ₁ = 10 mm, the diameter of the cylindrical cavity of the electrode cap 1 d ₂ = 14 mm and its length l = 4 mm (see drawing).

For the proposed device, the heat removed Q ₁ will be equal to

$$Q_{\mathrm{one}}=\alpha \Delta T\cdot F_{\mathrm{one}}\cdot \Delta \tau ,\left(6\right)$$

and for the prototype -

$$Q_2=\alpha \Delta T\cdot F_2\cdot \Delta \tau \left(7\right)$$

Their ratio will be written

$$\frac{Q_{\mathrm{one}}}{Q_2}=\frac{F_{\mathrm{one}}}{F_2}=\frac{0.785\cdot {\mathrm{fourteen}}^2+3.14\cdot \mathrm{fourteen}\cdot \mathrm{four}}{0.785\cdot {10}^2}=4.2\left(8\right)$$

Thus, the cooling efficiency of the electrode-cap in the proposed device increased by 4.2 times compared with the cooling effect of this cap of the prototype device, which increases the cooling efficiency of its front end and, therefore, the resistance due to the minimum temperature of its working surface to the beginning of the welding cycle parts or blanks among themselves.

By performing, for example, a cylindrical cavity at the bottom of the conical cavity of the electrode-cap for the formation of an annular gap between it and the holder, it is also simplified to manufacture the side surface of this cavity due to the exclusion of sticking of the cutting tool into this bottom, which is the case with the prototype. Moreover, its length 1 is determined by the size of the window (its diameter) + 1-2 mm, when it is made inclined relative to the longitudinal axis of the holder. For example, with a window diameter of 2 mm, the length l = 2 + (1-2) ≤4 mm (see the device drawing).

Thus, the proposed device increases the cooled surface of the electrode-cap and the cooling efficiency of the electrode-cap several times, which increases its resistance by at least 1.5-2 times.

Claims (1)

A device for contact spot welding, comprising a holder with an axial cavity, an electrode cap having a cavity with a conical side surface located on the conical surface of the front part of the hollow holder, and a refrigerant supply pipe installed in the axial cavity of the holder with a gap relative to its wall, characterized in that a cylindrical groove is made on the side surface of the electrode-cap, while the electrode-cap is placed on the surface of the holder with the formation of an axial clearance between the bottom ohm of the cavity of the electrode-cap and the front end of the holder and the annular gap between the lateral surface of the front of the holder and the surface of the groove, while the said annular gap is open in the axial clearance and connected by transverse windows made in the wall of the holder, with a gap in the cavity of the holder, which is sealed at the front end of the tube for supplying refrigerant open to said axial clearance.