Kohei Ando

On the Equation of the Transient Temperature Rise in Thin Plate due to Moving Point Heat

A new function mF0(δ) is introduced for the equation of the transient temperature rise, T=q/4πK·eX·mF0(δ) …(31) where mF0(δ), as well as m, δ are given in equ. (6), (32), (33). mF0(δ) has the following interesting characteristics mF0(δ)|m=1 = 1/2· mF0(δ)|m=∞ …(18)mF0(δ) + 1/mF0(δ) = ∞F0(δ) …(17)From equ. (17), the value of mF0(δ) for m>1 can be easily calculated from that of m<1.Fig. 3 shows the calculated results of mF0(δ) for range of m=0-1, in the form of ratio to ∞F0(δ), ∞F0(δ) being given in Table 1 for various values of δ.Equ. (18) suggests an interesting and useful understanding as to the transient temperature rise, namely when we neglect the radiation loss from the plate surface, the temperature of any point, whose distance from the arc point is equal to the distance of arc travel after arc starting, is just equal to the half of the quasi-stationary state value. See equ. (32).It is remarkable that the above mentioned relation expresed in equ. (18) holds true always independent of the thermal conduction constant of plate, arc traveling velocity and time elapsed after arc starting. The result holds under constant linear velocity with constant thermal input in thin plate.

A Consideration on the Mechanism of the Droplet from the Wire Tip in MIG Welding

The paper explains the reason why the wire tip takes a pencil-like form for the wire of low heat conductivity from the standpoint of the anode heating on the cylindrical wire surface. It explains also the reason why the pencil like-forming tendency is increased when the wire is preheated by .Joules loss.It is explained that the pencil-like forming of the solid part at the wire tip allows an easy detachment of the molten droplet and results in a lower temperature of the droplet arriving at the base metal.From the above mentioned idea, the following characteristics observed in MIG are welding are explained. For aluminum wire the heat content of the droplet increases as the current is increased until it reaches a nearly constant value in spray transfer range. The temperature is as high as the boiling point in spray transfer. The increase of the temperature is due to the quick heating of the droplet. For steel wire the heat content increases and reaches a maximum and then decreases as the current is increased under a constant wire extension The decrease of the heat content is related to the pencil forming.For any given current the heat content is smaller for longer wire extension because the pencil forming tendency is stronger. The decrease of the current corresponding to the maximum heat content above mentioned for longer wire extension is also attributed to the same cause.Lesnewich reports that the critical current in globular to spray transition decreases as the wire extension is increased. The reason is explained by the pencil forming. Salter reports that the melting speed is increased with decreasing of atmospheric pressure. The potential gradient of the arc column decreases in lower pressure and the arc foot climbs up along the wire. Therefore the pencil forming is increased and results in a decrease of the droplet temperature and an increase of the melting speed, because the equivalent anode melting voltage VmA=VA+VW+VT is presumed to be independent of the pressure which is not so much different from the atmospheric pressure.

Voltage Current Characteristics of Three Phase Rectifier Type D.C. Welder With Non-saturable A.C. Series Reactor

Voltage curent characteristics of three phase rectifier type d.c. welder with non-saturable series reactor (Fig. 1) are calculated for the cases when d.c. reactor Ln is zero and infinity, under the assumption that internal resistance is negligible compared to a.c. inductance L.. The results are shown in Fig. 2 and Fig. 3.It is worth to notice that in case of LD=0, the current wave form of d.c. side is similar to that of no load d.c. voltage for all part of the characteristics though the wave form of a.c. side varies according to the variation of the load resistance. See. Fig. 6. Point Q in Fig. 2 shows the critical point when the over lap angle u becomes less than 60°. Curve, QRS is given by equation (21).The curve in Fig. 3 can be divided into three parts PQ, QR, RS. Each of PQ and RS is linear and QR is circular. Equations for the parts are given in (36), (44), (48).The current wave forms of a.c. side are shown in Fig. 8. The range (a)-(b) of Fig. 8 is well known. In the range (b)-(d), the over lap angle u is constant and the phase angle φ increases from 30° to 60° as load resistance decreases. In the, range (d)-(f) which corresponds to RS of the characteristics shown in Fig 3, the phase angle rp increases from 60° to 90° and the angle β in which the phase current is equal to d.c. current ID which is maintained as constant due to infinite d.c. inductance decreases from 60° to zero as load resistance decreases to ideal short circuit.It is remarkable that for the interval 60-β, the load terminal is short circuited through the rectifiers of the sam polarity. The phase of the initiation of the short circuit is given in equation (38) for B phase. See Fig. 11.

Calculation of The Motion of Electrode of Resistance Spot Welder Operated Through Compressed Air

The variation of air pressures P1, P2 of the parts (1), (2) of the cylinder of a spot welder operated through compressed air, as well as the velocity ν and displacement z1 of the piston are calculated under the assumption that the pressure of the air source is maintained constant at the value PH at the inlet (1), Fig. 1.The results are shown in Figs. 2-5 and in Table 1, in which Fig. 2 is the case when the effect of moving mass M is assumed to be zero and Fig. 6 is the case when the gravity effect is taken into consideration.With the time constant Ta2 as defined in equ. (1), variations of P1, P2, v and z1 are related to time t in dimensionless forms as shown in the figures, the parameters being the dimensionless acceleration (equ. (9)), and the ratio of the effective sectional areas S1. S2 of air circuits (1), (2). The boundary conditions are shown in the figures, V10 being the initial volume of (1) and V0 the sum of volume of (1) and (2) : V0=V1+V2=V10+ V20.When the piston moves at the velocity ν0 as defined in equ. 5, the pressure P2 does not vary, and the air in (2) is discharged through S2 at sound velocity (See equ. (7)). This velocity is taken as the denominator of the dimensionless velocity.It is interesting to note that the accelerating force, which is proportional to (P1-P2) or (γ1-γ2) in dimensionless expression, decreases when J (or M) is decreased, and the time tm required for the piston to reach the bottom (i.e. V1=V0, z1=z0) varies only in small range even when j (or M) is changed in wider range.Calculation was made by the step-by-step method, i.e. dγ1, dγ2, dν/ν0, dz1/z0 corresponding to dt/ Ta2 were calculated from equ. (11), (12) and (18).It is assumed that equation (6) holds true for the whole range of P2.

Condenser Capacity Connected Continuously Parallel to A.C. Arc Welder

It is proved that the optimum current or kVA of condenser connected continuously parallel to A.C. welder, which is used intermittently with duty cycle ƒ¿ is equal to time averaged reactive wattless current or kVA of the welder proper, to mimimize the copper loss in the distribution line. In equations (3), (6), which show the result above mentioned, Ic I0, Ia mean the condenser current, no load magnetizing current, primary compensating arc load current respectively, Iw, IwI, being components of Ia.

A Consideration on the Heat Delivered to the Base Metal by Welding Arc : A Discussion on the Papers of Rosenthal

A paper of Rosenthal published in 1941 shows that the heat conducted to the electrode from the molten tip is 0.20 of the total arc heat V1, and so the heat delivered to the base metal is 0.65, 0.15 being the loss due to the radiation and convection of arc column. According to Rosenthal the above calculated result coincides well with the experimental data reported in 1938.It is evident from the paper that the heat part 0.20 is not radiated from the electrode surface, and that as the temperature rise does not exist in a remote part beyond about 1cm (1″/4) from the elec-trode tip, there is no heat flow and consequently no heat loss due to conduction can be observedni such a part. The heat conducted from the tip as far as 1cm is absorbed usefully to preheat the electrode metal before the metal reaches the arc surface. In other words, the heat energy conducted from the molten tip by the thermodynamic motions of metal molecules is transported back to the electrode tip as the metal part which absorbed the energy moves to the tip with the melting speed of the electrode. So the loss is only 0.15 instead of 0.35.In the experiment of 1938, the input arc power is calculated as V1, V and 1 being the effective values of arc voltage and current of a. c. respectively. But the wave from of arc voltage being nearly rectangular, so the power is 0.90 V1 and therefore the experimental data 0.65 becomes 0.72. The figure may get somewhat greater if the reduction of true power due to the instantenuous short circuits caused by irregular motions of molten tip metal is tanken into consideration, or if the input power is measured by a wattmeter or a watthourmeter. It is also remarkable that the base metal energy might be more incresed owing to the convection from the arc column, if the breadth of the base metal were greaterr than 12 mm and the protecting plate (forthermocouples) were uncovered as may be the case of practical welding.