JPS6021179A - Plasma cutting method of spiral welded pipe - Google Patents

Abstract

PURPOSE:To minimize generation of fumes by increasing an arc current value to the value optimum to the thickness of a spiral pipe only when a plasma-cutting torch passes through the weld seam part of the spiral pipe. CONSTITUTION:A timer T is provided to a driving source M of a flying cutter 4 and the time (t) until a cutting torch 6 intersects with a weld seam 3 where traveling starts is set to the timer T; at the same time, the timer T is so arranged that the signal therefrom is transmitted to an arc current regulator 10. The plasma arc current is increased up to the current value optimum for the thickness l+alpha of the weld seam 3 only during the time when the torch 6 passes through the seam 3 upon emission of the limit signal of the set time (t) from the timer T. Therefore, the torch 6 starts traveling and the plasma arc current value is automatically controlled at all times to the current value optimum for the thickness of a spiral pipe 5 until said torch finishes cutting the pipe.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma cutting method for spiffle welding which minimizes the generation of fumes.

Generally, as shown in Figure 1, Nuspiral steel pipes are made by forming a wide steel strip (1) into a spiral shape using a Nuspiral pipe making machine (2), and then welding the seam (3) from the inside and outside. By this, the pipe is continuously manufactured and cut into a predetermined length σ by a traveling cutting device (4).

By the way, although the plasma cutting method is widely used as the cutting means of the traveling cutting device (4), there is a problem that a large amount of fume is generated when the spiffle tube (5) is cut using the conventional plasma cutting method. Cheer.

That is, a plasma cutting torch (6) mounted on a traveling cutting device (4) that runs in synchronization with the pipe forming speed ('Vp)
The position is from the running nut position (7) to the sinupif/l/tube (
5) Continues to cut while it rotates once, and when it reaches position (8), the cutting is completed, but during this time the weld seam (3) must be cut at one location. However, as shown in Fig. 2, this weld seam part (3) is thicker than the other parts of the pipe (a) by the excess thickness α of the weld bead (9), and the 1Pfusma cutting torch (6) The flow "f" to the electrode of
'If the current value is adjusted according to the beating of the tube W, the welding seam part (3) will not have sufficient capacity, resulting in uncut phenomenon. Conventionally, the current applied to the electrode is I had adjusted the value according to the thickness of the close seam (3) (10 α), but when I did that, the weld seam (3)
) other than the normal pipe thickness (the force section will be cut at a higher current value than the proper current value, which will inevitably cause a large amount of fume to be generated. Nupaifuru Tube's plasma cutting factory, which generates a large amount of fume, was forced to install a large-scale fume collection device for environmental hygiene reasons.

The present invention was developed in consideration of such a protrusion, and the current value flowing through the electrode of the Buchsma cutting/closing torch (6) is adjusted to the thickness (t) of the bath weld seam portion (3) when the bath weld seam portion (3) is cut.
By providing a plasma cutting method for welded pipes, the value is automatically controlled so that 1/( is the optimum value for the pipe thickness (+α) and when cutting other parts. υ
, which attempts to prevent the occurrence of fumes.

The inventive method will be described in detail below.

In the method of the present invention, first, the seam pitch (v) of the spiral formed by the Nubaiful pipe-making machine (2) is calculated using the following formula 0 based on the pipe-making conditions of the Nubaiful pipe to be manufactured.

Pipe making machine <21 angle of approach p), W: 1 of steel strip (1)]
, t: Thickness of the band WI (1) 8, D = outer diameter of the Nispifle (5), that is, the seam pitch ■ of the Nuspifle tube to be manufactured, then Azuma cutting 1---F-(6) Since the traveling start position (7) of is always constant, it is possible to determine the position where the plasma cutting torch (6) completely passes through the welding seeding part (3).

For example, calculate the seam pitch [F] using the above formula, and plasma cut at the running start position (7) with respect to a point (Q') that is an integral multiple of the seam pitch P) from the spiral forming start point. When the position of the torch (6) is shifted by A pitch (90°') in the forward movement direction as in the case shown in 1) and 270° in the direction of arrow rotation (direction of arrow F) Now, the plasma cutting torch (6) will intersect the Tefa JV seam (3) when the spiffle welding tube (5) has rotated 180° (270°-90°). The running speed of the plasma cutting torch (6) is the pipe forming speed (Vp)
Therefore, in this case, the time required for the plasma cutting torch (6) to intersect the welding seam (3) after it starts running can be easily calculated using the following formula 0. be able to.

However, D = Nupaifu/I/outer diameter LS of tube (5): Nupaifu/L/peripheral velocity of tube (5) (vc'xcosθ)■C
: The speed at which the steel strip (1) enters the spiffle pipe making machine (2). Therefore, as shown in FIG.
A timer is provided in the drive source (goods) that starts its operation at the same time as the forward rotation of the drive source (goods), and the timer (T) is set in advance to the time (1>) set in the above formula 0. At the same time, the timer (TI) is connected to the arc current regulator αO of the lasma cutting circuit (6) so that the signal from the timer σ is transmitted to the arc current regulator QO.
At the same time as the limit signal of the above set time (1) from
If the plasma cutting torch (6) is configured to increase to the optimum current value for the thickness (t+α) of the welding seam only while it completely passes through the bath welding seam (3), the plasma cutting torch (6) will start running. Until the Spyful welded pipe (5) is finished cutting,
The plasma arc current value is always automatically controlled to the optimum current value for the pipe thickness, and no harmful fumes are generated in large quantities.

t7t, the present invention can be easily implemented using a limit switch instead of the above-mentioned timer.

In this case, the time (1) determined by the above formula 0 is further multiplied by the pipe forming speed (Vp) to determine the distance from when the plasma cutting torch (6) starts traveling until it intersects the bath contact seam (3). 1, a limit switch α is placed on the rail (1]) of the travel cutting device (4) from the travel start position (7) corresponding to the distance.
is installed so that when the arc current regulator C1O receives the signal from the limit switch (2), the fuser arc current value rises to the optimal value for cutting the weld seam (3). Just configure it.

As explained above, according to the present invention, Pfusma cutting 1
・Since it is possible to know in advance the point at which the torch (6) will pass the welding seam (3) of the Spyful Ying (5) while cutting, the plasma cutting torch (6) will pass the welding seam (
It becomes possible to perform automatic control to increase the plasma arc current value δ only when passing through step 3), and the spiral welded pipe can always be cut at the optimum current value for floating stones. Therefore, the generation of fume is significantly reduced, and favorable effects such as eliminating the need to install a fume recovery device, which is a big loss as in the past, can be obtained.

[Brief explanation of the drawing]

Fig. 1(a) is a schematic diagram showing the pipe manufacturing process of a spiral welded pipe, Fig. 1(b) is a sectional view taken along the line A-A in Fig. 1(a), and Fig. 2 is a welded seam ( 3) is a partially enlarged view showing the cross section of FIG. 3, and FIG. 3 is a block diagram of an automatic plasma arc current control circuit showing an embodiment of the present invention. l: Steel strip, 3: Welded seam part, 4: Traveling cutting device, 5 Nispi full welded pipe, 6: Fusuma cutting torch, 7: Traveling start position, 10: Arc current regulator

Claims (1)

[Claims] (1) When a spiffle welded pipe that has been spiral-formed and welded by a spiffle pipe making machine is cut to a predetermined length by a plasma cutting torch that moves in synchronization with the construction speed, the plasma cutting Predicting the time or travel distance for the torch to reach the weld seam of the Spyful pipe by calculating the distance per comb based on the construction conditions of the Spyful pipe;
The predicted value is set in a timer or a limit switch, and the signal is sent to the arc current regulator of the plasma cutting torch, so that the pipe thickness is adjusted only when the plasma cutting torch passes through the weld seam of the Nupaiwor pipe. A plasma cutting method for a spyful welded pipe, characterized in that an arc current value that has been adjusted to an optimal value is automatically increased to a value that is optimal for the thickness of a welded seam.