JPS6233025B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a plasma cutting method, and more particularly to a method for cutting a thin plate of metal material using a plasma arc.

[Conventional technology]

BACKGROUND ART When manually or semi-automatically cutting a thin sheet of metal material using a plasma arc, a hand-held plasma torch is convenient and has been widely used. In this case, argon (Ar) gas is mainly used as the plasma gas (cutting gas or working gas), and in rare cases hydrogen (H ₂ ) gas or nitrogen (N ₂ ) gas is added to Ar gas (Ar +
A mixed gas of H ₂ ) or (Ar+N ₂ ) may be used.

Note that N ₂ gas has a higher potential gradient than H ₂ gas.

Plasma cutting using Ar gas has the advantage of being very effective for repairs during processing such as making small cuts, drilling holes, and edge cutting, and for auxiliary work before and after welding. It has the disadvantage of extremely low ability. Therefore, the use of a mixed gas of (Ar+H ₂ ) and (Ar+N ₂ ) is effective in increasing the cutting ability, but when using a mixed gas of (Ar+H ₂ ), dross tends to adhere to the cut end. According to studies conducted by the present inventors, this is thought to be because the potential gradient of H ₂ is lower than that of N ₂ , and moreover, H ₂ is a reducing gas and does not easily enter the molten metal.

Particularly in plasma cutting operations using hand-held plasma torches, the main focus is on ensuring the quality of the cut surface, even at the expense of reducing the cutting speed. It is important that no dross adheres to the surface. In particular, when cutting thin plates with a thickness of 6 mm or less, there has been a strong demand for higher quality cut surfaces.
Various methods have been investigated to meet this demand, but at present no method has yet been found that is fully satisfactory.

On the other hand, it is known that water shield plasma cutting not only improves the quality of the cut surface, but also contributes to improving the working environment. For example, the special public official court in 1977-
Publication No. 9252 describes a method of cutting a material to be cut while spouting water from around a plasma arc to the cut end of the material to be cut. This cutting method is very effective in preventing sagging of the cut end of the material to be cut, preventing oxidation, and improving the quality of the cut surface, and is widely used mainly for high-speed automatic cutting of thick plates.

[Problem that the invention seeks to solve]

According to studies by the inventors of the present application, the causes of dross generation are that the amount of energy per unit area of the nozzle hole is low and that the molten metal has a high viscosity and is difficult to fall.

The cutting torch installed in the plasma cutting device disclosed in Japanese Patent Publication No. 47-9252 has a complicated structure and a large diameter (the torch is cooled by direct water cooling with a large current capacity), making it unsuitable for a hand-held cutting torch. . Not only that, but this device can also be used to create thin plates (thickness 6 mm).
Even if the following metal materials such as stainless steel and aluminum are cut, the problem of dross adhesion cannot be solved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a plasma cutting method that increases the cutting ability and enables dross-free cutting of thin plates.

[Means for solving problems]

In the plasma cutting method of the present invention, a nozzle hole at the tip of a plasma chip, which is also arranged at the internal tip of the plasma torch, is positioned in the direction of the tip of a non-consumable electrode rod built into the plasma torch via a collet.
When electricity is applied, a plasma arc is generated through this nozzle hole toward a metal material to be cut, and the metal material is cut by this plasma arc. In this case, the present invention is characterized by satisfying the following three conditions.

The current density i per unit area of the nozzle hole is 30
The nozzle hole and plasma current are selected to satisfy ≦i≦40 (A/mm ² ) to increase the density of the plasma arc.

The straight length l of the nozzle hole and the distance h from the tip of the nozzle tip to the tip of the electrode rod are 1.5l.
The density of the plasma arc is increased by satisfying the relationship ≦h≦3l.

A mixed gas of argon ( _Ar ) and _N2 with a nitrogen gas (N2) concentration of 60% or more is ejected from the nozzle hole.

In the present invention, although it is not directly connected to dross-free, since _N2 gas is used, in order to suppress the generation of harmful gases and the nitridation of the cut end, from between the nozzle cap and nozzle tip that constitute the tip of the plasma torch, It is desirable to cut the material by jetting water toward the cut end of the material.

[Effect]

By satisfying the above conditions, the amount of energy per unit area of the nozzle hole can be improved. Furthermore, by satisfying the above conditions, the amount of energy per unit area of the nozzle hole can be improved and the molten metal can fall more easily. In other words, _N2 gas has a high potential gradient, so it increases the voltage level and has the effect of increasing the amount of _energy.N2 gas dissolves into the molten metal as a promoter of oxidation and nitriding reactions, and can increase the amount of energy. It has the effect of raising the temperature and lowering the viscosity of the molten metal, making it easier to fall. That is, the object of the present invention is achieved by the synergistic effect of these conditions.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a plasma cutting machine to which a plasma cutting method according to the present invention is applied. In the figure, 1 is a small plasma torch that can be used for manual cutting, and the plasma torch 2
The torch has a function of ejecting water from the tip of the torch, the details of which will be described later. Reference numeral 3 denotes a torch cable connected to the control device 4 and the plasma torch 1, through which electricity, water, gas, etc. are supplied. 5 is a material to be cut, 6 is a DC power supply connected to the material to be cut 5 and the control device 4, and 7a and 7b are Ar gases stored in each cylinder.
The Ar gas and the N ₂ gas are supplied to the plasma torch 1 as a first plasma gas and N ₂ gas as a second plasma gas, respectively.

The control device 4 includes a DC power supply 6 and gases 7a and 7.
In addition to b, a cooling water for cooling the main body of the plasma torch 1 and a water source 8 for spouting water from around the plasma arc 2 to the cut end of the material to be cut 5 are connected. From the generation of the plasma arc 2 to the end of cutting, this control device 4 arbitrarily sets values such as plasma current, plasma gas flow rate, water amount, etc. as necessary, and controls the start and stop of supply as shown in FIG. It is configured so that it can be
9 is a torch switch for starting and stopping.

The details of the structure of the plasma torch 1 (hereinafter referred to as the torch) are as shown in Figure 2, and the torch main body 1a is a small, hand-held type with an outer diameter of about 25 mm, so that manual cutting can be easily performed. The torch main body 1a has components compactly housed within the torch body 1a. That is, a non-consumable electrode rod 10 that is energized through a collector 11 is installed in the center of the torch body 1a, and a small-diameter nozzle tip 12 is attached to the tip of the torch body 1a.
Plasma gas 7 and plasma arc 2 are injected from nozzle hole 13 of nozzle tip 12 toward workpiece 5 . Although the plasma gas 7 is shown to be of an axial flow type, it goes without saying that it may be swirled. The position of the electrode rod relative to the nozzle hole, the current density of the plasma arc, the plasma gas components, etc., which are important for achieving the purpose, will be described later.

The outer periphery of the nozzle tip 12 has an insulating ring 1
Metal nozzle cap 14 via 5a, 15b
surrounded by. For this reason, nozzle tip 1
2 and the nozzle cap 14 are electrically insulated, allowing the torch 1 to contact and cut the base material. A small groove is provided on the inner circumferential surface of the insulating ring 15b for uniformly jetting the cooling water 16 toward the material 5 to be cut as necessary. Also, the plasma torch body 1
Inside a is cooling water 17 for cooling itself.
is circulated, and a seal ring 18 is provided to prevent leakage of the plasma gas 7 and cooling water 16.
a, 18b, and 18c are provided. In the illustrated torch, cooling water 16 spouts from the outer circumference of the nozzle tip 12 and cooling water 1 for cooling the torch.
7 passages are provided independently, but it is also possible to integrate the two cooling water passages so that the cooling water supplied into the plasma torch body directly flows out to the torch tip (a single cooling water passage is provided). Water cools the torch and acts/reacts on the cut end of the material to be cut at the same time). Furthermore, the illustrated torch has a structure in which the amount of cooling water 16 can be arbitrarily varied.
In addition to cutting with cooling water jetting out, it is also possible to cut without jetting cooling water, so it can be used depending on the purpose of the work.

As described above, by downsizing and simplifying the shape of each component constituting the torch 1, a small torch that can be manually cut can be obtained.

Furthermore, with the torch 1, cutting is possible even when the nozzle cap 14 at its tip remains in contact with the workpiece 5, so the torch operation is easy, it is less susceptible to changes in arc length, and the cut surface It is possible to achieve uniformity and high quality.

Next, the plasma cutting control operation based on this embodiment will be explained with reference to FIG.

Figure 3 shows plasma current I and pilot arc A.
This figure shows how the supply of plasma gases G ₁ , G ₂ and water (Q _W ) changes with time from startup to stop and end. The first plasma gas G ₁ is Ar gas (for example, 3 to 10/min), and the second plasma gas G ₂ is N ₂ gas (for example, 10 to 30/min).
min), at the same time as the plasma arc 2 is generated, N ₂ gas is added and merged, and is injected from the nozzle hole as a (Ar+N ₂ ) mixed gas.

In addition, water supply in synchronization with this (for example, 30
~200c.c./min) is started. Nozzle tip 1
The small amount of cooling water 16 supplied to the outer periphery of 2
The plasma gas 7 and the plasma arc 2 are uniformly atomized and vaporized by the extremely high-temperature airflow, and the mixed fluid of water, spray, and steam acts to wrap around the plasma arc 2, resulting in a thermal pinch effect. As a result, the arc energy density is increased, and the heated spray and vapor fluid can effectively act on and react with the cut end of the material to be cut. When supplying this water, the amount of water that matches the cutting conditions may be set in advance. The appropriate amount is approximately 30
~200c.c./min; less than that may cause intermittent spraying or unstable plasma arc, and too much water may reduce cutting speed. It is.

In order to improve cutting performance, it is essential to increase the concentration of N ₂ gas, and it is necessary to increase the concentration of N ₂ gas to at least 60% or more. It is often thought that the use of N ₂ gas poses problems such as nitridation and oxidation of the cut surface and the generation of harmful gases such as NOx, but this is not an essential problem in countering dross. For example, to solve this problem, by spouting water arbitrarily from the tip of the torch as in this embodiment, the water sealing effect can prevent nitridation and oxidation of the cut surface, and also suppress the generation of harmful gases.

When performing dross-free cutting of thin plates, it is effective to increase the energy density of the plasma arc, but simply by reducing the nozzle hole diameter of the nozzle chip, the current density per unit area (A /mm ² ) alone cannot achieve dross-free cutting no matter how the cutting speed is adjusted. In order to obtain a high-quality cross-sectional area with a sharp cut and no dross adhering to it, several additional conditional factors must be understood.

As a result of various cutting experiments, it was found that the distance between the electrode inside the torch and the nozzle is an extremely important factor in achieving dross-free cutting of thin plates. Figure 4 shows the result of cutting a stainless steel plate with a thickness of 6 mm using the cutting torch shown in Figure 2, that is, the straight length l of the nozzle hole 13.
2 shows the arc voltage during cutting when the distance h from the lower end surface of the nozzle tip 12 to the tip of the electrode 10 is changed. V _p in the figure is the electrode 10
The voltage of the plasma arc generated from to the material to be cut 5, _VN is the divided voltage between the nostle and the electrode generated by the plasma arc. Argon-nitrogen mixed gas (Ar + 80% N ₂ ) is used as the plasma gas.
The conditions are constant: plasma current 70A, nozzle hole diameter 1.6mm, and amount of water added 70c.c./min.

When l is lengthened, V _p and V _N increase, and their values become higher as h becomes longer. However, it has been found that when the electrode tip approaches the upper end of the nozzle hole diameter and the condition is approximately l>h, the voltages V _p and V _N suddenly drop, and the cutting ability is significantly reduced. Further, under the above conditions, dross-free cutting was not possible. Even when cutting is performed with the torch lowered and in contact with the base metal, the values of V _p and V _N decrease relatively due to the voltage drop due to the reduction in arc length, but the above phenomenon is observed in the same way. (The dotted curve B in the figure is the base material contact cutting result). The reason why V _p and V _N suddenly drop under the condition of l > h is that the plasma arc cannot be narrowed down on the entire circumference of the nozzle hole, and the plasma arc is formed on one circumference of the tip of the nozzle hole. The arc constriction effect decreases. As a result, it is thought that the energy density of the arc decreases.

In Figure 5, the straight length l of the nozzle hole is 2.5 mm.
(constant), which shows the relationship between the distance h between the nozzle tip and the electrode and the plasma arc voltage _Vp . In addition, the results of cutting stainless steel plates with thicknesses (t) of 1 mm to 8 mm are summarized, and representative examples of the cut surfaces are illustrated. From this figure, it is clear that where h is short and l>h, V _p drops rapidly, and in this region a, the output of the plasma arc decreases and the cutting ability significantly decreases. Further, even if the cutting speed is adjusted, the cutting cannot be performed well, and as shown in the left figure (area a), the upper part of the cut end sag, and dross adheres to the lower part.

In contrast to the above, when h is increased, V _p increases almost in proportion to this, the energy of the plasma arc increases, and the cutting ability increases. In addition, as shown in the figure on the right (area b), the cut end is sharp with small shoulder sagging, hardly any dross adheres, and an extremely good cutting result with a gloss can be obtained.

As is clear from the above explanation, the condition l>h is extremely inappropriate for dross-free formation, and therefore l≦h is essential. More realistically, when the value of h is small and close to l, as shown in Figs. 4 and 5, the V _p and V _N values are close to the region where they tend to change up and down, so there is a problem in terms of cutting performance. It is stable.
Therefore, the lower limit value for h from the safe side should be set to 1.5, which is slightly larger than l.

By the way, in region c where h is too long and exceeds 8 mm, it is difficult to apply the pilot arc at startup and to transfer the plasma arc to the base material, which may impede the cutting operation. Also, since a high load is applied to the nozzle tip, the life of the nozzle tip is shortened.

This value of 8 mm is the value in this embodiment where l is 2.5 mm (therefore, h≈8 mm (〓2.5×3)).
That is, if the value of h is set to 3l or more, the tip of the electrode rod will be retracted too much into the interior of the torch, and the capacity of the power source will need to be increased due to the excessive increase in the values of V _p and V _N . Although this value is not particularly critical, it is a recommended and realistic value at the cutting site.

Therefore, in order to always obtain good cutting results with stable generation of plasma arc and dross-free without adversely affecting the cutting operation, the range should be limited to 1.5l≦h≦3l.

In this example, the nozzle hole diameter is 1.6 mm, but a nozzle chip with a smaller or larger nozzle hole diameter (for example, a nozzle hole diameter of 12 mm) is used.
mm, 2.0 mm), the above h and l
It has been confirmed that the relationship exists.

Furthermore, when changing the nozzle hole diameter, it is necessary to flow a plasma current commensurate with the hole diameter. According to the results of the study using the torch, the current density per unit area of the plasma arc passing through the nozzle hole i (A/
It has been found that it is optimal to flow the plasma current so that 30≦i≦40 (mm ² ) falls within the range of 30≦i≦40. If the value of i is too small than the above-mentioned appropriate range, it will be difficult to perform dross-free cutting using a plasma arc with insufficient heat input.On the other hand, if i is too large, it will be easy to induce double arc, which will lead to melting of the nozzle tip. (See Figure 6).

Conventionally, the influence of factors such as the distance between the electrode inside the torch and the nozzle tip has been limited to the factors that are said to be involved in plasma cutting, such as the plasma current, nozzle hole diameter, plasma gas, and cutting speed.
I was overlooked and won. However, as is clear from the examples shown in Figures 4 and 5, the settings of h and l are extremely important condition factors in achieving dross-free cutting of thin plates, so they must be carefully considered. It turns out there isn't.

As explained above, according to this embodiment, by downsizing and simplifying the shapes of the individual parts that make up the torch, it is possible to not only make a small torch that is easy to manually cut, but also to Accordingly, during cutting, a mixed fluid of water, spray, and steam can be easily applied and reacted to the cut end of the material to be cut, which prevents sagging of the cut end, reduces thermal effects, and prevents nitriding and oxidation. At the same time, it is possible to suppress the generation of harmful gases and improve the environment at the work site.

Furthermore, by setting the relationship between the length of the nozzle hole and the distance between the nozzle tip and the electrode to satisfy a predetermined condition, this embodiment improves the cutting ability, which was previously considered difficult to cut. Thickness 6mm
Dross-free cutting of thin plates is possible, and high quality cut surfaces can be achieved. In addition, cutting can be carried out even when the torch tip remains in contact with the material to be cut, so the torch is easy to operate, and even unskilled workers are less likely to damage parts such as the nozzle tip, ensuring stable cutting results. I can do it.

In addition, the function of spouting water from the tip of the torch not only allows for easy manual cutting, but also improves the quality of the cut surface and suppresses the generation of harmful gases, contributing to environmental improvements.

〔Effect of the invention〕

As explained above, the present invention has the effect of increasing the cutting ability of plasma cutting and making it possible to cut dross-free even thin plates.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a plasma cutting machine applied to a plasma cutting method according to an embodiment of the present invention, FIG. 2 is a longitudinal sectional view of a plasma torch used in a plasma cutting method according to an embodiment of the present invention, FIG. 3 is a control operation diagram of a plasma cutting method according to an embodiment of the present invention, FIGS. 4 and 5 are characteristic diagrams of an embodiment of a plasma cutting method according to an embodiment of the present invention, and FIG. 6 is a nozzle hole diameter FIG. 3 is a characteristic diagram showing the relationship between 1... Plasma torch, 1a... Torch body,
2... Plasma arc, 5... Material to be cut, 7...
Plasma gas, 10... Electrode rod, 12... Nozzle chip, 13... Nozzle hole, 14... Nozzle cap, 15... Insulating ring, 16, 17... Cooling water.

Claims (1)

[Claims] 1. A nozzle hole at the tip of a plasma chip, which is also placed at the tip inside the plasma torch, is positioned in the direction of the tip of a non-consumable electrode rod built into the plasma torch via a collet, and a plasma arc is caused by energization. In a plasma cutting method in which a plasma arc is generated through a nozzle hole toward a metal material to be cut and the metal material is cut, the current density i per unit area of the nozzle hole is 30≦i≦40 (A/ The nozzle hole and the plasma current are selected so as to satisfy mm ² ), and the straight length l of the nozzle hole and the distance h from the tip surface of the nozzle tip to the tip of the electrode rod satisfy the relationship of 1.5l≦h≦3l. A plasma cutting method characterized by increasing the density of the plasma arc so as to satisfy the following conditions, and further ejecting an argon-nitrogen mixed gas having a nitrogen gas concentration of 60% or more from the nozzle hole. 2. The plasma cutting method according to claim 1, characterized in that water is jetted toward the cut end of the material to be cut from between the nozzle cap and the nozzle tip that constitute the tip of the plasma torch to cut the material. plasma cutting method.