JPH0336625B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Application and Objectives of the Invention) The present invention relates to an improvement in a method for gas cutting a steel plate coated with a primer, and in particular, the present invention relates to an improvement in a method for gas cutting a steel plate coated with a primer. The purpose is to eliminate the need for additional work, reduce the chance of burnout of the primer coating, ensure that the shape of the cut end face is uniform and dimensionally accurate, and enable smooth cutting into sharp shapes. It was invented as.

(Conventional technology and its problems) For steel sheet materials, such as the side panels of huge outdoor tanks, which require a long period of six months or more from transporting the material to a processing factory to completing assembly on site, In order to protect steel sheets from corrosion, it is customary to apply various types of primers as a rust-preventive coating before shipping from the steel sheet manufacturer.

Conventionally, when using gas to perform cutting or beveling on steel plates coated with these primers, the components of the primer act as obstacles during cutting, making it difficult to cut at a stable speed or with good quality. It was not possible to obtain a cut shape.

Although primers with various components are commercially available depending on the required characteristics, an example of a steel plate coated with a zinc-rich primer will be explained here.

Zinc-rich primers are made of resin and metallic zinc powder. Especially in the case of tank plate materials, primers with a zinc content of 90% or more by weight are usually used to take advantage of the corrosion-preventing function of zinc as a sacrificial anode. ing. However, this metallic zinc powder causes various problems during cutting operations. That is, the metal zinc powder in the primer component reacts violently with oxygen in the high-temperature atmosphere during cutting, and further accompanies the molten metal and becomes sparks (spatter) that scatter around the cutting torch on the surface side of the steel sheet.

These spatters, which become fine particles and adhere to the periphery of the base material, damage the primer coated area and greatly impair the corrosion resistance and aesthetic appearance of the product. Furthermore, removing the sputters is usually a lengthy manual process using tools such as spatulas, grinders, chisels, and the like. In addition, the amount of work involved was considerable, including repair painting of the damaged primer. Also,
These spatters not only scatter around, but some of them also adhere to the gas outlet of the cutting torch, impeding the normal and stable flow of acetylene and cutting oxygen, and causing the cut shape of the workpiece to be cut. Failures occurred, and in some cases, a so-called flameout occurred, making cutting impossible.

To address these problems, conventionally, prior to cutting, the primer coating was removed by a predetermined width along the cutting line using a polishing machine such as a grinder. However, this polishing work and the repair work of the primer after cutting required a lot of labor, and problems still remained.

In addition, as an alternative to the conventional method, as shown in Figure 1, a torch 2 for destroying the primer coating is installed in advance of the torch 1 for cutting steel materials, and the primer coating is burnt and carbonized in advance to eliminate its effect. A method was also adopted in which the material was cleaned and then cut. According to this method, the effect of the scattering of primer components is certainly reduced, but it is necessary to operate the torch 2 for destroying the primer coating film in a place where the equipment required for the original cutting, flammable gas, and oxygen are present. The disadvantage of this method is that it costs nearly twice as much for equipment and gas fees as compared to a single torch, and no fundamental solution has been reached. In addition, the so-called heat-affected zone 4, which is the area where the primer coating is burned and carbonized, spans a wide area centered on the cutting line 3, and after cutting, it takes a lot of effort to repair the primer that has been burnt out due to the heat effect. There was no change.

(Structure of the Invention) As a result of research in view of the above points, the present inventor has
We discovered a method that allows stable cutting work without removing the primer coating beforehand.
The present invention has been accomplished.

The gist is that when gas cutting a steel plate coated with a primer, magnesium carbonate is applied to the surface of the part to be cut in advance, and then gas cutting is performed.

Note that the cutting device itself is a commonly used one.

Here, a specific method for adhering magnesium carbonate to the surface of the material to be cut is to suspend magnesium carbonate powder in water and spray it with a mist or apply it with a brush. In addition, in order to quickly adhere to the steel surface and dry it, a volatile solvent is used instead of water, and magnesium carbonate is suspended or dissolved in the solvent.
This may be applied by brushing.

Note that if this suspension or solution is filled into a spray can and used, the workability of application will be further improved.

The width over which the magnesium carbonate suspension is applied varies depending on the thickness of the material to be cut 5, but it is preferably about 100 mm along the cutting line 3.

(Operation of the invention) Next, how magnesium carbonate acts during cutting work will be explained.

Magnesium carbonate adhering to the upper surface of the primer coated on the steel surface prevents the carbonization reaction of the metallic zinc powder, which is a component of the primer, and suppresses the occurrence of fireworks. That is, the magnesium carbonate is thermally decomposed by the flame of the cutting torch to form a fire-resistant magnesium oxide film. This film protects the anti-rust primer paint around the torch from high-temperature flames, so there is no need to repaint the primer even after cutting. Furthermore, the magnesium oxide coating has the effect of suppressing the scattering of metallic zinc powder and molten metal.

Note that the magnesium oxide coating is an inorganic substance, and does not exhibit the phenomenon of burning after cutting, unlike conventional organic spatter inhibitors. That is, after cutting, the magnesium carbonate remains on the surface of the steel material in the form of ash-like magnesium oxide powder, and it is extremely easy to peel and clean it from the surface. It can be removed by wiping it with a cloth or by rubbing it lightly with a brush.

(Effects of the Invention) As described in detail above, the present invention is such that magnesium carbonate is preliminarily deposited with a predetermined width along the cutting line 3 on the surface of the material 5 to be cut, and then gas cutting is performed. This prevents spatter from scattering during gas cutting, and the magnesium carbonate oxide forms a fire-resistant film to minimize the heat-affected zone on the primer coating, reducing the amount of primer repair after cutting. This reduces the amount of labor required for cutting and repair work.
In addition, since there is little adhesion of the sputter to the torch nozzle, a stable cutting flame flow 7 can be obtained at all times.
Inevitably, the cut end surface of the material to be cut 5 is uniform, sharp, and accurate machining can be performed, resulting in excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a perspective view illustrating a conventional cutting method, that is, a cutting method using a cutting torch 1 and a torch 2 for destroying the primer coating film. In the method of the present invention, the torch 2 for destroying the primer coating becomes unnecessary. 1... Torch for cutting steel materials, 2... Torch for destroying primer coating film, 3... Cutting line, 4... Heat affected zone, 5... Material to be cut, 6... Automatic gas cutting device,
7... Cutting flame flow, 8... Guide rail.

Claims (1)

[Claims] 1. A method for gas cutting a primer-coated steel plate, which is characterized in that, when gas-cutting a steel plate coated with a primer, magnesium carbonate is preliminarily applied to the surface of the part to be cut, and then gas cutting is performed.