JPS5919009A - Mandrel mill mandrel bar lubrication treatment method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for lubricating hot working tools such as mandrel bars in mandrel mills.

In hot working of steel such as carbon steel, alloy steel, or stainless steel, it is used to reduce the frictional force generated during relative upward movement at the contact surface between the tool and the steel, seizure of the steel on the tool surface, tool wear, etc. It is extremely important to apply lubricant to the tool.

The type and application method of this lubricant vary depending on the processing method, but it is used in mandrel mill rolling (including full float method and retaining mandrel rolling method) in the hot working process of seamless steel pipes. The following explanation will be continued focusing on the case of lubrication.

In the mandrel mill rolling method, after a long mandrel bar is inserted into a hot perforated hollow shell, it is passed through a continuous rolling mill equipped with multiple stands with 2-high grooved rolls, and the rolling process is regulated by pars and grooved rolls. Thickness reduction processing is performed to the specified dimensions. However, lubricants are applied to the surface of the mandrel par, and the lubricants include liquid lubricants such as oil and solid lubricants such as graphite and molybdenum disulfide (MO82). Since the former has poor high temperature heat resistance, the latter is usually used. There are still three methods for attaching the latter graphite etc. to the mandrel bar. (1) If oil is not present, apply a mixture of heavy oil and graphite powder. (2) Apply a mixture of graphite in water or an aqueous solution containing an adhesion activator. (3) Graphite powder is mixed into an aqueous solution containing a quick-drying glue made of various water-soluble chemical conversion polymers, and after application the temperature of the mandrel bar (100 to 2
00°C) to dry the moisture and form a graphite' layer.

Among these methods, methods (1) and (2) are unstable in the amount of graphite per surface area, and the coating solution drips from the mandrel bar and contaminates the water in the factory. In addition, method (1) has the problem of generating black smoke.

Therefore, in recent years, method (3) has been gradually adopted.
According to the same law, quick-drying glue works effectively and graphite
It has the advantages of being able to easily control the amount (thickness) of each coat and generating less graphite.

However, even if a lubricant is applied using method (3), the steel surface [[
(Sufficient results cannot be obtained due to the scale of occurrence.

The inner surface of the hollow shell given to the mandrel mill is
A scale of 20/1 to 50μ is attached in a compacted state. A mandrel bar coated with graphite lubricant is inserted into this hollow shell, and the inner surface of the hollow shell is stretched according to the amount of stretching of the steel. It is plastically stretched in the longitudinal direction while being subjected to compressive stress in the radial direction. At this time, according to the findings of the present inventors, the scale deposited uniformly on the hollow shell is not stretched on the surface of the hollow shell in the same way as plastic stretching of steel; It became clear that the distribution was fragmented in different directions. It is as if bricks were roughly placed on the inner surface of the steel.

On the other hand, the graphite coated and fixed on the mandrel, as shown schematically in Figure 1, is torn off into brick-like pieces from the base metal of the hollow shell, and the coarsely distributed scale lumps 2 are It acts as if it were the surface of a file or the abrasive grains of a single whetstone, scraping the graphite 4 from the surface of the mandrel par 3, and conversely, the scraped graphite 4 fills the spaces between the scale lumps 2 and scrapes the graphite 4 from the surface of the bare metal of the hollow shell 1. It is thought that it will be dislocated to. As a result, the amount of graphite remaining on the surface of the mandrel bar becomes extremely small. In fact, experiments have shown that even when applying the method (3) above on a mandrel par with varying amounts of graphite adhesion within a thickness range of 10μ to 50μ, the amount of residual graphite is extremely small in each case. It is clear from Thus, if the amount of graphite is small compared to the amount of scale 1, the graphite will fall between the divided scale lumps and only the scale will be in contact with the armand lever with the tool. 9. The friction coefficient of the contact surface increases, and the scale accelerates the wear of the mandrel bar.

Therefore, one way to solve this problem is to increase the amount of graphite deposited. That is, when we investigated the relationship between various lubrication conditions and friction coefficients, we obtained the results shown in Table 1. The experiment was conducted using a stand model mandrel mill, with main pipe dimensions: 127φ x 18t (low carbon steel) rolled at a rolling temperature of 10
It was rolled at 70° C. and finished to a size of 114φX]3.87t (mandrel size of 86.26φ) (the unit of dimension is 0, the same applies hereinafter).

According to the results in Table 1, it can be seen that when the amount of graphite is 100 μm thick, the lubricity is considerably improved.

However, the use of large amounts of graphite is not only uneconomical, but graphite does not originally have completely plastic properties, and during the rolling process, it is distributed in lumps (drifts) and forms on the inner surface of the workpiece. It causes dents, which is undesirable.

In view of the above-mentioned conventional problems, it is an object of the present invention to provide a lubrication treatment method that can bring out the excellent lubrication performance originally possessed by solid lubricants even when the amount of solid lubricant used is minimal. That is.

That is, the lubrication treatment method for hot working tools of the present invention is as follows:
A first lubricant based on a solid lubricant that is difficult to flow during hot working is applied to the tool surface, and the surface of the first lubricant layer is coated with a first lubricant that has better fluidity than the first lubricant during hot working. In addition, a second lubricant that does not burn instantly is applied.

The first lubricant in the present invention is a solid lubricant that has a non-removal property even in the hot working temperature range of 800°C to 1150°C and even when applied external force, such as graphite or molybdenum disulfide MoS2. It is used either alone or with some additives added. As a method for applying the first lubricant, a spray method, particularly a high-pressure spray method, is generally used, but a dipping method, a roller transfer method, etc. can also be used instead.

Further, the coating thickness is preferably 10 to 150μ, preferably 20 to 50μ, because if it is less than 10μ, there is no lubrication effect, and if it exceeds 150μ, it will cause the same problems as in the conventional example. .

On the other hand, as the second lubricant, one is used that has better fluidity than the first lubricant during hot working, and a lubricant that burns off instantly in the working temperature range is avoided. Examples include inorganic substances such as common salt, rock salt, fine grains of borax, and fine grains of boric acid, or organic substances such as beef tallow or palm oil.

Furthermore, natural fats and oils such as heavy oil, Na+'Ca stearate, etc.
etc. can also be used.

Of these, beef tallow is the best example. As for the application method, the oil-based lubricant is used as it is, and the solid-based lubricant is mixed into a finely ground viscous solution and applied by a spray method.

The coating thickness varies from 5μ to 100μ depending on the amount of scale.
μ is preferable; if it is less than 5μ, the same result as the first lubricant alone will result, and if it exceeds 1ooμ, it is not economical.

By the way, it has been conventional practice to apply a mixture of the second lubricant and the first lubricant, but in this case, the mixture falls between the scale lumps and the mixture of the first lubricant, such as graphite, is mixed. Effective lubricity cannot be expected, and since the solid lubricant still lacks fluidity, the mixture cannot sufficiently fill in the spaces between scale lumps.

The present invention employs a two-layer coating method of a first lubricant and a second lubricant. As a result, during rolling, the behavior shown in FIG. 2 is exhibited. That is, the second lubricant 5 fills in between the divided scale lumps 2, and the first lubricant 4 does not fall between the divided scale lumps 2, but is interposed between the mandrel bar 3 and the scale lumps 2. It exhibits its original lubrication performance.

In order to confirm the effects of the present invention, a Bowden friction test (to determine the friction coefficient after 50 frictions) was conducted at 40°C. The results were as shown in Table 2.

Table 2 From the results, it was found that the method of the present invention was effective, so a test was subsequently conducted using an actual machine where scale was generated. The rolling mill is an 8-stand mill, main tube dimensions: 147φ x 1
4ot (low carbon steel), rolling dimension = 123φX 4. Ot
(mandrel size: 110φ) and rolling temperature: 950°C. The results were as shown in Table 3.

The coefficient of friction in Table 3 was calculated by measuring the rolling load and also measuring the holding force applied to the holding device of the mandrel bar, and dividing the former value by the latter value.

Further, Table 4 shows the results of similar tests conducted using different types of first and second lubricants.

Table 4 Note that the present invention is naturally applicable to the lubrication of not only mandrel bars but also plugs of plug mills, various guide shoes, molds of hot forging presses, and the like.

As described above, according to the present invention, excellent lubrication performance can be exhibited even with a small amount of solid lubricant used.
It is possible to reliably achieve prevention of seizure and tool wear.

[Brief explanation of drawings]

Figure 1 is a microscopic diagram showing the behavior of a conventional lubricant.
FIG. 2 is a microscopic schematic diagram showing the behavior of a lubricant treated by the method of the present invention. 1... Hollow Enoy workpiece material) 2... Scale lump 3... Mandrel bar (tool) 4... Graphite or first lubricant 5... Second lubricant

Claims (1)

[Claims] (1) A first lubricant based on a solid lubricant that is difficult to flow during hot working is applied to the tool surface, and the surface of the first lubricant layer is coated with a first lubricant that flows more than the first lubricant during hot working. A method for lubricating a tool for hot working, characterized by applying a second lubricant that has excellent properties and does not burn instantly.