JPH0219877B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for cold rolling a dense hexagonal metal plate, and more particularly to a method for producing the same metal plate with good productivity and almost no oil pits and a good surface quality. The close-packed hexagonal metal sheet to be subjected to cold rolling in the present invention is a general term for metal sheets having a close-packed hexagonal crystal structure, such as Ti, Ti alloy, Zr, and Zr alloy. In the cold rolling of metal plates, it is essential to use rolling oil to prevent seizure, but on the other hand, if too much rolling oil is supplied, fluid lubrication will occur between the rolling rolls and the material to be rolled, and high-pressure rolling oil will cause It is known that unevenness (so-called oil pits) occurs on the free surface of the rolled material in contact with it. In particular, in metals such as the dense hexagonal metals, which have significantly different deformation resistance depending on the crystal orientation,
Since crystals in orientations with low deformation resistance are easily deformed, oil pits are likely to occur; for example, in cold-rolled Ti plates, it is not uncommon for the pits to reach a depth of more than ten microns. Since these oil pits significantly impede the surface precision of the final product, how to reduce the size of the oil pits generated during the rolling process is an important issue in cold rolling of this type of difficult-to-work metal sheet. . The allowable limit for this oil pit varies depending on the required surface accuracy depending on the product's use, but the depth is 1 to 1.
It is often required that the thickness be 2 μm or less. By the way, as mentioned above, oil pits are thought to be caused by an excessive amount of lubricating oil intervening between the rolls and the rolled material, and it is necessary to minimize the amount of lubricating oil drawn in and make it uniform. If this is possible, it is believed that the oil pit can be made as shallow as possible. However, in this case, if the oil film runs out during rolling, a seizure problem will occur, so
When rolling metal plates such as Ti, Zr, or their alloys, which are prone to seizure, it is extremely important to uniformly apply the minimum amount of oil to the entire surface of the plate. However, with conventional lubricants, if an amount of lubricant that does not cause seizure occurs, oil pits will occur, whereas if the lubricant supply amount is reduced to the extent that oil pits do not occur, the oil film will run out and the problem of seizure will occur. occurs, and the above 2
It was not possible to solve two problems at the same time. The present inventors focused on these circumstances, and aimed to solve two problems simultaneously: occurrence of oil pits due to excessive supply of lubricant and occurrence of seizure due to lack of oil film of lubricant, targeting dense hexagonal metal plates. In an effort to establish a cold rolling method that would enable this, various studies have been carried out focusing on the particle size, saponification value, rolling speed, etc. of emulsion lubricants. The present invention was completed as a result of such research, and its composition uses an emulsion type lubricant containing an oily dispersoid with a center particle size of 6 μm or less and a saponification value of 80 or more, and has a dense hexagonal crystal structure. The gist is that a metal plate is cold rolled. In the present invention, as mentioned above, the particle size and saponification value of the dispersoid constituting the emulsion type lubricant are strictly specified, and the reason for this is as detailed below. That is, according to the inventors' various preliminary experiments, the lubricating performance of emulsion-type lubricating oil is determined not only by the emulsion concentration but also by
Since we obtained the knowledge that ``dispersoids are significantly affected by the saponification value and particle size,'' we proceeded with research to clarify these points quantitatively. And an emulsion type lubricant (concentration 1% or 0.5%) that uses various tallow oils with different saponification values as dispersants.
and conducted rolling experiments using each lubricant.
Reduction rate [εi=ln(ho/hi)] and average rolling pressure (Pm)
We investigated the relationship between However, the rolling conditions were as follows: a work roll diameter of 254 mm, a rolling speed of 12 m/min, a reduction rate of 10% per pass, and a pure titanium plate with a thickness of 1.0 mm was rolled to a thickness of 0.5 mm. The result is the first
As shown in the figure, the tendency for the average rolling power to increase as the rolling reduction rate increases varies markedly depending on the saponification value of tallow-based oil. It is thought that the pressure will increase rapidly and rolling operations will become virtually difficult. The higher the saponification value of tallow-based oil is, the smaller the tendency for the rolling pressure to increase will be. In this case, the rolling pressure becomes too high, making actual operation difficult. For products using tallow-based oil with a rating of 80 or higher, the above-mentioned increasing trend becomes relatively slow, and the average rolling pressure is approximately 170.
The average rolling pressure reaches a plateau below about Kg/ ^mm2 , and even if the reduction rate is increased, the average rolling pressure will not increase any further. As is clear from these results, in order to suppress the threading resistance during rolling and smoothly perform cold threading, the oil-based dispersoid that makes up the emulsion-type lubricant must have a saponification value of 80 or more. It turns out that you should choose one. Next, the following experiment was conducted to clarify the influence of the particle size and concentration of the oily dispersoid on the lubricating performance. However, the central particle size of the oil-based dispersoid referred to in the present invention refers to the particle size at the peak position in the emulsion particle size distribution as shown in Figure 2, for example, and the particle size distribution is measured using a Coulter counter (using a 50 μm aperture tube). Measured by In the experiment, tallow-based oil (saponification value: 185) was used as the oil-based dispersoid, and emulsion-type lubricants with different central particle diameters and concentrations of the dispersoid were prepared.
Ti plate (crystal grain size:
The oil pit depth was compared with the rolled sheet when cold rolling was performed by changing the sheet passing speed (approximately 5 μm). The results are shown in Table 1, and when using an emulsion-type lubricant in which the center particle size of the dispersoid is 6 μm or less, the oil pit depth can be kept to 1 to 2 μm or less regardless of the emulsion concentration or rolling speed. can. On the other hand, when using an emulsion type lubricant with a center particle size exceeding 10 μm, the rolling speed can be reduced.
Even if the speed is reduced to 50m/min, the oil pit cannot be made smaller. Also, the center particle size is 6~
When using a 10 μm emulsion lubricant, oil pits can be kept to a small level at low rolling speeds, but at speeds of 200 m/min or higher, which are used in actual cold rolling, oil pits become extremely deep. Become. When using an emulsion type lubricant with a center particle size of 6 μm or less,
The oil pit depth reaches a nearly saturated state at a rolling speed of 200 m/min, and the oil pit does not become deeper even if the rolling speed is increased beyond that. In other words, by using an emulsion-type lubricant that satisfies the specified requirements of the present invention, the oil pit depth can be made extremely small regardless of the rolling speed, and the oil pit depth can be made sufficiently small to meet the demand for improved productivity due to increased rolling speed. I can go. Figures 3 and 4 are micrographs (both magnified at 400x) showing the surface properties of Ti rolled plates.
When using an emulsion type lubricant with a diameter of 10 μm and a concentration of 2% (comparative example), Fig. 4 shows an emulsion type lubricant with a center particle size of 2 to 3 μm and a concentration of 2% using tallow-based oil as the dispersoid. When (example of the present invention)
are shown respectively. As is clear from a comparison of these photographs, oil pits formed on the surface of a rolled plate when using an emulsion type lubricant with a large center particle size are extremely noticeable (Figure 3), but oil pits that meet the specified conditions of the present invention are When a marsion lubricant with a small particle size is used, the number of oil pits is much smaller and the depth is as shallow as 1 to 2 μm (Figure 4).

【table】

[Table] Another criterion for determining the particle size structure of emulsion is to divide particles with a specific particle size as a boundary and divide them into particles with a content exceeding that particle size and particles with a content below that particle size, and calculate their content ratio ( Volume ratio: EDPI:Emu1−sion
One possible method is to compare using the distribution profile index (Distribution Profile Index). Therefore, the present inventors conducted the following experiment in order to clarify a suitable particle size configuration based on such judgment factors. That is, based on 6 μm, where the amount and depth of oil pits that occur suddenly change, we prepared various emulsion-type lubricants with different ratios of [(content rate of oil pits exceeding 6 μm)/(content rate of oil pits below 6 μm)].
A Ti plate was cold rolled using each lubricant (rolling speed: 200 m/min, emulsion concentration: 1
%, rolling roll: #320 emery polishing roll, 200
mmφ), the relationship between the depth of oil pits formed on the surface of the rolled plate and the above ratio was investigated. The results are shown in Figure 5 [The numbers in parentheses in the figure indicate the central grain size]
As shown in Figure 2, when the ratio exceeds 1, the oil pit tends to become deeper rapidly.
If it is less than 1, the oil pit depth can be kept to 1 to 2 μm or less. In this way, it is also meaningful to employ the above ratio as a determining factor for emulsion type lubricants. As described above, in the present invention, the saponification value and central particle size of the oil-based dispersoid are strictly defined in order to achieve the object, but other requirements are not particularly special. For example, the concentration of emulsion type lubricants is almost the same as the preferred concentration of conventionally known emulsion type lubricants, 0.5 to 10%, more preferably 0.5%.
~5% range. Furthermore, in the above explanation, an example was given in which the most common tallow-based oil is used as the oil-based dispersoid, but the oil-based dispersoid is not limited to tallow-based oil as long as it has the above-mentioned preferred saponification value.
Of course, it is also possible to use other fats and oils, fatty acids, etc. (specifically natural fats and oils such as palm oil and lard oil, synthetic fatty acids such as dimer acid, etc.). Furthermore, the method for producing an emulsion lubricant having the above-mentioned center particle size is not particularly limited. )
By adding this to oil, the oil particles are surrounded by water, creating an emulsion in which the oil particles are uniformly dispersed in water. The desired emulsion particle size can be obtained by changing the type and amount of the emulsifier and by appropriately selecting the stirring conditions after forming the emulsion. The present invention is constructed as described above, and its effects can be summarized as follows. Since oil-based lubricants have a high saponification value and good affinity with metals, they tend to form a thin oil film on the surface of the workpiece. Therefore, together with the fine central grain size, it is possible to reliably form a homogeneous, ultra-thin oil film at the bit part of the rolling roll, and the occurrence of oil pits due to excess lubricant can be suppressed as much as possible. Moreover, since the oil film is less likely to run out, seizure phenomena are less likely to occur, and the cold rolling of dense hexagonal metal plates can be carried out without any problems. As shown in Table 1 above, even if the rolling speed is increased, the oil pits remain shallow, and seizing is less likely to occur with high-speed rolling, so cold-rolled sheets with good surface accuracy are produced. It can be easily manufactured. In cold rolling of Ti plates, etc., in order to prevent oil pits, the diameter of the rolling rolls is made as small as possible to narrow the bite area, as disclosed in Japanese Patent Application Laid-open No. 56-165502. However, if an emulsion lubricant that satisfies the specified conditions of the present invention is used, it is possible to use rolling rolls with a considerably large diameter. Even if it is adopted, cold rolling can be performed without any problem, and it can contribute to improving productivity.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between rolling reduction [εi = ln [ho/hi]] and average rolling pressure (Pm) when tallow-based emulsion lubricants with different concentrations and saponification values are used. Figures 3 and 4 are diagrams to explain the meaning of the central grain size.
FIG. 5, which is a micrograph used as a drawing to show the surface properties of the plate, is a graph showing the influence of the content ratio of oil particles having a size around 6 μm on the oil pit depth.

Claims (1)

[Claims] 1. A method for cold rolling a dense hexagonal metal sheet, characterized by using an emulsion type lubricant containing an oily dispersoid with a center particle size of 6 μm or less and a saponification value of 80 or more.