JPH08218087A - Lubricant for hot rolling of stainless steel excellent in nozzle clogging resistance - Google Patents

Abstract

PURPOSE: To obtain a lubricant without causing trouble in clogging of a nozzle in jetting the lubricant for preventing the roll seizure in hot rolling of stainless steel on a roll during the rolling. CONSTITUTION: This lubricant for hot rolling of stainless steel excellent in resistance to nozzle clogging is obtained by using particles having <=50μm particle diameter as particles of the lubricant and suppressing the particle diameter of flocs produced in a dispersion to <=100μm in the lubricant for hot rolling of stainless steel containing 10-30wt.% particles of the lubricant dispersed in a viscous aqueous solution.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a lubricant for hot rolling of stainless steel. More specifically, during hot rolling of stainless steel, it prevents nozzle closing trouble when supplying a dispersion liquid of a solid lubricant from a nozzle between a material to be rolled and a rolling roll, and has a good surface property. The present invention relates to a stainless steel hot rolling lubricant suitable for obtaining a stainless steel plate product.

[0002]

2. Description of the Related Art In hot rolling equipment such as a tandem mill, when stainless steel, especially ferritic stainless steel, is hot-rolled, flaws easily occur on the surface of the steel sheet due to seizure of the stainless steel on a rolling roll. Once surface flaws occur, even minor flaws are unsuitable for mirror finishing applications and are subject to restrictions. In addition, a stainless steel plate having a surface flaw needs to be polished for surface maintenance or pickled again. If the degree of flaw is remarkable, it cannot be used as a product and is scrapped. Therefore, flaws on the surface of the steel sheet caused by seizure on the hot-rolled rolls cause a decrease in product yield and an increase in the number of process days, resulting in an increase in product cost.

In order to suppress the occurrence of the above-mentioned surface defects, various measures such as taking measures to reduce the load on the rolling rolls, selecting the rolling conditions, selecting the roll material, and improving the lubricant have been tried. Has been. Among them, as the lubricant, a method of supplying various oil-based lubricants such as animal oils, vegetable oils, mineral lubricating oils or synthetic lubricating oils to the surface of the rolling roll has been studied. In addition, a method of dispersing and mixing powder having lubricity in rolling oil and injecting it into the surface of the rolling roll by an injection method using a nozzle is also being studied.

However, in these supply methods using nozzles, the nozzle nozzle holes are unavoidably blocked during long-term use, and surface defects occur due to the extension of the nozzle replacement work time before rolling and the nozzle blockage during rolling. There is a problem.

Therefore, the inventors of the present invention disclosed in Japanese Patent Laid-Open No. 64-833.
No. 09 and its related applications proposed a lubricant for hot rolling of stainless steel in which iron oxide was dispersed in a viscous aqueous solution. This lubricant has advantages that the above-mentioned ones do not have, in that the liquid-feeding property is good and the iron oxide particles are uniformly dispersed.

[0006]

However, JP-A-64-
The lubricant in which iron oxide is dispersed in a viscous aqueous solution, which has been proposed elsewhere, can be uniformly dispersed immediately after the iron oxide powder is mixed in the aqueous solution, but when the lubricant is stored for a long time, it is oxidized in the storage tank. In some cases, the iron powder settled and stable retention of the iron oxide powder could not be obtained. If the dispersion holding is unstable, the iron oxide powder cannot be stably supplied to the surface of the rolling roll during hot rolling. It was also clarified that it causes nozzle clogging, and iron oxide accumulates on the joints of the guide tube that supplies the lubricant, causing problems such as clogging of the tube and insufficient supply of the lubricant.

Therefore, in the present invention, when a lubricant dispersion liquid obtained by dispersing lubricant particles in a viscous aqueous solution is jetted by a nozzle, it is improved so that the nozzle is not clogged during rolling and before and after rolling. The purpose of this is to eliminate nozzle replacement work, and to obtain a stainless steel hot-rolling lubricant suitable for obtaining products with good surface properties even for rolled steel strips. is there.

[0008]

According to the present invention, a lubricant for stainless steel hot rolling, comprising 10 to 30% by weight of lubricant particles dispersed in a viscous aqueous solution, is used as the lubricant particles. Disclosed is a lubricant for hot rolling of stainless steel, which is excellent in nozzle clogging resistance and is characterized in that particles having a diameter of 50 μm or less are used and the particle size of flocs generated in a dispersion is suppressed to 100 μm or less.

[0009]

[Function] As lubricant particles dispersed in a viscous aqueous solution,
If the particle size exceeds 50 μm, the particle size will be 10
Flocs exceeding 0 μm are easily formed. The term “flock” as used herein refers to a state in which lubricant particles are favorably dispersed and suspended in a viscous aqueous solution, but the particles attract each other for some reason and are adjacent to each other. It is said to be in the state of being dispersed and suspended in.

It has been found that there is a close relationship between the size of this floc and the nozzle clogging property. Even if the dispersed state is good, if the flocs having a particle size of more than 100 μm are dispersed, nozzle clogging is likely to occur. Therefore, to prevent nozzle clogging, it is important to control the particle size of flocs generated in the dispersion liquid. In order to reduce the floc particle size to 100 μm or less, the individual lubricant particles (also referred to as solid lubricant) dispersed in a viscous aqueous solution should be 50 μm.
That is, that is, substantially no particles exceeding 50 μm are present. As shown in the examples below,
If there are particles over 50 μm in the particle size distribution,
The particle size of the generated flocs also exceeds 100 μm.

The generation behavior of flocs varies depending on the type of thickener used to make a viscous aqueous solution, the type and form of the solid lubricant used, and the particle size distribution thereof. First of all, it is important to use a solid lubricant having a particle size not exceeding 50 μm. If necessary, a flocculant may be added by adding a dispersant such as a surfactant or a fluidizing agent. Suppress the generation of.

[Detailed Description of the Invention] The structure and action of the lubricant of the present invention will be specifically described below. In the following description, the lubricant particles dispersed in the viscous aqueous solution will be referred to as "solid lubricant". Further, when simply referred to as “lubricant”, it means a state after the solid lubricant is dispersed in the viscous aqueous solution.
The size of the flocs in the lubricant is called the "dispersed particle size."

In order to prevent nozzle clogging, the present inventors have
After investigating the actual condition of nozzle clogging and studying the sedimentation / aggregation behavior of the lubricant, the dispersed particle size when a solid lubricant was dispersed in a highly viscous aqueous solution greatly affected the nozzle clogging property, and the roll seizure occurred. Was also an important cause. That is, when the dispersed particle size in the lubricant becomes large, the solid lubricant accumulates in the nozzle tip hole, and this is dried and agglomerated by the radiant heat of the material to be rolled while waiting for rolling. Therefore, the dispersed particle size and soft agglomerate size must be smaller than the hole diameter of the filter part attached to the nozzle or the tip of the nozzle. For this purpose, it is most important to make the dispersed particle size of the solid lubricant in the viscous aqueous solution fine.

[Dispersed Particle Diameter in Lubricant] The dispersed particle diameter in the lubricant is a very important control point for nozzle sprayability and uniform sprayability on the roll surface. The smaller the dispersed particle size in the lubricant, the less likely nozzle clogging will occur. The larger the particle size of the solid lubricant, the larger the dispersed particle size in the lubricant, and the larger the particle size of the solid lubricant powder itself.

Generally, when the particles of the solid lubricant are less than 0.1 μm, they are aggregated or flocculated by Brownian motion and secondary aggregated. Also, when the particle size distribution is wide, it may be adsorbed and aggregated on relatively large particles. Therefore, the average particle size of the solid lubricant is 1 μm or less,
It is preferably 0.2 μm or more. That is, as shown in Example 1 described later, when the maximum particle size of the solid lubricant particles exceeds 50 μm, the maximum dispersed particle size of the lubricant also becomes 100 μm.
And the sedimentation also occurs. Therefore, to prevent sedimentation, that is, to prevent nozzle clogging and pipe clogging, all solid lubricant particles should be 50 μm or less, preferably 10 μm or less, and the particle size distribution should be 0.2 to 1 μm.
It is preferable that the degree of particles exceeds 50%.

By using a solid lubricant having such a particle size, the dispersed particle size in the lubricant can be made small. However, when the dispersed particle size exceeds 100 μm, as described above, the joint portion of the conduit, etc. It is easy for sedimentation and deposition to occur, and pipe clogging and nozzle clogging occur.
The thickness is less than or equal to μm, and more preferably less than or equal to 40 μm.

If necessary, an ultrasonic vibration device may be used, or an ordinary dispersant such as sodium pyrophosphate may be added in an appropriate amount so that the dispersed particle size does not exceed 100 μm.

[Type of Solid Lubricant] The solid lubricant to be dispersed in the viscous aqueous solution may be of any type as long as it has a seizure prevention function in hot rolling of stainless steel. For industrial use,
Further, considering that it is used for rolling stainless steel and treated with waste water, an iron-based solid lubricant is preferable.

FeO (OH), Fe as the iron-based substance
(OH) ₂ , Fe (OH) ₃ , FeO, Fe ₂ O ₃ , Fe ₃
Although O _{4 and the} like can be mentioned, Fe ₂ O ₃ has a high hardness and adversely affects wear of rolls, wear of nozzle holes, and the like. FeO
Is difficult to obtain industrially stable. Also Fe (O
H) ₂ and Fe (OH) ₃ are industrially unusable because they can exist during the process of producing FeO (OH). Regarding hardness, Fe ₃ O ₄ >FeO> FeO
Soft in the order of (OH). For these reasons, FeO (OH) is most preferable and practical among the iron-based solid lubricants.

[Compounding Amount of Solid Lubricant] The blending amount of the solid lubricant in the lubricant is limited in order to obtain stable nozzle jetting property and pipe liquid feeding property. When the content exceeds 30% by weight, an apparent viscosity increase is caused, an excessive discharge energy is required for spraying and supplying to the rolling rolls, and nozzle clogging practically occurs. If the amount of the thickener is reduced in order to suppress this increase in viscosity, the dispersed particle size of the solid lubricant becomes large, and the retention stability deteriorates, causing clogging in the liquid delivery pipe. And the increase of the content is also disadvantageous in terms of cost.
On the other hand, if the content of the solid lubricant is less than 10% by weight, a stable seizure preventing effect cannot be obtained. Therefore, the content of the solid lubricant needs to be 10 to 30% by weight.

[Viscous Aqueous Solution] The lubricant of the present invention is one in which a solid lubricant is dispersed in a viscous aqueous solution, and the viscous aqueous solution is used as a medium. This viscous aqueous solution is obtained by adding a thickener to water. Although various types of thickeners can be used, as shown in the examples below, polyacrylic acid type ones such as cross-linked acrylic acid polymer, polyacrylic acid soda, cellulose derivatives, etc. A thickening agent can be used, and the viscosity of the lubricant after compounding the solid lubricant is preferably about 1 × 10 ^{3 to} 5 × 10 ⁵ centipoise.

[Aspect of Use of Lubricant] When performing hot rolling of stainless steel using the lubricant according to the present invention, the lubricant of the present invention obtained by mixing water, a thickener and a solid lubricant is It is stored in a tank and is pumped from this tank to a nozzle near the rolling rolls through a conduit. The pump to be used may be appropriately selected, but since the viscosity is higher than that of simple water, a pressure of several tens of kgf / cm ² or more is usually required, and a plunger type pump or the like is suitable. The lubricant delivered by the conduit is sprayed from the nozzle at the tip to the roll in the rolling stand.

The rolling stand using this lubricant is not particularly limited, and is appropriately selected from a rough rolling stand and a finishing rolling stand in a hot strip mill. The position of the rolling roll on which the lubricant is sprayed may be appropriately selected in consideration of the degree of its effect. This lubricant may be sprayed over the entire width in contact with the rolled material, and seizure is relatively likely to occur due to the remarkable peeling of the oxide scale in the plastic deformation behavior in the widthwise rolling during rough rolling. It may be selectively sprayed in the vicinity of the rolled material edge portion.

The amount of the lubricant supplied to the rolling rolls is
By selecting the delivery pressure and the nozzle at the tip of the conduit,
It can be adjusted while taking into consideration the speed of the rolling roll and the like. At this time, the amount of the lubricant is preferably about 0.1 liter / m ² to several liters / m ^{2 with} respect to the area where the rolling roll contacts the rolled material. Although normal rolling lubricant may be used in hot rolling of stainless steel, the use of the lubricant according to the present invention does not prevent the lubricant from being used in combination, so that the rolling load can be reduced. Lubricating oil may be used together for the purpose.

[0025]

【Example】

[Example 1] As a solid lubricant, FeO (OH) powder having five kinds of particle size distribution shown in Table 1 was used, and as a thickener, a cross-linked acrylic acid polymer (Nippon Pure Chemical Co., Ltd.) was used. The lubricants of A to E in Table 1 were prepared using the product name Junron. Solid lubricant concentration is 10% by weight
The thickener was added in an amount of about 0.15% by weight so that the viscosity of the lubricant was 3000 centipoise. Solid lubricant,
The mixing time of water and the thickener is 30 minutes.

The dispersed particle size (average particle size and maximum particle size) of each of the obtained lubricants A to E was measured by a laser diffraction / scattering type particle size distribution measuring device. In addition, the sedimentation degree of each lubricant (volume of separated water / percentage of total volume) was determined by measuring the volume of water separated after mixing with the lubricant. The results are also shown in Table 1.

[0027]

[Table 1]

As shown in Table 1, the lubricants were produced under the same conditions except for the particle size distribution, but the dispersed particle size was different. That is, if solid lubricant particles exceeding 50 μm are present, the maximum dispersed particle size is 100 μm.
Will be exceeded. The larger the dispersed particle size, the greater the degree of sedimentation. Since the lubricants A and B do not have a solid lubricant exceeding 50 μm, the dispersed particle size is 100 μm or less and the sedimentation degree is low. Therefore, it is preferable as the lubricant of the present invention. From this example, to prevent nozzle blockage and pipe clogging,
All solid lubricant particles are less than 50 μm, preferably 1
It can be seen that the thickness needs to be 0 μm or less.

Example 2 In preparing a lubricant, first, a predetermined amount of a solid lubricant was added to water while stirring to obtain a suspension of the solid lubricant, and a suspension of the predetermined thickener was added to the suspension. After mixing and stirring, caustic soda was added to adjust to PH7. Table 2 shows the types of solid lubricants used, their contents and types of thickeners. As the thickener, a cross-linked acrylic acid polymer (trade name Junron manufactured by Nippon Pure Chemical Co., Ltd.), sodium polyacrylate (trade name Rheogic manufactured by Nippon Pure Chemical Co., Ltd.), and a water-soluble cellulose derivative (Shin-Etsu Chemical) The product name Metroze manufactured by Co., Ltd. was used. The maximum dispersed particle diameter of each obtained lubricant was measured in the same manner as in Example 1, and the results are shown in Table 2.

These lubricants were applied to actual stainless steel rolling. In hot rolling, first, a SUS430 stainless steel slab is heated to 1200 to 1250 ° C., rough-rolled into a rough bar having a thickness of 25 mm by a rough rolling mill, and then 7
With a finishing rolling mill group consisting of stands, a thickness of 3.0 mm
Rolled into a hot coil. In these, after changing the work rolls of the finishing rolling mill group (replacement with grinding-finished rolls), 20 slabs were continuously hot-rolled with the same work rolls, and one cycle of these 20 slabs was performed. The lubrication conditions were constant between the two.

The lubricant is supplied to the first to the last rolling mill groups.
A lubricant supply system was installed on the three-stand work rolls, and the lubricant was sprayed onto the rolls from five nozzles at the top and bottom respectively. To each nozzle, a lubricant was sent from a lubricant storage tank through a conduit with a plunger type pump at a pressure of 40 kgf / mm ² . Then, it was sprayed onto the roll surface from a hole having a nozzle diameter of 0.5 × 1 mm so that the supply amount was about 0.3 liter / m ² . The conventional rolling oil was supplied to the backup roll by water injection. The material of the work rolls of the first to third finish rolling mills was high speed steel.

The presence or absence of nozzle blockage and the presence or absence of roll seizure after rolling were examined, and the results are shown in Table 2. The number of nozzle blockages indicated is shown as a ratio to the number of nozzle inspections (30). The number of nozzles to be inspected is 10 in each of the first to third stands (three in each of the upper and lower stands), so there are a total of 30 nozzles.

[0033]

[Table 2]

As can be seen from the results in Table 2, when lubricants No. 3, 5 and 6 having a maximum dispersed particle size of 100 μm or less were used, there was no nozzle clogged and seizure of roll occurred. I didn't. On the other hand, the maximum dispersed particle size is 100
Nozzles were clogged above μm, the number of nozzles increased depending on the particle size, and roll seizure was observed.

[0035]

As described above, the lubricant of the present invention has excellent nozzle clogging resistance and enables stable injection onto the roll surface. In addition, damage to the rolling rolls is reduced and the roll unit consumption can be reduced. Further, since the manufactured stainless steel plate has a clean surface property, surface grinding can be omitted, and it is possible to manufacture a stainless steel plate having high productivity and high added value such as a mirror finishing application. .

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Claims (2)

[Claims] 1. A stainless steel hot rolling lubricant obtained by dispersing 10 to 30% by weight of lubricant particles in a viscous aqueous solution, wherein particles having a particle size of 50 μm or less are used as the lubricant particles and dispersed. The particle size of the flocs generated in the liquid is 1
Lubricant for hot rolling of stainless steel, which is excellent in nozzle clogging resistance, characterized by being suppressed to 00 μm or less. 2. The lubricant for hot rolling of stainless steel according to claim 1, wherein the lubricant particles are composed of FeO (OH) alone or a compound of FeO (OH) and other oxide particles.