JPH0354181B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a molten metal bath roll (hereinafter referred to as a bath roll) using a water plasma spraying apparatus and a method for manufacturing the same. In particular, it relates to bath rolls used as sink rolls, support rolls, etc. in molten metal plating bathtubs. (Prior Art) Conventionally, rolls for molten metal baths have been made of metal as is. Since it is immersed in corrosive molten metal, stainless steel, high chromium steel, etc., which have excellent heat and corrosion resistance, are used. This is a roll made by cutting an old metal bar into a small diameter journal by cutting both ends into a circle, leaving the middle part intact.
However, even if these corrosion-resistant and heat-resistant steel materials are used for a long period of time, scratches will occur on the roll surface due to the erosion effect of the molten metal. The scratches will also be transferred to plated steel plates etc. produced using this roll, resulting in defective products. Various measures have been taken to protect rolls from corrosion. Recently, thermal spray coatings of self-fusing alloys and ceramic materials have been used on roll surfaces for the purpose of improving corrosion resistance, wear resistance, and heat resistance. However, these attempts have a thin film thickness and 1
It was a thin film sprayed approximately 3mm thick. For this reason, there are various problems such as the adhesion between the thermal spray coating and the base material, and the bonding force between particles, and the current performance is that thermal spraying does not fully demonstrate its original performance. In the worst case, the surface alloy layer or ceramic layer of the roll may crack or peel off. Therefore, sufficient corrosion resistance and wear resistance cannot be obtained.
On the contrary, it shortens the life of the rolls and damages the plated steel plate pressed by the rolls. Sintered ceramic has excellent corrosion resistance, heat resistance, and wear resistance. This is a well-known advantage of ceramics. Therefore, a bath roll made entirely of sintered ceramic has been proposed. This is produced and used in some areas. This is done by placing ceramic powder in a mold, heating and compressing it, and sintering it, so it can be made all at once as a single component. However, ceramic chlorine has the following problems. In other words, sintered ceramic members are extremely brittle against impact forces. Significantly inferior toughness. Lack of toughness is a serious problem, especially in bath rolls that are subject to tension. Additionally, since sintered ceramics are made using molds, there are limits to the size and shape of the rolls. Also, in terms of cost, ceramic sintered rolls are very expensive. For example, we cannot afford to use such expensive products as bath rolls such as Metsuki Line. For these reasons, a sintered ceramic bath roll made entirely of ceramic is still not practical. (Problems to be Solved by the Invention) To solve the above problems and provide an innovative roll for a molten metal bath that is excellent in corrosion resistance, heat resistance, abrasion resistance, difficult wettability, toughness, and impact resistance, and is inexpensive. This is the object of the present invention. (Means for Solving the Problems) The roll for a molten metal bath of the present invention comprises a metal round bar having a uniform diameter, which has a journal portion at both ends and a coated portion in the middle, and an intermediate portion of the metal round bar. The thickness formed by water plasma spraying on the surface of
It is characterized by comprising a cylindrical ceramic layer of 20 to 50 mm. It is also possible to roughen the middle part of the metal round bar in advance, form a thin metal porous coating by thermal spraying, and then cover it with a thick ceramic layer by water plasma spraying as described above. good. The most significant feature of the present invention is that the shape of the base material, which is the material to be thermally sprayed, is a round bar, and the diameter of the round bar is only the diameter of the journal portion. In other words, the entire portion that was conventionally formed as the middle straight portion of the large-diameter body is made of ceramic material coated by water plasma spraying.
The film thickness depends on the dimensions of the target roll, but since it is water plasma spraying, it is possible to coat up to a film thickness of 50 mm, and the film thickness is generally 20 to 50 mm. Preferably it is 20 to 30 mm. (Function) The metal bath roll of the present invention having the above-described structure has features that are significantly different from conventional steel bath rolls. The bath roll of the present invention is characterized by a ceramic layer formed to a thickness of about 20 to 50 mm by water plasma spraying. When such a thick ceramic layer is formed by thermal spraying, it is very similar to a sintered ceramic material. Sintered ceramics have long been known to have excellent corrosion resistance, heat resistance, and wear resistance. To take advantage of this characteristic, some ceramic rolls made entirely of ceramic sintered bodies have been manufactured and used as bath rolls. However, as mentioned above, this material is weak against impact, has poor toughness, has limited shapes, and is expensive. Since the bath roll of the present invention is coated with a thick ceramic layer by thermal spraying, no molds or large sintering equipment are required. Furthermore, there are no restrictions on the size and shape of the roll. Its physical properties are very similar to those of sintered ceramics, and it has excellent corrosion resistance, heat resistance, and wear resistance. However, since there is a round metal bar in the center, it is resistant to impact. It is strong against bending and is suitable for use as a roll with high strength. It is cheaper because there are fewer equipment problems. In other words, the bath roll of the present invention has both the advantages of metal as a base material and the advantages of a ceramic layer coated with a thick metal. The method for manufacturing a roll for a molten metal bath according to the present invention will be explained below. The material of the round metal bar used as the base material of the roll will be described. Conventionally, expensive corrosion-resistant and wear-resistant materials such as stainless steel and high chromium steel have been used, but in the present invention, inexpensive materials can be used. This is because the coating is thick, at 20 to 30 mm, so the molten metal does not invade the base material. The ceramic layer completely protects the base material. This cannot be expected with a thin ceramic layer of 1 mm or less, or 1 mm to 3 mm. First, we will discuss the pretreatment of the metal round bar that is the base material. It is desirable that the base material surface has a certain degree of roughness. The purpose of this is to improve the adhesion between the first porous metal layer and the base material. A two-step process is preferably adopted for surface roughening. First, as shown in FIG. 1, a large number of grooves are cut in the middle part of a metal round bar 1, which is a base material. 1st
Figure A shows a thread-shaped spiral groove cut, and the grooved part is indicated by _S1 . Figure 1B shows the intersecting spiral grooves (knurlings) of a left-handed screw and a right-handed screw.The cross-spiral groove cutting section is indicated by _S2 .
In this way, large grooves are cut by machining, and then the surface is roughened, for example, by grid blasting. With Grid Blast,
The surface roughness is, for example, about 100 μm. Note that the roughening described above is not applied to both ends 1a, 1a of the round bar 1, which forms the journal of the bath roll. The purpose of the surface roughening is to minimize the effect of thermal expansion of the roll on the coating layer. This is also to increase the adhesion area between the metal round rod and the coating layer and strengthen the adhesion. Next, a porous coating layer of these metals is formed on the surface of the base material of the metal round bar 1 by plasma, arc, or flame spraying. Examples of metals used include nickel-aluminum alloy, nickel-chromium alloy, and stainless steel.
The thickness of the metal porous coating layer is preferably about 0.2 to 0.3 mm. The purpose of coating with the metal porous coating layer is to improve the adhesion between the second ceramic layer and the base material. Furthermore, a metal oxide capable of forming a ceramic is thermally sprayed onto the metal porous coating layer using a water plasma spraying apparatus to form a porous ceramic coating layer. The film thickness is 20 to 50 mm. Preferably 20-30
mm. The surface of this porous ceramic coating layer becomes the surface against which a steel plate or the like is pressed. The reason for limiting the construction method to water plasma spraying is as follows. In the case of gas plasma spraying, which is more widely used than before, Ar,
Expensive high-purity working gases such as He, No., and N are used. However, water plasma spraying is economical because it uses cheap water. It also has excellent thermal spraying ability, with water plasma spraying being 10 times more effective than gas plasma spraying. That is, water plasma spraying can form a film with a maximum thickness of 50 mm. The ceramic layer of the present invention is so thick that it cannot be applied other than by water plasma spraying. As the ceramic spraying material, metal oxides such as alumina, zirconia, titania, magnesia, silica, mixtures thereof, or other metal oxides are used. FIG. 2 is a perspective view of the bath roll made in this manner. A second ceramic coating layer 3 is coated around the middle portion of the metal rod 1 by thermal spraying. FIG. 3 is a sectional view. Both ends 1a, 1a of the metal round bar 1 serve as journal parts. It is made by selecting a round metal rod with a diameter equal to the diameter of the journal. Fourth
As shown in the partially enlarged sectional view of the figure, metal round bar 1
The surface has grooves along which a first metal porous coating layer 2 is coated, on which a second thick ceramic coating layer 3 is applied. When spraying ceramic materials, it is also effective to gradually change the particle size of the ceramic material depending on the type of sprayed metal, temperature, and other construction conditions. Alternatively, a multilayer coating layer may be formed by continuously spraying several different ceramic materials. (Example) An example of the present invention will be described. The target is a sink roll in a hot-dip galvanizing facility. The base material was a S45C round bar. The middle part of the base material, which was to become the long body part of the roll, was threaded as shown in Figure 1A. The cutting edge angle is 60°, and the thread pitch is
It is 0.4mm. The middle part of the base metal was further roughened by grid blasting. Two coating layers were formed on this by thermal spraying. As the first layer, nickel-aluminum alloy,
It was coated with arc spraying gas to a film thickness of 0.2 mm. The composition of the metal used and the spraying conditions are shown in Table 1.

[Table] A second layer of alumina ceramic material was coated onto the first layer using a water plasma spraying device to a thickness of 20 mm.
The thermal spraying conditions and ceramic material properties are shown in Table 2.

[Table] The surface of the roll thus created had some roughness from the thermal spraying process, so it was ground and polished to a level of about 3S. This is to prevent scratches from occurring on the surface of the galvanized steel sheet, which is to be pressed and fed with rolls, by making the outer circumferential surface smooth. The other purpose is to improve the wettability of the surface. The bath roll of the present invention and a conventional roll made of a heat-resistant and corrosion-resistant alloy were used as sink rolls in hot-dip galvanizing equipment, and their lives were investigated. FIG. 5 is a graph showing the results. The horizontal axis is the number of days of continuous use. A conventional roll made of a heat-resistant and corrosion-resistant alloy was used for about one week, and the surface of the roll became rough due to the erosion effect of molten zinc. This roll had to be replaced because there was a risk of defective Metsuki products. However, the bath roll of the present invention causes no problems even when used as a sink roll for 5 weeks. It continues to be used. The superiority of the sink roll of the present invention is clear. The reason for this is thought to be as follows. In this example, a ceramic coating layer as thick as 20 mm was formed, and this coating layer created a strong interparticle bonding force, and exhibited a stable corrosion prevention effect without peeling or falling off even in a zinc bath. . (Effects of the Invention) It is possible to provide a bath roll that has better corrosion resistance and a longer life than conventional metal bath rolls. This is because the ceramic layer is in contact with the molten metal through its surface, and ceramic has better corrosion resistance and wear resistance than metal. Because it has a long life, the number of times that the matsuki line, etc. must be stopped for roll replacement is reduced. The equipment has to be stopped every time the rolls are replaced, causing an increase in equipment costs. According to the present invention, this number of times is reduced, so equipment costs can be reduced. Furthermore, since the roll is prevented from being eroded by molten metal and peeling or cracking does not occur on the roll surface, it is possible to always provide high-quality plated products.

[Brief explanation of drawings]

Figures 1A and 1B show the surface processing performed before roughening the base metal surface by blasting in an embodiment of the present invention, and Figure 1A shows the surface processing of the metal by thread cutting. Side view of round bar,
Fig. 1B is a side view showing the state of surface processing by knurling, Fig. 2 is an external perspective view of a bath roll, that is, a sink roll, on which a ceramic spray coating layer has been formed, and Fig. 3 is a sink shown in Fig. 2. FIG. 4 is an enlarged sectional view of the part indicated by the arrow in FIG. 3, and FIG. 5 is a graph showing a comparison of durability between a conventional sink roll and a sink roll according to the present invention. The number of days it has been used in the tank is recorded. DESCRIPTION OF SYMBOLS 1... Metal round bar serving as a base material, 1a... End portion of the round bar 1 serving as a journal of the roll, 2... Metal porous coating layer, 3... Ceramic coating layer.

Claims (1)

[Scope of Claims] 1. A roll for a molten metal bath that is constantly immersed in a molten metal bath in a molten metal bath equipment and used under high temperature conditions in a corrosive melt, which includes portions that become journals at both ends and an intermediate portion. A round metal bar with a uniform diameter and a portion coated with
A roll for a molten metal bath, comprising a cylindrical ceramic layer of 20 to 50 mm. 2 A roll for a molten metal bath that is constantly immersed in a molten metal bath in a molten metal bath equipment and used under high temperature conditions in a corrosive melt, which has a smooth part that becomes a journal at both ends and a coating in the middle. a metal round bar with a uniform diameter having a roughened portion, a porous coating layer of metal thermally sprayed on the roughened portion in the middle of the metal round bar, and the porous metal coating layer. and a cylindrical ceramic layer having a thickness of 20 to 50 mm formed by water plasma spraying on the roll. 3. A process of roughening the middle part of a metal round bar with a uniform diameter, and applying a metal porous coating layer to the roughened middle part of the metal round bar by plasma, arc or flame spraying. and forming a ceramic-formable metal oxide as a porous ceramic coating layer on the metal porous coating layer of the metal round rod by water plasma spraying. How to make rolls.