Slide structure and continuous hot dipping apparatus having slide structure

A slide structure comprises a roll shaft and a roll bearing. A whole circumference of the roll shaft is made of a sintered ceramics body. A sliding surface of the roll bearing is constructed by inserting a cermet into a carbon-carbon reinforcing graphite member. A continuous hot dipping apparatus has a roll supported and rotated in a molten metal bath. A sliding surface of the roll shaft and the roll bearing employs the slide structure. The corrosion resistivity and the wearing resistivity can be improved and a long service life can be attained. The slide structure comprised of the roll shaft and the roll bearing can be smoothly rotated by decreasing the friction coefficient of the slide structure.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a slide structure and a continuous hot 
dipping apparatus having a slide structure, and more particularly to a 
slide structure and a continuous hot dipping apparatus having a slide 
structure having an excellent characteristic against the corrosion wearing 
with a molten metal and the wearing due to the load of a roll shaft 
provided on an end portion of a roll. 
The slide structure mainly comprises a roll bearing unit commonly having a 
pair of shafts (a pair of roll shafts) provided on both end portions of a 
roll and a pair of bearing members (a pair of roll bearings) for 
supporting the pair of roll shafts. 
The present invention relates to a slide structure and a continuous hot 
dipping apparatus having a slide structure, and more particularly to a 
slide structure in which by improving the bearing member (the roll 
bearing) structure of the slide structure a sliding portion formed between 
the roll shaft and the roll bearing can be smoothly rotated in accordance 
with the decrease a friction coefficient. 
2. Prior Art 
From the past, stainless steel, high chromium steel, super-hard steel or 
the like having the good corrosion resistivity is used as a material for a 
roll bearing in a continuous hot dipping apparatus in a form of an overlay 
member manufactured by the welding work or a sleeve member. 
However, there is a problem in that the plating characteristic is extremely 
degraded by the vibrations of the roll shaft and the continuous hot 
dipping apparatus due to the backlash and play formed between the roll 
shaft and the roll bearing, because the material is abraded in nearly one 
week, for example, in a molten zinc dipping bath. 
This reason has been clarified that it is difficult to completely eliminate 
the corrosion wearing with a molten metal such as the molten zinc even if 
a metal having a comparatively excellent corrosion resistibility such as 
stainless steel, high chromium steel, super-hard steel and so on is used. 
The corrosion wearing by the molten metal takes place as well as the 
friction wearing during the sliding portion of the roll bearing unit to 
lead to increase an amount in the friction wearing. 
Especially, when the corrosion progresses a certain degree, the friction 
wearing is accelerated by an occurrence of corrosion pits on the sliding 
surface formed between the roll shaft and the roll bearing in the slide 
structure. 
Therefore, in order to decrease the amount of wearing in the roll bearing 
unit, it is necessary to select a material having an excellent corrosion 
resistibility against the molten metal. 
From this standpoint, there are prepared some ceramics members which are 
hardly affected by the corrosion wearing of the molten metal. Such 
ceramics members are most suitable materials for the roll shaft of the 
roll bearing unit in the continuous hot dipping bath. 
The inventors of the present invention have proposed a roll bearing unit in 
a slide structure for a continuous hot dipping apparatus combining a 
sintered ceramics body as the material for the roll shaft and a 
carbon-carbon reinforcing graphite member as the material for the roll 
bearing, such a roll bearing unit in the slide structure is disclosed, for 
example, in Japanese patent laid-open No. 3-177,552 (1991). 
In this prior technique, the sintered ceramics body is fit to an outer 
periphery surface of the roll shaft through a metallic buffer member and 
the carbon-carbon reinforcing graphite member is provided on an inside 
periphery surface of the roll bearing. 
In the above stated prior technique, the combination of the sintered 
ceramics body employed in the roll shaft and the carbon-carbon reinforcing 
graphite member employed in the roll bearing does not take the problem of 
an actual operation in a continuous hot dipping apparatus into 
consideration. 
In other words, there has been revealed an entirely new problem in that in 
the continuous hot dipping apparatus. Namely, there exists an 
intermetallic compound produced by reaction of Fe eluted from a steel 
strip and so on with the molten metal such as Fe--Zn, Fe--Al and the like 
and ZnO and Al.sub.2 O.sub.3 produced in the early time of the operation 
of the continuous hot dipping apparatus. 
The intermetallic compound accelerates the wearing of the carbon-carbon 
reinforcing graphite member of the material for the roll bearing and 
further increases the friction coefficient in the sliding portion of the 
sintered ceramics body of the material for the roll shaft. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a slide structure and a 
continuous hot dipping apparatus having a slide structure wherein the 
corrosion resistivity and the wearing resistivity can be heightened in a 
combination of a sintered ceramics body employed in a roll shaft and a 
reinforcing graphite member such a carbon-carbon reinforcing graphite 
member employed in a roll bearing. 
Another object of the present invention is to provide a slide structure and 
a continuous hot dipping apparatus having a slide structure wherein a long 
service life can be attained in a combination of a sintered ceramics body 
employed in a roll shaft and a reinforcing graphite member such a 
carbon-carbon reinforcing graphite member employed in a roll bearing. 
A further object of the present invention is to provide a slide structure 
and a continuous hot dipping apparatus having a slide structure wherein 
between a roll shaft and a roll bearing constituted in the slide structure 
can be smoothly rotated by decreasing the friction coefficient of a 
sliding portion formed between the roll shaft and the roll bearing. 
A further object of the present invention is to provide a slide structure 
and a continuous hot dipping apparatus having a slide structure wherein a 
little roll rotating vibration caused by the rotation of a roll and a roll 
shaft constituted in the slide structure can be obtained. 
The above stated objects of the present invention can be attained by 
providing a slide structure having a roll bearing unit which comprises a 
roll shaft and a roll bearing, wherein a whole circumference of a sliding 
portion of the roll shaft is made of a sintered ceramics body, and the 
sliding surface of the roll bearing being constructed by inserting a 
cermet into a reinforcing graphite member such as a carbon-carbon 
reinforcing graphite member. 
The above stated objects of the present invention can be attained by 
providing a continuous hot dipping apparatus having a roll shaft supported 
with a roll bearing to rotate in a hot dipping bath, wherein a whole 
circumference of a sliding portion of the roll shaft of a roll is made of 
a sintered ceramics body, and a sliding surface of the roll bearing being 
constructed by inserting a cermet into a reinforcing graphite member such 
as a carbon-carbon reinforcing graphite member. 
According to the present invention, a continuous hot dipping apparatus has 
a sink roll and a support roll supported with a roll bearing and rotating 
in a hot dipping bath, wherein a whole circumference of a sliding portion 
of a roll shaft of at least one of the sink roll and the support roll is 
made of a sintered ceramics body, and a sliding surface of the roll 
bearing being constructed by inserting a cermet into a reinforcing 
graphite member such as a carbon-carbon reinforcing graphite member. 
According to the present invention, a continuous hot dipping apparatus has 
a sink roll and a support roll supported with a roll bearing and rotating 
in a hot dipping bath, wherein a whole circumference of a sliding portion 
of the roll shaft of the support roll is made of a sintered ceramics body, 
a sliding surface of the roll bearing being constructed by inserting a 
cermet into a reinforcing graphite member such as a carbon-carbon 
reinforcing graphite member, and the support roll rotating without any 
external driving unit. 
In accordance with the present invention described above, the sintered 
ceramics body employed in the roll shaft is one selected from a group of 
one or more of sialon, silicon nitride, silicon carbide, alumina, aluminum 
nitride, zirconia, boron nitrite and cermet. 
In accordance with the present invention described above, the cermet is 
formed by sintering at least one kind of a material having a high melting 
point and high hardness selected from a group of one or more of metal 
carbides, metal nitrides, metal borides, metal oxides and metal silicides 
with one selected from a group of a metal or an alloy. 
By using the sintered ceramics body for the sliding portion of the roll 
shaft and the carbon-carbon reinforcing graphite member for the sliding 
surface of the roll bearing, the corrosion wearing in the molten metal can 
be prevented. 
Since the carbon-carbon reinforcing graphite member employed in the roll 
bearing has an excellent solid lubricating capability and a sufficient 
mechanical strength, the friction coefficient in the sliding movement with 
the sintered ceramics body employed in the roll shaft is extremely small 
and is less than 0.1 and the limitation of surface pressure can be 
substantially increased above 50 kgf/cm.sup.2. 
However, in the hot dipping bath, there is generated a very hard 
intermetallic compound such as Fe--Zn or Fe--Al by reacting Fe eluted from 
a steel strip and the like with the molten metal. 
Entering of the intermetallic compound in the sliding surface formed 
between the roll shaft and the roll bearing increases not only the wearing 
of the comparatively soft carbon-carbon reinforcing graphite member by the 
abrasion wearing phenomenon but increases the wearing and the friction 
coefficient. 
This occurs since the hard intermetallic compound attaches to a ceramics 
sliding surface of the roll shaft to increase its surface roughness 
largely. 
In accordance with the present invention, in order to solve the above 
stated problems, the cermet is partially added on the sliding surface of 
the roll bearing in addition to the reinforcing graphite member such as 
the carbon-carbon reinforcing graphite member. 
As the material of the ceramics member used in the sliding portion of the 
roll shaft, sialon is most preferable, but SiC, Si.sub.3 N.sub.4, Al.sub.2 
O.sub.3, ZrO.sub.2, AlN, BN and cermet may be applicable. 
The cermet is formed by sintering at least one kind of a material having a 
high melting point and high hardness selected from a group of one or more 
of metal carbides, metal nitrides, metal borides, metal oxides and metal 
silicides with one selected from a group of a metal or an alloy. 
Especially, the cermet composed of molybdenum boride and Ni is preferable. 
Most of the matrix of the cermet becomes a three-element compound of 
B--Mo--Ni by controlling the contained amount of Ni and the sintering 
temperature, and the corrosion resistivity against the molten metal 
substantially increases to suppress the corrosion wearing. 
Further, the hardness of the cermet can be controlled to Hv=700-1400. In 
the combination with the ceramics member, by making the hardness of the 
cermet smaller than the hardness of the ceramics member by at least 20%, a 
sticking during the sliding movement at a high surface pressure (larger 
than 50 kgf/cm.sup.2) can be prevented and the abrasion wearing by the 
intermetallic compound such as Fe--Al and Fe--Zn can be also prevented 
since the cermet is harder than the intermetallic compound. 
As described above, by partially arranging the cermet on the sliding 
surface of the roll bearing in addition to the carbon-carbon reinforcing 
graphite member, it is possible to prevent the wearing of the abrasion 
wearing type due to the intermetallic compound such as Fe--Zn and Fe--Al 
in the hot dipping bath. 
Similarly, it is possible to prevent the wearing due to the surface 
roughness of the sliding surface of the roll shaft since the intermetallic 
composition attached on the ceramics sliding surface of the roll shaft can 
be removed according to the finishing effect. 
A further additional advantage is that since the cermet has the good 
wetness against the molten metal, the lubrication effect by the molten 
metal improves the wearing resistivity without increasing the friction 
coefficient. 
By making the above stated cermet composed of molybdenum boride and Ni in 
such that the most part consists of the three-element boride compound of 
B--Mo--Ni, the corrosion wearing can be suppressed since the cermet has 
the excellent corrosion resistivity against the molten metal. The friction 
coefficient can be decreased lower than 0.2 since the cermet has the good 
wetness against the molten metal. 
The oxide cermet used is composed of at least one selected from a group of 
one or more of ZrO.sub.2, Al.sub.2 O.sub.3, BeO, MgO and TiO.sub.2 and a 
metal or an alloy selected from at least one of Fe, Ni and Co. 
And also the cermet which is the above cermet further added with an alloy 
element selected from a group of one or more of Cr, Mo, W, Ti, Zr, Hf, Nb, 
Al and so on is used. It is preferable that the amount of the added 
element except for Cr is less than 5 wt %, besides the amount of the added 
Cr is less than 30 wt %. 
The carbide cermet used is a combination of at least one selected from a 
group of one or more of WC, TaC, NbC, VC, ZrC, Mo.sub.2 C and TiC and the 
metal or the alloy described above. 
The nitride cermet used is at least one of a group of one or more of BN, 
Si.sub.3 N.sub.4, AlN, TiN and ZrN. The boride cermet used is at least one 
of a group of one or more of ZrB.sub.2, Cr.sub.2 B, TiB.sub.2, HfB.sub.2, 
NbB.sub.2, Mo.sub.2 O.sub.5 and W.sub.2 B.sub.5. The silicide cermet used 
is at least one of a Group of one or more of Ti silicide, Zr silicide, Hf 
silicide, V silicide, Nb silicide, Mo silicide and W silicide. 
The containing amount of the ceramics member in the cermet is preferably 
more than 50 wt %, and particularly it is preferable to be 60-90 wt %. For 
the borides described above, it is preferable to contain the boride 
composition nearly 100%.

DESCRIPTION OF THE INVENTION 
Hereinafter, various embodiments of a slide structure employed in a 
continuous hot dipping apparatus according to the present invention will 
be explained referring to the drawing. 
Embodiment 1 
FIG. 1 is a cross-sectional view showing a continuous molten zinc dipping 
apparatus having a slide structure according to the present invention. 
In FIG. 1, a steel strip 7 supplied through a snout 6 is turned in its 
direction by a sink roll 1 in a dipping bath 5, and a pair of support 
rolls 3 prevent the steel strip 7 from deforming and vibrating. The steel 
strip 7 runs at a high speed of 20 to 200 m/minute. 
Further, the steel strip 7 extracted from the dipping bath 5 is blown with 
high speed gas flows from a pair of gas swiping nozzles 8 provided on both 
sides of the steel strip 7. The thickness of attached plating is regulated 
by adjusting the gas pressure and the angle of the blowing flow of the gas 
swiping nozzle 8. 
Both of the sink roll 1 and the support rolls 3 described above have a 
sliding type roll bearing unit 2 and sliding type roll bearing units 4 in 
the slide structure to be rotatable respectively. 
FIG. 2 is an enlarged cross-sectional view showing a roll shaft of the 
sliding type roll bearing unit portion of the sink roll 1 in the slide 
structure according to the present invention. 
In FIG. 2, sialon ceramics member is selected as a material for a 
cylindrical ceramics member 9 attached to a metallic roll shaft 16, the 
sialon ceramics member has a high corrosion resistivity against the molten 
zinc and also has a high strength and high hardness property. 
The chemical equation for the sialon is expressed by Si.sub.6-z Al.sub.z 
O.sub.z N.sub.8-z, where z may be an arbitrary value from 0 to 4.2, which 
is called as .beta.-sialon ceramics. 
In this embodiment, the sialon ceramics member is fabricated by using 
sialon powders having z=0.5, kneading them through a wet method using 
methanol after adding a little amount of binder, and then granulating 
through a spray dry method. 
Next, a cylindrical pressed powder compacting body is fabricated through a 
cold press method. After a degreasing treatment process, the obtained 
pressed powder compacting body is sintered at 1750.degree. C. in a 
nitrogen atmosphere so as to obtain a sintered sialon body 9. 
A sintered sialon body 9 is machined to form in an outer diameter of 165 mm 
and a length of 150 mm using a diamond grinder. 
Stainless steel having a comparatively high corrosion resistibility is used 
for the metallic roll shaft 16. In order to protect the cylindrical 
sintered sialon body 9 from the thermal expansion difference between the 
metallic roll shaft 16 and the cylindrical sintered sialon body 9, the 
metallic roll shaft 16 is wrapped with a stainless pipe made of SUS 316 
which acts as a buffer member 10. 
Then the metallic roll shaft 16 is inserted into the cylindrical sintered 
sialon body 9 and a pushing member 12 made of SUS 316L is pushed and fixed 
to an end edge portion of the cylindrical sintered sialon body 9 using a 
spring member 11 made of Inconel 750 and bolts 17 made of SUS 316L. 
Further, a thrust plate 13 made of SUS 316L is welded and fixed as shown in 
the figure to prevent the molten zinc from entering into a buffer member 
10. 
The main body portion 14 of the sink roll 1 is cylindrical and welded to 
the metallic roll shaft 16 to form a one-piece structure. An intermediate 
body 15 composed of a metallic ring is inserted between the cylindrical 
sialon body 9 and the metallic roll shaft 16. 
In a neck portion of the metallic roll shaft 16 there is provided a space 
18 to securely fix the cylindrical sintered sialon body 9. The cylindrical 
sintered sialon body 9 may be formed in a one-piece structure or in a 
structure separable into two (2) to four (4) pieces. 
FIG. 3 is a partially cross-sectional enlarged side view showing the roll 
bearing of the roll shaft. FIG. 4 is a front view showing an inner surface 
the roll bearing of the roll shaft of FIG. 3. 
In FIG. 3, ten (10) pieces of the carbon-carbon reinforcing graphite 
members 19 which form sliding surfaces of the bearing are arranged in dent 
portions formed in dovetail grooves on the inner surface of a metal casing 
21 made of SUS 316L arranging four rows to an axial direction as shown in 
figure. 
And seventeen (17) pieces of a cylindrical cermet members 20 having a 
diameter of 5 mm made of molybdenum boride and Ni are arranged as shown in 
the figure. 
An inner periphery of the sliding surface of the roll bearing is machined 
in a semi-circle shape as shown in the figure. The reason why the 
carbon-carbon reinforcing graphite members 19 in the right-half side are 
arranged three (3) rows to a peripheral direction is because the 
construction is chosen such that the arranged positions of the cermet 
members 20 in the right hand side and the left hand side are not come to 
the same positions on the peripheral direction. 
The reason why the carbon-carbon reinforcing graphite members 19 are formed 
in a swept-back shape seeing from the middle portion of the roll shaft is 
to prevent the dross from entering. 
The carbon-carbon reinforcing graphite members 19 are pushed and fixed to 
the metal casing 21 so as to contact to each other on their inner 
periphery. The carbon-carbon reinforcing graphite member 19 is made of a 
graphite sintered body containing carbon fibers having diameter of 1-10 
.mu.m by the amount of 50 volume %. 
The pushing metal plate 23 is for pushing and fixing the carbon-carbon 
reinforcing graphite members 19 to the inner surface side using a bolt 22. 
The cermet is a sintered body composed of molybdenum boride and Ni 
containing nickel of 35 wt %. The obtained cermet bodies 20 having special 
sizes ranging from 3-10 mm in a diameter and 5-20 mm in a length are 
formed into a cylindrical shape and then implanted or fit into the 
carbon-carbon reinforcing graphite members 19 described above to form a 
portion of the sliding surface with the graphite members. Thus, the 
members 19 serve as base members for the cermet bodies 20, surfaces of the 
two forming sliding surface of the bearing. 
The cermet bodies 20 are arranged in two rows as shown in FIG. 4 in such as 
not to come to the same positions on the peripheral direction. 
In the slide structure of this embodiment, a whole circumference of the 
sliding portion of the rotor shaft is made by the sintered ceramics body 
(the cylindrical sintered sialon body) 9 and a sliding surface of the 
rotor bearing is constituted by partially inserting the cermet body 20 
into the carbon-carbon reinforcing graphite member 19. 
Namely, in the sliding surface of the rotor bearing in the slide structure 
the cermet body 20 is partially exposed at the surface with a form of a 
block in the carbon-carbon graphite reinforcing member 19 and arranged to 
be surrounded by the carbon-carbon graphite reinforcing member 19. 
FIG. 5 is an assembling view of the roll shaft and the roll bearing having 
the above stated slide structure in the continuous molten zinc dipping 
apparatus. 
Using this slide structure, a slide test has been actually conducted in the 
molten zinc bath. The wearing speed of the bearing is less than 0.2 mm/day 
which is 1/10 of that in a conventional slide structure under the test 
condition of the zinc bath temperature of 450.degree.-480.degree. C., the 
roll shaft pressing load of 500 to 2500 kgf, rotating speed of 30-150 
min.sup.-1. The wearing of the sialon material in the roll shaft is hardly 
observed. 
The sliding surface of the slide structure is clean and smooth and has no 
intermetallic compound such as Fe--Zn attached. Further, the friction 
coefficient during the sliding movement is less than 0.05 which is less 
than 1/3 of that in a conventional slide structure. 
Embodiment 2 
FIG. 6 shows another embodiment of a small-size roll bearing for a support 
roll of the slide structure according to the present invention. 
In this embodiment, the materials of the roll bearing and the basic 
structure are the same as those in Embodiment 1. That is, carbon-carbon 
reinforcing graphite members 25 are used four (4) pieces in the left upper 
side and one (1) piece in the right side to construct the sliding portion 
of the roll shaft. 
Further, the cermet bodies 26 of 5 mm in a diameter and 10 mm in a length 
which are the same as those in Embodiment 1 are implanted or inserted into 
the carbon-carbon reinforcing graphite members 25 as shown in the figure, 
five (5) pieces and four (4) pieces, respectively. 
The implanted positions of the cermet bodies 26 are arranged in two rows, 
in the front side and in the back side to the direction of the roll shaft 
pushing load. The cermet bodies 26 are arranged in two rows as shown in 
FIG. 4 in such as not to come to the same positions on the peripheral 
direction. 
The carbon-carbon reinforcing graphite members 25 are arranged in one row 
to the axial direction. The fixing structure for the carbon-carbon 
reinforcing graphite members 25 in the portion not seen is the same as 
that shown in the cutaway portion. The carbon-carbon reinforcing graphite 
members 25 in the left hand side have a flat shape on the inner periphery. 
FIG. 7 is an assembling view of a roll shaft and a roll bearing in the 
slide structure. In this embodiment, the materials of the roll bearing and 
the basic structure are the same as those in Embodiment 1. 
A diameter of a cylindrical sintered sialon member 31 used in a sliding 
portion of the roll shaft is 80 mm. A cylindrical sintered sialon member 
31 is fixed by wrapping a metallic roll shaft with a stainless pipe made 
of SUS 316 in a certain length and fastened in the same manner as in 
Embodiment 1. 
A sliding test has been conducted using an actual continuous hot dipping 
apparatus. In the past, the support roll is driven using an external 
driving unit. However, by using the roll bearing unit in the slide 
structure according to the present invention shown in FIG. 6, the support 
roll can be smoothly rotated without any external driving unit. 
As the result, the vibration of the steel strip 7 can be substantially 
decreased and the deviation in thickness of plating can be decreased to 
less than one-half of that in the conventional continuous hot dipping 
apparatus. 
After ten days continuous operation of the continuous hot dipping 
apparatus, the amount of wearing of the roll bearing unit in the slide 
structure is hardly observed. Further, it is possible to prevent the 
generation of zebra marks (streaks) caused by the rotating runouts in the 
support roll. 
According to the present invention, by using the sintered ceramics body as 
the roll shaft having the excellent corrosion resistivity and the wearing 
resistivity for the sliding portion of the roll shaft and constructing the 
roll bearing using the reinforcing graphite member such as the 
carbon-carbon reinforcing graphite member and the cermet, the excellent 
slide structure can be constituted. 
Thereby, it becomes possible to decrease the wearing of the slide 
structure, to lengthen its service life capable of the continuous 
operation for the continuous hot dipping apparatus and to decrease the 
frequency of exchanging the roll bearing unit in the slide structure to 
improve the productivity in the continuous hot dipping apparatus. 
Further, it becomes possible to decrease the wearing of the slide structure 
in the continuous hot dipping apparatus, to lengthen its service life to 
be capable of the continuous operation for the continuous hot dipping 
apparatus of more than five times as long as that of the conventional 
slide structure in the continuous hot dipping apparatus, to decrease 
frequency of exchanging the slide structure to improve the productivity in 
the continuous hot dipping apparatus. 
Further, since the support roll is not directly driven to substantially 
decrease the rotating runouts in the rolls, it becomes possible to improve 
the quality of the products and to decrease the defective rate by 
decreasing the deviation in the amount of the plating thickness and by 
preventing the generation of streaks.