FIELD OF INVENTION
The present invention re-ates to sealed external galvanization of steel tubes. More particularly the present invention relates to hot dip galvanization of steel tubes on its outer surface only.
BACKGROUND OF THE INVENTION
Hot dip galvanization of steel tubes is a finishing operation used to protect the tubes from corrosion. It a semi-continuous operation where chemically cleaned and preheated tubes are transported through a molten zinc bath at a temperature range of 440 460°C such that a zinc coating of specified thickness gets metallurgically bonded to the metal surface. Galvanized products are automatically withdrawn rom the zinc bath and immediately treated to remove molten zinc in excess of coating specifications. Excess zinc is removed from the outside surface by "wiping" with compressed air, and from the inside by "blowing" with superheated stream.
As of now, in most of stee; plants across the world, the tubes are dipped inside the zinc bath during ga anization where along with the exterior surface, the interior surface also gets coated with zinc. With the exception of certain specific purposes (viz. irrigation ;>pes), in most applications zinc coating on the interior surface is unwanted an. even undesirable in many cases mostly in process industries. From the stee; manufacturers' point of view too, galvanization is detrimental as additiona ; inc loss takes place. In contemporary galvanization practices coating on tube nner surface gets solidified for more than one-third of its length before the stea-n blowing is carried out to remove the extra zinc and the final coating profile becomes wavy in nature.

Demerits of Internal Galvanization taking place in existing mechanism:
1. The layer of zinc thai is formed on the inside of the tube constitutes waste of zinc which increases cos? of the tubes.
2. Zinc tends to collect and/or forms beads on the interior surface which cannot be removed properly due to inaccessibility. These imperfections lead to surface roughness which interferes with optimum usage of the tube as it offers greater frictional resistance to the movement of materials through it.
3. The applied zinc coating has more hardness than that of steel core. When zinc coating is present on both the surfaces, the spaced hard layers impart some stiffness to the tube making it relatively inflexible. On the other hand, when there is a single hard laye present on the outside surface, the outer coating has little effect on the bendat^ity of the galvanized steel tube.
4. In many chemical industries, zinc on the inner surface reacts with the
material passing through t, which is undesirable.
OBJECTS OF THE INVENTION
1. It is therefore the objects of the invention to do sealed external galvanization of steel tubes which wi; galvanize only one external surface instead of both internal and external surface which reduces the cost of galvanization by 50%.
2. Another object of the nvention is to do sealed external galvanization of steel tubes which increases the oroductivity due to avoidance of unwanted zinc from the internal surface besides improving the quality of the product.
3. A further object of the nvention is to do external galvanization of steel tubes which reduces the cost of sjt up and its maintenance cost.
SUMMARY OF THE INVENTION
The present invention Ga /anization External aims to find a solution to the aforementioned problem of internal galvanization based on simple principles of venting air through end sea s clamped to both ends of the tubes to be

galvanized. This may eventually lead to reduction of the coating expenses to an extent around 50%.
The entire set up of tne invention consists of a horizontal table (1) with a longitudinal slot (2).
A pneumatic cylinder, vi: cylinder 1, is mounted on the table and is aligned with the slot. The piston head of cylinder 1 is connected to fixture 1 carrying a vertical pneumatic cylinder, viz cylinder 2, in such a way that the extension and retraction of the pistor of cylinder 1 moves fixture 1 linearly along the longitudinal slot in the direction AA.
Cylinder 2 carries fixture 2 which is free to move vertically up or down along with the piston of cylinder 2 ■•'. the direction BB. Fixture 2 carries the frame (3) for handling tubes to be galva lized.
The fixed arms of tr*e frame (3) is made of hollow tube bent in an L shape and has an end caps (5) at the lower end. The fixed arm is directly mounted on fixture 2. The movable a i of the frame is also made of similar hollow tube bent in an inverted L shape and carries a similar end cap (5) at the lower end. The end caps on both the arm;, of the frame are aligned such that they are coaxial with the tube (4) to be ga i anized.
The movable arm is connected at its top to pneumatic cylinder 3 such that movement of piston of cinder 3 moves the movable arm of the frame in the plane of Fixture 2.
Both the arms of the fran- e are provided with holes on the tube surface near their top ends which act as air bleed ports.

The whole frame (3) is mounted on fixture 2 in such a way that when the tube to be galvanized is held between the end caps, the axis of the pipe makes an angle of 15° with the horzontal. End caps are tapered with a taper angle of 60° for easy engagement with tube ends and to ensure its usability with tubes of different internal diameter?. They are drilled axially throughout their length so as to create an unrestricted a-r passage from one air bleed port to the other. Station 1, station 2 and station 3 are the positions of fixture 1 when cylinder 1 is retracted completely, extended halfway and extended completely respectively. The tube to be galvanized is placed directly beneath station 1 on an inclined plane of 15°. The hot zinc bath is directly beneath station 2 and the quenching chamber is directly beneaU station 3.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWING
Figure 1 - Process flow of pickling and galvanizing of steel tubes at existing set
up.
Figure 2 - current median ;m
Figure 3 - The entire set cu> of the lay out of the invention
Figure 4 - The frame holeog the steel tubes to be galvanized
Figure 5 - Different views of end cap that holds the steel tubes to be galvanized
Figure 6a, 6b, 6c - Clamping of the tubes at station No- 1
Figure 7a, 7b, 7c - Dipping of steel tubes at station No - 2
Figure 8a, 8b, 8c and 8d Stacking of tubes at station No -3
DETAILED DESCRIPTION OF THE INVENTION
Initially at station 1 fixture 1 is stationery with piston of cylinder 2 in retracted position and piston of cylinder 3 in extended position. The tube to be galvanized is directly below the arms of the frame.
Cylinder 2 is now actuar.ee and fixture 2 reaches is lowermost position such that the tube is now between tne end caps.

Cylinder 3 is retracted sucn that the tube is held firmly between the end caps of
both arms of the frame.
Cylinder 2 is retracted sun that fixture 2 reaches its topmost point along with
the tube.
Cylinder 1 is actuated such that fixture 1 moves along the horizontal slot and
reaches station 2.
Piston of cylinder 2 is extended such that the tube is dipped inside the hot zinc bath and is held as such for a predefined period of time.
Cylinder 2 is retracted such that fixture 2 reaches its topmost position along with the galvanized tube,
Piston of cylinder 1 is extended such that fixture 1 reaches station 3.
Cylinder 2 is extender, such that the galvanized tube is dipped inside the stacking chamber.
Cylinder 3 is actuated such that the end caps disengage. The tube stays inside the stacking chamber and-is ready for subsequent processes.
Cylinder 2 is retractec followed by retraction of cylinder 1 such that the assembly attains the initio position.
At the operational tempe ature the viscosity of Zinc prevents its flow past hole sizes of diameter lesser than 3/32". Under engaged condition the end caps prevent the flow of molfrj" zinc inside the hollow tube as the surface roughness of tubes along the edges .re of much smaller order as compared to that needed for free flow of molter inc. Thus the ends of the tubes to be externally galvanized are completelv sealed against any entry of zinc inside them.
The sealing of ends cane the air trapped inside to get heated and expand. Because of the inclination provided in the tube hot air rises in only one arm of the frame, after passing through the end cap, and is realized to the atmosphere through the air bleed port The vacuum created inside the tube due to this is

filled up by air pulled in 'hrough the other air bleed port which passes through the other end cap and reaches the inside of the hollow tube. Thus a natural draft of air is created and anv uressurization of the tube is prevented. This avoids the danger of splashing of 7 r c due to air leakage and also prevents disengagement of end caps.
Refactory metals will be used as the material for the frame. These are a class of metals that are extraordinarily resistant to heat and wear. They have a melting point above 2000°C and h gh hardness at room temperature. They are chemically inert and have a relative! v high density. The best option available is Mo-30W, an alloy of an alloy of 70°/ molybdenum and 30% tungsten. It has the following properties:
a) The high resistivity of Mo-30W against the attack of molten zinc makes it the ideal material for casting ;: nc.
b) It also has high mechanical and thermal shock resistance. This property is very useful because detrimental conditions are prevalent where solids are charged into the molten 7 <<. bath.
Advantages of the proposed invention:
1. Cost reduction: Since coating of one of the two surfaces can be prevented by this method, ideally cost cF coating can be reduced by 50 percent.
2. The following shows the possible applications of this technology: Structural tubes

- Structural elements as for example in airports where tubular structures, sealed from all sides are used.
- For construction purposes like scaffolding, where lower thickness pipes can be used, especially in coastal 3-eas.

Conveyance tubes
- Certain process indu-.tries and chemical plants emphasize on the use of
uncoated inner surface.
- For cold storage pipes wnich allow the passage of ammonia and liquid nitrogen. Other possible applications
- In firefighting operations, where the pipes don't require internal galvanization.
- Electric poles.
3. In the current set-.of, after the zinc tube comes out of the zinc bath, a superheated jet is blown nside the tube for a couple of seconds for removal of extra liquid zinc from tie interior surface. When internal galvanization is prevented the aforemeri