Pot for coating continuous metallic strip

A hot dip coating pot for containing a coating material in a liquid state. The coating pot comprises a substantially horizontal bottom and substantially vertical side walls. The bottom and the side walls define a first interior volume for containing the coating material. The bottom wall and a lower portion of each of the side walls defines a bottom portion which is separable from an upper portion of the side walls. The bottom portion has a predetermined interior volume less than the first interior volume.

FIELD OF THE INVENTION 
The present invention relates to hot dip coating of continuous metallic 
strip, and is particularly, but by no means exclusively, applicable to the 
coating of ferrous metals with zinc, aluminum, and other coatings. 
BACKGROUND OF THE INVENTION 
In coating of ferrous metals, such as in galvanizing, parts to be coated 
are immersed into a bath coating material after having been chemically 
pretreated and cleaned. The amount of time the parts stay immersed depends 
upon the material of the parts, their shapes, the bath temperature, the 
coating composition, and the desired coating thickness. 
Coating is frequently used to coat continuous strips of ferrous base metal 
to produce iron or steel strip stock having a thin coating of zinc, 
aluminum, or the like. In continuous-strip coating, the strip to be coated 
is first cleaned and pretreated, passed through a bath of molten coating 
material, and then withdrawn from the bath in a generally upward 
direction. The coating material adhering to the withdrawn strip is 
finished by coating rolls, air knives, or the like, and is subsequently 
solidified. 
The molten coating material, usually a molten metal such as zinc, for 
example, is contained in an externally-heated iron or steel pot. Metal 
coating pots have several disadvantages, however. They have a relatively 
short life. This is due to several factors, including rapid build-up of 
dross at the bottom of the pot. 
In normal operation, the coating pot is kept full with molten metal 
supplied via a launder from a premelter. Where a bottom dross generating 
alloy, such as a zinc alloy, is used, it becomes necessary to periodically 
empty the pot completely, and allow it to cool, to remove the dross which 
has collected at the bottom of the pot. To avoid this, it has been 
proposed to remove dross by using a circulating pump to continuously pump 
molten metal through a filter, to remove the dross, and return it to the 
coating pot. Zinc filtration is not yet a proven technology, however, and 
there is a need to provide an effective yet simple method of dross 
removal. The present invention fills that need. 
SUMMARY OF THE INVENTION 
The present invention is directed to a hot dip coating pot for containing a 
coating material in a liquid state. The coating pot comprises a 
substantially horizontal bottom and substantially vertical side walls. The 
bottom and the side walls define a first interior volume for containing 
the coating material. The bottom wall and a lower portion of each of the 
side walls defines a bottom portion which is separable from an upper 
portion of the side walls. The bottom portion has a predetermined interior 
volume less than the first interior volume.

DESCRIPTION OF THE INVENTION 
Referring now to the drawings, wherein like numerals indicate like 
elements, there is shown in FIG. 1 a coating installation 10 incorporating 
a coating pot 12 according to the invention. Installation 10 comprises, in 
addition to coating pot 12, a coreless induction melter 14 and a holding 
pot 16 located between the coreless melter 14 and the coating pot 12. 
Molten metal is supplied to coating pot 12 via a launder 18. The holding 
pot 16 holds molten coating metal, which is pumped from coating pot 12 via 
pump to holding pot 16 when it is desired to empty coating pot 12, and 
which is pumped from holding pot 16 to coating pot 12 when it is desired 
to refill coating pot 12. Molten metal pumps for transferring molten metal 
between coating pot 12 and holding pot 16 are commercially available, and 
are known per se to those skilled in the art. 
The coating installation 10 is supported on a deck or floor 20, except as 
will be described below. 
A vertical section through coating pot 12 is illustrated in FIG. 2. Coating 
pot comprises side walls 22 and a substantially horizontal bottom 24. 
Together, the side walls 22 and bottom 24 define an interior volume for 
containing molten coating material. Side walls 22 and bottom 24 are made 
of refractory materials, such as, for example, a "cold face" layer 26 and 
a "hot face" layer 28 of refractory material 30. More details of this 
aspect of the construction of coating pot may be had by reference to U.S. 
Pat. No. 5,354,970, assigned to the same assignee as the present 
invention, and which is incorporated herein by reference. 
A difference between coating pot 12 and prior coating pots is that each 
side wall 22 is divided into an upper portion 36 and a lower portion 38 
along a parting line 40. Lower portions 38 of side walls 22 are joined to 
bottom 24, and together define a bottom portion 42 which is separable from 
the upper portions 36 along the parting line 40. The lower portions 38 and 
bottom 24 define a predetermined interior volume which is less that the 
interior volume of coating pot 12. If desired, a suitable seal 44 may be 
provided between upper portions 36 and lower portions 38 of side walls 22, 
so that molten metal does not leak out of pot 12 along parting line 40. 
As seen in FIG. 1, coreless induction furnaces 41 are mounted on opposite 
side walls of the coating pot 12. Each coreless induction furnace 41 
defines an interior volume 43 therein in communication with the interior 
volume of the coating pot 12 for inductively heating the coating material. 
As seen in FIG. 3, coating pot 12 is located below the level of the deck 
20. Bottom portion 42 is supported and held in place against upper wall 
portions 22 by mechanical, hydraulic, or pneumatic jack screws 46 on 
transfer car 48, which is movable along a pair of rails 50 by means of 
wheels 52. Rails 50 are located on a floor below and spaced from deck 20. 
Transfer car 48 and bottom portion 42 are moved into place below coating 
pot 12, and then jack screws 46 are actuated to elevate bottom portion 42 
into contact with the upper portions 36 of side walls 22. 
As seen in FIG. 6, bottom portions 42 may be provided with a latch 
mechanism 54 which cooperates with projections 56 on the outer surface of 
upper portions 36 of side walls 22. The latch mechanism 54 is preferably 
remotely operable, such as by a hydraulic cylinder or by an 
electromechanical device (e.g., a solenoid). Latch mechanism 54 and 
projections 56 cooperate to secure bottom portions 42 to upper portions 
36. With the bottom portion 42 in place, molten coating metal can be added 
to coating pot 12 and the coating process of strip 34 can begin. 
Although the latch mechanisms 54 are shown as being located on bottom 
portion 42, they may also be located on the lower portions of side walls 
22. 
As the pot is used, dross is formed. In many cases, such as where the 
coating material is zinc, the dross is denser than the molten metal, and 
tends to sink and collect in the bottom portion 42. Periodically, the 
coating process must be stopped and the dross removed. This is easily done 
by lowering bottom portion 42, after coating pot 12 has been emptied of 
molten coating metal. When coating pot 12 has been safely emptied of 
molten metal, the locking clamps are released, the jack screws 46 are 
actuated, and bottom portion 42 is lowered downward onto the bed of 
transfer car 48, as seen in FIG. 4. Sufficient distance is provided so 
that, when lowered, bottom portion 42 clears the upper portions 36 of side 
walls 22. After bottom portion 42 has been fully lowered onto the bed of 
transfer car 48, transfer car is moved along rails 50 to a position away 
from installation 10 where bottom portion can be emptied. If desired, 
bottom portion 42 may be tilted for emptying, as illustrated in FIG. 5. 
As also seen in FIG. 6, several bottom portions 42 may be provided, each on 
its own transfer car 48, so that while one bottom portion is being 
conveyed away from coating pot 12 for emptying, another is put into place 
below coating pot 12, while a third is available for use when needed. In 
this manner, downtime of coating installation can be greatly reduced, 
since coating pot 12 can be used with a clean bottom portion while the 
previously used, dross-containing bottom portion is being emptied. 
For dross removal, coating pot 12 is emptied, such as by pumping molten 
metal out of it, to a level below parting line 40. While the jack screws 
46 support bottom portion 42, latch mechanisms 54 are released and bottom 
portion 42 containing the dross is lowered by jack screws 46 to the bed of 
transfer car 48. Bottom portion 42 containing the dross is conveyed by 
transfer car 48 to a tipping station, where it is tipped, as illustrated 
in FIG. 5, and its contents dumped. In the meantime, a new bottom portion 
42 is moved into place below coating pot 12, and raised into place by jack 
screws 46. Latch mechanisms 54 are the actuated to secure the new bottom 
portion 42 onto coating pot 12. After the new bottom portion 42 is secured 
to coating pot 12, coating pot 12 is filled, such as by pumping molten 
metal from one of the holding pots 16. 
An advantage of the invention is the speed with which the coating pot may 
be emptied of dross and refilled for subsequent use. Total elapsed time, 
including emptying the coating pot, exchanging bottom portions, and 
refilling the coating pot, is estimated to be only about an hour. 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof and, 
accordingly, reference should be made to the appended claims, rather than 
to the foregoing specification, as indicating the scope of the invention.