Cleanliness Enhancement of the Bath Surface within a ... - Pyrotek

Cleanliness Enhancement of the Bath Surface within a CGL Snout
C. H. Phillips, N. Staples, M. Bright
Craig H. Phillips and Neil Staples
Corus Research, Development and Technology
Metallic Coated Strip Products
Port Talbot SA 13 2NG, United Kingdom
Tel: 00 44 (0) 1639 603146
Fax: 00 44 (0) 1639 872308
Email: craig.h.phillips@corusgroup.com, neil.staples@corusgroup.com
Mark A. Bright
Metaullics Systems
Division of Pyrotek, Inc
31935 Aurora Road
Solon, Ohio 44139 U.S.A.
Tel: 440-349-8800
Fax: 440-349-8877
Email: marbri@pyrotek-inc.com
Key words: Snout, bath surface, dross, quality, zinc pumping
2005 Galvanizer’s Association Annual Meeting
Lexington, Kentucky
October 16 – 19, 2005

2
Cleanliness Enhancement of the Bath Surface within a CGL Snout
C.H.Phillips, N.Staples, M. Bright
Abstract
Many metallic coating defects can be attributed to poor quality of the galvanising bath surface
within the snout area. As the strip enters the bath any material that is less dense than zinc will
float on the bath surface (i.e. dross and zinc oxides) and due to the momentum of the strip can be
dragged onto the surface and cause subsequent defects.
Corus Research, Development & Technology, Port Talbot, Wales, has been working with
manufacturing teams at Corus' continuous strip galvanizing lines in order to identify ways and
means of reducing the afore mentioned defects.
The use of pumps within the snout area has been investigated and is reported. Water modelling
of the zinc bath in a test tank, in conjunction with Metaullics Systems Division, was used to
evaluate various pump inlet / outlet designs, the optimum position and flow of the pump
outlet/inlet, as well as evaluating different scenarios of using pumps to pull, push and various
combinations of the two.
New pumps have been commissioned on Corus' ZODIAC galvanising line and have helped to
dramatically reduce the volume and severity of snout bath surface related defects.

3
Cleanliness Enhancement of the Bath Surface within a CGL Snout
C.H.Phillips, N.Staples, M. Bright
Introduction
With the ever increasing quality demands of automotive manufacturers, producing defect-free
galvanised steel sheet is becoming more and more critical. The various types of sheet defects
have been well documented [Refs. 1-3] and investigations [Refs. 2, 4-8] have indicated that a
critical area where many defects are initiated is within the snout region of a continuous
galvanising line, at the point of initial insertion of the steel into the molten zinc. Specifically,
Chen and Patil [Ref. 2] have indicated that, if contaminants within the snout are not pumped out,
they may cause defects on the coating.
In 2004 there was an increase of a defect called “micro dross”/dross spots was reported on
galvanised strip produced at the Corus Zodiac line in Llanwern, South Wales and the surface of
the zinc bath was identified as a potential cause of this quality concern. Hence, the zinc bath
surface within the snout area was investigated to determine whether the overall cleanliness could
be improved and so reduce this type of defect (as well as others) caused by bath surface
cleanliness as the strip enters the bath from the annealing furnace. Addressing these issues was
vital to producing a high quality full finish product for use in the automotive market.
Previous industry research has extensively reviewed fluid flow patterns in the overall galvanising
pot [Refs. 7-12] and to a lesser extent the fluid dynamics of the snout area in the vertical crosssection
parallel to direction of sheet motion [Refs. 7, 8, 11, 12]. This study focused on the
physical modeling of fluid motion on the surface of the zinc bath along the width of the sheet
within the snout.
As part of this investigation, it was necessary to look at the current configuration of existing
snout dross pumping equipment and evaluate the benefits of adding a push pump. Consideration
needs within this critical area were: nozzle position, pump angle, bath level and potential flow
patterns as a result of using a push pump. The physical modelling work was best undertaken via
a water model, supplied by Metaullics Systems (Solon, OH).
The main aims to this physical modelling work were to investigate the following activities:
• The influence of the bath height on pump outlet and inlet
• The surface turbulence created by the push pump across the strip periphery
• Pull pump inlet, tundish design, orientation and position
• Push pump, position, orientation and tundish design

4
Water Model Configuration
Water modeling work was undertaken in close conjunction with Metaullics Systems at their
facility in Cleveland, U.S.A. Figure 1 outlines the water model and equipment used. At the start
of the trials, the pumps were in a central position as in Figure 1.
315mm
Push pump inlet
95mm
210mm
Snout
1195mm
Strip
Pull pump outlet
Fig. 1: - Basic plan outline of water model tank set up of the snout area
90mm
157.5mm
The model strip width was 30” [762mm] and was located in a stationary position within the
snout area. Snout dimensions were 47” x 12.5” x 5.5” [1195 x 315 x 140mm] (L x W x snout
depth into water) and the water tank dimensions were 70”x 47” x 31” [1778 x 1195 x 787mm] (L
x W x water depth). (See Figures 2 and 3 for additional details.)
The push pump arrangement for this investigation utilised a Metaullics D-13SD centrifugal
pump, constructed of MSA2000 (a Metaullics zinc-resistant superalloy). The pull pump was a
MetJet nitrogen propulsion gas-lift pump supplied again by Metaullics [Ref. 13]. The MetJet
works via a venturi effect, drawing zinc from one part of the bath to another without any moving
mechanical components.
The MetJet pull pump piping dimensions were 3.5” [90mm] diameter for the suction inlet with
an 8.5” [216mm] diameter discharge (external to the snout area). The push pump discharge that
was employed for these tests was configured with a 3.75” [95mm] fixed, oval outlet. Metaullics
recommended that the pull pump inlet be 1 to 4 inches deep and similarly, a 2 inch depth was
specified for the outlet of the push pump (i.e. 1/2 submerged).
The flow of the top surface of the bath was monitored indirectly by placing floating, perforated,
polyethylene discs (2.5cm diameter) to display movement of the surface. These could pass
through the MetJet without hindrance and be expelled into the bath freely.

140mm
60°
157.5mm
315mm
5
Pull pump inlet
Fig. 2 : - Side view of the water model bath
Strip
Fig.3 : Push system (left) and pull system (right)
Snout
Water model

6
Deduction from water model
It was found that the push flow must be tightly controlled to cause the flow of particles away
from the strip area but not too high as to cause a ‘wash’ effect at the snout walls where zinc dust
would be dislodged. Zinc may also solidify building up on the wall and increasing the surface
area hence more zinc oxide entrapment that would be harder to remove by mechanical means.
Too high a push flow causes major turbulence at the surface of the bath and is clearly visible
along the strip width.
The push pump is the dominant feature within the water model. The push flow has a greater
effect of particle tracking than that of the pull system. Therefore it was suggested that the pull
system be run continuously and at higher rate than the push system.
It must be ascertained the bath level that is most effective at removing surface oxides for both
push and pull systems. This is necessary as the surface tension and density of water to zinc is
vastly different but the knowledge gained from this exercise gives us an optimal starting point
for further modification on-line.
It was concluded from this work that the optimum shape of the pull system inlet was a weir
design as the zinc cascades over the weir and is removed efficiently from the snout area. This
would allow for the best arrangement so that the pull system should pull more than the push
system pushes. In this configuration the amount of dross that comes into contact with the strip is
minimised. More importantly this means that there is less chance of the surface tension being
broken and hence a loss in pull flow.
Care must be taken when considering any new designs for pull inlets, as any loss of surface
tension allowing the atmosphere can be pulled into the Metjet giving a loss of suction. The
width of the outlet must be less than any tracking that the strip may cover in the snout to prevent
contact with the strip.
Bath level effects
The level of the pot was crucial when the pumps were installed. The level of the pot needs to be
controlled tightly as the outlet of the push and the inlet of pull pump is highly sensitive to level
fluctuations. If the pot level is too high the pull outlet is below the surface of the bath and so the
flow of zinc that is supposed to push across the surface to help move surface contaminants to the
pull pump does not occur. Similarly at higher level the inlet to the pull pump is below the surface
and will then take sub-surface material and again the debris on top of the bath will remain.
Conversely, If the pot level is too low the push outlet will cascade out of the pump outlet and fall
into the bath. This increased flow of zinc appears on the surface of the strip as 'wash marks' and
hence is undesirable. Conversely the pull inlet is above the surface of the bath and hence cannot
collect any surface debris.

7
Plant installations
Based on the evidence of the water modeling experiments it was decided to try a push / pull
pump set-up, it was decide to centrally mount the collection tundish and the push (slot) within
the snout area (Fig. 4). A Metaullics D13 pump for the push and use the conventional
Metaullics M12 pump as the “puller”. Also the pull pump utilised the collection tundish.
However this required very precise positioning on the tundish in relation to the bath surface and
requiring a tight control of the bath height.
Fig. 4 : Collection tundish and push slot trialed within Zodiac snout
Additionally the position of the push slot is also critical to obtain the maximum benefit.
Defect reductions
Following on from the optimisation of the pump design and configuration a study was carried
out to identify the effect that this enhancement has had on snout related defects. The volume and
frequency of the three main defects that are attributed to the snout area are dramatically reduced
post the installation of the pumps. As can be seen in Figure 5 below.

Frequency rate
60
50
40
30
20
10
0
XMAS
TREE
2004
DROSS
SPOTS
2004
Defects attributed to the snout area
DIGS
2004
2004 2005
Defect
8
XMAS
TREE
2005
DROSS
SPOTS
2005
DIGS
2005
Frequency
Fig. 5 : Graph to illustrate the differences in the strip defects witnessed at ZODIAC in the first 5
months of 2004 compared to the same period in 2005.
The condition of the snout itself as seen from the camera system is clear to even the untrained eye. The
surface of the bath shows clear on the images shown below for both the outlet of the push pump (on the
left) and the inlet of the pull (shown on the right).
Fig. 6 : Improved surface with push and pull pumps installed
This much-improved surface as shown in figure 6 has lead to a dramatic reduction in surface
defects attributed to the snout bath surface.

9
Conclusions
The pictures from the snout clearly show that when the bath level control is maintained at the
agreed level then there is clearly a continuous flow of zinc into the tundish.
Similarly the collection tundish has performed exceptionally well at removing debris from within
the snout area. With poor bath level control surface scum built up but over a period of time when
bath height was controlled, the scum was captured along with subsurface zinc.
The installation of the pumping system within the snout has dramatically reduced defects, which
are attributed to the snout bath surface.

10
Acknowledgments
The authors would like to acknowledge Corus Strip Products UK and Metaullics Systems for
their willingness to promote the enclosed research.
References
1. Dunbar, F.C., “Defects of the 80’s – A Closer Look at the Critical Requirements of
Today’s Hot-Dip Galvanized”, 1988 Galvanizer’s Association Meeting, W. Middlesex,
Pennsylvania
2. Chen, F., Patil, R., “An In-Depth Analysis of Various Subtle Coating Defects of the
2000’s”, Galvatech 2004, Chicago, 2004, 1055-1066
3. Tang, N-Y., Coady, F., “Coating Defects: Origins and Remedies”, 2001 Galvanizer’s
Association Meeting, Portland, Oregon
4. Mallens, R., Treadgold, C., Vlot, M., Meijers, S., “Prevention of Dross Contamination in
the Corus Ijmuiden Hot Dip Galvanizing Line”, Galvatech 2001, Brussels, Belgium,
2001, 255-261
5. Komatsu, A., Andoh, A., Uchida, Y., “Initial Stages of Formation of Interfacial Alloy
Layers in Hot Dip Galvanizing”, Galvatech 2001, Brussels, Belgium, 2001, 337-344
6. Zermout, Z., Drillet, P., Houziel, J., “Reaction Mechanisms during Immersion of Low-
Carbon Steel in Zn-5wt.%Al Bath”, Galvatech 2001, Brussels, Belgium, 2001, 345-351
7. Pare, A., Binet, C., Ajersch, F., “Numerical Simulation of 3-Dimensional Flow in a
Continuous Strip Galvanizing Bath”, Galvatech 1995, Chicago, 1995, 695-706
8. Kato, C., Koumura, H., Mochizuki, K., Morito, N., “Dross Formation and Flow
Phenomena in a Molten Zinc Bath, Galvatech 1995, Chicago, 1995, 801-806
9. Evans, K., Treadgold, C., “Modelling and Measurement of Transient Conditions in the
Galvanising Pot”, 1999 Galvanizer’s Association Meeting, Jackson, Mississippi
10. Goodwin, F., “An Integrated View of Galvanizing Bath Flow and Dross Management”,
2001 Galvanizer’s Association Meeting, Portland, Oregon
11. Baril, E., DuBois, M., Gagne, M., “Investigation of Fluid Flow in the Snout of a
Continuous Galvanising Bath using Numerical Modelling”, Galvatech 2001, Brussels,
Belgium, 2001, 435-442
12. Ajersch, F., Ilinca, F., Perrault, M., Malo, A., Hetu, J-F., “Numerical Analysis of the
Effect of Operating Parameters on Flow in a Continuous Galvanizing Bath”, Galvatech
2001, Brussels, Belgium, 2001, 511-518
13. Becherer, G., “Utilizing Pumps to Continuously Remove Dross from Inside the Inlet
Snout”, 2001 Galvanizer’s Association Meeting, Portland, Oregon