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Improved casting quality through advanced
flow control technology
The introduction of modern graphite containing flow control systems
has brought a new dimension to the discharge of liquid metal from
bottom pour ladle systems. Previous technologies presented the
foundryman with a number of problems, any of which could have
resulted in a bad pour and possible defective castings. Using
the latest in both materials and design, the ROTOLOK* systems
incorporating either VISO* or VAPEX* refractories overcome
many of these issues and can lead to reduced costs and improved
productivity, says Rudi Bittniok of Foseco Germany.
The use of bottom pouring technology in steel foundries has become an
industry standard; in many foundries it has replaced the use of lip pouring
ladles for mould filling. The benefits of bottom pour ladles include: reduced
slag in the casting, easier filling of the mould, a reliable system, a controlled
pouring stream, and faster pouring.
In combination with modern lining materials, the foundry now has the
opportunity to achieve the high quality requirements demanded of many
castings. This can be achieved by reducing temperature loss from the ladle
during pouring, together with casting more moulds while the metal is at the
required pouring temperature. The shape of the stopper head and the nozzle
seat area are important parameters to obtain optimised control of the metal
flow.
Fig.1 Left: one-shot stopper
in KALTEK ladle, right:
ROTOLOK stopper head
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Bottom pour technology was introduced using
a disposable stopper rod system. This comprised
of a steel rod lined with ceramic sleeves and an
alumina-graphite stopper head; the ceramic sleeves
and the stopper head had to be glued together with
a high temperature resistant ceramic cement, like
SUREBOND. After assembling, it was necessary to
dry the system in an oven prior to use.
Foseco has improved this system by introducing the
ROTOLOK* stopper head for single use stopper rod
systems.
The unique ROTOLOK system comprises of
an alumina-graphite stopper head and a separate
ceramic thread. This ceramic thread is located on the
steel stopper rod. The alumina-graphite stopper head
is then screwed on to the thread and therefore on to
the stopper bar. This system ensures there is no direct
contact between the metallic rod and the graphite
head, preventing thermal stresses in the stopper head
during filling and casting. This is a significant benefit
compared to the old system where the metal rod was
screwed directly in the stopper head. The thermal
Fig.2
FTJ November 2012
Melting Technology
Fig.3 Different nose geometries
Fig.5 Nozzle flow capacities
Fig.6 Attachment possibilities
Fig.4 Surface contact areas by having different nose designs.
stress could cause cracks during the casting process.
This disposable system is the only way of applying
bottom-pouring technology with a stopper rod for
large and/or tall ladles, where the whole rod system is
longer than two metres.
The application of mono-block stopper
technology
Many modern steel foundries use multi-life monoblock stopper technology. The idea originates in steel
plants where similar technology is used for tundish
applications in long casting campaigns.
Foseco’s flow control products are available in two
main formulations - VAPEX* and VISO*.
VISO
VISO is based on carbon bonded alumina graphite,
produced using isostatic-pressing technology. The
products offer excellent thermal shock and oxidation
resistance, making them particularly suited as a
mono-block stopper for application with molten steel.
In steel foundry ladle applications the VISO stoppers
are normally removed from the ladle after the casting
period and cleaned before being reused.
VAPEX
VAPEX is a highly dimensionally accurate extruded
product, based on a refractory combination of graphite
and alumina. VAPEX offers excellent erosion and
oxidation resistance and maintains high mechanical
strength over a long operational time period. VAPEX
was originally designed to be used in iron foundries
with automated pouring; its excellent refractory
properties also qualified it as an ideal material for
nozzles used in ladle pouring of molten steel.
All standard nozzle shapes are available with a
range of inner bore diameters; products can also be
made to specific customer specifications.
The selection of the correct material and shapes for
the flow control system in a ladle or pouring box has a
significant impact on the pouring of the castings.
Inadequate flow control devices can result in
many problems. The stopper/nozzle can leak and
FTJ November 2012
Fig.7 Assembling of UNIROD
Fig.8 Stopper rod storage
Fig.9
Preheating
curve
occasionally fail, resulting in uncontrollable flow of molten metal from the
ladle - this is an obvious safety issue. A worn or blocked nozzle will give
inconsistent flow rates and mould fill times. Incorrect shape of the stopper
and nozzle will result in poor metal flow attributes; the metal will not flow
in a consistent stream and may spray out of the nozzle resulting in casting
defects from oxidation, air entrapment and erosion of the pouring cup by the
metal stream.
The use of VAPEX cross bore nozzles will further improve the integrity and
consistency of the metal flow into the mould. The system has already been
explained in the Foseco Foundry Practice 251(1).
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Melting Technology
Fig.12 Grinding tool
Fig.10 Preheating station
Fig.11 Cleaning station
The correct choice of the stopper geometry to prevent leakages
or the sticking effect
The choice of the correct stopper/nozzle design has a direct influence on the
performance of the system, and the prevention of molten metal leakage or
stopper sticking.
The golden rule is: ‘graphite to graphite’. Foseco always recommends
the use of VISO graphite containing stoppers along with a VAPEX graphite
containing nozzle to ensure the potential for sticking is minimised. The use of
pressed standard clay nozzles or pressed alumina nozzles with mono-block
stoppers which have different thermal expansions under hot load, can disturb
the casting process and impact on the flow of the metal stream.
Furthermore, the stopper head geometry will also influence the metal
stream. In steel foundry applications it is recommended to use a roundshaped stopper nose compared to a pointed head stopper nose to reduce
the contact area of the stopper/nozzle pair.
Different stopper head geometries
For very small casting weights and fast opening campaigns, the pointed
nose is suitable, as this provides improved control for small castings. This is
mainly applicable to iron auto-pouring furnaces.
The output of the nozzle and its flow rate is usually determined by the
inside diameter of the nozzles inner bore and the height of opening of the
stopper:
Attachment of the mono-block stopper
The attachment system for the stopper to the metallic rod connected to
the gooseneck, or ladle arm, is an important feature to assure an optimum
stopper movement control.
Foseco offers a choice of fully proven attachment systems:
• UNIROD attachment
• Roto-Rod attachment
• Tundish-Rod attachment
The UNIROD system is preferred by steel foundries and the Tundish-Rod
attachment is common practice in auto pouring lines in grey iron foundries.
The Roto-rod attachment is similar to UNIROD® (fig.7) but the thread is
incorporated on a ceramic insert. For both systems a special metallic stopper
rod is necessary, it is important that the metallic rod contains a central bore.
This vent hole allows for the escape of moisture from inside the stopper
during its temperature increase.
Preparation area
An adequately equipped area must be available for the preparation and
stocking of the flow control system. A rack which allows the vertical
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positioning of the stoppers is recommended to
facilitate all the assembly operations.
When such a rack is used, shock absorbing devices
are useful to protect the stopper glaze against damage
and cracks.
The unique attachment of UNIROD provides the
most rigid, secure and leak-proof assembly between
the stopper and the support-rod.
Preheating
The correct preheating of the stopper is an important
operation, which is too often neglected. Even when
the assembly, setting and handling operations of a
stopper have all been done correctly, it is possible to
damage the ceramic through poor preheating practice.
Correct preheating is important to avoid thermal shock
to the refractory components. The preheating must
follow a similar curve as shown in fig.9.
Cleaning of the stopper
The stopper can be used for up to 15 heats. After the
casting process and the cool down of the equipment,
the stopper should be cleaned carefully on a
horizontal cleaning station.
The slag should be removed carefully with a small
hammer. A suitable nozzle shaped device is used
to shape the stopper nose so that the radius fits the
nozzle. A special anti-sticking coating can be applied
to the stopper.
Outlook
The usage of the mono-block stopper technology
offers many benefits in the iron and steel foundry
casting process. With this multi-use system, the
foundry is able to cast many more heats before
replacing the stopper with a new one.
This reduces gas costs by reducing refractory
preheating and creates less waste than single use
stopper rod components.
In the future we will see increased application
of mono-block stoppers in conjunction with better
insulating ladle refractories like KALTEK*, where no or
minimal preheating of the system is necessary.
Contact: Paul Jeffs, UK technical manager, Vesuvius
UK Limited – Foseco Foundry Division, Tamworth,
Staffordshire B78 3TL UK. Tel: +44 (0) 1827 289999,
email: paul.jeffs@foseco.com web: www.foseco.com
1. Foseco Foundry Practice 251 is available direct
from the company as per the above contact
details. www.foseco.com
* ROTOLOK, VAPEX, VISO and KALTEK are Trade Marks of the
Vesuvius Group, registered in certain countries, used under licence.
FTJ November 2012