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Emergency Collecting Pits Protect Against Furnace Breakouts.

Ever since water-cooled electric furnaces have been used in smelting operations, these structures have required collection pits that are capable of taking up the entire furnace contents in the event of a furnace break-out or an emergency tapping. Now, they are being incorporated in foundry operations. Ideas and patent applications range from the "explosion-proof pit" (which is dimensioned sufficiently large and is solidly constructed to withstand a possible explosion) and the dry emergency collection pit (in which accumulating water is diverted in front of the emergency collection pit) to the emergency collection pit with drainage (in which water and liquid metal are separated at a point where it is still safe to do so).

The primary cause of explosions in foundry operations is contact between molten metal and water. Accordingly, the requirement for an emergency collection pit to be dry was incorporated in the German labor legislation at an early stage. An ECP is guaranteed to stop a molten metal/water explosion. In almost 30 years, SILMETA has built more than 300 ECPs that handled 150-plus breakouts with no injuries or damages. Large automotive companies rely on ECPs as well as a small art foundry that pours once every three months. In Germany, ECPs are mandatory and must be installed but are new to the North American market.

What was lacking, however, were instructions for keeping the furnace pit dry. What measures must be implemented when the pit is under water as compared to when the pit is only wet? How can the foundations--mainly in large plants--be effectively protected against thermal damage?

A Solid Material for Emergency Collection Pits

A solid drainage material was needed to increase the open evaporation surfaces--as in the case of steam expansion chambers--and to drain accumulating water not only in the bottom of the pit, but also through the pit's partitions and surrounding walls. The material would require the following characteristics:

* High open pore volume in order to drain water and steam as quickly as possible.

* Adequate refractoriness.

* Adequate strength to absorb both the static and dynamic forces during emergency tipping.

* High overall mechanical strength.

* Shock temperature resistance.

* Low reaction to liquid metal, if the drainage material is dry or wet.

* Rapid melting and sintering of the surface upon contact with molten metal.

Today, the modified ceramic foam suited for use in emergency collection pits is known under the trade name Thermofilter KS 91 (for iron alloys) and was designed and tested through the collaboration between SILMETA and the Seibersdorf Research Center (an Austrian equivalent to a U.S. national laboratory) in the early 1990s. The material is almost unchanged to this day and is always scaled to the amount of metal to be absorbed.

Emergency collection pits are now built to ensure drainage through the bottom as well as the chamber walls. As a result, the risk of a physical explosion is significantly minimized to essentially zero. The possibility of a structural explosion can be excluded as a large evaporation surface is provided. The required evaporation surface is provided by steam expansion zones above the collecting chambers, even when the pit is filled to capacity.

Large plants with pit contents exceeding 20 tons of molten metal have additional requirements in terms of thermal protection of the foundations. This issue prompted the "pit in the pit" design, based on a 1994 simulation of thermal behavior of the pits during the filling and solidification process. The simulation demonstrated that the load-bearing structures and reinforcements in the two-shelled structure used at SILMETA are not compromised, even without additional cooling measures (for example, due to the significant steam development and the unavailability of compressed air). Collection systems lined with firebricks, however, are only a conditionally suitable solution for heat dissipation and heat retention. The reinforcement of the pit foundations--for a 9.8 in (25 cm) thick brick lining--is heated to over 1,022F (550C).Thus, the foundations are essentially no longer suitable as load-bearing structures.

After publication of the proposed design, a data sheet was developed to describe the key features of the pit to "do-it-yourself contractors," and to challenge the industry to produce new solutions, subject to the condition that requirements of the data sheet be met. The data sheet defines the requirements for emergency collection pits and specifies the essential building materials suited for their fabrication (Figure 1). In addition, it requires that the pits be installed, "exclusively by qualified companies." This requirement is intended to prevent customers from being "used for experiments."

The European Union accepts the current VDG data sheet as the "state of the art" for emergency collection pits, including the ceramic foam, which these bodies identify as a suitable drainage material offering these required qualities:

* Water flows through without obstruction.

* Upon impact with molten metal, the pores close immediately.

Thus, the ceramic foam prevents contact with wet material and explosions are essentially eliminated in plants that comply with VE)G data sheet S 80. In addition, compliant installations prevent thermal stress to foundations in larger plants.
                              absorption of     gas
                              water following   permeability-
                              a momentary       dry [5]
                              contact in
                              % [5]

site--mixed concrete                n.d              --

waterproof concrete                 --               --

flooring plaster                    n.d              --

sieved gravel 20-50 mm              n.d              n.d
(double--washed)

moulding sand                       n.d              100

cupola slag 0.5-3 mm                17              1900
(clean, in granular form)

solid drainage material             14              2100
(foam ceramic)

fireclay bricks                      4               --

fireproof perforated plate           2               n.d
(clay graphite)

fireproof concrete (LCC)             6               --

fireproof ceramic                    4               --
(burnt fireproof concrete)

fireproof mortar                    n.d              --

steel sheets                        --               --

                              gas             resistance
                              permeability-   against molten
                              wet [5]         iron

site--mixed concrete               --              --

waterproof concrete                --              --

flooring plaster                   --              --

sieved gravel 20-50 mm             n.d             --
(double--washed)

moulding sand                      20               *

cupola slag 0.5-3 mm               55              --
(clean, in granular form)

solid drainage material            390              *
(foam ceramic)

fireclay bricks                    --               *

fireproof perforated plate         n.d              *
(clay graphite)

fireproof concrete (LCC)           --               *

fireproof ceramic                  --               *
(burnt fireproof concrete)

fireproof mortar                   --               *

steel sheets                       --             o (4)

                              foundations       slant
                              and surrounding   for water
                              structures        diversion

site--mixed concrete                --             --

waterproof concrete                 --             --

flooring plaster                    --             --

sieved gravel 20-50 mm               *             --
(double--washed)

moulding sand                       --             --

cupola slag 0.5-3 mm                 *            o (1)
(clean, in granular form)

solid drainage material              *              *
(foam ceramic)

fireclay bricks                     --             --

fireproof perforated plate          --             --
(clay graphite)

fireproof concrete (LCC)            --             --

fireproof ceramic                   --             --
(burnt fireproof concrete)

fireproof mortar                    --             --

steel sheets                        --             --

                              water      separation
                              drainage   of liquid
                                         iron and
                                         water

site--mixed concrete             *           *

waterproof concrete              *           *

flooring plaster                 --          *

sieved gravel 20-50 mm           --          --
(double--washed)

moulding sand                    --          --

cupola slag 0.5-3 mm             --          --
(clean, in granular form)

solid drainage material          --          --
(foam ceramic)

fireclay bricks                  --          --

fireproof perforated plate       --          --
(clay graphite)

fireproof concrete (LCC)         --          --

fireproof ceramic                --          --
(burnt fireproof concrete)

fireproof mortar                 --          --

steel sheets                     --          --

                              vapour         sections in
                              diversion in   contact with
                              the bottom     spilt iron
                              section

site--mixed concrete               --             --

waterproof concrete                --             --

flooring plaster                   --             --

sieved gravel 20-50 mm             *              --
(double--washed)

moulding sand                      --             --

cupola slag 0.5-3 mm             o (2)            --
(clean, in granular form)

solid drainage material            *              *
(foam ceramic)

fireclay bricks                    --             *

fireproof perforated plate         --             *
(clay graphite)

fireproof concrete (LCC)           --             *

fireproof ceramic                  --             *
(burnt fireproof concrete)

fireproof mortar                   --             *

steel sheets                       --             *

                              sections in    bottom of    walls of
                              contact with   collecting   collecting
                              flowing        chambers     chambers
                              iron

site--mixed concrete               --            --           --

waterproof concrete                --            --           --

flooring plaster                   --            --           --

sieved gravel 20-50 mm             --            --           --
(double--washed)

moulding sand                      --            --           --

cupola slag 0.5-3 mm               --            --           --
(clean, in granular form)

solid drainage material            *             *            *
(foam ceramic)

fireclay bricks                    *             --           --

fireproof perforated plate         *           o (3)          --
(clay graphite)

fireproof concrete (LCC)           *             --           --

fireproof ceramic                  *             --           --
(burnt fireproof concrete)

fireproof mortar                   *             --           --

steel sheets                       --            --           --

This table shows building materials from the data sheet.
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Title Annotation:CASTING INNOVATIONS
Publication:Modern Casting
Date:Dec 1, 2017
Words:1220
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