Metallurgical apparatus – Means for melting or vaporizing metal or treating liquefied... – Means to melt and separate metal from mass of diverse...
Reexamination Certificate
2001-12-27
2003-12-02
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means for melting or vaporizing metal or treating liquefied...
Means to melt and separate metal from mass of diverse...
C266S235000
Reexamination Certificate
active
06656415
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for precipitating solid compounds from the liquid zinc or liquid zinc-based alloys of a metal bath thereof.
The invention further relates to a device for precipitating solid compounds from a molten mass of liquid zinc or liquid zinc-based alloys, in particular from a metal bath thereof, for example, a galvanizing bath.
Finally, the invention relates to the use of the process and the use of the device for precipitating compounds and oxides, particularly intermetallic iron compounds from galvanizing baths, in particular from continuous sheet galvanizing systems.
2. Discussion of Background Information
Zinc is a metal with a comparatively low melting point of 419.6° C. and has a standard electrode potential of −0.762 V, and is therefore baser than iron with −0.447 V. In addition, zinc is relatively stable towards oxygen, because a zinc oxide layer formed on a zinc surface protects the zinc from the attack by oxygen. Thus, if a steel part is coated with a zinc layer, the zinc acts as an anode, i.e., protects the iron from oxidation, with the formed zinc oxide preserving the zinc layer from further oxidation. Because long-term rust protection of iron and steel can be achieved by zinc and zinc has a melting point that is lower by more than 1100° C., galvanizing parts in a liquid zinc bath is one of the most important protective measures against atmospheric and similar corrosion of steel components.
Galvanizing the steel parts takes mostly place by dipping them into a bath with liquid zinc or a zinc-based alloy to form a coating. Sheet metal is passed through a zinc bath, for example, which allows to achieve a thin, uniform and perfectly smooth surface coating.
Good adhesion of the zinc layer is ensured due to the solubility of the zinc in the alpha (&agr;)-mixed crystal of the iron of up to approximately 7.3 at. % at usual bath temperatures. On the other hand, iron is only slightly soluble in zinc at its melting temperature, with the three-phase equilibrium at 419.35° C. having an eutectic composition: zinc and 0.021 at. % or 0.018% by weight of iron. At higher temperatures of 530° C., for example, the solubility of iron in liquid zinc is 0.3 at. % or 0.25% by weight.
If iron is introduced into a galvanizing bath due to iron dust or the like adhering to the part as well as by system parts, then iron-zinc mixed crystals are formed, for example FeZn
3
, FeZn
7
, Fe
3
Zn
10
, Fe
5
Zn
21
. These FeZn mixed crystals may be heavier than pure zinc and enrich themselves at the bottom of quiescent liquid galvanizing baths as hard zinc or as so-called “dross” or “bottom dross.”
In order to improve the quality of the galvanizing or the zinc layer formation, in particular on metal sheet metal which passes through the zinc bath at a high speed, aluminum can be added at an order of magnitude of 0.1 to 0.2% by weight to form an alloy with the zinc bath. In the given case, the “bottom dross” interacts, in terms of reaction kinetics, with the zinc molten mass that due to subsequent alloying contains aluminum, and iron-aluminum mixed crystals with a configuration of Fe
2
Al
(5-x)
Zn
x
and a specific weight of significantly less than 6×10
3
kg/m
3
are formed.
The mixed crystals, in particular the compounds Fe
2
Al
(5-x)
Zn
x
form a pulp in the galvanizing bath, and with a continuation of the galvanizing treatments and further introduction of iron into the bath the particles become larger, reach a diameter of over 30 &mgr;m and agglomerates, so-called clusters, are generated. These coarse compound particles in the galvanizing bath, which may be in the form of lumps, can cause surface defects or can adversely affect the surface quality of the coating, especially in the galvanization of smooth sheet metal bands, such as those for the automobile industry, for example.
In order to purify galvanizing baths contaminated with intermetallic compounds, it is necessary to render the bath quiescent with respect to bath currents, if possible, whereafter the layer enriched on the surface with the compounds is skimmed off. Performing this kind of purification in sedimentation basins has already been proposed.
The previously known purification processes all have the disadvantages of low efficiency, high expenditure, reduced economic efficiency, and production safety, as well as productivity of the system.
The object of the invention is to eliminate the deficiencies of previous precipitation methods and to disclose a process by means of which even with large throughput quantities an insignificantly low content of solid compounds can be maintained in galvanizing baths.
An additional object of the invention is to provide a device for the optionally continuous precipitation of solid compounds from galvanizing and zinc baths, which device does not impede production.
SUMMARY OF THE INVENTION
The object is attained in a process of the type recited at the outset by subjecting partial amounts of the liquid metal phase containing the compound(s) and being above the melting temperature of zinc to an acceleration higher than the acceleration due to gravity and causing an at least partial demixing into fractions containing heavier and/or lighter components, whereafter the molten mass depleted of solid compounds is returned to the metal bath or made available in purified form for such a bath, and the part of the molten mass enriched with the desired compounds is discharged and/or supplied to a further separation process.
The additional object of the invention is attained with a device according to the species in that a hollow rotary body that can be driven about an axis and has conveyor means, such as conveyor impellers or pump impellers, projecting into the cavity in the feed or lower portion is introduced at least partially into the molten mass, which hollow rotary body is provided in its discharge or upper portion with at least one discharge opening for the depleted molten mass, which opening is eccentrically arranged in the wall of said body and, subsequent thereto with respect to the discharge side, with at least one further centrally and/or eccentrically arranged discharge opening for the liquid metal enriched with compounds wherein at least one of the upper molten mass discharge openings in the hollow rotary body opens into a discharge area of a housing which at least partially surrounds the hollow rotary body, which housing area has at least one discharge channel for the enriched molten mass and, optionally, a further one for the depleted molten mass designed to return to the metal bath.
The advantages of purifying a galvanizing bath of intermetallic compounds achieved in such a way can essentially be seen in that with a high acceleration of the metal contaminated with compounds of different densities a high degree of demixing can be achieved and utilized. A rapid and highly effective separation or accumulation of solid suspended particles, in particular Fe
2
Al
(5-x)
Zn
x
, in the center of a rotating molten mass, was surprising for the person skilled in the art because on the one hand the difference in the specific weights is to be considered as rather small and, on the other hand, the low particle size and especially the phase boundary tensions between the compound and the liquid metal counteract demixing. The further advantage according to the invention is that, as was found, larger intermetallic particles and particularly compound agglomerates, which can cause an especially large reduction in quality of the coating, can be concentrated and discharged fully and in a highly effective manner by high acceleration.
If in so doing the molten mass containing the compounds is subjected to a centrifugal acceleration of at least 1.2 times, preferably of at least 2.1 times, particularly of more than 10.1 times the acceleration due to gravity, an efficient purification effect can be achieved.
To achieve high productivity, it is advantageous for the precipitation of compounds to be conducted essentially continuou
Andritz Patentverwaltungsgesellschaft m.b.H.
Greenblum & Bernstein P.L.C.
Kastler Scott
LandOfFree
Process and device for precipitating compounds from zinc... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and device for precipitating compounds from zinc..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and device for precipitating compounds from zinc... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3167223