Patent Application
20060049160
This invention relates generally to annealing of strips. More specific it relates to method and arrangement for annealing of strips using direct resistance heating.
Narrow strips are usually slit from wide strip. Eventual annealing is made before slitting. Strand annealing is necessary if rapid cooling is needed. The required capacity for annealing can be reached by using moderate speeds up to 120 m/min. In some cases it would be desirable to process the strip as a narrow strip without slitting and anneal it as a single strip. In order to reach enough capacity, the strip speed needs to be higher. The required speed is up to 500 m/min. This means that the above described systems are not suitable for this kind of production.
An example of high speed annealing equipment can be found in wire industry, where 2000 m/min is a normal annealing speed. The annealing is done by using direct resistance heating. Such equipment is made with three or four contact rolls. In both cases the first and last rolls are connected electrically to each other and earthed to make the line electrically neutral. The system utilizes 3-phase current.
From the document EP 0 155 917 is also known a system for wire annealing plants. The wire is annealed with pair of consecutive rollers the rollers having plurality of electrically-conductive segments, which are insulated from each other. The segments are connected to the voltage source with electrical sliding contacts so that a voltage is not applied to the segments at the ends of the arc of winding. This is to avoid severe sparking or arching that happens and destroys the surface of the wire.
The object of the present invention is to produce a method and an arrangement, where the mechanical contact with the roller having electrically conductive segments and the strip is made before the electrical contact is connected and the electrical contact is disconnected before the mechanical contact is lost. The method and the arrangement are also much simpler than any prior art method and arrangement.
Another object of the invention is to produce a method and an arrangement where the strip is directed back to contact the same roller having electrically conductive segments twice and cut down the energy used in annealing.
These above mentioned objects are achieved by a method and an arrangement described later in the independent claims. In the dependent claims are presented other advantageous embodiments of the invention.
In the following the preferred embodiments are described in more details with reference to the accompanying drawings, where
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The electrically conductive segments 5 are insulated from each other with insulating segments 6. The conductive means can also be arranged outside of the commutator 2 contacting either the outer periphery of the commutator or the side of the commutator perpendicular to the rolling axis 20 of the commutator. The produced heat is conducted to the strip 1 to be annealed. After having the first contact with the commutator 2 the strip 1 is directed to the second rotable supported roller, which is a directing roller 7 directing the strip back to contact with the opposite side of the circumference of the same commutator. Then the strip 1 is directed further into the process. The brushes 4 and 5 inside the commutator 2 are arranged so that the mechanical contact between the strip 1 and the commutator is made before the electrical coupling is connected and lost after the electrical coupling is disconnected. This way the sparking or arching which are harmful to the surface and edges of the strip 1 are avoided.
By directing the strip 1 back to the same commutator 2 a significant amount of energy can be saved. At the exit side of the contact areas the hot strip 1 releases heat to the commutator 2 and at the entry side of the contact areas the hot commutator preheats the strip and the strip cools the commutator. In other words, we are using the cold incoming strip 1 to cool the hot strip and save energy. The energy saving aspect is not possible with a prior art arrangement annealing a wire because the contact surface for heat transfer between the wire and the commutator is very small and the prior art arrangements are using one commutator only once.
Theoretically, if the strip 1 was moving very slowly we could save almost 50% of the energy. For example, if the final temperature is 600K above the ambient temperature, then using the hot strip 1 it is possible to preheat the incoming strip to 300K above the ambient temperature and at the same time cool the outgoing strip to the same temperature. In production speeds it is not possible to achieve quite the theoretical saving but in any case the arrangement is very efficient as compared to the prior art methods.
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While the invention has been described with reference to its preferred embodiments, it is to be understood that modifications and variations will occur to those skilled in the art. Such modifications and variations are intended to fall within the scope of the appended claims.
