Electricity: measuring and testing – Electrolyte properties
Reexamination Certificate
2000-05-04
2002-05-28
Le, N. (Department: 2858)
Electricity: measuring and testing
Electrolyte properties
C324S629000, C324S439000, C324S438000
Reexamination Certificate
active
06396280
ABSTRACT:
TECHNICAL FIELD
This invention relates to an acid concentration measuring apparatus and an acid concentration measuring method which can measure for a sufficiently short period of time and accordingly at sufficient short measurement intervals the acid concentration of a pickling solution contained in a pickling tank of a continuous pickling line for steel stock, etc. It also relates to an acid concentration automatic control apparatus which, using the acid concentration measuring apparatus, can automatically control the acid concentration of a pickling solution contained in a pickling tank, such as an acid concentration automatic control apparatus and an acid concentration automatic control method which are suitable for use with a continuous pickling line of the type in which pickling solution contained in a pickling tank on a downstream side is made to successively overflow to adjoining pickling tanks on an upstream side.
TECHNICAL BACKGROUND
Pickling is a treatment process in which an oxide scale present on the surface of steel plates, such as cold rolled steel plates, hot rolled steel plates to be subjected to cold rolling, hot rolled steel plates which are in the form of final products, is removed by immersing the steel plates in a pickling solution of hydrochloric acid, sulfuric acid, etc., or by spraying a pickling solution at the surface of the steel plates. Pickling is performed, for example, by continuously passing steel plates through a continuous pickling line in which a plurality of pickling tanks containing a pickling solution are arranged in series in the direction of movement of the plates. In pickling performed using such a continuous pickling line, the acid concentration in each pickling tank, and particularly in the last pickling tank, greatly influences the efficiency of removal of oxide scale. Therefore, in pickling using such a continuous pickling line, it is necessary to accurately control the acid concentration.
In the past, in a continuous pickling line for steel strip, acid concentration measuring of pickling solution contained in a pickling tank and the supply of acid solution were performed by measuring the acid concentration of pickling solution contained in a pickling tank using a table-top measuring device and manually supplying acid solution to the pickling tank based on the results of measuring, or by installing the table-top measuring device on a pickling tank of the continuous pickling line to automatically measure acid concentration and automatically control the amount of acid solution supplied to the pickling tank based on the results of measuring.
However, when acid solution is manually supplied to a pickling tank, it is not possible to accurately cope with changes in the concentration of the pickling solution in the pickling tank. Therefore, it is easy for fluctuations in the concentration of the pickling solution to become large, and it is easy for the amount of acid solution which is supplied to become too great when trying to stay on the safe side. Therefore, the consumption of the pickling solution per unit of output tends to become poor when acid solution is manually supplied to a pickling tank.
A titration-type analyzer is used when automatically measuring the acid concentration of pickling solution in a pickling tank with a table-top measuring apparatus installed on the pickling tank. Measuring using a titration-type analyzer is performed by successively introducing a sample liquid, a reagent, and a pickling solution into a measuring cell. Therefore, the sample liquid flows intermittently into the measuring cell, so the retained sample liquid solidifies in piping and clogs up the piping, and measuring becomes impossible a short time after it is begun.
In addition, when performing measuring using a titration-type analyzer, only a minute quantity of sample liquid is supplied, so fine tubes within the piping system become clogged. If a filtering apparatus is provided to prevent clogging, a complicated piping system having a switching mechanism becomes necessary. An increase in the number of times the switching mechanism is switched leads to clogging of the piping.
In addition, a titration-type analyzer is expensive. Therefore, when a plurality of types of sample liquid are present, the sampling pipes much be connected in parallel to a single titration-type analyzer, and measuring is carried out by switching each sampling pipe. The switching of the sample pipes also causes clogging of the pipes to become frequent.
Furthermore, when measuring with a titration-type analyzer, approximately 15 minutes are required for one sampling from the introduction of the sample liquid until the output of data. Therefore, when sampling is carried out more than once using the same titration-type analyzer, the interval between data outputs is considerable, i.e., a minimum of 15 minutes. As a result, even if a titration-type analyzer is applied to an acid concentration control system for a continuous pickling line, it is actually impossible to output the measured acid concentration of the pickling solution at sufficiently short measurement intervals.
Thus, measurement of acid concentration using a titration-type analyzer has a long reaction time for chemicals, a long switching time by a pretreatment apparatus at the time of cleaning, and a long sampling time. Therefore, a time lag between sampling and measuring is unavoidable. Furthermore, when measuring acid concentration using a titration-type analyzer, data is output intermittently at considerable intervals. Thus, the responsiveness of control is extremely poor. Accordingly, it was difficult to control the acid concentration of a pickling solution using a titration-type analyzer with high accuracy.
In this manner, measuring the acid concentration of a pickling solution in a pickling tank requires much time. Therefore, particularly in a continuous pickling line of the type in which the pickling tanks are separated by partitions and pickling solution in a pickling tank on a downstream side successively overflows to pickling tanks on an upstream side and acid solution is supplied to the final pickling tank, normally the acid concentration of only the final pickling tank is measured to determine the amount of acid solution to be supplied, whereby the supply of acid solution is controlled in accordance with the acid concentration of the pickling solution in the final pickling tank.
However, in this type of continuous pickling line, reaction between the pickling solution and the scale layer on steel strip is actually more vigorous in more upstream pickling tanks than in the final pickling tank. Therefore, when fluctuation in the acid concentration of the pickling solution is grater in the upstream pickling tanks than in the final pickling tank, scale may remain on the steel strip.
If scale remains on steel strip, it becomes necessary to stabilize the acid concentration of the pickling solution in each pickling tank by lowering the line speed. In addition, in order to prevent scale from remaining, it is necessary to control the acid concentration of pickling solution in each pickling tank more rigorously than normally. Therefore, even if it is possible to measure the acid concentration and control the supply of acid solution in real time, increases in acid consumption per unit of output, i.e., in cost are unavoidable.
Therefore, in the past, various proposals have been made of ways to speedily control the acid concentration of a pickling solution with high responsiveness to compensate for the fact that the acid concentration of pickling solution in a pickling tank could not be measured as it continuously flowed.
For example, Japanese Published Examined Patent Application Sho 57-2275 discloses an invention in which, because of the fact that in feedback control of the acid concentration of pickling solution, hatching takes place if the gain is made large while the accuracy of a sensor decreases if the gain is made small and the sensor can't be used, instead of feedback control, feed-forward control is carr
Esaki Kazuto
Kataoka Takeo
Nonaka Toshihiko
Burns Doane , Swecker, Mathis LLP
Hamdan Wasseem H.
Le N.
Sumitomo Metal Industries Ltd.
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