CN103695830A - Method for controlling thickness of coating in hot galvanizing production process - Google Patents

Abstract

The invention provides a method for controlling the thickness of a coating in the hot galvanizing production process, which is characterized in that a coating thickness self-adaptive control unit, an air knife pressure feedback model control unit and an air knife position deviation control unit are additionally arranged in a hot galvanizing PLC (programmable logic controller), and a coating thickness self-adaptive feedforward control model, an air knife pressure feedback correction model and an air knife operation side and transmission side position deviation calculation model are respectively established. The invention can restrain the disturbance of the change of the linear velocity of the process section to the thickness of the coating, improve the response speed of the system, and respectively correct the thickness deviation of the coating and the position set values at the two sides of the air knife, thereby achieving the purposes of dynamically adjusting the position of the air knife and correcting the thickness deviation of the transverse coating and realizing the automatic control of the thickness of the coating in the galvanizing process. Therefore, the problem of overlarge thickness deviation of a galvanized layer caused by manual control of an operator is solved, the transverse uniformity of the thickness of the plated layer is effectively improved, the surface quality of a galvanized steel sheet product is improved, the consumption of zinc raw materials is reduced, and the production cost is reduced.

Description

Thickness of coating control method in a kind of pot galvanize production process

Technical field

The invention belongs to galvanizing process automation control area, particularly a kind of for pot galvanize production process thickness of coating control method.

Background technology

Pot galvanize product has very strong erosion resistance and good outward appearance, and therefore, its Application Areas is more and more extensive, has been widely used at present the industries such as automobile, building, electrical equipment, container, traffic, the energy, agricultural.Along with the continuous expansion of pot galvanize product application scope, people are also constantly improving its accuracy requirement.The level of control of hot dip galvanizing coating thickness will directly have influence on quality product, product cost and the competitiveness of product in market of heat zinc coating plate.

In strip steel Zn-plating process, the factor that affects strip coating thickness is complicated, nonlinear, causes the control accuracy of such Controlling System not high.At present, most production lines still mainly adopt traditional control method to the accurate control of thickness of coating, by operator, according to experience, set(ting)value are carried out to manual setting.Because manual intervention can be different because of operator's difference, thereby inevitably can cause the deviation on zinc coating thickness, thereby it is thin or blocked up that zinc layer is crossed, and finally causes galvanizing production Quality Down, and waste zinc raw material, such control situation is difficult to meet production requirement.

Each main hot dip galvanizing process producer of the world is summing up on knowhow basis, formed a set of oneself control method, all take and regulate air knife to leave with the spacing of steel and the pressure parameter of air knife nozzle purging air as main, but have their own characteristics each, in concrete control algolithm and steering logic, incorporated the knowhow of oneself and controlled tricks of the trade.

Number of patent application 200510024116.X discloses a kind of hot dip galvanized coating control method and device,, at band steel, electromagnetic generator is housed around, by regulating magneticstrength, adjust hot dip galvanizing coating thickness, by improving the method for technique, improve thickness of coating, but need to increase electromagnetism hardware device, could realize coating control, cost is higher.Japanese Patent JP10273766 provides a kind of thickness of coating control method, according to the thick air pressure of controlling of target plating in the thick setting model equation of plating, but the model equation structure proposing due to its is too complicated and will determine nearly 6 optimal coefficients, applies online and realize very difficult.Lin Lijun proposition system in the application document of Baosteel hot galvanizing unit layer weight control model adopts forecast Control Algorithm, on-line optimization model coefficient, and system possesses good robustness.But system adopts air knife nozzle gap Priority Control Schemes, and thickness of coating changes very sensitivity to air knife nozzle gap, easily causes the control overshoot of system, is unfavorable for the accurate control of thickness of coating.Dong Zhandong has proposed to control by improving air knife gaseous tension the method for zinc coating thickness in a kind of document of effective ways of controlling zinc coating thickness, adopt the air sword blower fan of connecting again to improve air quantity, thereby reduce the modification scheme of zinc coating thickness, but it is only to reduce Zinc Coating Thickness by improving air knife top hole pressure, cannot realize the accurate control of thickness of coating.

Summary of the invention

The object of the present invention is to provide and a kind ofly eliminate manual control and cause galvanized layer thickness deviation problems of too, thereby improve galvanizing production quality, reduce zinc raw material consumption, realize the method that in pot galvanize production process, thickness of coating is controlled automatically.

For this reason, the solution that the present invention takes is:

Thickness of coating control method in a kind of pot galvanize production process, it is characterized in that, in pot galvanize PLC, set up thickness of coating self-adaptive controller, air pressure feedback model control unit and air knife position offset control unit, realize the automatic control of thickness of coating in galvanizing process.Its concrete grammar is:

1, thickness of coating self-adaptive controller

Due to the requirement of zinc-plated production technique, unit speed can frequently change, and when unit speed improves suddenly or reduces, can produce very large impact to thickness of coating, so this thickness of coating adaptive control is very important.Therefore, according to thickness of coating target value and air knife cutter, apart from processing parameter, calculate the set(ting)value of air pressure, for thickness of coating provides an adaptive feedforward, control model, adaptive feedforward is controlled model formation and is:

$P_{\mathrm{top}}={\mathrm{kV}}^a{(D_{\mathrm{top}}+\mathrm{\ΔG}/2+\mathrm{\ΔS})}^b{H}_{\mathrm{tar}}^c,P_{\mathrm{bot}}={\mathrm{kV}}^a{(D_{\mathrm{bot}}+\mathrm{\ΔG}/2-\mathrm{\ΔS})}^b{H}_{\mathrm{bot}}^c$

In formula: P _topfor the air pressure feedforward set(ting)value with steel upper surface, P _botfor the air pressure feedforward set(ting)value with steel lower surface, D _topfor air knife with band steel upper surface apart from calculated value, D _botfor air knife with band steel lower surface apart from calculated value, △ G is change of distance value between upper and lower air knife, △ S is air knife framework side-play amount, H is target thickness of coating value, k, a, b, c are model constants.

2, air pressure feedback model control unit

Thickness of coating deviation can be corrected by feed forward control major part, but, the interference that some cannot be measured and affect thickness of coating again unpredictable variable exceeded feed forward control scope as belt plate shape, band steel shake etc., can only realize by feedback control.The strip coating thickness actual measured value of utilizing layer thickness meter to detect is compared and is obtained difference with target thickness of coating, according to this difference, calculates and revises the needed air pressure modified value of zinc plated plate plated layer thickness deviation; Air pressure feedback modifiers model formation is:

$P_{\mathrm{FBC}}=P_{\mathrm{act}}^n+{\mathrm{\α}}_n(H_{\mathrm{tar}}-H_{\mathrm{act}}^n)$

In formula: P _fBCfor air pressure feedback modifiers calculated value,

for actual air pressure detected value, α _nbe the proportional feedback gain of the n time scan cycle, H _tarfor target thickness of coating value, H _actfor actual thickness of coating value.

3, air knife position offset control unit

Air knife position offset control unit is for controlling the distribution bias of the horizontal thickness of coating of galvanized sheet.Bad or the uneven thickness of belt plate shape can cause strip width direction to produce and reverse, and makes air knife inhomogeneous with band steel both sides spacing.Therefore, dynamically adjust air knife position, sync bit correction is made in the two ends of same air knife, make the position of center line in upper and lower air knife with steel, to proofread and correct the deviation of the horizontal thickness of coating of galvanized sheet; By equilibrium calculation at the operating range with steel both sides upper surface and lower surface, correction tape steel distortion tilt error, forward migration variation can cause air knife with the increase of steel upper surface distance, air knife fore side and back side position calculations of offset model formation are:

$S_{\mathrm{set}}^{\mathrm{OS}}=S_{\mathrm{pre}}^{\mathrm{OS}}+(D_{\mathrm{bot}}^{\mathrm{OS}}-D_{\mathrm{top}}^{\mathrm{OS}})/2$

$S_{\mathrm{set}}^{\mathrm{DS}}=S_{\mathrm{per}}^{\mathrm{DS}}+(D_{\mathrm{bot}}^{\mathrm{DS}}-D_{\mathrm{top}}^{\mathrm{DS}})/2$

In formula:

be respectively air knife fore side and back side deviation post correction set(ting)value,

air knife fore side and back side deviation post currency,

for fore side air knife and band steel upper surface distance,

for back side air knife and band steel upper surface distance, for fore side air knife and band steel lower surface distance,

for back side air knife and band steel lower surface distance.

Beneficial effect of the present invention is:

The present invention calculates by the self-adaptation adjustment of air pressure, and the disturbance of the variation that has suppressed process section linear velocity to thickness of coating, has improved system response time; Adopt air pressure feedback model control method, by air pressure feedback modifiers is calculated thickness of coating deviation is revised; Adopt air knife position skew control method, the position setting value of air knife both sides has been carried out respectively to corrected Calculation, reach dynamic adjustment air knife position and proofread and correct horizontal thickness of coating deviation, realize the automatic control of thickness of coating in galvanizing process.Thereby solved operative employee and manually controlled caused galvanized layer thickness deviation problems of too, can effectively improve thickness of coating horizontal homogeneity, improved steel plate galvanized product surface quality, reduced zinc raw material consumption, reduced production costs.

Accompanying drawing explanation

Fig. 1 is thickness of coating adaptive control schema;

Fig. 2 is air knife position skew control flow chart.

Embodiment

Embodiment carries out at certain continuous hot galvanizing line, and this hot galvanizing line product orientation is building panel and appliance plate, and production technique adopts improvement Sendzimir method, about 400,000 tons of annual production.Air knife adopts German FOEN company, and apparatus for production line and electric and automatic control system originate from German SIEMENS company.Galvanized layer thickness scope is 80-276g/m ², plate is wide is 1004～1256mm, strip speed variation range is 80～150m/min.Concrete implementation step is as follows:

Step 1: as Fig. 1, when galvanizing process line speed changes, the zinc coating thickness of belt steel surface also can change, must adjust air knife distance and air pressure in time to keep thickness of coating constant.Gather current air pressure, speed and the abundant measured value of plating, then recalculate cutter apart from conduct feedforward adaptation coefficient, and cutter now apart from computation model is:

$D_{\mathrm{top}}={\left(\frac{P_{\mathrm{act}}^{\mathrm{top}}}{k{V}^a{H}_{\mathrm{act}}^c}\right)}^{1/b},D_{\mathrm{bot}}={\left(\frac{P_{\mathrm{act}}^{\mathrm{bot}}}{k{V}^a{H}_{\mathrm{act}}^c}\right)}^{1/b}$

Then by the cutter recalculating in value substitution adaptive feedforward control model:

$P_{\mathrm{top}}=k{V}^a{(D_{\mathrm{top}}+\mathrm{\ΔG}/2+\mathrm{\ΔS})}^b{H}_{\mathrm{tar}}^c$

Calculate the feedforward set(ting)value of air pressure, the air pressure value wherein collecting and thickness of coating value are band steel upper surface measured value, the air pressure feed forward control model of upper surface as shown in the formula:

$P_{\mathrm{top}}=k{V}^a{({\left(\frac{P_{\mathrm{act}}^{\mathrm{top}}}{k{V}^a{H}_{\mathrm{act}}^c}\right)}^{1/b}+\mathrm{\ΔG}/2+\mathrm{\ΔS})}^b{H}_{\mathrm{tar}}^c$

Air pressure feed forward control model with steel lower surface is:

$P_{\mathrm{bot}}=k{V}^a{({\left(\frac{P_{\mathrm{act}}^{\mathrm{bot}}}{k{V}^a{H}_{\mathrm{act}}^c}\right)}^{1/b}+\mathrm{\ΔG}/2-\mathrm{\ΔS})}^b{H}_{\mathrm{tar}}^c$

When with steel, skew occurs the position between upper and lower air knife, between upper and lower air knife, the side-play amount of distance G is:

△G=G ₂-G ₁

In formula: G1 is the distance of air knife up and down with before the skew of steel position, G2 is the distance of air knife up and down with after the skew of steel position.

The side-play amount that now departs from rolling centerline with steel is:

△S=S ₂-S ₁

In formula: S1 is the band steel position with before the skew of steel position, S2 is the band steel position with after the skew of steel position.

Step 2: occur belt plate shape in galvanizing process, during with steel vibration etc. these unpredictable interference volumes, need to revise the thick deviation of plating by feedback control.Thickness of coating feedback control depends on the thick measuring accuracy of plating, when weld seam passes through thickness tester, the strip coating thickness actual measured value that calculating layer thickness meter detects and the difference of target thickness of coating, then calculate and revise the needed compensation rate of thickness of coating deviation according to difference.Feedback control be take air pressure as main control quantity, the initial sum time length of feedback control is most important, when the impact that employing regulates when air pressure last time reaches thickness tester and Output rusults detected, air pressure is controlled the output that just can next time revise, by changing air pressure, dynamically reduces to plate thick error.

Air pressure feedback modifiers computation model is:

$P_{\mathrm{FBC}}=P_{\mathrm{act}}^n+{\mathrm{\α}}_n(H_{\mathrm{tar}}-H_{\mathrm{act}}^n)$

In formula: α _nbe the proportional feedback gain of the n time scan cycle, wherein, the proportional feedback gain alpha of the n time scan cycle _n(n>1) calculation formula is:

${\mathrm{\α}}_n=(P_{\mathrm{act}}^n-P_{\mathrm{act}}^{n-1})/(H_{\mathrm{act}}^n-H_{\mathrm{act}}^{n-1})$

thick with respect to the average plating of the i time detection

air pressure observed value, and feedback limiter is the part deviation of feedforward pressure pattern for the first time, feedback limiter α for the first time ₁calculation formula is:

${\mathrm{\α}}_1=\mathrm{ck}{V}^a{D}^b{H}_{\mathrm{tar}}^{c-1}$

In addition, compared with large pressure divergence, can cause being with the serious skew of steel and cannot revise thickness deviation, so when upper and lower surface pressure divergence transfinites, feedback control can amplitude limit upper and lower surface pressure divergence be 5kPa, if the poor P of upper and lower surface air pressure _top-P _bot>5kPa, reduces upper surface air pressure P _top, now

P _top=（P _top+P _bot）/2-2.5

Increase lower surface air pressure P simultaneously _bot, now

P _bot=（P _top+P _bot）/2+2.5

During normal work, feedback modifiers effectively starts to be just performed from scanning for the first time, because the time of response of feedback loop is long, depend on air knife and thickness tester propagation delay time, system regulates closed loop making time to need two sequential processes to change interval, if strip speed changes frequently, band steel will be only be controlled air pressure and feedback control is not carried out under feed-forward mode.

Step 3: as Fig. 2, owing to can cause the inhomogeneous defect of coating width when belt plate shape changes suddenly, so now call air knife framework torsion offset control unit, guarantee the thickness of coating uniformity coefficient in strip width direction, it is by regulating air knife operation and back side deviation post to make air knife frame position be parallel to band steel position of center line.

The triggering Rule of judgment of this control unit is:

In every meter of strip width direction, thickness deviation is more than or equal to 3g/m ², and be with steel position offset to be more than or equal to 0.4mm simultaneously.

The detection probe of coating thickness meter is consecutive periods scanning back and forth in strip width direction, along having 100 check points on air knife width.Thickness tester gathers a thickness data every a segment distance in belt steel surface broad ways, obtains the detected value that the multiple spot thickness of coating value in whole strip width direction is controlled as thickness of coating.

In every meter of strip width direction, thickness deviation calculation formula is:

$|H_{\mathrm{bot}}^{\mathrm{OS}}+H_{\mathrm{top}}^{\mathrm{DS}}-(H_{\mathrm{bot}}^{\mathrm{DS}}+H_{\mathrm{top}}^{\mathrm{OS}})|/2w$

In formula: for band steel fore side lower surface plates abundant measured value,

for band steel fore side upper surface plates abundant measured value,

for band steel back side lower surface plates abundant measured value,

for band steel back side upper surface plates abundant measured value, w is strip width.

Side-play amount calculation formula with steel positional distance rolling centerline is:

$|D_{\mathrm{bot}}^{\mathrm{OS}}+D_{\mathrm{bot}}^{\mathrm{DS}}-(D_{\mathrm{top}}^{\mathrm{OS}}+D_{\mathrm{top}}^{\mathrm{DS}})|/2$

In formula: band steel fore side air knife and lower surface cutter distance,

band steel back side air knife and lower surface cutter distance,

band steel fore side air knife and upper surface cutter distance,

band steel back side air knife and upper surface cutter distance.

Air knife fore side and back side deviation post correction model calculation formula as:

$S_{\mathrm{set}}^{\mathrm{OS}}=S_{\mathrm{per}}^{\mathrm{OS}}+(D_{\mathrm{bot}}^{\mathrm{OS}}-D_{\mathrm{top}}^{\mathrm{OS}})/2$

$S_{\mathrm{set}}^{\mathrm{DS}}=S_{\mathrm{per}}^{\mathrm{DS}}+(D_{\mathrm{bot}}^{\mathrm{DS}}-D_{\mathrm{top}}^{\mathrm{DS}})/2$

In formula:

for air knife operation and back side deviation post modified value,

respectively air knife fore side and back side deviation post currency.

In steady-state adjustment process, skew thickness is that thickness tester continuously scans through 4 times the mean value providing, and resets after the 4th scanning, determines whether to need air knife position correction, and every 4 scanning periods start a computation process.In feedback control, the minimum interval of two continuous position corrections was determined by transmission communication time and at least 4 sweep times, and this method can suppress noise and avoid unnecessary frequent adjustment action.

Claims (1)

1. thickness of coating control method in a pot galvanize production process, it is characterized in that, in pot galvanize PLC, set up thickness of coating self-adaptive controller, air pressure feedback model control unit and air knife position offset control unit, realize the automatic control of thickness of coating in galvanizing process, its concrete grammar is:

(1), thickness of coating self-adaptive controller

According to thickness of coating target value and air knife cutter, apart from processing parameter, calculate the set(ting)value of air pressure, for thickness of coating provides an adaptive feedforward, control model, adaptive feedforward is controlled model formation and is:

$P_{\mathrm{top}}={\mathrm{kV}}^a{(D_{\mathrm{top}}+\mathrm{\ΔG}/2+\mathrm{\ΔS})}^b{H}_{\mathrm{tar}}^c,P_{\mathrm{bot}}={\mathrm{kV}}^a{(D_{\mathrm{bot}}+\mathrm{\ΔG}/2-\mathrm{\ΔS})}^b{H}_{\mathrm{bot}}^c$

In formula: P _topfor the air pressure feedforward set(ting)value with steel upper surface, P _botfor the air pressure feedforward set(ting)value with steel lower surface, D _topfor air knife with band steel upper surface apart from calculated value, D _botfor air knife with band steel lower surface apart from calculated value, △ G is change of distance value between upper and lower air knife, △ S is air knife framework side-play amount, H is target thickness of coating value, k, a, b, c are model constants;

(2), air pressure feedback model control unit

The strip coating thickness actual measured value of utilizing layer thickness meter to detect is compared and is obtained difference with target thickness of coating, according to this difference, calculates and revises the needed air pressure modified value of zinc plated plate plated layer thickness deviation; Air pressure feedback modifiers model formation is:

$P_{\mathrm{FBC}}=P_{\mathrm{act}}^n+{\mathrm{\α}}_n(H_{\mathrm{tar}}-H_{\mathrm{act}}^n)$

In formula: P _fBCfor air pressure feedback modifiers calculated value,

for actual air pressure detected value, α _nbe the proportional feedback gain of the n time scan cycle, H _tarfor target thickness of coating value, H _actfor actual thickness of coating value;

(3), air knife position offset control unit

Air knife position offset control unit is for controlling the distribution bias of the horizontal thickness of coating of galvanized sheet; Dynamically adjust air knife position, sync bit correction is made in the two ends of same air knife, make the position of center line in upper and lower air knife with steel, to proofread and correct the deviation of the horizontal thickness of coating of galvanized sheet; By equilibrium calculation at the operating range with steel both sides upper surface and lower surface, correction tape steel distortion tilt error, forward migration variation can cause air knife with the increase of steel upper surface distance, air knife fore side and back side position calculations of offset model formation are:

$S_{\mathrm{set}}^{\mathrm{OS}}=S_{\mathrm{pre}}^{\mathrm{OS}}+(D_{\mathrm{bot}}^{\mathrm{OS}}-D_{\mathrm{top}}^{\mathrm{OS}})/2$

$S_{\mathrm{set}}^{\mathrm{DS}}=S_{\mathrm{per}}^{\mathrm{DS}}+(D_{\mathrm{bot}}^{\mathrm{DS}}-D_{\mathrm{top}}^{\mathrm{DS}})/2$

In formula:

be respectively air knife fore side and back side deviation post correction set(ting)value,

air knife fore side and back side deviation post currency,

for fore side air knife and band steel upper surface distance,

for back side air knife and band steel upper surface distance,

for fore side air knife and band steel lower surface distance,

for back side air knife and band steel lower surface distance.

Images