KR20040049607A - Method for Manufacturing Shipbuilding Steel Plate - Google Patents

Abstract

PURPOSE: A manufacturing method of steel plate for ship building is provided to manufacture the steel plate for ship building capable of satisfying both weight limit and thickness tolerance without increase of thickness defect by suggesting strict thickness tolerance. CONSTITUTION: The method comprises the steps of setting upper and lower thickness limit tolerances of the steel plate; setting a target rolling thickness using product thickness and lower thickness limit tolerance; rolling a rolling work to the target rolling thickness by controlling a rolling mill; longitudinally measuring thickness of central part and both edge parts of the steel plate using a thickness gauge after cutting width and length of the steel plate to ordered dimensions if the rolling completed steel plate is cooled to an ordinary temperature; calculating the minimum thickness and average thickness of the steel plate in the measured thickness values; rejecting the steel plate if the minimum thickness in the measured thickness values is less than a lower limit thickness, accepting the steel plate if the average thickness is less than an upper limit thickness, and waiting judgement of the steel plate if the average thickness is greater than the upper limit thickness; obtaining an actual weight of each product for accepted work and judgement standby work if rolling for order lot is completed; obtaining a weight ratio per each product using actual product weight for the judgement standby work and ordered product weight; accepting the steel plate if the total weight ratio is 1.015 or less after obtaining the total weight ratio by summing up weight of the selected product and weight of the accepted work after selecting a product having the lowest weight ratio (actual product weight/ordered product weight) in the judgement standby work; and finishing production if the accepted product entirely satisfies ordered product quantity after performing the foregoing processes for the judgement standby work, and repeating the foregoing processes by additionally producing shortfall until the accepted product satisfies the ordered product quantity if the accepted product does not satisfy the ordered product quantity.

Description

Method for Manufacturing Shipbuilding Steel Plate

The present invention relates to a method for manufacturing a ship steel sheet, and more particularly, to a method for manufacturing a ship steel sheet that can satisfy both the weight limit and thickness tolerance.

In general, the thickness inspection of the steel sheet is set to the upper and lower thickness tolerance for each product thickness, such as the thickness tolerance of shipbuilding steel shown in Table 1, and when the thick plate rolling is completed, the thickness is measured in the longitudinal direction and the width direction of the steel sheet If the thickness measurement is out of the upper and lower thickness tolerances even in one position, the product is defective.

Product thickness Product width Lower Thickness Tolerance Upper limit thickness tolerance Remarks 10.0 ~ 15.0mm 1500 to 5000mm -0.70 ~ 1.00mm 0.70 ~ 1.00mm Weight based on product width 15.0 ~ 25.0mm 〃 -0.80 ~ 1.10mm 0.80 ~ 1.10mm 25.0 ~ 40.0mm 〃 -0.90 ~ 1.20mm 0.90-1.20mm

On the other hand, the thickness deviation in a product includes the thickness variation in the longitudinal direction caused by the temperature variation in the longitudinal direction of the steel sheet and the warpage of the rolling roll caused by the rolling load during rolling. Considering these thickness deviations, thickness tolerances are set and operated for each product thickness.

In recent years, however, the number of ships carrying people, such as cruise ships, has increased, and as the ships become more advanced, ships are made using thin steel plates within the limit of securing the strength of the steel plates to transport as many people as possible in the same volume. It is light in weight to volume.

To this end, shipbuilding companies, which have a demand for shipbuilding steel sheets, have to reduce the thickness of the product as much as possible to reduce the weight of the ship in the material sector, unlike the thickness tolerance range set by the Society. Very stringent conditions are suggested, such as requiring within ± 1.5% of thickness.

That is, the lower limit of the thickness tolerance of -1.5% is for securing the strength of the material, and the upper limit of + 1.5% is for managing the ship's weight within + 1.5% of the target weight in the part of the material.

On the other hand, the thickness in the steel sheet is a deviation occurs in the longitudinal direction as shown in FIG.

These phenomena are caused by the temperature variation that occurs when heating slab, which is the material of the steel sheet, and the off-gauge at the tip portion where the steel sheet is first inserted during rolling, and as shown in FIG. The thickness shows the thinnest state.

In addition, in order to control the thickness of the tip, which is the thinnest position, within the thickness tolerance, the rolling target thickness must be set higher than the product thickness, so the average thickness of the product after rolling becomes thicker than the order thickness, so that the actual product weight is higher than the order product weight. It becomes heavy. In order to reduce the overweight caused by these phenomena, shipbuilding companies strictly demand the steel sheet manufacturers to limit the thickness.

Therefore, if the thickness tolerance is not applied to each conventional classification societies, and is set within ± 1.5% of the product thickness as required by the demand price, the thickness defect will increase significantly to meet the demand demand. If you can not do this, or if the demand of the demand is due to the increase in thickness, there is a problem that the profitability of the steel sheet manufacturer.

The present invention has been proposed to solve the problems of the prior art, to provide a shipbuilding steel sheet that can satisfy both the weight limit and the thickness tolerance without increasing the thickness defect by strictly presenting the thickness tolerance, the object.

1 is a schematic diagram showing the longitudinal thickness distribution of shipbuilding steel plate

2 is a schematic diagram showing a method for calculating a rolling target thickness according to the present invention.

Figure 3 is a thickness measurement position for calculating the minimum and average thickness of the product

Figure 4 is a schematic diagram showing the inspection results according to the thickness when manufacturing the steel sheet according to the present invention method

Explanation of symbols on the main parts of the drawings

One . . . Steel sheet in the state of complete rolling

2 . . . Steel plate produced as a product after rolling is completed

3. . . WS (right) thickness measurement position of steel plate

4 . . . CN (center) thickness measurement position of steel plate

5. . . DS (left) thickness measurement position of steel plate

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention comprises the steps of setting the upper and lower thickness tolerance of the steel sheet;

Setting a rolling target thickness using a product thickness and a lower limit thickness tolerance;

Controlling the rolling mill to roll the rolled material to a rolling target thickness;

After the rolled steel sheet is cooled to room temperature, after cutting the width and length to the order size, measuring the thickness of the center portion and both edges of the steel sheet in the longitudinal direction using a thickness meter;

Calculating a minimum thickness and an average thickness from the thickness measurements;

If the minimum thickness of the thickness measurement is smaller than the lower limit, reject processing; otherwise, if the average thickness is smaller than the upper limit, pass the processing; and if the average thickness is larger than the upper limit, waiting for determination;

When the rolling of the order lot is completed, calculating the actual weight of each product for the pass material and the determination air material;

Obtaining a weight ratio for each product using the actual product weight and the order product weight for the determination atmospheric material;

Selecting a product having the smallest weight ratio (actual product weight / order product weight) from the determination base material and adding the same together with the pass material to obtain the cumulative weight ratio, and then performing a pass process if the cumulative weight ratio is 1.015 or less;

After all the above processes are performed on the determination waiting material, the production is terminated if the passed product satisfies the total quantity of the ordered product. Otherwise, the above process is repeated by additionally producing a shortage until the order quantity is satisfied. It relates to a method for producing a ship steel sheet configured by.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

According to the present invention, in order to manufacture steel sheet for shipbuilding for tight tolerance of thickness tolerance, the upper and lower thickness tolerances of the steel sheet required by the orderer are set.

Next, the rolling error and the plate crown are compensated by the method shown in FIG. 2 using the product thickness and the lower limit thickness tolerance, and the rolling target thickness TATH is obtained by the following equation (1).

[Relationship 1]

TATH = PLTH-MTOL + ERR + Pcrown

[Here, PLTH: Product Thickness (mm)

MTOL: Product Lower Limit Tolerance (= Product Thickness * 0.015, mm)

ERR: Rolling error (inside thickness deviation + thickness deviation between plates)

Pcrown: Plate Crown (mm)]

The rolling error in Equation (1) includes the plate thickness deviation and the plate thickness deviation, and is obtained by regression analysis by collecting the deviation performance for each product thickness.

Here, the thickness deviation (Dinter) in the plate should be preceded by satisfying the lower limit thickness, so that the difference between the average thickness and the lower limit thickness for each product thickness is a dependent variable, and the product thickness (PLTH) is an independent variable. To derive

[Relationship 2]

Dinter = a × PLTH + b

In addition, the plate thickness deviation (Dintra) is derived from the difference between the target thickness and the average thickness for each product as a dependent variable, and the target thickness (TATH) as an independent variable to derive a regression equation as shown in Equation (3).

[Relationship 3]

Dintra = c × TATH + d

a, b, c, and d are regression coefficients determined by the plant's controllability, and are determined by experimental results.The preferred values are a: 0.004 to 0.008, b: 0.05 to 0.15, c: 0.008 to 0.015, d: 0.05-0.15 can be mentioned.

Next, the rolling mill is controlled to roll the rolled material to the rolling target thickness.

When the finished steel sheet is cooled to room temperature as described above, the width and length are cut to the product order dimension, and then the thickness of the center portion and both edge portions of the steel sheet is longitudinally measured as shown in FIG. Measure with

In FIG. 3, reference numeral 1 denotes a steel sheet in a completed rolling state, numeral 2 denotes a steel sheet produced as a product after rolling is completed, numeral 3 denotes a WS (right) thickness measurement position of the steel sheet, and numeral 4 denotes a CN (center part) of the steel sheet. The thickness measurement position, and reference numeral 5 denotes the DS (left) thickness measurement position of the steel sheet.

Next, the minimum thickness MinTH is calculated using the following equation (4) among the thickness measurements, and the average thickness AveTH is obtained using the following equation (5).

[Relationship 4]

MinTH = Min {∑ [MTHCN (i), MTHWS (i), MTHDS (i)]}

[Here, MTHCN: thickness of the steel sheet measured in the longitudinal direction in the center of the width direction

Average value (mm)

MTHWS: Average value of the thickness measured in the longitudinal direction from the WS (right) of the steel sheet (mm)

MTHDS: Average value of the thickness measured in the longitudinal direction from the DS (left) of the steel sheet (mm)

i: Each position measured in the longitudinal direction using a thickness meter]

[Relationship 5]

AveTH = [(MTHDS + MTHWS) / 2 + MTHCN] / 2

The reason for obtaining the average thickness is to find the actual weight of the steel sheet.

In other words, the weight increase in shipbuilding steel plate is equal to the thickness increase rate.

This is because the width and length of the steel sheet are used after cutting and welding.

Therefore, shipbuilders require strict control of thickness limits to achieve weight limits.

Next, as shown in FIG. 4, if the minimum thickness is smaller than the lower limit allowable thickness, the process is rejected. Otherwise, if the average thickness is smaller than the upper limit, the pass is processed. .

Here, if the minimum thickness is smaller than the lower limit, it is a problem for the strength of the steel sheet and must be rejected.However, even if the average thickness exceeds the upper limit, it does not exceed + 1.5% of the weight limit for the whole lot product ordered. If not, the decision is suspended.

Next, when the rolling of the order lot is completed, the actual weight (MCWt) for each product is obtained by the following equation (6) using the average thickness, width, and length of the pass material and the determination base material.

[Relationship 6]

MCWt = AveTH * WID * LEN * ρ / k

[WID: product width (mm)

LEN: Product length (mm)

ρ: specific gravity (g / ㎣)

k: unit conversion constant (1000)]

Next, the weight ratio (actual product weight / order product weight) for each product is determined by the following equation (7) with respect to the determination atmospheric material.

[Relationship 7]

WtRatio = MCWt / ODWt

[WtRatio: weight ratio of actual product to order weight

ODWt: Order Weight

Next, the products having the smallest weight ratio WtRatio are selected one by one, and the cumulative weight ratio is determined as the pass material. If the weight ratio is 1.015 or less, the pass processing is performed.

In this case, the reason why the average thickness is processed sequentially from the smallest product to the order thickness is to reduce the number of poor thickness products that may occur by selecting the product with the least influence on the weight.

Next, after all the above processes are carried out for the judgment-listing material, the production is terminated when the passed product satisfies the ordered product quantity. Therefore, it is possible to reduce the defects while satisfying both the thickness and weight for the shipbuilding steel sheet with a tight thickness tolerance.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example)

Product thickness: 10 ~ 15mm, product width: 2500 ~ 3500mm For each 1000 sheets, apply the thickness tolerance ± 1.5% considering the strength and weight of the product that the demand demands. The failure rate for the case and the case produced by the method of the present invention was investigated, and the results are shown in Table 2 below.

division pass fail Waiting for judgment Rejection rate Invention method 1st inspection 826 4 170 0.4% final check 170 0 - system 996 0 - Conventional method 825 175 - 17.5%

As shown in Table 2, in the case of the conventional method, the rejection rate was 17.5%, but in the case of the present invention, the rejection rate was significantly reduced to 0.4%.

As described above, in the present invention, the thickness inspection of shipbuilding steels for strict management of thickness tolerances to reduce the weight of ships and to secure the strength of materials by thinning the thickness of materials such as cruise ships is primarily performed. It is carried out by using the weight ratio of the actual product to the average thickness and the order weight at the end, it is possible to significantly reduce the thickness defects while satisfying both the thickness tolerance and the weight limit.

Claims (2)

Setting upper and lower thickness tolerances of the steel sheet; Obtaining a rolling target thickness (TATH) by the following equation (1); [Relationship 1] TATH = PLTH-MTOL + ERR + Pcrown [Here, PLTH: Product Thickness (mm) MTOL: Product Lower Limit Tolerance (= Product Thickness * 0.015, mm) ERR: Rolling error (inside thickness deviation + thickness deviation between plates) Pcrown: Plate Crown (mm)] Controlling the rolling mill to roll the rolled material to a rolling target thickness; After the rolled steel sheet is cooled to room temperature, after cutting the width and length to the order size, measuring the thickness of the center portion and both edges of the steel sheet in the longitudinal direction using a thickness meter; Obtaining a minimum thickness MinTH using the following equation (4) from the thickness measurements, and obtaining an average thickness AveTH using the following equation (5); [Relationship 4] MinTH = Min {∑ [MTHCN (i), MTHWS (i), MTHDS (i)]} [Here, MTHCN: average value of the thickness measured in the longitudinal direction at the center of the width direction of the steel sheet (mm) MTHWS: Average value of the thickness measured in the longitudinal direction from the WS (right) of the steel sheet (mm) MTHDS: Average value of the thickness measured in the longitudinal direction from the DS (left) of the steel sheet (mm) i: Each position measured in the longitudinal direction using a thickness meter] [Relationship 5] AveTH = [(MTHDS + MTHWS) / 2 + MTHCN] / 2 If the minimum thickness obtained is less than the lower limit allowable thickness, the process is rejected; if the minimum thickness is larger than the lower limit allowance, the process is passed if the average thickness is less than the upper limit thickness; ; Obtaining the actual weight (MCWt) for each product for the pass material and the determination base material by the following equation (6); [Relationship 6] MCWt = AveTH * WID * LEN * ρ / k [WID: product width (mm) LEN: Product length (mm) ρ: specific gravity (g / ㎣) k: unit conversion constant (1000)] Obtaining a weight ratio (actual product weight / order product weight) for each product with respect to the determination atmospheric material by the following formula (7); [Relationship 7] WtRatio = MCWt / ODWt [WtRatio: weight ratio of actual product to order weight ODWt: Order Weight Selecting the products having the smallest weight ratio (WtRatio) one by one from among the determination standby materials, and calculating the cumulative weight ratio together with the weight ratio of the passivating material, and if the weight ratio is 1.015 or less, passing the processing; and After all the above processes are performed on the determination waiting material, the production is terminated when the passed product satisfies the ordered product quantity, and if not, additionally produce a shortage until the order quantity is satisfied, and repeating the above process. Method of manufacturing steel plate for shipbuilding The rolling error (ERR) in the formula (1) is composed of an intraplate thickness deviation and an interplate thickness deviation; The thickness deviation Dinter is obtained by the following equation (2), and the thickness deviation Dintra is obtained by the following equation (3); And [Relationship 2] Dinter = a × PLTH (part thickness) + b [Relationship 3] Dintra = c × TATH + d In formulas (2) and (3), a is 0.004 to 0.008, b is 0.05 to 0.15, c is 0.008 to 0.015, and d is 0.05 to 0.15.