JPS5957109A - Method and apparatus for controlling film thickness of coated steel pipe - Google Patents

Abstract

PURPOSE:To control a film thickness into a uniform thickness, by regulating the temps. of the corresponding sections of a split type extrusion die on the basis of the measuring value in the entire peripheral direction of the film thickness of a coated plastic resin layer to control the resin emitting amount from each section. CONSTITUTION:In coating a plastic resin coated steel pipe, the film thickness of a coating layer is measured respectively directly after etching resistant layer coating-water cooling and directly after protective layer coating-water cooling by ultrasonic thickness meters 5, 5. That is, four ultrasonic probes 5a-5d are provided around the steel pipe P at 90 deg. intervals to be rotated 1/4 and the film thickness of the plastic resin layer applied to the steel pipe P is measured by using jet type water columns 50a-50d as couplings. The film thickness measuring values in the entire peripheral direction thus obtained by the probes 5a-5d are inputted to an information treating part 6 along with probe position angle pulses while the temp. information of the coating R is also measured by a surface thermometer 7 to be inputted to the treating part 6 where operation treatment is performed to carry out the compensation of the measured film thickness value and a real film thickness value is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for controlling the film thickness of a plastic resin-coated steel pipe.

BACKGROUND OF THE INVENTION Coating of steel pipes with plastic resin is done for the purpose of preventing corrosion of the steel pipes, and has conventionally been done by extruding and coating the steel pipes with plastic resin in a coating line as shown in FIG. However, the cross section of the plastic resin coating applied in this coating line has variations in film thickness in the circumferential direction, as shown in Figure 2, and the coating thickness unevenness (thickness unevenness - resin resin coating) is usually 10 to 30 inches. As mentioned above, the purpose of coating is to prevent corrosion, so it is required to guarantee a minimum coating thickness according to the specifications.For this reason, conventionally, in the pre-shipment process of the coated steel pipe manufacturing line, one The film thickness is measured using a micrometer or an electromagnetic thickness gauge at a frequency of 30 minutes to 150 minutes per line. However, since it does not control the film thickness, there is a drawback that an excess amount of plastic resin is coated depending on the thickness unevenness.

Therefore, the object of the present invention is to, in a glass resin coating line, immediately after coating with plastic resin,
Plastic resin-coated steel pipes that continuously measure the thickness of the coating in the entire circumferential direction and immediately control the coating thickness by feeding it back to operations, which reduces uneven thickness of the coating and improves the basic unit. An object of the present invention is to provide a film thickness control method and an apparatus for the same.

That is, the first invention measures the film thickness of the coating plastic resin layer in the entire circumferential direction in a plastic resin coating line for steel pipes, adjusts the temperature of the corresponding section of the split extrusion die based on the measurement result, and The main feature is that the film thickness can be controlled by controlling the amount of plastic resin discharged.

Further, the second invention includes n wall thickness gauges arranged around the steel pipe at intervals of 360°/n and measuring the wall thickness around the entire circumference of the steel pipe;
It is characterized in that it is divided into at least n sections, and the temperature of each section is adjusted based on the measurement results of the corresponding wall thickness gauge.

As shown in Figure 1, the plastic resin coating of steel pipes is
After descaling the steel pipe P by blasting, polishing 1, etc., an adhesive is applied using an adhesive applicator 2, and then a plastic resin is applied using a die 3 to form an anti-corrosion layer, which is then hardened by water cooling. After that, a protective layer is formed by coating the die 4 with a plastic resin, which is then cured by water cooling.

The film thickness measurement according to the present invention is carried out on the plastic resin coating line as described above, immediately after coating with an anticorrosive layer and cooling with water, and immediately after coating with a protective layer and cooling with water.

For example, an ultrasonic wall thickness meter is preferably used to measure the thickness of the plastic resin coating. Since the contact method may cause scratches on the coated surface, the measurement is performed using a non-contact method using water as a couplant.

In order to measure the film thickness around the entire circumference of the resin coating,
(1) When using one probe, the probe is rotated relative to the coating circumferential surface; (2) a large number of probes are fixedly arranged in the circumferential direction; (3) ) 360'/n (for example, 90°), n (4 in the case of 90°) probes are arranged, and each probe is set to the target ω: 3('i0'/n
Possible methods include rotating it relative to each other (by 90 degrees) or rotating it centrally. Among these, methods (1) and (2) are
(3)
In general, an ultrasonic wall thickness meter measures the time width of S echo S and B echo B of the measurement waveform (high frequency video waveform) as shown in Figure 3. Since the speed of sound varies depending on conditions and temperature, it is necessary to correct the film thickness according to these conditions. FIG. 4 shows the relationship between temperature and sound speed for coatings made of three different materials. In this way, when using an ultrasonic wall thickness meter, it is necessary to calculate the true film thickness from the actual thickness measurements of the anti-corrosion layer coating and protective layer coating, the surface temperature data of each coating, and the material data of the coating. It is.

Next, the present invention will be explained in detail with reference to embodiments shown in the drawings.

FIG. 5 is an explanatory diagram schematically showing a method for controlling the film thickness of a plastic resin-coated steel pipe according to the present invention.

According to FIG. 5, in the plastic resin coating line in FIG.
In this example, where the thickness of the coating layer is measured, four ultrasonic probes 5a to 5d are arranged around the steel pipe P at 90° intervals, and each probe 5a to 5d is The film thickness of the plastic resin layer R coated on the steel pipe P is measured by rotating the IA and using the jet-type water columns 50a to 50d as couplings.

The measurement trajectory is as shown in FIG. Now, probe 5
Assuming that a to 5d rotate 1/4 rotation in 10 seconds and the coating speed is 6 m/min, the distance t measured in 1/4 rotation is 1000 mm.

The specific configuration of the ultrasonic wall thickness meter 5 used in this example is explained in the eighth section.
9 and 9. The probes 5a to 5d are housed in a nozzle box (not shown) and mounted on a rotating ring 51 with a
They are spaced at ° intervals.

A gear is formed on the rotating ring 51 so that it can rotate 1/4 in both forward and reverse directions. The probes 5a to 5d, which are driven via the drive gear 54, are pivotable vertically and horizontally in order to make the ultrasonic beam incident perpendicularly to the thickness of the plastic resin coating layer R. It is attached.

55 indicates a pipe guide roll that conveys the steel pipe P in the direction of the arrow. Noguino guide roll 55 and probe 5a
The position of ~5d can be adjusted according to the diameter of the steel pipe P to be transported and measured.

Further, the iE iso guide roll 55 is preferably made of the same material as the covering material of the steel pipe P, and can be made to come into soft contact with the covering surface of the steel pipe. The pipe guide roll 55 and the rotating ring 51 are mounted on a support frame 56, and the support frame 56 is mounted on an outer frame 58 via a spring 57. Therefore, even if the coated steel pipe P vibrates somewhat vertically or horizontally during transportation, this vibration can be absorbed by the pipe following spring 57.

As described above, each probe 5a to 5d is rotated by 1/4, but the position of each probe 5a to 5d is determined by the rotation angle sensor (
(not shown), and the angular pulse is detected by the arithmetic processing unit 6.
is input.

Probes 5a of the ultrasonic wall thickness gauge 5 configured as described above
The film thickness measurement value in the entire circumferential direction of the coated steel pipe obtained by step 5d is inputted to the information processing section 6 together with the probe position angle and radius, as shown in FIG.

On the other hand, temperature information of the IMR target is measured by a surface thermometer 7, and the measurement result is input to the information processing section 6.

Information on the material of the covering R is input to the information processing section 6 via the keyboard 8. The information processing section 6 performs arithmetic processing on these inputs, corrects the measured film thickness value, and obtains the true film thickness value. This true film thickness value is given to dividing dies 3 and 4, which will be described later. In this case, the film thickness value given to the divided dies 3 and 4 is given as an average value of each division according to the division of the divided dies 3 and 4. Moreover, as a result of the calculation process, a film thickness profile as shown in FIG. 11 was obtained, and the average thickness was obtained.

Minimum wall thickness, thickness unevenness rate, etc. can be displayed. moreover,
What is displayed on the CRT display 1o by the printer 9'f6:
Can be recorded.

The dividing dies 3 and 4 have at least the same number of sections as the probes 5a to 5d or an integral multiple thereof, and in the example shown in FIG. 12, they are equally divided into eight sections. Each section is provided with a heating means 11 or a cooling means 12, and when the information processing section 6 is given a film thickness value corresponding to each section, the temperature of the corresponding section is adjusted according to each film thickness value.

As a result, the viscosity of the plastic resin is adjusted in each section, the amount of discharge thereof is adjusted, and the film thickness can be controlled to be constant.

As described above, according to the present invention, on the plastic resin coating line for steel pipes, the film thickness immediately after coating is continuously measured in the entire circumferential direction, and the temperature of each section of the dividing die is adjusted based on the measurement results. Since this method provides immediate feedback to the operation, it is possible to always achieve a uniform coating thickness in the entire circumferential direction. Therefore, there is no need to cover with excess resin, and the unit consumption can be improved.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing a conventional plastic resin coating line, Figure 2 is a conceptual diagram showing the uneven thickness of plastic resin coated steel manufactured on the conventional line, and Figure 3 is an ultrasonic wall thickness meter. FIG. 4 is a correlation diagram showing the relationship between temperature and sound velocity for each coating material. FIG. 5 is a schematic diagram showing the glass resin coating line according to the present invention. FIG. An explanatory diagram showing an overview of the film thickness measurement of the invention, Fig. 7 is a developed view of the coated steel pipe and a diagram showing the measurement locus, Fig. 8 is an explanatory side view showing the holding one rotation mechanism of the probe, Fig. 9 The figure is a front view of the same, and Figure 10 shows the temperature of the film thickness. FIG. 11 is a diagram showing a CRT display example, and FIG. 12 is a conceptual diagram showing a method for controlling the temperature in the circumferential direction of the die. ■... Scale processing, 2... Adhesive applicator, 3° 4... Dice, 5... Wall thickness gauge, 6... Information processing section, 7... Thermometer, 8... ... Keyboard, 9... Printer, 1o... CRT, 11... Heating means, 12.
...Cooling means, 5a to 5d...Ultrasonic probe, P...
・Steel pipe, R...Plastic resin plate covering.

Claims (2)

[Claims] (1) In the plastic resin coating line for steel pipes, measure the film thickness of the ring glass resin layer in the entire circumferential direction, adjust the temperature of the corresponding section of the split extrusion die based on the measurement results, and A method for controlling the film thickness of a coated steel pipe, characterized by controlling the film thickness by controlling the amount of plastic resin discharged. (2) n wall thickness gauges arranged around the steel pipe at intervals of 360°/n to measure the wall thickness around the entire circumference of the steel pipe, and at least n
1. A coating thickness control device for a coated steel pipe, characterized in that the coating is divided into sections, and each section is temperature-controlled based on the measurement results of a corresponding wall thickness meter.