JP4803104B2 - Crack inspection method and manufacturing method having the inspection method - Google Patents

Description

  The present invention relates to a method for nondestructively inspecting a crack of a member and a method for manufacturing a member having the inspection method.

  For example, a member such as a pump casing described in Patent Document 1 that requires oil-tightness is used to check the oil-tightness (oil leakage). It is necessary to check for liquid leakage by filling and applying internal pressure. And when internal pressure was applied to the pump casing, a crack sometimes occurred in the welded portion of the casing. If a pump casing is used with such cracks left unattended, the crack will progress after a predetermined time, and the pump casing will break and will not function.

  For this reason, the pump casing needs to be inspected for cracks in the welded portion after the oil-tight test. Conventionally, the presence or absence of cracks in the welded portion has been inspected by visual recognition through a camera. However, visual recognition was difficult when the crack width was 10 μm or less. Further, this visual inspection relies on the inspector's visual perception, and there are problems in reliability and cost.

  On the other hand, there is a technique described in Patent Document 2 as a crack inspection method for brittle materials such as ceramics. However, since the material used for the pump casing is not a brittle material such as ceramics, this crack inspection method cannot be adopted for the pump casing.

Japanese Patent Laid-Open No. 11-303771 JP 2006-30140 A

  The present invention has been made in view of the above problems, and an object thereof is not to provide visual inspection but to provide a crack inspection method excellent in reliability and cost and a manufacturing method having the inspection method.

The present invention provides, as means for solving the above-mentioned problems, a crack inspection method according to each of the claims and a manufacturing method having the inspection method.
According to the invention described in claim 1, the crack inspection method of the present invention comprises:
A step of applying a load to the object to be inspected 10, the first load pressing step S5 for applying a load up to the first load by displacing the pressurizing means 2 with respect to the object to be inspected 10 at a first speed;
A first load arrival time measuring step S6 for measuring a first load arrival time T1 required from the second load to the first load;
If the first load arrival time T1 is equal to or less than the reference value T0, it is determined that the predetermined part of the inspection object 10 has no cracks. If the first load arrival time T1 is greater than the reference value T0, the inspection object 10 A first product determination step S7 for determining a rejected product having a crack at a predetermined position of
It is characterized by having.

If there is a crack at a predetermined location of the object to be inspected, the first load arrival time required from the second load to the first load is roughly the displacement of the pressing means by the crack width to close the crack. The amount of time required for the inspection is larger than that of the inspection object without cracks. Using this principle, if the first load arrival time is equal to or less than the reference value, it is determined as an acceptable product without a crack at a predetermined location of the inspection object. As a result, it is possible to provide a crack inspection method that is excellent in reliability and cost rather than a visual inspection.
Furthermore, the crack inspection method of the present invention is characterized in that the predetermined portion of the inspection object 10 is a welded portion w of the inspection object 10. This is because the welded portion is likely to crack when subjected to stress.
Furthermore, the crack inspection method of the present invention is characterized in that the third load, the second load, and the first load are applied in a direction perpendicular to the plane including the welded portion w. The crack in the welded portion is open in the direction perpendicular to the plane including the welded portion. For this reason, it is effective to apply a test load in a direction perpendicular to the plane including the welded portion in order to realize a significant difference in the first load arrival time.
Furthermore, the crack inspection method of the present invention is characterized in that the object to be inspected 10 is a pump casing 50, a plurality of cylindrical members are laminated, and the mating surface outer peripheral portion w of the cylindrical member is welded. And The pump casing 50 includes a type in which a plurality of cylindrical members are stacked and the mating surface outer peripheral portion w of the cylindrical member is welded. After the welding, an oil-tight test is performed. At this time, an internal pressure is applied to the welded portion w, and a crack may occur. For this reason, the crack inspection method of the present invention is effective for such a type of pump casing.

According to the invention described in claim 2, the crack inspection method of the present invention comprises:
A step of applying a load to the object to be inspected 10, the first load pressing step S5 for applying a load up to the first load by displacing the pressurizing means 2 with respect to the object to be inspected 10 at a first speed;
A load measurement step S8 for measuring a load with respect to a time from the second load to the first load;
The load characteristic curve C with respect to the time from the second load to the first load has a first straight portion having a first gradient and a second straight portion having a second gradient, and the first straight portion and the second straight portion When the characteristic curve C is bent at the transition point S, it is determined as a rejected product having a crack at a predetermined location of the inspection object 10, and the characteristic curve C has only the first straight line portion having the first gradient, When not bent, it has an acceptable product second determination step (S9) for determining an acceptable product having no crack at a predetermined portion of the inspection object 10.

  If there is a crack at a predetermined location of the object to be inspected, the load increases rapidly when the pressurizing means is displaced by the crack width to close the crack. Using this principle, if the characteristic curve C has an inflection point, it is determined as a rejected product having a crack at a predetermined location of the inspection object. As a result, it is possible to provide a crack inspection method that is excellent in reliability and cost rather than a visual inspection.

According to invention of Claim 4 , the method of manufacturing the pump casing of the present invention comprises:
A pump casing welding step S1 in which a plurality of cylindrical members are stacked, and the mating surface outer peripheral portion w of the cylindrical members is welded to form the pump casing 50;
1st method step S10 which inspects the crack of the welding part w of the pump casing 50,
A step of applying a load to the pump casing 50, the first load pressurizing step S5 for applying a load up to the first load by displacing the pressurizing means 2 with respect to the pump casing 50 at a first speed;
A first load arrival time measuring step S6 for measuring a first load arrival time T1 required from the second load to the first load;
If the first load arrival time T1 is equal to or less than the reference value T0, it is determined that the welded portion w of the pump casing 50 is not cracked. If the first load arrival time T1 is greater than the reference value T0, the pump casing 50 A first pass determination step S7 for determining a rejected product having a crack in the welded portion w,
A crack inspection first method step S10 for applying a first load and a second load in a direction perpendicular to the plane including the weld w;
It is characterized by providing.
The first manufacturing method of the pump casing 50 having the first crack inspection method of the present invention is provided.

According to the invention described in claim 5 , the method for producing the pump casing of the present invention comprises:
A pump casing welding step S1 in which a plurality of cylindrical members are stacked, and the mating surface outer peripheral portion w of the cylindrical members is welded to form the pump casing 50;
A second method step S20 for inspecting the weld casing w for cracks in the pump casing 50, comprising:
A step of applying a load to the pump casing 50, the first load pressurizing step S5 for applying a load up to the first load by displacing the pressurizing means 2 with respect to the pump casing 50 at a first speed;
A load measurement step S8 for measuring a load with respect to a time from the second load to the first load;
The load characteristic curve C with respect to the time from the second load to the first load has a first straight portion having a first gradient and a second straight portion having a second gradient, and the first straight portion and the second straight portion When the characteristic curve C is bent at the transition point S, it is determined that the welded portion w of the pump casing 50 has a crack, and the characteristic curve C has only the first straight portion having the first gradient. And when it is not bent, it has an acceptable product second determination step S9 for determining that the welded portion w of the pump casing 50 has no crack, and
Crack inspection second method step S20 for applying the first load and the second load in the direction perpendicular to the plane including the weld w;
It is characterized by providing.
The second manufacturing method of the pump casing 50 having the second crack inspection method of the present invention is provided.

According to the invention described in claim 6 , the method for producing the pump casing of the present invention comprises:
A step of applying a load to the pump casing 50, a third load pressurizing step S3 for applying a load up to a third load by displacing the pressurizing means 2 with respect to the pump casing 50 at a second speed;
A third load removing step S4 for returning the third load applied to the pump casing 50 to zero by separating the pressurizing means 2 from the pump casing 50 is provided before the first load pressurizing step S5. And
The third load is applied in a direction perpendicular to the plane including the welded portion w.

  In addition, the code | symbol of said each step and each means shows the corresponding relationship with the specific step and means as described in embodiment mentioned later.

  Hereinafter, a crack inspection method according to an embodiment of the present invention and a manufacturing method having the inspection method will be described in detail with reference to the drawings. FIG. 1 is a flowchart showing a crack inspection method and a manufacturing method having the inspection method according to the first embodiment of the present invention. FIG. 2 is a flowchart showing a crack inspecting method and a manufacturing method having the inspecting method according to the second embodiment of the present invention. FIG. 3 is an overview of the crack inspection apparatus 1 used in the first embodiment of the present invention. FIG. 4 is a cross-sectional view of the pump device 10 including the rotary pump 11 that is the inspection object 10.

  In order to facilitate understanding, after the logic as a base of the crack inspection method and the manufacturing method having the inspection method is described with reference to FIGS. 3 and 4, the crack inspection method and the manufacturing method having the inspection method are illustrated in FIG. This will be described with reference to FIG.

  First, with reference to FIG. 4, the pump apparatus 10 (refer patent document 1) used as a to-be-inspected object is demonstrated. The pump device 10 includes two rotary pumps 11 for the first piping system and a rotary pump 13 for the second piping system. The pump casing 50 constituting the outer shape of the pump device 10 is constituted by first, second and third cylinders 71a, 71b and 71c and first and second central plates 73a and 73b.

  Then, the first cylinder 71a, the first center plate 73a, the second cylinder 71b, the second center plate 73b, and the third cylinder 71c are sequentially stacked, and the outer periphery w of the overlapping portion (the mating surface) is welded at four locations. A pump device 10 having an integral structure is formed. The rotary pumps 11 and 13 are built in the pump device 10. Specifically, the rotary pump 11 is disposed in a rotor chamber 50a formed by sandwiching a cylindrical first central plate 73a between a first cylinder 71a and a second cylinder 71b. The rotary pump 13 is arranged in a pump chamber 50b formed by sandwiching a cylindrical second central plate 73b between the second cylinder 71b and the third cylinder 71c.

  After the internal parts are assembled, the pump device 10 is welded at four locations on the outer periphery w of the mating surfaces (step 1). Next, an oil tightness test is performed (step 2). That is, an internal pressure of about 20 MPa is applied to the cylinder chamber for oil tightness (oil leakage) confirmation. Due to this internal pressure, cracks occur in the welded portion w at a rate of several of the 1000 pump devices. The welded portion w is likely to crack along a plane including the welded portion w (see FIG. 6). For this reason, it is necessary to perform a crack inspection test (steps 10 and 20) after the oil-tight test.

  Next, the crack inspection apparatus 1 used in the first embodiment will be described with reference to FIG. The crack inspection apparatus 1 used in the present embodiment includes a pressure unit 2 that applies a load to the inspection object 10, a load sensor 3 that measures the load applied to the inspection object 10, and a load measurement that captures the output of the load sensor. Unit 4, timer 5 for measuring time, and determination unit 6 that compares and determines the first load arrival time required from the second load to the first load and a reference value. Here, the inspection object 10 is the above-described pump device 10. In addition, since the crack inspection apparatus used for 2nd Embodiment has a little different function of the determination part 6, the description is abbreviate | omitted.

  The inspection object 10 is pressurized (a load is applied) to the pump casing 50 by the pressurizing unit 2. The pump casing 50 is applied with a load in a direction perpendicular to the plane including the welded portion w by the pressurizing unit 2. This is because, as will be described later, the cracks that are likely to occur in the welded portion w are in an open state with a gap perpendicular to the plane including the welded portion w (see FIG. 6).

  In this embodiment, the pressurizing unit 2 is driven by the pressurizing unit driving motor 7 and pressurizes the object 10 by moving up and down. Therefore, the pressurizing unit 2 includes a speed reduction mechanism, and further includes a mechanism such as a ball screw mechanism that converts the rotational motion of the pressurizing unit driving motor 7 into a linear reciprocating motion. The pressurization unit drive motor 7 is controlled by the pressurization control unit 8 so as to pressurize the object 10 by displacing the pressurization unit 2 downward at an appropriate predetermined speed. The pressurization control unit 8 may include a preprogrammed control procedure program and control the pressurization unit drive motor 7 in accordance therewith.

  The crack inspection method of this embodiment using the apparatus 1 will be described. First, the inspection object 10 is set on the table of the crack inspection apparatus 1. Next, the pressurizing unit 2 is displaced downward at a slightly high speed of 1 mm / sec (second speed) and is brought into contact with the inspection object 10 (step 3). Here, in order to determine the contact position, for convenience, the position at the time when a 5N load (third load) is detected is set as the contact position. That is, when the load applied to the inspection object 10 increases from 0N to 5N, the displacement of the pressurizing unit 2 is stopped. The third load may be a load that ensures that the object to be inspected 10 and the pressurizing unit 2 are in contact with each other, and may be a load of 1N to 50N, for example. The total length L of the inspection object 10 is slightly different for each inspection object 10. The difference range is, for example, 0.2 mm. For this reason, it is necessary to confirm the contact position for each inspection object 10. Confirmation of this contact position is necessary to accurately measure the first load arrival time described later. Moreover, the reason for displacing the pressurizing unit 2 at a slightly higher speed is to shorten the process work time.

  After confirming the contact position, the pressure unit 2 is displaced 0.05 mm upward, and the load applied to the object to be inspected 10 is returned to zero (step 4). By this upward displacement of 0.05 mm, the contact state between the object to be inspected 10 and the pressurizing unit 2 is surely released and separated from each other.

  From the next step, the load during pressurization that changes with time is measured by the load sensor 3 and the measuring unit 4 (step 8). The result is shown in FIG. FIG. 5 shows a typical load characteristic curve C when the inspection object 10 has a crack. The vertical axis in FIG. 5 indicates the load F applied to the inspection object 10, and its unit is (N). The horizontal axis indicates time t, and its unit is (msec).

  Then, from the position displaced 0.05 mm upward, this time, the pressurizing unit 2 is displaced downward at a very slow speed of 0.1 mm / sec (first speed) (step 5), and the inspection object 10 (Time t1). The reason for displacing at this very slow speed is to accurately measure a first load arrival time T1 described later. Even after the contact, the pressure unit 2 is continuously displaced downward at the same speed of 0.1 mm / sec. At time t2, the load becomes 10N (second load). Further, the pressurizing unit 2 is continuously displaced downward at the same speed of 0.1 mm / sec. Then, when a load of 150 N (first load) is detected (time t4), the rotational movement of the pressurizing unit drive motor 7 is temporarily stopped to stop the displacement of the pressurizing unit 2. Thereafter, the pressurizing unit 2 is displaced upward to return the load applied to the inspection object 10 to zero.

  As shown in FIG. 5, the load characteristic curve C forms a first straight line portion C1 having a first gradient from t1 to t3, and forms a second straight line portion C2 having a second gradient from t3 to t4. ing. The characteristic curve C is bent sharply at the transition point S between the first straight line portion C1 and the second straight line portion C2. The reason will be described with reference to FIG. FIG. 6 is a schematic diagram of the inspection object 10 having the crack k. The crack k is in an open state with a gap y at the entire circumference welded portion w.

  The pressurizing unit 2 descends at a constant speed of 0.1 mm / sec, and comes into contact with the end face 10a of the inspection object 10 at time t1 and starts applying a load to the inspection object 10. Then, the inspection object 10 starts to be compressed by the applied load, but the load gradually increases like the first gradient until the gap y of the crack k is closed by the load. This is because the substantial pressure receiving surface of the inspection object 10 is small until the gap y of the crack k is closed to zero by the load. When the gap y of the crack k is closed by the load at time t3, the substantial pressure receiving surface of the inspection object 10 increases rapidly. For this reason, the reaction force by the inspection object 10, that is, the load changes discontinuously, and the bending point S is formed. When the pressurizing unit 2 further descends at a constant speed, the load increases by forming a second gradient that is steeper than the first gradient.

  The above is the reason why the characteristic curve C is bent sharply at the transition point S between the first straight line portion C1 and the second straight line portion C2. Thus, the sharp curve of the characteristic curve C at the transition point S between the first straight line portion C1 and the second straight line portion C2 is a clear sign indicating the presence of a crack. Thus, by observing the shape of the characteristic curve C, it is possible to reliably determine whether or not a crack has occurred (step 9).

  On the other hand, the first load arrival time T1 required from the second load (10N) to the first load (150N) is measured (step 6), the first load arrival time T1 is compared with the reference value T0, Presence / absence can also be determined (step 7). The second load only needs to be a load that ensures that the object to be inspected 10 and the pressure unit 2 are in contact with each other, and can be a load of 1N to 50N, for example. In FIG. 5, the first load arrival time was T1, and the first load arrival time T1 was 1.5 seconds. In this example, the reference value T0 is 0.9 seconds. Thereby, since 1st load arrival time T1 was larger than the reference value T0, it determined with the to-be-inspected object 10 having a crack, and determined to-be-inspected object 10 as a disqualified product. In addition, when 1st load arrival time T1 becomes below the reference value T0, it determines with the to-be-inspected object 10 not having a crack, and makes the to-be-inspected object 10 a pass product (step 7).

  Based on the above, the crack inspection method of the present invention and the manufacturing method having the inspection method will be described with reference to FIGS. A first embodiment of the present invention is shown in FIG. 1, and a second embodiment is shown in FIG.

(First embodiment)
As shown in FIG. 1, first, in step 1, the pump casing 50 is formed by laminating a plurality of cylindrical members 71a, 71b, 71c, 73a, 73b, and there are four mating surface outer peripheral portions w of the cylindrical members, It is welded all around. Subsequently, in step 2, an internal pressure of 20 MPa is applied to the pump casing 50, and an oil tightness test is performed.

  Subsequently, a crack inspection first method step S10 for inspecting the presence or absence of a crack in the welded portion w is executed. The crack inspection first method step S10 includes steps 3, 4, 5, 6, and 7.

  Following step 2, step 3 is executed. Step 3 is a step in which a load is applied to the pump casing 50, and a third load is applied to the third load 5N by displacing the pressurizing means 2 with respect to the inspection object 10 at a second speed of 1 mm / sec. It is a load pressurization step. Subsequently, step 4 is executed. Step 4 is a third load removal step for returning the third load 5N applied to the pump casing 50 to zero by separating the pressurizing means 2 from the pump casing 50. Then step 5 is executed. Step 5 is a step of applying a load to the pump casing 50, wherein the pressurizing means 2 is displaced with respect to the pump casing 50 at a first speed of 0.1 mm / sec to apply a load up to a first load of 150N. One load pressurizing step. In parallel with step 5, step 6 is executed. Step 6 is a first load arrival time measurement step for measuring a first load arrival time T1 required from the second load 10N to the first load 150N. Following step 5 and step 6, step 7 is executed. Step 7 determines that the welded portion of the pump casing 50 has no crack if the first load arrival time T1 is equal to or less than the reference value T0, and if the first load arrival time T1 is greater than the reference value T0, This is a first determination step for a passed product that is determined as a rejected product having a crack in the welded portion of the inspection object 10.

  The above is the crack inspection first method step S10. The pump casing welding step S1, the oil tightness test step S2, and the crack inspection first method step S10 constitute a first pump casing manufacturing method.

(Second Embodiment)
Next, the second embodiment will be described, but the description of the same steps as those in the first embodiment will be omitted. As shown in FIG. 2, step 1 to step 5 are first executed continuously. Since these steps are the same as those in the first embodiment, detailed description thereof is omitted.

  Subsequent to Step 1 and Step 2, a crack inspection second method step S20 for inspecting the presence or absence of a crack in the welded portion w is executed. The crack inspection second method step S20 includes steps 3, 4, 5, 8, and 9.

  When Steps 3 to 4 are completed and Step 5 is started, Step 8 is executed in parallel with Step 5. Step 8 is a load measurement step of measuring a load with respect to time from the second load 10N to the first load 150N. Following step 5 and step 8, step 9 is performed. Step 9 includes a first straight line portion C1 having a first straight line portion C1 having a first gradient and a second straight line portion C2 having a second gradient in a load characteristic curve C with respect to time from the second load to the first load. When the characteristic curve C is bent at the transition point S between C1 and the second straight line portion C2, it is determined that the welded portion w of the pump casing 50 has a crack, and the characteristic curve C has the first gradient. It is an acceptable product second determination step in which the welded portion w of the pump casing 50 is determined as an acceptable product having no crack when it has only the first straight portion and is not bent.

  The above is the crack inspection second method step S20. The pump casing welding step S1, the oil tightness test step S2, and the crack inspection second method step S20 constitute a second pump casing manufacturing method.

  As described above, it was confirmed by a test that the occurrence of cracks in the pump casing or the like can be detected by the crack inspection method according to the present invention. The reference value used in the above test is merely an example, and varies depending on the type of the pump casing. Since the pump casing is loaded in the manufacturing (assembly) process, the crack inspection method of the present invention can be performed during the assembly operation as part of the manufacturing operation of the pump casing. Accordingly, if the test is included in the pump casing manufacturing operation, it can be seen that cracks can be detected by the test during manufacturing.

  In the embodiment described above or shown in the accompanying drawings, the object to be inspected 10 has been described as a pump casing. However, the present invention is not limited to this and may be a casing other than the pump casing. Other than that.

  The crack inspection apparatus described in the above embodiment is an example, and the present invention is not limited to this, and components, sensors, control devices, and the like that are not described may be added to the apparatus. A part of the crack inspection apparatus may be replaced by a known apparatus or the like.

  The above embodiment is an example of the present invention, and the present invention is not limited by the embodiment, is defined only by matters described in the claims, and other embodiments can be implemented. .

  As described above, according to the present invention, it is possible to provide a crack inspection method excellent in reliability and cost, and a manufacturing method having the inspection method, instead of visual inspection.

It is a flowchart showing the cracking inspection method which concerns on 1st Embodiment of this invention, and the manufacturing method which has this inspection method. It is a flowchart showing the crack inspection method which concerns on 2nd Embodiment of this invention, and the manufacturing method which has this inspection method. It is a general-view figure of the crack inspection apparatus 1 used for 1st Embodiment of this invention. It is sectional drawing of the pump apparatus which is a to-be-inspected object. It is a figure showing the characteristic curve of the load applied to the to-be-inspected object which has a crack. It is a schematic diagram of the to-be-inspected object which has a crack.

Claims (6)

In the crack inspection method for inspecting a crack at a predetermined location of the inspection object (10),
A step of applying a load to the object to be inspected (10), wherein the pressurizing means (2) is displaced with respect to the object to be inspected (10) at a first speed to apply a load up to the first load. 1 load pressurizing step (S5);
A first load arrival time measuring step (S6) for measuring a first load arrival time (T1) required from the second load to the first load;
If the first load arrival time (T1) is equal to or less than the reference value (T0), it is determined that the predetermined part of the inspection object (10) is not cracked, and the first load arrival time (T1). if there greater than the reference value (T0), possess the said first determination step accepted product determines that rejects that there is a crack in the predetermined portion of the object (10) (S7), and
The predetermined portion of the inspection object (10) is a welded portion (w) of the inspection object (10),
Applying the load in a direction perpendicular to the plane containing the weld (w),
The inspected object (10) is a pump casing (50), and a plurality of cylindrical members are laminated and a mating surface outer peripheral portion (w) of the cylindrical member is welded. Inspection method (S10). In the crack inspection method for inspecting a crack at a predetermined location of the inspection object (10),
A step of applying a load to the object to be inspected (10), wherein the pressurizing means (2) is displaced with respect to the object to be inspected (10) at a first speed to apply a load up to the first load. 1 load pressurizing step (S5);
A load measuring step (S8) for measuring a load with respect to time from a second load to the first load;
The load characteristic curve (C) with respect to the time from the second load to the first load has a first straight line portion having a first gradient and a second straight line portion having a second gradient, When the characteristic curve (C) is bent at the transition point (S) of the second straight line portion, it is determined that the predetermined part of the inspection object (10) has a crack, and the characteristic curve When (C) has only the 1st straight part which has the 1st slope, and is not bent, the acceptable product 2nd judgment step which judges with the acceptable product which does not have a crack in the above-mentioned predetermined part of the above-mentioned inspection object (10) and (S9), I have a,
The predetermined portion of the inspection object (10) is a welded portion (w) of the inspection object (10),
Applying the load in a direction perpendicular to the plane containing the weld (w),
The inspected object (10) is a pump casing (50), and a plurality of cylindrical members are laminated and a mating surface outer peripheral portion (w) of the cylindrical member is welded. Inspection method (S20). A step of applying a load to the object to be inspected (10), wherein the pressurizing means (2) is displaced with respect to the object to be inspected (10) at a second speed to apply a load up to a third load. 3 load pressurization step (S3),
A third load removing step (S4) for returning the third load applied to the inspection object (10) to zero by separating the pressurizing means (2) from the inspection object (10); The
It has before the said 1st load pressurization step (S5), The crack inspection method (S10, 20) of Claim 1 or 2 characterized by the above-mentioned. A pump casing welding step (S1) in which a plurality of cylindrical members are stacked, and a mating surface outer peripheral portion (w) of the cylindrical members is welded to form a pump casing (50);
A first method step (S10) for inspecting cracks in the weld (w) of the pump casing (50),
A step of applying a load to the pump casing (50), the first load applying a load up to a first load by displacing the pressurizing means (2) with respect to the pump casing (50) at a first speed; A pressurizing step (S5);
A first load arrival time measuring step (S6) for measuring a first load arrival time (T1) required from the second load to the first load;
If the first load arrival time (T1) is equal to or less than a reference value (T0), it is determined that the welded portion (w) of the pump casing (50) has no crack, and the first load arrival time ( If T1) is larger than a reference value (T0), it has an acceptable product first determination step (S7) for determining that the welded part (w) of the pump casing (50) has a crack, and
A crack inspection first method step (S10) for applying the first load and the second load in a direction perpendicular to a plane including the weld (w);
A method of manufacturing a pump casing, comprising: A pump casing welding step (S1) in which a plurality of cylindrical members are stacked, and a mating surface outer peripheral portion (w) of the cylindrical members is welded to form a pump casing (50);
A second method step (S20) for inspecting the weld casing (w) for cracks in the pump casing (50),
A step of applying a load to the pump casing (50), the first load applying a load up to a first load by displacing the pressurizing means (2) with respect to the pump casing (50) at a first speed; A pressurizing step (S5);
A load measuring step (S8) for measuring a load with respect to time from a second load to the first load;
The load characteristic curve (C) with respect to the time from the second load to the first load has a first straight line portion having a first gradient and a second straight line portion having a second gradient, When the characteristic curve (C) is bent at the transition point (S) of the second straight part, it is determined that the welded part (w) of the pump casing (50) has a crack, When the characteristic curve (C) has only the first straight line portion having the first gradient and is not bent, it is determined that the welded portion (w) of the pump casing (50) has no crack and is a qualified product. A second determination step (S9),
A crack inspection second method step (S20) in which the first load and the second load are applied in a direction perpendicular to a plane including the weld (w);
A method of manufacturing a pump casing (50), comprising: A step of applying a load to the pump casing (50), wherein the pressurizing means (2) is displaced with respect to the pump casing (50) at a second speed to apply a load up to a third load. A pressurizing step (S3);
A third load removing step (S4) for returning the third load applied to the pump casing (50) to zero by separating the pressurizing means (2) from the pump casing (50), Before the first load pressing step (S5),
The method for manufacturing a pump casing (50) according to claim 4 or 5 , wherein the third load is applied in a direction perpendicular to a plane including the weld (w).

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