Method for rapidly testing toughness of copper insert for plastic pipe fitting

Abstract

The invention discloses a method for quickly testing the toughness of a copper insert for a plastic pipe fitting, which comprises the following steps of: placing the copper insert to be tested in a cushion block, placing an expansion head on the copper insert to be tested, and applying load to the copper insert to be tested at a certain speed by using an electronic universal testing machine to expand, obtaining a stress-strain test curve and deformation and cracking conditions of the to-be-tested copper insert, comparing the stress-strain test curve of the to-be-tested copper insert with a stress-strain standard curve of a standard copper insert, and rapidly evaluating the toughness of the to-be-tested copper insert. The method disclosed by the invention is simple and convenient to operate, and the accuracy of a test result is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of pipe fitting testing technology, and specifically to a method for rapidly testing the toughness of copper inserts for plastic pipe fittings. Background Technology

[0002] Plastic pipe fittings are widely used in heating and water supply systems abroad due to their heat resistance, cold resistance, pressure resistance, rust resistance, corrosion resistance, aging resistance, and long service life. PP-R, PE, and PE-RT plastic pipe fittings, which are widely used, are themselves high-molecular polymers. While fittings can be directly heat-fused to pipes, most water-using equipment requires threaded connections. To achieve this threaded connection, threaded metal inserts are injection-molded together with the plastic.

[0003] PP-R, PE, PE-RT, etc. are crystalline plastics. After the products are manufactured, there will be a certain crystallization period. During the crystallization process, the product size and quality are unstable, and the material will shrink to a certain extent. This causes the metal inserts of existing wired pipe fittings to not fit well with the plastic interface, resulting in water leakage during actual use.

[0004] Currently, most manufacturers use copper (CW617N) for the metal inserts of wired pipe fittings. Copper itself has good toughness and machinability, which can largely prevent water leakage caused by poor bonding with the plastic interface. However, copper inserts are subjected to varying degrees of mechanical stress or chemical damage during continuous casting, cutting, hot stamping, sandblasting, precision machining, and electroplating processes. This makes the copper inserts prone to cracking during use, leading to water leakage and quality incidents.

[0005] While most manufacturers now use tempering to mitigate some damage, significant changes in processing and tempering techniques can lead to substantial fluctuations in the crack resistance (toughness) of different batches of copper inserts. Currently, the crack resistance (toughness) of copper inserts is primarily assessed through appearance, dimensions, and flattening tests. The flattening test applies uniaxial compressive stress; under this stress, the tested samples are less prone to crack propagation, resulting in minimal differences between samples. However, copper inserts are subjected to expansion forces generated during threaded connections during actual installation. The flattening test cannot simulate these expansion forces; therefore, using the flattening test to assess the toughness of copper inserts is inaccurate and cannot quantitatively reflect their toughness, serving only as a preliminary assessment method. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for rapidly testing the toughness of copper inserts for plastic pipe fittings. The method of this invention is simple, easy to operate, and significantly improves the accuracy of the test results.

[0007] The technical solution adopted to achieve the above-mentioned objectives of this invention is as follows: A method for rapidly testing the toughness of copper inserts for plastic pipe fittings includes the following steps: S1. Test the toughness of the copper inserts of the manufactured plastic pipe fittings by flattening test, and select the copper inserts with toughness that meet the standard as the standard copper inserts. S2. Place the standard copper insert in the center of the pad, and then place the expanding end of the expanding head inside the end of the standard copper insert facing away from the pad. At this time, the standard copper insert and the expanding head are coaxial. S3. Place the assembly of the pad, standard copper insert and expansion head on the lower platen of the electronic universal testing machine, then turn on the electronic universal testing machine and move the upper platen so that the center of the upper platen contacts the expansion head. S4. Apply a downward pressure load to the expansion head using the upper pressure plate, causing the expansion head to expand the standard copper insert. Observe the deformation and cracking of the standard copper insert during the expansion process. Simultaneously record the downward displacement of the expansion head and the expansion force applied by the expansion head to the standard copper insert in real time. When a clear crack is observed in the standard copper insert, stop the expansion. Obtain the expansion force-displacement curve for the entire expansion process, which is the stress-strain standard curve of the standard copper insert. The stress-strain standard curve shows multiple downward segments of expansion force. The first downward fluctuation of expansion force indicates that the standard copper insert has begun to crack. The expansion force corresponding to the highest point of the first downward fluctuation is F. d ; S5. Test the copper insert to be tested according to the methods in steps S2-S4 to obtain the stress-strain test curve of the copper insert to be tested. S6. Compare the stress-strain test curve of the copper insert to be tested with the stress-strain standard curve of the standard copper insert. First, determine whether the trend of the stress-strain test curve of the copper insert to be tested is the same as that of the stress-strain standard curve of the standard copper insert. If the trend of the stress-strain test curve of the copper insert to be tested is not the same as that of the stress-strain standard curve of the standard copper insert, then the toughness of the copper insert to be tested is deemed unqualified. If the trend of the stress-strain test curve of the copper insert under test is the same as that of the standard stress-strain curve of the standard copper insert, then compare the F values ​​on the stress-strain test curve of the copper insert under test. d ， Is it greater than F? d If F d ， Greater than F d If the toughness of the copper insert is good, then the toughness is acceptable; otherwise, it is unacceptable.

[0008] Furthermore, in step S4, when the upper pressure plate applies a downward pressure load to the expansion head, the downward pressure rate is 2~5 mm / min.

[0009] Furthermore, the pad is circular, and both ends of the pad are symmetrically provided with placement grooves for placing standard copper inserts or copper inserts to be tested. The placement grooves are coaxial with the pad, and the diameter of the placement grooves is the same as the outer diameter of the corresponding ends of the standard copper inserts and copper inserts to be tested.

[0010] Furthermore, the pad has a through hole, which is coaxial with the pad and is connected to the two placement slots respectively. The diameter of the through hole is not less than the inner diameter of the corresponding end of the standard copper insert and the copper insert to be tested.

[0011] Furthermore, the expanding side of the expanding head is truncated cone-shaped, and the expanding end of the expanding head is its smaller end.

[0012] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: This invention uses an electronic universal testing machine to clamp the expansion head and the copper insert. By applying a load to the expansion head using the electronic universal testing machine, the expansion head expands the copper insert to simulate the expansion force experienced by the copper insert during actual installation and application. This can realistically reflect the toughness changes of the copper insert under actual working conditions, thereby improving the accuracy and authenticity of the toughness test of the copper insert. Attached Figure Description

[0013] Figure 1 This is an assembly diagram for testing copper inserts.

[0014] Figure 2 The image shows the test results for the copper insert under test.

[0015] Among them, 1-upper pressure plate, 2-lower pressure plate, 3-pad, 4-placement groove, 5-through hole, 6-expansion head, 7-standard copper insert. Detailed Implementation

[0016] The present invention will now be described in detail with reference to specific embodiments, but these embodiments are not to be construed as limiting the scope of protection of the present invention in any sense.

[0017] Example 1 1. Test the toughness of the DN20 inner thread copper insert of the manufactured PPR pipe fitting by flattening test, and select the copper insert with the toughness meeting the standard as the standard copper insert 7.

[0018] 2. A cylindrical pad 3 is made from 45# steel. Placement grooves 4 are symmetrically formed at both ends of the pad, with the diameter of the grooves 4 being the same as the outer diameter of the standard copper insert 7. A through hole 5 is made at the bottom of one of the grooves 4, connecting to both grooves 4. The pad 3, grooves 4, and through hole 5 are coaxial. The diameter of the through hole 5 is the same as the inner diameter of the end of the standard copper insert located within the groove 4, ensuring that the sidewall of the standard copper insert 7 is completely in contact with the groove 4 during testing.

[0019] A cylindrical expansion head body is made using 45# steel bars. One side of the expansion head body is cut into a frustum shape to obtain expansion head 6. Expansion head 6 has one large end and one small end, with the smaller end being the expansion end.

[0020] 3. Place one end of the standard copper insert into the placement groove 4, and then place the expanding end of the expanding head 6 into the end of the standard copper insert 7 facing away from the pad 3. At this time, the standard copper insert 7 and the expanding head 6 are coaxial.

[0021] 4. For example Figure 1 As shown, the assembly of pad 3, standard copper insert 7 and expansion head 6 is placed on the lower pressure plate 2 of the electronic universal testing machine. Then, the electronic universal testing machine is turned on, and the upper pressure plate 1 is moved so that the center of the upper pressure plate 1 contacts the expansion head 6. 5. Apply a downward pressure load to the expansion head 6 at a downward pressure rate of 5 mm / min using the upper pressure plate, thereby causing the expansion head 6 to expand the standard copper insert 7. Observe the deformation and cracking of the standard copper insert 7 during the expansion process. Simultaneously record the downward displacement of the expansion head 6 and the expansion force applied by the expansion head to the standard copper insert 7 in real time. When a clear crack is observed in the standard copper insert 7, stop the expansion. Obtain the expansion force-displacement curve for the entire expansion process, which is the stress-strain standard curve of the standard copper insert 7. Figure 2 As shown, the stress-strain standard curve shows multiple downward segments of expansion force. The first downward fluctuation of expansion force indicates that the standard copper insert 7 has begun to crack (i.e., microcracks have appeared). The expansion force corresponding to the highest point of the first downward fluctuation of expansion force is F. d ; 6. Test the DN20 inner wire copper insert (the copper insert to be tested) according to the method in steps 3-5 to obtain the stress-strain test curve of the copper insert to be tested 7, such as... Figure 2 As shown; 7. Compare the stress-strain test curve of the copper insert under test with the stress-strain standard curve of the standard copper insert 7. Since the trend of the stress-strain test curve of the copper insert under test is the same as that of the standard copper insert 7, and the F on the stress-strain test curve of the copper insert under test is the same... d ， Greater than F d Therefore, it can be determined that the toughness of the copper insert under test is qualified.

Claims

1. A method for rapidly testing the toughness of copper inserts for plastic pipe fittings, characterized in that... Includes the following steps: S1. Test the toughness of the copper inserts of the manufactured plastic pipe fittings by flattening test, and select the copper inserts with toughness that meet the standard as the standard copper inserts. S2. Place the standard copper insert in the center of the pad, and then place the expanding end of the expanding head inside the end of the standard copper insert facing away from the pad. At this time, the standard copper insert and the expanding head are coaxial. S3. Place the assembly of the pad, standard copper insert and expansion head on the lower platen of the electronic universal testing machine, then turn on the electronic universal testing machine and move the upper platen so that the center of the upper platen contacts the expansion head. S4. Apply a downward pressure load to the expansion head using the upper pressure plate, causing the expansion head to expand the standard copper insert. Observe the deformation and cracking of the standard copper insert during the expansion process. Simultaneously record the downward displacement of the expansion head and the expansion force applied by the expansion head to the standard copper insert in real time. When a clear crack is observed in the standard copper insert, stop the expansion. Obtain the expansion force-displacement curve for the entire expansion process, which is the stress-strain standard curve of the standard copper insert. The stress-strain standard curve shows multiple downward segments of expansion force. The first downward fluctuation of expansion force indicates that the standard copper insert has begun to crack. The expansion force corresponding to the highest point of the first downward fluctuation of expansion force is F. d ; S5. Test the copper insert to be tested according to the methods in steps S2-S4 to obtain the stress-strain test curve of the copper insert to be tested. S6. Compare the stress-strain test curve of the copper insert to be tested with the stress-strain standard curve of the standard copper insert. First, determine whether the trend of the stress-strain test curve of the copper insert to be tested is the same as that of the stress-strain standard curve of the standard copper insert. If the trend of the stress-strain test curve of the copper insert to be tested is not the same as that of the stress-strain standard curve of the standard copper insert, then the toughness of the copper insert to be tested is deemed unqualified. If the trend of the stress-strain test curve of the copper insert under test is the same as that of the standard stress-strain curve of the standard copper insert, then compare the F values ​​on the stress-strain test curve of the copper insert under test. d ， Is it greater than F? d If F d ， Greater than F d If the toughness of the copper insert is good, then the toughness is acceptable; otherwise, it is unacceptable.

2. The method for rapidly testing the toughness of copper inserts for plastic pipe fittings according to claim 1, characterized in that: In step S4, when the upper pressure plate applies a downward pressure load to the expansion head, the downward pressure rate is 2~5 mm / min.

3. The method for rapidly testing the toughness of copper inserts for plastic pipe fittings according to claim 1, characterized in that: The pad is circular, and there are placement grooves symmetrically opened at both ends of the pad. The placement grooves are coaxial with the pad, and the diameter of the placement grooves is the same as the outer diameter of the corresponding ends of the standard copper insert and the copper insert to be tested.

4. The method for rapidly testing the toughness of copper inserts for plastic pipe fittings according to claim 3, characterized in that: The pad has a through hole, which is coaxial with the pad and is connected to two placement slots. The diameter of the through hole is not less than the inner diameter of the corresponding end of the standard copper insert and the copper insert to be tested.

5. The method for rapidly testing the toughness of copper inserts for plastic pipe fittings according to claim 3, characterized in that: The expanding head has a frustum-shaped expanding side, and the expanding end of the expanding head is its smaller end.

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