| Introduction |
| There are different methods
for hot-rolled steel bars with 40~60mm dia. in UT.For these bars,the
article is testing by means of direct contact with the circumferential
surface of bars using the straight
beam probe("S"probe),twin crystal probe which the probe face's
comtouring is suit to the bar curvature by make the initial plane of
probe face to curvature("SR"probe) and straight beam probe
with plastic delay block("SD"probe).According to the relation
between amplitude of echo from artifical reflector(traversed hole) in
the bar and its places,we drawn out the distribution state diagrams of
echo-sound pressure in the cross-section of the bar,and defined the
effective testing range.The reliability of these methods is compared and
analysed to seek the best testing method which is suit to inspecting in
field. |
| Test samples |
| The samples were cutted from
supplyed "No.45 steel"(a kind of middle-carbon steel)bars with
40,50 and 60mm normal dia. separately.There are 5 samples for each dia.
and they have the length of 60mm all.The two ends of every sample lathed
to plane,then drill hole perpendicular to the endface.The size of hole
is Φ1x20mm.so there are 10 places for the hole in the bar of each dia.
The arrangement of hole's place is in accordance with approximate equal
ratio array(table 1). |
| Table
1: The arrangement of hole's place |
| sample No. |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
|
distance from the
centre of the bar |
| sample dia. |
|
|
|
|
|
|
|
|
|
|
| 40mm |
0 |
3 |
6 |
8.5 |
11 |
13 |
14.5 |
16 |
17 |
18 |
| 50mm |
0 |
4.5 |
8.5 |
12 |
15 |
17.5 |
19.5 |
21 |
22 |
23 |
| 60mm |
0 |
5.5 |
10.5 |
14.5 |
18 |
21 |
23.5 |
25.5 |
27 |
28 |
|
| Testing method |
| The testing is
applied using 3 methods as shown in fig.1.
fig.1
(a)-"S"probe;(b)-"SR"probe;(c)"SD"probe
The internal line is 32 equal space,and the out short line is 64
equal space.
At first,we'll find up the
maximal echo-amplitude from the traversed hole on the sample's
centre,then adjust it to 50% height on the screen of ultrasonic
flaw detector(u.f.d) as basic level(0dB). |
|
|
| Afterward,we'll measure the
echo-amplitude from other 9 holes.The sample's cross-section is divided
into 32 equal spaces for measuring and the neighbourhood of
circumferential face is into 64 equal spaces due to the space
larger(fig.1).The measuring is operated along the lines of clockwise by
means of turning the sample.According to difference(dB) between the
basic level and echo-amplitude from these holes at different place,we
can draw out the distribution state diagrams of echo-sound pressure in
the cross-section of bars by analysis and treatment these data as shown
in fig.2,3 and 4(in it,the effective testing range for the bars is
within ＼6dB area-shaded and the empty area is ＼12dB). |
fig.2 |
1.The
"S"probe method is using the CTS-23 type u.f.d which
is made by SHANTOU city in China for matching.The probe is
2.5P20(2.5MHz,PZT,20mm dia.),2.5P14(2.5MHz,PZT,14mm
dia.),5P14(5MHz,PZT,14mm dia.) and 5N14(5MHz,14mm dia.-a narrow
pulse probe),above these probes were made by SHANTOU city in
China.In this testing,due to the 2.5P20,2.5P14 and 5P14(SHANTOU)
is possessed of widder initial pulse width so that the
observation to difficulty,so eliminated.The results shown in
fig.2.
2.The "SR"probe method
is using the CST-1 type u.f.d which is made by CHANGZHOU city in
China for matching.The probe is
5P12x10x2S3(5MHz,PZT,piezocrystal size is 12x10mm,two piece,its
initial incidence angle is 3＜ when the probe face is
plane,below is same),5P12x10x2S6 and 5P12x10x2S9.In this
testing,the 5P12x10x2S9 is possessed of narrower effective
testing range for the 60mm dia. so eliminated.The results shown
in fig.3.
3.The "SD"probe method
is using the CTS-26 type u.f.d which is made by SHANTOU city in
China for matching.The probe is 5P14,its delay block is made of
organic glass by ourself.The straight beam probe is fixed
together with the delay block using special tong on the probe.In
the outside of delay block it is set up sound-trap to eliminate
the interferences of echo within the delay block. |
|
fig.3 |
The delay block's
length ought to take the second interface-echo fall behind the
first back-echo exactly to avoid excessive attenuation of
sound-energy.In this testing,the delay block's length is 21,26
and 28mm for 40,50 and 60mm dia. separately.The results shown in
fig.4.
In fig.2,3 and 4,it shown that
"S"probe method is possessed of much small effective
testing rangge,but the "SR" and
"SD"probemethod is possessed of satisfactory
rangge.Apparently,when the inspection is applied around the
circumferential face of the bar,the effective testing range will
cover the cross-section of bar,therefore it will satisfy the
request of testing.In these figures,the solid-line indicated the
ideal sound-field defined by the edge of piezocrystal due to
diffusion in 0dB for reference and contrast,and the dotted-line
indicated the ideal sound-field due to diffusion in 3dB.The
effective range defined by testing is uncompletely concerned in
dostortion of real sound-field caused by the quality of the
probe itself,for example,the making-up technics of the probe,the
accuracy of the probe face's curvature,and etc. In addition,the
testing error is unavoidable due to the testing is operated by
hand.
Conclusion
Generally the twin crystal probe
is a |
|
fig.4 |
integrated
construction,it is don't repaired when it is wear out.But the
plastic delay block can be replaced easily if it is wear
out.Therefore,the "SR" and "SD"probe method
all can satisfy the request of testing reliability,but the
"SD"probe method is economic and convenience more than
the "SR"probe method due to the delay block can be
replaced so that the probe-itself is don't wear out.So the
"SD"probe method possess more practical purpose.
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