摘要
离心铸造比其它工艺方法生产的球铁管具有管壁薄、韧性好、强度高和耐蚀等优点被广泛应用于城镇供水、供气等工程项目。因其产量在不断扩大，离心球铁管的质量检测与控制也引起了人们的重视。其中球化率和管壁厚的检测尤为重要，因为球化率直接影响球铁的机械性能；而管壁厚不均匀或局部过薄则极易引起局部承载能力下降，导致爆管事故。
在一定的温度下，球墨铸铁的球化率和纵波声速的线性关系已经被大家所认同，长期以来，人们一直试图将超声声速法检测球化率的方法应用于离心球铁管的球化率检测，但由于管形铸件的特殊形状，在声路设置和声程的确定上受到管壁厚的影响，存在相当大的困难。
本文利用专门设计的探头架，让主声束在管壁内弦长方向传播，对离心球铁管横波声速进行了测试，得到了室温下横波声速与球化率的线性关系，并用于离心球铁管球化率超声无损检测，该方法克服了管壁厚度对声速检测的影响。在生产现场检测过程中，各个管壁温度不均，考虑到温度对声速的影响，本研究还测试了从室温到160℃范围内声速随管壁温度的变化规律，结果表明，横波声速随着温度升高而线性降低，并且声速的温度系数基本不受球化率的影响。据此，可将各个温度下测得的横波声速换算成室温下的声速，进而排除管壁温度对球化率检测的影响。
另外，管壁厚度也是影响球铁管质量的重要因素，而管壁厚度除了管两端外，很难用量具测量，为此，我们对在一定生产条件(相同铁液成分、相同基体状态等)下生产的球墨铸铁管的横纵波分别进行测量，得到其横纵波转化系数，将用前述方法测量的超声横波声速转化为纵波声速，用反射法测量了球铁管的厚度。
一次将球铁管的球化率和壁厚同时测量，可以对球铁管的质量进行综合评定。通过在生产现场应用此装置对球化率和厚度进行了测量，结果表明，基本符合生产上的要求。
Centrifugal Nodular Iron Pipe has been widely used in urban water supply, gas supply etc. project for its advandages such as thiner wall, better toughness, higher strength and better corrosion resistance and so on than Iron Pipe made from other process. With the expand of production increasingly, people pay more attention to the quality inspection and control of Centrifugal Nodular Iron Pipe. It is particularly important to test nodularity and the thickness for nodularity has impact on mechanical properties of Iron Pipe directly and thickness of pipe wall is uneven or part of pipe wall is too thin will cause the partial load capacity decline, then lead to accident of explosion.
With the temperature fixed,the linear relationship between the nodularity and ultrasonic velocity have already been identification by people. For a long time,people were trying to test the nodularity of the centrifugate spheroidal graphite iron pipe.But,there are multiple of difficulties as the special shape of the pipe in the settlement of the sound travel and the sound path.
This paper test the ultrasonic transversal wave velocity of the centrifugate spheroidal graphite iron pipe, making the main wave transmitting through the chord of the pipe by the specific designing probe device.The linear relationship of the nodularity and the transversal velocity in room temperature is obtained,and this method is used in the ultrasonic non-destructive test of the nodularity of centrifugate spheroidal graphite iron pipe.This method againsts the influence of the pipe thickness to the test of the velocity. Considering the effect of the temperature to the velocity,this study also test the law between the velocity and the temperature from room temperature to 160°C.The result shows that,the velocity linearly declined as the rising of the temperature and the temperature coefficient of velocity seems to no relationship with the nodularity .According to this,the velocity of various temperature can be converted to the velocity of room temperature,then the nodularity without temperature effect can be obtained.
The thickness is also a important factor of the pipe quality,but the thickness of the pipe is difficult to measure with measuring tool unless two end of the pipe. So we measure transversal wave velocity and longital wave velocity of nodular iron pipe separately which product under certain production conditions(the same ingredients of iron liquid, the same state of matrix etc.), and get its transfer coefficient of transversal wave velocity and longital wave velocity, we convert the transversal velocity to longital velocity,then measure the thickness of the pipe using the reflection method.
So we convert the transversal velocity to longital velocity,then measure the thickness of the pipe using the reflection method.
The nodularity and thickness are measured at the same time,then the quality of the pipe is intergrate evaluated. The results show that it meet production requirements by mesuring the nodularity and the thickness employed this device in the production field.
引文
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