Ultrasonic inspection in vehicle technology

1. Ultrasonic flaw detection principle,ultrasonic testing can be categorized to ultrasonic flaw detection and ultrasonic test thickness and ultrasonic gain size、test stress and so on,in ultrasonic flaw detection, there is pulse reflection method that according to echo and bottom echo of flaw to judge;penetration method that according to shadow of flaw to judge flaw condition; and there is resonance method that according to standing wave generated by object to judge flaw condition or judge thickness of plate;currently ,pulse reflection method is mostly used。Pulse reflection method uses longitudinal wave when do longitudinal wave flaw detection,uses horizontal wave when oblique incidence flaw detection,make ultrasonic shoot into a side of object ,then receive echo reflected from flaw in same side，according to echo condition to judge flaw,longitudinal wave and horizontal wave of  pulse reflected method has as follows flaw detection principle:

Vertical flaw detection method put voltage generated by pulse oscillator to chip,the chip vibration,and generate ultrasonic pulse。If the object is steel workpiece,ultrasonic spreads at fixed speed 590m/s in steel workpiece,when ultrasonic meets flaw, a part reflected to chip from flaw,another part ultrasonic that didn’t meet flaw will keep moving,until arrive the bottom of object and then reflected back。Therefore,reflected ultrasonic from flaw is first to go back to chip,bottom reflection goes back to chip。The ultrasonic back to chip and then transformed into high frequency voltage,by receiving 、amplifying to enter oscilloscope ,oscilloscope displays flaw echo and bottom echo on fluorescent screen,。Therefore ,the graphics on oscillograph tube can know whether it has flaw or not,position of flaw and size,for pulse reflected type ultrasonic flaw detector,time base line and exciting pulse of fluorescent are triggered at the same time。Namely they are working in synchronism 。When the probe is motivated and launch ultrasonic to workpiece,exciting pulse is also sent to receiving circuit，at the same time time base circuit is also begin to scan,so there is a strong pulse wave at the beginning socket in time base line，this wave is called initial wave;when probe receives sound wave that reflected from bottom ,right position of time base line relative present a pulse wave that means bottom reflection，called “bottom wave”, time base line  Is equal to travel time that ultrasonic pulse from probe to bottom and return back to probe,so the distance  represents thickness of workpiece。If there is flaw in workpiece , probe receives sound wave that flaw reflects back,time base line relatively present a pulse wave that represent flaw,called “flaw wave ”,use F represents。Apparently ,flaw wave use little time than bottom wave,so flaw wave F should be in the middle 。If flaw detector time base line is good,then utilize distance relationship,positioning flaw,in addition,because of flaw wave height is increasing with flaw increasing，so use flaw echo altitude to estimate flaw strength:when flaw is big,move probe,according to flaw range to get extended flaw dimension:

Oblique incidence flaw detection method ultrasonic vertical incidence longitudinal wave flaw detection and inclined incidence horizontal wave flaw detection are main flaw detection methods in ultrasonic flaw detection，the purpose of two methods are complementary,longitudinal wave flaw detection main find bigger flaw that parallel to detected surface or slight tilt,mainly used for steel plate、forging piece、Casting ,but oblique incidence horizontal flaw detection,mainly find flaw that perpendicular to detected surface or high inclined,mainly used for welding joint

Detection,due to ultrasonic is inclined transmission in object,ultrasonic up to bottom ,so this will not have bottom echo,therefore,can not use bottom wave to positioning flaw:but to know flaw position,need use suitable standard sample to adjust oscillograph tube horizontal coordinates to suitable condition,for this purpose,adopt CSK-IA and CSK-IIIA sample。

Sample of Ultrasonic flaw detection 

The purpose of sample in nondestructive testing technique,normally adopt the method that compare to known quantity to make sure condition of object。Such as in ray flaw detection,use penetrameter image as basis of comparison。In ultrasonic flaw detection ,use sample as basis of comparison ,there are many known features on sample,such as it has specific dimension so as to generate fixed acoustic features,or it has artificial flaw,use sample as instrument、quantitative flaw,is a feature of ultrasonic。 Development of ultrasonic flaw detection,is inseparable with sample researching、usage。Sample mainly has three purposes in ultrasonic flaw detection。

Make sure suitable flaw detection method。In ultrasonic flaw detection,can use sample with artificial flaw in some parts to grope flaw detection method，from this sample gets rule and method of flaw detection,can also be applied to flaw detection that with same material ，same form,same dimension。

Make sure flaw detection sensitivity and assess size of flaw。For different kinds ,thickness requirements workpiece,need different flaw detection sensitivity。For making sure sensitivity of flaw detection,then need many samples with different artificial flaw,use manual altitude of flaw wave to represent flaw detection sensitivity。For assessing flaw size in some depth in workpiece,compare to artificial flaw with different dimensions and sizes in same depth,artificial flaw with same depth and same wave altitude are similar to flaw with same depth ,same wave altitude ，this is flaw equivlent method in vertical flaw detection。

Calibrate instrument and test probe property。Use electronic device to measure ultrasonic detector property,always test electronic property of instrument,but ultrasonic flaw detection is use acoustic to do flaw detection,acoustic performance and ultrasonic flaw detection real property，always need to adopt samples to respectively measure instrument 、probe property or measure comprehensive properties that instrument combines with probe。The kinds of sample are according to the purpose of sample,there are three categories for commonly used sample:

Adjust instrument and sample of measuring probe ,such as CSK-1A;

Samples for Longitudinal wave flaw detection

Samples for horizontal wave flaw detection

The operation of Ultrasonic flaw detection ,use ultrasonic pulse reflection method A display single probe、directly connect longitudinal wave flaw detection 

Choose and decide flaw detection time,according to purpose,choose the most suitable flaw detection time,for assessing forging flaw can be produced by forging,,then it should do single probe vertical flaw detection to forge piece。

Choose flaw detection method,according to workpiece condition,choose flaw detection method,such as axis forging flaw detection,choose single probe vertical flaw detection method。

Choose flaw detector ,this is the third step of operation,after making sure flaw detection method,according to flaw detection method and workpiece condition,choose a flaw detector that satisfy workpiece flaw detection requirements to detect。 

Choose flaw detection direction。When Doing ultrasonic flaw detection,flaw detection direction is very important,the direction should find flaw,and decided by kinds and directions of flaw, such as rolled plate,the flaw inside steel is extended along with direction of rolling,projected area is the biggest when flaw on the thickness direction。Therefore steel plate use vertical flaw detection,along with steel plate surface to do flaw detection,make ultrasonic beam vertical launch on the biggest area of flaw,this flaw echo is the biggest。

Choices of Frequency 。According to thickness of workpiece and crystal size of material,reasonable choose flaw detection frequency,such as flaw detection on coarse grain,not better to choose high frequency,because high frequency has high attenuation ,always can not enough penetrating power。

Wafer diameter,angle of refraction.According to purpose of flaw detection,reasonable to choose wafer dimension and angle of refraction。Such as welding joint single inclined probe flaw detection mainly use 35°-70°angle of refraction,When thickness is big or no strengthen layer,use small angle of refraction,when small thickness plate or with strengthen layer,use big angle of refraction。

Flaw detecting surface and its repair。Not corresponding to detecting surface of detecting requirements，must do some suitable repair,in case not smooth surface affects flaw detection sensitivity and flaw detection results。

Choices of Coupling agent and coupling method 。For making ultrasonic launched by probe send to samples,it should use suitable coupling agent。Such as detect on rough surface,should choose water glass with strong viscidity or  paste as coupling agent;manual flaw detection ,for maintaining coupling stable,it should use hand or heavy things plus 1-2kg power,for make coupling more stable,when do hook face flaw detection,probe can arrange arc guide block。

Making sure flaw detection sensitivity。Using standard sample to make artificial flaw sample or undersurface with no flaw adjustable to a certain wave height,ensuring flaw detection sensitivity。

Doing rough flaw detection and precise flaw detection。 For probably know about flaw is existed or not and distributing states,use regulated flaw detection sensitivity or double times sensitivity to do rough flaw detection,qualitative 、quantitate 、positioning to flaw that discovered by rough flaw detection,this is precise flaw detection。

Features of Ultrasonic flaw detection 

Applicable range of ultrasonic flaw detection is extended，not only apply to plate、tube row material ,but also apply to processing product forging、cast、weld。When flaw detection,need to pay attention to choose scanning method of probe，,make acoustic wave vertical as much as possible toward flaw surface。According to elm processing condition，normally estimate direction of flaw and general position。Therefore,it can according to part and direction of flaw ,before flaw detection,it is better to research suitable flaw detection method。Features of Ultrasonic flaw detection 

Ultrasonic flaw detection to plane flaw,no matter how thin its thickness,only ultrasonic is vertically toward it ,then it can get very high flaw echo。But for sphere flaw ,if flaw is not considerable big,or not too intensive,then it can not get enough flaw echo。Therefore,ultrasonic has high chance to detect steel plate of layered and crack in welding joint、lack of penetration,but has little chance to test single air hole。

Detecting distance is big。In ultrasonic flaw detection,if detected object metal organization crystal particle is thin,ultrasonic can spread to relevant far distance,so it can do inside flaw detection to big forging with diameter is miters， this is not comparable for other nondestructive testing methods。 

Flaw detection result is not direct,no objective record,it needs high level experienced technique to judge flaw。Ultrasonic flaw detection is according to waveform on fluorescent screen to judge ,flaw displaying is not direct,flaw detection result is judged by analyzing waveform by operators。Ultrasonic testing device has developed into automatically save、digital instrument with printing function from past analog instrument，and automatic ultrasonic testing device is gradually replace manual operation;from past technology experiment applied to all accessories in vehicles ,such as new manufacture bent axle ultrasonic test,repairing wheel and axle ultrasonic testing ,welding  component welding joint ultrasonic test, cast steel 、side frame ultrasonic test、forging bent axle ultrasonic testing、cast iron brake disc ultrasonic test、vehicle wheel and wheel rim ultrasonic test、bearing shell bonding quality ultrasonic test、high phosphorus shoe ultrasound test、train hollow shaft ultrasonic test and rail ultrasonic test and so on。 Because of wide application and quick development of ultrasonic test technique,ensure railway vehicles transportation safety。