Ultrasonic wave helical welding steel tube weld automated flaw detection testing system

The article is firstly introduce automated ultrasonic flaw detection system used for helix weld steel tube weld inspection ,then introduced as mechanism and electrical structure of weld tracking institute of core of detecting device ,and introduce working process of system automatic flaw detection。

1 flaw detection system constitution

Weld flaw detection adopts pulse reflection type ultrasonic detecting technique is more effective,mainly due to judge whether it has flaw ,here we adopt type A to show (A scanning) ultrasonic flaw detection ,it takes advantage of reflection property of ultrasonic, On the fluorescent screen use ordinate to represent amplitude of reflection echo，use abscissa to represent travel time of reflection echo,according to amplitude and time of flaw reflection to make sure the size of flaw and the existing position，like graph 1,T is workpiece surface reflection echo,B is underside reflection echo。

2 flaw detection system constitution

Adopting to automated flaw detection system composition and structure of ultrasonic flaw detector like graph 2,the whole system is consist of ultrasonic flaw detector、traveling bogie and weld tracking constitute ,ultrasonic flaw detector uses for weld flaw detection,here adopting six angular probe that along with circularly symmetric distribution to detect the air hole、crack、slag、lack of penetration and lack of fusion in the weld;traveling bogie used for move steel tube,when detecting ,put steel tube on the traveling bogie and sent to below weld tracking system ，the bogie is moving forward with rotating steel tube ,the two kinds of movement combined into a helical motion of steel,under the ideal condition.Steel tube feeding will strictly keep pace with rotation,under the condition of keeping the steel tube weld helical angle same,weld is strictly located in flaw detection system,weld tracking system is the carrier of ultrasonic flaw detection ,used for track the center of steel tube weld ,for making sure detecting accuracy and reliability ,ultrasonic probe system needed to be arranged on the weld tracking system to work,the reasons are: (1) probe system of flaw detector has high requirement on position accuracy,due to ultrasonic probe system is restricted by its own principle and structure，requiring probe system must be equipped with very high level of positioning accuracy (2) weld condition restriction. Under Ideal condition ,steel tube weld is a helical line with fixed parameter 。But it maybe appear bias during the process of steel tube welding,generating steel tube weld geometrical parameter changed,so requiring detecting device can compensate this change,(3 ) due to traveling bogie doesn’t have accurate movement, it’s hard to guarantee feeding and rotation are strictly synchronous and lead to weld shifts relative to probe system,therefore,requiring detecting device must be able to track deviation of weld。

In the graph 2 system,adopting two sets of alternating current frequency conversion adjustable speed motor to realize traveling bogie rotation of feeding and steel tube，due to heavy steel tube ,the feeding and rotation of steel tube will not be strictly synchronous,it is especially important at the first stage, so the weld tracking system is the key part of weld automatic flaw detection device。The follows are emphatically introduce this section。

3. Weld tracking system mechanical structure

From the above we can know , automated ultrasonic flaw detection has high requirement on weld tracking system, Our designed weld tracking system is satisfied to the following indicator。

1) Suitable for steel tube range:spiral submerged arc welding pipe diameter φ337-φ1200mm,steel strip width is 550-1500mm,weld helical angle is 10° --75°，surplus height of seam ≥2mm weld width is 8-30mm。

2) Weld tangent movement speed:≤8m/min

3) Weld position tracking accuracy :±1mm

4) Horizontal tracking range :±300mm

5) Vertical tracking range :±150mm

According to index requirements,when designing weld tracking system,adopting two translational degree of freedom on the mechanism:one is vertical direction,and drive ultrasonic probe frame fluctuated;the other is horizontal direction,drive probe frame move along with steel tubular busbar in the horizontal plane,so as to realize track on the steel tube weld。Weld track system mechanical structure like graph 3 showed,probe frame installed on the vertical nut,two degree of freedom are adopt lead screw pair to realize translational movement,respectively adopts a alternating current servo motor to drive by reducer。Motor shaft to the guide screw axis reduction ratio is 9,screw pitch of lead screw is 6mm,the highest rotate speed of motor is 300r/min,from above parameter get Highest tracking line speed of Horizontal and vertical constitute is 2m/min,according to practical condition tested weld joint offset data,the system enable to satisfy tracking speed requirement,according to kind of drive and system mechanism structure parameter,put all the moment of inertia converted to the motor shaft,according to formula:

W额≥(3-4)W axis

Get two alternating current servo motor with rated power is 200W,above formula W is rated torque of motor,W axis is torque of motor shaft。

4 weld tracking system electrical system structure

constitute of Weld tracking system electrical parts like graph 4 showed,it mainly constitute of several parts 。

(1) industrial control computer 。 The system is not only need to realize every control function,but also need to be equipped with good operational interface。Adopting a Pentium586 industrial control computer as system host, and design a mode operational software that based on Windows95 graph ，which can real time display three dimensional information of weld joint appearance on the screen,and equipped with every kinds of condition display and warning hint,very easy to control and use。

(2) the digital quantity input card used for scanning operational button conditions of operational panel,the state of servo driver and zero position and limit switch of every direction of axis, by ISA buses to transmit to industrial motor， so as to make sure adopt operations。 Digital quantity input card is used for controlling power up 、operational mode 、and condition of indicator light of servo system。

(3) weld joint position sensor。 The current flaw detection tracking system mostly adopt electromagnetic type differential sensor and camera as weld joint position testing unit。In practical application，due to mostly adopt direct current welding machine, it will continue to do deslagging operation after weld,lead to weld joint has been magnetized before testing,simultaneously ,the shape of weld joint is not complete symmetry，these factors make application of electromagnetic differential sensor is not as ideal as we thought，it hard to achieve weld joint automatic track。Adopting camera as detecting unit to realize automatic track need to do graph processing ,its computation cost is high ,it has high requirements on calculating speed of controller，so it has a long distance to be used for high speed detection of weld joint。Current mainly used for manual operational tracking system，we design a scanning type weld joint position sensor that based on laser distance measuring principle ,it uses laser measuring distance sensor as distance sensitive element，adopting a reciprocating scanning constitute,providing to industrial control computer to extract steel tube weld information by scanning to get steel tube two dimensional image，used for automatic track on steel tube weld,this kind of sensor has high accuracy 、anti-interference 、easily database processing and so on advantages。

(4 ) weld joint sensor interface card。Weld joint position sensor itself is a servo system，needing real time control on scanning constitute , simultaneously adopt scanning position and the height of weld joint，so as to be convenient for industrial controller extract weld joint,for this reason,adopting single chip as controlling core to design computer system，by ISA buses connect to industrial controller,make system dependent work at certain time series,realizing control、weld position signal collecting and data preprocessing and transmit on scanning constitute。To realize optimization of scanning speed curve,adopting zero phase tracking method to control scanning constitute,so as to achieve sample data as much as possible,using small wave analytical method to extract the position of weld joint for achieved weld joint data .

（5）alternating servo motor and driver。Considering the positioning accuracy of device is high，adopting two alternating servo motor as two drive element of degree of freedom ,what weld joint position detecting unit achieved is the level of weld joint and diviation value vertical direction ,so servo motor are adopt position control ways, motor adopts optical-electricity encoder as feedback element，position servo accuracy can up to 5 pulsed quantity for highest,smaller than interval value of mechanical structure ,completely satisfy the requirements of system tracking accuracy。

(6) timer /counter used for controlling on two sets of servo motors。The counter used for measuring current position of system,providing industrial controller with closed loop that realizing whole system，timer used for send command to servo motor driver，controlling rotation speed and angle of rotation of motor so as to realize position control。

d on laser distance measuring principle ,it uses laser measuring distance sensor as distance sensitive element，adopting a reciprocating scanning constitute,providing to industrial control computer to extract steel tube weld information by scanning to get steel tube two dimensional image，used for automatic track on steel tube weld,this kind of sensor has high accuracy 、anti-interference 、easily database processing and so on advantages。

5 automatic testing process

The article introduces automatic ultrasonic flaw detection system,adopting as follows automatic detecting process：

（1 ） traveling bogie accepts steel tube,move to detecting original position ;

( 2 ) the photoelectric sensor on the rail detected steel tube front,giving signal of “steel tube is ready”,stop supplying of bogie, probe system and weld joint position sensor fall to steel tube surface，weld joint position sensor begin to scan,rotary steel tube looks for weld joint;

(3 ) weld joint original positioning ,initiate traveling bogie, detector，and begin to automatic flaw detection；

( 4 ) after detecting the terminal of steel tube ，uplift probe system ,flaw detector and tracking constitute restoration

(5 ) Traveling bogie moves steel tube to certain position,unload steel tube,continue to next detecting cycle。

During steel tube automatic flaw detection ,it can switch to manual ways at any time,at the moment,operator can according to weld joint three dimensional synthetic image on the screen to track weld joint manually,the system adopts multiple levels protection,can take relative operations when under emergency condition,so as to prevent system from being damaged。

6. Conclusion

Weld joint automatic nondestructive detection a key method to protect steel tube quality,but it is hard to implement。Due to adopt reasonable structure and detecting technique,especially the design and usage of weld joint position detecting unit about laser measures distance type ,make ultrasonic automatic flaw detector equipped with tracking speed and accuracy of doing weld joint ultrasonic flaw detection。 The model machine of this system has been tested in practical production environment,the result shows that system enable to satisfy fundamental requirements of helical weld steel tube weld joint detecting,it expresses that its design thought is right。Due to practical application environment is more complicated,existing much light、electricity interference and mechanical vibration of surrounding environment ,currently we need to do more step on anti-interference of the system and its miniaturization of detecting elements so as to make system enables to suitable for complicated environment during steel tube production。

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