Electric resistance welded pipe high frequency welding process

Electric resistance welded pipe high frequency welding process

Typical flow of electric resistance welded pipe:

Feeding -- inspection -- shear butt welding -- looper storage -- molding -- high-frequency welding -- burr removal -- cooling -- flaw detection -- sizing and straightening -- fly cutting -- intermediate inspection -- extraction of inner burr -- flat head chamfering -- packaging and storage.

1.Feeding inspection 

1.1Before and after unwinding, the steel grade or grade of the narrow strip shall be checked, and the specification (width × thickness) of the matched measuring tool (at least once/one large steel coil) shall be inspected in accordance with the steel grade or grade and specification (width × thickness) specified in the welded pipe specification of the shift; When the steel number of the same welded pipe specification is adopted in the second furnace/batch number due to large batch size, the production batch number must be listed in a single sub-batch number, mixed batch number is strictly prohibited;

1.2 The longitudinal edge burr direction of the narrow strip should be upward when the narrow strip coil is lifted up and uncoiling.

1.3 When the narrow strip coil is lifted to the uncoiling machine, the inner diameter of the narrow strip coil must be tightened on the mandrel of the uncoiling machine to prevent loose coiling phenomenon in the process of uncoiling and feeding; Make full use of the function of "manual unwinding, pneumatic braking, and interlocking with looper to prevent the uncoiler from dropping the belt or filling the looper with the tail";

1.4 The specification and steel number of the strip shall meet the requirements of the production specification of the welded pipe on duty. It is necessary to check each roll of the strip and meet the requirements of the "Benchmark Book for the Feeding Inspection of Narrow Strip".

1.5 It is necessary to conduct appearance inspection on the surface and longitudinal shear surface of narrow strip steel, and comply with the requirements of Feeding Limit Sample. If any abnormality is found, it shall be handled according to the operation instructions.

2. shear butt welding

2.1 It must be confirmed that the burr direction of narrow strip steel is upward;

2.2 During butt welding, about 3mm arc initiation and arc retraction are left on the two edges of the width direction of the narrow strip steel, and the welding gap joint material left just meets the arc cutting surface for removing the inner burr and reduces the possibility of damaging the inner burr blade;

2.3 The edges of the welded narrow strip in the width direction should be as close as possible, and the thickness direction should not be high or low. It is better to polish the welding spot after welding.

3. Looper storage material

3.1 Pinch roll is used only when charging at speed, and the rotation of the storage tray is used in the process of low speed or uniform charging.

3.2 For soft material, inclined roll with smaller Angle and transition roll with lower height are adopted, while for hard material, the reverse is true.

4. extrusion molding

4.1 Feed alignment adjustment 
(1) W roll pressure down will be directly related to the quality of forming,
 (2) extrusion roll front tube symmetry and weld height state
(3) removal of internal and external burr quality and smoothness;

4.2 After feeding alignment adjustment, the flowing water interface on the curved surface of the tube of the narrow strip passing through the W roller is basically consistent; From W roll to extrusion roll, the weld on both sides of the tube is basically two symmetrical cone lines, no wave shape bending;

4.3 The soft material is adjusted by open pressing "W roll just touches the strip or slightly presses down", and there is no obvious indentation on the inner surface of the tube's arc; For the hard material, including the hot rolled coil with small pipe diameter, the "W roll contacts the strip or a large amount of pressure" is adjusted by closed pressing, and there is no obvious indentation on the inner surface of the tube arc; The large amount of pressure is not good for the molding quality, especially the 
45° Angle of the finished product size in the diameter section is difficult to adjust; When the flaring ≥35% after welding and the flattening 2T test is not good, it can be properly used to adjust the fine forming section by open pressing.

4.4 When making the welded pipe of hot rolled coil, a large amount of water must be used to wash the oxide beside the W roll.

4.5 After the horizontal roller and vertical roller also adopt open or closed pressure adjustment, should pay special attention to the vertical roller set only plays an auxiliary role in forming quality, for soft material manual adjustment can be in place, at most add a certain pre-pressure! For hot rolled coil, the vertical roll set must be tightened to achieve stable edge forming effect.

4.6 After rough molding, the appearance of the tube has no edges and corners, which is conducive to the subsequent adjustment of the extrusion roller and the sizing section; If the outer edges of the tube can not be eliminated, the residual Angle will be 45° of the sizing size.

4.7 When the tube head is deformed and burrs, it must be removed without fretting through the rough forming machine, and it is absolutely not allowed to enter the finishing forming machine;

4.8 When the pass size of each pass of the finishing horizontal roll is not adjusted to the specified size, it shall not be moved through the finishing machine and enter the "welding extrusion roll";

4.9 Before the tube tube enters the "welding extrusion roll", the edges of the two sides of the tube tube to be welded are not allowed to appear uneven phenomenon, pipe seam distortion, pipe seam edge wave or bulge phenomenon; Must parallel alignment, continuous and stable into the "welding extrusion pass";

4.10 After the molding machine adjustment, molding tube should have the basic, correct cylinder shape, and conform to the size of the adjustment rules, and enough "extrusion amount (OD+0.45 ~ 0.8); After the welding test, it is checked that there is no internal and external overlap welding phenomenon. The internal and external burr formed by welding extrusion should be a smooth and uniform welding bar.

4.11 The sampling results of "process performance test: Flaring and flattening" after the test welding of the machine shall meet and meet the "specified value" of the execution standard of welded pipe specification in the production of the shift;

4.12 Sampling "internal burr residual height and quality" inspection after the test welding of the machine must meet and meet the "specified value" of the production welded pipe specification execution standard of the shift, and there is no internal overlap welding;

5. High frequency welding and burr removal

5.1 at the end of the weld quality stability also depends on the precision forming time and welding time intervals between extrusion, if the spacing is too large, forming tubes, the edge will be instability phenomenon, performance on the edge of the pipe barrel to weld large and small access to squeezing roller, chroma is a dark red outside burr after welding temperature, scraping except the burr, one large and one small

5.2 The front and rear components of the impedance device must be stainless steel or brass parts with or without magnetic function, and the components must have good water cooling ability; At any time, it is necessary to first test whether the impedance device leaks and the position point of the impedance device and the extrusion center. After confirming, the tube blank can be passed through the extrusion roller. In the normal production process, often after the joint flaming and flattening test will appear abnormal phenomenon, usually is the impedance device leakage must immediately stop inspection and replace or adjust to the watertight position. And to reconfirm the adjusted flaring and flattening test results.

5.3 The position between the head of the impedance device and the extrusion center line is 0.5mm.

5.4 Three steps of "three-roller" welding extrusion roll adjustment, any adjustment should be checked after welding diameter D+(0.45-0.80) :

5.5 "Slight indentation" means that the thin wall is about 1/4 T-1/3 t, while the thick wall is nearly 1/3 T.

5.6 When the upper roller is slightly pressed down, it is felt that the weld seam is closed, and the nails are used to check that there is no high or low state. The internal and external transverse adjustment of the upper roller is adopted to confirm that the weld seam must be smooth. Then, the upper roller is slightly pressed down to confirm that there is no groove in the weld seam.

5.7 any time start, start from specified start speed within the unit, namely the cooling water tank in three of the root canal time within the reach regulation speed, speed and welding power output rise evenly at the same time, as far as possible, the welding of high output power for a spark point welding quality is relatively appropriate fundamental principles of judgment! The most basic adjustment method is to increase the welding output power as much as possible by continuously taking out the outer burr, and it is based on the test results of flaring and flattening.

5.8 Under normal conditions, low speed welding is difficult to master due to the corresponding problems of welding output power time difference, and welding sparks or welding quality is easy to occur. Therefore, it should be quickly increased to the running speed after starting the machine.

5.9 During normal debugging, it is necessary to take off the inside and outside burr knife, and visually confirm the size of the inside and outside burr by sampling after a section of test welding, and then confirm the streamline state, and make a judgment according to the "Streamline Standard of Weld Metal".

5.10 After the weld line is confirmed to be qualified, test weld a section to confirm the removal status of internal and external burrs according to the internal and external burr knife, until the adjustment is qualified. The specific internal burr requirements are determined according to the "Welding Pipe Procedure Confirmation Table".

5.11 In the normal welding process, it is necessary to check whether the welding speed, temperature and welding power are within the prescribed range according to the items in the Welding Pipe Procedure Confirmation Table. If there is any abnormality, it should be reported and adjusted immediately.

5.12 During normal welding, it is necessary to take another sample to confirm the flow line status of the weld metal.

5.13 The flaring and flattening of any batch of welded pipes must be first inspected and inspected every time the machine is started and every joint must be inspected to ensure the stability and reliability of the welding quality and to ensure that there will not be any weld cracking problem due to the welding quality during the delivery to use. In addition to the conventional flaring and flattening of the welded pipe, continuous 2T vertical flattening test with a roll length was carried out to check whether there were spot-like micro-cracks in the vertical plane of the weld, and the test results were used to confirm that the welding quality was stable during the welding process.

6. cooling

6.1 The shape of welded pipe is irregular. For precision welded pipe, the welding strength and toughness should be maintained in the weld zone and its transition zone, which are not hardened and slowly cooled due to water cooling, by using the state of air cooling as far as possible at the first stage of the cooling process. In this way, the original welding performance can be retained whether the welded pipe is delivered directly or the DOM pipe is delivered after cold rolling or cold drawing.

6.2 At the same time, due to the mild cooling of the weld area, the whole irregular welding has equal strength, which is more conducive to obtaining satisfactory accuracy of outer circular dimension in the diameter section.

7. inspection

7.1 The flaw detector shall be corrected before production every day and again after production with standard sample tubes to ensure that all the detected tubes are in normal operation of the equipment.

7.2 The production of flaw detection sample tube shall be performed according to GB/T7735 Grade B standard, and the standard hole shall be checked every year.

7.3 After each replacement of the welded pipe specifications, the removed probe and guide sleeve must be cleaned in time, and the probe and guide sleeve must be stored for future use after confirming that there is no damage.

7.4 It is necessary to verify whether the three functional states of the flaw detection equipment (alarm, marking and automatic sorting) are normal every day.

8. sizing straightening and flying saw

8.1 The outer diameter and ellipticity of the welded pipe after adjusting the sizing section must be adjusted to the qualified range.

8.2 After the sizing section, it is necessary to confirm the surface scratches, indentation and other defects. If any defects are found, it is necessary to test or polish the rolls.

8.3 The straightness needs to be adjusted after adjusting the sizing size, and the outer cylinder needs to meet customer requirements. DOM pipe generally ensures that the steel pipe can roll freely on the flat head rack.

8.4 Cut according to the length of the production plan.

9. Intermediate inspection

9.1 For welding precision tubes with conventional requirements, "intermediate inspection" shall be carried out in accordance with the following requirements, and "process control method" shall be carried out in case of special requirements;

9.2 Before starting welding operation of each unit, the welded pipe through the "flying saw process" must strictly implement the "three inspection system for the first product (self-inspection, mutual inspection and special inspection)", and the unit can only be formally produced after the first piece passes the inspection; First piece inspection (short sample) should be processed after batch specification is completed;

9.3 The dimensional accuracy and appearance quality of the first piece shall be more than three welded pipes in a row. The specific inspection method shall be carried out according to the Welding Pipe Inspection Instruction.

9.4 The internal and external surfaces of the welded pipe shall be smooth, and no surface defects such as cracks, folds, lap welding, fake welding, burrs, lamination, indentation, lines or scratches are allowed;

9.5 After removing burrs, the outer weld should be smooth, feel without edges, and be stable bright yellow or light blue;

9.6 The internal weld is uniform, without obvious sharp tooth shape, and no melting drops are allowed;
9.7 After removing the inner burr of the inner weld, it shall meet the standard requirements in the "Welding Pipe Procedure Confirmation Table";

10. Extract inner burr and flat head chamfer

10.1 After cutting off by flying saw, the qualified welded pipe shall be transferred from the "discharge roller" to the rear "genuine material storage platform", and the water in the pipe shall be controlled and dried as far as possible on the "genuine material storage platform"; And before entering the "double head flat mouth chamfering machine", the "inner burr iron filings" in the tube will be pulled out with tinier pliers; Then use the high-pressure air nozzle will be in the pipe "broken debris" flushed clean.

10.2 When the water in the pipe is controlled and dried, the "iron chip" is drawn out and the "broken chip" is washed clean, the appearance quality of the welded pipe, the condition of the inner burr of the pipe end and the removal quality of the inner burr should be observed anytime and anywhere. If there is any abnormality, the operator of the welded pipe unit should be informed immediately so as to eliminate the defects in time.

10.3 Only the welded pipe that has been cleared of iron in the pipe can enter the "double-end flat chamfering machine".

10.4 Main safety operation requirements for iron chip extraction process:

10.4.1 At all times during the process of removing iron filings, the hands or feet should be prevented from being injured by iron filings scattered on the ground.

10.4.2 "Safety first" should be taken as the leading role in the process of removing iron filings to prevent personal safety accidents.

10.4.3 The welded pipe should be allowed to enter the double-end flat chamfer process only after it has been fully verified that there are no internal and external defects or impurities that may affect the "delivery, double-end flat chamfer process".

10.4.4 After the chamfer of flat head is completed, it is necessary to confirm whether the end face is chamfered evenly and whether there are still harmful burrs.