In high frequency welding of tube & pipe, there is a phenomenon called "Strip Edges Meeting Too Soon". It means that the two strip edges can meet several inches ahead of the center line of the weld box. When this phenomenon happens, the risk of weld defect goes up.
There can be two possible causes for this phenomenon, too small a vee angle or too much squeeze out. People can easily understand the influence of too small a vee angle, but rarely realize the role of the squeeze out. Theoretically speaking, when the squeeze out is none, the two strip edges will meet at the center line of the weld box. However, a squeeze out is necessary for the high frequency welding of tube and pipe. When the squeeze out is bigger than zero, the two strip edges will meet ahead of the center line of the weld box. The bigger the squeeze out is, the sooner the two strip edges meet.
To achieve a good weld, a certain amount of squeeze out is needed. Typically the squeeze out is directly related with the strip thickness. The thicker the strip is, the bigger the squeeze out should be. People often use the difference of girth out of last fin and weld as the squeeze out. Since the girth can grow between the last fin and the weld, this way of calculation may result in too much squeeze out.
Additional attention should be given to tube of heavy wall. Since it needs a bigger squeeze out, the strip edges will meet sooner if the vee angle is still the same. In reality people just use one set of fin rolls for all the gauges. This set of fin rolls might work fine for light gauges but have trouble with heavy gauges. So, a bigger vee angle is needed for heavier gauges.
The vee angle is related with the following factors: the last fin thickness, the tube diameter, the distance from last fin to the center line of weld box, the wall of tube, the yield strength of the strip material, the constraint of the weld rolls, and even the amount of fin reduction. The last fin thickness is set in the roll design. If it is found too narrow, it can be widened by a redesign and regrind. The wall of tube and the yield strength can affect the spring back after last fin and the closing process before the weld rolls. Large diameter weld rolls applies a stronger constraint to the tube and will reduce the vee angle. When the upper weld rolls have a narrow working width, the lower weld rolls can apply a strong constraint to the tube and thus reduce the vee angle. The amount of fin reduction can affect the spring back after last fin. The last fin thickness, the tube diameter, the distance from last fin to center line of weld box, and the constraint of weld rolls are set by design, but other factors can vary with each setup. So, the vee angle can vary from setup to setup.
To get rid of the phenomenon of "Strip Edges Meeting Too Soon", you first have to check whether you are doing too much squeeze out. If it is fine, you will have to increase the vee angle.
Saturday, June 25, 2011
Saturday, May 28, 2011
Vee Angle-Related Defects in High Frequency Welding of Tube & Pipe
The Vee Angle affects the weld quality in high frequency welding of tube & pipe. The following weld defects can be related with it.
(1) Entrapments (Black Penetrators). This type of defect is usually a metal oxide that has been trapped on the bond plane instead of being squeezed out with the molten metal. These oxides are formed on the surface of the molten metal edges in the vee. When the vee angle is too small, the strip edges can be over heated, producing too much molten metal mixed with oxides. The normal squeeze out does not completely remove the larger than normal liquid volume and an entrapment results.
(2) Pre-Arcs. When the vee angle is too small, a pre-arc can occur when the HF current jumps across the vee ahead of the apex, usually as a result of a silver or bit of scale falling across the vee. The short-circuit diverts the current momentarily, robbing the vee of heat. The very short duration of the diverted current leaves only a short defect, often no longer than the wall thickness. It is easily observed when the weld is broken open and has a flat, shiny surface surrounded by the woody fracture of the rest of the weld area.
(3) Open Seam. When the vee angle is too big, the strip edges might not get sufficient weld heat. The edges usually show a blue heat tint suggesting that some heat was input. However, the edge face remains flat and smooth, showing no signs of having been molten.
As a conclusion, the Vee Angle may not be too small or too big. When it stays within an appropriate range, It becomes much easier to achieve a consistent and solid weld.
References
Robert K. Nichlos, Comman HF Welding Defects, Thermatool Corp.
(1) Entrapments (Black Penetrators). This type of defect is usually a metal oxide that has been trapped on the bond plane instead of being squeezed out with the molten metal. These oxides are formed on the surface of the molten metal edges in the vee. When the vee angle is too small, the strip edges can be over heated, producing too much molten metal mixed with oxides. The normal squeeze out does not completely remove the larger than normal liquid volume and an entrapment results.
(2) Pre-Arcs. When the vee angle is too small, a pre-arc can occur when the HF current jumps across the vee ahead of the apex, usually as a result of a silver or bit of scale falling across the vee. The short-circuit diverts the current momentarily, robbing the vee of heat. The very short duration of the diverted current leaves only a short defect, often no longer than the wall thickness. It is easily observed when the weld is broken open and has a flat, shiny surface surrounded by the woody fracture of the rest of the weld area.
(3) Open Seam. When the vee angle is too big, the strip edges might not get sufficient weld heat. The edges usually show a blue heat tint suggesting that some heat was input. However, the edge face remains flat and smooth, showing no signs of having been molten.
As a conclusion, the Vee Angle may not be too small or too big. When it stays within an appropriate range, It becomes much easier to achieve a consistent and solid weld.
References
Robert K. Nichlos, Comman HF Welding Defects, Thermatool Corp.
Thursday, March 31, 2011
Vee Gauge for High Frequency Welding of Tube & Pipe
The Vee Gauge has been developed for the precise measurement of small vee angle from one to five degrees. The vee angle has two edges and one apex, where the two edges meet with each other. The first application can be for high frequency welding of steel tube and pipe.
The Vee angle is an important parameter for High Frequency welding of steel tube and pipe. First, it affects the quality of the weld; Secondly, it affects the power consumption in the welding process.
However, the vee angle can be difficult to measure. One reason is that it is a small angle, usually in a range of 1 to 5 degrees; Another reason is the tight space surrounded with weld rolls, induction coil or weld shoes; The third reason is the limited lighting on the shop floor.
One way that people have adopted is to use play dough. Apply the dough to the vee and then measure the vee printed on the dough with a protractor. Another way is to use a small twist drill, a tape measure, and a calculator and then do a trigonometry calculation. These ways are "quick & dirty", not so accurate, not so quick, not so easy.
The newly developed Vee Gauge, as shown in the photo below, will revolutionize the way to measure the small vee angle.
(1) With the Vee Gauge, you can measure the vee angle accurately. It has a resolution of 0.1 degree.
(2) With the Vee Gauge, you can measure the vee angle quickly. It can be done in 10 seconds.
(3) With the Vee Gauge, you can measure the vee angle easily. You simply slide the pin into the vee until it touches both edges of strip, and then read at the apex. And the reading is directly in degree.
(4) It is built to last and comes with a life long warranty. It is made of stainless steel and the pin is hardened to stand against the sharp strip edges. It is Made inUSA
(5) It comes with the recommended vee angle for different tubing such as OCTG and Fire Protection, Stainless, and Structural. It will help to reduce the scrap when the weld is critical. One piece less scrap will recover your investment in this innovative instrument.
(6) It has two sides. One side is for a right-hand mill and another side is for a left-hand mill.
The Vee angle is an important parameter for High Frequency welding of steel tube and pipe. First, it affects the quality of the weld; Secondly, it affects the power consumption in the welding process.
However, the vee angle can be difficult to measure. One reason is that it is a small angle, usually in a range of 1 to 5 degrees; Another reason is the tight space surrounded with weld rolls, induction coil or weld shoes; The third reason is the limited lighting on the shop floor.
One way that people have adopted is to use play dough. Apply the dough to the vee and then measure the vee printed on the dough with a protractor. Another way is to use a small twist drill, a tape measure, and a calculator and then do a trigonometry calculation. These ways are "quick & dirty", not so accurate, not so quick, not so easy.
The newly developed Vee Gauge, as shown in the photo below, will revolutionize the way to measure the small vee angle.
Photo 1. The Vee Gauge measuring a tube of (3) degrees of vee angle.
(1) With the Vee Gauge, you can measure the vee angle accurately. It has a resolution of 0.1 degree.
(2) With the Vee Gauge, you can measure the vee angle quickly. It can be done in 10 seconds.
(3) With the Vee Gauge, you can measure the vee angle easily. You simply slide the pin into the vee until it touches both edges of strip, and then read at the apex. And the reading is directly in degree.
(4) It is built to last and comes with a life long warranty. It is made of stainless steel and the pin is hardened to stand against the sharp strip edges. It is Made in
(5) It comes with the recommended vee angle for different tubing such as OCTG and Fire Protection, Stainless, and Structural. It will help to reduce the scrap when the weld is critical. One piece less scrap will recover your investment in this innovative instrument.
(6) It has two sides. One side is for a right-hand mill and another side is for a left-hand mill.
(7) It measures any vee angle between (1) degree and (5) degree. This basically covers the whole range of the vee angle in the real world.
(8) The mahogany wooden case, which has been specially made for the Vee Gauge, will provide the best life-long protection to the Vee Gauge.
Photo 2. The Vee Gauge in a Mahogany Wooden Case
(9) It can be used for tube and pipe of 1-3/4" OD and above.
(10) The Vee Gauge can not only be used for the welded tube and pipe, but also for the precise measurement of any small vee angle from 1 to 5 degree. The small vee must have an apex.
(11) If you want to buy the Vee Gauge, go to www.ebay.com. Type "Vee Gauge" in the search box, and you will see the listing. You can buy it right from ebay.
(12) If you have any question, please email to VeeGauge@comcast.net
(10) The Vee Gauge can not only be used for the welded tube and pipe, but also for the precise measurement of any small vee angle from 1 to 5 degree. The small vee must have an apex.
(11) If you want to buy the Vee Gauge, go to www.ebay.com. Type "Vee Gauge" in the search box, and you will see the listing. You can buy it right from ebay.
(12) If you have any question, please email to VeeGauge@comcast.net
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