Experimental study of roll forming of weld neck flanges
A roll forming situation of a weld neck flange is introduced. Through the test rolling of several flange blanks, it is concluded that the flange is challenging to roll forming. Still, it provides a solid basis for the combination of casting and rolling creating to improve the quality of the flange. The method can be used as a reference for the new process of manufacturing weld neck flanges.
Flanges are widely used as pipe coupling parts. The flange is generally produced by casting molding or forging punching. Casting flange internal organization is loose and uneven, strength and quality are difficult to be guaranteed; forging molding is more consumables, energy consumption, and high cost, and the intersection of disk and neck is easy to produce stress concentration and affects the strength, rolling molding can avoid the above problems. Because of the continuous circumferential distribution of the fibers of the rolled parts, the metal grain arrangement is tight and neat, forming fast, energy consumption is small, saving metal materials, good surface quality, and high-quality molding; many advantages make the flange roll forming rapid development.
Although many models of flanges have been rolled in developed countries, yet to be seen in China, to promote the flange moving forming process vigorously, we selected the weld neck flange, which is challenging to roll forming as the test object, expecting that through the weld neck flange rolling test, grasp the general law of flange rolling.
1. Test process
The test is carried out in the metallurgical machinery laboratory of taiyuan heavy machinery institute whz-200 a ring rolling machine. The test is for a factory import and export company exporting a model of flange products.
1.1 Test material
The lead deformation at room temperature is similar to the deformation of steel in a hot state. It can be stopped at any time for observation and measurement, so the lead is chosen as the test metal material.
1.2 Hole design
Because the flange rolling process is a continuous rolling process in a hole pattern, the hole pattern tests the external contour of the object as a reference. To facilitate the flow of metal and to prevent the occurrence of local stress concentration phenomenon, the intersection of the neck and the disc is designed as a circular arc; to avoid metal in the deformation of the phenomenon of clamping, the groove design in the hole pattern to have a certain slope.
1.3 Blank design
Flange rolling forming has a great relationship with the blank design; different models have different size designs. So far, have yet to see a definite formula to calculate the size of the flange blank. From the information, flanges with shaped cross-section ring rolling blank design, mostly based on experience or approximate cross-section of the product design to give the rough shape of the blank, through the test machine, correction and then to determine the best size of the blank. For the weld neck flange in this test, we first gave three blank shapes, see Figure 1.
Figure.1 Shape of flange blank
2. Deformation and analysis of results
Because the internal organization of the cast billet is loose, the initial rolling, from loose to dense at this stage, and the inner diameter changes rapidly. In contrast, the radial dimension of the external profile does not change significantly. After this stage, it enters the roll-forming stage, and due to the different conditions of each part of the billet, the changes are various. The Flange schematic diagram in Figure 2 shows the rolling process measurement results in Table 1 – Table 4.
Figure.2 Flange schematic diagram
The flange neck in the rolling is more or less typical of the rectangular section ring rolling, slightly different from the neck is not entirely rectangular. The flow of metal along the roll body is also a little different. At this time, the height of the contact side with the primary roll is greater than the height of the contact side with the core roll, so the top of the “fishtail” defect formation is also very irregular in the ring rolling mill with end-rolling equipment, to remove this defect has a great role. But the test mill is without end-rolling equipment, so this defect must be eliminated.
The formation of the flange disk part is more complicated. From the molding situation, the lower part of the three blanks that only a tiny amount of the disk into the hole shape; the reason is: ① the weld neck flange disk’s inside diameter is small, large outside diameter. If you take a large amount of pressure to squeeze the metal into the hole pattern and the formation of the disk, the inner diameter of the flange will also expand to a size that exceeds the requirements; the flange disk part into the hole pattern, but from the surface of the rolled parts can be observed on the outer thickness of the disk is reduced trend, which is the formation of circumferential fibers into the hole pattern but still free disk edge has a strong pull caused by this deformation affects the accuracy of the product (3) the limited capacity of the mill, does not allow a large amount of pressure, so the deformation is mainly concentrated in the formation of circumferential fibers and the growth of the neck height.
2.3 Inner and outer diameter and height
The inner diameter expands rapidly, making the flange smaller. Internal diameter size is always met or exceeded when the external profile has not been formed. The reason is:
- ① flange billet for the cast billet, the internal organization is loose;
- ② core roll diameter is small, the local metall pressure is more significant, and the metal flow is faster, leading to more immediate inner diameter expansion.
It can be seen from the information that the roll-forming flange’s inner diameter and outer diameter ratio are more significant. The outer diameter of the flange mainly refers to the outer diameter of the disc, which changes slowly. In order to make the disk part of the molding, a more significant amount of pressure makes the part of the deformation faster, uniform deformation under a certain amount of deformation, but more than a certain amount of unrounded situation, the reasons are more complex, such as uneven internal materials, holding roller force asymmetry, uneven deformation can cause these situations. The height change of the flange is mainly reflected in the change of the neck height; the neck height increases quickly after rolling, “fishtail” phenomenon is also more obvious, which is the inevitable result of the flow of metal along the roll body.
3. Blanks after the improvement of the rolling situation
From the above three kinds of blank forming situation, the most into the hole pattern of the empty forming good, according to the design of a blank, and then rolled, rolling process as above, the results are shown in Figure 3, the measured value is shown in Table 4.
Figure.3 flange forming photos
The outer contour size of this blank is basically the same as the sample size, the outer contour and roll contact; the final rolling results show that the inner diameter of the flange expanded, the height increased, the outer contour of the surface is smooth, the size is basically consistent. This indicates that the outer contour of the constrained rolling contact, the formation is much better.
- Through the careful design of the blank, the weld neck flange can be rolled into shape.
- For the small internal diameter and external profile size of the flange, it is difficult to roll forming with a simple shape blank, but the critical value, that is, what is the ratio of internal and external diameter, is to be studied later.
- The traditional casting flange process combined with casting and the rolling process can improve the flange’s quality to compete and have certain social and economic benefits worthy of vigorous promotion.
Source: China Pipe Flange Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)