11.What is the difference between elbow and bend pipe?
Both elbows and bends are pipe fittings that change the flow direction of pipelines. The elbow only has the bent part of the pipeline; Bends include straight pipes at both ends in addition to bent parts, and also refer to a manufacturing method.
Elbow is a kind of pipe fitting commonly used in pipeline installation, which connects two pipes with the same or different nominal diameters to make the pipes turn at a certain angle. Elbows can be classified according to production process, bending degree, material and connection mode. For example, the same elbow can be cast steel elbow, 90 elbow, stainless steel elbow, threaded elbow, etc.
Bend pipe, in addition to connecting pipe fittings, also refers to a manufacturing method. Bending is to bend a straight pipe by machining means, so as to achieve the purpose of changing the flow direction of the pipeline. Its manufacturing process and finished products are called bent pipes. Bends are made of straight pipes, so there is a problem of uneven thickness. However, bends can be made on site as required and at special angles.
The bending radius of bend pipe is usually larger than that of elbow. The mechanical strength per unit area of elbow is usually greater than that of bend pipe. You can choose according to your needs in use. For example, in order to deal with the erosion of pipe fluid on the bend, thick-walled elbow can be selected to achieve the purpose of erosion resistance; It is also possible to reduce (disperse) the scouring force by means of large radius bend pipe.
22.How to measure it when there is a bend? What dimensions are measured?
Measure an elbow, mainly measuring its YBC data: Y: the feeding distance DBB(Distance Between Bends) between two pipes, the distance from the end point to the tangent point of a straight line and an arc, or the distance between the tangent point of a straight line and two arcs. For pipe benders, it is the straight-line feeding distance before each bend; B: Spatial corner POB(Plane Of Bend) is the angle between the plane where the second bend lies and the plane where the first bend lies. For a pipe bender, it is the rotation angle of the chuck holding the pipe. The chuck can rotate forward or backward. C:. bending angle DOB(Degree Of Bend). It is the outer included angle between the center line of the second straight line segment and the center line of the first straight line segment. For the pipe bender, it is the turning angle of the bending arm; CLR; pipe diameter; wall thickness and materials need of be input of the pipe bender before processing.
33.What are the common defects of elbow?
(1) For the pipe fitting with severe flattening outside the arc, the pressing die can be designed to have anti-deformation groove when making coreless pipe bending. When making coreless pipe bending, the appropriate mandrel (if necessary, the flexible mandrel assembled by multi-section mandrels) should be selected and installed correctly. When installing the die, the axis of the pipe groove of each component should be on the same horizontal plane.
(2) The thinning of the outer side of the arc in small radius bending is determined by the bending process characteristics, which is inevitable. In order to avoid excessive thinning, the commonly used effective method is to use a pipe bender with a boosting device on the side or a pushing device on the tail, to offset part of the resistance during pipe bending by boosting or pushing, to improve the stress distribution on the cross section of the pipe, and to make the neutral layer move outwards, so as to achieve the purpose of reducing the thinning of the outer wall of the pipe.
(3) In case of bending and cracking on the outer side of the pipe arc, firstly, ensure that the pipe has a good heat treatment state, then check whether the pressure of the pressing die is too high, and adjust it to make the pressure appropriate. Finally, ensure that there is good lubrication between the mandrel and the pipe wall, so as to reduce the bending resistance and the friction between the inner wall of the pipe and the mandrel.
(4) For the wrinkling inside the arc, corresponding measures should be taken according to the wrinkling position. If the front tangent point is wrinkled, the core rod position should be adjusted forward to achieve reasonable support for the pipe when bending; if the back tangent point is wrinkled, the anti-wrinkle block should be installed to make the anti-wrinkle block installed correctly and adjust the die force to be appropriate; If the inner side of the arc is full of wrinkles, it means that the diameter of the mandrel used is too small, so that the gap between the mandrel and the pipe wall is too large, or the die force is too small, which can not make the pipe fit well with the pipe bending die and anti-wrinkle block during bending. Therefore, the mandrel should be replaced, and the pressing die should be adjusted to make the pressing force appropriate.
(5) Compensation method and correction method are mainly used to control the phenomenon of bending springback. Compensation method is to estimate the amount of springback in advance by comprehensively analyzing the influencing factors of springback in bending, according to various conditions and springback trends during bending, and to correct the dimensions and geometric shapes of the working parts of the male and female dies when designing and manufacturing dies, so as to realize "over-positive" bending. The correction method is to take measures on the die structure, so that the correction force is concentrated at the corner, change the stress state, and try to eliminate the elastic deformation and overcome the rebound. For example, in the stretch bending process, tensile force is applied while bending, so that the whole section is under the action of tensile stress. When unloading, the elastic recovery is consistent with the deformation direction, which can obviously reduce the springback.