# 90 degree push elbow

Pushing elbow push system is made of elbow, elbow now push type is made when a bend forming production process, mainly because of the push type made elbow is push system elbow production speed, and then push the system elbow when production can be made into mass production, is in the elbow push system, the quality of elbow push system the molding process is now bend the main forming production process.

The main parameters of the push-elbow - the geometric shape are radius of curvature R, the section unroundness perpendicular to the radius of curvature (the actual section diameter Ds - the standard section diameter Db) and the wall thickness (see figure 1). The technological parameters that affect the geometry of the push elbow are: material, wall thickness and outside diameter of the push elbow, material and shape of mandrel head, heating temperature and its distribution, and propulsion speed. The influence of process parameters on the geometry of push elbow is discussed. (1) influence of blank material, wall thickness and outside diameter on the geometry of pusher elbow materials commonly used in thermal power industry include WB36 and A335P22, etc. The high temperature strength of WB36 is less than that of A335P22, the high temperature plasticity of WB36 is less than that of A335P22, and the thermal conductivity of WB36 is less than that of A335P22. Therefore, the fitting performance of WB36 with the die is less than A335P22 when the blank has the same outer diameter, wall thickness and mandrel head. Push elbow needs normalizing + tempering heat treatment, machining port, wall thickness should be reserved for burning loss and machining allowance. The general allowance is 10% ~ 20% of the theoretical wall thickness of elbow. The smaller the ratio of the elbow wall thickness to the section diameter D, the better the fitting performance with the die, but the easier the inner arc of the elbow will be unstable and wrinkle. According to the characteristics of constant volume of metal under plastic deformation, constant wall thickness (actually slightly thinner) and equal length of outer arc of elbow and tube billet, the formula of outer diameter of tube billet is deduced:

Dp -- outer diameter of tube blank; R -- radius of curvature of elbow;

Delta -- -- elbow wall thickness;

D -- -- diameter of elbow section.

If the actual selected diameter ratio of the tube billet is smaller than the Dp value calculated by the formula, it has good fitting performance with the die, but the inner arc of the elbow is prone to instability and wrinkling. If the actual diameter ratio of the selected blank is larger than the Dp value calculated by the formula, the result is exactly the opposite. According to the above principles, the push tube blank used for the push elbow in this test is shown in table 1 (A is the left section of the bend).

(2) the material and shape of mandrel head is an important technological parameter, which is directly controlled by design and manufacture.

Mandlet head materials generally include ZG1Cr18Ni9Ti, ZG3Cr20Ni14, ZG1Cr25Ni20Si2, ZG0Cr20Ni25, etc. High temperature strength and abrasion resistance gradually increase, and the price also increases correspondingly. For small batch production, ZG1Cr18Ni9Ti and ZG3Cr20Ni14 are available. If it is mass production, ZG3Cr25Ni20 Si2 and ZG0Cr20Ni25 should be selected, but the price of ZG0Cr20Ni25 is too high, so the material of mandlet head in this test is ZG1Cr25Ni20 Si2. Mandrels are divided into single curvature, double curvature and multiple curvature according to the radius of curvature. With single curvature, double curvature and multi-curvature mandrels, the thrust decreases gradually and the production cost increases gradually. Double curvature mandrel was selected in this experiment. According to the shape of the section, there are two kinds of circular section and elliptic section. The circular section is simple to make and low in cost, but the ellipticity and thinning rate of the push elbow are too large. The elliptic section is complex and expensive, but the ellipticity and thinning rate of the push elbow are small. Elliptic section mandrel was selected for this test. There are two types of mandrel head according to whether there is a plastic section: one with plastic section mandrel head and the other without plastic section mandrel head. Plastic section mandrel making complex, high cost, long use time; Non-plastic section mandrel is simple to make, low cost, but the front wear fast. Plastic section mandrel was selected for this test.