Riser is a kind of structure for storing liquid metal in the mold, which is used to compensate the possible shrinkage during the forming process of the casting and prevent the shrinkage cavity and porosity of the casting. According to the design principle of riser, the solidification time of riser should not be less than that of the feeding part of casting. Riser size can be calculated by solidification time. There are square root law and modulus method to calculate solidification time. In this paper, the riser size is calculated by the square root law.
Where, δ Is the thickness of solidified layer (riser size); K is the solidification coefficient; T is the solidification time.
(1) solidification time: the solidification time of the riser should not be less than that of the feeding part of the casting. The solidification time of the casting is the basis for determining the riser size. According to the principle of electric heating riser area solidification time > insulation brick riser area solidification time > ordinary sand mold riser solidification time > roll body solidification time, the riser solidification time of the casting should be more than that of the feeding part of the casting, After repeated production test and evaluation, it is determined that the best proportion of solidification time of each part is (3.0 ~ 4.5) ∶ (1.5 ~ 2.0) ∶ (1.2 ~ 1.4) ∶ 1.
(2) solidification coefficient: through the test and inquiry of relevant professional data, the metal mold riser is 2.6, the sand mold riser is 1.3, and the insulating brick riser is 1.0-1.2 (production experience value).
(3) calculation of riser diameter: the roller position diameter is known, according to the δ = The diameter of riser can be calculated by TK2 formula and solidification time ratio.
(4) calculation of riser height: according to the riser design principle, the shrinkage amount provided by the riser shall not be less than the volume shrinkage of the casting, and the volume shrinkage coefficient shall be calculated as 3% – 5%. From the formula WC × ( 3% ～ 5%) = WR (WC is the amount of water in the casting, WR is the amount of water in the riser), the value of WR can be calculated, and the riser height can be calculated from the riser diameter calculated in step (3). In order to avoid the electric heating molten pool in the finished roll diameter, in step
(4) the height of riser is increased by 300-600 mm, and the insulation brick is located in the middle 1 / 3 area of riser height direction.
According to the above design ideas, repeated experiments and optimization, the best riser design method and principle are obtained, and applied to production. The product surface quality is significantly improved, the surface is free of porosity and shrinkage defects, and the bottom wave is clear in UT detection.
As the above scheme adopts the riser design combining electric heating riser feeding and heat preservation refractory, the riser diameter and height are greatly reduced while improving the product quality, and the net to gross ratio can be increased by more than 30%.