RU2077410C1 - Method of casting of iron castings without sinkheads - Google Patents

Abstract

FIELD: foundry; applicable in production of solid highly tight iron casting without sinkheads. SUBSTANCE: after pouring of molten iron into mold, it is given rotary motion round horizontal axis with angular velocity of 1-60 revolutions per minute. This formation of sink hole separated with hard connector from nonsolidified region of casting in which at the stage of eutectic crystallization excessive volume appears. Owing to this, excessive volume fills shrinkage cavity but it does not result in exterior expansion of casting. This is why the iron castings have no sinkheads. EFFECT: higher efficiency.

Description

 The invention relates to linear production and can be used to obtain dense high-pressure castings without profits.

 To obtain cast iron castings without shrinkage defects, casting molds are usually made with a special cavity (profit), from which the castings are fed during solidification. At the same time, a large amount of metal is spent on profit, often commensurate with the casting itself, especially when castings are made from ductile iron.

 At the same time, graphite is precipitated during the solidification of cast iron, which is accompanied by an increase in volume and compensation of shrinkage caused by cooling of molten cast iron and its transition to a solid state. Thus, it would seem that there is every opportunity to obtain dense castings of cast iron without profit. But in practice this does not happen for the following reason. In the absence of profit at the initial stage of solidification of the olive, a shrinkage shell is formed in it due to nutritional deficiency during this period. At a later stage of solidification of the casting, in particular at the eutectic crystallization stage, an excess volume is formed due to the intensive release of graphite and the removal of cast iron overheating mainly by this time. Excess volume, if it does not break into the previously formed shell, is completely spent on the pre-expansion (external) expansion of the casting. The casting is obtained with a large shrink shell. If the excess volume breaks into the shrink shell, then the latter is completely or partially filled with cast iron. But, as research has shown, the casting cannot be recognized as qualitative, even if the originally formed shell was completely filled with cast iron due to excess volume. There is a low strength of cast iron at the boundary of the former shrink shell, probably due to the oxidation and insufficient weldability of the cast iron in this place.

 These defects are eliminated by the invention. The essence of the invention is that after casting iron into a mold, it is brought into rotation around a horizontal axis. In this case, the resulting shrinkage void is sequentially moved to the heat center. This eliminates the formation of a shrink shell with access to the surface of the casting, as well as a solid bridge (bridge) between the shrink shell and the uncured volume of metal. Due to this, the excess volume that occurs in the casting at the eutectic crystallization stage is spent on filling the shrinkage void, and not on the pre-expansion expansion of the casting. If there is no exit of the shrink shell to the surface of the casting, rarefaction occurs in it and external (atmospheric) pressure also helps to reduce the volume of the shrink shell. The quality of cast iron in the area of the filled shrink shell does not decrease, since there is no oxidation.

 The optimum angular speed of rotation of the mold is 1 60 rpm. A speed of more than 60 revolutions per minute significantly increases costs, without a subsequent improvement in quality. A speed of less than 1 revolution per minute no longer ensures uniformity of the layer-by-layer solidification of the casting, as well as a more uniform distribution of non-metallic inclusions and the exclusion of black spots. The upper layers of nodular iron castings during conventional casting (without rotation) often have a “black spot” defect due to the surfacing of non-metallic inclusions formed during the interaction of molten iron with a modifier. The rotation of the mold eliminates this defect due to a more uniform distribution of non-metallic inclusions over the casting and provides greater uniformity of mechanical properties and tightness in the casting.

 The proposed method has the following sequence of operations: 1) pouring cast iron into a mold; 2) casting the mold into rotation around a horizontal axis with an angular speed of 1 60 rpm.

 By technical nature, the prototype of the proposed method is a centrifugal casting method [1, 2] which has the following sequence of operations: 1) casting the mold into rotation around horizontal, vertical, etc. axis with an angular speed of hundreds and thousands of revolutions per minute; 2) pouring metal into a mold.

 Thus, the difference between the proposed method and the prototype consists in a different sequence of operations and in that the rotation speed of the mold in the proposed method is hundreds of times lower compared to the centrifugal casting method.

 These differences are of fundamental importance.

 In the centrifugal casting method, the liquid metal and the void are located symmetrically about the axis of rotation due to the action of significant centrifugal forces. Liquid metal is in rotation with the hardened part of the casting.

 In the proposed method, centrifugal forces are practically absent and therefore the liquid metal is always located below, and the shrinkage void above the liquid metal. The inner surface of the shell of the crystallized casting, as it were, is run in by liquid iron. The combination of run-in with layer-by-layer freezing of cast iron creates the effect of moving the shrinkage void towards the uncured region of the casting.

 In conventional casting (without rotation of the mold) non-metallic inclusions float, enriching the upper parts of the casting; during centrifugal casting, they are removed in the direction of the axis of rotation due to the "weight of the metal", enriching the inner layers of the casting; in the proposed method, non-metallic inclusions are simply uniformly distributed over the casting section, excluding the formation of a black spot defect typical of high-strength cast iron.

 Only axisymmetric castings can be made in a centrifugal way in order to avoid destruction of the installation due to vibration. The proposed method can be obtained cast iron castings without profits, manufactured in any form of almost any configuration and size.

 In the proposed method, the rotation of the mold around a horizontal axis can be performed using various devices: in particular, tilters, rotators, manipulators, industrial robots. It can be completely nontrivial devices. The choice of devices and their design depends on a number of factors: on the mass, dimensions and configuration of the casting molds, the seriality of castings, production experience, etc.

Claims (1)

1 A method for producing non-profit cast iron castings, comprising casting cast iron into a mold brought into rotation about a horizontal axis of rotation, and subsequent crystallization, characterized in that the cast mold is brought into rotation after casting of cast iron is completed at a speed of 1 60 rpm min