Technical analysis and quality control points of riser design for steel castings

Overview

In the production process of steel castings, riser design is a key link to ensure the integrity and mechanical properties of castings. Its role is to compensate for the shrinkage of metal solidification, regulate the temperature gradient, and prevent the occurrence of casting defects such as shrinkage cavities and shrinkage. Reasonable riser design needs to comprehensively consider the structural characteristics of the casting, alloy composition and casting process parameters and achieve efficient shrinkage compensation by optimizing the size, shape and layout.

1.Core technical framework of riser design

Riser design must follow three core principles: smoothness of the shrinkage compensation channel, controllability of the solidification sequence, and coverage of the hot zone area. The shrinkage compensation channel should avoid sharp angles, and the ratio of channel length to diameter is recommended to be controlled within 3:1 to ensure a smooth flow of liquid metal. The solidification sequence design adopts the modulus method or computer simulation to ensure that the riser area solidifies last and forms an adequate shrinkage compensation pressure. Hot zone analysis requires the identification of thick and large parts of the casting through three-dimensional modeling, and the riser should accurately cover these areas. Usually, the riser modulus needs to reach 1.2-1.5 times the modulus of the hot zone of the casting.

Riser size parameters must be strictly calculated. For carbon steel castings, the root diameter of the riser is usually 1.1-1.3 times the diameter of the hot section of the casting, and sufficient molten metal reserves must be guaranteed in the height direction. In an actual case, a wind turbine gearbox casting reduced the shrinkage defect rate from 18% to 3% by increasing the riser height by 20%. In terms of shape design, cylindrical risers are suitable for simple castings. In contrast, oval or spherical risers are ideal for complex structures, and their curved surface transition can reduce stress concentration.

2. Differentiated cooling system design strategy

The design of the cooling system directly affects the shrinkage compensation efficiency of the riser. When adopting a differentiated cooling strategy, the casting body uses a common sand mold, and the riser area uses a chilled material or a water-cooled copper sleeve to establish a directional solidification gradient. The production data of a particular automobile engine cylinder block shows that after the cooling rate in the riser area is increased by 50%, the grain size is refined by 25%, and the mechanical properties are improved by 12%. It should be noted that the cooling system must match the casting temperature, and an excessive cooling rate may cause the casting to crack.

3.Analysis of typical scenarios of industry applications

International general standards have precise requirements for riser design. ISO 17874 stipulates that the riser volume calculation formula must include shrinkage, safety factor and shrinkage compensation efficiency factor, and the safety factor is usually 1.3-1.5. ASTM B189 provides a detailed parameter table for copper alloy riser design, and its principle can be used for reference in steel design. In actual inspection, ultrasonic flaw detection or X-ray inspection is often used to verify the shrinkage compensation effect of the riser.

Different industries have different requirements for riser design. For large steel castings in energy equipment, the riser design needs to consider the deformation of the casting’s weight and a multi-riser collaborative shrinkage compensation solution is usually adopted. Key automotive parts emphasize the convenience of riser removal, and sufficient processing allowance must be reserved during design. The parametric riser design system developed by an engineering machinery company automatically generates an optimization plan by inputting a three-dimensional model of the casting, shortening the design cycle by 40% and increasing material utilization by 15%.

The riser design of steel castings is a key link in the casting process chain, and its rationality directly affects the quality of castings and production costs. Through accurate hot spot analysis, scientific parameter calculation and innovative cooling system design, combined with a strict quality control system, the casting yield rate can be effectively improved.