Design dimensions and application reference of edge pressing riser for castings with different shapes of edge pressing riser corresponding to castings

Pressure riser is a commonly used riser design method in casting production. This is because the edge feeder has the advantages of simple structure, easy removal, and good shrinkage effect. Nowadays, more and more foundries are applying edge pressing risers to castings made of materials such as cast iron and non-ferrous metals. The size of castings has also been expanded. Originally mainly used for small parts, now several hundred kilograms, several tons, and even larger castings also use edge pressing risers. However, in the actual production of the foundry, the foundry practitioners are not yet familiar with the specific characteristics of the edge pressing riser, which shapes of castings correspond to different shapes of edge pressing risers, and the design of edge pressing riser size. Below, we will focus on these issues.

One The principle of size design for edge feeder includes the edge width (W) and edge length (L), and the following conditions need to be considered during design:

1. The shrinkage channel does not solidify in advance: the edge width should be small enough to delay the solidification time of the riser neck, but too small will increase the shrinkage resistance.

2. Shrinkage coverage of hot joints: The edge length needs to cover the hot joint area to ensure the effective shrinkage path.

3. The empirical formula for edge pressing is W=(0.4-0.6) xT, where T is the thickness of the hot joint of the casting and the edge pressing length L=(1.5-2.0) xT, which needs to cover the length of the hot joint area. Note: For cast iron castings, graphite expansion should be considered, and the edge pressing width can be taken as 0.4-0.5

II How to match the shape of castings with different shapes of edge feeders

1. Circular riser

Characteristics: Compact structure: The circular structure allows it to provide a relatively stable shrinkage channel while occupying a small space, which is beneficial for the shrinkage of locally thick parts of castings. Uniform heat dissipation: The circular geometric shape allows for more uniform heat dissipation during the solidification process of the riser, which can prolong the retention time of the molten metal in the riser and improve the efficiency of shrinkage compensation. Easy to process: Whether in casting model making or post casting processing, the shape of the circular edge pressing riser is easy to process and clean, and its smooth surface helps reduce stress concentration. Suitable for wheel castings such as gears, pulleys, etc. These castings usually have structures of different thicknesses such as wheel hubs and spokes. Circular edge pressing risers can be placed in thick areas such as wheel hubs according to their structural characteristics for effective shrinkage filling, preventing defects such as shrinkage holes and looseness. Disc castings: such as flanges, brake discs, etc., circular edge pressing risers match the shape of disc castings and can be arranged at the edges or center of the disc to provide sufficient metal liquid for the solidification process and ensure the quality of castings. Cylinder block and cylinder head castings: These types of castings have complex structures with many areas of alternating thick and thin walls. Circular edge feeders can be flexibly placed in thick walled areas, such as around the cylinder barrel and at water channel connections, for precise shrinkage and to meet the density requirements of the castings.

2. Square/rectangular edge feeder

Easy to arrange: Square or rectangular shapes can better fit the edges or specific areas of the casting, especially suitable for casting parts with right angles or straight edges, making it easy to arrange reasonably in limited space to achieve effective shrinkage. Enhanced shrinkage channel: Its shape can provide a wider shrinkage channel, which is conducive to the flow of molten metal in the horizontal direction. For some castings that require shrinkage from a specific direction during solidification, square or rectangular edge pressing risers can better meet the requirements. Beneficial for heat concentration: Square or rectangular structures are relatively regular, and during the solidification process of castings, heat distribution is relatively concentrated, which helps to prolong the solidification time of the molten metal in the riser and improve the shrinkage effect. Suitable for flat castings such as machine tool workbenches, flat measuring tools, etc. These castings usually have large flat dimensions. Square or rectangular edge pressing risers can be set along the edges or thickness changes of the flat plate to provide uniform shrinkage for the castings and prevent defects such as shrinkage marks. Box type castings: such as transmission cases, engine cases, etc., due to their mostly square or rectangular shell structures, square or rectangular edge feeders can be reasonably arranged at the corners and near the reinforcing ribs of the box according to the shape and wall thickness distribution of the box, effectively supplementing the shrinkage of the castings during solidification. Frame type castings: such as steel frame node castings used in construction, frame castings in mechanical structures, etc., whose structures are mostly connected by square or rectangular members. Square or rectangular edge pressing risers can be conveniently set at nodes or intersections of members to supplement and improve the overall quality of castings in areas prone to shrinkage.

3. Elliptical edge pressing riser

Strong shape adaptability: Elliptical shapes have some characteristics of both circular and square shapes. They are not as compact in certain directions as circles, nor do they have obvious edges and corners like squares. They can better adapt to castings of various shapes, especially those with complex shapes that have both curved and straight wheel profiles. Optimization of shrinkage channel: The long axis direction of the ellipse can be oriented according to the solidification shrinkage direction of the casting, allowing the molten metal to flow more smoothly to the parts that need to be shrunk, optimizing the shrinkage channel, and improving shrinkage efficiency. Uniform stress distribution: The elliptical arc-shaped structure ensures relatively uniform stress distribution during solidification, reducing the possibility of cracking in castings due to stress concentration and improving the quality and reliability of castings. Suitable for impeller castings: impellers usually have complex curved shapes, and elliptical edge pressing risers can be flexibly set at the connection between the blades and the hub or other thick parts according to the blade shape and hub structure of the impeller, providing good shrinkage for the solidification of the impeller and ensuring its internal quality. Valve body castings: The shape of the valve body is usually irregular, with various inlet and outlet ports and complex internal cavity structures. The elliptical edge pressing riser can be reasonably arranged in the thick walled parts of the valve body, such as the valve chamber, flange connection, etc., according to the specific shape of the valve body, effectively compensating for the shrinkage during casting solidification and preventing defects such as shrinkage and porosity.

4. Trapezoidal edge pressing riser

High shrinkage efficiency: The trapezoidal shape allows for a larger contact area between the riser and the casting, resulting in a larger edge pressure. This is beneficial for the metal liquid to flow more smoothly towards the solidification shrinkage area of the casting under gravity, thereby improving shrinkage efficiency. Good heat dissipation characteristics: The trapezoidal structure has certain advantages in heat dissipation. The area ratio of its side and bottom surfaces is different, and it can be adjusted according to the heat dissipation needs of the casting, so that the metal liquid in the riser can remain liquid for a suitable period of time, continuously supplementing the shrinkage of the casting. Easy to shape: Trapezoids are relatively regular, and in the casting process, whether manually or using molds, they are relatively easy to achieve. Compared with other shapes of risers, they are easier to match the shape of the casting, making them easy to install and fix. Suitable for conical castings, such as the blanks of bevel gears. The trapezoidal edge pressing riser can connect the narrow edge to the small end of the casting and the wide edge to the large end, and make up for shrinkage along the taper direction of the casting, which can better adapt to the shrinkage trend of the metal liquid during the solidification process of conical castings. Step shaft castings: For shaft castings with different diameter steps, trapezoidal edge pressing risers can be placed at the transition part of the step, and their shape can be adjusted according to the size changes of the step, providing effective shrinkage for shaft castings during solidification and preventing defects such as shrinkage holes at the step. Certain special shaped shell castings: When the shape of the shell casting has a certain degree of inclination or a trapezoidal contour, the trapezoidal edge pressing riser can tightly adhere to the edge of the shell, and compensate for the shrinkage characteristics of the shell during solidification, which helps to ensure the uniformity of the wall thickness and overall quality of the shell.

5. Combination edge pressing riser

Combination edge feeding riser is a type of riser that combines different shapes and sizes of risers or risers with other auxiliary devices for use. It has the following characteristics and is suitable for castings: flexible filling and shrinking: different types of risers can be flexibly combined according to the shape, thickness, and solidification characteristics of different parts of the casting to achieve more accurate and comprehensive filling and shrinking. Improving process yield: By reasonable combination, the overall size and weight of the riser can be effectively reduced while meeting the demand for shrinkage, thereby increasing the utilization rate of metal materials and improving the process yield. Improving solidification sequence: Different arrangements and combinations of risers can be used to adjust the solidification sequence of various parts of the casting, promote sequential solidification, and concentrate defects such as shrinkage and porosity in the riser area, thereby improving the quality of the casting. Suitable for large and complex structural castings, such as large machine tool bed bodies, ship engine cylinder bodies, etc. These castings have complex structures, large differences in wall thickness in different parts, and complex solidification processes. The combination of edge pressing risers can be used to combine different shapes and sizes of risers for different wall thickness areas, ensuring that each part can be well compensated. Precision castings: Castings such as aircraft engine blades and precision molds that require extremely high dimensional accuracy and internal quality. The combination of edge pressing and riser can achieve precise control over the solidification process of castings through precise design and combination, reduce casting defects, and ensure high quality and precision of castings.

Choose Suggestions

1. Prioritize the shape of the hot section: When the hot section is circular or symmetrically distributed, circular risers are preferred; When the hot section is elongated or stepped, elliptical or trapezoidal risers are preferred.

2. Combining process parameters: When the pouring temperature is high, the size of the riser should be appropriately increased, and the shape should be a circular or elliptical shape with uniform heat dissipation; When the mold stiffness is insufficient, avoid using sharp edged square risers and instead use trapezoidal or circular ones.

3. Coordination with other processes: If cold iron is used to accelerate local cooling, trapezoidal or combined risers can be used to shorten the shrinkage distance; For thin-walled castings, priority should be given to small-sized and precisely positioned trapezoidal or elliptical risers. Attention to riser size: It needs to be calculated using the modulus method or the hot spot circle method to ensure that the riser volume is sufficient to cover the hot spot. Process validation: Verify the effectiveness of the riser shape through trial casting or simulation analysis (such as MAGMASOFT) to avoid shrinkage and porosity defects. Cold iron assistance: When used in conjunction with cold iron in thick and large areas, it can reduce the volume of the riser and improve the efficiency of filling and shrinking.

Summary: The shape selection of the edge pressing riser for gray cast iron parts should be based on the matching of hot nodes. Circular and elliptical risers are suitable for most scenarios, and complex structures can be selected as trapezoidal or combined. The final design needs to be optimized based on process parameters and casting requirements, and the effectiveness should be verified through practice.