Basic Principles Of Design Of Precision Casting Gating System

1. Ensure the smooth filling of molten metal

(1) Control the flow rate and flow of molten metal to avoid the phenomenon of molten metal flowing and splashing, and prevent the inclusion of gas and inclusions.
Reasonably design the shape and size of the runner so that the molten metal flows smoothly in the runner, gradually accelerates into the cavity, and reduces impact and disturbance. Use appropriate gate forms, such as flat gates, trapezoidal gates, etc., to reduce the flow rate of molten metal, which is conducive to smooth filling.

(2)Ensure that the rising speed of molten metal in the cavity is uniform to prevent defects such as local overheating or cold shut.
Reasonably arrange the position and number of inner runners so that the molten metal can evenly fill all parts of the cavity.
According to the shape and size of the casting, calculate the appropriate filling time and molten metal flow rate to ensure a uniform rising speed.

2. Favorable for exhaust and slag removal

(1) Design a reasonable exhaust channel to facilitate the smooth discharge of gas in the cavity.
Set up outlets, risers, etc. in the casting system so that the gas can escape in time to avoid defects such as pores in the casting.
The layout of the runner should be conducive to the flow and discharge of gas to avoid gas accumulation in the cavity.

(2)Promote the floating and removal of inclusions.
Utilize the shape and flow characteristics of the runner to enable inclusions to float to the riser or slag bag during the flow of molten metal.
Reasonably set the position and size of the slag bag to collect and remove inclusions.

3. Control the solidification sequence

(1) Guide the molten metal to solidify in a predetermined solidification sequence to obtain good casting quality.
By adjusting the size, position and number of the runner, control the cooling rate and solidification direction of the molten metal.
The principle of sequential solidification can be adopted to make the casting solidify from a position away from the riser,
and gradually advance toward the riser to ensure the density of the casting.

(2)Reasonably set the riser and chill to adjust the solidification process of the casting.
The riser is used to compensate for the shrinkage of the casting during solidification to prevent defects such as shrinkage cavities and shrinkage.
According to the shape and size of the casting, determine the position, size and number of the riser.
Cold iron can accelerate the local cooling rate of castings, change the solidification sequence, and improve the quality of castings.

4. Easy to clean and operate

(1) The structure of the pouring system should be simple, easy to clean and remove residues such as runners and risers.
Avoid designing overly complex runner shapes and connection methods so that the pouring system can be easily separated from the casting during the casting cleaning process.
The location of the gate should be selected in a position that does not affect the appearance and performance of the casting, which is convenient for subsequent processing and treatment.

(2)Consider the operability of the casting process and improve production efficiency.
The design of the pouring system should be compatible with the casting equipment and process, and easy to operate and control.
Reasonably arrange the location of the gate, riser, etc., so as to perform operations such as pouring, shrinkage compensation and exhaust during the casting process.

Sand pouring and floating sand have their own advantages and disadvantages in the shell making process.

Advantages of sand pouring:

(1)The sand particle distribution is relatively uniform, which can better ensure the uniformity of the thickness of the shell.

(2)For some castings with complex shapes, sand pouring can better cover all parts. Disadvantages of sand casting:
The equipment requirements are relatively high, and special sand casting equipment is required.
More dust may be generated during the operation.

Advantages of floating sand:

(1)The operation is relatively simple and the cost is low.

(2) The thickness of the sand layer can be adjusted as needed.

Disadvantages of floating sand:

(1)distribution of sand particles may not be as uniform as that of sand casting, and it is easy to be too thick or too thin in some areas.

(2)For castings with complex shapes, there may be problems with incomplete coverage.

In general, the choice of sand casting or floating sand depends on specific production requirements, casting shape, cost and other factors. If the quality requirements for the shell are high,and there are corresponding equipment and technical support,sand casting can be considered. If you pursue simple operation and low cost, floating sand may be an option. At the same time, you can also conduct experiments and optimization according to the actual situation to determine the most suitable shell making method