Design of gating system for fixture casting (part 1)

The pouring system is a channel to guide liquid metal into the mold cavity, which is composed of sprue cup, direct sprue, transverse sprue and internal sprue.

Selection of gating system type

1.Closed gating system:

F refers to the gating system in which the cross-sectional area from the bottom hole of the sprue cup to the internal sprue is gradually reduced, and the choke element is the internal sprue.

F. this kind of pouring system is full quickly and has good slag retaining capacity. It is not easy for liquid metal to bring air and oxidation into the sprue, with less metal consumption and convenient cleaning.

F disadvantage: the linear velocity of liquid metal entering the mold cavity is high, which is easy to damage the mold and cause splashing, oxidation and gas entrapment of liquid metal.

F is mainly applicable to all kinds of iron castings that are not easy to oxidize, non-ferrous alloy castings that are easy to oxidize and steel castings that are cast by plunger casting.

2.Open gating system:

F the cross-sectional area from the bottom hole of the sprue cup to the inner sprue increases gradually, and the flow blocking section is located at the bottom hole of the sprue cup or the upper gate of the sprue.

Advantages: when entering the mold cavity, the liquid metal flow speed is small, the mold filling is stable, the scouring force is small, and the metal oxidation is small.

F disadvantage: poor slag retaining effect, large internal sprue, and more liquid metal consumed.

F is suitable for non-ferrous alloy castings, ductile iron castings and medium and large-scale steel castings which are easy to oxidize.

The above two kinds are not suitable for the characteristics of large-scale production of small steel castings in this design, so they are not selected.

In view of this design, check the foundry engineer’s Manual: in the mass production of small steel castings, subcontracting pouring is often used, and the filling pouring system is mostly used, which can not only strengthen the slag capacity, but also reduce the spray. The ratio of the cross-sectional area of the commonly used pouring system is within a

: a horizontal: a straight = 1.0: (0.8-0.9): (1.1-1.2)

Determine the position, number and metal introduction direction of the inner runner on the casting

The external dimension of the fixture is 285mm * 120mm * 140mm. According to table 5-7 of the foundry process equipment design manual, we can see that the sandbox size a * b * H = 350mm * 250mm * 200mm is selected, and one box is selected for casting according to the minimum sand load,. In order to facilitate the molding, the internal sprue is arranged on the parting surface. Because the casting is cast with the base facing up and the casting is all located in the lower box, so the casting solidification sequence is from bottom to top, which is conducive to the solidification of the important part of the support and get the feeding, so the inner sprue is set at the bottom side to introduce the liquid metal.

Determining the position and height of the sprue

It has been proved that too low sprue makes the filling and liquid feeding pressure insufficient, and it is easy to have defects such as unclear edge angle and contour of casting, and concave casting on the upper surface. The height of the primary design sprue is equal to the height of the upper sandbox by 200mm. However, the height should be checked for adequacy.

The inspection basis is that the residual pressure head shall meet the requirements of pressure angle, as follows:

HM > Ltg

Where HM – minimum residual pressure head

L — horizontal projection distance from the center of sprue to the highest and farthest point of casting

а – pressure angle

According to table 6-79 in the foundry engineer’s manual, it can be concluded that a = 4

Ltgа=2600*tg4≈180mm

Since the castings are all located in the lower tank, the residual pressure head HM is equal to the height of the upper tank by 200mm

It is verified that the residual pressure head meets the requirements of pressure angle.

Calculate pouring time and metal rising speed

Calculate the volume of single casting v = 0.9479dm3 according to the casting drawing

The density of steel casting is 7.9kg/dm3

One box and one piece, M = 7.49kg

Considering the machining allowance, it is calculated as 8%, M = 8.09kg

Considering the proportion of gate riser to casting 20% – 40%, take 40% m = 11.33kg

The process yield of mass production of fixture is about 85%, and the total weight of molten iron in mold can be estimated

G=11.33/85%≈13.33kg

Casting relative density kV = g / v = 13.33kg/v = 2.78kg/dm3

According to table 6-98 of foundry engineer manual, C = 1.0, k = 0.7 kg / cm2. S

According to table 1.4-61 of practical casting manual, the preliminary calculation of pouring time can be obtained

T=C√G=2.2*√13.33≈3.65s

Calculated rising speed of molten iron level V = L / T = 140 / 3.65 = 38.36mm/s

According to table 6-94 of foundry engineer’s manual, the minimum rising speed of molten steel v = 15mm / s, but it should not exceed 30mm / s, so the coefficient C should be corrected. Taking C = 1.3, the pouring time t = 4.75s, the rising speed of molten iron is 29.5mm/s, which meets the requirements.

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