Causes preventive measures of porosity defects in castings

Bore hole is a common casting defect, its shape is generally spherical, oblate strip.The reason for the formation of pores is that the local gas pressure in a certain part of the casting exceeds the metal pressure when the metal liquid solidifies.Gas always flows along the path of least resistance, usually towards the top of the casting.Intrusion of pores precipitation of pores will also make the surface of the casting appear concave cystic holes the formation of subcutaneous pores.

1. Casting profile design

(1) Insufficient core head vent;

(2) The unreasonable casting design causes insufficient metal hydraulic head;

(3) When gas converges on the parting surface, pores will be generated at the parting surface.

2. Sand box its preparation

(1) the box belt is too close to the mold surface;

(2) the box wall is too close to the mold surface;

(3) the upper box is too shallow;

(4) the straight runner riser are too close to the box belt the box wall;

(5) The air vent on the metal wall for centrifugal casting is enough.

3. Sprue riser system

(1) the pressure head is too low;

(2) the gating system causing turbulence;

(3) a gating system that can cause flow interruption;

(4) the height size of the riser is enough;

(5) improper design of straight runner inner runner.

4. The sand

(1) Too much moisture in molding sand;

(2) poor air permeability of molding materials;

(3) foreign impurities are mixed in the molding sand;

(4) there are small clumps of clay in the molding sand;

(5) Poor mixing of molding sand;

(6) the particles of the gas generating material are too coarse;

(7) the content of gas material in the coating is too much.

5. Core

(1) The sand core is dried hardened;

(2) excessive amount of binder added;

(3) the air permeability of the sand core is poor;

(4) the sand core exhaust is smooth;

(5) Metal liquid enters the outlet hole;

(6) excessive amount of sand core binder excessive moisture;

(7) the coating layer of the sand core is too thick, damaged dried;

(8) too much gas material in the core sand paint;

(9) the sand core in the storage process in the sand mold moisture absorption;

(10) hook, wire sphanger is exposed outside the sand core;

(11) the cold iron joint filling material in the sand core is dry;

(12) The sand-core hook hanger is dried after sand-filling;

(13) Inclusions such as grass roots, leaves, coke coal are mixed into the sand core;

(14) Poor mixing of core sand.

6. Modelling

(1) Cold hot materials meet;

(2) poor ventilation of sand type;

(3) the sand is dry enough;

(4) improper sanding method under specific conditions;

(5) the sand hook, sand fixation wood, core bone box belt is too close to the appearance;

(6) the mud dipped on the sand hook is too thick;

(7) wet repair excessive repair;

(8) the sealing mud strip is too wet too close to the mold cavity;

(9) the sprue cup gating system are too wet;

(10) Insufficient sand filling in the sand box;

(11) Excessive release agent dosage;

(12) sand coating ointment is too thick dried.

7. Metal composition

All the factors that can change the gas solubility in the liquid metal are the main factors related to the stomatal defects.

8. Smelting

(1) steel: the metal liquid in the furnace for a long time intense boiling, can make the gas in the metal liquid escape;

(2) cast iron: scrap iron castings due to pores, most of which are caused by the low temperature of molten iron poured into the sand mold;

(3) Non-ferrous metals: most non-ferrous metals are very inspiratory.

9. Pouring

(1) use cold, wet unbaked crucible pouring bag;

(2) the molten metal casting temperature is low;

(3) the flow is cut off during pouring;

(4) the pouring bag crucible is too high when pouring;

(5) slow pouring.

10. Other

(1) the use of rusty, galvanized poor, oxidized moisture absorption cold iron, core support, core wire, etc.;

(2) Centrifugal casting is enough centrifugal force low speed.