In casting production, the quality of marine castings should be controlled and inspected. The process rules and technical conditions for the control and inspection of each specific product from raw materials and auxiliary materials shall be formulated first. Each process shall be controlled and inspected in strict accordance with the process rules and technical conditions. After that, the quality of finished castings shall be inspected. Reasonable testing methods and appropriate testing personnel shall be provided. Generally, for the appearance quality of the casting, the surface roughness of the casting can be judged by comparing the sample blocks; Fine cracks on the surface can be inspected by coloring method and magnetic particle method. For the internal quality of marine castings, audio, ultrasonic, eddy current, X-ray and γ X-ray and other methods.

The casting defects of sand mold casting include: cold shut, insufficient pouring, air hole, sand sticking, sand inclusion, sand hole, sand expansion, etc.

1. Cold shut and insufficient pouring: the filling capacity of liquid metal is insufficient or the filling condition is poor. Before the cavity is filled, the metal liquid will stop flowing, which will cause the casting to have insufficient pouring or cold shut defects. Insufficient pouring will make the casting unable to obtain a complete shape; During cold shut, although the casting can obtain a complete shape, the mechanical properties of the casting are seriously damaged due to incomplete fusion joints.

Prevent under pouring and cold shut: improve pouring temperature and pouring speed.

2. The porosity gas does not escape in time before the metal liquid crusts, and the porosity defects are generated in the casting. The inner wall of the pores is smooth, bright or slightly oxidized. The effective bearing area of the casting will be reduced after the porosity is generated, and the stress concentration around the porosity will reduce the impact resistance and fatigue resistance of the casting. Porosity can also reduce the compactness of castings, resulting in the scrapping of some castings required to withstand hydrostatic testing. In addition, the porosity has a bad effect on the corrosion resistance and heat resistance of the casting.

Prevent the generation of air holes: reduce the air content in the molten metal, increase the permeability of the sand mold, and add an air outlet riser at a higher place in the mold cavity.

3. Sticky sand: a layer of sand particles that are difficult to remove are adhered on the surface of the casting. Sand sticking not only affects the appearance of the casting, but also increases the workload of casting cleaning and cutting, and even affects the service life of the machine. For example, if there is sand on the surface of the casting teeth, it is easy to damage. If there is sand in the pump or engine and other machine parts, it will affect the flow of fuel oil, gas, lubricating oil, cooling water and other fluids, and will stain and wear the whole machine.

Prevention of sand sticking: adding pulverized coal to the molding sand and brushing anti sand coating on the surface of the casting mold.

4. The groove and scar defects formed by sand inclusion on the surface of the casting are very easy to occur when wet casting thick and large plate castings.

Most of the parts with sand inclusion in the casting are in contact with the upper surface of the sand mold. The upper surface of the mold cavity is easily arched and warped due to the radiation heat of the metal liquid. When the warped sand layer is continuously scoured by the metal liquid flow, it may be broken and left in place or brought into other parts. The larger the upper surface of the casting, the larger the volume expansion of the molding sand, and the greater the tendency of sand inclusion.

5. Sand holes are holes filled with molding sand inside or on the surface of the casting.

6. Defects caused by the movement of the mold wall and the local expansion of the casting under the pressure of the molten metal during sand pouring. In order to prevent sand expansion, the strength of the sand mold, the rigidity of the sand box, the pressing force or fastening force when the box is closed should be increased, and the pouring temperature should be appropriately lowered to make the surface of the molten metal crust early, so as to reduce the pressure of the molten metal on the mold.