(1)If the coated sand is used,local bonded core box appear which is mainly caused by uneven resin coating. Another reason is that there is too much fine powder in the sand or the added powdery auxiliary material which blocks the vent plug.It will also lead to an increase in the amount of resin usage.For the coated sand with powdery material,to mix it correctly,we should add powder first, mix for a few seconds before adding resin, otherwise it will not be easy to make mixing uniform, also affects the overall strength of the coated sand. 

(2)Refractoriness of coated sand resin, thick cast iron, cast steel Parts and castings that require high temperature pouring, the resin must have high fire resistance which does not react chemically with sand at high temperature. The raw sand is required to have a higher SiO2 content, and appropriately add

carbonaceous refractory accessories, using ceramsite sand, zircon sand and sprayed refractory paint etc 

(3)Coated sand needs to be heated for curing and the core box must be heated evenly. The nozzle position should be able to shoot fully empty cavity, and try to avoid shooting on the casting in order to remove it. The position of the vent should pay attention to “dead corners” when setting, and set more places far away from the nozzle vent. The core box should be cleaned of the adhered sand layer frequently, and the molds that are not in use should be coated with anti-rust oil for maintenance after cleaning. 

(4) The strength of the coated sand should be determined according to the requirements of the sand core.High strength inevitably increases the amount of resin added, and the amount of outgassing will also increase.

(5) Phase change should be used for sand cores with severe thermal creep in the inner cavity sand, special sand, and various auxiliary materials are added.

(6) The sand core is thin, slender and surrounded by molten metal in the core The gas generated at high temperature is difficult to discharge, so you must use a thicker source sand, such as 50/100 mesh, 40/70 mesh, external coating (preferably water base paint), forcing the gas to escape from the voids of the sand grains.

(7) The coated sand has a large amount of gas, and the gas is slow, and it is sticky in the soil sand mold, the gas must be led out through the core head, otherwise it is easy to appear choke pores, sand molds "fire" leaks, break sand molds, and explosive stickiness sand. 

(8) The coated sand at the lower part of the longer casting will collapse prematurely, without method to hold up the nearly solidified castings, it is easy to form the castings sinking, cracks, preheating The preventive measures are as follows: ①Fast pouring, speed up cooling, make the casting shape intensity; ②The lower mold can use the sand-coated iron mold process.

 (9) The coated sand shell of the stacking box pouring must be in the molding Time to extend the baking time and reduce the amount of gas, otherwise due to the molten metal bottom-up filling type, drove the gas to the top, due to the original pressure Because the top few layers are easy to cause choking and insufficient pouring.

 (10) The sand-coated iron type is to coat the surface of the metal cavity with a layers of coated sand, with a thickness of 4-20 mm, adjust the gold with the thickness of the sand depending on the cooling rate of the liquid, the sand layer should be thin in the part where the casting wall thickness is larger.The sand layer should be thicker in the part where the wall thickness of the casting is thinner. The mold rigidity is good, and the casting size is more accurate. Due to iron type,good thermal conductivity, fast cooling of molten metal, better self-feeding good, the riser can be used less or no riser, the process yield rate is improved, and the casting.The compactness of the parts is strong and the mechanical properties will be improved.