Teach you the problems and solutions in the application of coated sand

There are many kinds of core making methods, which can be divided into two categories: thermosetting method and cold curing method. Coated sand core-making belongs to the thermosetting method. Any core-making method has its own advantages and disadvantages, which mainly depends on the comprehensive factors such as product quality requirements, complexity, production batch, production cost, product price, etc. It is very effective to use coated sand core-making method for sand cores with high requirements on the surface quality of the inner cavity of castings, high dimensional accuracy and complex shape. For example: the intake and exhaust port sand core, water channel sand core, oil channel sand core of the cylinder head of a car engine, the water channel sand core and oil channel sand core of the cylinder block, the shell core sand core of the intake manifold and exhaust manifold, The flow channel sand core of the hydraulic valve, the air passage sand core of the automobile turbocharger, etc., but there are still some problems in the use of coated sand. Here is just a brief talk about the experience in the work.

1. Control the supply quality of coated sand

The coated sand must be accompanied by the supplier's quality assurance information when entering the factory, and the enterprise shall check according to the sampling standard, and the inspection shall be qualified before storage. When the enterprise fails to pass the sampling test, the quality assurance and technical departments will make the processing results, which is a concession to accept or return to the supplier.

2, qualified coated sand in the core of the sand core fracture deformation

The fracture deformation of the sand core during core making is usually considered to be caused by the low strength of the coated sand. In fact, sand core fracture and deformation will be involved in many production processes. If there is an abnormal situation, the real reason must be found before it can be completely solved. The specific reasons are as follows:

(1) The movable mold and the static mold are not parallel or on the same center line. Under the pressure of the oil cylinder or air cylinder during mold closing, the front end of the positioning pin has a slope, and the mold will still close tightly. However, the movable mold and the static mold will still return to their original state when the mold is opened, causing the sand core to break or deform. In this case, the sand will run when shooting sand, and the size of the sand core will become larger. The solution is to adjust the parallelism and coaxiality of the mold in time.

(2) When the hollow sand core is produced on the shell core machine, when the unhardened coated sand is poured out from the sand core and needs to be reused, the unused coated sand must be mixed according to the ratio of 3:7 before use, so as to ensure the surface quality of the shell core sand core and the strength of the sand core.

(3) The temperature of the mold and the time of the mold during core making are related to whether the hardening thickness of the sand core shell meets the process requirements. The process parameters specified in the process need to have a range, which needs to be adjusted by the skills of the operator. The lower limit of the mold retention time can be taken at the upper limit of the mold temperature, and the upper limit of the mold retention time is taken at the lower limit of the mold temperature. Operators need to be constantly trained to improve operational skills.

(4) phenolic resin and sand particles will stick to the mold during core making, which must be cleaned in time and sprayed with release agent, otherwise the sand core will be broken or deformed when more and more molds are opened.

(5) The spring ejector rod on the static mold of the hot core box mold will cause elastic failure due to long-term work at high temperature and cause the sand core to break or deform. The spring must be replaced in time.

3, the strength of the film sand and the determination of the amount of gas.

Under the premise of the quality of raw sand and resin, the key factor affecting the strength of coated sand is mainly the addition of phenolic resin. If the amount of phenolic resin is added, the strength will be improved, but the gas emission will also increase and the collapsibility will be reduced. Therefore, in the production application, it is necessary to control the strength of the coated sand to reduce the gas emission and improve the collapsibility, and a balance point must be found in the formulation of the strength standard. This balance point is to ensure the surface quality of the sand core and the strength under the premise of no deformation and no core breakage during pouring. In this way, the surface quality and dimensional accuracy of the casting can be guaranteed, and the gas emission can be reduced, the pore defects of the casting parts can be reduced, and the sand performance of the sand core can be improved. For sand core storage, station equipment and sand core trolley can be used in the process of handling, and 10mm ~ 15mm thick sponge is laid on it, which can reduce the loss rate of sand core.

4. Storage period of coated sand core

Any sand core will absorb moisture, especially in the southern region of the relative humidity of the air, the storage period of the sand core must be specified in the process documents, the use of lean production first-in-first-out production methods to reduce the storage capacity and storage period of the sand core. Each enterprise should determine the storage period of the sand core according to its own plant conditions and local climatic conditions.

This article is finished by coated sand, the point of view of this article does not represent the point of view of this site.