Coated sand has better circulation and storage properties

Definition: Before moulding design and core making, the surface of sand grains has been covered with a layer of solid resin film, and the core sand is called coated sand, also known as shell sand.

Coated sand has good circulation and storage, used to make the core of high strength, high precision processing, and is conducive to long-term storage.

In our country in 1997 to formulate the forging sand machinery industry standard (JB/T8583-1997), clear film sand grading and model expression:

Coated sand for forging according to the bending strength at room temperature strength classifications

Particle size distribution of coated sand sieve number numbering

Classification number of burnishing reducer

Bending strength at room temperature strength grade classification No.

Film-coated sand for forging (cover, film, sand Chinese pinyin alphabet)

Characteristics of coated sand

Compared with other resin sand casting, coated sand has the following main characteristics:

 Suitable strength characteristics, can be made into a high-strength shell core coated sand, can also be made into a medium strength hot core box coated sand, can also be made into a low-strength non-ferrous metal with coated sand;

Good flowability, clear contour of the produced type (core), high density of the mechanism, can produce manufacturing complex sand core, such as cylinder head, cylinder head water cooler core;

Sand core surface cost-effective, less or not on the construction of paint, you can get a better surface quality of castings, surface roughness of the surface to Ra = 6.3 ~ 12.5um, machining accuracy can reach CT7 ~ CT8 level;

Good collapsibility, castings are very easy to remove;

The sand core is strong against water absorption and has a long storage time, which is good for storage, delivery and use;

Main disadvantages: expensive, relatively large energy consumption, need to cause pungent odour in the process of moulding design, core making and pouring, long term storage at high temperature, high and low temperatures may produce agglomerates, etc.

Storage of coated sand

Laminating sand can be stored for a long time, generally not more than 5 months, if it is put into a vessel or bag with good sealing, under the dry and agitated environment of indoor temperature (≤20℃);

Specific production process generally do not have the above storage standards. Laminating sand using two-layer bag (inner bag, outer bag) outer packaging, storage of dry, natural ventilation conditions in a good warehouse, the next layer should be used to support the mat of carpentry boards, carpentry boards under the natural ventilation, in order to ensure that the sand does not return to the moisture, not agglomerated. If the agglomeration is slight, it can be pounded and used normally after screening.

Types of coated sand

It consists of quartz sand, thermosetting plastic urea-formaldehyde resin, urotropin and calcium stearate. Suitable for general casting iron parts.

High strength and low outgassing type of coated sand

It is the upgraded enterprise product of general coated sand, which is equipped with new technology according to the addition of relevant additives, and its strength is more than 30% higher than that of general coated sand, and the amount of gassing is significantly reduced, so it is suitable for the production and manufacture of complicated and high-precision casting iron parts.