SAND CASTING EQUIPMENT.

Mechanical sand is also known as metal liquid permeable sand, which is formed by liquid metal or metal oxide drilling into the sand particle clearance on the cavity surface through capillary penetration or gas phase permeation. The metal and sand particles are mechanically mixed adhesive layer on the surface of the casting. The metal luster can be seen when the sand layer is removed. The surface of mechanical sand is spongy and sticks firmly to the surface of the casting. It usually occurs near the spout and the core surface where the sand mould and sand core are heated and the sand mould is low in compactness, such as near the spout, the thick and large section of the casting, the inner Angle and the groove.

Mechanical sand casting not only affects the appearance quality of casting, and even leads to scrap, so enough attention must be paid to mechanical sand casting to improve the yield of products. Based on years of experience and reference to relevant materials, Xinyuanzhu Group talks about the causes of mechanical casting sand adhesion and its preventive measures.

1.Casting and pattern design
If the casting and pattern structure will give the sand mold a sharp, overhanging, or protruding shape, or have a flat and thin sand table or core, the design will promote mechanical sand adhesion. Because the casting of this kind of structure will concentrate the local heat of sand mold and sand core, its normal performance will be damaged, the surface of sand mold and sand core will break up in advance, and the molten metal or metal oxide will be easy to infiltrate and produce mechanical sand adhesion. For this purpose, special sand types, such as zirconium sand or olivary sand, can be used in places where heat is concentrated to improve their ability to be heated for a long time or irradiated by high temperature.

2.Appearance
(1)The shape of the process design is not good, so that the sand type compaction is not compactness or compactness is uneven, will cause the cavity surface rough or loose, mechanical sand has a direct impact. The following mistakes are often made in the appearance process design:
1.1Improper selection of parting surface, resulting in excessively high upper mold, or forming deep cavity in sand mold.
1.2Improper layout of the pattern on the bottom plate makes it difficult to spring the depression, which may be caused by the pattern being too close to the box wall or the pattern being too densely arranged. Overcrowding of the pattern will cause sand expansion in the casting, and mechanical sand adhesion will occur even if there is no obvious sand expansion. Since the source of the defect is the same, mechanical sand and sand swelling may occur on the same casting.
1.3Improper placement of the straight runner, riser and runner will lead to pits that are not easy to spring, which is related to the layout of the riser system.
1.4Starting die slope & LT; At 1.5°, even if the entire sand mold is properly compacted, it will tear the surface of the sand mold, making it easy to infiltrate the metal or metal oxide.
(2)The appearance of the process structure is poor, resulting in the metal liquid static pressure is too high. Due to the increase of static pressure, the load of sand mold is also increased, so it is necessary to adopt special sand mold or more compact modeling method to resist the seepage pressure of metal liquid on sand mold.

3.sand box
The design and construction of sand box is not reasonable, resulting in uneven compaction of sand or sand too soft.
The general reasons for these problems are as follows:
(1)Improper location of the box belt prevents the compaction of some depressions, resulting in local excessive softness of the sand mold, causing swelling or mechanical adhesion of sand.
(2)Due to the sand box is too small, the sand is not solid.
(3)The box belt is not properly positioned, so that the straight runner and riser cannot be placed in the proper position, so that the moulding sand between the riser or the straight runner and the shape is not tight. and because of the heat concentration inevitably caused by the place, the mechanical sand more serious. Therefore, if the position of the runner or riser cannot be changed, one or all of the belt must be cut off.
(4)The top case is too high. Mechanical sand is usually related to the permeability resistance of the cavity surface and the static pressure of the metal liquid. The size of the metal liquid pressure is related to the density of the metal and the height of the upper box. If the casting needs to be filled, the upper box should be of a certain height, but the molding sand performance must be improved accordingly.

4.Gate and riser system
(1)Improper location of the riser leads to local overheating of the sand mold, thus causing premature destruction of the cavity surface. Metal liquid or metal oxide formed at high temperature is more likely to penetrate into the cavity surface.
Typical examples of such situations are as follows:
1.1If the straight runner or riser is too close to the mold surface, a hot spot area will be formed. If the sand type in this hot spot is not ground, the mechanical sand adhesion defects will be very serious.
1.2Excessive flow of metal liquid over a certain cavity surface will heat the mold surface to the point of destruction. If the initial solidification of the hard shell in the cavity is remelted by the later inflow of liquid metal, the sand adhesion is more serious.
1.3At the time of pouring, any factor which may cause excessive liquid pressure of the metal may cause mechanical sand-sticking of the casting. This is especially true when the liquid metal is not only at high pressure but also at high temperature.
(2)Improper proportion of cross section of straight runner, cross runner and inner runner causes the metal liquid to be continuously oxidized during pouring, which increases the amount of metal oxide and leads to the melting aid of molding sand. During pouring, the pouring system should always be filled with liquid metal, otherwise, the liquid metal can be oxidized in any part of the pouring system.
(3)The riser neck size is too large, which will cause the sand around it to overheat, which is a relatively common problem. This problem is often caused by the riser neck being too long, so that the metal liquid in the riser neck does not solidify prematurely, the size of the riser neck must be increased. If the riser neck is not retractable due to improper design, it is better to shorten the riser neck to prevent solidification rather than increase its size. A smaller riser neck reduces sand heating.
(4)Improper design of the runner cup or straight runner will lead to the involvement of air in the pouring process and cause liquid metal oxygenation, which is usually caused by turbulence. Mechanical sand adhesion will be caused by the continuous accumulation of oxide film on the surface of liquid metal.

5.sand
(1)Uneven distribution of original sand grain size will result in low compactness of sand mold, and the distribution of original sand grain size has a direct impact on the maximum compactness of sand mold.
(2)Poor fluidity and molding properties of molding sand.
(3)The resin coating on shell molding sand is too thin, will reduce the shell local strength and local sand is not covered by the resin, often because of this simple reason, the casting mechanical sand.
(4)The air permeability of the mold is too high, which is another reflection that the molding sand particles are too thick. Air permeability and compactness are two factors influencing each other. Low compactness leads to good air permeability and vice versa.
(5)The lack of carbon materials or deoxidizing substances in molding sand will produce too much metal oxide, making the oxide wet sand and easy to infiltrate.

6.core-making
(1)Uncoated sand core sand is too coarse or the distribution of particle size is not good, and the original sand particle size distribution is not uniform, has an impact on the generation of mechanical sand.
(2)Unground sand cores have the same properties as unground sand types, which have a significant impact on mechanical sand adhesion.
(3)The rough or porous surface of the sand core will cause mechanical sand adhesion. Molten metal or metal oxide infiltrates into the sand core after it has infiltrated the rough or porous surface.
(4)The sand core is hygroscopic during storage. For cores, too much water is more of a problem. Because the sand core moisture is too much to detect. Some cores look dry, but they are actually quite high in moisture. 
(5)The sand core in handling careless operation, or in the paint is still in the wet state handling and lead to damage or scratch coating. The consequence is that there is not enough paint on the sand core to prevent metal or metal oxides from penetrating the core. The damage to the paint is like opening an air vent in the sand core, causing the molten metal to boil and produce mechanical sand.
(6)Sand core coating immersion too shallow, will directly cause mechanical sand adhesion.
(7)Low high temperature strength of sand core coating. Because the clay in coating is insufficient, or the solvent is too much, as a result, binder content decreases, cause coating high temperature strength to reduce and cause mechanical adhesion sand.
(8)The poor mixing of core sand makes the strength of some parts of the core too low, causing collapse during pouring and resulting in mechanical sand adhesion.
(9)Poor cleaning and dressing of sand core will directly cause mechanical sand adhesion. To strengthen the inspection of sand core, such defects should be able to be avoided.
(10)The sand core is not dried again after immersion or coating spraying. With the sand core in the sand hygroscopic moisture, the coating is not easy to occur peeling and peeling.
(11)If the core box is not clean, the core sand will stick to the core box, resulting in rough surface of the core. The sand core with good quality has dense surface layer, and the sand core with dense surface layer cannot be obtained if the core box is not clean.

7.modelling
(1)Uneven softness and compactness of the sand. In most cases, sand compaction is as important as uniformity. However, sometimes uneven compactness is more harmful than overall softness of sand mold.
(2)Sand mould is not repaired properly. Sand repair surface rough and loose, will cause mechanical sand; Excessive repair or excessive moisture in the repair site will also cause boiling of metal liquid and mechanical sand.
(3)The parts with bad sand filling are rough and loose, and mechanical sand adhesion will occur.
(4)Sand mold coating uneven or insufficient.
(5)Table dry coating drying uneven or not fully dried.
(6)Excessive amount of demoulding liquid will weaken the surface strength of sand mold and promote the boiling of metal liquid, resulting in mechanical sand adhesion of casting.
(7)The baume of sand type coating is too low, coating can be inhaled by sand type, consequently coating falls off skin, chip or flake and cause mechanical adhesion sand.
(8)The surface sand covered by the surface is insufficient, which is a common operational oversight.
(9)Hot and cold materials (sand core, sand mold, core brace, chiller, etc.) contact with each other. When hot and cold materials meet, water will condense. Water can cause boiling mechanical sand, and at the same time greatly increase the rate of formation of oxides, which subsequently occur in the infiltration of metal oxides. This is the general reason for mechanical sand, but also the main reason for high pressure molding mechanical sand.

8.Metal composition
(1)It is easy to form metal oxides with good fluidity, which are more likely to cause mechanical sand adhesion than those with high surface tension or viscous metals.
(2)Alloys containing low melting point components, such as lead in lead bronze, can easily cause mechanical sand adhesion. Because lead is still flowing at a much lower temperature than the base metal.
(3)Alloys requiring high temperature casting. Due to the good fluidity of the alloy, mechanical sand adhesion is easy to occur. In addition, due to the high casting temperature, the formation speed of oxide is accelerated, so it has a tendency to form oxidizing mechanical sand.

9.pouring
(1)When the casting temperature is too high, it will not only improve the liquidity of the metal liquid, but also make the metal liquid oxidize rapidly, thus accelerating the occurrence of oxidizing mechanical sand.
(2)Excessive lifting of the ladle is the same as excessive lifting of the upper box, which will form excessive metal head and promote the metal or metal oxide to enter the pores of the sand mold.

The above is the summary of Xinyuanzhu Group. We welcome samples and drawings for casting production, and also welcome customers to visit the factory