Mechanical sticky sand, also known as liquid metal infiltration sticky sand, is composed of a liquid metal or metal oxide by capillary permeation or gas permeation manner drilled cavity surface grit gap, formed on the surface of the metal in the casting and sand mechanically mixing the adhesive layer. Clear visible metallic luster sticky sand shovel. Sand surface mechanical sticky spongy, firmly adhere to the casting surface, occurs in strongly heated sand and sand core surface effects and low sand compaction of the site, such as Riser nearby, casting Heavy cross-section, inside and concave grip.

　　Mechanical sticky sand casting quality not only affects the appearance, and even cause scrapped, so the sticky sand casting machinery must be taken seriously enough to improve product yield. We combine years of practical experience and refer to relevant information, to talk about the causes of sticky sand casting machinery and the precautions.

　　1. casting and pattern design

　　If the appearance of structural castings and sand will have sharp corners, overhanging or protruding shape, or having flat thin sand table or sand core, then this design will facilitate mechanical sticky sand production. Because such structures will cast sand, sand core local heat concentrated damage its normal performance, sand, sand core surface ahead of collapsing, the molten metal or metal oxide is easy to penetrate and create mechanical sticky sand. In this regard, the heat can be concentrated in the special parts of sand, such as zircon sand or olivine sand, to increase its capacity by prolonged heat or high temperature radiation.

　　2. appearance

　　Poor process design (1) look like, so that Chung is not compacted sand or uneven compaction will cause cavity surface rough or loose, have a direct impact on the generation of mechanical sticky sand. Process design often look like the following error:

　　One parting poor choice, causing the type is too high, or the formation of a cavity deep in the sand.

　　Second, look at the position of the upper mold base plate arranged properly, so difficult Chung real depression, which may be due from the tank wall look too close, or too dense arrangement appearance due. Since the appearance of overcrowding arrangement, it will cause inflation to produce sand casting, even if there is no obvious swelling sand, mechanical sticky sand will happen. For the same root cause of defects, mechanical sticky sand and sand expansion occurs on the same cast.

　　Third sprue, riser and runner position arranged properly, there will be real difficult Chung sunken part, this layout Riser system related.

　　Fourth, draft angle <1.5 °, even if the entire sand compaction appropriate, also make sand surface tear, easy to penetrate the metal or metal oxide.

　　Adverse process structure (2) the appearance of lead metal hydrostatic pressure is too high. Due to increased static pressure, sand the load will increase, requiring the use of special sand or firmer modeling methods to withstand the molten metal on the sand of the osmotic pressure.

　　3. sand box

　　Sand box design and construction unreasonable, resulting in uneven sand compaction rammer or too soft.

　　General causes of these problems are as follows:

　　Improper position (1) box with and prevent some parts of the Chung real depressed, resulting in localized sand too soft, causing swelling or mechanical sticky sand sand.

　　(2) the sand box is too small to cause rammer is not true.

　　(3) box with improper position, so that the sprue and riser not in the right position, so that the riser or sand between Chung sprue and pattern is not tight. Because where the focus will inevitably lead to heat, mechanical sticky sand more serious. Therefore, as the position of the sprue or feeder can not be changed, it must be cut off a piece of tape or a whole box removed.

　　(4) the box is too high. Mechanical sticky sand usually associated with anti-penetration and molten metal cavity surface static pressure is related to the density of the size of the metal hydraulic pressure, and metal boxes and on highly relevant. As from the casting feeding needs, the box should have a certain height, but sand performance must be improved along.

　　4. Riser System

　　(1) Riser position improper sand local overheating, thus contributing to premature destruction of the cavity surface, a metal oxide formed at high temperature metal solution or even more easily penetrate the cavity surface.

　　More typical examples of such cases are the following:

　　First, sprue or riser distance profile too close, forming a hot spot area, sand this hot spot area Chung if not real, then sand sticking mechanical defects will be very serious.

　　Second, certain excessive molten metal flowing through the cavity surface, type of surface will be heated to a degree sufficient to destruction. If the initial cavity was later flows into the crust solidified molten metal remelting, the sticky sand is more serious.

　　Third, at the time of casting, where molten metal can cause any factors that excessive pressure, are likely to lead to a mechanical sticky sand casting. When the metal was not only pressure is high, and the temperature is high, the situation is particularly serious.

　　(2) sprue, improper cross-section ratio of the runner and runner, so that the molten metal in the pouring constantly being oxidized, increasing the amount of metal oxides and lead fluxing action on the sand. In the casting process, the gating system should always be filled with liquid metal, otherwise, in any part of the system are to make the casting of molten metal by oxidation.

　　(3) riser neck size is too large, it will cause overheating of the surrounding sand, which is a relatively common problem. This problem is often caused due to the riser neck too long, in order to make the riser without premature solidification of liquid metal neck, you have to increase the size of the neck. If the riser neck design because improper feeding less, then it is better to shorten the riser neck to prevent clotting, rather than increasing its size. Smaller riser neck size can be reduced sand heated.

　　Improper (4) gate or sprue cup design that involved air oxidation caused by pouring the molten metal, which is usually due to turbulence caused by the accumulation of liquid metal with the surface oxide film can cause mechanical sticky sand.

　　5. Sand

　　(1) The degree of uneven distribution of sand, can cause low sand compaction, the original sand particle size distribution has a direct impact on the sand of the greatest firmness.

　　(2) sand flowability and poor moldability.

　　(3) the resin coated sand shell is too thin, the local intensity will decrease and partial shell sand is not covered with resin, often because of this simple reason, the casting mechanically sticky sand.

　　(4) high permeability of the mold, which is too coarse sand particles another reflection. Permeability and compaction are the two factors that influence each other. Compaction is low permeability, and vice versa.

　　(5) The shortage of sand in the carbon material or deoxy substances, will produce excessive metal oxide, an oxide wet sand and easy to penetrate.

　　6. The system core

　　(1) No paint brush sand core sand is too coarse or poor particle size distribution, and the uneven distribution of the original, like sand, sand sticking to a mechanical impact.

　　(2) Chung sand core is not real, and the sand is not the real nature of Chung, have a significant effect on the mechanical sticky sand.

　　(3) The sand core surface rough or porous, cause mechanical sticky sand. It will penetrate sand core of molten metal or metal oxides such infiltration rough or porous surfaces later.

　　(4) sand core moisture during storage. Sand core, the water too much more trouble. Too much water because of the sand core imperceptible. Some look like dry sand core, but in fact its water remains high.

　　(5) The sand core in the handling careless operation, or handling incurred damage or scratch the coating when the coating is still in a wet state. The consequences are caused by paint sand core is not enough, that it can not prevent the infiltration of metal or metal oxide sand core. Paint breakage if the sand core opened as a vent, causing the liquid to boil and generate mechanical metal sticky sand.

　　(6) immersed in shallow sand core paint, it will directly cause mechanical sticky sand.

　　(7) high-temperature strength of the sand core paint is low. Due to lack of clay coatings, solvent or too much, so that the binder content is reduced, causing the coating to reduce high-temperature strength and cause mechanical sticky sand.

　　(8) core sand mixed system is bad, so that the individual parts of the sand core strength is too low, causing the avalanche in the pouring, resulting in mechanical sticky sand.

　　(9) The sand core cleaning and poor finishing, it will directly cause mechanical sticky sand. Strengthen inspection of the sand core, such gaps should be able to avoid.

　　(10) The sand core in dip, spray paint is not drying again. And sand core in the absorbent damp sand as prone to flaking coatings quit and peel.

　　(11) core box is not clean, it will adhere to the core sand core box, resulting in a rough surface of the sand core. Good quality sand core has a dense surface layer, core box is not clean will not get the quality of the sand core having a dense surface layer.

　　7. Modeling

　　(1) Chung soft sand and uneven compaction. In most cases, Chung sand compaction and compaction even equally important. However, sometimes uneven compaction is greater than the overall soft sand hazards.

　　(2) sand repair bad. Sand repair loose surface roughness, cause mechanical sticky sand; repairing excessive or repair parts water is too high will cause the liquid to boil and cause mechanical metal sticky sand.

　　(3) poor parts coarse sand fill, loose, mechanical sticky sand occur.

　　(4) sand coating uneven or insufficient.

　　(5) Table dry paint drying or full drying unevenness.

　　(6) the amount of excess fluid release will weaken the sand surface strength, contributed to the boiling liquid metal casting machine to produce sticky sand.

　　(7) Baume sand coating is too low, the coating will be sand sucked, thereby causing the paint to peel, flake or peel off and cause mechanical sticky sand.

　　(8) the amount of sand the surface appearance of surface coverage deficiency, which is common in operating negligence.

　　(9) Hot and cold material (sand core, sand, stud, cold iron, etc.) contacts together. Hot and cold materials meet, make water condensation. Boiling water can cause mechanical sticky sand, while dramatically increasing the production rate of the oxide, followed by the metal oxide infiltration will occur. This is a general cause mechanical sticky sand, is mainly due to mechanical sticky sand to produce high-pressure molding.

　　8. The metal component

　　(1) easy to form a free-flowing metal oxide, a metal of high specific surface tension and good mobility, or more likely to cause a thick metal mechanical sticky sand.

　　(2) containing a low-melting alloy components, such as lead bronze Lead is easy to cause mechanical sticky sand. Because lead is lower than the parent metal temperature much time remains in the running state.

　　(3) requires a high temperature cast alloys. Since the alloy mobility, prone to mechanical sticky sand. In addition, due to the pouring temperature is high, the accelerated production rate of the oxide, it tends to form an oxide more mechanical sticky sand.

　　9. Casting

　　(1) When the pouring temperature is too high, not only will improve the flowability of molten metal, but also the rapid oxidation of the liquid metal, which accelerates the oxidation of the occurrence of mechanical sticky sand.

　　(2) ladle lift too high and the box is too high as the formation of the high metal pressure head, prompting a metal or metal oxide into the sand pores.