Mechanical sticky sand, also known as metal liquid permeation sticky sand, is composed of liquid metal or metal oxide through the capillary infiltration or gas infiltration way into the cavity surface sand gap, the surface of the Automobile Casting metal and sand mechanical mixture of adhesive layer. Qinghe sticky sand layer can be seen when the metal luster. Mechanical sticky sand surface was sponge-like, firmly adhere to the surface of the Automobile Casting, and more occurred in the sand and sand core surface heat and strong sand tightness of the low parts, such as pouring near the mouth, Automobile Casting thick section, Groove.
The mechanical sticky sand not only affects the appearance quality of the Automobile Casting Automobile Castings, but also causes scrapping, so the mechanical sticky sand of the Automobile Castings must be given enough attention to improve the product yield. I combined with years of practical experience in production and refer to the relevant information, talk about the cause of Automobile Casting sand and its prevention measures.
1, Automobile Casting and design
Such a design will promote the production of mechanical sticks if the cast and pattern will cause the sand to have a sharp, overhanging or protruding shape, or a flat sand or sand core. Because this kind of structure of the Automobile Castings will sand, sand core local heat concentration, its normal performance is destroyed, sand, sand core surface in advance collapse, molten metal or metal oxide easy to penetrate and produce mechanical sticky sand. In this regard, in the heat concentrated parts of the use of special sand, such as zircon sand or olivine sand, in order to improve its long-term heat or high temperature radiation capacity.
2, looks like
(1) the appearance of the poor design process, so that the sand is not tight or compact compaction, will cause the cavity surface rough or loose, there is a direct impact on the production of mechanical sticky sand. Appearance of the process design often appear the following error:
First, the mold part of the wrong choice, resulting in the type is too high, or in the sand form in the formation of deep cavity.
Second, the appearance of the mold on the bottom of the layout of the improper position, so that depression is difficult to Chung, this may be due to the pattern from the wall too close, or the appearance of too close. Due to the arrangement is too crowded, will cause the Automobile Casting to produce swelling sand, even if there is no obvious swelling of the sand, there will be mechanical sticky sand. Due to the same origin of the defect, mechanical sticky sand and bulging will appear on the same Automobile Casting.
Third, the sprue, riser and runner position improperly arranged, there will be easy to Chung real depression, which is the layout of the riser system.
Fourth, from the mold slope <1.5 °, even if the sand tightness of the appropriate, will make the sand surface tear, easy to make metal or metal oxide infiltration.
(2) the appearance of the poor structure of the process, resulting in metal liquid static pressure is too high. Due to the increase in static pressure, sand load will increase, so the need for special sand or more compact modeling method to resist the metal liquid on the sand type of osmotic pressure.
3, sand box
The design and construction of the sand box is unreasonable, resulting in uneven sand compactness or Chung sand is too soft.
The general causes of these problems are as follows:
(1) improper position of the box, hinder some of the sinking of the Chung real, resulting in local sand too soft, causing swelling sand or mechanical sticky sand.
(2) due to the sand box is too small to cause Chung sand is not real.
(3) improper position of the box, so that the sprue and riser can not be placed in the right place, so that the riser or sprue and the type of sand between the compaction is not tight. And because the Department will inevitably lead to heat concentration, so that the mechanical sticky sand is more serious. Therefore, if the position of the sprue or riser can not be changed, the box must be cut off or removed from the whole.
(4) the box is too high. Mechanical sticky sand is usually associated with the impermeability of the cavity surface and the static pressure of the molten metal, the size of the metal liquid pressure, and the metal density and the height of the upper box. If you need to start from the Automobile Casting shrink, the box should have a certain height, but the sand performance must also be improved.
4, pouring riser system
(1) improper position of the riser caused the local overheating of the sand, thus causing the cavity surface to be destroyed prematurely. The metal liquid or the metal oxide formed at high temperature is more likely to penetrate the cavity surface.
Examples of such cases are the following:
First, the sprue or riser from the surface too close to form a hot section, the hot section of the sand type if not Chung, the mechanical sticky sand defects will be very serious.
Second, in a certain cavity on the surface of the flow of metal too much, will be heated to the extent of enough to destroy the extent. If the initial solidified hard shell in the cavity is later infiltrated by the molten metal, the sticky sand is even more serious.
Third, in the pouring, where can cause the metal liquid pressure is too high any factors, may lead to Automobile Castings produce mechanical sticky sand. When the metal liquid is not only high pressure, and the temperature is high, the situation is particularly serious.
(2) the proportion of the cross-section of the sprue, the runner and the runner is improper, so that the molten metal is continuously oxidized during pouring, increasing the number of metal oxides and causing the fluxing of the molding sand. During the pouring process, the gating system should always be filled with molten metal, otherwise the metal solution can be oxidized at any part of the Automobile Casting system.
(3) riser neck size is too large, will cause its surrounding sand overheating, which is a more common problem. This problem is often caused by the riser neck is too long, in order to keep the metal in the bottom of the mouth is not prematurely solidified, you have to increase the neck size. If the design of the riser neck is not due to improper filling, it is best to shorten the riser neck to prevent the solidification, rather than increase its size. Smaller riser neck, can reduce the sand type heat.
(4) gate cup or sprue improper design, so that when pouring into the air caused by oxidation of metal liquid, which is usually caused by turbulence, with the metal surface oxide film will continue to accumulate the mechanical adhesion sand.
(1) the original sand particle size distribution is not uniform, will cause sand compactness is low, the original sand particle size distribution of the maximum compactness of the sand has a direct impact.
(2) sand flow and poor formability.
(3) shell sand on the resin is too thin film, will make the shell of the local strength and local sand is not covered by resin, often because of this simple reason, so that the formation of mechanical sand sticking.
(4) The permeability of the mold is too high, which is another reflection of the sand particles too thick. Breathability and compactness are two factors that affect each other. Low degree of tightness is good ventilation, and vice versa.
(5) sand carbon material or deoxidizing material is insufficient, will produce too much metal oxide, so that the oxide wet sand and easy to penetrate.
6, the core
(1) Uncoated paint sand core sand too coarse or poor particle size distribution, and the original sand particle size distribution is not uniform, the impact of the formation of mechanical sticky sand.
(2) sand core is not Chung, and sand type is not the same as the nature of the same, the mechanical sticky sand has a significant impact.
(3) sand core surface rough or porous, will cause mechanical sticky sand. The molten metal or metal oxide infiltrates this rough or porous surface and then infiltrates the core.
(4) sand core during storage of moisture. For the sand core, the water is too much trouble. Because the sand core too much water is not easy to detect. Some sand cores look like dry, but in fact the water is still very high.
(5) the sand core in the handling of careless, or in the paint is still in the wet state when handling and lead to damage or abrasion coating. The consequence is that the coating on the core is not sufficient to prevent metal or metal oxides from penetrating into the core. Paint at the damage Department as if the sand core to open a hole, causing the metal liquid boiling and produce mechanical sticky sand.
(6) sand core coating immersion too shallow, will directly cause mechanical sticky sand.
(7) sand core coating high temperature strength is low. Due to lack of clay in the paint, or too much solvent, so that the binder content decreased, resulting in lower strength of the coating caused by mechanical adhesion sand.
(8) core sand mixed poor, so that individual parts of the sand core strength is too low, resulting in caving when pouring, resulting in mechanical sticky sand.
(9) sand core cleaning and poor repair, it will directly cause mechanical sticky sand. The sand core to strengthen the inspection, such defects should be able to avoid.
(10) sand core in the dip, spray paint did not dry again. And sand core in the sand in the wet tide like the same, the coating is not easy to peel off and peel off.
(11) core box is not clean, will make the core sand attached to the core box, resulting in sand core surface roughness. High quality sand core has a dense surface layer, the core box is not clean and can not get a dense surface layer of high quality sand core.
(1) Chung sand soft and compact degree of uneven. In most cases, it is equally important to have uniform and compactness. However, sometimes the compactness of the sand is more uniform than the overall softness of the sand.
(2) sand repair bad. Sand repair surface rough loose, will cause mechanical sticky sand; repair over or repair parts of the water is too high, will cause the metal liquid boiling and cause mechanical sticky sand.
(3) fill the bad parts of the rough, loose, there will be mechanical sticky sand.
(4) sand coating uneven or inadequate.
(5) dry-type paint dry or uneven drying.
(6) excessive amount of mold release fluid will weaken the sand surface strength, contributed to the molten metal boiling and produce mechanical Automobile Casting sand.
(7) sand coating is too low, the coating will be sand inhalation, resulting in paint off, falling or peeling caused by mechanical sticky sand.
(8) the surface of the surface covered with insufficient amount of sand, which is a common operating negligence.
(9) hot and cold materials (sand core, sand, core, cold iron, etc.) come together. Hot and cold material meet, will make water condensation. Moisture can cause boiling-type mechanical sticky sand, while a substantial increase in the rate of production of oxides, followed by metal oxide infiltration. This is the general cause of mechanical sticky sand, but also the main reason for high pressure modeling of mechanical sticky sand.
8, metal composition
(1) easy to form a good flow of metal oxides, good mobility of metal than the surface tension or thicker metal is more likely to cause mechanical sticky sand.
(2) alloys containing low melting point components, such as lead bronze in the lead easily lead to mechanical sticky sand. Because the lead is still in the flow state when the temperature is much lower than the parent metal temperature.
(3) the need for high temperature Automobile Casting alloy. As the alloy flow is good, easy to produce mechanical sticky sand. In addition, since the pouring temperature is high, the rate of formation of the oxide is accelerated, and therefore, there is a tendency to form oxidative mechanical sticky sand.
(1) pouring temperature is too high, not only will improve the fluidity of molten metal, but also rapid oxidation of metal liquid, thus accelerating the occurrence of oxidative mechanical sticky sand.
(2) the ladle is too high and the upper box is too high, will form too high metal indenter, to promote the metal or metal oxide into the sand-type pores.