Lost Foam Casting Method Application And Pouring System Design Features

Top injection type (including rain pouring); B. measured injection type; measured on the note which was divided; measured note, C. ladder pouring; D. antes style; also known as the return type or the lower end of Rainfall ; E. string pouring ceremony.

A. Top injection type:

Top injection type generally used for small parts production, the advantages are; gating system set up to facilitate the group box modeling easy process yield increase, the drawback is; is not conducive to slagging exhaust.

B. Bottom injection type

Note for note with the top end and side note can not satisfy the requirements of casting liquid metal filling advantage is smooth, very conducive to liquid metal slag produced by the front end, air is discharged upward; disadvantage; process yield lower group box modeling difficult, liquid metal flow increases, the front is easy to cause casting defects due to low temperature.

C. Side pour type

Side pour type is pouring from the side for the form, including the sprue from the center after the introduction of the lateral injection castings, its focus on the bottom and the top note note the advantages of a higher process yield, group box modeling is also convenient, slag, gas and other impurities are easily discharged. LFC is the most commonly used form of casting.

D. Multistep type

Multistep type is actually a special side note type, which is characterized by multi-lateral injection points; side note relative to the general formula, and its advantages are; due to increased stratification of the liquid metal is formed on the mold filling relay mode, avoid long flowing liquid metal, is conducive to increasing pouring temperature, casting speed, to avoid wrinkled skin, cold shut, pouring lack of defects; should be noted that, step inside the runner must have enough to eat between the amount of sand , to prevent the baking of foam; ladder ingates must have a certain slope to prevent the molten metal into the mold upper prematurely.

E. String type

String type; Because the unit casting is small, to cast easily and improve efficiency, increase the production rate of the casting pouring taken way, a single casting can take the form of any one of the previous four kinds, they are combinations of clusters according to certain rules, share a set of gating system, the formation of strings pouring.

1. Gating system design points

Gating system in the entire casting process, it is introduced directly into the liquid alloy mold cavity, it enters the alloy liquid velocity, temperature (high and low temperature heat distribution), slag, gas exclude such a direct impact on the quality of castings, therefore, in addition to follow the gating system design sand casting and investment casting of principles, it features also need to reconsider.

The white sand mold casting system (vertical, horizontal, inside runner) and connection castings, must melting, cracking, decomposition, gasification out, the entire space so that the liquid alloy injection. Average temperatures than pouring liquid alloy sand casting raise 30 --- 50 ℃, thin-walled parts to 80 ℃, so raising the temperature, there is enough heat to melt away all the white mold. To improve the pouring temperature 50 ℃ 1500 ℃ high manganese steel pouring sieve, for example, the top note (vertical, horizontal, inside runner unity), such as pipes pouring cup then under the straight, horizontal, inside runner, runner too large, the high side, then into the cavity of molten steel temperature is too high too fast, so that the cavity overheating, resulting defects: sticky sand, chemical sticky sand, coating cracking, spalling caused by swelling of sand, scarring, bulging, and more meat, etc., collapsed sand, liquid steel into the cavity too fast too fast impact force is too large, the temperature is too high, so that the local sand collapse collapse, collapse scattered, the casting scrap; same superheat pouring temperature, while the use of bottom Note, straight, horizontal, inside runner cross-section is too small, too few, so that the molten steel into the cavity when the rate slows slows down, time and too long, prompting the temperature drops off very, resulting in localized melting of white mold completely clean, and produce flaw: wrinkled skin, coke, Lippi, sticky sand, mechanical sticky sand, liquid steel, sand, white mode decomposition residual liquid, solids and tar lustrous carbon, bonded together, difficult to clean, pouring less than lack of meat, heavy leather, slag, inclusions, entrained air --- and so on. It is necessary to consider a gating system to adapt to the casting, straight, horizontal, inner cross-sectional area of the cavity in order to control access to the appropriate speed, the temperature and the thermal field distribution in order to obtain qualified castings.

Therefore, before trying to enter the inner runner straight, horizontal, inner end or both ends of the runner left set slag pit (package) to facilitate centralized, so ingates section can curb flow, flow, so that the horizontal pouring slag file Road two ends prisoners set; temperature of molten alloy into the cavity with a certain fluidity to allow slag floating, while leaving some time for the slag can float to the surface; ingates sectional size, distribution, angle, so Entry alloy liquid chamber does not produce turbulence, adverse scum, but to calm and steady rise, which will help surfaced slag, slag mixed into these last riser or set the residue collection package, so the gating system design must be carefully considered set slag slag and other process measures.

White mold in the casting system and the model volume (size, structure, shape, weight and layout) plays a decisive role, together with the pouring temperature, casting speed, direct impact on gas evolution, since gas evolution at different temperature ranges are not the same first control fortunately white mold casting process gas evolution, pouring temperature is too high, fast speed, especially sprue stubby, prone to gas eruptions, coupled with vacuum suction is too small, resulting in anti-spray, endangering safety , design control white modulus (density, size), so that a smooth and orderly gas evolution; pouring in a smooth and orderly, the white sand mold and produce gas in the gas and the liquid alloy precipitates out of gas, timely sucked out by a vacuum pump or through the gating system riser (strain relief), set the residue riser escape. Must coordinate the vacuum from the flask, the middle, the bottom suction direction, and the heat rise of the law, the gas suction clean, otherwise the sand bottom suction, the suction pump is small, and the generated gas and lot, so there somewhere section castings, heat rises, breathing down both stalemate and produce large pores.

Cross-sectional area of each unit gating system, riser set

Casting the structure, shape, size, thickness, dimensions, weight, etc. initially determine its structure, the current general sand casting is still determined according to the common cross-sectional area ratio of each unit and the specific size of each unit proven in a larger cross-sectional area changes in the scope, will be eligible for warranty castings. Experience Sand calculation:

 (1) Experience in France, the traditional sand technology, the look-up table or empirical formula obtained Σ, the general increase of 10% -25% and then you can, try before you time to adjust.

 (2) Theoretical method to calculate the formula ΣF hydraulics class = G / (Mt0.31 √ Hp) (see related books).

Adopt closed type: Steel Castings: F Inside: F Black: F value = 1:1.1:1.2

                                Iron Castings: F Inside: F Black: F value = 1:1.2:1.4

Adopt open type: Finside: F Black: F value = 1: (1.1 --- 1.3): (1.2 --- 1.5)

The gate of the size, dimensions, shape, orientation (angle), directly affects the white mold melted alloy liquid into the cavity as speed, temperature (thermal field), stream trends, if applied early in triangular sand casting gate or flakes gate, take the side of the gate, its capacity is less liquid alloy, heat the surrounding area and more, dramatically reducing the liquid alloy into the cavity temperature, equal to the set of the strangle hold the cold zone, affecting the white mold melted, it is appropriate type of variable cross-section inside the gate, but with white mold (cast iron appearance) junction, the gate section thickness should be less than the casting wall thickness 1/2, no more than 2/3 of the formation of small hot thick section will produce fall feeding, so that roots (junction) produce shrinkage, shrinkage and even small slag, porosity. Ingates length should be as short as possible, too long, easy alloy flow heat loss, but also easy to form a small dead zone which affect the stream, generally according to the casting size 20mm-100mm.

Riser Set: riser Apart from feeding, to obtain dense conventional casting the role, but also improves the liquid alloy castings last padding set slag temperature and the role of feeding and set plays the role of the riser slag also known as the residue collection riser.

2. Setting principles：

(1) It should be placed on possible shrinkage or shrinkage of the hot spot or wall area, in order to provide solidification feeding;

(2) In the final filling liquid alloy parts, both out gassing, set the residue, but also serve to improve the effect of temperature where liquid alloy;

(3) white mold riser dead zone settings to set residue, while avoiding as to generate cushion effect caused by casting lack of meat, the outline is not clear.

Riser shape: spherical, cylindrical, cube-shaped, rectangular prism, etc.; Ariake riser, dark riser. In the lost foam casting process conditions spherical minimum surface area due to large volume, the solidification time is long; modeling commonly dark riser, so that the entire casting process remains in a closed vacuum.