About LFC V Casting Method By Carbon And Inclusion Of Quality Defects

Abstract: This thesis EPC casting method with V characteristics by carbon, carbon mechanism to do a more in-depth research. Clear on these two processes in terms Carbon differences and why.  The V method in the production of ordinary carbon steel casting advantage is recognized.

Keywords: Carbon, just melt do not burn to burn mainly, but also burn it melt, and instantly by carbon.

1 Introduction

EPC with V casting method application in our country for decades of history, from the first edition published in 1990, "Casting Handbook" will be listed as new technology V-method [1] (P881-P888), to 2002 in the second edition of "casting Handbook" [2] became a full sand craft (P85-88), 2011 Third Edition "casting Handbook" [3] (P70) four kinds of sand craft, lost foam casting and vacuum casting to become two of them, making it the primary means of casting modeling. Production quality defects encountered in the application to become the focus of our foundry workers overcome. This increases with the inclusion of carbon steel casting production has become a top priority. Our company consists of a casting plant (also known as the test base, referred to as pilot plant) two processes coexist, this branch of the mission is to provide programs promote the use of lost foam casting process or V France casting process units, visit, study, training operation of the workers. We also promote the use of these two processes to solve technical problems in the test sites. Our production is generally found in carbon steel castings produced by lost foam castings often occur by carbon and mixed quality defects, but with the V method of casting steel casting, carbon and inclusion phenomenon is not serious. Production casting surface finish, wrinkled skin defects rarely occur, especially after machining, internal inclusions rarely occur. This phenomenon has aroused our attention, and to put this issue as a research topic. Below we summarize the findings out research references for colleagues, welcomed criticism.

2. Lost foam casting process casting process with V France similarities and differences

2.1 The same point: dry sand, vacuum, plastic

 (1) dry sand, negative almost identical. We believe that dry sand Strictly speaking, the best selection of EPC 20/40 coarse particles, enabling foam pyrolysis products discharged by vacuum casting, reducing the casting and mixed by carbon impact. However, due to the coexistence of two processes we experimental plant, to facilitate the production, simplify sand processing equipment, lost foam casting foundry with V-method are used 40/70 dry sand, a few years to produce more normal, vacuum systems share.

(2) Plastics: lost foam casting EPS (polystyrene) foam.

V method for casting EVA (ethylene - vinyl acetate copolymer) plastic film EPS, EVA are petrochemical products, the main material are hydrocarbons, in the casting process will occur with high temperature pyrolysis liquid steel and its products but also with liquid steel effect, both physical changes but also chemical reactions, and the results will result in increased carbon steel castings and inclusions. Inclusion of this article refers to the residue caused by the inclusion of plastic. Excluding inclusions caused by melting and pouring.

2.2 Differences: cavity vent

(1) Cavity: Lost molded type, no cavities, so called solid casting. And even make the same foam riser is sealed in the sand box. Pouring molten steel using its own high-temperature pyrolysis of the foam, the occupation of space by replacing its formation castings. V method with the traditional casting foundry, have a upper and lower boxes, boxes can be combined to form the core under the sand, there are cavities. Cavity with air, The air containing 20% oxygen.

(2) Vent: LFC no vent riser is also enclosed in the sand within the film.

V casting method must have a vent to atmosphere and environment for the cavity, before pouring in the box together, so that the cavity and being drawn into the vacuum system of the sand particles to form a negative pressure differential, the establishment of the cavity shape, hardness and strength. Pouring, heat vent dramatic expansion of the cavity in the gas and plastic film cast exhaust gases produced by combustion.

3. EPC with V Cast Carbon and mixed method

3.1 EPC Carbon and inclusion [5] [6]

EPC in the foam due to mold, is sealed in a vacuum system is pumped into the vacuum dry sand, pouring, is anaerobic conditions, foam only pyrolysis, is a typical "just melt do not burn." Formation of pyrolysis products:

(1) Gas: CO, CO2, H2, CH4, and low molecular weight styrene and their derivatives thereof. Gas is easily removed by a vacuum system pumped through the paint layer, dry sand, to the atmosphere.

(2) Liquid: There are benzene, toluene, ethylene, composed of glassy polystyrene.

(3) Solid phase: mainly by pyrolysis of polystyrene into lustrous carbon and tar-like residue components.

The pyrolysis products are hydrocarbons, can not be discharged in casting mold, and poured into contact with molten steel, which then spread to the carbon steel, resulting in increased carbon and mixed casting. Some information will these pyrolysis products called "carbon pool" [7], and the lower the carbon content of castings, carbon trend is. Production of iron castings, cast iron itself due to high carbon content, the molten iron flow is good, slagging ability, carbon and inclusion phenomena have little effect. But the production of steel castings, due to low carbon content steel, poor mobility, slagging ability is poor, especially in less carbon 0.45% carbon steel castings [5] (P335), Carbon and became mixed major problem affecting the quality of castings, production requirements than 0.04% carbon low carbon stainless steel castings even become a problem.

3.2 V casting method by carbon

Speaking in front of V-process casting process is the cavity, the cavity has a special vent to atmosphere and the environment to make the cavity, the cavity with air, oxygen content of about 20%, the vacuum system will only sand particles between air pumped, in principle, allow pumping cavity gases. In practice, EVA sealing film, sometimes partially damaged, causing leakage. Local leak sand box, said partial vacuum leak, the vacuum system has become a means to maintain the intensity of negative pressure. V-process molding process at address leak repair, sticky seal to minimize leakage, ensure that the vacuum system vacuum intensity values.

Casting, the previous result of sufficient oxygen in the cavity, when the EVA film of liquid steel in contact with the combustion occurs mainly when the oxidation reaction of carbon in the plastic film, the oxygen in the air, react to generate CO2, along with the thermal expansion the hot air, the cavity escapes through the vent hole to the atmosphere, this phase does not occur by carbon. Pouring medium, because the filling of liquid steel mold, the cavity smaller. Pre-casting, to produce CO2, resulting in consumption of large quantities of oxygen, the oxygen content decreased cavity, when the carbon, oxygen, the reaction will produce some CO, is due to CO gas, with the hot air will escape to the atmosphere through the vent hole medium. During this period, still does not happen by carbon, generally speaking, less and less oxygen in the mold, the output of CO more and more. To pouring the late serious shortage of oxygen in the oxidation reaction is getting worse, the phenomenon occurs by carbon. Especially to the cast full of the moment, only to melt without burning will occur, will be like a lost foam casting, as generated by carbon and inclusions. However, due to shrinkage of liquid steel casting, need to have sufficient to complete the casting of molten steel feeding. Therefore, a larger riser volume set, you can focus a considerable amount of liquid steel pouring into the slag collecting bag, set carbon package, set the air bag. Pouring the last moment the production of plastic residues are concentrated in the riser body, in the clearing of castings, cut riser as recycled waste removed, and the casting is intact, no interference by carbon defects.

In actual production, we carefully observe the casting process, the mold of the gas changes have fully proved this phenomenon, with the balance of pouring oil block as an example. (See the balance schematic block casting)

          Pouring oil balance block schematic

The structural characteristics of castings, is a large flat castings, plastic film A surface accounted for 35%, B side accounted for 35%, C plane (vertical) one week, about 30%. Start pouring the molten metal burning A face first, because of the surface area is large, then the cavity enough oxygen, burning, the amount of CO2 produced more casting will see a hint of smoke from three strands three ventilation emerge mouth, burning in the liquid metal vertical line A to B cable film, casting a large plane, the slower rise in the liquid metal, the film is slow burning, the smoke vent almost invisible. When pouring the height close to line B, due to hypoxia, B side is also burned membrane into the melt phase, when the cavity is full of water becomes almost instantaneous melting only does not burn, will produce carburizing time, the resulting residue also form inclusions. This conclusion is drawn with a few years of observational studies. From pouring in, the changes to take smoke vent fully explain V France casting casting process, the change from the plastic film to burn mainly to also burn it melt, and then to melt based. As long as there is oxygen, will produce CO2, CO gas, CO2, CO gas will be from the vent (vent riser) self-discharge mold, it does not produce carbon growth and inclusion. Late in the casting melt just do not burn the moment, due to the casting riser, play sets slag, set carbon, gas gathering role, carbon and inclusions greatly reduce the harm.

V-process foundry castings produced by carbon and less inclusions Another reason is the V casting method consuming than lost foam casting plastic plastic consumed less.

Theoretical calculations, tons of steel casting, lost foam material consumed 1 ÷ 7.6 * 20 = 2.63kg (where 1 is 1m3 foam, 7.6 for the steel weight 7.6t / m3, 20 for the EPC proportion kg / m3) if riser consumption rate will go, consumption 3.5kg / t above.

V method is a film casting cavity surface of the sealing body wrapped. EVA film accounted for 0.98, EPS foam proportion 0.02,0.98 ÷ 0.02 = 49. EPS foam EVA film that is 49-fold. Film thickness to 0.1mm calculations, V France cast a considerable thickness of 4.9mm foam board with a foam made of hollow appearance, the literature [5] [6] [7] have pointed out that the use of hollow foam appearance is to reduce the growth of carbon and plastic residues effective measures. Moreover, when V of the coating film casting method, a significant portion of the film is stretched to a thickness of 0.05 ~ 0.08mm, the plastic residue can be more reduced. V t casting casting method consumed quantity of the film thickness of the casting, the greater the consumption of less thickness. It should be pointed out that the carbon content of 0.15% or less production of carbon steel castings by carbon when plastic film can not be ignored.

More than 0.15% carbon steel castings, V casting method can produce high-quality steel castings, in recent years, China has been mass-produced automobile front axle, the axle, rear axle, railway locomotive side frames, bolsters, hooks, etc. steel castings, steel castings are these safety critical parts. Through the national rigorous assessment of such castings have been exported to the United States, Australia, Russia, Ukraine, Kazakhstan and other countries, the full description V method casting process, production of carbon steel castings is a good technique worthy of recognition.

Some small steel castings, due to the limitations of the casting process V method, using the V method is not appropriate. I believe that the efforts of our foundry workers will overcome difficulties, making progress. Literature [4] [5] [6] [7] are more in-depth clarification of the appropriate control measures can refer to the application.

Refrence:

[1] Chinese Mechanical Engineering Society Foundry Institute "Casting Handbook" First Edition May 1990

[2] Chinese Mechanical Engineering Society Foundry Institute "Casting Handbook" Second Edition January 2002

[3] Chinese Mechanical Engineering Society Foundry Institute "Casting Handbook" third edition September 2011

[4] Branch of Chinese Mechanical Engineering Society Foundry Casting Lost Foam Technology Committee with the V France's Sun Ye Sheng-ping into a "lost foam casting foundry with V-method" in February 2010

[5] Zhang Zhou Wang Chunjing Deng Everest "Lost Foam Casting Handbook" January 2011

[6] Kelvin Huang Naiyu "lost foam casting technology," May 2004

[7] Cuichun Fang Deng Everest "lost foam casting technology and application" in June 2007     

About the author:

Ma Huairong, born in 1937, Weifang, Shandong, in 1960 graduated from the Shandong Institute of Machinery Casting, assigned to the Shandong Metallurgical Machinery Plant, engaged in casting technical work and retired in 1997, after retirement has been engaged in casting technology services, service units hundred, Pu Tong incumbent Zibo Vacuum Equipment Co., Ltd. technical adviser. a senior engineer The branch of the National Institute of Mechanical Engineering Casting Lost Foam Casting Technology Committee in V method. In recent years, he focused on the EPC with V casting method.

Contact: 13793332726