The Adaptability Conditions and Applicable Countermeasures Analysis of Lost Foam Casting

Crusher & Mining Industry Projects

1. Introduction

Lost foam casting is a significant casting technology in the foundry industry. It has unique process characteristics and application scopes. However, in the actual production process in China, it faces various challenges, such as high defect rates in some enterprises and difficulties in mastering the technology. This article aims to comprehensively analyze the adaptability conditions, common defects, and applicable countermeasures of lost foam casting, as well as predict its development trend in the Chinese context.

2. The Current Situation of Lost Foam Casting in China – The Onset of the Crucial Stage

2.1 The “Lost Foam Casting Dilemma”

The Up – Surge of Lost Foam Casting: Currently, in China, the lost foam casting industry is experiencing a boom. According to incomplete estimates, there are approximately 2,500 – 3,000 large – scale lost foam casting enterprises, and the actual number is even larger, with the number still on the rise. The equipment types, production organization methods, raw and auxiliary materials, and process technologies in the industry are diverse and uneven.
Negative Impacts: Some enterprises, especially small and micro – enterprises, suffer from a high scrap rate of castings. They often rely on post – repair to maintain production even for low – end castings, and the phenomenon of “easy to understand but difficult to operate” persists for a certain period.
The Dilemma: Although lost foam casting has many advantages, many small and medium – sized enterprises that have adopted this technology encounter difficulties in production. They struggle to produce high – quality castings, while those that manage to overcome these difficulties can move forward on the right track. This situation puzzles numerous small and medium – sized enterprises.

2.2 The Crucial Stage

An Empirical Technology: Lost foam casting is an empirical technology in the Chinese context, with many restrictive conditions and complex mechanisms. Some enterprises have mastered the key points and can operate smoothly, while others, despite numerous experiments, still cannot find the proper way. The complex basic principles of lost foam casting make it different from ordinary sand casting. Applying the methods of ordinary sand casting to lost foam casting usually leads to failure.
Differences in Enterprise Performance: Large and medium – sized enterprises are gradually entering a stage of stable mass – production quality in lost foam casting. Their strong technical strength, high – quality awareness, precise operation, and fine management of processes and equipment play a crucial role. In contrast, most small and micro – enterprises have weak technical strength, and their actual operations deviate from process specifications. Since lost foam casting is affected by many factors, the cumulative effect of improper operations in multiple processes leads to the failure of final casting quality to meet the requirements. For example, as shown in Table 1, if there are ten processes in the casting production, and the pass rate of each process is 90%, the overall pass rate is only 38.5%. When the pass rate of each process is increased to 95%, the overall pass rate is close to 60%, and when it reaches 99.9%, the overall pass rate is 99%. In small and micro – enterprises, the large number of inexperienced workers, manual operations, and variable raw and auxiliary materials make the quality of castings more unstable.
| Pass Rate of Each Process | Overall Pass Rate |
|—|—|
| 90% | 38.5% |
| 95% | 60% |
| 99% | 90.4% |
| 99.9% | 99% |
| Table 1: Relationship between the Pass Rate of Each Process and the Overall Pass Rate |

2.3 Complex Mechanisms of Lost Foam Casting

Defect – Causing Mechanisms: The mechanism research of lost foam casting is challenging. Common defects in lost foam castings include slag inclusion, carbon deposition, and porosity. Slag inclusion is caused by the mixing of foreign inclusions into the cavity or the residues formed by the burnout and gasification of the white mold. Carbon deposition occurs when the high – carbon white mold burns out and gasifies at high temperatures, transforming into elemental free carbon and other carbon compounds. These inclusions have complex movement laws in the molten iron. Although they generally float upward due to their low density, the negative pressure disrupts this known law, causing them to gather in a certain area on the surface of the casting, forming the “scab” defect.

2.4 Disruption of Normal Laws by Negative Pressure

Impact on Physical Laws: For the filling and solidification of molten iron in a cavity mold, various physical laws such as temperature field, flow velocity field, gravity field, negative pressure field, and crystallography can be predicted under normal circumstances. However, under the action of negative pressure, these laws are disrupted. The negative pressure causes a strong wall – attachment effect, making the molten iron flow form turbulence. The temperature field is also affected by the intense turbulence of the molten iron and is no longer the same as that in a cavity mold without negative pressure. The gas overflow channels generated by the disappearance of the white mold are narrow and tortuous, and the acceleration of gas flow has a significant impact on the temperature field and velocity field.
Consequences of Law Disruption: The original laws are disrupted, and new laws have not been fully understood. Traditional measures to overcome defects are no longer effective. For example, the phenomenon of mold collapse in some enterprises is often caused by the negative pressure field. The complex structures of castings have different blocking effects on the negative pressure air flow. For large and closed casting cavities, installing negative pressure mechanisms inside the cavity can significantly help prevent mold collapse. Pouring with gas is an important cause of sand adhesion and even mold collapse in castings.

2.5 Overcoming the Irregularities

Difficulty in Dealing with Irregular Defects: It is not difficult to overcome single – type defects, but the challenge lies in the irregular appearance of defects and the interweaving of several defects. In this case, various measures must be coordinated. For security – related castings and high – pressure – sealed castings, special care is needed. Although lost foam casting has some difficulties in China, it is not impossible to produce high – quality castings. Since some enterprises have achieved good results, it shows that there are laws in lost foam casting, but these laws are complex and difficult to discover and master. Therefore, it is necessary to launch a crucial battle to make lost foam casting successful under Chinese conditions.

3. Existing Problems in the Application of Lost Foam Casting

Technically, lost foam casting is just one of the casting process methods. It has its own applicable scope and is not a panacea. It has advantages for some casting productions but may be disadvantageous for others. Finding the suitable application of lost foam casting is the correct way for its development. Although it has many advantages, it also has some disadvantages, deficiencies, and inapplicable situations.

3.1 Turbulent Molten Iron Flow

The flow of molten iron in lost foam casting is disorderly, which easily leads to internal slag inclusion and gas entrapment.

3.2 Low – Quality White Molds

In China, most of the white molds used in lost foam casting are construction – grade or packaging – grade white molds. Their raw materials are leftovers from packaging and construction materials, and they usually contain a flame retardant, which increases the amount of slag.

3.3 Negative – Pressure – Induced Problems

The use of negative pressure in lost foam casting to fix the mold makes the molten iron flow more disorderly. The negative pressure also causes the wall – attachment effect, which blocks the discharge of slag and gas.

3.4 Temperature Difference and Carbon Deposition

During the pouring process of lost foam casting, the white mold absorbs heat, which increases the temperature difference between the front and rear of the molten iron entering the mold. The low – temperature molten iron at the front causes poor gasification of the white mold, resulting in carbon deposition.

3.5 Air Entrainment and Its Consequences

During the pouring process, a large amount of air is brought into the mold by the sprue as the molten metal fills the mold. This causes oxidation of the molten iron, a decrease in the negative pressure in the mold cavity, and damage to the local coating, resulting in sand adhesion, and in severe cases, mold collapse.

3.6 High Dependence on Coating Quality

Lost foam casting is highly dependent on the quality of the coating. The large amount of gas generated during pouring can only be discharged through the narrow gaps in the coating. Therefore, the quality of the coating has a significant impact on the casting process.

3.7 Sensitivity to Moisture

Lost foam casting is very sensitive to the moisture in the mold and its coating. High moisture content generates a large amount of gas, which hinders the discharge of carbon – containing gas and seriously aggravates the carbon deposition defect in the casting.

3.8 Impact on Casting Hardness

Lost foam casting uses dry sand for molding. The thermal conductivity of dry sand is lower than that of wet sand, which is likely to cause a decrease in the hardness of the casting.

3.9 Toxic Gas Emission

The gas generated by the gasification of the white mold in lost foam casting is basically a pyrolysis product of benzene, which is a toxic gas. If it is not harmlessly treated, it will pollute the air.

3.10 Problems in Casting Aluminum Parts

When producing aluminum castings by lost foam casting, the relatively low pouring temperature makes the gasification of the white mold poor. The liquefied white mold contaminates the dry sand, reducing its permeability and increasing the probability of porosity in the aluminum castings.

3.11 White Mold – Related Issues

The white mold in lost foam casting has low strength. It is easy to deform during the dry sand vibration molding process. For castings with complex internal cavities, it is difficult to fill and compact the dry sand during the vibration filling process, which is likely to cause local sand adhesion in the internal cavity.

3.12 Lack of Theoretical Clarity

The theoretical laws of lost foam casting have not been fully understood. It is basically an experimental and empirical technology. Experience needs to be accumulated, and beginners lack relevant experience.

4. Process Characteristics and Applicable Scope of Lost Foam Casting

Compared with other casting process technologies, lost foam casting has its unique advantages. The most significant advantage is that after the white mold is buried in the molding sand, there is no need for mold removal, that is, there is no mold – release process. This greatly simplifies the casting process, improves the dimensional accuracy and surface quality of the castings, and makes the appearance quality close to that of investment – casting precision castings. Other advantages of the lost foam casting process are derived from this.

4.1 Process Advantages

No Need for Sand Cores: No matter how complex the casting is, only one white mold is needed, which is different from the complex sand – core – related problems in sand casting for complex castings.
No 分型面: Lost foam casting does not require a parting surface for molding, which makes the casting process design more flexible.
Flexible Gating and Riser Design: The gating and riser design in lost foam casting is very flexible. The ingate can be easily placed at any position on the casting, and the riser can be installed in any direction.
Convenient Sand Removal and High Sand Reuse Rate: Lost foam casting uses dry sand for molding without adding any binder. Casting sand removal is very convenient, and the sand reuse rate is high.
High Production Efficiency and Low Labor Intensity: Lost foam casting has high production efficiency, requires fewer workers, is easy to be mechanized and automated, has low initial investment, occupies a small area, and has low labor intensity.
Increased Casting Density: Due to negative – pressure pouring and solidification, the density of lost foam castings increases.
Good Workshop Environment: During pouring, the negative pressure in the sand box makes it easy to collect, treat, and discharge the gas generated by the gasification of the white mold, creating a good workshop environment.

4.2 Requirements for Production Conditions

Lost foam casting requires relatively strict production conditions. The quality of castings is sensitive to the performance and stability of raw and auxiliary materials, and various conditions have cross – effects with complex influencing laws that have not been fully understood. It is also sensitive to process design, and the design is usually customized for each casting. To do a good job in lost foam casting, the following points need to be achieved:

Stable Raw and Auxiliary Materials: The performance, source, and composition of raw and auxiliary materials such as foam beads, adhesive glue, coatings, and dry sand should be stable.
Suitable Vibration Table: The vibration table should be able to meet the requirements of dry – sand vibration filling in the complex internal cavities of the white mold and maintain the dimensional stability of the white mold.
Proper Sand Cooling: The cooling of dry sand and recycled sand should meet the requirement of not causing thermal deformation of the lost – foam white mold, including controlling the treatment temperature and flow rate.
Accurate White Mold Bonding: The bonding of white – mold pieces should be accurate and stable. It is recommended to use a machine – bonding machine.
High – Quality Coating: The coating should be applied evenly with good coating adhesion, leveling, permeability, normal – temperature and high – temperature strength, and collapsibility. It is recommended to use a coating – leveling machine.
High – Precision White Mold Molds: The white – mold molds should have high precision, hardness, wear resistance, and stability. It is recommended to use integral white molds as much as possible to reduce the number of mold pieces and bonding seams.
Skilled Engineering and Technical Personnel: There should be a group of engineering and technical personnel who are proficient in the basic principles of lost foam casting, master production operation details, can design and manage, and have a sense of responsibility.
Appropriate Casting Selection: Engineering and technical personnel should master the suitable casting materials, structures, and sizes for lost foam casting. Different materials, structures, and sizes of castings require different lost – foam casting process designs.

4.3 Applicable Scope of Lost Foam Casting

Lost foam casting is not a universal process. Based on the basic process principles of lost foam casting, the flow law of molten iron during filling after pouring, the gasification of the white mold and the movement law of gas residues, as well as the common defect laws such as slag inclusion and carbon deposition, under the current technical level in China, lost foam casting is more suitable for the following types of castings:

By Material: As shown in Table 2, lost foam casting is most suitable for gray iron castings, followed by ductile iron, then cast steel, and finally cast aluminum.
By Structure: It is most suitable for castings with uniform wall thickness, complex structure, and a wall – thickness range of 10 – 20 mm, such as box – type and shell – type castings.
By Size: It is most suitable for medium – sized castings with a weight ranging from a dozen to several hundred kilograms.
For Cast Steel Parts: It is most suitable for non – machined or less – machined cast steel parts with low requirements for internal defects, such as wear – resistant, heat – resistant, and corrosion – resistant castings.
For Large Castings: For large castings, resin – sand molding is preferred. Lost foam casting is most suitable for automotive – covering – part stamping dies and machine – tool bed castings. When using dry – sand vibration molding for large castings, some special measures are required.
By Production Batch: For small and medium – sized castings, the most suitable production batch is more than 10,000 pieces. The white mold is formed by a mold, and the pouring is carried out on a production line. For large castings, the white mold is processed by plate cutting and CNC machine tools, and resin – sand molding is used with normal – pressure or negative – pressure pouring (with smoke and dust removal).
| Casting Material | Suitability Ranking |
|—|—|
| Gray Iron | 1 |
| Ductile Iron | 2 |
| Cast Steel | 3 |
| Cast Aluminum | 4 |
| Table 2: Suitability Ranking of Lost Foam Casting for Different Casting Materials |

5. Common Defects in Lost Foam Castings and Corresponding Process Measures

In China’s lost foam casting, slag inclusion and carbon deposition are the most common casting defects. Each defect has its specific causes and corresponding countermeasures.

5.1 Treatment of Slag Inclusion Defects

Causes of Slag Inclusion: The slag inclusion in lost foam casting is mainly caused by three aspects. First, the closed dry – sand cavity is easy to be damaged, and dry – sand grains are easily sucked into the cavity. Second, the surface of the white mold is not very smooth, and pits, holes, gaps, and bonding seams of mold pieces can soak into the coating, and the coating burrs formed during pouring are washed into the cavity. Third, the gasification residues of the white mold are mostly high – carbon organic materials, which are dispersed into a certain range under the upper surface of the casting by the combined action of molten iron and negative pressure.
Countermeasures: The principle of overcoming slag inclusion defects is to block the source. The dry – sand cavity seal must be tight, especially at the joints of the white mold, the gating system, and the connection between the pouring cup and the sprue. In case of inevitable entry of foreign matter, external discharge measures such as slag – discharge and gas – discharge risers, burning while pouring, overflow risers, and vent holes (ropes) should be taken. For complex – structured castings where foreign matter cannot be completely discharged, measures should be taken to disperse the foreign matter, such as top – pouring and multi – gating. These measures can be summarized as “strictly prevent entry, expel, and break up”, or “seal, discharge externally, and disperse”.

5.2 Treatment of Carbon Deposition Defects

Causes of Carbon Deposition: Carbon deposition defects are common in lost – foam – cast steel and ductile – iron castings. The main reason is the low – quality white mold, poor permeability of the coating, which makes it difficult for carbon – containing gas to be discharged smoothly. In addition, the unique filling method of molten iron and the negative – pressure effect in lost foam casting make it difficult for the pyrolysis products of the white – mold residue to be completely discharged out of the mold or evenly distributed.

5.3 Treatment of Sand – Adhesion Defects

Types and Causes of Sand – Adhesion: There are two types of sand – adhesion in castings: mechanical sand – adhesion and chemical sand – adhesion. Lost – foam casting is mostly related to mechanical sand – adhesion, and only in the case of cast – steel parts and the slender inner – hole parts of castings, there is a certain degree of chemical sand – adhesion. The main causes of sand – adhesion include low coating strength. During drying, handling, and assembly, the coating may experience local peeling, bubble bursting, and cracking. Molten iron overflows from these areas, wraps the sand grains, and quickly solidifies due to rapid cooling, forming sand – adhesion. A thin coating also has low strength and is more likely to be damaged. During pouring, if a large amount of gas is entrained from the sprue and the negative – pressure system cannot discharge it in time, the local negative pressure in the mold cavity will decrease, the dry sand will lose its density, and the support for the coating will be weakened, resulting in coating damage and sand – adhesion. In severe cases, mold collapse may occur. In addition, if the dry sand does not fill the inner cavity of the complex pattern well and the compactness is insufficient, a gap will be formed between the local pattern coating and the sand – filling layer. The huge pressure of the molten iron during pouring will break the coating and enter the sand mold, wrapping the sand grains and causing sand – adhesion. For cast – steel parts or the slender inner – hole parts of castings, after pouring, the dry sand in these areas is surrounded by a large amount of heat for a long time. Excessive heat causes the coating and some sand grains to sinter and liquefy, and a chemical reaction occurs with some elements in the molten iron, generating a new substance that firmly combines the external sand grains with the casting matrix, that is, chemical sand – adhesion, which is difficult to remove and usually requires machining and chipping.
Countermeasures: To overcome sand – adhesion defects, corresponding measures should be taken. Improve the normal – temperature and high – temperature strength of the coating to prevent coating damage during the operation process. The coating thickness should be appropriate to ensure a certain overall strength without reducing its permeability. Strengthen the filling and compacting effect of the vibration table on the dry – sand during molding, especially for complex – structured castings. The vibration table is one of the key equipment in lost – foam casting. A vibration table with the ability to fill and compact long, thin, blind holes opening downward is urgently needed in lost – foam casting. During pouring, control the entrainment of gas, and keep the sprue full during large – flow pouring. Currently, the vibration tables of American companies such as Fukun and GK have certain effects on solving the filling and compacting problems of dry sand for complex – structured castings. Among domestic vibration tables, the Tianzhe vertical elliptical – motion vibration table has a relatively good effect on filling blind holes. For cast – steel parts and parts with long, thin, downward – opening inner holes, special local process measures should be taken, such as using high – temperature – resistant coatings.

5.4 Treatment of Deformation Defects

Causes of Deformation: Deformation is a common defect in lost – foam castings, especially for thin – walled and large – volume castings with low stiffness. The reasons for casting deformation in lost – foam casting are more complex than those in sand casting. The white mold may be deformed before sand filling and molding. The processes of white – mold formation, drying, and handling may all cause deformation. For example, an unreasonable mold structure, charging method, cooling method, and mold – removal method can lead to white – mold deformation. During the drying process of the white mold, uneven contact with the support base and side surfaces may cause inconsistent shrinkage of different parts of the white mold due to water loss, resulting in deformation. During the assembly and handling of the white mold, human – caused collisions, drops, and distorted support bases can also cause deformation. During the dry – sand filling and vibration molding process, uneven filling heights of dry sand in the inner cavity and around the white mold, as well as inconsistent lateral pressures of granular sand on the white mold, and 不协调的 vibration parameters of the vibration table can cause the dry sand around and inside the white mold to flow directionally, strongly impacting the side walls of the white mold and causing deformation. During the molten – iron pouring and filling process, the high – temperature baking of the molten iron in the flowing – through area on the non – flowing – through area of the white mold can cause local shrinkage deformation of the white mold. During the solidification process of the casting, different shrinkage amounts of each part and restricted shrinkage can easily generate internal stress, leading to casting deformation.
Countermeasures: To prevent casting deformation, corresponding measures should be taken according to the causes of deformation. Design a reasonable mold structure to ensure that the formed pattern does not deform in shape and size. Pay attention to smooth mold opening and pattern removal to avoid excessive stress on the pattern with high moisture content and low strength. The charging method and layout of the charging ports in the mold cavity should be reasonable, and the structure of the charging gun should be designed to make the density of the pre – expanded beads filled into the mold cavity uniform, without loose or overly – dense areas. The cooling method of the mold should be reasonable to ensure uniform cooling of the overall pattern formed by the expansion and fusion of the pre – expanded beads in the mold cavity, and consistent cooling and solidification effects of each part. For complex – structured patterns, spray cooling is more effective than “flood – like” cooling. When removing the newly formed pattern from the opened mold, handle it gently and place it on a conforming support bracket on the drying rack to avoid uneven stress. When drying the pattern pieces, use a conforming support bracket to place the pattern pieces, and pay attention to appropriate drying temperature and heating rate to prevent inconsistent shrinkage of different parts of the pattern during the drying process. During the handling, bonding, coating, and post – coating drying of the pattern pieces, avoid human – caused collisions, drops, and distorted support bases to ensure the stability of the shape and size of the pattern in each link. When bonding and assembling the patterns, apply the adhesive evenly, ensure accurate docking and uniform stress. For thin – walled large – sized parts with low structural stiffness and easy to deform during molding, attach a certain number of rib – bracing strips of wood or other materials at the port. The bonding direction and interval of the rib – bracing strips should be determined reasonably according to the specific structure. It is recommended to dip – coat the combined patterns as a whole. For the combination of multiple castings in series, use a support bracket to fix them to facilitate overall dipping – coating and one – time placement in the sand box, avoiding difficulties in sealing the bonding parts in the sand box. Use a vibration table with good performance. For general thin – walled castings, the vibration table should not cause overall directional sand flow and should be able to fill the inner cavity of the pattern with dry sand. For simple – structured castings without horizontal downward – opening blind holes, a general vibration table can be used. When filling the sand box with dry sand during dry – sand molding for castings with large inner cavities and thin walls, pay attention to adding sand evenly and simultaneously inside and outside the casting to keep the stress on the thin – walled pattern balanced. When designing the series – casting combination scheme, pay attention to the appropriate interval between each pattern piece, the distance between the gating system and the casting pattern, and the distance between the pattern and the sand – box wall. Prevent the heat of the pre – filled molten iron from causing the shrinkage deformation and gasification of the patterns that have not yet come into contact with the molten iron, which may lead to casting deformation and pouring mold collapse. When designing the casting process, pay attention to the solidification form and sequence of the casting. Different shrinkage amounts of each part during the solidification process and restricted shrinkage can easily generate internal stress, leading to casting deformation.

5.5 Treatment of Porosity Defects

Causes of Porosity: Lost – foam castings are prone to porosity defects. The main reasons are as follows: the pyrolysis and gasification of the white mold increase the amount of gas. Poor permeability of the coating makes it impossible for the gas generated by the gasification of the white mold and the various components in the molten iron to be discharged out of the mold in a timely and sufficient manner. During the pouring process, the exhaust channels are narrow, and only the coating layer around the narrow gap between the front of the molten iron and the un – gasified white mold can form a narrow exhaust channel, while other parts are blocked. The negative – pressure pouring causes a strong wall – attachment effect during the filling of the molten iron. The thin layer of molten iron near the wall solidifies rapidly due to rapid cooling, forming a solid thin shell near the surface of the casting, which blocks the subsequent discharge of gas. If the white mold and its coating are not thoroughly dried, the moisture in them will form a large source of gas, posing a hidden danger to the formation of porosity defects in the casting. Before the solidification of the casting, if the gas wrapped in the molten iron is not discharged out of the casting in time, it will remain in the solidified casting, forming spherical holes with smooth inner walls.
Countermeasures: To overcome porosity defects in castings, measures should be taken from the root causes. Control the pre – expansion and molding density of the white mold appropriately. Under the premise of ensuring the stiffness and non – deformation of the pattern, reduce the density of the pattern as much as possible to reduce the solid content of the pattern and thus the gas – generation amount. Good coating permeability, especially high – temperature permeability, is more important for overcoming porosity defects. In fact, the normal – temperature and high – temperature strength, normal – temperature and high – temperature permeability, and sufficient refractoriness of the lost – foam coating are the three main working properties of the coating. Consider the design of the exhaust channels in the process design. Setting exhaust and overflow risers on the upper side of thick – walled parts is a good choice to overcome porosity defects. It is very important to dry the pattern and its coating thoroughly because the gas – generation amount of water is much larger than that of the white mold. Moist coatings and white molds greatly increase the overall gas – generation amount of the pattern cluster, which is likely to cause porosity defects in the casting. Design the position, number, and direction of the ingates reasonably to avoid excessive shrinkage and porosity caused by long – term overheating in the area near the ingates. Unreasonable negative – pressure pouring is one of the reasons for porosity defects in cast – steel parts. The negative pressure should be uniform, stable, and consistent in all parts of the entire mold cavity, especially in the large inner cavity of the casting, where sufficient negative pressure should be maintained. However, excessive negative pressure is also likely to cause a strong wall – attachment effect, forming a skin – layer in the casting surface and blocking the overflow of gas.

5.6 Treatment of Mold – Collapse (Cavity – Collapse) Defects

Causes of Mold – Collapse: Mold – collapse, also known as cavity – collapse, is a serious defect often encountered in the production of large – sized lost – foam castings. It not only causes the scrapping of castings but also may lead to safety accidents, so special precautions are needed. The root cause of mold – collapse is that when the negative pressure in different parts of the sand box is unbalanced to a certain extent, under the combined action of the strong heat – flow impact during pouring of molten iron and the gas – flow impact of white – mold gasification, the difference in the strength of the dry – sand mold between high – and low – negative – pressure areas causes the sand body to move directionally, forming a “sand – free blank” area locally. Under the action of the gravity and impact force of the molten iron, the coating layer is easily broken through, and the molten iron enters the blank area and solidifies with the sand grains. The subsequent molten iron continues to advance through the new channels formed by the breakthrough of the front – end molten iron. The advancing direction is out of the range of the casting cavity. The white – mold cavity that has not yet received the molten iron shrinks and pyrolyzes under the thermal and momentum impacts of the disorderly molten – iron flow, creating more blank areas. A series of chain reactions occur instantaneously, and the phenomenon observed is that the sand on the top surface of the sand box sinks rapidly, resulting in mold – collapse.
Countermeasures: Although mold – collapse is a serious defect, the solution measures are not complicated. Generally speaking, it is necessary to maintain the balance of the negative pressure in the sand grains around and inside the white mold in the sand box during the pouring process and not to break this balance. At the same time, a sufficient air – extraction speed and air – extraction volume should be maintained.

It can be seen that the influencing factors of lost – foam casting defects are diverse and the result of the comprehensive influence of multiple factors. Therefore, lost – foam casting requires precision, and each process must be carried out in place. There should be special personnel to check the connection of each process. Once the process is stable, it should not be changed casually. It is necessary to establish and improve the process operation and execution specifications of lost – foam casting and strictly implement them without being affected by individuals.

6. The Development Direction of Lost Foam Casting under Chinese Conditions

The development process of lost – foam casting in China has been long and tortuous. Since the mid – 1960s when it started to be developed, 60 years have passed. In the past half – century, the development of lost – foam casting in China has not been smooth. Many enterprises have gone through arduous struggles, paid a high price, and finally achieved success, while some enterprises failed at the initial exploration stage.

With the development of China’s foundry industry, the advantages of lost – foam casting have become more prominent. The research and exploration of lost – foam casting have been continuously deepened, and a number of applicable production technologies suitable for China’s national conditions have emerged. A group of large and medium – sized enterprises have seized the opportunity, continuously explored and improved on the R & D path of combining basic theories with their own conditions, and achieved leap – forward development in lost – foam casting. However, due to weak technical strength, low management levels, and shallow understanding of lost – foam casting, small and micro – enterprises still have their cognitive concepts stuck in sand casting and do not pay enough attention to the special process of lost – foam casting. As a result, the quality of lost – foam castings is relatively low, mostly low – end castings, such as non – machined, non – inspected, and locally defective castings that do not affect performance. The high – requirement casting pass rate has been difficult to increase and is unstable.

From the overall situation in China, lost – foam casting still has a period of continuous development. The development speed during this period will increase, mainly in terms of qualitative leap and quantitative expansion.

6.1 Qualitative Aspect

The number of high – end casting production enterprises will gradually increase, and breakthroughs will be made in the production of complex and irregular castings. Breakthroughs will mainly be achieved in large and medium – sized state – owned enterprises and some joint – stock cooperative enterprises. In addition, some enthusiasts and persistent pursuers of lost – foam casting also have the hope of making breakthroughs in certain aspects. It is hoped that enterprises with strong strength and 雄厚的技术力量 will take the lead in conducting basic research and development on the application of lost – foam casting, promoting the transformation of personalized and empirical lost – foam casting technology into universal and theoretical technology, and clarifying the basic principles and basic technologies of lost – foam casting forming.

6.2 Quantitative Aspect

A considerable number of enterprises will turn to lost – foam casting. It should be noted that the lost – foam process is not a universal process. It has its suitable casting types and structures. Foundry enterprises should keep a clear head, analyze whether the product structure type is suitable for the lost – foam process, and not blindly believe and rush into production just because of its advantages. They should also analyze the disadvantages of lost – foam casting. There are still many unsolved problems, both in theory and in practical stability.

As the professional branch of lost – foam casting of the China Foundry Association, it has the responsibility and obligation to provide good – quality services to enterprises, including policy consultation, market consultation, development consultation, and technical consultation. It aims to provide enterprises with a direction for sound development and gradual improvement of benefits, give full play to the advantages of lost – foam casting, avoid and overcome its disadvantages, and promote the healthy, sustainable, and sound development of China’s lost – foam casting industry, so as to contribute to the improvement of the overall level and the growth of China’s foundry industry.

In conclusion, lost – foam casting in China has both opportunities and challenges. By addressing the existing problems, clarifying the applicable scope, and strengthening technological research and development, the lost – foam casting industry in China can achieve better development and occupy a more important position in the international foundry market.