Chapter One Introduction of Lost-in-vaning mode Development of 1.1


Chapter 1 Introduction to Lost Foam

 

1.1 Lost Foam Development

1.1.1 Overview of Lost Foam Casting Development

Lost foam casting technology is to use foam plastic (EPS, STMMA or EPMMA) to make a shape exactly the same as the structure and size of the casting, to bury it in a special sand box for dry sand modeling after dipping and drying with refractory adhesive coating (for strengthening and smooth effect), to compact it through three-dimensional or two-dimensional micro-vibration and negative pressure, and to pour molten alloy liquid without mud core, live block or even riser, the whole process maintains a certain negative pressure, so that the pattern is heated, gasified and decomposed and then replaced by alloy liquid one-time molding casting new process. Lost foam casting has a variety of different names, mainly called dry sand casting, negative pressure casting, referred to as EPC casting. Foreign names are mainly lost foam process (United States), policast process (Italy) and so on. Compared with the traditional casting technology, it has great advantages, and is praised as "the casting technology of the 21st century" and "the green revolution of the casting industry" by the casting industry at home and abroad ".

Lost foam casting combines "magnetic mold casting" and "V method casting". In 1956, American H.F.Shoyer began the experiment of using polystyrene foam plastic for casting, and achieved success, which aroused great interest. In 1958, it was published in the form of a patent, which was called "cavity-free casting". At first, this method was only used to make metal statues and art castings. After years of practice and exploration, the former Federal Republic of Germany introduced patents from the United States in 1962, and the lost foam casting method was gradually developed and applied and promoted in industry. A survey conducted by the University of Wisconsin in 1999 showed that 6% of aluminum alloy castings in 1990 were made using this process. Since 1997, gray cast iron and ductile iron have also increased rapidly, reaching 15% in 2009.

The history of China's research and development of lost foam casting is basically similar to that of foreign countries. Some aspects such as STMMA foam plastics have approached or reached the foreign technical level, and have unique features. After the 1980 s, a number of units manufactured expandable polystyrene pre-foaming machines and foaming molding machines, of which Fuyang Lianfa Lost Foam Molding Equipment Factory developed simultaneously with EPS and STMMA pellets. China's lost foam casting technology has also been promoted by the state, the lost foam industry has a certain scale, become an important part of the casting industry, the proportion of production castings in the casting industry continues to increase, lost foam casting has become the transformation of traditional foundry factory application of the most extensive one of the high-tech. But in general, there is still a gap between the production and application level of lost foam casting in China and developed countries.

At present, the lost foam casting technology is mainly used in the following aspects in China.

(1) the application of casting alloy type aluminum alloy, magnesium alloy, copper alloy, gray cast iron, ductile iron, special cast iron (high chromium cast iron, wear resistant cast iron, corrosion resistant cast iron), ordinary carbon steel, medium and high carbon low alloy wear resistant steel, special cast steel (high manganese steel, nickel chromium heat resistant steel, corrosion resistant steel) and stainless steel.

(2) Typical castings with successful application

Anti-wear castings: chromium grinding ball, high manganese steel liner, high chromium cast iron hammer, excavator shovel teeth (bainitic steel, high chromium cast iron), etc;

Heat-resistant castings: heat-resistant cast iron cast steel grate bar, heat-treated base plate, material cabinet, material rack, etc;

Pipe fittings: various specifications of gray cast iron, ductile iron pipe fittings and rolled steel pipe lined with high chromium cast iron or above composite pipe fittings;

Valve castings: cast steel ZG25, ZG35 valve body, valve cover, ball iron valve body valve cover;

Construction machinery: ADI castings of ductile iron for bucket teeth, gears, racks, forklift steel castings;

Box (shell) body castings: gearbox housing, differential housing, steering gear housing, motor housing, fire hydrant housing, shell housing, etc;

Automobile brake system castings: brake drum, brake disc;

Crankshaft: compressor crankshaft, automobile engine crankshaft;

Intake and exhaust pipes: aluminum intake pipe, ductile iron 4-cylinder automobile exhaust pipe, gray cast iron 6-cylinder diesel engine exhaust pipe, etc;

Rear axle castings: cast steel, cast iron rear axle housing;

Bracket castings: railway 25 steel support plate, automobile spring support, highway railing, ZG35 support, etc;

Cylinder block and cylinder head castings: compressor cylinder block, single-cylinder engine cylinder block, automobile 4-cylinder cylinder block and cylinder head;

Other parts: sewing machine head, pedal, bracket, agricultural machinery crank bracket, plow head, plow guide plate, etc.

1.1.2 Lost Foam Casting Process

lost foam casting process:

1. Make a foam white mold, combine the gating system, brush the surface of the gasification mold, spray special high temperature resistant coating and dry it.

2. Place the special interlayer sand box on the vibration workbench, fill in the bottom sand (dry sand), vibrate and level it, place the dried gasification mold on the bottom sand, fill with dry sand, and level the box mouth at an appropriate time by micro-vibration.

3. Cover with plastic film, put on the gate cup, connect with the vacuum system to suck vacuum, dry sand is fastened and formed, pouring is carried out, the white mold disappears by gasification, and the metal liquid replaces its position.

4. Release the vacuum, turn over the box after the casting condenses, and take out the casting from the loose dry sand.

1.1.3 Classification and characteristics of lost foam casting process

Lost foam casting according to its mold material can be divided into self-hardening sand lost foam casting (and moisture type with binder) and dry sand (dry type without binder) lost foam casting; according to the pouring conditions can be divided into ordinary (atmospheric pressure) lost foam casting and vacuum negative pressure lost foam casting. Compared with the traditional sand casting, mass-produced lost foam casting has the following process characteristics.

① The shape is completely consistent with the shape of the casting, and the foam plastic pattern with only the difference in size and metal shrinkage is retained in the casting mold to form a "real mold" casting mold, rather than a "cavity" casting mold (I. e., empty mold) of a traditional sand mold.

② sand type is dry quartz sand without binder, moisture and any additives, or magnesium olivine sand, chrome sand, magnesia sand, treasure sand, etc. according to the type of alloy.

③ When pouring, the foam plastic pattern is continuously decomposed, cracked and gasified under the action of high-temperature liquid alloy, and the alloy liquid-pattern replacement process occurs, which is different from the traditional "cavity" (empty mold) casting, which is a liquid alloy liquid filling cavity process. Making a casting is about "disappearing" a foam pattern.

④ The foam plastic pattern can be molded in blocks and then bonded and combined. The shape of the pattern (and the shape of the casting) is basically not subject to any restrictions (manual cutting, machine forming, combination bonding can be).

Table 1-1 is a comparison of the characteristics of mass-produced traditional clay sand casting and lost foam casting processes.

Table 1-1 Comparison of the characteristics of mass-produced traditional clay sand casting and lost foam casting processes

 

Project

traditional sand casting

lost foam casting

Mold
Type
Work
Art


Parting open edge

Must be split

No (parting) open edges required

Draft

Must have a certain draft

Little or no draft

Composition

Composition with outer core

single model

Number of Applications

One model is used multiple times

One type at a time

Material

Metal or wood

foam plastic

Build
Type
Work
Art


molding sand

Binder, water, appendages passing through
Mixed core sand

No interference of binder, any additives and water

Sand filling method

Mechanical sand filling

Self-weight microseismic sand filling

Tightness mode

Mechanical force compaction

Physical (self-weight, microseismic, vacuum) action compactness

Sand box features

Prepare special sand box according to the characteristics of each part

Simple universal sand box

casting mold

The cavity consists of the core assembly

cavity solid type

Coating layer

Most without coating

Must have paint

Pouring
Note
Work
Art


Filling characteristics

Just fill the cavity with metal and model

physical and chemical action

Main factors affecting the filling speed

Gating System and Pouring Temperature

It is mainly affected by the pressure state of the gas in the mold, the gating system, and the pouring temperature.

Falling
Sand
Qing
Li


Falling sand

Strong vibration is required to turn over the box or lift out the casting.

Automatic separation of casting and sand

Cleaning

Flash burr and gate to be polished

Only need to polish the in-gate, no flash burr

 

(1) Problems that should be paid attention to when using the lost foam casting process: Although the lost foam casting has unparalleled advantages, any casting process is only suitable for a certain range. Therefore, the use of lost foam casting process must seriously consider the following issues.

① Comprehensive economic benefits should be considered: detailed economic assessment, cost accounting and technical ability assessment should be made for specific castings, materials, sizes, shapes, structures, batches, prices, etc. For example, some factories use lost foam casting to produce several different types of cast iron motor housings and oil pump bodies with small batches, and only provide them to the next factory as casting blanks, but the other party's subscription price per ton is not high. Even if EPS is used, the cost of its appearance is 0.03 ~ O.04 yuan/g, coupled with unstable process and many scrap rates, it is found to be unprofitable or even lose money after being put into production for a period of time. Had to return to the clay sand casting process to produce. If as the unit of the casting blank, even if the profit is guaranteed, but the overall for the next machining to create the conditions is also desirable, because the casting quality is uniform.

② process technology to be fully prepared: copy, imitation, or rush on the lost foam production line is not desirable. For example, a factory quickly loaded the production line of ball iron pipe fittings. There were neither technical engineers nor pipe fittings product salesmen. After a period of time, due to changes in the market, pipe fittings were unsalable, so the line was stopped in a hurry and the production line was shelved.

③ To consider the use of material castings: copy, copy, not combined with the actual casting of our factory, on the lost foam casting production line will also be full of problems. For example, a factory imported a 1000t/year small lost foam casting steel casting plant from elsewhere with equipment of 200000~300000 yuan. since a set of processes is matched according to the casting process of high manganese steel, magnesium olivine sand is used as dry sand, and its powder is used as coating aggregate, the qualified rate of castings is very high, and the quality of finished products is very good, which is favorable and desirable. However, after arriving at the small factory, the casting was ZG25. The exporting party did not understand the ZG25 production process, and the importing party was eager for the other party to solve the problem. Therefore, it took a long time to explore the way to produce ZG25 castings and lost a lot.

④ Factors of production development should be considered: the lost vanishing mold production line has been installed, and there is no room for production development. For example, several enterprises have installed the lost vanishing mold production line and introduced pipe fittings and anti-wear parts to produce. Originally, one or two shifts were considered. After that, the demand for castings in this area has increased rapidly, and two or three shifts are needed for production. The substantial increase in production has exposed the lack of stamina stamina, affecting the deformation and cooling capacity, if you want to go to the production capacity equipment, you can't afford to go to the production line with large production capacity. if you want to go to the production line, you can't go to the production line. if you want to go to the production capacity, you can't go to the production capacity. if you want to go back, you can barely support it for a period of time. No long-term casting business was identified and launched. A 3000t/year cast steel lost foam production line was installed in a factory. After completing 1/3 of the tasks, there was no casting production task due to various reasons, and the machine was shut down for the task.

⑤ Castings that are not suitable for lost foam casting process: for example, low chromium cast iron grinding balls are cast with lost foam. Due to the slow cooling rate of dry sand, quenching, normalizing and other heat treatments are required to improve hardness and wear resistance, but the performance is not as good as that of metal mold casting grinding balls. Metal mold casting can obtain a cast hard shell with uniform carbide size and shape distribution on the surface of grinding balls-corresponding grinding balls. Second, low cost can adopt cast normalizing or fog quenching, so as to reduce the cost, the cost of foam pattern O.03 ~ 0.04 yuan/g can be exempted.

⑥ Correctly understand and scientifically treat lost foam casting process: some people are engaged in sand casting, visited some lost foam casting factories or nearby lost foam production workshops, especially those adopting simple lost foam casting factories. they think it is simple and convenient. foam patterns can be cut, processed and pasted by buying waste products or plates of EPS packaging materials, self-made coatings, self-made three-dimensional vibrating tables, purchased vacuum pumps and put into lost foam production, after more than half a year's ordeal, we still re-purchased lost foam casting machinery and equipment and white area foam molding equipment to produce anti-wear lining plates and pipe fittings.

A high manganese steel foundry completely copied the lost foam casting liner and hammer head of the same industry. The sand box was imitated and the box wall was drilled by electric drill. The appearance was cut and bonded by waste packaging foam materials. It was never stable after production because the appearance quality was never uniform.

To sum up, where serious, systematic, comprehensive analysis, overall planning, the use of lost foam casting process of large and medium-sized manufacturers, can get good results. Some small and medium-sized foundries on the random lost foam production process often appear the above situation, but can not reflect the advantages and characteristics of the lost foam casting process.

(2) the lack of lost foam casting process

① Complex large castings, mold manufacturing is more complex, high cost, time-consuming, a mold a casting, one-time investment more.

A bubble can only be used once. Only one mold can be used to make the foam pattern. The cycle of making the foam pattern is long and the debugging is labor-expensive.

The price of EPS is 1/5~1/4 of STMMA(C5 H8), but the application has limitations, the latter is more expensive, which is not good for reducing the cost of castings.

The design of the gating system process requirements are higher, in order to avoid the cold insulation of aluminum alloy, gray cast iron, ductile iron casting carbon defects.

The problem of EPS carburization for low carbon steel can only be controlled through the change of pellets and the design of the process, and the improper process is easy to produce pores.

The process system is closely linked, and the management must be strict and serious.

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