Lost foam casting

Investment castings can be made from an extremely wide range of ferrous and non-ferrous metals. 

The ferrous range covers low alloy, carbon and tool steels as well as corrosion and heat-resistant steels. The non-ferrous range covers aluminium and zinc alloys and the copper-based alloys, brasses, bronzes and gunmetal. 

The lost foam casting process originated in 1958 but due to strong patents that covered the process early development was restricted. Only 

After a short stabihsing period, the completed pattern is strengthened by dipping in a refractory material which coats the foam pattern leaving a thin heat-resistant layer which is then air dried. This ceramic coating also provides a good surface finish for the finished casting. 

When drying is complete the coated foam is suspended in a steel container which is vibrated while traditional green sand, with no binders or other additives, is poured around the coated pattern providing mechanical support to the thin ceramic layer. During the sand pouring operation, the vibration causes a layer of sand near the pattern surface to fluidise ensuring all voids are filled, and shapes supported, while the whole mass of sand is compacted. 

A patented process has been developed known as counter gravity low pressure air melt (CLA) casting process, which is the same as has been described, up to the metal pouring stage. 

Once the fully dried mould has been dewaxed and fired to 1000°C it is placed inside a casting chamber and sealed. The casting chamber is then located in position and vertically lowered towards the furnace and the molten metal so that the open neck is below the liquid surface. Fig. 18.8. 

A vacuum is then applied to the casting chamber forcing molten metal up into the mould and so filling it at a consistent and even rate. After a predetermined cycle time the vacuum is released leaving the solidified components intact but allowing the runner, which is still in a molten state, to return to the furnace for use on the next mould. 

Due to this vacuum technology there are a number of additional advantages over gravity pouring. 

Alternative moulding/core-making methods Lost Foam casting 

The general principles of Lost Foam casting have been described in Section 2.5.7.1. Due to the absence of binders, the technique produces a reduced amount of solid waste and emissions compared to sand casting methods. 

The technique allows the production of pieces with tighter tolerances, less feeder and riser channels and better as-cast features. This all results in less machining and clean-up time. 

Lost foam foundries include a foam workshop, a melting shop and a casting shop. They do not have an extensive core-making shop and finishing shop. The foam shop involves foaming machines, steam generators and coolers and ambient air dryers. 

The Lost Foam models are made of polystyrene (EPS) or PMMA, with small amoimts of pentane, glue and a mineral coating. Since both EPS and pentane are pure hydrocarbons, organic carbons are formed upon pyrolysis of the model. In order to minimise emissions of the organic decomposition products of EPS, post combustion of the off-gases is performed. 

---

Ceramic Filter. The ceramic filter collects, volatilizes, and destroys particulates and condensible organics emitted from industrial process streams, such as paint spray, lost foam casting, condensible organics, tenter frames, and cured rubber... 

Boston, Ma., 7th-llth May 1995, p.2178-82. 012 PHYSICOCHEMICAL ANALYSIS OF POLYMERS USED IN THE LOST FOAM CASTING PROCESS Shivkumar S Y Celotto M A Worcester,Polytechnic Institute (SPE)... 

This process, commonly called "Lost Foam casting , was developed 30 years ago and its commercial growth was initially rather slow. However, during the last 10 to 15 years, it is has become used more often, primarily for the mass production of automotive parts or similar products, in spite of significant set-up difficulties. 

US Dept, of Energy (1998). "Advanced Lost Foam Casting", Office of Industrial Technologies, http //www.oit.doe.gov/factsheets/metalcast/pdfs/lostfoam.pdf... 

INVESTMENT CASTING, LOST FOAM CASTING AND SHELL MOULDING... 

After compaction, molten metal is poured into the mould causing the foam to burn up and vaporise as the molten metal replaces the foam pattern, exactly duplicating all the features of the original pattern. Like other investment casting methods, for each new casting produced, a new pattern must be made hence the name lost foam casting. 

Characteristics of lost foam casting Design freedom to produce complex shapes. 

Briefly describe the lost foam casting process. 

Where required, chapters have heen updated in line with current developments, e.g. lost foam casting and metal injection moulding. 

Investment casting, lost foam casting and shell moulding... 

The lost foam casting process originated in 1958 but due to strong patents that covered the process early development was restricted. Only when the patent expired around 1980 was free development possible and during the 1990s much work was done and the lost foam casting process is now a technical and commercial success. 

---