Shell molding is a process to create molds using a special type of sand that is coated with resin to form the fabricated mold. The shell molding provides a far superior accuracy in dimensional measurements and thus is far more in use than sand casting or any other method of molding. The process of shell molding has been the same over the years but the major development has been in the technology related to the shell molding machines. |
WHAT ARE SHELL MOLDING MACHINES?
The shell molding machines are the machines that are used in the shell molding process. The credit for the invention of the shell molding machine goes to the German inventor Johannes Croning. It is to this effect that the process of shell molding is also referred to as “Croning method”. A standard shell molding process has 5 to 7 steps involved that include creating the pattern for the mold, creating the design of the mold, assembling the mold, pouring of metal, cooling of the metal, and removal of casts.
Products manufactured by the shell molding process are used in the automobile industry, high precision instruments, and many other industries. The shell molding process was developed in Germany during the early 1940s. The earlier shell molding machines built were heavy and required frequent human intervention. With the advancement in technology the machines have become fully automated and are cost effective with large scale production.
PROCESS OF SHELL MOLDING IN SHELL MOLDING MACHINES
In a typical shell molding machine the mold is heated up to 300 to 400 degrees Celsius. Once the required temperature is achieved for a particular mold, resin-coated sand is unloaded from the machine sand container on the mold to achieve a particular pattern. The resin-coated sand sticks on the mold giving it a smooth finish and strong binding. Any excess sand is then deposited back in the box at the end of the station. The mold is then ejected automatically.
TYPES OF SHELL MOLDING MACHINE
There are many types of shell molding machines available in the market. It depends on the suitability and requirement of the industry and product specifications. The most commonly used machines are the two stations and four station machines. The four-station machines are generally fully automatic machines that are designed to produce molds in huge quantities. Usually there is only one operator that is required to supervise the machines. The two station machines are relatively faster than the four station machines. They are able to produce shell molds in huge quantities at a faster rate. A third type of the machine is the core shooter machine. It is comparatively lighter and the sand is shot to difficult designs to create an intricate mold. The cycle time for each mold varies with the design and type of product. Usually a cycle of 2 to 4 minutes is considered to be good for a particular type of machine. The machines are also available in automatic and semiautomatic types. Even in a semi-automatic type the number of operators required is not more than 2 to 3. In an automatic type too only a single operator is required.
The machines have optional accessories available like winch, mold unloading, optical guard, etc.
ADVANTAGES OF SHELL MOLDING MACHINE
The use of shell molding machine creates a lot of advantages for the manufactures. The molding process initially is time consuming but once the mold is created, the machine facilitates large scale production. The shell molding machine helps in reducing wastage by making accurate and precision molds and thus reducing re-machining. The machines are used to make connecting rods, crankshafts, head of cylinders, molding cores, and gears.
There is a major advantage in terms of the machine using less energy as compared to other molding machines. The machine can be operated by a single operator thus there is very limited human intervention. One of the main features to look in a shell molding machine is the cycle time required to produce a single mold.
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