Types of Moulding Machines | Squeezers , Jolt Machines , Sand Slingers
Molding is a technique through which a material, often plastic, but also metal, rubber, or powder mixtures is shaped on the outline of a die or mold. There are many different techniques for molding materials, just as there are many different applications for each process.
There are two primary types of plastics: thermosets and thermoplastics. The main difference between these two types of plastics is that thermosets permanently cure. This means that once the plastic is melted into a shape, it cannot be melted back down to molten plastic. Once the plastic takes a shape, it will retain that shape. If the plastic is melted, it simply burns. This is different from thermoplastics, which can be cured into a shape, then melted back down to molten plastic and reformed through further curing.
Type 1. Squeezers:
The working principle of a squeezer type moulding machine is shown in Fig. . The pattern plate is clamped on the machine table, and a flask is put into position. A sand frame is placed on the flask, and both are then filled with sand from a hopper.
Next, the machine table travels upward to squeeze the sand between the pattern plate and a stationary squeeze head. The squeeze head enters into the sand frame and compacts the sand so that it is level with the edge of the flask. These machines rammed the sand harder at the back of the mould and softer on the pattern face. Squeezer machines are very useful for shallow patterns.
Type 2. Jolt Machines :
In this machine sand is compressed through the application of compressed air or other suitable force transmitted through a piston-table arrangement which squeezes the sand against a platen.
The ramming is best at the sand platen interface from where pressure is applied and not near the pattern, whereas in Jolt machine the ramming is best around pattern. Therefore, combination of jolting and squeezing gives best results and both the operations can be carried out in a single machine called Jolt-squeeze moulding machine (Fig. ). In pure squeezing, both the parts of the mould could be formed at the same time if the depth is not too great. It is generally limited to rather shallow work.
Type 3. Sand Slinging Machine :
In this machine the moulding sand is thrown by impeller device which causes packing of the sand into the flask through inertia. In this method the sand density is most uniform at all the levels and it is, therefore, best suited method for any type of mould.
The density can be controlled by changing the speed of the impeller which normally varies between 1200 and 1800 R.P.M. However it is best adapted to work ranging from medium to very large size. The machine is generally available in various capacities with sand moving at a speed of about 3000 m/mt. The moulding sand should be mixed with suitable binders etc., so that it can flow into place readily and afterwards binder should become hard.
Various other moulding machines are explained in fig. , the schematic sketches of which are self- explanatory.
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