The following points highlight the three main types of sand moulding machines used in industries. The types are: 1. Jolt Machine 2. Squeezing Machine 3. Sand Slinging Machine.
Type # 1. Jolt Machine:
This machine is equipped with adjustable flask lifting pins to permit the use of flasks of various sizes within the capacity of the machine. The flask is placed on the machine table and during operation the machine table raises the flask at short distance and then the flask is allowed to fall freely under gravity.
This sudden action causes the sand to be packed evenly around the pattern. The density of the sand is greatest around the pattern and at the parting line. Further away from pattern, the density keeps on decreasing. Since the moulding sand is firmly packed around the pattern, the mould is very strong and there is very less possibility of swells, scabs or run-outs.
After the moulding is complete the lifting pins on the machine engage the flask and raise it from the match plate. Thus it is obvious that jolt machines can take care of only one part of a flask at a time and are, therefore, suited specially to large work.
Apart from the sand ramming, every moulding machine has to perform several other functions also. After ramming one part of the complete mould, the first part is rolled over so that other part may also be made and the pattern from the first part removed. Pattern is usually rapped in the sand with the help of air or electrically operated vibrator attached to the pattern plate or may be removed by hand.
Jolting is generally done in combination with other operations on the same machine, such as in the Jolt-squeeze machine, Jolt-pin lift machine, Jolt-roll-over-draw machine etc.
Type # 2. Squeezing Machine:
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.
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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. 3.59). 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.
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Various other moulding machines are explained in (Figs. 3.57 to 3.60), the schematic sketches of which are self- explanatory.
