The following points highlight the top five methods of sand moulding used in industries. The methods are: 1. Bench Moulding 2. Floor Moulding 3. Plate Moulding 4. Pit-Moulding 5. Machine Moulding.
Method # 1. Bench Moulding:
Bench moulding is carried out on a convenient bench and the moulds prepared are relatively small. By bench moulding, green sand, dry sand or skin-dry sand moulds can be made. In this, hand ramming with loose patterns is employed and as such, it is a slow and laborious method.
Methods of Bench Moulding:
Various methods of bench moulding are described below:
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(i) Two Box Moulding:
It uses the moulding box made in two parts (upper is called cope and lower one drag). Two parts are fitted with a suitable clamping and locating device. Clamping prevents the cope from lifting due to the pressure of the molten metal while pouring. Locating device enables the two parts to maintain proper alignment at all times.
In this method, the drag and pattern are placed on the moulding board and the sand is rammed in drag. The drag is then rolled over the board. The other part of the pattern is fitted over bottom one, and cope is placed over the drag.
Sprue-pin and riser pin are placed in position, and sand filled in the cope and rammed. Mould is vented, sprue and riser pins removed. Mould is then parted off, pattern withdrawn, mould cavity cleaned and gate cut in the drag. Core is placed in position and reassembled and clamped to make the mould ready for pouring.
(ii) Three-Box Moulding:
When the pattern is of flanged type, two box moulding becomes inconvenient. To facilitate moulding work in such cases, three boxes are used (middle box being called ‘cheek’). During pouring of metal, all the three boxes are clamped properly. Fig. 3.30 shows the various steps involved.
(iii) Stacked Moulding:
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When a large number of small size castings are required, each having one flat surface, this method can be used. Both sides of one half of the mould can be made use of by stacking them as shown in Fig. 3.31. There will be a common passage for the molten metal running through the stock of the intermediate boxes. A number of parts can thus be cast in a single pouring operation.
Method # 2. Floor Moulding:
In this method, the moulding of medium and large moulds is directly carried out on the floor. Green sand, dry sand, or skin-dry moulds can be made by this method on the floor with the proper flasks. It is also a slow and laborious method as it requires ramming with loose patterns.
The floor moulding is generally carried out using two part boxes (top and bottom, known as cope and drag). These boxes consist of two stout frames with pins and holes to ensure accurate location. The ground surface is first levelled and half part of pattern placed over it and then box frame is placed around the pattern.
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Box is packed with sand, and sand is rammed and levelled off. The packed box is then turned over and second box placed on top, ensuring correct location by inserting dowel pins into the holes in side lugs on the boxes. The other half of pattern is placed over earlier half and sand is filled and rammed in top box and levelled off.
Two boxes are then opened and pattern is removed. If any repair is required, same is carried out and gates for pouring metal made. If cores have to be located to form holes, these are placed in position. Boxes are again put back into position and usually clamped to prevent the upper box floating on the liquid metal.
Method # 3. Plate Moulding:
The patterns in case of floor moulding are usually constructed of wood and are split on an appropriate horizontal parting-line. The two portions of the pattern have to be located together with dowels. However, in plate moulding, the pattern consists of a flat plate usually of metal instead of wood for long life, with portions of the pattern permanently assembled in alignment on each side.
For very large quantity production, and for very heavy castings, two plates may occasionally be used— one to assist in the making of copes, the other for drags. The plate incorporates some locating arrangement for the moulding boxes, which could be pegs in the plate, but more usually consists of holes for locating pegs.
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The use of a plate normally calls for moulding boxes which incorporate lugs having holes for location. Fig. 3.32 shows a typical double- sided plate used for hand or machine moulding, and shows how provision is made for six castings from one pouring. The plate includes runners, gates, part of pourer and part of riser, thus reducing the time considerably to finish the mould after the extraction of the pattern equipment.
This method is usually used for large quantity production. The use of a particular plate is restricted to a certain range of moulding boxes.
Method # 4. Pit-Moulding:
In this method, the moulding is carried out in the pits and generally, very large moulds are made, the pit serving the purpose of flask. Generally, green sand is used in pit moulding but cement bonded sand sections may also be used. For large moulds, this is the only method of moulding and is quite slow and laborious.
Method # 5. Machine Moulding:
A variety of machines are used in this method for carrying out the moulding of small, medium and large moulds. This method is faster and gives uniform mouldings, but requires mounted patterns. By this method also, green-sand, dry-sand and skin-dry moulds can be prepared.