Moulding Machines | Molding Press | Compression Molding Press

Moulding Machines:

Moulding processes may be classified as hand moulding or machine moulding according to whether the mould is prepared by hand tools or with the aid of some moulding machine. Hand moulding is generally found to be economical when the castings are required in a small number.

Advantages:

· When the number of castings is substantial, the additional cost of metallic patterns and other equipment is compensated by the high rate of production, and the overall cost per piece works out lower than in the case of hand moulding.

· It affords great saving in time, especially when a large number of similar castings in small sizes are required.

· A semi-skilled worker can do the machine job whereas hand moulding requires skilled craftsmanship.

· The castings obtained are more uniform in size and shape and more accurate than those obtained by hand moulding due to steadier lift of the pattern.

Types of Moulding machine:

1. Hand Operated molding machine

a. Pattern draw type

b. Pattern draw and Squeeze type

c. Pin Lift type machine

d. Roll Over type machine

2. Power operated Molding Machine

a. Squeeze machine

b. Jolt machine

c. Jolt squeeze machine

d. Jolt squeeze roll over pattern draw machine

e. Sand Slinger

 

Squeeze machine

A squeeze machine is very useful for shallow patterns. A squeezer (squeeze head) plate or presser board slides inside the flask to compress the sand above and around the pattern.

For squeezing action the squeeze piston may by forced upward, pushing the flask up against the squeezer or presser board the presser board being forced into the flask.

The sand is rammed harder at the back of the mould and softer on the pattern face. In other words sand has greatest density at the surface where pressure is applied to sand and sand density decreases progressively towards the pattern.

Moulding force (Mf) = P (π. d2/4)-W

Where, P – Pressure in squeeze cylinder

d – Piston diameter

W – Weight of flask pattern and sand

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Jolt-Squeeze machine

It combines in single machine the operating principles of the jolt and squeeze machines. Combination of jolting and squeezing produces beneficial compaction effects on sand density and thus a more uniform hardness throughout the mould is attained. A jolt-squeeze machine makes use of match plate moulding.

Sand slinger

The sand slinger consists of a base, a sand bin, a bucket elevator, a swinging or movable arm, a belt conveyor and the sand impeller. Prepared sand lying in the sand bin is picked up by the elevator buckets and is dropped on to the belt conveyor which takes the same to the impeller head.

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Inside the impeller head, rapidly rotating cup shaped blade picks up the sand and throws it downward into the moulding box as a continuous stream of sand with machine gun rapidity and great force.

The sand is discharged into the moulding box at a rate of 300 to 2000kg/minute. This force is great enough to ram the mould satisfactorily.

In moulding boxes, sand is filled and rammed at the same time. The density of sand which is the result of sand’s inertia is uniform throughout the mould.

Squeeze Casting-Auto Jolting Machine with Sand Slinger

Cupola Furnace | How To Build A Cupola | Iron Melting Furnace

Furnaces in casting:

Melting furnaces used in the foundry industry are of many diverse configuration The selection of the melting unit is one of the most important decisions foundries must make with due consideration to several important factors including:

· The temperature required to melt the alloy

· The melting rate and quantity of molten metal required

· The economy of installation and operation

· Environmental and waste disposal requirements

 

Several types of furnaces are most commonly used in foundries:

· Cupolas

· Direct fuel-fired furnaces

· Crucible furnaces

· Electric-arc furnaces

· Induction furnaces

 

Selection of the most appropriate furnace type depends on factors such as the casting alloy; its melting and pouring temperatures; capacity requirements of the furnace; costs of investment, operation and maintenance and environmental pollution considerations.

Cupolas

A cupola is a vertical cylindrical furnace equipped with a tapping spout neat its base. Cupolas are used only for melting cast irons, and although other furnaces are also used the largest tonnage of cast iron is melted in cupolas.

01-Cupola Furnace-Cupola Furnace construction-Cupola Furnace Operation-Cupola Furnace Working

It consists of a large shell of steel plate lined with refractory. The charge, consisting or iron, Coke, flux and possible alloying elements, is loaded through a charging door located less than halfway up the height of the cupola.

The iron is usually a mixture of pig iron and scrap (including risers, runners, and sprues left over from previous castings). Coke is the fuel used to heat the furnace. Forced air is introduced through openings near the bottom of the shell for combustion of the coke.

The flux is a basic compound such as limestone that reacts with coke ash and other impurities to form slag. The slag serves to cover the melt, protecting it from reaction with the environment inside the cupola and reducing heat loss. As the mixture is heated and melting of the iron occurs, the furnace is periodically tapped to provide liquid metal for the pour.

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Cupola zones

Combustion or Oxidizing zone

It is the zone where combustion takes place. It extends from the top of the tuyeres to a surface boundary below which all the Oxygen of air is consumed by combustion, chemical reaction that takes place in the zone is

C(coke) + 02 (from air) -> C02 + Heat

The temperature in this zone is about 1800°C.

Reducing zone

It extends from the top of the combustion zone to the top of the initial coke bed. The CO2 produced in the combustion zone moves up and is reduced to CO. The temperature also drops to 1650°C.

C02 + C2 -» CO – Heat

Melting zone

It includes the first layer of pig iron above the initial coke bed. In this zone, the pig iron is melted. The following reaction takes place.

3 Fe + 2 CO -» Fe3C + C02

Preheating zone

It includes all the layers of cupola charges placed above the melting zone to the top of the last charge. The layers of charges are heated by the out-going gases. The temperature in the zone may be up to 1050°C.

Stack:

It is the zone beyond the pre-heating zone, through which the hot gases go to the atmosphere.

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