MELTING PROCESS IN FOUNDRY

Raw Materials

a) Controlling Raw Materials

Raw materials for the manufacture of castings must be selected and controlled to ensure that castings have the mechanical properties and chemical composition desired by the customer and are free from defects.

Amongst the various raw materials input into the foundry, metallic take the lion’s share both in terms of technology and economics.

Metallic Raw Materials

I) Steel scrap

ii) Bought cast iron scrap

iii) Pig iron

iv) Return scrap

Ferro Alloys

Each of these materials should be purchased to:

 range of compositions

 range of quality

 range of physical form.

The selections and quantity requirements of these metallic will depend on the melting method and techniques, the types and grades of irons to be produced, the skill of the operators and possibly local factors such as scrap availability.

b) Ferrous Scrap

Steel scrap has quite deliberately been placed as the number one raw metallic.

Over the last decade technical advances in cupola techniques, electric furnace melting and metallurgical skills have resulted in an increase in the use of steel scrap in foundry melting operations.

The scrap industry has made considerable efforts to ensure that it supplies the qualities of scrap required by the foundry industry. Many scrap merchants have geared their business to local foundries. However, it is up to the individual foundry to:

specify the quality and quantity requirement

 carry out the necessary visual check on every individual load of scrap – remember that visual inspection means checking before and after tipping

 visit the scrap merchant’s yard on a regular basis to ensure continuity of quality and supply.

The scrap merchant’s quality is only as good as his scrap source, plus his processing equipment. The former can change, especially when prime steel is at a premium, resulting in scrap of unknown qualities being introduced into the system.

Bought Cast Iron Scrap

Similar remarks concerning quality control apply to cast iron scrap as to steel scrap.

Categories and approximate ranges of composition for the main types of cast iron scrap are shown in Exhibit L.

The controlling element in bought cast iron scrap is considered to be phosphorus and even relatively medium phosphorus contents of 0.3% or less are detrimental to the production of the higher strength grey irons.

However, with certain specific exceptions, the phosphorus levels of cast iron scraps have reduced considerably over the last 20 to 30 years. In fact, the only commercial way to produce a high phosphorus iron is to add ferro phosphorus.

Control

As with steel scrap loads, a visual inspection of each individual load is essential, and again check before and after tipping, including the bottom of the transport vehicle.

Attention must be paid to possible sources of contamination such as: gas works scrap		high sulphur
enamelled scrap	–	lead, boron and antimony
petrol engine scrap	–	lead, aluminium, etc, plus the possibility of small quantities of chromium

The vast majority of cast iron borings originates from low phosphorus sources and as such are a useful, relatively low cost raw material for many iron foundries.

It can be briquetted, packed in canisters and used in cupola operations. Commercial success depends on the quality of briquette or canning operations as there can be serious losses in the melting operation.

The coreless induction furnace is an ideal melting unit providing the borings are dry and relatively free from rust and foreign matter.  Briquetted cast iron borings should be free from corroded lumps and excessive cutting fluids.