Direct-chill casting

Direct-Chill aluminium casting machines

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Explore the world of direct-chill aluminium casting and the advantages of using vertical DC (VDC) casting machines for extrusion ingots production.

Vertical and horizontal direct-chill (DC) casting machines

For direct-chill aluminium casting of extrusion ingots, two types of casting machines are used in the world:

vertical DC (VDC) casting machines
horizontal DC (HDC) casting machines.

A general view of a vertical casting machine is shown as part of other equipment in Figure 1, and a horizontal casting machine is shown in Figure 2. The most widely used are vertical casting machines. They will be discussed below.

Figure 1 – An vertical direct-chill (VDC) casting machine and other related equipment [1]

Figure 2 – An horizontal direct-chill (HDC) casting machine [1]

Vertical DC casting machines

Main parts

Vertical DC (Direct-Chill) casting machines are usually concidered as a complement of the follow main parts [4]:

The casting machine wich fitts into the casting pit.
The platen drive mechanism, hydraulic or mechanical.
The platen and stools.
The mould table completed with moulds, spray rings, starter blocks.
The control water system.
The control system.

The types of DC casting machines

There are two basics types of casting machines:

cable type and
hydraulic.

Both types of machines have the same type of mould table.

Cable type casting machines have two options:

Cable operated casting machines.
Suspension cable casting machines.

The primary role

The primary role of the DC casting machine is [1]:

to lower the platen, starting head base, and starting heads, together with the forming cast product, into the casting pit, at the set rate (Vcast)
to maintain the whole system in a horizontal or coplanar position with respect to the moulds
to minimise any rotational movement (<1′ of arc) during the total casting process.

Mechanical DC casting machines

Cable operated DC casting machnes

Figure 3 shows a cable type casting machine. It has a working capacity up to 5 tons. Machines of this type are used in small remelt shops.

These machines provides:

a low cost
ease of installation
the minimum of foundation work.

The cable type of casting machine has the platen raised and lowered by a wire rope which passes the system of capstans and pulleys [2]:

There must be a tensioning arrangement to accommodate the rope extension as the load increases and give suffucient back tension to ensure that the rope does not slip during casting .
These machines have electrical power supply and therefore require a backup source of electricity in case of an accident to allow the cast to be stopped safely.

Figure 3 – A cable operated DC casting machine [2]

Suspension cable DC casting mashines

Figure 4 shows a typical suspension cable casting machine. Such machines are often installed in small remelt casting shop of extrusion plants to remelt their own scrap. They usually have a load capacity of about 5 tons.

An platen support frame is suspended by four ropes of equal length to prevent any unequal extension during casting. The suspension cable machines requires no equipment to be installed in the casting pit below the floor level.

Figure 4 – A suspension DC casting machine [2]

Some advantages of suspension cable DC casting machines [2]:

Low capital cost.
Reduced depth of casting pit.
No part of casting machine attached to casting pit.
No guides.
Simple maintenance.
All operating equipment is accessible from shop flor level.

Hydraulic DC casting machines

Hydraulic DC casting machines are most suited for drop weight more 10 tons. They uses a hydraulic ram to raise and lower the platen.

Back in the 90s the industry standard had been a simple displacement ram with guide rails. These guide rails provided the platen support and alignment. The guide rails were attached to the casting pit walls. The platen was fitted with guide slides or wheels which ran against the rails.

Modern DC casting machines have self guiding rams which are strong enough to support the platen loading without guide rails. These ram have an internal guide which prevents the platen rotating. These rams are very effective but of higher cost. A cost compromisw can be made by using a self supporting ram with an external antirotation guide [2].

Figure 5 shows a 60 tons hydraulic DC casting machine for rolling ingots with a tilting mould table.

Figure 5 – An hydraulic DC casting machine for rolling ingots [2]