Auxilary equipment of extrusion press
In addition to the extrusion press itself, any line for extruding aluminum profiles includes about a dozen units of various auxiliary equipment. Typically, a distinction is made between auxiliary equipment BEFORE the press and auxiliary equipment AFTER the press [1-3]. The equipment before the press includes, but is not limited to (Fig. 1):
- Log/Billet Feed Table
- Log/billet heater
- Hot log shears
- Billet Transfer Conveyor to Press
- Billet and Dummy Block Lubricants (no shown)
Log/Billet Feed Table
- The equipment for feeding logs or pre-cut billets into log/billet furnace.
- Usually it a gravity-feed table on which logs or billets are loaded individually or in bundle form.
- They are allowed to roll down to a stop where an indexing device feeds them out, one-by-one as called for.
- Also this equipment often includes chain-feed tables or conveyors (Fig. 2) .
Figure 2 – Log feed table [Tecalex]
Gas heating furnaces heat the logs or billets to a predetermined temperature. The main task of these furnaces is to ensure an accurate and constant temperature of the billets for immediate feeding into the press container.
Most log heating furnaces use direct heating from burner flames. Hot gas combustion products are then directed towards the incoming logs (billets) for their preheating. This results in significant energy savings . Contact thermocouples are installed in each heating zone of the furnace, which provide control of the heating temperature of the log (billet) (Figure 3).
Figure 3 – Log furnace [Tecalex]
Hot log shears
Hot cutting shears cut the billet from the log to the optimal length, which depends on the pressing parameters, including the type of die and profile design (Figure 4). When loading pre-cut billets into the furnace, this is achieved by sequentially feeding billets of different lengths.
The system for cutting heated billets has special cutting dies that ensure minimal curvature of the log from the impact of cutting forces. After the billet of a given length is cut, the remainder of the log is returned to the furnace, where it is heated until the next cycle of cutting the log. Typically, the remaining short end of the log is connected to a shortened piece from the next log to obtain the specified full length of the billet. Due to certain difficulties in processing short pieces of logs, it is common to try not to leave log remnants shorter than a certain minimum length. This is achieved using special programs for programmable logic controllers.
Figure 4 – Hot log shears [Tecalex]
Billet Transfer Conveyor to Press
The conveyors which transport hot billets from the billet heater or log shear to the press are critical to press performance, because they often cause excessive downtime and require constant operator attention. Many of the older systems in use are difficult to maintain because the components are inaccessible. Billets don’t stay aligned, so the operator must watch each billet, ready to grab a pry bar and help the billet into position; this keeps the operator tied to the press and prevents truly automatic operation .
Billet and Dummy Block Lubricants
To prevent the billet from sticking to the dummy block, the ends of pre-cut billets have traditionally been lubricated by painting with graphite dispersions, in a base of either kerosene or water. However, increasing use of fixed dummy blocks, combined with hot-sheared billets, has forced the development of alternatives which may be automatically applied, for example after the billet is sheared.
At the present time there are three popular methods of applying lubricant to the surface between billet and dummy block :
- Flame application of carbon (soot) to the billet face. The billet is paused at some point of its
transfer to the press, while a carbon-rich flame applies a coating of “soot” or carbon to the end of
the billet. Usually an acetylene flame burns for 3 to 4 seconds with a visibly black smoke. Typically, every billet is coated.
- Automatic spraying of proprietary liquid arting compounds to the dummy block. An automatic applicator descends from above by means of a pneumatic cylinder to align with the dummy block during the press dead cycle. Typically, the block is sprayed every 5 to 10 billets.
- Electrostatic application of Boron Nitride (BN) powder to the billet and/or other tooling surfaces. BN powers are expensive. Usually spraying intermittently – for example, every 3 to 5 billets.
Figure 5 – Device for applying acetylene sooth to the butt of billet