Vehicles, Cranes and Other Moveable Objects

This subsection specifies commonly used vehicles, cranes, and other moveable objects in more detail. This subsection first addresses vehicles involved in the aluminum smelter. Next, crane operations are discussed. Then, other moveable objects that play a role in the logistics are outlined. As shown in Table B.1, some tasks can be performed by multiple operating entities. We focus on elucidating objects that are of importance for the transportation of anodes.

2.2.2.1 Vehicles

A number of vehicles and related substitutes can be identified in an aluminium smelter. Besides pedestrians and personnel vehicles, vehicle movements involved in an aluminium potroom include, for example:

• anode pallet transporters (e.g., see Figure 1.4); • crucible transporters (e.g., see Figure 1.1d); • forklifts;

• vacuum cleaners;

• cavity cleaners (e.g., see Figure 1.1c); • bath tapping vehicles;

• anode changing vehicles (e.g., see Figure 1.1b).

Some vehicle may interfere with the anode pallet transporter. For example, pedestrians, personnel vehicles, vacuum cleaners, cavity cleaners, forklifts, bath tapping vehicles, crucible transporters, and anode changing vehicles can interfere with activities of the considered AGV. However, in general, these vehicles can maneuver freely and without blocking paths required for other activities, due to the way the shift-based working routine is arranged (see Subsection 2.2.3).

Furthermore, due to the availability of highly magnetic fields, areas or pathways may be blocked for vehicle movements. Some positions in a potroom facility are infested by this phenomena and

consequently limited or no vehicle movement is possible. In this thesis, we consider the vehicles dis- cussed below in detail.

Automated Guided Anode Pallet Transport vehicle (AGAPTV)

The Automated Guided Anode Pallet Transport Vehicle (AGAPTV) (see Figure 2.10) is responsible for transporting anode pallets. Anode pallets may be empty or contain a certain amount of either new or used anodes. Pallets with new anodes are transported from the rodding shop to nearby the cell. Empty pallets or pallets with burned anodes are transported from nearby the cell to the rodding shop. The pickup of pallets should be done by executing a special backward driving maneuver because physical vehicle properties prohibit the AGAPTV to pick-up pallets by forwards driving. More details about this maneuver and the tasks carried out by the AGAPTV is given in Subsection 2.3.

(A) AGAPTV with an open bucket. (B) AGAPTV with a closed bucket.

FIGURE2.10: Automated guided anode pallet transport vehicle

The AGAPTV can drive both forward and backward at the same speed. Although the vehicle’s speed can be much faster, it is considered as safe to let the AGAPTV drive at most the regular walk- ing speed of pedestrians (4.5km/h). To avoid possible collisions and to maneuver freely it is rec- ommended to keep AGAPTVs at least a certain number of meters (usually10 meters) away from other vehicles. Furthermore, the AGAPTV is an electric vehicle and therefore needs regular charging. Charging details and other vehicle properties are summarized in the overview in Appendix C.

Ladle Transport Vehicle (LTV)

The Ladle Transport Vehicle (LTV) (see Figure 2.11) is designed for the transport of pallets with filled or empty crucibles. A variant of the LTV is the LTV with the ability to tilt the crucible for operations carried out in the casthouse (e.g., see Figure 1.1d).

The LTV occupies quite some space to move and to conduct its driving maneuvers safely. It is important that the LTV can proceed its job without too much delay because a delayed arrival in the casthouse can affect continuity and efficiency of both the potroom and the casthouse. However, in general, the LTV can execute its tasks without much interruption. That is because the LTV mostly drives on main roads (so-called metal roads) in which other vehicles can pass the vehicle without too much interruption. Also, the LTV would only active in a limited number of sections at the same time because of the shift-based working routine (see Subsection 2.2.3). Furthermore, as LTV’s drop-off and pick-up crucibles in main roads and cross aisles, they do limitedly interfere with the traffic in the cell segments. In addition, there are some other technological challenges to overcome before they are sufficiently mature for driving autonomous.

Although crucible transporters provide an interesting direction for automation by means of AGVs, there is no urgent reason to incorporate the logistics of this vehicle in detail. The exclusion of crucible transporters could subvert the validity of the model because these vehicles may cause deadlocks that

2.2. Common Factory Characteristics 23

(A) LTV without crucible. (B) LTV with crucible palette.

FIGURE2.11: Ladle transport vehicle.

could have a significant impact on AGAPTV (and smelter) performance. However, the (explicit) in- volvement of crucible transporters would make the goal of an operational planning and control tool for the AGAPTV increasingly more complex. Therefore, the management decides to not explicitly involve crucible transporters.

Other Vehicles

Besides these two type of vehicles, forklifts are used for a variety of (mainly supporting) purposes in an aluminium potroom as well. Forklifts can, for example, be used to assist anode setting and pot change out. Forklifts may also be used for transportation of crucible tapping lids and (emergency) anode pallets. Nevertheless, most of its executing tasks can be carried out by other equipment such as cranes as well. Furthermore, forklifts are human-driven and usually maneuver freely in between the available trajectories while coping appropriately with blocking situations. This vehicle plays a supportive role in the smelters we consider.

2.2.2.2 Cranes

Several cranes can be identified in an aluminium smelter. Examples are construction cranes, pot displacement cranes, and pot-tending cranes. Some crane types may serve multiple purposes. The crane operator can change the tool attached to the crane to make it suitable for different purposes. Because of safety regulations, the immense presence of the (overhead) cranes (e.g., see Figure 2.4), and the often limited space, areas could be (temporary) blocked for other vehicles during a specific shift (see Section 2.2.3). Furthermore, cranes need maintenance or could break. Crane behavior is not explicitly considered in this study. However, the processes involved are examined on a high-level (as time delay and operating sequence).

2.2.2.3 Moveable Objects

Moveable objects that are transported throughout the production facility include, for example, an- odes and anode pallets, crucibles, and muck trays. Below we discuss them more detailed.

Anodes and Anode Pallets

Anodes are placed on pallets (see Figure 2.12). The pallets are transported by means of the AGAPTV (e.g., see Figure 2.10). Currently, the pallets can hold at most three (regular size) anodes, but Hencon wishes to investigate the impact of transporting a pallet containing pallets with an increased capacity as well. Figure 2.10b illustrates an AGAPTV with a pallet that can hold at most four anodes.

(A) Anode pallet with fresh anodes. (B) Fresh Anode.

FIGURE2.12: Graphical illustration of the anode and anode pallet object. The rods are asymmetric attached to the anodes. Anode orientation can be observed through the

small cove at the block width side.

Furthermore, the orientation of the pallet (i.e., north, south, east, west), is of importance because anode blocks (including their rods) are not symmetrical (see Figure 2.3b) and require a certain orien- tation in the cell. Notice that quite some cranes cannot easily rotate the anode 180 degrees and only align anodes for placing in the cell. Anodes are prepared such that they are suitable according to a specific orientation required in the cell, either for the front position (see Figure 2.7a) or rear position (see Figure 2.7b) of cells. During anode pallet transport, the pallet can be driven in according the re- quired orientation by letting the transporter drive forward/backward in a section. For safety reasons (to avoid electrical short cut) and to enable drive through by other traffic, pallets cannot be placed anywhere. Subsection 2.3 gives attention to the anode transportation and pallet placement.

Crucibles

A crucible (also known as ladle) is a large metal bucket for transport of liquid aluminium. Cru- cibles are transported by means of crucible transport vehicles (e.g., see Figure 1.1d and Figure 2.11) and could be empty, filled or partly filled. A crucible is completely filled with metal after a certain amount of tapped pots. A lid is placed on the crucible before it is being transported. Crucibles and crucible lids are not considered in this study because this is part of the crucible transporter which is not embodied in the scope.

Muck Trays

Bath tapping fills a muck tray with bath material. This material is collected in a tray and after a certain amount of tapping, the muck tray is full and requires a transport to the bath conveyor belt where it is further handled. Muck trays are not considered in this study.