Round bars of aluminium, which are used as the starting material for forging operations, have to be delivered in the form of hexagonal bundles. For metallurgical reasons the leading, middle and trailing portions of the extruded bars have to be packed separately. This working step, which until now had to be carried out manually, has now for the first time been automated at the extrusion plant of Aluminium Laufen AG. The new round bar stacker with a sorting function was developed by H+H Herrmann + Hieber.
Whereas at the other presses in the plant, after the layer saws the profile sections are automatically stacked in racks and transported, until now round bars had to be handled manually. The necessary manpower incurs costs and with weights per metre of up to 10 kg or more, can be physically very demanding for the workers. Aluminium Laufen therefore decided to automate this difficult work station.
The preferred packing mode for such material is a hexagonal bundle, the number of bars in each bundle varying according to the dimensions. This form of stacking makes it necessary to use special holders with inclined sidepieces on both sides. Since the bundle size varies depending on the bar diameter, the sidepieces can be adjusted horizontally.
The important work steps during stacker operation are:
- Programming: The job number, the number of bars per layer, the bar diameter and the nature of the material (leading, middle or trailing portion) are input into the stacking program. For this, a maximum of 99 job numbers are available. With these data in each case the layer required can be assembled. For this it is not only necessary to determine the number of bars, but also the leading, middle or trailing portions have to be distinguished.
- Isolating and preparing the layer: The sections cut off by the layer saw are placed on a conveyor belt. To be able to assemble the layer, the sawn bar packet has to be isolated. For this is used a lifting device, the so-termed “Isolator”. This takes up the required number of bars, raises them up and transports them to the nearby preparation belt. When leading ends are being stacked and the next layer is a layer of middle portions (which have to be stacked separately), the stacking machine places the remaining bar offcuts into a mobile bar offcut store from which they can be recovered later as necessary.
- Transporting and deposition: Transport takes place with the help of a mobile gripper gantry, on which are arranged a total of five grippers. This prevents sagging in the case of long, thinner bars. The fixed and clamped layer of bars is moved to its target position over the rack concerned and deposited there. In this special case three racks, one each for leading, middle and trailing portions respectively, are arranged in fixed positions next to one another.
- Packing: The filled racks are taken to the packing station where the bundles are weighed and automatically strapped with interposition of spacer layers. After that the goods are immediately ready to be transported away.
The new stacker for round bars began operating in September 2011 and has since then been working without problems. In continuous operation it replaces two workers who used to be subjected to considerable physical stress. The capacity of the unit is sufficient for the higher production planned for the future. A contribution to the economic success of this new equipment is that damage of the bars is virtually excluded.