The world hungers for steel. 1.343 billion tons of crude steel have been produced last year alone. 2007 has been the 5th year in succession with an average growth index beyond 7 %. Driving force are above all the emerging markets in Asia and Latin America but also the CIS countries. As successful as this development is, the manufacturers already reach the limits of their capacity. In the area of quenched and tempered steel for instance, the demand exceeds supply for a long time already. This is why in the past, the steel manufacturer SSAB had no other alternative but to turn away new customers. Due to the development of an additional painting line in the Swedish Oxelösund, the production now will be enlarged and the capacity considerably increased on a long-term basis. "Criteria for the increase in production is the new painting line and in addition a warehouse with sufficient place and fast functional intralogisitcs systems", explains Magnus Rådh, project manager at SSAB Oxelösund: "We therefore plan to increase the capacity of delivery for prepainted steel plates by 30 % up to the year 2009. "Within a period of 12 months only, the Vollert plant engineering company, specialists for many years in intralogistics systems for heavy loads, developed in its capacity as general contractor a so far unique solution in the steel area: a high-bay warehouse for up to 6000 tons of steel with access in a matter of seconds.
As soon as the 3rd painting line runs with SSAB in the Oxelösund factory from 2009 with full efficiency, every 60 seconds a sheet steel board of up to 15 x 3.5m size comes out of production. After blasting and painting and prior to order-picking a barcode will be directly printed with ink on the sheet plate by use of a new procedure that prints among others the type of steel plate, the weight and the customer allocation. After this a crane will set the steel plate onto a pallet, which at the desired time will have been brought, arranged and then at the end of the process, returned to be stacked and stored in the warehouse, by one of the two AS/RS stacking devices. The central control system automatically allocates the pallets to certain customers or to supply contracts so that different steel plates of one order can be assorted and compiled according to order-picking, ready for delivery.
Short cycle times at extreme loads
The challenge for the Vollert engineers has been to manage short reaction time and simultaneously high loads. Only three minutes prior to the production exit, the control system transfers the information to the central storage management system stating to which customer - and onto which pallet - the steel plate belongs to. Now everything must be carried out quickly: One of the two AS/RS starts running and takes the right pallet out of the warehouse where some tons of order-pre-picked steel may already be set. The two AS/RS developed by Vollert, so-called mega AS/RS are working in overhead execution and each one lifts a payload of 32 tons. With the double-storey structure of the AS/RS stacking devices, the simultaneous transport of two pallets of 16 m length and 3,5 m width can be carried out. Hence, two pallets can be exchanged in one working step thus reducing the cycle time and increasing the storage capacity. The facility, in an extreme case must run a distance of 80m as well - that is the length of the warehouse with its 500 places. At the same time high speeds grant short cycle times: The equipment manages at the rack storage and retrieval process a speed of 2.2 m/second and on the way through the warehouse of up to 4.5 m/second regardless of the total equipment weight of 140 tons. Due to this it is possible to move 60 pallets in our hour, hence.
Calculated with maximum values, 64 tons of steel dash up to 60 times per hour with 4.5 m/second through the storage aisle. In practice 5000 tons of steel on average are weekly transferred at approx. 10 tons of steel per pallet. "Short cycle times due to high speeds at large payload -our pre-settings are fulfilled at best with this equipment", according to Magnus Rådh.
Simultaneous storage and order picking
The interface between SSAB and Vollert is between painting and packing. The central storage management system that controls the driving jobs of the AS/RS decides autonomously where which pallets are stored. Customer orders at SSAB can only be carried out parallel, not side by side since the individual production steps always allow a certain steel plate type only, for instance with a certain amount of thickness. This is why different steel plates ordered are picked one after another on a pallet. This pallet is automatically asked for by the warehouse management system as soon as one steel plate is ready for the allocated customer. After de-stacking the steel plates the AS/RS stores the pallet back to the warehouse till it is required again for order-picking or for delivery to the customer. An optimum coordination of components and control system between SSAB and Vollert achieves a trouble-free connection of the production and warehouse control system.
Shorter ways thanks to high-bay warehouse
On the one hand the increase of capacity is based upon the high speeds of both AS/RS. However due to the high loads, the limits of feasibility are quickly reached. The second challenge at transfer therefore has been to shorten the distances. Instead of the hitherto existing surface warehouse, a high-bay warehouse had to be built with the necessary stability to withstand the strain. The storage system plus the hall that has been accomplished is unique and one of the largest of this type worldwide. "With our high-bay warehouse for heavy loads we set the trend to convert from surface to high-bay warehousing in the steel industry" Andreas Gebhart explains, project leader in the sector of intralogistics systems for metals and automotives from the Vollert plant engineering company. "Shorter ways mean shorter cycle times and at the same time space saving". In addition the Vollert logistic solution offers utmost security. With the double execution of the AS/RS stackers and the parallel arrangement of both aisles, a fail-safe production on 365 days/year and 24 hours can be implemented round the clock. Even the annual maintenance of the equipment can be carried out under running production.