Modernized stacker cranes for BHS tabletop

Anyone who goes out to eat in hotels, pubs or restaurants is very likely to have their food served on porcelain from BHS tabletop. The company is the world market leader for out-of-home porcelain and produces the collections of its three brands Bauscher, Tafelstern and Schönwald exclusively in Germany. On their way from production to the customer, all items stop off at the decoration and logistics center at the company headquarters in Selb, Bavaria. There, plates, cups, bowls and other porcelain items for the catering and hotel industry are stored on 120,000 spaces. Customer-specific decoration of the articles and shipment processing are also carried out from Selb. Reliable logistics are essential to ensure that the packaging, shipping and delivery of up to 40 million parts per year are carried out on time. The starting point for all goods movements is an automatic small parts warehouse (AKL), in which BHS tabletop stocks its porcelain over a length of 75 meters and a width of 30 meters. The connection between the miniload and the shipping department is ensured by an automatic storage and conveyor system: the goods are transported from the twelve-aisle warehouse to the decoration area via roller conveyors and a container lifter and are then shipped. Storage and retrieval is carried out with the help of twelve 18-meter high single-mast stacker cranes (SRMs). These are equipped with a telescopic table for holding two containers at the same time. They are the core element of logistics, as they significantly control the flow of goods. However, after 19 years of full operation, the impeller bearings of the RBGs began to malfunction: As a result, individual units failed again and again, leading to shutdowns in the warehouse. “The stacker cranes became a risk factor for us,” says Heiko Benker, Head of Distribution and Technology at BHS tabletop, describing the situation. “We never knew how long it would be before the next disruption and which device would be affected.” Emergency repairs also did not provide a permanent solution. Here, the material damage to the bearing flanges was repaired by buildup welding and subsequent boring of the bearing bores. “Through the emergency repairs, we were able to restore the function of the impeller bearings, but we had no guarantee that this would last in the long term,” Benker said. The aim of BHS tabletop was therefore to take preventive action and counteract unplanned failures at the RBGs in advance.

On the trail of the cause

The contract for the technical clarification of the failures, the development of suitable repair measures and the implementation of the modernization was awarded to TELOGS GmbH. BHS tabletop decided in favor of the service provider from Wettenberg near Giessen primarily because of its great expertise in the field of retrofitting and its existing experience in dealing with comparable storage and retrieval systems. “Our first step was to take a detailed inventory on a storage and retrieval machine,” says Manuel Maus, a design engineer at TELOGS, describing the course of the project. The maintenance expert thus determined the causes of the failures: The company noticed heavy wear on the bearing seats in the travel frame of the SRMs. This was due, among other things, to the fact that the impeller bearing is continuously exposed to high pressures during continuous operation of the plant. If it can no longer withstand these, material damage occurs, resulting in unpleasant noise and unplanned RBG failures. Furthermore, the wheels and track wear out quickly. This results in high costs for maintenance and spare parts. In addition, BHS tabletop had no process reliability in the operation of its RBGs due to the failures and malfunctions.

New design according to requirements

As part of a feasibility study, TELOGS developed proposals for a new design of the impeller bearings that would permanently prevent the bearing seats in the travel frame from deflecting. “Our biggest challenge was to intervene constructively in an existing system and to implement all conversion measures on site with mobile tools,” specifies Manuel Maus. The most economical and targeted solution for BHS tabletop was to select bearing flanges made of a higher-strength material and to use wider rolling bearings. This required machining of the chassis on all SRMs: TELOGS removed the bearing seats welded in there and replaced them with new, bolted bearing flanges with wider spherical roller bearings. The width of 43 millimeters exceeds the dimensions of the old bearings by 14 millimeters. This leads to a reduction in surface pressure, which prevents wear and tear and deflection of the bearing seats. In addition, the maintenance service provider also replaced the conductor rails with substructure as well as the brackets of the current collectors as part of the modernization. As a result, the energy supply and thus also the availability of the warehouse improved.

Flexible project management

TELOGS worked for a total of two months on the planning and design of the new solution. On-site implementation took around three days per RBG and was carried out while the plant was in operation. Only the alley where the reconstruction took place was shut down. Thus, the modernization hardly affected day-to-day business. “We are very satisfied with the consulting and project handling by TELOGS,” summarizes Heiko Benker. “We were particularly impressed with the company’s flexibility.” For example, during the rebuild on one RBG, failures of a second and third unit suddenly occurred. The maintenance service provider made additional personnel available at short notice for this requirement, which was outside its remit. This meant that the equipment that had unexpectedly broken down was quickly put back into operation and BHS tabletop did not suffer any supply bottlenecks for its products. Thanks to the repair of the stacker cranes based on the TELOGS solution, the porcelain manufacturer is now operating its SRMs trouble-free again. The availability of the warehouse now meets the requirements of the company. Another positive effect of modernization is predictable costs for maintenance and spare parts.