Two orders for a total of 14 new cranes completed the overhead material handling requirements at a new production plant for insulated doors. Uwe and Dieter Ehrenfels, owners of the company founded by their grandfather Bruno in 1922 in Karlsburg, Germany, are proud of their modern E6m factory.

Production processes and material flow have been completely restructured according to latest production thinking. The building was designed by Josef Reindl, an industrial buildings specialist, and his team from Nürnberg.

Manufactured at the plant are insulated doors to isolate cold stores and other temperature controlled areas such as climatic chambers in the motor industry which can measure up to 4m x 6m and up to 180mm thick. The Ehrenfels company, which employs around 50 people, has strong competition in Germany but Dieter Ehrenfels is optimistic for the future as his door products are becoming more popular in other European countries and there are high expectations for a recently introduced series of insulated stainless steel doors for residential and office buildings.

R Stahl Fördertechnik GmbH, which first supplied chain hoists to Ehrenfels more than 30 years ago, has supplied all of the overhead material handling equipment for the new factory. One suspension crane, five portal cranes, six single girder EOTs and two pillar jib cranes transport the frames and door panels and, combined with vacuum lifters, provide assistance in the final assembly and despatch of the completed doors.

Crane systems on two levels

The heart of the lifting system is the work station craneage where the insulated doors are assembled. Fred Weber, Stahl sales specialist, planned the portal type single girder EOTs on a 2.8m high runway. This allows a good height of lift and at the same time prevents assembly personnel from being injured by cranes travelling on the ground.

All the cranes at Ehrenfels use Stahl T and ST series chain hoists for a maximum load of 1,000kg. The five workshop cranes are small portals with 7m span and 1t SWL. An EOT and a suspension crane, both with 12.5m span and 1t SWL, travel above them at a height of 12.5m. These cranes transport the insulated doors from one assembly bay to another, bring materials, and hoist the packed doors to the despatch area in transport racks.

The EOT for the despatch area can travel on its runway out of the production bay into the despatch area, after a flap at the side of the bay is opened, where it is used to load the stacks of completed doors directly onto trucks. An intelligent solution needed a sophisticated control system to prevent collisions with goods stored in the despatch area and to ensure a well-ordered flow in the outside area. Proximity switches on the runway prevent collisions but interlocking the suspension crane and the EOT with the five portal cranes was considerably more complicated: the EOT and suspension cranes can only deliver material when the relevant portal crane has been moved to the rearmost position of its 5,7m long runway. Stahl solved the problem of interlocking the suspension and EOTs with the portal cranes using an HBC-radiomatic radio remote control. This does not release the travel path (a total of 31m) of the suspension and EOTs until the portal cranes at the lower level have been moved to their final position.

Five more single girder EOTs of 500kg SWL each, manually operated and divided among two parallel runways, assist with assembly of smaller doors. They are equipped with vacuum turning equipment and during the manufacturing process they turn the doors from front to back and vice versa. The two pillar jib cranes, with 6m and 7m jibs and 250kg SWL, are installed at the foaming machine and the subsequent assembly stations.

The new Ehrenfels production comprises 21 cells (15 cells for production and six for storage) and has been operating since early this year. Each cell has a grid dimension of 15.3m x 15.3m and is roofed over with large tent-shaped concrete slabs. The crane runways and raised runways for the portal cranes were attached to the roof slabs and to the longitudinal girders of the roof structure.