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issue: March 2004 APPLIANCE Magazine

Production - Refrigerators/Freezers
Flexible Production of Insulating Foams


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The Electrolux factory in Mariestad, Sweden has implemented new equipment for applying foam insulation to refrigerator and freezer doors. The equipment is said to combine high efficiency and flexibility with a relatively small footprint.

As one of the world's largest manufacturer of home appliances and garden equipment, The Electrolux Group produces a wide range of products - from refrigerators, cookers, and washing machines to chain saws, lawn mowers, and garden tractors. Apart from the Electrolux brand itself, the company's brand portfolio includes names such as AEG, Zanussi, Frigidaire, Eureka, Flymo, and Husqvarna.

 


Pictured is an eight-station Rotostar foaming line for insulating refrigerator and freezer doors.
At its Mariestad plant, Electrolux manufactures refrigerators and upright freezers up to 400-L in capacity. With approximately 1,100 employees, the plant ships more than 500,000 appliances annually.

In order to increase efficiency at the plant, Electrolux recently installed a new Rotostar line from Krauss-Maffei Italiana (Milano, Italy) to insulate the refrigerator/freezer doors with PU foam. The automated Rotostar has eight mould carrier stations mounted on a drum rotating on a horizontal axis. The mould carrier at each station is large enough (2,000 by 900 mm) to process doors for the full range of refrigerators and freezers sold in Europe.

The processing cycle begins by inserting the metal door to be foamed into a mould together with the plastic inner door. Next, the pallet-mounted mould is unloaded from the mould carrier onto the pallet conveyor system.

The pallet-mounted mould is then loaded onto the open mould carrier on the drum. The mould carrier is then closed, and two mixing heads inject the PU foam into the mould, and it expands with the help of cyclopentane and cures.

" Krauss-Maffei mixing heads ensure a high foam mixing quality and eliminate all the problems involved with the use of cyclopentane," notes Fredrik Bolin, production engineer at the Electrolux Mariestad plant.

After 45 sec, the drum on which the eight mould carriers are mounted indexes one station. A new pallet-mounted mould is then loaded, and the mould with the finished foamed door is unloaded from the drum mould carrier.

The mould then travels around the drum on a roller and belt conveyor system. First, it is transported to a tilting conveyor, where a robot removes the foamed doors. Then, the operator loads the metal door and the inner door. The pallet-mounted mould moves ahead to the next station, where the mould is reinserted in a mould carrier and the cycle starts again.

Rotostar is said to have a number of features designed to ensure a high level of efficiency and reliability and to keep maintenance efforts low. For example, the hoses carrying the water for mould temperature control are integrated in the aluminium mould carriers. The complete water distribution system is installed on the rotating drum.

To prevent foam leaks, a mechanism integrated in the upper mould carrier platen automatically closes the injection hole as soon as the PU system has been discharged into the mould. The mould carrier parallel stroke opening system is hydraulically driven through a cam system. This, Mr. Bolin says, keeps operating costs down and noise levels lower than conventional opening systems. "The use of the cam system decreases the initial investment cost of the equipment and improves the time required for plant maintenance as well," he confirms.

The drum is fully hydraulically driven for high reliability and precision control. A proportional valve is used to slow the drum's rotation at the beginning and end of each indexing movement.

 


During loading and unloading, a pinion mechanism controls the position of the mould-bearing pallets.
Specific features of the RotoStar system proved to be important for the production of Electrolux's range of models, which require handling different door designs. An automatic recognition system detects the door type before loading the pallet-mounted mould into the drum. This information is transmitted to the main control panel and used to select the correct shot time. Mould loading and unloading is very fast, with the position of the pallets controlled by a rack and pinion system driven by a servomotor.

The Rotostar equipment is said to take up less floor space than most foaming systems built on an oval or carousel design. Fewer mould carrier stations are required because loading of the metal door and inner plastic door and removal of the finished insulated doors takes place outside the production cycle.

Electrolux's Mariestad plant marks the launch of a new Krauss-Maffei RotoStar product family. The supplier says the equipment with four- and seven-mould carrier stations are soon to be installed for other customers in the U.S. As the product's first customer, Electrolux says it is pleased with the results. "We really appreciate Krauss-Maffei RotoStar because it improved our cycle time and allowed a higher manufacturing flexibility," says Mr. Bolin.

 

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