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.
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.
Pictured is an eight-station Rotostar foaming line for insulating
refrigerator and freezer doors.
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
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
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.
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.
During loading and unloading,
a pinion mechanism controls the position of the mould-bearing
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