While the number of cabinet sizes is fairly standardised within countries; the number of permutations of door components and internal arrangements for shelves is very large.
It is not always possible for a refrigerator maker to have a foaming line dedicated to foaming one type of refrigerator door, for example. While it may make sense from a production point of view to have large scale production of one model in a dedicated factory, the logistics of shipping empty refrigerators often means that smaller, flexible plants are more economically viable. Such plants may also have to produce several models of refrigerator, and this can lead to a situation where a plant has several foaming lines dedicated to an individual model or range of models.
Drum units are a good solution. They have good flexibility, and it is possible to change tooling if needed.
Banging the drum
Stationary fixtures have similar characteristics and advantages, but can give only a low output. A drum unit can provide medium levels of output, but the drum has a larger footprint than a stationary fixture or a mould clamp.
A centralised door foaming line can be used for the next level of production. This can be anything from a paternoster with a vertical arrangement to a horizontal oval conveyor.
Paternosters and conveyor systems give much higher production and greater flexibility than drum units because they can hold a much greater number of moulds. Unfortunately, they also have a much larger footprint, and cannot handle a variety of cure-times efficiently. The entire line is sequenced together, and therefore is limited by the longest curing part on the carousel.
Centralised systems are well known in the industry, and are common for really large volume manufacturers.
Hennecke recently had an enquiry from a customer who needed a foam line with a medium level of output. This had to be slightly higher than a traditional drum unit or stationary fixture would give them, but they did not need quite as much volume as a centralised system like a conveyor or paternoster can provide.
The customer also needed the system to be very flexible to produce multiple models, and they wanted to run between five and eight models on the door foaming line at the same time. A further complication was the lack of space in the plant.
Although the customer had little horizontal space, its production hall had height, so we used that and developed the Hennecke KTT system.
The KTT is a discontinuous machine that can handle eight to 10 different doors at the same time. It can handle a wide range of curing times, too, without limitations in output.
At the heart of the system lies a vertical storage unit. This is split into two parts, separated by a central lifting and lowering device. Each side of the storage unit is either four or five units high.
Moulding a refrigerator door on the KTT model foam line starts at the operator station, which has fixed guarding and a floor scanner.
The operator station is designed to enable the plastic liners to be inserted directly into the moulds, which are mounted into intelligent mould carriers. The operator loads the metal door pans directly on top of the liners in an open pour application. After the parts are loaded, the carrier moves into the foaming station.
When it reaches the station, it closes. It then locates and holds the metal door pans by magnet, vacuum, or clips built into the upper tool itself. This opens to present the liner to the mix heads for foaming. The door pan is on top.
The KTT machine uses two MT18 mix heads with a double x-y axis electrical manipulator to lay the foam patterns directly onto the liners.
After foaming, the upper fixture closes. This brings the metal door pan down onto the liner, and the carrier indexes back to the lifting device. This takes it into the curing station, and puts it into a vacant slot on one of the levels.
In the foam line each of the levels is independent; mould carriers can be moved to the right or the left for storing. The mould carrier is heated during curing. Heating energy is taken from the electrical busbar. The busbar runs through the machine. The carriers are also equipped with on-board pneumatics with an accumulator.
The mould carrier’s position and residence time in each location is tracked by the machine’s PLC. When the part has cured, the mould carrier is removed, and taken by the central lift to the automatic unloading station. The mould carriers open and close themselves via an electrically controlled crank drive. There is no need for a separate station. The mould carriers are designed so the bottom platen can move downwards by up to 20 mm before the lid is opened. This is useful for deep liners.
After the mould is opened, a robot unloads the door and the carrier moves back to the loading station and the operator. Alternatively, the mould can be swapped at this point in the cycle. A friction drive is used for speed.
The lift is counter-weighted and uses a triple chain drive system. This reduces wear and to increases reliability.
Hennecke’s KTT machine has a number of advantages over other foam line machinery configurations.
Firstly, because each slot in the tower is independent, it is possible to have parts in the tower with cure times of 5 minutes along with parts with cure time of 3, 4, 7 or any other number of minutes. The plant has been used with parts that were complete in a 36 second cycle. It could be possible to handle cycle times of 25 seconds. That is around half the cycle time of a drum unit.
Compact, higher output
The foam line plant covers 1,333 sq ft (124 m2) and has twice the volume output of a two-drum unit system. Drum units typically cover 2,500 sq ft. If space is tight, and if the factory has an area that is 25 ft (7.5 m) high, then it could be advantageous to exploit that height.
The Hennecke KTT sits right between two drum units and a carousel unit in terms of production capacity. An oval conveyor would cover around 3,000 sq ft. It could produce doors on a 20 second cycle, but that is much more area to cover.
In summary, the KTT has a compact footprint compared to drum and conveyor door systems, and offers highly flexible production for mixtures of models. Using independent intelligent carriers eases the problems which can arise with mixtures of components that cure at different times.