Maersk Brings Automation to Refrigerated Container Manufacture

It's not surprising that the world's largest manufacturer of refrigerated containers is also the most automated. What is surprising is the high degree of automation that is used to achieve both a low cost and high quality in this cost-driven industry.

Maersk Container Industri AS (MCI) and its parent, the A P Moller Group, built its first container manufacturing plant in 1990. The goal was to provide a more stable source for dry freight boxes closer to the Maersk Lines corporate headquarters in Copenhagen, Denmark. The only way it could be competitive in Denmark against the low-wage container builders in the Orient was to automate. Two-thirds of the cost of the $35-million plant went for fixtures and equipment, including some 40 robots plus automatic seam-welders and other automatic handling equipment. An eight-page article on this MCI plant in Tinglev, Denmark, appeared in the July 1992 Trailer/Body Builders. Since startup, this plant has produced more than 100,000 40-ft dry freight ISO cargo containers.

Five years later, MCI added another even more automated plant alongside the dry freight plant - this one dedicated solely to refrigerated ISO containers. And at the end of 1998, Maersk Container Industri acquired the assets of Jindo's modern reefer container plant in Qingdao, China. These two plants, both built in 1996 but on opposite sides of the world, give Maersk Container Industri the ability to produce 450 refrigerated containers a week. Together, the two plants have 35% of the world market for refrigerated containers.

40-ft Refrigerated Containers Before designing the highly automated plant in Denmark, MCI first developed a new generation of 40-ft refrigerated containers to meet customer demands of a competitive price and low tare weight for highest payload potential. Extremely robust, the container and its insulation are designed for a 15-year trouble-free life. Easy to clean, its appearance both inside and outside is expected to stay presentable for foodstuffs throughout its life. And its tightly sealed construction makes it suitable for controlled atmosphere.

One of the unusual features of the Maersk Sea-Land design is a completely flat bottom that has no crossmembers. The sandwich construction uses a core material of Dow's extruded polystyrene. This block foam is sandwiched between a steel bottom plate and the container interior floor of extruded aluminum T-section planking. Elimination of the crossmembers reduces the tare weight and provides an even distribution of stress with no thermal bridges.

A key element of the bottom design is the damage-resistant bottom rail of 4 mm (0.1575") high tensile steel. This bottom rail angle is sloped upward at the sides of the container in order to deflect obstacles when lowering the container, such as forgotten twist locks at the 20-ft container position. This steel bottom rail is fully welded to the 1.2 mm (0.047") bottom sheet and the side cladding so there are no free flanges or edges that can be caught when handling.

Foam-in-Press Sandwich The sides and roof are also of sandwich construction, but here the insulation is foamed during panel manufacture using R-141b as a blowing agent. The sandwich has high-grade stainless steel cladding on the outside of the container and aluminum cladding on the interior, without joints or rivets or other fasteners. There are no side sheet stiffeners or spacers. Thermal bridges are thus eliminated.

Both the stainless steel exterior and the aluminum interior are fully welded so there can be no water penetration into the insulation foam through joints. The metal cladding prevents diffusion of the cell gas from the foam insulation. Therefore, the insulation properties of the foam can be expected to last the 15-year container lifetime, says Bjarne Kolbo Nielsen, director of sales and marketing at Maersk Container Industri.

The MCI design eliminates thermal bridges and contact between the inner aluminum cladding and the stainless steel exterior cladding. A high-density PUR foam separates the different metals and provides good support at the rear frame of the doors. This PUR foam separation avoids any galvanic connection between the aluminum and steel, and also provides mechanical flexibility between inside and outside skins to absorb thermal expansion.

Rear doors are also of sandwich construction. Here the exterior door plate is 4 mm (0.1575") galvanized steel, the interior lining is high-grade stainless steel, and the core material is polyurethane foam. The door gasket is a single frame of extruded EPDM.

The MCI design is the lightest steel refrigerated container on the market, says Nielsen. The MCI 40-ft high-cube container with a standard picture-frame refrigeration unit installed has a tare weight of 4200 kg (9,250 lb). He says it's also the most air-tight and the most robust reefer container with the best mechanical strength.

Automated Manufacture Manufacturing the MCI insulated container is pretty much a hands-off operation. Robots do most of the work. The process starts with welding sheets of stainless steel together. A robot arm picks up individual stainless steel sheets from a stack and feeds them into the automatic seam welder. The output from the seam-welder is a dimensionally accurate side sheet for one sidewall of a 40-ft container. Another seam welder does the same for the aluminum interior lining, then welding the complete 40-ft sheet to the extruded aluminum scuffband at the bottom of the sidewall and the extruded cove rail at the top.

The complete exterior sidewall skin is transferred to the foaming press, where liquid polyurethane is mixed and distributed over the whole length of the sheet, by automatic machine, of course. The inner lining is mechanically placed on top of the liquid foam, which then expands under heat and pressure to form the core of the sandwich. Thus, the complete sidewall is foamed inside a dimensionally stable mold, guaranteeing precision accuracy of the sidewall.

The container roof is foamed in a similar manner. The stainless steel roof sheet is first formed with lateral corrugations to provide more strength against bending or sagging. The sidewalls and roof foam are blown with R-141b HCFC.

Block Foam in Floor The floor assembly is insulated in a different way. The 1.2 mm (0.047") steel bottom sheets are seam welded, and then welded to the 4 mm (0.1575") bottom rail angle. Blocks of Dow's extruded polystyrene foam are picked up individually by a robot arm and placed on this metal pan with adhesive in a prescribed pattern that assures a high-strength bonded floor. The seam welded T-section floor is bonded to the top of the foam, completing the sandwich. Around the metal-framed gooseneck tunnel, the floor is insulated with pour-in-place polyurethane foam.

Box Assembly The completely insulated floor assembly, two sidewalls, and roof panel are clamped in an assembly fixture with the two steel endframes that have been fabricated in another Maersk plant across the Baltic Sea 600 miles east of Denmark in the Republic of Estonia.

With the whole box clamped tightly in the assembly fixture, human welders perform one of the few manual operations in the highly automated plant: They tack weld the box together. It is then transferred to another rotating fixture where seam-welding robots complete the welds.

On the outside, the stainless steel sidewall cladding is welded to the bottom rail and the roof rail, as well as to the end frames. Inside, the aluminum ceiling lining is welded to the cove rail at the top. At the bottom the scuffband extrusion is welded to the aluminum floor. In areas where the welding is already backed up with polyurethane foam, the hollow aluminum extrusion has an air pocket as insulation to prevent burning the foam. For example, the joint between the roof and the sidewall is already completely foamed. After the box is assembled, only the void in the joint at the base of the sidewall and floor assembly needs to be foamed.

Painted Stainless Steel After assembly welding is completed, the corner voids are foamed and the grit-blasted steel end frames are galvanized by a hot zinc spray. In the paint booth, these galvanized end frames are primed, along with the stainless steel sidewalls and roof followed by an eight-minute flash-off, then top-coated wet-on-wet. The Maersk blue seal and black logo in three-ft-high letters are both painted on by a robot arm without masking. The paint is then baked at 65C (150F).

After cooling, the rear doors are mounted and the picture-frame refrigeration unit installed as the front wall. Applying decals is another job that robots have not mastered yet, but the position of each decal is indicated by laser beams. The completed containers are then moved outside the plant for certification of the refrigeration equipment. Every 100th container gets a more rigorous thermal check inside a test chamber.

This reefer container plant runs three shifts a day, five days a week. Its output fills three trains a day, for transfer to the port of rhus, Denmark, 100 miles to the north, or the port of Hamburg, Germany, 100 miles to the south. At the end of the year 2000, more than 30,000 of these MCI-produced refrigerated containers were in operation.

Maersk Factory in China Acquisition of the modern Jindo reefer container plant in Qingdao, China, gives Maersk Container Industri a lot more capacity and much more flexibility. While the highly automated MCI home plant in Denmark produces a single model, the 40-ft ISO refrigerated container in stainless steel, the new plant in China produces several models, including lengths of 20-ft and 45-ft.

The Qingdao plant produces refrigerated containers of aluminum, steel, muffler-grade stainless steel, or high-grade stainless steel, in standard and high-cube heights, and with the normal reefer T-floor or with a flat aluminum floor. With this number of models and options, it gives up some of the capability for automation that is possible with a more standardized product. The Qingdao factory employs about 1,000, compared to the 500 employees in the Tinglev plant.

The outstanding development of the Qingdao factory is the 45-ft refrigerated Euro container that meets all European road regulations. The standard 45-ft container, designed in the US to make marine containers more cube competitive with truck trailers, has been a legal problem in Europe. The front corners stick out too far beyond the maximum 2040 mm (80") swing radius from the kingpin. Because of the size discrepancy, some countries have banned 45-ft containers from the highways, limiting their travel to the port area. Other countries have limited their highway travel to a specified number of kilometers from the port.

Euro-Legal 45-ft Box The MCI 45-ft Euro container avoids all this enforcement hassle by simply complying. It complies with all European Union regulations for transport equipment. It complies with all ISO standards for strength and size. It offers full intermodality between road, rail, and sea transport. It can be handled by all existing multifunctional lifting and transport equipment for containers and swap bodies. Yet it offers the same capacity as other 45-ft containers - 32 Euro pallets or 26 ISO pallets.

The 45-ft Euro container does all this by the simple expedient of chamfering the front corner posts and the front corner castings. Equipped with the standard all-electric picture-frame refrigeration unit, it meets both the maximum length regulations and the front swing radius requirements. However, when equipped with the optional diesel-electric truck trailer refrigeration unit, there is a small front end bulge extending 45 mm (1 3/4") beyond the maximum front end swing radius.

Inside length with either reefer unit is 13,100 mm (43'). Minimum inside width is 2,435 mm (96"). Exterior width can be either 2,556 mm (100.6") or 2,600 mm (102.36"). Exterior height can be either 2,896 mm (9'6") or 2,770 mm (9'1").

Seven-High Stacking The Euro container has dual end frames at both the 40' and 45' position. Lifting spreaders can use either the 40' or 45' corner castings. For stacking, the 40' frames have a three-high stacking limit, while the 45' frames have a seven-high stacking capability. Manufactured with muffler-grade stainless steel cladding on the outside and high-grade stainless steel liners on the inside, the high cube model (9'6" high) has a tare weight of 6,000 kg (13,230 lb) with an electric refrigeration unit installed. Substituting the optional diesel-electric truck trailer unit would add 800 kg (1,765 lb).

The standard 45-ft Euro container has end frames of CorTen steel that is further protected by hot spray zinc galvanizing. Substituting high tensile Domex steel end frames would reduce the tare weight by 700 kg (1,545 lb). The standard floor is flat aluminum (upside-down T-bar) with a flat aluminum plate welded to it for scuffband. The option of turning the T-bar floor over for better air circulation is without weight penalty. Another option is an aluminum exterior skin instead of the MGSS.

Foam-in-Place Sidewalls The MCI Qingdao plant uses a combination method in which only the floor and roof are constructed as sandwich panels. The container is then assembled and the entire sidewall is then foamed in place. The expanding foam effectively fills the entire sidewall, leaving no voids at the top and bottom of the sidewall.

The 45-ft Euro reefer was developed after a request by the Norfolk Line, one of the Maersk Group of companies. This intermodal operator uses 45-ft Euro containers in its service between Ireland, the UK, and the Continent. It also serves Scandinavia and the UK, and it has its own trains connecting Scandinavia and Italy.

Maersk Lines and Sea-Land Service also use 45-ft containers. These wider and longer containers must be carried on deck. The benefits of reduced transport costs and providing a cube-competitive refrigerated container outweigh the nuisance of special handling for the larger container that won't fit into the below-deck cells.

The 45-ft refrigerated container is a more efficient transport method that could lower transportation costs, says Nielsen. The larger box can help reduce traffic density. However, to succeed, it must have better access to the whole intermodal transport sector. This means an expanded rail capacity with the capability to haul the more efficient size inland, in addition to the highway network.

The world market for temperature controlled intermodal transport is still growing, Nielsen says. The total reefer container fleet was about 300,000 TEU (twenty-foot equivalent units) in 1990. Today the fleet is two-and-a-half times larger, at about 800,000 TEU. It will continue to grow for the next several years at a rate of about 50,000 TEU each year, he believes.

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