EP2794428A1

EP2794428A1 - Transport container and floor thereof

Info

Publication number: EP2794428A1
Application number: EP12858888.6A
Authority: EP
Inventors: Ilpo Maaranen; Jukka SILTANEN; Ville-Matti NURMELA
Original assignee: Rautaruukki Oyj
Current assignee: Rautaruukki Oyj
Priority date: 2011-12-23
Filing date: 2012-12-20
Publication date: 2014-10-29
Also published as: EP2794428A4; WO2013093206A1; CN103171835A; FI20116324A

Abstract

The present invention relates to a floor structure (2) for transport container (1)and to a transport container. The floor structure (2) comprises a first surface layer (8) forming a floor surface and a support arrangement (10, 11, 24) for supporting the first surface layer (8). The invention is based on the idea of omitting the plywoodboards and using a hardened martensitic steel sheet for forming the floor surface of the floor structure (2) of the transport container(1). According to the present invention the first surface layer (8) is formed from hardened martensitic steel sheet.Anadvantage of the present invention is that when the floor structure (2) of the container is formed from hardened martensitic steel sheet, the floor structure (2) of the container has very good stiffness and good impact resistance characteristics together with excellent abrasion resistance.

Description

TRANSPORT CONTAINER AND FLOOR THEREOF

FIELD OF THE INVENTION

The present invention relates to a floor structure for transport container and more particularly to a floor structure according to the preamble of claim 1 . The present invention further relates to a transport container and more particularly to a transport container according the preamble of claim 18.

BACKGROUND OF THE INVENTION

Transport containers, and so called general transport containers or dry transport containers, are used for transporting different kinds of cargo. The transport containers conventionally comprise a support frame and floor structure, wall structure and roof structure attached and supported to the support frame. The floor structure usually comprises separate support beams attached to the support frame and such that they extend in the transversal direction in relation to the longitudinal direction of the floor structure. The support frame is usually provided from tubular elements and the support beams from I-beams or the like. A floor surface is provided by one or more thick plywood boards installed on the support beams. The plywood boards are thick enough such that they stiffen the floor structure and carry the load caused by operations performed on it. From the underside the floor structure is typically open such that the support beams are exposed.

The problem with the prior art transport containers and especially floor structures thereof is that the lifetime of the plywood boards is limited. Worn or otherwise damaged surface sheets may even lead to accidents during loading the container. Thus the plywood boards have to be regularly replaced. Replacing the plywood boards decreases the effective operating time and increases maintenance time. Furthermore, the used plywood is hazardous waste and which has to be specially treated. Another problem with plywood is that the boards have to be thick, for example in some applications boards with 28 mm thickness are used, for reaching adequate stiffness and impact strength. Furthermore, the availability of plywood is limited. However, the advantage of the plywood boards is their lightness. BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is therefore to provide a floor structure for a transport container and a transport container so as to solve or at least alleviate the above mentioned problems. The objects of the present in- vention are achieved by a floor structure for a container which is characterized in that the first surface layer is formed from hardened martensitic steel sheet, as defined the characterizing portion of claim 1 . The objects of the present invention are further achieved by a transport container provided with a floor structure comprising a first surface layer formed from hardened martensitic steel sheet, as defined in the characterising portion of claim 18.

The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea of omitting the plywood boards and using a hardened martensitic steel sheet for forming the floor surface of the floor structure of the transport container. The martensitic steel sheet may be hardened by conventional post hardening method in which the steel is first heated in a hardening oven to hardening temperature and then rapidly cooled down, ie. quenched for hardening the steel. The martensitic steel sheet may also be direct hardened steel, i.e. direct quenched steel, meaning that the steel is hardened directly in the hot-rolling production process immediately after the final hot-rolling pass and before the steel strip is coiled. This way a thin hardened martensitic steel sheet with very good flatness, and impact strength properties is achieved, this kind of steel sheet being especially suitable for floor structures of transport containers. In addition, such a martensitic steel has ex- tremely high hardness and strength. High hardness and strength give high resistance to abrasion and loadings.

An advantage of the present invention is that when the first surface layer of containers floor structure is formed from hardened martensitic steel sheet, the floor structure of the container has very good stiffness and good im- pact resistance characteristics together with excellent abrasion resistance. Due to the above mentioned viewpoints the required maintenance of the work of the containers is decreased as there is no need for regularly replacing the hardened steel sheet. Additionally the steel is fully recyclable material and produces no hazardous waste material after use. The hardened martensitic steel sheet may be less than 6 mm thick for reaching the required stiffness and impact strength of the floor structure of the transportation container. Furthermore, this kind of steel sheet or plate combined with the floor structure according to the present invention provides a very light weight and flat base for the container.

Therefore, the present invention may provide increased cargo space which has considerably transportation and cost advantages. The considerable effect of the present invention is that the above mentioned advantages are achieved without substantially increasing the weight of the container and the floor structure thereof due to the decreased thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figure 1 is shows schematically a transport container;

Figures 2A and 2B show schematically the structure of the transport container of figure 1 ;

Figures 3A and 3B show schematically one embodiment of the floor structure of the present invention;

Figure 4 shows schematically an alternative embodiment of the floor structure of the present invention; and

Figure 5 shows schematically yet another alternative embodiment of the floor structure of the present invention.

LIST OF THE REFERENCE NUMBERS

Transport container 1

Floor structure 2

Floor frame 3

Roof structure 4

Support frame 5

Wall structure 6

Floor frame 7

First surface layer 8

Connection piece 9

Profile beam 10 I-beam 1 1

Laser weld 12

Laser weld 13

Top surface layer 14

Web 15

Ridge section 16

First flange 17

Second flange 19

Web section 18

Flange section 20

Second surface layer 21

Weld 23

Profile beam 24

Ridge section 25

Web section 26

Fillet or corner weld 27

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 is shows schematically a general transport container 1 for transporting dry cargo. The transport container 1 is substantially rectangular and comprises a wall structure 6, roof structure 4 and floor structure 2. The container 1 further comprises a support frame 5 to which the wall, roof and floor structures are supported. The container 1 is further provided with a loading door (not shown) at the shorter vertical side, i.e. at the end of the container. The wall and roof structures 6, 4 are usually formed from profiled sheets of steel, which may be coated with zinc and/or paint or some other coating material.

Figure 2A shows the transport container 1 from one end thereof. As may be seen the support frame 5 forms a substantially rectangular cargo space together with the roof, wall and floor structures 4, 6, 2. The floor structure 2 comprises a first surface layer 8 forming the floor surface of the cargo space of the container 1 . Figure 2B shows the floor structure 2 of the transport container 1 from above. The floor structure 2 comprises a first surface layer 8 forming a floor surface and a support arrangement for supporting the first sur- face layer 8. The support arrangement comprises the elements arranged to support the first surface layer 8.The support arrangement comprises a floor frame 7, 3 which may be part of the support frame 5 of the transport container 1 . The support arrangement further comprises separate beams 10, provided on the underside of the first surface layer 8 and shown with dotted lines figure 2B. The separate beams 10 may be attached to the underside of the first surface layer (8) adjacent and/ or in parallel direction to each other. The beams 10, are attached to the floor frame 3 from their ends and further to the first surface layer 8. The floor frame 7 surrounds the beams 10 in lateral direction. The floor frame 3, 7 may be formed from tubular elements which are joined togeth- er by connection pieces 9. Alternatively the load-bearing floor frame 3, 7 may be formed from profile beams such as, U-beam or the like. Profile beam means a beam that is produced by profiling the shape of the beam, i.e. not produced by welding. The floor frame 3, 7 may also be formed from I-beams or other welded beams. The wall structure 6 may be supported to the upper surface of the floor frame 3, 7.

Figure 3A shows one embodiment of the present invention in which the floor structure 2 comprises a first surface layer 8, separate profile beams 10 and a second surface layer 21 . As shown in figure 3A the floor structure 2 forms honeycomb structure in which the support arrangement or the profile beams 10 forms the core elements of the honeycomb between the first and second surface layers 8, 21 . Especially the above mentioned solution having first surface sheet formed from thin hardened martensitic steel sheet is a flat, light-weight and very rigid structure for the base of the transportation container 1 .

Referring to the figure 3A, the first surface layer 8 forms the floor surface of the cargo space and the second surface layer 21 forms the bottom surface of the floor structure. The profile beams 10 are attached to the first and second surface layer 8, 21 by welding, laser welding or mechanically or by fusion. In figure 3A the separate profile beams 10 are delta-beams having a ridge section 16, web section 18 and flange sections 20. The ridge section 16 is attached by laser welds 13 to the second surface layer 21 and the flange sections 20 are attached to the first surface layer 8 by laser welds 12. In an alternative embodiment the profile beams have Z-, U- or V-profile or some other profile.

The profile beams 10 mean beams which are produced by profiling, forming or bending steel material, such as steel sheet or steel plate into a form of beams. Thus the profile beams 10 are beams 10 which are not produced by welding separate parts together. The profile beams 10 are manufactured from steel thin sheet, and specifically they may be manufactured from high strength steel that may be galvanized or weathering steel. The profile beams 10, 24 may have material thickness in the range 0,5 to 3 mm, preferably in the range 1 to 2 mm. High strength steel means that steel includes yield strength more than 400MPa, more preferably more than 500MPa.

According to the present invention the first surface layer 8 is formed from hardened martensitic steel sheet. The first surface layer 8 may be manu- factured from post hardened martensitic steel or from direct hardened martensitic steel. However, the post hardening may have some drawback relating to produce a thin enough steel sheet having excellent flatness. Thus the steel sheet provided by post hardening may not provide fully straight and thin floor 2 surface. Therefore the martensitic steel sheet of the first surface layer 8 is preferably direct hardened for providing a thin and smooth floor surface with excellent impact strength. The post hardening furthermore may enable only limited size sheets to be hardened due to the limited size of the hardening oven. Thus the floor may have to be formed from several separate post hardened steel sheets, especially in the longitudinal direction of the container. According to one embodiment of the present invention the microstructure of the steel sheet that is formed from hardened martensitic comprises, in terms of volume percentages, at least 70% martensitic phases, preferably at least 80% martensitic phases and more preferably at least 90% martensitic phases. The residual main phases may include ferrite, perlite, residual austenite and/or bainite, for instance.

It should be noted that the first surface layer 8 may be made from fully martensitic steel or martensitic-bainitic steel. Therefore it should be understood that the term martensitic includes also martensitic-bainitic steel.

According to one embodiment, a tempering heat-treatment is per- formed for martensitic steel after hardening and also before forming the floor structure 2. This means that steel sheet is hardened and tempered and thereby including tempering-martensitic microstructure. Therefore it should be understood that the term martensitic includes also tempering-martensitic steel.

It is however advantageous that the hardness of the martensitic steel in first surface layer 8 is at least 270 HBW, preferably at least 360 HBW and most preferably at least 420 HBW. The hardness is measured in Brinell units (HBW) in compliance with EN ISO 6506-1 on a milled surface 0.3-2 mm below sheet surface.

First surface layer 8 made of martensitic steel may also include yield strength at least 900MPa which provides excellent resistant against plastical failures for example locally in the surface sheet between the beams.

Preferably the first surface sheet 8 made from hardened martensitic steel sheet is covering the whole floor 2 of the container structure 1 .

The thickness of the first surface layer 8 may be less than 6 mm or less than 5 mm, or even in the range 1 to 4 mm such as in the range 1 ,5 to 3 mm. Even low thickness of martensitic steel sheet can contribute in achieving the necessary stiffness and impact strength for the floor structure 2. The first surface layer 8 may be formed from steel plates or alternatively and even more preferably from steel strip. Therefore said steel sheet can be also considered as steel plate or cut to length steel strip.

As shown in figure 3A the floor structure 2 may further comprise a second surface layer 21 for closing the floor structure 2 and providing the honeycomb structure. The second surface layer 21 may be formed from weathering steel sheet or hardened weathering steel sheet. The thickness of the second surface layer 21 may be less than 6 mm, or less than 5 mm preferably in the range 1 to 4 mm, most preferably in the range 1 ,5 to 3 mm.

Figure 3B shows an alternative embodiment in which a further top surface layer 14 is arranged on the first surface layer 8 for forming the top floor surface. This top surface layer 14 is for example provided by a thin plywood board or some other corresponding material.

However, it may be desired to omit the second surface sheet 21 for providing lighter weight base and avoiding or reducing number of closed shells in which the humidity may cause corrosion related problems. Figure 4 shows yet an alternative embodiment of the present invention in which there is no second surface layer 21 and the bottom structure 2 is open from the underside. In this embodiment the support beams 1 1 are formed from I-beams 1 1 having a first flange 17, web 15 and second flange 19. The I-beams 1 1 are attached to the first surface layer 8 by welds 23. The I-beams 1 1 may be replaced by other beams 10, 24 such as U-beams or the like and they may be attached also by laser welds, mechanically or by fusion to the first surface layer 8. The beams 1 1 may be manufactured from high strength steel that may be galvanized or weathering steel. Additionally the beams 1 1 may be coated with paint. High strength steel means that steel includes yield strength more than 400MPa, more preferably more than 500MPa and even more than 700MPa.

According to preferred embodiment, the profile beams 10 made of high strength steel are attached, by welding for instance, only to the first sur- face layer 8 made of hardened martensitic steel sheet and there is no second surface layer 21 whereby the floor structure 2 is open from the underside. It is most desired that in this embodiment, the separate profile beams 10 are delta-beams having a ridge section 16, web section 18 and flange sections 20. The flange sections 20 are attached to the first surface layer 8 and the ridge sections are forming the bearing surface to be against the ground during use of the container.

Figure 5 shows an alternative embodiment of the present invention in which the floor structure comprises a first surface layer 8 and separate profile beams 24. The first surface layer 8 forms the floor surface of the cargo space and the floor structure 2 is open from the under underside such that the support arrangement, or the profile beams 24 are exposed and may be subjected to environmental conditions. The profile beams 24 are attached to the first layer by welding, and especially with fillet or corner welds 27, as shown in figure 5. Corner or fillet welds 27 may be formed by laser welding, for instance. In figure 5 the separate profile beams 24 are V-beams having a ridge section 25 and web sections 26. The web sections 26 are attached with the corner welds 27 to the first surface layer 8 and the ridge sections 25 are forming the bearing surface to be against the ground during use of the container.

The profile beams 24 may be manufactured from steel thin sheet, and specifically they may be manufactured from high strength steel that may be galvanized or weathering steel. The profile beams 24 may have material thickness in the range 0,5 to 3 mm, preferably in the range 1 to 2 mm. High strength steel means that steel includes yield strength more than 400MPa, more preferably more than 500MPa.

It should be noted that the floor structure 2 may also comprise one or more separate second surface layers 21 for forming one or more separate honeycomb sections to the floor structure 2. This means that the floor structure 2 does not have to be closed but it may be only partially closed. In other words, bottom structure may be completely or partially open from the underside.

In one embodiment the floor structure 2 may be divided to two sections, the first section comprises a gooseneck for connecting to a transport ve- hide and has a structure open from the underside as shown for example in figure 4, and the second section has a structure closed form the underside as shown for example in figures 3A or 3B. However the first surface layer 8 may be continuous over the both first and second sections.

In one possible embodiment the first surface layer 8 may be a low honeycomb element in which the upper sheet is the hardened martensitic steel sheet as discussed above. The height of the honeycomb element may be for example 10 to 30 mm. In a yet alternative embodiment of the present invention the hardened martensitic steel sheet may be provided on top of an existing plywood board for forming a steel surface for the cargo space.

According to the above mentioned the present invention also provides use of hardened martensitic or martensitic-bainitic steel sheet for forming the floor 2 of a transport container 1 , or use of direct hardened martensitic or martensitic-bainitic steel sheet for forming the floor 2 of a transport container 1 . This provides the technical benefits discussed above.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A floor structure (2) for transport container (1), the floor structure (2) comprising:

- a first surface layer (8) forming a floor surface; and

- a support arrangement (10, 11, 24) for supporting the first surface layer (8),

characterized in that the first surface layer (8) is formed from hardened martensitic steel sheet.

2. A floor structure (2) according to claim 1, characterized in that first surface (8) layer is formed from direct hardened martensitic steel sheet.

3. A floor structure (2) according to claim 1 or 2, characterize d in that the first surface layer (8) is formed from fully martensitic steel or martensitic-bainitic or tempering-martensitic steel.

4. A floor structure (2) according to any of claim 1 to 3, c h a r a c - t e r i z e d in that the first surface layer (8) is

a. ) having Brinell hardness at least 270 HBW, or

b. ) include yield strength at least 900MPa

5. A floor structure (2) according to any one of claims 1 to 4, characterized in that thickness of the first surface layer (8) is less than

6 mm.

6. A floor structure (2) according to any one of claims 1 to 5, characterized in that the support arrangement comprises separate beams (10, 11, 24) or profile beams (24) attached to the underside of the first surface layer (8) adjacent and/or in parallel direction to each other.

7. A floor structure (2) according to the claim 6, characterized in that beams (10, 11, 24) or profile beams (10, 24) have I-, Z-, U- V- or delta-profile.

8. A floor structure (2) according to the claim 6 or 7, character i z e d in that the profile beams (10) have material thickness in the range 0,5 to 3 mm, preferably in the range 1 to 2 mm.

9. A floor structure (2) according to any one of claims 6 to 8, characterized in that beams (11 ) or profile beams (10, 24) are formed from high strength steel, having yield strength more than 400MPa, and that beams (11) or profile beams (10, 24) may optionally be made of galvanized or weathering steel.

10. A floor structure (2) according to any one of claims 1 to 9, characterized in that the floor structure (2) further comprises a second surface layer (21 ) attached to the support arrangement (10, 11, 24) for forming a honeycomb in which the support arrangement (10, 11) forms the core of the honeycomb between the first and second surface layers (8, 21).

11. A floor structure (2) according to claim 10, characterized in that the floor structure (2) comprises one or more separate second surface layers (21) for forming one or more separate honeycomb sections to the floor structure (2).

12. A floor structure (2) according to claim 10 or 11, characterized in that the second surface layer (21) is formed from weathering steel sheet or hardened weathering steel sheet.

13. A floor structure (2) according to any one of claims 10 to 12, characterized in that the thickness of the second surface layer (21 ) is less than 6 mm, preferably 1 to 4 mm.

14. A floor structure (2) according to any one of claims 1 to 9, characterized in that the floor structure (2) is open from the under underside such that the support arrangement (10, 11, 24) is exposed or that ridge sections (25) of profile beams (10, 24) are forming the bearing surface to be against the ground during use of the container.

15. A floor structure (2) according to any one of claims 1 to 14, characterized in that the support arrangement (10, 11, 24) is attached to the first surface layer (8) or first and second surface layer (8, 21) by welds, laser welds, mechanical fasteners or they are fused together.

16. A floor structure (2) according to any one of claims 1 to 15, characterized in that the floor structure (2) comprises a plywood board (14) provided on the first surface layer (8).

17. A floor structure (2) according to any one of claims 1 to 16, characterized in that support arrangement comprises a floor frame (3,7) surrounding the beams (10, 11 ,24) or profile beams (10, 24) in lateral direction, the ends of the beams (10, 11, 24) or profile beams (10, 24) being attached to the load-bearing frame (3).

18. A transport container (1) comprising a floor structure (2), a roof structure (4), a wall structure (6) and a support frame (5) for defining a cargo space, the floor structure (2) comprising:

- a first surface layer (8) forming the floor surface of the transport container (1); and

- a support arrangement (10, 11, 24) for supporting the first surface layer (8) to the support frame (3),

characterized in that the first surface (8) layer is formed from hardened martensitic steel sheet.

19. A transport container according to the claim 18, characterize d in that first surface (8) layer is formed from direct hardened martensitic steel sheet.

20. A transport container according to the claim 18 or 19, c h a r- acterized in that the first surface layer (8) is formed from fully martensitic steel or martensitic-bainitic or tempering-martensitc steel.

21. The transport container according to the claim 18 or 20, characterized in that the first surface layer (8) is a. ) having Brinell hardness at least 270 HBW, or b. ) include yield strength at least 900MPa

22. A transport container according to any one of claims 18 to 21, characterized in that thickness of the first surface layer (8) is less than 6 mm.

23. A transport container according to any one of claims 18 to 22, characterized in that the floor structure (2) is a floor structure accord- ing to the any one claims 1 to 17.

24. Use of hardened martensitic or martensitic-bainitic or tempering martensitic steel sheet for forming the floor of a transport container.

25. Use of direct hardened martensitic or martensitic-bainitic or tempering-martensitic steel sheet for forming the floor of a transport container.