Patent Application
20120298657
The present invention relates to freight containers. The invention particularly relates to the impact resistance of freight containers, particular to impacts from handling equipment.
To enable efficient supply chain systems to be implemented, freight containers are preferably of a standard size, such as freight containers conforming to the ISO standards for containers. An ISO (International Standards Organization) container is a freight or shipping container that complies with one or more relevant ISO container standards, such as the ISO 1496 series.
Types of freight containers may vary according to their application, but include nominal 20 and 40 foot ISO containers and 10, 25, 30 and 45 foot containers and SWAP bodies for conveyance of goods by road, rail and/or sea. The containers of the present invention include general purpose, thermal (e.g. insulated, refrigerated, heated) or bulk containers as described in the ISO 1496 series, but also include non ISO containers and SWAP bodies.
The ISO container standards provide minimum structural properties relating to the strength of the walls, roof and floor. Rigidity and weatherproofing standards are also set. The standards ensure that the containers are suitable for purpose as freight, shipping or cargo containers.
Heretofore, freight or shipping containers generally have used a metal framework with composition board (usually steel or aluminium sheathed) or other composite material panels attached to the framework by bolts, rivets or welding. Corner fittings are then attached, in accordance with ISO standards, to each corner of the shipping container. The corner fittings are used to secure cables and other components to the shipping containers during loading, unloading and handling of the containers, as well as to secure the containers to one another and to the transport vehicle.
Due to the tremendous loads routinely placed on the corner fittings, these components sustain a significant amount of wear and tear damage. Use of damaged and/or worn ISO corner fittings presents a safety risk that can have disastrous consequences. For example, in applications that require the shipping container to be lifted or hoisted in the air, a damaged and/or worn corner fitting can result in the container being dropped. Handling equipment, such as attachment hooks, top loaders, spreaders may also impact against areas adjacent to the corner fitting, thereby damaging the roof and/or walls.
Therefore, it is absolutely vital that maintenance be performed regularly and frequently on the corner fittings (or other attachment points) and surrounding area to repair or replace damaged and/or worn fittings and panels. Regular maintenance and repair helps keep the corner fittings and surrounding area in good operating condition and can extend the service life of the much more expensive and harder to replace shipping containers.
The abovementioned problem has been addressed in U.S. Pat. No. 7,059,488 in which removable corners are fitted to a composite material shipping container. The removability of the corner fitting enables efficient maintenance and repairs, thus saving time, effort and costs. However, panels, particularly those immediately adjacent to the corner fittings or forklift attachment points are still prone to damage. This necessitates time consuming repairs involving welding operations to ensure that the structural integrity; the weatherproof nature; and the security of the container are maintained.
For composite containers added protection in the form of aluminum or impact resistant plates placed on the roof adjacent to each of the ISO corner fittings, as suggested in U.S. Pat. No. 7,334,697, addresses this problem. For the currently applied steel containers, a thick steel plate or bar is in practice placed on the roof in the surrounding of each of the attachment points. However, the use of impact resistant plates to protect the immediate roof area around the corning fitting through deflecting the impact, often merely transfers the impact to an adjacent region of the impact resistant plate. Further, as the impact resistant plates may not extend more than 750 mm from either end of the container to conform to the requirements of ISO 1496-1, protection does not extend to areas affected by deflected impacts and/or impacts from wayward crane operators.
Therefore, further improvements to the impact resistance of containers are still required. In particular, increasing the resistance of freight containers against impact put on the container via an attachment point or on a region surrounding the attachment point.
The solution to this problem is addressed in the present invention in which a first aspect provides a freight container comprising:
a frame; a roof, a floor and walls,
an attachment point for a lifting device to attach to the container; and
at least a wall, roof or floor comprising:
(a) an impact resistant portion proximal to the attachment point; and
(b) a portion, distal from the attachment point (distal portion);
wherein the modulus of elasticity of the distal portion is at least 20% greater than the modulus of elasticity of the impact resistant portion.
The terms “impact resistant portion” and “proximal portion” may be interchangeable used.
As used herein, an attachment point for a lifting device includes fittings containing the attachment means (e.g. apertures to receive a hook from a handling device) and also includes fork pockets (for use in lifting the container with forklift trucks). In particular, an attachment point refers to a fitting containing attachment means (e.g. apertures to receive a hook from a handling device).
Preferably, the container passes the tests described in section 6 of ISO 1496-1 (fifth edition) and/or tests described in section 8 of ISO 1496-2 (fifth edition). All dimensions of the container and panels therein are typical of those used in freight containers and preferably also comply with ISO requirements.
In a preferred embodiment, the freight container comprises a frame to which the walls, roof and floor are attached by means of for example bolts, rivets or welding.
Preferably, the attachment point is a fitting attached to the roof or to the frame on the roof side. More preferably, the attachment point is a fitting attached to the frame on the roof side.
The combination of an impact resistant portion or zone that at least partially absorb the impact energy and an energy dissipating portion or zone (i.e. distal portion) adjoining the impact zone enables the roof, floor or wall containing such an impact resistant and distal portion to more effectively absorb and dissipate impacts during handling. Surprisingly, considering conventional techniques (rigid impact resistant plates), this has been achieved through making the portion of the wall, roof or floor proximal to the attachment points more flexible (lower modulus of elasticity) relative to a portion distal therefrom.
For convenience, the term “modulus” will refer to the modulus of elasticity (E-modulus in bending), unless otherwise stated.
Preferably, the modulus of elasticity of the distal portion is at least 30%, more preferably at least 40%, even more preferably at least 50%, even more preferably at least 100%, even more preferably at least 200%, even more preferably at least 300%, even more preferably at least 500%, even more preferably at least 700% and most preferably at least 900% greater than the modulus of elasticity of the impact resistant portion. As used herein, the modulus of elasticity refers to E-modulus in bending. Depending on the material and construction of the portion, the person skilled in the art will know to choose the applicable norm for measuring the modulus of elasticity. For example, for a sandwich construction the modulus of elasticity is measured according to ASTM D7249; for an unidirectional fibre-reinforced composite monolayer the modulus of elasticity is measured according to ISO 527; for a polyurethane rubber monolayer the modulus of elasticity is measured according to ASTM D412.
The impact resistant portion is required to have the sufficient mechanical properties to withstand impact from attachment forks or hooks which in some cases weigh around 1500 kg. This weight may be drop, fall or swing onto the portion or region immediately surrounding the attachment point, with a contact area of for example about 1000 mm2 (0.001 m2). Thus, the impact energy that this region must absorb or dissipate, if the hook falls from a height of just 0.1 meter, is approximately 1.5 kJ (1500 kg (mass)×9.81 m/s2 (gravitation acceleration)×height (0.1 m)).
Preferably, the impact energy resistance of the impact resistant portion is at least 0.2 kJ, more preferably at least 0.5 kJ, even more preferably at least 1.0 kJ, yet even more preferably at least 2.0, yet still more preferably at least 5 kJ and most preferably at least 10 kJ. The dimensions and material of the impact resistant portion are chosen such that the impact resistant portion has an impact energy resistance of preferably at least 0.2 kJ, more preferably at least 0.5 kJ, even more preferably at least 1.0 kJ yet even more preferably at least 2.0, yet still more preferably at least 5 kJ and most preferably at least 10 kJ. The impact energy resistance of the impact resistant portion and of the distal portion is measured with the charpy impact test according to ISO179-1. The impact resistant portion has an impact energy resistance of for example at least 0.7 kJ in case the impact resistant portion is able to receive an impact energy of at least 0.7 kJ put on the container via the attachment point or on a region surrounding the attachment point with a contact area of about 1000 mm2 without resulting in that the impact resistant portion either shows permanent deformation or abnormality which will render it unsuitable for use.
The impact energy resistant test performed on the container preferably uses an attachment hook, attachment fork (i.e. from fork lift), spherical or hemispherical object (e.g. steel ball or dart) having a minimum contact radius of about 5 mm and a minimum weight of about 5 kg. Suitable impact testing equipments includes the Instron® range of impact testers including the 9200 and 8100 series (e.g. the 8120 model with a 100 kg impact object). On successful completion of the test, the container should not show either permanent deformation or abnormality which will render it unsuitable for use, consistent with the pass criteria used in ISO 1496-1. The specific energy absorption (SEA) of the impact resistant portion is preferably at least 10 J/kg/m2, more preferably at least 50 J/kg/m2, even more preferably at least 80 J/kg/m2, yet even more preferably at least 100 J/kg/m2 and most preferably at least 120 J/kg/m2. The higher the specific energy absorption, the lighter the impact resistant portion may be for the same impact energy resistance.
To achieve the required impact energy resistance, the impact resistant portion preferably has a modulus of elasticity of at least 1 MPa, more preferably at least 3 MPa, even more preferably at least 5 MPa and most preferably at least 10 MPa. Preferably, the modulus of elasticity is no more than 1000 MPa, more preferably no more than 500 MPa, even more preferably no more than 200 MPa and most preferably no more 100 MPa. Higher modulus values may result in poor dampening efficiency (i.e. increased chance of failure due to brittle fracture), while lower modulus values may not be sufficient to prevent excessive deformation, which may result in damage to the payload.
The ratio of the stored modulus (E′) (or stored elastic energy) to the loss modulus (E″) also known as tan delta (E″/E′) is used to measure the material's damping effectiveness or the material's ability to dissipate energy. The higher tan delta, the greater the material's ability to dissipate energy.
As is known in the art, tan delta may be used to infer the amount of energy dissipated as heat during deformation of a foam and plastic deformation. It is preferred that the impact resistant portion has a tan delta value that does not vary greatly (e.g. <35% variation) over the operating temperature range (e.g. −30 to 70° C.). This is particularly so when the impact resistant portions forms part of a broader energy dispersion system, such as that defined in the present invention.
The ability of a panel of a container to absorb energy through material deformation may be also quantified using the ball rebound test (DIN EN ISO 8307).
Other measures of rigidity include the flexural modulus and rigidity index as described in WO 90/05633 pages 28 to 31 under the relevant headings.
In a special embodiment, the first aspect of the invention is modified (with the other features remaining the same unless otherwise stated) such that it provides a container comprising an impact resistant portion (Pi) which has relatively high energy absorbing properties compared to a distal portion (Pd), as characterized by Pi having a % difference compared to Pd (i.e. (Pi−Pd)/Pi×100) of at least 20%, more preferably at least 30%, even more preferably at least 40%, even more preferably at least 50%, even more preferably at least 100%, even more preferably at least 200%, even more preferably at least 300%, even more preferably at least 500%, even more preferably at least 700% and most preferably at least 900%, of at least one of the following properties:
Ball rebound test (positive % difference)
Tan delta (positive % difference)
Modulus of elasticity (negative % difference);
Flexural modulus (negative % difference); and
Rigidity index (negative % difference);
Preferably, the container has at least two, more preferably at least three, even more preferably at least four and most preferably all of the above properties. Preferably, these improved energy absorbing characteristics are present across the operating temperature range (−30 to 70° C.).
The ability for the impact resistant portion proximal to the attachment point to disperse energy, which has not been already absorbed, is dependant upon the energy dispersive properties of the portion of the panel distal from the attachment point and indeed the whole container. In contrast to the impact resistant portion which preferably dissipates energy through flexing, compressing and other non-permanent elastic deformation, the distal portion preferably dissipates energy through vibration. This is preferably achieved through the distal portion having a higher modulus of elasticity or higher rigidity. The vibration of the distal portion results in energy being dissipated through the movement and optionally through transfer into seals and fasteners where energy is also dissipated through non-permanent material deformation.
The impact resistant portion and the distal portion may form part of the same contiguous panel or they may be separate panels which are connected by a fastening means, such as a clamp, rivet, bolt, glue and/or adhesive. Preferably an adhesive is applied which adhesive preferably has a composition comprising an elastomeric polymer.
In embodiments in which the two functional components (e.g. impact resistant portion and distal portion) are within the same contiguous panel, the two components are preferably connected through thermal fusing or polymer welding techniques.
In a preferred embodiment, the impact resistant portion is an impact resistant panel and the distal portion is a distal panel and the distal panel and impact resistant panel are separate panels.
The impact resistant portion is preferably affixed to the frame by a resilient fastening means, which preferably comprises a spring loaded bolt and/or an adhesive.
The impact resistant portion and distal portion according to the present invention may be present in part or all of the side walls, end wall, front wall (doors), floor wall and/or roof wall of the container. Preferably, the impact resistant portion and distal portion according to the present invention are present in the roof of the container, as this is where most impacts from handling equipment occur. Unless otherwise indicated, reference to the term panel will mean reference to the wall, roof, floor of the container or part thereof.
The impact resistant portion may for example be a monolayer or may be a laminate construction. Preferably, the laminate comprises an outer layer, a core layer and an inner layer (e.g. sandwich construction).
In one embodiment, the impact resistant portion is a monolayer. The desired rigidity of the ultimate panel will greatly influence the choice of material. In the preferred embodiments of the invention, the impact resistant monolayer comprises a low modulus polymer selected from the group consisting of a low density polyethylene; a polyurethane rubber; a flexible epoxy; a filled elastomer vulcanizate; and a thermoplastic elastomer. In a more preferred embodiment of the invention, the impact resistant monolayer portion comprises a polyurethane rubber. In an even more preferred embodiment of the invention, the impact resistant monolayer is made of a polyurethane rubber. The thickness of the monolayer is preferably between 10 and 30 mm.
In another embodiment, the impact resistant portion is a laminate construction. Herein below, preferred embodiments are described for the impact resistant portion in case it is made of a laminate construction. The thickness of the laminate construction is preferably between 20 and 30 mm.
The outer layer is preferably formed from a material sheet having a high tensile strength.
The desired rigidity of the outer layer and/or ultimate panel will greatly influence the choice of material. In the preferred embodiments of the invention, the outer layer of the impact resistant portion comprises a low modulus polymer selected from the group consisting of a low density polyethylene; a polyurethane; a flexible epoxy; a filled elastomer vulcanizate; and a thermoplastic elastomer. The modulus of the outer layer is preferably less than 50 MPa.
In a more preferred embodiment of the invention, the outer layer of the impact resistant portion comprises a polyurethane rubber. In an even more preferred embodiment of the invention, the outer layer of the impact resistant portion is made of a polyurethane rubber.
The outer layer of the impact resistant portion preferably has an elongation to break (determined at 23° C. and 5 mm/min, according to ISO 527) in the range between 2 to 700%, more preferably in the range between 30 to 700% and even more preferably in the range between 500 to 700%.
The core layer preferably comprises a polymeric material that provides a relatively light (in terms of weight) means of providing flexibility to the wall. The polymeric material is preferably a polymeric foam as this provides a low density structural material. Suitable foamed materials include plastic foams, for example polyurethane foam, polyethylene foam, polypropylene foam, a foam of an ethylene—propylene copolymer, phenolic foam, or any other plastic foam known to the person skilled in the art may also be used. Suitable polymeric foams exist as closed cell, syntactic cellular polymer compositions, which in a preferred embodiment have a density of about 20 to 300 kg/m3. The density of the foam may be graduated, with the region immediately adjacent to the attachment point having the highest density.
For the purposes of the present invention foamed materials include materials comprising polymeric or ceramic hollow microballoons or hollow microspheres.
Preferably, the polymeric foam is a closed cell polyethylene foam as such foams have excellent energy dissipating properties. Preferably, the foam has a glass transition temperature (Tg) equal or less than 0° C. with a change in the ratio of the loss modulus to the stored modulus of no more than 50% from the median value measured over the temperature range of from about −20° C. to about 50° C. This ensures that the foam has good impact resistance over its operating range.
Preferably, the Tg is less than −10 and more preferably less than −20° C. The change in tan delta between about −20° C. to about 50° C. is preferably no more than 40% and even more preferably no more than 30%.
The glass transition temperature (Tg) is preferably determined by Dynamic Mechanical Thermal Analysis (DMTA) in accordance with ASTM D4065-93, adapted to measure Tg at the onset of the drop in the elastic modulus.
The inner layer may be of the same construction of the outer material, thereby forming what is commonly referred to as a sandwich panel. The inner layer of the impact resistant portion preferably comprises a polyurethane rubber. In an even more preferred embodiment of the invention, the inner layer of the impact resistant portion is made of a polyurethane rubber.
The distal portion may be made of a metal, for example aluminium, may be made of a metal alloy, preferably steel, more preferably stainless steel or weathering steel (also known as cor-ten steel), but may be also of a laminate construction. Preferably, the laminate comprises an outer layer, a core layer and an inner layer (e.g. sandwich construction). The thickness of the laminate construction is preferably between 20 and 30 mm.
Herein below, preferred embodiments are described for the distal portion in case it is made of a laminate construction.
The outer layer of the distal portion preferably comprises a reinforced composite material. The composite material is preferably reinforced with fiber or yarn. Suitable yarns include aramid fibers, E glass or S-glass fibers, fibers of high tenacity polyester and yarns comprising ultra-high molecular weight polyethylene fibers. These type of yarns or fibers have a good combination of high strength and modulus of elasticity which may them particularly suited to withstanding impacts.
Suitable Yarns are aramid fibers, for example sold under the trade name Kevlar™ and Twaron™. Yarns comprising high tenacity polyester fibers are for example sold under the trade name Vectran™, yarns comprising ultra-high molecular weight polyethylene fibers are for example sold under the trade name Dyneema™ and Spectra™. The fibers or yarn may form part of a woven or non-woven fabric.
The fiber or yarn preferably has a tensile strength of at least 0.5 GPa, more preferably at least 1.2 GPa, even more preferably at least 2.5 GPa and yet even more preferably at least 3.0 GPa.
The fibers or yarn are preferably arranged in a plurality of layers, more preferably in at least 3 layers. Preferably, the adjacent layers having fibers or yarn which are disposed an angle of at least 30°. More preferably, the adjacent layers have fibers or yarn disposed an angle of about 90°. Each layer is preferably embedded into a matrix comprising a thermoplastic or thermosetting resin matrix. As used herein “thermoplastic resins” are resins which can be heated and softened, cooled and hardened a number of times without undergoing a basic alteration, and “thermosetting resins” are resins which cannot be resoftened and reworked after molding, extruding or casting and which attain new, irreversible properties once set at a temperature which is critical to each resin.
The outer layer and/or ultimate panel of the distal portion preferably comprises a fiber reinforced composite comprising a modulus of at least 50 MPa and preferably at least 80 MPa. The rigidity of this matrix is especially suited to rigid fibers such as the glass reinforcing fibers. The amount of fibre, in particular glass fibre, in the outer layer is preferably at least 40 volume %.
The outer layer is preferably a reinforced composite sheet, although a metal sheet such as an aluminium sheet may also be used. A polymeric liner may be used, such as PP or PE, either alone or as part of a laminate construction.
The core layer preferably comprises a polymeric material that provides a relatively light means of providing rigidity to the wall. The polymeric material is preferably a polymeric foam as this provides a low density structural material. Suitable foamed materials include metal foams, for example aluminum foam, glass foams or plastic foam, for example polyester foam, such as polyethylene terephtalate foam, polyvinyl chloride foam, polyurethane foam, polystyrene foam, polyethylene foam, polypropylene foam, a foam of an ethylene—propylene copolymer, phenolic foam, or any other plastic foam known to the person skilled in the art. may also be used. The core layer may also be made of:
Preferably the core layer of the distal portion comprises a polyester foam, such as polyethylene terephtalate foam, or a polyvinyl chloride foam.
The core layer may be made of essentially one piece and of essentially one material. The core layer may be made also of reinforced fibrous material. It is however also possible to use a core layer comprising two or more superimposed layers. The two or more superimposed layers may be made of the same or a different material. Suitable two layer systems are described in U.S. Pat. No. 4,101,704. One or more layers may be made of reinforcing fibrous material.
The reinforcing fibrous material may be the same or different material as used in the outer layer.
The core layer may comprise structural support inserts to improve the impact resistance of the wall. The inserts may be honeycomb-like or wave-like structure. Preferred inserts are further described in EP1596024, particularly
The inner layer may be of the same construction of the outer material, thereby forming what is commonly referred to as a sandwich panel. The inner layer of the distal portion is preferably a reinforced composite sheet.
In one embodiment, the inner layer functions as a skeletal frame connecting the proximal portion and the distal portion together. In one aspect of this embodiment, the skeletal frame forms part of the same panel as the proximal and distal portions. In another aspect, the skeletal frame is able to receive more than one panel, each panel comprising an outer layer and a core layer as previously described. Within this aspect, the skeletal frame is able to directly transfer energy to the core layer of the distal portion, thereby reducing vibration compared to panels which form the entire cross-section of the wall, roof or floor.
The modulus of elasticity of the distal portion is preferably at least 1 GPa, more preferably at least 10 GPa, even more preferably at least 15 GPa, most preferably at least 20 GPa. A high resistance to bending results in the distal portion having sufficient rigidity to structurally support the impact resistant portion, such that the container as a whole satisfies the tests described in section 6 of ISO 1496-1 (fifth edition) and/or tests described in section 8 of ISO 1496-2 (fifth edition).
Preferably, the impact resistant panel covers a geometric portion of the panel which has the highest risk of impact. For example, the impact resistant panels preferably extend to a radius of more than 300 mm, more preferably more than 500 mm, even more preferably more than 750 mm and yet even more preferably more than 1000 mm. To enable the container to conform to the required ISO structural requirements, the impact resistant portion is preferably no more than 2500 mm and more preferably no more than 2000 mm.
Preferably, the impact resistant portion covers less than 50% of the surface area of the wall, roof or floor, more preferably less than 30% and even more preferably less than 10% and yet even more preferably less than 5% of the area of the wall, floor or roof of the container.
In one embodiment, the impact resistant panels extends from the attachment fitting containing the attachment means (e.g. apertures to receive a hook from a handling device) towards the closest adjacent end corner fitting. The panel is preferably rectangular with a length to width ratio of preferably more than 1.5 to 1, with the length measured in the direction of the closest adjacent attachment fitting.
Preferably, the distal portion comprises one or more panels which separate the proximal portions adjacent to each attachment fitting. Preferably, the distal panels represent at least 50%, more preferably at least 70% and even more preferably at least 90% and yet even more preferably at least 95% of the area of at least the wall, floor or roof of the container.
The impact resistant panel and the distal panel are preferably attachable and detachable to the frame to enable more efficient and effective repairs to the panel(s).
Preferably, at least the wall, roof or floor comprises at least four, more preferably at least six, even more preferably at least eight and yet even more preferably at least ten panels. Preferably, at least the wall, roof or floor comprises less than twenty and more preferably less than fifteen panels.
The more panels there are the more attachment means are required to connect the impact resistant and distal portions together. Each attachment means is a source of energy dissipation and therefore the greater the number of attachment means the more effective the energy dissipation is from the impact zone.
An energy dissipation means is also preferably integrated into the attachment means of the panels to the frame. Preferably the means to attach and/or seal the panels to the frame comprises a polymeric composition having a modulus of less than 50 MPa and preferably less than 25 MPa or a resilient coil (e.g. spring load bolts).
Detachable, for the purposes of the present invention, means that the layers in question may be separated such that the layers do not show either permanent deformation or abnormality which will render it unsuitable for use, consistent with the pass criteria used in ISO 1496-1. (i.e. the layers can be taken apart and then reused).
The containers of the present invention are preferably nominal 10, 20, 30, 40 or 45 foot containers. In an even more preferred embodiment the container is a nominal 45 foot container, as these containers are particularly used for transportation by road, in which the frequency of handling (and thus risk of damage) is often greater than in other modes of transport.
Unless otherwise stated all references herein are hereby incorporated by reference.
Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
Features, integers, characteristics and compounds described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.
The invention is now been further described with specific reference to a preferred embodiment.
With reference to
The frame is preferably connected to impact resistant panels 30 which is immediately adjacent, and preferably abutting, the frame. Preferably, the impact resistant panel is connected to the frame by means of a spring loaded bolt 40, which secure the panel from above and/or below. Further attachment points may be made from the frame directly into the core layer.
In
In an embodiment (see
In another embodiment (see
The central panels 100/100′, which are distal from the attachment points preferably comprise an outer 50′, core 60′ and inner 70′ layer. The central panels 100/100′ may also be of a metal or metal alloy, such as steel. The modulus of elasticity of the distal portion is at least 20% greater than the modulus of elasticity of the impact resistant portion.
The containers of the present invention may also be suitable used and/or modified for other applications, such as building construction.
Rigid sandwich panels (to be used for the distal portion) and flexible sandwich panels (to be used for the impact resistant portion) are made and tested.
Both the top and bottom composite skins of the rigid sandwich panels are made of 2 layers of triaxial (−45/90/+45) fiberglass commercially available from Saertex, Germany impregnated with vinyl ester resin (ATLAC 430, commercially available from DSM Composite Resins, Switzerland) resin. Total thickness of the fiberglass reinforced skins is 1.8 mm.
Two sets of rigid sandwich panels are produced; one series is manufactured by using poly vinyl chloride (PVC) 80 kg/m3 25 mm thick foam core (brand name C70.75, commercially available from Airex, Switzerland) and the other series by using polyethylene terephthalate (PET) 100 kg/m3 25 mm thick foam core (brand name T90.100, commercially available from Airex, Switzerland). For both series the composite skins are the same as described above. Total thickness of rigid sandwich panels made with PVC and PET foam cores is approximately 28 mm.
Both series of rigid sandwich panels are manufactured by hand lamination, where fiberglass mats are impregnated with vinyl ester resin by hand; foam core is placed in between the two “wet” fiberglass skins so that the top and bottom surfaces of the core material are also impregnated with vinyl ester resin.
The panels are then left for 24 h at room temperature for the resin to cure; afterwards they are placed in an oven for post-cure at 60° C. for 24 h.
On a large industrial scale, the rigid sandwich panels (with PVC and PET foam core materials) are preferably produced in a two-step process; first the composite skins are manufactured by preferably continuous lamination where fiberglass triaxial mats are impregnated with vinyl ester resin in a continuous way. After the resin is cured, rigid foam core materials are bonded to the composite skins by using a polyurethane adhesive of which the final strength can be reached after a number of days.
Both the top and bottom skins of the flexible sandwich panels are made of castable polyurethane (PU) (Bolipur 160, commercially available from Bolidt, the Nethlerlands); the PU skins are produced by mixing part A and part B with a mix ratio of 86:14 by weight. Both top and bottom PU skins are 2 mm thick.
The core of the flexible sandwich panels is made of closed-cell polyethylene (PE) foam 20 mm thick.
A one-component liquid primer is applied on the top and bottom surfaces of the PE foam and left to cure for 24 h at room temperature; as such the PU mix of part A and part B is poured on the foam surfaces and evenly spread out. The system is left to cure at room temperature for 24 h.
Total thickness of the flexible sandwich panels is approximately 24 mm.
Tests with Rigid and Flexible Sandwich Panels
Rigid sandwich panels made with PVC and with PET foam cores are tested in 4-point bending (apparatus used is of Zwick with a 20 kN load cell). Sample length is 1200 mm and width is approximately 62 mm; the distance between the testing supports is 1000 mm while the distance between the two loading members is 180 mm.
Flexible sandwich panels are tested in 3-point bending (apparatus used is of Zwick with a 20 kN load cell). Sample length is approximately 600 mm and width is 65 mm; the distance between the testing supports is 300 mm.
From the flexural test results, E-modulus in bending of rigid sandwich panels made with PVC foam core is 5.35 kN/mm2, E-modulus in bending of rigid sandwich panels made with PET foam core is 5.28 kN/mm2, while E-modulus in bending of flexible sandwich panels is 0.00278 kN/mm2.
Charpy impact tests are performed with rigid sandwich panels made with PVC and PET foam cores and with flexible sandwich panels. The sample width is approx. 15 mm; and the sample thickness is approx. 28 mm.
Specific impact energy (Specific impact energy=Impact energy in J (measured by the testing machine)/(sample width x sample thickness)) of rigid sandwich panels with PVC foam core is 101 kJ/m2; specific impact energy of rigid sandwich panels with PET foam core is 45 kJ/m2, while specific impact energy of flexible sandwich panels is at least 126 kJ/m2 since at this value they do not fail in impact but return to their original shape with no damage after having been hit.
The large difference in values of E-modulus between rigid and flexible sandwich panels explains the improvement in impact resistance of the container when flexible sandwich panels are used at places where the container is hit instead of rigid ones.
Once hit, the flexible sandwich panels are capable of withstanding an elastic deformation greater than 40 mm (this value is determined by the 3-point bending tests where a flexural load is applied and the elastic deformation is recorded; once a value of deformation of 40 mm is obtained, the load is removed and the hysteresis behaviour is recorded: almost immediately the panels come back to their original shape with close to no deformation, therefore a deformation of at least 40 mm is “elastic”, since it is not a permanent deformation; after the load is removed they return to their original shape with no damage).
On the other hand, the rigid panels are not capable of withstanding such large elastic deformations and they break at much lower deformations.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09178680.6 | Dec 2009 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/069364 | 12/10/2010 | WO | 00 | 8/14/2012 |
