Background Art In general, it is known that a steel door having a good security and fire-protection has been employed as the entrance door in a detached house, a semi-detached house, or an apartment building. A conventional steel door is shown in FIGS. 1 to 3.

FIG. 1 is a partially exploded perspective view showing the conventional steel door. FIG. 2 is a cross-sectional view taken along the line I-I in FIG. 1, and FIG. 3 is an enlarged view of the portion A in FIG. 2.

As shown in the figures, the conventional steel door 1 is composed of two opposing steel plates 2a, 2b spaced anart from each other, and reinforcement bodies 3a, 3b installed inside the steel plates 2a, 2b and having a honeycomb structure formed of a

paper material.

In the fabrication of the above conventional steel door 1, first, urethane foams 4a, 4b having an adhesive characteristic is coated, with a certain desired thickness, on the inner face of the steel plates 2a, 2b of a desired size. On top of the urethane foams 4a, 4b coated on the steel plates 4a, 4b is installed the reinforcement bodies 3a, 3b of a honeycomb structure, which is formed of a paper material. Then, the steel plates 2a, 2b with the reinforcement bodies 3a, 3b installed thereon are superimposed in opposite relationship to each other and hot-pressed. Therefore, the reinforcement bodies 2a, 2b are integrally attached and fixed to the steel plates 2a, 2b, by means of the curing effect due to foaming of the urethane foams 4a, 4b. Thereafter, the finishing process around the steel plates 2a, 2b is conducted.

The above conventional door 1 has the reinforcement bodies 3a, 3b made of a paper material such that the steel plates 2a, 2b forming the door 1 are reinforced and therefore deformation such as a dent or depression by an external impact can be avoided, along with other functions such as heat-insulation and fire-protection.

However, the conventional steel door 1 having the above- described construction has several problems resulting from structural faults of the reinforcement bodies 3a, 3b.

The reinforcement bodies of the conventional door 1 are made of a paper material, so that it is vulnerable to moisture or heat and consequently loses its function as a reinforcement body. Thus, the life of the door is shortened.

In addition, during the manufacturing process of the door, when the steel plates 2a, 2b are opposed, the honeycomb portions of the reinforcement bodies 3a, 3b remains internally in a vacuum state except for part of its external portions.

Accordingly, the urethane foams 4a, 4b, which are placed near the honeycomb structure and coated in the surface of the steel plates 2a, 2b, also is in the vacuum envsteelment. This vacuum state acts as a hindrance in the foaming process of the urethane foams 4a, 4b, since urethane foaming is easily activated and cured under the condition of air-circulation, and otherwise its inherent properties may remains after forming. Resultantly, the reinforcement bodies are not properly attached to the steel plates, leading to the production of poor-quality or inferior doors.

Disclosure of Invention The present invention has been made to solve the above problems in the art, and it is an object of the invention to provide a steel door having a reinforcement body, which is made of a metallic material resistant to heat, moisture, and impact.

Another object of the invention is to provide a steel door having a reinforcement body made of a metallic material, which can be easily received and carried.

In order to accomplish the above objects, according to one aspect of the present invention, there is provided a steel door comprises: a door body being composed of a pair of steel plates, the steel plates being superimposed on each other to form a space for receiving a urethane foam, the steel plate having a certain desired width, wherein the urethane form is foamed to fix the steel plates ; and a reinforcement body disposed in the inner face of and between the steel plates, the reinforcement body being formed of a plurality of metallic members each having a certain desired length, each metallic member having a cut slit formed in certain intervals along the length thereof, through which the metallic members are fitted into each other to form the reinforcement body consisting of a plurality of rectangular lattices, wherein the urethane foam can be filled in the rectangular lattice 136a and cured, thereby attaching the reinforcement body integrally to the steel plates; wherein the metallic member has a through-hole formed in certain intervals along the longitudinal direction thereof such that the urethane foam flows across the rectangular lattices through the through- holes and is cured, thereby attaching the metallic members firmly to the steel plates by means of the cured urethane inside

the through-holes.

In the above structure, preferably a latching step is formed in the inner face of the cut slit, and a latching plate is formed in that portion of the metallic member corresponding to the latching step, such that the latching plate is entrapped in the latching step when assembled, thereby preventing the metallic members from releasing from each other.

In addition, the latching plate is preferably formed in such a manner that a portion of the metallic member is cut and raised up in a slanted form.

The cut slit is preferred to include an inlet portion having an outwardly flared slant face for guiding.

According to another aspect of the invention, there is provided a steel door comprises: a door body having a pair of steel plates superimposed on each other such that a space for receiving a urethane foam is provided, the steel plate having a certain desired width, wherein the urethane foam is foamed in order to fix the steel plates; a reinforcement body disposed in parallel in the inner face of the steel plates and consisting of a plurality of metallic members, each metallic member being formed of a thin plate of metallic material and having a rectangular shape having a certain length, the metallic member having a large hole formed in certain intervals along the length thereof and a small hole around the large hole, wherein the

urethane foam flows through the large and small holes and then is cured, thereby affixing the steel plates integrally by means of the cured urethane inside the large and small holes; and a connector formed in certain intervals along the longitudinal direction thereof, every other connectors of the metallic member being connected with those of a neighboring metallic member such that the connected metallic members can be spread to form a honeycomb structure for receiving the urethane foam.

In the above structure, preferably the connector is detachably formed through a fitting plate and a fitting projection projected respectively from opposing faces.

In addition, the connector may be formed through a fusion- bonding by a welding or through an adhesive-bonding using an adhesive.

Brief Description of Drawings Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a partially exploded perspective view showing a conventional steel door; FIG. 2 is a cross-sectional view taken along the line I-I in FIG. 1 ; FIG. 3 is an enlarged view of the portion A in FIG. 2;

FIG. 4 is an exploded perspective view of a steel door according to the first embodiment of the invention; FIG. 5 shows an enlarged cross-section taken along the line II-II in FIG. 4; FIG. 6 is an enlarged view of the portion B in FIG. 5 ; FIG. 7 is a perspective view showing metallic members for forming a reinforcement body of the steel door of the invention; FIG. 8 is an exploded perspective view of a steel door according to a second embodiment of the invention; FIG. 9 shows an enlarged cross-section taken along the line ILS-TITI in FIG. 8; FIG. 10 is an enlarged view of the portion C in FIG. 10 ; FIG. 11 shows a reinforcement body before assembled ; FIG. 12 is an enlarged view of the portion D in FIG. 11 ; FIG. 13 illustrates a partially enlarged view of a reinforcement body after assembled; FIG. 14 is an exploded perspective view of a steel door according to a third embodiment of the invention; FIG. 15 shows an enlarged cross-section taken along the line IV-IV in FIG. 14; FIG. 16 illustrates a reinforcement body before assembled; FIG 17 is a partially enlarged view of the reinforcement body of FIG. 16 when assembled; FIG. 18 illustrates a reinforcement body in a folded state;

and FIG. 18 shows the reinforcement body of FIG. 17 in a spread state.

Best Mode for Carrying Out the Invention The preferred embodiments of the invention will be explained in detail with reference to the accompanying drawings.

FIG. 4 is an exploded perspective view of a steel door according to the first embodiment of the invention, in which the steel door is generally denoted at 10. FIG. 5 shows an enlarged cross-section taken along the line II-II in FIG. 4, and FIG. 6 is an enlarged view of the portion B in FIG. 5.

As shown in the figures, the steel door 10 according to the first embodiment of the invention is provided with first reinforcement bodies 30a, 30b installed between a pair of first steel plates 12a, 12b having a certain desired width, so that the first steel plates 12a, 12b are reinforced by the reinforcement bodies and thus prevented from being deformed.

Each of the first reinforcement bodies has the same structure and will be explained, with reference to the reinforcement body denoted by a reference numeral 30a in FIG. 4.

Dissimilar to the conventional reinforcement body made of a paper material, the first reinforcement body 30a of the invention is formed of metallic members 32a, 34a fitted into

each other. The first metallic members 32a, 34a may be plural steel plates having a certain thickness and a length and width corresponding to those of the first steel plates 12a, 12b.

These steel plates are fitted, in certain intervals, into each other in the form of a lattice to thereby form the first reinforcement body 30a comprising a plurality of first rectangles. The first metallic members 32a, 34a constituting the first reinforcement body 30a have first'through-holes 38a formed in certain intervals along the metallic member 32a, 34a.

The first reinforcement bodies 30a, 30b having the above construction may be assembled into the steel door 10 in the same manner as in the conventional one, which is described above in conjunction with FIGS. 1 to 3. That is, the first reinforcement body 30a, 30b is disposed on top of the first urethane foams 40a, 40b, which is coated on the inner face of the first steel plates 12a, 12b with a certain thickness. Thereafter, the first steel plates 12a, 12b are superimposed in such a manner that the first reinforcement bodies 30a, 30b thereinside are faced with each other, and then hot-pressed. Due to the curing effect by the foaming of the first urethane foams 40a, 40b, the foams 40a, 40b are integrally affixed to the first steel plates 12a, 12b to thereby form the steel door 10.

In the above-described process for fabricating the steel door 10 according to the first embodiment of the invention, the

first reinforcement bodies 30a, 30b have a first rectangular lattice 36a formed by the first metallic members 32a, 34a. The first rectangular lattice 36a is fluid-communicated with the outside of the door through the first through-holes 38a, which are formed in the first metallic members 32a, 34a, as denoted by an arrow in FIG. 5 and 6.

As described above, according to the invention, the first rectangular lattice 36a of the first reinforcement bodies 30a, 30b is internally fluid-communicated with the external atmosphere of the door, rather than in a vacuum state of the prior art. Therefore, during the hot-pressing, the first urethane foam 40a, 40b disposed inside the first rectangular lattice 36a can be actively foamed so that the reinforcement bodies 30a, 30b can be more firmly attached to the first steel plates 12a, 12b. Thus, the reinforcement bodies 30a, 30b are prevented from easily being released due to external impact or moisture.

In addition, during the foaming of the first urethane foams 40a, 40b, the urethane foam coated on the steel plates 12a, 12b can flow through the first through-holes 38a formed in the first reinforcement bodies 30a, 30b. Therefore, the first urethane foam 40a, 40b remains in part in the through-holes 38a and then is cured as it is. The cured urethane inside the through-holes act as a connection hook so that the first reinforcement bodies

30a, 30b can be more firmly attached to the first steel plates 12a, 12b.

FIG. 7 is a perspective view showing the metallic members for forming the reinforcement of the steel door of the invention.

Each of the first metallic members 32a, 34a, which form the reinforcement body 30a, has a first cut slit 35a formed in certain intervals along the longitudinal direction thereof. The metallic members are fitted with each other by means of the first cut slit 35a to thereby form the reinforcement body 30a comprising a plurality of first rectangular lattice 36a (see FIG.

4). The first metallic members 32a, 34a can be assembled into the first reinforcement body 30a by means of the first cut slit 35a and also the reinforcement body 30a can be disassembled into the first metallic members 32a, 34a. In addition, since the first cut slit 35a provides flexibility to the whole structure of the reinforcement body, the assembled first reinforcement body 30a can be folded and contracted due to an external force.

FIG. 8 is an exploded perspective view of a steel door according to a second embodiment of the invention, where the steel door of the invention is in general denoted by a reference numeral 100. FIG. 9 shows an enlarged cross-section taken along the line III-III in FIG. 8, and FIG. 10 is an enlarged view of the portion C in FIG. 10. FIG. 11 shows a reinforcement body before assembled, and FIG. 12 is an enlarged view of the portion

D in FIG. 11. FIG. 13 illustrates a partially enlarged view of a reinforcement body after assembled.

As shown in the figures, similar to the first embodiment of the invention, the steel door 100 of the second embodiment comprises a door body having a pair of second steel plates 112a, 112b superimposed on each other such that a space for receiving a second urethane foam 140a, 140b is provided. The steel plates 112a, 112b have a certain desired width and the second urethane foam 140a, 140b is foamed in order to fix the second steel plates 112a, 112b. The steel door 100 includes a second reinforcement body 130a, 130b integrally affixed to the second steel plates 112a, 112b. The reinforcement body 130a, 130b is disposed inside the space between the steel plates 112a, 112b, and formed of a plurality of second metallic members 132a, 134a each having a certain desired length. Each second metallic member 132a, 134a has a second cur slit 135a formed in certain intervals along the length thereof, through which they are fitted into each other to form the second reinforcement body consisting of a plurality of second rectangular lattices 136a.

The second urethane foam 140a, 140b can be filled in the second rectangular lattice 136a and cured, thereby firmly attaching the second reinforcement body to the second steel plates. The second metallic members 132a, 134a have a second through-hole 138a formed in certain intervals along the longitudinal

direction thereof. Similarly, the second urethane foam 140a, 140b remains in part in the second through-holes 138a and then is cured as it is. The cured urethane inside the second through-holes act as a connection hook so that the second metallic members 132a, 134a can be more firmly attached to the second steel plates 112a, 112b.

The steel door 100 according to the second embodiment of the invention may be fabricated in the same manner as in the steel door 10 of the first embodiment. For example, the second reinforcement body 130a, 130b can be formed in the same way as in the first embodiment. Accordingly, the steel door 100 of the second embodiment has the same functions and effects as that of the first one. Therefore, details will not be repeated here.

In the above-described construction, the steel door 100 of the invention is provided with a latching step 151a, 151b and a latching plate 152 formed in the second metallic members 132a, 134a, so that the metallic members are prevented from being released from each other when assembled.

The latching steps 151a, 151b are projected in the inner face of the second cut slit 135a, and the latching plates 152 are projected in one side of the second metallic members 132a, 134a, facing the second cut slit 135. As shown in FIG. 9, when the second metallic members 132, 134a are fitted with each other, the latching steps and plates are entrapped to each other such

that the second metallic members 132a, 134a can not be easily disassembled.

For the purpose of simplifying and unifying the manufacturing process, preferably the latching step 152 may be formed in such a manner that a portion of the second metallic member 132a, 134a is cut and raised up in a slanted form.

In addition, the latching steps 151 are preferably formed in pairs. If the latching steps 151a, 151b are formed in the form of a single step, the operator must consider the orientation of each second metallic members 132a, 134a due to the position of the single latching step 151a. Therefore, the latching steps are desired to be formed in pairs facing each other.

Furthermore, the cut slit 135a has an inlet portion 160 with a slanted face 161 formed such that it is expanded outwardly so as to guide other metallic members when fitted together. Therefore, this structure of the cut slit 135 enables the metallic members 132a, 134a to be easily and simply assembled.

FIG. 14 is an exploded perspective view of a steel door according to a third embodiment of the invention, where the steel door of the invention is generally denoted at 200, and FIG.

15 shows an enlarged cross-section taken along the line IV-IV in FIG. 14. FIG. 16 illustrates a reinforcement body before

assembled, and FIG 17 is a partially enlarged view of the reinforcement body of FIG. 16 when assembled. FIG. 17 illustrates a reinforcement body in a folded state, and FIG. 18 shows the reinforcement body of FIG. 17 in a spread state.

As shown in the figures, the steel door 200 of the third embodiment of the invention comprises a door body having a pair of third steel plates 212a, 212b superimposed on each other such that a space for receiving a third urethane foam 240a, 240b is provided. The third steel plates 212a, 212b have a certain desired width and the third urethane foam 240a, 240b is foamed in order to fix the third steel plates 212a, 212b. The steel door 200 of this embodiment comprises a third reinforcement body 230a, 230b disposed in parallel in the inner face of the third steel plates 212a, 212b and consisting of a plurality of third metallic members 232a, 234a. The third metallic members are formed of a thin plate of metallic material and each has a rectangular shape having a certain length. The third metallic member 232a, 234a has a large hole 238a formed in certain intervals along the length thereof and a small hole 238b around the large hole 238a. The third urethane foam 240a, 240b remains in part inside the large and small holes 238a, 238b and then is cured as it is. The cured urethane inside the large and small holes act as a connection hook so that the third metallic members 232a, 234a can be more firmly attached to the third

steel plates 212a, 212b. The third metallic member 232a, 234a has a connector 234a formed in certain intervals along the longitudinal direction thereof. Every other connectors 234a of a third metallic member are connected with those of a neighboring metallic member, such that the connected third metallic members can be spread to form a honeycomb structure for receiving the third urethane foam 240a, 240b.

The steel door 200 according to the third embodiment of the invention may be fabricated in the same manner as in the steel door 10 of the first embodiment. For example, the third reinforcement body 230a, 230b can be formed in the same way as in the first embodiment. Accordingly, the steel door 200 of the third embodiment has the same functions and effects as that of the first one. Therefore, details will not be repeated here.

In the above-described construction, the connectors 235a may be embodied as a fitting mode for assembling and disassembling, a fusion-bonding mode such as the spot welding, or an adhesive-bonding mode using an adhesive.

Among them, a fitting mode of the connector 235a is achieved by forming a fitting plate 250a and a fitting projection 250b in a facing face F1, F2 of the third metallic members 232a, 234a, as shown in the figures. That is, in the connector 235a of fitting type, the fitting plate 250a and the fitting projection 250b to be detachably fitted into the fitting

plate 250 are formed in the facing faces F1, F2 of the neighboring parallel third metallic members 232,234, such that they can be correspondingly fitted into each other. When the fitting plate 250b is fitted into the fitting plate 250a, the third reinforcement body 230 is formed and can be spread into a honeycomb structure, in which the third urethane foam 240a, 240b is received. The fitting plate 250a and the fitting projection 250b may be formed alternately in the facing faces F1, F2.

The fitting plate 250a is formed in such a manner that a portion of the third metallic member 232a, 234a is cut, raised up, and then bent in a"r"shape. The fitting projection 250b is formed by cutting a portion of the third metallic members 232a, 234b, which is corresponding to that of the fitting plate 250a. Then, the portion between the cut portions is raised up in, a projected form.

As illustrated in FIG. 18, the third metallic members 232a, 234b can be spread into a honey structure of the third reinforcement body 230a by means of the above-described connector 235a. As shown in FIG. 19, the third metallic members 232a, 234b may be contracted in its longitudinal direction to thereby reduce the volume thereof, thereby enabling an easy transportation and installation of the third reinforcement 230a.

It is understood to those skilled in the art that, in the first, second, and third embodiment of the invention, the

through-holes, and the large and small holes may be formed in any shape as long as they do not do any harm to the mechanical strength of the metallic members.

Industrial Applicability As described above, according to the invention, the reinforcement body used with the steel plates is formed of high-strength metallic members, and the metallic member has through-holes formed along the length thereof, so that the urethane foam can be actively foamed through the through-holes to thereby affix the reinforcement body to the steel plates.

Therefore, the reinforcement body is not easily released from the steel plates and deformed by an external impact or moisture, and its heat insulation and fire-protection performances are improved, thereby extending the life of the steel door.

In addition, the reinforcement body of the invention is assembled such that it can be spread or contracted, thereby enabling an easy transportation and installation of the reinforcement body made of metallic members.