BACKGROUND ART FIG. 1 is a rear perspective view of a general microwave oven. The microwave oven 1 has a casing 2 forming a cooking chamber, a front plate 3 attached to the front side of the casing 2, and a rear plate 4 attached to the rear side of the casing 2. The casing 2 is covered with an outer casing (not shown) forming an appearance of the microwave oven 1.

The microwave oven 1 has a magnetron for generating microwaves.

As the microwaves generated by the magnetron are irradiated into the cooking chamber, the food in the cooking chamber is cooked.

On the central area of the upper side of the casing 2, as shown in FIG. 2, a plurality of discharge holes 11 for discharging gas in the cooking chamber are formed, and a discharge pipe 15 communicating with the discharge holes 11 is installed on the upper side of the casing 2. The discharge pipe 15 is extended to the rear side of the casing 2.

A guide member 25 is installed on the rear side of the casing 2. The

guide member 25 forms a discharge opening 17 opened upward so that the gas is discharged upward.

A covering member 20 is installe on the rear side of the casing 2 over the guide member 25. The covering member 20 partially covers the discharge opening 17, thereby preventing entrance of dirt into the discharge pipe 15 through the discharge opening 17.

The microwaves generated by the magnetron are irradiated into the cooking chamber through a wave guide (which is not shown), and then the food in the cooking chamber is cooked. While the food is being cooked, gas such as humidity or smoke generated in the cooking chamber flows into the discharge pipe 15 through the discharge holes 11, and then the gas is discharged upward from the rear side of the microwave oven 1 through the discharge opening 17.

In general, the microwave oven 1 is used in a kitchen, and accordingly, due to carelessness of a user, linear metallic matters such as chopsticks may enter into the discharge pipe 15 through the discharge opening 17. In FIG. 2, a wire 40 is shown as an example of such a metallic material, which may be inserted into the discharge pipe 15 through the discharge opening 17. If the wire 40 enters, the microwaves generated during the operation of the microwave oven 1 will leak to the outside of the microwave oven 1, which may cause a damage on a human body. Therefore, the microwave oven 1 should undergo a wire insertion test as to whether a wire can be inserted thereto or not, and such a wire insertion test is obligatory in many countries.

In order to prevent the insertion of the wire 40 into the microwave oven 1, a plurality of walls partially closing the discharge pipe 15 have been disposed alternately in the discharge pipe 15. However, in order to install the walls, the walls have to be manufactured separately and attached into the discharge

pipe 15, so the manufacturing cost of the microwave oven 1 increases and the process for manufacturing is complex.

DISCLOUSRE OF INVENTION The present invention has been proposed to overcome the above- described problems in the prior art, and accordingly it is the object of the present invention to provide a microwave oven capable of preventing entrance of linear metallic matters such as wire or chopsticks into the discharge pipe, which has a simple construction and can be manufactured easily.

To achieve the above object, the present invention provides a microwave oven comprising: a casing forming a cooking chamber, the casing being formed with a discharge holes at a side thereof, the discharge holes for discharging gas in the cooking chamber; a discharge pipe being installed at an outer surface of the casing and having a discharge opening opened at an outer side of the casing so as to provide a passage for the gas to be discharged outward; and a protrusion formed in the discharge pipe on an area adjacent to the discharge opening so as to obstruct entrance linear metallic matters into the discharge pipe through the discharge opening.

It is preferable that the protrusion is formed with the casing in a single body. Entrance of the linear metallic matters such as wires or chopsticks into the discharge pipe is obstructed by the protrusion. Therefore, the leakage of microwaves through the linear metallic material is prevented.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a rear perspective view of a general microwave oven; FIG. 2 is a partial enlarged side sectional view of FIG. 1; and FIG. 3 is a partial enlarged side sectional view of a microwave oven according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to FIG. 3. Respective parts of the microwave oven which have been illustrated in relation to FIG. 1 will not be described repeatedly, and will be referred to with the same reference numerals.

The casing 2 of the microwave oven 1 forms a cooking chamber, and a plurality of discharge holes 11 for discharging gas in the cooking chamber are formed on the central area of the upper side of the casing 2. A discharge pipe 15 communicating with the discharge holes 11 is installed on the upper side of the casing 2. The discharge pipe 15 is extended to the rear side of the casing 2.

A guide member 25 is installed on the rear side of the casing 2. The guide member 25 forms a discharge opening 17 opened upward so that the gas is discharged upward.

Furthermore, a covering member 20 is installed on the rear side of the casing 2 over the guide member 25. The covering member 20 partially covers the discharge opening 17, thereby preventing entrance of dirt into the discharge pipe 15 through the discharge opening 17.

While the food in the cooking chamber is being cooked by the microwaves generated by a magnetron, gas such as humidity or smoke generated in the cooking chamber flows into the discharge pipe 15 through the discharge holes 11, and then the gas is discharged upward from the rear side of the microwave oven 1 through the discharge opening 17.

A protrusion 30 is formed in the discharge pipe 15 on an area adjacent to the discharge opening 17. The protrusion 30 protrudes from the plane of the casing 2, so it is formed in a single body with the casing 2.

Entrance of a wire 40 into the discharge pipe 15 through the discharge opening 17 is obstructed by the protrusion 30, so it cannot enter further into the discharge pipe 15. Moreover, if an exterior force is applied to the wire 40, the front end portion of the wire 40 will be bent upward by the protrusion 30 as shown in FIG. 3. Therefore, the entrance of the wire 40 into the discharge pipe 15 is prevented, and thereby the leakage of microwaves toward the outside of the microwave oven 1 through the wire 40 is prevented.

Furthermore, walls manufactured separately need not be installed in the discharge pipe 15, so the manufacturing cost for microwave oven 1 is reduced and the manufacturing process thereof becomes simple.

As described above, according to the present invention, the entrance of the linear metallic matters such as wire or chopsticks into the discharge pipe is prevented by the protrusion, and leakage of microwaves through the linear metallic material is prevented. In particular, since the protrusion is formed together with the casing, it is easy to manufacture the microwave oven and the manufacturing cost is reduced.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, wherein the spirit and scope of the present invention is limited only by the terms of the appended claims.