TIE LOCKING DEVICE BACKGROUND OF THE INVENTION 5 1. Field of the Invention The present invention relates generally to a tie locking device, and more particularly to a tie locking device in which the press cover can be easily pressed down onto the main body to fix the tie 10 in a tightened state. 2. Description of the Related Art A conventional tie, rope or the like is used to tie an article. A 15 locking device can be used in cooperation with the tie to tighten and fix the article. The locking device includes a main body and a shift member equipped with a lock head. One end of the shift member is pivotally rotatably connected with the main body. After the rope is passed through the main body to tie the article, a worker pulls 20 up the shift member, whereby one end of the shift member bites the rope. Then the worker can use a key to rotate the lock head to lock the shift member and keep the rope bitten by the shift member. When the worker holds the main body and pulls up the shift member 25 to bite the rope with both hands, it is very hard for the worker to further use the key to rotate the lock head. As well known by those who are skilled in this field, after the shift member is pulled
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up to bite the rope and then locked to keep the rope fixed, the locking device will prot rude from the main body to enlarge the volume. In this case, during transfer, the locking device is likely to collide with other objects. As a result, the lock device may be 5 damaged to unlock the shift member. Under such circumstance, the rope will be released to untie the article. This is not what we expect. The conventional tie locking device has some shortcomings in use 10 and structural design that needs to be overcome. It is therefore tried by the applicant to provide a tie locking device to eliminate the shortcomings existing in the conventional tie locking device so as to widen the application range of the tie locking device. For example, in the conventional tie locking device, the shift member 15 is pulled up to bite the rope (or the tie). In contrast, the tie locking device according to an embodiment of the present invention employs a press cover, which is pressed down to bite the tie. Therefore, the lock head will not protrude from the main body so that the volume is minified without occupying much room. In this 20 case, the locking device is prevented from colliding with other objects and protected from being damaged. Moreover, in operation of the locking device, a worker can press the press cover and the main body with one hand and use a key to rotate the lock head and lock the press cover with the other hand. Therefore, the operation 25 of the tie locking device according to an embodiment of the present invention is simple. 2 SUMMARY OF THE INVENTION An embodiment of the present invention seeks to provide a tie locking device, which can be easily operated. 5 Alternatively or additionally, an embodiment of the present invention seeks to at least provide the public with a useful choice. The tie locking device of the present invention includes a main body and a rotatable press cover. The main body includes a fixing section 10 and at least one wall connected with the fixing section. The press cover has a pivoted end pivotally connected with a pivoted section of the main body. The pivoted end of the press cover and the pivoted section of the main body together define an inlet for a tie to enter the main body. A valve board is disposed on the main body and movable 15 within the main body between a first position distal from the inlet and a second position proximal to the inlet. The valve board is formed with a toothed section. After the valve board is moved to the second position, the toothed section bites the tie and the press cover is pressed onto the main body to fix the valve board and the 20 tie. The tie locking device according to an embodiment of the present invention overcomes the shortcomings of the conventional tie locking device that the conventional tie locking device cannot be 25 easily operated by one single worker and the volume of the conventional tie locking device is larger. 3 In the above tie locking device, the press cover has an arm. When the valve board is moved to the second position, the press cover is pressed down, whereby the arm hinders the valve board from moving to the first position and the free end of the arm bites the tie to 5 help the toothed section of the valve board in fixing the tie. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described, by way of non-limiting 10 example only, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of the present invention, showing that the press cover is positioned in a locking position and closed onto the main body; 15 Fig. 2 is another perspective view of the present invention, showing that the press cover is positioned in an unlocking position and opened from the main body; 20 Fig. 3 is a perspective exploded view of the present invention, showing the structures of the main body, the press cover and the valve board; Fig. 4 is a sectional view of the present invention, showing the 25 operation thereof, in which the valve board is positioned in the first position and the tie is passed through the main body and the press cover; 4 Fig. 5 is another sectional view of the present invention, showing the operation thereof, in which the valve board is moved to the second position to bite the tie; and 5 Fig. 6 is still another sectional view of the present invention, showing the operation thereof, in which the press cover is pressed down to a locking position to bite the tie and is locked with the main body by the lock head. 10 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Please refer to Figs. 1, 2 and 3. The tie locking device of the present invention includes amain body 10 and a rotatable press cover 15 20. The main body 10 includes a fixing section 11 and a pivoted section 12. The fixing section 11 is formed with a cavity 13 and an opening 14 in communication with the cavity 13. One end 41 of a tie 40 (as shown in Fig. 4) is fixed in the cavity 13. The tie 40 extends out from the opening 14. At least one side or two sides 20 of the main body 10 are formed with walls 15 connected with the fixing section 11 and rails 16 disposed on the walls 15 for mounting a valve board 30. The main body 10 is assembled on a seat 70. The seat 70 has a head 25 section 71 corresponding to the main body 10 for at least partially enclosing the fixing section 11 of the main body. An opening 72 is formed on the head section 71 corresponding to the opening 14 of 5 the main body. Two sides of the seat 70 are formed with sidewalls 73 for at least partially enclosing the walls 15 of the main body 10. 5 In a preferred embodiment, the wall 15 of the main body 10 is formed with a recess 17. The support sections 31 of two ends of the valve board 30 can be mounted into the rails 16 through the recesses 17. The valve board 30 is movable along the rails 16 between a first position and a second position. The valve board 30 is a board body, 10 having apush face 33 anda toothed section 32 disposed under abottom face of the valve board 30. When the valve board 30 is moved toward the second position, the toothed section 32 is used to bite the tie 40. (This will be further described hereinafter). The push face 33 is a roughened face for increasing the frictional force between a 15 finger and the valve board 30. Please refer to Fig. 4. It should be noted that a push angle 0 is contained between the push face 33 and the rails 16 (or the moving path from the first position to the second position). The push angle 20 0 is about 10' ~45 . Please refer to Figs. 3 and 4. The press cover 20 has a pivoted end 21 pivotally connected with the pivoted section 12 of the main body 10, whereby the press cover 20 is freely rotatable. An inlet 18a 25 is defined between the pivoted section 12 of the main body and the pivoted end 21 of the press cover. The other end 42 of the tie 40 can enter the main body 10 from the inlet 18a. A restriction section 6 19 is disposed on the main body 10 in the form of a plate. The restriction section 19 is connected with the walls 15. An outlet 18b is defined between the restriction section 19 and the fixing section 11. The other end 42 of the tie 40 can extend out of the 5 main body 10 through the outlet 18b. The press cover 20 is equipped with a lock head 50 and a lock plate 51 controlled by the lock head 50 to lock or unlock. In this embodiment, the press cover 20 has at least one arm 22 positioned 10 between the lock head 50 and the pivoted end 21 for hindering the valve board 30 from moving. The arm 22 has the form of a finger and perpendicularly or nearly perpendicularly protrudes from the press cover 20. The arm 22 has a free end 23. After the press cover 20 is pressed down, the free end 23 will bite the tie 40 to help the 15 toothed section 32 of the valve board in fixing the tie 40. Please refer to Figs. 4 and 5. Fig. 4 shows that the valve board 30 is positioned in the first position of the main body 10 or the rails 16, where the valve board 30 permits the tie 40 to be pulled 20 tight or released. Fig. 4 also shows that the other end 42 of the tie 40 enters the main body 10 from the inlet 18a to pass through the valve board 30 and extend out of the main body 10 through the outlet 18b. After the tie 40 is pulled tight to tie an article 60, a worker pushes the valve board 30 from the first position to the 25 second position, whereby the toothed section 32 of the valve board 30 bites the tie 40. 7 Fig. 6 shows that the press cover 20 is pressed down and the arm 22 hinders the valve board 30 from moving to the first position. Also, the free end 23 of the arm 22 bites the tie 40 to help the toothed section 32 of the valve board 30 in fixing the tie 40. In 5 this operation mode, the worker can press the press cover 20 and the main body 10 with one hand and use a key to rotate the lock head 50 and the lock plate 51 with the other hand, whereby the lock plate 51 is moved into the restriction section 19 to lock the press cover 20. Under such circumstance, the valve board 30 and the tie 40 are 10 fixed. The press cover 20 can be opened to release the tie 40 from the valve board 30 only when the worker uses the key to unlock the lock plate 51. In comparison with the conventional device, the tie locking device 15 of the present invention has the following advantages: 1. The locking device, the main body 10, the press cover 20 and the relevant components are redesigned and different from the conventional device in use and operation form. For example, the 20 valve board 30 is formed with the toothed section 32 and is movable between the first and second positions of the main body 10 or the rails 16 to release or bite the tie 40. The press cover 20 has the arm 22 to hinder the valve board 30 from moving. The locking device of the present invention is free from the shift member of 25 the conventional device, which is pulled up to bite the rope or the tie. 8 2. The main body 10 and the press cover 20 structurally cooperate with each other to facilitate the operation of the locking device. That is, a worker can easily use a key to rotate the lock head 50 and the lock plate 51 to lock the press cover 20 so as to fix 5 the valve board 30 and the tie 40. Moreover, the locking device will not protrude from the main body so that the volume is minified without occupying much room. In this case, the locking device is prevented from colliding with other objects and protected from beingdamaged. Accordingly, the tie cankeep ina tightened state. 10 The above embodiments are only used to illustrate the present invention, not intended to limit the scope thereof. Many modifications of the above embodiments can be made without departing from the spirit of the present invention. 15 The term 'comprising' as used in this specification and claims means 'consisting at least in part of'. When interpreting statements in this specification and claims which include the term 'comprising', other features besides the features prefaced by this term in each 20 statement can also be present. Related terms such as 'comprise' and 'comprised' are to be interpreted in similar manner. In this specification where reference has been made to patent specifications, other external documents, or other sources of 25 information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents 9 is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art. 5 10