CN217817981U

CN217817981U - Heating device and oven

Info

Publication number: CN217817981U
Application number: CN202221743702.5U
Authority: CN
Inventors: 詹宗颖; 郑鸿峙
Original assignee: Zhisheng Technology Guangzhou Co Ltd
Current assignee: Zhisheng Technology Guangzhou Co Ltd
Priority date: 2021-12-07
Filing date: 2022-07-06
Publication date: 2022-11-15
Anticipated expiration: 2032-07-06
Also published as: CN116242116A

Abstract

The utility model provides a heating device and oven is applicable to the heating work piece. The heating device comprises a base unit and a heating unit. The base unit comprises a transport table adapted for placing said work pieces. The heating unit comprises a first heating mechanism arranged on one of the upper side and the lower side of the base unit, and the first heating mechanism is provided with a first heating plate used for heating the workpiece. Through heating unit first heating mechanism set up in one of them side about the base unit, first heating mechanism can be right carry the platform heating, reduce by a wide margin the required time of heating chamber intensification effectively promotes whole work efficiency.

Description

Heating device and oven

Technical Field

The utility model relates to a heating device, in particular to heating device and oven.

Background

The processes for substrates can be divided into a process requiring heating of the substrates and a process not requiring heating of the substrates, and basically, the two processes must be divided into two different production lines, so that more space is required to accommodate the production lines of the different processes, which is a challenge in the case of decreasing space.

In addition, the conventional oven must be preheated before use to convey the workpiece to be heated into the oven for heating and baking. After the baking is finished, the workpiece can be conveyed to the next station only after the workpiece is cooled, so that the temperature of the oven must be reduced after the baking is finished. However, the conventional oven requires a long time for warming up and warming down after baking, and has room for improvement.

SUMMERY OF THE UTILITY MODEL

Therefore, one of the objectives of the present invention is to provide a heating device that can solve at least one of the above problems.

Therefore, another object of the present invention is to provide an oven capable of solving at least one of the above problems.

Thus, the present invention provides a heating device adapted to heat a workpiece, the heating device comprising: a base unit comprising a transport table adapted for placement of the workpiece; and the heating unit comprises a first heating mechanism arranged on one of the upper side and the lower side of the base unit, and the first heating mechanism is provided with a first heating plate for heating the workpiece.

Heating device, first heating mechanism can move from top to bottom, heating unit can remove between heating position and heat dissipation position during the heating position, first heating mechanism is close carry the platform during the heat dissipation position, first heating mechanism interval just keeps away from carry the platform, first heating mechanism is in during the heat dissipation position extremely carry the distance of platform and compare during the heating position extremely carry the distance of platform long.

Heating device, the heating unit still including set up in the second heating mechanism of opposite side about the base unit.

Heating device, second heating mechanism can move about from top to bottom during the heating position, first heating mechanism reaches second heating mechanism is close respectively carry the platform during the heat dissipation position, first heating mechanism reaches second heating mechanism separates respectively and keeps away from carry the platform, second heating mechanism is in during the heat dissipation position extremely carry the distance of platform and compare during the heating position extremely carry the distance of platform long.

Heating device, the base unit still including set up in carry the interior air supply piece of platform, be used for right carry the platform to blow the air current.

Heating device, carry the platform to have two lateral walls spaced each other, first heating mechanism have can from top to bottom movably set up in base unit's last mount pad and set up in go up the mount pad orientation carry the first hot plate on platform's surface during the heating position, go up the mount pad with the lateral wall driving fit each other, just first heating mechanism carry the platform to reach second heating mechanism defines out the heating chamber jointly.

Heating device, heating unit is still including setting up in the hot blowing piece of one of them lateral wall, be used for it is right during the heating position the heating chamber blows the hot gas flow, it still includes the guide plate that the slope set up to go up the mount pad, the guide plate is in be located during the heating position the gas outlet department of hot blowing piece for direct the hot gas flow downwards to the heating chamber.

Heating device, the heating unit still including set up in the hot blowing piece of base unit and set up in the guide plate of first heating mechanism, the hot blowing piece is used for right carry the platform to blow the hot gas flow, the guide plate is located the gas outlet department of hot blowing piece for guide the hot gas flow downwards to carry the platform.

Heating device, carry the platform have the entrance side and be on the contrary the outlet side of entrance side, the base unit still including set up in carry the exhaust mechanism of platform and two set up in the piece of blowing of first heating mechanism, exhaust mechanism have two set up respectively in the entrance side reaches the air inlet of outlet side, the piece of blowing is located respectively the air inlet top can be facing to respectively the air inlet blows, with the separation carry platform and external gas flow.

The utility model discloses the oven is applicable to the heating work piece, the oven contains: a case unit including a case; and the heating device is arranged in the box body.

Oven, the box have the pan feeding mouth and be located the discharge gate of pan feeding mouth opposite end, the box unit still include two set up respectively in outside the box just be located the pan feeding mouth reaches the wind wall of discharge gate top blows the piece, the wind wall blows the piece and blows the air current downwards respectively in order to form the wind wall for separation outside air flows in inside the box.

Oven, carry the platform have the entrance side and be on the contrary the outlet side of entrance side, the base unit still including set up in carry the exhaust mechanism of platform and two set up in the piece of blowing of box, exhaust mechanism have two set up respectively in the entrance side reaches the air inlet of outlet side, the piece of blowing is located respectively the air inlet top can be facing to respectively the air inlet blows, with the separation carry the platform and flow with external gas.

The beneficial effects of the utility model reside in that: through heating unit first heating mechanism set up in one of them side about the base unit, first heating mechanism can be right carry the platform heating, reduce by a wide margin heating chamber intensification required time effectively promotes whole work efficiency, so can reach cost utility model's purpose really.

Drawings

Fig. 1 is a fragmentary, schematic plan view of a first embodiment of the toaster of the present invention, illustrating a heating unit in a heat dissipating position;

FIG. 2 is a schematic plan view of another perspective of the first embodiment illustrating the heating unit in the heat dissipating position;

FIG. 3 is a schematic cross-sectional view taken along line III-III of FIG. 1 illustrating the heating unit in the heat dissipating position;

FIG. 4 is a fragmentary plan view of the first embodiment illustrating the heating unit in a heating position;

FIG. 5 is a schematic plan view of the first embodiment illustrating the heating unit in the heating position;

FIG. 6 is a schematic cross-sectional view taken along line VI-VI of FIG. 4 illustrating the heating unit in the heating position; and

FIG. 7 is a schematic plan view taken along line VII-VII of FIG. 3 illustrating the distribution of air flow from a hot air blower of the heating unit and a blower of a cabinet unit;

figure 8 is a schematic cross-sectional view similar to figure 3 illustrating a second embodiment of the oven of the present invention with the heating unit in the heat dissipating position;

figure 9 is a schematic cross-sectional view similar to figure 6 illustrating a second embodiment of the oven of the present invention with the heating unit in the heating position;

FIG. 10 is a fragmentary plan view illustrating the venting mechanism and blowing members of the base unit of the second embodiment;

FIG. 11 is a schematic plan view taken along line XI-XI in FIG. 10, illustrating the positional relationship of the air discharging mechanism and air-blowing members with respect to the conveying table; and

fig. 12 is a schematic cross-sectional view similar to fig. 3 illustrating a third embodiment of the oven of the present invention with the heating unit in the heat dissipating position.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings and examples.

Referring to fig. 1 to 3, a first embodiment of the oven of the present invention is adapted to heat a workpiece 1, and after the workpiece 1 is cooled, the next process can be performed, and the workpiece 1 can be, for example, a printed circuit board. The oven includes a case unit 2 and a heating device 3.

The box unit 2 includes a box 21, an air blowing member 22 disposed in the box 21, two air wall blowing members 23 disposed outside the box 21, two baffles 24 movably disposed in the box 21 up and down, and an air exhausting member 25 disposed in the box 21. The box body 21 has a feeding port 211 and a discharging port 212 located at the opposite end of the feeding port 211, and the air wall blowing member 23 is located above the feeding port 211 and the discharging port 212, respectively, and can blow air downward to form an air wall for blocking the outside air from flowing into the box body 21. The blower 22 can continuously blow the air flow into the case 21, and can reduce the amount of dust in the case 21. The baffle 24 can move upward to close the inlet 211 and the outlet 212. The exhausting member 25 can exhaust the air flow blown by the blowing member 22 out of the box body 21 to form a flow field inside the box body 21.

The heating device 3 includes a base unit 4 and a heating unit 5. The base unit 4 comprises a transport table 41 adapted for placing the work piece 1, the transport table 41 having two side walls 411 spaced apart from each other. The heating unit 5 includes an upper heating mechanism 51 (i.e., a first heating mechanism), an upper lifting mechanism 52 connected to the upper heating mechanism 51, a lower heating mechanism 53 (i.e., a second heating mechanism), a lower lifting mechanism 54 connected to the lower heating mechanism 53, and a hot blowing member 55 disposed on one of the sidewalls 411 of the conveying table 41. The upper heating mechanism 51 and the lower heating mechanism 53 are respectively disposed at the upper and lower sides of the conveying table 41, and both are movable up and down relative to the conveying table 41 by the upper lifting mechanism 52 and the lower lifting mechanism 54, respectively. The upper heating mechanism 51 has an upper mounting base 511 disposed on the conveying table 41 in a vertically movable manner and an upper heating plate 512 disposed on the upper mounting base 511 facing the upper surface of the conveying table 41. The upper mounting seat 511 includes a main body 511a, two side bars 511b connecting two sides of the main body 511a, two side bars 511c disposed on two side edges of the main body 511a facing the surface of the conveying platform 41, and a baffle 511d obliquely disposed on one side bar 511 c. The side strips 511b are provided with adhesive tapes on their surfaces to be respectively adhered to the side walls 411, and the upper heating plate 512 is provided between the side strips 511c and the main body 511 a. The lower heating mechanism 53 has a lower mounting base 531 movably disposed on the conveying table 41 up and down and a lower heating plate 532 disposed on the lower mounting base 531 facing the lower surface of the conveying table 41. The upper heating plate 512 and the lower heating plate 532 are, for example, but not limited to, electric heating plates. In other embodiments, the lower heating mechanism 53 may be fixed, i.e. the lower lifting mechanism 54 can be omitted, and is not limited to this embodiment.

With reference to fig. 4 to 6, the heating unit 5 can move between a heating position and a heat dissipation position, the distance from the first heating mechanism to the conveying table at the heat dissipation position is longer than the distance from the first heating mechanism to the conveying table at the heating position, and the distance from the second heating mechanism to the conveying table at the heat dissipation position is longer than the distance from the second heating mechanism to the conveying table at the heating position. In the heating position, the upper heating mechanism 51 and the lower heating mechanism 53 move downward and upward to approach the conveying table 41, the side strips 511b of the upper mounting seat 511 of the upper heating mechanism 51 and the side walls 411 are sealed with each other, the lower mounting seat 531 of the lower heating mechanism 53 abuts against the conveying table 41, the upper heating mechanism 51, the conveying table 41 and the lower heating mechanism 53 define a heating cavity 412 together, and the guiding plate 511d is located at the air outlet of the hot blowing piece 55 to guide the hot air blown from the hot blowing piece 55 to the heating cavity 412 downward to the heating cavity 412, so as to raise the temperature in the heating cavity 412 quickly, and to make the overall heating process more efficient. In the heat dissipation position, the upper heating mechanism 51 and the lower heating mechanism 53 are spaced apart from the conveying table 41. It should be noted that, by means of the upper heating mechanism 51 and the lower heating mechanism 53 being movable up and down relative to the conveying table 41, the maintenance personnel can operate in a more flexible space during maintenance, compared with the existing heating device with a flip-top structure, one side of the cover is fixed to the housing and pivoted by the rotating shaft, such a structure results in a reduced maintenance space, and only maintenance can be performed from above, which is not easy to maintain, and the heating device 3 of the present invention is convenient for maintenance.

The utility model discloses the oven is as follows to this heating chamber 412 preheating step and heat dissipation step: first, the oven is in an unheated state in an initial state, that is, the heating unit 5 is located at the heat dissipation position as shown in fig. 1 to 3, and then if the next batch of workpieces 1 needs to undergo the heating step, the oven is first started to perform the preheating step, so that the oven is converted from the unheated state to the heating state as shown in fig. 4 to 6, that is, the heating device 3 moves to the heating position and opens the upper heating plate 512 and the lower heating plate 532 to heat the heating cavity 412, and the baffle 24 moves upward to respectively close the material inlet 211 and the material outlet 212, so that the inside of the oven body 21 becomes a closed space, and the air flow is continuously blown downward by the air wall blowing member 23, thereby reducing the situation that the air flow inside the oven can communicate with the outside, and avoiding the external temperature from affecting the heating inside of the oven. Referring to fig. 7, the hot air blowing element 55 can blow hot air to the entire heating chamber 412, so as to quickly raise the temperature of the heating chamber 412, and it takes several tens of seconds to raise the heating chamber 412 to the operating temperature. When the heating chamber 412 rises to reach the corresponding working temperature, the baffle plate 24 is separated from the material inlet 211 and the material outlet 212, and the air wall blowing part 23 and the hot air blowing part 55 are closed, so that the workpieces 1 sequentially enter the material outlet 212 from the material inlet 211 and are output without pause in the middle until the batch of workpieces 1 to be heated completely passes through and the next batch of workpieces 1 does not need to be heated or the oven is cooled when the next batch of workpieces 1 does not exist.

In the heat dissipation step, the heating unit 5 moves to the heat dissipation position and closes the upper heating plate 512 and the lower heating plate 532 to stop heating the heating chamber 412, and blows air into the heating chamber 412 through the air blowing member 22 to achieve the effect of rapid cooling, and the temperature can be lowered to the corresponding working temperature as long as several tens of seconds, so that the next batch of workpieces 1 which do not need to be heated can pass through sequentially, i.e., enter the discharge port 212 from the feeding port 211 and are output without pause. That is, in a production line, workpieces 1 to be heated can be produced simultaneously by adding the oven, and workpieces 1 not to be heated can also be produced. The mechanism designed by the scheme can be used for calculating the temperature rise and fall time in tens of seconds, so that the production efficiency is greatly improved.

In another embodiment, the heating and heat dissipating steps of the oven for the workpiece 1 are substantially as follows: firstly, the workpiece 1 enters the conveying table 41 through the feeding port 211, at this time, the heating unit 5 is located at the heat dissipation position, after the workpiece 1 is positioned on the conveying table 41, the heating device 3 moves to the heating position, and the baffle 24 moves upward to respectively seal the feeding port 211 and the discharge port 212, so that the interior of the box body 21 becomes a closed space, and air flow is continuously blown downward by matching with the air wall blowing piece 23, so that the interior of the oven can be isolated from the outside as much as possible, and the influence of the outside temperature on the heating inside the oven is avoided. Referring to fig. 7, at this time, the hot blowing element 55 can blow the hot air to the entire heating cavity 412, so as to rapidly raise the temperature of the heating cavity 412 to heat the workpiece 1, which takes several tens of seconds to raise the temperature of the workpiece 1. After the heating is completed, the workpiece 1 needs to be cooled, the heating unit 5 is moved to the cooling position, and at this time, the baffle 24 is moved downward to open the inlet 211 and the outlet 212, the hot air blowing device 55 stops blowing hot air, and the air blowing device 22 blows air into the box 21, so that the space inside the box 21 and the workpiece 1 can be cooled quickly, and the corresponding working temperature can be reached in tens of seconds. The utility model discloses the oven has all shortened the required time by a wide margin on heating up and heat dissipation cooling relatively down, has effectively promoted whole work efficiency.

Referring to fig. 8 to 11, a second embodiment of the oven of the present invention is similar to the first embodiment, and the difference is that the base unit 4 of the heating device 3 further includes two inner air blowing members 42 disposed on the conveying platform 41, an exhaust mechanism 43 disposed on the lower side of the conveying platform, and two air blowing members 44 disposed on the box body, and the conveying platform 41 has an inlet side 413 and an outlet side 414 opposite to the inlet side 413. The heating unit 5 only includes the upper heating mechanism 51 and the upper lifting mechanism 52, the lower heating mechanism 53, the lower lifting mechanism 54 and the hot blowing part 55 are omitted, and the air guiding plate 511d of the upper heating mechanism 51 is omitted. The inner blowing members 42 are, for example, L-shaped, and stand on two opposite sides of the conveying table 41, and an opening of one inner blowing member 42 faces the inlet side 413, and an opening of the other inner blowing member 42 faces the outlet side 414, the inner blowing member 42 can blow an air flow to the conveying table 41 before the workpiece 1 enters the oven to reduce the amount of dust on the conveying table 41 and around the conveying table 41, so as to avoid the contamination of the workpiece 1 with dust when entering the oven, and in addition, the inner blowing member 42 can change the operation mode to blow hot air to the heating cavity 412 when the upper heating mechanism 51 moves to the heating position, thereby accelerating the temperature-increasing efficiency of the oven. The exhaust mechanism 43 has two air inlets 431 respectively disposed on the inlet side 413 and the outlet side 414, the blowing members 44 are respectively located above the air inlets 431 and can respectively blow air against the air inlets 431 to block the air flow between the conveying table 41 and the outside, on the other hand, the air flow blown by the inner blowing member 42 is also sucked into the exhaust mechanism 43 through the air inlets 431, so as to enhance the air flow function and achieve the effect of improving cleanliness, and of course, the air flow guided into the exhaust mechanism 43 can be recycled and reused according to the user's requirement, and blown out through the inner blowing member 42. The heating unit 5 is also movable between the heating position and the heat dissipation position. In the heating position, the upper heating mechanism 51 moves downward to approach the conveying table 41, and the side strips 511b of the upper mounting seat 511 of the upper heating mechanism 51 and the side walls 411 are tightly sealed, so that the upper heating mechanism 51 and the conveying table 41 jointly define the heating cavity 412.

Referring to fig. 12, a third embodiment of the oven of the present invention is similar to the second embodiment, and the difference is that the lower heating mechanism 53 is not omitted in the third embodiment, i.e. the lower heating mechanism 53 is fixedly disposed at the lower side of the conveying table 41 and cannot move up and down. However, although the hot blowing element 55 and the air deflector 511d are omitted in the second and third embodiments, in other embodiments, the hot blowing element 55 and the air deflector 511d are not required to be omitted, and the effect of greatly reducing the time required for heating the heating chamber 412 can also be achieved. The inner blowing elements 42 can be disposed in any embodiment or any heating mechanism, and the number of the inner blowing elements 42 can be only one, and can be adjusted (e.g., increased) as required to match with the exhaust mechanism 43, so that each implementation mode is not described again.

The blowing member 44, the blowing member 23 and the baffle 24 are similar in function and are suitable for blocking the mutual flow of the internal and external air during the heating process as much as possible, so that a user can select any mode according to actual requirements to complete the process, and the enhanced blocking function can be designed at the same time. Of course, the position where the blowing member 44 is provided is not limited to the upper heating mechanism 51, and may be provided in the case 21.

To sum up, the utility model discloses the oven sets up respectively in this both sides of this base unit 4 and all can move from top to bottom through this last heating mechanism 51 of this heating unit 5 and this lower heating mechanism 53, can closely heat this heating chamber 412 when this last heating mechanism 51 and this lower heating mechanism 53 are close to this base unit 4, and borrow the steam of this hot blowing spare 55 simultaneously, reduce this heating chamber 412 required time of intensification by a wide margin, in addition, when this heating chamber 412 need not be heated or maintain operating temperature, this base unit 4 just is kept away from to this last heating mechanism 51 and this lower heating mechanism 53, close this hot blowing spare 55 simultaneously, and let this air supply spare 22 blow and form the gas flow field, help this heating chamber 412 to dispel the heat to another operating temperature that corresponds fast, can reduce the required time of this heating chamber 412 cooling down equally, effectively promote whole work efficiency. The heating and cooling mechanism can be rapidly achieved through the oven, so that the workpiece 1 which is not required to be heated and is required to be heated can be produced simultaneously in a single production line, and the occupation of space is greatly reduced. Furthermore, since the upper heating mechanism 51 and the lower heating mechanism 53 of the heating device 3 can move up and down, the space is large and convenient during maintenance, so as to achieve the purpose of the present invention.

In addition, the number and the moving mode of the heating mechanisms can be correspondingly adjusted according to the requirements of users, and the effect of optimizing the processing efficiency of the production line can be achieved after the adjustment.

The above description is only for the preferred embodiment of the present invention, but it is not intended to limit the scope of the present invention, and any person skilled in the art can make further modifications and variations without departing from the spirit and scope of the present invention, therefore, the scope of the present invention should be determined by the appended claims.

Claims

1. A heating device adapted to heat a workpiece, the heating device comprising:

a base unit comprising a transport table adapted for placement of the workpiece; and

and the heating unit comprises a first heating mechanism arranged on one of the upper side and the lower side of the base unit, and the first heating mechanism is provided with a first heating plate for heating the workpiece.

2. The heating device according to claim 1, wherein the first heating means is movable up and down, and the heating unit is movable between a heating position in which the first heating means is close to the conveyance table and a heat radiation position in which the first heating means is spaced apart from the conveyance table, and wherein the distance from the first heating means to the conveyance table in the heat radiation position is longer than the distance from the first heating means to the conveyance table in the heating position.

3. The heating apparatus as claimed in claim 1, wherein the heating unit further comprises a second heating mechanism provided on the upper and lower sides of the base unit.

4. The heating apparatus as claimed in claim 2, wherein said heating unit further comprises a second heating mechanism provided on the other side of said base unit.

5. The heating device according to claim 4, wherein the second heating means is vertically movable, and in the heating position, the first heating means and the second heating means are respectively close to the transport table, and in the heat radiation position, the first heating means and the second heating means are respectively spaced apart and distant from the transport table, and in the heat radiation position, the distance from the second heating means to the transport table is longer than the distance from the second heating means to the transport table in the heating position.

6. The heating apparatus according to any one of claims 1 to 5, wherein the base unit further comprises an inner blowing member provided to the conveying table for blowing an air flow to the conveying table.

7. The heating apparatus according to claim 4 or 5, wherein the conveying table has two side walls spaced from each other, the first heating means has an upper mounting seat movably disposed up and down on the base unit and a first heating plate disposed on a surface of the upper mounting seat facing the conveying table, the upper mounting seat and the side walls are in close contact with each other in the heating position, and the first heating means, the conveying table and the second heating means collectively define a heating chamber.

8. The heating apparatus as claimed in claim 7, wherein the base unit further comprises an inner blowing member provided to the conveying table for blowing an air flow to the conveying table.

9. The heating apparatus as claimed in claim 7, wherein the heating unit further comprises a hot air blowing member disposed on one side wall thereof for blowing hot air to the heating chamber in the heating position, and the upper mounting base further comprises an inclined baffle plate disposed at an air outlet of the hot air blowing member in the heating position for guiding the hot air to the heating chamber.

10. The heating apparatus as claimed in claim 1, wherein the heating unit further comprises a hot blowing member provided to the base unit for blowing a hot air flow to the conveying table, and a baffle plate provided to the first heating mechanism at an outlet of the hot blowing member for guiding the hot air flow to the conveying table.

11. The heating apparatus as claimed in any one of claims 1 to 5 and 10, wherein the conveying table has an inlet side and an outlet side opposite to the inlet side, the base unit further comprises an exhaust mechanism provided on the conveying table and two air blowing members provided on the first heating mechanism, the exhaust mechanism has two air inlets provided on the inlet side and the outlet side, respectively, and the air blowing members are respectively located above the air inlets and capable of blowing air against the air inlets to block the flow of air from the outside.

12. The heating apparatus as claimed in claim 7, wherein the conveying table has an inlet side and an outlet side opposite to the inlet side, the base unit further comprises an exhaust mechanism disposed on the conveying table and two blowing members disposed on the first heating mechanism, the exhaust mechanism has two air inlets disposed on the inlet side and the outlet side, respectively, and the blowing members are respectively located above the air inlets and can blow air against the air inlets respectively to block the conveying table from flowing with the outside.

13. The heating apparatus as claimed in claim 11, wherein the base unit further comprises an inner blowing member provided to the conveying table for blowing an air flow to the conveying table.

14. An oven adapted to heat a workpiece, the oven comprising:

a case unit including a case; and

a heating device as claimed in any one of claims 1 to 10, provided in the tank.

15. The oven of claim 14 wherein said housing has an inlet and an outlet at opposite ends of said inlet, said housing unit further comprising two air wall blowers disposed outside said housing and above said inlet and said outlet, respectively, said air wall blowers blowing air downward to form air walls to block the flow of outside air into said housing.

16. The toaster of claim 14, wherein said conveyor has an inlet side and an outlet side opposite to said inlet side, said base unit further comprises an air exhausting mechanism disposed on said conveyor and two air blowing members disposed on said housing, said air exhausting mechanism having two air inlets disposed on said inlet side and said outlet side, respectively, said air blowing members being positioned above said air inlets and capable of blowing air against said air inlets, respectively, to block the flow of air from said conveyor to the outside.