Belt conveyor freezer

Abstract

For example, we provide a belt conveyor freezer that enables stable operation of the belt conveyor even when cooling or freezing objects in low-temperature environments below -40°C. [Solution] The belt conveyor freezer 1 according to the present invention comprises a belt 25 for conveying objects, a plurality of pulleys for driving or supporting the belt 25, and a cooling tunnel 9 for cooling or freezing objects conveyed by the belt 25 in a low-temperature space, and is characterized by comprising a pulley heating means 7 for heating the pulleys so that the outer surface temperature of the pulleys is higher than the dew point of the atmosphere of the operating environment.

Description

Technical Field

[0001] The present invention relates to a belt conveyor freezer capable of continuously cooling or freezing objects in a low-temperature space while conveying the objects by a belt conveyor.

Background Art

[0002] Conventionally, in fields such as the food industry, belt conveyor freezers that cool or freeze objects while conveying the objects by a belt conveyor have been used. The belt of a belt conveyor is formed in an endless shape and supported by a plurality of rotatably provided pulleys. One of these pulleys is connected to a drive device composed of a motor or the like, and the belt runs when the drive device applies rotational force to this pulley. A pulley connected to a drive device is referred to as a drive pulley, and the drive systems of belt conveyors are classified according to how the drive pulley is arranged.

[0003] As drive systems for belt conveyors, there are mainly head drive type and intermediate drive type. In a head drive type belt conveyor, one of the pulleys arranged at both ends of the belt conveyor serves as the drive pulley. In the case of the head drive type, this drive pulley serves as the head pulley (the foremost pulley in the conveying direction), and only forward operation conveying in only one direction is possible. An example of a belt conveyor freezer using a head drive type belt conveyor is disclosed in, for example, Patent Document 1.

[0004] On the other hand, in an intermediate drive type belt conveyor, a drive pulley is arranged at an intermediate portion of the belt conveyor. A pair of pulleys is arranged near the drive pulley so as to sandwich the drive pulley, and the pair of pulleys and the drive pulley generate the frictional force required for the belt to run. In the case of the intermediate drive type, either of the pair of pulleys arranged at both ends of the belt conveyor may serve as the head pulley, and both forward operation and reverse operation are possible.

[0005] Head-driven systems have a tension adjustment mechanism on the rearmost pulley (tail pulley) in the conveying direction, which results in variations in machine length due to tension adjustments. Therefore, they are not easy to integrate with existing equipment, but they have the advantage of being inexpensive to construct due to the small number of parts. On the other hand, while the intermediate drive system has more parts and therefore higher costs, it does not have length fluctuations because the tension adjustment mechanism is installed on a pulley located in the middle of the belt conveyor. Therefore, it is easy to combine with existing equipment and the machine can be made smaller compared to the head drive system, making it suitable even when installation space is limited.

[0006] In all drive systems, the belt is supported by each pulley with a constant tension applied to it. This creates friction between the drive pulley and the belt, which in turn transmits the rotational force of the drive pulley to the belt. For a belt conveyor to operate stably, the tension mentioned above must be applied evenly across the width of the belt.

[0007] If the tension distribution becomes uneven for any reason while the belt is running, the belt will move in the width direction (axis direction of the pulley). This phenomenon is called meandering. If the belt misaligns, it can disrupt production by causing the conveyor belt to operate stably, and furthermore, the belt may fall off the pulley, potentially stopping the machine.

[0008] Therefore, conventional belt conveyors are equipped with devices to suppress belt meandering and devices to detect and correct meandering. In the freezer device described in Patent Document 1, a rubber protrusion is provided on the back surface of one side edge of the belt, and a recess is provided on the outer surface of the pulley. By running the belt while the rubber protrusion is loosely fitted into the recess, the belt is prevented from meandering.

[0009] Furthermore, Patent Document 2 discloses a belt drive device capable of controlling the meandering of the belt. In the belt drive device described in Patent Document 2, a light-emitting element and a light-receiving element are arranged above and below the belt, and belt meandering is detected when the light sent from the light-emitting element to the light-receiving element is blocked by the belt deviating from the reference range. Furthermore, when belt meandering is detected, the belt is moved back into the reference range by tilting the drive pulley and / or other pulleys (drive roller and driven roller in Patent Document 2) to control the belt's meandering. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Re-table No. 2012 / 001797 (patent application 2010-542459) [Patent Document 2] Japanese Patent Publication No. 2008-195463 (Japanese Patent Application No. 2007-29930) [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] Conventional belt conveyor freezers have a cooling tunnel on the conveying path of the belt for cooling or freezing the object to be cooled. The inside of this cooling tunnel is a low-temperature space, for example, below -40°C, and objects are cooled and frozen by being transported through the cooling tunnel on a belt.

[0012] When an object passes through a cooling tunnel, the belt that carries the object is also cooled, which can cause frost or condensation to form on the belt's surface. Additionally, the pulleys supporting the belt also become cold, which can cause frost or condensation to form on their outer surfaces. In particular, if the belt conveyor is of the intermediate drive type as described above, the surface of the belt comes into contact with the outer surface of some of the pulleys, so frost or condensation that forms on the surface of the belt adheres to the pulleys.

[0013] When frost accumulates on the outer surface of the pulley, the frost adds extra tension to the belt, disrupting the belt's tension balance and causing it to meander. Furthermore, if condensation occurs on the outer surface of the drive pulley, moisture can get between the drive pulley and the belt, reducing friction and potentially causing the drive pulley to spin freely, resulting in a so-called slip phenomenon where rotational force is not transmitted to the belt. As described above, conventional belt conveyor freezers have been plagued by problems such as meandering and slipping caused by frost and condensation accumulating on the outer surface of the pulleys.

[0014] As mentioned above, Patent Document 1 prevents belt meandering by loosely fitting rubber protrusions provided on the back surface of the belt into recesses provided on the outer surface of the pulley while the belt is running. However, in low-temperature environments below -40°C, the rubber protrusions on the belt may break due to low-temperature brittleness. Furthermore, even if the rubber protrusions on the belt are not damaged, the anti-sway function may be lost if the recesses in the pulleys become filled with frost.

[0015] Patent Document 2 describes a method for correcting meandering by tilting a pulley when meandering is detected. However, if there is a large amount of frost accumulation, tilting the pulley may not be sufficient to control the meandering. Also, if the frictional force between the belt and the pulley is reduced due to condensation, the intended meandering control function may not be achieved.

[0016] As described above, Patent Documents 1 and 2 were intended for use in a general temperature range and were not sufficient to suppress meandering and slippage caused by frost and condensation, which are problems in belt conveyor freezers that cool and freeze objects in low-temperature spaces of -40°C or below.

[0017] The present invention was made to solve the above-mentioned problems, and aims to provide a belt conveyor freezer that enables stable operation of the belt conveyor even when cooling or freezing objects in a low-temperature space of -40°C or lower. [Means for solving the problem]

[0018] (1) A belt conveyor freezer according to the present invention comprises: a belt that conveys an object; a plurality of pulleys that drive or support the belt; and a cooling tunnel that cools or freezes the object conveyed by the belt in a low-temperature space, wherein the belt conveyor freezer comprises pulley heating means for heating the pulley such that an outer surface temperature of the pulley becomes higher than a dew point of an atmosphere of a usage environment.

[0019] (2) Furthermore, in the device according to (1) above, the pulley has a hollow cylindrical structure, the pulley heating means includes a heated fluid and a supply pipe that circulates and supplies the heated fluid to each pulley in a parallel state, and the pulley is heated by circulating and supplying the heated fluid from the supply pipe into the interior of the pulley.

[0020] (3) Furthermore, in the device according to (2) above, the pulley heating means supplies the heated fluid such that the heated fluid flows from one end of the pulley to the other end thereof, and a flowing direction of the heated fluid in each pulley is alternately opposite in an arrangement order of the respective pulleys with respect to the belt. Effects of the Invention

[0021] In the present invention, the provision of the pulley heating means for heating the pulleys makes it possible to prevent formation of frost and condensation on the outer surfaces of the pulleys in a belt conveyor freezer that cools or freezes objects in a low-temperature space. As a result, meandering and slipping of the belt are less likely to occur, and stable operation can be achieved.

[0022] Furthermore, since the formation of frost and condensation on the pulleys can be prevented, the pulleys can be arranged in the vicinity of the cooling tunnel regardless of the driving system of the belt conveyor. This makes it possible to make the machine smaller than conventional models, resulting in a space-saving belt conveyor freezer. [Brief explanation of the drawing]

[0023] [Figure 1] This is an explanatory diagram of a belt conveyor freezer according to an embodiment. [Figure 2] Figure 1 is a plan view of the belt conveyor section and the freezer section. [Figure 3] Figure 1 is a front view of the belt conveyor section and the freezer section. [Figure 4] This is a cross-sectional view of the support pulleys in the belt conveyor section. [Figure 5] This is an explanatory diagram of another embodiment of the belt conveyor freezer according to the embodiment. [Figure 6] This is an explanatory diagram of another embodiment of the pulley heating means. [Modes for carrying out the invention]

[0024] Figure 1 shows a belt conveyor freezer 1 according to one embodiment of the present invention. As shown in Figure 1, the belt conveyor freezer 1 of this embodiment includes a freezer section 3 for cooling or freezing an object such as food, a belt conveyor section 5 for transporting the object so that it passes through a cooling tunnel 9 of the freezer section 3, and a pulley heating means 7 for heating the pulleys of the belt conveyor section 5. The following describes each component in detail.

[0025] <Freezer section> Figures 2 and 3 show the plan view and front view of the freezer section 3 and belt conveyor section 5 of the belt conveyor freezer 1 shown in Figure 1. As shown in Figures 2 and 3, the freezer section 3 includes a cooling tunnel 9, which has a low-temperature interior, and a refrigerant supply means (not shown) for supplying refrigerant into the cooling tunnel 9.

[0026] The cooling tunnel 9 comprises an insulated tank 11, a fan 13 provided on the ceiling of the insulated tank 11, a fan motor 15 for driving the fan 13, and a temperature sensor 17 for measuring the temperature inside the insulated tank 11.

[0027] The insulated tank 11 has a sealed structure except for the entrance and exit areas where objects are brought in and out. Inside the insulated tank 11, a refrigerant is supplied by a refrigerant supply means, and the fan 13 distributes it within the insulated tank 11, thereby creating a low-temperature space inside the insulated tank 11. The internal temperature of the insulated tank 11 is constantly monitored by a temperature sensor 17 and maintained at a predetermined set temperature (e.g., -40°C).

[0028] The refrigerant supply means includes a valve for controlling the amount of refrigerant supplied, and piping for supplying the refrigerant to the insulated tank 11. As the refrigerant, a liquefied gas such as liquid nitrogen is used. Based on the temperature inside the insulated tank 11 measured by the temperature sensor 17, feedback control is performed, that is, the amount of refrigerant supplied is controlled by comparing the target temperature with the current temperature, thereby maintaining the temperature inside the insulated tank 11 at a predetermined set temperature.

[0029] <Belt Conveyor Section> As shown in Figure 3, the belt conveyor section comprises a frame 19, support pulleys 21a to 21h and a drive pulley 23 provided on the frame 19, a belt 25 stretched between the support pulleys 21a to 21h and the drive pulley 23, and a drive pulley motor 27 for driving the drive pulley 23. Note that in Figures 1 and 2, pulleys that overlap vertically in a plan view are not shown, and only some of the pulleys are illustrated.

[0030] The belt conveyor section 5 is of the intermediate drive type, with a drive pulley 23 provided in the center of the frame 19. A drive pulley motor 27 is provided near the drive pulley 23 and connected to it. In addition to the drive pulley 23, the frame 19 is provided with eight support pulleys 21a to 21h, and the endless belt 25 is supported by these nine pulleys, including the support pulleys 21a to 21h and the drive pulley 23 (see Figure 3). In this embodiment, the belt 25 is made of urethane, but the material of the belt is not particularly limited in the present invention.

[0031] In this specification, all pulleys other than the drive pulley 23 are referred to as "support pulleys," but their functions vary from one to another. For example, support pulleys 21a and 21h function as head pulley and tail pulley, respectively, positioned at the head and tail of the belt conveyor. The space between support pulleys 21a and 21h forms the conveying path for transporting the object. Although Figures 1 to 3 show the direction of belt travel (direction of object transport), as mentioned above, intermediate-drive belt conveyors can operate in both forward and reverse directions, so operation in the opposite direction to those shown is also possible. In that case, support pulley 21h becomes the head pulley and support pulley 21a becomes the tail pulley.

[0032] In addition, some of the support pulleys 21a to 21h function as tension pulleys that add tension to the belt, and others function as bend pulleys that change the direction of the belt's movement, but we will omit explanations of their individual functions. When simply referring to "pulley," it means both the drive pulley 23 and the support pulleys 21a to 21h.

[0033] Each pulley has a hollow cylindrical structure. As an example, a cross-sectional view of support pulley 21a is shown in Figure 4. The support pulley 21a has a shaft portion 29 and socket portions 31 provided at both ends of the shaft portion 29, and the belt 25 is supported on the shaft portion 29. The shaft portion 29 and the socket portion 31 each have a hollow structure, and the overall structure is a stepped hollow cylindrical structure.

[0034] As shown in Figure 4, the support pulley 21a has a hollow cylindrical structure, which allows the hot fluid described later to flow through the inside of the support pulley 21a from one end to the other, specifically from one socket portion 31 to the other socket portion 31, or from the other socket portion 31 to the first socket portion 31.

[0035] The above shows the internal structure of the support pulley 21a as an example, but the support pulleys 21b to 21h and the drive pulley 23 also have a similar hollow cylindrical structure, and all pulleys are capable of allowing hot fluid to flow through their interiors.

[0036] As shown in Figure 2, rotary joints 33 are provided at both ends of each pulley. Both ends of each pulley are connected via the rotary joints 33 to the supply pipes 35 of the pulley heating means 7, which will be described later. This allows hot fluid to be supplied to each pulley from the supply pipe 35 while each pulley is in a rotatable state.

[0037] In the belt conveyor section 5 configured as described above, the drive pulley motor 27 is driven to rotate the drive pulley 23, and the frictional force generated at that time causes the belt 25 to move.

[0038] When an object is placed on the upper surface of the belt 25 on the entry side (support pulley 21h side) of the cooling tunnel 9, the object is transported by the moving belt 25 and brought into the cooling tunnel 9. The object is cooled or frozen while moving within the low-temperature space inside the insulated tank 11, and then transported out through the cooling tunnel 9.

[0039] <Pulley heating method> The pulley heating means 7 heats the pulley so that the outer surface temperature of the pulley is higher than the dew point of the ambient air in the operating environment. Here, the dew point is the temperature at which moisture in the air in the room where the belt conveyor freezer 1 is installed begins to condense. As shown in Figure 1, the pulley heating means 7 of this embodiment includes a supply pipe 35, a hot fluid (not shown) filled in the supply pipe 35, a pump 37 for circulating the hot fluid in the supply pipe 35, and a hot fluid heating unit 39 for heating the temperature of the hot fluid to a predetermined temperature.

[0040] The supply pipe 35 is connected to rotary joints 33 provided at both ends of each pulley so as to circulate and supply the hot fluid to each pulley in parallel. The supply piping 35 consists of a supply pipe 41 located downstream of the heater 45 (described later) and a return pipe 43 located upstream of the heater 45.

[0041] The supply piping 41 consists of a single main pipe 41a extending downstream of the heater 45 and nine branch pipes 41b branching off from the main pipe 41a. Each branch pipe 41b is connected to a rotary joint 33 located on the right side of each pulley relative to the direction of travel of the belt 25. The return piping 43 consists of nine branch pipes 43a connected to a rotary joint 33 located on the left side of the direction of travel of the belt 25 at each pulley, and one main pipe 43b to which these branch pipes 43a are connected. The main pipe 43b is connected to the main pipe 41a of the outgoing piping 41. In Figure 1, not all pulleys are shown, so only six branch pipes 41b and 43a are depicted, but branch pipes 41b and 43a are connected to all nine pulleys in the same way. The black triangles in the diagram indicate the direction of flow of the warm fluid.

[0042] The warm fluid is a heat transfer medium for heating the pulley, and in this embodiment, it is water (hot water). The warm fluid is heated and maintained at a predetermined temperature by the warm fluid heating unit 39 so that the pulley can be heated to a temperature higher than the dew point in the operating environment.

[0043] In this embodiment, water was used, but the hot fluid of the present invention is not limited to water; any type of fluid that can be heated to the desired temperature is acceptable. For example, other liquids or gases may be used, specifically antifreeze, alcohol, or air (hot air). However, considering economic efficiency, safety, heat capacity (specific heat), etc., water is preferred as the thermal fluid in this invention.

[0044] The dew point varies depending on the temperature and relative humidity of the operating environment, and therefore the temperature required for the warm fluid also changes depending on the environment. For example, if the room temperature is low and the room is dry, the dew point will be low, and the temperature required for the warm fluid will also be low. The following is an example of a temperature setting for a hot fluid.

[0045] The Ministry of Health, Labour and Welfare's "Manual for Hygienic Management of Mass Catering Facilities" recommends that food businesses maintain a temperature of 25°C or lower and a relative humidity of 80% or lower as part of their facility temperature and humidity control. Therefore, if we assume that the environment of a typical food factory is 25°C and 80% RH relative humidity, the dew point in that environment will be approximately +22°C. If the dew point in the room where the belt conveyor freezer 1 is installed is approximately +22°C, the temperature of the hot fluid should ideally be around +30 to +40°C, taking into account that it will be cooled as it flows through the supply pipe 35 and pulleys.

[0046] As described above, the temperature of the hot fluid is determined by the dew point of the operating environment, but it is also advisable to set it appropriately by considering the heat resistance temperature of the belt 25 and a temperature that does not hinder the cooling or freezing of the object. For example, if the temperature of the hot fluid is too high, it can put a heat load on the belt 25, and the food being frozen will also be heated, which is undesirable as it can lead to product defects. Also, if the pulley becomes too hot, there is a risk of workers getting burned. Therefore, it is desirable to determine the temperature of the warm fluid within a range that is above the temperature at which the outer surface temperature of the pulley can be heated to be higher than the dew point, and below the heat resistance temperature of the belt 25, and more preferably below +40°C.

[0047] The hot fluid heating unit 39 consists of a heater 45(H) that heats the hot fluid, an indicator controller 47(TIC) that controls the heater 45 so that the temperature of the hot fluid reaches a predetermined temperature, and a temperature sensor 49(TE) that measures the temperature of the hot fluid, thereby heating and maintaining the hot fluid in the supply pipe 35 at a predetermined temperature. As mentioned above, the temperature of the hot fluid is determined according to the dew point of the operating environment of the belt conveyor freezer 1 and is preset in the indicator controller 47. The indicating controller 47 controls the heater 45 based on the set value and the measurement value from the temperature sensor 49, maintaining the hot fluid at a predetermined temperature.

[0048] Figure 1 shows an example in which the warm fluid is passed through each pulley from right to left relative to the direction of travel of the belt 25. However, the system is not limited to this, and the warm fluid may also be passed through from left to right relative to the direction of travel of the belt 25.

[0049] Next, we will explain the operation of the belt conveyor freezer 1 configured as described above. First, the pump 37 is started to circulate the water filled in the supply pipe 35. A temperature sensor 49 measures the temperature of the water circulating in the supply pipe 35, and based on this measurement, an indicator controller 47 controls the heater 45 to heat the water until it reaches a predetermined temperature.

[0050] The hot water heated by the heater 45 is supplied to each pulley by splitting from the main pipe 41a of the supply pipe 41 into nine branch pipes 41b. The hot water supplied to each pulley flows through the inside of each pulley from one end to the other and is discharged into the branch pipes 43a of the return pipe 43. As the hot water flows through the inside of each pulley, the heat from the hot water is transferred to the pulley, and each pulley is heated. The hot water discharged into the nine branch pipes 43a merges in the main pipe 43b and is supplied to the outflow pipe 41, circulating through the outflow pipe 41, each pulley, and the return pipe 43.

[0051] When the outer surface temperature of each pulley rises above the dew point of the operating environment, the freezer unit 3 and the belt conveyor unit 5 are activated to begin cooling or freezing the object. When the object is cooled or frozen, the belt 25 is cooled as it passes through the cooling tunnel 9, so the temperature of each pulley in contact with the belt 25 also decreases.

[0052] As the temperature of each pulley decreases, the temperature of the hot water flowing through the pulley also decreases. However, the indicator controller 47 controls the heater 45 in response to the decrease in the temperature of the hot water, heating the hot water, so that each pulley is always supplied with hot water at a predetermined temperature. As a result, although each pulley is in contact with the low-temperature belt 25, its outer surface temperature is maintained at a temperature higher than the dew point.

[0053] Conventionally, the belt 25, cooled by passing through the cooling tunnel 9, lowered the outer surface temperature of each pulley, causing condensation or frost to form on the outer surface of the pulleys, which led to the belt 25 meandering or slipping. In contrast, in this embodiment, hot water is constantly circulated and supplied inside each pulley, and the outer surface temperature of the pulley is maintained at a temperature higher than the dew point of the operating environment, thereby suppressing the occurrence of condensation and frost. Consequently, meandering and slippage of the belt 25 can be prevented, enabling stable operation.

[0054] Figure 1 shows an example where hot fluid is passed through each pulley from right to left in the direction of travel of the belt 25. In this case, the right side of each pulley (the inlet side of the hot fluid) heats up relatively easily, while the left side (the outlet side of the hot fluid) heats up less easily. Therefore, the temperature of the belt 25 in contact with these pulleys will be relatively higher on the right side in the direction of travel than on the left side. A large temperature difference between the left and right sides of belt 25 is undesirable because it may lead to uneven cooling and freezing of the object. Furthermore, if there is a large temperature difference between the left and right sides of the belt 25, the higher temperature area will expand and the lower temperature area will contract, which may disrupt the tensile balance applied to the belt 25 and could cause it to meander.

[0055] As described above, if hot fluid is passed through each pulley in the same direction, a temperature difference is likely to occur between the left and right sides of the belt 25, which may result in insufficient cooling of the product or belt meandering. Therefore, Figure 5 shows an example in which the pulley heating means 7 is configured to minimize temperature differences between the left and right sides of the belt.

[0056] The belt conveyor section 5 in Figure 5 is the same as the belt conveyor section 5 described in Figures 2 and 3. However, in Figure 5, pulleys that are not normally visible in a plan view are also shown in order to clarify the direction of flow of the hot fluid through each pulley. Figure 5 shows an example where the direction of hot fluid flow through each pulley is alternately opposite to the direction of flow through each pulley relative to the belt 25.

[0057] Here, the order in which each pulley is arranged relative to the belt 25 specifically refers to the order in which the pulleys are arranged so that a certain part of the belt 25 makes contact with it when the belt 25 is in motion. For example, if we designate a certain point on the belt 25 as point A in Figure 3, as the belt 25 moves, point A first contacts the support pulley 21a, then the support pulley 21b. Subsequently, point A on the belt contacts the support pulleys 21c, 21d, 23, 21e, 21f, 21g, and 21h in that order. In other words, in this embodiment, the order of the pulleys relative to the belt 25 is: support pulleys 21a to 21d, drive pulley 23, and support pulleys 21e to 21h.

[0058] In the embodiment shown in Figure 5, the main pipe 41a of the supply pipe 41 branches into two pipes. One of these branches into five branch pipes 41b, which are connected to the left rotary joint 33 of the support pulleys 21a, 21c, drive pulley 23, support pulleys 21f, and 21h. The other branch of the main pipe 41a branches into four branch pipes 41b, which are connected to the right rotary joint 33 of the support pulleys 21b, 21d, 21e, and 21g. Furthermore, five branch pipes 43a of the return pipe 43 are connected to the right-side rotary joint 33 of the support pulleys 21a, 21c, drive pulley 23, support pulleys 21f, and 21h, and four are connected to the left-side rotary joint 33 of the support pulleys 21b, 21d, 21e, and 21g, and these are connected to the main pipe 43b.

[0059] As the supply piping 35 is arranged as described above, the hot fluid flows from left to right in the direction of travel of the belt 25 through the support pulleys 21a, 21c, drive pulley 23, support pulleys 21f, and 21h. Therefore, the temperature of these five pulleys will be relatively higher on the left side than on the right side. On the other hand, in the support pulleys 21b, 21d, 21e, and 21g, the warm fluid flows from right to left with respect to the direction of travel of the belt 25, so the temperature on the right side of these four pulleys is relatively higher than that on the left side.

[0060] As a result, when point A in Figure 3 reaches support pulley 21a, the left side of belt 25 heats up more easily, and when it then reaches support pulley 21b, the right side of belt 25 heats up more easily. This process is repeated alternately, and after point A reaches support pulley 21h, it passes through the cooling tunnel 9, cools down, and returns to the position shown in Figure 3. In this way, as point A of the belt 25 moves, it alternately contacts the warm pulley on the left side and the warm pulley on the right side relative to the direction of travel of the belt 25, making it less likely for a temperature difference to occur between the left and right sides of the belt 25. This is true not only at point A but also along the entire length of belt 25. Therefore, in the embodiment shown in Figure 5, it is possible to heat each pulley while minimizing temperature differences between the right and left ends of belt 25. As a result, the tension distribution of belt 25 can be maintained uniformly, which suppresses meandering and allows for more stable operation.

[0061] As described above, in this embodiment, a pulley heating means 7 is provided to heat the pulley so that the outer surface temperature of the pulley is higher than the dew point of the ambient environment in which it is used. As a result, even when cooling or freezing an object in a low-temperature space of -40°C or lower, for example, condensation or frost is less likely to form on the outer surface of the pulley. This prevents belt 25 from meandering or slipping, enabling stable operation.

[0062] In the above embodiment, an intermediate-drive type belt conveyor freezer 1 was used as an example, but the present invention is not limited to this and can also be applied to a head-drive type belt conveyor freezer. However, since frost is more likely to accumulate on the pulleys in intermediate-drive belt conveyor freezers than in head-drive belt conveyors for the reasons described below, this invention is more effective in intermediate-drive belt conveyor freezers.

[0063] In the intermediate drive system, some of the pulleys are positioned to contact the surface of the belt 25 (support pulleys 21b, 21d, 21e, and 21g in Figure 3). As a result, frost that forms on the belt surface may adhere to the outer surfaces of these pulleys, making it easy for frost to accumulate on the outer surfaces of the pulleys and causing meandering. Therefore, in belt conveyor freezers where frost formation is a concern, the intermediate drive type is more difficult to operate stably than the head drive type, making the present invention more effective.

[0064] Furthermore, in the above embodiment, the cooling method for the freezer section 3 was a so-called liquefied gas type, in which liquid nitrogen was supplied to the cooling tunnel 9 to form a low-temperature space, but the present invention is not limited to this. The cooling method for the freezer section 3 may be a refrigeration type, such as that used in household refrigerators, that is, a method that uses a refrigerant such as fluorocarbon gas, carbon dioxide, or ammonia, and forms a low-temperature space within the cooling tunnel by a refrigeration cycle of the refrigerant.

[0065] Furthermore, the pulley heating means 7 of the above embodiment may also be provided with a storage tank for storing the hot fluid. By combining the storage tank with the supply piping 35, the temperature and flow rate of the hot fluid can be stabilized. However, if the temperature and flow rate of the hot fluid can be stabilized solely by the volume of the supply pipe 35, then the configuration without a storage tank, as in the embodiment, may be used.

[0066] Furthermore, although the above embodiment describes an example in which the pulley has a hollow cylindrical structure and is heated by passing a warm fluid through its interior, the pulley heating means of the present invention is not limited to this. Another example of a pulley heating method is shown in Figure 6.

[0067] The pulley heating means 51 in Figure 6 includes a heater 53, electrical wiring 55 that supplies power to the heater 53, and a slip ring 57 that electrically connects the heater 53 and the electrical wiring 55. The heater 53 has a heating element and is incorporated inside the pulley 59 so that the heat from the heating element is transferred to the pulley 59. The slip ring 57 is a rotary connector configured to supply power from a stationary body to a rotating body, and power supplied from a power source (not shown) to the electrical wiring 55 is supplied to the heater 53 via the slip ring 57. Since power is supplied to the heater 53 via the slip ring 57 in this way, the electrical wiring 55 will not get tangled or twisted even when the heater 53 rotates together with the pulley 59.

[0068] In the pulley heating means 51 configured as described above, the pulley 59 can be heated so that its outer surface temperature is higher than the dew point of the ambient environment in use. Furthermore, the temperature of the pulley 59 can be maintained even while the belt conveyor freezer is in operation, so the same effects as in the embodiment can be expected. [Examples]

[0069] We conducted specific experiments to confirm the effects of the belt conveyor freezer of the present invention, and the results are described below. In this example, a belt conveyor freezer configured similarly to that shown in Figure 1 was used, and experiments were conducted under the conditions shown in Table 1 below.

[0070] [Table 1]

[0071] The conveyor belt used was a urethane belt measuring W400 x L4000 mm, and it was operated at a speed of 2.6 m / min. Liquid nitrogen was supplied as a refrigerant to the cooling tunnel, maintaining the interior temperature at -40°C. The hot fluid used was hot water, and the set temperature for the hot water was +40°C. The direction of hot water flow to each pulley was the same for all pulleys, flowing from right to left relative to the direction of belt movement. Under these conditions, the belt conveyor freezer was operated for a certain period of time, and it was visually inspected whether frost or condensation occurred on the support pulleys or drive pulleys, as well as to check for any abnormal stops due to poor belt meander control or slippage.

[0072] In addition, as a conventional example, a belt conveyor freezer was operated for a certain period of time under the same conditions as described above, without passing hot fluid through the pulley. Table 2 shows the experimental results for the inventive example and the conventional example.

[0073] [Table 2]

[0074] As shown in Table 2, in the example of the invention, no frost or condensation was observed on the support pulley and drive pulley, and the belt conveyor freezer continued to operate stably. On the other hand, in conventional cases, belt slippage and other issues occurred shortly after starting operation, and the system became unable to operate normally after approximately one hour.

[0075] As described above, in this embodiment, it was confirmed that by applying the present invention, condensation and frost formation on the outer surface of the pulley can be prevented, and stable operation can be obtained. [Explanation of Symbols]

[0076] 1. Belt conveyor freezer 3 Freezer section 5. Belt conveyor section 7. Pulley heating means 9 Cooling tunnel 11 Insulated tank 13 Fans 15 Fan motors 17. Temperature sensor 19. Stand 21a~21h Support pulley 23 Drive pulley 25 belts 27 Motor for drive pulley 29 Shaft section 31 Socket part 33 Rotary Joint 35 Supply piping 37 Pumps 39 Hot fluid heating section 41 Outlet piping 41a Main piping 41b Branch pipe 43 Return piping 43a Branch pipe 43b Main piping 45 Heater 47 Indicating controller 49 Temperature sensor 51 Pulley heating means (other embodiments) 53 Heater 55 Electrical Wiring 57 Slip Rings 59 Pulley

Claims

1. A belt conveyor freezer comprising a belt for transporting objects, a plurality of pulleys for driving or supporting the belt, and a cooling tunnel for cooling or freezing the objects being transported by the belt in a low-temperature space, A belt conveyor freezer characterized by comprising a pulley heating means for heating the pulley so that the outer surface temperature of the pulley is higher than the dew point of the ambient temperature in the operating environment.

2. The aforementioned pulley has a hollow cylindrical structure, The pulley heating means comprises a hot fluid and a supply pipe that circulates and supplies the hot fluid to each pulley in parallel. The belt conveyor freezer according to claim 1, characterized in that the pulley is heated by circulating the hot fluid from the supply pipe into the inside of the pulley.

3. The pulley heating means supplies the hot fluid so that it flows from one end of the pulley to the other end. The belt conveyor freezer according to claim 2, characterized in that the direction of flow of the hot fluid in each pulley is alternately opposite in the order in which the pulleys are arranged with respect to the belt.

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