Bag making machine heat sealing device and temperature control method thereof

Abstract

The invention discloses a heat sealing device of a bag making machine and a temperature control method of the heat sealing device. An electric heating plate of a transverse sealing device and an electric heating plate of a longitudinal sealing device in the heat sealing device each comprise two main electric heating pipes symmetrically arranged in the length direction. An electric heating plate in the longitudinal sealing device comprises a set of compensation electric heating pipes arranged between two sections of main electric heating pipes and two sets of compensation electric heating pipes arranged on the outer sides of the two sections of main electric heating pipes, and an electric heating plate in the transverse sealing device at least comprises a set of compensation electric heating pipes arranged between the two sections of main electric heating pipes. According to the invention, through the distribution of the main electric heating tube and the compensation electric heating tube on the electric heating plate and the design of a temperature control method of the heat-sealing hot knife, heat accumulation in the middle of the heat-sealing hot knife is effectively reduced, so that the heat-sealing hot knife realizes smaller temperature difference in the heat-sealing process, and the heat-sealing quality is further ensured; and on the other hand, through the design of the water cooling plate temperature control method, accurate control over the flow speed of condensate water is achieved, heat balance of the water cooling plate is achieved, and then the sealing quality is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of heat sealing, and in particular to a heat sealing device for a bag making machine and a temperature control method thereof. Background Art

[0002] The surface temperature difference of the heat-sealing knife of a bag-making machine is an important factor affecting the heat-sealing quality of plastic films. It is of practical significance to study how to reduce the surface temperature difference of the knife. The electric heating plate is an important component of the heat-sealing device of a bag-making machine. In recent years, great progress has been made in the research on the distribution of the temperature field of the electric heating plate. However, most of these studies are used on the electric heating plates of large-scale production equipment such as rubber injection machines and vulcanizers that use a large number of electric heating tubes. Compared with these electric heating plates, the electric heating plates of the heat-sealing device of a bag-making machine are relatively small in size, and the number of electric heating tubes used is also small. In addition, the traditional design of the electric heating plate of a bag-making machine ignores the heat transfer characteristics of the hot plate, which often causes a high surface temperature difference of the knife. Therefore, considering the influence of the internal structure design of the electric heating plate of the heat-sealing device of a bag-making machine on the distribution of the temperature field of the heat-sealing knife is an important way to study how to reduce the temperature difference of the heat-sealing temperature field of the bag-making machine.

[0003] The heat sealing device of the existing bag making machine generally includes a heat sealing mechanism and a water cooling mechanism, wherein the hot air mechanism includes an electric heating plate and a heat sealing knife, and the heat source is generally provided by two symmetrically arranged electric heating tubes of the same length as the electric heating plate. However, the temperature of the heat sealing knife's heat surface varies greatly, and the highest temperature appears at the center of the knife, and the lowest temperature appears at both ends of the knife;

[0004] In addition, current research on water cooling mechanisms in existing bag-making machine heat-sealing devices mostly focuses on improving cooling efficiency. However, the key is how to achieve thermal balance of the cooling plate by controlling the cooling water flow to achieve higher sealing quality.

[0005] Therefore, it is necessary to invent a heat sealing device and a temperature control method for a bag making machine which can reduce the temperature difference of the hot knife surface in the heat sealing mechanism and ensure that the cooling plate in the water cooling mechanism achieves thermal balance. Summary of the invention

[0006] In view of the above problems, the present invention proposes a heat sealing device for a bag making machine and a temperature control method thereof, and the technical scheme adopted is as follows:

[0007] A heat sealing device for a bag making machine, comprising a transverse sealing device, a longitudinal sealing device, a temperature monitor and a controller, wherein the transverse sealing device and the longitudinal sealing device both comprise a heat sealing mechanism and a water cooling mechanism; the heat sealing mechanism comprises a heat sealing knife 6 and an electric heating plate 7 arranged in the heat sealing knife 6, the water cooling mechanism comprises a cooling platen and a water cooling plate arranged in the cooling platen, and a cooling pipe is arranged in the water cooling plate; the temperature monitor is used to monitor the corresponding temperature values ​​in the heat sealing mechanism and the water cooling mechanism set by the controller; the characteristic is that the electric heating plate 7 in the transverse sealing device and the longitudinal sealing device The hot plates 7 each include two sections of main electric heating tubes 8 symmetrically arranged in the length direction; wherein, the hot plate 7 in the longitudinal sealing device includes a group of compensating electric heating tubes 9 arranged between the two sections of the main electric heating tubes 8 and two groups of compensating electric heating tubes 9 arranged outside the two sections of the main electric heating tubes 8, and the hot plate 7 in the transverse sealing device includes at least one group of compensating electric heating tubes 9 arranged between the two sections of the main electric heating tubes 8; temperature monitors are provided in the middle of the heat sealing knife 6 and at both ends of the working area, and temperature monitors are provided on the water inlet cooling pipe fittings and the return water cooling pipe fittings in the water cooling plate.

[0008] A temperature control method for a heat sealing device of a bag making machine, characterized in that it includes a heating step S1 of a heat sealing knife 6 in a heat sealing mechanism and a cooling step S2 of a cooling plate in a water cooling mechanism, specifically as follows:

[0009] The step S1 of heating the heat sealing knife 6 in the heat sealing mechanism comprises:

[0010] S11, according to the properties of the plastic film to be sealed, determine the final temperature T, the upper limit of the temperature difference X1 and the fall temperature difference X2 of this heating;

[0011] S12, using the main electric heating tube 8 to heat the electric heating plate 7, and recording the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area;

[0012] S13, according to the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area measured in step S12, calculate the local temperature difference ΔTa in the working area of ​​the heat sealing knife 6, if the local temperature difference ΔTa is less than the upper limit of the temperature difference X1, continue to use the main electric heating tube 8 to heat the electric heating plate 7 until the middle temperature value T1 and the temperature values ​​T2 at both ends of the working area reach the final temperature T or the local temperature difference ΔTa is greater than the upper limit of the temperature difference X1; when the middle temperature value T1 and the temperature values ​​T2 at both ends of the working area reach the final temperature T, the heating step S1 is completed; when the local temperature difference ΔTa is greater than the upper limit of the temperature difference X1, start the compensation electric heating tube 9 for heating, and proceed to step S14;

[0013] S14, the compensation electric heating tube 9 heats the electric heating plate 7 with the compensation power W1, and records the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area, and calculates the local temperature difference ΔTa of the working area of ​​the heat sealing knife 6, until the local temperature difference ΔTa is less than the fall temperature difference X2, and then turns off the compensation electric heating tube 9;

[0014] S15, based on step S14, determine whether the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area have reached the final temperature T. If the final temperature T has not been reached, continue to step S12 for heating; if the final temperature T is met, the heating step is completed;

[0015] The cooling step S2 of cooling the pressing plate in the water cooling mechanism comprises:

[0016] S21, setting the condensing water temperature T3, the initial flow rate V1, and setting the maximum value of the temperature rise ΔTb of the water cooling plate to X3;

[0017] S22, a water cooling plate cools the plastic film after sealing and hot stamping;

[0018] S23, measuring the temperature rise ΔTb of the water cooling plate after one operation;

[0019] S24. According to the temperature rise ΔTb of the water cooling plate after one operation obtained in step S23, compare ΔTb with the maximum value X3. If ΔTb is greater than the maximum value X3, it is considered that the water cooling plate is heated up too fast, and condensed water is added at a flow rate V2 for cooling until ΔTb is less than the maximum value X3. If the local maximum temperature difference ΔTb is less than the maximum value X3, it is considered that the water cooling plate is heated up normally, and the water cooling plate continues to work under the set environment.

[0020] Furthermore, the material properties of the plastic film include thermal conductivity, temperature of the fluid medium, thermal diffusion coefficient, material density, material specific heat, heat resistance temperature and melting temperature.

[0021] Further, in step S14, the compensation power W1 is determined as follows:

[0022] S141, according to the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area measured in step S12, a temperature T-distance S function relationship curve of the heat sealing knife 6, as well as the temperature, heat flux density and entropy of the fluid medium are obtained by simulation;

[0023] S142. Determine the compensation heating amount Q according to the data obtained in S141. The specific expression is as follows:

[0024]

[0025] In the formula, α = λ / ρc is the thermal diffusion coefficient, λ is the thermal conductivity of the object, c is the specific heat of the material, t f is the temperature of the fluid medium, p is the working pressure of the hot knife, ρ is the material density, and s is the entropy;

[0026] S143, determining the compensation power W1 according to the compensation heating amount Q obtained in S142,

[0027] When the electric heating plate 7 in the horizontal sealing device only includes a group of compensation electric heating tubes 9 arranged between two sections of main electric heating tubes 8, the compensation power W1 of the compensation electric heating tubes 9 in the horizontal sealing device is expressed as follows:

[0028]

[0029] In the formula, Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density;

[0030] The compensation power W1 of the compensation electric heating tube 9 in the longitudinal sealing device is expressed as follows:

[0031]

[0032] In the formula, Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density;

[0033] When the electric heating plates 7 in the horizontal sealing device and the vertical sealing device both include a group of compensating electric heating tubes 9 arranged between the two sections of the main electric heating tubes 8 and two groups of compensating electric heating tubes 9 arranged outside the two sections of the main electric heating tubes 8, the expressions of the compensation power W1 of the compensating electric heating tubes 9 in the horizontal sealing device and the vertical sealing device are both as follows:

[0034]

[0035] Where Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density.

[0036] Further, in step S24, the flow rate V2 is determined as follows:

[0037] S241, according to the temperature rise ΔTb of the water cooling plate measured in step S23, the condensed water Reynolds number, heat flux density and entropy are obtained by simulation;

[0038] S242, determine the flow rate V2 according to the data obtained in S241, and the specific expression is as follows:

[0039]

[0040] Where Re is the Reynolds number, ΔTb is the temperature rise of the water cooling plate when it works once, L is the length of the working area of ​​the water cooling plate, λ is the thermal conductivity of the object, ρ is the material density, and c is the specific heat of the material.

[0041] Since the present invention adopts the above technical solution, the present invention has the following advantages:

[0042] The present invention effectively reduces the heat accumulation in the middle of the heat sealing knife through the distribution of the main electric heating tube and the compensation electric heating tube on the electric heating plate and the design of the heat sealing knife temperature control method, so that the heat sealing knife achieves a smaller temperature difference during the heat sealing process, thereby ensuring the heat sealing quality; on the other hand, through the design of the water cooling plate temperature control method, the precise control of the condensed water flow rate is achieved, so that the water cooling plate achieves thermal balance, thereby effectively improving the sealing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the assembly structure of the transverse sealing device and the longitudinal sealing device in the heat sealing device of the bag making machine of the present invention.

[0044] Figure 2 Schematic diagram of the heat sealing mechanism structure of the transverse sealing device in an embodiment of the present invention.

[0045] Figure 3-4 Schematic diagram of the heat sealing mechanism structure of the longitudinal sealing device in an embodiment of the present invention.

[0046] Figure 5 The figure is a schematic flow chart of the temperature control method of the heat sealing device of the bag making machine of the present invention.

[0047] Figure Number:

[0048] 1-plastic film; 2-heat sealing mechanism of longitudinal sealing device; 3-water cooling mechanism of longitudinal sealing device; 4-heat sealing mechanism of transverse sealing device; 5-water cooling mechanism of transverse sealing device; 6-heat sealing knife; 7-electric heating plate; 8-main electric heating tube; 9-compensation electric heating tube. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further specifically described below by way of embodiments and in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0050] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "up", "down", "in", "out", "front", "back", etc. are based on the directions or positional relationships shown in the accompanying drawings, or are the directions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0051] like Figure 1-4 As shown, a heat sealing device for a bag making machine includes a transverse sealing device, a longitudinal sealing device, a temperature monitor and a controller. Both the transverse sealing device and the longitudinal sealing device include a heat sealing mechanism and a water cooling mechanism. The heat sealing mechanism includes a heat sealing knife 6 and an electric heating plate 7 arranged in the heat sealing knife 6. The water cooling mechanism includes a cooling platen and a water cooling plate arranged in the cooling platen. A cooling pipe is arranged in the water cooling plate. The temperature monitor is used to monitor the corresponding temperature values ​​in the heat sealing mechanism and the water cooling mechanism set by the controller. The electric heating plates 7 in the transverse sealing device and the longitudinal sealing device include symmetrically arranged in the length direction. Two sections of main electric heating tubes 8; wherein, the electric heating plate 7 in the longitudinal sealing device includes a group of compensating electric heating tubes 9 arranged between the two sections of the main electric heating tubes 8 and two groups of compensating electric heating tubes 9 arranged outside the two sections of the main electric heating tubes 8, and the electric heating plate 7 in the transverse sealing device includes at least one group of compensating electric heating tubes 9 arranged between the two sections of the main electric heating tubes 8; temperature monitors are provided in the middle of the heat sealing knife 6 and at both ends of the working area, and temperature monitors are provided on the water inlet cooling pipe and the return water cooling pipe in the water cooling plate; in this embodiment, the temperature monitor can be an infrared temperature measuring camera or a temperature measuring camera;

[0052] In this embodiment, Figure 1 As shown, the heat sealing device of the bag making machine includes a longitudinal sealing device heat sealing mechanism 2, a longitudinal sealing device water cooling mechanism 3, a transverse sealing device heat sealing mechanism 4 and a transverse sealing device water cooling mechanism 5 which are arranged in sequence from front to back.

[0053] The temperature control method of the heat sealing device of the bag making machine in this embodiment includes a heating step S1 of the heat sealing knife 6 in the heat sealing mechanism and a cooling step S2 of the cooling plate in the water cooling mechanism, which are specifically as follows:

[0054] The step S1 of heating the heat sealing knife 6 in the heat sealing mechanism comprises:

[0055] S11, according to the properties of the plastic film to be sealed, determine the final temperature T, the upper limit of the temperature difference X1 and the fall temperature difference X2 of this heating;

[0056] S12, using the main electric heating tube 8 to heat the electric heating plate 7, and recording the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area;

[0057] S13, according to the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area measured in step S12, calculate the local temperature difference ΔTa in the working area of ​​the heat sealing knife 6, if the local temperature difference ΔTa is less than the upper limit of the temperature difference X1, continue to use the main electric heating tube 8 to heat the electric heating plate 7 until the middle temperature value T1 and the temperature values ​​T2 at both ends of the working area reach the final temperature T or the local temperature difference ΔTa is greater than the upper limit of the temperature difference X1; when the middle temperature value T1 and the temperature values ​​T2 at both ends of the working area reach the final temperature T, the heating step S1 is completed; when the local temperature difference ΔTa is greater than the upper limit of the temperature difference X1, start the compensation electric heating tube 9 for heating, and proceed to step S14;

[0058] S14, the compensation electric heating tube 9 heats the electric heating plate 7 with the compensation power W1, and records the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area, and calculates the local temperature difference ΔTa of the working area of ​​the heat sealing knife 6, until the local temperature difference ΔTa is less than the fall temperature difference X2, and then turns off the compensation electric heating tube 9;

[0059] S15, based on step S14, determine whether the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area have reached the final temperature T. If the final temperature T has not been reached, continue to step S12 for heating; if the final temperature T is met, the heating step is completed;

[0060] The cooling step S2 of cooling the press plate in the water cooling mechanism comprises:

[0061] S21, setting the condensing water temperature T3, the initial flow rate V1, and setting the maximum value of the temperature rise ΔTb of the water cooling plate to X3;

[0062] S22, a water cooling plate cools the plastic film after sealing and hot stamping;

[0063] S23, measuring the temperature rise ΔTb of the water cooling plate after one operation;

[0064] S24. According to the temperature rise ΔTb of the water cooling plate after one operation obtained in step S23, compare ΔTb with the maximum value X3. If ΔTb is greater than the maximum value X3, it is considered that the water cooling plate is heated up too fast, and condensed water is added at a flow rate V2 for cooling until ΔTb is less than the maximum value X3. If the local maximum temperature difference ΔTb is less than the maximum value X3, it is considered that the water cooling plate is heated up normally, and the water cooling plate continues to work under the set environment.

[0065] In this embodiment, the material properties of the plastic film include thermal conductivity, temperature of the fluid medium, thermal diffusion coefficient, material density, material specific heat, heat resistance temperature and melting temperature.

[0066] In step S14, the compensation power W1 is determined as follows:

[0067] S141, according to the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area measured in step S12, a temperature T-distance S function relationship curve of the heat sealing knife 6, as well as the temperature, heat flux density and entropy of the fluid medium are obtained by simulation;

[0068] S142. Determine the compensation heating amount Q according to the data obtained in S141. The specific expression is as follows:

[0069]

[0070] Where α = λ / ρc is the thermal diffusion coefficient, λ is the thermal conductivity of the object, c is the specific heat of the material, t f is the temperature of the fluid medium, p is the working pressure of the hot knife, ρ is the material density, and s is the entropy;

[0071] S143, determining the compensation power W1 according to the compensation heating amount Q obtained in S142,

[0072] When the electric heating plate 7 in the horizontal sealing device only includes a group of compensation electric heating tubes 9 arranged between two sections of main electric heating tubes 8, the compensation power W1 of the compensation electric heating tubes 9 in the horizontal sealing device is expressed as follows:

[0073]

[0074] In the formula, Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density;

[0075] The compensation power W1 of the compensation electric heating tube 9 in the longitudinal sealing device is expressed as follows:

[0076]

[0077] In the formula, Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density;

[0078] When the electric heating plates 7 in the horizontal sealing device and the vertical sealing device both include a group of compensating electric heating tubes 9 arranged between the two sections of the main electric heating tubes 8 and two groups of compensating electric heating tubes 9 arranged outside the two sections of the main electric heating tubes 8, the expressions of the compensation power W1 of the compensating electric heating tubes 9 in the horizontal sealing device and the vertical sealing device are both as follows:

[0079]

[0080] Where Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density.

[0081] In step S24, the flow rate V2 is determined as follows:

[0082] S241, according to the temperature rise ΔTb of the water cooling plate measured in step S23, the condensed water Reynolds number, heat flux density and entropy are obtained by simulation;

[0083] S242, determine the flow rate V2 according to the data obtained in S241, and the specific expression is as follows:

[0084]

[0085] Where Re is the Reynolds number, ΔTb is the temperature rise of the water cooling plate when it works once, L is the length of the working area of ​​the water cooling plate, λ is the thermal conductivity of the object, ρ is the material density, and c is the specific heat of the material.

[0086] The following is further described in conjunction with the embodiments:

[0087] In this embodiment, since the width of the plastic film is relatively small, the electric heating plate 7 in the transverse sealing device is set to include only one set of compensation electric heating tubes 9 arranged between two sections of main electric heating tubes 8;

[0088] The material of the electric heating plate 7 and the heat sealing knife 6 is cast aluminum, with a density of ρ=2700kg / m3, a specific heat of 880J / (kg·℃), and a thermal conductivity of 235W / (m·℃). The natural convection heat transfer coefficient of the electric heating plate 7 and the heat sealing knife 6 is 8.45W / (m2·℃), the initial temperature and the ambient air temperature are 22℃, and the input power of each electric heating tube is 1.5kW.

[0089] The heating step S1 of the heat sealing knife 6 in the heat sealing mechanism in the initial state is implemented as follows:

[0090] S11. According to the properties of plastic film, the suitable heat sealing temperature is 289-292°C, and the upper temperature difference X1 is set to 3°C and the lower temperature difference X2 is set to 1.5°C;

[0091] S12, start the main electric heating tube 8 to heat the electric heating plate 7, and record the middle temperature T1 of the heat sealing knife 6 and the temperature T2 at both ends of the working area;

[0092] S13, after heating for 1 minute, according to the middle temperature of the heat sealing knife 6 measured in S12 is 287°C, and the temperature values ​​at both ends of the working area are 292°C. At this time, the local temperature difference ΔTa is greater than the temperature difference value of 4°C, so the compensation heating tube is activated and step S14 is performed;

[0093] S14, the compensating electric heating tube 9 heats the electric heating plate 7 with a power of W1=962W, and records the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area;

[0094] In step S14, the compensation power W1 is determined as follows:

[0095] S141, according to the middle temperature value T1 of the heat sealing knife 6 and the temperature values ​​T2 at both ends of the working area of ​​the heat sealing knife measured in step S12, a function relationship curve of the transverse sealing temperature T-transverse distance S, as well as the temperature, heat flux density and entropy of the fluid medium are obtained by simulation, wherein the fluid medium is an ideal gas (an ideal gas is a physical model for studying gas properties);

[0096] S142. Determine the compensation heating amount Q according to the data obtained in S141. The specific expression is as follows:

[0097]

[0098] Where α = λ / ρc is the thermal diffusion coefficient, λ is the thermal conductivity of the object, c is the specific heat of the material, t f is the temperature of the fluid medium, p is the working pressure of the hot knife, ρ is the material density, and s is the entropy;

[0099] S143, determining the compensation power W1 according to the compensation heating amount Q obtained in S142,

[0100] The compensation power W1 of the compensation electric heating tube 9 in the horizontal sealing device is expressed as follows:

[0101]

[0102] In the formula, Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density;

[0103] The compensation power W1 of the compensation electric heating tube 9 in the longitudinal sealing device is expressed as follows:

[0104]

[0105] In the formula, Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density;

[0106] The local temperature difference ΔTa of the heat sealing knife 6 is calculated. After heating for 3 minutes, when the local temperature difference ΔTa drops back to the drop temperature difference X2, the compensating electric heating tube is turned off.

[0107] S15. On the basis of step S14, determine whether the middle temperature value T1 and the temperature values ​​T2 at both ends of the working area meet the final temperature T. At this time, the middle temperature value T1 and the temperature values ​​T2 at both ends of the working area have not reached the final temperature of 298-292°C, then continue step S12 for heating. After 2 minutes of heating, the temperature values ​​at both ends are monitored to be 292°C, and the middle temperature value is 290°C. Calculate whether the local temperature difference ΔTa is higher than the temperature difference value 4°C / mm. The local temperature difference ΔTa falls back to the range of X2 after 2 minutes, and the heating is completed.

[0108] The cooling step S2 of cooling the press plate in the water cooling mechanism is implemented as follows:

[0109] S21, the initial temperature T3 of the water cooling plate is 20°C, and the temperature rise during the cooling process is required to be always less than X3 by 2°C / mm;

[0110] S22, passing condensed water, and the water cooling plate cools the plastic film after sealing;

[0111] S23, measuring the temperature rise ΔTb of the cooling plate after one operation;

[0112] S24. According to the temperature rise ΔTb of the cooling plate after one operation obtained in step S23, compare ΔTb with the maximum value X3. If ΔTb is greater than the maximum value X3, it is considered that the water cooling plate is heated up too fast, and condensed water is added at a flow rate V2 for cooling until ΔTb is less than the maximum value X3. If the local maximum temperature difference ΔTb is less than the maximum value X3, it is considered that the water cooling plate is heated up normally, and it continues to work under the set environment.

Claims

1. A heat sealing device for a bag making machine, comprising a transverse sealing device, a longitudinal sealing device, a temperature monitor and a controller, wherein the transverse sealing device and the longitudinal sealing device both comprise a heat sealing mechanism and a water cooling mechanism; the heat sealing mechanism comprises a heat sealing knife (6) and an electric heating plate (7) arranged inside the heat sealing knife (6), the water cooling mechanism comprises a cooling platen and a water cooling plate arranged inside the cooling platen, and a cooling pipe is arranged inside the water cooling plate; the temperature monitor is used to monitor the corresponding temperature values ​​in the heat sealing mechanism and the water cooling mechanism set by the controller; and the characteristics are as follows: The electric heating plate (7) in the transverse sealing device and the longitudinal sealing device both include two sections of main electric heating tubes (8) symmetrically arranged in the length direction; wherein, the electric heating plate (7) in the longitudinal sealing device includes a group of compensating electric heating tubes (9) arranged between the two sections of the main electric heating tubes (8) and two groups of compensating electric heating tubes (9) arranged outside the two sections of the main electric heating tubes (8), and the electric heating plate (7) in the transverse sealing device at least includes a group of compensating electric heating tubes (9) arranged between the two sections of the main electric heating tubes (8); temperature monitors are provided in the middle of the heat sealing knife (6) and at both ends of the working area, and temperature monitors are provided on the water inlet cooling pipe and the return water cooling pipe in the water cooling plate.

2. The temperature control method of a heat sealing device of a bag making machine according to claim 1, characterized in that: The method comprises a heating step S1 of a heat sealing knife (6) in a heat sealing mechanism and a cooling step S2 of a cooling plate in a water cooling mechanism, which are specifically as follows: The step S1 of heating the heat sealing knife (6) in the heat sealing mechanism comprises: S11, according to the material properties of the plastic film to be sealed, determine the final temperature T, the upper limit of the temperature difference X1 and the fall temperature difference X2 of this heating; S12, using the main electric heating tube (8) to heat the electric heating plate (7), and recording the middle temperature value T1 of the heat sealing knife (6) and the temperature values ​​T2 at both ends of the working area; S13, according to the middle temperature value T1 of the heat sealing knife (6) and the temperature values ​​T2 at both ends of the working area measured in step S12, the local temperature difference ΔTa of the working area of ​​the heat sealing knife (6) is calculated. If the local temperature difference ΔTa is less than the upper limit of the temperature difference X1, the main electric heating tube (8) continues to heat the electric heating plate (7) until the middle temperature value T1 and the temperature values ​​T2 at both ends of the working area reach the final temperature T or the local temperature difference ΔTa is greater than the upper limit of the temperature difference X1; when the middle temperature value T1 and the temperature values ​​T2 at both ends of the working area reach the final temperature T, the heating step S1 is completed; when the local temperature difference ΔTa is greater than the upper limit of the temperature difference X1, the compensation electric heating tube (9) is started to heat, and step S14 is performed; S14, the compensating electric heating tube (9) heats the electric heating plate (7) with the compensating power W1, and records the middle temperature value T1 of the heat sealing knife (6) and the temperature values ​​T2 at both ends of the working area, thereby calculating the local temperature difference ΔTa of the working area of ​​the heat sealing knife (6), until the local temperature difference ΔTa is less than the fall temperature difference X2, and then the compensating electric heating tube (9) is turned off; S15, based on step S14, determine whether the middle temperature value T1 of the heat sealing knife (6) and the temperature values ​​T2 at both ends of the working area have reached the final temperature T. If the final temperature T has not been reached, continue to step S12 for heating; if the final temperature T is met, complete the heating step S1; The cooling step S2 of cooling the pressing plate in the water cooling mechanism comprises: S21, setting the condensing water temperature T3, the initial flow rate V1, and setting the maximum value of the temperature rise ΔTb of the water cooling plate to X3; S22, a water cooling plate cools the plastic film after sealing and hot stamping; S23, measuring the temperature rise ΔTb of the water cooling plate after one operation; S24. According to the temperature rise ΔTb of the water cooling plate after one operation obtained in step S23, compare ΔTb with the maximum value X3. If ΔTb is greater than the maximum value X3, it is considered that the water cooling plate is heated up too fast, and condensed water is added at a flow rate V2 for cooling until ΔTb is less than the maximum value X3. If the local maximum temperature difference ΔTb is less than the maximum value X3, it is considered that the water cooling plate is heated up normally, and the water cooling plate continues to work under the set environment.

3. The temperature control method of a heat sealing device of a bag making machine according to claim 2, characterized in that: The plastic film material properties include thermal conductivity, temperature of the fluid medium, thermal diffusion coefficient, material density, material specific heat, heat resistance temperature and melting temperature.

4. The temperature control method of a heat sealing device of a bag making machine according to claim 2, characterized in that: In step S14, the compensation power W1 is determined as follows: S141, according to the middle temperature value T1 of the heat sealing knife (6) and the temperature values ​​T2 at both ends of the working area measured in step S12, a temperature T-distance S function relationship curve of the heat sealing knife (6), as well as the temperature, heat flux density and entropy of the fluid medium are obtained by simulation; S142. Determine the compensation heating amount Q according to the data obtained in S141. The specific expression is as follows: Where α = λ / ρc is the thermal diffusion coefficient, λ is the thermal conductivity of the object, c is the specific heat of the material, t f is the temperature of the fluid medium, p is the working pressure of the hot knife, ρ is the material density, and s is the entropy; S143, determining the compensation power W1 according to the compensation heating amount Q obtained in S142, When the electric heating plate (7) in the transverse sealing device only includes a group of compensation electric heating tubes (9) arranged between two sections of main electric heating tubes (8), the compensation power W1 of the compensation electric heating tubes (9) in the transverse sealing device is expressed as follows: In the formula, Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density; The compensation power W1 of the compensation electric heating tube (9) in the longitudinal sealing device is expressed as follows: In the formula, Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density; When the electric heating plates (7) in the horizontal sealing device and the vertical sealing device both include a group of compensating electric heating tubes (9) arranged between two sections of the main electric heating tubes (8) and two groups of compensating electric heating tubes (9) arranged outside the two sections of the main electric heating tubes (8), the expressions for the compensation power W1 of the compensating electric heating tubes (9) in the horizontal sealing device and the vertical sealing device are both as follows: Where Q is the compensation heating amount, t is the time required for a complete sealing, λ is the thermal conductivity of the object, ρ is the material density, c is the specific heat of the material, and q is the heat flux density.

5. The temperature control method of a heat sealing device of a bag making machine according to claim 2, characterized in that: In step S24, the flow rate V2 is determined as follows: S241, according to the temperature rise ΔTb of the water cooling plate measured in step S23, the condensed water Reynolds number, heat flux density and entropy are obtained by simulation; S242, determine the flow rate V2 according to the data obtained in S241, and the specific expression is as follows: Where Re is the Reynolds number, ΔTb is the temperature rise of the water cooling plate when it works once, L is the length of the working area of ​​the water cooling plate, λ is the thermal conductivity of the object, ρ is the material density, and c is the specific heat of the material.

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