A multilayer composite film soft-pack battery and a production process thereof

Abstract

The application provides a multilayer composite film soft package battery and a production process thereof, relates to coordinated control of deformation amount and temperature of a heating mold, preheating of a multilayer composite film, pit punching and temperature control, slow demolding when the temperature drops to 50-100 DEG C at a cooling speed of 0-50 DEG C / min; tab rubber is coated in advance on the surface of a tab, and then the multilayer composite film is heated and combined on both sides of the tab, and the application adopts a proper temperature control process to ensure the integrity of the multilayer composite film structure in stamping deformation, and even can obtain deep stamping performance superior to that of an existing aluminum plastic film.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soft package battery, in particular to a multi-layer composite film soft package battery and a production process thereof. BACKGROUND

[0002] Aluminum-plastic film soft package battery, as an advanced battery packaging technology, is widely used in new energy vehicles and other portable electronic devices. The following are its main advantages: high energy density: soft package battery is packaged by aluminum-plastic film, which can be more closely attached to the internal structure of the battery, so as to pack more active substances in the same volume, thereby improving the energy density of the battery. Good safety: compared with steel shell or aluminum shell battery, soft package battery usually only bulges or cracks from the sealing part to release energy when encountering safety hazards, without explosion, improving the safety in use. Design flexibility: the shape of soft package battery can be customized according to customer requirements, suitable for various irregular application scenarios, providing greater design flexibility. Light weight: due to the light weight of aluminum-plastic film material, soft package battery is about 40% lighter than steel shell lithium battery and 20% lighter than aluminum shell battery of the same capacity, which helps to reduce the total weight of the device, improve the portability and energy efficiency. Small internal resistance: lower internal resistance reduces battery self-consumption, improves battery efficiency and performance.

[0003] However, there are also some obvious disadvantages: short circuit risk, the aluminum foil layer in the aluminum-plastic film can effectively block the passage of water, but it also has good electrical conductivity, and the charge is conducted through the aluminum foil, which can easily cause local battery short circuit. Weak deep drawing ability, when the aluminum-plastic film production engineering is in the process of stamping forming, the stamping depth is increased, the plastic deformation ability of the aluminum foil layer and the inner layer is different, which can easily cause local rupture, and the resin layer inside the aluminum-plastic film is prone to splitting. This splitting causes the electrolyte to directly contact the aluminum foil layer, forming a local battery reaction, affecting the product qualification rate and long-term use safety.

[0004] The soft package battery with multi-layer composite film structure uses a multi-layer structure composite as a barrier film without using aluminum foil as a water barrier layer, forming a composite layer film with certain strength and toughness, for example, patent CN115195234A. The composite film uses an intermediate layer mixed with organic and inorganic water blocking agents to achieve the same water blocking effect. At the same time, due to the resin-based intermediate layer, it can protect and avoid the rupture of the inner layer resin, causing local short circuit.

[0005] The production process of the existing aluminum-plastic film soft-pack battery is as follows: aluminum-plastic film forming: the aluminum-plastic film is punched under heating conditions by using a mold to form a pit capable of accommodating the battery cell, which is called shell filling, pit punching or pit forming. Top side sealing process: including top sealing and side sealing, the top sealing is used to close the tab, and the side sealing forms the battery shell, during which the liquid injection port is left. Liquid injection and pre-sealing: electrolyte is injected into the formed aluminum-plastic film cavity, and preliminary sealing (one sealing) is performed to isolate the internal and external environments. Two sealing: after liquid injection and formation, the final sealing is performed to ensure the sealing of the battery.

[0006] However, there are the following significant differences between the production process of the multi-layer composite film soft-pack battery and the existing aluminum-plastic film preparation process: 1) the outer layer of the aluminum-plastic film is PE (nylon), the middle layer is aluminum foil, and the inner layer is PET resin. The aluminum-plastic film has an intermediate aluminum foil layer, which ensures uniformity of the whole film temperature during heating due to the thermal conductivity of the aluminum foil. The multi-layer composite film does not have such conditions; 2) the intermediate aluminum foil layer has a certain plastic deformation resistance, which can facilitate shell filling production, but the multi-layer composite film is a viscoelastic structure, which is prone to curling during cold stamping due to viscoelastic deformation. The aluminum foil layer in the aluminum-plastic film cannot completely recover the deformation characteristics after plastic deformation, while the resin often has viscoelasticity, and its plastic deformation characteristics can be significantly recovered when the temperature is not uniform. In the production of lithium batteries, the pit punching performance is an important guarantee for battery forming.

[0007] The existing production process of the aluminum-plastic film soft-pack battery cannot be directly applied to the production of multi-layer composite films and soft-pack batteries, which is reflected in the following two points: 1) weak shell filling capacity, which cannot be applied to subsequent battery production; 2) difficulty in temperature control for top side sealing, which is not easy to achieve. Direct application of the existing production process of the aluminum-plastic film soft-pack battery to the multi-layer composite film can easily cause battery bulging or liquid leakage. SUMMARY

[0008] In order to overcome the deficiencies in the prior art, the present application provides a multi-layer composite film soft-pack battery and a production process thereof. The multi-layer composite film mentioned in this paper is different from the aluminum-plastic film, which is a composite film without a metal layer in the middle, and the application number is 202211019003.0.

[0009] The present application adopts appropriate temperature control process to ensure the integrity of the multi-layer composite film structure in the stamping deformation, and even can obtain better deep drawing performance than the existing aluminum-plastic film.

[0010] To achieve the above-mentioned purpose, the present application provides a pit punching method of multi-layer composite film, which comprises the following steps,

[0011] The heating mold deformation and temperature coordination control: the heating mode of filamentous thermocouple arrangement is adopted, the temperature gradient is controlled to be 0-5℃ / cm according to the distance from the deformation center, the temperature of the edge of the deformation of the multilayer composite film is controlled to be higher than the overall mold temperature by 0-20℃;

[0012] The preheating of the multilayer composite film, the pit punching and temperature control: the multilayer composite film is preheated by hot air at 30-100℃, the lateral tension of the multilayer composite film is controlled to be 0-10N, the pit is punched at the temperature of 120-200℃, and the lateral tension is released when the pit is punched;

[0013] The cooling and demolding: the temperature is reduced to below 50-100℃ at the cooling speed of 0-50℃ / min, and the demolding is slowly performed;

[0014] The shell removing and top and side sealing: the multilayer composite film is heated and compounded on both sides of the pole ear to which the pole ear glue has been coated, the pole ear is heated to the surface temperature of 180-230℃, the top sealing pressure is controlled to be 2.5-3kgf / cm², the top sealing is completed, the temperature during the side sealing is lower than the aluminum plastic film side sealing temperature by 0-10℃, and the pressure maintaining and heat preservation time is controlled to be 3-20s.

[0015] Preferably, the heating mold deformation and temperature coordination control: the temperature gradient is controlled to be 1-3℃ / cm according to the distance from the deformation center, and the temperature of the edge of the deformation of the multilayer composite film is controlled to be higher than the overall mold temperature by 5-10℃.

[0016] Preferably, the preheating of the multilayer composite film, the pit punching and temperature control: the multilayer composite film is preheated by hot air at 50-90℃, the lateral tension of the multilayer composite film is controlled to be 0-2N, the pit is punched at the temperature of 120-200℃, and the lateral tension is released when the pit is punched.

[0017] Preferably, the cooling and demolding: the temperature is reduced to below 50-70℃ at the cooling speed of 5-20℃ / min.

[0018] Preferably, the shell removing and top and side sealing: the multilayer composite film is heated and compounded on both sides of the pole ear to which the pole ear glue has been coated, the pole ear is heated to the surface temperature of 190-220℃, the top sealing pressure is controlled to be 3.5-4kgf / cm², the top sealing is completed, the temperature during the side sealing is lower than the aluminum plastic film side sealing temperature by 3-6℃, and the pressure maintaining and heat preservation time is controlled to be 10-15s.

[0019] The application provides a system for implementing the pit punching method of the multilayer composite film.

[0020] The temperature control compensation heating mold: the temperature of the heating mold is controlled by the filamentous thermocouple, the filamentous thermocouple is adjusted according to the feedback of the temperature sensor, and the heating mold deformation and temperature coordination control of the multilayer composite film is realized.

[0021] Hot air preheating device: including hot air equipment and tension equipment, before the multilayer composite film enters the punching die, the hot air equipment and the tension equipment heat and apply tension to the multilayer composite film;

[0022] Punching die: heating and temperature adjustment of the punching die are realized by a filament thermocouple;

[0023] Cooling device: used for cooling the multilayer composite film after the punching is completed;

[0024] Demolding device: capable of slow demolding at a suitable temperature, avoiding the influence of the viscoelastic deformation rebound of the multilayer composite film on subsequent processing;

[0025] Top sealing device: including an induction heating device and an infrared thermometer, used for heating and composite of the tab rubber to complete the top sealing operation.

[0026] Preferably, the punching die and the heating die are combined by adjusting the arrangement of the thermocouples.

[0027] Preferably, the clamping end of the hot air preheating device is provided with a load sensor and a position actuator.

[0028] The beneficial effects of the present application are as follows:

[0029] In the punching process, the present application controls the temperature gradient, thereby reducing the deformation coordination ability of the composite film after punching. In the tab top sealing process, the tab rubber method and the surface induction heating method are adopted, which improves the bonding strength of the tab and the top sealing edge, and does not affect the sealing edge structure that has been bonded in other parts. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Schematic diagram of a heating fixed die;

[0031] Figure 2 Schematic diagram of a temperature gradient;

[0032] Figure 3 Arrangement of a filament thermocouple;

[0033] Figure 4 Schematic diagram of a soft package battery after folding and packaging;

[0034] Figure 5 Schematic diagram of a multilayer composite film soft package battery punching system structure. DETAILED DESCRIPTION

[0035] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in combination with specific embodiments.

[0036] The present application is based on the multi-layer composite film in patent 202211019003.0, in which the middle layer is a composite film of inorganic matter. The structure of this composite film includes an inner connecting layer film and an outer skeleton layer film.

[0037] Inner connecting layer film: made of a mixture of heat-bonding polymer (such as polypropylene or modified polypropylene) and water-blocking additives, which can be inorganic (such as titanium nitride, aluminum nitride, etc.) or organic (such as perfluorinated compounds) type, the amount of additive is 0.01-1 parts by weight, preferably 0.06-0.8 parts by weight.

[0038] Outer skeleton layer film: made of a mixture of high-melting-point polymer (such as polyethylene terephthalate or nylon) and water-blocking additives. The melting point of the high-melting-point polymer is in the range of 200-350℃, and the amount of water-blocking additive is the same as that of the inner layer, i.e. 0.01-1 parts by weight, preferably 0.06-0.8 parts by weight.

[0039] Overall, this composite structure enhances the waterproof performance of battery packaging by adding water-blocking agents in the inner and outer layers. The resulting battery after packaging does not leak and does not bulge during continuous charging and discharging.

[0040] Example 1

[0041] This example is based on the punching process in the production process of lithium batteries, and provides a punching process method of multi-layer composite film, the steps are as follows:

[0042] 1) Temperature coordination control of deformation amount and temperature of multi-layer composite film heating mold

[0043] The multi-layer composite film mentioned in this paper is different from the aluminum-plastic film, which is a composite film without metal layer in the middle, and the reference is application number 202211019003.0. Since the temperature uniformity of the multi-layer composite film is relatively sensitive, temperature compensation control needs to be performed on the heating mold. The temperature range of the overall mold is 120℃-200℃, for the commonly used soft shell (soft pack battery package) of the folded battery, the temperature of the folded edge is higher than the overall mold temperature by 0-20℃, preferably 5-10℃, and according to the distance from the deformation center, the temperature gradient is set to 0-5℃ / cm, preferably 1-3℃ / cm,

[0044] Temperature control is achieved through the arrangement of heating resistors, such as Figure 3 The arrangement of the fine filament thermocouple is shown in the figure, which is similar to the PT1000 fine filament thermocouple produced by the American PPG company. Through the dense arrangement of the thermocouple and the feedback of the temperature sensor, the temperature accurate control method is realized,

[0045] 2) Preheating multi-layer composite film, punching and temperature control

[0046] Pre-punching preheating control, before the multilayer composite film enters the mold pit of the punching mold, hot air of 30-100°C, preferably 50-90°C, is used to preheat the multilayer composite film, and the preheating time is 5-10 seconds, so that the mold base temperature is uniform,

[0047] During the preheating process, the two ends of the film are clamped by applying a weight of 0-1 kg, which is linked through a pulley to provide a restraining force; or a load sensor and a position actuator are applied to the clamped end to achieve closed-loop control of the preset load. The lateral tension of the composite film is controlled between 0-10N, preferably 0-2N. During the punching process, the lateral restraining force is released;

[0048] Generally, the punching temperature of the multilayer composite film varies depending on the type, thickness, and production process of the aluminum-plastic film material used, and for the multilayer composite film, the punching process temperature range is approximately 120-200°C. The punching temperature of the multilayer composite film is similar to that of the aluminum-plastic film, and needs to be determined according to the film thickness and material type, but is generally slightly lower than that of the aluminum-plastic film;

[0049] In this application, the heating mold and the punching mold are combined into one, that is, by modifying the arrangement of the thermocouple in the punching mold, the thermocouple arrangement wraps the heating mold and the punching mold at the same time, realizing the combination of the two for synchronous control, such as Figure 2 、 Figure 3 .

[0050] 3) Cooling and demolding

[0051] Referring to the aluminum-plastic film, after the punching is completed, the film is quickly demolded and enters the next production process. Due to the viscoelastic deformation characteristics of the multilayer composite film, rapid demolding will cause slow rebound, affecting subsequent production. Therefore, the cooling temperature and demolding speed need to be controlled, and the film is gradually demolded at a suitable temperature. It is recommended to use air cooling to reduce the temperature at a cooling speed of 0-50°C / min, preferably 5-20°C / min, and slowly demold when the temperature drops to below 50-100°C, preferably to below 50-70°C.

[0052] 4) Top side sealing of multilayer composite film

[0053] The main problem of side sealing of multilayer composite film occurs at the tab position, and excessive melting of the outer layer of the tab glue often leads to battery leakage or top sealing failure. Therefore, the top sealing process of the multilayer composite film at the tab position is different from that of the traditional aluminum-plastic film.

[0054] The tab glue is pre-coated on the tab surface, and then the multi-layer composite film is heated and laminated on both sides of the tab to complete the top seal operation. To improve the top seal reliability of the multi-layer composite film, the present invention proposes an induction heating method, using thermocouple heating in conjunction with an infrared thermometer, and the temperature is controlled between 180-250°C, preferably 200-230°C. The tab surface temperature is raised to the pre-fabrication temperature of 180-230°C, preferably 190-220°C, and then the top seal pressure is controlled between 2.5 and 5 kgf / cm², preferably 3.5-4 kgf / cm².

[0055] The side seal temperature is 0-10°C lower than that of the aluminum-plastic film, preferably 3-6°C. The side seal pressure is controlled between 2.5 and 3 kgf / cm², preferably 2.8-3.0 kgf / cm². The temperature is controlled between 150-200°C, preferably 180-200°C. The side seal pressure is the same as that of traditional aluminum-plastic film. The pressure and heat holding time is 3-20 seconds, preferably 10-15 seconds. Appropriately slowing the cooling rate is beneficial to the stability of the side seal.

[0056] After top and side sealing, the injection and side sealing processes are the same as with traditional aluminum-plastic film. Injection holes are left at the side seal edges to inject electrolyte into the battery pack. Furthermore, the secondary sealing process is the same as with traditional aluminum-plastic film. After injection, the side seal is completed at the injection hole location.

[0057] The present invention precisely controls the temperature through a temperature gradient during the punching process, thereby reducing the deformation and coordination ability of the composite film after the punching. When performing the tab top seal, the tab glue method and surface induction heating are used to improve the bonding strength between the tab and the top seal without affecting the already bonded edge seal structure of other parts.

[0058] Example 2

[0059] The present invention controls the temperature gradient during the flushing process to achieve balanced control of the temperature field. Specifically, the temperature sensor is arranged at the following positions: Figure 3 As shown in the figure, there are 6 groups of temperature sensors. Since the heating mold used in the preparation method is in a horizontally symmetrical state, the sensors are arranged in the upper or lower part, or in both the upper and lower parts as shown in the figure. Then, the quadratic curve is used to Figure 3 Data simulation is performed on the temperature region shown in the figure. Based on the target temperature range and gradient, a data model for the data temperature distribution is established. The collected independent data points are fitted to a quadratic curve using the least squares method. The temperature difference between the fitted quadratic curve and the independent region in the quadratic curve of the data model is evaluated. Based on the temperature difference, a PW wave with a duty cycle is used to control the heating thermocouple to ensure that the temperature measurement curve is as close to the target curve as possible. The specific steps are as follows:

[0060] 1. Data Collection:

[0061] Use sensors (such as thermocouples) to collect independent temperature data points within the target temperature range. These data should cover the entire temperature range to accurately reflect the temperature distribution;

[0062] 2 Data modeling:

[0063] According to the collected temperature data points, use the least squares method to fit these points to a quadratic curve. The equation of the quadratic curve is:

[0064] T(x)=ax 2 +bx+c,

[0065] Where T(x) is the temperature, x is the position coordinate, a, b, c are fitting parameters;

[0066] 3. Evaluate the fitting effect:

[0067] Calculate the temperature difference: compare the fitted quadratic curve with the target temperature range. The fitting effect can be evaluated by calculating the temperature difference at each independent temperature data point:

[0068] ΔTi=T target (xi)−T fitted (xi),

[0069] Where ΔTi is the temperature difference, T target( xi ) is the target temperature, T fitted( xi ) is the temperature of the fitted curve, Xi is the coordinate point in the distance direction, and Figure 2 The temperature measurement points of the crater mold are evenly spaced in the length or width direction, such as in the length direction, with an interval of 1mm, there are multiple data points, and only at a few specific positions there is temperature detection. Therefore, by comparing the temperature measurement value of the corresponding coordinate point Xi with the target value, the temperature difference ΔTi is calculated;

[0070] 4. Control strategy

[0071] PWM wave control heating: according to the temperature difference ΔTi, adopt pulse width modulation (PWM) control heater (such as heating thermocouple) to control heating. The duty cycle of the PWM signal can be adjusted according to the temperature difference to achieve precise temperature control, and the control algorithm is:

[0072] Duty Cycle=K⋅∣ΔTi∣

[0073] Where K is a proportional constant used to adjust the response speed of PWM control, Duty Cycle is the duty cycle, which is the ratio of the duration of high level to the total time of a period. It is usually expressed in percentage:

[0074] Duty Cycle = (Thigh / Ttotal) x 100%

[0075] Where T Thigh is the duration of the PWM signal at high level, T Ttotal is the time of a complete period. ΔTi is the difference between the target temperature and the actual temperature, reflecting the current system temperature control error, which can be expressed as:

[0076] ΔTi = Ttarget - Tactual

[0077] ΔTi is positive, indicating that the heater needs to heat up to reach the target temperature, i.e. when Δ Ti >= 0, K = 0, not to provide heating; negative value indicates the need to reduce temperature, i.e. when Δ Ti <0, K > 0, control the heating system to heat up;

[0078] The value of the proportional constant K determines the degree of influence of temperature difference on duty cycle. Higher K value will make the system more sensitive to temperature changes, with faster response; while lower K value will result in slower system response, which may cause larger temperature fluctuations;

[0079] 5. Real-time adjustment using cyclic feedback control:

[0080] In practical applications, continuous monitoring of temperature changes and real-time adjustment of PWM signal duty cycle are required to ensure the best approximation of temperature measurement curve to target curve. PID control strategy can be used to optimize the temperature control process, and the control effect can be verified by experiment to observe whether the temperature curve is stable within the target range. If necessary, adjust the control parameters (such as proportional constant K) to optimize performance.

[0081] The inorganic composite film involved in the present application has an inner layer of thermally bonded polymer polypropylene with a thickness of 60 microns, and an outer layer of nylon skeleton layer with a thickness of 80 microns, and a total thickness of about 140 microns. Using the traditional method without temperature gradient control (traditional thermocouple mold process), 100 sets of soft pack batteries are prepared, and using the method involved in the present application, 100 sets of soft pack batteries are prepared. Since the electrolyte in the battery is gray-black, and the soft pack battery is completely transparent, it can be judged by visual inspection. After a certain period of testing, the product soft pack battery does not leak and does not separate, which is considered to pass. The pass rate test results of the soft pack battery prepared by the above composite film are shown in Table 1:

[0082] Table 1. Test results of pass rate of composite film prepared soft-pack battery

[0083] .

[0084] Finally, it should be noted that the above examples are merely intended to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for preparing a multi-layer composite film soft-pack battery, characterized in that: The multilayer composite film includes an inner connecting layer film and an outer skeleton structure layer film. The multilayer composite film is different from the aluminum-plastic film in that it is a composite film without a metal layer in the middle. The preparation method of the multilayer composite film includes the following steps: Coordinated control of mold deformation and temperature: Using a heating method with a filamentary thermocouple arrangement, the temperature gradient is controlled at 0-5°C / cm according to the distance from the deformation center. The temperature of the folded edge of the multi-layer composite film at the deformation point is controlled to be 0-20°C higher than the overall mold temperature. The overall mold temperature range is 120°C-200°C. Preheating the multi-layer composite film, punching holes and temperature control: Use 30-100℃ hot air to preheat the multi-layer composite film, control the lateral tension of the multi-layer composite film to 0-10N, punch holes at 120-200℃, and release the lateral tension during punching; Cooling and demoulding: Lower the temperature to below 50-100℃ at a cooling rate of 0-50℃ / min, and demould slowly; Shelling top and side sealing: The multi-layer composite film is induction heated and laminated on both sides of the tabs coated with tab glue, and the tabs are heated to a surface temperature of 180℃-230℃. The top sealing pressure is controlled at 2.5-3kgf / cm² to complete the top sealing. The side sealing temperature is 0-10℃ lower than the side sealing temperature of the aluminum-plastic film. The side sealing temperature is controlled between 150-200℃, and the pressure holding and heat holding time are controlled at 3-20s during side sealing.

2. The method for preparing a multi-layer composite film soft-pack battery according to claim 1, wherein: Coordinated control of mold deformation and temperature: The temperature gradient is controlled at 1-3°C / cm according to the distance from the deformation center, and the temperature of the folded edge at the deformation of the multi-layer composite film is controlled to be 5-10°C higher than the overall mold temperature.

3. The method for preparing a multi-layer composite film soft-pack battery according to claim 1, wherein: Preheating the multi-layer composite film, punching holes and temperature control: Use 50-90℃ hot air to preheat the multi-layer composite film, control the lateral tension of the multi-layer composite film to 0-2N, punch holes at a temperature of 120-200℃, and release the lateral tension during punching.

4. The method for preparing a multi-layer composite film soft-pack battery according to claim 1, wherein: Cooling and demoulding: reduce the temperature to below 50-70℃ at a cooling rate of 5-20℃ / min.

5. The method for preparing a multi-layer composite film soft pack battery according to claim 1, wherein: Shelling top and side sealing: Heat and laminate the multi-layer composite film on both sides of the tabs coated with tab glue, heat the tabs to their surface temperature of 190℃-220℃, control the top sealing pressure to 3.5-4kgf / cm², complete the top sealing, and the side sealing temperature is 3-6℃ lower than the side sealing temperature of the aluminum-plastic film during side sealing. Control the pressure holding and heat holding time to 10-15s.

6. A system for implementing the method for preparing a multi-layer composite film soft-pack battery according to any one of claims 1 to 5, characterized in that: include, Temperature control compensation heating mold: Use fine-wire thermocouples to control the temperature of the heating mold. Adjust the density of the fine-wire thermocouples according to the feedback from the temperature sensor to achieve coordinated control of the deformation and temperature of the heating mold of the multi-layer composite film. Hot air preheating device: including hot air equipment and tensioning equipment. Before the multi-layer composite film enters the punching die, the hot air equipment and tensioning equipment heat the multi-layer composite film and apply tension; Punching mold: The punching mold is heated and the temperature is adjusted by a thin-wire thermocouple; Cooling device: used to cool the multi-layer composite film after the punching is completed; Demolding device: It can slowly demould at a suitable temperature to prevent the multi-layer composite film from rebounding due to viscoelastic deformation and affecting subsequent processing; Top sealing device: includes induction heating equipment and infrared thermometer, which is used to heat and compound the ear glue to complete the top sealing operation.

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