A stress-guided cryogenic cutting device and a cutting method thereof

Abstract

The application discloses a stress-guided low-temperature cutting device and a cutting method thereof, and relates to the technical field of brittle material cutting. The stress-guided low-temperature cutting device comprises a roller and a spraying module which are installed in a main body. Periodic distribution of indentation teeth is arranged on the surface of the roller to press periodic grooves on the surface of a plastic strip, form a stress concentration guide belt, make the stress of a cutting hob release along the groove path, and then spray refrigerant to the groove in a direction through the spraying module to realize local embrittlement, so that the groove preferentially breaks under the stress of the cutting hob. Through the synergistic effect of the pre-indentation stress and the refrigerant directional embrittlement, the material fracture behavior is changed from random fracture to controllable fracture, the neatness of the cutting section is improved, and the precise and efficient cutting of the plastic strip is realized. Not only the problems of irregular section or material tearing caused by stress diffusion in the traditional cold cutting process are avoided, but also the cutting load is significantly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the brittle material cutting technology field, in particular to a stress guiding low-temperature cutting device and a cutting method thereof. BACKGROUND

[0002] In the plastic granulation process, the extruder pushes the molten plastic to the multi-hole die, and under the constraint of the die, the molten plastic is transformed into a continuous strip. Then, the strip is quickly cooled and solidified in water to avoid adhesion. Subsequently, the solidified strip is cut into particles of uniform size using a cutting hob.

[0003] When the strip is made of heat-sensitive materials such as PLA and PHA, they are sensitive to temperature changes, and large changes in cooling temperature can cause large thermal stress in the material, which in turn increases the brittleness of the material. The increased brittleness undoubtedly increases the risk of material rupture during the subsequent granulation process, which may cause the formation of irregular cross-sections during cutting, affecting the quality of granulation. SUMMARY

[0004] One of the purposes of the present application is to solve the problem of brittle materials in the prior art that are difficult to form a neat cross-section during cutting, affecting the quality of granulation.

[0005] The second purpose of the present application is to provide a stress-guided low-temperature cutting method.

[0006] To achieve the above-mentioned one of the purposes, the present application adopts the following technical scheme: a stress-guided low-temperature cutting device, comprising a guide mechanism and a cutting hob arranged on the side of the guide mechanism, the guide mechanism comprising: a main body provided with a guide hole, the guide hole guiding the plastic strip for cutting granulation by the cutting hob.

[0007] The surface of the roller rotatably installed in the main body is provided with periodic distribution of indentation teeth to press periodic grooves on the surface of the plastic strip in the guide hole, forming a stress concentration guide belt, so that the stress of the cutting hob is released along the groove path.

[0008] The main body also has a jet module for directional jetting of refrigerant, which is configured to directionally jet refrigerant to the groove to achieve local embrittlement, so that the groove preferentially breaks under the stress of the cutting hob.

[0009] The present application has the following advantages:

[0010] The present application realizes precise and efficient cutting of the plastic strip through the synergistic effect of pre-indentation guidance and refrigerant directional embrittlement.

[0011] Specifically, the periodic indentation teeth on the roller surface press regular grooves on the surface of the plastic strip, forming a controllable stress concentration guide belt, so that the cutting stress is released along the predetermined path (thereby reducing the situation that the material is randomly broken to form a neat cross section), and the refrigerant injection module fills the grooves with low-temperature refrigerant, thereby enhancing the brittleness of the material through local ultra-low temperature and weakening the molecular chain bonding force in the groove area to guide the material to break at a specific location.

[0012] The present application changes the material breaking behavior from random breaking to controllable breaking by guiding the cutting stress through the groove structure of the plastic strip and by regulating the material of the groove structure through temperature, thereby improving the neatness of the cutting cross section. Not only does it avoid the irregular cross section or material tearing problem caused by stress diffusion in the traditional cold cutting process, but it also significantly reduces the cutting load (the plastic strip is easy to break, the overall plastic strip is not easy to bend and shake, and the cutting effect is better).

[0013] Further, in the embodiment of the present application, the plastic strip is a biobased degradable material, including at least one of polylactic acid, polyhydroxyalkanoate, and polybutylene succinate, and the groove depth is adapted to the material shrinkage rate.

[0014] Further, in the embodiment of the present application, the refrigerant is selected from at least one of liquid nitrogen, liquid carbon dioxide, dry ice particles, or low-temperature compressed air.

[0015] Further, in the embodiment of the present application, the main body is provided with a liquid nitrogen hole, the injection module is sealingly connected with the liquid nitrogen hole, the liquid nitrogen hole is in communication with a liquid nitrogen supply channel of the main body, and the liquid nitrogen supply channel is connected with a pump of a liquid nitrogen tank outside the main body through a liquid nitrogen delivery pipeline.

[0016] Further, in the embodiment of the present application, a negative pressure channel is arranged on the guide hole and in communication therewith, the negative pressure channel is located between the roller and the injection module, and the gas in the groove is discharged through the negative pressure channel to inhibit local heat convection.

[0017] Further, in the embodiment of the present application, the negative pressure channel is in communication with an air pressure channel of the main body, and the air pressure channel is connected with an air pressure pump outside the main body.

[0018] To achieve the above-mentioned purpose two, the present application adopts the following technical scheme: a stress-guided low-temperature cutting method, comprising the following steps:

[0019] A roller with periodic indentation teeth on the surface is used to press periodic grooves on the surface of the plastic strip, the groove depth is 0.05-0.3mm, and a stress concentration guide belt is formed.

[0020] The refrigerant is sprayed into the groove to rapidly reduce the temperature of the groove area to -200℃ to -50℃, thereby achieving local embrittlement.

[0021] The cutting hob is controlled to cut the plastic strip along the groove path.

[0022] Further, in the embodiment of the present application, a negative pressure of -30kPa to -80kPa is applied to the groove area before the refrigerant is sprayed to discharge gas and inhibit heat convection.

[0023] Further, in the embodiment of the present application, the refrigerant is selected from at least one of liquid nitrogen, liquid carbon dioxide, dry ice particles or low-temperature compressed air, and the refrigerant flow rate and the roller pressure satisfy the following relationship: wherein Q is the refrigerant flow rate, P is the roller pressure, T is the real-time temperature of the groove, is the reference temperature, and K is the material coefficient.

[0024] Further, in the embodiment of the present application, when the plastic strip is polylactic acid, the refrigerant is liquid nitrogen and the groove depth is 0.1-0.2mm; when the plastic strip is polyhydroxyalkanoate, the refrigerant is liquid carbon dioxide and the groove depth is 0.15-0.25mm. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic diagram of a plastic pellet production line according to an embodiment of the present application.

[0026] Figure 2 is a perspective view of a stress-guided low-temperature cutting device according to an embodiment of the present application.

[0027] Figure 3 is a plan view of a stress-guided low-temperature cutting device according to an embodiment of the present application.

[0028] 1. cutting hob;

[0029] 10. main body, 11. guide hole, 12. roller, 13. spraying module, 14. liquid nitrogen supply channel, 15. negative pressure channel, 16. air pressure channel. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions of the present application clear and complete, and the advantages more clear and apparent, the embodiments of the present application are further described in detail below with reference to the drawings. It should be understood that the specific embodiments described herein are part of the embodiments of the present application, rather than all the embodiments, and are only used to explain the embodiments of the present application, and do not limit the embodiments of the present application, and all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0031] In the description of the present application, it needs to be explained that the terms "center", "middle", "upper", "lower", "left", "right", "inner", "outer", "top", "bottom", "side", "vertical", "horizontal" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "one", "first", "second", "third", "fourth", "fifth", "sixth" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0032] In the description of the present application, it needs to be explained that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0033] For the purpose of simplicity and illustration, the principles of the embodiments are mainly described by reference to examples. In the following description, many specific details are presented to provide a thorough understanding of the embodiments. However, it is obvious that these embodiments can not be limited to these specific details in practice. In some examples, the well-known stress-guided low-temperature cutting method and structure are not described in detail to avoid unnecessarily making the embodiments difficult to understand. In addition, all embodiments can be used in combination with each other.

[0034] As shown in Figure 1 , the plastic granulation production line contains an injection molding machine, a multi-hole mold, a cooling tank, a drying box, a stress-guided low-temperature cutting device and a granulating equipment from left to right. The injection molding machine melts the raw material at high temperature, injects it into the multi-hole mold to form a continuous long plastic strip, and then the plastic strip enters the cooling tank for cooling and solidification, and is guided to the drying box through the guide wheel for drying, and then is sent to the stress-guided low-temperature cutting device for processing, and finally the processed plastic strip is cut by the cutting hob 1 in the granulating equipment to cut the plastic strip into granular material. Embodiment 1

[0035] It should be noted that the drawings in the specification are part of the content of the specification, and the structure shape, connection relationship, fitting relationship and positional relationship that can be obtained without doubt in the drawings should be understood as the content of the specification.

[0036] A stress-guided low-temperature cutting device, as shown inFigure 2 As shown, the device includes a guiding mechanism and a cutting hob arranged on the side of the guiding mechanism, the guiding mechanism comprises a main body 10 provided with a guiding hole 11 for guiding the plastic strip for pelletizing processing by the cutting hob.

[0037] As shown, Figure 2 , Figure 3 The roller 12 is rotatably installed in the main body 10, and the surface of the roller 12 is provided with periodic indentation teeth for pressing periodic grooves on the surface of the plastic strip in the guiding hole 11 to form a stress concentration guide belt, so that the stress of the cutting hob is released along the groove path.

[0038] The roller 12 can be driven to rotate by a driving motor.

[0039] The main body 10 is also provided with a spray module 13 for directional spraying of refrigerant, which is configured to spray refrigerant to the groove for local embrittlement, so that the groove preferentially breaks under the stress of the cutting hob.

[0040] The present application realizes precise and efficient cutting of the plastic strip through the synergistic effect of pre-indentation guiding stress and refrigerant directional embrittlement.

[0041] Specifically, the periodic indentation teeth on the surface of the roller 12 press regular grooves on the surface of the plastic strip, forming a controllable stress concentration guide belt, so that the cutting stress is released in a predetermined direction (thereby reducing the situation that the material cannot form a neat cross section due to random breaking); at the same time, the refrigerant spray module 13 fills the groove with low-temperature refrigerant, enhances the brittleness of the material through local ultra-low temperature, weakens the molecular chain bonding force of the groove area, and guides the material to break at a specific location.

[0042] The present application changes the material breaking behavior from random breaking to controllable breaking by guiding the cutting stress through the groove structure of the plastic strip and by the mechanism of temperature regulation of the material in the groove structure, and improves the neatness of the cutting cross section. Not only avoids the problem of irregular cross section or material tearing caused by stress diffusion in traditional cold cutting process, but also significantly reduces the cutting load (the plastic strip is easy to break, the overall plastic strip is not easy to bend and shake, and the cutting effect is better).

[0043] Specifically, the plastic strip is a biobased degradable material, including at least one of polylactic acid (PLA), polyhydroxyalkanoate (PHA), and polybutylene succinate (PBS), and the groove depth is adapted to the material shrinkage rate. For example, a groove depth of 0.1-0.2mm is suitable for a material PLA shrinkage rate of about 3-5%, avoiding the risk of insufficient stress caused by too shallow or material breaking caused by too deep.

[0044] In particular, the coolant is selected from at least one of liquid nitrogen (-196°C), liquid carbon dioxide (-78.5°C), dry ice particles (-78.5°C) or cryogenic compressed air (-50°C to -100°C).

[0045] More particularly, the body 10 is provided with a liquid nitrogen hole, the injection module 13 is sealingly connected to the liquid nitrogen hole, the liquid nitrogen hole is in communication with a liquid nitrogen supply channel 14 of the body 10, and the liquid nitrogen supply channel 14 is connected to a pump of a liquid nitrogen tank outside the body 10 through a liquid nitrogen delivery pipeline.

[0046] The injection module 13 is selected from a micro product capable of being used for low-temperature fluid injection and having high-precision injection amount control (0.001 ml), such as a Bartels piezoelectric micropump, which has a small volume (30 mm x 15 mm x 3.8 mm), can perform hundreds of pumping cycles per second, and can accurately control the pumping flow by adjusting the bending degree, amplitude and vibration frequency of the piezoelectric diaphragm. Not only can the microliter flow (such as 0.001 ml) output be controlled, but intermittent pumping can also be realized.

[0047] The cost of the directional cooling treatment scheme of spraying the coolant in the groove of the plastic strip is very low, such as a plastic particle with a groove with a width of 0.5 mm, a depth of 0.2 mm and a length of 10 mm. According to the calculation, it generally contains 0.001 ml of liquid nitrogen (the actual situation will be slightly larger than 0.001 ml, because the liquid nitrogen contacts the normal temperature medium and will vaporize).

[0048] As for liquid nitrogen, the price of industrial-grade liquid nitrogen is 1.5-2.0 yuan per kilogram. Under ideal conditions, without considering volatilization and other issues, one kilogram of liquid nitrogen can fill about 800 billion grooves, that is, 800 billion plastic particles are cut out. 800 billion PLA plastic particles are about 400,000 kilograms. The market price of PLA raw material cost is usually 20,000-30,000 yuan per ton. The cost of 800 million PLA plastic particles is at least 8 million yuan. Moreover, under the condition that the liquid nitrogen spraying effect requirement is not high and the liquid nitrogen consumption is small, the total cost of the liquid nitrogen tank, liquid nitrogen conveying pipeline, Bartels piezoelectric micropump, and liquid nitrogen pump is estimated as follows: 50 liters of liquid nitrogen tank (YDS-10-50 low-temperature storage liquid nitrogen tank) purchase price 815 yuan, assuming a 5-year use, monthly depreciation of about 13.58 yuan; liquid nitrogen conveying pipeline selects ordinary rubber hose, such as inner diameter 1 / 4 inch, length 5 meters, price about 10 yuan per meter, 5 meters total 50 yuan. Assuming a 5-year use, monthly depreciation of about 0.8 yuan; Bartels piezoelectric micropump (precise control of 0.001 ml of spraying amount), single price calculated at 550 yuan, assuming a 2-year use, monthly depreciation of about 22.9 yuan; pump selection pedal type liquid nitrogen pump, price about 950 yuan. Assuming a 1-year use, monthly depreciation of about 79 yuan. Finally, the monthly additional cost is basically not more than 150 yuan, and most factories can produce hundreds of millions of PLA plastic particles in one or two months, so the cost is extremely low.

[0049] Specifically, the guide hole 11 is provided with a negative pressure channel 15 in communication therewith, which is located between the roller 12 and the spraying module 13, and the gas in the groove is discharged through the negative pressure channel 15 to suppress local heat convection.

[0050] Because liquid nitrogen will quickly vaporize after contacting the normal temperature environment, it is easy to form a nitrogen film to hinder the subsequent penetration of liquid nitrogen (it can be understood that the air pressure in the groove increases, and if the pressure is not reduced in time, it is easy to prevent the subsequent liquid nitrogen from entering). Therefore, by applying negative pressure to discharge the gas in the groove, the liquid nitrogen can be guided to quickly fill the groove and fully soak the groove.

[0051] Moreover, the negative pressure can also inhibit the local heat convection caused by the nitrogen film (after the air in the groove is discharged, the gas medium condition of the heat convection is destroyed, so it is not easy to produce local heat convection, and the situation of local high or low temperature is formed), so that the cooling temperature field distribution is more uniform.

[0052] By using the negative pressure scheme to solve the airflow interference medium flow and solve the local heat convection phenomenon, the cooling temperature distribution is uniformized to form stable material embrittlement.

[0053] The present application not only guarantees sufficient immersion of liquid nitrogen to the groove (avoiding nitrogen film interference), but also provides stable temperature field conditions for local ultra-low temperature embrittlement (inhibiting heat convection), so that the stress concentration area and the embrittlement area are accurately matched, and the groove structure and the subsequent cooling and fracture are important 'bridges'.

[0054] More specifically, the negative pressure channel 15 is in communication with the air pressure channel 16 of the main body 10, which is connected with an air pressure pump outside the main body 10. Embodiment 2

[0055] A stress-guided low-temperature cutting method, comprising the following steps:

[0056] A periodic groove is pressed on the surface of the plastic strip by the roller 12 provided with periodic indentation teeth on the surface, the groove depth is 0.05-0.3mm, and a stress concentration guide belt is formed.

[0057] The refrigerant is sprayed into the groove in a directional manner, so that the temperature of the groove area is suddenly reduced to-200℃ to-50℃, and local embrittlement is realized.

[0058] The cutting hob is controlled to cut the plastic strip along the groove path, the cutting direction forms an angle of 30°-90° with the feeding direction of the plastic strip, and the cutting force is 50-300N.

[0059] The present application pre-processes a'stress concentration guide belt' through the indentation of the roller 12, and combines negative pressure-assisted liquid nitrogen local ultra-low temperature treatment, so that the groove area is preferentially embrittled to form a 'preset fracture path'. By utilizing the synergistic effect of structure and temperature field, the material fracture behavior is changed from random fracture to controllable fracture, and the neatness of the cutting section is improved. The problem that brittle materials are difficult to form a neat section during cutting in the prior art is solved, and the problem of affecting the granulation quality is solved.

[0060] Specifically, before the refrigerant is sprayed, a negative pressure of-30kPa to-80kPa is applied to the groove area to discharge gas and inhibit heat convection.

[0061] Because liquid nitrogen will quickly vaporize after contacting the normal temperature environment, it is easy to form a nitrogen film to hinder the subsequent penetration of liquid nitrogen (it can be understood that the air pressure in the groove increases, and if the pressure is not reduced in time, it is easy to prevent the subsequent liquid nitrogen from entering). Therefore, by applying negative pressure to discharge the gas in the groove, liquid nitrogen can be guided to quickly fill the groove and fully immerse the groove.

[0062] In addition, the negative pressure can also inhibit the local heat convection caused by the nitrogen film (after discharging the air in the groove, the gas medium conditions for heat convection are destroyed, so it is not easy to produce local heat convection, and the situation of local temperature being too high or too low is formed), so that the cooling temperature field distribution is more uniform.

[0063] The present application not only guarantees the full infiltration of liquid nitrogen into the groove (avoiding nitrogen film interference), but also provides stable temperature field conditions for local ultra-low temperature embrittlement (inhibiting thermal convection), so that the stress concentration area and the embrittlement area are accurately matched. This design is an important "bridge" for the groove structure and subsequent cooling and fracture.

[0064] The negative pressure scheme solves the airflow interference medium flow and the local thermal convection phenomenon, so as to uniformize the cooling temperature distribution and form a stable material embrittlement.

[0065] Specifically, the refrigerant is selected from at least one of liquid nitrogen, liquid carbon dioxide, dry ice particles or low-temperature compressed air, and the refrigerant flow and the roller 12 pressure satisfy the following relationship: Wherein, Q is the refrigerant flow (L / min), P is the roller 12 pressure (N), T is the real-time temperature of the groove (K), T is the reference temperature (293 K), and K is the material coefficient (PLA takes 0.02-0.05, and PHA takes 0.03-0.08). represents the nonlinear attenuation effect of temperature on refrigerant flow, reflecting the exponential decline law of refrigerant demand when the temperature rises, when the groove temperature T tends to the reference temperature T (293 K, about 20℃), ≈0.368, the refrigerant flow is reduced to 36.8% of the reference value.

[0066] Reference temperature It needs to be adjusted according to the material properties, for example, the It can be set to the glass transition temperature (60℃, i.e. 333K), so that the formula adapts to the transition zone from brittle to ductile.

[0067] The formula balances the nonlinear relationship between the roller 12 pressure and the refrigerant demand through the exponential function, avoiding error amplification in the high and low temperature range. More specifically, when the plastic strip is polylactic acid (PLA), the refrigerant is liquid nitrogen (-196℃), and the groove depth is 0.1-0.2mm; when the plastic strip is polyhydroxyalkanoate (PHA), the refrigerant is liquid carbon dioxide (-78.5℃), and the groove depth is 0.15-0.25mm.

[0068] Although the above describes the specific embodiments of the present application illustratively, so that those skilled in the art can understand the present application, the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, all inventions utilizing the concept of the present application are within the protection scope of the present application as long as various changes are within the spirit and scope of the present application defined and determined by the appended claims.

Claims

1. A stress-guided cryogenic cutting method, characterized in that, This method is based on a stress-guided cryogenic cutting device, which includes a guiding mechanism and a cutting roller disposed on the side of the guiding mechanism. The guiding mechanism includes a main body with a guiding hole, which guides a plastic strip for the cutting roller to perform pelletizing. The roller mounted in the main body has periodically distributed indentation teeth on its surface to press periodic grooves on the surface of the plastic strip in the guide hole, forming a stress concentration guide band, so that the stress of the cutting roller is released along the groove path; The main body also has a spray module for directional spraying of refrigerant, which is configured to directionally spray refrigerant into the groove to achieve local embrittlement, so that the groove will fracture preferentially under the stress of the cutting roller. The groove depth is adapted to the shrinkage rate of the plastic strip material; A negative pressure channel is provided on the guide hole and communicates with it. The negative pressure channel is located between the roller and the injection module. Gas in the groove is discharged through the negative pressure channel to suppress local heat convection. The stress-guided cryogenic cutting method includes the following steps: Periodic grooves are pressed onto the surface of a plastic strip using a roller with periodic indentation teeth. The groove depth is 0.05-0.3mm, forming a stress concentration guide zone. A coolant is directionally injected into the groove, causing the temperature in the groove area to drop rapidly to -200°C to -50°C, thereby achieving localized embrittlement. Control the cutting roller to cut plastic strips along the groove path; Before refrigerant injection, a negative pressure of -30 kPa to -80 kPa is applied to the groove area to expel gas and suppress thermal convection.

2. The stress-guided cryogenic cutting method according to claim 1, characterized in that, The plastic strip is a bio-based biodegradable material, including at least one of polylactic acid, polyhydroxyalkanoate, and polybutylene succinate, and the groove depth is adapted to the material shrinkage rate.

3. The stress-guided cryogenic cutting method according to claim 1, characterized in that, The refrigerant is selected from at least one of liquid nitrogen, liquid carbon dioxide, dry ice particles, or cryogenic compressed air.

4. The stress-guided cryogenic cutting method according to claim 3, characterized in that, The main body is provided with a liquid nitrogen hole, and the injection module is sealed to the liquid nitrogen hole. The liquid nitrogen hole is connected to the liquid nitrogen supply channel of the main body, and the liquid nitrogen supply channel is connected to the pump of the liquid nitrogen tank outside the main body through a liquid nitrogen delivery pipe.

5. The stress-guided cryogenic cutting method according to claim 1, characterized in that, The negative pressure channel is connected to the air pressure channel of the main body, and the air pressure channel is connected to an external air pressure pump of the main body.

6. The stress-guided cryogenic cutting method according to claim 1, characterized in that, The refrigerant is selected from at least one of liquid nitrogen, liquid carbon dioxide, dry ice particles, or cryogenic compressed air, and the injection flow rate and roller pressure satisfy the following relationship: Where Q is the refrigerant flow rate, P is the roller pressure, and T is the real-time temperature of the groove. The reference temperature is K, and the material coefficient is K.

7. The stress-guided cryogenic cutting method according to claim 1, characterized in that, When the plastic strip is made of polylactic acid, liquid nitrogen is used as the refrigerant and the groove depth is 0.1-0.2 mm; when the plastic strip is made of polyhydroxyalkanoate, liquid carbon dioxide is used as the refrigerant and the groove depth is 0.15-0.25 mm.

Images