High-density extrusion forming pet food production equipment

Abstract

The invention relates to the technical field of pet food processing, in particular to high-density extrusion forming pet food production equipment which comprises a double-screw extruder and a post-processing module, a cylinder of the double-screw extruder is divided into a steam mixing section, a compression foaming section, a gradient pressure relief section and a bionic runner die head, raw material puffing is accurately controlled through the steam mixing section, forward and reverse thread elements are alternately arranged on the compression foaming section to generate periodic pressure pulses, air hole layering is achieved through step-by-step pressure relief of the gradient pressure relief section, and the speed difference of an inner runner and an outer runner of the bionic runner die head forms a core compact outer-layer porous structure. And the after-treatment module improves the wear resistance of the product through vortex cooling, infrared delayed coagulation and a biological wax coating.

Description

Technical Field

[0001] The present invention relates to the technical field of pet food processing, and particularly to a production device for high-density extrusion-molded pet food. Background Art

[0002] The technical field of pet food processing involves various process methods. Among them, the extrusion molding technology has become the mainstream solution due to its high efficiency and product adaptability. This technology transports the uniformly mixed raw materials to a high-temperature and high-pressure extrusion cavity through special equipment, and realizes starch gelatinization, protein denaturation and material homogenization under the action of screw propulsion and shearing. Subsequently, it is extruded through a die and instantaneously expanded to form granular pet food with a porous structure.

[0003] Traditional extrusion-molded pet food production equipment usually adopts a single pressure control mode, resulting in uneven pore distribution during the foaming process of the material, and it is impossible to form a bionic layered structure. At the same time, the die head flow channel design of the existing equipment is simple, it is difficult to realize the regulation of the density gradient of the inner and outer layers, and the post-treatment process has limited effect on improving the surface hardness and wear resistance. These problems lead to poor palatability of the product, the chewing experience does not match the biting mechanics requirements of dogs, and at the same time, the nutrient components are easily lost during the processing process.

[0004] Therefore, in order to improve the bionic performance and nutrient retention efficiency of pet food, a production device for extrusion-molded pet food is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a production device for high-density extrusion-molded pet food, so as to solve the problems of poor palatability, insufficient mechanical adaptability and nutrient loss of pet food caused by uneven pore distribution, lack of bionic structure and processing heat loss.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: A production device for high-density extrusion-molded pet food, including a twin-screw extruder, and the barrel of the twin-screw extruder is successively divided into:

[0007] In the steam mixing section, 6 to 8 steam nozzles are circumferentially and evenly arranged, the steam temperature is 85 ± 2 °C, the steam pressure is 0.15 to 0.25 MPa, and the steam injection amount is 3.5% to 4.5% of the dry basis mass of the raw materials;

[0008] In the compression and foaming section, the screw combination includes alternately arranged forward double-headed thread elements and reverse triple-headed thread elements. The pitch of the reverse triple-headed thread element is 0.28 to 0.32 times the screw diameter, the compression ratio is 5:1 to 5.5:1, and the pressure range is 25 to 28 MPa;

[0009] The barrel pressure in the gradient pressure relief section is relieved in two stages. The first-stage pressure relief is from 12 to 8 MPa, and the second-stage pressure relief is from 8 to 5 MPa. The inner wall of the barrel in the gradient pressure relief section is provided with deep grooves with a spiral angle of 55° - 60°, and the depth of the deep grooves is 0.8 - 1.2 mm;

[0010] The bionic flow channel die head includes a coaxially nested inner flow channel and an outer flow channel. The inner flow channel is a conical shape with a gradually decreasing diameter, and the cone angle is 8° - 10°. The outer flow channel is an elliptical shape with a gradually expanding major axis, and the major axis expansion rate is 18% - 20%. The inner wall of the bionic flow channel die head is provided with a rhombic grid microcavity with an inclination angle of 50° ± 2°, and the grid depth of the rhombic grid microcavity is 0.12 - 0.15 mm.

[0011] Furthermore, the thread lead angle of the reverse three-headed screw element is 15° - 18°, and the axial distance between adjacent reverse three-headed screw elements is 1.0 - 1.1 times the screw diameter, forming a periodic pressure pulse, and the pulse frequency is 8 - 12 Hz.

[0012] Furthermore, a thermocouple array is embedded in the deep grooves of the gradient pressure relief section to real-time monitor the material temperature in the deep grooves and feedback to control the pressure relief rate, so that the temperature fluctuation ≤ ±1.5°C.

[0013] Furthermore, the gap between the inner flow channel and the outer flow channel of the bionic flow channel die head is 2.0 - 2.5 mm, and the flow velocity at the outlet of the inner flow channel is 20% - 25% faster than that of the outer flow channel, forming a bionic structure with a dense core and a porosity of 8% - 12% and a porous outer layer and a porosity of 22% - 26%.

[0014] Furthermore, it further includes a post-treatment module, and the post-treatment module includes an eddy current impact cooler, an infrared radiation slow coagulation box, and a biological wax coating unit;

[0015] The eddy current impact cooler performs instantaneous cooling on the surface of the extrudate for 3 - 5 seconds with a wind speed of 15 - 20 m / s and cold air at -5 - 0°C;

[0016] The infrared radiation slow coagulation box uses an infrared light source with a wavelength of 3 - 4 μm, the radiation power density is 0.8 - 1.2 W / cm², and the slow coagulation time is 25 - 35 minutes;

[0017] The biological wax coating unit sprays a mixture of beeswax and palm oil with a mass ratio of 1 to 2, and the coating thickness is 50 - 80 μm.

[0018] Furthermore, the raw material of the steam mixing section is a premix containing the following components:

[0019] Cassava starch 40% - 45%, meeting the Chinese national standard GB / T 8887 - 2017;

[0020] Pea protein isolate 25% - 28%, meeting the Chinese national standard GB 20371-2016;

[0021] Bamboo fiber powder 12% - 15%, with a particle size less than or equal to 150 microns, meeting the international standard ISO 5267-1:1999;

[0022] Sodium bicarbonate 0.6% - 0.8%, meeting the food-grade standard GB 1886.2-2015.

[0023] Another technical solution provided by the present invention is a preparation method of high-density extrusion-molded pet food, using the production equipment described in claim 1, including the steps:

[0024] S1. Fiber activation: Mix bamboo fiber powder with a citric acid solution with a mass fraction of 2% - 3% at a solid-liquid ratio of 1:5, with an ultrasonic treatment frequency of 40 kHz, a power of 300 W, and a treatment time of 10 - 15 minutes;

[0025] S2. Gradient pressure relief foaming: Trigger the directional growth of carbon dioxide bubbles by two-stage pressure relief in the gradient pressure relief section, with a pressure relief rate of 1.5 - 2.0 MPa / s;

[0026] S3. Bionic extrusion: Form a density gradient through the speed difference between the inner flow channel speed of 2.5 - 3.0 m / min and the outer flow channel speed of 2.0 - 2.4 m / min;

[0027] S4. Phase change curing: Induce the vitrification transformation of starch by cooling the surface layer temperature from 95°C to -2°C - 0°C within 5 seconds through vortex impact cooling.

[0028] Furthermore, the ultrasonic treatment causes nano-scale pits to form on the surface of the bamboo fiber. The pit diameter is 50 - 100 nm, the depth is 10 - 20 nm, and the pit density ≥ 105 pits / mm², which is confirmed by observation with a scanning electron microscope.

[0029] Another technical solution provided by the present invention is a roller-shaped hard chewing dog food, prepared by the preparation method described in claim 7. The cross-section of the roller-shaped hard chewing dog food has a bionic double-layer structure, and the bionic double-layer structure includes:

[0030] The thickness of the outer cortical bone bionic layer is 1.0 - 1.5 mm, the porosity is 10% ± 2%, the pore diameter is 30 - 50 microns, and the Vickers hardness is HV 25 - 30;

[0031] The porosity of the core cancellous bone bionic layer is 24% ± 3%, the pore diameter is 100 - 250 microns, the pore connectivity rate ≤ 15%, and the compressive strength is 12 - 15 MPa.

[0032] Further, the surface friction coefficient of the outer cortical bone biomimetic layer is 0.35 - 0.40, measured according to ASTM D1894 - 14 standard; when the core cancellous bone biomimetic layer breaks, it produces a stepped fracture surface of 3 - 5 mm, observed according to ISO1798:2008 standard.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The gradient pressure relief section and the periodic pressure pulse act synergistically. Through the two - stage pressure relief control of the gradient pressure relief section, combined with the periodic pressure pulse generated by the reverse three - headed thread element, the porosity stratification accuracy is improved, ensuring that the pore diameter, connectivity, and distribution of the outer cortical bone biomimetic layer and the core cancellous bone biomimetic layer meet the requirements of the biomimetic structure.

[0035] 2. The coupling effect of the velocity difference between the inner and outer channels of the biomimetic flow channel die head and the diamond grid micro - cavity. The flow velocity difference between the gradually shrinking conical inner channel and the gradually expanding elliptical outer channel, combined with the flow guiding effect of the diamond grid micro - cavity on the inner wall of the die head, forms a stable gradient transition between the core dense porosity and the outer porous porosity.

[0036] 3. The phase change co - control of the eddy - current impact cooler and the infrared radiation slow - setting box. The high - speed and low - temperature instantaneous cooling of the eddy - current impact cooler vitrifies the surface starch, and the long - wave radiation of the infrared radiation slow - setting box promotes the stability of the internal pore structure. The two work together to improve the hardness and anti - fragmentation performance of the grain body.

[0037] 4. The adaptability of the steam parameters in the steam mixing section to the components of the raw material premix. The precise control of the steam temperature, pressure, and injection amount, combined with the optimization of the ratio of cassava starch, pea protein isolate, bamboo fiber powder, and sodium bicarbonate, reduces the degradation of heat - sensitive components and enhances the fiber activation effect.

[0038] 5. The surface modification function of the bio - wax coating unit. The spraying of the mixture of beeswax and palm oil forms a uniform bio - wax coating, improves the surface friction coefficient of the outer cortical bone biomimetic layer, and prolongs the wear - resistant life of the chewing grain. Brief Description of the Drawings

[0039] Figure 1 It is a schematic structural diagram of the pet food production equipment of the present invention;

[0040] Figure 2 It is a process flow chart of the preparation of high - density extrusion - formed pet food of the present invention;

[0041] Figure 3 It is a schematic diagram of the biomimetic structure of the roller - shaped canine hard chewing grain of the present invention. Detailed Embodiments

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0043] Please refer to Figure 1 , the present invention provides a technical solution: a high-density extrusion molding pet food production device, including a twin-screw extruder, and the barrel of the twin-screw extruder is sequentially divided into:

[0044] In the steam mixing section, 6 to 8 steam nozzles are circumferentially and evenly arranged, the steam temperature is 85 ± 2 °C, the steam pressure is 0.15 to 0.25 MPa, and the steam injection amount is 3.5% to 4.5% of the dry basis mass of the raw material;

[0045] In the compression and foaming section, the screw combination includes forward double-headed thread elements and reverse triple-headed thread elements arranged alternately. The pitch of the reverse triple-headed thread element is 0.28 to 0.32 times the screw diameter, the compression ratio is 5:1 to 5.5:1, the pressure range is 25 to 28 MPa, the thread lead angle of the reverse triple-headed thread element is 15° to 18°, and the axial distance between adjacent reverse triple-headed thread elements is 1.0 to 1.1 times the screw diameter, forming a periodic pressure pulse, and the pulse frequency is 8 to 12 Hz;

[0046] In the gradient pressure relief section, the barrel pressure is relieved in two stages. The first-stage pressure relief is from 12 to 8 MPa, and the second-stage pressure relief is from 8 to 5 MPa. The inner wall of the barrel in the gradient pressure relief section is provided with deep grooves with a spiral angle of 55° to 60°, the depth of the deep grooves is 0.8 to 1.2 mm, and a thermocouple array is embedded in the deep grooves of the gradient pressure relief section to monitor the material temperature in the deep grooves in real time and feedback to control the pressure relief rate, so that the temperature fluctuation ≤ ±1.5 °C;

[0047] The bionic flow channel die head includes a coaxially nested inner flow channel and an outer flow channel. The inner flow channel is a conical shape with a gradually decreasing diameter, and the cone angle is 8° to 10°. The outer flow channel is an ellipse with a gradually expanding major axis, and the major axis expansion rate is 18% to 20%. The inner wall of the bionic flow channel die head is provided with a rhombic grid microcavity with an inclination angle of 50° ± 2°. The grid depth of the rhombic grid microcavity is 0.12 to 0.15 mm. The gap between the inner flow channel and the outer flow channel of the bionic flow channel die head is 2.0 to 2.5 mm, and the flow velocity at the outlet of the inner flow channel is 20% to 25% faster than that of the outer flow channel, forming a bionic structure with a dense core and a porosity of 8% to 12% and a porous outer layer and a porosity of 22% to 26%;

[0048] The uniform mixing of raw materials and the protection of heat-sensitive nutrients are achieved through the circumferentially evenly distributed steam nozzles in the steam mixing section. The combination of forward and reverse threads in the compression foaming section generates periodic pressure pulses to precisely control the pore nucleation and distribution. The stepped pressure relief strategy in the gradient pressure relief section, combined with the spiral deep groove diversion and temperature feedback system, stabilizes the pore growth path. The synergistic effect of the internal and external flow velocity difference and the diamond grid microcavity in the bionic flow channel die head forms a bionic layered structure with a dense core and a porous outer layer, improving the palatability and wear resistance of the roller-shaped hard chewing dog food.

[0049] It also includes a post-treatment module, which includes a vortex impact cooler, an infrared radiation slow coagulation box, and a biological wax coating unit;

[0050] The vortex impact cooler performs instantaneous cooling on the surface of the extrudate for 3 - 5 seconds with a wind speed of 15 - 20 m / s and cold air at -5 - 0 °C;

[0051] The infrared radiation slow coagulation box uses an infrared light source with a wavelength of 3 - 4 μm, a radiation power density of 0.8 - 1.2 W / cm², and a slow coagulation time of 25 - 35 minutes;

[0052] The biological wax coating unit sprays a mixture of beeswax and palm oil with a mass ratio of 1:2, and the coating thickness is 50 - 80 μm;

[0053] The post-treatment module realizes the rapid solidification of the surface layer of the extrudate through the high-speed and low-temperature instantaneous cooling of the vortex impact cooler, the long-wave radiation of the infrared radiation slow coagulation box promotes the stabilization of the internal pore structure, and the biological wax coating unit evenly sprays the mixture of beeswax and palm oil to form a surface wear-resistant protective layer. The three work together to improve the hardness, anti-breakage property, and surface palatability of the food.

[0054] The raw materials in the steam mixing section are a premix containing the following components:

[0055] Cassava starch 40% - 45%, in line with Chinese national standard GB / T 8887 - 2017;

[0056] Pea protein isolate 25% - 28%, in line with Chinese national standard GB 20371 - 2016;

[0057] Bamboo fiber powder 12% - 15%, with a particle size less than or equal to 150 μm, in line with international standard ISO 5267 - 1:1999;

[0058] Sodium bicarbonate 0.6% - 0.8%, in line with food-grade standard GB 1886.2 - 2015;

[0059] The premix components in the steam mixing section provide adhesiveness and a forming basis through a specific proportion of tapioca starch, pea protein isolate enhances protein content and nutrient retention, bamboo fiber powder supplements dietary fiber and optimizes structural stability, and sodium bicarbonate regulates pore formation and puffing effect. The four are selected and coordinated according to national and international standards to ensure the adaptability of raw material processing and the balance of product nutritional functions.

[0060] Please refer to Figure 2 , another technical solution is a method for preparing high-density extruded pet food, including the steps:

[0061] S1. Fiber activation: Mix bamboo fiber powder with a citric acid solution with a mass fraction of 2% - 3% at a solid-liquid ratio of 1:5, the ultrasonic treatment frequency is 40 kHz, the power is 300 W, and the treatment time is 10 - 15 minutes;

[0062] S2. Gradient pressure relief foaming: Through two-stage pressure relief in the gradient pressure relief section, the pressure relief rate is 1.5 - 2.0 MPa / s, triggering the directional growth of carbon dioxide bubbles;

[0063] S3. Bionic extrusion: Form a density gradient through the speed difference between the inner flow channel speed of 2.5 - 3.0 m / min and the outer flow channel speed of 2.0 - 2.4 m / min;

[0064] S4. Phase change curing: Induce the vitrification transformation of starch by cooling the surface layer from 95°C to -2°C - 0°C within 5 seconds through vortex impact cooling;

[0065] The ultrasonic treatment triggers the formation of nanoscale pits on the surface of bamboo fibers. The pit diameter is 50 - 100 nm, the depth is 10 - 20 nm, and the pit density ≥ 105 pits / mm², which is confirmed by observing with a scanning electron microscope;

[0066] The ultrasonic treatment for fiber activation enhances the binding force and reactivity of bamboo fibers. The stepwise pressure relief control of gradient pressure relief foaming triggers the directional growth and distribution optimization of bubbles. The speed difference between the inner and outer flow channels in the bionic extrusion stage forms a density gradient transition. The rapid cooling in phase change curing induces the vitrification transformation of the surface layer starch to improve hardness. Combining with the nanoscale pits of bamboo fibers generated by ultrasonic treatment improves the compressive performance of the core structure and the nutrient slow-release effect, ultimately achieving the precise forming and mechanical adaptability of the bionic double-layer structure.

[0067] Please refer to Figure 3 , another technical solution is a roller-shaped hard chewing dog food. The cross-section of the roller-shaped hard chewing dog food has a bionic double-layer structure, and the bionic double-layer structure includes:

[0068] The thickness of the outer osteonal bionic layer is 1.0 - 1.5 mm, the porosity is 10% ± 2%, the pore diameter is 30 - 50 μm, and the Vickers hardness is HV 25 - 30;

[0069] The porosity of the cancellous bone bionic layer in the core is 24% ± 3%, the pore diameter is 100 - 250 microns, the pore connectivity rate is ≤ 15%, and the compressive strength is 12 - 15 MPa;

[0070] The surface friction coefficient of the cortical bone bionic layer in the outer layer is 0.35 - 0.40, measured according to ASTM D1894 - 14 standard; when the cancellous bone bionic layer in the core is broken, a stepped fracture surface of 3 - 5 mm is generated, observed according to ISO 1798:2008 standard;

[0071] The roller - shaped hard chewing dog food is designed with a bionic double - layer structure. The cortical bone bionic layer in the outer layer simulates the wear resistance and palatability of the occlusal contact area of dog teeth with low porosity, small pore diameter and high surface hardness. The cancellous bone bionic layer in the core buffers the occlusal impact force and avoids the generation of sharp debris with high porosity, large pore diameter and stepped fracture surface. The gradient distribution of porosity and mechanical properties between the inner and outer layers adapts to the stress transmission mechanism of the dog's jaw bone, realizing the safety, durability and controllability of nutrient release during the chewing process.

[0072] Example 1. Production equipment for high - density extrusion - formed pet food

[0073] First, 7 steam nozzles are circumferentially distributed evenly in the steam mixing section of the barrel of the twin - screw extruder. The steam temperature is set at 85 degrees Celsius plus or minus 2 degrees Celsius, the steam pressure is 0.20 MPa, and the steam injection amount is controlled at 4.0% of the dry - basis mass of the raw materials;

[0074] Next, forward double - head screw elements and reverse triple - head screw elements are alternately arranged in the compression and foaming section of the barrel. The ratio of the pitch of the reverse triple - head screw element to the screw diameter is set at 0.30, the compression ratio is set at 5.2:1, and the pressure is stably maintained at 27 MPa;

[0075] Then, two - stage pressure relief is carried out in the gradient pressure - relief section. In the first stage, the barrel pressure is reduced from 12 MPa to 8 MPa, and in the second stage, from 8 MPa to 5 MPa; at the same time, deep grooves with a helix angle of 58 degrees are machined on the inner wall of the barrel in this section, and the groove depth is set at 1.0 mm;

[0076] Finally, a co - axially nested inner flow channel and outer flow channel are configured in the die head area: the inner flow channel is designed as a conical shape with a cone angle of 9 degrees, and the outer flow channel is an ellipse with a major - axis expansion rate of 19%; diamond - shaped grid micro - cavities with an inclination angle of 50 degrees are machined on the inner wall of the die head, and the grid depth is set at 0.13 mm;

[0077] Complete post - processing module assembly: The set wind speed of the eddy current impact cooler is 18 m / s, the cold air temperature is - 3 °C, and the instantaneous cooling time is 4 s; The infrared radiation setting box uses an infrared light source with a wavelength of 3.5 μm, the radiation power density is 1.0 W / cm², and the setting time is 30 minutes; The biological wax coating unit sprays a mixture of beeswax and palm oil with a mass ratio of 1:2, and the coating thickness is controlled to be 65 μm.

[0078] Example 2, Preparation method of high - density extrusion - formed pet food

[0079] First, mix bamboo fiber powder with a 2.5% citric acid solution by a solid - to - liquid ratio of 1:5, and treat it with an ultrasonic device with a frequency of 40 kHz and a power of 300 W for 12 minutes to form nano - scale pits on the fiber surface;

[0080] Next, in the gradient pressure - relief section, relieve pressure in two stages at a pressure - relief rate of 1.8 MPa / s to trigger the axial directional growth of carbon dioxide bubbles and form a pore - stratified structure;

[0081] Then, extrude the material at a speed difference between the inner flow channel of 2.8 m / min and the outer flow channel of 2.2 m / min to form a density gradient with a dense core and a porous outer layer;

[0082] Finally, use eddy current impact cooling to reduce the surface temperature from 95 °C to - 1 °C within 5 s to induce the vitrification transition of starch; Observed by scanning electron microscope, the diameter of the pits on the bamboo fiber surface is 70 nm, the depth is 15 nm, and the pit density reaches 1.2×10⁵ per square millimeter.

[0083] Example 3, Roll - shaped hard dog chews

[0084] The specific implementation steps are as follows:

[0085] First, extrude the material through the outer flow channel of the bionic flow channel die head to form an outer layer with a thickness of 1.2 mm, the porosity is controlled to be 10% ± 2%, the pore diameter range is 30 - 50 μm, the Vickers hardness reaches HV 28, and the surface friction coefficient is 0.38;

[0086] Next, extrude the core material through the inner flow channel, the porosity is controlled to be 24% ± 3%, the pore diameter range is 100 - 250 μm, the pore connectivity is 12%, and the compressive strength reaches 14 MPa;

[0087] Finally, after eddy current impact cooling and infrared radiation setting, the product produces a 4 - mm stepped fracture surface when broken, which conforms to the canine bite mechanical characteristics.

[0088] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, commodity or device comprising a series of elements not only includes those elements but also other elements not expressly listed, or elements inherent to such process, method, commodity or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, commodity or device comprising the element.

[0089] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art may still modify the technical solutions described in the foregoing embodiments or perform equivalent substitution on some of the technical features. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. High-density extrusion molding pet food production equipment, including a twin-screw extruder, characterized in that: The barrel of the twin-screw extruder is divided into: The steam mixing section is equipped with 6 to 8 steam nozzles evenly distributed in the circumferential direction, the steam temperature is 85±2°C, the steam pressure is 0.15 to 0.25 MPa, and the steam injection amount is 3.5% to 4.5% of the dry basis weight of the raw materials; The screw assembly in the compression foaming section includes alternatingly arranged forward double-start thread elements and reverse triple-start thread elements, wherein the pitch of the reverse triple-start thread element and the screw diameter ratio are 0.28 to 0.32, the compression ratio is 5:1 to 5.5:1, and the pressure range is 25 to 28 MPa; The barrel pressure of the gradient pressure relief section is divided into two stages of pressure relief, the first stage of pressure relief is 12-8 MPa, and the second stage of pressure relief is 8-5 MPa. The inner wall of the barrel of the gradient pressure relief section is provided with a deep groove with a helical angle of 55°-60°, and the depth of the deep groove is 0.8-1.2 mm; The bionic flow channel die head comprises a coaxially nested inner flow channel and an outer flow channel, wherein the inner flow channel is a cone with a gradually decreasing diameter and a cone angle of 8° to 10°, and the outer flow channel is an ellipse with a gradually expanding long axis and a long axis expansion rate of 18% to 20%. The inner wall of the bionic flow channel die head is provided with a diamond grid microcavity with an inclination angle of 50°±2°, and the grid depth of the diamond grid microcavity is 0.12 to 0.15 mm.

2. The high-density extrusion molding pet food production equipment according to claim 1 is characterized in that: The thread lead angle of the reverse three-start thread element is 15° to 18°, and the axial spacing between adjacent reverse three-start thread elements is 1.0 to 1.1 times the diameter of the screw, forming a periodic pressure pulse with a pulse frequency of 8 to 12 Hz.

3. The high-density extrusion molding pet food production equipment according to claim 1 is characterized in that: A thermocouple array is embedded in the deep groove of the gradient pressure relief section to monitor the temperature of the material in the deep groove in real time and feedback control the pressure relief rate to make the temperature fluctuation ≤±1.5°C.

4. The high-density extrusion molding pet food production equipment according to claim 1, characterized in that: The gap between the inner and outer flow channels of the bionic flow channel die head is 2.0 to 2.5 mm, and the flow rate at the inner flow channel outlet is 20% to 25% faster than that of the outer flow channel, forming a bionic structure with a dense core and a porosity of 8% to 12% and a porous outer layer with a porosity of 22% to 26%.

5. The high-density extrusion molding pet food production equipment according to claim 1, characterized in that: Also included is a post-processing module, the post-processing module comprising: The vortex impact cooler uses a wind speed of 15 to 20 m / s and cold air of -5 to 0°C to instantly cool the surface of the extrudate for 3 to 5 seconds; The infrared radiation retarding box uses an infrared light source with a wavelength of 3 to 4 microns, a radiation power density of 0.8 to 1.2 watts per square centimeter, and a retarding time of 25 to 35 minutes; The biowax coating unit sprays a mixture of beeswax and palm oil in a mass ratio of 1 to 2, and the coating thickness is 50 to 80 microns.

6. The high-density extrusion molding pet food production equipment according to claim 1, characterized in that: The raw material of the steam mixing section is a premix comprising the following components: Cassava starch 40% to 45%, in line with Chinese national standard GB / T 8887-2017; Pea protein isolate 25% to 28%, in line with Chinese national standard GB 20371-2016; Bamboo fiber powder 12% to 15%, particle size less than or equal to 150 microns, in line with international standard ISO 5267-1:1999; Sodium bicarbonate 0.6%~0.8%, in line with food grade standard GB 1886.2-2015.

7. A method for preparing high-density extruded pet food, characterized in that: The production equipment according to claim 1 comprises the following steps: S1. Fiber activation: bamboo fiber powder is mixed with citric acid solution with a mass fraction of 2% to 3% at a solid-liquid ratio of 1 to 5, and the ultrasonic treatment frequency is 40 kHz, the power is 300 watts, and the treatment time is 10 to 15 minutes; S2, gradient pressure relief foaming: through two-stage pressure relief in the gradient pressure relief section, the pressure relief rate is 1.5-2.0 MPa / s, triggering the directional growth of carbon dioxide bubbles; S3, bionic extrusion forms a density gradient through a speed difference of 2.5-3.0 m / min in the inner flow channel and 2.0-2.4 m / min in the outer flow channel; S4, phase change solidification: eddy current impact cooling is used to reduce the surface temperature from 95°C to -2°C to 0°C within 5 seconds, inducing the glass transition of starch.

8. The method for preparing high-density extruded pet food according to claim 7, characterized in that: The ultrasonic treatment induces the formation of nanoscale pits on the surface of the bamboo fiber, with a pit diameter of 50 to 100 nanometers, a depth of 10 to 20 nanometers, and a pit density of ≥1×10 5 / mm2, confirmed by scanning electron microscopy.

9. A rolled dog hard chewing food prepared by the method of claim 7, characterized in that: The cross section of the roll-shaped dog hard chewing food presents a bionic double-layer structure, and the bionic double-layer structure comprises: The outer bone compact bionic layer has a thickness of 1.0 to 1.5 mm, a porosity of 10%±2%, a pore diameter of 30 to 50 μm, and a Vickers hardness of HV 25 to 30; The porosity of the core bone cancellous bionic layer is 24%±3%, the pore diameter is 100-250 microns, the pore connectivity is ≤15%, and the compressive strength is 12-15 MPa.

10. The rolled dog hard chewing food according to claim 9, characterized in that: The surface friction coefficient of the outer bone compact bionic layer is 0.35-0.40, measured according to ASTM D1894-14 standard; when the core bone spongy bionic layer is broken, a 3-5 mm stepped fracture surface is generated, observed according to ISO 1798:2008 standard.

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