A drying and milling device for blood meal processing

Abstract

This invention relates to the field of blood meal processing equipment technology, specifically disclosing a drying and grinding device for blood meal processing, including a base, a drum-type processing chamber, a left support bushing, a right support bushing, a screw conveyor, a feed drive motor, a rotating main shaft, a rotating drive motor, multiple scraper blades, multiple grinding roller assemblies, a cylinder rotation drive mechanism, and an inclination adjustment mechanism. The scraper blades and grinding roller assemblies are both mounted on the rotating main shaft, and the grinding rollers form a grinding gap with the inner wall of the processing chamber. The cylinder rotation drive mechanism drives the processing chamber to rotate independently. The inclination adjustment mechanism consists of a support seat and a lifting device, used to adjust the inclination angle of the processing chamber. This invention achieves dynamic drying and flexible grinding through the combined motion of the processing chamber rotation and the main shaft rotation. The scraper blades continuously clean the inner wall to prevent sticking and coking, and the inclination adjustment allows for online control of material residence time, significantly improving processing uniformity, product quality, and thorough discharge.

Description

Technical Field

[0001] This invention relates to the field of blood meal processing equipment technology, and specifically discloses a drying and grinding device for blood meal processing. Background Technology

[0002] In the current blood meal processing, the cooked wet blood material needs to be dried and milled sequentially to obtain a blood meal product with qualified moisture content and uniform particle size. However, the existing equipment has the following two core defects:

[0003] The processing chambers of existing devices are mostly fixed structures, or can only achieve single chamber rotation. The internal stirring and grinding components have simple movements and insufficient material agitation. This not only leads to uneven heating during drying, but also causes wet materials to easily stick to the chamber wall and form a coking layer that cannot be effectively processed. At the same time, incomplete grinding can easily lead to agglomeration and uneven particle size, which seriously affects product quality.

[0004] The existing equipment has a fixed installation angle for the processing chamber, which cannot be flexibly adjusted according to factors such as the initial moisture content of the raw materials and the processing progress. This results in the inability to control the residence time of materials in the chamber, leading to low processing efficiency. In addition, because the angle is not adjustable, material residue and incomplete discharge are likely to occur during discharge, increasing cleaning costs and material loss. Summary of the Invention

[0005] This invention proposes a drying and grinding device for blood meal processing. By combining the combined motion of cavity rotation and spindle rotation with online tilt angle adjustment, it achieves uniform heating, anti-sticking, flexible grinding, and flexible control of material residence time during the drying and grinding process of blood meal, significantly improving product quality, processing efficiency, and thorough discharge.

[0006] This invention is implemented as follows: a drying and grinding apparatus for blood meal processing, characterized in that it comprises:

[0007] Base;

[0008] A horizontally positioned and rotatable drum-type processing chamber;

[0009] The left and right support bushings are coaxially and rotatably fitted onto and connected to the two ends of the processing cavity via bearings, and the outer ends of the left and right support bushings are both closed structures.

[0010] A screw conveyor is coaxially and rotatably disposed inside the left support bushing, and a feeding port is provided on the cylinder wall of the left support bushing;

[0011] The feed drive motor is fixed to the outer end of the left support bushing, and its output end is coaxially fixed to the screw conveyor.

[0012] A rotating spindle is coaxially and rotatably mounted on the right support sleeve and extends into the processing cavity;

[0013] A rotary drive motor is fixedly mounted on the outer end of the right support bushing, and its output end is coaxially fixedly connected to the rotary spindle.

[0014] Multiple scraper blades are vertically arranged along the axial direction of the rotating main shaft and divided into upper and lower groups, located on the upper and lower sides of the outer wall of the rotating main shaft, respectively. The scraper blades on the upper and lower sides are staggered in the axial direction. The free end of each scraper blade slides in contact with the inner wall of the processing chamber to continuously clean the material adhering to the inner wall.

[0015] Multiple grinding roller assemblies are distributed back and forth along the axial direction of the rotating main shaft and are divided into two groups, located on the front and rear sides of the rotating main shaft respectively. The grinding roller assemblies on the front and rear sides are staggered in the axial direction. Each grinding roller assembly includes a U-shaped mounting frame with the opening facing outward and a grinding roller rotatably disposed in the mounting frame. The closed end of the mounting frame is fixedly connected to the rotating main shaft. A grinding gap is formed between the roller surface of the grinding roller and the inner wall of the processing chamber.

[0016] A cylinder rotation drive mechanism is used to drive the processing chamber to rotate around its own axis. It includes a gear ring fixedly sleeved on the outer wall of the processing chamber, a drive gear meshing with the gear ring, and a chamber drive motor fixed on the left support bushing or the right support bushing. The output end of the chamber drive motor is coaxially and fixedly connected to the drive gear.

[0017] An angle adjustment mechanism is used to adjust the angle between the axis of the processing chamber and the horizontal plane. It includes a support base and a lifting device. The upper end of the support base is hinged to the outer wall of the left support bushing, and its lower end is fixed to the base. The fixed end of the lifting device is hinged to the base, and its telescopic end is hinged to the outer wall of the right support bushing.

[0018] As a preferred embodiment of the drying and grinding apparatus for blood powder processing according to the present invention, the processing chamber is provided with a heating jacket inside the cylinder wall, and heating elements are arranged inside the heating jacket.

[0019] As a preferred embodiment of the drying and grinding apparatus for blood powder processing according to the present invention, a temperature and humidity sensor is installed in the inner wall of the right support bushing near the processing chamber, and the temperature and humidity sensor is electrically connected to the control unit of the heating element.

[0020] As a preferred embodiment of the drying and grinding apparatus for blood powder processing according to the present invention, the outer wall of the processing chamber is wrapped with a heat insulation layer, and the heat insulation layer covers the outside of the heating jacket.

[0021] As a preferred embodiment of the drying and grinding apparatus for blood meal processing according to the present invention, the lifting device is a hydraulic push rod or an electric push rod.

[0022] As a preferred embodiment of the drying and grinding apparatus for blood powder processing according to the present invention, a discharge port is provided at the lower part of the outer wall of the processing chamber, and a sealing valve is installed at the discharge port.

[0023] As a preferred embodiment of the drying and grinding apparatus for blood powder processing according to the present invention, multiple sets of scraper blades are arranged along the axial direction of the rotating main shaft, each set comprising multiple scraper blades evenly distributed circumferentially, and adjacent sets of scraper blades are staggered in the circumferential direction.

[0024] As a preferred embodiment of the drying and grinding apparatus for blood meal processing according to the present invention, the width of the grinding gap is 0.1mm-0.5mm.

[0025] Preferably, in a drying and grinding apparatus for blood meal processing according to the present invention, the chamber drive motor rotates in the opposite direction to the rotary drive motor.

[0026] In a preferred embodiment of the drying and grinding apparatus for blood powder processing according to the present invention, the outer walls of both the left and right support bushings are covered with heat-insulating protective sleeves.

[0027] The beneficial effects of this invention are:

[0028] 1. This invention achieves a composite motion of cavity rotation and spindle rotation by setting up an independently driven drum-type processing chamber and a rotating main shaft with scraper and grinding roller, with the chamber drive motor and the rotation drive motor rotating in opposite directions. The scraper continuously cleans the inner wall to completely solve the problem of sticking and coking, while the grinding roller rotates with the main shaft to perform flexible grinding of the material. Combined with the material throwing and tumbling caused by the rotation of the cavity, the blood material is always in a dynamic dispersion state during the drying process, with uniform heating and thorough grinding, effectively avoiding agglomeration and uneven particle size, and improving product quality.

[0029] 2. This invention, by setting up an angle adjustment mechanism consisting of a support base and a lifting device, allows the angle between the axis of the processing chamber and the horizontal plane to be continuously adjusted online. According to the initial moisture content of the raw materials, processing progress and other requirements, the inclination angle of the chamber can be flexibly adjusted, thereby accurately controlling the residence time of the material in the chamber and optimizing the drying and grinding efficiency. When discharging, the chamber is adjusted to a negative inclination angle to achieve gravity-assisted discharge, eliminate material residue, and reduce cleaning costs and material loss. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0031] Figure 1This is a schematic diagram of the overall structure of the present invention.

[0032] Figure 2 This is a three-dimensional schematic diagram of the present invention.

[0033] Figure 3 This is a schematic diagram of the internal structure of the drum-type processing chamber of the present invention.

[0034] Figure 4 This is a schematic diagram of the scraper, mounting frame, and grinding roller structure of the present invention.

[0035] Figure 5 This is a schematic diagram of the heating interlayer and heat insulation protective sleeve structure of the present invention.

[0036] The markings in the diagram are: 1. Base; 2. Processing chamber; 3. Left support bushing; 4. Right support bushing; 5. Bearing; 6. Screw conveyor; 7. Feed port; 8. Feed drive motor; 9. Rotary spindle; 10. Rotary drive motor; 11. Scraper; 12. Mounting frame; 13. Grinding roller; 14. Gear ring; 15. Drive gear; 16. Chamber drive motor; 17. Support seat; 18. Lifting device; 19. Heating jacket; 20. Heating element; 21. Temperature and humidity sensor; 22. Insulation layer; 23. Discharge port; 24. Sealing valve; 25. Thermal insulation sleeve. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments to aid in understanding its content. Unless otherwise specified, the methods used in this invention are conventional methods; the raw materials and apparatus used, unless otherwise specified, are conventional commercially available products.

[0038] Please see Figure 1-5 A drying and grinding apparatus for blood meal processing, comprising:

[0039] Base 1;

[0040] A horizontally positioned and rotatable drum-type processing chamber 2;

[0041] The left support bushing 3 and the right support bushing 4 are coaxially and rotatably fitted onto and connected to the two ends of the processing cavity 2 via bearings 5, respectively. The outer ends of the left support bushing 3 and the right support bushing 4 are both closed structures.

[0042] The screw conveyor 6 is coaxially and rotatably installed inside the left support bushing 3, and the left support bushing 3 has a feeding port 7 on its cylindrical wall.

[0043] The feed drive motor 8 is fixed to the outer end of the left support bushing 3, and its output end is coaxially fixed to the screw conveyor 6.

[0044] The rotating main shaft 9 is coaxially and rotatably inserted through the right support sleeve 4 and extends into the processing cavity 2;

[0045] A rotary drive motor 10 is fixed to the outer end of the right support bushing 4, and its output end is coaxially fixed to the rotary spindle 9.

[0046] Multiple scraper blades 11 are vertically arranged along the axial direction of the rotating main shaft 9 and are divided into upper and lower groups, located on the upper and lower sides of the outer wall of the rotating main shaft 9 respectively. The scraper blades 11 on the upper and lower sides are staggered in the axial direction. The free end of each scraper blade 11 slides in contact with the inner wall of the processing chamber 2 to continuously clean the material adhering to the inner wall.

[0047] Multiple grinding roller assemblies are distributed back and forth along the axial direction of the rotating spindle 9 and are divided into two groups, located on the front and rear sides of the rotating spindle 9 respectively. The grinding roller assemblies on the front and rear sides are staggered in the axial direction. Each grinding roller assembly includes a U-shaped mounting frame 12 with the opening facing outward and a grinding roller 13 rotatably disposed in the mounting frame 12. The closed end of the mounting frame 12 is fixedly connected to the rotating spindle 9, and a grinding gap is formed between the roller surface of the grinding roller 13 and the inner wall of the processing chamber 2.

[0048] The cylinder rotation drive mechanism is used to drive the processing chamber 2 to rotate around its own axis. It includes a gear ring 14 fixedly sleeved on the outer wall of the processing chamber 2, a drive gear 15 meshing with the gear ring 14, and a chamber drive motor 16 fixed on the left support bushing 3 or the right support bushing 4. The output end of the chamber drive motor 16 is coaxially fixedly connected to the drive gear 15.

[0049] The tilt adjustment mechanism is used to adjust the angle between the axis of the processing chamber 2 and the horizontal plane. It includes a support base 17 and a lifting device 18. The upper end of the support base 17 is hinged to the outer wall of the left support bushing 3, and its lower end is fixed to the base 1. The fixed end of the lifting device 18 is hinged to the base 1, and its telescopic end is hinged to the outer wall of the right support bushing 4.

[0050] In this embodiment: the feed drive motor 8 is started to drive the screw conveyor 6 to rotate, quantitatively feeding the wet blood material into the drum-type processing chamber 2 from the feeding port 7 on the left support bushing 3; at the same time, the rotation drive motor 10 drives the rotating main shaft 9 to rotate, and the scraper 11 installed on the main shaft rotates with the main shaft, its free end closely adhering to the inner wall of the processing chamber 2, continuously scraping off the material adhering to the wall surface to prevent coking; similarly, the grinding roller 13 installed in the U-shaped mounting bracket 12 on the main shaft revolves with the main shaft, and its roller surface maintains a grinding gap with the inner wall of the processing chamber 2 to squeeze and grind the material; at the same time, the cylinder rotation drive mechanism drives the drive gear 15 through the chamber drive motor 16, driving the gear fixed to the outer wall of the processing chamber 2. The gear ring 14 causes the entire processing chamber 2 to rotate around its own axis. The material inside the chamber is continuously turned over and scattered under the dual action of the chamber rotation and the main shaft rotation, and spirals forward along the inner wall. The heating element 20 in the heating jacket 19 heats the chamber, so that the material is uniformly heated and dehydrated during the dynamic process. The tilt adjustment mechanism changes the height of the right support bushing 4 by extending and retracting the lifting device 18, thereby adjusting the angle between the axis of the processing chamber 2 and the horizontal plane. When it is necessary to extend the material residence time, the feed end is lower than the discharge end (positive tilt angle). When it is necessary to discharge the material quickly, the feed end is higher than the discharge end (negative tilt angle). After processing, the sealing valve 24 of the discharge port 23 is opened, and the finished blood powder is discharged under the action of gravity and the rotation of the chamber.

[0051] Multiple scraper blades 11 and multiple grinding roller assemblies are arranged in an alternating manner. Through the above-mentioned spatial staggered layout, the scraper blades 11 and the grinding roller assemblies are staggered in both the circumferential and axial directions of the rotating main shaft 9. This not only achieves all-round scraping and anti-sticking of the inner wall of the processing chamber 2, but also avoids interference between the grinding roller 13 and the scraper blades 11 during the grinding process, ensuring the continuous and stable operation of the drying and grinding process.

[0052] As a technical optimization of the present invention, a heating jacket 19 is provided inside the cylinder wall of the processing cavity 2, and a heating element 20 is arranged inside the heating jacket 19.

[0053] In this embodiment: a heating jacket 19 and a heating element 20 are provided on the wall of the processing chamber 2 to provide a stable heat source for the processing chamber 2, thereby achieving efficient drying of wet blood materials and ensuring drying efficiency.

[0054] As a technical optimization of the present invention, a temperature and humidity sensor 21 is installed in the inner wall of the right support bushing 4 near the processing cavity 2. The temperature and humidity sensor 21 is electrically connected to the control unit of the heating element 20.

[0055] In this embodiment: the temperature and humidity sensor 21 is electrically connected to the control unit of the heating element 20 to monitor the temperature and humidity in the processing chamber 2 in real time, realize the automatic control of the heating process, ensure the drying effect is stable, and avoid material coking or incomplete drying.

[0056] As a technical optimization of the present invention, the outer wall of the processing cavity 2 is wrapped with a heat insulation layer 22, which covers the outside of the heating interlayer 19.

[0057] In this embodiment, a heat insulation layer 22 is provided on the outer wall of the processing chamber 2 to reduce heat loss from the heating interlayer 19, reduce energy consumption, and at the same time maintain stable temperature inside the chamber and improve drying uniformity.

[0058] As a technical optimization of the present invention, the lifting device 18 is a hydraulic push rod or an electric push rod.

[0059] In this embodiment, the specific type of the lifting device 18 (hydraulic push rod or electric push rod) ensures that the tilt adjustment mechanism can stably and flexibly adjust the tilt angle of the processing chamber 2 to adapt to different processing requirements.

[0060] As a technical optimization of the present invention, a discharge port 23 is provided at the lower part of the outer wall of the processing chamber 2, and a sealing valve 24 is installed at the discharge port 23.

[0061] In this embodiment, a discharge port 23 and a sealing valve 24 are provided at the lower part of the processing chamber 2 to facilitate the convenient and thorough discharge of blood powder after processing, while ensuring the sealing of the processing chamber 2 during processing to avoid heat loss and material leakage.

[0062] As a technical optimization of the present invention, multiple scraper blades 11 are arranged in multiple groups along the axial direction of the rotating main shaft 9. Each group includes multiple scraper blades 11 evenly distributed in the circumferential direction, and adjacent groups of scraper blades 11 are staggered in the circumferential direction.

[0063] In this embodiment, the distribution of the scraper blades 11 makes the scraping of the inner wall of the processing chamber 2 more comprehensive and uniform, effectively preventing wet material from sticking to the chamber wall and forming a coking layer, while improving the material turning effect.

[0064] As a technical optimization of the present invention, the width of the grinding gap is 0.1mm-0.5mm.

[0065] In this embodiment, the distribution and grinding gap of the grinding roller 13 assembly are adapted to meet the particle size requirements of the finished blood meal, ensuring that the blood meal particle size is uniform after grinding, and obtaining a blood meal product with uniform particle size (meeting the gap requirements of 0.1mm-0.5mm), thereby improving product quality.

[0066] As a technical optimization of the present invention, the chamber drive motor 16 and the rotary drive motor 10 rotate in opposite directions.

[0067] In this embodiment, the chamber drive motor 16 rotates in the opposite direction to the rotary drive motor 10, which enhances the tumbling, impact and grinding effect of the material in the processing chamber 2, and further improves the drying uniformity and grinding thoroughness.

[0068] As a technical optimization of the present invention, the outer walls of both the left support bushing 3 and the right support bushing 4 are covered with heat-insulating protective sleeves 25.

[0069] In this embodiment, heat insulation protective sleeves 25 are provided on the outer walls of the left support bushing 3 and the right support bushing 4 to reduce heat conduction, protect the support components and drive motor, and prevent operators from being burned by high temperature, thereby improving the safety of the device.

[0070] Working principle and usage process of this invention:

[0071] Before starting the equipment, the tilt angle of the processing chamber 2 is preset according to the initial moisture content of the raw materials through the tilt angle adjustment mechanism; the heating element 20 is started to preheat the processing chamber 2 to the set temperature, and then the feeding drive motor 8, the rotation drive motor 10 and the chamber drive motor 16 are started simultaneously; the wet blood material is fed into the feeding port 7 and quantitatively pushed into the rotating processing chamber 2 by the screw conveyor 6; inside the chamber, the rotating main shaft 9 drives the scraper 11 to continuously scrape the inner wall to prevent the material from sticking to the wall and coking; the grinding roller 13 revolves with the main shaft to continuously crush the material; the rotation of the processing chamber 2 itself causes the material to spirally roll along the inner wall and fully contact the heated chamber wall to achieve uniform drying; the temperature and humidity sensor 21 monitors the state inside the chamber in real time and feeds it back to the heating control unit to automatically adjust the heating power; during the processing, the lifting device 18 can be dynamically adjusted as needed to change the tilt angle of the chamber to control the material residence time; after the processing requirements are met, the chamber is adjusted to a negative tilt angle (lower discharge end), the discharge port 23 and the sealing valve 24 are opened, and the finished blood powder is discharged under the action of gravity and rotation.

[0072] In the description of this invention, it should be understood that the terms "left", "right", "up", "down", "top", "bottom", "front", "back", "inner", "outer", "back", "middle", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0073] However, the above are merely specific embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made in accordance with the scope of protection of the present invention should still fall within the scope of the claims of the present invention.

Claims

1. A drying and grinding apparatus for blood meal processing, characterized in that, include: Base (1); A horizontally set and rotatable drum-type processing chamber (2); The left support bushing (3) and the right support bushing (4) are coaxially and rotatably fitted onto and connected to the two ends of the processing cavity (2) via bearings (5), respectively. The outer ends of the left support bushing (3) and the right support bushing (4) are both closed structures. A screw conveyor (6) is coaxially and rotatably disposed inside the left support bushing (3), and a feeding port (7) is provided on the cylinder wall of the left support bushing (3). The feed drive motor (8) is fixed to the outer end of the left support bushing (3), and its output end is coaxially fixed to the screw conveyor (6); The rotating spindle (9) is coaxially and rotatably inserted through the right support sleeve (4) and extends into the processing cavity (2); A rotary drive motor (10) is fixed to the outer end of the right support bushing (4), and its output end is coaxially fixed to the rotary spindle (9); Multiple scraper blades (11) are vertically arranged along the axial direction of the rotating main shaft (9) and divided into upper and lower groups, located on the upper and lower sides of the outer wall of the rotating main shaft (9) respectively. The scraper blades (11) on the upper and lower sides are staggered in the axial direction. The free end of each scraper blade (11) slides in contact with the inner wall of the processing chamber (2) for continuously cleaning the material adhering to the inner wall. Multiple grinding roller assemblies are distributed back and forth along the axial direction of the rotating main shaft (9) and divided into two groups, located on the front and rear sides of the rotating main shaft (9) respectively. The grinding roller assemblies on the front and rear sides are staggered in the axial direction. Each grinding roller assembly includes a U-shaped mounting frame (12) with the opening facing outward and a grinding roller (13) rotatably disposed in the mounting frame (12). The closed end of the mounting frame (12) is fixedly connected to the rotating main shaft (9). A grinding gap is formed between the roller surface of the grinding roller (13) and the inner wall of the processing chamber (2). The cylinder rotation drive mechanism is used to drive the processing chamber (2) to rotate around its own axis. It includes a gear ring (14) fixedly sleeved on the outer wall of the processing chamber (2), a drive gear (15) meshing with the gear ring (14), and a chamber drive motor (16) fixed on the left support bushing (3) or the right support bushing (4). The output end of the chamber drive motor (16) is coaxially fixed to the drive gear (15). The tilt adjustment mechanism is used to adjust the angle between the axis of the processing chamber (2) and the horizontal plane. It includes a support base (17) and a lifting device (18). The upper end of the support base (17) is hinged to the outer wall of the left support bushing (3), and its lower end is fixed to the base (1). The fixed end of the lifting device (18) is hinged to the base (1), and its telescopic end is hinged to the outer wall of the right support bushing (4).

2. The drying and grinding apparatus for blood meal processing according to claim 1, characterized in that: The processing chamber (2) has a heating jacket (19) inside its cylindrical wall, and heating elements (20) are arranged inside the heating jacket (19).

3. The drying and grinding apparatus for blood meal processing according to claim 2, characterized in that: A temperature and humidity sensor (21) is installed in the inner wall of the right support bushing (4) near the processing cavity (2), and the temperature and humidity sensor (21) is electrically connected to the control unit of the heating element (20).

4. The drying and grinding apparatus for blood meal processing according to claim 2, characterized in that: The outer wall of the processing chamber (2) is wrapped with a heat insulation layer (22), which covers the outside of the heating interlayer (19).

5. The drying and grinding apparatus for blood meal processing according to claim 1, characterized in that: The lifting device (18) is a hydraulic push rod or an electric push rod.

6. The drying and grinding apparatus for blood meal processing according to claim 1, characterized in that: The lower part of the outer wall of the processing chamber (2) is provided with a discharge port (23), and a sealing valve (24) is installed at the discharge port (23).

7. The drying and grinding apparatus for blood meal processing according to claim 1, characterized in that: Multiple scraper blades (11) are arranged in multiple groups along the axial direction of the rotating main shaft (9), each group containing multiple scraper blades (11) evenly distributed in the circumferential direction, and adjacent groups of scraper blades (11) are staggered in the circumferential direction.

8. The drying and grinding apparatus for blood meal processing according to claim 1, characterized in that: The width of the grinding gap is 0.1mm-0.5mm.

9. The drying and grinding apparatus for blood meal processing according to claim 1, characterized in that: The chamber drive motor (16) rotates in the opposite direction to the rotary drive motor (10).

10. A drying and grinding apparatus for blood meal processing according to claim 1, characterized in that: The outer walls of both the left support bushing (3) and the right support bushing (4) are covered with heat-insulating protective sleeves (25).

Images