CN115653968A

CN115653968A - Hydraulic oil cylinder

Info

Publication number: CN115653968A
Application number: CN202211301020.3A
Authority: CN
Inventors: 朱志峰; 袁松; 陈阳阳
Original assignee: Jiangsu Xugong Construction Machinery Research Institute Co ltd
Current assignee: Jiangsu Xugong Construction Machinery Research Institute Co ltd
Priority date: 2022-10-24
Filing date: 2022-10-24
Publication date: 2023-01-31

Abstract

The application discloses hydraulic cylinder. The hydraulic oil cylinder comprises a cylinder barrel and a piston rod. The cylinder barrel is provided with a first oil port and a second oil port. When the first oil port takes oil, the piston rod extends out. When the oil is fed from the second oil port, the piston rod retracts. The hydraulic oil cylinder further comprises a first heat insulation cylinder body and a second heat insulation cylinder body. The first heat insulation cylinder body is used for insulating heat of the piston rod. The bottom wall end of the first heat insulation barrel is fixedly connected with the piston rod to move relative to the cylinder barrel along with the piston rod, and the first heat insulation barrel is sleeved on the outer side of the cylinder barrel. The second heat insulation cylinder body is used for insulating heat of the cylinder barrel. The bottom wall end of the second heat insulation cylinder is fixedly connected with the cylinder barrel. The first heat insulation barrel is always sleeved on the outer side of the extending portion of the piston rod, the piston rod is not directly exposed in a high-temperature environment, and the risk that external heat is transferred to the oil cylinder along the piston rod is reduced. The second heat insulation barrel is sleeved on the outer side of the cylinder barrel and insulates heat of the cylinder barrel. The two heat insulation barrels prevent the oil temperature in the hydraulic oil cylinder from suddenly rising, and the reliability of the hydraulic oil cylinder in a high-temperature environment is improved.

Description

Hydraulic oil cylinder

Technical Field

The application relates to the field of engineering machinery, in particular to a hydraulic oil cylinder.

Background

With the continuous development of the engineering machinery industry, the application scene is more diversified, and the applicability of the hydraulic oil cylinder in a high-temperature environment is an important research direction. Sometimes, the fire engine is required to continuously work for several hours in a high-temperature environment of 600 ℃, a cylinder barrel and a sealing element of a common oil cylinder cannot be qualified for the high-temperature working condition, and the normal work of a hydraulic system and the normal fire rescue work are influenced due to the sealing failure.

It should be noted that the statements in this background section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

Disclosure of Invention

The application provides a hydraulic cylinder to improve the reliability of hydraulic cylinder in high temperature environment.

The application provides a hydraulic cylinder, including cylinder and piston rod, cylinder have first hydraulic fluid port and second hydraulic fluid port. When the first oil port is filled with oil, the piston rod extends out. When oil is fed from the second oil port, the piston rod retracts. The hydraulic oil cylinder also comprises two heat insulation cylinders. The two heat insulation cylinders comprise a first heat insulation cylinder and a second heat insulation cylinder. The first heat insulation barrel is used for insulating heat of the piston rod. The bottom wall end of the first heat insulation barrel is fixedly connected with the piston rod so as to move relative to the cylinder barrel along with the piston rod, and the first heat insulation barrel is sleeved on the outer side of the cylinder barrel. The second heat insulation barrel is used for insulating heat of the cylinder barrel. The bottom wall end of the second heat insulation cylinder is fixedly connected with the cylinder barrel.

In some embodiments, the second insulating cylinder is sleeved outside the first insulating cylinder.

In some embodiments, the first insulating cylinder has an outer diameter greater than an inner diameter of the second insulating cylinder.

In some embodiments, the second oil port is housed inside the first heat-insulating cylinder. The first heat insulation cylinder body is provided with an oil port channel communicated with the second oil port. The oil port channel penetrates through the first heat insulation cylinder in the wall thickness direction, and extends in the axial direction, so that the second oil port is always located in the extending length of the oil port channel in the process that the first heat insulation cylinder extends out or retracts along with the piston rod.

In some embodiments, the second insulated cylinder further comprises a first opening and a second opening opened in the cylinder wall. The first opening is used for being communicated with the first oil port. The second opening is used for being communicated with the second oil port.

In some embodiments, the insulation cartridge includes a cartridge body and an insulation material layer disposed inside the cartridge body.

In some embodiments, the second insulating cylinder is sleeved outside the first insulating cylinder. The first heat insulation cylinder body also comprises a communicating seam arranged on the cylinder body. The communication seam penetrates in the wall thickness direction of the cylinder body of the first heat insulation cylinder body so that the heat insulation material layer of the second heat insulation cylinder body is in contact with the heat insulation material layer of the first heat insulation cylinder body through the communication seam.

In some embodiments, the insulating material layer has elasticity.

In some embodiments, the insulating cylinder further comprises a metal mesh. The metal grid net sets up and lays on the metal grid net at the inboard thermal insulation material layer of barrel body.

In some embodiments, the thermally insulated barrel further comprises a thermal barrier coating. The thermal barrier coating sets up the outside at the barrel body.

In some embodiments, the open end of the insulating cylinder is provided with a rounded chamfer.

Based on the technical scheme that this application provided, hydraulic cylinder includes cylinder, piston rod, first hydraulic fluid port and second hydraulic fluid port. The first oil port and the second oil port are arranged on the cylinder barrel. When the first oil port takes oil, the piston rod extends out. When the oil is fed from the second oil port, the piston rod retracts. The hydraulic oil cylinder also comprises two heat insulation cylinders. The two heat insulation cylinders comprise a first heat insulation cylinder and a second heat insulation cylinder. The first heat insulation barrel is used for insulating heat of the piston rod. The bottom wall end of the first heat insulation barrel is fixedly connected with the piston rod so as to move relative to the cylinder barrel along with the piston rod, and the first heat insulation barrel is sleeved on the outer side of the cylinder barrel. The second heat insulation barrel is used for insulating heat of the cylinder barrel. The bottom wall end of the second heat insulation cylinder is fixedly connected with the cylinder barrel. Under the condition that the piston rod stretches and retracts in a reciprocating mode, the first heat insulation barrel is sleeved on the outer side of the extending portion of the piston rod all the time, the piston rod cannot be directly exposed in a high-temperature environment, and therefore the risk that external heat is transmitted to the interior of the oil cylinder along the extending piston rod is reduced. The second heat insulation cylinder body is static relative to the cylinder barrel and is sleeved on the outer side of the cylinder barrel all the time, so that a heat insulation effect is achieved on the cylinder barrel. The first heat insulation barrel and the second heat insulation barrel are matched together, so that the oil temperature of hydraulic oil in the hydraulic oil cylinder cannot suddenly rise, the reliability of the hydraulic oil cylinder in a high-temperature environment is improved, and the applicability of the engineering machinery in operation in the high-temperature environment is improved.

Further features of the present application and advantages thereof will become apparent from the following detailed description of exemplary embodiments thereof, which is to be read in connection with the accompanying drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:

FIG. 1 is a schematic overall view of a hydraulic ram according to an embodiment of the present disclosure.

FIG. 2 is a schematic view of the first insulated barrel of FIG. 1.

FIG. 3 is a schematic view of the second insulated barrel of FIG. 1.

Fig. 4 is a schematic view of the first heat-insulating cylinder of fig. 1 having a heat-insulating material layer disposed inside.

Fig. 5 is a schematic view of the second heat-insulating cylinder of fig. 1 with a heat-insulating material layer disposed inside.

In the figure:

1. a first heat insulation cylinder; 11. a first cylinder body; 12. an oil port channel; 13. a communicating seam; 14. a first metal grid; 16. a first arc structure; 2. a second heat insulation cylinder; 21. a second cylinder body; 22. a first opening; 23. a second opening; 24. a second metal grid; 25. a second arc structure; 3. a cylinder cover; 4. a cylinder barrel; 5. a piston rod; 6. a first oil port; 7. a second oil port; A. a layer of thermal insulation material; B. and (4) a thermal insulation coating.

Detailed Description

The technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only some embodiments of the present application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the application, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The relative arrangement of the components and steps, the numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present application unless specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description. Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be discussed further in subsequent figures.

For ease of description, spatially relative terms such as "over 8230," "upper surface," "above," and the like may be used herein to describe the spatial positional relationship of one device or feature to other devices or features as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is turned over, devices described as "above" or "on" other devices or configurations would then be oriented "below" or "under" the other devices or configurations. Thus, the exemplary terms "at 8230; \8230; above" may include both orientations "at 8230; \8230; above" and "at 8230; \8230; below". The device may be otherwise variously positioned and the spatially relative descriptors used herein interpreted accordingly.

In the prior art, a heat insulation and cooling mechanism is usually arranged outside a cylinder barrel of the hydraulic oil cylinder, a piston rod heat insulation protection technology is lacked, high temperature in the environment can be transmitted to the inside of the oil cylinder along a piston rod, sealing failure is caused, the actual application capability of the hydraulic oil cylinder in a high-temperature environment is poor, and the working time in the high-temperature environment is limited. In order to solve the problem, the application provides a hydraulic cylinder. Referring to fig. 1, the hydraulic cylinder includes a cylinder tube 4 and a piston rod 5. The cylinder 4 has a first port 6 and a second port 7. When the first oil port 6 is fed with oil, the piston rod 5 extends out. When the oil is fed into the second oil port 7, the piston rod 5 retracts. The hydraulic oil cylinder also comprises two heat insulation cylinders. The two heat-insulating cylinders include a first heat-insulating cylinder 1 and a second heat-insulating cylinder 2. The first heat insulation cylinder 1 is used for heat insulation of the piston rod 5. The bottom wall end of the first heat insulation cylinder body 1 is fixedly connected with the piston rod 5 so as to move relative to the cylinder barrel 4 along with the piston rod 5, and the first heat insulation cylinder body 1 is sleeved on the outer side of the cylinder barrel 4. The second heat insulation cylinder 2 is used for insulating the cylinder 4. The bottom wall end of the second heat insulation cylinder 2 is fixedly connected with the cylinder barrel 4. Under the condition that the piston rod 5 stretches back and forth, the first heat insulation barrel 1 is always sleeved on the outer side of the extending part of the piston rod 5, so that the piston rod 5 is not directly exposed in a high-temperature environment, and the risk that external heat is transmitted to the inside of the oil cylinder along the extending piston rod 5 is reduced. The second heat insulation cylinder 2 and the cylinder barrel 4 are relatively static and are sleeved on the outer side of the cylinder barrel 4 all the time, so that the cylinder barrel 4 is heat-insulated. The first heat insulation barrel body 1 and the second heat insulation barrel body 2 are matched together, so that the oil temperature of hydraulic oil in the hydraulic oil cylinder cannot suddenly rise, the reliability of the hydraulic oil cylinder in a high-temperature environment is improved, and the applicability of the engineering machinery in operation in the high-temperature environment is improved.

It should be noted here that the heat insulation cylinder includes a bottom wall and an opening, and the bottom wall has a mounting hole. For example, for the first heat-insulating cylinder 1, the bottom wall thereof has a mounting hole for mounting the piston rod 5. For the second heat-insulating cylinder 2, the bottom wall thereof has a mounting hole for mounting the cylinder 4. In the description of the embodiments of the present application, one end of the opening of the heat insulation cylinder is referred to as an open end. The end opposite the open end of the insulating cylinder, i.e., the end of the bottom wall, is referred to as the bottom wall end. The end of the cylinder 4 intended to be hinged to the body of the working machine is called the cylinder mounting end. An end of the piston rod 5 to be articulated with a working mechanism (e.g., a telescopic arm) of the construction machine is referred to as a piston rod attachment end. Therefore, the first heat-insulating cylinder 1 and the second heat-insulating cylinder 2 are detachable, and the cylinder mounting end is inserted from the open end of the second heat-insulating cylinder 2 and is made to leak out from the mounting hole on the bottom wall end of the heat-insulating cylinder during mounting, and then the second heat-insulating cylinder 2 and the cylinder 4 are fixedly connected through a clamp or a bolt. In a similar way, the piston rod mounting end is inserted from the open end of the first heat insulation cylinder 1 and leaks out from the mounting hole of the bottom wall end, and then the first heat insulation cylinder 1 is fixedly connected with the cylinder 4 through a hoop or a bolt. After the installation is completed, the open ends of the first heat-insulating cylinder 1 and the second heat-insulating cylinder 2 are oppositely oriented, so that the first heat-insulating cylinder 1 and the second heat-insulating cylinder 2 are also convenient to detach and replace.

In order to improve the heat insulation performance and the protection performance of the hydraulic oil cylinder, in some embodiments, referring to fig. 1, the second heat insulation cylinder 2 is sleeved outside the first heat insulation cylinder 1. Specifically, the first heat insulation barrel 1 is located between the second heat insulation barrel 2 and the cylinder barrel 4, and the extension length of the second heat insulation barrel 2 is at least equal to the length of the cylinder barrel 4, so that the cylinder barrel 4 is always sleeved with the second heat insulation barrel 2 in the inner side in the process that the first heat insulation barrel 1 moves along with the piston rod 4. The extension length of the first heat insulation cylinder 1 is similar to the length of the piston rod 4, so that when the piston rod 5 completely extends out of the cylinder 4 (i.e. the first heat insulation cylinder 1 completely extends out of the second heat insulation cylinder 2), the piston rod 5 is still sleeved inside by the first heat insulation cylinder 1. First thermal-insulated barrel 1 and the thermal-insulated barrel 2 of second can also play the guard action to piston rod 5 and cylinder 4 except playing thermal-insulated effect, thereby reduce hydraulic cylinder and external environment collision and take place the risk of losing efficacy in the course of the work.

In some embodiments, the first heat-insulating cylinder 1 may also be disposed outside the second heat-insulating cylinder 2.

In some embodiments, the outer diameter of the first heat-insulating cylinder 1 is larger than the inner diameter of the second heat-insulating cylinder 2. Specifically, the first heat insulation cylinder 1 and the second heat insulation cylinder 2 are configured to be interference fit to avoid generating a gap, thereby improving a heat insulation effect.

In some embodiments, referring to fig. 1 and 2, the second oil port 7 is housed inside the first heat-insulating cylinder 1. The first heat-insulating cylinder 1 has an oil port passage 12 communicating with the second oil port 7. The port passage 12 penetrates in the wall thickness direction of the first heat-insulating cylinder 1 and extends in the axial direction X so that the second port 7 is always located within the extended length of the port passage 12 in the process of extending or retracting the first heat-insulating cylinder 1 along with the piston rod 5. In the operation process, hydraulic oil needs to enter the first oil port 6 or the second oil port 7 through the oil pipe to realize the telescopic function of the piston rod 5, so that the oil port channel 12 needs to be reserved to prevent the first heat insulation cylinder 1 from extruding the oil pipe when moving along with the piston rod 5, and meanwhile, the first heat insulation cylinder 1 can smoothly slide along with the piston rod 5. Further, the size of the port passage 12 is adapted to the size of the oil pipe.

In some embodiments, referring to FIG. 1, the second insulated cylinder 2 further includes a first opening 22 and a second opening 23 opened in the cylinder wall. The first opening hole 22 is for communication with the first oil port 6. The second opening 23 is for communication with the second port 7. The oil pipe comprises a first oil pipe and a second oil pipe, the first oil pipe is communicated with the first oil port 6 through the first opening hole 22, and the second oil pipe is communicated with the second oil port 7 through the second opening hole 23, so that the telescopic function of the hydraulic oil cylinder is realized. In the telescopic process of the piston rod 5, the first oil pipe and the second oil pipe are relatively static with the first heat insulation cylinder 1, and the first oil pipe and the second oil pipe are relatively movable with the second heat insulation cylinder 2. Furthermore, the oil pipe, the oil port and the opening hole formed in the second heat insulation cylinder 2 are matched in size and shape.

In some embodiments, the heat insulating cylinder includes a cylinder body and a heat insulating material layer a disposed inside the cylinder body.

In some embodiments, the insulating cylinder further comprises a metal mesh. The metal grid sets up and lays on the metal grid at the inboard heat-insulating material layer A of barrel body.

The arrangement of the heat insulating cylinder and the heat insulating material layer a will be described in detail with reference to fig. 4 and 5. Specifically, fig. 4 shows a partial enlarged view of the first heat insulation cylinder 1, in which a black thick solid line represents a cylinder body of the first heat insulation cylinder 1, that is, the first cylinder body 11, a first metal grid 14 is arranged inside the first cylinder body 11, and a heat insulation material is laid on the first metal grid 14 to form a heat insulation material layer a, so that the first heat insulation cylinder 1 has a heat insulation function, and the first metal grid 14 plays a role of fixing the heat insulation material. Further, the first metal grid 14 is fixedly connected (e.g., welded) to the inside of the first cylinder body 11. Referring to fig. 5, the second heat insulation cylinder 2 has the same structure as the first heat insulation cylinder 1, i.e., has a second cylinder body 21, a second metal mesh 24 fixedly attached to the inside of the second cylinder body 21, and a heat insulation material layer a formed of a heat insulation material laid on the second metal mesh 24.

In some embodiments, the wire diameter of the metal grid comprises 0.2 to 0.5mm. The fixing effect of the metal grid net on the heat insulation material can be enhanced through the arrangement.

To further promote protection of the hydraulic ram, in some embodiments, the cartridge body comprises a metal foil. The thickness of the metal sheet is 2-5 mm. In particular, the metal sheet may be a cylindrical structure itself to constitute the cylinder body. Of course, the metal sheet may be an arc-shaped sheet having an equal curvature, and the cylindrical body may be formed by joining a plurality of arc-shaped sheets to each other.

In some embodiments, the foil comprises a stainless steel and/or an aluminum alloy.

In some embodiments, the insulation material layer a has elasticity. Specifically, the heat-insulating material layer A is made of aerogel felt and is coated by high silica cloth. The aerogel felt is a flexible heat-insulating felt which is prepared by using nano silicon dioxide or metal aerogel as a main body material and compounding the aerogel felt with carbon fiber or ceramic glass fiber cotton or pre-oxidized fiber felt, and is characterized by low heat conductivity coefficient and certain tensile and compressive strength.

In some embodiments, the insulation material layer a is silica aerogel blanket. Silica aerogel felt has high resilience, consequently can kick-back closed path breach after the hydraulic fluid port (first hydraulic fluid port 6 or second hydraulic fluid port 7) passes through as it, ensures protective structure integrality.

In some embodiments, the first insulating cylinder 1 further comprises a communication slit 13 (see the dashed line in fig. 2) opened on the cylinder body thereof. The communication slit 13 penetrates in the wall thickness direction of the cylindrical body of the first heat-insulating cylindrical body 1 so that the heat-insulating material layer a of the second heat-insulating cylindrical body 2 contacts the heat-insulating material layer a of the first heat-insulating cylindrical body 1 through the communication slit 13. Specifically, the number of the communication slits 13 may be plural, and circumferentially spaced on the first cylinder body 11. The heat insulation effect can be further improved by the contact of the heat insulation material layers A of the two heat insulation cylinder bodies through the communication seams 13.

In some embodiments, referring to fig. 4 and 5, the thermal cylinder also includes a thermal barrier coating B. The heat insulation coating B is arranged on the outer side of the cylinder body. Specifically, the thermal insulation coating B is uniformly coated on the outer side of the cylinder body to further increase the thermal insulation effect. Specifically, the thermal insulation coating B can be a high-temperature resistant ceramic coating, and the thickness of the coating is 2-8 mm.

In some embodiments, referring to fig. 1-3, the open end of the insulating cylinder is provided with a rounded chamfer. Specifically, the open end of the first heat-insulating cylinder 1 has a first circular arc structure 16, and the open end of the second heat-insulating cylinder 2 has a second circular arc structure 25. The shape and size of the first circular arc structure 16 and the second circular arc structure 25 are adapted to reduce the wear of the inner surface of the second insulated cylinder 2 and the outer surface of the first insulated cylinder 1 during the extension and contraction of the piston rod 5.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solutions of the present application and not to limit them; although the present application has been described in detail with reference to preferred embodiments, those of ordinary skill in the art will understand that: modifications can be made to the embodiments of the application or equivalents may be substituted for some features; all of which are intended to be encompassed within the scope of the claims appended hereto without departing from the spirit and scope of the present disclosure.

Claims

1. The utility model provides a hydraulic cylinder, includes cylinder (4) and piston rod (5), cylinder (4) have first hydraulic fluid port (6) and second hydraulic fluid port (7), during first hydraulic fluid port (6) oil feed, piston rod (5) stretch out, during second hydraulic fluid port (7) oil feed, piston rod (5) withdrawal, its characterized in that, hydraulic cylinder still includes two thermal-insulated barrels, two thermal-insulated barrels include:

the first heat insulation barrel (1) is used for insulating heat of the piston rod (5), the bottom wall end of the first heat insulation barrel (1) is fixedly connected with the piston rod (5) so as to move relative to the cylinder barrel (4) along with the piston rod (5), and the first heat insulation barrel (1) is sleeved on the outer side of the cylinder barrel (4); and

the second heat insulation barrel (2) is used for insulating heat of the cylinder barrel (4), and the bottom wall end of the second heat insulation barrel (2) is fixedly connected with the cylinder barrel (4).

2. The hydraulic oil cylinder as claimed in claim 1, characterized in that the second heat-insulating cylinder (2) is sleeved outside the first heat-insulating cylinder (1).

3. Hydraulic ram according to claim 2, characterized in that the external diameter of the first insulating cylinder (1) is greater than the internal diameter of the second insulating cylinder (2).

4. The hydraulic oil cylinder according to claim 1, wherein the second oil port (7) is covered inside the first heat insulation cylinder (1), the first heat insulation cylinder (1) is provided with an oil port channel (12) communicated with the second oil port (7), the oil port channel (12) penetrates in the wall thickness direction of the first heat insulation cylinder (1) and extends in the axial direction (X) so that the second oil port (7) is always located within the extension length of the oil port channel (12) in the process that the first heat insulation cylinder (1) extends or retracts along with the piston rod (5).

5. The hydraulic ram according to claim 1, characterized in that the second insulating cylinder (2) further comprises a first opening (22) and a second opening (23) opening on the cylinder wall, the first opening (22) being intended to communicate with the first oil port (6) and the second opening (23) being intended to communicate with the second oil port (7).

6. Hydraulic ram according to claim 1, characterised in that the thermally insulated cylinder comprises a cylinder body and a layer (a) of thermally insulating material arranged inside the cylinder body.

7. The hydraulic oil cylinder as claimed in claim 6, wherein the second heat insulation cylinder (2) is sleeved outside the first heat insulation cylinder (1), the first heat insulation cylinder (1) further comprises a communication seam (13) formed in a cylinder body of the first heat insulation cylinder, and the communication seam (13) penetrates in the wall thickness direction of the cylinder body of the first heat insulation cylinder (1) so that the heat insulation material layer (A) of the second heat insulation cylinder (2) is in contact with the heat insulation material layer (A) of the first heat insulation cylinder (1) through the communication seam (13).

8. A hydraulic ram according to claim 6, characterised in that the layer (A) of insulating material is elastic.

9. Hydraulic ram according to claim 6, characterized in that the insulating cylinder further comprises a metal grid which is arranged inside the cylinder body and on which the layer of insulating material (A) is laid.

10. The hydraulic ram of claim 6, wherein the thermal barrier cylinder further comprises a thermal barrier coating (B) disposed on an exterior side of the cylinder body.

11. The hydraulic ram according to any one of claims 1 to 10, wherein the open end of the heat insulation cylinder is provided with a rounded chamfer.