DE202005006035U1 - Outer cover e.g. for super vacuum isolation tank deep-cold liquid gas, has cylinder and two curved surfaces at both ends and reinforcing ring at exterior surface of cylinder of outer cover - Google Patents

Abstract

The outer cover has a cylinder and two curved surfaces at both ends and a reinforcing ring at the exterior surface of the cylinder of the outer cover. Each curved surface has an intensified structure distributed around mounting holes of the curved surface. The structure is a plate and together with the curved surface a smooth curved surface forms. An independent claim is included for a super vacuum isolation tank.

Description

Field of the invention

The The invention relates to a type of storage or transport device for deep-frozen LPG, and in particular an outer shell and a super vacuum isolation tank, the latter in the efficient transport of cryogenic LPG used.

Description of the state of the technique

The capacity from cryogenic tanks was created by the 1909 evolved vacuum powder insulation technology greatly improved. By the end of the 30s, the vacuum powder insulation technology was found Widely used in the whole range of cryogenic technology, the air separation and the liquefaction technique being typical Examples are. At the beginning of the 50s came the multilayer super vacuum insulation technology on which a very significant evolution in the story the cryogenic isolation technology was. In particular, increased by the end of the 50s with the development of space technology the consumption of liquid hydrogen and liquid helium strong, what the research and the application of multi-layer super vacuum insulation technology stimulated, being tanker trucks and tank container for cryogenic liquid gas the main ones Were product applications.

On Low-temperature technology refers to the field of cryogenic technology LPG on the gas in liquid Condition and with a temperature below -160 ° C, such as liquid oxygen, Liquid nitrogen, Liquid argon, Liquid hydrogen, Liquid helium, Liquid methane and liquid natural gas (LNG - Liquified Natural gas), etc. Since the volume of the above-mentioned gases in the liquid State in comparison with that in the gaseous state to the more reduced by 600 times, these are often transported in a liquid state. The devices for transporting cryogenic LPG include tanker trucks, Tank container, etc. The tank is with a double layer structure and a vacuum intermediate layer formed between the inner container and the outer shell arranged are, which by means of a support structure with each other are connected. Due to the requirement of transport regulations should all transport devices (such as tankers, tank containers etc.) the restriction comply with the maximum overall size, and within the limit will be the effective volume for the charge is determined by the thickness of the vacuum layer.

Currently, tank trucks and tank containers with vacuum powder insulation are widely used as cryogenic transporters. 1 shows the main structure of a transport device formed according to the prior art 10 which an outer shell 1 , an inner container 2 , an isolation structure 3 , several radial supports 4 and a front longitudinal support 15 and a rear longitudinal support 16 between the outer shell 1 and the inner container 2 , and a stiffening device 6 having. Between the inner container 2 and the outer shell 1 is a super-vacuum layer 8th formed, in which material, such as perlite may be included to realize the heat insulation. To achieve a satisfactory thermal insulation effect, the super-vacuum layer 8th designed so that it has a large thickness dimension, which is often in a range of 200 mm to 300 mm. However, the actual loading volume of such a device is reduced, and the perlite gradually settles during transportation, affecting the performance of the thermal insulation. For this reason, the multi-layer insulation technology has been developed with its improvement in practical use, particularly with respect to the cryogenic LPG receiving devices.

According to the multi-layer insulation technology are in the above-mentioned transport device 10 Heat insulation materials outside the inner container 2 is wound around, and the insulating layer is formed by emptying the plurality of layers of heat insulating material having vacuum intermediate layer to a super-vacuum state. The thinner the vacuum interlayer, the more charge the tank can accommodate and transport. However, the difficulty is that as the insulating layer becomes thinner, the supporting structure between the inner container and the outer shell is more difficult to form, the degree of vacuum is lower, and more heat is transferred from the outer shell to the inner container.

Currently must be used in most multi-layer insulation techniques, as described for example in the Chinese patent ZL 00249960.6 and ZL 01272605.2 are disclosed for attaching the radial support in the vacuum layer the thickness of the vacuum layer about 100 mm.

In fact, the supporting structure between the inner container and the outer shell should not only take up the load of the liquid, the weight of the tank and the forces caused by shock acceleration, but further reduce as much as possible the heat input caused by itself, and therefore it is a key task Construct supporting structure of a cryogenic tank. In the above-mentioned Transportvorrich tung 10 has the support structure radial supports 4 , the front longitudinal support 15 and the rear longitudinal support 16 on. Take the rear longitudinal support 16 as an example, this has a reinforcing plate 23 and a steel support tube 24 for the inner container 2 , an insulating support ring 26 and its retaining ring 25 , a steel support tube 32 for the outer shell 1 and a reinforcing rib 33 on. The steel support tube 24 for the inner container 2 is through the reinforcement plate 23 through with the outer surface of the rear arched bottom of the inner container 2 welded, and the steel support tube 32 for the outer shell 1 is with the inner surface of the rear arched bottom of the outer shell 1 welded. The steel support tube 24 for the inner container 2 extends through the insulating support ring 26 and the retaining ring 25 through and over this from the steel support tube 32 for the outer shell 1 held. The stiffening device 6 has an insulation filler block 28 , an inner nut 27 as well as a pressure nut 29 for the insulation filler block 28 , an axle journal 30 and a carrying lid 31 on. The stiffening device 6 is by means of the inner nut 27 with the steel support tube 24 coupled, with the pressure nut 29 with the carrying lid 31 is welded and the carrying lid 31 with the steel support tube 32 for the outer shell 1 is welded. It can be seen that the structure of the above-mentioned isolation filler block 28 between the inner container 2 and the outer shell 1 neither the problem that the heat input through the support structure is very high because of the narrow gap between the multiple super-vacuum insulation layers nor the problem that thermal expansion or cold shrinkage can damage or break the multiple super-vacuum insulation layers can effectively solve. Second, it is very difficult to place the stainless steel over-tube between the domed bottoms of the inner container 2 and the outer shell 1 train. Finally, the distance between the domed bottoms of the inner container 2 and the outer shell 1 big and the impact resistance is low.

A other support structure for cryogenic containers referred to as a "hanging" structure, which However, it can not effectively solve the problem that the impact resistance due to thermal expansion or from cold shrinkage subsides. If the supportive ability the hanging structure made of stainless steel is, takes the heat transfer to, and therefore, the evaporation losses of the cryogenic container will increase and the storage efficiency for Cryogenic fluid is lose weight.

Chinese patent ZL 00216678.X discloses a type of support structure 40 for the cryogenic container to absorb strong shocks, as in 2 shown. The support structure 40 has a radial support on the inner surface of the outer shell 44 is provided at each end of the cryogenic container, and a longitudinal support which is provided at the one end of the cryogenic container, whereas the other end is formed as a free end. The radial support has a radial support ring 41 , a support tube 42 for the outer shell 44 and a reinforcing rib 43 on. One end of a support tube 51 for the inner container 50 is in the middle of the outer surface of each domed bottom of the inner container 50 welded, and the other end is in the radial support ring 41 used. The support tube 42 , the reinforcement rib 43 and the outer shell 44 are connected to a unity. The longitudinal support has a longitudinal support rod 45 , a longitudinal support plate 47 , which with the support tube 51 is screwed and positioned by means of welding, a glass fiber reinforced plastic backing plate 46 , which at each end of the longitudinal support plate 47 is mounted, a pressure bar 48 , which with the longitudinal support plate 47 cooperates such that it the glass fiber reinforced plastic backing plate 46 tightly compresses, and a transitional connector 49 on, by means of which the longitudinal support rod 45 with the curved bottom of the outer shell 44 is welded. In the above-mentioned support structure, since each end of the cryogenic container is provided with both radial support and longitudinal support, a greater distance must be left between the domed bottoms, which reduces impact resistance, and the contact gap increases during transition from a normal one or ambient temperature to a low temperature.

The Development of storage or transport containers for cryogenic LPG pursues the objective, the effective volume for cryogenic LPG and the impact resistance increase within the limited size.

Description of the invention

Accordingly It is an object of the present invention to provide an outer shell of a To provide super vacuum isolation tanks, which has a cylinder, two arched Floors and Further, a plurality of reinforcing rings on the outside, to protect the outer shell, essentially the design problems of the prior art solve that the heat insulation layer the tank thinner training to produce a good insulation performance, and the for a greater effective volume provides.

Another object of the present invention is to provide a super vacuum insulation tank using the outer shell, which substantially obviates one or more of the problems due to the limitations and disadvantages of the prior art Technology triggers.

Around these goals in agreement with the intention of the present invention, as they embodied herein and is generally described, includes an outer shell of a Super vacuum insulation tanks for cryogenic liquid gas a cylinder and two arched ones Floors on Both sides of the cylinder, wherein a plurality of reinforcing rings on the outer surface of the Cylinder of the outer shell provided are. About that In addition, each vaulted Ground a reinforced Structure on, around the mounting holes of the arched floor are distributed. Especially the reinforced structure is a plate and makes a smooth and arched one surface along with the arched one Floor off. Besides that is a plate on each receiving bore for sealing the receiving bore arranged, and a reinforced Plate is on the inner surface the arched floors arranged.

In Another aspect includes a super vacuum isolation tank for deep-frozen LPG a frame and a tank body, the tank body an outer shell, the a cylinder with two domed ones Includes soils, an inner container, one cylinder and two arched ones Includes soils, a super-vacuum insulation layer between the outer shell and the inner container includes, and a support structure, the outer shell and the inner container connecting, wherein a plurality of reinforcing rings on the outside surface of the Cylinder of the outer shell are provided. Each arched Floor continues to show a reinforced Structure on which is distributed around the mounting holes.

According to the invention combined support structure only between the inner arched floor and the outer arched floor provided at both ends of the tank, and has the radial support no direct contact with the outer shell, what the heat conduction area of support between the inner container and the outer shell reduces, whereby a better insulation performance is achieved. simultaneously can the super vacuum insulation layer between the inner container and the outer shell through the absence of radial support reduced in the straight section in the thickness dimension to 50 mm which increases the effective volume of the inner container and increases the loading capacity.

Further shows the outer shell of the tanks according to the invention two arched floors, a cylinder and a plurality of stiffening or reinforcing rings on. In contrast to the prior art, the reinforcing rings on the outside provided the outer shell, what kind of the outer shell one lower material consumption, lower weight and lower Cost causes while the Requirements met are that the outer shell the same inside diameter and the reinforcing rings have the same size. At the same time the reinforcing rings act as a protection device for the outer shell. The domed Floors of the inner container and the outer shell (im Hereafter referred to as the inner and outer domed bottoms) are in opposite directions Direction arranged, and the inner container is multi-layered of thermal insulation material wrapped. The inner container is with the outer shell by means of the formed between the inner and outer curved bottoms at both ends of the tank according to the invention combined support structure connected, which simultaneously forces in the radial direction and in longitudinal direction receives. Because the vaulted floors of the inner container and the outer shell in the opposite direction can be arranged, the combined support structure within the inner arched Bodens are formed, which is the distance between the inner and the outer arched bottom reduced. Therefore, achieved at the same size of the outer shell of the inner container of the tanks according to the invention a bigger effective one Volume.

Brief description of the drawings

The The invention will be explained in more detail with reference to the drawing. In the drawing show:

1 a schematic sectional view of a tank for cryogenic liquid gas according to the prior art;

2 a schematic view of a shock-resistant support structure, which is provided in a cryogenic container according to the prior art;

3 a perspective view of a multi-layer super vacuum insulation tank according to the invention for cryogenic liquid gas;

4 a schematic vertical sectional view of the in 3 illustrated tanks;

5 a perspective sectional view of a first curved bottom of the in 3 illustrated tanks;

6 a perspective sectional view of a second curved bottom of the in 3 illustrated tanks.

Detailed description the preferred embodiment

Referring to the drawings a preferred embodiment of the invention described.

3 shows a perspective view of a multi-layer super-vacuum insulation tank according to the invention for cryogenic liquid gas. As in 3 is shown, the tank points 100 a frame 101 and a tank body 102 which are welded together in a special way.

With regard to a tanker truck, the frame is concerned 101 the structure that the tank body 102 attached to the automobile chassis. Regarding a tank container, the frame is concerned 101 the structure that the tank body 102 attached in the predetermined area of the container. Further, on the outer surface of the tank 100 a plurality of stiffening or reinforcing rings 103 intended.

4 shows a schematic vertical sectional view of the in 3 shown tanks 100 , Referring to 4 points the tank body 102 an outer shell 110 with a cylinder 111 , a first arched ground 112 and a second arched floor 113 that serve the cylinder 111 each at its two ends to close, and an inner container 120 on, inside the outer shell 110 is arranged and a cylinder 121 , a first arched ground 122 and a second arched floor 123 which serve to the cylinder 121 each at its two ends to close. Between the outer shell 110 and the inner container 120 is a super vacuum insulation layer 104 formed, with multiple layers of insulation material 105 around the outer surface of the inner container 120 are wound.

Referring to 4 and 5 shows 5 a perspective sectional view of a first curved bottom of the in 3 illustrated tanks. In particular, the first curved floor 122 of the inner container 120 a first main body 1221 , a first small, inverted dome-shaped end 1222 which is from the middle of the first main body 1221 in the inner container 120 is formed lowered, so that consequently the curved surface of the first small, inverted curved bottom 1222 to the curved surface of the corresponding arched bottom 112 the outer shell 110 is opposite, and a first extension approach 1223 on, between the first small, inverted arched floor 1222 and the first main body 1221 welded and which forms a rounded structure and the internal tension of the inner container 120 reduced. In addition, a stiffening or reinforcing plate 1224 on the inside of the arched floor 122 of the inner container 120 be provided to increase the impact resistance. Referring to the 4 and 6 has the second arched floor 123 of the inner container 120 a second main body 1231 , a second small, inverted arched floor 1232 which is from the middle of the second main body 1231 in the inner container 120 is formed lowered, so that consequently the curved surface of the second small, inverted curved bottom 1232 to the curved surface of the corresponding arched bottom 113 the outer shell 110 opposite, and a second extension approach 1233 on, between the second small, inverted arched bottom 1232 and the second main body 1231 welded and which forms a rounded structure and the internal tension of the inner container 120 reduced. In addition, a reinforcing plate 1234 on the inside of the arched floor 123 of the inner container 120 be provided to increase the impact resistance.

To ensure sufficient strength, the first curved bottom points 112 the outer shell 110 Further, a main body 1121 , a stiffening plate 1122 in the middle of the main body 1121 is provided, a reinforcing tube 1123 attached to the stiffening plate 1122 is attached, and a reinforcing plate provided thereon 1124 for reinforcing the structure. Preferred is on the inside of the first arched bottom 112 a reinforcing plate 1126 provided the strength of the first arched floor 112 to increase. To meet the mounting requirements, the second arched floor points 113 the outer shell 110 a main body 1131 , a support tube 1132 from the center of the main body 1131 is mounted, a stiffening plate 1133 in the middle of the main body 1131 is provided and to the support tube 1132 is attached, a reinforcing tube 1134 attached to the stiffening plate 1133 is attached and the support tube 1132 surrounds and on which a reinforcing or stiffening plate 1135 is provided to increase the strength of the structure, and a reinforcing plate 1136 on the inside of the second arched floor 113 is provided. The abovementioned, inventive construction of the tank body 102 makes it possible, taking advantage of the distance between the curved bottom of the outer shell 110 and the domed bottom of the inner container 120 to arrange a combined support structure.

Referring to 4 the combined support structure has separately from each other a radial support structure and a longitudinal support structure. The radial support structure has a first radial support structure 210 that with the first arched ground 122 of the inner container 120 cooperates, and a second radial support structure 220 on top, with the second arched floor 123 of the inner container 120 interacts. The first radial support structure 210 and the second radial support structure 220 each have an inner mounting ring 2101 respectively. 2201 , an outer mounting ring 2102 respectively. 2202 and a first radial support plate 2103 or a second radial support plate 2203 on. The inner mounting ring 2101 respectively. 2201 and the outer mounting ring 2102 respectively. 2202 are in turn at predefined positions on the inside of the extension lug 1223 respectively. 1233 or on the small, inverted arched floor 1222 respectively. 1232 attached. The respective radial support plate 2103 respectively. 2203 is between the inner mounting ring 2101 respectively. 2201 and the outer mounting ring 2102 respectively. 2202 attached and works closely with the transition tube (extension approach 1223 respectively. 1233 ) or the small, inverted arched floor 1222 respectively. 1232 together. Because the arched floors 122 . 123 of the inner container 120 each having a rounded structure, it can be seen that the radiant from the extension approach 1223 . 1233 to the small, inverted arched floor 1222 . 1232 gradually decreases, so that the contact gap between the radial support plate 2103 . 2203 and the arched floor 122 . 123 self-adjusting. Therefore, when transitioning from the normal temperature state to the low temperature state, although on the inner container 120 a thermal expansion effect or a cold shrinkage effect occurs, the first radial support plate 2103 and the second radial support plate 2203 but still on the small, inverted arched floor 1222 respectively. 1232 or at the extension approach 1223 respectively. 1233 be engaged without a gap is formed therebetween. Of greater importance is that, since the radial support directly on the curved bottom 122 . 123 of the inner container 120 is provided, the super-vacuum insulation layer between the inner container 120 and the outer shell 110 in its thickness can be reduced to 50 mm, which is the effective volume of the inner container 120 additionally increased.

Further, between the first arched floor 112 the outer shell 110 and the first arched ground 122 of the inner container 120 the longitudinal support structure 230 provided, extending through the first radial support plate 2103 extends through. The longitudinal support structure 230 has a support tube 2301 attached to the stiffening plate 1122 the outer shell 110 is mounted and on the inside of an enlargement or a collar 2302 is provided as a spacer, a support axis 2303 at the center of the first small, inverted arched floor 1222 is mounted and facing the support tube 2301 extends, a locking piece 2304 at the end of the support axis 2303 is provided, a first filler block 2305 that is between the locking piece 2304 and the ring collar 2302 is held, and a second filler block 2306 on, between the first small, inverted arched floor 1222 and the ring collar 2302 of the support tube 2301 is held. The reinforcing tube 1123 and its reinforcing plate 1124 surround the support tube 2301 to the structure of the support tube 2301 to reinforce. During a movement of the tank 100 expresses a leftward or rightward longitudinal force passing through the inner container 120 and the charge is caused, the second filler block 2306 and the first filler block 2305 together and then over the support tube 2301 to the outer shell 110 transfer. Using a program for finite element calculation and heat transfer calculation, the inner support structure that meets the requirements for heat input and stresses at maximum transport capacity is constructed in a controlled manner, and the gap of the first domed floors 122 . 123 that are provided with the longitudinal support structure should only meet the mounting requirements, which in fact achieves the inner support structure that fits well with the multilayer super vacuum insulation structure. According to the invention, the end of the tank body provided with the longitudinal support structure 102 the distance between the arched floors 122 and 112 of the inner container 120 or the outer shell 110 for transferring longitudinal force through the liquid seal of the pipe for transfer of liquid or gas and through the necessary gap for compensating the thermal expansion effect or the cold shrinkage effect, for example, the gap may be about 300 mm. In addition, the support tube 2301 . 1132 be provided with a reinforcing structure to the strength of the support tube 2301 . 1132 to increase.

The first radial support structure 210 takes along with the second radial support structure 220 the radial force coming through the inner container 120 and the transported medium is caused. The outer diameter of the respective support plates 2103 . 2203 stands with the arched ground 122 respectively. 123 in the inner container 120 in sections, which is advantageous for arranging the longitudinal support structure and reducing the heat input caused by the longitudinal support structure. The support plates 2103 . 2203 are with their inner diameters on the support tubes 2301 respectively. 1132 engaged, which on the curved floors 112 respectively. 113 the outer shell 110 mounted, which compensates for the radial force and improves the reliability of the support structure. At the same time a good insulating performance is achieved, wherein the longitudinal heat transfer surface between the inner container 120 and the outer shell 110 is only the load surface of the inner support structure, and in other areas of the container heat is transferred only by heat radiation, which successfully eliminates the prior art problem of heat input to the longitudinal support. Furthermore, at the same time as a result of clotting distance between the inner arched bottom and the outer arched bottom improves the transport ratio. The support plate of the tank according to the invention 100 is made of suitable glass fiber reinforced plastic material. By a finite element analysis and by experimental tests, it is possible to make the gap on the inner ring and the outer ring self-adaptive so that it changes little in the transition from the normal temperature state (ambient temperature) to the low temperature state, which the impact resistance of the structure in the radial direction improved and advantageous in assembly and gap control at normal temperature.

Furthermore be in the tank according to the invention the advantageous properties of glass fiber reinforced plastic material exploited in which the ratio from compressive strength to thermal conductivity coefficient is larger as the heat transfer resistance, what the ability the support structure improves radial force absorption and heat input reduced, creating the difficult, occurring in the prior art Problem that the enlargement of the Cold gap in terms of impact resistance is disadvantageous eliminated becomes. By means of the section where the arched floor of the inner container in the inner container extends into it, the length is of the filling block made of glass fiber reinforced Plastic in the longitudinal direction extended, what the heat input the longitudinal support structure reduces and solves the existing prior art problem, according to which impossible is, the heat input at the support structure longitudinal to control. At the same time the maximum volume is guaranteed, with the liquid limited overall size of the tank can be included, and the paradox between the internal voltage and the thermal insulation is eliminated.

The tank according to the invention is suitable for installation. First, the second arched floor 113 with the cylinder 111 welded to form a combined section. Second is the first arched floor 122 , the second arched floor 123 and the cylinder 121 welded together so that they are the inner container 120 form.

Next, multiple layers of heat insulating material around the outer surface of the inner container 120 wound. During further assembly, first the second radial support plate 2203 and arranged on the inside, inner mounting ring 2201 in the inner container 120 inserted, and then the outer mounting ring 2202 used, and the outer mounting ring 2202 is pressed at its inner diameter using a special tool. Thereafter, the outer fastening ring 2202 as a corner joint with the second extension approach 1233 of the inner container 120 welded to conveniently the assembly part of the outer shell 110 install it so that it guides the horizontal mounting process tube to the second radial support plate 2203 includes. Second, the first radial support plate 2103 and arranged on the inside, inner mounting ring 2101 in the inner container 120 used, then the outer mounting ring 2102 used, and the outer mounting ring 2102 is pressed at its inner diameter by means of a special coating tool. The outer mounting ring 2102 is used as a corner joint with the first extension approach 1223 welded, and then the second filler block 2306 on the support axis 2303 placed. Finally, the first arched floor 112 the outer shell 110 installed so that it is the first radial support plate 2103 includes, and the first arched floor 112 becomes with the assembly part of the outer shell 110 welded. The next step is the first filler block 2305 in the support tube 2301 used and on the support axle 2303 by means of the closing element 2304 clamped so that the first filler block 2305 and the second filler block 2306 be compressed, and the closing element 2304 is used as a corner joint with the support axle 2303 welded, so that the assembly of a combined support structure is realized. Last is the first sealing plate 1125 as a corner joint with the first stiffening plate 1122 welded to seal the first receiving bore, and the second stiffening plate 1133 is used as a corner joint with the second sealing plate 1137 welded, which seals the second mounting hole, causing the tank body 102 is trained. By pumping a super-vacuum is between the outer shell 110 and the inner container 120 a super vacuum insulation layer 104 educated. Thereafter, the stiffening or reinforcing rings 103 the outer shell 110 to the outer surface of the outer shell 110 welded.

For the average expert It is apparent that various modifications and variations of the present invention. It is intended, that the present invention covers the modifications and the Variations of the present invention disclosed within the scope of the appended claims and their equivalents occur.

Claims (10)

An outer shell of a super vacuum LPG tank with a cylinder and two domed bottoms at both ends of the cylinder, wherein a plurality of stiffening rings on the outer surface of the barrel of the outer shell are provided le. Outer shell according to claim 1, each being domed Ground a reinforced Structure distributed around receiving holes of the domed floors is. Outer shell according to claim 2, the reinforced Structure is a plate and together with the arched ground forms a smooth and arched surface. Outer shell according to claim 3, wherein for sealing the receiving bore a plate on each receiving bore is provided. Outer shell according to claim 4, with a reinforced Plate on the inner surface of the arched floor is arranged. A super vacuum isolation tank for cryogenic LPG with a frame and a tank body, the tank body having: - one Outer shell, the a cylinder and two arched Having bottoms; - one Inner container, one cylinder and two arched ones Having bottoms; A super-vacuum insulation layer between the outer shell and the inner container; and - one Support structure, which the outer shell and the inner container connects, where - one Plural of stiffening rings is provided on the outer surface of the cylinder of the outer shell. Tank according to claim 6, with each arched bottom a reinforced one Structure that surrounds around mounting holes of the domed floor is distributed. The tank according to claim 7, the reinforced Structure is a plate and together with the arched floors one smooth and arched surface forms. The tank according to claim 8, wherein for sealing the receiving bore a plate on each receiving bore is provided. The tank according to claim 9, with a reinforced Sheet metal plate is provided on the inner surface of the curved bottom.