WO2010009590A1

WO2010009590A1 - Sight glass assembly

Info

Publication number: WO2010009590A1
Application number: PCT/CN2008/071714
Authority: WO
Inventors: Miao YAN; Jia He; Bingyuan Huang
Original assignee: Danfoss (Tianjin) Ltd.
Priority date: 2008-07-22
Filing date: 2008-07-22
Publication date: 2010-01-28
Also published as: CN102099641B; CN102099641A

Abstract

A sight glass assembly (300) comprises a main body (310) which has an annular extension (320), the annular extension (320) defines a bore (321) which communicates with a cavity (312) formed in the main body (310); and a cylindrical or disk- like glass member (330), which is firmly held in the bore (321) of the annular extension (320), achieving a gas and fluid tight sealing between the periphery of the glass member (330) and the inner surface of the annular extension (320). The main body (310) is made of stainless steel, and the glass member (330) is joined to the annular extension (320) through sintering process. And a process of joining a stainless steel member and a glass member (330) by sintering is provided.

Description

SIGHT GLASS ASSEMBLY

Field of the Invention

The invention relates to a sight glass assembly and a process of joining a stainless steel member and a glass member by sintering.

Background of the Invention

As well known in the art, sight glass assemblies permit visual inspection or monitoring of the conditions of fluids in a vessel or in a pipeline. Taking a refrigeration system as an example, sight glass assemblies are used to monitor flow, level, state or condition and moisture content of system refrigerant, so as to determine whether the refrigeration system is in a normal operation condition.

Fig.l is a longitudinal sectional view of a conventional sight glass assembly. As shown in Fig. 1, the sight glass assembly 100 comprises a main body 110 made of brass, short lengths of conduit 120 and 130 which are attached to the main body 110. The main body 110 is generally cylindrical and has a bore 111, and a diameter enlarged cavity 112 is formed at the center. The main body 110 is further provided with an annular extension 113, which is used to accommodate a transparent cylindrical or disk-like member 150 and defines a counterbore in communication with the cavity 112, an annular shoulder 115 is formed between the cavity 112 and the counterbore. An annular groove 116 is formed in the inner surface 117 of the annular extension 113 to receive a sealing ring 160 which is made of Teflon. The cylindrical or disk-like member 150, which is made of transparent material, such as glass, is accommodated in the annular extension 113 as shown in Fig.l; and furthermore, the sealing ring 160 is received in annular groove 116. After installation of the cylindrical or disk-like member 150 and the sealing ring 160, the rim of the annular extension 113 is inwardly turned so as to press the sealing ring 160 onto the cylindrical or disk-like member 150. The sight glass assembly 100 further comprises support means 170 and an indicator 180. As shown in Fig. 1, the support means 170 comprises a spring 171 and a spring holder 172 which is the form of a sleeve with one end closed. The spring holder 172 is affixed in a notch 118 formed in the inner surface of the cavity 112, and the spring 171 is received in the spring holder 172 with the indicator 180 provided between the spring and the member 150. By the biasing force of the spring, the indicator 180 is held in place.

When in use, the sight glass assembly 100 is connected or coupled in a suitable manner into a fluid carrying pipe through the two conduits 120 and 130. When the fluid flows through the sight glass assembly, inspection can be made to monitor various conditions of a fluid such as the flow, level, state or condition and moisture content of the fluid.

For the conventional sight glass assembly, the main body is made of brass by hot forging, so such a sight glass assembly has a relatively good corrosion resistant property.

However, there are several drawbacks with this kind of sight glass assembly. 1. Since the main body is made of brass which is relatively expensive, so such a sight glass assembly is costly; 2. The support means is complicated in structure, because it needs a spring holder to hold the spring in place, leading to the increase of the number of the components and thus resulting in the increase of production cost;

3. Since the support means is provided in the flow passage of the fluid, the flow resistance is increased, resulting in the increase of energy consumption. 4. The glass member is held by inwardly turned rim of the annular extension 113, and thus has a poor pressure- withstanding capability and a poor sealing effect.

Furthermore, there is known a conventional sintering process for joining a metal member and a glass member. However, this conventional sintering process can only be used to sinter a metal member made of special steel and a glass member made of special glass, the special steel is Kovar which is an alloy material and is specially used to metal-glass joining, and the special glass is 7052 glass. Moreover, an additive needs to be added for the sintering process. So, with the conventional sintering process, the sintered product is very expensive and the glass is not transparent after being subjected to the sintering process.

So, there is a need for a sight glass assembly, which can work under higher operation pressure and which have better corrosion resistant properties, as well as a sintering process for joining a stainless steel member and a glass member.

Summary of the Invention

In consideration of the above, the object of the invention is to provide a sight glass assembly which can withstand higher pressure, has a better corrosion resistant property and is economically effective, as well as a method of manufacturing the sight glass assembly.

To achieve the above objects, according to one aspect of the invention there is provided a sight glass assembly, comprising: a main body which has a cavity and an inlet from which fluid to be inspected flows into the cavity; an annular extension which extends from the main body and is made of stainless steel, the annular extension defining a bore which communicates with the cavity formed in the main body; a cylindrical or disk-like glass member, the glass member being firmly held in the bore of the annular extension, with a gas and fluid tight sealing being formed between a periphery of the glass member and an inner surface of the annular extension; wherein said main body is made of stainless steel.

According to another aspect of the invention, there is provided a process of joining a stainless steel member and a transparent glass member by sintering, the stainless steel member having a first surface portion for joining with a second surface portion of the glass member, the process comprising the steps of: providing a stainless member; providing a transparent glass member; placing the stainless member and the glass member in a graphite holder, with the first surface portion being immediately adjacent to the second surface portion; placing the graphite holder with the stainless member and the glass member provided thereon in a furnace; sintering the stainless member and the glass member; and cooling the sintered the stainless member and the glass member.

With the sight glass assembly of the invention, the main components, including the main body and the ring member, are made of stainless steel which is cheaper than brass; and furthermore, since stainless steel has higher strength than brass, so the wall thickness of these components can be made thinner through casting or deep drawing, leading to less material consumption. Therefore, the production cost and the overall weight can be reduced.

The glass member and the ring member are joined together through sintering, the pressure withstanding capability and the sealing effect of the sight glass assembly are greatly increased.

Furthermore, the main body and the ring member are fixed together though laser welding, a good sealing is achieved between the connected members.

Moreover, since a claw support is used to provide support for the indicator, and the claw support is not provided in the flow passage of the fluid, thus causing no flow resistance to the flowing fluid and resulting in the decrease of energy consumption. And furthermore, the production cost of the claw support is lower than the support means with a spring and a spring holder.

With the sintering process of the invention, the following advantages can be obtained:

1. the sintering process is carried out in a reduction gas atmosphere, so the stainless steel is prevented from being oxidized;

2. since high purity graphite is used to manufacture the graphite holder which has a low heat transfer coefficient, energy consumption is reduced; furthermore, by using caps to cover the transparent glass members, the contact area between the glass member and the reduction gas is reduced, thus preventing the glass from reacting with the reduction gas at high temperature 3. a slow cooling manner is used to cool the sintered ring member and glass member, so the glass member and the stainless steel member is prevented from becoming fragile;

4. additives are not needed;

5. the sintering process of the invention can be used to sinter ordinary stainless steel and ordinary glass.

Brief Description of the Accompanying Drawings

The invention will be described in detail with reference to the accompanying drawings, in which

Fig. 1 is a longitudinal cross-sectional view of a conventional sight glass assembly; Fig. 2 is a longitudinal cross-sectional view of a sight glass assembly in accordance with the first preferred embodiment of the invention;

Fig. 3 is a perspective view of the sight glass assembly shown in Fig. 2; Fig. 4 is a plan view of the claw support;

Fig. 5 is sectional view of the claw support taken along line A-A in Fig. 4; Fig. 6 is perspective view of the claw support;

Fig. 7A is a longitudinal cross-sectional view of a sight glass assembly in accordance with the second preferred embodiment of the invention, and Fig. 7B is a perspective view of the sight glass assembly;

Fig. 8 A is a top view of the sight glass assembly in accordance with the third preferred embodiment of the invention, and Fig. 8B is an axial sectional view taken along line A-A in Fig. 8A;

Fig. 9 is an axial sectional view of the ring member; Fig. 10 is a perspective view of the glass member;

Fig. HA is a plan view of the graphite base plate, and Fig. HB is a sectional view taken along line A-A in fig. 1 IA;

Fig 12 is a front view of the graphite support member;

Fig. 13A is top view of the graphite cap, and Fig. 13B a sectional viewtaken along line A-A in Fig. 13 A; Fig. 14A is a top view of a graphite holder with the ring member and the glass member installed therein; and Fig. 14B is a sectional viewtaken along line A-A in fig. 14A.

Detailed Description of the Preferred Embodiments

First embodiment

Reference is now made to Fig. 2 which is a longitudinal sectional view of a sight glass assembly in accordance with the first preferred embodiment of the invention.

As shown in Fig. 2, the sight glass assembly 200 mainly comprises a main body 210, a ring member 220; a cylindrical or disk-like member 230; a claw support 240; an indicator 250 and two tubes 260.

The main body 210 is made of stainless steel and is formed through deep drawing. The main body 210 takes the form of a cup defining a cylindrical cavity 216 and has an inlet 217 and an outlet 218.

The ring member 220 takes the form of a bush with a bore 221 therethrough and is made of stainless steel. The ring member 220 includes a large-diameter portion 224 and a small-diameter portion 225 which is diametrically substantially equal with the cylindrical cavity 216, forming an annular shoulder 226 therebetween. Adjacent to the inner end of the ring member 220 which faces the main body 210, there is formed an annular groove 222 in the inner surface of the ring member 220; and at the outer end of the ring member opposite to the inner end, there is formed a counterbore 223, forming a shoulder between the counterbore 223 and the bore 221. On the axial end face of the ring member 220 opposite to the main body, indicia 228 can be provided to coordinate with the indicator (which will be described later) so as to facilitate the inspection of the various states or parameters of the fluid to be monitored, as shown in Fig. 3.

The cylindrical or disk-like member 230 is made of glass such as soda lime glass and etc, and is preferably made of soda lime glass.

The claw support 240 is a resilient member which provides support for the indicator 250, and can be made of any suitable material such as stainless steel, so long as the material is corrosion resistant to the fluid to be inspected.

Fig. 4 is a plan view of the claw support, Fig. 5 is sectional view of the claw support taken along line A-A in Fig. 4, and Fig. 6 is perspective view of the claw support.

As shown in Figs. 4-6, the claw support 240 comprises a central body 241 having a bore 242 and a counterbore 243, forming an annular shoulder 244 therebetween. The bore 242 provides access for the fluid to the indicator. Three claws 245, which are spaced from each other by 120°, extend from the central body 241. It should be noted that the number of the claws is not limited to three, four or more claws are also possible. And furthermore, it is obvious to one skilled in the art, the claw support may take various forms so long as it can provide desired support for the indicator 250.

The indicator 250 may be of any type designed to monitor the states of a fluid, depending on the application of the sight glass assembly. For example, the indicator 250 can be one which is used to indicate the moisture state or dry state by changing its color; to indicate whether a fluid has been fully filled and etc.

Returning to Fig. 2 and 3, two sleeve-like protrusions 266 and 267 are provided to surround the inlet 217 and outlet 218, and are preferably made of the same material as the main body 210 and are made as an integrated part of the main housing. The two tubes 260 are made of a suitable material such as copper or copper plated steel, and are attached to the main body by being connected with the sleeve-like protrusions 266 and 267 respectively through any suitable connecting process, such as induction welding, furnace brazing and etc. Though various welding methods can be used for this purpose, induction welding is preferred when attaching the two tubes, since an induction-welding joint exhibits excellent sealing performance. When in use, the sight glass assembly is connected or coupled in a suitable manner into a fluid carrying pipe through the tubes 260.

Upon assembly of the sight glass assembly 200, the cylindrical or disk-like member 230 is fitted in the bore 221 of the ring member and is fixed to the ring member through sintering process (which will be described in detail later), achieving gas and fluid tight sealing between the cylindrical or disk-like member 230 and the ring member.

Then, the claw support 240 is fitted in the annular groove 222, with the indicator 250 being disposed between the claw support 240 and the cylindrical or disk-like member

230. The indicator is installed in the counterbore 243 of the claw support 240 and is seated on the shoulder. Due to the resilience of the claw support 240, the indicator 250 is biased into close contact with the cylindrical or disk-like member 230 and thus is fixed in place.

Hereby, a subassembly comprising ring member 220, glass member 230, claw support and indicator 250 is defined.

Then, the ring member 220 is inserted into the cylindrical cavity 216 with its small-diameter end, until the shoulder 226 abuts an end face of the main body 210. Then, the main body 210 and the ring member 220 are fixed together though welding, such as laser welding, plasma welding and etc, along the seam 268 between the main body 210 and the ring member 220, so as to fix the ring member 220 relative to the main body 210 and achieve the sealing therebetween, with the ring member 220 constituting an annular extension of the main body. Though various welding methods can be used to connect the ring member 220 and the main body, laser welding is preferably used, because excellent sealing effects can be achieved by laser welding. This kind of sight glass assembly can be used, for example, to detect the water content or moisture content in a refrigerant. When the refrigerant comes into contact with the indicator, the indicator will change its color, if the water or moisture content reaches a predetermined level. An operator makes a determination based on the corresponding indicia on the sight glass assembly, whether the refrigerant is in moisture condition or dry condition, so as to change the desiccant in time. This kind of sight glass assembly can also be used to inspect whether a fluid has been fully filled based on, for example, whether there exist bubbles between the cylindrical or disk-like member and the fluid surface.

Second embodiment

Fig. 7A is a longitudinal cross-sectional view of a sight glass assembly in accordance with the second preferred embodiment of the invention, and Fig. 7B is a perspective view of the sight glass assembly.

As shown in Figs. 7A and 7B, the sight glass assembly 300 comprises a main body 310, a ring member 320, a cylindrical or disk-like member 330, a claw support 340 and an indicator 350.

The main body 310 is generally cylindrical and is made of stainless steel, and is preferably formed through casting. The main body 310 has a bore 311 therethrough, a diameter enlarged cylindrical cavity 312 is formed at the center, and a cylindrical hole 313 is formed on the wall of the cavity 312. The two axial ends of the main body 310 are externally threaded.

The ring member 320 takes the form of a bush with a bore 321 therethrough and is made of stainless steel. The ring member includes a large-diameter portion 324 and a small-diameter portion 325, forming an annular shoulder 326 therebetween. Adjacent to the inner end of the ring member which faces the main body, there is formed an annular groove 322 in the inner surface of the ring member; and at the outer end of the ring member opposite to the inner end, there is formed a counterbore 323, forming a shoulder between the counterbore 323 and the bore 321.

The cylindrical or disk-like member 330 is made of glass such as soda lime glass and etc, and is preferably made of soda lime glass. The claw support 340 is a resilient member which provides support for the indicator 350, the structure of the claw support 340 is substantially the same as that of the claw support 240 described in connection with the first embodiment, so its detailed description is omitted.

Upon assembly of the sight glass assembly 300, as described in connection with the first embodiment, the cylindrical or disk-like member 330 is fitted in the bore 321 of the ring member and is fixed to the ring member through sintering process, achieving gas and fluid tight sealing between the cylindrical or disk-like member 230 and the ring member.

And next, the claw support 340 is fitted in the annular groove 322, with the indicator 350 being disposed between the claw support 340 and the cylindrical or disk-like member 330. Due to the resilience of the claw support 340, the indicator 350 is biased into close contact with the cylindrical or disk-like member 330 and is thus fixed in place.

Then, the ring member 320 is inserted into the hole 313 with its small-diameter end, until the shoulder 326 abuts the end face of the wall defining the hole 313. Then, the main body 310 and the ring 320 are fixed together through laser welding along the seam between the main body 310 and the ring 320, with the ring member 320 constituting an annular extension of the main body.

As an alternative to the second embodiment, one axial end or both axial ends of the main body may be otherwise configured. For example, one axial end or both axial ends of the main body is not externally threaded, but instead, is internally threaded.

Third embodiment

Reference is now made to Figs. 8 A and 8B which shows a sight glass assembly in accordance with the third preferred embodiment of the invention. Fig. 8 A is a top view, and Fig. 8B is a sectional view taken along line A-A in Fig. 8 A.

As shown in Figs. 8A and 8B, the sight glass assembly 400 of the third embodiment has a generally cylindrical main body 410 having a through bore 411 and a counterbore 416 formed at one end of the bore 411, forming an annular shoulder 418 therebetween. The main body has a hexagonal head 412 adjacent to one end, and the other end of the main body is externally threaded as shown in Fig. 8A or internally threaded. And the sight glass assembly 400 further comprises a cylindrical or disk-like member 430, a claw support 440, an indicator 450, a support net 460 and floating balls 470.

The main body 410 is made of stainless steel, and is preferably formed through casting, though other methods can be used to manufacture the same. Adjacent to the end where the hexagonal head 412 is located, an annular groove 413 is formed in the inner surface of the main body which is used to receive the claw support 440; and adjacent to the other end of the main body, another annular groove 415 is formed in the inner surface of the main body which is used to receive the support net 460.

The cylindrical or disk-like member 430 is made of glass such as soda lime glass and etc, and is preferably made of soda lime glass.

The claw support 440 is a resilient member which provides support for the indicator 450, its structure is substantially the same as that of claw support 240 described in connection with the first embodiment, so its detailed description is omitted.

The support net 460 is made of a suitable material such as metal, resin and etc, but preferably stainless steel, and is used to let a fluid pass through on one hand and prevent the floating balls from coming out of the sight glass assembly on the other hand.

The floating balls are made of a suitable material such as polymethylpenten, so long they can float in the fluid to be inspected or monitored, and can be bright colored so as to facilitate observation. This kind of sight glass assembly can be used, for example, to inspect whether a container has been filled up with a fluid. When in use, the sight glass assembly is disposed with its axis substantially parallel (or sometimes perpendicular) to the ground plane, the floating balls will locate at a lower position in the cavity due to the gravity if the container is not filled up with fluid, and will locate at the top of the cavity due to the buoyancy when the container is filled up with fluid.

Upon assembly of the sight glass assembly 400, as described in connection with the first and second embodiments, the cylindrical or disk-like member 430 is fitted in the through bore 411, and is fixed to the main body through sintering process, achieving gas and fluid tight sealing between the cylindrical or disk-like member 230 and the main body.

Then, the claw support 440 is fitted in the annular groove 413, with the indicator 450 being disposed between the claw support 440 and the cylindrical or disk-like member 430. Due to the resilience of the claw support 440, the indicator 450 is biased into close contact with the cylindrical or disk-like member 430 and is fixed in place.

The support net 460 is fitted in the annular groove 415 after the floating balls are put inside the bore 411, thus the floating balls are restrained in the space defined by the support net 460 and the cylindrical or disk-like member 430.

On the axial end face of the main body opposite to the threaded portion, indicia 480 can be provided to coordinate with the indicator 250 so as to facilitate the inspection of the various states or parameters of the fluid to be monitored.

When in use, the sight glass assembly 400 is screwed into a screw hole provided in a target object such as refrigerant pipe, refrigeration system and etc, so that at least part of the sight glass assembly 400 is immerged in the fluid to be monitored.

Unlike the first and second embodiments in which the main body includes a separate ring member which is attached to the main body, in the third embodiment, the part of the main body, which is used to accommodate the glass member, the indicator and the claw support, is coaxially integrally formed with the main body and forms the annular extension.

Following is a detailed description about the sintering process for joining the cylindrical or disk-like glass member and a ring member made of stainless steel.

1. material selection and manufacturing of the ring member

Stainless steel is selected as the material for manufacturing the ring member.

A section of rod or tube is first prepared as a blank, and then is processed and formed into a finished ring member 100 as shown in Fig. 9. The processing method includes, but not limited to, deep drawn, lathe turning and etc.

Thereafter, the ring member is subjected to cleaning-up which includes decreasing, alkali wash, drying and etc.

2. material selection and manufacturing of the glass member

Various glasses can be selected as the material for manufacturing the glass member, which include, but not limited to, soda lime glass and etc, preferably soda lime glass is used to manufacture the glass member. Preferably, a coefficient of thermal expansion of the glass, which is used to manufacture the glass member, is between 7-9 (10^"6/°C).

The glass member 101 is formed into a cylindrical or disk-like shape (as shown in Fig.

10) through e.g. grinding, and is adapted to fit in the bore of the ring member.

The glass member is a "finished" prefused glass member. This is different with known processes, where pressed and pre-baked glass powder parts are fused together with stainless steel parts in furnaces, by use of graphite tools. 3. Placing the ring member and the glass member into a graphite holder

First, the structure of the graphite holder is described, which comprises a graphite base plate, a plurality of glass member support members and a plurality of graphite caps. Preferably, high purity graphite is used to manufacture the graphite holder, because it has a high thermal conductivity and low heat capacity, thus energy consumption can be reduced.

Fig. HA is a plan view of the graphite base plate, and Fig. HB is a sectional view taken along line A-A in Fig. 1 IA.

As shown in Figs. HA and HB, the base plate 102 is formed with a plurality of holding holes or positioning holes for holding the support members, each holding or positioning hole is a shoulder hole including a bore 721 and a counterbore 722, so an annular shoulder 723 is formed between the two bores.

As shown in Fig. 12 which is a front view of the graphite support member, the support member 103 is a step diametered graphite member with a small diameter portion 131 and a large diameter portion 132, and is used to position the ring member and provide support for the glass member. When fitting the support members, the small diameter portion 131 is inserted into the bore 721 until the end face of the large diameter portion 132 abuts the shoulder 723, thus positioning the support member in the holding hole.

As shown in Figs. 13A and 13B which show the structure of the graphite cap, Fig. 13 A is top view of the graphite cap, and Fig. 13B a sectional view taken along line A-A in Fig. 13 A. The graphite cap 104 takes the shape of a shallow cup including a cylindrical side wall 911 and a bottom wall 912, its internal diameter is substantially identical to the external diameter of the ring member, thus covering the ring member with the glass member located inside. There is formed a hole 913 in the bottom wall of the graphite cap which allows a reduction gas to pass.

The following is a description about the fitting of the ring member and the glass member into the graphite holder.

Reference is made to Figs. 14A and 14B, in which Fig. 14A is a top view of a graphite holder, and Fig. 14B is a sectional view taken along line A-A in fig. 14A. First, the graphite base plate 102 is placed on a table and the support members 103 are installed in the respective holding holes; then the ring members 100 are fitted over the support members; after that, the glass member is installed in the bore of the ring member, with the glass member being centrally positioned relative to the bore of the ring member and is supported by the support member. And next, the caps are attached to the ring members to cover the glass member. By using the caps to cover the glass members, the contact area between the glass member and the reduction gas is reduced, thus preventing the glass from reacting with the reduction gas at high temperature.

Please note that the structure of the graphite holder is not limited to that described above, various modification can be made to realize the same function.

For example, in the embodiment described above, the base plate and the support members are discrete components, but they can also integrally formed; furthermore, the discrete caps can be replaced with a cover plate which is provided with a plurality of circular recess, or a cover plate which is provided with a plurality of ring-like annular protrusions to receive the respective ring members and cover the same.

4. sintering the ring member and the glass member

The sintering process will be described in connection with some examples which are only illustrative but not limitative.

Sintering the ring member and the glass member is carried out in a furnace such as a vacuum oven and a tunnel furnace.

When a vacuum oven is used, the graphite holder together with the ring member and the glass member to be sintered is first placed in the furnace; then the inside of the vacuum oven is vacuumized so that the ring member and the glass member can be sintered in a vacuum atmosphere. And thereafter, the furnace is heated to a first predetermined preheating temperature, and the inside temperature of furnace is maintained at this first predetermined preheating temperature for a period of time to preheat the ring member and the glass member at this first predetermined preheating temperature; after this period of time elapses, the inside temperature of the furnace is increased to a second predetermined preheating temperature, and is maintained at this second predetermined preheating temperature for a period of time to preheat the ring member and the glass member at this second predetermined preheating temperature; and after this, the inside temperature of the furnace is increased to a third predetermined sintering temperature, and is maintained at this third predetermined sintering temperature for a period of time to sinter the ring member and the glass member at this third predetermined sintering temperature, thus completing the sintering process. The first and second predetermined preheating temperatures are selected from the temperature range from 500 °C to 1000 ⁰C , and the third predetermined sintering temperature is selected from the temperature range from 1000°C to 1100°C. The period of time for preheating the ring member and the glass member at each of the predetermined preheating temperatures and the period of time for sintering the ring member and the glass member at the predetermined sintering temperature can be determined based on various factors such as the particular materials of the ring member and glass member, the temperature values of the preheating temperatures and sintering temperature(s) and etc.

When the sintering process is finished, inert gas such as argon gas, helium gas and etc, is introduced into the furnace to cool the furnace together with the graphite holder as well as the sintered ring member and glass member. The purpose of introducing inert gas into the furnace is to expedite the cooling process, otherwise it will take too long a time to cool the furnace under a vacuum condition. When the furnace is cooled to the room temperature, the graphite holder together with the sintered ring member and glass member is taken out of the furnace, and the furnace is ready for the next sintering process. The used inert gas can be recycled after purification.

Preferably, the graphite holder together with the sintered ring member and glass member is slowly cooled down so as to prevent the glass member and the stainless steel member from becoming fragile, and the cooling time can be set, for example, at about 40 minutes. However, it should be noted that the cooling time is not limited to about 40 minutes and can be varied so long as the quality of the sintered product can be ensured, and furthermore, the cooling time can vary with various factors such as the particular materials of the ring member and glass member, the cooling conditions and etc.

By this sintering process, the ring member and the glass member are sintered and joined with each other, achieving a gas and fluid tight sealing between the joining surfaces of the ring member and the glass member.

In the embodiment described above, the inside temperature of the furnace is maintained unchanged for a period of time at two predetermined preheating temperatures and one predetermined sintering temperature, however the invention is not limited to this. The number of the predetermined preheating temperatures, at which the inside temperature of the furnace is maintained unchanged for a period of time, can be less or more; and the number of the predetermined sintering temperatures, at which the inside temperature of the furnace is maintained unchanged for a period of time, can be two or more. Moreover, each predetermined temperature is not necessarily limited to a particular value, and can be selected within a temperature range described above ; and furthermore, it is obvious that each predetermined temperature may vary with the number of the predetermined preheating temperatures and the number of the predetermined sintering temperatures, at which the inside temperature of the furnace is maintained unchanged for a period of time. Furthermore, the furnace can also be heated continuously to a predetermined final sintering temperature without being held at an intermediate preheating temperature, which is lower than the final predetermined sintering temperature, for a period of time.

As noted above, sintering process can also be carried out by using a tunnel furnace.

When a tunnel furnace is used, preferably, the internal space or the internal cavity of the tunnel furnace is divided into several temperature zones such as three temperature zones in the direction along which the graphite holder moves, with the last temperature zone being the sintering zone and the others being the preheating zones. During sintering process, each of the temperature zones is set to a predetermined temperature. Taking a three-zone tunnel furnace as a example, the first and the second preheating zones are selected from the temperature range from 700 °C to 1000 ⁰C, and the third sintering zone is selected from the temperature range from 1000°C to 1100°C. Furthermore, the tunnel furnace is provided with a cooling section which performs the cooling of the sintered ring member and glass member. It should be noted that the cooling section can be integrated with the tunnel furnace, or the cooling section can be a separate section which is combined with the furnace when is use.

At the beginning of the sintering process, nitrogen gas is first introduced into the furnace at room temperature, and at the same time the furnace is heated until the inside temperature reaches a predetermined temperature.

When the inside temperature reaches the predetermined temperature, the introduction of nitrogen gas is stopped and instead a reduction gas such as hydrogen or carbon monoxide is introduced into the furnace. In the case of using hydrogen as the reduction gas, the predetermined temperature may be set at, e.g. 700⁰C, and in the case of using carbon monoxide as the reduction gas, the predetermined temperature may be set at, e.g. 550⁰C. The reason for introducing a reduction gas after the predetermined temperature is reached lies in that: the reduction gas such as hydrogen will explode when meeting with oxygen at a temperature lower than its dew point temperature (about 700⁰C for pure hydrogen), so in order to prevent hydrogen from exploding and thus protect the furnace, hydrogen is not introduced until the inside temperature of the furnace reaches the first predetermined temperature.

The nitrogen gas is gradually discharged with the progress of the introduction of the reduction gas, and at the same time, the three temperature zones are respectively heated to their predetermined temperatures and are maintained at such temperatures afterwards. When each of the three temperature zones reaches its predetermined temperature, the graphite holders together with the ring members and the glass members are placed successively in the furnace for sintering in the reduction gas atmosphere.

During the sintering process, a first graphite holder with the ring member and the ring member to be sintered is moved into the first temperature zone which is kept at a first predetermined preheating temperature and stays in this temperature zone for a period of time, e.g. 6 to 7 minutes, and then is moved to the second temperature zone which is kept at a second predetermined preheating temperature which is higher than the first predetermined preheating temperature, and at the same time a second graphite holder is moved into the first temperature zone. After a period of time, e.g. 6 to 7 minutes, elapses, the first graphite holder is moved into the third temperature zone which is kept at a third predetermined sintering temperature which is higher than the second predetermined preheating temperature, and at the same time the second graphite holder is moved into the second temperature zone and a third graphite holder is moved into the first temperature zone, and the ring member and the ring member are sintered at the third temperature zone for e.g. 6 to 7 minutes. In this way, the sintering process can be carried out continuously, and a conveyor band can be used to transmit the graphite holders through the three temperature zones successively.

The ring member and the glass member are sintered after being subjected to the three-zone heating and sintering. Then, the graphite holder together with the sintered ring member and glass member is moved into the cavity of the cooling section to be cooled down gradually to a room temperature. It is preferred that the graphite holder together with the sintered ring member and glass member is slowly cooled down and the cooling time can be set, for example, at about 40 minutes. However, it should be noted that the cooling time is not limited to about 40 minutes, and it can vary with various factors such as the particular materials of the ring member and glass member, the cooling temperature inside the cavity of the cooling section and etc. Preferably, the cavity of the cooling section is kept at a constant temperature through cooling medium such as water which circulates around the cavity.

The purpose of introducing a reduction gas into the furnace during the sintering process is to react with residual oxygen in the cavity of the furnace to produce water (when the reduction gas is hydrogen) or carbon dioxide (when the reduction gas is carbon monoxide), so as to prevent the stainless steel from being oxidized and thus protect the sintering process. A certain amount of reduction gas is consumed during the sintering process, so the tunnel furnace is continuously supplemented with reduction gas, while surplus reduction gas is burned at the inlet and outlet of the cavity of the furnace by igniting the same.

By the sintering process, the glass member and the ring member are joined together, achieving a gas and fluid tight sealing between the joining surfaces of the ring member and the glass member.

In the above embodiment, the tunnel furnace is described as containing three temperature zones: two preheating zones and one sintering zone. However, the invention is not limited to this, the number of the preheating zones is not limited to two, and more or less preheating zones are also possible; and the number of the sintering zones is not limited to one, two or more sintering zones are also possible. Furthermore, in the above embodiment, the sintering process is described as lasting about 20 minutes, however it is obvious to one skilled in the art that the period of time for the sintering process will vary with various factors such as the particular materials of the ring member and glass member, the temperature values of the preheating temperatures and sintering temperature(s) and etc.

And moreover, the members can also be sintered in a tunnel furnace with only one temperature zone. In this case, the graphite holder with the ring member and the ring member to be sintered is placed in the furnace at a predetermined temperature after introducing a reduction gas.

And furthermore, the temperature set for each temperature zone is not limited to a particular value but can be varied, depending on various operation conditions and particular materials of the members to be sintered. Furthermore, the temperature set for each temperature zone may vary with the number of the preheating zones and/or the sintering zones. Although the invention has been described in connection with the some embodiments, those skilled in the art will appreciate that the embodiments are only exemplary but not limitative, various modifications are possible without departing from the spirit and scope of the invention.

For example, in the above embodiments, the sight glass assembly is provided with an indicator and a claw support. However, the indicator and the claw support can be omitted when the sight glass is only used to observe the fluid surface. Likewise, the floating balls can also omitted from the third embodiment, and further the floating balls can also be used in connection with the sight glass assembly of the first and second embodiments.

In the above embodiments, the sintering process is described in connection with a stainless steel ring member and a cylindrical or disk-like glass member which are used in a sight glass assembly. However, the present invention is not limited to this. The sintering process of the invention can be used to sinter any stainless steel member and glass member which need to be joined together, and the stainless steel member and glass member can take any forms.

Claims

1. A sight glass assembly, comprising: a main body which has a cavity and an inlet from which fluid to be inspected flows into the cavity; an annular extension which extends from the main body, the annular extension defining a bore which communicates with the cavity formed in the main body; a cylindrical or disk-like glass member, the glass member being firmly held in the bore of the annular extension, with a gas and fluid tight sealing being formed between a periphery of the glass member and an inner surface of the annular extension; wherein said main body and the annular extension are made of stainless steel.

2. The sight glass assembly of claim 1, wherein said glass member is joined to the annular extension through sintering process.

3. The sight glass of claim 1, wherein said glass member is a soda lime glass member.

4. The sight glass assembly of claim 1, wherein the annular extension is formed by a ring member which has a bore therethough and is attached to the main body.

5. The sight glass assembly of claim 4, wherein the ring member and main body are connected through laser welding.

6. The sight glass assembly of claim 1 wherein the main body takes the form of a cup manufactured through deep drawing and further has an outlet, the inlet and the outlet are formed in a side wall of the main body, and the sight glass assembly further comprises two tubes, which are attached to the main body at the inlet and outlet.

7. The sight glass assembly of claim 6 wherein the two tubes are made of copper and are attached to the main body through induction welding.

8. The sight glass assembly of claim 1 wherein the main body has two axial ends which extend from the main body, and each of the two axial ends is either externally threaded or internally threaded, the main body is manufactured by casting.

9. The sight glass assembly of claim 1, wherein the main body is generally cylindrical, the annular extension is coaxially integrally formed with the main body by casting.

10. The sight glass assembly of claim 9, wherein a hexagonal head is formed around the annular extension, and an end of the main body opposite to the annular extension is externally threaded or internally threaded.

11. The sight glass assembly of claim 1 , further comprising an indicator and support means for supporting the indicator against the glass member.

12. The sight glass assembly of claim 11 , wherein the support means is a claw support which has a central body and a plurality of claws extending from the central body; an annular groove is formed in an inner surface of the annular extension, and the claw support is held in the bore of the annular extension by the claws being received in the annular groove.

13. The sight glass assembly of claim 12, wherein the central body of said claw support has a bore and a counterbore which has a larger diameter than the bore, with an annular shoulder formed therebetween, the indicator is positioned between the shoulder and the glass member.

14. The sight glass of claim 9, further comprising a floating ball and a support net, the support net allows fluid to pass and prevents the floating ball from coming out of the sight glass assembly; an annular groove is formed in the inner surface of the cylindrical main body, and the support net is held in the main body by its periphery being received in the annular groove and defines a space for accommodating the floating ball between it and the glass member.

15. The sight glass assembly of claim 14, wherein said support net is made of stainless steel, and said floating ball is made of polymethylpentene.

16. The sight glass assembly of claim 1, wherein an outer end surface of the annular extension is provided with an indicia.

17. The sight glass assembly of claim 4, wherein the ring member is manufactured by deep drawing or lathe turning.

18. A refrigeration system, comprising a sight glass assembly as claimed in any one of the preceding claims.