CA1135091A - Sight glass with laminated lens assembly - Google Patents

Abstract

SIGHT GLASS WITH LAMINATED LENS ASSEMBLY

ABSTRACT OF THE DISCLOSURE

A safety sight glass assembly can be mounted in a standard pipe joint flange and has a sleeve with an inturned flange at the outer end and an outwardly extending flange at the inner end. A
pair of cylindrical lenses inside the sleeve are interspaced by a plastic sheet that also extends axially between the inner lens and the sleeve and outwardly over the outwardly extending flange.
Both lenses and the sheet are bonded together and to the sleeve by a transparent, plastic material.

Description

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¦ SIGH~ GLASS WITH LAMINATED LENS ASSEMBLY

¦ BACKGROUND OF THE INVENTION

¦ This invention relates to sight glasses which are used to ¦view the interior of pressure vessels, and more particularly to ¦sight glasses that are adapted to resist corrosion and erosion by ¦the contents of the vesselr to withstand variations in temperature ¦and pressure and to resist leakage even when the glass may hecome ¦cracked or broken.
l Sight glasces have long been used to allow visual exami-¦nation of the interior of certain vessels or containers under a ¦wide range of conditions. A sight glass must be large enough, ¦depending upon the application, to allow adeauate visual inspec-~tion of the interior of the container and must be made resistant ¦to the physical and chemical forces that tend to damage the sight ¦glass. For example, the glass may be exposed to various tempera-¦tures and pressures which~apply high stresses to the glass, and it ¦may be subject to chemical corrosion depending upon the contents ¦of the vessel. The result of these forces acting on the sight glass tends to make it subject to breakage and suhsequent leakage of the contents, and also chemical attacks may make the glass hecome opaque so that it must be replaced with a clear glass to allow proper visual inspection. Thus, the sight glass must be mounted to provide adeauate sealing against leakage~ and must also he mounted in such a wav that it can easily and quickly be replaced if it becomes damaged.

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While in the beginning single prisms of glass, usually circular in shape and having parallel front and rear sides, were used, it has been discovered that the use of two or more separate g]ass lenses in a suitable mounting provides better resistanc2 to breakage. It has also been discovered that when the glass lenses are subjected to compressive forces, their strength is greatly increased and it is possible to have one of the lenses crack with-out resulting in any leakage. Furthermore, in order that replace-ment may be done quickly and easily with a minimum of downtime, the glass has been mounted as a subassembly on a flange with a suitable cover so that the placement can be done simply by unbolt-ing the cover, inserting a replacement subassembly, and then re-fastening the cover in place on the flange.
Other improvements made in such sight glasses include the bonding together of the separate glass lenses by plastic laminat-ing material, the use of a plastic laminating material as a seal-ing agent around the outer periphery of the lenses between the lenses and a metal shell which supports them, and the use of chemically resistant matePials on the inner facing of the glass lens for protection of the glass against chemical attack by the contents of the vessel.
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According to the present invention there is provided a lens assembly including a lens containing member having an axially extendin~ sidewall with an outwardly extending surface at one end and an inwardly extending surface at the other end.
A first lens is provided in the member and having a first side adjacent the inwardly extending surface, and a second lens is provided having a first side adjacent the outwardly extending surface, the opposite sides of the lenses being adjacent each other. A sheet of transparent flexiblé phastic matérial extends between the lenses, between the outer periphery of the second lens and the sidewall of the~member and extending along the outer side of the outwardly extending surface.
The present invention provides a unitary, self-contained glass lens assembly which can be mounted in place on a pressure vessel using a standard pipe flange mounting.
In a specific embodiment of the invention, the lens containing member is in the form of a metal ferrule member which maybe formed by spinning from a piece of t~in-walled tubing having an original outer diameter allowing a slight clearance within the bore in the standard pipe flange. The ferrule has an annular, inturned lip or flange at the outer end and an outwardly extending flange at the inner end which is clamped between the two pipe flanges. The pair of cylindrical glass lenses are mounted within the ferrule with the outer lens bearing against a gasket at the inturned lip. The sheet or web of suitable plastic material extends between the two lens discs, inwardly along the outer periphery of the inner lens disc, and then radially outward along the inner side of the ferrule flange.
This sheet is tm/ ~ ~3-: ,:

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bonded to both lenses and the radial space between the lenses and the ferrule is filled with a suitable plastic potting compound. Finally, another sheet of plastic material extends over the inner face of the inner disc to which it is bonded. This sheet also extends radially outward overlying the other sheet to which it is also bonded. In some applications, the thickness of the two plastic sheets may serve as a gasket between the ferrule flange and the inner pipe flange, but optionally a separate sealing gasket may be used at this location.
Because the two glass discs are bonded and laminated together, it is possible that even both of the discs can be broken without allowing any leakage from the assembly. Furthermore, if tm~l~ -3a-~.
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¦it is necessary to replace the sight glass assembly, it is only ¦necessary to remove the bolts holding the outer flange, substitute la new sight glass assembly and gasket, and again rebolt the flange ¦in place.

BRIEF DESCRIPTION OF THE DRAliINGS

PIG. 1 is an elevationa]. view of a sight glass according to the present invention;

FI~. 2 is a cross sectional view, taken on line 2-2 of FI~ l; and FIG. 3 is an enlarqed, cross sectional view showing details of the ferrule and the mounting of the glass lens discs. .

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; ~ ' ¦ DESCRIPTION OP THE PREFERR~ED EM~ODIMENT

As shown in FIGS. 1 and 2, the lens assembly 10 is mount-ed against the raised face 12 of the inner flange 11 in line with the bore 13. It will be understood that the flange 11 is secured to the vessel on which the sight glass assembly is to be used in any convenient manner, and that the bore 13 communicates with the interior of the vessel so that any liquid or gas in the vessel is free to contact the lens assembly 10, depending upon the condi-tions on the interior of the vessel.
Outwardlv of the raised face 12, flange 11 has a plural-ity of tapped bolt holes 14 to secure in place the outer flange 1 bv suitable means, such as holts or cap screws 17, which pass through holes 18 in the outer flange and engage the tapped holes 14. Of course, other methods, such as studs or exterior clamp bolts, could also be used, but under the present circumstances it should be appreciated that the inner flange 11 has the basic dimensions of a standard, raised face pipe flange and the outer flange 16 has the basic dimensions of a standard lap joint pipe flange made to the standard dimensions specified for these flanges. Accordingly, the outer flange lfi is provided with a planar inner face 19 and an axial bore 20 which are joined at a radiused relief, as shown at 21, in accordance with the standard dimensions for a lap joint pipe flange. Furthermore, the flange 16 is provided with a raised central boss 22 extending around bore 20 and terminating in a planar outer face 23~
The lens assembly 10 is shown in greater detail in FIGS.

2 and 3, and includes a metal ferrule member 26 within which the other parts are mounted, as will be described in greater detail i . - - - . . .~, .

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hereinafter. The ferrule 26 is preferably formed from a piece of steel tubing by a spinning operation, but, of course, it may also be machined from a solid bar or fabricated by welding. The fer-rule 26 includes a cylindrical wall 28 extending the full distance from the ferrule and having outer and inner peripheral sides 29 and 31. At its outer end, the ferrule 26 has an inturned or inwardly projecting flange 33 which extends radially inward to terminate in an inner edge 34 defining reduced diameter visual opening in the lens assemblyO l~hile the opening 34 in the ferrule 26 has been shown as being circular in cross section, it is under-stood that the lens assembly 10 may also be oval, elliptical, or rectangular in shape, and the circular form shown and described herein is selected because it is the most widely used arrangement.
At the inner or lower end, the ferrule 26 has an outward-ly extending flange 38 having a planar upper side 39 which con-tacts the inner face 19 of outer flange 16 when the lens assembly is clamped in place on the inner flange 11.
Mounted within the ferrule 26 are outer and inner glass lenses 43 and 44, respect~vely. These glass lenses have parallel surfaces and cylindrical outer peripheral surfaces having a diam-eter slightly less than the inside diameter of the cylindrical wall 28 of the ferrule. Of course, if the ferrule is noncircular, the lenses have a shape substantially in conformance with the shape of the ferrule. While it is normally contemplated that both of the lenses can be made of the same material, such as a tempered soda-lime glass, it is understood that they may be made of special glasses such as borosilicate glass or fused quartz.

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In order to prevent direct glass-metal contact, an annu-lar gasket 46 of asbestos or similar material is positioned between the outer surface of the outer glass lens 43 and the inner face 35 of the inturned flange 33, and this gasket 46 not only provides a cushioning action but a sealing action which is of value during assemhlv, as will be descrihed in greater detail hereinafter. A cup 48 of a plastic-resin material is positioned between the inner and outer glass lenses to have a flat portion 49 hetween the lenses and a cvlindrical sidewall portion 51 extending around the outer periphery of the inner glass lens 44. The cup 48 then also includes a horizontally extending flange portion 52 which extends outwardly from the sidewall portion ~1 along the lower side 41 of the ferrule flange 38. Thus, the inner glass lens 4~ is positioned entirely within the cup 48, which therefore forms a barrier between the inner and outer lenses to prevent leakage in the event that either or both of the glass lenses should be cracked or broken. The cup 48 is formed from a sheet of transparent plastic material, such as a fluorocarhon polvmer, and can be formed bv vacuum fo~rming to the indicated shape using a mold sized according to the exact dimensions of the inner glass lens 44.
All of the parts of the complete lens assembly are honded together by means of a suitable adhesive resin, such as an epoxy novalac resin, which is used not only in thin layers to cause parts to adhere to each other hut also to fill all of the interior spaces within the assemhly. Accordingly, there is a thin resin layer 54 between the outer side of the flat portion 49 of the plastic cup 48 and the inner side of outer glass lens 43 to bond I . '',',.,. '~
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.' . ':: '.', . -' '' I ' _ _ - 1 1135~91 these two members together, and a resin layer 56 also fills the peripheral space between the outer glass lens 43 and the sidewall 51 of cup 48 and the inner surface 31 of the cylindrical ferrule wall 28. This resin layer also extends in a portion indicated at 57 between the cup flange 42 and the inner surface 41 of the fer-rule flange 380 In similar manner, there is a thin resin layer 59 between thè inner side of the flat portion 49 of cup 48 and the outer sur-face of the inner glass lens 44. The same resin laYer extends at 61 between the outer periphery of lens 44 and the cup sidewall 51.
In the preferred embodiment of the invention, the inner surface of the inner glass lens 44 is protected by another plastic sheet or disc 63 that extends across the entire inner surface of the lens assembly, including an outer peripheral portion 66, which extends outwardly for the full diameter of the ferrule flange 38.
This disc 63 is honded to both the lens 44 and the cup flange 52 by a simi].ar thin resin layer 64.
When the lens assembly 10 is mounted between the flanges 11 and 16, it is possible that the plastic materials of the cup flange 52 and the disc outer portion 6S may be sufficiently com-pressible that no gasket is re~uired. However, as shown in FIG.
2, it is generally preferred to use a soft compressible gasket at 68 which extends over the raised face 12 on flange 11. It should be noted that the central portion of the assembly where the discs are has a slightly lesser thickness than the peripheral portion at the flange 38, so that when the outer flange 16 is clamped in place, compression exists only between the ferrule flange 38 and .
the inner flange raised face 12, and no compression pressure is ..

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`I 1135091 therefore exerted directly on the glass lenses 43 and 44. Fur-thermore, it should be noted that the diameter of the glass lens discs 43 and 44, and hence of the entire lens assembly 10, is selected to be slightly greater than that of the bore 13 in the inner flange 11, and the unit is preferably sized so that the bore in the inner flange is substantially equal to the opening 34 on the inturned flange 33 on the ferrule.
The assembly of the component parts of lens assembly 10 --is done by first thoroughly cleaning all of the surfaces to which the epoxy resin is to be bonded and then treating the surfaces with any bonding agents or adhesion-enhancing agents that may be necessary. After this is done, the metal ferrule and the glass lenses are preheated in an oven to a working temperature such as 90 C. to enhance the subsequent curing of the epoxy material and avoiding sudden temperature changes that may cause the glass lenses to fracture. The epoxy resin is then mixed and heated to a high enough temperature to lower its viscosity so that it is able to flow readily and form ~hin layers. After the epoxy resin has been mixed, the ferrule is placed in an inverted position, with the outer inturned flange resting on a horizontal surface. The gasket 46 is then set in place, followed by the outer lens 43.
The epoxy resin is then poured into the ferrule to cover the inner face of outer lens 43, as well as to fill the annular peripheral gap between the lens 43 and the ferrule filled with the resin layer 56. At the same time, the entire rest of the interior of the ferrule is covered by the resin, including the inner face 41 f flange 38. Also at the same time, the resin is poured into the interior of the cup 48 to coat its inner surface and the inner , ,:, ' . -., . - .:

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¦glass lens 44 is placed into the cup and sufficient pressure ¦applied to eliminate any air bubbles that would form in the layers ¦59 and 61.
¦ After the above has been aone, the cup 48, including the ¦inner lens 44, is placed into the ferrule, again forcing out air bubbles to ensure clarity in the resin layer 54, which should be as thin as practically possible. Of course, any excess resin material is thus forced outward into the space between the cup flange 52 and the ferrule flange 38, and may be removed as neces-sary.
At this point, it will be seen that the gasket 46 serves as a seal to prevent leakage of the liquid resin during assembly, as well as its cushioning effect when the lens assembly is in use. It should be noted, however, that in many cases it is desir-able to use a slightly porous material, such as asbestos, for the gasket 46, in which case a small amount of the epoxy may flow through the gasket and form a bead at the exterior junction between the gasket 46 and the outer surface of lens 43, but this is in no way undesirable.
After the inner lens 44 and cup 48 have heen assembled together and all air bubbles removed, an additional amount of the epoxy resin is poured over the inner face of the inner glass lens 44 and the exposed flange 52 of the cup 48. The disc 63 is then pressed in place and, again, care is taken to ap~ly suitable pressure to exclude all air bubbles from the resin layer 64.
~ he next step is to place the inverted assembly into a clamping fixture which applies separate pressures to the lens area and outer flange area. By first applying pressure to the lens and . .
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then to the flange, any distortion of the disc 63 is eliminated and there is no chance for air bubbles to enter the liquid resin.
After the necessary clamping has taken place, it is then necessary only to place the assembly into a curing oven to complete the curing of the epoxY resinO
It is understood that different materials may be used for the lenses 43 and 44, and various suitable plastic or resinlike materials can be used for the cup 48 and disc 63. ~owever, when the assembly is bonded together in the manner described and clamped between the flanges, no compression pressure ;s placed on the glass lenses 43 and 44. Nevertheless, if either or even both of the lenses should be broken, the assembly will not leak as long as the cup member 46 is unbroken, since it forms as a unitary mem-ber a complete seal across the assembly, which is sealed at the ferrule flange 38. With this arrangement, the glass lenses 43 and 44 serve no sealing function, but merely provide strength against the pressure in the vessel to which the sight glass is attached and permit the visual inspection of the interior.
It is also understood that in certain applications the disc 63, and hence the resin laYer 64, may be eliminated so that the inner surface of inner lens 44 is exposed to the interior of the pressure vessel, and it is also understood that the gasket 68 may be eliminated, since the flange portion 52 of cup 48 does have a certain amount of resilience to function as a gasket or seal under certain conditions.
It is also understood that the disc 63 may be made of various transparent materials that are selected solely for their resistance to chemical and physical attack by the contents of the '; , ,:
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~135091 pressure vessel, since, although the disc 63 can perform a sealing function if the glass lenses are broken, this i5 entirely a secondary function since the cup 48 proviaes the primary sealing function under such conditions. - . :
While the preferred embodiment of the present invention has been disclosed and descrihed in particular detail, it is to be understood that various modifications and rearrangements may be made without departing from the scope of the invention as defined in the following claims.

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Claims (16)

WHAT IS CLAIMED IS

1. A lens assembly for a sight glass comprising a fer-rule, said ferrule having an axially extending sidewall with an outwardly extending flange at one end and an inwardly extending flange at the other end, a first lens in said ferrule having a first side adjacent said inwardly extending flange, a second lens in said ferrule having a first side adjacent said outwardly ex-tending flange, the opposite sides of said lenses being adjacent each other, and a sheet of transparent flexible plastic material extending between said lenses, between the outer periphery of said second lens and said ferrule sidewall and extending along the outer side of said outwardly extending flange.

2. A lens assembly as set forth in claim 1, wherein said sheet is bonded to said opposite sides of said lenses.

3. A lens assembly as set forth in claim 2, wherein said sheet is also bonded to said ferrule wall and said outer side of said outwardly extending flange.

4. A lens assembly as set forth in c]aim 3, including a second sheet of transparent flexible plastic material bonded to said first side of said second lens and to the portion of said first sheet extending along said outwardly extending flange.

5. A lens assembly as set forth in claim 3, including a gasket between said first side of said first lens and said inward-ly extending flange, and bonding material filling the space between the outer periphery of said first lens and said ferrule sidewall.

6. A sight glass comprising a first pipe flange adapted to be attached to a pressure vessel, a second pipe flange secured to said first flange and defining an opening, a lens assembly clamped between said flanges and extending through said opening, said lens assembly comprising a ferrule, said ferrule having an axially extending sidewall within said opening, said ferrule also having an integral outwardly extending flange at the inner end clamped between said pipe flanges and an integral inwardly extend-ing flange at the other end, a first lens in said ferrule having a first side adjacent said inwardly extending flange, a second lens in said ferrule having a first side adjacent said outwardly ex-tending flange, the opposite sides of said lenses being adjacent each other, and a sheet of transparent flexible plastic material extending between said lenses, between the outer periphery of said second lens and said ferrule sidewall and along said outwardly extending flange adjacent said first pipe flange.

7. A sight glass as set forth in claim 6, wherein said flexible plastic sheet is bonded to said opposite sides of said lenses.

8. A sight glass as set forth in claim 7, wherein said flexible plastic sheet is also bonded to said ferrule wall and the outer periphery of said second lens and to said outwardly extend-ing flange.

9. A sight glass as set forth in claim 8, including a second sheet of transparent flexible plastic material bonded to said first side of said second lens and extending completely across said first side of said second lens and across said portion of said first sheet adjacent said outwardly extending flange.

10. A sight glass as set forth in claim 8, including a gasket between said first side of said first lens and said inward-ly extending flange and bonding material filling the space between the outer periphery of said first lens and said ferrule sidewall.

11. A sight glass as set forth in claim 9, including a second gasket positioned between said second sheet and said first pipe flange.

12. A lens assembly comprising a lens containing member having an axially extending sidewall with an outwardly extending surface at one end and an inwardly extending surface at the other end, a first lens in said lens containing member and having a first side adjacent said inwardly extending surface, second lens in said lens containing member having a first side adjacent said outwardly extending surface, the opposite sides of said lenses being adjacent each other, and a sheet of transparent flexible plastic material extending between said lenses, between the outer periphery of said second lens and said sidewall of said lens containing member and extending-along the outer side of said outwardly extending surface.

13. A lens assembly as set forth in claim 12, wherein said sheet is bonded to said opposite sides of said lenses.

14. A lens assembly as set forth in claim 13, wherein said sheet is also bonded to said sidewall of said lens containing members and said outer side of said outwardly extending surface.

15. A lens assembly as set forth in claim 14, including a second sheet of transparent flexible plastic material bonded to said first side of said second lens and to the portion of said first sheet extending along said outwardly extending surface.

16. A lens assembly as set forth in claim 14, including a gasket between said first side of said first lens and said inwardly extending surface, and bonding material filling the space between the outer periphery of said first lens and said sidewall of said lens containing member.

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