WO2002031383A2

WO2002031383A2 - Seals with improved corrosion resistance and a method for manufacturing same

Info

Publication number: WO2002031383A2
Application number: PCT/US2001/042547
Authority: WO
Inventors: Christopher M. Kappes; John J. Vajo; Ronghua Wei
Original assignee: Hrl Laboratories, Llc; Delphi Technologies, Inc.
Priority date: 2000-10-12
Filing date: 2001-10-08
Publication date: 2002-04-18
Also published as: WO2002031383A9; TW588107B; AU2001297005A1; WO2002031383A3

Abstract

A combination seal comprising two chemical seals (4a, 4b), each between a first surface of a sealant (2a) and a surface of a substrate (2b) and a physical seal (5) between a second surface of first chemical seal and a second surface of a second chemical seal. The chemical seals are formed by applying the sealant to two substrates and curing the sealant. The physical seal is formed by clamping the chemical seals together. The resulting combination seal has good corrosion resistance of a chemical seal and is re-sealable allowing easy re-work. A method for forming the combination seal.

Description

SEALS WITH IMPROVED CORROSION RESISTANCE AND A METHOD FOR

MANUFACTURING SAME

I. BACKGROUND OF THE INVENTION

1. Field of the Invention.

This invention relates to the field of seals with enhanced resistance to corrosion. More particularly, it pertains to the use of re-sealable seals in housings when seals are used to protect the contents enclosed within such housings from corrosion.

2. Description of the Related Art.

There are two commonly known types of seals used to protect housings from corrosion — re-sealable, or physical seals, and non-re-sealable, or permanent chemical seals. These seals are used to protect all kinds of housings, including housings fabricated of a metal, such as, for instance, steel, aluminum or a sheet metal, and those fabricated of a non-metal. Physical seals are always preferred if the housing is to be unsealed for rework. However, chemical seals usually have better corrosion resistance than physical seals.

A commonly known method for manufacturing physical seals comprises clamping an elastomeric sealant, such as an 0-ring, between two halves of the module's housing, followed by physical compression between the sealant and the housing. Two physical seals are formed in this fashion on each half of the housing. These seals may be opened and released allowing rework. This method of manufacturing physical seals is frequently used in fabricating electronic module control housings . The second method involves dispensation of an uncured sealant on one half of the housing followed by curing to form a permanent chemical seal on the housing. After curing, the module is assembled by clamping the half with the cured sealant to the mating half. As a result, one permanent chemical seal and one re-sealable physical seal are formed. The corrosion resistance of the chemical seal is good, while that of the physical seal is relatively poor.

Finally, a chemical permanent seal can be made by dispensation of an uncured sealant on one half of the housing, assembling the housing by clamping the mating half, followed by curing the completely assembled module. Two permanent chemical seals are thus made, attached to both halves of the housing. They have good corrosion resistance, but re-opening of the seal becomes very difficult thus making rework difficult .

The inventors are unaware of prior art describing a seal in housings which is having good corrosion resistance of the sealant-to-metal chemical seals and is re-sealable allowing rework by inserting sealant-to-sealant physical seal at the same time. Yet, there is a necessity for such a seal combining these two important characteristics.

The present invention proposes such seal and method of manufacturing thereof.

II. SUMMARY OF THE INVENTION

The present invention is directed to a seal, and particularly to a seal for electronic control module housings. Instead of using of a common sealant-to-metal physical seal or a sealant-to- sealant chemical seal, the seal of this invention comprises a combination of two seals: a sealant-to-metal chemical seal and a sealant-to-sealant physical seal. Such combination provides the superior, compared to conventional physical seals, corrosion resistance, while allowing, as needed, easy re-work not available for conventional chemical seals.

Housings are made of any appropriate metal, for instance, steel, sheet metal or aluminum, or of a non-metal . The choice of a material for fabrication of a housing is made based on criteria known to those skilled in the art. Housings for automotive electronic control modules are preferably made of a metal, more preferably, of cast aluminum.

The housings are manufactured in two halves. After the contents, which the housing is designed to protect, for instance, an electronic board, has been installed in one piece of the housing, the second piece of the housing is clamped together with the first piece of the housing to enclose and protect the board from the environment .

Prior to such clamping, two permanent chemical seals are dispensed and cured separately on each half of the housing. When the housing is eventually assembled, the two surfaces, the sealant coating having been formed on them, are clamped together to form a physical seal. The physical seal is, therefore, of a sealant-to-sealant type and does not touch the housing. The corrosion resistance is high as a result.

The present invention is further directed to the method of fabrication of the aforementioned seals.

III. BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

FIG. 1(a) is a schematic diagram showing the general structure of the seal of this invention before the process of sealing.

FIG. 1(b) is a schematic diagram showing the general structure of the seal of this invention after the process of sealing.

FIG. 1(c) is a schematic diagram showing the general structure of a traditional seal.

FIG. 2 is a cross sectional view through a housing for an electronic control module or other object to be protected thereby, the housing being sealed in accordance with the present invention .

IV. DETAILED DESCRIPTION OF THE INVENTION

A general assembly of the seal is schematically shown on FIG. 1(a) . A bead of sealant 1 is dispensed onto two plates 2a and 2b. Plates 2a and 2b are made of any material used for housings, including metals, such as aluminum, steel, sheet metal, and non- metals. The choice of material for the plates 2a and 2b is made according to criteria known to those skilled in the art. The thickness of the bead of sealant is the common and usual thickness used by those skilled in the art for fabricating seals .

Two beads are used. Preferably, the first bead 1 is hemispherical and the second bead is preferably directly dispensed in a shape having a rectangular cross section 3. Alternatively, the second bead having a rectangular cross section 3 can be obtained by cutting down a hemispherical bead to form such rectangular cross section 3. The methods of dispensing as a rectangular are known to those skilled in the art . The process of cutting the bead 1 down to obtain the rectangular cross section 3 is conducted, if necessary, according to usual procedures using usual equipment known to those skilled in the art.

Al ernatively, each of the two beads dispensed can be hemispherical in cross-section. In this alternative case, there is no cutting down the bead 1 down to obtain the rectangular cross section 3 and both beads remain hemispherical in the cross-section.

The beads are dispensed onto the two plates 2a and 2b to achieve the desired thickness using usual methods of dispensing and thickness control known to those skilled in the art.

A material used for the sealant 1 is an elastomeric material selected according to usual criteria used by those skilled in the art, depending on particular requirements to a particular seal. The elastomeric material is preferably a silicon polymeric material. Following the dispensation of the sealant 1, it is cured under usual curing conditions known to those skilled in the art .

Plates 2a and 2b are then clamped together using clamps, C- cla ps, pressure, bolts, or by any other method creating pressure sufficient to form a physical seal. The amount of pressure is normally expressed as a degree of compression of the seal, usually shown as percentage of compression. The degree of optimal compression can vary and is determined by the manufacturer of the unit. Both the amount of required pressure, the methods to achieve it, and the time during which the plates 2a and 2b remain under such pressure are known to those skilled in the art. As a result a combination seal of this invention, comprising two chemical seals 4a and 4b and a physical seal 5, is formed, as shown on FIG. 1(b) .

Example 1.

Two individual beads of sealant are dispensed onto two metal plates 2a and 2b, respectively. The thickness of the beads of sealant 1, with approximately hemispherical cross section, is preferably about 3.5 millimeters (0.14 inches); on the plate 2a the hemispherical cross section bead is cut down to a rectangular cross section 3. The rectangular cross section 3 preferably has a thickness of about 0.75 millimeters (0.03 inches ) .

A material used for the sealant 1 is an elastomer, preferably, a silicon polymeric material.

The plates 2(a) and 2(b) are preferably made of 380 cast aluminum.

Plates 2a and 2b are then clamped together using #14 (0.158 inch diameter) bolts, with the torque of about 8 in-lbs applied. The degree of torque can vary and is determined as the torque necessary to achieve the above-mentioned percentage of compression specified by the manufacturer of the unit.

As a result, a combination seal of this invention, shown on FIG. 1 (b) , is formed, comprising two chemical seals 4a and 4b (between the sealant and metal plates 2a and 2b) and a physical seal 5 (between the layers of sealant 1 and 3) .

For comparison purposes another, traditional, seal is prepared. This control seal is prepared by applying the sealant 1 to the same plate 2b and in the same fashion as described above. The other plate, 2a, remains untreated. The two plates are then clamped together with the same type bolts and with the same torque as described above for the seal of this invention to form a physical seal 6 as shown on FIG. 1(c) .

The two fixtures, the seal of this invention of FIG. 1(b) and the control seal of FIG 1(c), are then tested for corrosion side-by-side using the salt spray system for 40 days, under conditions similar to the American Society for Testing Materials' (ASTM's) Test Designation B117-90 and to the Joint Electron Device Engineering Council's (JEDEC's) Test JESD 22- A107-A.

The control seal of FIG. 1(c) is only slightly corroded (less than 1 millimeter deep) under the sealant-to-aluminum chemical seal 4b. However, at the same time, extensive corrosion areas (approximately 7.5 millimeters deep) appear under the sealant- to-aluminum physical seal 6. Such 7.5 millimeters depth of corrosion constitutes the failure of the seal since the seal is approximately only 5.5 millimeters wide.

The seal of this invention of FIG. 1(b), in contrast, shows no evidence of corrosion through the sealant-to-sealant physical seal 5 and, similar to the control seal, only very minor corrosion (less than 1 millimeter) under the chemical seals 4a and 4b. In addition, the sealant-to-sealant seal 5 separated easily without any sticking of the seal 5 surfaces, thus allowing easy re-work.

This invention is not limited to seals only to be used on modules having two parts. The seal of this invention can also be used, among other things, with a door or a hatch cover on a much larger structure, such as a hatch on a plane or a boat, or to seal an electrical box on the outside of a building.

FIG. 2 depicts, in a cross sectional view, a housing 2 for protecting an electronic control module 7 or other object meriting protection. The housing could be used in an automobile or in any other environment where it is desirable to protect a relatively delicate object such as the aforementioned electronic control module 7. The housing 2 is preferably formed of cast aluminum and has a top 2a and a bottom portion 2b. The top portion 2a has a peripheral surface 2c for receiving sealant 1 and the bottom portion 2b likewise has a peripheral surface 2d for receiving sealant 1. In plan view the housing can be rectangular, circular or another other convenient shape for housing the module 7. The top portion 2c and the bottom portion 2d are sealed using the chemical sealing techniques as previously described with reference to FIGs . 1(a) and 1(b) . One of the two deposited bodies of sealant 1 may be formed with or cut to assume a rectangular cross section as shown at numeral 3. FIG. 2 shows the two portions 2a and 2b of the housing 2 being brought together just as the sealants on each portion touch. Then pressure is applied between the two portions 2a, 2b, then a mechanical seal at numeral 5 is fully formed as shown by FIG. 1(b) . Chemical seals are also formed at numerals 4a and 4b, as previously described.

Having described the invention in connection with several embodiments thereof, modification will now suggest itself to those skilled in the art. As such, the invention is not to be limited to the described embodiments except as required by the appended claims.

Claims

CLAIMSWE CLAIM :

1. A method for fabricating a seal comprising a combination of a physical seal disposed between two chemical seals, said method comprising the steps of:

(a) applying a sealant to a first substrate followed by curing of said sealant on said first substrate to form a first chemical seal, said first chemical seal comprising a first exposed surface of said sealant;

(b) applying said sealant to a second substrate followed by curing of said sealant on said second substrate to form a second chemical seal, said second chemical seal comprising a second exposed surface of said sealant; and

(c) clamping together said first exposed surface of said sealant and said second exposed surface of said sealant to form a physical seal between said first chemical seal and said second chemical seal .

2. The method according to Claim 1, wherein a material of said first substrate and of said second substrate comprises a metal .

3. The method according to Claim 1, wherein said sealant comprises elastomers.

4. The method according to Claim 1, wherein said sealant comprises silicon polymeric materials.

5. The method according to Claim 1, wherein in said step of applying said sealant to said first substrate, said sealant forms a bead.

6. The method according to Claim 1, wherein said step of applying said sealant to said second substrate further comprises dispensing said sealant in a rectangular form.

7. The method according to Claim 1, wherein in said step of applying said sealant to said second substrate, said sealant is cut to form a rectangular cross section.

8. The method according to Claim 1, wherein in said step of clamping together, said first exposed surface of said sealant and said second exposed surface of said sealant are brought into a contact and a clamping force is applied to said first and second substrates.

9. The method according to Claim 1, wherein said combination seal is used to seal automotive electronic control modules .

10. A combination seal, comprising:

(a) a first chemical seal between a sealant and a first substrate, said first chemical seal having two surfaces, a first surface of said first chemical seal attached to a surface of said first substrate and a second surface of said first chemical seal, said second surface of said first chemical seal being exposed;

(b) a second chemical seal between said sealant and a second substrate, said second chemical seal having two surfaces, a back surface of said second chemical seal attached to a surface of said second substrate and a face surface of said second chemical seal, said face surface of said second chemical seal being exposed; and

(c) a physical seal between said second surface of said first chemical seal and said face surface of said second chemical seal.

11. The seal according to Claim 10, wherein a material of said first substrate and of said second substrate comprise a metal .

12. The seal according to Claim 10, wherein said sealant comprises elastomers.

13. The seal according to Claim 10, wherein said sealant comprises silicon polymeric materials.

14. The seal according to Claim 10, wherein said second surface of said first chemical seal has a shape of a bead.

15. The seal according to Claim 10, wherein said face surface of said second chemical seal has a shape of a rectangular .

16. The seal according to Claim 10, wherein said combination seal is used to seal automotive electronic control modules .