GB2190923A

GB2190923A - Metal sheet for sealing to soft glass

Info

Publication number: GB2190923A
Application number: GB08711142A
Authority: GB
Inventors: Akio Fujii; Koji Mukai
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 1986-05-13
Filing date: 1987-05-12
Publication date: 1987-12-02
Anticipated expiration: 2007-05-12
Also published as: DE3715397C2; GB2190923B; FR2600638B1; DE3715397A1; JPH0665737B2; FR2600638A1; GB8711142D0; JPS62267449A; NL8701055A

Description

GB 2190923 A 1

SPECIFICATION

Metal sheetfor sealing to soft glass The present invention relates to plated Fe-Cr alloy sheets suitable for sealing to soft glass used forfluorescent 5 tubes,etc.

Conventional known alloys for sealing to soft glass include, for example Fe-42%M-6%Cr alloy and Fe 18%Cr alloy. These alloys are used for sealing to soft glass since they have a coefficient of thermal expansion close to that of soft glass. For sealing to soft glass a metal sheet is formed into a desired shape by etching or punching. It is then oxidized at 900-1 1000C in an atmosphere of wet hydrogen gas for about 10 minutes in 10 orderto form a chromium oxide film of about 0.5 [Lm thickness on the alloy. The metal sheet is then sealed to the glass through the oxide film. Subsequently, the metal sheet is solder- plated to permit attachment of lead pins for making electrical connection with external terminals. Forthesolder-plating, the oxide film has to be removed by mechanical grinding orthe like. Unfortunately, with a Fe-Cr alloy adhesion of solder cannot be achieved by ordinary solder plating because the Fe-Cr alloy soon forms a firm passive state film onthe 15 surfaceafterthe removal of the oxide coating film. Forthis reason, despite their low price, the Fe-Cr alloys are not generally used to seal fluorescent tubes forwhich solder-plating is needed.

Itwould thus be desirable to be able to provide a metal alloy sheet suitable for sealing to soft glass and which is capable of being solder-plated afterthe removal of the oxide film. We have nowfoundthatcertain Fe-Cralloy sheets, which sheets are plated with Ni are useful for sealing to soft glass, are both inexpensive 20 and have astable and good affinity for glass and can be solder-plated.

According to the present invention, there is provided a metal alloy sheet for sealing to soft glass, the alloy containing 16-30%byweightCr, not more than 0.06% byweight C, 25 not morethan 0.06% byweight N, not more than 1.0% byweightSi and not more than 1.0% byweight of Mn, the remainder being Fe,apartfrom impurities and incidental ingredients, a surface of the said sheet being plated with nickel. 30 In the sheets according to the present invention the alloy has a Crcontent of 16-30%. With an amount smallerthan 16%,the alloy has a coefficient of thermal expansion excessively largerthan that of softglass.

With an amount greaterthan 30%,the alloy is poor in workability.

The content of C should be as low as possible in orderthat the alloy has improved corrosion resistance.

Some carbon is in general practically unavoidable but an amount smallerthan 0.06% causes no significant 35 problem in practical use.

Si in an amount smallerthan 1% is sufficientto promotethe internal oxidation of the alloy during oxidation treatment and to improve the adhesion of the oxide film to the alloy.

Mn forms a spinel type oxide (MnCr204) in the surface layer, thereby improving thewettability with glass.

However, an alloy containing more than 1 % of Mn has an excessively high coefficient of thermal expansion. 40 In general the alloy may contain up to 0.04% of P, up to 0.03% of S and up to 0.5% of Ni as unavoidable impurities (ASTM Standard).

Thethickness of the Ni plating should generally be sufficient such that NI remains uniformlyon thesurface layerof the alloy afterthe oxide film has been removed. On the other hand, the thickness of the Ni plating affects the thickness of the chromium oxide coating film to beformed on the Ni plating layer. Thus,the 45 thickness of theformed chromium oxidefilm varies depending not only on the temperature and duration of oxidation butalso on thethickness of the Ni plating layersince chromium in the alloy diffusesto thesurface through the plated Ni layerwherebythe chromium oxide coating film isformed onthe outermost layer. It is necessary therefor to select a thickness for the Ni plating layerwhich, underthe oxidation conditionsto be used, i.e. thetemperature and period of the oxidation treatment, allowsthereto be obtained an oxidecoating 50 film having a thickness adequateto effect sealing to soft glass. In general the nickel plating layerwill prefer ably have athickness not lessthan 1 gm. When oxidation is carried outat 1000'C, a 2-4 pm thick Ni plating layer provides a chromium oxidefilm suitable for sealing to softglass.

The Ni plating can be performed in the usual way,for example by degreasing a suitable Cr-Fe alloysurface, an optional activation treatmentstep, NI strike plating, and regular plating in a conventional manner. 55 The invention will now be further illustrated byway of thefollowing working Examples.

Example 1

An Fe-Cr alloy containing 26.73% Cr, 0.03% C, 0.035% N, 0.40% Si, 0.50% Mn, 0.022% P and 0.009% S was prepared in the usual manner. Test pieces were subjected to Ni plating in various thicknesses in the usual 60 manner. The Ni-plated test pieces were oxidized at 1 000'C for several minutes in an atmosphere of wet hydrogen gas which was obtained bybubbling hydrogen through water at35'C so that an oxide film about 0.5 firn thick was formed. The oxide film on the test piece was removed by rubbing with sand paper.lm mediately thereafter, a flux was applied to the surface of the test pieces and they were dipped inasolderbath at 250'C. Thus treated test pieces were examined to determine the area (as a percentage) covered with solder. 65 2 GB 2 190 923 A 2 The results are shown in Table 1.

Table 1

Thickness of Ni plating (Lm) 0 1 2 4 6 5 Area covered with solder (%) 55 100 100 100 100 SolderedArea X 100 (%) 10 Dipped area It is apparentfrom Table 1 thatthetest piecewhich has no Ni plating was notadequately covered with solder, even though itwas dipped in the solder bath immediately afterthe removal of the oxidefilm. In contrast, test pieces with Ni plating thickerthan 1 lim were 100% covered with solder. 15 Examp/62 Test pieces of the same alloy as in Example 1,with orwithouta 2 1Lm thick Ni plating film, were subjectedto oxidation treatment in the same manneras in Example 1. Then,thetest pieceswere dipped in the solderbath after different periods of timefollowing the removal of the oxidefilm. Thetest pieceswere examinedto 20 determine the area (as a percentage) covered with solder. The results are shown in Table 2.

Table 2

Time (min) before dipping in solderbath 25 0.5 1 2 5 120 Without Ni plating 55% 30% 20% 20% 20% With 2 Lm Ni plating 100% 100% 100% 100% 100% It is noted from Table 2thatthetest pieceswithout Ni plating were poor in theiradhesion of soldereven 30 when thetest pieceswere dipped in the solderaftera comparatively short period of time and the covered area decreased with an increase in thetime before dipping. In contrast, in the cast of test pieces with 2 Lm thick Ni plating,the adhesion of solderwas good regardless of thetime interval before the dipping in the solder bath.

35 Example 3

Test pieces of the same alloy as in Example 1, with or without a 2 [Lm thick Ni plating, were subjected to oxidation treatment in the same manner as in Example 1. The test pieces were then sealed to soft glass plates and 50 samples of the glass plates were examined for cracking. The results are shown in Table 3.

40 Table 3

With 2 pm Without Niplating Niplating Cracked samples (%) 0 0 45 It is noted from Table 3 that like the test pieces having no Ni plating, test pieces with 2 gm thick Ni plating were capable of good sealing without causing cracking in the glass.

Example4

Test pieces of cold-rolled sheet (0.7 mm thick) were prepared from the same alloy as in Example 1. Thetest 50 pieces, with orwithout a 2 Km thick Ni plating were subjected to oxidation treatment under the above mentioned conditions. The test pieces were sealed to soft glass. The bonding strength was measured by applying a tensile shear loaded to the sealed part. The results are shown in Table 4.

Table 4 55

With 2 Lm Without Niplating Niplating Tensile shear strength 2.1 kglmm2 2.0 kg/m M2 It is noted from Table 4thatthe test pieces with a 2 Km thick Ni plating exhibited adequate bonding strength 60 as did the test pieces with no Ni plating.

Claims

1. A metal alloy sheet for sealing to soft glass, the alloy containing: 65 3 GB

2 190 923 A

3 16-30%byweightCr, not morethan 0.06% byweightC, not morethan 0.06% byweightN, not morethan 1.0% byweightSiand not more than 1.0% byweight Mn, 5 the remainder being Fe, apart from impurities and incidental ingredients, a surface of the said sheet being plated with nickel. 2. A sheet according to Claim 1 which is plated with nickel in a thickness of not less than 1 [Lm. 3. A sheet according to Claim 2 wherein the plated nickel thickness is from 2 to 4 [Lm.

4. A metal alloy sheet according to claim 1 substantially as herein described. 10

5. A metal alloy sheet according to claim 1 substantially as herein described in any one of Examples 1 to 4.

6. Each and every novel method, process and product herein disclosed.

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