CA1066221A - Tin orientation on tinplate - Google Patents
Tin orientation on tinplateInfo
- Publication number
- CA1066221A CA1066221A CA251,596A CA251596A CA1066221A CA 1066221 A CA1066221 A CA 1066221A CA 251596 A CA251596 A CA 251596A CA 1066221 A CA1066221 A CA 1066221A
- Authority
- CA
- Canada
- Prior art keywords
- tin
- outer layer
- tinplate
- brightened
- flow
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D51/00—Making hollow objects
- B21D51/16—Making hollow objects characterised by the use of the objects
- B21D51/26—Making hollow objects characterised by the use of the objects cans or tins; Closing same in a permanent manner
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/48—After-treatment of electroplated surfaces
- C25D5/50—After-treatment of electroplated surfaces by heat-treatment
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/20—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Crystallography & Structural Chemistry (AREA)
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Mechanical Engineering (AREA)
- Electroplating Methods And Accessories (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Method of making tinplate container component to give improved resistance to corrosion from E. G. milk products includes selecting steel plate coated with flow brightened electrolytic beta tin, the tin having particular crystallo-graphic textures.
Method of making tinplate container component to give improved resistance to corrosion from E. G. milk products includes selecting steel plate coated with flow brightened electrolytic beta tin, the tin having particular crystallo-graphic textures.
Description
~Q~6Z2~
This invention relates to tinplate container component and methods of making them. It is especially concerned with tinplate components suitable for, but not confined to foodstuff containers which are partly or entirely of tinplate, and par-ticularly to components for containers for milk products.
A typical foodstuff container consists of a can having either two or three components, comprising a can body with a separate can end member seamed on to each end, or a can body closed integrally at one end and having a separate end memb0r seamed onto the other end. Any, both or all components may be ; of tinplate, formed from sheet consisting of steel having a flow-brightening coating comprising an outer layer of metallic tin and usually also a relatively thin layer of alloy between , the steel and the metallic tin outer layer. The alloy layer, which is formed during the flow-brightening process, consists entirely or mainly of the inter-metallic compound FeSn2. In addition a relatively thin passivation layer containing chromium may be applied over the tin coating, and it is common in compo- ;
nents for foodstuff containers to apply a suitable protective lacquer over the tin coating (or over the passivation layer i~ present).
There are various ways of preventing corrosion of the tin coating by the contents of a container, beyond the mere use of lacquer and passivation layers, which in many instances may not be sufficient in themselves. Among such additional methods may be mentioned the use of a reducing or substantially chem~cally~
! inert atmo~phere in the container headspace, and the modification of the lacquer by the use of additives. Nevertheless, such expedients do tend to add to the cost of packaging the container contents and to be somewhat limited as to their application.
We have discovered, ~urprisingly, that there is a posi-tive relation~hip between, on the one hand, the grain orientation - 1 - ~` ' ' ..
' ' ' "
of the metallic tin in commercially-produced flow-brightened electrolytic tinplate and, on the other hand, the resistance of the tin outlet layer itself to corrosion when used in com-ponents for containers for certain foodstuffs, in particular certain milk products. This grain orientation is usually referred to as the texture of the metal, and this is the term that will be used hereinafter. We have also discovered that the texture of the tin coating as deposited electrolytically undergoes a marked change due to the flow-brightening process, and that it i9 the extent to which this change has taken place that can be correlated with the said corrosion performance.
The invention accordingly provides a method of making a tinplate container component (particularly though not neces-i sarily for use with milk products), which method includes the selection of tinplate sheet having certain predetermined characteristics, and in particular the textural characteristics which we have found prevent or substantially prevent corrosion of the tin outer layer (de-tinning by milk products).
These textural characteristics are best defined in terms of test results which may conveniently be those obtained using known techniques, in particular those of the measurement of the texture of the metallic tin outer layer by X-ray diffrac-tion. These X-ray diffraction measurements can be conveniently displayed in various ways, for example on a pole figure, from which both qualitative and quantitative information regarding the characteristics of the texture can be drawn. Quantitive information as to the texture can be ohtained from measurements of the inten~itie~ of selected certain reflection5 or in terms of the ratio of the peak intensities of ~elective reflections obtained u~ing an X-ray diffractometer. The latter type of measurement i~ more convenient, quicker and cheaper than pole figure determination~, ~y ~0662~
The purpose of these texture measurements is to deter-mine the degree to which the texture of the original as-electrolytically deposited tin (hereinaf~er called the " as-depositedl' tin coating) has been transformed to the texture which is characteristic of fully flow-brightened tin. The term ' ~'partially flow-brightened" means that the tin coating has been ~ubjected to an incomplete flow-brightening process, for example, by passing it between the brightening rolls with the latter set to roll the tin coating so lightly as to change its grain `, 10 orientation to a certain extent in plastic flow without melting ~, it. The tin coatings which are found to be substantially resis-! tant to corrosion by milk products have textures which are ' ~ ' neither one o~ these two extremes but rather are interrnediate between them;this intermediate texture can be expressed in terms of the aforesaid texture measurements~ ~ , We have al~io found that there is a relationship between these texture measurements using on the one hand, X- '' , ray diffraction and, on the other, oxide reduction potential ,-measurements, so that oxide reduction potential measurements may also be u~ed to express the degree of flow-brightening achieved. We have found a satiisfactory correlation between the result3 obtained in corrosion tests using milk products on variou~ samples of tinplate, on the one hand, and on the other , the reqults of experiments to determine the degree of flo~-brightening in terms of the texture and other characteris-tics of the outer layer by both of the above-mentioned techniques. "~
Accordingly, in a first aspect the invention provides ~ , a method of making a tinplate container component, comprising the steps of (i) 3electing tinplate sheet having predetermined characteristic3 and (ii) forming the,component therefrom, the isaid characteristici~ being that:
. ~
", , ' :, ~ ' " , ' , ' . ' , . ' 662~1 a) The tin coating of the tinplate includes an outer layer of unalloyed, electrolytic beta-tin, partially flow-brightened ~as hereinbefore defined), the degree of severity of flow-brightening being defined by (b) as follows:
b) X-ray diffraction measurement shows that the preferred grain orientation of the tin in said outer layer is intermediate between, and different from, that of fully flow-brightened t~n (as hereinbefore defined) and that of as-deposited tin, and j 10 c) The tin coating is substantially resistant to corrosion by milk products.
The texture of the outer layer is specified by means of X-ray diffraction measurements so as to define the required degree of transformation of the texture from that obtaining for the as-deposited (non-flow brightened) tin coating to that -obtaining for the required partially-flow brightened tin coating.
What i~ shown by the diffraction measurement is most conventionally expressed in terms of the ratio between the inten~ities of two preselected reflections of the metallic tin outer layer. Preferably the intensity ratio af the two preselected reflections obtained by X-ray diffraction is such a~ to indicate a texture of said outer layer intermediate between, and different from, both that of as-deposited tin and that of fully flow-brightened tin (as hereinbefore defined).
Preferably, said ratio has a value greater than 0.1 where the said reflections are the (101) and (200) reflections.
In a second aspect, the invention provides a method of making a tinplate container component, comprising the steps of ~i) selecting tinplate sheet having predetermined characte ristics and (ii) forming the component therefrom, the said ~;
characteri~tic~ being that:
~': ' . . , . : ., " ' ' , '', ' ` '` " ~' . "', '` '' ' ' '. '' ' ' ' ..
1~662~iL
a) the tin coating of the tinplate includes an outer layer of unalloyed partially flow-brightened electrolytic ; beta-tin, b) the tin coating has reduction characteristics such that after oxidation, from a substantially oxide-free state, for 24 hours at iimbient temperature, a first current peak will occur at a reduction potential measured from a set potential of -600 mV in the range -600 mV ta -930 mV; and c) the tin coating is substantially resistant to corrosion by milk products.
According to the invention in a third aspect, there i8 provided a container component of tinplate whose tin coating :
includes an outer layer of unalloyed, electrolytic beta-tin, substantially resistant to corrosion by milk products and flow-brightened (as hereinbefore defined) to a degree of severity ~uch that X-ray diffraction ~how3 that the preferred grain orien- .
tation of the tin in said outer layer is intermediate between, and different from, that of fully flow-brightened tin (as here-inbefore defined) and that of as-deposited tin.
According to the invention in a fourth aspect, there :
is provided a container component of tinplate whose tin coating includes an outer layex of unalloyed, electrolytic beta-tin, substantially resistant to corrosion by milX products and partially flow-brightened (as hereinbefore defined), said outer layer having reduction characteristics such that, after oxidation from a substantially oxide-free state for 24 hours at ambient temperature, a first current peak will occur at a reduction potential, mea~ured from a set potential of -600 mV, in the range -600 mV to -930 mV.
It is to be understood that in each of the above definition~ of the method of the invention in its first and '.
. ~' ` ~0~
:
second aspect~, the determination or evaluation of characteristics of the metallic tin outer layer under (b) is not a step in the method, but rather as a convenient way of defining the charac-teristics concerned.
Embocliments of the invention will now be described by way of example only, and partly with reference to the accompanying drawings, of which:
, Figure l is a pole figure for the (321) re~lection of the metallic tin outer layer of a sample of as-deposited tinplate, Figure 2 is a pole figure for the (200) reflection of the metallic tin outer layer of a sample of as-deposited tinplate, Figure 3 is a pole figure for the (200) reflection of the metallic tin outer layer of a sample of fully flow-brightened tinplate not having the characteristics required for making a component according to the invention, Figure 4 i8 a pole figure for the (200) reflections of the metallic tin outer layer of a ~ample of tinplate having the characteristics for such a component and not being fully flow-brightened, and ; Figure 5 i5 a general view of a typical tinplate container.
In a methocl of making a tinpla-te can end member lO, Flgure 5, according to the invention, the can end is made from ~heet material, by any convenient known technique, which u~ually means stamping in a conventional press and which need not be described further here. A can body ll may be made of similar material to the end member lO, and a complete container i~ made by securing the member 10 onto the open end of the body 11 by conventional means well known in the art.
., .
. . .
. ~ ,,, ,, ,, - , , . , , ~
.. . .
~)6GZ21 The sheet material selected for the can end 10 is - -electrolytic tinplate in which the tin coating includes an outer layer of unalloyed metallic beta-tin which has been partially flow-brightened for example as discussed earlier herein. There will usually also be a relatively thin layer of the iron-tin alloy FeSn2 between the metallic tin outer layer and the steel substract. The sheet material is further cho~en so as to be substantially resistant to corrosion by milk product~, and it preferably has a coating of a suitable protective lacquer over the surface of the tin outer layer, with a very thin passivation layer containing chromium between the tin and the lacquer.
The material is selected for its corrosion resistance according to the grain orientation characteristics of the tin ; in the outer layer. This may be determined by various methods as already set forth herein. Specific examples of these methods will now be described. In each case the samples used are of unlacquered, partially flow-brightened electrolytic tinplate whose tin coating has an outer layer of beta-tin as above described.
; 20 Example 1 In this example X-ray diffraction techniques ha~e been used, and their results are expressed in pole figures,four of which are represented by Figures 1 to 4. The numerals marked on the pole figures are "contours'7 on a scale of 1 to 10, 10 being the maximum. These contours are directly proportional in each Figure to the numberof counts per second in the X-ray test concerned.
Figure 1 is a pole figure for the (321) reflection for a sample of an as-deposited non-flow-brightened tinplate. The contour scale 1 to 10 represents a range of 1 to 14 counts per second. A pole figure using this reflection is quite useful for characterising the texture of the outer layer 662~
of the tin coating of tinplate in this condition because the loops of contours at its centre which are close together indicate - -~that there is a si~nificant proportion of the tin grains with their (321) plane parallel to the surface of the specimen.
Figure 2 is a pole figure for the (200) reflection for a sample of an as-deposited non-flow-brightened tinplate (the contour scale of 1 to 10 representing a range of 1 to 60 counts per second) which is useful for following the transformation of the texture of the outer layer with the flow-brightening process, since for this sample the minimum in the centre of the pole figure indicates that a high proportion of the tin grains do not have the (100) planes parallel to the surface of the specimen, whereas:
Figure 3 which is a pole figure for the t200) reflection for a sample of fully flow-brightened tinplate, (as hereinbefore -defined) with the contour scale 1 to 10 representing a range of 1 to 180 counts per second, shows a pronounced maximum at the centre of the pole figure, indicating that a significant proportion ` , of the tin grains in the outer layer have the (100) planes parallel to the surface of the specimens.
The sample which was the subject of Figure 3 was proved to have unsatisfactory resistance to corrosion by milk product~.
Figure 4 is a pole figure for the (200) reflection for a sample of tinplate which proved to have satisfactory re-sistance to corrosion by milk product5. The contour scale 1 to 10 represents a range of 1 to 80 counts per second.
Thi~ pole figure i~ le~s clear cut than the others, indicating a more complex texture in the tin outer layer situation.
Thereis a maximum near the centre of the pole figure, but it is markedly less prononced than that in Figure 3 and there are also . .
- 8 - :
,^
. ", il;
~ 6;2~
contours over most of the figure which is not the case in Figure 3.
Example 2 A number of different tinplate samples were subjected to conventional X-ray diffraction analysis. The same samples were also each subjected to a standard electrochemical test carried out as follows.
The chromium passivation layer was removed electro-chemically from each sample in an electrolyte bath under controlled conditions. The samples were rinsed and cathodically cleaned in a separate electrolyte bath under known conditions ;~
to remove any tin oxides present, before being rinsed and dried in warm air. The samples were then exposed to air at ambient temperature for 24 hours, at the end of which the resulting oxide layer was measured in a mixed borate solution under deaerated conditions. The reduction peak was measured poten-tio-dynamically from a set potential of -600 mV with respect to a N/10 calomel reference electrode, scanning in a cathodic direction. The potential at which the first current peak occurred i.e. the so-called reduction potential at which the ; oxide was reduced and current rose to a peak value and then fell, waa recorded.
In the following table, the second column indicates re~is~ance of the relevant sample to corrosion by milk products.
; The third column shows the ratio R between the maximum intensity of preferred grain orientation in the outer layer of metallic tin, obtained by the X-ray tests in the (101) plane, to that obtained by the X-ray tests in the (200) plane.
The fourth column shows the potential at which the first reduction peak, above mentioned,03Curred for each sample in the electrochemical tests.
'~
.
~' ~ ' ', __.__ , , . _-` -- -'': _ _ ~
Sample Performance R Reduction :
~o. _ Potential (mV) :~
. . .___ _...................... . . _ 1 Satisfactory 0.80 -917 to -920
This invention relates to tinplate container component and methods of making them. It is especially concerned with tinplate components suitable for, but not confined to foodstuff containers which are partly or entirely of tinplate, and par-ticularly to components for containers for milk products.
A typical foodstuff container consists of a can having either two or three components, comprising a can body with a separate can end member seamed on to each end, or a can body closed integrally at one end and having a separate end memb0r seamed onto the other end. Any, both or all components may be ; of tinplate, formed from sheet consisting of steel having a flow-brightening coating comprising an outer layer of metallic tin and usually also a relatively thin layer of alloy between , the steel and the metallic tin outer layer. The alloy layer, which is formed during the flow-brightening process, consists entirely or mainly of the inter-metallic compound FeSn2. In addition a relatively thin passivation layer containing chromium may be applied over the tin coating, and it is common in compo- ;
nents for foodstuff containers to apply a suitable protective lacquer over the tin coating (or over the passivation layer i~ present).
There are various ways of preventing corrosion of the tin coating by the contents of a container, beyond the mere use of lacquer and passivation layers, which in many instances may not be sufficient in themselves. Among such additional methods may be mentioned the use of a reducing or substantially chem~cally~
! inert atmo~phere in the container headspace, and the modification of the lacquer by the use of additives. Nevertheless, such expedients do tend to add to the cost of packaging the container contents and to be somewhat limited as to their application.
We have discovered, ~urprisingly, that there is a posi-tive relation~hip between, on the one hand, the grain orientation - 1 - ~` ' ' ..
' ' ' "
of the metallic tin in commercially-produced flow-brightened electrolytic tinplate and, on the other hand, the resistance of the tin outlet layer itself to corrosion when used in com-ponents for containers for certain foodstuffs, in particular certain milk products. This grain orientation is usually referred to as the texture of the metal, and this is the term that will be used hereinafter. We have also discovered that the texture of the tin coating as deposited electrolytically undergoes a marked change due to the flow-brightening process, and that it i9 the extent to which this change has taken place that can be correlated with the said corrosion performance.
The invention accordingly provides a method of making a tinplate container component (particularly though not neces-i sarily for use with milk products), which method includes the selection of tinplate sheet having certain predetermined characteristics, and in particular the textural characteristics which we have found prevent or substantially prevent corrosion of the tin outer layer (de-tinning by milk products).
These textural characteristics are best defined in terms of test results which may conveniently be those obtained using known techniques, in particular those of the measurement of the texture of the metallic tin outer layer by X-ray diffrac-tion. These X-ray diffraction measurements can be conveniently displayed in various ways, for example on a pole figure, from which both qualitative and quantitative information regarding the characteristics of the texture can be drawn. Quantitive information as to the texture can be ohtained from measurements of the inten~itie~ of selected certain reflection5 or in terms of the ratio of the peak intensities of ~elective reflections obtained u~ing an X-ray diffractometer. The latter type of measurement i~ more convenient, quicker and cheaper than pole figure determination~, ~y ~0662~
The purpose of these texture measurements is to deter-mine the degree to which the texture of the original as-electrolytically deposited tin (hereinaf~er called the " as-depositedl' tin coating) has been transformed to the texture which is characteristic of fully flow-brightened tin. The term ' ~'partially flow-brightened" means that the tin coating has been ~ubjected to an incomplete flow-brightening process, for example, by passing it between the brightening rolls with the latter set to roll the tin coating so lightly as to change its grain `, 10 orientation to a certain extent in plastic flow without melting ~, it. The tin coatings which are found to be substantially resis-! tant to corrosion by milk products have textures which are ' ~ ' neither one o~ these two extremes but rather are interrnediate between them;this intermediate texture can be expressed in terms of the aforesaid texture measurements~ ~ , We have al~io found that there is a relationship between these texture measurements using on the one hand, X- '' , ray diffraction and, on the other, oxide reduction potential ,-measurements, so that oxide reduction potential measurements may also be u~ed to express the degree of flow-brightening achieved. We have found a satiisfactory correlation between the result3 obtained in corrosion tests using milk products on variou~ samples of tinplate, on the one hand, and on the other , the reqults of experiments to determine the degree of flo~-brightening in terms of the texture and other characteris-tics of the outer layer by both of the above-mentioned techniques. "~
Accordingly, in a first aspect the invention provides ~ , a method of making a tinplate container component, comprising the steps of (i) 3electing tinplate sheet having predetermined characteristic3 and (ii) forming the,component therefrom, the isaid characteristici~ being that:
. ~
", , ' :, ~ ' " , ' , ' . ' , . ' 662~1 a) The tin coating of the tinplate includes an outer layer of unalloyed, electrolytic beta-tin, partially flow-brightened ~as hereinbefore defined), the degree of severity of flow-brightening being defined by (b) as follows:
b) X-ray diffraction measurement shows that the preferred grain orientation of the tin in said outer layer is intermediate between, and different from, that of fully flow-brightened t~n (as hereinbefore defined) and that of as-deposited tin, and j 10 c) The tin coating is substantially resistant to corrosion by milk products.
The texture of the outer layer is specified by means of X-ray diffraction measurements so as to define the required degree of transformation of the texture from that obtaining for the as-deposited (non-flow brightened) tin coating to that -obtaining for the required partially-flow brightened tin coating.
What i~ shown by the diffraction measurement is most conventionally expressed in terms of the ratio between the inten~ities of two preselected reflections of the metallic tin outer layer. Preferably the intensity ratio af the two preselected reflections obtained by X-ray diffraction is such a~ to indicate a texture of said outer layer intermediate between, and different from, both that of as-deposited tin and that of fully flow-brightened tin (as hereinbefore defined).
Preferably, said ratio has a value greater than 0.1 where the said reflections are the (101) and (200) reflections.
In a second aspect, the invention provides a method of making a tinplate container component, comprising the steps of ~i) selecting tinplate sheet having predetermined characte ristics and (ii) forming the component therefrom, the said ~;
characteri~tic~ being that:
~': ' . . , . : ., " ' ' , '', ' ` '` " ~' . "', '` '' ' ' '. '' ' ' ' ..
1~662~iL
a) the tin coating of the tinplate includes an outer layer of unalloyed partially flow-brightened electrolytic ; beta-tin, b) the tin coating has reduction characteristics such that after oxidation, from a substantially oxide-free state, for 24 hours at iimbient temperature, a first current peak will occur at a reduction potential measured from a set potential of -600 mV in the range -600 mV ta -930 mV; and c) the tin coating is substantially resistant to corrosion by milk products.
According to the invention in a third aspect, there i8 provided a container component of tinplate whose tin coating :
includes an outer layer of unalloyed, electrolytic beta-tin, substantially resistant to corrosion by milk products and flow-brightened (as hereinbefore defined) to a degree of severity ~uch that X-ray diffraction ~how3 that the preferred grain orien- .
tation of the tin in said outer layer is intermediate between, and different from, that of fully flow-brightened tin (as here-inbefore defined) and that of as-deposited tin.
According to the invention in a fourth aspect, there :
is provided a container component of tinplate whose tin coating includes an outer layex of unalloyed, electrolytic beta-tin, substantially resistant to corrosion by milX products and partially flow-brightened (as hereinbefore defined), said outer layer having reduction characteristics such that, after oxidation from a substantially oxide-free state for 24 hours at ambient temperature, a first current peak will occur at a reduction potential, mea~ured from a set potential of -600 mV, in the range -600 mV to -930 mV.
It is to be understood that in each of the above definition~ of the method of the invention in its first and '.
. ~' ` ~0~
:
second aspect~, the determination or evaluation of characteristics of the metallic tin outer layer under (b) is not a step in the method, but rather as a convenient way of defining the charac-teristics concerned.
Embocliments of the invention will now be described by way of example only, and partly with reference to the accompanying drawings, of which:
, Figure l is a pole figure for the (321) re~lection of the metallic tin outer layer of a sample of as-deposited tinplate, Figure 2 is a pole figure for the (200) reflection of the metallic tin outer layer of a sample of as-deposited tinplate, Figure 3 is a pole figure for the (200) reflection of the metallic tin outer layer of a sample of fully flow-brightened tinplate not having the characteristics required for making a component according to the invention, Figure 4 i8 a pole figure for the (200) reflections of the metallic tin outer layer of a ~ample of tinplate having the characteristics for such a component and not being fully flow-brightened, and ; Figure 5 i5 a general view of a typical tinplate container.
In a methocl of making a tinpla-te can end member lO, Flgure 5, according to the invention, the can end is made from ~heet material, by any convenient known technique, which u~ually means stamping in a conventional press and which need not be described further here. A can body ll may be made of similar material to the end member lO, and a complete container i~ made by securing the member 10 onto the open end of the body 11 by conventional means well known in the art.
., .
. . .
. ~ ,,, ,, ,, - , , . , , ~
.. . .
~)6GZ21 The sheet material selected for the can end 10 is - -electrolytic tinplate in which the tin coating includes an outer layer of unalloyed metallic beta-tin which has been partially flow-brightened for example as discussed earlier herein. There will usually also be a relatively thin layer of the iron-tin alloy FeSn2 between the metallic tin outer layer and the steel substract. The sheet material is further cho~en so as to be substantially resistant to corrosion by milk product~, and it preferably has a coating of a suitable protective lacquer over the surface of the tin outer layer, with a very thin passivation layer containing chromium between the tin and the lacquer.
The material is selected for its corrosion resistance according to the grain orientation characteristics of the tin ; in the outer layer. This may be determined by various methods as already set forth herein. Specific examples of these methods will now be described. In each case the samples used are of unlacquered, partially flow-brightened electrolytic tinplate whose tin coating has an outer layer of beta-tin as above described.
; 20 Example 1 In this example X-ray diffraction techniques ha~e been used, and their results are expressed in pole figures,four of which are represented by Figures 1 to 4. The numerals marked on the pole figures are "contours'7 on a scale of 1 to 10, 10 being the maximum. These contours are directly proportional in each Figure to the numberof counts per second in the X-ray test concerned.
Figure 1 is a pole figure for the (321) reflection for a sample of an as-deposited non-flow-brightened tinplate. The contour scale 1 to 10 represents a range of 1 to 14 counts per second. A pole figure using this reflection is quite useful for characterising the texture of the outer layer 662~
of the tin coating of tinplate in this condition because the loops of contours at its centre which are close together indicate - -~that there is a si~nificant proportion of the tin grains with their (321) plane parallel to the surface of the specimen.
Figure 2 is a pole figure for the (200) reflection for a sample of an as-deposited non-flow-brightened tinplate (the contour scale of 1 to 10 representing a range of 1 to 60 counts per second) which is useful for following the transformation of the texture of the outer layer with the flow-brightening process, since for this sample the minimum in the centre of the pole figure indicates that a high proportion of the tin grains do not have the (100) planes parallel to the surface of the specimen, whereas:
Figure 3 which is a pole figure for the t200) reflection for a sample of fully flow-brightened tinplate, (as hereinbefore -defined) with the contour scale 1 to 10 representing a range of 1 to 180 counts per second, shows a pronounced maximum at the centre of the pole figure, indicating that a significant proportion ` , of the tin grains in the outer layer have the (100) planes parallel to the surface of the specimens.
The sample which was the subject of Figure 3 was proved to have unsatisfactory resistance to corrosion by milk product~.
Figure 4 is a pole figure for the (200) reflection for a sample of tinplate which proved to have satisfactory re-sistance to corrosion by milk product5. The contour scale 1 to 10 represents a range of 1 to 80 counts per second.
Thi~ pole figure i~ le~s clear cut than the others, indicating a more complex texture in the tin outer layer situation.
Thereis a maximum near the centre of the pole figure, but it is markedly less prononced than that in Figure 3 and there are also . .
- 8 - :
,^
. ", il;
~ 6;2~
contours over most of the figure which is not the case in Figure 3.
Example 2 A number of different tinplate samples were subjected to conventional X-ray diffraction analysis. The same samples were also each subjected to a standard electrochemical test carried out as follows.
The chromium passivation layer was removed electro-chemically from each sample in an electrolyte bath under controlled conditions. The samples were rinsed and cathodically cleaned in a separate electrolyte bath under known conditions ;~
to remove any tin oxides present, before being rinsed and dried in warm air. The samples were then exposed to air at ambient temperature for 24 hours, at the end of which the resulting oxide layer was measured in a mixed borate solution under deaerated conditions. The reduction peak was measured poten-tio-dynamically from a set potential of -600 mV with respect to a N/10 calomel reference electrode, scanning in a cathodic direction. The potential at which the first current peak occurred i.e. the so-called reduction potential at which the ; oxide was reduced and current rose to a peak value and then fell, waa recorded.
In the following table, the second column indicates re~is~ance of the relevant sample to corrosion by milk products.
; The third column shows the ratio R between the maximum intensity of preferred grain orientation in the outer layer of metallic tin, obtained by the X-ray tests in the (101) plane, to that obtained by the X-ray tests in the (200) plane.
The fourth column shows the potential at which the first reduction peak, above mentioned,03Curred for each sample in the electrochemical tests.
'~
.
~' ~ ' ', __.__ , , . _-` -- -'': _ _ ~
Sample Performance R Reduction :
~o. _ Potential (mV) :~
. . .___ _...................... . . _ 1 Satisfactory 0.80 -917 to -920
2 Satisfactory 0.47 -920
3 Satisfactory 0.34 -917 Satisfactory 0.18 -910 to -915 ~
Unsatisfactory 0.09 -940 6 Unsatisfactory 0.07 -935 7 Unsatisfactory 0.03 -933 to -935 . . Unsatisfactory 0.02 -932 ' From the table it can be seen that for the samples with satisfactory corrosion resistance, the ratio R was over 0.10 with reference to the two planes chosen. Similarly, it will be seen that the reduction potential at which the current -peak occurs lie~ within a predetermined range when the required characteri~tics are present, being, in the above examples, in the range -910 to -920 mV and in any event within the range .
-600 mV to -930 mV.
.' ':' .
,. .
""," -- 10 i .. ,,, ' , ' , , , ~ ~ .
Unsatisfactory 0.09 -940 6 Unsatisfactory 0.07 -935 7 Unsatisfactory 0.03 -933 to -935 . . Unsatisfactory 0.02 -932 ' From the table it can be seen that for the samples with satisfactory corrosion resistance, the ratio R was over 0.10 with reference to the two planes chosen. Similarly, it will be seen that the reduction potential at which the current -peak occurs lie~ within a predetermined range when the required characteri~tics are present, being, in the above examples, in the range -910 to -920 mV and in any event within the range .
-600 mV to -930 mV.
.' ':' .
,. .
""," -- 10 i .. ,,, ' , ' , , , ~ ~ .
Claims (11)
1. A method of making a tinplate container component, comprising the steps of (1) selecting tinplate sheet having predetermined characteristics and (II) forming the component therefrom, the said characteristics being that:-a) The tin coating of the tinplate includes an outer layer of unalloyed electrolytic beta-tin, partially flow-brightened to a degree of severity defined by (b) as follows:
b) An X-ray diffraction measurement shows that the preferred grain orientation of the tin in said outer layer is intermediate between, and different from, that of fully flow-brightened tin and that of as-deposited; and c) The tin coating is substantially resistant to corrosion by milk products.
b) An X-ray diffraction measurement shows that the preferred grain orientation of the tin in said outer layer is intermediate between, and different from, that of fully flow-brightened tin and that of as-deposited; and c) The tin coating is substantially resistant to corrosion by milk products.
2. A method according to Claim 1, wherein the in-tensity ratio of two preselected reflections obtained by X-ray diffraction is such as to indicate a texture of said outer layer intermediate between, and different from, both that of as-deposited tin and that of fully flow-brightened tin.
3. A method according to Claim 2, wherein the said reflections are the (101) and (200) reflections.
4. A method according to Claim 2, wherein said ratio has a value greater than 0.1.
5. A method of making a tinplate container component comprising the steps of (1) selecting tinplate sheet having predetermined characteristics and (II) forming the component therefrom, the said characteristics being that:-a) The tin coating of the tinplate includes an outer layer of unalloyed electrolytic beta-tin, partially flow-brightened, b) The said outer layer has reduction characteristics such that, after oxidation peak will occur at a reduction potential measured from a set from a substantially oxide-free state, for 24 hours at ambient temperature, a first current potential of -600 mV, in the range -600 mV to -930 mV; and c) The tin coating is substantially resistant to corrosion by milk products.
6. A method according to Claim 5, wherein the said range is -917 mV to -920 mV.
7. A container component of tinplate whose tin coating includes an outer layer of unalloyed, electrolytic beta-tin, substantially resistant to corrosion by milk products and flow-brightened to a degree of severity such that X-ray diffrac-tion shows that the preferred grain orientation of the tin in said outer layer is intermediate between, and different from, that of fully flow-brightened tin and that of as-deposited tin.
8. A component according to Claim 7, wherein the intensity ratio of two preselected reflections obtained by X-ray diffraction is such as to indicate a texture of said outer layer intermediate between, and different from, both that of as-deposited tin and that of fully flow-brightened tin.
9. A component according to Claim 8, wherein the said intensity ratio of the (101) and (200) reflections has a value greater than 0.1.
10. A container component of tinplate whose tin coating includes an outer layer of unalloyed, electrolytic beta-tin, substantially resistant to corrosion by milk products and partially flow-brightened, said outer layer having reduction characteristics such that, after oxidation from a substantially oxide-free state for 24 hours at ambient temperature, a first current peak will occur at a reduction potential, measured from a set potential of -600 mV, in the range -600 mV to -930 mV
11. A container having at least one component according to Claim 6 or Claim 10.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1812875A GB1552221A (en) | 1975-05-01 | 1975-05-01 | Container components |
| BE1007553A BE845146A (en) | 1975-05-01 | 1976-08-13 | PROCEDURE FOR MANUFACTURING SPARE PARTS OF VERTIND BLIK, A RESERVOIR PART THIS MANUFACTURE AND A RESERVOIR FITTED WITH AT LEAST SUCH A RESERVOIR PART |
| BE845146 | 1976-08-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1066221A true CA1066221A (en) | 1979-11-13 |
Family
ID=27159454
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA251,596A Expired CA1066221A (en) | 1975-05-01 | 1976-04-30 | Tin orientation on tinplate |
Country Status (4)
| Country | Link |
|---|---|
| BE (1) | BE845146A (en) |
| CA (1) | CA1066221A (en) |
| FR (1) | FR2309428A1 (en) |
| GB (1) | GB1552221A (en) |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1391299A (en) * | 1964-03-25 | 1965-03-05 | Du Pont | Process for obtaining tinplate with high corrosion resistance |
-
1975
- 1975-05-01 GB GB1812875A patent/GB1552221A/en not_active Expired
-
1976
- 1976-04-28 FR FR7612497A patent/FR2309428A1/en not_active Withdrawn
- 1976-04-30 CA CA251,596A patent/CA1066221A/en not_active Expired
- 1976-08-13 BE BE1007553A patent/BE845146A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BE845146A (en) | 1976-12-01 |
| GB1552221A (en) | 1979-09-12 |
| FR2309428A1 (en) | 1976-11-26 |
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