FR2696421A1 - Steel for opening packaging by breaking a line of least resistance. - Google Patents

Abstract

The packaging according to the invention is of the type in which the lid is to be opened by breaking a line of lowest strength arranged in a part of the wall made of steel sheet. The steel of which the sheet consists has a carbon content of between 0.02 and 0.08 % by weight and a boron content of between 0.002 and 0.004 % by weight, the steel also containing nitrogen, the ratio of the boron content to the nitrogen content being higher than 0.8 and the remainder being chiefly iron and residual elements.

Description

The present invention relates to the packaging of the

  opening type by breaking a line of least resistance

  So called easy opening box.

  We know of such packages which are for example intended to contain a drink, canned or

others products.

  They have a cover in which is arranged a line of least resistance, for example a

  incision, delimiting an opening panel.

  An actuating ring is fixed on the panel

opening using a rivet.

  The opening is caused by a tensile force on the actuating ring so as to break the metal at the level of the incision, the opening panel possibly being able to include a zone of connection with the cover so as not to come off. completely from the latter. Such packaging can be produced in

  aluminum but they are then relatively expensive.

  When made from steel, for

  reduce their cost, we commonly use a sheet metal

  standard low carbon steel shot annealed

  continuous at approximately 680 OC and tinned.

  The mechanical characteristics of such a steel in the tinned state are as follows: yield strength (Re) in transverse direction of the order of 415 M Pa, breaking load (Rm) in transverse direction of

around 430 M Pa.

  The steel used for the production of such packaging must make it possible, on the one hand, to form the fastening rivet of the opening ring and, on the other hand, to break the line of least resistance easily without having

  to exert too much effort.

  For this, the breaking load Rm must not be too high because otherwise the opening force to be exerted to break the line of least resistance must be significant. Likewise, the yield strength ratio Re on breaking load Rm must be close to 1 so that the steel is sufficiently weakened to cause a

easy opening.

  However, this Re / Rm ratio should not be too high, that is to say too close to 1, because in this case, the steel being very weakened, it becomes almost impossible to form the rivet, this operation requiring

  deep drawing of the steel of the cover of the

  ballage. Now, the standard steel commonly used, the elastic limit Re of which is equal to approximately 415 M Pa and the tensile strength Rm of the order of 430 M Pa results in a

Re / Rm ratio of the order of 0.96.

  An easy-opening cover made with such a steel has a high opening force, due to the value of Rm and a residual thickness at the level

  relatively large incision.

  In addition, the yield point

  is important, which causes the formation of vermiculu-

  apparent when stamping the packaging,

  detrimental to the aesthetic appearance of the latter.

  To overcome these drawbacks, the object of the invention is to provide a packaging of the type with opening by breaking a line of least resistance, for which the overall effort required for opening is reduced, while having an improved appearance. after stamping the packaging, and good ability to form the rivet.

  To this end, the invention relates to a packaging

  metal beam of the opening type by rupture of a line of weakest resistance arranged in a wall part of steel sheet, characterized in that the steel constituting the sheet has a carbon content of between 0.02 and 0, 08% by weight and a boron content of between 0.002 and 0.004% by weight, the steel also containing nitrogen, the ratio of the boron content to the nitrogen content being greater than 0.8 , the rest being

  mainly iron and residual elements.

According to other characteristics:

  the weight composition of the steel

  killing the sheet is preferably as follows, in thousandths of a percent: carbon: 50 manganese: 200 phosphorus: 10 nitrogen: 3.5 aluminum: 30 silicon: 5 boron: 3

  the remainder being iron and elements

  duels. The invention also relates to a steel sheet intended for the production of a packaging and

  characterized in that the ratio of its elastic limit

  cited on its breaking load is between 0.87 and

  0.96, preferably between 0.91 and 0.92.

  The invention also relates to a method of

  manufacture of a sheet suitable for carrying out the em-

  embossing according to the invention, in which the sheet is obtained by continuous rolling, and characterized in that after this continuous rolling, the sheet is subjected to an annealing on base carried out for 8 to 10 hours at a temperature

  between 550 and 6500 C approximately, the rise in temperature

  turing from room temperature being carried out in approximately 20 hours, then the sheet is subjected to cold re-rolling with an elongation rate of between 5% and%. The invention will be better understood on reading

  the detailed description which will follow, given as

example.

  Reducing the effort required to open

  ture involves the use of a steel having a relatively low yield strength, which further facilitates the winding of the opening panel after breaking

  the incision, and by a high Re / Rm ratio.

  On the contrary the good aptitude for the formation of the rivet passes by the use of a steel having a report

Low Re / Rm.

  The appearance of the packaging and its corrosion resistance are improved by the use of a sheet

  having a structure with fine equiaxed grains and not presenting

  as long as there is no elastic limit plateau.

  Obtaining the required mechanical characteristics and the equiaxial microstructure are the result of: the use of a sheet made of steel having a determined composition, the adaptation of a sheet manufacturing process comprising annealing on the basis and a re-rolling at

cold.

  More precisely, the packaging according to the invention is produced from a steel sheet whose carbon content is between 0.02 and 0.08% by weight and the boron content is between 0.002 and 0.004% by weight, the steel also containing nitrogen in an amount less than 0.005%, the ratio of the content of

  boron on the nitrogen content being greater than 0.8.

  A carbon content of less than 0.02% is difficult to achieve with conventional production processes and can lead to mechanical resistance

insufficient cover.

  If the carbon content was greater than 0.08% by weight, the tensile strength Rm of the sheet intended to produce the packaging would be too great.

  It has been found that to obtain a sheet per-

  making it possible to produce a packaging according to the invention, the structure of which is equiaxial, the ratio of the boron content to the nitrogen content must be greater than 0.8, the boron being limited to 0.004% because, for a higher content, there is an increase in the mechanical characteristics of the sheet and we see a preferential oxidation appear on the edge of the product, which is unacceptable from an aesthetic point of view. The weight composition of the steel constituting the sheet intended for packaging according to the invention is preferably as follows, in thousandths of a percent: carbon: 50 manganese: 200 phosphorus: 10 nitrogen: 3.5 aluminum: 30 silicon : 5 boron: 3

  the remainder being iron and elements

  duels. The process used to make the suitable sheet

  for packaging according to the invention, consists in that a

  After continuous rolling of the steel described above, the sheet is subjected to annealing on a basis carried out for 8 to 10 hours at a temperature between approximately 550 and 6500 C, the rise in temperature from ambient temperature being carried out Approximately 20 hours The sheet is then subjected to a cold re-rolling with a rate

  elongation between 5 and 10%.

  The combination of the composition of steel and

  suitable manufacturing process makes it possible to obtain the

  following mechanical characteristics: Re = 310 M Pa approximately, Rm = 340 M Pa approximately. The ratio of the elastic limit to the

  breaking load is between 0.91 and 0.92.

  A package is thus obtained, the opening of which is fairly easy and having good aptitude for formation

of the rivet.

  On the other hand, such steel allows to support

  a significant indentation before damage redhibi-

  that is, the incision can be more pro-

  based, thereby allowing an opening effort

lesser.

  Indeed, in the case of standard low carbon steel, the remaining thickness at the bottom of the incision should not

  not be less than 70 microns under penalty of damage-

  prohibitive, while this remaining thickness at the bottom of the incision can drop to 50 microns in the

case of the steel according to the invention.

  This packaging made from a sheet metal

  fine-grained equiaxed structure avoids, when forming

  tion of the rivet, the appearance of deformation roughness due to sagging, which is detrimental to

  the appearance of the packaging and the holding of a possible varnish

  tuel. The presence of boron also makes it possible to slow down the coalescence of the cementite which results in a greater regularity of the effort to be provided during

opening the package.

Claims (4)

  1 Metallic packaging of the type with opening by breaking of a line of weakest resistance arranged in a wall part of sheet steel, characterized in that the steel constituting the sheet has a carbon content of between 0.02 and 0.08% by weight and a boron content   between 0.002 and 0.004% by weight, the steel contains   also with nitrogen, the ratio of boron content to nitrogen content being greater than 0.8, the rest   being mainly iron and residual elements.   2 Packaging according to claim 1, charac-   characterized in that the weight composition of the steel   titrating the sheet is preferably as follows, in thousandths of a carbon percent: 50 manganese: 200 phosphorus: 10 nitrogen: 3.5 aluminum: 30 silicon: 5 boron: 3   the remainder being iron and elements   duels. 3 Sheet steel for packaging according to   claims 1 or 2, characterized in that the ratio   of its yield stress on its breaking load is between 0.87 and 0.96.   4 sheet steel according to claim 3,   characterized in that the ratio of its elastic limit   quoted on its breaking load is between 0.91 and 0.92. Method of manufacturing a sheet according to   claims 3 and 4, comprising rolling in   continuous, characterized in that after this continuous rolling, the sheet is subjected to a basic annealing carried out for 8 to 10 hours at a temperature between approximately 550 and 6500 C, the rise in temperature from ambient temperature being carried out 20 hours approximately, 5 then the sheet is subjected to a cold re-rolling with a   elongation rate between 5 and 10%.