Practical procedure for preparing a technical sheet defining the right metal for a container body type “3 pieces”



We have already discussed this topic in another work on this website, but it was focused on the specific case of funds. We refer to the article:

– Specifications of tinplate for lids

We return to it now, but focusing on the case of bodies for containers “3 pieces”. As we said in that work, it is important to have a good document on the basic matter in the metal sector, tinplate, TFS, aluminum … It is useful for a multitude of departments or tasks. Among others:

– Technical office

–          Base document to define the order of raw materials by the Purchasing Department.

–          Calculation of costs.

–          Base document in the coil cutting operation.

–          Preparation of photoliths by the corresponding Study.

–          Preparation of printing plates and rollers for lithography.

–          Production: Base document for the adjustment of equipment: Scroll, presses, shears …

–          Quality control, for verification of records and cuts.

–         Etc.



We are going to focus on this work, on how to prepare a metal specification, for packaging bodies with side seam, round or in any other way. We will see what data are the most convenient to include in it, and how each of them is calculated.

To follow the procedure better we will do it taking a practical example, in our case it will be the one corresponding to an aerosol container of diameter 52 and height 132 mm. It is designated by the diameters of the body, bottom and dome, followed by its height. In this case it would be: RO – 52/50/48 x 132.

The first data that must be known is the dimension of the rectangle of material, from which the body of the container is going to be formed, that is, what we will call the “development of the body”. For our case, the values ​​are 165.8 x 135.6. The calculation necessary to carry these values ​​we assume that it will not present difficulties for our readers. With it we can deduce the dimensions – width and length – of the sheet that will be obtained from a coil. We will not enter into this calculation either, since he himself is easily deduced as it will be seen throughout the article

Known the dimensions of the sheet, it will be possible to begin to make the specifications of the specification, drawing the sheet and detailing all the dimensions that define its geometric composition. See figure # 1. We will comment on these drawings later. As you can see, this sheet has two parts. A first superior, with a series of boxes where the data that we are calculating will be reflected, and the lower one that will present the drawing of the sheet with all its data.

The first five boxes are purely informative and they specify:

–          Designation of the element

–          No. of line that will manufacture it, if applicable.

–          Date of completion of this document

–          Basic characteristics of the body.

–          Lost or overlap for welding the side seam

Figure No. 1: Specification of metal for aerosol bodies RO 52/50/48 x 132

 Then we enter the definition of the sheet of material to be used. To determine the ideal width and length of the same, we must take into account a number of factors that the size of the sheet must meet, the main ones are:

–          Tin price of purchase price, so as not to incur extra costs for dimensions. We must ensure that they adapt to the minimum rate for measures.

–          Maximum and minimum dimensional capacity of the coil cutting line. They must be within this capacity

–          To be included between the maximum and minimum dimensions allowed by the varnishing and printing lines.

–          Dimensional capacities of the cutter of the production line, that is to say for the cutting of the bodies.

The analysis of all this, and the corresponding calculation, will result in a valid tinplate measurements to be used during the process without problems. The length of the sheet is a multiple of the measure of the development of the cylinder of the body of the container, plus additional cuts. The width of the blade – and therefore of the coil – is a multiple of the measurement of the height of the cylinder of the body, plus additional cuts. That length and width of the sheet is what must be taken into account for the dimensional limitations of the equipment.

The additional cuts must be the minimum that allow an adequate work of the line cutter. These are usually between 2 to 3 mm. Sometimes the same sheet dimension can be used for several uses, as is the case of the example shown, and then they can be higher. The use of a sheet for multiple uses is permissible when the consumptions in each packaging format are low.

Once the coil width is known, the rolling direction of the base steel, ie the direction of the grain , is automatically set. In the case of bodies, it must be parallel to the base thereof.

Depending on the dimensions of the body of the container, its mechanical strength and its use, we will be given another set of data such as:

–          Tin coating

–          Annealing

–          Passivation

–          Surface finish

–          Quenching

–          Thickness

We do not stop to delve into these parameters because they are well known, and if required you can consult the works of this Web:

Basic notions about tinplate 

All these values ​​must be written down on the corresponding boxes of the specification card.

We now enter into the determination of a series of interesting data, valid for later calculations in other phases of the process.

Units per sheet : Indicates the number of bodies obtained per sheet, 25 in our example.

Leaves by% 0 : Shows the number of sheets needed to make a thousand bodies. It is obtained by dividing 1000 by the number of units per sheet. (1000/25 = 40)

Both data are interesting to calculate the number of precise sheets to cover a specific packaging order.

Surface per sheet: It gives us in m2 the area of ​​the sheet. It is obtained by the product of the length (cutting line pitch) by the coil width expressed in m. (0.840 x 0.686 = 0.57624m2)

m2 per% 0 : Required tinplate surface to make 1000 bodies. It is the product of the surface per leaf per leaves per% 0 . (0. 57624 x 40 = 23,049 m2)

Ratio : Indicates the ratio of size between the surface of the sheet and that of the sheet taken as a unit in the tinplate market, which is a sheet of dimensions 20 “x 14” (508 x 355.5 mm = 180594 mm2 = 0.180594 m2) .

Ratio = 0.57624/0.180594 = 3.1899

Base box by% 0 : Before determining this data, we will define what is “base box”. It is a unit of measurement widely used in the tinplate market. It is a multiple of the unit sheet (20 “x 14”). There are two types of “base box”:

American base box : Tinplate media unit per surface. It is equal to the surface of 112 sheets of dimensions 20X14 inches or what is the same, 31,360 square inches and equivalent to 20.23 square meters. It is used mostly in the American market. 1 base box = 1.1201 European base box = 0.2023 places

European base box: Tinplate media unit per surface. It is equal to the surface of 100 sheets of dimensions 20X14 inches or what is the same, 28,000 square inches and equivalent to 18.06 square meters. It is used preferably in the European market. 1 European base box = 0.8928 base box = 0.1806 places

Therefore the data ” base box per% 0 ” reflects the base boxes needed for tinplate to make 1000 funds. It is determined by dividing the surface m2 by% 0 by the surface of the base box. According to the American or the European would be used:

American base box by% 0 : 23.049 / 20.23 = 1.1393

European base box per% 0 : 23.049 /18.06 = 1.2762

Sita by% 0: It is another way of expressing the same previous data. The SITA is another unit of measurement per surface of the tinplate and is defined:

–          SITA: Tinplate measurement unit per surface, equal to 100 square meters (International System Timplate Area). Equivalent to 4,943 base boxes or 5,537 European base boxes

Therefore, “by% 0 ” is the number of sites needed to manufacture 1000 bodies and is calculated by dividing the surface m2 by% 0 by the surface of a site. (23,049 / 100 = 0.23049 places)

All this data obtained: Surface per sheet, ratio, m2 per% 0, base box per% 0, and per% 0 , have several utilities, among others:

–          Calculation of the cost of a tin order to the steel industry, the rates according to the country of origin of the merchandise, can use any of these units.

–          Calculation of the cost of an order of lithography or varnishing of sheets. When you use third parties to perform this work, your rates also use these units.

–          Internal consumption calculations.

Weight per sheet: It is determined from the volume of a sheet by the density of the steel. Expressed in Kg. Would be:

 Weight per sheet = = (57.624 x 0.19 / 100) x 7.85 = 0.8594 Kg

Weight per% 0 : It is the weight of tinplate necessary to manufacture 1000 bodies. The equal to the weight per sheet multiplied by the leaves by% 0.

                Weight by% 0 = 0.8594 x 40 = 34.377 Kg

Weight box 100 sheets : It is the weight of a pack of 100 sheets of this material.

Weight box 100 sheets: Weight sheet x 100

Weight box 100 sheets: 0.8594 x 100 = 85.94

These last two data are useful for:

–          Calculation of the transport price.

–          With certain suppliers, for the calculation of the price of the material.

% utilization: It informs of the net percentage of metal used to manufacture the bodies.

% utilization = body area x number of bodies x 100 / surface per sheet.

% profit = 165.8 x 135.6 x 25 x 100/576240 = 97.54%

This information is necessary for the calculation of the standard cost of the body.

Determined all these values ​​are reflected on their corresponding boxes.

It could add other data depending on the particular needs of each one, such as: tinplate lubrication, internal code of this material, etc.

As we have already indicated above, the specification is completed with the drawings:

1º.- Of a developed body, that is to say the rectangle of metal necessary for its formation with its measurements. These include:

–          The measures of the rectangle

–          The necessary reserves of varnish and lithography in the welding area. To represent both faces – interior and exterior – you can draw the fragmented body, see drawing # 1.

–          The limits of texts, ie the areas of both ends of the body that will be affected by the closure, and therefore should not have texts or codes, as they can disappear when closing the container.

2º.- Of the complete sheet of metal, with the distribution of bodies on it and their corresponding margins. It will indicate:

–          The measurements of the sheet.

–          The margins for trimming and the net measures for obtaining the bodies.

–          The distance to the edge of the sheet, from where the texts can start (14 mm in our case).

–          The reference points for lithography and varnishing operations (tweezers and bowl). In our example they are represented by small triangles ..

–          The feed senses of the sheet in lithography, varnishing and cutting operations. They are represented by arrows.

–          The orientation of the images and texts in the print, in relation to the sheet. It is indicated by the word “Impression”.

All these data are very useful for a correct use of the metal packages during the whole process.

We have ended the preparation of the tinplate specification.

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