THE EXTRUSION

In this process the aluminum is not liquid, but a malleable solid. Thus, it can take the form we want through pre-fabricated molds at the time of extrusion. The process resembles a tube of toothpaste that, when pressed, expels the cream into the shape of the tube spout.


Extrusion


- For the extruded products, the tolerances contained in ABNT NBR 8116 - aluminum and its alloys - are based on ASTM (ANSI H35.2 - M).

- Due to the constant updating of the NBR 8116 standard, due to the advances of the aluminum producing industries and the increasing needs of the industries that use extruded profiles, the values in this table are subject to change.

- In this work, we will present only the most usual table, and additional information may be obtained with the FEP technicians.

- The table shows the standard tolerances.

- When no tolerance is shown it must be established by mutual agreement between the buyer and the supplier.
Rectilinearity
Length
Final Cut
Permissible deviation of the frame ± 1 °

(1) For nominal diameter rebar, for bars nominal width.

(2) In order to obtain the permissible deviation in bars of more than one meter in length multiplies the value of the length in meters by the value of the deviation by meter.

(3) When there are two adjacent flaps, it is considered the least thick.

(4) When the space limited by the angle is all metal, the smallest metal thickness at the vertex of the angle is considered.
Height and width


(1) Not applicable in O tempering, tubes in rolls or tubes with a wall thickness of less than 0,5 mm or 2,5% of the outer diameter or diameter of the equivalent circumference (diameter of the circle whose circumference measures the perimeter of the tube) .

(2) Example: In an extruded rectangular tube of 76,20 x 34,10 mm the width tolerance (76,20) is ± 0,63 mm and in the height (38,10) it is ± 0,89 mm.
Wall Thickness - Drawn Tubes
Rectilinearity- Drawn Tubes
Profile Transversal Section Tolerance
Rebar, bars and extruded profiles. Tolerances at transversal section in millimeters for more or less. These tolerances apply to extruded profiles except for annealing O (baking state) and tempering F (as manufactured).

(A) These standard tolerances apply to common profiles; larger tolerances may be required for some profiles and narrower tolerances for others may be possible depending on the prior agreement between the buyer and the supplier.

(B) Tolerances for extruded profiles in special alloys and tempers shall be be agreed between the buyer and the supplier.

(C) The tolerance applicable to a composite dimension of two or more components is the sum of the tolerances of the component dimensions, if all are indicated.

(D) If a specified dimensional tolerance is not symmetric, then the standard tolerance value to be applied is the one that would be applied to the average of the maximum and minimum dimensions permissible for the tolerance initially specified.

E) (E) These tolerances do not apply to the "X" and "Z" dimensions of the example, even when "Y" is 75% or more of "X". For tolerances applicable to dimensions "X" and "Z" use columns 4, 5, 6, 7, 8 and 9 depending on the distance A.

(F) The tolerance in the wall thickness of the tubular or semi-tubular profiles shall be agreed between the buyer and the supplier when the nominal thickness of one wall is three or more times larger than the opposite wall.

(G) At points situated at 5 mm or less from the beginning of the flap, the tolerances for column 2 shall apply.

(H) The following tolerances are applied in the case of tubular profiles:

• for the width (L), the tolerance is given in column 4 for height (H);

• for height (H), the tolerance is given in column 4 for width (L);

• In no case can the tolerance for the width or height be less than the tolerance for the corners (column 2, dimensions of the metal).

Example of a tubular profile having rectangular outer dimensions of (25 x 75 mm):

• the tolerance at the width is ± 0.46 mm and the tolerance at the corners (column2), dimensions of the metal) is 0.60 mm for the width and ± 0.25 mm for the height. Note that the tolerance of 0.46 mm in column 4 should be adjusted to 0.60 mm in order not to be less than the tolerance in column 2.

(l) When the specified dimensions are external and internal. Instead of the wall thickness itself, the permissible deviation (eccentricity) indicated in column 3 applies to the average wall thickness.

(J) In the case of standard tubular profiles, the standard tolerance for the standard thickness, for the wall thickness of the extruded round tubes is applied.

Examples:

(a) internal void dimensions (tubular profiles): all dimensions indicated by "Y" are classified as "metal dimensions" within the tolerances given in column 2. Dimensions indicated by "X" are classified as "dimensions including internal voids" , the applicable tolerances being determined by column 4, unless 75% or more of the size is metal, in which case column 2

(b) dimensions of the voids not totally circumscribed by metal. The tolerances applicable to dimension "X" can be classified in one of the following three cases:

• Localize the dimension (X) in column 1;

• Determine which column, from 4 to 9, is applicable, depending on the distance (A);

• Localize the correct tolerance between columns 4 and 9, in the same line as dimension (X);

• localize the distance (B) in column 1;

• determine which column, from 4 to 9, is applicable depending on distance (A);

• localize the correct tolerance between columns 4 and 9, on the same line as the value chosen in column 1;

• the tolerances applicable to the dimensions (X) are not determined by the scale but by the standard tolerances applicable to the angles (A).

Torsion
Angularity
Diameters


(1) Not applicable in O tempering, tubes in rolls or tubes with a wall thickness of less than 0,5 mm or 2,5% of the outer diameter or diameter of the equivalent circumference (diameter of the circle whose circumference measures the perimeter of the tube) .

(2) Example: In an extruded rectangular tube of 76.20 x 34.10 mm the width tolerance (76.20) is ± 0.63 mm and the height (38.10) is ± 0.89 mm .
Wall Thickness - Extruded Tubes


Length - Drawn Tubes