HEADING 90.24 - MACHINES AND APPLIANCES FOR TESTING THE HARDNESS STRENGTH COMPRESSIBILITY ELASTICITY OR OTHER MECHANICAL PROPERTIES OF MATERIALS (FOR EXAMPLE METALS WOOD TEXTILES PAPER PLASTICS).
78 COMMODITIES
9024.10 - Machines and appliances for testing metals
9024.80 - Other machines and appliances
9024.90 - Parts and accessories
This heading covers a wide range of machines and appliances for testing the hardness elasticity tensile strength compressibility or mechanical properties of various materials (e.g. metals wood concrete textile yarns and fabrics paper or paperboard rubber plastics leather). It therefore excludes :
(a)Instruments or appliances for examining the microscopic structure of materials (e.g. metallographic or other microscopes - heading 90.11 or 90.12) or for analysing materials or measuring properties such as porosity thermal expansion etc. (heading 90.27).
(b)Instruments or apparatus designed only for ordinary measurement or checking of width thickness etc. (e.g. of machined parts wire metal goods) (heading 90.17 or 90.31).
(c)Instruments for detecting faults fissures cracks or other defects in materials (heading 90.31).
The machines and appliances of this heading are generally used in industrial or research laboratories for testing manufactured articles (usually carefully selected or standard specimens). They may also be used during manufacturing processes in constructional work (in workshops building sites etc.) or to check goods on delivery in warehouses etc.
They may range from large mechanically electrically or hydraulically operated machines of considerable weight (several tons) to small portable or even pocket size instruments. Some " universal " types (e.g. for metal testing) can be used for hardness tensile bending etc. tests by means of separate attachments. Although they usually operate on the " start-stop " principle some are designed for automatic or semi-automatic operation (e.g. for testing large output off an assembly line). Test results may be ascertained either by direct reading (sometimes with the aid of a simple optical device such as a magnifying glass or even a built-in microscope or profile projector) or by separate microscopic examination of the test-piece (e.g. observation of ball-test marks on metal). In addition certain machines may have provision for recording the stresses strains etc. borne by the test-piece.
(I) MACHINES AND APPLIANCES FOR TESTING METALS
This group covers machines and appliances for :
(A) Tensile testing on test-pieces bars wire cables springs etc. Tensile tests are used to ascertain the elasticity breaking stress and many other important properties of a metal. Tensile testing machines are of various types (e.g. vertical or horizontal endless screw or hydraulic load types); basically however they each comprise jaws or clamps for holding the sample under test.
(B) Hardness tests on test-pieces bars machined parts etc. the hardness of a metal being measured in terms of resistance of that metal to indentation. These tests include :
(1) The steel ball indentation test (hardened steel or metallic carbide ball) or Brinell test. The indentation is produced by applying a continuous pressure (not by impact or by repeated blows) to the steel ball by means of a lever spring or piston; the diameter of the imprint is then measured with a microscope.
(2) The diamond pyramid indentation test. This test may be made by the Rockwell method (in which the depth of the indentation is measured with a dial comparator) or by the Vickers method (microscope measurement of the area of the indentation). Other forms of these tests are also used (Monotron Shore Knoop etc.) and there are also instruments for testing soft metals by means of a steel indenting tool (e.g. Rockwell method). The above three tests may be carried out by the same machine.
(3) The rebound test carried out by the aid of scleroscopes or sclerographs. A small hammer (usually tipped with a diamond pyramid) is released from a pre-determined height on to the surface of the piece under test. The harder the metal the higher will be the rebound of the hammer.
(4) The pendulum hardness test in which the oscillations of a pendulum resting on the specimen are observed. The pendulum consists of an inverted U-shaped cast iron body fitted in the middle with a steel ball.
(C) Bending tests.
(1) Impact tests carried out on bars (whether or not notched). The bar rests on two supports and is subjected to the repeated impacts of a ram until it breaks; its limiting resistance is thus determined.
(2) Pressure tests (mainly for bars) bending tests (springs).
(D) Ductility tests mainly used to test sheet metal. An indenting tool usually tipped with a steel ball is gradually pressed into the sheet up to the point of perforation; the first contact is recorded and the stress and deflection are then measured.
(E) Folding tests (sheets bars and wire) compression tests and shearing tests (mainly for cast iron).
(F) Fatigue tests. Test-pieces are not only submitted to simple stresses as described above but are also subjected to compound and varying stresses. These tests are carried out by means of rotating bending machines (the specimens rotate at high speed) or reversal torsional machines (in which the torsional direction is alternately reversed) electro-magnetic fatigue-testing machines etc.
(II) MACHINES AND APPLIANCES FOR TESTING TEXTILES
The main tests carried out by machines of this group include :
(1) Extensibility and resistance to rupture tests elasticity or tensile strength under strain tests and the like (and combinations of such tests). The material under test may be raw fibres or yarns ropes or cables ordinary fabrics webbing belts etc. These tests are made with the aid of dynamometers of various types usually named after their operating principle (e.g. pendulum or balance-lever dynamometers) or according to the material for which they are most frequently used (e.g. single yarn twisted yarn or rope glass fibre hank or skein fabric dynamometers); these tests may also be made by the use of extensometers.
Some dynamometers are equipped with a ball device for perforation tests on fabrics.
(2) Tests to detect changes in the dimensions of textile samples. The expansion or shrinkage of a sample of fabric is measured after it has been stretched in the dry and in the wet states.
(3) Wear and tear tests. These are carried out on textile goods liable to be exposed to friction (sheets cloths table linen etc.) and sometimes also on the yarn itself. These tests are carried out by means of abrasion-testers wear-testers etc.
A strip of cloth stretched at a suitable tension is progressively worn away by a friction instrument (an abrasive disc a rotating cylinder fitted with metal flanges a steel milling wheel etc.). Wear and tear resistance is measured by the number of revolutions required for the friction instrument to cause the fabric to break. The heading does not include instruments used to inspect textile materials (e.g. yarn uniformity testers; strain-testers to determine the tension to which yarn is subjected on warping-frames on spoolers etc.; yarn torsion counters and torsiographs to measure the torsion of yarns (heading 90.31).
(III) MACHINES AND APPLIANCES FOR TESTING PAPER PAPERBOARD LINOLEUM FLEXIBLE PLASTICS OR FLEXIBLE RUBBER
These tests are mainly concerned with tensile strength (measuring of extensibility break-load etc.) or resistance to perforation. They are effected by means of dynamometers similar in basic design to those used for textiles.This group includes bursting strength testers fold testers etc. (e.g. for paper) elasticity meters reboundimeters tensile testers abrasion machines plastimeters (e.g. for rubber or plastics).
(IV) MACHINES AND APLIANCES FOR TESTING OTHER MATERIALS
Most of these materials (e.g. wood concrete hard plastics) are subjected to tensile bending hardness compression shearing abrasion etc. tests by means of machines and apparatus similar in principle to those used for metal testing (by ball- imprint impact etc.).
The heading also includes a large number of instruments usually small in size designed to determine the tensile strength resistance to bending compression etc. of test-pieces moulded from foundry moulding sand. It also covers instruments designed for measuring the surface hardness of finished foundry moulds or mould cores.
PARTS AND ACCESSORIES
Subject to the provisions of Notes 1 and 2 to this Chapter (see the General Explanatory Note) parts and accessories of apparatus or appliances of this heading remain classified here.
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