ISO/DIS 8442-5

ISO/TC 186

Secretariat: SAC

Date: 2025-11-10

Materials and articles in contact with foodstuffs — Cutlery and table holloware —

Part 5:
Specification for sharpness and cutting wear resistance test of cutlery

DIS stage

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Contents

Foreword

Scope

Normative references

Terms and definitions

Sharpness testing

Wear resistance testing

General

Test length

Apparatus

Test medium

Test procedure

Evaluation / Expression of results

Calibration method

(normative) Sharpness testing

(normative) Apparatus for wear resistance testing

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

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This document was prepared by Technical Committee ISO/TC 186, Cutlery and table and decorative metal hollow-ware, in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 194, Utensils in contact with food, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This second edition cancels and replaces the first edition (ISO 8442-5:2004), which has been technically revised.

The main changes compared to the previous edition are as follows:

• Introduction of the term sharpness
• description of the foil pressure cutting test and foil pull cutting test
• introduction of a new evaluation method for cutting wear resistance test
• revision of the wear resistence test medium

A list of all parts in the ISO 8442 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found atwww.iso.org/members.html.

Materials and articles in contact with foodstuffs — Cutlery and table holloware —

Part 5:
Specification for sharpness and cutting wear resistance test of cutlery

This document specifies the sharpness and wear resistance of knives, which are designed for professional and domestic use in the preparation of food of all kinds, specifically of those knives intended for hand use.

This document describes test methods for sharpness measurement and for the evaluation of wear resistance of the cutting edge.

This document does not apply for hunting knives, pocket knives, razors or tool or utility knives (with trapezoidal blade for cutting carpets etc.). Knives with special shapes, e.g. herb chopping knives or highly curved boning knives, can only be tested in the style of this document since not all properties and test methods are applicable in a meaningful manner.

There are no normative references in this document.

For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

knife

cutlery intended to be used for the preparation of food, manually guided and in general having a cutting edge which can be featured with a serration or micro serration

sharpness

parameter, which reflects the force needed to cut into a defined test material with a defined cutting movement (see ISO 8442-1)

wear resistance

resistance of the cutting edge against wear, tested by cutting into an abrasive test material (see ISO 8442-1)

The test methods focus on the micro cutting wedge and its cutting edge. It is not the aim to measure the influence of the friction between the blade and the test material. At the beginning of the test procedure the test material is deformed. The force measured in the first moment of material separation (cutting) is defined as sharpness.

The apparatus for sharpness testing are described in Annex A.

NOTE Specific requirements are under study.

This test shall be carried out before any other physical or mechanical test so that edge performances are assessed in the “as received” condition.

The portion of the cutting edge of the blade to be tested shall be straight except for a maximum deviation of ±1 mm. The stroke length is 40 mm.

The apparatus for wear resistance testing is described in Annex B.

The test medium is described in Clause B.8.

Determine the portion of the blade (50 mm = 40 mm stroke + 10 mm test card width) which meets the straightness criterion (±1 mm deviation over the stroke length of 40 mm, see 5.2) and mark with a suitable marker. Mount the blade (edge uppermost) in the fixture and set the length to be tested level to within 0.5 mm at either end.

Load the apparatus with the test card and weights which combine to give the required 50 N test load (in the static condition) at the start of a new test.

Clamp the card in the holder with approximately 24 mm protruding and lower the assembly until the protruding medium rests on the edge of the blade and position of contact is 3 mm from the clamped edge.

Release any retaining clamp on the transverse slide and move the blade in forwards and backwards cutting strokes of 40 mm with the test card contacting the cutting edge of the blade throughout the whole cycle. Measure the depth of cut through the card pack at the end of each cutting cycle. Do not allow the blade cutting edge to contact the metal support bar. When more card is required, lift the card pack off the blade and feed forwards the whole pack by approximately 3 mm. Return the transverse slide back to the starting position with respect to the card clamped edge and carry out more cutting strokes.

Record the depth of cut on each cutting cycle, repeating until the predetermined number of cycles is completed for that type of blade. Tabulate the results showing cumulative card cut as per the example in Table 1.

Table 1 — Method of recording results (example)

A cutting cycle is defined by one forward plus one reverse stroke of the designated length of the blade against the test material. The depth of paper cut (in mm) during one cutting cycle is called c(i), where i is the index for the cycle number.

The following values are defined:

The decay factor (a) is defined in Formula (1) as

(1)

The starting value ( c(0) ) is calculated in Formula (2) as

(2)

The ideal curve for the cutting wear resistance follows the Formula (3)

(3)

The expected lifetime factor (ELF) is calculated in Formula (4) as

(4)

The theoretical total cutting performance (TTCP) is given in Formula (5) by

(5)

Initial Cutting Performance (ICP) in Formula (6) as

(6)

Total Cut Card (TCC) in Formula (7) as

(7)

A new calibration method is under study.

1. 
   (normative)
   
   Sharpness testing
   1. Test medium

The test medium is a PTFE foil with a defined thickness and width.

NOTE Thickness and width are still under study.

It should be used at room temperature in the test environment.

• 1. Test apparatus

The test apparatus consists of a motorized linear axis for the cutting movement, a blade holder to fix the test blade, a foil holder to fix the test medium and a load cell for measuring the cutting force.

• 1. Test procedure

Foil pressure cutting test(Figure 1 a)) : The test blade is moved in a unidirectional motion at a constant cutting speed v_c,D through the test medium, which is clamped in a radius profile. During the cutting movement, the force acting against the cutting direction is measured. The characteristic value is the maximum force when the cutting edge penetrates the test medium. This allows evaluation of the cutting edge sharpness and pressure cutting capability.

Foil pull cutting test(Figure 1 b) ): The blade is moved in a biaxial motion through the test medium at a constant cutting speed v_c,Z and v_c,D. The foil is clamped on one side only. During the cutting movement, forces act both in the plane of the foil and perpendicular to it. Characteristic values are the penetration force into the foil assessing the sharpness of the cutting edge, the pull cutting capability, and the resulting force profile. This profile enables conclusions about the homogeneity of the grinding quality.

a) Principle foil pressure cutting test

b) Principle foil pull cutting test

Key

v_c,D velocity of cutting towards the test medium

v_c,Z velocity of cutting perpendicular to the test medium

Figure A.1 — Principles of sharpness measurements

NOTE The exact test procedure is still under study.

1. 
   (normative)
   
   Apparatus for wear resistance testing
   1. General

A suitable apparatus for performing the wear resistance test is shown in Figure B.1 and comprises the elements of Clause B.2to Clause B.7.

Key

1 vertical slide

2 test blade

3 blade fixture

4 motor

5 longitudinal slide

6 transverse slide

7 cutting stroke direction

8 test medium

9 test medium holder

F downward force (50 N)

Figure B.1 — Schematic arrangement of a suitable test apparatus

• 1. Card strip holder

A rigid holder with a 10 mm wide aperture to hold the strips of card (max. 50 mm deep). The holder shall provide sideways restraint against the cutting force of the knife and a support bar above the card, which protrudes, from the holder to provide the reaction against the 50 N test load throughout the test. The card pack shall be clamped by a force of 130 N ± 2.5 N on the inboard side of the cutting line and any cut card shall be allowed to fall away freely (see Figure B.2).

No test shall be performed within 25 mm of the start of the new pack.

Dimensions in mm

NOTE x ≈ 20° , ICF - Independent clamping force 130 N ± 2.5 N

Figure B.2 — Arrangement of test medium, clamp and blade presentation

• 1. Counterbalance arrangement

An arrangement of add-on or counterbalance weights, which in conjunction with the card and holder, vertical slide element and all its fitting shall result in a total vertical static load at the interface between card and blade of 50 N + 2 N (average over the working range) at the beginning of each new test.

• 1. Blade fixture

A fixture, which holds the blade and presents the cutting edge uppermost and provides support against the test load and also a means of easy levelling of the test lengths. The centre line through the section of the blade shall be vertical.

When held in the fixture, the cutting edge of the blade shall be capable of cutting through strips of card cleanly without any undue frictional influences excepting that from the blade’s sharpened bevel against the face of the uncut card. The cutting edge of the blade shall be prevented from coming into contact with the metal support bar by means of an independent depth stop.

• 1. Transverse blade slide unit

A transverse frictionless slide unit, on which the blade fixture shall be mounted to reduce the influence of friction forces between the blade’s sharpened bevel and stack of the uncut card. This will allow movement of the blade away from the card holder during the cutting strokes, normal to the direction of the cutting strokes. At the beginning of the first stroke through each strips of card (50 mm thick) the point at which the blade starts its cut shall be 3 mm ± 0.2 mm away from the edge of the card holder/clamp. The end of the card pack should be straight and aligned to an approximate angle of 20° to the vertical to allow an approximately equal length of card beyond the cutting point.

• 1. Longitudinal blade slide unit

A longitudinal frictionless slide table, which provides the motion to the blade in the direction of the cutting strokes. It shall have a drive system, which is capable of producing a nominal 50 mm/s cutting speed, which is achieved by maintaining a more or less constant speed of 50 mm/s over at least 90 % of the specified stroke, with rapid acceleration and deceleration at the ends. This parameter will be verified over several non-cutting cycles and the result shall be 45 mm/s ± 0.5 mm/s average speed. The stroke shall be repeatable within 45 mm/s ± 0.5 mm/s average and verified over several non-cutting cycles of the table.

• 1. Card cut amount transducer

A displacement transducer, capable of measuring the depth of cut through the card pack at each cutting cycle, with a minimum resolution of 0.1 mm (i.e. 1/3 card thickness).

• 1. Test medium

A specially developed chemical pulp is produced in the form of sheets of card containing a controlled amount of abrasive material i.e. quartz. This card shall be pure chemical soda pulp without any other chemical additive except for the addition of silica in the proportion of 5 % ± 0.5 % by weight.

The average grain size of the quartz powder d_50% is 8 µm to 16 µm, the upper grain size d_95% is 25 µm to 50 µm.

The purity of the quartz powder should be at least 97.5 % SiO₂. Minor additions of Al₂O₃, Fe₂O₃, CaO, MgO, Na₂O or K₂O are allowed.

EXAMPLE Suitable silica powders are Millisil C400 or Sikron SH500. Millisil C400 and Sikron SH500 are examples of suitable products available commercially. This information is given for the convenience of users of this document and does not constitute an endorsement by CEN of these products

To satisfy the test arrangement the card is cut into 10 mm wide strips (with the fibres of the card grain flowing across the strip) and compiled into a pack maximum 50 mm deep when clamped under pressure of 130 N ± 2.5 N in a holder as shown in Figure B.2.

The physical properties of each strip shall be as specified in Table B.1.

Table B.1 — Physical properties

Before use, the test medium shall be conditioned in a controlled atmosphere of 55 % ± 5 % relative humidity at 20 °C ± 2 °C for a period of 24 h. The card shall be open to this atmosphere and used within 4 h of removal from it.