Foreword
ISO (International Organization for Standardization) is a global federation of national standards bodies (ISO member institutions). The work of formulating international standards is usually carried out through ISO technical committees. Each member institution interested in the subject of the technical committee has the right to represent the committee. Governments and non-governmental international organizations in contact with ISO also participated in this work. On all issues of electronic technology standardization, ISO works closely with the International Electrotechnical Commission (IEC).
International standards are drafted in accordance with the rules given in Part 2 of the ISO/IEC Directive.
The main task of the technical committee is to prepare international standards. The draft international standard adopted by the technical committee has been distributed to member institutions for voting. To be published as an international standard, at least 75% of the voting authority must be approved.
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ISO 21181 is prepared by technical committee ISO/TC 41, pulleys and belts (including belts), subcommittee SC 3, conveyor belts.
This International Standard is based on EN 1723:1999 developed by CEN/TC 188.
Introduction
Many applications of lightweight conveyor belts require it to be tensioned first, and then to change its length by adjusting any rollers. In this case, the tension in the belt will change throughout the life of the belt. This is due to the following two effects: permanent stretching and relaxation of the belt, both of which will change its actual elastic modulus . It is important to have a way to determine how the tension changes. The test performed cyclic stretching between two defined elongation states in two cycles. It has been found through experiments that the tension decreases exponentially. You can measure the tension and then calculate the “relaxed modulus of elasticity” defined here. It is important to note that this is not a true modulus of elasticity, because it includes elements that are permanently stretched; however, it has great practical value in determining the final tensile force, except in the case of larger permanent stretch. This International Standard aims to meet the requirements of such applications.
1 Scope
This International Standard specifies a test method for determining the relaxation modulus of light-duty conveyor belts according to ISO 21183-1 or other conveyor belts that do not apply to ISO 9856.
2 Normative references
The following reference documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated reference documents, the latest version (including all amendments) is applicable to this standard.
ISO 7500-1:2004, Metallic materials-Verification of static uniaxial testing machines-Part 1: Tension/compression testing machines-Verification and calibration of force measurement systems
ISO 9856, Conveyor belts-Elasticity and permanent elongation and elasticity Determination of modulus calculation
ISO 18573: 2003, Conveyor belts-Test atmosphere and conditioning period
ISO 21183-1, Lightweight conveyor belts-Part 1: Main characteristics and applications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
Modulus of Elasticity
The force per unit width of the conveyor belt.
Note 1: It is expressed in Newtons/mm belt width and is represented by the symbol M in ISO 9856.
Note 2: The definition of this term is different from the definition usually used in engineering. The definition is expressed in stress units, that is, the force per unit cross section, and is expressed by the symbol E; (for example, see ISO 527-4).
3.2
Elastic modulus
The force required to extend the original length of a representative optical conveyor belt test piece, in Newtons per unit width.
Note 1: The force is represented by the symbol k, so the elastic modulus is represented by the symbol k 1%. This value is also referred to as “a tensile force with 1% elongation per unit width” or “k 1% value”. It is expressed in Newtons per millimeter.
Note 2: In EN 10002-1:2001, the symbol k is used to indicate the scale factor.
3.3
Relaxed elastic modulus
After 500 cycles between the predetermined extension limit, the elastic modulus of the light conveyor belt.
Note 1: The k 1% value of the new conveyor belt is higher than the k 1% value of the loose conveyor belt in use. The relaxation occurs after the exponential function.
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References
[1] ISO 527-4, Plastics—Determination of tensile properties—Part 4: Test conditions for isotropic and orthotropic fiber-reinforced plastic composites
[2] EN 10002-1: 2001, Metallic materials-Tensile test-Part 1: Test method at ambient temperature
