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1、= 4851903 0617923 dl12 TECHNICAL REPORT IS0 TR 11444 First edition 1995-07-1 5 Quality of sawn wood used for the construction of pallets Qualit des bois utiliss pour la fabrication de palettes Reference number ISOTTR 1 1444:1995(E) COPYRIGHT International Organization for Standardization Licensed by
2、 Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services ISO/TR 11444:1995(E) = Li851903 Ob37924 759 Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0
3、member bodies). The work of preparing International Standards is normally carried out through IS0 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, govern
4、mental and non-governmental, in liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The main task of technical committees is to prepare International Stan- dards, but in ex
5、ceptional circumstances a technical committee may pro- pose the publication of a Technical Report of one of the following types: - type 1, when the required support cannot be obtained for the publi- cation of an International Standard, despite repeated efforts; - type 2, when the subject is still un
6、der technical development or where for any other reason there is the future but not immediate possibility of an agreement on an International Standard; - type 3, when a technical committee has collected data of a different kind from that which is normally published as an International Standard (”sta
7、te of the art”, for example). Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they can be transformed into Inter- national Standards. Technical Reports of type 3 do not necessarily have to be reviewed until the data they provide are consi
8、dered to be no longer valid or useful. ISOflR 11444, which is a Technical Report of type 2, was prepared by Technical Committee ISOflC 51, Pallets for unit load method of materials handling. This document is being issued in the type 2 Technical Report series of publications (according to subclause G
9、.4.2.2 of part 1 of the ISO/IEC Di- rectives, 1992) as a “prospective standard for provisional application” in the field of sawn wood used for the construction of pallets because there is an urgent need for guidance on how standards in this field should be used to meet an identified need. 8 IS0 1995
10、 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Ca
11、se Postale 56 CH-121 1 Genve 20 Switzerland Printed in Switzerland II COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services Y853903 Ob37925 695 8 IS0 ISO/TR
12、 11444:1995(E) This document is not to be regarded as an “International Standard”. It is proposed for provisional application so that information and experience of its use in practice may be gathered. Comments on the content of this document should be sent to the IS0 Central Secretariat. A review of
13、 this type 2 Technical Report will be carried out not later than two years after its publication with the options of: extension for another two years; conversion into an International Standard; or withdrawal. Annex A of this Technical Report is for information only. . 111 COPYRIGHT International Org
14、anization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services ISO/TR 11444:1995(E) N 4BSI1903 0637926 523 0 IS0 Introduction Components of wooden pallets typically exhibit major differences i
15、n physical and mechanical properties between pieces of identical shape, size and species. These differences are caused by natural variations in the growth of a living tree, the anisotropic characteristics of wood, and the manufacturing practices used in the conversion of wood into industrial and con
16、sumer products. Each of these differences significantly alters the physical, mechanical and aesthetic properties of wood and wood by- products. The properties of wooden pallets of like design will vary significantly if the size, frequency, location and type of variation are not controlled. For ex- a
17、mple. a large knot located above the notch cut into a wooden stringedbearer can cause potentially catastrophic failure of a pallet in bending, even when the pallet is carrying well below its rated load. Some of the variations affecting the physical and mechanical properties of wood are a direct resu
18、lt of infestation or plant diseases such as Amer- ican or European chestnut blight and Dutch elm disease. The unrestricted intercontinental distribution of pallets containing infested wood can and has resulted in the devastation of unresistant timber species. Reasons for recognizing natural variatio
19、ns in wood in order to control the quality of sawn wood in pallets include: - assembly of the most cost-effective pallet; - selection of a superior pallet at minimal cost; - determination of the life cycle cost between pallets of differing grades and quality; - prediction of the strength of pallets
20、of like design; - prevention of potentially dangerous failure; - control of the spread of plant disease. The Technical Committee ISO/TC 51 has therefore decided to publish these guidelines, prepared by Working Group WG 5, in the form of a Technical Report. In view of the way in which current IS0 tes
21、t methods and performance requirements for pallets are specified and the general move by national and international standardization bodies away from specifying strict ma- terial quality standards, this Technical Report does not provide grading rules intended to ensure a minimum strength quality of w
22、ood. It is es- sential that it remains possible to meet the performance requirements specified in ISO/TR 10233 using any hardwood or softwood, from any country in the world, by modifying the wood or fastenings content to achieve the required performance. iv COPYRIGHT International Organization for S
23、tandardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services = q53903 Ob17927 468 8 IS0 ISO/TR 11444:1995(E) The guidelines, although related primarily to wooden pallets, may also be of value in relation t
24、o the construction of wooden packaging for industrial or agricultural purposes. A list of International Standards related to this Technical Report is given in annex A. V COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organiz
25、ation for Standardization Licensed by Information Handling Services m Y851903 Ob17728 3T4 TECHNICAL REPORT Q IS0 ISO/TR 11444:1995(E) Quality of sawn wood used for the construction of pallets I Scope This Technical Report gives information on the faults and features which may affect sawn wood used f
26、or the construction of pallets, and provides guidance on their effects in relation to the physical and mechanical properties of both components and complete wooden pallets. It is strongly recommended that these guidelines be followed when wooden pallets are constructed for testing in accordance with
27、 IS0 861 1, while their use in pallet manufacture should provide a more consist- ent level of performance. NOTE 1 In view of the different timber species used for pallet construction in various parts of the world, it may be appropriate for member bodies adopting this Technical Re- port to add inform
28、ation about the characteristics of species used for the construction of pallets in their respective countries. 2 Moisture content 2.1 A proportion of the water in wet wood (around 25 %) is chemically bound in varying degrees to the wood fibres. Living trees and freshly felled sawn tim- ber can conta
29、in even more water than this (up to 200 % of free water, with even more in certain species). 2.2 There are two methods of measuring moisture content in common use. The most common method, a rapid test using an electrical moisture meter, is an essentially non-destructive test which is based upon the
30、principle that the electrical resistance of wood varies with its moisture content. Meters are com- monly marked to indicate a range between 6 % and 50 % moisture content, but their accurate range is normally from 9 % to 25 %. A skilled user can obtain results between these limits within +_ 2 % of th
31、e true moisture content. They are particularly appropriate for pallet work where extreme accuracy is not needed. The other method used takes at least several hours to achieve a reading and is destructive, in that it in- volves taking the whole piece of wood (or a tiny rec- tangular cut sample), weig
32、hing it to determine the mass of wood plus the water it contains, drying it to obtain the dry mass and calculating the moisture content as follows: Percentage moisture content = (mass of wet wood - mass of dried wood) mass of dried wood x 100 NOTE 2 mass of dry wood has a moisture content of 1 O0 %.
33、 Wood in which the mass of water is equal to the Known as the “oven-drying method“, this is the more precise method, but is only necessary for accurate testing or for research work. 2.3 Before wood is stored or used to construct pallets, it is usually necessary to remove a portion of the water it co
34、ntains. The reason for drying prior to storage is that wood of many species will decay if kept at a high moisture content for long periods and, even in the short term, susceptible species will suffer from mould and staining (see clause 4). Examples of this are the blue stain that particularly affect
35、s pine species, although spruces and others are also sus- ceptible. Below about 20 % moisture content, a level known as the decay safety line (timber line), wood is generally safe from such discoloration or damage. 1) Moisture content can be above 100 % because of the method of definition where the
36、mass of water is expressed as a percentage of the oven-dry mass of the wood. I COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services - 9 Li853903 Ob37929 23
37、0 9 Common Origin Botanical name name ISO/TR 11444:1995(E) Mean bending strength (N/mm2 1 20 % moisture Green content (air dry) 2.4 Wet pallets are less stiff (.e. bend more under a given load) and less strong (.e. have a lower break- ing strength and a lower maximum working load) than dry pallets.
38、Allowance needs to be made for this both during the test and in actual usage, since their per- formance when under load can vary enormously with a change in moisture. The change can be typically, for Douglas fir, a reduction of 19 % in terms of strength comparing green timber with air-dry, or a 23 %
39、 change for European redwood (see table1 for ex- amples). Pseudofsugal 54 I 66.6 I menziesii Douglas 1 Canada 1 fir I I I I I I I I I 44 I 57,l I Eastern Redwood I Europe 1 $: a grain detection tool may be needed. 8.3 Slope o f grain weakens wood under bending stress in that, as the gradient of slop
40、e increases, a greater proportion of stress is carried across the grain rather than along the grain. Since in wood the ratio of strength across the grain to strength along the grain is very low (typically 1 :50), substantial strength loss can result from excessive grain slope. 8.4 If critical compon
41、ents do not have grain slope exceeding 1 :8, then no significant strength reduction occurs. Less critical elements can tolerate the small strength loss associated with grain slope of 1:6. Figure 3 - Grain slope in pallet stringer Unit length - - Figure 4 - Measurement of slope of grain 4 COPYRIGHT I
42、nternational Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services 0 IS0 ISO/TR 11444:1995(E) 9 Rate of growth 9.1 spacing of annual rings on board ends. pressed in kilograms per c
43、ubic metre. The mass of wood in a given volume changes with the shrinking and swelling caused by changes in moisture content, so the term “rela- tive density“ is indefinite unless the conditions under which it is determined are specified. In all standard wood testing, the convention of using a nomin
44、al density is generally The rate of growth of timber is Seen as the 9.2 some of the finest and most widely used adopted. This iS based on the VolUme Of the wood at the time of test (normally at a moisture content of 12 %, 20 % or green) and its mass when oven dried. The formula used species for pall
45、ets have, typically, a high rate of growth (widely separated rings). Even with this high rate of growth, these species frequently exceed the for determining nominal density for strength and suitability of species with slower rates of growth. Rate of growth cannot be used to define acceptable qualiti
46、es of sawn wood for pallets, al- though it still remains as a measure of quality in cer- tain national standards. In certain circumstances, rate of growth may be coupled with other factors to as- sess density (see note 4). A common method of defining growth rate is in “number of rings per 25 mm“. NO
47、TE 4 The mass of wood of a given species for given dimensions, such as might be evident on lifting a pallet board, is not an indication of density unless the moisture content is known. An approximate visual method can be used by technologists with experience of the growth habits of a species. This i
48、nvolves making radial measurements of the spring and summer wood visible at the end grain. If the average density for the species is known, the percentages of spring and summer wood can be calculated and adjust- ment made above or below the published mean density. Some national standards use this te
49、chnique. Oven-dry mass Volume at 12 % moisture content 10.3 Low density indicates weakness and high density indicates strength in pallet wood. These dif- ferences within a single species are frequently suf- ficient to pass or fail identical design pallets by significant margins when carrying out tests in accord- ance with IS0 861 1 in relation to the performance requirements of ISO/TR 10233 (see table 1). Density control is essential in important pallet tests. 10.4 Density variation within a species can reduce or increase strength and stiffness by as much as one-fifth either side of pu