www bzfxw com BRITISH STANDARD BS EN 519 1995 Structural timber — Grading — Requirements for machine strength graded timber and grading machines The European Standard EN 519 1995 has the status of a B[.]
BRITISH STANDARD Structural timber — Grading — Requirements for machine strength graded timber and grading machines The European Standard EN 519:1995 has the status of a British Standard BS EN 519: 1995 BS EN 519:1995 Committees responsible for this British Standard The preparation of this British Standard was entrusted by Technical Committee B/518, Structural timber, to Subcommittee B/518/2, Solid timber, upon which the following bodies were represented: British Timber Merchants’ Association British Woodworking Federation Council of the Forest Industries of British Columbia Department of the Environment (Building Research Establishment) Forestry Commission Institute of Building Control Institution of Civil Engineers National House-Building Council Nordic Timber Council (UK) Southern Pine Marketing Council Timber Research and Development Association Timber Trade Federation Trussed Rafter and Fabricators’ Association UK Softwood Sawmillers’ Association This British Standard, having been prepared under the direction of the Sector Board for Building and Civil Engineering, was published under the authority of the Standards Board and comes into effect on 15 October 1995 © BSI 12-1998 Amendments issued since publication Amd No Date Comments The following BSI references relate to the work on this standard: Committee reference B/518/2 Draft for comment 91/14706 DC ISBN 580 24627 标准分享网 www.bzfxw.com 免费下载 BS EN 519:1995 Contents Committees responsible National foreword Page Inside front cover ii Foreword Text of EN 519 National annex NA (informative) United Kingdom requirement for machine strength graded timber Figure NA.1 — Example of a mark on machine strength graded timber List of References 19 19 Inside back cover ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ © BSI 12-1998 i BS EN 519:1995 National foreword This British Standard has been prepared by Subcommittee B/518/2 and is the English language version of EN 519:1995 Structural timber — Grading — Requirements for machine strength graded timber and grading machines published by the European Committee for Standardization (CEN) It supersedes the following sections and appendices of BS 4978:1988 Specification for softwood grades for structural use: sections and 5, B.3, B.4 and appendices E, F and G These are in the process of being withdrawn by revision of BS 49781) Cross-references Publication referred to Corresponding British Standard EN 336:1995 BS EN 336:1995 Structural timber — Coniferous and poplar — Sizes — Permissible deviations EN 338:1995 BS EN 338:1995 Structural timber — Strength classes EN 384:1994 BS EN 384:1995 Structural timber — Determination of characteristic values of mechanical properties and density EN 408:1995 BS EN 408:1995 Timber structures — Structural timber and glued laminated timber — Determination of some physical and mechanical properties A British Standard does not purport to include all the necessary provisions of a contract Users of British Standards are responsible for their correct application ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ Compliance with a British Standard does not of itself confer immunity from legal obligations Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the EN title page, pages to 20, an inside back cover and a back cover This standard has been updated (see copyright date) and may have had amendments incorporated This will be indicated in the amendment table on the inside front cover 1) In preparation © BSI 12-1998 ii 标准分享网 www.bzfxw.com 免费下载 EUROPEAN STANDARD EN 519 NORME EUROPÉENNE February 1995 EUROPÄISCHE NORM ICS 79.040 Descriptors: Wood, sawn timber, laminated board, timber construction, filing, mechanical strength, test equipment, specifications English version Structural timber – Grading – Requirements for machine strength graded timber and grading machines Bois de structure — Classement — Spécifications pour le bois classé par machine pour sa résistance et les machines classer Bauholz für tragende Zwecke — Sortierung — Anforderungen an mashinell nach der Festigkeit sortiertes Bauholz und an Sortiermaschinen ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ This European Standard was approved by CEN on 1995-02-22 CEN members are bound to comply with the CEN/CENLEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom CEN European Committee for Standardization Comité Européen de Normalisation Europäisches Komitee für Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels © 1995 All rights of reproduction and communication in any form and by any means reserved in all countries to CEN and its members Ref No EN 519:1995 E EN 519:1995 Foreword Page This European Standard has been prepared by the Technical Committee CEN/TC 124, Timber structures, of which the secretariat is held by DS This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by August 1995, and conflicting national standards shall be withdrawn at the latest by August 1995 In accordance with the CEN/CENELEC Internal Regulations, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom Contents Foreword Introduction Scope Normative references Definitions Symbols Requirements for machine strength graded timber Requirements for the company producing graded timber, on the operation of strength-grading machines Requirements for the acceptance of strength-grading machines 7.1 Requirements for all systems 7.2 Additional requirements for machine-controlled systems 7.3 Additional requirements for output-controlled systems Requirements for the derivation of machine settings 8.1 Requirements for machine-controlled systems 8.2 Requirements for output-controlled systems Requirements for production testing in output-controlled systems 9.1 General 9.2 Sampling from production 9.3 Procedure for testing samples from production 9.4 Cusum control constants Page 3 4 9.5 Use of cusum control charts and resulting action Annex A (informative) Additional requirements for the certification body on the operational control of grading machines Annex B (informative) Example of cusum control charts Annex C (normative) Measurement of visually-assessed characteristics Figure — Amounts of wane Figure — Fissures Figure — Measurement of bow, spring and twist Figure — A Graph of variables A and B for use in the determination of cusum control constants for modules of elasticity Figure B.1 — Cusum control from (in control) Figure B.2 — Cusum control from (out of control) Figure B.3 — Cusum chart of data from Figure B.1 and Figure B.2 Table — Visual override requirement Table — Visual override requirements for non-fully machine-graded portions ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ 11 14 14 15 7 12 16 17 18 6 5 5 9 10 10 10 11 11 11 11 11 © BSI 12-1998 标准分享网 www.bzfxw.com 免费下载 EN 519:1995 Introduction There are basically two methods of strength grading: visual grading and machine grading This standard deals with machine grading Machine strength is in common use in a number of countries Its greater predictive accuracy compared with visual grading enables higher yields of higher strength classes to be achieved The countries use two basic systems, referred to as “output controlled” and “machine controlled” Both systems require a visual override inspection to cater for strength-reducing characteristics that are not automatically sensed by the machine The output-controlled system is suitable for use where the grading machines are situated in sawmills grading particular sizes, species and grades in repeated production runs of around one working shift in duration This enables the system to be controlled by testing timber specimens from the daily output These tests together with the cusum statistical procedure are used to monitor and adjust the machine settings to maintain the required strength properties for each strength class If the cusum procedure indicates that the process is in control then the machine settings may be modified to maximize yield If the cusum procedure indicates that the process is out of control then, after further checks, the settings shall be modified to ensure the strength requirements are met and the timber may need to be re-graded With this system it is permissible for machine-approval requirements to be less demanding and for machines of the same type to have non-identical performance The machine-controlled system was developed in Europe around 1969 Because of the large number of sizes, species and grades used it was not possible to carry out quality-control tests on timber specimens drawn from production The system relies therefore on the machines being strictly assessed and controlled, and on considerable research effort to derive the machine settings, which remain constant for all machines of the same type The requirements in this standard are based on machines in current use and on future types of machines as far as these can be foreseen It is recognized that additional clauses or standards may be required if unforeseen developments take place Because of the complexity of the subject, the standard is structured to facilitate use by the various interested parties as follows a) A specifier or user of machine strength graded timber, should refer to clauses to inclusive b) A company carrying out machine strength grading should refer to clauses to inclusive and Annex A and Annex C If it is intended to operate the machine in an “output-controlled” system, then clause and and Annex B should also be studied c) A company manufacturing grading machines, should be familiar with all clauses and annexes, but, most importantly, clause d) A certification body should refer to all clauses and annexes Scope This European Standard specifies the requirements for assessing and operating machine strength grading systems, to strength grade structural timber and laminates for glulam NOTE Whilst it is permitted to use this standard to determine machine settings and to grade to any possible strength profile for a given species, this standard refers to the strength classes of EN 338 to provide suitable strength profiles and dictate the visual override requirements necessary to make machine grading to this standard possible In addition, guidance is given for the degree of quality control necessary to ensure the reliability of timber graded by strength grading machines These requirements are given for both “machine-controlled” and “output-controlled” systems for grading timber ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ © BSI 12-1998 Normative references This European Standard incorporates by dated or undated reference, provisions from other publications These normative references are cited at the appropriate places in the text and the publications are listed hereafter For dated references, subsequent amendments to, or revisions of, any of these publications apply to this European Standard only when incorporated in it by amendment or revision For undated references the latest edition of the publication referred to applies EN 336, Structural timber — Coniferous and poplar — Sizes, permissible deviations EN 338, Structural timber — Strength classes EN 384, Structural timber — Determination of characteristic values of mechanical properties and density EN 408, Timber structures — Structural timber and glued laminated timber — Determination of some physical and mechanical properties EN 519:1995 Definitions For the purposes of this standard the following definitions apply 3.1 batch timber of one species population and size graded in one working shift 3.2 coefficient of determination 3.10 species population timber from an identifiable source and of a species or species combination that is, or is intended to be, strength graded and marketed as a commercially defined product 3.11 timber size sawn or processed dimensions with respect to the permitted tolerances given in EN 336 square of the correlation coefficient 3.12 thickness 3.3 depth dimension perpendicular to the longitudinal axis of a timber beam, in the plane of the bending forces 3.4 indicating property measurement or combination of measurements closely related to strength, from which the machine determines the grade of each increment of length of a piece of timber 3.5 machine-derived modulus of elasticity lesser dimension perpendicular to the longitudinal axis of a piece of timber 3.13 width greater dimension perpendicular to the longitudinal axis of a piece of timber Symbols A B Ba cusum control parameter cusum control parameter cusum parameter associated with acceptable quality level cusum parameter associated with rejectable quality level width of cross section (in mm) theoretical modulus of elasticity (in N/mm2) actual modulus of elasticity measured in a proof load test (in N/mm2) modulus of elasticity in bending (in N/mm2) machine-derived modulus of elasticity (in N/mm2) characteristic mean modulus of elasticity parallel to grain (in N/mm2) applied force (in N) proof load (in N) characteristic bending strength (in N/mm2) proof stress (in N/mm2) depth of cross section (in mm) cusum control parameter size factor run length in acceptable region for cusum control run length in rejectable region for cusum control cusum control parameter thickness (in mm) deflection or deformation (in mm) cusum control parameter cusum control parameter ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ value of modulus of elasticity calculated directly from an indicating property measurement and associated with the position of that measurement on the piece of timber NOTE The calculation formula may assume the timber to be homogeneous within the machine’s measuring span and may ignore the effects of shear deflection and minor end moments 3.6 sample number of specimens of timber of one size and representative of one species population Br b E Ea Em Emac 3.7 settings E0,mean values associated with the variable controls of a grading machine which determine the acceptance to each strength class of timber graded by the machine F Fp fm,k fp h K kh La 3.8 strength-reducing characteristic weakness in a piece of timber resulting from natural growth of the tree (e.g knots, slope of grain) or changes in moisture content (e.g fissures) or resulting from conversion of the log (e.g the inclusion of wane) or caused by attack from fungi, insects or mechanical damage 3.9 strength class classification of timber based on particular values of mechanical properties Lr N t w Y Z © BSI 12-1998 标准分享网 www.bzfxw.com 免费下载 EN 519:1995 Requirements for machine strength graded timber 5.1 The grading system shall operate in either a machine-controlled or output-controlled system 5.2 The visual characteristics of each piece of timber shall meet the requirements of Table and Table when measured in accordance with Annex C Where a machine does not fully grade to the ends of each piece of timber (as in bending-type machines) these non-fully graded portions shall be visually examined If the diameter of knots and slope of grain in the non-fully graded portions exceeds the size of such defects in the fully graded portion of the same piece of timber, and exceeds the limits given in Table 2, then the piece shall be rejected 5.3 The timber shall meet the requirements of EN 336 including one of the two tolerance classes 5.4 Each piece of machine-graded timber shall as a minimum give the following information clearly and indelibly indicated by marking or stamping on one face or edge: a) grade and/or strength class; b) species or species combination; c) number of this standard; d) information whereby the company and the machine responsible for the grading may be identified In exceptional circumstances the end use of timber may require marking to be omitted for aesthetic reasons In such cases, when the customer specifically requests/orders timber to be free from marks, each parcel of timber of a single class shall be despatched under the cover of a certificate of compliance stating the following minimum information in addition to that listed in a), b), c) and d) above: e) serial number and date of the certificate; f) customer’s name and address; g) customer’s purchase or order number; h) timber dimensions and quantities; i) date the timber was graded; j) signature of the operator of the grading machine 5.5 If the grading has been carried out before processing, provided that the processing reduction is not greater than mm from the target size or not greater than mm from the target size for dimensions over 100 mm, the grade shall not be considered to have been changed If the marking or stamping is removed by such processing, the timber shall be re-marked or re-stamped with its original grade or strength class, the species or species combination, the standard to which it is graded and the name of the surfacing company Requirements for the company producing graded timber, on the operation of strength-grading machines 6.1 Machine strength grading operations shall be carried out by personnel and grading companies, under the supervision of a certification body NOTE Requirements essential to the operational control of grading machines for inclusion in the procedures of certification bodies are given in Annex A 6.2 The number of grades or strength classes that can be graded on one pass through the machine will depend upon the accuracy and capabilities of the machine and the settings available Timber rejected by a machine must not be re-graded unless the method of determining settings has made allowances for the changed species population 6.3 The strength-grading machine shall be calibrated in accordance with the manufacturer’s specification (see 7.1.1) 6.4 Additional requirements for quality control testing for output-controlled systems are given in clause ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ © BSI 12-1998 Requirements for the acceptance of strength-grading machines NOTE The requirements for strength-grading machines are based on experience with the bending-type machines in common use and also machines that use radiation techniques to predict the strength of timber Should new machines be developed with different principles of operation then it may be necessary to add additional clauses 7.1 Requirements for all systems 7.1.1 To enable acceptance to be considered, the manufacturer of the machine shall provide a specification to the certification body which shall include the following information: a) specification and description of the mechanical and electrical operation of the machine; b) range of environmental conditions under which the machine is to operate; c) maintenance and operating instructions; d) frequency and extent of calibration procedures; e) species populations, sizes, tolerances, surface finish, moisture content, strength classes, grades, temperatures, throughput speed and limits of distortion of the timber to be graded EN 519:1995 Table — Visual override requirement Strength class according to EN 338 C18 and below Max permissible length of fissuresa Maximum distortion (in mm) over m of lengthb (see Figure 3) Through the thickness Not greater Twice width of piece than 600 mm in any m length Not through the thickness Unlimited Half length of piece Bow Spring Twist 20 mm 12 mm mm/25 mm width 10 mm mm mm/25 mm width Wane (see Figure 1) Resin pockets and bark pockets Wane must not reduce the full edge and face dimensions to less than 2/3 of the basic dimensions of the piece Not through the thickness Unlimited if shorter than the width of the piece otherwise the same limits as for fissures Through the thickness Unlimited if shorter than half the width of the piece, otherwise the same limits as for fissures Insect damage Abnormal defects NOTE Above C18 No active infestation is permitted Wood wasp holes are not permitted and worm and pin holes shall be assessed as abnormal defects ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ Where the reduction in strength caused by the abnormal defect is obviously less than caused by other defects permitted by this table, the piece may be accepted provided the defect is of a type that will not increase after conversion and drying Sapstain is not a structural defect and is acceptable without limitation a Limitations b on fissures may be disregarded if research confirms that they have no effect on strength Limits of distortion will be less if required by the method of operation of the grading machine Table — Visual override requirements for non-fully machine-graded portions (see 5.4) These maximum limits are only applicable where the size of knots and slope of grain in the non-fully graded portion exceeds the size of similar characteristics in the fully graded portion of the same piece Strength class according to EN 338 C18 and below Above C18 Knot diameter on face 1/2 × width of piece 1/4 × width of piece Knot diameter on edge 3/4 × thickness of piece 1/2 × thickness of piece Slope of grain in in 10 NOTE The knot diameter is measured perpendicular to the longitudinal axis of the piece of timber For arris knots the above limits apply to the portion of the knot visible on the particular face or edge being considered © BSI 12-1998 标准分享网 www.bzfxw.com 免费下载 EN 519:1995 ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ Figure — Measurement of bow, spring and twist 7.1.2 The grading machine shall comply with the manufacturer’s specification 7.1.3 A theoretical examination of the machine’s principle of operation shall be carried out to evaluate its sensitivity to isolated strength-reducing characteristics within a piece of timber Where the machine predicts strength by measuring a machine-derived modulus of elasticity Emac, the theoretical examination shall indicate that Emac is not more than 45 % higher than the modulus of elasticity E value assumed for the strength-reducing characteristics In this evaluation, the strength-reducing characteristics shall be assumed to be 150 mm in length and have an E value of 0,5 times that for the remainder of the piece and situated at the most sensitive position in the span NOTE The purpose of this clause is to assess theoretically the effects of a machine’s dimensions and configuration on its sensitivity to changes in modulus of elasticity caused by a defect It is therefore assumed that for a piece of homogenous timber the machine would measure E exactly, i.e E = Emac· NOTE Where the indicating property of a machine is completely independent of strength-reducing characteristics greater than 75 mm from the measuring position (unlike bending machines), sensitivity to isolated defects is limited by the requirements of 7.2.3, 7.2.4 and 7.2.5 for machine-controlled systems 7.1.4 The grading machine shall not damage the timber during the grading operation In particular, damage shall not be caused by large compressions perpendicular to grain stresses and/or large bending stresses © BSI 12-1998 标准分享网 www.bzfxw.com 免费下载 EN 519:1995 7.1.5 Ten pieces of timber of various cross-sectional sizes shall be passed through the machine five times in the same orientation to determine any differences in the indicating property measurements at the same position on the pieces The average value of the maximum difference for each piece, at each position it occurs, shall not be greater than % of the average indicating property values at each of those positions Where the speed can be varied this shall be carried out at two throughput speeds, i.e at low speed and at the maximum speed 7.1.6 The effects on the indicating property of timber size, surface finish, moisture content, throughput speed, timber tolerances, distortion, temperature and orientation (both end to end and side to side) for use in determining grade settings shall be established 7.1.7 The grading machine shall measure its indicating property or properties, at increments of not greater than 150 mm Grading machines whose indicating property measurements are influenced by strength-reducing characteristics away from the measuring position (as in bending-type machines) shall measure the indicating property to within 800 mm of each end of the piece of timber Where the indicating property is influenced only by strength-reducing characteristics at the measuring position (as in radiation-type machines) then the measurements shall be made to within 500 mm of each end 7.1.8 The grading machine shall be capable of comparing each of its indicating property measurements with pre-set boundary settings which correspond to individual grades and of marking each piece of timber according to the lowest grade sensed within the length of that piece 7.1.9 All measuring transducers that are part of the grading machine shall be accurate to within ± % of the actual measurements 7.1.10 For grading machines which measure their indicating properties in digital form, the digital increments shall represent not more than % of the actual indicating property measurements for any size, grade and species within the range required for the machine 7.1.11 The infeed and outfeed equipment shall provide the correct height and angle of entry for the timber into the grading machine and shall not interfere significantly with the sensing of the indicating property, even when the timber is distorted within the limits given in item e) of 7.1.1 7.1.12 The grading machine shall be fitted with a means to enable calibration of all measuring transducers and of parameters critical for the correct operation of the machine 7.2 Additional requirements for machine-controlled systems 7.2.1 All machines of the same type shall have an identical performance to within acceptable manufacturing tolerances 7.2.2 The machine shall have locking devices on the setting controls, and a means by which the grade settings are displayed in a form different from that used to insert the settings to help ensure that, as an additional check, the operator refers back to the tabulated setting data 7.2.3 For each species population given by the manufacturer’s specification (see 7.1.1) a sample or combination of samples of at least 200 specimens shall be tested to verify the requirements in 7.2.4 and 7.2.5 7.2.4 Where machine settings are estimated from an equation between the lower percentile bending strength, tested in accordance with EN 408, and the indicating property, then the equation shall be determined from the combined sample data for each species, to reduce the effects of sample variability The regression equation between bending strength and the indicating property for the combined sample shall have a coefficient of determination of not less than 0,45 (see 7.2.3) 7.2.5 The relation between the bending modulus of elasticity Em as measured in EN 408 and the machine’s indicating property shall have a coefficient of determination of not less than 0,5 (see 7.2.3) ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ © BSI 12-1998 7.3 Additional requirements for output-controlled systems For output-controlled systems there are no requirements in addition to those given in 7.1 It follows that a machine approved for use in a machine-controlled system is automatically acceptable for use in an output-controlled system EN 519:1995 Requirements for the derivation of machine settings 8.1 Requirements for machine-controlled systems 8.1.1 Where the machine is required to grade a large range of sizes and species it is necessary to derive a mathematical model that relates the machine’s indicating properties to species population, strength class and size It is also necessary to carry out sufficient testing using samples containing a minimum number of 100 specimens each, to establish the effects of all the variables listed in 7.1.1 (i.e species population, size, tolerances, surface finish, moisture content, strength classes, temperature, throughput speed and limits of distortion) These effects must be taken into account when determining settings To avoid the enormous amount of testing that this would entail it is permissible to interpolate and, having established the effects on one species, extrapolate to other species provided the species can be shown to behave similarly with respect to the variable being considered Where the effect of a particular variable can be established totally or partly from theory (e.g tolerances) this is acceptable 8.1.2 The mathematical model referred to in 8.1.1 may also vary the settings according to the number and combination of strength classes graded in one pass through the machine Where this is carried out it is important that the grading machine operator fully understands that the combination of strength classes cannot be changed without changing the settings 8.1.3 Data shall be provided to verify that timber graded to settings determined as in 8.1.1 has characteristic strength properties, calculated in accordance with EN 384, that meet the requirements of the grade or strength class These data shall involve testing a number of samples containing a minimum of 40 specimens of each species population The test shall be carried out as follows a) Proof load (using Fp as specified in 8.2.5) in accordance with EN 408, a random sample of 60 specimens of the strength class/species/size/source combinations, ignoring pieces graded by visual overrides, edgewise over a span of 18 times the depth of the specimens and using third-point loading with the tension edge selected at random and the estimated weakest cross section positioned where possible within the centre third of the span b) Determine the actual modulus of elasticity Ea (as specified in 8.2.5) by measuring the deflection at the span centre, with the tension edge selected at random and the estimated weakest cross section positioned where possible within the centre third of the span The rate of applied stress shall be 110 N/mm2/min If more than one strength class is to be graded in one pass through the machine in production, then these classes shall also be graded in one pass to obtain specimens for the assessment tests If the results not meet the requirements of 8.2.3, then the settings shall be modified and the tests repeated ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ 8.2 Requirements for output-controlled systems 8.2.1 Apparatus For assessment and quality-control purposes, a static proof loading machine shall be used This machine shall be capable of bending each specimen using edgewise third-point loading and a span of 18 times the specimen depth according to EN 408 The deflection and load transducers shall be accurate to within ± % of the actual measurement 8.2.3 Assessment of machine settings for each strength class/species/size/source combination When tested in accordance with 8.2.2, the initial settings for the machine shall meet the following requirements: a) the mean actual modulus of elasticity Ea of the 60 specimens shall be not less than the strength class characteristic mean value E0, mean; b) no more than two specimens shall fail to sustain the proof load Fp (see 8.2.5) 8.2.4 Test records The following records shall be kept: a) species population; b) timber size and surface finish (planed or sawn); c) number of specimens in each strength class and the number of pieces rejected by the machine; d) all machine settings; e) results of tests; f) date of test; g) identification number or name of the machine operator and the identification number of the grading machine 8.2.2 Procedure NOTE Initial estimated settings should be deduced from any relevant available information on relations between bending strength and indicating property © BSI 12-1998 10 标准分享网 www.bzfxw.com 免费下载 EN 519:1995 8.2.5 Calculations The applied proof load Fp is given by the equation: t hf FP = P18 Where fp is the proof stress = 0,96khfm,k; kh is the size factor for h as given in EN 384; fm,k is the characteristic bending strength for 150 mm depth The measured actual modulus of elasticity Ea is given by the equation: 242FEa = -tw Where F is the applied force; w is the deflection at the span centre Requirements for production testing in output-controlled systems 9.1 General NOTE For an example see Annex B 9.4 Cusum control constants To carry out the quality-control procedures, three cusum control constants K, Y and Z need to be entered on the cusum control charts These are determined as follows For control of bending strength: K=1 Y=1 Z=6 For control of characteristic mean modulus of elasticity parallel to grain: K = E0,mean – 345 where E0,mean is equal to the mean modulus of elasticity for the strength class ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ Grading accuracy shall be monitored by testing samples drawn from production and analysing the results using the cusum procedure described in this clause 9.2 Sampling from production Only machine settings that have been assessed in accordance with 8.2 shall be used Five specimens of the strength class to be tested shall be counted, then the sixth specimen shall be selected for the test sample This procedure shall be repeated to select two five-specimen samples from each class produced during each working shift This process shall be repeated at approximately equal intervals during the shift period For the first three working shifts the sampling rate shall be doubled using newly assessed settings 9.3 Procedure for testing samples from production The tests shall be carried out as follows, using the apparatus described in 8.2.1 a) Proof load (using Fp as specified in 8.2.5) each specimen edgewise over a span of 18 times the piece depth and using third-point loading with the tension edge selected at random and the estimated weakest cross section positioned where possible within the centre third of the span © BSI 12-1998 b) Determine the actual modulus of elasticity Ea (as specified in 8.2.5) by measuring the deflection at the span centre, with the tension edge selected at random and the estimated weakest cross section positioned where possible within the centre third of the span The rate of applied stress shall be 110 N/mm2/min The number of specimens that fail under the proof load and the values of Ea shall be recorded on the cusum control charts A constant “A” shall be calculated from the equation A = 7012/E0,mean and used in Figure to determine two values of B expressed as Ba when La = 150 and Br when Lr = The remaining control constants Y and Z are then calculated from: Y = 0,0492E0,meanBa N = 0,0492E0,meanBr Z=Y+N 9.5 Use of cusum control charts and resulting action 9.5.1 All results from the tests on quality-control specimens from production shall be entered on the control charts NOTE There are two charts, one for use when the process is “in control” (see Figure B.1) and one for use when the process is “out of control” (see Figure B.2) If the process goes out of control then, irrespective of which or how many properties are involved, the out-of-control chart shall be used An example showing the method of filling in the control charts is given in Annex B 9.5.2 Directions for determining cusum values on “in-control” charts Proceed as follows a) If sum is or less, then cusum equals b) If sum is between and Y, then cusum equals sum (For bending strength, Y = 1, therefore this condition does not apply) 11 EN 519:1995 ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ Figure — A graph of variables A and B for use in the determination of cusum control constants for modulus of elasticity c) If sum is greater than or equal to Y, then cusum equals Z and the process is out of control Use “out-of-control” chart 9.5.3 Directions for determining cusum values on “out-of-control” charts Proceed as follows a) If sum is greater than Y and less than or equal to Z, then cusum equals sum b) If sum is less than or equal to Y, then cusum equals and the process is now back in control Use “in-control” chart 9.5.4 Actions to be taken If the cusum charts indicate that the production is in control then the timber can be released for delivery If the manufacturer wishes to maximize grade yields, the grade-boundary settings can be adjusted in increments of % or less After each adjustment, results from 12 five-specimen samples shall be tested and entered on the cusum charts which shall indicate that the production remains in control If the cusum charts indicate that the production is out of control, then all timber represented by that sample shall be held pending results of confirmation tests as set out below Upon determining the production is out of control, the grading machine shall be checked for basic calibration and accuracy of grade settings The proof load test equipment shall be checked for accurate calibration Following machine and test-equipment checks, the operator can undertake one of the following actions a) No machine adjustment If no adjustment is made the operator shall select 30 specimens from production by choosing every third piece, sequentially numbered in six samples of five specimens each Tests shall be made in accordance with 9.3 When control charts indicate in control, after one or more of the six samples have been tested and evaluated, the production can continue and graded timber can be released for delivery If the control charts indicate the process is still out of control, the operator shall proceed to either b) or c) © BSI 12-1998 12 标准分享网 www.bzfxw.com 免费下载 EN 519:1995 b) Setting adjustment of % or less If a single % or less adjustment is made, the operator shall select 30 specimens representative of production following the adjustment by choosing every third piece, sequentially numbered in six samples of five specimens each Tests shall be made in accordance with 9.3 If, after the adjustment, the control charts indicate in control, after one or more of the six samples have been evaluated, the production can continue and graded softwood can be released for delivery If the control charts indicate the process is still out of control, the operator shall proceed to c) c) Setting adjustment of greater than % If machine settings are adjusted by more than %, then the grade marks on the graded timber being held shall be obliterated The production process shall only be considered back in control after appropriate steps have been taken to correct the process and a subsequent test (in accordance with 9.3), of 30 pieces representative of production, selected as every third piece to give six samples of five specimens shows the process to be in control After this action, the quality-control sampling rate shall be doubled for the first three working shifts 9.5.5 Cusum graphs Graphs of the cusum values provide an overall representation of how the production is fluctuating over long periods of time It is easier to visualize general material characteristics and small changes in the process by a visual approach rather than by looking at numbers NOTE A graph of the example in Annex B is shown in Figure B.3 ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ © BSI 12-1998 13 EN 519:1995 Annex A (informative) Additional requirements for the certification body on the operational control of grading machines A.1 This annex does not attempt to include other necessary parts of an acceptable third-party certification scheme, i.e organizational responsibility, legal considerations, dispute procedures, etc (see ISO/IEC Guide 28) A.2 In addition to meeting the requirements of this annex, all certification bodies shall comply with the requirements of ISO/IEC Guide 40 A.3 The certification body’s representative shall, at least twice per year for machine-controlled systems and at least four times per year for output-controlled systems, carry out a check on the strength-grading machine, unannounced, to ensure that the performance and operation of the machine complies with the requirements of this standard The equipment used for calibration shall not be that used by the company A.4 When, on inspection of a parcel of graded timber, it is ascertained that not more than 10 % of the pieces exceed the permissible visual override limits in Table and Table 2, and provided that no piece exceeds the limits by more than 25 %, the parcel shall be considered as complying with the grade Where the parcel contains less than 50 pieces, the permissible limits shall not be exceeded d) number of pieces in each strength class and the number of pieces rejected by the machine; e) all machine settings; f) date and working shift; g) identification number or name of the machine operator and the identification number of the grading machine; h) for output-controlled machines: results of quality-control tests and cusum control charts and plots Annex B (informative) Example of cusum control charts Refer to Figure B.1, Figure B.2 and Figure B.3 At the heading of the chart enter the following: a) size, species, grade and surface finish; b) values for Fp, E0,mean, K, Y and Z from 9.3 and 9.4; c) machine settings used and the date and shift in the first column Lines to Enter Ea values for the five test specimens (see 9.3) Line Enter the mean value from lines to Line Enter the cusum value from the previous column If no previous column exists for this species/grade/size combination, then cusum is Line Enter K for mean modulus of elasticity Line Enter the sum of lines and Line 10 Enter the mean value of Ea from line Line 11 Enter sum by subtracting line 10 from line Line 12 Enter cusum determined from sum and 9.5.2 (or 9.5.3 for out-of-control chart) Line 13 Enter a tick if process is in control, otherwise write “no” (see 9.5.2 and 9.5.3) Line 14 to 18 If a test piece failed during proof loading, write the failure load, otherwise add a tick Line 19 Enter the number of failures Line 20 Enter the cusum value from the previous column Line 21 Enter the sum of lines 19 and 20 Line 22 Enter K for bending strength Line 23 Enter sum by subtracting line 22 from line 21 ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ NOTE The deviation in grading is allowed to take into account practical difficulties in measuring certain visual characteristics and consequent difference of opinion A.5 The company carrying out the grading shall nominate a representative who will be responsible for the operation of the strength-grading machine, test equipment and associated personnel and review the grading records on a weekly basis A.6 Equipment used for calibration of the strength-grading machine shall be subject to certification in respect of its accuracy every years A.7 No modifications shall be made to the machine without authorization by the certification body A.8 The results of routine service and maintenance to the strength-grading machine and ancillary equipment shall be recorded together with the results of calibration checks A.9 The following records shall be kept for each batch of graded timber: a) job or order number and customer’s name, if known; b) timber species population; c) timber size and surface finish (planed or sawn); © BSI 12-1998 14 标准分享网 www.bzfxw.com 免费下载 EN 519:1995 Line 24 Line 25 Enter cusum determined from sum and 9.5.2 (or 9.5.3 for out-of-control chart) Enter a tick if process is in control otherwise write “no” (see 9.5.2 and 9.5.3) Annex C (normative) Measurement of visually-assessed characteristics C.2 Distortion The methods of assessing distortion are shown in Figure Bow, spring and twist shall be assessed over a m length Longitudinal curvature in square section pieces shall be assessed using the limits for bow NOTE Because distortion and fissures are influenced by moisture content, the limits apply only at the time of grading NOTE This annex will be deleted when a CEN Standard is written to cover this topic C.1 Fissures The size of a fissure shall be taken as the distance between lines enclosing the fissure and parallel to a pair of opposite faces, see Figure a) If a transverse plane cuts through two or more fissures on opposite faces then the sum of their sizes shall be taken as the size of the defect, see Figure b) The depth of fissures may be assessed by the use of a feeler gauge not exceeding 0,2 mm in thickness ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ © BSI 12-1998 15 EN 519:1995 Size: Species: red/whitewood Grade: XX K Y Z Mean E: 10 215 336 812 Bending strength: 1 35 × 97 Fp:3 898 Surface finish: planed Machine settings Date 5.5.80 6.5.80 7.5.80 8.5.80 9.5.80 10.5.80 11.5.80 12.5.80 13.5.80 14.5.80 Shift Day Day Day Day Day Day Day Day Day Day Ea value 10 632 10 432 10 710 735 10 220 206 962 510 626 10 312 Ea value 529 304 601 10 680 110 10 280 10 424 10 425 10 917 846 Ea value 10 011 12 842 10 100 10 240 632 690 10 681 12 681 12 467 11 567 Ea value 873 700 890 910 465 12 490 10 310 10 276 832 341 Ea value 10 356 10 123 10 460 10 390 915 976 11 262 987 11 428 10 878 Mean Ea 10 080 880 10 152 10 191 668 728 10 527 10 175 10 653 988 135 470 533 557 104 0 40 Last cusum K +10 215 Subtotal Mean Ea 10 215 ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ +10 215 +10 215 +10 215 +10 215 +10 215 +10 215 +10 215 +10 215 +10 215 10 350 10 685 10 748 10 772 11 319 10 215 10 215 10 255 10 215 – 10 080 – 880 – 10 152 – 10 191 – 668 – 728 – 10 527 – 10 175 – 10 653 – 988 10 Sum 135 470 533 557 104 591 – 312 40 – 398 227 11 Cusum 135 470 533 557 104 812 40 227 12 In control? Ï Ï Ï Ï Ï Test result Ï Ï Ï Ï Ï 820 Ï Ï Ï Ï Ï‘ Ï Ï Ï 805 Ï Ï Ï Ï Test result Test result Ï Test result Ï 796 Test result Ï No failed Ï Ï No Ï Ï Ï Ï 13 672 Ï Ï Ï Ï 14 Ï Ï Ï 504 Ï Ï Ï Ï 16 Ï Ï Ï Ï Ï 17 Ï Ï Ï Ï Ï 18 Ï 563 15 1 0 0 19 +0 +0 +0 +0 +0 +0 +0 +0 +0 +0 20 Subtotal 1 0 0 21 K 1 1 1 1 1 22 Sum 0 –1 –1 –1 –1 –1 –1 23 Cusum 0 0 0 0 24 Last cusum In control? Ï Ï Ï Ï Ï No Ï Ï Ï Ï 25 Operator Figure B.1 — Cusum control form (in control) © BSI 12-1998 16 标准分享网 www.bzfxw.com 免费下载