1、BRITISH STANDARD CONFIRMED DECEMBER1990 BS 2797:1976 Incorporating Amendment No. 1 Specification for Leathers for gas meter diaphragms UDC 675.061.1/.2:681.122.36BS2797:1976 This British Standard, having been prepared under the directionof the Leather StandardsCommittee was published under the autho
2、rityofthe ExecutiveBoardon 30 July 1976 BSI 12-1999 First published in two Parts: Part1 December 1956; Part2February 1962 First revision July 1976 The following BSI references relate to the work on this standard: Committee reference TCM/17 Draft for comment 75/50593 DC ISBN 0 580 09322 0 Co-operatin
3、g organizations The Leather Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government department and scientific and industrial organizations: British Leather Federation* British Leather Manufacturers Research Associatio
4、n* Hide and Allied Trades Improvement Society Ministry of Defence Shoe and Allied Trades Research Association Society of Leather Technologists and Chemists* Tropical Products Institute The scientific and industrial organizations marked with an asterisk in the above list, together with the following,
5、 were directly represented on the committee entrusted with the preparation of this British Standard: British Gas Corporation Department of Energy, Gas Standards Institution of Gas Engineers Society of British Gas Industries Amendments issued since publication Amd. No. Date of issue Comments 4962 Nov
6、ember 1985 Indicated by a sideline in the marginBS2797:1976 BSI 12-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 References 1 3 Definitions 1 4 Requirements 1 5 Marking 1 Appendix A Method of manufacture of E.I. sheepskin diaphragm leather (type 1) 2 Appe
7、ndix B Method of manufacture of split hide diaphragm leather (type 2) 2 Appendix C Procedure for the determination of iron content 2 Appendix D Procedure for the determination of shrinkage in boiling water 3 Figure 1 Test piece holder for determination of shrinkage in boiling water 5 Publications re
8、ferred to 6BS2797:1976 ii BSI 12-1999 Foreword BS 2797 was originally published in two Parts; Part 1:1956, “E.I. Sheep skin leather” and Part 2:1962, “Split hide leather”. In this first revision the two Partshave been combined as a single document superseding Parts 1 and 2 which are now withdrawn. M
9、inor changes have been made; in particular, the requirement for the boil test has been modified to remove a discrepancy left after an amendment to the first editions. Other changes are mainly editorial, for example, to take into account the revision in1974 of BS1309, and to make clear that the use o
10、f suitable fillers during manufacture is not excluded by the requirements of the standard. Certification. Attention is drawn to the certification facilities described on the inside back cover of this standard. A British Standard does not purport to include all the necessary provisions of a contract.
11、 Users of British Standards are responsible for their correct application. 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, pages1 to 6, an inside back cover an
12、d 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.BS2797:1976 BSI 12-1999 1 1 Scope This British Standard specifies requirements for finished leathers for use in diaphr
13、agms of gas meters intended for use with natural gas. Two types of leather are specified. Type 1. E.I. sheepskin leather, manufactured as described in outline inAppendix A. Type 2. Split hide leather, manufactured as described in outline inAppendix B. 2 References The titles of the British Standards
14、 referred to in this standard are listed on page 6. 3 Definitions For the purposes of this British Standard, thedefinitions given in BS2780 apply. 4 Requirements 4.1 pH value. When determined as described in BS1309, the pH value of the finished leather shall be not lower than3.5. 4.2 Iron. When dete
15、rmined by the method described inAppendix C, the iron content of the finished leather at a volatile matter content of14%(m/m), determined as described in BS1309 shall not exceed 5004g (Fe) per gram of leather. 4.3 Shrinkage in boiling water. When the finished leather is tested by the procedure descr
16、ibed inAppendix D, the mean percentage decrease in the diameter of the test piece shall not exceed3.0%. 4.4 Chromium. When determined by either the perchloric acid method or the alkaline fusion method for chromic oxide content described in BS1309, the chromic oxide content of the finished leather at
17、 a volatile matter content of14% (m/m), determined as described in BS1309 shall be not less than2.5% Cr 2 O 3 . 4.5 Thickness 4.5.1 Type 1. The thickness of finished type1 leather, measured by the procedure described in BS3144, and the permissible variation in thickness, shall be subject to agreemen
18、t between the purchaser and the vendor. 4.5.2 Type 2. When determined as described in BS3144, the thickness of the finished type2 leather shall be not less than1.20mm at any point within the area which will form a diaphragm. The difference between the maximum thickness and minimum thickness within t
19、his area shall not exceed0.30mm. Providing that finished type2 leather complies with these requirements, the mean thickness and the tolerance on the thickness shall be the subject of agreement between purchaser and vendor. 5 Marking The finished leather shall be indelibly marked so that the followin
20、g information will appear on each diaphragm. a) Manufacturers name or identification mark. b) Manufacturers batch or lot number. c) “BS 2797 type 1” or “BS 2797 type 2”, asappropriate. NOTEOther information may be added if required. Addition of the date of rettanage is recommended.BS2797:1976 2 BSI
21、12-1999 Appendix A Method of manufacture ofE.I. sheepskin diaphragm leather (type 1) A.1 Raw material Well preserved E.I. tanned Persian sheepskins are used. Skins used are chosen to be of good tannage and free from harmful materials, holes, flaying defects and serious imperfections of fibre structu
22、re. Skins are selected for thickness so that during shaving (seeA.2.1) the thickness is reduced by a minimum. A.2 Tannage A.2.1 Shaving. The flesh side is slightly shaved and the skin is finished to the required thickness (see4.5.1) on the grain side. A.2.2 Retanning. Skins are retanned with basic c
23、hromium sulphate so that the finished leather will meet the requirements of4.4. A.2.3 Inert materials. At an appropriate stage, the manufacturer may incorporate into the leather inert materials (known as “fillers”) which do not prevent the finished leather from complying with the requirements of thi
24、s standard. A.3 Fat-liquoring The leather is treated (fat-liquored) with oil (excluding oil derived from marine animals) and with soap flakes complying with the requirements of BS1912, to yield a finished leather containing3% (m/m) added oil and2% (m/m) added soap both calculated on a basis of14% (m
25、/m) volatile matter in the finished leather. NOTE 1The use of neatsfoot oil is recommended. NOTE 2Bar soap, complying with the requirements of BS1911, is an alternative to soap flakes, provided that the quantity used is adjusted to compensate for any difference in fat content. Appendix B Method of m
26、anufacture of split hide diaphragm leather (type 2) B.1 Raw material The raw material used is good quality vegetable-tanned split hide made from either: a) UK market hides, or b) good quality wet-salted hides of European origin. The split hides are selected so that during shaving (seeB.2.1) no more
27、than0.5mm of the leather need be removed. Hides used are selected so that they are free from harmful material and so that the areas from which the diaphragms will ultimately be cut are free from ticks, holes, healed or partially healed warble holes, brands, score marks and other serious imperfection
28、s of the grain or fibre structure. B.2 Rettanage B.2.1 Shaving. The hides are shaved so that the finished leather complies with the requirements of4.5.2. As a final operation, the leather may be lightly shaved or buffed on the grain side. B.2.2 Retanning. The split hides are retanned with basic chro
29、mium sulphate so that the finished leather will meet the requirements of4.4. B.2.3 Inert materials. At an appropriate stage the manufacturer may incorporate into the leather inert materials (known as “fillers”) which do not prevent the finished leather from complying with the requirements of this st
30、andard. B.3 Fat-liquoring The leather is treated (fat-liquored) with oil (excluding oils derived from marine animals) and with soap flakes complying with the requirements of BS1912, to yield a finished leather containing3% (m/m) added oil and2% (m/m) added soap both calculated on a basis of14% (m/m)
31、 volatile matter in the finished leather. NOTE 1The use of neatsfoot oil is recommended. NOTE 2Bar soap, complying with the requirements of BS 1911, is an alternative to soap flakes, provided that the quantity used is adjusted to compensate for any difference in fat content. Appendix C Procedure for
32、 the determination of iron content C.1 Reagents Use reagents of recognized analytical reagent quality and water complying with the requirements of BS3978. The following reagents are required. C.1.1 Ammonia solution, dilute. Mix ammonia solution (d = 0.880) with an equal volume of water. C.1.2 Hydroc
33、hloric acid, dilute (approximately 6N). Mix concentrated hydrochloric acid (d = 1.18) with an equal volume of water. C.1.3 Potassium thiocyanate solution. 400gperlitre. C.1.4 Standard iron solution (104g Fe per millilitre). Dissolve0.7022g of ammonium ferrous sulphate, (NH 4 ) 2SO 4 .FeSO 4 .6H 2 O,
34、 in water. Add1ml to2ml of concentrated nitric acid and evaporate the solution to dryness on a water bath. Dissolve the residue in10ml of the dilute hydrochloric acid and dilute to1000mlwith water. From this solution prepare a 1+9 dilution 104g of iron (Fe) per millilitre immediately before use.BS27
35、97:1976 BSI 12-1999 3 C.2 Apparatus Usual laboratory apparatus is required and, in particular, the following. C.2.1 Platinum dish, iron-free. C.2.2 Nessler cylinders, 50ml, complying with the requirements ofBS612. C.2.3 Microburette C.2.4 One-mark volumetric flask, 100ml, class B, complying with the
36、 requirements of BS1792. C.3 Procedure Weigh5 0.1g of the leather into the platinum dish and heat it carefully, at the minimum temperature necessary, below500 C, to form an ash free from carbonaceous particles. Take care that at no time does any part of the dish reach a bright red heat. NOTEThe low
37、ignition temperature prevents fusion of alkali salts present. If necessary, to eliminate carbonaceous particles, cool the dish, moisten the ash with a few drops of water, dry carefully and then heat again to a temperature below500 C. Cool the dish, add1ml to2ml of the dilute hydrochloric acid to the
38、 ash and evaporate to dryness on a water bath. Dissolve the residue in1ml to2ml of the dilute hydrochloric acid, dilute with water, boil and filter. Dilute the cooled filtrate to100ml in the volumetric flask. Transfer a10.0ml aliquot portion into a Nessler cylinder, dilute with water, add5ml of the
39、dilute hydrochloric acid then add5ml of the potassium thiocyanate solution. Dilute to50ml with water andmix. Into a second Nessler cylinder containing5ml of thedilute hydrochloric acid,5ml of the potassium thiocyanate solution and approximately37ml of water, gradually add standard iron solution from
40、 the microburette until the colour of the solutions in the two Nessler cylinders matches when the solutions are viewed vertically from above with the cylinders held over a white surface. Note the volume of standard iron solution added. C.4 Expression of result Calculate the result as follows. Iron c
41、ontent (4g Fe per gram) = 1 720 V/(100 x) where V is the volume, in millilitres, of standard iron solution used; x is the percentage volatile matter content of the leather, determined as described in BS1309. Appendix D Procedure for the determination of shrinkage in boiling water D.1 Apparatus and m
42、aterial Use the following apparatus and material. D.1.1 Glass dish, flat bottom, circular, diameter between75mm and105mm, capacity at least350ml. D.1.2 Glass rods, each approximately2.5mm in diameter,100mm in length, and bent in the middle to an angle of60 . D.1.3 Beaker, 250ml. D.1.4 Desiccator or
43、similar glass vessel, which can be evacuated and which will contain the glass dish. D.1.5 Vacuum pump, capable of reducing the absolute pressure in the desiccator to less than25mbar 1)within120s of being switched on. D.1.6 Scale, calibrated in millimetres. D.1.7 Stopclock D.1.8 Pressure vessel, cons
44、tructed of aluminium or aluminium alloy, in which water can be boiled at a pressure greater than atmospheric pressure. The vessel shall incorporate the following features. D.1.8.1 Lid that can be rapidly removed and replaced. D.1.8.2 Thermometer covering the range100Cto105 C. NOTEThermometer F 125C/
45、100, complying with the requirements of BS593, is suitable. The thermometer shall be fitted in the lid near one side, so that with the lid in position the thermometer bulb extends to within20mm of the bottom of the vessel. D.1.8.3 Gas ring capable of heating the vessel so that the temperature of1000
46、ml of water in the vessel is raised from98 C to100 C in less than60s. D.1.8.4 Adjustable release valve, spring-loaded, capable of adjustment (in conjunction with the gas flow to the gas ring) so that the temperature of water boiling in the vessel is maintained at102.0 0.3 C. NOTEA domestic pressure
47、cooker may be modified to form a suitable pressure vessel for the test. The volume of water in the pressure vessel is unlikely to be of critical importance; losses as steam are restricted by following the method described. 1) 1 bar = 10 5N/m 2= 100kPaBS2797:1976 4 BSI 12-1999 D.1.9 Test piece holder
48、, to prevent the test piece from curling during heating in boiling water. The holder (seeFigure 1) shall have a brass plate Aof diameter about100mm and thickness about3mm standing on legs formed by brass screws which raise it about10mm. The test piece B, when in position, (shaded) shall rest on plat
49、e A, anda bent copper wire of diameter about1mm shall rest on the test piece (for clarity, the wire is drawn thicker than1mm in the plan ofFigure 1). On the wire shall rest another similar brass plateA, which shall carry a bridge formed by two brass screws and a brass rod. When the holder has been assembled with the test piece in position, a brass nut shall be screwed on to each of the three vertical screws attached to the lower plate, so that the holder can be lifted from boiling water by a bent wire hooked under the bridge, but the holes in the upper
