1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7900 : 1998 ICS 77.140
2、.80 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Specification for Examination of the surface texture of precision steel castingsBS 7900 : 1998 This British Standard, having been prepared under the direction of the Engineering Sector Board, was published under the authority
3、 of the Standards Board and comes into effect on 15 May 1998 BSI 1998 The following BSI references relate to the work on this standard: Committee reference ISE/6 Draft for comment 96/713267 DC ISBN 0 580 28932 X Amendments issued since publication Amd. No. Date Text affected Committees responsible f
4、or this British Standard The preparation of this British Standard was entrusted to Technical Committee ISE/6, Steel castings, upon which the following bodies were represented: BEAMA Ltd. British Pump Manufacturers Association British Valve and Actuator Manufacturers Association Castings Development
5、Centre Hopkinsons Limited Institute of British Foundrymen Lloyds Register of Shipping Ministry of Defence Railway Industry AssociationBS 7900 : 1998 BSI 1998 i Contents Page Committees responsible inside front cover Foreword ii Specification 1 Scope 1 2 Definitions 1 3 Description of tactile compara
6、tor set 1 4 Information to be supplied by the purchaser 1 5 Assessment of surface texture 2 6 Recording of results of examination 2 Annex A (informative) Examples of comparator plates 3ii BSI 1998 BS 7900 : 1998 Foreword This British Standard is aimed at facilitating a better understanding between t
7、he casting producer and purchaser regarding the natural surface finish produced by four precision casting processes. It is intended to prevent misunderstandings arising from imprecise descriptions at the enquiry and order stage and subsequent customer disappointment at the goods received stage. The
8、casting process characteristically produces randomly oriented irregularities on surfaces created by the moulding medium and subsequent fettling. These irregularities may be depressions or protrusions of widely varying shapes and sizes. The use of tactile comparators for the evaluation of surface qua
9、lity is superior to methods based on photographs which can introduce uncertainties concerning interpretation, particularly with regard to the profile of these surface irregularities. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This d
10、ocument comprises a front cover, an inside front cover, pages i and ii, pages 1 to 6, an inside back cover and a back cover. BSI 1998 1 BS 7900 : 1998 1) For information on the availability of comparators contact the BSI Information Centre, British Standards House, 389 Chiswick High Road, London W4
11、4AL. 2) An example of this is the Replicast process. Replicast is the trade-name of the Castings Development Centre. This information is given for the convenience of users of this standard and does not constitute an endorsement of the product named. Equivalent products may be used if they can be sho
12、wn to lead to the same results. Specification 1 Scope This British Standard specifies levels of surface roughness/texture on steel castings produced by the resin shell, lost wax, lost polystyrene and Shaw moulding processes (see 2.5 to 2.8 for a brief description of each process). Surfaces created b
13、y subsequent fettling operations (see 2.4) are also included. In addition to the definitive requirements, this standard also requires the items detailed in clause 4 to be documented. For compliance with this standard, both the definitive requirements and the documented items have to be satisfied. NO
14、TE. Acceptance levels should be agreed between the casting producer and purchaser by reference to a set of reference tactile comparators which represent the surfaces produced by the four moulding processes after blasting, and also, surfaces created by subsequent fettling operations. Annex A contains
15、 full size photographs of the comparator plates to assist in making a rapid review of the overall content of the set. It is emphasized, however, that the comparators and not the photographs should be used to form the basis of agreement 1) Agreement and acceptance is by visual examination and touch.
16、2 Definitions For the purpose of this standard, the following definitions apply. 2.1 surface texture The surface of the castings after blasting. 2.2 precision castings Castings exhibiting high external and internal integrity and exceptional dimensional accuracy. 2.3 tactile Relates to the sense of t
17、ouch. 2.4 fettling Removal of feeder heads and ingates by cutting and/or grinding operations. 2.5 resin shell process A precision moulding process that uses metal pattern and corebox equipment and resin-bonded sand. 2.6 lost polystyrene process 2) A precision moulding process that uses expanded poly
18、styrene patterns and thin ceramic shell moulds. 2.7 Shaw process A precision casting process that uses wooden/resin pattern and corebox equipment and ceramic block moulds. 2.8 lost-wax process A precision casting process that uses wax patterns and ceramic shell moulds. 3 Description of tactile compa
19、rator set The comparators are plastic replicas of actual cast steel surfaces. They comprise five categories, each with two or three levels of surface texture increasing in roughness from 1 to 2 or 3 (level 1 is the smoothest), as follows: resin shell process (three levels V1, V2, V3); lost polystyre
20、ne process (three levels W1, W2, W3); Shaw process (three levels X1, X2, X3); lost-wax process (two levels Y1, Y2); fettled surfaces (three levels Z1, Z2, Z3). Full size photographs of the comparators are shown in annex A for information purposes only. 4 Information and requirements to be agreed and
21、 documented The following information to be supplied by the purchaser shall be fully documented. Both the definitive requirements specified throughout the standard and the following documented items shall be satisfied before a claim of compliance with the standard can be made and verified: a) the ar
22、eas on the casting to be examined; b) whether the results of inspection are to be recorded; c) the acceptance category(ies) for each of the relevant areas on the casting.2 BSI 1998 BS 7900 : 1998 2) An example would be a 100 W bulb suspended approximately 1 metre above an object. 5 Assessment of sur
23、face texture 5.1 The following procedure shall form the basis of an assessment for a casting in the as supplied condition, prior to any coating operation. 5.2 The comparator, or comparators, used shall be representative of both the casting process and the surface acceptance criteria. 5.3 The compara
24、tor and casting surface shall be viewed together in lighting conditions of at least 350 lux 2) . 5.4 The assessment shall be satisfactory if, in the required area of the casting, the surface texture is equal to, or better than, the reference comparator selected in accordance with 6.3. NOTE. Difficul
25、ties may arise in accessing surfaces of castings covering a range of size and section thickness using standard comparators measuring 60 mm3 60 mm. It is emphasized, however, that it is not intended that areas of the casting should be divided up into areas of equivalent dimensions. 6 Recording of res
26、ults of examination The casting producer shall, if requested by the purchaser, keep a record of the examination and provide a report. The report shall contain the following information: a) casting identification; b) identification and authorization of the person undertaking the examination; c) compa
27、rator(s) used versus area of the casting examined; d) result determined as an actual level of roughness.BS 7900 : 1998 BSI 1998 3 Annex A (informative) Examples of comparator plates4 BSI 1998 BS 7900 : 1998 BSI 1998 5 BS 7900 : 1998BSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | |
28、 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BSI British Standards Institution BSI is the independent national body re
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