1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7918-1:1999 ICS 01.040
2、.83; 83.060 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Visual imperfections in rubber products Part 1: VocabularyThis British Standard, having been prepared under the direction of the Sector Committee for Materials and Chemicals, was published under the authority of the S
3、tandards Committee and comes into effect on 15 April 1999 BSI 04-1999 The following BSI references relate to the work on this standard: Committee reference PRI/73 Draft for comment 95/124810 DC ISBN 0 580 29519 2 BS 7918-1:1999 Amendments issued since publication Amd. No. Date Text affected Committe
4、es responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee PRI/73, Industrial rubber products, upon which the following bodies were represented: British Rubber Manufacturers Association Ltd. British Structural Bearings Manufacturers Associa
5、tion Construction Confederation Department of the Environment, Transport and the Regions (Highways Agency) Institute of Biomedical Science Ministry of Defence Royal Society of Chemistry Tun Abdul Razak Research Centre University of North LondonBS 7918-1:1999 BSI 04-1999 i Contents Page Committees re
6、sponsible Inside front cover Foreword ii 1 Scope 1 2 Terms and definitions 1 Bibliography 11 Figure 1 Surface depressions (air entrapment) 1 Figure 2 Two plate mould with split line 2 Figure 3 Blister 2 Figure 4 Flash thickness 3 Figure 5 Removal of inclusions 4 Figure 6 Knit lines 4 Figure 7 Surfac
7、e depressions (laking) 5 Figure 8 Surface depression in a rubber covered roller as an example of localized bond failure 5 Figure 9 Off-register 6 Figure 10 Pitting 6 Figure 11 Scorch (localized and generalized) 7 Figure 12 Trimming 8 Figure 13 Surface splits 9 Figure 14 Cellular porosity and roughen
8、ed texture 10 Figure 15 Witness marks 10ii BSI 04-1999 BS 7918-1:1999 Foreword This part of BS 7918 has been prepared by Technical Committee PRI/73. BS 7918 has been published in order to assist manufacturers and inspectors in making objective assessments of a products conformity to a given specific
9、ation. It is intended that BS 7918 will be published in three parts: part 1, a vocabulary of terms and illustrations of those terms by way of example; part 2, a system of sampling and inspection and part 3, a system of classifying imperfections into a scheme which can be tailored to the needs of the
10、 individual contract of supply or can be included within a manufacturers quality control procedures. Parts 2 and 3 are currently in development. A British Standard does not purport to include all necessary provisions of a contract. Users of British Standards are responsible for their correct applica
11、tion. 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, pages 1 to 11 and a back cover. BSI 04-1999 1 BS 7918-1:1999 1 Scope This British Standard defines terms
12、used to describe the visual imperfections sometimes found in rubber products. The vocabulary is supplemented by schematic drawings which illustrate the terms. Imperfections in cellular products, for example gloss and colour imperfections, and instrumental methods of measurement are outside the scope
13、 of this standard, as are toroidal sealing rings (O-rings), for which reference should be made to BS 6442. 2 Terms and definitions 2.1 air entrapment entrapment of large quantities of air between the rubber and mould surface producing a large, often single surface depression (see Figure 1) NOTE 1 Wi
14、th certain rubbers, e.g. natural rubber, this is often accompanied by localized stickiness. NOTE 2 Dulling of the surface around the air trap can also occur due to the burning effect of the localized hot air. Figure 1 Surface depressions (air entrapment)2 BSI 04-1999 BS 7918-1:1999 2.2 backrind spli
15、ts and roughness running along a depression in the surface directly coincident with the mould split line (see Figure 2) NOTE Backrind can occur during moulding at the split line of a mould. It is caused by the mould opening slightly during the moulding process and the vulcanized surface layer being
16、forced through the opening. This movement of rubber breaks and cracks the moulded surface. Figure 2 Two plate mould with split line 2.3 blister trapped air in a component due to incomplete removal of air from the rubber during processing, resulting in surface blisters which, when cut, reveal a void
17、beneath them (see Figure 3) Figure 3 Blister 2.4 colour uniformity the visual perception that the hue and depth of shade throughout the entire surface area is not variable NOTE 1 At high magnifications or using comparative instrumental techniques, this visual perception may be challenged. NOTE 2 The
18、 visual perception of non-uniformity of colour is more noticeable in light-coloured articles and may have several causes, such as: contamination, for example by other materials and lack of cleanliness during production; sulfur spotting, which causes brown specks in sulfur-vulcanized components; or p
19、oor pigment dispersion giving rise to variations in hue. BSI 04-1999 3 BS 7918-1:1999 2.5 flash thickness an unwanted additional thickness of rubber at the interfaces between different segments of the mould or at a join in a component NOTE Excess flash can influence the dimensions of the finished pa
20、rt and may, therefore, be detectable by normal dimensional checks, but it may be necessary to specify limits on the size of flash on a component independently in some instances. See Figures 4a) and 4b). a) O-ring cross-section b) Block cross-section Figure 4 Flash thickness4 BSI 04-1999 BS 7918-1:19
21、99 2.6 inclusions foreign matter, e.g. grit, fibres, metal or vulcanized flash embedded in the surface of the component; or solid ingredients in the rubber compound, such as carbon black, which have not been properly dispersed (see Figure 5) NOTE Depending on the nature of the inclusion, it may or m
22、ay not be proud of the surface. If the inclusion is proud of the surface, it may be capable of being removed by a fingernail, leaving a pit in the rubber surface; flexing of the component may also release the inclusion. Fibrous matter may not be removable from the surface. Figure 5 Removal of inclus
23、ions 2.7 knit lines witness marks visible on the surface of a moulding under certain lighting conditions where two flow fronts have joined but not intimately merged (see Figure 6) NOTE Knit lines differ from flow lines in that a split in the surface is not detectable except under high magnification.
24、 It might be assumed that as knit lines are only a visible imperfection they are purely a cosmetic problem; they can, however, act as a point of failure under applied stress. Figure 6 Knit lines BSI 04-1999 5 BS 7918-1:1999 2.8 laking small surface depressions resulting from small quantities of air
25、being trapped between the rubber and the mould surface (see Figure 7) NOTE This imperfection is most common on moulded sheets. Figure 7 Surface depressions (laking) 2.9 localized bond failure in rubber-to-metal bonded components, the lack of a rubber-to-metal bond in a localized area on a component,
26、 resulting in a slight surface depression over the area (see Figure 8) Figure 8 Surface depression in a rubber covered roller as an example of localized bond failure 2.10 mould fouling build up of deposits on the mould which remain attached to the mould, but which cause localized depressions in the
27、rubber surface6 BSI 04-1999 BS 7918-1:1999 2.11 off-register misalignment of mould halves (see Figures 9a, 9b and 9c) NOTE In BS 6442 the term “mismatch” is defined as the difference resulting from a dimensional difference in mould halves, as in the second and third illustration in Figure 9a. In BS
28、3558-1, the terms “off-register” and “mismatch” are synonymous and confined to misalignment of mould parts. a) O-ring cross-section b) Block cross-section c) Jointed ring Figure 9 Off-register 2.12 pitting discrete single pits, visible on the surface of the component and not localized (see Figure 10
29、) NOTE Components produced by casting polyurethane materials can exhibit this effect where air bubbles in the mixed liquid have risen to the surface of the casting. Figure 10 Pitting BSI 04-1999 7 BS 7918-1:1999 2.13 scorch marks and distortion premature vulcanization occurring during processing whi
30、ch can lead to dull, matt, roughened or grainy surface texture in localized areas or of the whole part (see Figure 11) NOTE 1 Knit lines (see 2.7) may also be visible. NOTE 2 Distortion can also be caused by premature removal of the part during vulcanization, anisotropic flow patterns during flow an
31、d contact with other components during storage and transit (see BS 3574). Such distortion is usually of a gross nature, without necessarily changes in surface texture, and can cause dimensional changes. Figure 11 Scorch (localized and generalized) 2.14 surface abrasion and excessive trimming flats o
32、r slight depressions at the split line of a moulding caused by excessive surface abrasion or trimming of flash (see Figures 12a and 12b) NOTE Abrasion and trimming are two methods by which the flash produced during moulding may be removed from the finished component, the trimming involving the use o
33、f a knife either manually or in an automated process (see Figures 12a and 12b).8 BSI 04-1999 BS 7918-1:1999 2.15 excessive trimming method by which the flash produced during moulding may be removed from the finished component using a knife, either manually or in an automated process (see Figures 12a
34、 and 12b) NOTE Excessive trimming may result in flats or slight depressions at the splits. a) O-ring cross-section b) Block cross-section Figure 12 Trimming 2.16 surface contamination contaminant, such as rubber dust from a buffing operation, bloom of an ingredient from the compound or liquids appli
35、ed to prevent sticking of the finished components during transit, not moulded into the component surface, but merely residing on it NOTE While surface contamination may be regarded as being merely a cosmetic problem, it might, in certain circumstances, affect performance. 2.17 surface depressions lo
36、calized areas where the nature of the rubber surface is exactly the same as elsewhere on the component, but which are slightly depressed due to mould fouling (2.10), laking (2.8), air entrapment (2.1) or localized bond failure (2.9) BSI 04-1999 9 BS 7918-1:1999 2.18 surface splits splits in the surf
37、ace generally having a length in excess of the width of the split. They may vary in depth depending on their cause NOTE Splits in the surface can be caused by several factors such as those listed below: a) flow lines formed when the compound has not totally flowed together during processing (see Fig
38、ure 13a); b) failure to bond to metal at the rubber to metal interface in a composite component (see Figure 13b); c) failure to achieve total adhesion at a joint between two sections of rubber (see Figure 13c); d) removal of the part from the mould; e) cuts due to careless trimming operations; f) co
39、ntact with other parts during storage and transit. a) O-ring and segment section b) Bonded joint section c) Adhesion failure in bonded ring Figure 13 Surface splits10 BSI 04-1999 BS 7918-1:1999 2.19 surface porosity under-curing of a vulcanized component due to inadequate moulding pressure or someti
40、mes by slight under-filling of a mould cavity (see Figure 14) NOTE 1 The effect may, in certain circumstances, be extremely localized on a component. The presence of surface porosity can usually be detected by a change in surface texture and colour. NOTE 2 The porosity may be seen to be of a cellula
41、r nature as might be expected, but may also be seen as an area of roughened texture, if the degree of under-filling of the cavity is slight. Figure 14 Cellular porosity and roughened texture 2.20 witness marks pipes from injection or feed ports and flash pipes, or the pits that can result from their
42、 intentional or accidental removal (see Figure 15) NOTE The presence of such pipes may present either cosmetic or functional problems. Figure 15 Witness marks BSI 04-1999 11 BS 7918-1:1999 Bibliography Standards publications BS 3574, Specification for the controlled storage and packaging of vulcaniz
43、ed rubber and rubber products. BS 6442, Specification for limits of surface imperfections on elastomeric toroidal sealing rings (“O”-rings). BS 3558-1, Glossary of rubber terms Part 1: International terms.BSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | | | | | | | | | | | | | | |
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