MIL-STD-413C Visual Inspection Guide for Elastomeric O-Rings

NOTE: MIL-STD-413 has been redesignated as a Test Method Standard. The coverpage has been changed for Administrative reasons. There are no other changesto this Document.

MIL-STD-413C 8 DECEMBER 1980

SUPERSEDING MIL-STD-413B

28 FEBRUARY 1969

AMSC N/A FSC 5330

DISTRIBUTION STATEMENT A. Approved for public release; distribution isunlimited.

DEPARTMENT OF DEFENSETEST METHOD

VISUAL INSPECTION GUIDEFOR

RUBBER ELASTROMERIC O-RINGS

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MIL-STD-413C8 December 1980

DEPARTMENT OF DEFENSE

WASHINGTON, DC 20360

Visual Inspection Guide forRubber O-Rings

MIL-STD-413C

1. This Military Standard is mandatory for use by all Departmentsand Agencies of the Department of Defense.

2. Beneficial comments (recommendations, additions, deletions) andany pertinent data which may be of use in improving this document shouldbe addressed to: Commander, Naval Sea Systems Command, SEA 3112,Department of the Navy, Washington, DC 20362 by using the self-addressedStandardization Document Improvement proposal (DD Form 1426) appearingat the end of this document or by letter.

ii



FOREWORD

Government material acquisition specifications have been primarilyconcerned with detailing composition, construction, and necessary physicalrequirements. However , little attention has been paid to defining thelimits of acceptable quality regarding manufacturing imperfections otherthan such generalizations as "the workmanship shall be first class." Insuch a diverse industry as that of rubber manufacturing, individual plantsvary considerably in their production and quality control techniques.Imperfections are likely to occur from many causes, such as variation inthe quality of the basic materials and variations in manufacturingprocesses and finishing operations. Therefore, the quality generalizationsused in this standard must, of necessity, cover a considerable range whichrepresents the best available judgement. This standard is issued as apractical yardstick which quality assurance personnel will use to appraisethe acceptability of O-rings concerning visible imperfections.

iii



CONTENTS

Paragraph 1.1.11.2

2.2.1

3.

4.4.14.24.3

5.5.15.25.3

Figure 1.2.3.4.5.6.7.8.9.

10.11.

12.

13.

14.

15.

16.

17.

18.

19.

SCOPE . . . . . . . . . . . . . . . . . . . . . 1Purpose . . . . . . . . . . . . . . . . . . . . 1Scope . . . . . . . . . . . . . . . . . . . . . 1

REFERENCED DOCUMENTS . . . . . . . . . . . . . . 1Issues of documents . . . . . . . . . . . . . . 1

DEFINITIONS . . . . . . . . . . . . . . . . . . 1

GENERAL REQUIREMENTS . . . . . . . . . . . . . . 3Examination conditions . . . . . . . . . . . . . 3Identification of imperfections . . . . . . . . 3Evaluation of imperfections . . . . . . . . . . 3

DETAILED REQUIREMENTS . . . . . . . . . . . . . 4Nondestructive tests . . . . . . . . . . . . . . 4Rejection of individual O-rings . . . . . . . . 4Sampling . . . . . . . . . . . . . . . . . . . . 4 & 5

FIGURES

Backrind, unacceptable, W = 0.070" (1.78 mm) . . 9Backrind, unacceptable, W = 0.103" (2.62 mm) . . 10Backrind, unacceptable, W = 0.103" (2.62 mm) . . 11Backrind, unacceptable, W = 0.103" (2.62 mm) . . 12Backrind, acceptable, W = 0.103" (2.62 mm) . . . 13Backrind, acceptable, W = 0.103" (2.62 mm) . . . 14Backrind, unacceptable, W = 0.139" (3.53 mm) . . 15Backrind, acceptable, W = 0.139" (3.53 mm) . . . 16Backrind, acceptable, W = 0.210" (5.33 mm) . . . 17Backrind, unacceptable, W = 0.210" (5.33 mm) . . 18Parting line indentation, acceptable, W = 0.070"(1.78 mm) . . . . . . . . . . . . . . . . . . . 19

Parting line indentation, acceptable, W = 0.070"(1.78 mm) . . . . . . . . . . . . . . . . . . . 20


Parting line indentation, unacceptable,w = 0.070" (1.78 mm) . . . . . . . . . . . . . 22Parting line indentation, acceptable, W = 0.103"(2.62 mm) . . . . . . . . . . . . . . . . . . . 23

Parting line indentation, acceptable, W = 0.103"(2.62 mm) . . . . . . . . . . . . . . . . . . l 24


Parting line indentation, unacceptable,W = 0.103" (2.62 mm) . . . . . . . . . . . . . 26Parting line indentation, unacceptable,w = 0.139" (3.53 mm) . . . . . . . . . . . . . 27

iv

Page


MIL -STD-413C8 December 1980

CONTENTS (Continued)

Page

Figure 20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

41.

42.

43.



Parting line indentation, unacceptable,w = 0.210" (5.33 mm) . . . . . . . . . . . . . 32Foreign material, acceptable, W . 0.103"(2.62 mm) . . . . . . . . . . . . . . . . . . . 33

Foreign material, unacceptable, W = 0. 103"(2.62 mm) . . . . . . . . . . . . . . . . . . . 34

Foreign material, acceptable, W . 0. 103"(2.62 mm) . . . . . . . . . . . . . . . . . . . 35

Foreign material, unacceptable, W = 0.103"(2.62 mm) . . . . . . . . . . . . . . . . . . . 36

Foreign material, acceptable, W = 0.139"(3.53 mm) . . . . . . . . . . . . . . . . . . . 37

Foreign material, unacceptable, W = 0. 139"(3.53 mm) . . . . . . . . . . . . . . . . . . . 38

Foreign material, acceptable, W = 0.139"(3.53 mm) . . . . . . . . . . . . . . . . . . . 39

Foreign material, unacceptable, W = 0.210"(5.33 mm) . . . . . . . . . . . . . . . . . . . 40

Foreign material, unacceptable, W = 0.275"(6.98 mm) . . . . . . . . . . . 41

Excessive trimming, acceptable, W = 0.103"

(2.62 mm) . . . . . . . . . . . . . . . . . . . 42Excessive trimming, unacceptable, W = 0.103" (2.62 mm) . . . . . . . . . . . . . . . . . . . 43

Excessive trimming, acceptable, W = 0.103"(2.62 mm) . . . . . . . . . . . . . . . . . . . 44

Excessive trimming, unacceptable, W = 0.103"(2.62 mm) . . . . . . . . . . . . . . . . . . . 45





Excessive flash, unacceptable, W = 0.l03"(2.62 mm) . . . . . . . . . . . . . . . . . .

Excessive flash, unacceptable, W = 0.l03" (2.62 mm) . . . . . . . . . . . . . . . . . . . 51

v

50




Figure 44.

45.

46.

47.

48.

49.

500

51.

52.53.54.55.56.

58.59.60.61.

62.

63.

64.

65.

66.

67.

68.

69.

70.71.72.73.74.75.76.

Excessive flash, unacceptable, W = 0.103"(2.62 mm) . . . . . . . . . . . . . . . . . .

Excessive flash, acceptable, W = 0.103"(2.62 mm) . . . . . . . . . . . . . . . . . .


Excessive flash, unacceptable, W = 0.139"(3.53 mm) . . . . . . . . . . . . . . . . . .Excessive flash, acceptable, W = 0.139"(3.53 mm) . . . . . . . . . . . . . . . . . .




Non-fill, unacceptable, W = 0.070" (1.78 mm) .Non-fill, unacceptable, W = 0.103" (2.62 mm) .Non-fill, acceptable, W = 0.139" (3.53 mm) . .Non-fill, unacceptable, W = 0.139" (3.53 mm) .Non-fill, unacceptable, W = 0.139" (3.53 mm) .Non-fill, unacceptable, W = 0.210" (5.33 mm) .Non-fill, unacceptable, W = 0.210" (5.33 mm) .Non-fill, acceptable, W = 0.275" (6.98 mm) . .Non-fill, unacceptable, W = 0.275" (6.98 mm) .Mold deposit indentations, unacceptable,W = 0.070" (l.78 mm) . . . . . . . . . . . .Mold deposit indentations, acceptable,W = 0.l03" (2.62 mm) . . . . . . . . . . . .

Mold deposit indentations, acceptable,W = 0.139" (3.53 mm) . . . . . . . . . . . .Mold deposit indentations, unacceptable,W = 0.139" (3.53 mm) . . . . . . . . . . . .

Mold deposit indentations, unacceptable,W = 0.139" (3.53 mm) . . . . . . . . . . . .Mold deposit indentations, unacceptable,W = 0.139" (3.53 mm) . . . . . . . . . . . .Mold deposit indentations, acceptable,W = 0.139" (3.53 mm) . . . . . . . . . . . .Mold deposit indentations, acceptable,W = 0.210" (5.33 mm) . . . . . . . . . . . .Mold deposit indentations, unacceptable,W = 0.275" (6.98 mm) . . . . . . . . . . . .Flow marks, unacceptable, W = 0.070" (1.78 mm)Flow marks, unacceptable, W = 0.139" (3.53 mm)Flow marks, acceptable, W = 0.139" (3.53 mm) .Flow marks, unacceptable, W = 0.139" (3.53 mm)Flow marks, acceptable, W = 0.139" (3.53 mm) .Flow marks, unacceptable, W = 0.139" (3.53 mm)Flow marks, unacceptable, W = 0.139" (3.53 mm)

. 52

. 53

. 54

. 55

. 56

. 57

. 58

59. 60. 61. 62. 63. 64

65. 66

67. 68

. 69

. 70

. 71

. 72

. 73

. 74

. 75

. 76

. 7778

. 79

. 80

. 81

. 8283

. 84

vi

Page

57.




Page

Figure 77.78.79.

80.

81.

82.

83.

84.

85.

86.

87.

Table I.

II.

III.

Flow marks, acceptable, W = 0.139" (3.53 mm) . . 85Flow marks, acceptable, W = 0.210" (5.33 mm) . . 86Off-register and/or mismatch, unacceptable,w = 0.070" (1.78 mm) . . . . . . . . . . . . . 87Off-register and/or mismatch, unacceptable,w = 0.103" (2.62 mm) . . . . . . . . . . . . . 88

Off-register and/or mismatch, unacceptable,w = 0.139" (3.53 mm) . . . . . . . . . . . . . 89Off-register and/or mismatch, acceptable,w = 0.139" (3.53 mm) . . . . . . . . . . . . . 90Off-register and/or mismatch, acceptable,w = 0.139" (3.53 mm) . . . . . . . . . . . . . 91

Off-register and/or mismatch, acceptable,w = 0.139" (3.53 mm) . . . . . . . . . . . . . 92Off-register and/or mismatch, acceptable,w = 0.210" (5.33 mm) . . . . . . . . . . . . . 93Off-register and/or mismatch, unacceptable,w = 0.210" (5.33 mm) . . . . . . . . . . . . . 94Supplementary illustrations of surfaceimperfections . . . . . . . . . . . . . . . . . 95

TABLES

Index to photographs of representative accept-able and unacceptable surface imperfections . . 6

Quantitative classification of imperfections,maximum acceptable dimensions in inches . . . . 7Quantitative classification of imperfections,maximum acceptable dimensions in millimeters . 8

vii/viii



1. SCOPE

1.1 Purpose. The objective of this standard is to assureacquisition of elastomeric O-rings with a surface quality level adequatefor their intended use. To achieve this objective, this standard:

(a) Includes illustrations and supplementary definitions anddimensions to identify O-ring surface imperfections forthe purpose of inspection, and

(b) Establishes quantitative levels of acceptance for O-ringsrelative to surface imperfections, type, size and quantity.

1.1.1 In general, this standard is intended to supplement theinspection procedure of a particular specification for O-rings. Whereno such procedure is provided, this standard becomes the primary guide.In the event of conflict between this standard and the inspection procedureof an end item specification or a specification for O-rings, the basicspecification shall govern.

1.2 Scope. This document covers only visible imperfections ofO-rings.

2. REFERENCED DOCUMENTS

2.1 Issues of documents. The following documents, of the issuein effect on date of invitation for bids or request for proposal, forma Part of this standard to the extent specified herein.

STANDARDS

MILITARYMIL-STD-105 - Sampling Procedures and Tables for Inspection

by Attributes.MIL-STD-109 - Quality Assurance Terms and Definitions.

(Copies of specifications, standards, drawings, and publicationsrequired by contractors in connection with specific acquisition functionsshould be obtained from the contracting activity or as directed by thecontracting officer.)

3. DEFINITIONS

3.1 MIL-STD-105 and MIL-STD-109 define critical, major and minordefects. The classification of an O-ring defect as "critical" requiresknowledge of the end use; therefore, critical defects are not includedin this standard but must be, considered in the basic specification(s).O-rings inspected for surface imperfections in accordance with thisstandard are determined to be either acceptable or unacceptable. Theconcept of minor defects is not applicable.

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3.2 Theimperfections

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

(1)

following word descriptions apply to the visiblecovered in this standard:

Backrind. A longitudinal recess of wide angle U-like orW-like cross-sections, oriented circumferentially andlocated at parting lines, caused by thermal expansion oversharp mold edge or by premature cure.

Blister. A void or a hole in the body of the O-ring, whichmay or may not cause protrusion on the surface and maybe covered or open, caused by air being trapped duringcure.

Bloom. Material which has migrated from the body of theO-ring to the O-ring surface.

Excessive trimming. Flat spots or nicks, producing out-of-tolerance cross-section, caused by excessive buffing ortrimming of flash. An O-ring is considered excessivelytrimmed only if a flat area results to the extent thatan out-of-tolerance condition exists. Even when an O-ringhas not been "excessively trimmed", it could have animperfect trim or buff condition. "lImperfect trim or buff"is a condition, wherein abrasion, scuffing or tearing,generated when removing flash or parting line projection,result in a substantially coarser texture. ProtrudingO-ring material or a heavily abraded surface are theindicators of "imperfect trim" and are not acceptable onany size O-ring.

Flash. Very thin gage, sometimes film-like, material whichextends from parting line projection, resulting from moldseparation or inadequate trim.

Flow mark. A thread-like recess, usually curved, of veryslight depth in the unflexed state, with normal surfacetexture and radiused edge. It is caused by incompleteflow and knit of the material.

Foreign material. Any extraneous, embedded matter (suchas contamination, dirt, or undispersed pigment) ordepression, formed by its removal.

Mismatch. The cross-sectional radius in one ring halfis unequal to that of the other half. It is caused bythe dimensional difference in mold halves.Mold deposit indentations. Surface indentations, irregularin shape, with rough surface texture, caused by a build-upof hardened deposits, adhering to the mold cavity.

Non-fill. A randomly spaced, irregularly shaped, surfaceindentation, having a coarser texture, than the normalO-ring surface.

Off-register. Misaligned O-ring halves, caused by thelateral shift of one mold cavity plate, relative to theother.

Parting line indentation. A shallow, saucer-like recess,located on the parting line, caused by a deformity in moldedge.

2



(m) Parting line projection. A continuous ridge of material,situated on the parting line, caused by worn or otherwiseexcessively rounded mold edges.

(n) Porosity. Presence of numerous minute voids or sponginess,showing up usually in a cross-section cut.

4. GENERAL REQUIREMENTS

4.1 Examination conditions. The illumination during examinationshall be 400-foot candles, minimum. Bloom or surface dust, if presenton the O-ring, shall be removed before inspection.

4.2 Identification of imperfections.

4.2.1 Enlarged photographs of representative, acceptable andunacceptable imperfections are included to aid inspection (see figures1 through 86). The grid sizes are 0.1, 0.2, 0.3, 0.5 and 1.0 inch forlx, 2x, 3x, 5x, and 10X magnification, respectively.

4.2.2 Arrows have been added to selected 10X magnificationphotographs for aid in identifying the imperfection shown. 3X powermagnification , however, shall be used to aid in the detection ofimperfections, unless otherwise specified by the contract.

4.2.3 All photographs are indexed in table I, according to figurenumber, O-ring size (W), type of imperfection and classification ofimperfection (acceptable and unacceptable) . For some types of imper-fections, exaggerated line drawings are included to supplement the photo-graphs and to illustrate the nature of the imperfections more vividly (seefigure 87).

4.2.4 It should be borne in mind that this standard has includedphotographs of only the most common imperfections that occur during thefabrication of elastomeric O-rings. It is not feasible to obtain photo-graphs to show clearly all possible imperfections in all sizes. Further ,the definitions of imperfections in this standard do not abrogaterequirements of a particular specification , contract or order. Where othertypes of imperfections such as cracks or ruptures are found , the generalworkmanship criteria of 5.1 shall govern.

4.3 Evaluation of imperfections.

4.3.1 For the purpose of visual examination, it is recommended thatinspectors use , for reference and comparison, wire gauges or other typedevices in diameters of 0.002; 0.005; 0.010: 0.015; and 0.020 inch (or0.05; 0.13; 0.25; 0.38; and 0.51 millimeters (mm)). Such gauges shallbe positioned adjacent to imperfections for their size determination.

4.3.2 Quantitative classification of acceptable and unacceptableimperfections is shown in table II (showing dimensions in inches) and intable III (showing dimensions in mm). When any dimension of an imper-fection exceeds the value specified in tables II or III, as applicable,this constitutes an unacceptable imperfection for any O-ring having a cross-sectional width, "W", within the range shown. Otherwise , the imperfection

3



is classified as acceptable. In general, the dimensional limits of imper-fections are related to the O-ring cross-sectional width. For O-ring sizesappreciably larger than 0.275 inch (6.98 mm) cross-sectional width, qualityasurance personnel should refer to the particular specification involvedfor quantitative dimensional limits of imperfections.

5. DETAILED REQUIREMENTS

5.1 Nondestructive tests. In all cases, including where a conflictexists with this standard , the requirements of the applicable specificationshall govern. Workmanship and finish shall be in acordance with thehighest grade practice in manufacturing this kind of product. Manufac-turing practices shall be such that the physical properties of the finishedproduct shall be uniform in quality and condition, clean, smooth and freefrom cracks, ruptures, porosity, blisters, foreign materials or otherimperfections detrimental to the performance of the parts, as furtherdefined herein.

5.1.1 Each O-ring sampled shall be carefully examined for visiblesurface imperfection s (see section 4, and tables I, II, and III).Unacceptable imperfections (those which exceed the dimensional limits intables II and 111, as applicable, or those described in 5.2), shall because for rejection of O-rings.

5.2 Rejection of individual O-rings. Rejection of individualO-rings shall be based on the following:

(a) Each O-ring found to have out-of-tolerance dimensions shallbe rejected.

(b) Visual surface imperfections shall be cause for rejection,as follows:

Any O-ring with one or more unacceptable surfaceimperfection.

Any O-ring with radially oriented flow mark, regardlessof length.Any O-ring exhibiting poor general appearance, as definedin 5.1.

Such rejection applies equally to surface imperfections found on O-ringsinspected for any requirement under the applicable specification. Also,any O-ring which was part of a sample shall be rejected if it containsone or more unacceptable imperfections , regardless of whether its lot orbatch as a whole is accepted or rejected.

5.3 Sampling. All O-rings shall be subjected to one or moreMIL-STD-105 sampling procedures, as specified by the contracting activity,except where the material specification includes a sampling plan. Unlessspecified otherwise in the material specification, purchase order or

4



contract, an Acceptable Quality Level (AQL) of 1.5 percent defective shallused . Acceptance or rejection of the lot, sublot or batch shall be onthis basis, except where already rejected in 5.1. In the application ofMIL-STD-105 to this standard, the following shall be noted:

(a) Inasmuch as inspection to this standard is to determinewhether O-rings are either acceptable or unacceptable andin view of 3.1, minor and critical defects do not apply.

(b) Any sampled O-ring which is rejectable, as indicated in5.2, shall be considered defective for the determinationof the acceptance or rejection of the lot it represents.

Custodians : Preparing activity:Army - M I Navy - SHNavy - SH (Project 5330-0532)Air Force - 99

Review activities:Navy - OS, ASAir Force - 11

User activities:Army - ATNavy - MC



6



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MIL-STD-413C Visual Inspection Guide for Elastomeric O-Rings

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