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Module 17. Closures for Glass 

Containers 

Section 9 CFR 431.2(c) 

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Purpose and Objectives 

 Purpose of Module 17: 

• Provide knowledge of common closures 

and techniques to evaluate closures for 

glass containers. 

 Performance Objectives: 

• Can evaluate glass closure examinations 

and determine whether recorded results 

are complete and within specification. 

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The Basic Parts of a Glass Container 

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 Finish: Holds cap or closure 

 Body: Made in body mold 

 Bottom: Made in bottom plate 

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The Finish 

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 Sealing Surface: Contacts sealing gasket 

 Glass Thread or Lug: Protruding ridges for 

fastening closure 

 Transfer Bead: aids in transfer of container 

 

 

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The Finish (2) 

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 Vertical Neck Ring Seam: A line from 

matching the two parts of neck ring 

Parting Line 

Neck Ring 

 Neck Ring Parting Line: Horizontal line from 

matching neck ring parts with body-mold 

parts 

VERTICAL , ... · · ,CK 

RIN'O SEAM 

 

 

 

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The Body 

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 Shoulder: Top portion where diameter decreases 

 Side Wall: Area between shoulder and heel 

 Heel: Curved portion at bottom 

 Mold Seam: Vertical line from matching two parts 

of body mold 

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MOLD SEAM 

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S[DB WALL I BODY 

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HEEL 

 

 
eorm·M P'LATE 

PARTINO LINE 

BEARr,_o SURF .- CE 

 

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The Bottom 

 Bottom Plate Parting Line: Horizontal line 

from matching body-mold parts with bottom 

plate 

 Bearing Surface: Portion on which container 

rests 

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Discussion of the Finish 

 Hundreds of different finishes 

 Specific finishes are designed for specific 

closures 

 Glass finishes are standardized 

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Terms for Glass Closures 

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 Panel: Flat center of cap top 

 Radius of Shoulder: Connects panel and 

skirt 

 Skirt: Side of cap that serves as gripping 

surface 

PANEL 

RADIUS 

SKIRT 

 

 

 

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Terms for Glass Closures 

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 Lug: Protrusion from curl that holds cap in 

place 

 Thread: Spiral groove on continuous thread 

closures 

 

 

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Terms for Glass Closures (4) 

 Coatings: Protect cap metal, adhere gasket 

material and decorate closure 

 Gasket: Sealing member of cap 

 Plastisols: Gasket material 

 Safety Button or Flip Panel: Raised, circular 

area in panel center used in dud detection 

and as an indicator to consumer 

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Factors Affecting Vacuum Formation 

The vacuum within the container plays a vital 

role in forming and maintaining a good seal. 

1. Headspace 

2. Product sealing temperature 

3. Air in product 

4. Capper vacuum efficiency 

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3 Principal Vacuum Closure Types 

 Low-acid products: 

• Lug or twist cap 

• PT (Press-on Twist-off) cap 

 Acidified products: 

• Lug or twist cap 

• PLCT (plastisol-lined continuous thread) 

closure 

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Closure Evaluation 

 Visual examinations (non-destructive) 

 Closure examinations and tests (destructive) 

• These examinations must be made either 

before or after thermal processing 

• The establishment must have specification 

guidelines for closure integrity on file and 

available for review by Program employees 

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lii'til)::-==LU_G_B_E_N==T =O=UT====l=, LUG BENT IN 

APPEARS NORMAL 

NO SCRATCHES 

SLIGHT BEND 

,------- LIGHT SCRATCHES 

LUG BENT IN 

HEAVILY SCRATCHED 

SHALLOW 

IMPRESSION 

MODERATE BEND 

HEAVY SCRATCHES 

[ 

CURVED CREASE 

IN TOP PANEL 

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TO ONE SIDE 

Tests and Observations for Closure 

Application and Defects 

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CRUSHED LUGS 

[ tzmm:::1111111111 :l 

[ SLIGHT BEND INWARD 

ALL LUGS 

ALL LUGS SCRATCHED 

SEVERE TO SLIGHT 

IMPRESS ION EVEN BUT LIGHT 

STRIPPED CAP 

NOTE OUT OF ROUND 

CONDITION 

BARE METAL VISIBLE 

ON I NS I DE OF EACH LUG 

IMPRESSION LIGHT AND SLIGHTLY 

IRREGULAR 

Tests and Observations for Closure 

Application and Defects 

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Frequency of Inspection 

 Must be inspected by a trained technician at 

regular intervals to ensure satisfactory 

closures 

 Includes both visual and destructive tests 

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Visual Examinations 

 At least one container from each capper 

 Include an examination for closure and 

container defects 

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Visual Examinations 

 Defects must be recorded along with 

corrective actions 

 Should examine every 30 minutes 

 Must examine at start of production, after 

container jam, and after machine adjustment 

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Cocked-Cap Detectors and Ejectors 

 Serve to eliminate problem containers at 

capper 

 Signal that problem exists 

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Dud Detectors 

If properly maintained and checked, will monitor 

seal quality and serve as useful tool. 

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Physical Examinations 

 Must be conducted EITHER before OR after 

thermal processing 

 Should be made at intervals not to exceed 

four hours of continuous closing machine 

operation 

 Results along with any necessary corrective 

action must be promptly recorded 

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Physical Examinations 

 Additional examinations should be made at 

start of production, after a container jam, and 

after machine adjustment 

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Security 

 Most reliable measurement of proper lug cap 

application 

 Security value ranges are specified by 

closure manufacturer 

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Security Value Measurement 

 Make vertical line on cap and jar 

 Open cap until vacuum is broken and 

reapply until it is finger-tight 

 Measure distance between vertical lines 

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\\ 

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' \ Mark applied by 

Inspector 

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-+141+-

'---- Security 

Measurement 

(in 1 /16th in.) 

Security Value Measurement 

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Security Value Measurement 

After processing and cooling values will be 

lower. 

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Key Notes 

 Headspace, product temperature, entrapped 

air in the product, and capper vacuum 

efficiency affect vacuum formation. 

 Examinations of cap application should be 

done to assure that the cap is level and 

properly seated on the finish, vacuum is 

adequate and for gasket impression checked 

after processing. 

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Key Notes (2) 

 Lug cap application should be evaluated for

level cap, pull-up, security, adequate vacuum 

and gasket impression after processing. 

 PT cap application should be evaluated for

level cap, adequate vacuum and gasket 

impression after processing. 

 Corrective action must be taken when 

readings outside of specifications exist or 

when caps are loose. 

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Questions 

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Questions?