Gasket Fabricators Association

Technical Handbook

994 Old Eagle School Rd., Suite 1019, Wayne, Pennsylvania 19087-1802Phone: 610-971-4850

Fax: 610-971-4859E-Mail: info@gasketfab.com

Web Site: www.gasketfab.com

©Copyright 1998 - Gasket Fabricators Association994 Old Eagle School Road, Suite 1019Wayne, PA 19087-1866

No duplication without the written consent of the Gasket Fabricators Association

I Introduction

A. Gasket Fabricator Definition------------------------------B. Types of Materials Fabricated - Processing Equipment-

II Standard Practices------------------------------------------

A. Dimensional Characteristics-------------------------------B. Material Thickness Tolerances----------------------------C. Measurement------------------------------------------------D. Part Identification-------------------------------------------E. Labeling (Standard Label Format)------------------------F. Lot Traceability---------------------------------------------G. Quality Assurance ------------------------------------------H. Statistical Process Control---------------------------------

Table of Contents

11

3

310111213141515

INTRODUCTION

Gasket Fabricator Defined

G askets are an integral compo-nent of any device whichrequires the confinement of a

gas or liquid. They compensate for theunconformity of mating surfaces.These surface irregularities may beminute or large depending on thepurpose of the device but in all cases,the gasket is required to compensatefor the difference while limiting theflow of fluid in either direction.

Gaskets differ from seals in thatgaskets are normally cut from sheets orrolls while seals are formed individu-ally in their own configuration. A flatcut gasket is derived from material ofspecific thickness and to a configura-tion that is designed for a specificapplication.

Organizations which convertmaterial in sheet or roll form to func-tional gaskets are designated as “gasketfabricators,” gasket cutters,” or simply“converters.” “Gasket fabricators” aregenerally perceived to be those organi-zations which have dedicated theirassets toward optimal accuracy andefficiency in their gasket fabricatingactivities. They have made major invest-ments in sophisticated fabricating equip-ment. Gasket fabrication for originalequipment production line applicationsrequires consistency and precision on anever-improving scale. Organizations thatare sensitive to these needs, invest in therequired equipment and process controls.

Members of the Gasket FabricatorsAssociation are professionals dedicatedto the continuous improvement ofthese activities.

Types of MaterialFabricated—ProcessingEquipment

I f the gasket material is in sheet orroll form, a gasket fabricator canconvert it into parts. However,

the material characteristics will deter-mine the personality of the end prod-uct. Gasket materials that are hardand thin can be fabricated to tighterdimensional tolerances than gasketmaterials that are soft and thick.Accordingly, 90 durometer rubber 1/32

inch thick can be cut to more preciserequirements than 30 durometerrubber 1/8 inch thick.

Some gasket fabricators special-ize in certain types of material. Onefabricator may have unique capabili-ties in the processing of sponge rubberproducts where another fabricatormay have acquired equipment moresuitable for elastomeric rubber.

Another specialization is theability to process sheets rather thanroll goods. One fabricator may beheavily invested in platen presseswhile another may specialize in slittersand punch presses with continuousfeed and takeoff.

Typical gasket fabricating equip-ment utilized by gasket fabricatorsare:1. Steel Rule Dies— Most commonly used

for moderate volume parts. Tool-ing is economical and can be usedin platen presses, roll presses,mechanical presses or rotary diemachines.

1

2. Male and Female Blanking Dies—Generallyused in high volume productionwhere very close tolerances arerequired. Tooling is more costlybut generally longer lasting.

3. Laser Cutting Machines—Laser technologyoffers excellent tolerance control withessentially no tooling wear. Equip-ment is expensive and used primarilyin very specific applications.

4. Water Jet Cutting Machines—New tech-nology with limited use, except inreinforced fiberglass compositecutting. Offers excellent tolerances.

5. Wire Electrical Discharge Machines (EDM)—For small volume or prototypework. Very good for intricatedesigns.

In summary, all gasket fabricatorsare not alike. They differ in their con-verting capabilities and accordingly, theydiffer in the types and forms of materi-als processed.

2

STANDARD PRACTICES

DIMENSIONAL CHARACTERISTICS

General

T he objective of the followingspecifications and capabilitiesfor cut gaskets is to acquaint the

user of gasketing products with accept-able methods, procedures and dimen-sional characteristics used in the industry.The enclosed information and data isoffered as a guide to the designer ofgaskets as well as an aid to the purchas-ing facility using cut gaskets.

The specifications outlined hereinwere developed from the present stateof the art with respect to known manu-facturing techniques. Depending uponmaterials, product design and/orindividual manufacturing techniques,the dimensional specifications outlinedin the report may vary.

Application

I n general, a gasket is used to sealtwo imperfect mating surfaces. Inany part designed as a gasket, only

the designer knows which dimensionsare critical. If all are critical, thisshould be clearly indicated. In gasketdesigns, the bolt hole location and holesize are normally the most important.Port hole position and size may also beof prime concern. Thickness of thegasket as well as the material physicalcharacteristics play an important partin gasket design and capability. Theessential design elements shouldalways be specified on drawings. Inexamining a gasket drawing the pro-ducer of a gasket frequently questionsif corners must be as sharp as shown

or whether radii are acceptable; do allholes and ports actually require thesame close tolerances; and does thetitle block tolerance properly reflectactual gasket requirements versusstandards for machined parts? Thedesigner should be certain he needseverything he specifies. Unnecessaryrequirements can result in needlesscosts in producing the parts. Consulta-tion with the gasket fabricator willoften lead to cost saving in tooling orproduction of the part.

M e t h o d s

A lthough cutting methods forindividual gaskets can varywidely, the most conventional

cutting tools used are: Steel rule dies,solid steel dies, or a combination ofboth. The most widely used is the steelrule die. Steel rule dies have beendescribed as “glorified cookie cutters.”A steel rule die consists of a basematerial such as high grade plywood orphenolic composition which becomesthe holder for a strip of hard thin steelsharpened on one edge known as “steelrule.” Sharpened hole punches knownas “tubes” are incorporated along withrubber stripper pads to complete thetool. Depending upon the dimensionalaspects of the part, different procedurescan be used in the construction of thecutting tool. These various methodsgreatly dictate the accuracy of the cutpart.

The illustrations on page 7 and 8outline steel rule construction methods.

3

4

Tooling Types The two most common types of

tooling used are steel rule dies and allsteel dies. Volume, quantity, tolerance,and cost are the variables that helpdetermine the type of tooling used.

Steel Rule DiesThere are multiple ways to construct asteel rule die. However, the objective ofany method is to cut a pattern of the partinto the base material, and then insert asteel rule that has been bent into thesame pattern, into the base material.

The various methods used tomake a steel rule die are:n To obtain the pattern cut into the

dieboard, the customer’s print or partpattern can be either hand or machinedrafted onto the dieboard. Thedieboard is then hand cut with ajigsaw.n Another method is to program the

customer’s print into a computercontrolled laser cutting machine andlaser cut the pattern into the dieboard.n Once the pattern is cut into the

dieboard, the steel rule is bent into thesame pattern and inserted into theboard. The bending of the steel rulecan be done either by hand or by usinga computer driven rule bendingmachine.

As shown in the chart on thefollowing page, these methods havedifferent tolerances associated withthem.

All Steel ToolingDepending upon the complexity

of the design, the type of material andthe volume of the part, all steel maleand female tooling is often used toproduce a gasket. Unlike blanking orcutting ferrous or nonferrous materi-als, most gasketing materials do notrequire clearance between the punch

and the die in all steel tooling. Thecommon practice is to construct allsteel tooling with minimum clearancebetween the punch and die. In manyinstances, the punch may be hard witha soft die which allows the die to be“peened” against the punch to providezero clearance conditions. Zero clear-ance provides clean cut parts. As theedges of the punch and die becomerounded due to the abrasive action ofthe material being cut, the quality ofthe cut part may diminish.

Dimensional tolerancing for allsteel tooling can be controlled to a fewthousandths of an inch. The improvedaccuracy of all steel tooling over ruledie tooling results in more accuratepart dimensional capabilities. Althoughthe all steel tooling used to produce agasket may be built to very closetolerances, the tolerance of the partdepends upon the gasketing material.The material may pull or stretch duringthe cutting action. The cut part may besubject to shrinkage or expansiondepending on the atmospheric condi-tions after cutting. To maintain maxi-mum dimensional stability on partsproduced from all steel tooling, the dieshould be maintained in a sharp condi-tion and the parts should be packagedin a stable environment.

Dimensional Capabilities for Steel Rule Dies

5

I t is important to know that the dimensions of the diecut part are determined not only by the die, but also bythe material type, hardness, density, thickness, and

variations of these factors. The greater the variation ofthese factors, the greater the variance of the die cut dimen-sions.

Different types of tooling have different dimensionaltolerances.

All steel tooling provides the most accurate tolerances.These can vary depending on type of tool constructionmethods, but generally +/-.002 to +/-.005 can be held.

Steel rule tooling also varies with the type of construc-tion method. The most accurate is laser cut board withautomated bent rule. Depending on length of rule, toler-ances can range from +/-.005 to +/-.015. The longer the ruleis, the more variation can be expected.

Steel rule dies that are laid out by hand and jigsaw cutcan not be held this tight and will generally vary +/-.030.

Holes that are cut using punches will have the sametolerance regardless of die construction method. Theindustry accepted variation on punch dimensions are asfollows:

Hole diameter—less than 3/4” +/-.002Hole diameter—from 3 /4”-15/8 +/-.003Hole diameter—greater than 15/8 +/-.005

Hole position tolerance is again best achieved usinglaser cutting and automated rule bending. Depending ondistance between holes +/-.005 to +/-.015 can be expected. Ifthe die is laid out by hand and jigsaw cut, the tolerancescould be +/-.010 to +/-.030.

These tolerances are general guidelines and can varybased upon die building equipment and the skills of the diemaker.

6

Steel Rule Die Making Methods

The die making process begins with the layout. The layout can bedone either manually or by C.A.D.

A computer controlled laser cutsthe die board.

The pattern is cut with a preci-sion jig saw.

The steel rule ishand cut and bentto proper con-figuration.

(Right) A com-puter controlledmachine cuts andbends the rule.

The steel rule is inserted into thedie board.

The steel rule die is complete.

7

Dimensional VerificationVarious methods are used to check dimensions on

production tooling or parts. In most cases, it is difficult tomeasure the dimensions on the steel rule die itself, becauseof the many types of bevels and position of the cutting edge.

It is not recommended to use the gasket as a measuringdevice since the part is usually flimsy and unstable. Somegasket materials are subject to change due to atmosphericconditions, such as humidity.

Die impressions are commonly used to check dimen-sions. The impression should be made on stable material.These materials are not subject to change due to tempera-ture or moisture conditions. Mylar, plastics and tag paperare commonly used. An impression is created by eithercutting partially into the plastic material, which gives a cleardefined line to measure against, or a dark line impressioncan be obtained by placing carbon paper between the dieand manila tag. If a coordinate measuring machine is usedfor checking, the plastic impression is best to use since adefined line is present in which to position the stylus. Cau-tion should be used when making the impression. Distortioncan result if the impression is too deep which can causeerrors in measurement.

Manila tag impressions can be easily measured usingstandard drafting techniques or they can be used withcoordinate measuring machines similar to plastic impres-sions.

Punched holes dimensions should be measured bymeans of plug gauges in the punched hole of the gasket.The hole should be measured opposite the initial piercedside. On relatively thin materials, there will be little, if any,size variation from one side or the other. On thick materi-als, the bevel of the punch tube may distort the hole to somedegree.

Hole true position can best be determined by coordi-nate measuring machines. All positional tolerance require-ments are to be based upon maximum material conditions(MMC) unless otherwise specified.

An example of hole location tolerance for floatingfasteners and tolerances for radius with an unlocated centeris illustrated at the top of the next page.

SingleDoubleBevel

CreasingRule

Single Bevel Double Bevel DoubleDouble Bevel

8

Toleranced Radii.A toleranced radius with an unlocated center creates a

tolerance zone defined by arcs tangent to adjacent surfaceswithin which the part contour must have a faired curvewithout reversals. The part contour falls entirely within thezone between the minimum radius and the maximumradius, regardless of the actual shape of the part. Theradius at all points of the part contour shall neither besmaller than the specified minimum limit nor larger than themaximum limit. See illustration.

9

MATERIAL THICKNESS TOLERANCES

T o perform their function, gaskets are expected to be compressible andresilient. Materials are often selected for specific applications becauseof their compressibility.

Since the material is intended to be compressed, original thickness andthickness tolerances are important only to the extent that sufficient materialremains after compression to fill the gap between flange surfaces. Accordingly,in general, soft compressible materials (sponge, cork) have greater thicknesstolerances than firm, less compressible materials (compressed sheet). In no caseshould these resilient materials be specified with the same thickness tolerancesas non-resilient materials such as steel.

Typical thickness tolerances for resilient gasketing materials are listedbelow.

10

MEASUREMENT

I n the previous section “Dimensional Characteristics,” it was suggested thatdimensional verification of tooling be made on die impressions rather thanon cut gaskets due to the dimensional instability of some materials. This

procedure may be acceptable in the fabricator’s workplace but it may not satisfythe needs of the gasket user. Accordingly, attention must be given to the gasketdimensions at the place of application. If the gasket material shows significantdimensional change in changes of atmospheric conditions, the gasket must beprotected from these influences. In recognition of this characteristic, gasketsfabricated from cork containing materials are generally packaged in polyethylenebags. Although cellulosic materials are subject to dimensional change in varyingenvironmental conditions, some cellulose based materials have been reinforcedwith inorganic fibers to reduce atmospheric dimensional change.

Notwithstanding the above information, there are times when fabricatedgaskets must be checked for their dimensional conformance to blueprint orapplication requirements. In order to achieve verifiable and accurate dimen-sions, consideration must be given to atmospheric conditioning of the gasket.ASTM Standard F104-83, Paragraph 8, details the currently accepted condition-ing practices.

Measuring devices available and commonly used by gasket fabricators are:n Calipersn Coordinate Measuring Machinesn Durometer Gage - instrument to check hardness of rubber and rubber-

like materialn Gage Pins - straight, unflanged pins with specific diameters and ex-

tremely close tolerancesn Light Section MicroscopenMetal Hardness Tester-device to determine hardness of steel being

fabricatednMicrometersn Optical Comparatorsn Radius Gages - precision ground metal strips with accurate radius

machined on each endn Scales - 6” 12” 18”n Shadow Graph Machinesn Templates - Soft (thin plastic or mylar) Hard (1/8” to 1/2” thick plastic

or mylar with steel pins)n Tolerance Gauge - Tool for visual pass/fail dimensional inspection.

11

PART IDENTIFICATION

S ome manufacturing operations utilize a multitude of similar gaskets.Accordingly, it is frequently desirable to individually identify differentparts by number and/or supplier. This identification provides for:

1) Traceability2) Inventory Verification3) Efficient Application

There are a number of identification alternatives which can be arranged. Amongthem:1) Rubber Stamp with ink - Part Number and/or Supplier Logo2) Metal Stamp - No ink - Indent Material with Part Number and/or Supplier Logo3) Screen Print - Part Number and/or Supplier Logo4) Tie In Bundles and Tag5) Package Specific Quantities in Printed Envelopes6) Shrink Pack Specific Quantities - Label7) Color Code with Rubber Stamp or Screen Printing8) Notch Edge of Gasket According to Prearranged Code

NOTE: Special operations may add to cost of gasket.

12

LABELING

E ffective labeling is an important component of good customer/supplierrelationships. It is important that labels be placed for easy viewing fromany vantage point, they must be visually clean, and they must include all

of the information pertinent to the transaction.In many cases, all of the required information cannot be provided and

should not be provided on the same label. Many companies prefer shippinginformation be separated from product information. In other cases, format is theprime consideration. In any case, these details can always be negotiated betweencustomer and supplier. Typical labels are as follows:

13

LOT TRACEABILITY

Ø Ø Lot Traceability SystemGasket manufacturers should establish a system for positive identification

and record keeping for use when required by customers. The lot identificationnumber for finished gaskets should provide traceability to major manufacturingoperations, inspection, testing, and significant raw materials. The method of lotcontrol and identification should be developed by the gasket manufacturer,consistent with their manufacturing facilities and operations, and should includethe elements discussed below.

Ø Ø Lot IdentificationThe lot identification and lot size should be determined by one of the major

manufacturing, testing or inspection operations. Significant raw materials mayalso be considered for lot size and identification. In continuous operations, itmay be necessary to select a specific length of time, such as a shift, one day, oneweek, etc. to determine lot size. In all cases, the lot number assigned to finishedgaskets must provide traceability to major manufacturing operations, inspectionand test records and significant raw materials.

The gasket supplier should assign only one lot code to a lot, regardless ofthe number of shipping designations. When successive subdivisions of the lot arenecessary, the principal code must be supplemented by additional subordinatecodes to identify each of the sublots. Each shipping container must be identifiedwith the principal and subordinate codes.

The supplier may ship more than one lot on a pallet, but each container onthe pallet must contain parts from only one lot. The packing slip must state thenumber of containers comprising each lot.

Ø Ø Lot Traceability ControlThe gasket supplier must establish a system for identifying lots so that:· Records indicating inspection or tests results contain the principal and subordi-

nate lot code.· The final inspection reports are cross-referenced to supporting inspection and

test documents and the supplier’s code.

14

QUALITY ASSURANCE

PolicyFabricators will employ appropriate operating procedures and controls to

assure that parts supplied conform to customer specification requirements.

ProceduresA. Fabricators will establish and maintain written procedures covering all

phases of the control system. These procedures will be dated and signed by anauthorized individual and will be available for review by customer representa-tives.

B. Records of conformance will be retained for 12 months, or as requiredby the customer after shipment of parts. Retained records will include:Ø Supplier evidence of conformance to specificationØ Fabricator evidence of manufacturing process capabilityØ X and R Charts of critical characteristics

References& Harvey C. Charbonneau and Gordon L. Webster. Industrial Quality

Control, Prentice-Hall, Inc. 1978& Eugene L. Grant and Richard S. Leavenworth . Statistical Quality

Control, McGraw-Hill, Inc. Fifth Edition, 1980.& J.M. Juran, Frank M. Gryna, Jr., and R.S. Bingham, Jr. Quality

Control Handbook, McGraw-Hill, Inc., Third Edition, 1979.

H. STATISTICAL PROCESS CONTROL (S.P.C.)S.P.C. provides a means for changing the emphasis of quality control from

detection of defects to prevention of defects.S.P.C. operates by:o Returning control of quality to the place where it starts; the operator, tool setter, supervisor.o Detecting changes in process at the earliest possible point.o Providing sound knowledge of reasons for a process change.o Determining the inherent variations in a process.

S.P.C. provides:o Knowledge of the place and time to take corrective action and avoid continued production of bad parts.o A road map which enables a manufacturer to better his process.

Results of a good S.P.C. program are:o Improved customer satisfaction.o More realistic processes and tolerances on any given product.o A formal program for “best of quality” output.o Lower costs.

15

994 Old Eagle School Rd., Suite 1019, Wayne, Pennsylvania 19087-1866Phone: 610-971-4850

Fax: 610-971-4859E-Mail: info@gasketfab.com

Web Site: www.gasketfab.com