Testing systems forfoodstuffs and packaging

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Zwick Roell AG - Over a century ofexperience in materials testing

Mechanical technological testing is the oldest disciplinein materials testing. Leonardo da Vinci and Galileo Galileipondered over flexural loading and the elastic behaviourof materials. Further knowledge has been gained overthe years. The first test machines appeared in France inthe middle of the 18th century.

The firm Amsler (previously in Schaffhausen, Switzerland)began dealing with materials testing, as did Roell &Korthaus from 1920 onwards. In 1937 Zwick began withthe construction of devices, machines and systems formechanical technological materials testing. Long beforethis, as far back as 1876, Professor Seger founded achemical laboratory as a scientific technological advisorycompany for the earth and stone industry. Today’s ToniTechnik developed from these beginnings during the20th century as one of the leading specialists for buildingmaterial test systems. Excellent performances havebeen furnished by MFL (Mohr & Federhaff), groundedas early as 1870, by the way, Carl Benz was one of itsemployees.

These firms constitute the company group Zwick Roellsince 1992. Whereby the firms Dartec, Rosand, Kelseyand Indentec in Great Britain joined them in the twoyears following.

The Zwick Roell company group was reorganized toform Zwick Roell AG, a public limited company (joint-stock company), in July 2001. It encompasses thefirms Zwick, Toni Technik, Indentec Ltd. and Zwick RoellControllers Ltd. These companies supply acomprehensive program for materials, building materialsand function tests; from manually operated hardnesstesters up to complex test systems that can be usedfor production accompanying applications. Inclusion ofthe French company Acmel Labo in 2002 supplementsthe Zwick Roell AG product program with laboratoryproducts for the cement, plaster and lime industry.

Zwick has many years of experience resulting from thesupply of a multitude of equipment. This iscomplemented by continuous communication with

the users of such equipment. The company suppliesan extensive program of efficient products based onthis solid basis. These products range from economicstandard machines to special complex models designedfor special test tasks. State of the art mechanics,efficient electronics and the applications orientedsoftware constitute the prerequisites for the versatilityand high “intelligence” of these modern test machinesand systems.

The Zwick Roell AG, however, offers a lot more thanjust the supply of products. The company was certifiedto DIN EN ISO 9001 as far back as 1994 and thusvouches for constant high product and service quality.Accredited DKD(1 or UKAS(2 calibration laboratoriesauthorise the Zwick Roell AG companies to check andcalibrate test devices, and to document it withinternationally recognised certificates.

(1 DKD: Deutscher Kalibrier-Dienst (German calibrationauthorities)

(2 UKAS: United Kingdom Accreditation Service

Fig. 1: Zwick headquarters

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1. Foodstuff testing

1.1 Foodstuff testing in general anddefinitions of terms

Foodstuffs are the raw or processed basic elements ofour nourishment. There are animal and vegetable foods.

Animal foods are meat, animal fats, milk, eggs and thefoods which are prepared from these e.g. cheese,butter, sausage, canned foods.

Vegetable foods are the grain foods (e.g. the flours andbaked goods processed from them), fruit, nuts,vegetables, starchy vegetables (potatoes, soy beans,etc.) and the foods processed from them.

In addition to the foodstuffs, there are also foods eatenonly for enjoyment (luxury foods). As opposed to thefoodstuffs, these have little or no nourishment value.They do not serve to nourish the human body, but theyhave a stimulating affect via the central nervous system,sometimes increasing the physical and mentalperformance. Some luxury foods are tobacco, coffee,tea, cola and alcoholic drinks.

Foodstuffs have various “material characteristics”according to type, consistency, make-up and physicalcondition. These greatly determine the rheologicalcharacteristics of a foodstuff.

Picture 3: Gelatine

Picture 2: Optical and sensorical pizza testing

Contents

1. Foodstuff testing .................................................................................................................................................... 31.1 Foodstuff testing in general and definitions of terms .......................................................................................... 31.2 Overview: Foodstuffs and typical test methods ................................................................................................ 61.3 A typical measurement curve from foodstuff testing with description of results .................................................. 81.4 Zwick Roell test devices with applications examples ........................................................................................ 9

2. Packaging test .................................................................................................................................................... 152.1 General to packaging testing ......................................................................................................................... 152.2 Zwick Roell testing devices with applications examples .................................................................................. 16

3. Testing machines ................................................................................................................................................. 233.1 Load frame.................................................................................................................................................... 233.2 Measurement, control and regulating system................................................................................................. 263.3 Test software testXpert® ................................................................................................................................ 273.4 Load cells ...................................................................................................................................................... 293.5 Test units and test tools ................................................................................................................................. 293.6 Temperature and climate chambers .............................................................................................................. 313.7 Extensometers .............................................................................................................................................. 31

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RheologyThe rheological characteristics of a foodstuff can bedescribed as follows: Rheology is the science ofmechanical behaviour of fluid, pasty and viscousmaterials during their deformation.

A more technical definition of rheology is the relationshipbetween stress and strain, or, the material´s behaviourwhich is indicated by stress, strain and time effects.

Tscheuschner wrote about the basic rheologicalcharacteristics: Foodstuffs serve as nourishment forpeople. They must have rheological characteristicswhich satisfy the requirements of biting off, chewing andswallowing, while generating impressions which aresensed as textures of the food and give them a quality.

Rheological tests can be manifold and often have themost varying reasons. Some of today´s tests on foodstuffs are performed for the following reasons:

• Evaluation of the quality and processingcharacteristics of raw foodstuffs.

• Characterisation of the structure and structuralchanges during technical processing.

• Rheological process control for rheological relevantchanges in conditions.

• Process planning and system calculations forrheological processes.

• Creation of foodstuffs with a desired texture.

• Quality control of finished products in relation to theirrheological characteristics and texture.

TextureTextures are the characteristics of a foodstuff which canbe determined from a combination of physicalcharacteristics and the percepted feelings such astouching (including the feeling in the mouth), look andacoustic behaviour. Thereby, size, form, number of cellsand their structure, influences the texture characteristicsof the foodstuff.

Examples of texture characteristics are the crispness offrankfurters, the firmness of cheese or the crispness ofwaffles.

Picture 5: Viscosity test on mustard

Picture 4: „Zwick penetrates the food market!“

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Texture and viscosity testing of food stuffsThe texture of foodstuffs describes the physical nature ofeach foodstuff. It results from the structural compositionand is determined through mechanical deformation.

Texture characteristics are dependent upon the forcesapplied, the failure of the molecular structure and theflow characteristic under loading influence. It isrepresented as a function of time, mass anddeformation.

Viscosity can be described as the inner friction of aliquid, or the tendency of a liquid to resist flowing.

Rheology involves itself with both parts of foodstufftechnology; viscosity and texture testing. The differencebetween texture and viscosity is found in the basicmaterial. Texture is measured in a solid foodstuff,viscosity is measured in a liquid, or pasty, food stuff, e.g.biting an apple, cutting cheese or bread with a knive.

Texturecharacteristicsof foodstuffs

Hardness

Composition,cohesion

Elasticity

Adhesiveness

Viscosity

Sensoric designationsof foodstuffscharacteristics

softsolidhard

crumblycrispbrittle

plasticelastic

adheresstickyvery sticky

highly fluidsemifluid

Picture 6: Testing of foodstuffs are taken from everyday practice

Picture 7: You can test foodstuffs of all types with Zwick testingtools

Table 1: Texture characteristics of foodstuffs with sensoricdescriptions

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Foodstuff Type of test Tool/Test device Sensoriccharacteristics

Bread and baked goodsBread Compression, Compression test device, Firmness

penetration test Compression die (AACC 74-09:cylindrical die dia. 36 mm)

Cake, pastry, cookies, Penetration, flexure, Compression die (ball), Firmness, hardness,waffles shear test 3-point flexure test kit, breaking strength

Warner-Bratzler test deviceCroutons Compression test Compression test device, Hardness, crispyness

OTMS test device with rod bladesDough Tensile, compression Dough tensile test device, Elasticity, adhesiveness

test Compression test deviceSalted snacks Compression, Compression test device, Flexure, breakinge.g. pretzel sticks flexure test OTMS test device with rod blades, strength, crispyness

3-point flexure test kitPeanut flips Compression, Compression test device, Crispyness, hardness

extrusion test Kramer shear test deviceChips, rice cracker Compression, Compression test device, Crispyness, hardness

extrusion test OTMS test device with rod bladesNoodle and rice productsCooked spaghetti Shear, compression Shear and compression units Hardness, strength

(adhesiveness test) (AACC 66-50) adhesivenessRaw noodle products Bending tests 3-point flexure test kit Flexure, breaking strengthCooked Gnocchi Compression test Compression test device Hardness, strength,

adhesivenessCooked noodle products Compression test Warner-Bratzler test device, Hardness, strength,

Compression test device adhesivenessCooked rice Compression test Compression test device Hardness, strength,

adhesivenessRice pudding Penetration test Compression die (cylinder) StrengthSweetsBreakfast cereals Compressibility test OTMS test device with Crispyness, hardness

sealing plateChewable hard candy, Compression test Cutting knive Hardness, (cuttingsugar-coated drops strength)Chewing gum Tensile test Dough tensile test device ElasticityIce creme Indentation test Compression die (ball) StrengthChocolate bar Compression test, Compression test device, Hardness, strength,

extrusion test Kramer shear test device crispynessChocolate creme Indentation test Compression die Strength, hardness,

(ball, pyramid) spreadabilityChocolate (raw mass) Viscosity test Back extrusion test device Viscosity, consistency

1.2 Overview: Foodstuffs and typical test methods

Table 2: Overview of test methods (1 American Association of Cereal Chemists

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Foodstuff Type of test Tool/Test device Sensoriccharacteristics

Milk productsButter, margarine Cutting, spreading, Butter-cutting unit, Firmness,

penetration test Compression die (ball, pyramid) spreadability, hardnessCheese spread, Spreading, Compression die (ball, pyramid) Spreadability,soft cheese penetration test firmness, hardnessHard cheese Penetration test Compression die (ball, cylinder) HardnessYoghurt, mousse, Penetration test Compression die (cylinder) Firmness (surface)Peanut butter Viscosity test Back extrusion test device ViscositySauces, pastes, gels, oil, ...Mayo, mustard, ketchup, Viscosity test Back extrusion test device Viscosity, consistencyveg. oil, marmelade, honeyMayo, mustard, ketchup, Penetration tests Penetration die (cylinder) Firmness, consistencyveg. oil, marmelade, honeyGelatin Compression test to Bloom penetration die (dia. 1/2") Bloom hardness

BloomFruit, vegetablesApples, pears Penetration test Compression die (ball, cylinder) Firmness, hardness

penetration test deviceGrapes, berry fruits Penetration test Penetration test device, Surface hardness,

compression die (cylinder) elasticityPotatoes Shear test Warner-Bratzler test device Firmness, shear workPotatoe salad, mashed Extrusion test OTMS test device with Extrusion work,potatoes perforated insert firmnessPeas Compression, shear, Compression, penetration Firmness (surface),

penetration test Kramer shear test device hardnessCorn Compression, Compression test device, Firmness, hardness

shear test Kramer shear test deviceBeans Extrusion test OTMS test device with rod blades Extrusion work,

firmnessPickles, canned goods Shear test Kramer shear test device Firmness,

shear strengthSausage, meat and fish productsChicken Shear test Warner Bratzler test device, Shear strength,

Kramer shear test device toughnessCrab Shear test Kramer shear test device Shear strengthMeat, fish Shear test, Warner Bratzler test device, Shear strength,

penetration test Compression die (cylinder) toughnessFrankfurters Penetration test, Penetration test device (needle), Crispness,

shear test Warner Bratzler test device shear strengthSausage Penetration test, Compression die (cylinder, ball), Firmness,

shear test Warner Bratzler test device shear strengthAnimal foodCanned food Extrusion test OTMS test device with rod blades Extrusion work

Dry food Compression test, Compression test device, Hardness, firmnesspenetration test compression die (cylinder)

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F11

F12

F13

F14

Fv

- Fv

F15

s11 s12 s13 s14s15s16 s20 s21 s24s25s26

F23

F24

Fv

- Fv

F25

S11

S21

E11 E12

E13E14

E21 E22

E23E24

First cycle Second cycle

Force Force

Table 3: Measurement results of the Zwick test program for texture analysis

English German Test result

Modulus Steigung s11, s21

Specimen height Probenhöhe H0

Fracturability Bruchneigung F11

Brittleness Sprödigkeit F11 - F12

Hardness Härte F13

Indentation Stauchweg S13

Cohesion strength Bindekraft F15

Adhesiveness Klebneigung E13 + E14

Springiness Rückfederung (S23-S20) / (S13)Gumminess Zäh-elastisch, klebrig F13 * (E21 + E22) / (E11 + E12)Chewiness Kauverhalten F13 * (E21 + E22) / (E11 + E12) * (S23-S20) / (S13)

Extensionor

travel

Extensionor

travel

1.3 A typical measurement curve fromfoodstuff testing with description ofresults

Picture 8: Typical graphical evaluation of a texture test with 2 cycles, with individual evaluation by the testXpert®-texture analysis-program

In the following table and the example test curve (force-path-diagram), of a typical texture test, the importantresults necessary for the determination of foodstuffscharacteristics are shown.

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1.4 Zwick Roell test devices withapplications examples

Back extrusion test deviceBack extrusion testWith the back extrusion test, a die is moved up anddown in a fluid test material. The measured forces atdefined speeds, determine the viscosity .

Setup and performing a testThe back extrusion cell consists of a cylindrical containerand a cylindrical compression die. The container is fixedto the machine to prevent lifting during the reversestroke. A certain volume (min. 75 % of the container´svolume) of the test material is filled into the cell. The diepushes into the specimen with a defined speed andcontinues until a pre-set position has been reached.When this position has been reached, the die drivesback to the beginning position. During this movement,the specimen material flows through a ring slot betweenthe container and the piston into the other containerarea. The force required for this action allows theviscosity to be determined.

Kramer shear test deviceKramer shear testThe Kramer shear cell was developed in 1959by Kramer & Twigg and it is the most widely usedtest method in the area of foodstuffs testing.It simulates as nearly as possible, the single biteof prefragmented foodstuffs.

Setup and performing a testThe Kramer shear cell consists of a box, which has afloor with slotted openings. The specimen material isfilled into this box. The rectangular shaped cutters areaffixed via guides (the Kramer shear cell is available intwo options, with 5 or with 10 cutters). The cell ismounted on a basic platform so that a free spaceremains underneath. Here the specimen material whichis pushed out can be collected. The advantage of aKramer shear cell is that not only one position ismeasured, but 5 or 10 positions at the same time.Local texture deviations are compensated for with thismethod. The cutters drive at a constant speed throughthe specimen material, compressing and shearing thespecimen until it is pushed through the floor of the cell.The force-path or force-time curve is the result andconclusions as to the chewing characteristic, thecrispiness or the freshness can be made.

Applications• Testing of viscosity, consistency or cohesion of fluid

and pasty masses, e.g. joghurt, pudding, mustard,tomato paste, oils

Applications• Simulates as nearly as possible, the single bite of pre-

fragmented foodstuffs.• Texture characteristics of small sized fruit and

vegetable products, cereals, etc.

Picture 9: Viscosity testing ofketchup with the back extrusiontest device

Picture 10: Shear testing of cereals with the5-blades Kramer shear test device fordetermination of crispiness

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OTMS test deviceOttawa Texture Measuring System (OTMS) TestThe Ottawa Texture Measurement was developed bythe Engineering Research Service of Agriculture, Cana-da under P. Voisey, 1971. The test simulates thechewing characteristic through compression anddisplacement of the specimen.

Setup and performing a testThe OTMS cell consists of a rectangular container withopen floor in which various inserts can be mounted.There are different inserts (see picture 11), e.g. withrod blades, with perforations, with wire blades or aclosed insert (sealing plate). A rectangular or round diecompresses the specimen material through the variousinserts. The OTMS cell is available with various volumes(depending on the reduction insert or die used).The die moves down with a constant speed(e.g. 200 mm/min), compressing the specimen andpushes it through the insert. The force-path or force-time curve is the result. From the type of curve,parameters can be taken which indicate the crispiness,hardness, ripeness or the extrusion work.

Applications• Determination of the hardness/softness of vegetables• Determination of the hardness/crispiness of granola,

Cornflakes etc.• Comparable simulation of the chewing characteristic

through compression and displacement of thespecimen

Warner-Bratzler test deviceWarner-Bratzler testThe Warner-Bratzler Test was developed in 1932 byL.J. Bratzler in his Masters Thesis, Kansas StateUniversity, Manhattan, and has been in use since the1950s. The test gives information about the softness/toughness of meat and fish products as well as bakedgoods.The cutter simulates the edges of teeth during biting.Because of the good reproducibility of the results, thistest is used very often and is considered as a type of“Standard”.

Setup and performing a testThe Warner-Bratzler test device consists of a slitplate, on which round or rectangular specimen areplaced, and additional blades. The blades (straightblade for rectangular specimen or notched blade forround specimen) have a thickness of 3 mm. Thespecimen are placed on the base plate and the cutterdrives down with a constant speed and cuts thespecimen. The force-path or force-time curve is theresult. The shear characteristic can be seen from thistest curve.

Applications• Comparable simulation of biting characteristic

(“cuspid teeth”) on fish, meat and baked goods• Determination of the softness/toughness of meat and fish products• Determination of the shear behaviour of baked goods

Picture 11: OTMS extrusiontesting on fresh cheese

Picture 12: Warner-Bratzler testwith notched blade on salami, tosimulate the biting characteristic

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Compression test unitCompression testWith the compression test we simulate the stackingbehaviour of fruit. The test is also suitable for testingthe freshness (aging behaviour) of bread or fruit, cheese,fish and other comparable foodstuffs.

Setup and performing a testThe test unit consists of a basic plate and acompression die. Attention must be paid that thespecimen is smaller than the compression die. Thespecimen is compressed to a certain degree and(in a cyclic test) decompressed. In a force-path orforce-time curve the compression and decompressioncharacteristics are shown. Conclusions as tocomposition, freshness or degree of ripeness of theproduct can be made.

Applications• Testing of bread, fruit, cheese fish• Testing of the compression sensitivity of products

which must be stacked when stored

Penetration test devicePenetration testThe penetration test, also called „puncture test“ or„force penetration“, was used the first time in 1925 tojudge gelatin masses. In the meantime, it is used moreand more to test the degree of ripeness in fruits andvegetables.

Setup and performing a testThe penetrator (needle) is pushed into the specimen to acertain depth.The force-path and force-time curves are drawn. Initially,the force increases greatly. As soon as the needlepenetrates the specimen, the force reduces since theskin (biggest strength) has been penetrated. The degreeof freshness can be read from the drawn curve.

Applications• Determination of the degree of freshness on fruit and

vegetables• Determination of the freshness of baked goods

Picture 13: Compression test on hardcheese to determine the degree ofripeness

Picture 14: Penetration test on fruit, todetermine the degree of freshness

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Dough tensile test deviceDough tensile testThe dough tensile test is performed on dough and gluten(protein binders). The special dough tensile test devicemakes it possible for dough and baked goods producersto determine the material characteristics of dough. Theelasticity and strength of various doughs and glutenscan be determined. Mechanical testing of dough canshow the characteristics through technically measuredproof. Various recipes, processing types- and times, aswell as admixed material, can be improved in order tohave the optimal end product.The increasing use of automated dough processingrequires the most constant product characteristicspossible to which the machine parameters are set.Through constant monitoring of these characteristicswith the dough tensile test device, product quality aswell as processing steps can be optimised.

Setup and performing a testThe dough tensile test device consists of a specimentable which holds the dough specimen, and a tensilehook for deformation of the specimen. A device forspecimen preparation is used to produce identicalspecimen (dough strands).Specimen preparation: Approx. 200 to 300 g dough isplaced into the special device for specimen preparationwhich is also supplied with the dough tensile test device.By compression several identical specimen strips getformed which are placed via a piece of paper in the testdevice.

Test: After the specimen has been placed on the testingtable and the table mounted in the test device, thedough is deformed with the hook. Thereby force andtravel are acquired and evaluated by the testingmachine.

Applications:• Determination of dough characteristics for bread and

baked goods• Determination of the elastic characteristics of chewing

gum

Butter cutting test deviceButter cutting testThis test is used to determine the spreading quality andfirmness of butter or cheese specimen to DIN 10331 /ISO 16305. A stainless steel wire with dia. 0.3 mm cutsthrough a block of butter. The force required is acquiredby the testing machine. This test is very dependent ontemperature and should only be performed underdefined temperatures (see temperature chamber,page 14, picture 21).

Setup and performing a testA complete block of butter (500g) is placed on theuniversal work platform. The cutting fixture, which cutsthrough the complete block of butter, is affixed to themoving crosshead of the testing machine. The forcerequired to cut through the butter is acquired by thetesting machine. Information as to the butter´scharacteristics such as hardness and spreadability canbe determined from the force-path curve.

Applications:• Determination of hardness and cutting tenacity of

butter• Determination of hardness and cutting tenacity of

cheese, eggs, vegetables, fruit

Picture 15: Dough tensile test fordetermination of the processingcharacteristics of dough

Picture 16: Butter cutting testto ISO 16305

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3-point flexure test kitSetup and performing a testThe 3-point flexure test kit consists of a flexure table onwhich 2 supports can be fixed at variable distances toeach other. The specimen is placed on these supportsand centrally loaded with a flexure fin.

Applications:• Determination of the flexure strength (breaking

characteristic) of baked goods (cookies, waffles,pastries,...), dough products (noodles, lasagne,...),chocolate bars and fruits

Compression dies for hardness penetration testPenetration testThe determination of the hardness of foodstuffs using apenetration test is of great importance for the qualitytesting of the most various foodstuffs. This test is widelyused and finds its application with many foodstuffs sincethe hardness of a foodstuff has a great influence on thesensoric characteristics of a product.In order to test a multitude of foodstuffs, Zwick offerspenetration dies with various diameters and materials(stainless steel, plexiglass, aluminium,...), cylindrical, ball,beveled or conical.

Setup and performing a testWith the penetration test care should be taken that thespecimen has as flat a test surface as possible, and aflat under surface as well.

Picture 17: 3-point flexure teston a waffle to determine itscrispness

Picture 18: Penetrationtest on butter todetermine the firmness

Applications:• Determination of hardness of fruits, vegetables, milk

products, sausages, dough products, gelatins

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Bloom – test unit(hardness testing on gelatin)The hardness test on gelatin according to Bloom is welldefined in the British Standard BS 757. The test isrecognized and accepted outside the borders of GreatBritain and is used by many gelatin producers.

Setup and performing a testA cylindrical compression die is pushed into the gelatinwith a constant speed. The maximum force required topenetrate 4 mm into the gelatin, gives information as tothe firmness (“Bloom value”) of the gelatin.

Applications:• Determination of the “Bloom-Firmness” on gelatin

Hardness test on sausage productsThe sausage hardness tester is a modified analogueShore A hardness tester. A compression cylinder with asurface area of 1 cm² is used as the penetrator. Thisunit is used especially in the quality control of sausagesand luncheon meat. A comparable quality control canbe performed using comparable measurements of thehardness of a sausage.

Foodstuffs testing under defined temperatureFoodstuffs are products which are usually verysensitive to temperatures. In order to receivereproducible and comparable test results fromfoodstuffs, a test under defined, constant temperature isvery important, since the products characteristics areoften influenced greatly.Zwick offers a temperature chamber which fits on thetexture testing machine (zwicki) especially for theserequirements.The chamber has a temperature range of -30°C to+130°C. Almost all foodstuffs can be tested in thisrange. The cooling is performed with liquid nitrogenand warming is performed with a bar heater.Typical testing under defined temperature is, forexample, the testing of ice cream at a storagetemperature of –20°C, or the testing of pizza cheeseat approx. +80°C.

Picture 19: Bloom teston gelatin to determinethe Bloom-hardness

Picture 20: Sausagehardness testing with a ShoreA hardness tester

Picture 21: Food stuff testing in a temperaturechamber

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2. Packaging test

2.1 General to packaging testingThe development of packaging is very stronglyinfluenced by the requirements of the foodstuffs industry.The foodstuffs industry always demands improvedstorage and transport characteristics from packaging.

Packaging should be, as much as possible, thefollowing:

• Stable• Practical• Inexpensive• Simple to produce and process• Temperature insensitive• Non-poisonous• Secure• User friendly• Light• Storable / stackable• Leakproof• Easy to compress• Easy to open

Not only the foodstuffs industry, but almost all producingindustries require packaging which have the optimumcharacteristics for their special requirements. Not onlythe original characteristics of the packaging areimportant here, but also the protection of a product.

Other factors, e.g. product marketing and environmen-tal considerations receive more and more importance.Since packaging nowadays is made of the most variousmaterials, it must fulfill the most varying requirements. Asmall overview of the most important packagingmaterials follows.

Packaging of paper / cardboard• Carton• Paper packaging (paper sacks, paper bags)• Corrugated cardboardThe most important applications: Foodstuffs, luxuryfoodstuffs, industry packaging, transport packaging.

Packaging made of plastic• Foils• Bottles, canisters• Cases, containers, pails• BeakerThe most important applications: Foodstuffs, chemicals,industry packaging, transport packaging.

Packaging made of metal• Cans• Barrels• ContainersThe most important applications: Drinks, chemicals,industry packaging.

Packaging made of glass• BottlesThe most important applications: Drinks, foodstuffs,chemicals, cosmetics.

Other packaging• Packaging made of textile, composites (bags, sacks,

Big Bag)• Packaging made of wood (crates, palettes)

Constant materials testing is required so that the listedpackagings can be optimally used. The most importanttesting on finished packaging is described on thefollowing pages. Mainly, mechanical testing of finishedpackaging is described in this prospectus. Informationfor specific material testing of other materials can beseen in other prospects (plastic, metal, paper, textile).

Picture 23: Packaging of foodstuffs

Picture 22:Variouspackagings

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2.2 Zwick Roell testing devices withapplications examples

Testing of plastic packagings

Stacking test (ISO 12048, DIN 35526-1)During a stacking test, the packaging is loaded witha force which corresponds to a defined number ofpackaging units which would be stacked on top of it.In this test, it can also be seen if the foreseen stackingheight can be reached. A packaging unit is loadeduntil it fails. The force required to destroy the packagingunit can be used to calculate the maximum stackingheight. This test is usually not performed on individualpackagings. Plastic beakers are almost alwaystransported in trays (cardboard holders for beakers,e.g. joghurt). In order to receive test results whichare close to practice, completely filled trays are loadedin a compression test.

greatly, there is very often no Standard available. Forthis reason, most testers orient themselves to thegeneral material Standards and try to recreate thefinished product´s function or a production problem usinga testing machine.

Determination of inherent rigidityThe packaging unit is loaded until failure. This test givesinformation mainly used in the processing of packaging,since this unit has a certain load applied when it isclosed (when the lid is put on), and the packaging unitmust withstand this closing process without problem.

Picture 24: Stacking test on plastic pails

Picture 25: Compression test onplastic packagings (plastic barrel,joghurt beaker)

Compression test on plastic beakers, canisters,pails and barrelsThe compression test is one of the most common testsin the packaging industry. Since a lot of packaging ismade of plastic, it is very understandable that amultitude of compression tests are performed on thesepackagings. Since the form of the packaging varies

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Testing of packaging foils

Tensile test on plastic foilsThe tensile test on plastic foils is clearly described inStandard, DIN EN ISO 527-3. It serves to exactlydetermine the single axis stress-strain-characteristic. Itis important that the test speed is exactly maintainedsince plastics also have visco-elastic characteristics.This sometimes changes the stress-strain-characteristicgreatly.Plastic foils can display a strong anisotropy (the stress-strain-characteristic is dependent upon the directionthe specimen is taken from the basic material).The stress-strain-diagram contains additional informationwhen the test temperature is varied. Tests undertemperature are necessary in cases where the foil isexposed to temperature swings during use, and thechance of the foil failing is greater.

Tear testStandards DIN 53515 and DIN 53363 exist for tear testson plastic foils. The test simulates the behaviour ofpackaging foils when the package is opened.When opening a plastic bag, the initial tearing strengthshould be approximately as much as the continuingtearing strength. If the maximum force at initial tearing is

too high, the danger exists that the plastic bag willsuddenly tear completely open and the contents will spillout. The ideal behaviour is not easy to adjust becausethe tear resistance (as well as the tensile strength), isvery direction dependent with stretched foils.

Picture 26: Tensile test onplastic foils with differentelasticity

Picture 27: Seam strength test on heat sealed packaging foils

Seam strengthThe seam strength test is described in the Standard,DIN 55543.This seam strength test determines the strength of theglued or heat sealed seam on packaging bags andsacs.

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Friction testThe friction test is described in Standards, ISO 8295,ASTM D 1834 and DIN 53375.The coefficient of friction ratio is a dimension fordetermination of a foils quality. However, it is also usedto evaluate the behaviour of a foil in packaging orprinting machines. The following can be determined:• The static friction ratio µS and/or• the sliding friction ratio µD

and these as coefficient of friction of foil against foil or foilagainst a different material.

Picture 28: The device for testing the frictional behaviour, mounted

Picture 29: Penetration test on foil strips

Picture 30: Peel-off teston glued beaker top/“push-out“ test onmedical packaging

Penetration test on packaging foilThe penetration test device was developed for thedetermination of the penetration resistance of elasticpackaging materials. With this device, penetration testson foils can be simply and quickly performed accordingto DIN EN 14477. The possibility of placing an endlessstrip specimen in the device ensures cost effectivetesting. Using a collet, different penetration dies can beexactly mounted with a few easy steps.

Customer specific test devices for functionaltesting on foilsOn the basis of customer specific requirements, varioustesting units and tools for testing of plastic packagingand other components, can be developed and producedon short notice.Examples are shown here. To the left is a unit todetermine the „push-out“ force on blister packs and, tothe far left, a test device to determine the peel-off forceon packaging beakers.

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Testing of paper packaging

Box compression test and stacking test oncardboard boxesThe box compression and stacking tests are describedin Standard, ISO 12048.Both tests serve to determine the strength and thestacking capabilities of cardboard boxes. The completecarton is loaded until failure or until its nominal loadingvalue is reached. In the box compression test, thecardboard carton is quickly loaded to the nominalloading value or until failure. In the stacking test, anagreed upon maximum load is held constant for adetermined time, or until failure of the box.

Picture 31: Box compression test on a large cardboard box

Picture 32: 4-point flexure test on cardboard

Flexure test on cardboardThe 4-point flexure test on cardboard is described inStandard, ISO 5628.The 4-point flexure test is used to test single or multi-layered cardboard, heavy cardboard, heavy fiberboardor cardboard with fiber reinforcement, as well as testingof structural materials, e.g. honeycomb constructions.The supports integrated into the testing device aremade especially for cardboard testing and do not haveany influence on the measurements. Specimen from200 to approx. 400 mm can be simply and exactlytested with this device.

Compression test on compound paper boxesThe compression test on full and empty compoundpaper boxes serves to determine the strength of thesepackagings. The most varied box shapes can be simplyand efficiently tested in a special horizontal testingmachine. The specimen can be placed exactly andquickly into the testing unit with two guidance units.

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Testing of metal packaging

Compression testing of metal barrels, cans,canisters etc.The compression tests on metal barrels, canisters etc.are defined in various directives (e.g. the directive forproduction and test standards for packaging, largepacking items, large packagings...).Accordingly, metal containers must be loaded for5 minutes with a force that is equal to 1.8 times themaximum gross mass weight with which such apackaging is allowed to be loaded.The packaging is not allowed to have any permanentdeformations after the test is over.Often, it is also of interest to determine the maximumpossible loading of a packaging unit. Here the packagingunit is loaded until failure and the maximum load requiredfor this is determined.

Peel-off test on a packaging beaker withaluminium coverWith the flexible testing unit for peel-off testing on foodstuffs beakers (e.g. joghurt, soft cheese, coffeecream,...), the peel-off forces which are required toopen a glued beaker cover can be determined.Various sizes and shapes of beakers can be held withthe variably adjustable unit. A clamp is affixed to the pull-off tab of the cover. This is connected to the load cell onthe moving crosshead with a thin cord via a guide roller.When the moving crosshead is driven upwards, thecover is peeled-off and the force required is determined.

Picture 34: Compression test on a metal barrel

Picture 35: Peel-off test on a packaging beaker

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Testing of other packaging materials

Torsion testing on packaging materialsScrew cap closings are more and more important in thepackaging industry and they find increasingly moreapplications. Bottles, canisters, compound paper boxesetc. are fitted with screw cap closings. In order to testthese closings, a testing machine is necessary fortorsion testing.In addition, torsion testing on complete packagingmaterials (e.g. cigarette boxes) is becoming moreimportant.Zwick offers a variable use test machine series exactlyfor these applications with various specimen sizes andthe different torque moments required.

Tests on textile packaging materials (sacks,bags, ”Big Bag”, ...)Tests are not performed on the end product ofpackaging materials made of textile, but on definedspecimen.The most important test on these materials is the tensiletest. Similar to the Standards EN ISO 13934, 13935 and13937, the specimen are loaded in a tensile test untilthey tear.Another important test on such textile sheets is the diepenetration test. Similar to the Standard EN ISO 12236,a penetration body is forced through a specimen. Theforce required, as well as the deformation determined,gives important information about the characteristics ofthe end product.

Pull-out test on wine bottle corksThe pull-out test on corks of wine bottles is a veryspecial test which has been developed for a small circleof users. However, it is a good example of the flexibilityand Zwick´s customer orientation.

Picture 36: Torsion testing on a carton

Picture 37: Tensile andpenetration tests ontextiles

Picture 38: Illustration ofthe cork pull-out test ona wine bottle

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Flexible testing components for food stuffs/packaging testing

BasicLine Toolbox: Quick action chuckFor flexible compression and penetration tests, variouspenetration needles or compression dies can be simplyand precisely held with the quick action chuck. Thequick action chuck is adapted to the Zwick connectionsystem which gives the customer the possibility ofquickly and simply integrating his own testing tools intothe system.

BasicLine Toolbox: T-Slot platesThe T-Slot plates are used for universal mounting of themost varied testing tools. Zwick Roell tools, as well ascustomer specific units and tools, can be adapted viathese plates. For example positioning units, hinge sets,vices and many more can be used.

Picture 39: Pull-off test on a marmalade container which is held ina parallel vice. The pull-off is performed by a small screw clamp

Picture 40a/b:Penetration testson foodstuffspackaging

BasicLine Toolbox: VicesSeveral universally usable vices make possible thegripping of the most varied specimen and components.According to application, a highly precise parallel vice,an easy to open and close quick action vice, or anuniversal vice, can be adapted to the machine for usein many universal ways.

BasicLine Toolbox: Screw clampA multiple application clamp finds use in foodstuffstesting in pull-off, tensile and pull-out tests. The clamp,which is connected to the moving crosshead with athin cord, can be used e.g. for pull-out tests on fruitstems, or as well for pull-off tests on joghurt beakers.

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3. Testing machines

Zwick Roell develops and produces testing machines forforces from the mN range up to more than 6000 kN.As opposed to the often offered single-purpose testinginstruments, Zwick Roell offers testing machines withindividual solutions for each testing requirement. Acustomer specific testing machine is put together foreach testing application.

Following is an overview of the different variations of loadframes, the multitude of testing tools and devices, theadvantages of the testing software testXpert®, as wellas several of the options available.

We would also be happy to specify the correct testingmachine for you and your application.

3.1 Load frame

Basic conceptThe Zwick Roell program has table-top and floormachines with various measurement, control andregulating systems, different drives and many multi-useaccessories.

In order to be able to offer the correct machine with theoptimum price-performance ratio, the Zwick Roellmachine concept has three machine series which arevery different in their equipment, performancecharacteristics and in their expansion possibilities:

Picture 43a/b: Testing machines of the Allround series:A 1-column table-top machine (left) and a floor machine (right)

Picture 42a/b: Testing machine of the BasicLine:A 1-column (left) and 2-column (right) table-top machine

Picture 41a/b: Testing machines of the Standard series:A 1-column (left) and 2-column (right) table-top machine

• The BasicLine is especially suited for routine andfunctional testing of components and for simplematerials testing.

• With the Standard series the user who wants testsreliably performed to test requirements of Standards,receives a solid solution which is cost favourable.

• The Allround series is the expandable machinefor demanding test requirements in research anddevelopment. It enables the connection of specialsensors, allows multi-channel measurementtechnology and can be expanded modularly.

In each of these series we offer:• 1-column table-top machines („zwickis“)

• 2-column table-top machines

• Floor machines (not in the BasicLine)

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Picture 44: By equipping a testing machine with several testingpositions, a maximum degree of use is achieved at low cost

1-column table-top machinesThese transportable load frames are based on a verystiff extruded aluminium profile. The working area isfreely accessable from three sides which predestinates itfor functional and component testing on specimen whichhave small front-to-back depths when mounted fortesting. The lower force limits are determined by theload cell which is used: They begin in the mN range andgo up to 2.5 kN.

2-column table-top machinesThese load frames are outfitted with steel columns(BasicLine), or carrying and guiding columns of patentedextruded aluminium profile (Standard and Alllroundseries).

The load frames of the BasicLine are of a simpleconcept. That means, with fewer functions, but still withhigh quality, which offers an inexpensive alternative tothe Standard and Allround series.

Picture 45: The BasicLine offers inexpensive solutions for simpletesting

The load frames of the Standard and Allround series arevery light but with high bending stiffness because of theextruded aluminium profiles. The profiles also serve asguidance and protection for the spindles.T-slots on the outer sides enable simple mounting ofaccessories. These load frames can be optionallyequipped with profile legs for optimum positioning of theworking area to a user friendly height.

Floor machinesThe load frames of the floor machines are equipped withtwo or four chromium plated round columns and twoprecision ball-lead screw spindles. They are especiallysuitable for testing with high forces, materials with highextension, large specimen or components.

Electro-mechanical driveAll electro-mechanical drives are based on play-free andwear resistant ball-lead screws and digitally controlleddrives. They are used for load frames with testing loadsup to 600 kN. Together with the digital measurement,control and regulating system, they offer the followingadvantages:

• Extremely large, stepless, speed range

• Very small speeds can be set(from approx. 0.5 µm/min)

• Highly precise and exactly reproducible positioning andspeeds

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Overview of the Zwick Roell load frame series and their specifications/functions

BasicLine Standard series Allround seriesSpecification/function

Load frames•Model

- Table-top machine (Nom. force) 500 N to 20 kN 1 to 100 kN 1 to 100 kN- Floor machine (Nom. force) - 50 to 250 kN 50 to 600 kN

•Number of testing areas 1 1, optionally 2 1, optionally 2•Wider and/or higher models

available - √ √

Drive system•Electro-mechanical

- Number of ball lead screws 1 or 2 1 or 2 1 or 2- DC-Motor √ only „zwicki“ only „zwicki“- AC-Motor - √ (except „zwicki“) √ (except „zwicki“)

Measurement, control and regulation system•BasicLine (Stand Alone / PC operation) √ - -•testControl (PC operation) - √ √•testControl Stand Alone - optional optional

Test software• Test software testXpert® (for PC operation) optional optional optional

- with Standard test programs √ √ √- with Master test programs - √ √

Measuring transducers•Strain-gauge load cell 1 (exchangeable) 1 (optional up to 2) 1 (optional up to 3)•Digital crosshead travel monitor integrated integrated integrated

Connection and control of externalmeasurement systems - √ √

Control of external systems•Specimen grips (motor driven,

pneumatic, hydraulic) - à åExtension measurement systems - semi-automatic fully-automatic

Optional accessories for special applications•Torsion drive - - optional•Torque transducer - optional optional•Temperature and climate chambers - optional optional

Table 4: Overview of Zwick Roell load frames

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3.2 Measurement, control and regulatingsystemThe testing machine components which decide theperformance capability and degree of functionality arethe measurement, control and regulating system. Itsperformance capability determines which drive can beregulated, which sensors can be connected and whichfunctions can be controlled. Therefore, it determines thescope of applications and the extension possibilities ofthe testing machine.

Measurement, control and regulating systemtestControl of the Standard and Allround seriesFor the extensive functionality of the Standard andAllround series, the measurement, control and regulatingsystem „testControl“ developed by Zwick Roell is used.Through the use of the most modern technology andthe highest quality standards, testControl offers long-term investment security and the greatest measure oftechnical performance:

• Time synchronised test value acquisition with highresolution and measuring frequency.

• Real-time evaluation of the test values with 500 Hzacquisition rate.

• Adaptive regulation for exactly reproducible test speedand positioning.

When used with a PC, all advantages of the Zwick Roelltesting software testXpert®, are available. Theelectronics, „Stand Alone“, is also optionally available.Here the operation can be performed simply andsecurely without PC, with a decade keyboard and a fewfunction keys. A printer can be connected for output ofthe test results.

Measurement, control and regulating system ofthe BasicLineThe proven electronics used for the BasicLine can beused for simple tests, e.g. on components, with orwithout PC (Stand Alone). When used with a PC, alladvantages of the Zwick Roell testing softwaretestXpert®, in connection with Standard test programs,can be used.

Picture 46: The measurement, control and regulating system forthe BasicLine can be operated with or without PC

Picture 47: The measurement, control and regulating systemtestControl is operated via PC, or with the option „Stand Alone“also without PC (see inset picture)

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3.3 Test software testXpert® Modular systemThe test programs have been created by Zwick Roellwith several hundred software modules. The modulesare separated into classes such as test parameters,test sequence phases, screen masks etc. They arecontinually updated and expanded with new insightsand required supplements. This makes testXpert®, anintelligent software and thereby makes it possible torealise test programmes which follow Standards exactly,but which are also practice oriented (Picture 48). Theirvariety makes it possible to use testXpert® universallyfor a wide applications spectrum and with most typesof testing machines.

Test programsTest programs describe how a test is to be performed.Their basis is selected software modules which arelinked together and pre-configured by fixed parameterscorresponding to the required functions. The userreceives a finished „test template“ from Zwick Roell,into which he must only enter variable parameters.

For the various requirements in practice, the followingthree variations are available:• Master test programs• Standard test programs• Customer specific test programs

testXpert® is theuniversal test softwarefrom Zwick formaterials, componentsand functional testing.Its area of use reachesfrom material testingmachines (tensile,compression, flexureand materials testingmachines), hardnesstesting machines,pendulum impact testers, melt flow rate instruments,balances, automatic testing systems etc., up to themodernisation of testing machines of the most variedconstruction types and makes.

Tasks and functionsThe basic functions of testXpert® are:• Preparation and/or changeover to different tests of

the test machine• Parametrisation of the test or test series• Performance of the test, evaluation and

documentation• Data management• Quality management• Data exchange between testXpert® and other

applications (Word, Excel etc.)

testXpert® supports the user in all tasks with Software-Assistants and Editors, guiding pictures and videosequences, situation specific user tips, warnings, errormessages and online help.

Future oriented conceptThe testing software testXpert® uses the characteristicof object oriented programming for a clear organisationof tasks and functions. Structure and performance aredetermined from applications and software know-howfrom Zwick Roell. The testXpert®-concept is a guaranteeof highest flexibility and functional security, as well asbeing simple to use. The important features are:• Uniform basic software for all applications• Software modules for Standards• Software tools for operator support

Picture 48: Screenshot in testXpert®: Penetration test on bread

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International Quality Standard The most simple operationWith standard applications, the operational effort isreduced to one-button operation, that is, the pushing ofthe start button. This is possible because testXpert®

automatically acquires the test values, and dependingon these, controls and monitors the test sequence anddetermines and documents the test results.

The preparation of a test series only requires 2 steps:• Call-up of the test program• Input of the variable parameters

Optimum operator informationAll displays which are required for the performance of atest can be clearly collated in one screen mask. Theseinclude:• Input fields for specimen specific test parameters• Individual or multiple diagram curves• Tables for test results• Tables for results statistics

Data storage for later useCorresponding to the requirements in the test Standard,all data, or only selected data, of a test or test seriescan be stored. The storage of all data offers thepossibility to trace the development of the results all theway back to the configuration and set-up of themachine. In the simulation mode, the test data can berepeatedly displayed and reevaluated to other criteria.

TraceabilityThe system data is stored along with other test data.Then, according to ISO 9000 ff, it can be traced backas to which testing machine, in which configuration, andwith which settings, the test was performed.

Video-CapturingtestXpert® supports the operator not only with „helpvideos“, but also with video sequences which can betaken at the same time as the test. With a videocamera and a video-capture card, multimedial testingcan be performed. The videos run synchronous to therespective test values. Therefore, they can be evaluatedand the video can be repeated as often as desired.

A software product can onlymeet International QualityStandards when each versionhas continuity, is documentedin all phases of development,and is archived for 10 years.The test software testXpert®

fulfils these requirements andeven the especially strictguidelines of the GoodManufacturing Practices (GMP).

The complete developing process of software and itscomponents is carefully documented and archived fromsource code up to the software tools used for eachversion, and for every phase of the analysis of thespecification, design, implementation and finally, testing.The conformity to Standard, ISO 9000-3 is confirmedwith the audit report number QM-F-96/1016.

testXpert® is available in various languages, e.g.German, English and French.

Safety in detailtestXpert® takes over a safety relevant task with themonitoring and control of machines: Machine damageand danger to people must be eliminated. For thisreason, in the testing mode, testXpert® has nooverlapping windows, as is known in Windows, whichcan cover important displays or buttons.

Automatic read-in of system dataVarious testing tasks require testing machines withdifferent components which are usually exchangeable.Their specific characteristics are recorded in the systemdata (nominal force, travel, speed range, test set-upheight, calibration factors, etc.). Organisational datasuch as serial number or the date of last calibration isalso necessary.

testXpert® automatically reads-in the data directly afterprogramme start• For the required settings,• To determine the safety limit values,• For correct evaluation of the measured values.

In addition, testXpert®, checks if• The test can be performed with this configuration,• All settings have been made,• The data for the actual test has been changed.

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3.4 Load cellsLoad cells for nominal loads from 5 N to 2,000 kN canbe supplied. Together with the digital measurement,control and regulation system, they offer manyadvantageous characteristics:

• Automatic identification and acquisition of all set-upand calibration parameters via the sensor plug. Thismakes the changing of load cells very simple and aninput of set-up data or calibration is not necessary.

• Automatic zero point and sensitivity adjustment

• Temperature drift compensation

• High measuring frequency

• High measurement value resolution

• Measurement accuracy:Class 0.5 (0.5 % of measured value) from 1 to 100 %of the nominal loadClass 1 (1 % of measured value) from 0.2 to 120 %of the nominal load (1 to 100 % for load cells with anominal load ≤ 500 N)

• Overload protection

• Manufacturer´s test certificate for proof of factorycalibration

Picture 49: A load cell from our large selection: The load cell type„KAF“ for loads up to maximum 5 kN

3.5 Test units and test toolsTest units and test tools are divided into:

• Specimen grips

• Test tools for compression and flexure tests and testtools for special applications

• Tool elements for variable specimen holding(„BasicLine Toolbox“)

Since chapters 1 and 2 had information about thetesting devices and tools that are often used in foodstuffs and packaging testing, the following is only a basicoverview.

Specimen gripsZwick covers a multitude of applications areas with awide spectrum of specimen grips. The quality of aspecimen grip and its match to the specimen is veryimportant to the quality of the test.

The following criteria is used to select specimen grips:

• Force-locking and form-locking specimen grips: Withthe force-locking principle, the specimen is held byapplying a tensile force. With the form-lockingprinciple, the form of the specimen holds it in the gripitself, therefore there is no force application from thespecimen grip.

• Externally operated and self-clamping specimen grips:Specimen grips which are operated by external energyalways have a parallel clamping gripping principle,whereby the gripping force is indepenent of the tensileforce. Examples are screw and pneumatic specimengrips. With the self-clamping specimen grips, theclamping force is taken from the test force andamplified via levers, wedges, cams, or similar, andtransferred to the jaw faces. Examples here arewedge and pincer grips.

• Nominal force: Within the various categories ofspecimen grips, there are also various maximumnominal forces available. For example: There arescrew grips with Fmax from 20 N up to 50 kN.

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Picture 51: The „Mc Kee-testing machine“ contains the mostvarying testing units especially for packaging / paper testing

Picture 50: An individually specified test arrangement: Above is aspecimen grip and below are elements of the BasicLine Toolbox

An important criteria is also the selection of thematching jaw inserts. A secure and slip-free clampingof the specimen depends on the correct jaw inserts.For example: There are jaw faces with rubber smoothsurface, or steel corrugated, smooth, with V-slot etc.

Test tools for compression and flexure tests andtest tools for special applicationsThere is a multitude of testing tools of various types anddimensions, as well as of different test forces, forperforming compression and flexure tests. Completecompression and flexure test kits are available, but thereis also a complete line of individual elements availableso that a unit can be specified to any application.There also exist test tools for special applications,which are developed explicit for a test. For example:The device for testing the frictional behaviour (seepicture 28).

Toolbox elements for variable specimenclampingSome „unwieldy“ specimen require a suitable specimenclamping when there is no special testing unit available.For these cases, Zwick Roell offers the „BasicLineToolbox“. This is a product programme which containsmany elements which can be combined with oneanother. Examples can be seen in the pictures onpage 22.

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3.7 ExtensometersCrosshead travel monitorsAll Zwick Roell material testing machines are equippedwith a digital crosshead travel monitor. This measuresthe travel of the moving crosshead with high precisionand exactly reproducibility. This means that manyapplications in foodstuffs and packaging testing canuse indirect measurement of the extension (withoutadditional extensometer direct on the specimen).

Direct extension and reduction-in-widthmeasurementSome tests require measurement of the extensiondirectly on the specimen in order to eliminate anymeasuring errors which could occur due to machinedeformation, over-run of test tools or partial slippageof the specimen.There are various measurement systems for measuringextension:

• Mechanical exensometers for contact measurementdirectly on the specimen, also for long-travel lengths.

• Contact-free extensometers which do not affect thespecimen and measure the extension with opticalmethods.

• Clip-on extensometers which measure with highresolution and are clipped directly onto the specimen.

3.6 Temperature and climate chambersFoodstuffs and many packagings change theircharacteristics greatly depending on the humidityand environmental temperature.

According to the application of the „material“, thesechanges can have important effects. For example:When heated sauces are filled into containers, thetemperature can effect the production process.

Zwick Roell offers a complete product range oftemperature chambers corresponding to the manydifferent requirements.

Picture 52: A temperature chamber especially for the zwicki. Usedhere for testing on foodstuffs

Picture 53: Mechanical extensometer for high resolution, directextension measurement on the specimen.