Cruas Tiontú Cairt, Áireamhán & Trialacha do Rockwell, Brinell, Vickers agus níos

Réamhrá: Cad é Cruas

Is Cruas maoin de chuid aon ábhar a deformations a cruth resist nuair a bheidh sé faoi réir fórsa seachtrach. Tá tástáil Cruas tábhachtach d'iarratais teicniúla agus innealtóireachta mar cabhraíonn sé chun a chinneadh an hardness agus neart teanntachta na n-ábhar.

Cabhraíonn sé chun tuiscint shoiléir ar cibé an bhfuil an t-eiseamal á thástáil oiriúnach do iarratais ar leith a fhorbairt. Cabhraíonn sé tionscail a dhéanamh ar tháirgí deiridh sábháilte agus ar ardchaighdeán a chomhlíonann na rialacháin sábháilteachta agus na treoirlínte arna leagan síos ag na húdaráis ábhartha.

Na cineálacha éagsúla de chruas agus modhanna éagsúla tástála chruas agus lena gcinntear na luachanna cruas Pléitear thíos:

Cruas scratch

Is cruas Scratch ar chumas d'ábhar dhífhoirmiú chun seasamh in hiondúil ag scratches agus abrasions. Is cruas Scratch ceann amháin an chineáil chruas a thomhas nuair a dromchla eiseamal scríobtha ag stylus a dragged feadh a dromchla faoi ualach tástála seasta.

Scratch hardness method defines the resistance of a material to plowing by a hard stylus. It measures the hardness of the material and its ability to resist scratches and abrasions. Generally, a scratch hardness tester consists of a stylus, portable sample holding stage, load-applying device, and a data processing and display unit.

The earliest scratch hardness tests were conducted by Friedrich Mohs in 1820 who also developed the Mohs scale. The scratch hardness test measures the resistance of the specimen to fracture or permanent deformation due to friction caused by the stylus along its surface.

Úsáideann an triail ábhar níos deacra a scratch an dromchla eiseamal atá déanta d'ábhar réasúnta níos boige. Nuair is gá duit a cótaí thástáil, scratch ansin tagraíonn cruas leis an bhfórsa is gá a ghearradh tríd an scannán leis an tsubstráit. Tá Mohs scála a úsáidtear le haghaidh a thomhas an fhriotaíocht scratch ábhair chomh maith le gléas a thomhas ar a dtugtar sclerometer.

Cruas eangaithe

Tagraíonn cruas eangaithe don cruas d'abhar is gcinneann dhéanamh eangú ar a dhromchla ag baint úsáide as indenter cuí faoi ualach tástála.

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There are many different indentation testing methods which measure the depth of indentation made on the specimen surface for measuring its hardness. Indentation hardness tests can be further subdivided into two categories- macro indentation tests and micro-indentation tests. Macro indentation tests make use of large test loads in excess of 1Kgf and can go up to 3000Kgf in some cases.Uathoibríoch turret Digiteach Taispeáin Íseal Luchtaigh Vickers Cruas Tester

The prominent type of macro indentation testing methods includes Rockwell hardness testing method, Brinell method, Vickers test, Knoop hardness testing method, etc. Micro-indentation testing, on the other hand, is used for measuring the hardness of soft metals, thin and small specimen, etc.

The test loads applied for micro-indentation hardness tests are much lower and can range between 1 to 1000gf. Micro-indentation tests can be used for measuring changes in hardness on a microscopic scale. Vickers method and Knoop hardness testing methods are two popular micro-indentation hardness testing methods.

Indentation hardness tests can be prone to errors. The main sources of errors while measuring hardness include poor technique, improper calibration of the testing equipment, improper finishing of the specimen surface, etc. The test surface needs to be free from any dirt, oxidation, or lubrication to get reliable estimates of hardness. The indenter should also be perpendicular to the specimen surface as any inclination will result in faulty hardness measurements.

rebound Cruas

Rebound hardness which is also known as dynamic hardness measures the hardness of a material by determining the height to which a diamond-tipped hammer bounces when it is dropped from a height on to the specimen. This type of hardness is related to elasticity.

Rebound hardness is generally measured using the Leeb rebound hardness test. This method was developed in 1975 by Leeb and Brandestini by using a portable hardness tester. This tester provided a new alternative to the usually intricate and complex traditional hardness testing equipment.Taispeáin Uathoibríoch turret Cláraithe Digiteach Vickers Cruas Tester

The Leeb rebound hardness testing method follows standardized procedures. The velocity of the body ranges between 1.4 m/s to 3 m/s. Under this method, the velocity of the body before and after the impact is measured to determine the hardness of the specimen.

The ratio of the impact velocity to the rebound velocity gives the dynamic Leeb hardness of the test specimen. The object used for making the impact on the specimen can be tungsten carbide cobalt, ceramic or diamond, or a ball-shaped indenter with different radius.

The sample hardness determined by this method is represented as (example) 750 HL D in which 750 denotes the hardness value, HL denotes “Hardness according to Leeb” and D represents Leeb method with spherical impact body of tungsten carbide-cobalt with a radius of 1.5 mm and weight of 4.5 grams.

Roghnú na Modh Tástála Cruas Fearr

The hardness of a material depends on a number of factors like homogeneity of the material, type of material, its size, and condition.

There are different types of methods for hardness testing which needs to be selected carefully for getting the most accurate and reliable hardness measurements.

Computer microhardness Tester (Semi-uathoibríoch) do Cláraithe Iompróir Tábla
Computer microhardness Tester (Semi-uathoibríoch) do Cláraithe Iompróir Tábla

Factors which need to be considered before selecting the ideal hardness testing methods include- the type of material to be tested, the hardness of the material to be tested, homogeneity of the material, size of the specimen, if mounting is necessary for hardness testing, thickness of the specimen, etc.

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Rockwell Cruas Tástáil

Rockwell hardness testing is the most common and fast method for testing hardness. It is generally ideal for testing hardness of larges sized samples.

It can be used either on the assembly line or in laboratories for testing hardness. It uses a steel ball or diamond-tipped cone indenter for measuring hardness depending upon the hardness of the material to be tested.

To start the Rockwell test, a minor load of generally 10Kgf is applied on the indenter. The indenter then moves under the test load on to the specimen surface. While the indenter is still under the influence of the minor test load, an additional major test load is also applied to it. This ensures better indentation on the specimen surface which is clear and measurable.

The Rockwell method of hardness testing is popular as it is not influenced by either the operator’s bias or the roughness of the surface whose hardness is being tested.

It does not make use of any sophisticated or costly optical equipment for measuring the hardness of specimen, which makes it a cost-effective method for hardness testing. It is a non-destructive method for hardness testing which means that the sample specimen being tested is not destroyed and it can be used for other purposes after the testing procedure is completed.Rockwell Cruas Tester (Clasaiceach Cineál)

This method has its drawbacks also as it is not very accurate compared to other methods of hardness testing. Small deviation in measuring the indentation depth can throw off the hardness readings considerably.

If the indenter in this method is worn out, then it can provide faulty hardness measurements which are non-reliable.

Tá luach cruas Rockwell ríomh ag úsáid na cairteacha chomhshó. Tá beagnach 30 scálaí Rockwell ach is mó de na n-ábhar atá clúdaithe ag Rockwell C agus B scálaí. Tá ionadaíocht na luachanna hardness i dtástáil Rockwell mar (shampla) 70 HRB nuair atá 60 an léamh chruas ar an scála B.

 

Brinell Tástáil Cruas

Tá an tástáil cruas Brinell ar cheann de na modhanna is sine agus is mó a úsáidtear go forleathan le haghaidh tástála chruas na n-ábhar. Forbraíodh an modh seo ag JA Brinell sa bhliain 1900. Is sé iontach do thomhas an chruas heiseamail atá ró-gharbh nó cúrsa a thomhas trí mhodhanna eile.

I gceist leis an modh Brinell úsáid ualaí tástála níos airde is féidir a théann suas go dtí 3000Kgf agus indenter liathróid go ginearálta 10mm ar trastomhas.Leictreach Dromchla Rockwell Cruas Tester

Chun tomhas cruas miotal softer agus cóimhiotail, ualaí tástála níos lú de suas le 500Kgf a úsáid freisin. Is é an t-ualach tástála réamhshocraithe i bhfeidhm ar an indenter spherical a bhíonn ar siúl ar an dromchla eiseamal ar feadh i gcoitinne ar feadh 10-15 soicind agus ansin ar athraíodh a ionad.

Is é an doimhneacht eangú a rinne an indenter ar an dromchla eiseamal thomhas ansin agus staidéar ag úsáid trealamh optúil chun cinn a chinntíonn cruinneas níos fearr agus iontaofacht.

Is é an chairt comhshó Brinell úsáid ansin a thiontú ar an trastomhas meánach an eangú tugadh don luach chruas comhfhreagrach Brinell. Ag baint úsáide as na cairteanna a chomhshó, is féidir leis an luach cruas Brinell a aistriú freisin i an neart teanntachta comhfhreagrach.

The Brinell method of hardness testing comes with few drawbacks also. The operator can make mistakes in measuring the indentation depth on the specimen surface which can considerably impact the hardness measurements.

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Since the method involves advanced and sophisticated optical equipment for measuring the specimen hardness, it is costlier compared to the Rockwell method. It also takes more time to test hardness as the specimen surface needs to be prepared before testing.

The Brinell method will also not work accurately if the specimen surface is too thin i.e. less than 9.6 mm.

The hardness readings using the Brinell method are represented as 600 HBW where 600 denotes the hardness value and HBW denotes “Brinell Hardness” with tungsten ball indenter. If steel ball indenter is used then the readings will be represented as 600 HBS where HBS denotes “Brinell Hardness” with steel ball indenter.

Vickers Tástáil Cruas

The Vickers test uses the same principle as the Brinell method with the only exception being the type of indenter being used.

The type of indenter needs to be changed under the Brinell method depending on the type of material being tested. However, the same diamond indenter is used in the Vickers method for measuring the hardness of all specimen types.Uathoibríoch turret Digiteach Taispeáin Íseal Luchtaigh Vickers Cruas Tester

The indenter used in this method is in the form of a right pyramid. A test load is applied on the indenter which presses itself against the specimen surface thereby leaving an indentation.

The diagonal lengths of these indentation marks are measured using optical systems, resulting in highly accurate hardness readings. The dwell time- the time for which the test force is applied through the indenter on the specimen surface- is generally between 10-15 seconds in this method.

The Vickers test using micro-test loads which are much lesser compared to the Brinell method. It is a microhardness testing method which is best suited for measuring the hardness of materials which are too thin or small for macro hardness testing.

Tá an modh seo oiriúnach i do thomhas an cruas na bileoga tanaí de mhiotail, a bhfuil samplaí beag, etc Is é an tástáil Vickers modh neamh-millteach a chinntíonn gur féidir an t-eiseamal a úsáid tar éis an t-tástála a chomhlánú. Tá roinnt teorainneacha an modh Vickers.

Éilíonn sé an dromchla eiseamal a bheith saor ó aon imperfections agus dá bhrí sin tá am ag teastáil le haghaidh ullmhú an dromchla eiseamal roimh seoladh na tástála. Bíonn sé ar a laghad 30-60 soicind do sheoladh an tástáil agus an t-am eisiach an am a thógann sé chun ullmhú an dromchla eiseamal.

Ní tástáil Vickers molta le haghaidh táirgeadh an mórchóir i línte cóimeála agus tá sé níos oiriúnaí le haghaidh tástála saotharlainne. Na tomhais chruas sa tástáil Vickers Tá ionadaíocht mar 700 HV / 10 nuair atá 700 an luach cruas Vickers atá Thángthas trí úsáid a bhaint lucht tástála 10Kgf.

Knoop Tástáil Cruas

Knoop hardness testing method is an alternative to the Vickers method. It is a microhardness measuring method which is suitable for measuring the hardness of fragile and brittle materials like ceramics. It is also useful for hardness testing of small elongated areas like coatings.

The Knoop method also uses a pyramidal diamond as indenter, but the indenter is elongated instead of being a right pyramid as in the Vickers method. Since the method is used for hardness testing of fragile materials, it uses micro loads of up to 1Kgf.

The indenter used in this method penetrates the specimen surface only half as deep as in the Vickers method, which makes it perfect for hardness testing of the brittle specimen.

Mar gheall ar an cruth ar an indenter, is é an modh Knoop oireann níos fearr do thomhas heiseamail níos faide elongated nós bratuithe. Tá sé tábhachtach a thabhairt faoi deara gur chóir an dromchla eiseamal bheith ullmhaithe go cuí sula atá ag déanamh an tástáil Knoop as a chinntiú tomhais cruas cruinn agus iontaofa.

 

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