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  TERM PAPEr

MEC 201TOPIC: Write a report on property called

hardness.what does it depend upon ,howit increase or decrease it.In what

application it is important.what is the

disadvantage of hardness?how is

hardness measure?

SUBMITTED BY: SUBMITTED TO:

RAUSHAN SUDHANSHU MR.ASHISH

K.G.SARAN 

10901326

K4901

K4901B42

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ACKNOWLEDGEMENT:-I take this opportunity to present my votes of thanks to all those guidepost who

really acted as lightening pillars to enlighten our way throughout this

 project that has led to successful and satisfactory completion of this

study.

We are really grateful to our HOD for providing us with an opportunity to

undertake this project in this university and providing us with all the

facilities. We are highly thankful to our subject teacher Mr. AshishK.G.Saran for his active support, valuable time and advice, whole-

hearted guidance, sincere cooperation and pains-taking involvement

during the study and in completing the assignment of preparing the said

 project within the time stipulated.

Lastly, We are thankful to all those, particularly the various friends , who have

 been instrumental in creating proper, healthy and conductive environment

and including new and fresh innovative ideas for us during the project,

their help, it would have been extremely difficult for us to prepare the

 project in a time bound framework.

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Contents :-

• Introuduction .

• Hardness Measuring

• Dependence of hardness

• Mohr scale of hardness

• Applications

• Advantage of hardness

•  Testing of Hardness & Measuring method

• References

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  Introduction:-

What is Hardness?

Hardness is the property of a material that enables it to resistplastic deformation, usually by penetration. However, the termhardness may also refer to resistance to bending, scratching,

abrasion or cutting.

 The Metals Handbook  defines hardness as "Resistance of 

metal to plastic deformation, usually by indentation. However,

the term may also refer to stiffness or temper or to resistance

to scratching, abrasion, or cutting.

It is the property of a metal, which gives it the ability to resist

being permanently, deformed (bent, broken, or have its shape

changed), when a load is applied. The greater the hardness of 

the metal, the greater resistance it has to deformation.In

mineralogy the property of matter commonly described as the

resistance of a substance to being scratched by another

substance.

In metallurgy hardness is defined as the ability of a materialto resist plastic deformation.

 The dictionary of Metallurgy defines the indentation

hardness as the resistance of a material to indentation. This is

the usual type of hardness test, in which a pointed or rounded

indenter is pressed into a surface under a substantially static

load.

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Hardness is the measure of how resistant solid matter is tovarious kinds of permanent shape change when a force isapplied. Macroscopic hardness is generally characterized bystrong intermolecular bonds, however the behavior of solid

materials under force is complex, therefore there are differentmeasurements of hardness: scratch hardness, indentationhardness, and rebound hardness.

 Typically defined as resistance to indentation under specific

conditions, the hardness of an elastomer is more accurately

thought of as two related properties: inherent hardness and

processed hardness. As a result of chemical structure, each

elastomer has its own inherent hardness. This inherent

hardness can be modificompoundingvulcanizationHardness in

molded rubber articles (processed hardness) is a factor of 

cross-link density (and the amount of fillers). The more cross-

linking a given material undergoes during vulcanization, the

harder the final molded part will be. When judging the potential

effectiveness of a molded seal, processed hardness is one of 

the most common criteria in the rubber industries.

Hardness is the property of a material that enables it to resistplastic deformation, usually by penetration. However, the termhardness may also refer to resistance to bending, scratching,abrasion or cutting.

Measurement of Hardness:-

Hardness is not an intrinsic material property dictated byprecise definitions in terms of fundamental units of mass,

length and time. A hardness property value is the result of adefined measurement procedure.

Hardness of materials has probably long been assessed byresistance to scratching or cutting. An example would bematerial B scratches material C, but not material A.Alternatively, material A scratches material B slightly andscratches material C heavily. Relative hardness of minerals canbe assessed by reference to the Mohs Scale that ranks the

ability of materials to resist scratching by another material.Similar methods of relative hardness assessment are still

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commonly used today. An example is the file test where a filetempered to a desired hardness is rubbed on the test materialsurface. If the file slides without biting or marking the surface,the test material would be considered harder than the file. If 

the file bites or marks the surface, the test material would beconsidered softer than the file.

 The above relative hardness tests are limited in practical useand do not provide accurate numeric data or scales particularlyfor modern day metals and materials. The usual method toachieve a hardness value is to measure the depth or area of anindentation left by an indenter of a specific shape, with aspecific force applied for a specific time. There are three

principal standard test methods for expressing the relationshipbetween hardness and the size of the impression, these beingBrinell, Vickers, and Rockwell. For practical and calibrationreasons, each of these methods is divided into a range of scales, defined by a combination of applied load and indentergeometry.

What depend upon hardness:- 

1-How does a water treatment system remove hardness?

Hardness is removed by a process called "ion exchange."

Hardness-causing particles and debris are positively charged.

 The water runs through the resin system, which has millions of 

negatively charged sites. As the water flows past these sites,

calcium, rock, iron and magnesium attach to the sites and are"bumped off .

2-Does granite can have pits?

Natural stone Granite have pits that are the part of stones

structure. But pits can be minimized by applying sealer to the

surface of counter top.

MOHS' SCALE OF HARDNESS:-

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more brittle). Often only the surface of a metal is treated forhardness and hardness is also related to crack propagationunder certain circumstances.

*Another advantage of hardness testing is that it can beperformed on lighter and less expensive equipment than tensiletesting. It usually involves simply indenting a specimen with adiamond indenter as opposed to the large equipment requiredfor tensile testing.

What are the defects and advantages of hard water?Removal of 

hardness of water?

I don't know of any advantages of having a hard water.Disadvantages are easier to come by. In normal use hard waterwill not allow soap to make suds, this makes washing machinesand dishwashers less effective. So you will have to add moresoap to do the same job, this will cost more money to do thesame job as a softer water. Hard water also has some long termproblems. It can cause scaling on the inside of your pipes andfaucets. The scaling will build up over time and reduce the

inside diameter of your pipes. This can cause blockage or lowpressure from your showers and faucets. It will also causewater heaters to fail sooner, raising the cost of replacement.Since most hardness is caused by the minerals calcium andmagnesium they can be removed with a couple of differentprocesses. A water softener works on the principle of cation orion exchange in which ions of the hardness minerals areexchanged for sodium or potassium ions, effectively reducingthe concentration of hardness minerals to tolerable levels.Some softeners use zeolites but most use sodium chloride, alsoknown as table salt. Hardness can also be reduced with a lime-soda ash. The addition of lime causes a reaction in which thehardness minerals precipitate out of solution and can then beremoved through filtration.

Use Pencil Hardness to Your Advantage:-

When starting the preliminary drawings for any project it is bestto keep the lines light and sketchy. A 2H pencil hardness is

ideal for this.

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 This is one thing I have definitely learned over the years thathas greatly impacted my design and the process of which Iwork. When I was in high school there was a fellow artist's workthat I admired for the skill and and overall style his pieces

possessed. While watching him work one day I noticed he onlyused two or maybe three different pencils on his pieces: a 2Bpencil and an Ebony pencil. These pencils are on the softer sideof the spectrum when it comes to pencil hardness.

Hardness Testing & measure method:-

1-Rockwell Hardness Test

2-Rockwell Superficial Hardness Test

3-Brinell Hardness Test

4-Vickers Hardness Test

5-Microhardness Test

6-Mohs Hardness Test

7-Scleroscope and other hardness testing

methods

Hardness Conversion or Equivalents:-

Hardness conversion between different methods and scalescannot be made mathematically exact for a wide range of materials. Different loads, different shape of indenters,homogeneity of specimen, cold working properties and elastic

properties all complicate the problem. All tables and charts

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should be considered as giving approximate equivalents,particularly when converting to a method or scale which is notphysically possible for the particular test material and thuscannot be verified. An example would be converting HV/10 or

HR-15N value on a thin coating to the HRC equivalent.

Property of hardness:-

1.-Tensile Strength:-

 To better understand tensile strength, first recall that thereare intermolecular forces (known as van der Waals forces)helping to hold long polymer chains in place. These forcesare at their weakest when, due to structural irregularities,themolecules cannot fit closely together, resulting in a non-regimented, amorphous structure. Some polymers,however, have their constituent molecules aligned in veryregular patterns. The combination of this regularity and theintermolecular forces may be enough to “fit” the chainsinto a rigid, crystalline pattern. Tensile strength largelydepends on an elastomer’s ability to partially strain

crystallize when stretched. With greater crystallizationcomes increased strength and resistance to stress. Naturalrubber is an example of an elastomer with a very regularchain structure that strain crystallizes. As a result, naturalrubber has high tensile strength. Of course, the temporarynature of strain crystallization allows natural rubber toregain its original shape once the stress is removed. Anelastomer with inherently poor tensile strength, suchasstyrene butadiene, can be improved through the addition

of highly particulate reinforcing agents.

2-Tear Resistance:-

 Tear resistance can be gauged via the same ASTM D 412apparatus used in the testing of tensile strength, modulus,andelongation. As described in ASTM D 624, different

specimen types can be used to measure both tear initiation

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(resistance to the start of a tear and tear propagation(resistance to the spread of a tear . Either way, the sampleis placed in the tester’s grips, which then exert a uniform

pulling force until the point of rupture. This force may thenbe divided by the specimen’s thickness to arrive at the tearresistance for that particular sample. Three separatesamples are typically tested and an average calculated.

.

3-Compression Set:-

Compression set is the end result of a progressive stressrelaxation, which is the steady decline in sealing force thatresults when an elastomer is compressed over a period of time. In terms of the life of a seal, stress relaxation is likedying, whereas compression set is like death.

 Though it is very difficult to accurately quantify stressrelaxation, compression set is easy to measure. ASTM D395 details compression set testing for rubber that will becompressed in air or liquid media. Two methods aredescribed (“A” for constant force; “B” forconstant deflection), but the basic methodology issubstantially the same. Testing generally involves use of cylindrical disk compression set test buttons (0.49" thick by1.14" diameter). In lieu of buttons, die-cut plied (stacked)samples (0.070" thick by 1.14" diameter) may besubstituted. The buttons or plied samples are placedbetween steel plates. In method A the plates are thenforced together using either a calibrated spring or a pre-defined external force , a bolt-tightened device and steel

spacers are used. Either way, compression (normally 25%of original thickness) is held for a given time (e.g. 22 hours)at a specific temperature (e.g. 100° C), these last twovariables based on anticipated serviceconditions.

4-Abrasion Resistance:-

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Measured as a loss percentage based on originalweight,abrasion resistance is the resistance of arubber compound to wearing away by contact with a

moving abrasive surface. Whereas the cutting or nicking of a seal’s surface is an instantaneous event, abrasiverubbing or scraping is much more of a progressivephenomenon that develops over time. Seals in motion aremost susceptible to abrasion. Hardcompounds tend toexhibit less abrasive wear than soft compounds, but use of a harder compound can also increasefriction in dynamicseals, and increased friction generates seal-degrading heat.

Because of the many potential variables (including heatfluctuation and surface contamination), abrasion resistanceis hard to accurately measure. Testing typically involvesthe uniform application of an abrasive material (such assandpaper) to the surface of a sample. ASTM standardsdescribe three different abraders: D 1630 relies on aNational Bureau of Standards (NBS) abrader ; D 2228 usesa Pico abrader (see Figure 22); and D 3389 (also known as

 Taber Abrasion) employs a double-head abrader and a

rotary platform. Regardless of the specific test method, therelative amount of sample material that is lost due toabrasion is a good indication of abrasion resistance.

5-Resilience:-

As detailed in ASTM D 2632, resilience (also known asrebound) refers to a compound’s ability to regain itsoriginal size and shape after temporary deformation.Resilience testing typically involves the dropping of a smallweight onto a test specimen (such as a compression setbuttonThe extent to which the weight bounces back is thennoted as a percentage of the initial drop height. A highlyresilient material (one that can rapidly regain itsdimensions) might engender a 70% rebound value, butvalues in the range of 40 to 50% are more typical for themajority of elastomers tested. Thoughcompounding may

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improve an elastomer in this area, it can also detract fromgood resilience, which is largely an inherent property. As ageneral rule, resilience is most critical indynamic seals.

References:-

1-www.sciencedirect.com

2-www.wikipidia.org

3-^ Correlation of Yield Strength and Tensile Strength withHardness for Steels , E.J. Pavlina and C.J. Van Tyne, Journal of Materials Engineering and Performance, Volume 17, Number 6 /December 20084-^ G.L. Kehl, The Principles of Metallographic LaboratoryPractice, 3rd Ed., McGraw-Hill Book

5-^ H.M. Rockwell & S.P. Rockwell, "Hardness-Tester," USPatent 1 294 171, Feb 1919.6-^ S.P. Rockwell, "The Testing of Metals for Hardness,

 Transactions of the American Society for Steel Treating,