<![CDATA[karthik Kumarasamy - My Blog]]>Fri, 15 Jan 2016 23:58:46 +0000Weebly<![CDATA[Casting Defects]]>Mon, 03 Aug 2015 10:50:43 GMThttp://krishengineer.weebly.com/my-blog/casting-defectsBelow are descriptions of defect types and their correct terminology.

1. Upon machining, small, narrow cavities appear on your casting faces.Defect: Dispersed Shrinkage--Characteristic of cast iron, these cavities are most often perpendicular to the casting surface, with depths as great as 0.8 in. (2 cm). The casting defect is most commonly caused in iron components by low carbon content or high nitrogen content in the melt.
Picture
Dispersed shrinkage
2. Several castings in your shipment are showing thin bits of metal at the parting line.Defect: Flash--Projections at the parting line occur when clearance between the top and bottom of the metal casting mold halves is great enough to allow metal to enter and solidify. The metalcaster must take more care in pattern, mold and coremaking to eliminate flash or remove it in the cleaning room after pouring.

3. One of your iron castings fractures and reveals smooth, slightly curved facets on the fracture face.Defect: Conchoidal or “Rock Candy” Fracture--This defect is characterized by separation along the grain boundaries of primary crystallization. The resulting configuration is often compared to the appearance of rock candy. The defect is caused in steel castings by elevated aluminum and nitrogen levels.
Picture
Blowholes-Pinholes

4. Your casting has smooth-walled, rounded cavities of various sizes clumped together in one area.Defect: Blowholes/Pinholes--The interior walls of blowholes and pinholes can be shiny, more or less oxidized or, in the case of cast iron, covered with a thin layer of graphite. The defects can appear in any region of a casting. They are caused when gas is trapped in the metal during solidification.

5. Your iron casting has folded, shiny films in its walls.Defect: These folded or wrinkled films are distinctly outlined and found within the walls of iron castings, causing a linear discontinuity in the structure. Generally, they are seen only upon fracturing a casting. The defects form when materials from mold or core additives and binders volatize, decompose and become entrained in the melt.
Picture
axial shrinkage
6. Upon x-ray, you observe a cavity in the middle of your casting.Defect: Axial Shrinkage--All metal shrinks as it solidifies. Axial (or centerline) shrinkage, most often plate-like in shape, occurs when the metal at the center of the casting takes longer to freeze than the metal surrounding it. The defect is partly a function of the section thickness designed into the casting, but it also can be influenced by the metalcaster’s pouring temperature, alloy purity, riser use and pouring speed.

7. A protrusion of metal is sticking out of a 90-degree corner of one of your castings.Defect: Fillet Vein--These types of metallic projections can divide an interior casting angle in half. This defect can occur when too much binder in the sand causes a crevice to form in a mold or core during mold preparation or casting. The metalcaster will reduce or modify its binder usage to alleviate the defect.

8. All your casting dimensions are incorrect in the same proportion.Defect: Improper Shrinkage Allowance--All casting alloys shrink as they solidify, but each does so at a different rate. This defect can occur when the patternmaker uses a shrink rule (constant) that differs from the actual shrinkage of the alloy used. The pattern will have to be remade to account for this defect.

9. Your casting is essentially complete except for more or less rounded edges and corners.Defect: Misrun--This defect can occur with the use of any casting alloy, but in the case of iron, the surface is generally shiny and easily cleaned. The problem can come about due to a lack of alloy fluidity, slow mold filling, inadequate venting of the mold and (in permanent molding) low temperatures.
Picture
expansion scab
10. Your casting has a partial separation in one of its walls.Defect: Cold Shut--Cold shuts vary in depth and can extend either partially or all the way through a casting section. This defect may be accompanied by rounded casting edges (also common to misruns, detailed in question 9). Cold shuts generally occur on wide casting surfaces in thin, difficult-to-fill sections, or where two streams of metal converge in the mold during filling.

11. Your casting has been stored for some time, and when you pull it out for assembly, you notice it has bent out of specification.Defect: Warped Casting--Distortion due to warpage can occur over time in a casting that partially or completely liberates residual stresses. Common practice in iron casting is normalizing heat treatment to remove residual stress. In aluminum casting, a straightening between quench and aging might be required.

12. Your iron casting has branched grooves of various lengths with smooth bottoms and edges.Defect: Buckle--Occurring in all ferrous alloys and sometimes in copper-base castings, the defect is caused by the expansion of silica sand. The defect distinguishes itself from a scab (see question 18) in that it does not allow penetration of the metal into the adjacent cavity below.

13. Very small grooves (less than 0.5 in.) on the surface of your casting are almost covered by a folded edge.Defect: Rat Tail--This shallow defect occurs in ferrous and nonferrous green sand castings. Rat tails most often extend from the area where the metalcaster gates the casting. Rat tails may be accompanied by other projection-like defects. Metalcasters can alleviate this defect by altering their sand mixture.

14. Your iron casting has spherical particles coated with oxide inside it. The particles are the same chemical composition as the base metal.Defect: Cold Shot (Shot Metal)--Not to be confused with a cold shut, this defect occurs when small droplets of metal fall into a metalcasting mold, solidify and fail to remelt when the remaining metal is introduced to the mold. The defect is caused primarily by faulty pouring practices, but it also can be influenced by misplaced runners and risers. Metalcasters can stop the defect from occurring by improving pouring conditions and protecting the mold openings against metal splashing.
Picture
lustrous carbon
15. Small, gray-green, superficial cavities in the form of droplets or shallow spots appear on your iron castings.Defect: Slag Inclusions--A reaction between the mold and ferrous metals can cause the formation of a low-melting slag, which can adhere to the casting surface. When the inclusions are dislodged during shot-blasting, a rounded cavity is left behind. The defect is especially common in steels with high chromium contents. The metalcaster will reduce pouring temperatures and cool the castings in a reducing atmosphere to correct the problem.

16. Irregular projections crop up on one side of a vertical casting surface near the parting line.Defect: Ramoff/Ramaway--This defect is characterized by a thickening of the casting in the vicinity of the parting line or an increase in dimension of a surface parallel to the parting line. It is caused by improper mold creation (ramming), which has in turn caused the sand to separate from certain vertical walls of the pattern.

17. Plate-like metallic projections with rough surfaces jut up parallel to the casting surface.Defect: Kish Graphite Inclusions--This ferrous casting defect appears as coarse (not smooth) porosity, filled with graphite. It generally becomes visible upon casting machining. The defect is caused by an excessive carbon equivalent in the melt, slow cooling or great differences in section thickness. A redesign on the part of the casting end-user may be in order to address this defect.
Picture
Seams or Scars

18. Your iron casting shows local accumulations of coarse graphite. The graphite has moved into the shrinkage cavities.Defect: Expansion Scab--Another defect caused by the expansion of molding or core sand, expansion scabs can occur in ferrous or copper-based castings. The thin metallic projections with sharp edges are generally parallel to the surface of the casting and have very rough surfaces. They are usually attached to the casting at only a few points and are otherwise loose.

19. Waves of fold markings without discontinuities appear on your casting.Defect: Seams or Scars--This defect, which generally occurs on horizontal or convex surfaces of thin castings, distinguishes itself from a rat tail in that the two edges of each individual groove are at the same level. The defect may appear in conjunction with kish graphite (detailed in question 17). Sand is not the cause of this defect. Rather, it is metallurgical.

20. Lines of extra metal that look like veins appear on your casting surface.Defect: Veining--This defect occurs when cracks appear on a sand mold due to sand contraction, which is caused by heat. The metal caster must regulate its sand composition and heating to keep veining from occurring.
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<![CDATA[Sri Sastha Bhujangam]]>Mon, 01 Jun 2015 10:19:41 GMThttp://krishengineer.weebly.com/my-blog/sri-sastha-bhujangam
Translated by
P.R.Ramachander

(I was not aware of this stotra and it is not in the list of works of Adhi Sankara who specializes in Bhujanga stotras. It was brought to my notice by sri Sudha Haran Chennicherry. The transliteration is also by him.)

1.Shridhaa nanda chinthamani shreenivasam
Sada sacchidaananda purna prakasham 
Udhaaram Sadhaaram Suraadhaara meesham
Param jyothi rupam bhaje bhootha naatham 

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who is the son of Lakshmi , who is a wish giving gem and is the residence of wealth,
Who always has the full sparkle of the true divine happiness.
Who is generous , who is with respect and the God who protects devas.

2.Vibhum veda vedaantha vedhyam varishtam
Vibhoothi pradam vishrutham brahma nishtam
Vibhaaswath prabhaava prabhum pushka leshtam
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who is the lord , Who is worshipped by Vedas and Vedanthas, who is the greatest,
Who provides in plenty , who is famous and one who does penance to brahma,
Who shines as the lord with great power and is the dear of Pushkala.

3.Parithraana dhaksham parabrahma soothram 
Suraschaaru gaathram bhava dhwaantha mithram
Param, prema paathram pavithram vichithram 
Param jyothi rupam bhaje bhootha naatham 

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who protects with great interest , Who is the one who defines parabrahmam,
Who is the god with pretty body , Who is the friend of those seeking divine,
Who is divine , who is the one to be loved , Who is holy, Who is of varied types,

4.Paresham prabhum purna kaarunya rupam 
Girishaadi peeto jwala chcharu deepam
Sureshaadi samsevitham suprathaapam 
Param jyothi rupam bhaje bhootha naatham 

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who is the highest lord , who is the form of complete mercy,
Who is the pretty lamp which lights the place of Lord Shiva,
Who is being served by Indra and other devas and who has good fame.

5.Gurum purna lavanya paadadi kesham 
Gareeyam mahatkoti surya prakasham
Karaambhoru hanya sthavethram suresham 
Param jyothi rupam bhaje bhootha naatham 

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who is the teacher, who is completely pretty from head to foot,
Who is most venerable, who has shine of billions of Suns,
Who has thighs like an elephants trunk , kills and is praised by the lord of devas.

6,Hareeshaana samyuktha shakthyey ka veeram
Kiraathaa avathaaram kripaa paanga pooram 
Kireetaavatam sojjwalath pinjcha bhaaram 
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who along with Vishnu and Shiva is a hero of great strength,
Who has taken the incarnation of a hunter , Who is full of mercy to others,
Who shines along with his crown and is elegant with a decorated feather

7.Mahaayoga peeto jwalantham mahaantham
Mahaavaakya Saaro Padesham sushaantham
Maharshi praharsha pradam Jnaana kaantham 
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who shines in the seat of great yogis , who is great,
Who teaches the meaning of great sayings, , who is greatly peaceful,
Who makes great sages happy , and who likes wisdom.

8.Mahaaranya madbaava saantarnivaasam
Ahankaara durvaara himsaan mrugadeen
Nihantham kiraata avataram charantham
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who lives in the great forest and is the essence of peace,
Who troubles, people with pride and bad habits and those who trouble animals,
Who has an incarnation as a hunter and who keeps on travelling.

9.Pruthivyaadi bhoota prapanchaantarastham
Pruthagbhoota chaitanya janyam prashashtam
Pradhaanam pramaanam puraanam prasiddham
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who is within the beings of the earth other planets,
Who separately creates intelligence in all beings , who is famous,
Who is the chief of Pramadhas and who is well known in the epics.

10.Jagaj jeevanam paavanam paavaneeyam
Jagadvyaapakam deepakam mohaneeyam
Sukhaadhaara maadhaara bhootam tureeyam
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who lives in this world , who is holy and makes others holy,
Who is spread throughout the world like the light of a pretty lamp,
Who supports pleasant life and is the most holy support of all beings.

11.Ihaamutra satsaukhya sampannidaanam
Mahadyoni mavyaah gataatmaabhidhaanam
Ahar pundareekaananam deepyamaanam
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who gives wealth of good pleasure filled life, here and there,
Who goes unimpeded and put together the life of great beings,
Who during day and night lights up the forest where elephants live.

12.Trikaala sthitam susthitam jnaanasanstham
Tridhaama trimoortyaa tmakam brahma sanstham
Trayeemoorti maartich chidam shaktiyuktam
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who is in the past , present and future, who laughs nicely, who is the store house of knowledge,
Who is in earth, heaven and hell, Who is like Shiva, Vishnu and Brahma, who is with Brahma ,
Who is perceived as the presence of the three gods and Shakthi.

13. Idaam pingalaam satsushumnaam vishantam
Sphutam brahmarandhra svatantram sushaantam
Dridham nitya nirvaanam udpadayayantam
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who keeps the ida, Pingala and Sushumna Nadis in absolute peace,
Who has opened his Brahmarandhra , who is independent and peaceful,
Who is stable, who is always detached and who does not have a second.

14.Anu brahmaparyanta jeevaikya bimbam
Gunaakaara matyanta bhakta anukampam
Anargyam shubhaadormarga valambam
Param jyothi rupam bhaje bhootha naatham

I sing about the Lord of Bhoothas , who is the form of light of love ,
Who is the form which is the amalgam of all beings from atom to Brahma,
Who protects good qualities, and has great concern about his devotees,
Who is priceless and always follows only the auspicious path.]]>
<![CDATA[Possible Mistakes In The Sampling System ]]>Fri, 20 Mar 2015 18:41:23 GMThttp://krishengineer.weebly.com/my-blog/possible-mistakes-in-the-sampling-systemManaging an analytical instrumentation operation is no small task. Experienced staff members are in short supply and you can’t spend time training new hires on your own–you’re expected to manage increasingly complex operations with limited technician and engineering time. But issues with your sampling system due to outdated skills can spell major problems for you including: analyzer down
time, unexpected maintenance costs, and even damage to your team’s credibility as analytical instrumentation professionals. Your sampling system design or routine operations and maintenance training and procedures may be the culprit – and it’s harming your operation more than you think. 
1) You haven’t checked your system for simple errors. You can improve the reliability of your analyzers by auditing and then eliminating simple mistakes from your sample system installations. When you look for them, simple mistakes like reversed check valves blocking your sample flow or a fast loop flowing backwards are easy to find, and the remedies are obvious.
2) Your gas sampling system has too much volume upstream of the first regulator. High pressure gas can ruin an otherwise well designed sampling system by causing condensation in the lines and excessive time delay due to gas compressibility. Furthermore, high pressure gas can cause a safety concern due to the rapid decompression in the event of a component failure. So, it’s best to reduce the pressure of a gas as soon as you can by minimizing the sample system volume on the upstream side of a regulator

3) Your liquid sampling pressure is too low. Liquid samples are just the opposite. Letting the pressure drop may release a dissolved gas, thus causing the liquid to bubble or foam. It’s best to keep the pressure of a liquid sample as high as possible.

4) You haven’t paid much attention to the surfaces your sampling system needs. When sample fluid touches a surface, a few molecules stick. Loss of molecules due to adsorption can spoil your sample. Pick the proper materials for filter elements, regulator diaphragms, tube walls, or gas cylinders when designing or maintaining your system.

5) You’re using elastomer seals not compatible with your sample fluid. Material that is mismatched to your sample fluid may cause a failure like sample leakage or even a blockage within the sampling device leading to the degraded accuracy of your analysis.

6) You’re sampling from a stagnant line. For a representative sample, make sure you’re sampling from an active process line. Remember that the timeliness of your sample is also dependent on the time it takes the sample to flow from the process to the extraction point. The location of the sample point can be a critical aspect of a successful sampling system.

7) You’re not spot ting dead legs in your sample-transport line. Dead legs or unpurged volume allow molecules to diffuse into the sample causing a slow analyzer response and continuous contamination of your system.

8) Your vaporizer is too hot. A hot vaporizer body could boil the incoming sample, causing it to fractionate. Make sure you understand temperature requirements of the chemicals in your system and appropriate equipment settings to prevent errors

9) Your sample flow is too slow. The slower your sample flow, the more viscous drag is placed on the interior wall of your tubing, causing solids to form. A faster flow is recommended for good sample mixing, cleaner sample lines and faster response time

10) You’re not looking for the causes of time delay in your sampling system. If your measurement does not follow your process, you have time delay in your system. Other symptoms are blurred or muted response, laboratory disagreement, and poor performance of a control scheme
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<![CDATA[Rp vs G screw thread interchangeability]]>Thu, 19 Mar 2015 18:53:09 GMThttp://krishengineer.weebly.com/my-blog/rp-vs-g-screw-thread-interchangeabilitySimilarities
The G-series and the Rp-series British Standard Screw Threads have much in common:
a. Both are British Standard Pipe Parallel.
b. Both have the Whitworth 55° included thread angle form with Full Form rounded root and crest of thread.
c. In all situations the G-series can be used when the Rp-series is specified, but the reverse is not true. 

Differences
The differences between the G-series screw thread and the Rp-series screw thread include:
The G-series screw thread is made to ISO-228 while the Rp-series screw thread is made to ISO-7 or BS-21 or EN 10226-1.
The G-series screw thread may be internal screw thread or external screw thread; where the Rp-series screw thread is only internal screw thread.
The G-series screw thread is not intended for a seal being made on the screw thread where the Rp-series screw thread is specifically designed to seal when mated with an R-series tapered external screw thread.

Comparison of Pitch Diameters
I think a basic understanding of the two screw threads is embodied in a comparison of their effective pitch diameters. Below is a chart displaying the G1” effective pitch diameters compared with the Rp1” effective pitch diameters

Similarities
The G-series and the Rp-series British Standard Screw Threads have much in common:
a. Both are British Standard Pipe Parallel.
b. Both have the Whitworth 55° included thread angle form with Full Form rounded root and crest of thread.
c. In all situations the G-series can be used when the Rp-series is specified, but the reverse is not true.

Differences
The differences between the G-series screw thread and the Rp-series screw thread include:
The G-series screw thread is made to ISO-228 while the Rp-series screw thread is made to ISO-7 or BS-21 or EN 10226-1.
The G-series screw thread may be internal screw thread or external screw thread; where the Rp-series screw thread is only internal screw thread.
The G-series screw thread is not intended for a seal being made on the screw thread where the Rp-series screw thread is specifically designed to seal when mated with an R-series tapered external screw thread.

Comparison of Pitch Diameters
I think a basic understanding of the two screw threads is embodied in a comparison of their effective pitch diameters. Below is a chart displaying the G1” effective pitch diameters compared with the Rp1” effective pitch diameters

Conclusion
Notice how the G-series will always be within the specified parameters for the Rp-series, but the Rp-series may be smaller than the G-series. Based on this the G-series is always useable when a Rp-series is requested, but an Rp-series may not work when a G-series is requested.The reason for this is that both the G-series screw thread and the Rp-series screw thread have the same Basic Effective Pitch Diameter. The Internal G-series screw thread then has an amount of tolerance applied to the positive and none applied to the minus of the Basic Effective Pitch Diameter. The Rp-series has the same amount of tolerance added to the positive side of the Basic Effective Pitch Diameter AND an equal amount applied as a minus from the Basic Effective Pitch Diameter.

A word on Gages
We recommend that you use gauges which are defined in a specification. In this case:
- BS-21 Rp internal screw threads should be checked with BS-21 Rc Tapered Screw Thread Plug Gage.
- EN-10226 Rp-series internal screw threads should be checked with EN-10226 Rc Tapered Screw Thread Plug Gages: EN-10226 Gage-1* AND EN-10226 Gage-2*.
- ISO-7 Rp-series internal screw threads should be checked with ISO-7 Rc Tapered Screw Thread Plug Gages: ISO-7 Gage-1* AND ISO-7 Gage-2*.
- ISO-228 G-series internal screw threads should be checked with G-series Screw Thread Plug Gauges.
* EN-10226 gages are interchangeable with ISO 7 gages.

Disclaimer
This information given is my opinion from my study of the standards. I have no authority and my opinion thus has no value. If you intend on acting on this information;

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<![CDATA[Rs vs G screw thread interchangeability]]>Sun, 01 Feb 2015 20:01:35 GMThttp://krishengineer.weebly.com/my-blog/rs-vs-g-screw-thread-interchangeabilityNOTE
The Rs-series per BS 21 is an obsolete thread series and should not be used in new designs; however; you may find a requirement for Rs-series screw threads on an older product/part design drawing.

Similarities
The G-series and the Rs-series British Standard Screw Threads have much in common:
a. Both are British Standard Pipe Parallel.
b. Both have the Whitworth 55° included thread angle form with Full Form rounded root and crest of thread.
c. In all situations the G-series can be used when the Rs-series is specified, but the reverse is not true.
Differences
  • The differences between the G-series screw thread and the Rs-series screw thread include:
  • The G-series screw thread is made to ISO-228 while the Rs-series screw thread is made to BS-21 Appendix C.
  • The G-series screw thread may be internal screw thread or external screw thread; where the Rs-series screw thread is only external screw thread.
  • The G-series screw thread is not intended for a seal being made on the screw thread where the Rs-series screw thread is specifically designed to seal when mated with an Rc-series tapered internal screw thread.

Comparison of Pitch Diameters
I think a basic understanding of the two screw threads is embodied in a comparison of their effective pitch diameters. Above is a chart displaying the G1” effective pitch diameters compared with the Rp1” effective pitch diameters: 

Conclusion
Notice how the G-series will always be within the specified parameters for the Rs-series, but the Rs-series may be smaller than the G-series. Based on this the G-series is always useable when a Rs-series is requested, but an Rs-series may not work when a G-series is requested.The reason for this is that both the G-series screw thread and the Rs-series screw thread have the same Basic Effective Pitch Diameter. The Internal G-series screw thread then has an amount of tolerance applied to the minus and none applied to the positive of the Basic Effective Pitch Diameter. The Rs-series has the same amount of tolerance added to the positive side of the Basic Effective Pitch Diameter AND an equal amount applied as a minus from the Basic Effective Pitch Diameter.

A word on Gages
We reccommend that you use gages which are defined in a specification. In this case:
- BS-21 Rs external screw threads should be checked with BS-21 R-series Tapered Screw Thread Ring Gage.
- ISO-228 G-series external screw threads should be checked with G-series Screw Thread Ring Gauges.

Disclaimer
This information given is my opinion from my study of the standards. I have no authority and my opinion thus has no value.

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