Bugra Cengiz 030060178 13th week

Traditional composites

Traditional composites constructed from matrix and solid and/or porous fillers they feature high filler content and high hardness, their young modulus is dentin-like and their radioopocity is good. Depending on degree of milling. The surface is rough to nearly smooth. Depending on time and distrubition wear of the restoration and antagonists is low to high.

Andreas Mortensen,Concise encyclopedia of composite materials. P. 197

Polyethylene

Polyethylene, a linear polymer, is made by an addition reaction.  It is started with an initiator, such as H2O2, which gives free, and very reactive -OH radicals. One of these breaks the double-bond of an ethylene molecule,  C2H4, when it is heated under pressure, to give

The left-hand end of the activated monomer is sealed off by the OH terminator,

but the right-hand end (with the star) is aggressively reactive and now attacks

another ethylene molecule, as we illustrated in Fig. 22.1. The process

continues, forming a longer and longer molecule by a sort of chain reaction.

The OH used to start a chain will, of course, terminate one just as effectively,

so excess initiator leads to short chains. As the monomer is exhausted the

reaction slows down and finally stops. The DP depends not only on the amount

of initiator, but on the pressure and temperature as well.

Michael F. Ashby

David R. H. Jones Engineering Materials 2. An Introduction to Microstructures, Processing and Design. P. 280

Nitrocarburizing

Nitrocarburized microstructures also develop in gaseous atmospheres when ammonia is blended with a carbon-emitting gas Gas nitrocarburizing is widely applied, with the use of additional gases such as endogas, exogas, carbondioxide , methylamine, and methanol resulting in several processing variants.

In nitrocarburizing, an ammonia atmosphere is blended with carbon and oxygen containing

gases that are usually based on carbon dioxide or allow carbon dioxide to be generated.  In accordance with the homogeneous water gas reaction. carbon dioxide reacts under near equilibrium conditions with the hydrogen generated according to the react ion

                                                                             CO2 + H2 --->H2O+  CO

Given a constant ammonia partial pressure, this leads to a drop in the hydrogen partial pressure and arise in the nitriding characteristic

A state of near-equilibrium is also maintained in the react ion of ammonia with carbon monoxide from an additional gas

NH3 + CO ---> HCN + H2O        where hydrogen cyanide (HCN) is generated

In addition to reaction nitrogen transition is furthermore promoted by the reaction

HCN ---> N(a) +C(a) + (1/2)H2

in which carbon too diffuses into the steel. Carbon, moreover , diffuses into the steel via the Boudouard reaction and the heterogeneous water gas reaction

The Effect of nitrocarbuzing 

George, E, Totten, Steel Heat Treatment Handbook Mettallurgy and Technologies. P. 458. 472-473. 477

Cryogenic Treatment ( Subzero Cryogenic Treatment)

Subzero cryogenic treatment may be applied to transform the retained austenite to martensite, substantially lowering its amount, sometimes to as little as about 1 vol%, which cannot be detected metallographically but only by x-ray diffraction

Decreasing the amount of retained austenite achieves

1. Increase in hardness and consequently in wear resistance
2. More dimensional stability in the finished part (smaller change in dimensions due to structural volume change in use)
3. Less susceptibility to the development of cracks at grinding


Figure 6.124 shows a heat treatment cycle that includes subzero treatment. The most
important parameters of the treatment are (1) the temperature below 0 C (328F) that should be attained and (2) the cooling capacity of the equipment. In some cases, temperatures of - 80 to -100 C ( -112 to - 148  F) are sufficient, but for other steels, especially high-alloy ones, ower temperatures of - 140 C (- 280  F) or even -180 C (- 292 F) are necessary. Holding time at low temperature is unimportant, because the transformation of retained austenite to martensite does not depend on time, but only on the temperature to which the metal has been cooled. Only that portion of the retained austenite will be transformed to martensite that corresponds to the cooling temperature realized. Further transformation will take place only if the temperature is lowered further.

George, E, Totten, Steel Heat Treatment Handbook Mettallurgy and Technologies. P. 400-401

Bugra cengiz 11th week

Duplex Stainless Steel

In early 1980's, various steel companies developed a steel with both ferritic and austenitiv microstructure called duplex stainless steel. It contains the characteristics of ferritic steel such as high yield strength and good weldability with resistance to generak corrosion, pitting and stress corrsion cracking Duplex steels from different mills each have slightly have diffrent chemical copmpositions.,
C(max)= %0,03
Si (max)=%1
Mn(max)= %2
P(max)= %0,03
S(max)= %0,02
Cr=%22
Ni=%5.5
Mo= % 3

Pitting and crave corrosion protection depends on chromium and molydenum present in the steel. Because its ferritic properties duplex steel has high resistance to erosion corosion. The relatively low nickel content may make duplex steel more economical than austenitic steels. That of course, depend on pricing policies of the steel mills: Duplex stainless steels resist the cavitation and caviation corrosion.


Uno Wahren,Practical introduction to pumping technology P.98

Transverse Cracking 


Transverse cracks in weld metal formed when predominanr contraction are in directionof the weld axis They can be hot cracks which seperates intergranularly as the result of hot shortness or localized planar shrinkage, or thet can be transgranular separations produced by stresses exceeding the strength of the material. Tranverse cracks lie in a plane normal to the axis of the weld. and are usually open to the surface. They usually extend across the entire face of weld and usually open the surface. They usually extend the across the entire face of weld and  sometimes porpagete into the base metal.
  Tranverse cracks in base metal occur on surface in or near the HAZ. They are result of the high residual stresses induced by thermal cycling during welding. high hardness excessive restraint and the precense of hydrogen promote theri formation. Such crack propoganete  ino the weld or beyond the HAZ into the base metal. as far as needed to relive the residual stresses.

Steve Lampman,ASM International, Weld integrity and performance: a source book adapted from ASM international


Poke Yoke (Poka Yoke)

Althought the concept of poka yoke has existed for a long time in various forms, iı was japanese manufacturing engineering Shigeo Shingo who developed idea into the formiable tool for achieving zero defects and evantually eliminating quality control inspection.The method he avocates were formerly called "fool-proofing" reconizing that this is label could often many workers, Shingo came up with the term poka-yoke generally translated as " mistake proofing" or " fail safing". The idea behind the poka-yoke is to respect the intelligence of workers. By taking over respetitive tasks or actions that depend on vigilance or memory, poka-yoke can free a worker's time and mind to pursue more creative and value-adding activities
    Many thing can go wrong in complex enviroment of workplace; every day there are opportunities  to make mistake that will result in defective products. Defects are wastefull and if they are not discovered they disappointed the costumer expectations of quality. Behind poka- yoke is the conviction that is not accepteable to produce small number of defective goods.. To become world class competitor. a company mus adopt not only philosophy but a producing zero defects. Poka-yoke methods are simple concepts for achieving this goal.


Poka-yoka, Improving Product Quality by Preventing Defects, P. XI 

Flux Cored Arc Welding

http://www.robot-welding.com/arc_weld_processes.htm

Flux Cored Arc Welding  is a fusion welding process in which weld heating is produced from an arc between the work and a continiously fed filter metak electrode. Atmosferic shielding is provided in complately or in part by the flux sealed within the tubular electrode.Extra shielding may or may not supplied through a nozzle in the same way in GASW.

     Although the process was introduced in 1950's it represented less than % 5 of the total amount of welding done in 1965. In 2005  it passed the %50 of mark and still is rising

Advantages.
High Deposition Rate
Minimum Electrode aste
Ecellent controll.

Larry Jeffus,Lawrence Bower,Welding Skills, Processes and Practices for Entry-Level Welders, P.114

Buğra Cengiz 030060178 10th week

Compression Test

The compressive stress-strain curve is similar to the tensile stress-strain curve up to the yield strength. Thereafter, the progressively increasing specimen cross section causes the compressive stress-strain curve to diverge from the tensile curve. Some ductile metals will not fail in the compression test. Complex behavior occurs when the direction of stressing is changed, because of the Bauschinger effect, which can be described as follows: If a specimen is irst plastically strained in tension, its yield stress in compression is reduced and vice versa.

Mark's Standard Hanbook For Mechanical Engineers, P. 5-5

Cold Rolling

Cold Rolling is practical in production of thin coil stock with the more ductile metals. The number of passes or amount of reduction between anneals is determined by the rate of work hardening of the metal. Successive stands of cold-rolling help to retain heat generated in working. Tension provided by mill reels and between stands helps to increase the practical reduction per step. Bright annealing in a controlled atmosphere avoids surface pockmarks, which are difficult to get out. For highfinish stock, the rolls must be maintained with equal finish.

Mark's Standard Hanbook For Mechanical Engineers, P.13-16

Polycarbonate

     Polycarbonates show excellent dimensional stability, with good impact resistance and ductility. They are employed as a base for photographic film and also for lenses. Their toughness makes them appropriate for the manufacture of safety helmets.     ( John Martin, Materials For Engineering, Third Edition, P.160 )

      Polycarbonates, one of the strongest, toughest, and most rigid thermoplastics, are not generally considered good barrier materials. It is possible to use polycarbonate as the structural layer in a composite (co-extruded) film for use in barrier application. In such cases, polycarbonate contributes
toughness and heat resistance to the final product while other components in the composite film may provide the barrier properties
Processing Methods: Injection molding, extrusion, blow molding, and rotational molding
Applications:
• Packaging. Milk bottles, baby bottles, food containers.
• Medical. Dialysers, artery cannulas.
• Electrical. Distribution box lids, fuses, sockets, lamp holders, and covers.

Liesl K. Massey, Permability properties of Plastics And Elastomers. Chapter 26




Process Flow Chart

        Process Flow Charts are to manufacturing as road maps are to drivers. They provide detailed view of the process, and increase understanding of how the process flow. With a process flow chart teams repetitive steps, bottlwnecks, and inefficiencies in the process wich in turn helps the team identify potential failures, effects and solutions.
        The best way to create a flowchart  is to walk through the process as if you were the thing being processed or created. the process steps should be followed sequentally and notes should be taken during walk through.
         once the walk through is complate each steps should be listed on a self stick-stick note. It helps to have several people do this as each will contribute  ideas  that others missed. The steps should then be grouped and organized according to their order in the process
        For complicated process  with a several steps  and substeps it helps to create a top-down flowchart, where each of major steps in the process listed in order of flow across the top of the chart and sub-steps are listed underneath each major steps

Robin E. McDermott,Raymond J. Mikulak,Michael R. Beauregardi The Basics of  FMEA, P. 59

Buğra Cengiz 030060178 9th week

Vibratory Casting
The same conventional castables , made up and placed in the same way , may be vibratory cast. The consistency may be exactly the same or a little drier, but not much. The apperiance of small nodulus , in a wad of material sparated by cracks, signifies that it is too dry.

Recalling that castable mixes are thixotropic, they can be kept fluid more or less throughout by been kept in constant shear throughout.This end is achiaved by the use of >= 10 kilohertz vibrators, working either on the forms or in channal geometry via the top surface of the fill. Wheather this techniques is better than those of conventional manual placement, above, may be matter of geometry and size of casting or  to some degree one of the local preference and style. Where it is feasible vibratory casting gives superior density and strenght 

Stephen C. Carniglia, Gordon L. Barna Handbook of industrial refractories technology: principles, types, properties, and applications, P. 564

Dry Film Lubricant

Stamping lubricants can be divided into oil-based liquid lubricants and dry film or coil
lubricants (DFL). The liquid lubricants may be mineral oils or emulsions. Dry film
lubricants are divided into water-soluble dry film lubricants and water-free dry film
lubricants (the so-called “hotmelts”). Water-soluble dry film lubricants are applied in
amount of 0.5-1.5g/m2 at the rolling mill. They stick to the surface of the stamped sheet
parts and offer sufficient corrosion protection but are not compatible with most
adhesives used in automotive body construction The water-free dry film lubricants are also applied on the sheet material in small amounts at the rolling mill. Besides their superior drawing performance compared to oil-based lubricants, the most important advantage is their compatibility with almost all commonly used adhesives. In today’s automotive stamping plants, DFL is increasingly popular, due to improved performance cleanliness and reduced requirements for recycling and disposal In addition, DFL: a) provides uniform coating thickness on the sheet blanks, b) reduces the amount of lubricant (typically 0.5-1.5 g/m2 vs. oil-based lubrication 1.5-3.0 g/m2), c) may eliminate washing of stampings which are necessary with wet lube, d) is compatible with assembly operations (welding, bonding, clinching and riveting), e) is more environmentally benign than the petroleum based wet lubes. On the other hand, DFL has no cooling effect and makes it difficult to remove deposits of metal debris left on the die surface.

Tribology of Manufacturing Processes, Volume 1, P.16

 Liquid Laser

Lasers that use liquids as active medium have advantages of being more concantretad than a gas and of being able to be circulated and cooled. In 1966 Peter, P. Sorokin and J.R Lankard at IBM corporation's watson Research center in Yorktown heights. New york, demonstared the first dye laser. Since then hundreds of flourecent dyes have been found  to produce laser action. Dyes can emit laser beams with with a wide range of wavelenghts and thus have the great advantage being tuneable.  Liquid dye lasers can emit the laser beams from about the 250 nanometers in the ultraviolent throught the whole visible spectrum to 1,800 nanometers in the infrared.

   In a liquid dye laser, the dye is active medium. It is usually dissolved in a liquid solvent such as alcohol or ethylene glycol. The source of energy for a liquid dye laser is usually a flashlamb  of another laser.

Charlene W Billings, Lasers: New Technology Of Light. P. 25

Excimer Laser

An excimer laser belongs to a famşly of gas lasers that produce nanosecond-long powerfull pulses at wavelenghts near of in the ultraviolent portion of the electromagnetic spectrum. These lasers use the mixures of gases. The bulk of the gas mixture is a gas such as helium or neon that aids in energy trasnfer . A rare gas is source of laser actiın and usually makes up only one half the 12 percent of the total mixture. The important excimer laser gases are krypton flouride, xenon flouride, argon flouride and xenon chloride. An exicemr laser can generate pulses of over one bilion watts of power.

Charlene W Billings, Lasers: New Technology Of Light. P. 25

 

Bugra Cengiz 030060178 8th week

Stiffness
Stiffness is a measure of  a systems's resistance to deformation. A rubber band is easily deformed by hand but a steel wire or rod of the same cross-sectional area is not. The stiffness of steel is greater than that of rubber.

Frederick A. Leckie,Dominic J. Dal Bello, The strength and the stiffness of The Engineering Systems, P.48 

Implsion (Implosion Hazard)


The pressure differance (0,1MPA) between inside of the vacuum enclosure and outside initiate an accidental implosion of an evacuated birttle containeer, resulting in flying fragments. Glass and perspex viewports represen an implosion hazard. 

R. Hellborg, Electrostatic accelerators: fundamentals and applications, P.366

Flexible Systems (Flexible Productio Systems)
Mass production is predicated largely on the principles of Frederick W. Taylor. one of the leaders of the scientific management movement in the early 1901s.  According to Taylor, workers had to be told every detail of their work methods and were incapable of planning their own tasks. By comparison.Lean production makes use of worker teams to organize the tasks to be accomplished and worker involvement to solve technical problems. One of the findings reported in The Machine thai Changed the World was that workers in Japanese "lean production" plants received many more hOUTSof training than their U.S, counterparts (380 hours of training vs.46 hours).Another finding was the lower number of job classifications in Japanese lean plants. The study showed an average of 11.9 job classifications in Japanese plants versus an average of 67.1 in L:.S. plants. Fewer job classifications mean more cross-training among workers and greater nexttunty ill the work force.                                  
     In mass production, the goal is to maximize efficiency. This is achieved using long
production runs of identical parts. Loeg production runs tolerate long setup changeovers, In lean production. procedures are designed to speed the changeover. Reduced setup times allow for smaller batch sizes. thus providing the production system with greater flexibility. Flexible production systems were needed in Toyota's comeback period because of the much smaller car market in Japan and the need to be as efficient as possible.


Groveer, Automation, Production Systems and CIM, P. 835