030070010 Celal Selçuk Tiftik 8th week

Three - Plate Mold (new)

 The three - plate mold  is becoming more
widely used, with gate placement not restricted to the edge of parts. It uses
separate plates for the runner system and cavity/core. The part and runner are
automatically degated when the mold opens; the runner systems can be downsized,
thereby obtaining shorter fl ow paths. Such central gating of parts can
reduce weld lines and mold - in stresses, as well as provide shorter fl ow paths
for the material fi lling the mold/part cavity. It uses conventional ejection
techniques, with minor limitations on cooling channel placement. Although
more expensive than two - plate molds, it can run automatically, with no operator
required for part/runner separation.

(Total Quality Process Control for Injection Molding Second Edition M. Joseph Gordon, Jr. p.184)

Three-Plate Mold 00:10 14.04.2011    (old)

The two-piate mold is the most common mold in injection molding. An alternative is a three-plate mold, shown in Figure 13.24, for the same part geometry as before. There are advantages to this mold design. First, the flow of molten plastic is through a gate located at the base of the cup-shaped part, rather than at the side. This allows more even distribution of melt into the sides of the cup. In the side gate design in the two-plate mold of Figure 13.23, the plastic must flow around the core and join on the opposite side, possibly creating a weakness at the weld line. Second, the three-plate mold allows more automatic operation of the molding machine. As the mold opens, it divides into three plates with two openings between them. This forces disconnection of runner and parts, which drop by gravity (with possible assistance from blown air or a robotic arm) into different containers beneath the nioid.

(Mikell P. Groover, Fundamentals of Modern Manufacturing, Materials, Processes and Systems ,page 279-280)

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Seebeck effect (new)

A temperature difference between two points in a conductor or a semiconductor results in a 

voltage difference between these two points. This phenomenon is called seebeck effect.  The 

magnitude and the direction of thermo-emf developed in a thermocouple depend upon the nature 

of metals forming the thermocouple and the differences in temperature of the two junctions. The 

seeback effect is reversible i.e. if the hot and the cold junctions are interchanged the direction of 

thermoelectric current is reversed.

Seeback series is listed in the box below.

Bismuth     -      Constant     -     Nickel    -     Platinum    -      Mercury    -     Aluminium         
Lead    -    Silver    -     Gold       -   Copper     -    Zinc      -   Iron      -    Nichrome      -   Antimony


     When any two of these metals form a thermocouple, current flows through the hot junction from 
a metal occurring earlier to a metal occurring later in the series. For a given differences of 
temperature of two junctions the larger is the gap in seeback series between the metals forming 
the thermocouple, the greater will be the thermo-emf generated.
     The electron-density (no. of electrons per unit volume) of a conductor depends on the material of 
the conductor. When two different metals are brought into contact at the junction, the free 
electrons tends to diffuse from the metal with greater free electron density to the other with lower 
free electron density. Due to this diffusion, a potential difference developed at the junction of the 
two metals called contact-potential. When both the junctions are at the same temperature, the 
contact potentials at the two junctions will be the same. Hence no current flows in the 
thermocouple. But if one junction is heated up, the rate of diffusion of free electrons at that 
junction will change, which results in difference in the contact potential of the two junctions 
called thermo-emf.



(Thesis Submitted for the Award of the Degree of Master of Science By KALYANI BHOI p.21)

THE SEEBECK EFFECT: (09.04.2011, 22:40) (old)

In 1826, Seebeck discovered the thermoelectric effect, which after his name is also known as Seebeck effect. The phenomenon of production of an e.m.f. causing an electric current to flow in a thermocouple, when its two junctions are kept at two different temperatures, is known as Seebeck effect. To study this effect, two wires of different materials, say copper and iron are joined at their ends so as to form two junctions. A sensitive galvanometer is included in the circuit. This arrangement is called a copper-iron thermocouple. When one junction of the thermocouple is kept hot and the other cold, the galvanometer gives deflection indicating the production of current in the arrangement. The current so produced is called thermoelectric current. Further the continuous flow of current in the thermocouple indicates that there must be a source of e.m.f. in the circuit, which is causing flow of current. This e.m.f. is called thermoelectric e.m.f.

(Sharma H.C., Kharb R., Sharma R., Comprehensive Physics for Engineers, p.161)

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Vacuum Coating

Vacuum coating is used to increase the reflectivity of a mirror surface. A metal

material is evaporated onto the surface and becomes a thin layer of deposition.

Before the coating, the old film should be removed from the mirror surface. Then
the surface is cleaned. The cleaning of the surface is a process of chemical and
mechanical reaction. Usually a detergent or a mixture of mild sulfuric and
chromic acids is used. After cleaning with acid, the mirror surface should be
washed with water. Then the mirror dries in air. Some observatories also use dry
ice for the mirror surface cleaning though this process is usually used between
coatings to remove dust from the mirror surface.
The coating is done inside a vacuum chamber. The chamber is a large barrellike
container. If the mirror to be coated has a larger dimension, it is usually
placed vertically in the chamber. In this position, no metal fuses or other objects
will fall on the mirror surface. Metal fuses are arranged at equal distances around
the mirror. Then the chamber is evacuated. When the air pressure reaches 10 4
to 10 5 mmHg (1 mmHg = 1.33 10 2 Pa) and can be maintained at this level,
the coating process can be started. If a single layer of aluminum film is needed,
the coating material, usually aluminum filaments, is placed above a few tungsten
heating coils. When the temperature of the filaments is over 6008C, the
aluminum melts and attaches to the heating coils. When the temperature
reaches 1,2008C, the aluminum evaporates. The evaporating aluminum molecules
radiate to the mirror and deposit on the surface. In the visible wavelength
range, aluminum coating is widely used. For infrared wavelengths, gold or silver
has a higher reflectivity. The obvious drawbacks of the silver coating are a low
adhesive force and the tendency to oxidize. These can be solved by an additional
coating of Al2O3 or SiOx. Gold, or silver, or platinum are also used for mirrors in
X-ray imaging systems.



(The Principles of Astronomical Telescope Design Jingquan Cheng p.125)


*There is no old definition...


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Deflection Temperature Under Load (DTUL) (new better)

      There are several short term , standard tests that are commonly used to indicate the relative high temperature capabilities of plastic materials. The most commonly used test is known as the deflection  temperature under load  (DTUL) test.  The test is often referred to as the heat distortion temperature (HDT)  test. The DTUL test provides a rough measure of he temperature  at which a beam like  specimen subject to three – point bendings deflects a fixed distance under a specified load.

       For amorphous  materials, the DTUL  value is generally close to the transition temperature of the polymer,  the DTUL value has no relation to glass transition .  The DTUL test provides a measure of the  temperature at which  a polymer achieves  a certain flexural modulus value , but does not provide any indication as to the shape of the modulus-temperature curve for the  polymer .As such , the DTUL test is suitable only for initial material screening  and should not  be used  for final material selection and design.

(Plastic Part Design for Injection Molding: An Introduction Yazar: Robert A. Malloy p.170)

Deflection Temperature Under Load (DTUL) (April 14, 2011 - 13:42) (old)

Deflection temperature under load (DTUL) is a technique which follows the deflection of a beam of material under fixed stress as the temperature is increased. The temperature at which the beam deforms by a specified strain (0.2% for plastics and 0.1% for composites) is the DTUL. This technique was previously known as heat deflection temperature (HDT).

(Mulligan D.R., Cure Monitoring for Composites and Adhesives, 2003, pg.15)