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September 30, 2018

“Injection molding is a manufacturing process for producing parts by injecting material into a mould. Injection moulding can be performed with a host of materials, including metals, glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed, and forced into a mould cavity where it cools and hardens to the configuration of the cavity. After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mouldmaker (or toolmaker) from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars.”
Plastic housing is one of the most common finished products of injection moulding, used to produce thin-walled plastic parts. Plastic housing is a thin-walled enclosure, many a time demanding many ribs and bosses on the inside. These houses are used in an array of products including household appliances, consumer electronics, power tools, and as automotive dashboards. Injection moulding is also used to manufacture valves and syringes that are used in the medical industry.
The moulding procedure is complex. Hence, parts to be injection moulded needs to be designed with sufficient care keeping into account, the substance used for the part, the desired shape and features of the part, mould material and also the various properties of the moulding machine.
An interesting variety of injection moulding is Compression Injection Moulding.
Compression Injection Moulding (CIM) aims “to combine the high productivity of Conventional injection moulding with the Stress Free moulding obtained by Compression Moulding. It is well suited for articles with a high Flow path/wall thickness ratio. It is possible to mould articles on a lower Clamp tonnage than conventional Injection moulding.”
If we look into the past, compression moulding would come out to be the initial grounds on which moulding of plastics began to develop itself from. Most Thermosets are compression moulded till date, though most thermoplastics are indeed injection moulded. They are melt-processible, making it ideal for injection moulding.
The plastics industry, especially injection moulding companies have witnessed an aggressive change in the economics. With the automotive and electronics business eyeing the east and a continual necessity to keep costs at check, it becomes imperative to better operations within the industry. A possibility could be building a new profile of potent customers in a new feasible market environment.
Let us talk about moulding in the medical industry.
And why not? If one would like to explore such avenues CEOs and CFOs must be ready so as to be able to make those crucial decisions.
Medical Injection Molding (MIM) is a process that is much more than the field of just plastics. It has a process that involves more than just a machine, mould or any other material. Quality control capacities and operation-controls – these are aspects that just cannot be compromised. An ISO systems of checking or standardizing quality is being followed and mostly that is at an ISO-13485 mark. This means that for standing out to medical devices buyers, one would need such quality control system compliant output.
Raw materials are significant too- a thorough review of the material used that includes colourants, processing aids, stabilizers, etc is mandatory. Maintaining records and bringing in a lot control is another requirement. Cleanliness and hygiene, again are crucial in the medical industry. There are separate standards for these as well that need to be maintained in production units. Design of the final output – can either be a contribution chance or an impediment!
When it comes to technology, one would want to look at hygiene, process control and automation, data retention/control and other equipment that would contribute largely to the total moulding, process.
In a nutshell, injection moulding can well be “moulded” according to needs of the market and demand.

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September 30, 2018
Cold spring is the process of offsetting (or pre-loading) the piping system with displacement loads (usually accomplished by cutting short or long the pipe runs between two anchors) for the purpose of reducing the absolute expansion load on the system.
Cold spring is used to do the following:
1.    Hasten the thermal shakedown of the system in fewer operating cycles.
2.    Reduce the magnitude of loads on equipment and restraints, since often, only a single application of a large load is sufficient to damage these elements.
Several things should be considered when using cold spring:
1.    Cold reactions on equipment nozzles due to cold spring should not exceed nozzle allowables.
2.    The expansion stress range should not include the effect of the cold spring.
3.    The cold spring should be much greater than fabrication tolerances.
Note: No credit can be taken for cold spring in the stress calculations, since the expansion stress provisions of the piping codes require the evaluation of the stress range, which is unaffected by cold spring (except perhaps in the presence of non-linear boundary conditions, as discussed below). The cold spring merely adjusts the stress mean, but not the range. Many engineers avoid cold spring due to the difficulty of maintaining accurate records throughout the operating life of the unit.
Future analysts attempting to make field repairs or modifications may not necessarily know about (and therefore include in the analysis) the cold spring specification. Due to the difficulty of properly installing a cold sprung system, most piping codes recommend that only 2/3 of the specified cold spring be used for the equipment load calculations.
The cold spring amount is calculated as:
Where:
1.    Ci = length of cold spring in direction i (where i is X, Y, or Z), (inches)
2.    Li = total length of pipe subject to expansion in direction i, (inches)
3.    α = mean thermal expansion coefficient of material between ambient and operating temperature, (in/in/°F)
4.    dT = change in temperature, (°F)
Note that the 1/2 in the equation for the cold spring amount is used such that the mean stress is zero. In some cases it is desirable to have the operating load on the equipment as close to zero as possible. In this latter case the 1/2 should be omitted.
The maximum stress magnitude will not change from a system without cold spring, but will now exist in the cold case rather than the hot. To model a cold spring in CAESAR II specify the elements as being made of cut short or cut long materials. Cut short describes a cold sprung section of pipe fabricated short by the amount of the cold spring, requiring an initial tensile load to close the final joint.
Cut long describes a cold sprung section of pipe fabricated long by the amount of cold spring, requiring an initial compressive load to close the final joint. The software models cut shorts and cut longs by applying end forces to the elements sufficient to reduce their length to zero (from the defined length) or increase their length to the defined length (from zero) respectively.
(It should be remembered to make the lengths of these cold spring elements only 2/3 of their actual lengths to implement the code recommendations.) This is effectively what occurs during application of cold spring. The end forces applied to the elements are then included in the basic loading case F (for force), whereby they can be included in various load combinations.
Special material numbers 18 and 19 are used to signal CAESAR II that the element currently in the spreadsheet actually represents a length of pipe that is to be cut short or long during fabrication.
1.    Material # 18 – Cut Short
2.    Material # 19 – Cut Long
The user should be sure to reset the material property on the element following the cold spring element. The following load cases are recommended when analyzing a cold spring system:
Cold spring is allowed to reduce the magnitude of equipment loads because, often, only a single application of a large load is sufficient to cause damage to rotating machinery.
Cold spring does not change the “range” of stresses that the piping system is subject to, and so, no allowance is given for stress reduction. (The maximum value of the stress is lowered, but the range is unchanged.) Both the sustained loads and the operating loads should be within the manufacturer’s allowables for the particular piece of equipment. If the designer isn’t careful, the installation of the cold spring in the ambient state can overload a piece of rotating equipment as the unit starts up.




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September 30, 2018
One of the uses of eddy current instruments is for the measurement of electrical conductivity. The value of the electrical conductivity of a metal depends on several factors, such as its chemical composition and the stress state of its crystalline structure. Therefore, electrical conductivity information can be used for sorting metals, checking for proper heat treatment, and inspecting for heat damage.
The technique usually involves nulling an absolute probe in air and placing the probe in contact with the sample surface. For nonmagnetic materials, the change in impedance of the coil can be correlated directly to the conductivity of the material. The technique can be used to easily sort magnetic materials from nonmagnetic materials but it is difficult to separate the conductivity effects from the magnetic permeability effects, so conductivity measurements are limited to nonmagnetic materials. It is important to control factors that can affect the results such as the inspection temperature and the part geometry.

Conductivity changes with temperature so measurements should be made at a constant temperature and adjustments made for temperature variations when necessary. The thickness of the specimen should generally be greater than three standard depths of penetration. This is so the eddy currents at the back surface of the sample are sufficiently weaker than the variations in the specimen thickness that are not seen in the measurements.
Generally large pancake type, surface probes are used to get a value for a relatively large sample area. The instrument is usually setup such that a ferromagnetic material produces a response that is nearly vertical. Then, all conductive but nonmagnetic materials will produce a trace that moves down and to the right as the probe is moved toward the surface. Think back to the discussion on the impedance plane and these type of responses make sense. Remember that inductive reactance changes are plotted along the y-axis and resistance changes are plotted in the x-axis. Since ferromagnetic materials will concentrate the magnetic field produced by a coil, the inductive reactance of the coil will increase. The effects on the signal from the magnetic permeability overshadow the effects from conductivity since they are so much stronger.
When the probe is brought near a conductive but nonmagnetic material, the coil's inductive reactance goes down since the magnetic field from the eddy currents opposes the magnetic field of the coil. The resistance in the coil increases since it takes some of the coil's energy to generate the eddy currents and this appears as additional resistance in the circuit. As the conductivity of the materials being tested increases, the resistance losses will be less and the inductive reactance changes will be greater. Therefore, the signals will be come more vertical as the conductivity increases, as shown in the image above.
To sort materials using an impedance plane device, the signal from the unknown sample must be compared to a signal from a variety of reference standards.  However, there are devices available that can be calibrated to produce a value for electrical conductivity which can then be compared to published values of electrical conductivity in MS/m or percent IACS (International Annealed Copper Standard). Please be aware that the conductivity of a particular material can vary significantly with slight variations in the chemical composition and, thus, a conductivity range is generally provided for a material. The conductivity range for one material may overlap with the range of a second material of interest, so conductivity alone can not always be used to sort materials. The electrical conductivity values for a variety of materials can be found in the material properties reference tables.



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September 30, 2018
You do not have to move from home to assist those affected by disasters. Volunteering at the local office of relief organisations may provide them with much needed support. You may be able to help with campaigning or awareness-raising work and disaster preparedness activities. Note that organisations are unlikely to want new volunteers at the time of a disaster when all their energies are on the relief effort.

 

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September 30, 2018
Have you ever seen a monument erected for Marine Engineers?
Wondering what it is and where is it?
Coming back to the memorial, here is a picture which I took from internet.
I am sure When Engineers see such a monument, they will definitely be happy and be proud too.
The intention of this article, is to let our dear Marine Engineers know the location so that they can visit if they have time.
Name:       Memorial to the Engine Room Heroes of the “Titanic”.
Location:  Liverpool.

This memorial stands on Pier Head in Liverpool. It is inscribed on the north face

“IN HONOUR OF  ALL HEROES OF THE  MARINE ENGINE ROOM  THIS MEMORIAL  WAS ERECTED BY  INTERNATIONAL SUBSCRIPTION” inscription
and on the south face

“THE BRAVE DO NOT DIE THEIR DEEDS LIVE FOR EVER  AND CALL UPON US  TO EMULATE THEIR COURAGE  AND DEVOTION TO DUTY” inscription
Comprises a granite column with a carved Egyptian scene at the top and statues of engineers by Goscombe John on the West face. There are depictions of Water,Earth,Sea and Fire on each corner.
The memorial commemorates the 122 Engineers who died when RMS Titanic sunk on 15 April 1912.





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September 30, 2018
An important application of the diode is one that takes place in the design of the rectifier circuit. Simply put, this circuit converts alternating current (AC) to direct current (DC). This is an essential circuit in AC-to-DC power-supply design.

The Rectifier Circuit

In order to power any circuit, a power supply is needed; and if you want to power electronic devices from an AC supply, a rectifier is needed.
Figure 1.1 illustrates a schematic diagram of a DC power supply. There is a 120 V (rms), 60 Hz AC line that feeds the power supply, which delivers a voltage VO to the electronic circuit (load block). VO must be a stable DC voltage to ensure that the electronic circuitry functions correctly.

Figure 1.1

Looking at the diagram, first we see the transformer. This transformer is a step-down transformer that “steps down” the high AC input voltage to a lower AC voltage to be inputted into the rectifier. This transformer consists of two separate coil windings (primary and secondary windings) that have a different number of turns, N1 for the primary and N2 for the secondary. Thus, the AC voltage vS­ can be written as 120(N2/N1) V (rms) and is measured between the two terminals of the secondary winding.
Next, the diode rectifier converts the AC voltage vS to a DC voltage. This voltage will exhibit large variations and thus will not be suitable for electronic circuitry. A filter is used to smooth out these variations.
Even after filtering, though, the voltage will exhibit small variations known as ripple. Consequently, a voltage regulator is used to greatly reduce the ripple and establish a reliable DC supply rail.

Half-Wave Rectifier Circuit

The half-wave rectifier eliminates the negative portions of the input sinusoid. In Figure 1.2 (A), the half-wave rectifier is illustrated. In this article, we will use the constant voltage drop (CVD) model of a diode owing to its simplicity. From this model, we are provided with

v0=0v0=0
  when 
vS<VDvS<VD
   
Equation 1.1 (A)

v0=vS−VDv0=vS−VD
  when 
vS≥VDvS≥VD
   
Equation 1.1 (B)

where VD ≈ 0.7 V. The above equations lead to the transfer characteristic illustrated in Figure 1.2 (B). Figure 1.2 (C) illustrates the voltage output that is provided when the input voltage vS is sinusoidal.
Figure 1.2 (A) The half-wave rectifier


Figure 1.2 (B) Transfer characteristics of the rectifier circuit

Figure 1.2 (C) Input and output waveforms

When determining which diodes to use in a rectifier circuit, there are two things to take into consideration: 1) the diode's ability to handle current, which must be chosen based on the largest current that is expected to be conducted by the diode, and 2) the peak inverse voltage (PIV), which is the highest reverse voltage to which the diode will be subjected; the diode must be able to withstand the PIV. Looking at Figure 1.2 (A), we can observe that when the voltage vS is negative, the diode will be cut off and the voltage vO will have a value of zero, leading to a reverse voltage across the diode of magnitude vS. Thus, the PIV is the peak ofvS:

PIV = VS    
Equation 1.2

where VS (with an uppercase V) represents the peak amplitude of the input sinusoid.
One thing worth noting is that the circuit clearly will not operate effectively when the input sinusoid's peak amplitude is not significantly higher than VD. For example, a sinusoidal input with peak amplitude of 200 mV will not be rectified at all because the diode will never "turn on," i.e., it will never conduct significant amounts of current. 

Full-Wave Rectifier Circuit

Unlike the half-wave rectifier, the full-wave rectifier can utilize both the negative and the positive portion of the AC input voltage. In order to achieve a unipolar output, the negative portion of the sinusoidal waveform must be inverted. This can be accomplished by using the circuit shown in Figure 1.3 (A).

FIGURE 1.3 (A) Full-wave rectifier circuit; the transformer has a center-tapped secondary winding

In this configuration, the step-down transformer's secondary winding is what is called "center-tapped." A center tap, or CT, is an electrical contact made halfway along the winding. This CT is used to provide two equal voltages, vS, across the two halves of the transformer's secondary winding. When the input voltage is positive, both vS signals will also be positive, and when the input voltage becomes greater than VD, diode D1 will be conducting and diode D2 will be reverse-biased. The current that flows into diode D1 will also flow through resistor R and then back to the CT. The circuit behaves just like the half-wave rectifier during the positive half-cycle of an input sinusoid.
During the negative half-cycle, both vS voltages will be negative. Now, diode D1 is reverse-biased and diode D2 is conducting. The current that flows through D2 will then flow through resistor R and back to the CT.
Thus, current flows during both half-cycles, and furthermore the current through the resistor will always flow in the same direction. The result is a unipolar output voltage, as shown in Figure 1.3 (C).

If we consider the circuit's operation during a positive half-cycle, the voltage at the cathode of D2 is (vS - VD) and the voltage at the anode of D2 is -vS. Thus, the PIV is (VS - VD) - (-VS):
PIV = 2VS - VD
Equation 1.3

Note that this PIV is roughly double that of the half-wave rectifier.

Figure 1.3 (C) Input and output waveforms

Conclusion

In this article, we discussed the purpose of a rectifier circuit as well as two specific types of rectifiers: the half-wave rectifier and the full-wave rectifier. Rectifiers are essential circuits for power supplies that convert an AC input voltage into a DC voltage supply that can be used to power electronic circuits. We saw that the half-wave rectifier utilizes alternate half-cycles of the input sine wave whereas the full-wave rectifier utilizes both positive and negative half-cycles.




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