Wear Resistant Coating

Wear is the loss of material due to friction with another surface caused by motion.  Wear causes weakening of components and ultimately breakdown of materials. 

Wear resistance, therefore, is a highly desirable property in materials.  Wear can be minimized by selecting proper materials which can withstand the expected wear during the design stage itself.

Nevertheless, no matter how good the material selection is, there will always be some wear during operation.

Wear resistant coatings increase the wear resistance by forming a protective layer over the surface experiencing friction.  These coating can be applied as a spray or by means of a special forming process.

There are different types of wear resistant coatings. Ceramic Coatings, Phenolic coatings, Polymer and Epoxy coatings are some of the types of coatings available. 

The type of coating is chosen based on the working environment and the degree of protection desired.

Wear Resistance in Materials

In engineering, wear resistance refers to the property of materials to resist wear and tear during normal operation.  Wear resistance is a desirable property in moving parts such as bearings, wheels and tyres etc.

There are different mechanisms of wear.  Some of them are adhesive, erosive, cavitation and fretting.  Wear generally occurs as a combination of different mechanisms. 

All materials have wear resistance as a standard specification of materials.

Wear resistance is evaluated by specialized tests which simulate normal operation. 

By understanding the level of wear expected during normal operation, materials can be made wear resistant.  Wear resistance can be achieved by special manufacturing process and appropriate choice of materials. 

There are also other types of wear resistance methods such as special coatings and sprays.

What are the losses in a pump ?

The losses in the pump can be categorized into three categories

Mechanical Losses
The first type of losses is the mechanical loss.  This loss is due to friction between the pump components such as the impeller and the bearings.

Hydraulic Losses
These losses occur due to the energy expended in overcoming the friction between the fluid and the impeller surface

Volumetric Losses
Volumetric Losses occur due to re-circulation of the fluid within the pump.  This does not contribute towards the development of pressure.

Leakage Losses
Leakage Loss is caused due to leakage of the liquid from the pump due to reasons such as malfunctioning of seals, etc.

Stroboscopic Effect in Fluorescent Lamps

The Stroboscopic Effect in Fluorescent lamp is a phenomenon which causes running or moving equipment to appear stationary or appear to be operating slower than they actually are.

In an AC supply, the voltage drops 100 times a second to zero volts as the supply frequency is 50 Hz.  When a Fluorescent lamp is operating with an AC supply, the light intensity drops 100 times a second.  This flicker is not noticeable to the human eye due to the persistence of vision. 

When a worker in a factory observes a running machine, say a flywheel under the illumination of a fluorescent light, the flywheel may appear to be stationary or to be operating at reduced speed.  This can result in accidents and is highly dangerous.

A sewing machine whose needle moves up and down may appear to be stationary and the operator can prick the fingers.  These are some examples where the stroboscopic effect in the Fluorescent lamps can prove to be dangerous.  When using fluorescent lamps around rotating or moving machinery, two lamps powered by two different phases should be used.  This ensures that both the lamps do not flicker due to the zero crossing at the same time. 

If another phase is not available, a capacitor can be added in series to one lamp.  This ensures that there is a phase lag between the two lamps. The Stroboscopic effect can be eliminated by  using electronic ballasts where the supply to the lamps is of a very high frequency of the order of kiloHertz.

Structure of an Optical Cable

Optical Cables are used extensively in the field of telecommunication.  They have numerous advantages over conventional communication on wires.  They are efficient, quick and secure.  Optical Communication Cables are designed to provide high efficiency of transmission.  They are also designed to withstand the challenges of the external environment such as corrosion, heat and physical stress.
The Optical Cable has the following main components. 
Core
The Core provides the pathway for the light to travel.  It is made of glass or transparent plastic material. 
Cladding
The cladding is the layer that covers the core.  The function of the Cladding is to reflect the light which may come out of the core back into the core.  This results in Total Internal Reflection which ensures that there is no loss of the light signal. 
Buffer
The Buffer is a coating which is outside the Cladding.  The Buffer serves to protect the optical fibre. 
Aramid Yarn Protection
The Aramid yarn which surrounds the buffer provides crush protection to the cable.
Protective Jacket
The protective jacket offers mechanical protection to the cable. 

How do Electronic Ballasts in Fluorescent lights work ?

A Ballast in a fluorescent light is necessary to get the light glowing.  The Ballasts generates a high voltage by means of the would coil which acts as an inductance.  When the starter interrupts the supply to the inductance, a powerful voltage is generated.  These are called magnetic ballasts. 

However, magnetic ballasts take time to get the lamps to start.  They also have an undesirable hum.  They also produce a flicker before the tube lights up continually.

Electronic eliminate the problem of initial flicker and hum.  They also reduce power consumption.
Electronic Ballasts work by converting the AC supply into DC first.  This rectified DC is then chopped by a chopper circuit to generate high voltages to start the discharge in the lamp.  The chopped AC waveform is t a very high frequency of the order of kHz.  This ensures that the flicker is reduced to a minimum.

The efficiency of the lamp is also increased.  Electronic Ballasts are 10% more efficient than magnetic ballasts. Electronic Ballasts can generate harmonics.  This, however, is insignificant as the amount is very small.

Why does the resistance of metals increase when they are heated ?

Conductivity in metals is due to the presence of free electrons in the atomic lattice.  When the metal is heated, the atoms in the lattice vibrate.  This results in reduced movement of the electrons as they hit against the vibrating atoms.

This results in an increase in resistance of the metals. 

Most Metals have positive temperature coefficient of resistance. There are , however, exceptions such as carbon and semiconductor metals such as Silicon and Germanium.  Some Alloys have zero temperature coefficient of temperature which means that the resistance does not change with increase of temperature.  Manganin is an example.