Mechanical engineer interviews questions

It will clean the surface of the parts. It will be cooling agent of the engine. It is used to lubricate the parts.

Oil scraper ring is on the piston that scrapes the excess oil off the liner wall on the down stroke of the piston.

When the Machine is running, torsional vibration due to varying cyclic torques built up. There will be a natural frequency for the whole system and if the frequency of the vibration is equal to multiple of the natural frequency, a condition of resonance is set up. Resonance will cause unacceptable torsional vibration and stresses to be induced.

Bent foot is the condition when the foot is touching the base on the outside portion, but the inside of the foot is bent, creating an angle between the base and the bottom of the foot. When the hold-down bolt is tightened, the foot will deflect and distort the machine frame, depending on what portions of the frame will bend. A bent foot is a type of soft foot that occurs when the bottom of foot is not coplanar, meaning that the foot slopes from one corner to another. The foot may also be bent upward so that the outside edge is not touching the base and the deflection occurs along the outside of the foot. The best way to correct bent foot is to remove the equipment and machine the foot, the base plate, or possibly both.

Soft foot is the common term used for the improper contact between a machine casing, and the base plate used to support it. It may be either an angular or parallel soft foot, but often it is a combination of the two. This condition is identified when there is an unequal gap at all four corners of a foot. A soft foot can occur when one leg of the driver is too short, when the foot mounting pad is not in the same plane as the other(s), or The foot has an inadequate amount of shim under it. If the alignment process has been started, and an accurate or consistent alignment cannot be obtained, it is likely that there is a soft foot condition present.

Shims are used in the shaft alignment process to correct the vertical position of a movable machine so it will be in alignment with the stationary or reference machine. Shims should be clean and flat. Shim stock or precut shims are used to raise the driver during the alignment process. When angular soft foot is present, it is advisable to cut a shim to fill in the void from the angular soft foot.

Bolt-bound is when the movable machine is up against the hold down bolts preventing further adjustment in the direction needed to complete the horizontal alignment. It is used to describe a condition that occurs during the alignment process, where the driver or pump cannot be moved any further.

If the misaligned shaft center lines are parallel but not coincident, then the misalignment is said to be parallel (or offset) misalignment. Or when the equipment shaft center lines are parallel, but are offset from each other, it is called parallel misalignment.

Misalignment is a condition where the center lines of coupled shafts do not coincide. Angular misalignment is the term used when two shaft center lines are at an angle to each other. If the misaligned shafts meet at a point but are not parallel, then the misalignment is called angular misalignment.

This is also called fluid-film, thick-film or flooded lubrication. This type of lubrication is done in those cases where liquid lubricants having minimum viscosity under working conditions are used and at the same time, it should remain in place and separate the moving or sliding parts of the machine. A thick film of lubricant is interposed between the surfaces of bodies in relative motion. The frictional resistance to the movement of the sliding parts is only due to the internal resistance between the particles of the lubricant. In the fluid film lubrication, the liquid lubricant fills the grooves or irregularities of the sliding surfaces, and forms a thick layer in between them so that there is no direct contact between the sliding surfaces.

Where thick film lubrication fails, thin film lubrication is done. Thin film or boundary Lubrication is done for those cases in which the continuous film of lubrication cannot persist and direct metal to metal contact is possible. A Shaft starts moving from rest The speed is very low Load is very high and iv) viscosity of lubricating oil is very low.

MTBF tells us the most frequent failures within a process. Mean Time means, statistically, the average time. Mean Time Between Failures is two important KPI's in plant maintenance. In other words, the mean time between failures is the time from one failure to another. Mean Time Between Failures = Total up time / number of breakdowns = (Total calendar days-Failure days)/ number of breakdowns

Mean Time To Repair  Mean time to repair (MTTR) is the average time required to troubleshoot and repair failed equipment and return it to normal operating conditions. It is a basic technical measure of the maintainability of equipment and repairable parts. Mean Time means, statistically, the average time. Mean Time To Repair is two important KPI's in plant maintenance. Mean Time To Repair = Total down time / number of breakdowns = (Total Failure days)/ number of breakdowns 

Impeller types can be radial, mixed flow, axial and peripheral and are selected on the basis of the pump design and the application. The number of vanes will affect the efficiency; in general more vanes are more efficient. Open impellers   Vanes are attached to the central hub, without any form, sidewall, or shroud, and are mounted directly onto a shaft. Open impellers are structurally weak and require higher NPSHR values. The impeller to volute or back plate clearance must be adjusted when the pump is at operating temperature and all axial thermal growth has occurred.

Transformations at constant temperature (Delta T = 0) An isothermal process is a thermodynamic process in which the temperature of the system remains constant. The heat transfer into or out of the system typically must happen at such a slow rate that the thermal equilibrium is maintained. In a phase diagram, an isothermal process is indicated by following a vertical line along a constant temperature.  Therefore, if the pressure and volume change, it is possible for a substance to change its state of matter even while its temperature remains constant,

Thermodynamic Definition of Enthalpy (H): H = E + P x V E = energy of the system P = pressure of the system V = volume of the system Consider a process carried out at constant pressure. If work is of the form –Delta V, then: Delta E = q x p + w Delta E= q x p – P Delta V

The cooling capacity of a refrigeration system – is the rate of heat removal from the refrigeration space – is often expressed in terms of Ton of Refrigeration(TR).

The international deference in dimensions of mating mechanical parts that permits them to move relative to each other.

Bearing is a machine element, which supports another moving machine element permitting the relative motion between the Contact surfaces with minimal friction.

Lubrication is the some oily or greasy substance in order to diminish friction. Lubrication oil is thick fatty oil is used to lubricate machinery. Oil and grease are the most common. Grease is composed of oil and a thickening agent to obtain its consistency,

The primary function of a lubricant film is to provide protection for moving parts. Thereby reducing friction and wear of the machine. Cooling and debris removal are the other important benefits provided by a fluid film lubricant.

Vibration is the oscillation (periodic back-and-forth motion) of an object about a static position. Example of vibration is a weight suspended from a spring. Vibrations fall into two categories: free and forced. Free vibrations occur when the system is disturbed momentarily and then allowed to move without restraint.

In this bearing moving parts are in direct line contact with one another. The plain bearing consists of a shaft, also called a journal, and a supporting component, which may be a shell around the shaft called a sleeve, a half shell that the shaft fits into, two half shells (top and bottom parts) or a multipart shell. They can absorb more force than rolling bearings, but due to higher friction, plain bearings are subject to higher wear.

Effluent Treatment Methods Effluent can be treated in a number of different ways depending on the level of treatment required. These levels are known as preliminary, primary, secondary and tertiary treatment.  The mechanisms for treatment can be divided into three broad categories:

Main parameters in the water quality discharge standards are briefly discussed in below: pH pH is a measure of the concentration of hydrogen ions in the waste water and gives an indication of how acid or alkaline the waste water is. This parameter is important because aquatic life such as most fish can only survive in a narrow pH range between roughly pH 6.5-8. Oil and Grease This includes all oils, fats and waxes, such as kerosene and lubricating oils. Oil and grease cause unpleasant films on open water bodies and negatively affect aquatic life. They can also interfere with biological treatment processes and cause maintenance problems as they coat the surfaces of components of ETPs. BOD Measurement of the oxidisable organic matter in waste water is usually achieved through determining the 5-day biological oxygen demand (BOD5), the chemical oxygen demand (COD) and total organic carbon (TOC).

Organizations should have a clear work description of what a planner’s role is. The role may vary between organizations, mainly due to plant size. Some organizations have combined planners/supervisors. Some have dedicated planners for shutdowns/turnarounds. Planner/Scheduler position is responsible for the effective execution of all maintenance work control processes. He / she is responsible to the Maintenance Manager for the efficient and effective use of planning and scheduling

Contaminants In Waste water Treatment are given below: Heavy metals  Heavy metals are usually discharged to waste water from commercial and industrial activities and have to be removed if the waste water is to be reused Suspended solids Lead to the development of sludge deposits and anaerobic conditions when untreated waste water is discharged into the aquatic environment. Dissolved inorganics Inorganic constituents such as calcium, sodium, and sulfate are added to the original domestic water supply as a result of water use and may have to be removed if the waste water is to be reused.

Chemicals industry A range of industries manufacture or use complex organic chemicals. These include pesticides, paints and dyes, petro-chemicals, pharmaceuticals, plastics, detergents, paper pollution, etc. Waste waters can be contaminated by feed-stock materials, by-products, product material in soluble or particulate form, washing and cleaning agents, solvents and added value products such as plasticizers. Treatment facilities that do not need control of their effluent typically opt for a type of aerobic treatment. Food and beverages industry Waste water generated from agricultural and food operations has distinctive characteristics that set it apart from common municipal waste water managed by public or private sewage treatment plants throughout the world. It is biodegradable and nontoxic,

What is Pretreatment process ? Screening The influent water is screened to remove all large objects like cans, rags, sticks, plastic packets etc. carried in the sewage stream. This is most commonly done with an automated mechanically raked bar screen in modern plants serving large populations, whilst in smaller or less modern plants a manually cleaned screen may be used. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The solids are collected and later disposed in a landfill or incinerated. Bar screens or mesh screens of varying sizes may be used to optimize solids removal. If gross solids are not removed they become entrained in pipes and moving parts of the treatment plant and can cause substantial damage and inefficiency in the process. Grit Removal Pre-treatment may include a sand or grit channel or chamber where the velocity of the incoming waste water is adjusted to allow the settlement of ...