Skip to main content

Why molybdenum steel valve seats are used?



The valve lead and valve seat work under most demanding conditions. These must remain tight when the valve is seated. When the exhaust valve just starts to open the gases at high pressure and temperature escape at great velocity that may cause erosion of the valve and seat material. Such erosion also take place if some dirt or grit from ash gets lodged between the valve and seat and there is leakage of gas.

If the fuel contains elements such as sodium and vanadium, at high temp a viscous and sticky compound is deposited that is very corrosive. At low temperature there may be dew formation and sulphur oxides produce during combustion coming in contact with water may form acid causing corrosion of parts.

The valve seat therefore require periodic servicing. If the seat were an integral part of exhaust valve cage or the cylinder cover, then the entire cage or cover may need to be replaced, which would be very expensive. For this reason detachable valve seats made of high quality heat resistant material is fitted.





Valve Seats main functions:
  • Compression gas sealing – Prevents compressed gaseous bodies and combustion gas from leaking into the manifold.​
  • Heat transfer – Releases heat in the valve to the cylinder head
  • Strength – Holds tight when the valve is mounted.​
  • Wear-resistance – Hard to wear down under high heat and high load.
Properties of molybdenum
Molybdenum is hard slivery metal with very high melting point. It is primarily use to make alloys with other metals. The most common alloy of molybdenum are those with steel. Molybdenum improve strength, toughness, resistance to wear and corrosion and ability to harden steel.

Comments

Popular posts from this blog

Load Line & Why it is Important

Merchant ships have a marking on their hull know as the Plimsoll line or the Plimsoll mark, which indicates the limit until which ships can be loaded with enough cargo, internationally, the Plimsoll line on a ship is officially referred to as the international load line. Every type of ship has a different level of floating and the Plimsoll line on a ship generally varies from one vessel to another.  All vessels of 24 meters and more are required to have this Load line marking at the centre position of the length of summer load water line. There are two types of Load line markings:- Standard Load Line marking – This is applicable to all types of vessels. Timber Load Line Markings – This is applicable to vessels carrying timber cargo. These marks shall be punched on the surface of the hull making it visible even if the ship side paint fades out. The marks shall again be painted with white or yellow colour on a dark background/black on a light background.  The comp

Difference Between A, B & C-Class Divisions?

IMO Symbol A Class Division  IMO Symbol B Class Division  SOLAS has tables for structural fire protection requirement of bulkheads and decks. The requirements depend on the spaces in question and are different for passenger ships and cargo ships. The Administration has required a test of a prototype bulkhead or deck in accordance with the Fire Test Procedures Code to ensure that it meets the above requirements for integrity and temperature rise. Types of Divisions: "A" Class "B" Class "C" Class "A" Class: "A" class divisions are those divisions formed by bulkheads and decks which comply with the following criteria: They are constructed of steel or equivalent material They are suitably stiffened They are constructed as to be capable of preventing the passage of smoke and flame to the end of the one-hour standard fire test. they are insulated with approved non-combustible materials such that the average tempera

Pump Shaft Alignment Procedure

Types of shaft alignment methods: Visual Line-Up Straightedge/Feeler Gauge Rim and Face Cross Dial Reverse Dial Laser Visual Line-Up The visual line-up method is the most common method of alignment. Used in initial installations, visual line-up allows technicians to analyze the working conditions and feasibility of installation. Straightedge/Feeler Gauge Straightedges are used to determine the offset between coupling halves. Corrections are made under all four of the machines feet. Feeler gauges or taper gauges measure the gap between coupling halves at the bottom and top of the coupling. Rim and Face This method is similar in principle to using a straightedge and feeler gauge, but more accurate since dial indicators are used. The rim reading measures the offset between the coupling halves. The face reading measures the angular difference between the faces of the coupling. Changes are calculated with the same formula as the straightedge/feeler gauge met