Monday, October 14, 2019

Material Selection For Valve Guides

Material Selection For Valve Guides
Valves are very important devices that are used to regulate or control the flow of media such as gases, liquids or slurries. The use of valves is common in a lot of industries such as the car industry. Valves are important components in the engine of modern day cars and they are responsible for the flow of fuel vapor in the engine.
Just like other devices, a valve is a combination of several different parts that are assembled together to work in unison as a valve. One of the very important parts of a valve is the Valve Guide. A valve guide is a cylindrical piece of metal that is either casted or pressed into the cylinder head, with a valve reciprocating inside it. The major function of the valve guide is to absorb the transverse forces generated by the engine which could affect the valve stem. Together with the valve spring, the valve guide works to precisely center the valve so it can make proper contact with the valve seat. It also helps to conduct a proportion of the heat generated from the valve head to the cylinder head through the valve stem where it may be taken up by the cooling system.
Due to the strenuous task of the valve guide, the quality of valve guides mostly depends on the properties of the materials it is made with.


Contrary to general belief, steel has not been and probably never will be a good choice of material for valve guides. Material selection for valve guides is majorly down to cast iron and brass. Generally, material that will be used for making valve guides must have good gliding and thermal conductivity properties. Grey cast iron and brass materials with some selected alloy components have been particularly proven to be best suited for making valve guides.


Grey cast iron with pearlitic structure – this material is characterized by having good wear resistance. This material is best suited for making valve guides that will be used under normal strain conditions.


Grey cast iron with pearlitic basic structure and increased proportion of phosphorus. This material has higher resistance to wear and better emergency run properties due to the reticular formation of the phosphorus that is added. This material is best suited for making valve guides that will be used under medium strain conditions.


Grey cast iron with pearlitic basic structure and increased proportions of phosphorus as well as chromium content. This material has a very high resistance to wear and is best suited for manufacturing valve guide that will be used in highly supercharged engines.


CuZnAl (Brass) alloy. This material is characterized by high sliding properties and good resistance to wear. Best suited for valve guides under normal and medium strain.


Valve guides are very important parts in a valve that are meant for carrying out a very important task in the valve. They undergo a lot of strain in order to achieve this task, hence, they wear easily. The choice of material for making valve guides is important as the quality or functionality of the valve guide depends on it. Materials selected should have good wear resistance.