Why valve and valve seat ring and other accessories to wear?
Valve valve working conditions are very bad working conditions.
First of all, the valve directly contact with high temperature gas, heat, and heat dissipation difficulties, so the valve temperature is very high.
Secondly, valve gas under physical strength and the function of valve spring force, and the distribution of the movement mechanism of inertial force make the valve seat when hit.
Third, the valve in the lubrication condition is very poor at high speed under the condition of opening and closing and make high-speed reciprocating motion in the valve guide.
In addition, the valve due to contact with the corrosive gases in high temperature gas under corrosion.
The material of valve inlet valve generally made of carbon in the alloy steel, such as chrome steel, chrome molybdenum steel and nickel chrome steel, etc.
The exhaust valve of heat-resisting alloy steel manufacturing, such as silicon chromium steel, chrome molybdenum steel silicon, silicon chromium manganese steel, etc.
Of the valve structure of automobile engine inlet and exhaust valves are mushroom valve, made up of two parts of the valve head and valve stem.
At the top of the valve are flat, concave and convex head shape.
Application at present most is flat valve and its structure is simple, easy to manufacture, heating area is small, inlet and exhaust valves can be used.
Between valve and valve seat or valve seat by taper sealing.
The Angle between the valve cone and the top of the valve is called the valve cone Angle.
Inlet and exhaust valve cone Angle of the door in general are 45 & deg;
, only a handful of engine inlet cone Angle is 30 & deg;
Of the valve head to accept part of the valve seat ring heat to the cylinder cover;
Others through the valve stem and valve guide to the cylinder head, have been in the cylinder cover water jacket coolant to be taken away.
In order to enhance heat transfer, seal cone of the valve and valve seat ring must be tight fit.
To this end, both to match grinding, grinding after not interchangeable.
Valve stem has high machining precision and lower roughness, and valve guide keeping fit clearance, to reduce the wear and tear, and direction and good heat dissipation effect.
The shape of the end of a valve is decided by the fixed way of valve spring seat.
Using split into two and a half and the outer surface of the cone valve lock clamp to fix the valve spring seat, simple structure, reliable operation, easy disassembling, therefore has been widely used.
Inner surface has a variety of shapes, valve lock clamp valve end accordingly have different shape of valve lock clamp slots.
In some highly intensive engine with hollow valve stem of the valve, designed to reduce the valve quality and reduce the inertia force of the valve.
In order to reduce the temperature of the exhaust valve, enhance the exhaust heat dissipation capacity, on many car engine by using sodium cooled valve.
The valve is in the hollow valve rod fill half of metallic sodium.
Because the melting point of sodium is 97.
8 ℃, boiling point is 880 ℃, so in the valve work, become liquid sodium, violently shaking up and down inside the valve stem, constantly absorbing heat and to the valve stem from the valve head, then through valve guide to the cylinder head, valve head is cooling.
We again to say these components easily damaged reasons: one of the most common, the burning of the valve to the exhaust valve, its basic reason is that the distortion of the valve seat and the carbon deposit.
In addition, such as excessive valve clearance adjustment, wear also can lead to valve burning.
When distortion valve seat, valve and valve and seat sealing surface temperature between the partial pressure increase at the same time.
Valve seal surface often appear groove, the high temperature gas scour will form the burning.
When the valve and valve seat sealing surface carbon deposition seriously, make the heat transfer conditions deteriorate, also easy to deformation, lead to valve burning 2, the function of the valve guide is the movement of valve guide, ensure the valve as a straight line reciprocating movement, valve and valve seat or valve seat can fit properly.
In addition, will also accept part of heat to the cylinder head valve rod.
Valve guide working temperature is higher, and poor lubrication condition, work valve-train by the lubricating oil splash up when the valve stem and valve guide hole.
Valve guide by gray cast iron, nodular cast iron or iron base powder metallurgy production.
In certain interference to press the valve guide into the cylinder cover on the valve guide hole after, fine hinge valve guide hole again, to ensure the right fit clearance of valve guide and valve stem.
3, (1) cylinder head bolt tightness.
(2) the valve seat ring around the cylinder material (
Cast iron or aluminum alloy)
Uneven cooling intensity (
More commonly used bearing hole of the cylinder heated to 100 ℃ or so)
(3) cylinder or cylinder cover & other;
Aging & throughout;
Cylinder block and cylinder head casting can produce stress, after a long time, the phenomenon of the stress go away)
(4) valve seat ring geometry surface processing or Mosaic process quality is not high, cause with bearing hole of the seat is not tight, lead to bad heat transfer, the seat is overheating, resulting in serious deformation.
(5) bearing hole and seat material without reasonable matching.
General seat materials should be chosen in the working temperature smaller plastic deformation and hardness of high alloy.
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