Engine Performance, Valve Seals and the Minimum Chip
The seal between valve seats and their respective valves is not a myth!
It would be wrong to minimize the importance of precision valve seat machining in internal combustion engines.
Cylinder seals and their reliability over the long term, is a "holy grail" for many engine developers. It is well established that this is the key to a “successful and perfect engine".
The cylinder seal at the piston ring level, at the valve level, two different problems successfully dealt with through metallurgical progress, machining and control means progress, advances in surface coatings and various heat treatments.
Seals at the cylinder segments level has evolved considerably, to the point of practically no longer being a problem in advanced engines.
Valve seals remains a costly problem; machining only valve guides and valve seats represents a significant percentage of the overall cost of machining a conventional internal combustion engine.
Significant progress in this area are related to improving machining precision, which machining accuracies are made even more difficult to obtain because of the new materials used to manufacture valve seats and valves.
Valve seat materials typically are sintered metals allowing a better heat dissipation, improved abrasion resistance to gas lamination, and a better resistance to compaction as a result of the repeated impacts of valve closures.
The precision machining of valve seats permits contact over the entire contact surface. A form that is incompatible between the valve seat and the valve leads to too small a surface, limited to a tiny area which is pounded over due to the fact that all the pressure is concentrated on too reduced a surface.
Concentricity defects (run out) or shape defects (circularity) yield the same effects, the crushing of the contact surface, making unlikely a perfect seal and reduces the durability of the cylinder head components.
To be completely compatible, valve seat shapes and valves must be perfect and completely identical. A circularity defect exceeding 0.005mm (0.00019”) will hardly be corrected by the crushing of the material. Likewise, an angle difference of more than 0.15 degree will have a negative effect on the life of parts, valve seats and valves.
To achieve a perfect seal during the closing of a valve every one hundredth of a second, requires accurate geometric shapes and a flawless guiding of the valve within its valve guide. The brevity of the contact does not allow for the slightest defect and if the valve must "drag" on the seat to get to find its closed position, the seal will be poor and the combustion imperfect.
The seal is definitely linked to the achievement of very high precision machining operations in materials that are particularly suited for this function.
The high precision can only be obtained by making very light machining passes, forming a metal chip as close as possible to the mechanically feasible minimum.
The size of the minimum chip is different depending upon the nature of the materials to be machined and, for this, the choice of tools must be especially adapted to each case. The tool must be extremely rigid, prerequisite for the cutting edge to effectively cut the material. The new machining technologies have transformed the approach to metal finish cutting and cutting edges are handled with precision; "the minimum chip" and therefore the precision of the machining operations depend on all these parameters which will yield to excellence.
This search for the absolute definitely eliminates machining operations that generate significant cutting efforts; such as the recessing used for nearly a century to machine valve seats. The high-level precision, the search for the minimum chip has been made possible thanks to the advent of the numerical control that allows to drive with extreme precision a tool that gets its rigidity from a preloaded kinematics which is also resistant to all cutting efforts.
NEWEN® has, for its part, developed a tool travel kinematics with absolute rigidity, resorting to the use of the most efficient alloys, and most advanced/best performing linear movement control techniques.
NEWEN® has done everything, worked to achieve a completely rigid tool kinematics, capable of withstanding cutting forces with a rigidity superior to the micron. The use of the most advanced components and techniques available to date on the world market do that the FIXED-TURNING® allows maximum precision machining, often higher than what would be obtained by a grinding wheel process.
NEWEN® uses the best components from high precision mechanical industries from Germany, Japan, Switzerland, USA, etc…
FIXED-TURNING® provides machining managers with a tool that, in addition to providing total freedom of forms, guarantees a near perfect precision level.