From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Journal page discussing engine valve seat inserts and different designs for internally cooled valves.
| Identifier | ExFiles\Box 158\5\ scan0025 | |
| Date | 1st March 1939 | |
| 116 S.A.E. JOURNAL (Transactions) Vol. 44, No. 3 Fig. 14 — This figure illustrates the benefit of carrying the guide-boss cooling as close to the valve seat as possible Fig. 15 — Comparative tests of the straight-hole versus the hollow-head type of internally cooled valves indicate a marked reduction in operating temperatures with the latter type [Figure 14 Left Side] VALVE & GUIDE COLOR AT 2200 R.P.M. FULL LOAD APPROACHING BRIGHT RED BRIGHT RED DOWN INTO GUIDE DULL RED BLACK 19 SECONDS REQUIRED FOR VALVE TO TURN BLACK AFTER THROTTLE IS CUT TO IDLE [Figure 14 Right Side] VALVE & GUIDE COLOR AT 2200 R.P.M. FULL LOAD BLACK DULL RED BLACK 6 SECONDS REQUIRED FOR VALVE TO TURN BLACK AFTER THROTTLE IS CUT TO IDLE [Figure 15 Left Valve] NORMAL OUTPUT SECTION 'A' TO 'B' AT APPROXIMATELY 1200°F AT MAXIMUM OUTPUT WHOLE HEAD INCLUDING SEAT OPERATING AT 1200°F OR HIGHER STRAIGHT HOLE TYPE OF INTERNALLY COOLED VALVE [Figure 15 Right Valve] AT HIGH OUTPUT VALVE OPERATING BLACK INDICATING TEMPERATURE UNDER 1000°F.{Mr Friese} CAVITY OR HOLLOW HEAD TYPE OF INTERNALLY COOLED VALVE [Main Text] degree by applying a material that will harden and produce a good wear-resistant surface. However, in spite of all the precautions taken, valve-seat burning can and will occur if it is operating against, first, unsuitable material or, second, in cylinder seats that distort to the extent that leakage can occur under severe operating conditions. Seat Inserts The major factors in the development of suitable inserts, or seat rings, have been: 1. Proper material to resist corrosion, or what is commonly called “seat sinkage.” 2. The ability of the seat ring to remain an integral part of the cylinder head into which it is fitted. Measurement of the temperatures of a seat ring installed in cast iron indicated that the seat ring operated at an average temperature approximately 150 F higher than the adjacent cylinder material and, since it is believed this is a representative differential, the ideal ring material from the viewpoint of its ability to remain tight would be that which has an expansion coefficient less than the material into which it is fitted, by the amount that would be equivalent to the differential in average temperature so that the stresses developed do not vary to a great degree from those set up by the original room-temperature interference fit. There exists a temperature gradient through the ring, it being maximum at the seat and tapering down as it approaches the bottom. If the temperature is sufficiently high, thermal strains are set up which tend to overstress the section nearest the seat, causing it to take a permanent set. If the depth is sufficient, there still remains a considerable portion of the ring that is not overstressed, and it will maintain its original interference fit, whereas the section near the seat might reduce sufficiently in diameter to lose its original tightness. In addition to thermal strains set up by temperature differentials, there is always the possibility of distortion of the counterbore from both mechanical and thermal distortion and, without consideration of these factors, it is doubtful if a ring of any type can be kept in its proper position. The method of installation is quite variable, but we believe that the simplest form of construction ofttimes gives the best results and, in the case of seat rings, the plain straight-ground ring, shrunk in with the proper interference fit at room temperature, gives the most satisfactory results – particularly where the face of the ring is left slightly below the counterbore so as not to expose any of the outside diameter of the ring to the flame. The ability of the material to resist corrosion or seat sinkage appears to be correlated to the valve difficulties in that materials that resist oxidation and corrosion when used in valves appear to do likewise when used as a seat-ring facing. Aluminum-bronze has been and is still used to a considerable extent but, as outputs and consequent temperatures, distortion, and so on, increase, it is very likely to cause difficulties and, where this trouble has occurred, the aluminum-bronze has been replaced by an austenitic type of steel. Apparently the conductivity of the seat ring material is not of prime importance since the austenitic steel has a lower thermal conductivity than aluminum-bronze and overcomes difficulties that have caused failure with the aluminum-bronze type. In some engines it has been found necessary to go a step further and apply a Stellite facing to the backing material, as Stellite has the necessary characteristics that make it one of the most pronounced materials as far as resistance to this so-called seat sinkage is concerned – this condition probably being due to its inherent stainless qualities in addition to its ability to maintain hardness at elevated temperatures. | ||