PRODUCT. Piston Rings. Sealing under extreme conditions POSTER INSIDE

Transcription

1 Piston Rings Sealing under extreme conditions PRODUCT I N F O R M A T I O N POSTER INSIDE

2 Under pressure KOLBENSCHMIDT piston rings. Controlled application of force. Inertia and gas loads as well as high temperatures put high demands on piston rings. It is only by making the correct adjustment to the relevant engine that optimum service life and compliance with the exhaust gas regulations can be achieved. Type, dimensions and material adaptations together with a precise production process are indispensable factors for applying controlled force that determines the function of the rings. Casting process for piston ring castings (die casting) Grinding the piston ring sliding surface Molybdenum coatings To protect the rings against scuffing, the sliding surfaces of the rings can be filled or coated all over with molybdenum. The flame spraying or plasma spraying procedure can be used for this purpose. Thanks to its high melting point (2620 C), its porous structure and lubricating effects, molybdenum warrants a higher stability of the piston ring sliding surfaces. Internal lathe Manufacturing the inner contour Phosphate-coating plant

3 KOLBENSCHMIDT piston rings more than just a seal. Temperature management is a vital function of the piston rings. Most of the heat that is absorbed by the piston in the course of the combustion process is dissipated by the piston rings to the cylinder. Without this continuous heat dissipation the aluminium piston would melt within a few minutes. absorbed quantity of heat 45% Pressure is essential because only the proper amount of combustion pressure will enable compression rings to fully perform their sealing function. The given tangential load of the rings only assumes the basic function which is to establish contact to the cylinder wall. The far higher pressure force representing up to 90% of the total pressure force is generated by the combustion pressure during the combustion cycle. As can be seen in the illustration, the pressure is applied behind the piston ring and presses it even tighter again the cylinder wall. 20% 5% Compression rings dissipate up to 70% of the piston temperature to the engine block. Two are better than one with two oil scraper lands (rails) on the oil control rings ensuring that the oil film thickness of 1-2 μm required for lubrication is always achieved and never ex-ceeded. Low oil consumption and a low mixture flow rate as well as a long service life of the associated parts are thus translated into practice in an almost ideal way.

4 Motorservice Group. Quality and service from a single source. The Motorservice Group is the sales organisation for the global aftermarket activities of KSPG (Kolbenschmidt Pierburg). It is one of the leading suppliers of engine components for the independent aftermarket, including the premium brands KOLBENSCHMIDT, PIERBURG and TRW Engine Components, as well as the BF brand. Our comprehensive product range allows our customers to obtain engine components from a single source. As a problem solver for dealers and garages, Motorservice offers extensive service and the technical expertise that you would expect from the subsidiary of one of the largest automotive suppliers. KSPG (Kolbenschmidt Pierburg). Renowned supplier to the international automotive industry. As long-standing partners to the automotive industry, the companies in the KSPG Group develop innovative components and system solutions with acknowledged competence for air supply and emission control, for oil, water and vacuum pumps, for pistons, engine blocks and engine bearings. The products comply with the high demands and quality standards of the automotive industry. Low emissions, reduced fuel consumption, reliability, quality and safety these are the forces that drive innovation at KSPG. Motorservice Partner: Headquarters: MS Motorservice International GmbH Wilhelm-Maybach-Straße Neuenstadt, Germany /14 EN MS Motorservice International GmbH

5 Piston Rings Function and Design Incorrect reconditioning Piston impact on cylinder head Maintenance faults Worn-out ring grooves If the sealing surface of an engine block is reconditioned and a piston with standard compression height fitted, this may cause mechanical impact by the piston on the cylinder head in the case of diesel engines. The same occurs if cylinder head gaskets with the wrong thickness are fi tted. Due to these hard im-pacts, the piston rings start to flutter and vibrate, dislodging the lubri cation film and as a consequence sealing is no longer effectively. The result: High oil consumption and high cylinder wear (see also Fuel Flooding ). Remedy: Compliance with the correct piston protrusion; use of correct cylinder head gaskets. Dirt that reaches the combustion chamber settles in the ring grooves where it causes abrasive wear in the ring grooves and at the flanks of the piston ring. This results in excessive ring height clearance and consequently to a deterioration of the guidance of the piston rings in the ring grooves. The rings will become bent during use and start to flutter. If the rings are severely worn at the sides, they can break. The result: High oil consumption and poor performance. Remedy: Regular air filter main-tenance, especially in very dusty areas. Ring joint clearance too small The piston ring joint clearance is comparable to the valve clearance. When the parts are warmed up, the components are thermally heated which results in a change in length. As long as the machine is cold, the joint clearance prevents the pistons in the cylinder from being jammed when the machine is hot. If the joint clearance is too small when the machine is cold, there will be an excessive rate of wear on the piston ring, sealing problems and engine failure could occur when the machine is hot. Asymmetric piston wear pattern Deformed connecting rods, which often occur as a result of engine failure, can cause the piston to have an incorrect attitude in the cylinder. The piston rings consequently take on an elliptical form and no longer rotate in the piston. This results in uneven wear and piston ring fluttering. The result: Premature piston ring wear, piston seizure and high oil consumption. Remedy: It is essential that the minimum joint clearances are complied with a reduction of the joint clearance by the repair shop is not permitted. The result: High wear, ring fractures and excessive oil consumption. Remedy: Check the connecting rod for deformation and torsion prior to installing it. Abnormal combustion Jammed piston rings Piston rings must be able to rotate freely in their ring grooves during operation (exception: two-stroke engines). If the piston rings are blocked by carbon deposits or dirt in the ring grooves they are no longer able to seal properly and will not wear uniformly. If the rings are clamped in the grooves, the sealing effect is no longer warranted. This causes a blow-by of combustion gases on compression rings, and results in the penetration of oil into the combustion chamber on oil rings. Knocking combustion and glow ignition The result: Piston seizure, high wear and high oil consumption. Remedy: Regular air filter maintenance and the use of engine oil with the prescribed oil specification for the engine. Installation of worn-out parts Out-of-round cylinders Knocking combustion or glow ignitions result in excessive pressure peaks in the cylinder as well as high mechanical stress of the parts. The piston rings start to flutter and can break. On moly-bdenumplated rings, the moly-b denum layer can break away. The result: Piston seizure, loss of engine power and/or high oil consumption. Remedy: Use of high-grade fuels. To p When machining the cylinder bores, it is essential to make sure that the geometry is perfect. The piston rings can still seal slightly oval cylinders. However, sealing becomes more difficult with out- of-rounds of the 3rd or 4th order. These are often caused by tension stressing from the cylinder head bolts. The crescent-shaped gap caused by out-of-roundness between the piston ring and the cylinder will result in leakages. The result: Poor performance, excessive oil consumption and engine failures. Remedy: Observe the tightening specifications for the cylinder head or exclude out-of-rounds during cylinder machining. Out-of-rounds: Sliding friction Fuel flooding The oil film is washed off due to incomplete combustion of the in-jected fuel or to excessive injected fuel. This causes mixed friction or even dry friction of the piston in the cylinder. The metal parts rub against each other without a protective oil film. The result: High ring and cylinder wear, high oil consumption. Remedy: Correct function and setting of the fuel system. 3rd order 4th order Mixed friction Ring joint clearance too great MS Motorservice International GmbH /15 EN An excessive joint clearance on the piston rings appears after a long running period and high wear on the cylinder and piston rings. The joint clearance is too great if it has doubled its size compared to its new condition. Clearance exten-sions of up to 0.3 mm are irrelevant. They contribute neither to a loss of engine power nor to excessive oil consumption. Slightly enlarged piston ring joint clearances are often over-estimated. On this topic, also see Ring joint clearance too small. Worn-out cylinders If new pistons and piston rings are fitted into a worn-out cylinder, the piston rings often hit the upper wear edge of the cylinder. As a result, the piston rings start to flutter and can no longer seal effectively. Also see Piston impact on cylinder head and Worn-out ring grooves. Remedy: Replace worn-out pistons and cylinders. d The result: Higher oil consump tion and premature wear. Remedy: Replacement of the cylinder liner or remachine the cylinder bore (drilling, honing). Details on this subject can be found in our brochure Piston Rings for Combustion Engines. Further information can be obtained directly from your local Motorservice partner or at The Motorservice Group is the sales organisation for the global aftermarket activities of KSPG (Kolbenschmidt Pierburg). It is one of the leading suppliers of engine components for the independent aftermarket, including the premium brands KOLBENSCHMIDT, PIERBURG and TRW Engine Components, as well as the BF brand. Our comprehensive product range allows our customers to obtain engine components from a single source.