About piston rings

A piston ring is an expandable split ring used to provide a seal between the piston and the cylinder wall. Piston rings are commonbly made from cast iron. Due to the new sulphur cap 2020 regulations MAN B&W have introduced cermet coated piston rings. For older types or engines that use for example scrubbers and keep running on HFO we have types such as aluminium, bronze and ceramic coated versions. 

Other options are piston rings with gas tight lock and left-hand, right-hand executions and models with different dimensions such as 9, 11, 12,5 and 14 mm.

Piston rings in a marine diesel engine

Similar to other types of internal combustion engines, a marine diesel engine operates with three or more types of piston rings. The smooth and efficient operation of a marine diesel engine relies heavily on the secured sealing of the piston rings liners.

Functions of marine diesel piston rings

In general there are four functions known that piston rings fulfill. 

Compression gas seal; Compression piston rings guarantee that there is limited leakage, which can result in decreased gas compression pressure. A leak in gas compression will lead to insufficient power to fuel the engine and a significant increase in fuel consumption. 

Lubricating oil; Piston rings also spread the lubricating oil as it moves up and down the cylinder liner thousands of times per minute. This makes the piston operate smoothly, reducing the risk of friction and scuffing between metal parts

Heat regulation; During gas ignition, the temperature inside a piston can go up to 300°C. If this goes further, intense undistributed heat can damage the engine. Piston rings help regulate the temperature inside by releasing the transferring heat from the piston crown to the cylinder.  With new 

Form a barrier; A piston ring acts as a barrier between the piston and the cylinder wall, which prevents frictional force and eventually engine failure.

Damen Schelde Marine Services has been contributing to the shipbuilding industry throughout the world for over 140 years as former manufacturer and supplier of internal combustion engine components including piston rings.

In particular, the piston rings for marine use internal combustion engines, boasting high quality and performance have been held in high repute amoung worldwide users. The piston rings are based on specifications that are standardized by original engine manufacturers and exist out of many different materials of special cast iron and coatings.

The production of a piston rings is based on the following processes from tapping, machining, rough grinding, cutting-off GAP and further treatment starting with plasma spray, side surface finish, gap sizing and ending up with marking the parts.

Composition of piston rings

Our piston ring programme contains different compositions of material. Several factors are important and related to different chemical compositions. For example size, value of modulus of elasticity, value of transverse test strength, hardness and coefficiten for detoriation of tension. These factors are all applicable to the known Cast iron executions such as Nodular Graphite, Compacted Vermicular Graphite and Flake Graphite.

Configuration of marine piston rings

Within these configuration we split the cross-section types in compression rings and oil control rings. When talking about compression rings we have the following types:

Type Section Application and features

Plane

  Basic geometry of compression ring
Grooved   Effective for retaining lubrucation oil
Tapered face   Effective for controlling the oil film on the cylinder wall
Tapered balance undercut   Used mainly as the lowest stage pressure ring of 4 stroke diesel engines
Symmetry barrel face   Prevents edge loading during the initial run-in operation
Internal bevel barrel face   Feature a twist effect
Asymmetry barrel face   Effective for facilitating the initial run-ing operation

Oil control rings are known to us in the following configurations:

Name Section Application and features
Cutter   Ordinary oil ring geometry
Bevel cutter   Smaller rubbing surface to enhance oil control capability
Bevel cutter   Effective for suppressing the reduction of surface pressure due to circumferential wear
Bevel cutter with coil   Greater oil control capability using a coil expander
Bevel cutter with coil   Used for reducing lubrication oil consumption for medium-size, medium-speed diesel engines
Bevel cutter with coil   Permits larger coil diameter for larger tension

Besides the shape of rings for the configuration it is also relevant what shape of joints are used depending on the application and wanted features. Below we describe the types.

Name Appearance of joint Face or section Application and features
Butt joint     Commonly used for various engines
Right angle joint     Used for relatively large size engine
Left angle joint      
Right step joint     Low speed engine and hyraulic equipment
Left step joint      
Double angle joint     In order to give gastight state at joint, these types are used for hydrualic cylinder and large size, low speed engine
Double round joint      
Double step joint      

Surface treatment for marine use rings

Plating are known with the following films

  • CPN
  • Cr
  • RQBM
  • CPC

Sprays are known with the following films

  • Ceramic; 
  • molybdenum and Ni-Cr; 
  • Cu; and
  • Graphite-Cu-Sn

Notes for use of ring

  1. Store rings in a low-humidity environment and store them horizontally;
  2. During assembly, take care not to hit the ring against a hard object;
  3. To assemble a ring onto the piston, use the ring-mounting tool. The gap, enlarged before installtion, should be at most eight or nine times larger than the thickness of the ring. A gap that is too large may cause the material to break or deform;
  4. For rings that have an asymmetrical section, mount it with the marked surface facing upwards.

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