GB2445566A

GB2445566A - An oil scraper seal system for a two-stroke crosshead diesel engine

Info

Publication number: GB2445566A
Application number: GB0700411A
Authority: GB
Inventors: Ernest Stephenson Terry
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-01-10
Filing date: 2007-01-10
Publication date: 2008-07-16
Anticipated expiration: 2027-01-10
Also published as: GB0700411D0; GB2445566B

Abstract

An oil scraper seal for a two-stroke crosshead diesel engine comprises a carrier ring (g) including a built-in oil reservoir res, with lower castellated slots (e) and slots from the reservoir which allow oil to free flow to the sump. The carrier rings (g) are flanged with guide pins and a special bolt that is radially loaded using Belleville Spring Washers (see Figure 1. The carrier rings (g) have removable scraper seals (f) with a 4{ male dovetail matching a corresponding carrier ring dovetail as a light interference fit. Scraper segments are set at a 45{ scarfe (see Figure 7)to ensure continuous scraper seal effect. The scraper seals preferably use High Density Polymers, though metallic scrapers can be used to the same design criteria. This invention prevents oil retention within its design as there are no obstructions over any drain slots in either the carrier ring or scraper seals.

Description

SUBMISSION OF INDUSTRy INFORMATION.

For many years attempts have been made to create an efficient piston rod sealing/scraping stuffing box system for Marine and Power Station 2 stroke crosshead diesel engines To date many of the systems in use have been developed from a previous mechanical age using designs and materials that have not adapted as well as expected to the modem two stroke diesel engine.

Some of the problems have been caused by the need to have separate systems of lubrica-tion for the engine cylinders using a type of oil with an average TBN of 70. The engine sump uses an oil of 30, and the fuel oil can be anything from light diesel oil to heavy fuel oil. To pre-vent the mix of all the oil types a Stuffing box Is placed between the two systems to prevent any mixing Should the stuffing box system be worn or damaged then the 3 oil types can mix which Is very detrimental to the engine mechanically, also very expensive when replacement's need to be made.

Information Sketch 1 shows a cross section of a typical stuffing box which is divided into 3 sections Upper/MjdJLower, each section has Its own priority of operation. The Lower section should effectively scrape off the system oil from the piston rod as it passes through the boiç the prime scrape off being on the upward stroke, the Mid section has a dual purpose of scrap-ing off in both directions of movement but on the down stroke the oils scraped off should be directed to a neutral space or waste tank The Upper section should seal and scrape but also be gas tight to prevent transmission of gas in either direction from above or below the stuffing box.

011 loss from the crankcase system can be considerable in any one operational year and make up of oil to the system can cost many thousands of or US$. Currently if a vessel has a make up requirement of 3000 1tt per month an annual cost at US$1.45/hr would be around $48,000.00. Contamination of the system oil by fuel oil and cylinder oil In the worst Instance would require a total system clean and refill with system oiL Many solutions have been tried over the last 10/15 years but current designs still tend to use outdated spring solutions to hold sections of seal/scraper rings In place within the confines of the stuffing box configuration.

Because the stuffing box system has three distinct areas of designation and operation this Invention must be in two parts, Part 1 covers the Bottom and Mid scraper/seal areas and Part 2 must cover the Upper area which has a more complex operation to seal and scrape, this invention will also go far beyond current designs and materials, the Upper Ar-ea has to be treated in a different manner in materials and design to the Lower Area.

(**(c Conseil International Des Machines a Combustion, CIMAC reference Is to 21st International Congress on Combustion Engines.) Description of Retro Two-Stroke Oil Scraper System.

This invenhlon relates primarily to the bottom end or lower scraper rings of the conventional two-stroke crosshead engine piston rod stuffing box and mid seal or scraper system of one or Iwo rings that scrapes off excess oil to the neutmi space. In this invention the mid scraper/seal rings will be inverted to allow the castellated sections more efficient scrape off should the Up-per Scrape Rings not work effectively. Historically the siffinp Iin h hgvi

Description continued.

machined to create a good scrape off of oil from new, and as the ring weaxs then the sur-face contact area of each lip increases In surface area to maintain a good scrape off effect until the ring system needs replacement through operational wear. The scraper ring Is the other part of the dovetail In the carrier ring the location Into the carrier ring can be seen In Figure 4 & 5.

This design removes dependency on fine lip seals Figure 9, which can be prone to damage (I11rIra I i._... --This invention will be more efficient at removing oil from the piston rod during operation as there Is no retention caused by springs covering the drain holes or slots Info Sketch 4 and Fig-ure 9 show conventional conditions. By using the Belleville system of loading the carrier rings the slots In the scraper rings Flgurel (h) and carrierriri CDRN dPI h unrestricted flow first into the carrier ring reservoir Figures Res and then free flow from the reservoir to the return sump of the engine. As there Is no pump back to the piston rod normal-ly caused by springs covering the drain slots/boles there will be a greater volume of oil scraped from the piston rod during all normal operational speeds. Belleville washers can be used on veiy high loads with small deflections and yet maintain a constant load dependant upon the design criteria This invention will be able to retro-fit to all current two stoke crosshead engine types, and each engine type and size can be accommodated to suit available dimensions, and will be able to fit single or stacked spaces as per Information Sketch 1.

The flexibility in design of this invention Is such that should design require the Carrier ring system can be cast as single height, double height, or triple height to give rigidity of structure.

Machining to accommodate the scraper ring would be the same except a single casting could take one, two or three scraper ring systems in each cast configuration. The flanging arrange-ment would be the same as the flange loading would be for a single carrier ring arrangement and the spherl-bolt and Belleville Spring Stacking arrangement would remain as a constant and torqued to suit operational conditions.

In this Retro PolyDuplex System the Belleville Washer system on the spherl-bolt and between the flange faces Is torqued to permit load and off load during engine operations and also the set torque will maintain the correct force on the scraper ring system sections.

The actual flanged face is designed to fit the various stuffing box configurations of existing two stroke crosshead engines, and also with minimum modification to new engine designs proves the flexibility of this design. Though the spherl-bolt Is shown as the prune securing bolt, hex-agonal cap screws can be used into a Teflon Spheri Sleeve should dimensional restrictions ap-ply.

A further advantage of the RPDS design is the ability to trim the Polymer Scraper rings to suit the change In piston rod diameter, from one section a piece can be removed using the sup-plied cutting gauge, or conversely should an extra piece of segment be needed then a small section can be cut from a spare segment and added into the carrier rings. Versatility of design allows many functions of alteration to be made without affecting the system performance or efficiency. This design Is probably the only system to be tailor made to suit every piston rod on any engine, even If there were three differing piston rod sizes on an engine Ic:-308 mm! 310 mm, 306 mm. Normally of course the piston rods would all be the same diameter, however the mixing of rod diameters Is not unknown and the abthty to adapt the scraper rings Figure 7 (f) to suit conditions Is Important to ensure continuous efficient operation.

Claims

Claims: 1 The Retro PolyDuplex System (RPDS) invention is a

technologicai step for-ward to efficiently scrape the maximwn amount of system oil from the piston rods of two stroke crosshead diesel engines in the Lower and Mid areas of the stuffing box, by using an entirely different approach to scraper design and a carrier ring system with m built oil reservoir for containing scraper seals, and for the first time to remove the ungainly and less efficient peripheral / garter springs from the stuffing box systems in operation currently on all two stroke crosshead diesel engines.
2 The RPDS scraper system as claim 1, uses a system of Belleville Washers on the special bolt designed for this application called a spheri-bolt, this bolt and the carrier ring flanges are loaded by use of Belleville Washers to maintain a constant load to compensate for expansion and Contraction during engine operation and close down, this constant is preferable to periphexy springs which tend to be dynamic during operation, can elongate, stretch and break
3 The RPDS scraper system as in claim 1 will be able to scrape off oil from the piston rod more effectively as there are no dynamic springs blocking the oil drain slots or holes as in a conventional system, on the piston rod up stroke the oil will be scraped off by oil exit through castellated slots directed by the lower scraper lip, and from the scraper lips via the drain slots to the carrier ring reservoir and directly then to the engine crankcase lube oil sump.
4 The Reiro PolyDuplex System as in claIm 1 composes of a carrier ring ma-chined with a 4 dovetail arrangement to hold the scraper ring with the male 4 dovetail fitting butts up to the limitation shoulder at the reservoir recess, the scraper ring sections are scarfed at 450 according to good seal practice for sealing reciprocating rods, the number of scraper sections can be 4 for new rods and up to 7 sections for rods with slight ovality.
RPDS as in claim 3 will be able to scrape oil from a piston rod efficiently as there are no barriers over the drain slots in either the scraper rings or the car-rier rings, and therefor the possibility of oil being drawn back onto the piston rod during operation Is reduced to a minimum, also the reservoir behind the scraper ring allows easy flow of oil away from the rod into the engine crank-case oil Bump.
6 The RPDS claim 3 is more efficient as there is no drawback onto the piston rod as occurs with conventional systems purely because the drain slots in the RPDS scraper rings and carrier ring do not impede the oil scrape off from the piston rod, therefor as the oil free flows down to engine crankcase sump it can not be drawn back on to the piston rod by suction of the piston rod as it travels through the stuffing box scraper/seal ring system.
7 Though the RPDS design as in Claim 1, is primarily intended for installation into existing design two stroke crosshead diesel engines it is equally adapta- ble into new designs of engine with the minimum of modification to the origi-nal concept of a scraper seal system that performs efficiently without the use of conventio periphezy / garter springs with adaptability to all forms of stuffing boxes in use and those in design stages for new engines.