Orkot Marine Bearings: Engineering Manual - Trelleborg.com.au

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Orkot ® Marine BearingsEngineering Manual for Rudder and Water Lubricated Propeller Shaft Bearings5. Manufacture a simple lance from 10 mm (.40") orsimilar copper tube, drill approximately twenty 1mm (.40") diameter holes through both walls ofthe pipe and fit a bleed valve to the pipe to controlthe flow of liquid nitrogen. Ensure that you sealthe open end of the lancee.The diagram (Figure 8) illustrates a method ofensuring the bush is square before the fitting starts.6. Place the plywood disk on top of the bearing,and connect the lance to a pressurised liquidnitrogen tank.7. Turn the valves to control the flow on nitrogenuntil vapour can be seen escaping, under pressurefrom the lance. If liquid starts to exit the lance thenthe flow should be reduced until it stops.8. Place the lance though the hole in the centre ofthe disk and into the bearing. Wrap the bearing inan insulating blanket to reduce energy loss from itssurface.9. During the procedure the nitrogen flow will need tobe monitored and adjusted from time to time.Measure the od at the top of the bearing periodically.Housing-1mmFigure 8: Method of ensuring the bush is squarebefore the fitting starts.Bearing operating temperature:-30°C-10°C-20°C 0°C6020mmstep10. Once sufficient clearance between the bearing andthe housing has been achieved then the bearingcan be transported to the housing for fitting.11. The apparatus used to transport the bearing afterfreezing will need to be resistant to the cryogenictemperatures they will encounter (e.g. polyesterslings) and suitable to support the weights involved.Tonnes504030201012. Ensure that the reduced bearing can be locatedquickly and easily. Once it comes into contact withany conductive surfaces the rate with which it willreturn to its original dimensions increases greatly.13. Slide the bearing into position, ensuring that it isheld there while its temperature normalises. Oncethe bearings surfaces have cleared of the ice thatforms on them during normalisation then anysupports can be removed.Method 3:Using dry ice and alcoholFreeze fitting using dry ice and alcohol will onlyprovide the required clearance when using very lightinterferences. As such it is rarely a viable method in itsown right and will often also require press fittingFitting with Hydraulic Press orCentre Pull JacksIf a bearing is to be press fitted, installers should ensurethat they have equipment available to deliver adequateforce to press the bearing fully into the housing. Theease of fitting will vary dependent on the finish of thehousing and this should be considered when calculatingthe force required. When press fitting a bearing it isimportant that it is in line and square with the borebefore the operation beings, an adequate chamfer onthe housing will prevent shaving of the bush.0150 250 350 450 550 650 750 850100 200 300 400 500 600 700 800Diameter (mm)Figure 9: Fitting force (Tonnes)Tons6655443322110Bearing operating temperature:-22°F-14°F-4°F 32°F6 10 14 18 22 26 3 344 8 12 16 20 24 28 32Diameter (inches)Figure 10: Fitting force (Tons)Figures 9 and 10 show the typical fitting force of abearing, length/diameter ratio 1:1An initial force to move the bearing may be higherthan given in the graphThe actual force will vary dependent on the conditionof the housing, leading chamfers and the length/diameter ratio.15
Orkot ® Marine BearingsEngineering Manual for Rudder and Water Lubricated Propeller Shaft BearingsBondingThe method of fixture will depend upon the designemployed, however the key point to be emphasisedhere is that in addition to traditional mechanicalfixing, Orkot ® materials can be bonded to both itselfand metallic substrates. Please note that if theassembly is to experience in excess of 60-70°C theninterference fitting should be replaced withadhesive bonding.Numerous adhesives are compatible with Orkot ® andhave been tested within our laboratory facilities.Generally the most suitable adhesives are:● Epoxies.● Acrylics .● Cyanoacrylates.● Polyurethanes.The following is a list of adhesive suppliers whoseproducts have been tested and are approved for usewith Orkot ® materials:● Araldite● Belzona● Bisonite● Chockfast● Loctite● PermabondFor specific details of bonding agents and conditionsplease contact our Technical department.General terms and preparations are requiredirrespective of the adhesive to be used.Terms:● The bonding agent is referred to as the adhesive.● The material/surface to which the Orkot ® is to bebonded is the substrate.● The distance between the Orkot ® and the substrateis the gap.● The ability of the adhesive to bridge and fill the gapis the gap fill.Preparations:● Suitable substrates are Orkot ® materials themselvesand various metals (including stainless steel).● Plastics such as polyethylene, polypropylene,polycarbonate, PVC, PTFE are unsuitable substratesfor bonding to Orkot ® materials.● The key to effective adhesion is in the preparationof the substrate and the material to be bonded.● Ensure no boundary layers such as oxides or greaseare present. Degrease with a suitable solventensuring local health and safety guidelines arefollowed. Orkot ® can be degreased by using a quickwipe with a solvent such as acetone, but exposure tothe solvent must be kept brief so as not to attackthe Orkot ® material. Oxides can be removed by useof fine abrasive paper or wire wool.● Roughen the surface. Ideally where metals areinvolved use shot blasting. Ensure any remainingparticulates are removed from the surface. Generallythe slightly fibrous surface of Orkot ® does notrequire roughening, though the use of abrasivepaper is acceptable so long as any dust is removed.● The assembled components may need support whilethe adhesive sets. This cure time will vary with theconditions under which the adhesive is used.Typically a rule of thumb is that the cure time willhalf for every 10°C increase in temperature.● In terms of assembly, avoid butt joints in favour oflap, so that loads applied to the adhesive joint willact across the assembly in shear.16
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