Specifying the most suitable bearing for your vessel, as the seals and bearings experts, AtZ can specify and supply white metal aft and forward stern tube bearings, along with intermediate shaft bearings. Made of cast iron lined with white metal, they’re suitable for a variety of applications.
The Sterntube is a watertight tube enclosing and supporting the propeller shaft. It consists of a cast-iron or casted steel cylinder fitted with bearings within which the propeller shaft, rotates. The Sterntube bearings are typically oil-lubricated and usually consisting of two bushes pressed into the stern-tube. The bearing is a cast iron bush lined with a white metal having excellent load handling and lubricating property.
The Sterntube bearing serves an important purpose – to withstand load. The propeller which hangs at the aft end exerts load on the shaft, as do the rotational loads of the propellor shaft. All these loads are imparted on the Sterntube bearings.
White metal bearings as the name suggests are light in colour owing to the running surface of the bearing being made from lead historically and now tin based alloys. The backing element of the bearing is a harder shell made from steel which has the softer tin-based lining material deposited on it using a rotational moulding process with molten metal known as babbiting. The stiffer backing material provides structural support for the bearing while the softer lining gives optimum friction and wear properties.
Designed, installed and maintained correctly – white metal bearings can last the lifetime of a vessel – perhaps as long as 25 years. While the wear surfaces of the bearings are relatively thin compared to their thickness, when operating correctly the shaft is supported on a full fluid film which prevents any contact between the surfaces other than when they are at rest.
AtZ supply top quality bearings in tin and lead, white metal base with centrifugal castings. We provide ultrasonic non-destructive and Chalmers destructive test methods for proving white metal bonding integrity. Our bearings are available in all sizes to accommodate any vessel type or application and come with class inspection certification, on request.
AtZ offers on-site engineering support to project manage the full design, machining and installation of all sterntube bearing systems to the highest engineering standards for tolerance and fit. We utilise our own specialist engineers for the design and supervision of sterntube bearings incorporating shaft alignment protocols in accordance with class rules.
If the seawater has caused loss of hydrodynamic film, then you should see temperature spikes from your bearing sensors. Also, check your Sterntube oil sample in a laboratory, if there are traces of tin (from the white metal) it is likely they are damaged
The process may vary slightly dependent on the stern design of a vessel but generally would follow thus:
Drain sterntube oil and remove aft seal arrangement
Remove propellor and tail shaft
Check alignment of all bearings in sterntube
Remove damaged bearing
Check condition and dimensions of the sterntube inside diameter, in way of bearing.
Machine new bearing outside diameter to match sterntube bore, typically achieving an interference of 0.02 -0.05mm
Hydraulically press new bearing into sterntube ensuring cleanliness, lubrication and eradication of any sharp edges. Failure to adhere could result in pick up and damage to your new bearing
Once the bearing is in position and settled, re-check alignment of bearings
Insert tail shaft, mount seal and mount propellor
Fill sterntube with oil.
AtZ can typically manufacture, class inspect and deliver a new white metal bearing in less than 2 weeks, sometimes quicker.
Our team of technical experts offer industry-leading consultation services, equipment sales and support and with a wealth of project management and technical experience, we plan and deliver. We work with you to ensure a smooth project from design specification to onsite installation. Our impartial guidance and multi-supplier approach mean we are focused on finding you the best solution meaning you can be confident in both our services and products.
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