Propeller Shaft Repair

Bearing Area Buildup

Worn bearing areas can be repaired with reasonable success by utilizing one of the two following methods:

Metalizing (either oxyacetylene arc-spray or plasma flame methods)

This method requires the work temperature to be low, approximately 200 to 400 Fahrenheit (93 to 204 Celsius), to minimize distortion.  The bond to the pre-roughened area is mostly mechanical. The plasma flame process gives the densest coating as oxide formation is kept to a minimum. Type 304 stainless is the most readily available coating to be considered for metalizing propeller shafts. The effect on the base metal is regarded to have little or no effect. A problem may arise with regards to the questionable reliability of the shaft coating bond.

Weld Overlay Fusion Process

A metallurgically intact bond is attainable when matching fillers are used in combination with the appropriate expertise for weld overlay and full welded joints. No pre-heating is necessary. To lessen distortion, a semiautomatic process (gas metal arc) is utilized by clamping a welding torch to a lathe tool holder for indexing as the shaft rotates in the lathe under the weld head. If this is not possible, longitudinal  verlay weld beads may be placed alternately 180 degrees opposite the previous overlay. For WBM shafts, matching weld overlay fillers are preferred. If availability is a problem, there are alternate fillers as shown in the Matching Filler Table. However, the alternate fillers may not possess the hardness, strength and corrosion resistance as that of the base metal.

A note of caution is noted with regards to the weld overlay fusion process for Aqualoy 17 alloy. Welding Aqualoy 17 will create a small area of untempered martensite in the shaft which results in lower ductility. However, this area of the shaft should be adequate for normal sea  water service. To restore the mechanical properties of the weld area to almost that of the shaft, perform a post-weld heat treatment at 1150 degrees Fahrenheit (621 degrees Celsius) for four hours. Re-straightening the shaft will most likely be necessary after this process.  Aqualoy 19 and Aqualoy 22 in their as-welded conditions have mechanical properties which closely match the base metal in diameters 3 inches (76mm) and over. Under 3 inches (76mm) diameter, a decrease in such properties will most likely occur. Additionally, Aqualoy 22 retains basically the same corrosion resistance properties when overlaid using the matching fillers. When welding dissimilar metals, it is recommended the matching filler or alternate filler for the particular grade be used.

Straightening

One technique often used to improve straightness is heat straightening. However, special consideration must be given to limiting the temperature to 1000 degrees Fahrenheit (538 degrees Celsius) in order to avoid introducing changes in metallurgical structure. These changes may have a detrimental impact on the mechanical properties and corrosive resistance of the shaft which could result in premature failure. The use of Tempil sticks is recommended to avoid excessive temperatures. If possible, cold straightening is preferred.  While this method requires a separate piece of equipment, it will not affect the metallurgical structure of the steel.