INTRODUCTION TO WORN SHAFT REPAIR
Shaft Wear and Damage
Shafts are a critical component of rotating equipment. Shafts are used to transmit power from one part to another or from a machine that produces power to a machine that absorbs power. Shafts are usually operated in immersed or semi-immersed conditions and are subject to damage by corrosion or chemical attack. In the mining industry, shafts can become worn or damaged due to vibration, friction and abrasive media. In the marine industry, gland packing and bushing damage to the shaft together with sand abrasion and sea water exposure can lead to erosion-corrosion on shafts. Additionally, oversized keyways, a crucial component that connects the rotating equipment to the shaft, may cause shaft dysfunction. Worn and damaged shafts can shut down the entire machine. Therefore, worn shafts may hamper or halt production and result in revenue loss.
Conventional Repair Methods of a Worn Shaft
Worn and damaged shafts are conventionally repaired using a hot process (welding/machining or hot metal spray/machining). If not carefully controlled, these conventional methods will cause residual damage to the shaft. They also require the disassembly of the machine. There are problems associated with welding and thermal spraying. Welding can create heat stresses that will tamper and distort the metal, lowering its load bearing capacity. Metal spraying can only be used to repair damage up to a few 1000s of an inch. These problems and limitations can be avoided by using a combination of polymer tehnology and proven Belzona application techniques.
The problems and limitations of conventional methods can be avoided by using a combination of polymers and proven Belzona application techniques. Belzona 1000 series polymers provide cold applied repair solutions, which can often be carried out in situ. Thus, downtime and production costs that can be incurred are minimized.
The Belzona solution requires that a surface be prepared to achieve a rough, irregular profile. The product is then easily applied with simple hand tools and allowed to cure. Since Belzona paste grade compounds are heat sensitive, the entire curing process can be accelerated by adding heat to the repaired surface. This helps reduce your repair time and allows the shafts to quickly return to service, thus minimizing downtime.
Worn Shaft Repair Drawing
Worn Shaft Repair Using a Former and Belzona 1111
For this repair, we used Belzona 1111 (Super Metal), a pre-fabricated stainless steel former, Belzona 9111 (Cleaner/Degreaser), Belzona 9411 (Release Agent), and a few tools from our machine shop. First, we cleaned the repair area, applied release agent onto the internal surface of the former and the area surrounding the repair area. Next, Belzona 1111 was thoroughly mixed and applied onto the internal surface of the former and the repair area of the shaft, forming a peak towards the center. Then, the former was clamped around the shaft and secured in place with fasteners. Exuded product was carefully removed. Once cured, the former was removed and the repair area was smoothed out with an emery cloth to eliminate any sharp edges.
SUPPLIES AND TOOLS NEEDED FOR A WORN SHAFT REPAIR WITH A FORMER AND BELZONA 1111
STEP-BY-STEP INSTRUCTION OF A WORN SHAFT REPAIR WITH BELZONA 1111
Step 1: Thoroughly clean the area to remove all the grease, dirt and other surface contaminants.
Step 2: Use a mechanical grinder fitted with a suitable disk to undercut the shaft by 1/16″ (1.5 mm) around the circumference.
Step 3: Clean the prepared area with Belzona 9111 (Cleaner/Degreaser) to remove all surface contaminants.
Step 4: Apply Belzona 9411 (Release Agent) to the internal surface of the former.
Step 5: Apply Belzona 9411 (Release Agent) to the area surrounding the repair area.
Step 6: Thoroughly mix Belzona 1111 until a uniform color, free of any streakiness, is achieved.
Step 7: Apply a thin layer of the mixed Belzona 1111 on the internal surface of the former.
Step 8: Apply a thin layer of the mixed material onto the shaft, pressing down firmly into the roughened profile.
Step 9: Form a peak towards the center of the application area.
Step 10: Position the former around the shaft.
Step 11: Secure the former in position with fasteners ensuring that the excess material is extruded from the ends of the former.
Step 12: Remove excess material and allow the applied material to cure.
Step 13: Once cured, carefully remove the bolts and the former.
Step 14: Smooth out the surface of the application area with an emery cloth.