Repairing hardened gear teeth requires specific welding techniques and careful consideration of the gear’s material and condition.
In this blog post, we will provide a step-by-step guide on how to effectively weld repair hardened gear teeth.
We will cover the repair methods for surface damage, broken teeth, gear cracks, and permanent deformation. Each section will outline the necessary steps to ensure a successful repair.
Best Welding rod for Gear Tooth Repair
Gears are wear-out elements, so repairing gear teeth is necessary to restore the functionality of the mechanisms.
When it comes to selecting the best welding rod for gear tooth repair, it’s important to consider the specific requirements of the repair job.
The choice of welding rod depends on factors such as the type of gear material, the severity of damage, and the desired mechanical properties of the repaired gear tooth.
Here are some welding rods commonly used for gear tooth repair:
- Low Hydrogen Electrodes (AWS E7018):
Low hydrogen electrodes are a popular choice for gear tooth repair due to their excellent strength and low moisture absorption. They provide good impact resistance and produce high-quality welds with low hydrogen content, reducing the risk of cracking. These electrodes are suitable for repairing medium to high carbon steels commonly used in gear manufacturing.
- Nickel Electrodes (AWS ENiCrFe-2):
Nickel electrodes are often used for repairing gears made from nickel alloys or other non-ferrous materials. They offer excellent corrosion resistance and high-temperature strength. Nickel electrodes are suitable for repairing gear teeth that operate under harsh conditions or require resistance to wear and abrasion.
- Cobalt-Based Electrodes (AWS CoCr-A):
Cobalt-based electrodes are ideal for repairing gears made from heat-resistant alloys or those subjected to high temperatures and wear. These electrodes provide exceptional hardness and wear resistance, making them suitable for repairing gear teeth in high-stress applications.
- Stainless Steel Electrodes (AWS E309/E310):
Stainless steel electrodes are commonly used for repairing gears made from stainless steel or when a high level of corrosion resistance is required. They offer good strength, toughness, and resistance to heat and corrosion. Stainless steel electrodes are suitable for repairing gear teeth in applications where hygiene, chemical resistance, or elevated temperatures are a concern.
- Cast Iron Electrodes (AWS ENi-CI):
Cast iron electrodes are specifically designed for repairing gears made from cast iron. They provide good machinability and thermal conductivity, making them well-suited for repairing gear teeth in cast iron gearboxes or machinery.
Gear Weld Repair methodlogy
To develop a technology for surfacing and restoring gear teeth, you need to know the answers to the following questions:
- what area of the tooth needs to be fused with a restoration layer;
- what is a worn tooth surface: are there any cracks in the tooth, corrosion damage to the tooth, the amount of hardening of the tooth, possible remnants of the previous surfacing of the gear tooth;
— technology for removing damaged areas for surfacing;
— what wear loads will the restored part of the gear teeth be subjected to;
- what metal the gear is made of and the hardness of the teeth;
— what surfacing method is recommended for the gear material;
- what should be the temperature regime for surfacing the tooth and gear;
— sequence of technological operations when restoring teeth and gears;
— necessary equipment and materials for restoring the tooth profile;
— the required properties of the surfacing material for the gear tooth, its composition and diameter.
I. Repair Method for Surface Damage of Gear Teeth:
- End Face Reversal Method:
- Assess the gear’s wear pattern and determine if it is suitable for end face reversal.
- If the gear is symmetrical in the axial center plane, use the axial turning method to repair the worn tooth surface.
- Adjust the gear head, if applicable, to improve impact degree or replace worn-out parts.
- Surfacing Method:
- Evaluate the severity of gear wear, pitting, or spalling.
- Prior to welding, anneal the gear to relieve stress.
- Clean the gear surface thoroughly.
- Perform welding to build up the damaged tooth surface.
- Machine the welded area to achieve the desired profile.
- Apply heat treatment to restore the gear’s mechanical properties.
- Finish the repaired gear to ensure its functionality.
- Hot Forging Method:
- Identify gears with seriously worn working surfaces and reduced tooth thickness.
- Utilize hot forging to extrude metal from the tooth top onto the working surface.
- Achieve the required tooth thickness, considering machining allowances for shape repair.
- Apply a weld overlay on top of the gear teeth to complete the repair.
II. Repair Method for Broken Gear Teeth:
- Tooth Insert Method:
- Assess the extent of the broken tooth and ensure the surrounding teeth are intact.
- Determine if the gear’s precision and working speed allow for repair through the insert method.
- Use an appropriate insert to replace the broken tooth and ensure proper alignment.
- Splicing Method:
- Cut off the damaged part of the gear using gas welding or a toothless saw.
- Restore the deformed gear to its original shape using specialized tools.
- Obtain a replacement part from the same gear or create a new part with similar material and dimensions.
- Weld the replacement part into the notch, ensuring uniform pitch alignment.
- Perform mechanical processing on the welded area to achieve the desired finish.
- Surfacing Method:
- Analyze the broken tooth pattern before proceeding with the surfacing repair.
- Clear any cracks, especially fatigue cracks, before welding.
- Submerge the gear in water, exposing only the welding area to minimize heat influence.
- Use asbestos cloth to cover the adjacent surface near the welding area.
- Perform the surfacing welding to repair the broken tooth.
III. Repair of Gear Cracks:
- Repair of Gear Fatigue Cracks:
- For initial fatigue micro-cracks, drill passivation holes in front of the crack propagation to prevent further expansion.
- For more severe fatigue cracks, saw off the residual teeth along the crack propagation direction.
- Follow the repair method for broken teeth to address the fatigue crack and restore functionality.
- Repair of Gear Surface Cracks:
- Remove growing surface or subsurface cracks through grinding or filing.
- Ensure the removal of the deformation layer at the crack tip during the repair.
- Repair of Internal Gear Cracks:
- Localize and quantify internal cracks using non-destructive testing.
- Evaluate the residual life using fracture mechanics and determine the appropriate repair method.
IV. Repair of Permanent Deformation of Gears:
- Repair of Slight Plastic Deformation:
- File or trim burrs, small indentations, or ridges caused by slight plastic deformation.
- Consider surface strengthening or local hardening treatments, such as shot peening.
- Improve lubrication conditions if necessary.
- Repair of Serious Plastic Deformation:
- Utilize the end face reversal method or hot forging for gears with severe plastic deformation.
- Apply the appropriate repair method for the specific damage, while considering load and environmental factors.
- Repair of Serious Bending Plastic Deformation of Gear Shaft:
- Use pressure or cooling straightening methods, depending on the gear shaft’s diameter and deformation.
- Apply heat treatment for smaller gear shafts to overcome elastic failure and ensure straightening recovery stability.
How to repair a gear?
The appearance of malfunctions and defects in a gear requires urgent repairs, since the use of faulty gears leads to their destruction and mechanism failure. Gears are restored in various ways.
- When the teeth on one side wear out, the wheels are turned over. For asymmetrical elements, attach a bushing or trim the hub.
- A ring for the ring gear is made according to the size of the worn gear. The remaining part of the assembly is pressed onto it, the workpiece is ground, and the teeth are cut.
Gear repair by surfacing
The teeth are fused with rods using copper templates. The work is carried out using arc and gas welding. If the teeth are small, the material is welded in a continuous layer. After surfacing, thermal and mechanical treatment is carried out.
- To repair large wheels with a diameter of more than 5 mm, welding or linings are used. If cracks appear on the rim, they are welded, pulled together and fixed with pads that are secured with screws. The cracked hub is ground and a bandage ring is pressed onto it.
- Defects in the mounting hole are eliminated by boring and surfacing or installing a repair sleeve.
Restoring a gear by welding
- inserts in place of worn teeth, the crown is fixed by welding. When one wheel in the block wears out, the defective element is ground off, pressed on and a new part is welded.
- During operation of the gear train, the teeth may become jammed at the end. This defect can be eliminated by grinding or turning the end of the wheel.
- In transmissions with quiet running and low load, broken teeth are removed by milling. An insert is made according to the original dimensions of the tooth and installed in a milled groove. The element is fixed by welding and screw connections.
Repairing hardened gear teeth requires a systematic approach and adherence to specific repair methods.
By following the step-by-step guide outlined in this blog post, you can effectively weld repair hardened gear teeth, ensuring their functionality and extending their service life.
Always consider the gear’s material and condition, and consult industry standards and best practices for a successful repair.