Laser Cladding Repair Process for Filter Press Shaft

As a key equipment for solid-liquid separation in industrial production, the stable operation of the filter press plays a crucial role in production efficiency and product quality. Shaft components, as the core transmission parts of the filter press, are prone to wear, deformation, and other failure issues due to complex mechanical stress, friction, wear, and corrosion during long-term high-load operation. Once a filter press shaft fails, it not only causes equipment downtime and production interruptions but may also result in significant economic losses. Traditional repair methods often have many limitations when addressing shaft failures, such as the tendency for welding repairs to cause thermal stress concentration leading to shaft deformation or even fracture, and the limited thickness and insufficient bonding strength of electroplated coatings, which are prone to peeling.

Laser cladding technology, as an advanced surface repair and strengthening technique, has been widely applied in the field of filter press shaft repair in recent years. This technology uses a high-energy laser beam as a heat source to rapidly melt and solidify specific alloy powders or ceramic powders with the shaft substrate surface, forming a high-performance cladding layer metallurgically bonded to the substrate. This effectively restores the shaft's dimensional accuracy and significantly enhances its wear resistance, corrosion resistance, and fatigue resistance, providing a new solution for the efficient and reliable repair of filter press shafts.

Laser Cladding Repair Process for Filter Press Shafts

1. Shaft Surface Pretreatment

<1> Cleaning

Thoroughly clean the surface of the filter press shaft using organic solvents (such as alcohol) to remove oil stains, dust, and other contaminants, ensuring the smooth progress of subsequent processes. After cleaning, ultrasonic cleaning equipment can be used to further enhance the cleaning effect and ensure surface cleanliness.

<2> Grinding

Use grinding tools (such as sandpaper or grinding wheels) to treat worn, corroded, or deformed areas on the shaft surface, removing the oxide layer, fatigue layer, and damaged layer to expose fresh metal substrate. During grinding, strictly control the grinding depth and roughness to avoid excessive damage to the substrate while ensuring a smooth surface for uniform cladding layer application.

<3> Nondestructive Testing

Use nondestructive testing methods such as magnetic particle testing, penetrant testing, or ultrasonic testing to conduct a comprehensive inspection of the cleaned and ground shaft to identify defects like cracks, pores, or sand holes on the surface or inside the shaft. Precisely mark the location and size of defects. For larger defects, pre-treatment such as mechanical removal of the defective area is required before laser cladding repair.

2. Cladding Material Selection

Selecting the appropriate cladding material based on the working environment, failure mode, and performance requirements of the filter press shaft is crucial. Commonly used cladding materials include nickel-based alloys, cobalt-based alloys, iron-based alloys, and ceramic particle-reinforced metal matrix composites.

<1> Nickel-Based Alloys

Nickel-based alloys offer good corrosion resistance, high-temperature stability, and oxidation resistance, making them suitable for repairing filter press shafts operating in corrosive or high-temperature environments. For example, using nickel-based alloys as cladding material in filter presses handling corrosive materials can effectively enhance the shaft's corrosion resistance and extend its service life.

<2> Cobalt-Based Alloys

Cobalt-based alloys exhibit excellent high-temperature hardness, wear resistance, and thermal fatigue resistance, performing exceptionally well under high-temperature, high-load, and severe wear conditions. For filter press shafts operating in high-temperature environments with frequent starts and stops, and subjected to significant mechanical stress and wear, cobalt-based cladding materials can significantly improve wear and heat resistance, enhancing shaft reliability and stability.

<3> Iron-Based Alloys

Iron-based alloys are relatively low-cost and offer high strength and hardness, making them suitable for general wear and moderate corrosion environments. For filter press shaft repairs where cost sensitivity is a concern and working conditions are relatively mild, iron-based alloys are an economical and practical choice.

2. Ceramic Particle-Reinforced Metal Matrix Composites

Ceramic particles (such as tungsten carbide WC or titanium carbide TiC) possess high hardness, excellent wear resistance, and good chemical stability. Composites formed by adding ceramic particles to a metal matrix combine the high wear resistance of ceramics with the good toughness of metals, significantly improving the hardness, wear resistance, and erosion resistance of the cladding layer. For filter press shafts facing severe abrasive wear, using ceramic particle-reinforced metal matrix composites as cladding material can effectively resist solid particle erosion and wear, significantly extending the shaft's service life.

3. Laser Cladding Operation

<1> Determining Process Parameters

Through preliminary testing and simulation analysis, combined with the shaft material, dimensions, repair area, and selected cladding material characteristics, determine the optimal laser cladding process parameters, including laser power, scanning speed, powder feed rate, spot diameter, and overlap rate. These parameters are interrelated and decisive for the quality and performance of the cladding layer. For example, excessively high laser power may cause overheating of the molten pool, leading to coarse cladding layer structure and defects like pores and cracks, while too fast a scanning speed may result in insufficient melting of the cladding material, affecting the bonding strength between the cladding layer and the substrate. Therefore, repeated testing and optimization are necessary before actual operation to obtain the optimal parameter combination.

<2> Powder Feeding and Laser Cladding

After determining the process parameters, feed the selected cladding powder uniformly into the laser action area using a powder feeding device. The main powder feeding methods are synchronous feeding and pre-placed powder. Synchronous feeding involves delivering powder directly into the molten pool while the laser scans, allowing real-time control of powder addition and synchronization with laser energy, which is conducive to obtaining high-quality cladding layers and is widely used in actual production.

As the laser beam scans the shaft surface along a predetermined path, the cladding powder rapidly melts under the laser energy, fusing with the thin surface layer of the shaft substrate to form a continuous and dense cladding layer. During the cladding process, closely monitor the state of the molten pool, such as its temperature, shape, and fluidity, and adjust process parameters to ensure the stability of the cladding process and the consistency of the cladding layer quality.

4. Post-Repair Treatment

<1> Heat Treatment

To eliminate residual stress generated during laser cladding, improve the microstructure and properties of the cladding layer, and enhance the bonding strength between the cladding layer and the substrate, perform appropriate heat treatment on the repaired filter press shaft. Common heat treatment methods include stress relief annealing and tempering. Stress relief annealing is typically performed at lower temperatures, holding for a period to release internal residual stress and prevent shaft deformation or cracking during subsequent use. Tempering treatment can adjust the hardness, toughness, and other mechanical properties of the cladding layer according to the material and performance requirements, ensuring it meets actual working needs.

<2> Machining

After laser cladding and heat treatment, the thickness and dimensional accuracy of the cladding layer may not fully meet usage requirements, necessitating machining. Use machining methods such as turning or grinding to precisely process the repaired area of the shaft, ensuring that dimensional accuracy, roundness, cylindricity, and other geometric tolerances meet design requirements. During machining, select appropriate tools and cutting parameters, control machining allowances, and avoid damaging the cladding layer to ensure the repaired shaft can fit well with other components and operate normally.

<3> Quality Inspection

Conduct comprehensive quality inspection of the repaired filter press shaft to ensure repair effectiveness and safe, reliable operation. Key inspection items include visual inspection, dimensional accuracy inspection, hardness testing, metallographic analysis, and nondestructive testing.

Visual inspection checks whether the cladding layer surface is smooth and free of obvious defects such as pores, cracks, or peeling. Dimensional accuracy inspection uses measuring tools (such as calipers, micrometers, or coordinate measuring machines) to measure key dimensions of the shaft, ensuring they meet design drawing requirements. Hardness testing uses a hardness tester to evaluate the hardness of different parts of the cladding layer and substrate, assessing the strengthening effect of the cladding layer. Metallographic analysis uses a metallographic microscope to observe the microstructure of the cladding layer, determining its uniformity, density, and bonding with the substrate. Nondestructive testing again employs methods like magnetic particle testing, penetrant testing, or ultrasonic testing to conduct a comprehensive inspection of the shaft, checking for internal defects in the repaired area and the entire shaft to ensure safety during use.

Conclusion

Laser cladding technology, with its unique advantages, shows broad application prospects in the field of filter press shaft repair. Through in-depth analysis of the failure modes and causes of filter press shafts and the adoption of a scientific and reasonable laser cladding repair process, it is possible to efficiently and accurately repair defects such as wear and corrosion, significantly improving the surface performance and service life of the shaft, thereby providing strong support for the stable operation of the filter press. With the continuous development and improvement of laser technology, along with ongoing research into cladding materials and processes, laser cladding repair technology for filter press shafts will continue to innovate and optimize, playing an increasingly important role in industrial production and helping enterprises achieve efficient, green, and sustainable development.