Laminar cooling rollers are used in rolling mills for the transportation and laminar cooling of finished strips. During the transportation process of hot-rolled strips, laminar cooling rollers must not only withstand the load impact of the hot strips but also have high bonding strength guarantees. Wear properties of rollers.

Laminar Roller Laser Repair

1. Laminar flow roller repair needs

Laminar cooling rolls are used for conveying and laminar cooling of finished strips in rolling mills. They are located between the finishing rolling and curling machines. During the transportation process of hot rolled strips, laminar cooling rolls must withstand the load impact of the hot strips. At the same time, it must have high bonding strength to ensure the wear performance of the roller table. Traditional laminar flow rollers are manufactured using Ni60 spray welding technology, but the bonding strength between the Ni60 spray welding layer and the substrate is low and the working life is short.

In view of the working environment of the laminar flow roller table, laser cladding is used in the additive process for its remanufacturing. LC-SR-31 powder (hereinafter referred to as 31 powder) is selected as the laser cladding material. The metal roller surface material is 45# steel and the material at both ends is Q345D. Therefore, the hardness material required for surface cladding of conventional laminar rollers is used. Traditional submerged arc welding technology has large welding heat input and easy deformation of the workpiece; large base metal dilution rate and heat-affected zone, poor performance guarantee rate; pre-welding preheating and post-welding heat treatment are required, making the process complex and cumbersome. Laser cladding technology has small heat input during the cladding process, deformation of the workpiece, small dilution rate of the base metal, and small heat-affected zone, and no heat treatment is required after welding.

2. Repair technical requirements

• The metallographic sample is found to be defect-free (laboratory stage);
• The unilateral cladding thickness of the roller surface is 1.5-2mm, and the unilateral cladding thickness of the bearing part is 1.5mm;
• No defects in PT flaw detection;
• Meet the drawing size and accuracy requirements.
• The hardness of the working layer of the laminar cooling roller is 55-60HRC.

3. Laminar flow roller uses powder

The cladding material used in the laminar flow roller is LC-SR-31 powder (hereinafter referred to as 31 powder), with a particle size of 60-150um and a chemical composition as shown in Table 3.1.

4. Research content and technical difficulties

• Process performance:
  Based on the characteristics of the cladding material powder, by adjusting process parameters such as power, scanning speed, powder feeding amount, and overlap, a cladding layer without defects such as cracks, inclusions, and pores can be obtained to meet product quality requirements.
• Mechanical properties:
  According to the product requirements of hardness 55-60HRC, corrosion resistance, etc., the powder is selected for laser cladding to test the hardness, and a powder that meets the hardness requirements is obtained.
• Size inspection:
  As the laser cladding height progresses, there will be a tendency for the molten pool to move downwards. There is a thickness difference between a single layer and multiple layers of laser cladding on a flat plate. Therefore, each layer of cladding must be accurately measured after completion to ensure laminar flow. Machine-added size (the size before cladding is at least 1mm larger on one side than after machine-added).
• Technical Difficulties:
  Since the laminar flow roller table is hollow and requires high surface hardness, the size shrinkage is relatively large before and after laser cladding, which can easily cause cracks.

5. Test results

Metallographic:
According to GB/T 13298-2015, the metallographic test of the simulated parts is shown in Figure 5, and the corrosive liquid is aqua regia. As can be seen from Figure 3.1, there are no defects such as cracks, pores, or lack of fusion on the surface of the tissue.

Hardness Testing:
The hardness test results are shown in Table 3.2. According to the hardness test results, the average Rockwell hardness of the cladding layer is 57.8HRC, the average Vickers hardness of the heat-affected zone is 173.6 HV, and the average Vickers hardness of the base material is 166.5 HV.

6. Industrialization stage

• Clamping:
  A horizontal turntable is used for clamping. Compared with a turntable, the horizontal turntable clamping can effectively reduce the impact of circular runout on cladding, and will not provide support on the cladding surface. It will not be used during the second layer of cladding. There may be an overall jump of the workpiece due to the unevenness of the first layer.
• Sanding and cleaning:
  Use angle grinder and steel brush for grinding and cleaning to remove rust and oil on the surface of the workpiece.
• Cleaning:
  Use alcohol, copper brush and dust cloth to clean to remove oil stains on the surface of the workpiece.