Taking the high-quality mirror-finished roller as an example, a wet belt polishing machine is used to focus on polishing the roller surface before electroplating to reduce shading and ensure surface roughness requirements. After electroplating, through grinding with abrasive belts of different meshes, a roller with stable coating thickness and mirror effect can be obtained.

The ironing roller is one of the important parts of the ironing machine. The roller is usually made of low carbon steel seamless pipe. In order to make the fabric surface have a high gloss, the surface of the roller requires hard chromium plating. The surface roughness value Ra=0.01~0.025μm is required, and the mirror effect is achieved after polishing.

General processing methods include mechanical polishing, electrolytic polishing, etc. For the roller with an outer diameter of 415 mm, a mechanical abrasive belt polishing method was used to obtain a mirror roller with a surface roughness value R a = 0.02 μm. During the processing, it was found that the quality of rough polishing before electroplating has an important influence on the fine polishing after electroplating. By controlling the rough polishing quality, a high-quality hard chromium layer mirror polishing effect can be obtained.

Analysis of roller processing problems

The roller is made of 20# seamless steel pipe. Since there are edges on the surface of the roller, its function is to beat and comb the rough surface of the fabric. Therefore, the edges cannot be squeezed by force during the processing, and it must be ensured that there are no round edges during grinding. The corners appear. At the same time, during the abrasive belt polishing process, due to the existence of ribs, the polishing head is in an intermittent polishing state. Therefore, abrasive belt shading often appears during the surface changing process, especially during rough polishing, which will appear on the surface of the roller. Continuous shading of varying shades. Because if the surface roughness cannot be guaranteed before electroplating, it will be difficult to process to achieve a mirror effect after being covered with a high-hardness chromium plating layer, so the shading process before electroplating is crucial.

Process analysis

The process route after roller grinding is:

grinding → rough polishing → electroplating → fine polishing → subsequent processing.

After the roller is ground, the surface roughness value reaches Ra=0.8μm, and the processing marks are slightly discernible on the surface.

After the roller is fixed and debugged on the polishing machine, the roller surface must be cleaned to prevent grinding wheel particles from adhering to the roller surface, otherwise the final mirror effect may be affected.

Adjust the head swing frequency according to the mesh number of the abrasive belt, the specific rough polishing → electroplating → fine polishing process.

When polishing, the abrasive belt surface reciprocates in the axial direction perpendicular to the roller surface. After polishing the 250# abrasive belt twice, the roller surface will have continuous radially distributed shading. At the same time, the roller surface will have a dark glossy surface, which is darker than before. There are obvious differences in the grinded roller. This kind of shading is mainly caused by the different sizes of sand grains on the surface of the abrasive belt. The lower the mesh number of the abrasive belt, the higher the particle non-uniformity, and the more obvious the traces left on the surface of the roller during polishing. At the same time, the roller surface runout also has an impact on polishing. To a certain extent, the runout affects the pressure of the abrasive belt on the roller surface, resulting in different shades of shading.

For the special roller of the ironing roller, the shading mainly exists near the edges. The intermittent contact between the abrasive belt and the roller surface will cause the grinding degree of the sand grains at the notch to be higher than that at the roller surface. At the same time, the roller rotates It is easy to turn the edge into an arc edge, so it is very important to control the contact pressure between the abrasive belt and the roller surface. After polishing with 500# and 1000# abrasive belts, the shading is refined. When light shines on the roller surface, it is diffusely reflected by the shading. It needs to be observed along the direction of the light, and compared with the surface roughness standard sample to determine whether Need to use 1500# abrasive belt for polishing.

After rough polishing, the surface roughness value Ra is guaranteed to be less than or equal to 0.1μm, and the processing marks are basically invisible on the surface. A 1500# abrasive belt shading is allowed in the direction facing the light.

After electroplating, the surface of the roller appears bright and shiny, but the shading still exists. The surface roughness value before electroplating is directly proportional to the surface roughness value after electroplating, and the thickness of the plating layer also affects the surface roughness of the roller surface after electroplating.

The increase in coating thickness makes the roller surface rougher. According to the current peak effect, the current density is high at the peak bulges of the microscopic unevenness of the workpiece substrate. The electroplated metal ions are deposited there first, causing the coating to thicken quickly at the peak. As the electroplating time increases, the coating becomes thicker and the surface Becoming rougher, the coating thickness is required to be ≥80μm.

The electroplated roller is fixed on the polishing machine for final processing. Different from the previous rough polishing, the lower limit of the head swing frequency is selected during fine polishing, so as to allow the new abrasive belt to contact the roller surface as much as possible to improve the shading removal rate. After polishing with abrasive belts of different mesh sizes, confirm the surface roughness of the roller surface before final glazing (surface roughness value Ra≤0.03μm). If it is not reached, continue polishing with a 1500# abrasive belt. 3000# polishing sanding belt can basically remove the residual shading. Finished roller.

This time, a wet belt polishing machine was used to focus on processing the roller surface before electroplating. By controlling the rough polishing quality, a high-quality mirror polishing effect of the hard chromium layer was obtained.

1) The lower the surface roughness value of the roller surface before electroplating, the lower the surface roughness value of the electroplated layer, and the fewer shading in the subsequent fine polishing process, making it easier to obtain a high-quality mirror roller. Abrasive belts of different mesh sizes can gradually refine the shading until it is basically removed.

2) The roller and the polishing belt rotate in opposite directions, which can improve the grinding efficiency while protecting the edge notches.

Diamond sanding abrasive belt can be widely used for grinding steel, stone, glass, ceramics, monocrystalline silicon, polysilicon, zirconia, alumina, metal-nonmetallic synthetic materials, cemented carbide, aluminum-magnesium alloy, aluminum beryllium alloy, titanium alloy and etc. hard brittle materials. Moresuperhard have resin and electroplated diamond abrasive belt for polishing thermal spray  coating.

---EDITOR: Doris Hu

---POST: Doris Hu