Contact Us
You are here: Home > Tech Blog

How to regrind the slitter knife, should we grind the outer circle or the surface?

Views : 2769
Author : Ping Cai
Update time : 2021-03-17 16:14:03
Slitter knife regrinding is crucial for coils processors. How to regrind the knife and how often to regrind the knife depends on the material and hardness of the knife and the material processed by each factory. Only by mastering the correct grinding method and finding the most suitable grinding cycle can the service life of the slitter knife be extended to the greatest extent, thereby saving production costs. Is it to grind the outer circle or to grind the surface? This is the first question we should think about.
To answer this question, we must first understand the manufacturing process of the knife, as well as the structure of the slitting machine and trimming machine. In the precision cutting slitter knife manufacturing plant, they have to take many complex technological measures to ensure the long-term and stable extremely high precision of the slitter knife, such as using multiple tempering to eliminate internal stress, and the experienced old workers will manually flatten it. Knife manufacturer spent a huge sum of money to purchase very precise machine tools and test equipment, so that the flatness, parallelism, verticality of slitter knife can be in the best level. Only in this way, the runout of the knife surface can reach micron level. For nearly all coils processors, it is impossible to reach this level. Therefore, when we regrind the knife, we must retain the extremely precise inner hole and the verticality of the surface processed by the original knife factory, which means that after the knife is reground, the surface runout of 1 ~ 2 μm level can be maintained. From this point of view, we can only regrind the outer circle of the knife. If you don’t know this reason, regrind the surface of the knife to regain the sharpness of the cutting edges. It is quite good to keep the surface runout at the level of 0.01mm, but for strip cutting, it is not enough.
After grinding the outer circle, in order to make the round knife still work normally, the center distance of the upper and lower axes must be adjusted. Therefore, all slitting machines have considered such a mechanism. But there are exceptions, that is the trimming machine. There are two types of edge trimming machines: the newer ones are all with adjustable center distance, and the edge trimming knives are reground by outer circle, so the thickness is thinner. The other is the non-adjustable center distance. In this case, its knife cannot grind the outer circle during regrind, but can only rely on the surface of the round knife. This kind of edge trimming machine is generally suitable for thick plates without high requirement for burrs, and its knife is relatively thick to ensure that the knife has sufficient regrind times and thus has sufficient service life. When regrinding the side surface of the knife, be careful not to use an ordinary surface grinder. Because this kind of grinder cannot guarantee the verticality of the axis of the inner hole of the knife and the surface, it cannot guarantee the runout of the knife after regrind. At this time, we must use a horizontal axis grinder with a rotating table. Even if this kind of machine is inaccurate, it may grind the knife into a concave dish shape or convex umbrella shape at most, but the main axis of the inner hole is always perpendicular to the surfaces, and the runout is still not so bad, which will minimize the impact on the cutting clearance. Figure 1 and Figure 2 are two photos of this machine.

Fig. 1 Rotary Table and Grinding Wheel of Surface Grinder

Fig. 2 Surface Grinder with Rotary Working Table