The introduction of cylinder superfinishing has become widely adopted to guarantee a consistent high-quality print. For this reason printing cylinders are of paramount importance to the rotogravure and flexographic production processes where quality improvements are continuously demanded.
The superfinishing method is strongly influenced by the type of printing process whether it be rotogravure or flexographic.
Both these technologies use printing cylinders which are manufactured and applied in different ways. The cylinders are in continuous development in order to improve the print quality of the finished product and the efficiency and competitiveness of the overall print process.
Rotogravure is a type of intaglio printing which requires the engraving of the printed image onto an image carrier. This image is engraved onto the cylinder which like the flexographic process is then installed into the rotary printing press.
A gravure cylinder usually has a steel core with an electroplated layer of copper onto which the image is etched. The surface of the copper layer is then finished to the required dimensional and surface specifications whilst removing any inaccuracies inherent in the copper plating.
Superfinishing technology is an additional operation to grinding. Cylinder superfinishing using micro-abrasive film is a highly recommended method to remove excess copper which may occur in the plating process particularly on the cylinder edges. Due to the soft nature of the bonding system necessary for a grinding application, damage to the grinding wheel can easily occur.
Superfinishing of copper plated cylinder
After copper plating and polishing, the gravure cylinder is engraved and then chrome plated to increase surface hardness and to lower the coefficient of friction.
Due to the thinness of the chrome layer, any damage or defect in the copper plating not removed by the polishing process cannot be corrected by chroming.
Following chrome plating, an additional superfinishing process is required to regenerate the surface roughness created on the copper in order to guarantee Rz consistency; the roughness of the surface is essential to prevent doctor blade wear or damage – if too smooth, the surface does not allow enough lubrication for the doctor blade and results in excessive chrome wear.
Superfinishing of chrome plated cylinder
Gravure cylinders have applications in markets with high volume production using fully automated machines running 24/7. The markets include flexible packaging, tobacco products, decoration and publishing. In order to reduce machine downtime for the replacement of the used superfinishing roll, we can advise the customer on the optimum length of roll in order to maximise production time. Standard lengths are always available, but we can also offer non-standard lengths to accommodate customer specific requirements.
Abrasive sheets are also available for manual application.
Anilox is a method used to provide a specific amount of ink to a flexographic printing plate.
An anilox cylinder usually has a steel or aluminium core which is ceramic coated by a thermal spray process.
The sprayed substrate must be ground and finished in order to remove any porosity in the surface, thus creating an ideal base for the subsequent laser engraving. It is advised to use diamond products for this process due to the hardness of the coating.
In order to achieve the required roughness and structure, cylinder superfinishing with diamond polishing film is used giving the customer a fast, reliable, easy to clean and free of contamination machining process when compared to other finishing techniques.
Today, anilox cylinders are laser engraved creating cells which, depending on the specification, determine the amount of ink to be transferred to the printing plate.
Laser engraving results in the cell walls having a rough finish.
Cylinder superfinishing with micro-abrasive film is a key process to remove the roughness of the re-casted materials and to achieve the required cell volume.
In order to meet the ever-increasing demand for improved print quality, the cells are becoming smaller. Consequently, the micro-abrasive film used in the superfinishing process must have the capability of producing a soft abrasive action to prevent damage to the thin cell walls without over polishing the surface.
Anilox cylinder superfinishing
Precision Polishing offers the best solutions even for the smaller screens, thanks to the extensive range of products and grit sizes available.
Precision Polishing will be exhibiting at ICE 2019 in Munich on March 12-14th Hall A5 Stand 1456. We will be presenting our complete portfolio for cylinder superfinishing focusing on printing applications.