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Which is best for heating roller surface treatment? Hard chromium, Teflon or ceramics?

2020-07-27 20:36:17

The common treatment methods of roller surface include chromium plating, Teflon spraying and ceramic spraying. There are often people tangled, which one is better?


Let's start with the characteristics of these methods.


        Among the three methods, chromium plating is the most commonly used. Chromium electroplating is divided into two categories: decorative chromium and hard chromium. The plating on the surface of the roller is basically hard chromium.


The thickness of chromium plating is mostly 0.1 ~ 0.2mm. Of course, it can be thicker or thinner, depending on the needs. If it is a hot roller, it is generally recommended not to be too thick. The main reason is that the coefficient of thermal expansion of chromium is relatively small, only half of that of steel. If it is too thick and heated quickly, it is easy to cause cracks on the surface of chromium layer. Therefore, the chromium layer thickness of most hot rollers is less than 0.012 mm, and the chromium layer of high temperature roller is as low as 0.03 ~ 0.05 mm. If it is an ordinary roller, there is no such requirement, and thickening the chromium layer is a common method to compensate for insufficient diameter.


The surface of the chromium coating is not good-looking and rough, which requires fine grinding. If you want to be mirror like, you have to polish it. After polishing, the roughness of chromium layer can be very high, up to grade 14 (RA < 0.0125 mm). Hard chromium can work stably at 500 ℃.


There are two types of Teflons:
       1) . PTFE: usually green, some gray. PTFE also known as "king of plastic", chemical name is polytetrafluoroethylene. The spraying thickness is generally 0.03-0.04mm;
       2) . PFA: gray, spraying thickness is generally 0.05-0.06mm, or thinner.


The surface roughness of Teflon is not high, most of which are in the range of ra0.5 ~ 1.5. However, due to the chemical properties of Teflon surface, it is usually used in occasions where anti sticking is needed. Subject to the melting point of Teflon (usually in 300 ~ 320 ℃), its using temperature is usually not higher than 260 ℃.


There are many kinds of industrial ceramics, the most common is tungsten carbide (WC). It can achieve mirror surface (Ra0.025 ~ 0.03), the coating thickness is generally ≥ 15 wires (0.15mm), and the maximum thickness can reach 30-40 wires (0.3-0.4mm). The hardness is high, which can reach hrc75 ~ 76. But the price is expensive, the unit area price is about 10 times that of chromium plating or spraying Teflon.


There are two main ceramic thermal spraying methods: HVOF spraying and plasma spraying. Conventional HVOF spraying materials: WC-12% Co; WC-20Co-7Ni; WC-10Co-4Cr; Cr3Cr2-20 ~ 25% NiCr; 316 stainless steel; Ni series superalloy, etc. Conventional plasma spraying materials: Al2O3; Al2O3-3% TiO2; Al2O3-13TiO2; Al2O3-40TiO2; Co2O3; ZrO2-8% Y2O3; TiO2, etc. The surface roughness of sprayed ceramics is better than that of fluorone, but not as good as that of hard chromium. Considering WC, the best roughness is about Ra0.025


Generally speaking, hard chromium plating is the most common method with high cost performance; the main purpose of spraying Teflon is anti sticking; spraying ceramic has many functions, among which the most used is wear resistance.


Which is better, or according to the needs of their own technology.

 


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