Which surface treatment is best for heating rollers? Hard chrome, Teflon, or ceramic?

Common surface treatments for rollers include chrome plating, Teflon coating, and ceramic coating. Many people wonder which one is better.

This requires discussing the characteristics of each method.

Of the three methods, chrome plating is the most common. Chrome plating is divided into two main categories: decorative chrome and hard chrome. The plating on roller surfaces is basically hard chrome.

The thickness of the chrome plating is usually 0.1-0.2mm, although it can be thicker or thinner depending on the needs. For heating rollers, it is generally recommended not to make the plating too thick, mainly because the thermal expansion coefficient of chromium is relatively small, only half that of steel. If it is too thick and the heating is too fast, it can easily cause cracking of the chrome layer. Therefore, the chrome layer thickness of most heating rollers is less than 0.012mm, and the chrome layer of high-temperature rollers is even as low as 0.03-0.05mm. For ordinary rollers, this requirement does not apply, and thickening the chrome layer is a common method to compensate for insufficient diameter.

The surface of the plated chrome layer does not look good; it is very rough, requiring precision grinding. To achieve a mirror finish, polishing is also necessary. After polishing, the chrome layer can have a very high surface roughness, up to level 14 (Ra < 0.0125mm). Hard chrome has a relatively high operating temperature and can usually work stably at 500℃.

Teflon comes in two types:

1). PTFE: Usually green, sometimes gray. PTFE is also known as "plastic king," and its chemical name is polytetrafluoroethylene. The coating thickness is generally 0.03-0.04mm;

2). PFA: Gray, with a coating thickness generally of 0.05-0.06mm, or even thinner.

Teflon has a low surface roughness, mostly Ra 0.5-1.5, but due to its chemical properties, Teflon surfaces are usually used in applications requiring non-stick properties. Due to the melting point of Teflon (usually 300-320℃), its operating temperature is usually no higher than 260℃.

There are many types of industrial ceramics, the most common being tungsten carbide (WC). It can achieve a mirror-like finish (Ra 0.025~0.03), with a coating thickness generally ≥15 microns (0.15mm), and a maximum thickness of 30-40 microns (0.3-0.4mm). It has high hardness, reaching HRC 75~76. However, it is expensive, with a price per unit area approximately 10 times that of chrome plating or Teflon coating.

There are two main methods for ceramic thermal spraying: supersonic flame spraying and plasma spraying. Common spraying materials for supersonic flame spraying include: WC-12%Co; WC-20Co-7Ni; WC-10Co-4Cr; Cr3Cr2-20~25%NiCr; 316 stainless steel; Ni-based superalloys, etc.

Common spraying materials for plasma spraying include: Al2O3; Al2O3-3%TiO2; Al2O3-13TiO2; Al2O3-40TiO2; Co2O3; ZrO2-8%Y2O3; TiO2, etc. The surface roughness of sprayed ceramics is worse than Teflon, but not as good as hard chrome. Taking WC as an example, the best roughness can only reach about Ra 0.025.

In general, hard chrome plating is the most common method, offering high cost-effectiveness; Teflon coating is mainly used for non-stick properties; ceramic spraying has many functions, the most common of which is wear resistance.

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