Paper & Printing Industry
Thermal spray technology has found several useful applications in the paper and printing industry, contributing to improved equipment performance, durability, and overall production efficiency.
Thermal Spray application for paper & printing industry
Rollers and Cylinders
Wear Resistance:
In the paper manufacturing process, rollers and cylinders play crucial roles. For example, the press rollers in a paper machine are constantly in contact with the wet paper web, subjecting them to significant wear due to friction. Thermal spray coatings with materials like tungsten carbide or chromium carbide can be applied to these rollers to enhance their wear resistance. This helps maintain the proper surface finish of the rollers, ensuring consistent paper quality and reducing the frequency of roller replacements.
Corrosion Protection:
In some cases, especially in the presence of moisture or chemicals used in the papermaking process, rollers and cylinders may be prone to corrosion. Ceramic or corrosion-resistant alloy coatings via thermal spray can act as a protective barrier, preventing corrosive substances from reaching the underlying metal surface and thus prolonging the lifespan of these components.
Printing Press Components
Wear and Tear Reduction:
Printing press components such as printing plates, cylinders, and gears are subject to continuous wear during operation. Thermal spray coatings, such as those made of hard metals or ceramic composites, can significantly reduce wear and tear on these parts. For instance, a coating on the printing plate can maintain its sharpness and printing quality for a longer period, as it protects against abrasion caused by the ink and paper interaction.
Heat Dissipation:
Some printing press operations generate a significant amount of heat, which can affect the performance and lifespan of the components. Thermal spray thermal barrier coatings (TBCs), typically made of ceramics like zirconia, can be applied to relevant parts to reduce heat transfer. This helps in maintaining a more stable operating temperature, preventing overheating of components and potentially improving the overall efficiency of the printing press.
Drying Cylinders
Enhanced Heat Transfer:
Drying cylinders are used to remove moisture from the paper during the manufacturing process. Thermal spray coatings can be applied to the surface of drying cylinders to improve their heat transfer efficiency. For example, a coating with a high thermal conductivity material can help the drying cylinder absorb and dissipate heat more effectively, reducing the drying time and increasing the production rate of the paper machine.
Surface Protection:
The surface of drying cylinders may also face issues such as scaling or corrosion due to the high temperatures and moisture involved. Thermal spray coatings can provide protection against these problems, ensuring the smooth operation of the drying cylinders and maintaining their performance over time.
Cutting and Slitting Equipment
Wear Resistance:
Cutting and slitting equipment used to cut the paper into desired sizes and shapes experience significant wear due to the continuous contact with the paper. Thermal spray coatings with wear-resistant materials can be applied to the cutting blades and other components to improve their wear resistance. This helps in maintaining the sharpness of the cutting edges and reduces the need for frequent blade replacements, thereby saving costs and ensuring consistent cutting quality.
Corrosion Prevention:
In environments where the cutting and slitting equipment is exposed to moisture or chemicals, corrosion can be a concern. Thermal spray coatings can offer corrosion protection, keeping the equipment in good working condition and prolonging its service life.
Thermal Spray Techniques Used in the Paper & Printing Industry
1. Plasma Spray
Plasma spray is a commonly used thermal spray technique in the paper and printing industry. It creates a high-temperature plasma arc by passing an electric current through a gas (usually argon or a mixture of gases). The plasma arc melts the coating material, which is then sprayed onto the surface of the equipment in the form of fine droplets. Plasma spray is particularly suitable for applying ceramic coatings, such as those used for heat dissipation or surface protection on printing press components and drying cylinders. It offers precise control over coating thickness and quality, making it a preferred choice for applications where high precision is required.
2. Flame Spray
Flame spray is another thermal spray technique utilized in the paper & printing industry. It uses a fuel gas (such as acetylene or propane) and an oxidizer (usually oxygen) to create a flame that melts the coating material. The melted material is then sprayed onto the surface in the form of droplets. Flame spray is often used for applying coatings with a wide range of materials, including metals, alloys, and some ceramics. It is a relatively simple and cost-effective technique, suitable for on-site repairs or coating large surfaces where high precision is not as crucial. For example, it can be used to coat the exterior of large drying cylinders or to repair worn areas on rollers.
3. High-Velocity Oxy-Fuel (HVOF) Spray
HVOF spray is a thermal spray technique that combines high velocity and high temperature to deposit coating materials. It uses a mixture of fuel and oxygen to create a high-temperature, high-velocity jet that melts and accelerates the coating material towards the surface to be coated. HVOV spray is known for its ability to produce dense and high-quality coatings, especially with materials like tungsten carbide and chromium carbide. It is highly suitable for applications requiring wear resistance, such as coating the cutting blades of cutting and slitting equipment or the rollers of paper machines. The high velocity of the sprayed material results in better adhesion to the surface and a more uniform coating, which contributes to its excellent performance in enhancing wear resistance.
The Application Process of Thermal Spray in the Paper & Printing Industry
1. Surface Preparation
Before applying any thermal spray coating, the surface of the equipment must be properly prepared. This typically involves cleaning the surface to remove dirt, grease, rust, and other contaminants. For example, using solvents to clean oily surfaces or mechanical methods like sandblasting to remove rust and roughen the surface. The surface roughening is important as it improves the adhesion of the coating to the surface. In some cases, chemical etching may also be used to further enhance the adhesion, especially for certain types of coatings and materials.
2. Coating Selection
Based on the specific requirements of the equipment (such as wear resistance, corrosion resistance, or heat dissipation), the appropriate thermal spray coating material is selected. For example, if the goal is to provide wear resistance for a cutting blade, a coating material like tungsten carbide may be chosen. If it’s for corrosion protection of a drying cylinder, a ceramic or corrosion-resistant alloy coating may be selected. The selection also takes into account factors such as the operating environment, temperature range, and the nature of the interaction with other components.
3. Spraying Operation
Once the surface is prepared and the coating material is selected, the thermal spray operation is carried out. The spraying technique (such as plasma spray, flame spray, or HVOF spray) is used according to the requirements of the coating material and the application scenario. During the spraying process, parameters such as spraying distance, angle, velocity, and temperature are carefully controlled to ensure the quality of the coating. For example, in plasma spray, the plasma arc temperature and the spraying distance need to be optimized to obtain a uniform and high-quality coating. The spraying operation may be carried out in a dedicated spraying booth to control the spread of dust and fumes and to ensure a clean and safe working environment.
Benefits of Thermal Spray in the Paper & Printing Industry
1. Extended Equipment Service Life
By providing wear resistance, corrosion protection, and heat dissipation functions, thermal spray coatings can significantly extend the service life of paper and printing industry equipment. This reduces the need for frequent replacements and repairs, saving costs in the long run. For example, a printing press with properly applied thermal spray coatings on its components may last several years longer than one without such coatings.
2. Improved Equipment Performance
Thermal spray coatings can enhance the performance of paper and printing industry equipment in several ways. For example, wear-resistant coatings on rollers and cutting blades can improve the quality of paper production and cutting operations respectively. Heat dissipation coatings on printing press components can maintain a more stable operating temperature, preventing overheating and improving the efficiency of the printing press.
Enhanced heat transfer coatings on drying cylinders can reduce the drying time and increase the production rate of the paper machine.
3. Cost Savings
The extended service life of equipment due to thermal spray coatings means fewer replacements and repairs, which directly translates into cost savings. Additionally, improved equipment performance can lead to increased productivity, which further contributes to cost savings. For example, a paper machine with better heat transfer coatings on its drying cylinders can produce more paper in the same amount of time, thereby increasing revenue while reducing costs associated with production time.
In conclusion, thermal spray technology has become an important tool in the paper and printing industry, offering numerous benefits such as extended equipment service life, improved performance, and cost savings.