Das Sandstrahlverfahren beherrschen: Optimale Oberflächenbehandlung erreichen

August 27, 2024

The sandblasting process is a crucial step in surface treatment, determining the final quality and performance of the workpiece. From setting up the sandblasting equipment to every detail of the operation, it requires not only technical support but also the meticulousness and precision of the operator. This article will guide you through the various aspects of the sandblasting process, helping you master this process from start to finish to ensure each operation achieves the desired results.

Preparation for Sandblasting

Preparing for sandblasting is key to ensuring the final treatment effect and workpiece quality. This process can be divided into the following important aspects: workpiece preparation, selection of sandblasting media, and equipment selection and setup.

1. Workpiece Preparation

Before sandblasting, initial cleaning of the workpiece is crucial. The cleaning steps can remove grease, dirt, rust, or other loose surface materials to ensure the uniformity and effectiveness of the sandblasting. Different materials of workpieces have different preparation requirements:

• Metal Workpieces: First, remove surface grease and dirt using solvent cleaning, mechanical scrubbing, or chemical cleaners. For iron workpieces, rust removal is usually done with brushes or chemical agents. The cleaned workpiece should be thoroughly dried to avoid residual moisture affecting the sandblasting result.
• Plastic Workpieces: Plastic is relatively fragile and needs careful handling. Use mild cleaners and soft cloths to wipe the surface, removing grease and dirt. For stubborn stains, use specialized plastic cleaners. Be especially careful with rough brushes or strong cleaners as they may damage the plastic surface.
• Ceramic Workpieces: Ceramic workpieces are relatively hard and typically have natural grease or dust on the surface. Use a soft brush or air flow to blow away the dust, then wash with warm water and neutral detergent, and finally, thoroughly dry.

2. Selection of Sandblasting Media

The choice of sandblasting media directly affects the sandblasting process and final results. Therefore, selecting the appropriate sandblasting media based on workpiece material, desired surface effect, and treatment requirements is crucial. Common sandblasting media include:

• Aluminium-Oxid: With high hardness and wear resistance, suitable for applications requiring strong abrasion, ideal for treating metal surfaces, removing oxides, or old coatings. Due to its higher cost, it is usually used for high-end applications or special treatments.
• Glasperlen: Softer, suitable for fine surface treatments, such as consumer electronics housings. Glass bead sandblasting effectively removes surface contaminants, improves surface smoothness, and does not cause excessive wear to the workpiece.
• Ceramic Media: With moderate hardness, between aluminum oxide and glass beads, suitable for processes requiring higher surface roughness. Ceramic media are often used for deburring or surface strengthening of metal parts, providing uniform roughness and good durability.
• Stahlkugel: Suitable for large-scale metal surface cleaning, such as steel structure anti-corrosion treatment. Steel shot is hard and wear-resistant, effectively removing rust and old coatings.

3. Equipment Selection

The choice and setup of sandblasting equipment also impact the sandblasting effect. Major types of equipment include:

• Pressure Feed Sandblasting Equipment: Uses compressed air to deliver abrasives to the nozzle, suitable for applications requiring high flow and pressure. Equipment usually includes air pressure control, abrasive storage, and nozzle components. When setting, adjust the blasting pressure, typically between 4 to 8 bar, depending on the treatment requirements.
• Suction Feed Sandblasting Equipment: Utilizes air flow to draw abrasives into the nozzle, suitable for smaller workpieces or precise operations. When setting, adjust the nozzle diameter and blasting angle, which are usually more flexible and adjustable as needed.

4. Equipment Parameter Settings:

• Blasting Pressure

Blasting pressure is one of the core parameters in the sandblasting process, directly affecting blasting speed and treatment effect. Blasting pressure is typically measured in pressure units (e.g., psi or bar). In the sandblasting process, the blasting pressure determines the impact force of the abrasives. Higher blasting pressure increases the speed of abrasives, enhancing their impact on the workpiece surface and removal efficiency. However, excessive blasting pressure may cause over-wear or even damage to softer or finer workpiece surfaces.

• Nozzle Diameter

The nozzle diameter determines the spraying range and uniformity of abrasives. The diameter of the nozzle is usually measured in millimeters. Larger nozzle diameters (typically between 6-12 mm) increase the coverage area and improve treatment efficiency, suitable for large surface tasks such as rust removal from metal bodies or cleaning concrete surfaces. However, a larger nozzle diameter may cause uneven blasting, especially for finer surfaces, leading to over-treatment or under-treatment in some areas.

• Blasting Angle

The blasting angle is another important parameter in the sandblasting process, set by adjusting the equipment bracket or nozzle itself. The blasting angle directly affects the direction and uniformity of abrasive impacts. Typically, the blasting angle should be adjusted based on the workpiece’s geometry and treatment requirements to ensure even surface treatment. The angle can influence the fineness of the sandblasting effect. Common blasting angles range from 30° to 90°. When the nozzle is perpendicular to the workpiece surface (90°), the impact force of abrasives is strongest, suitable for thorough cleaning of flat surfaces. This angle ensures abrasives evenly strike the entire surface, especially for large or uniform surfaces; larger blasting angles (60°-90°) are suitable for large-scale cleaning but may cause uneven local treatment; smaller blasting angles (30°-45°) are suitable for detailed treatment, providing higher surface quality.

By accurately adjusting these parameters, the sandblasting process can achieve more efficient and precise surface treatment, meeting the needs of different application fields. Understanding and mastering these parameter settings are crucial for optimizing sandblasting effects and improving production efficiency.

Careful attention to the above preparation work ensures the smooth execution of the sandblasting process, achieving the desired treatment effect.

Specific Sandblasting Operation Process

• Setting Blasting Parameters:
  • Pressure Setting: Discuss how to set the blasting pressure based on workpiece material and media type, and the impact of setting pressure too high or too low.
  • Blasting Angle and Distance: Analyze the relationship between the blasting angle and the workpiece surface’s flatness and roughness, and the impact of distance on treatment effects.
  • Nozzle Movement Speed: Explain how the speed of the nozzle’s movement across the workpiece surface affects the uniformity and efficiency of sandblasting.
  • Workpiece Positioning and Fixing: Ensure the workpiece remains stable during sandblasting for a uniform surface treatment effect.
  • Common Workpiece Fixing Methods and Devices: (See image below)

• Sandblasting Operating Procedure:
  • Start Blasting:  Start the sandblasting equipment, gradually increase the blasting pressure to the set value. Begin blasting from one end of the workpiece and move gradually to the other end, ensuring the entire surface is covered. Maintain smooth movement of the nozzle, avoid staying in one position too long to prevent over-wear, and ensure comprehensive coverage, including edges and hard-to-reach areas.
  • Check Surface Condition: Regularly check the workpiece surface during processing to ensure it meets the desired roughness or cleanliness. Adjust blasting pressure, nozzle angle, or nozzle diameter as needed based on inspection results to optimize treatment effects.
  • Multiple Passes:  If necessary, perform multiple passes, especially for complex surfaces, where step-by-step treatment may be more effective.
• Post-Sandblasting Treatment and Inspection:
  • Post-Sandblasting Cleaning: Use air blowers, brushes, or vacuum cleaners to remove residual abrasives and dust from the workpiece surface. Carefully check to ensure no residual abrasives or other impurities are left on the surface.
  • Surface Inspection and Measurement: Use surface roughness measuring instruments to check the surface quality of the workpiece, ensuring it meets the requirements. If surface treatment is uneven or incomplete, perform necessary repairs or additional sandblasting.

Common Detection Instruments Include:

1. Surface Roughness Measuring Instruments: Includes contact-type roughness gauges (which record surface variations via a probe) and optical roughness gauges (which use lasers or optical systems for non-contact surface measurement) to evaluate the surface roughness of sandblasted workpieces by comparing test values with set standards.
2. Roughness Testers: Includes handheld roughness meters (convenient for field operation and suitable for different workpiece shapes) and benchtop roughness meters (suitable for laboratory environments, providing higher measurement accuracy) to record roughness values and compare with design requirements.
3. Profilometers: Mainly used for measuring workpiece surface profiles and shapes to ensure consistency in sandblasting treatment.
4. Abrasive Particle Size Analyzers: Used to measure the particle size distribution of sandblasting media to ensure media compliance with requirements.
5. Pressure Gauges: Measure air or fluid pressure in sandblasting equipment to ensure it operates within the set range.
6. Thermometers: Measure the humidity of the sandblasting environment to prevent moisture from affecting sandblasting effects and abrasive quality.
7. Gas Flow Meters: Measure the gas flow during sandblasting to ensure stable blasting effects.
8. Wear Testers: Measure the degree of wear of the workpiece surface by abrasives during sandblasting to ensure wear is within allowable limits.

Maintenance of Sandblasting Equipment

• Clean the Equipment: Regularly clean the sandblasting equipment, especially the nozzles and pipes, to prevent clogging or wear.
• Check for Wear: Inspect various parts of the sandblasting equipment, such as the nozzles, pressure gauges, and pipes, to ensure they are functioning properly.
• Replace Nozzles: Replace nozzles regularly based on usage, especially when the sandblasting effect deteriorates.
• Maintain Equipment: Perform maintenance and upkeep according to the equipment manufacturer’s recommendations to ensure long-term stability and performance.

Common Problems in Sandblasting Process and Their Solutions

• Incorrect Media Selection: Using media that is too coarse or too fine may cause surface damage or insufficient processing. Therefore, first ensure the distance and angle between the nozzle and the workpiece are consistent, then adjust the nozzle diameter to make the spray pattern more uniform, and lastly, regularly check and clean the sandblasting equipment to prevent clogging or uneven spraying.
• Nozzle Wear and Clogging: Nozzles are prone to wear under high-pressure spraying, which can reduce sandblasting efficiency and cause uneven media dispersion. Use nozzles made of wear-resistant materials, such as boron carbide or tungsten carbide. Control the spraying pressure during use to avoid accelerated nozzle wear due to excessive pressure. Remember to regularly check the condition of the nozzles and replace those that are severely worn.
• Insufficient or Fluctuating Equipment Pressure: Improper control of spraying pressure can lead to uneven surface treatment or increased equipment wear. If necessary, use a pressure regulator to precisely control the spraying pressure, avoiding pressure that is too high or too low. Adjust the pressure to an appropriate range based on the material and shape of the workpiece. Regularly check the pressure system as well.
• Safety Issues for Sandblasting Operators: If operators do not take appropriate safety measures during sandblasting, it may lead to personal injury. To avoid this, provide comprehensive safety training for operators, emphasizing operational procedures and protective measures. Ensure operators wear necessary protective gear, such as gloves, goggles, and protective clothing, during equipment operation.
• Low Efficiency of Media Recovery: Low media recovery efficiency can increase production costs and may affect the environment. Optimize the sandblasting equipment’s recovery system to ensure effective recovery of media after use. Additionally, regularly check and clean the recovery system to prevent clogging or damage, or use high-quality media that can be recycled multiple times.

 

Mastering the sandblasting process involves careful preparation, accurate equipment setup, and precise operation. By understanding and controlling the parameters of sandblasting, such as pressure, nozzle diameter, and angle, as well as regular inspection and maintenance, you can achieve optimal surface treatment results. Whether for cleaning, deburring, or surface finishing, mastering the sandblasting process ensures that each operation meets the highest standards, contributing to the overall quality and performance of the workpiece.