What is surface finishing?
Surface finishing is a series of industrial processes with the main goal to alter the surface of a certain workpiece in order to obtain specific properties. This can be performed chemically, mechanically, or even electronically with the aim of removing, altering, adding or reshaping the material that is being treated.
Industries that use surface finishing techniques
Surface finishing techniques are used by most industries that manufacture industrial parts (e.g., metals, wafers, tools, and more). The use of surface finishing processes has been on the rise globally and is expected to grow further. An article published by Grand View Research (2019) predicted that the market size for metal finishing chemicals is expected to grow to $13.52 billion USD by 2025.
People mostly think about polishing and sanding when surface finishing is brought up, but it is much more than that. Several industries use different processes to treat surfaces with the main objective of obtaining the highest product quality. According to Grand View Research, the top three industries with the biggest market share for metal surface chemicals are automotive and aerospace, semiconductors, and the metal industry (e.g., industrial machinery, construction).
Figure 1 (repurposed from Metal Finishing Chemicals Market Global Forecast to 2021) shows that surface finishing is mainly used in the automotive industry. Here, electroplating and electroless plating are the main processes used to protect against corrosion. The electroplating process consists of using electricity to coat a material (e.g., copper) with a thin layer of another material (e.g., nickel). Electroless plating is accomplished with chemical processes that reduce metal cations in a bath and deposit them as an even layer, even on non-conductive surfaces.
Next is the semiconductor industry, which includes the manufacturing and cleaning surface process of electrical and electronic parts as well as silicon wafers. This industry involves plating processes (e.g., electroless plating) as well as chemical cleaning baths. Chemical cleaning baths are used here to remove any contaminants from the wafer surfaces.
Finally comes the metal industry, responsible for creating the infrastructure that our modern world depends on. Here, the process of galvanization is used to make metal corrosion- and heat-resistant. Galvanization is an anti-corrosive measure taken with iron and steel (as well as other metals) by applying a protective zinc coating which does not allow oxidation to occur. The zinc also acts as a sacrificial anode which still protects the underlying metal in the event of a scratch in the galvanized surface. Pickling baths are another common surface finishing process for this industry. These acidic baths are used to remove the oxide layer which formed on the surface during the hot strip mill. If the base steel is over-pickled, it can result in pitting of the metal surface, leading to an undesirable rough, blistered coating in the subsequent galvanizing steps and also excessively consumes the pickling acid (e.g., HCl).
Much more than just decorative coatings
Do appearances matter? When talking about products, absolutely! One of the reasons product surfaces are treated is so they have a more pleasant appearance for consumers, but also for more technical reasons that go beyond looks. Since surface finishing processes are used in a broad range of industries, they serve different purposes depending on the uses of the final products.
In the semiconductor industry, any defect on the components (e.g., silicon wafers, microelectronics, printed circuit boards, etc.) can impact the performance of the final product. Therefore, maintaining the proper concentrations of all components in the chemical cleaning bath ensures a repeatable etching process, which for this purpose means the elimination of surface defects.
Another example includes phosphating baths, which are used to improve corrosion resistance of the product parts used in the automotive and aerospace industry. This process is performed prior to any painting to protect the body structure from environmental factors. Phosphating baths also need to be kept consistent to guarantee the correct (and identical) thickness of the protective layer in each of the products subjected to this process.
Check out our free webinar about how Process Analytical Technology (PAT) brings analytical measurements directly to the process for real-time decision-making, ensuring a high level of control for coating and finishing baths and eliminating unnecessary risk to plant personnel. Learn about real-world case studies and field-tested applications that demonstrate the advantages of optimized bath chemistry and PAT in the surface treatment industry.
Challenges in surface finishing processes: daily bath maintenance
Like any process, surface finishing has day to day challenges which can be improved upon. Improvement can only come from knowing the bath composition and how it affects the final product. Generally, monitoring the concentration of chemical baths is done via manual sampling and titration in a laboratory on site (in some cases, by a contract lab offsite). While this method works, it can lead to long waiting times from the moment the sample is taken until the final result—therefore the results are no longer representative of the current process conditions. Because of this delay, bath replenishment can be impaired by over- or under- dosing components, leading to suboptimal bath composition and resulting product quality (Figure 2).
Manual bath analysis and chemical dosage based on old data directly influences the company’s bottom line since the manufacturer loses money either by overusing bath chemicals or producing subpar products. The larger the plating bath volume, the greater the cost of chemicals utilized. Surface finishing baths can be as large as 3,500 L (1,000 gallons) or more. Thus, it is extremely important to optimize chemical dosing to reduce unnecessary costs and waste while still providing maximum quality.
If the baths are overdosed, more chemicals are used than necessary which increases overall operational costs. However, if the baths are underdosed based on old data, then the final products may be defective, which results in increased operational costs as well.
Additionally, surface finishing processes involve many hazardous substances. When carrying out any risk assessment, the first resort is the use of personal protective equipment (PPE), and any potential exposure risks should ideally be engineered out of any process.
Automated analysis of the bath components with an online or inline process analyzer completely eliminates the risk of exposure by plant personnel to the hazards associated with the chemicals used, as well as taking care of the sample preconditioning and sampling itself. With a closed loop control, quick measurements are obtained which lead to fast results and response times for optimized process adjustments.
The solution: operate more safely and efficiently with automated process analysis
Process analysis by manual titration typically takes several steps: sample collection, sample preconditioning, volumetric manipulations, calculation, logging and checking results, and finally sending feedback to the process. All of these can be totally eliminated by using online and inline analysis.
The benefits of this are very clear. By limiting the manual handling steps, any risk of exposure to hazardous chemicals is removed. Sampling error, volumetric errors, and end point ambiguity from analyst to analyst are no longer an issue. Furthermore, sampling can be carried out on a timed basis and can be programmed to occur more frequently than possible with manual methods, giving much greater process control.
The analyzer can be used to fully control a process with direct feedback of results for the correct dosage of chemicals to aging baths. Data is automatically recorded and calculated. On-screen plots and signals can warn about deviating process conditions along with alarm outputs to notify operators of bath issues. The user interface is programmed by simple intuitive operation, and can be performed even by non-chemists.
Benefits of online and inline analysis in surface finishing processes:
- Decrease manual labor – save time and money
- Safer working environment – avoid contact with hazardous chemicals
- Faster response time to process changes – better product quality
- Optimized chemical consumption – less waste, reduced costs
Metrohm Process Analytics has more than 45 years of experience in process analysis and optimization. The following examples show our expertise with configuring inline and online process analyzers for different surface finishing processes.
Learn about the differences between inline, online, atline, and offline measurements in our previous blog post.
Automated monitoring of clean and etch baths
Metal surfaces can have scratches, impurities, and other imperfections which may interfere with further manufacturing processes (e.g., plating or painting). Therefore, clean and etch baths are a key step to obtain clean, polished, and undamaged surfaces.
Traditionally, these bath chemicals are measured offline in the lab after taking a sample from the process. However, as mentioned earlier, manual laboratory methods result in long response times in case of process changes (e.g., reaction mixture, moisture levels, etc.), and the sample preparation can also introduce errors, altering the precision of the analysis. Additionally, it can be quite cumbersome since different operating procedures need to be implemented to analyze multiple parameters including alkalinity, ammonium hydroxide, hydrogen peroxide, and more.
Another example of cleaning baths are mixed acid baths, generally comprised of sulfuric acid, hydrofluoric acid, and nitric acid. Titration only provides the acid value of the sample analyzed; therefore, it is not possible to know how much of a specific acid is present in the baths. However, near infrared spectroscopy (NIRS) is the perfect analytical technique to monitor each acid individually.
Reagent-free NIRS XDS Process Analyzers enable comparison of real-time spectral data from the process to a primary method (e.g. titration) to create a simple, yet indispensable model for process optimization. NIRS is economical and fast, enabling qualitative and quantitative analyses that are noninvasive and nondestructive. Integration of inline spectroscopic techniques allows operators to gain more control over the production process and increase overall safety.
In addition to NIRS process analyzers, Metrohm Process Analytics can design and customize flow-through cells (Figure 5). These clamp on to tubing already present onsite for easy installation with no need to modify the existing setup.
Download our free Process Application Note below for more information.
Automated monitoring of phosphatizing baths
The phosphatizing process produces a hard, electrically non-conducting surface coating that adheres tightly to the underlying metal. This layer protects against corrosion and improves the adhesion of paints and organic finishes to be subsequently applied.
Phosphatization consists of two parts: an etching reaction with phosphoric acid which increases the surface roughness, and a second reaction at the surface between the alkali phosphates and the previously generated metal ions. This coating is quite thin and offers only basic corrosion protection. The addition of metal cations (such as zinc, manganese, and calcium) to the phosphatizing bath results in the formation of very resistant zinc phosphates with a coating thickness between 7–15 times thicker, perfectly suited for outdoor use.
In the cleaning, degreasing, and rinsing baths, and also in the phosphatizing bath itself (Figure 6), the various parameters involved in the process must be kept stable. Conductivity, pH value, free alkalinity, and total alkalinity are among the main parameters that must be determined in the degreasing and rinsing baths. Free and total acids, accelerator, zinc, and fluoride are monitored in phosphatizing baths. The 2060 Process Analyzer from Metrohm Process Analytics (Figure 7) monitors, records, and documents all of these critical parameters at the same time. The combination of different analytical methods within one system as well as the intuitive handling via the well-arranged user interface ensure easy and reliable monitoring of the entire process.
Check out our free related Process Application Note to learn more.
Online and inline process analyzers from Metrohm Process Analytics are the ideal solution to automate the analysis of surface finishing processes because of the comprehensive benefits they provide:
- No manual sampling needed, thus less exposure of personnel to dangerous chemicals
- Extended bath life by tightening process windows (less chemicals required)
- Minimize risk of downtime with faster and more precise data
- Easier compliance with final product requirements by process automation