Continuous Control of Total Solids and Ash Concentration for an Accurate Solution Restoration

 

 

Abstract

This application note describes the use of the in-line Polispec NIR system for monitoring the concentration of ash and total solids dispersed in cataphoresis tanks at an industrial vehicle manufacturing plant. The system provides real-time data on pigment and resin concentrations, enabling precise restoration of the coating solution when necessary, optimizing the uniformity and quality of the coating process.

 

 

 

Introduction

In industrial vehicle production, chassis undergo a cathodic electrocoating (CDC) process to apply a uniform base layer. This electrochemical process binds pigments and resins to the chassis, ensuring a durable and homogeneous coating. However, maintaining the correct balance of pigments and resins in the cataphoresis tanks is essential to ensure the quality of the final product. In the past, it was challenging to determine when and how much restoration of the coating solution was needed.

The in-line Polispec NIR system was implemented in the recirculation duct of the CDC tanks to continuously monitor the concentration of dispersed ash and total solids, allowing for the establishment of a precise set point for solution restoration.

 

Objectives

The objectives of this application are:

• To monitor the real-time concentrations of ash and total solids in the CDC tanks.
• To establish a set point to ensure precise restoration of pigments and resins.
• To improve the consistency and quality of the base coating process.

 

 

 

Methodology

The coating solution, contained in the CDC tanks where chassis are immersed, is kept in constant recirculation to prevent sedimentation and ensure the quality of the production process. Each time a chassis is immersed in the tank, the activated electrochemical process causes part of the pigment to adhere to the metal, resulting in the removal of resins and pigment from the tank.

By implementing the Polispec NIR measurement system in the recirculation duct of the tanks, continuous measurements of solids and ash concentrations in the solution can be taken, providing real-time feedback that is essential for the correct restoration of concentrations.

 

 

 

 

Steps

1. Chassis Preparation: The chassis are immersed in the cataphoresis tanks.
2. Electrochemical Coating: Pigments and resins bond to the chassis during the electrochemical process.
3. In-Line Monitoring: The Polispec NIR system continuously monitors the coating solution, detecting the levels of dispersed solids and ash.
4. Restoration: When the concentration of solids falls below the predefined set point, the system signals for the precise restoration of the solution.

 

Results and Discussion

The integration of the Polispec NIR system has enabled the company to:

• Maintain optimal concentrations of pigments and resins in the CDC tanks.
• Restore the solution accurately and promptly, avoiding both overdosing and underdosing.
• Improve the uniformity of chassis coating, reducing process variability.

By monitoring the solution in real time, the company has enhanced the overall quality and operational efficiency of the coating process, eliminating the need for periodic sample checks that require dedicated laboratory personnel and waiting times for sample drying and incineration.

 

Conclusions

The in-line Polispec NIR system has proven to be an effective tool for quality control in the cataphoretic coating process in the industrial vehicle sector. The ability to monitor ash and total solids in real-time has enabled precise control of the coating solution, reducing waste and improving product quality, eliminating lengthy and repetitive sample checks, and decreasing analysis response times.

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