Paint


Improving Cost Effectiveness in Automotive Finishing

The automotive industry consumes millions of litres of paint annually. Quality control systems currently in place don’t tell the whole story. We will show you how to save up to 5% of your paint spend. In fact any organisation or industry that spends more than $ 1 million on coatings annually will benefit with amazingly short payback periods often less than half a year.


Paint Volume Solids Measurement – Benefits to the Automotive Industry

The PVS instrument has 3 main areas of use – in production to help control film build, in quality control to evaluate paint supply consistency, and as a research tool.

Background

The paint volume solids machine provides information about:
  • how much cover you will get per litre of paint at a specified thickness (you can optimize the precise coating time needed per car as a function of each specific colour and each specific paint batch), and
  • how thick your finished paint coating will be for a given set of coating conditions.


Use In Production

Automotive finishing represents an expensive stage of car manufacture and needs tight control for efficiency, cost control, and product quality. Excess paint application means more cost, more overspray that needs to be treated, and more wear and tear of spray and coating equipment. Insufficient paint means expensive re-spraying operations the incidence of which must be absolutely minimized. Given the high cost of total paint purchases considerable savings can be achieved with improved quality control.

In-line automotive spraying is an automated relatively fast process via advanced high tech car paint lines. The spray process is automated and the spray head handles a large number of colours programmed to meet the production schedule. Knowing the paint volume solids property for paint will allow the development of a superior menu based control program for the spray heads to more accurately apply paint within a tighter band of finished dry paint film thickness. At a 50% paint volume solids content a 2% variation in this property results in a 4% shift in dry film build. 2%to 4% variation from paint to paint represents a very typical range seen from colour to colour and sometimes from batch to batch. Knowing the value for each paint batch can save a significant amount of paint and improve quality consistency.


Use In Quality Control

The paint volume solids machine allows monitoring the consistency of supplier deliveries on a batch to batch basis. The relationship between colour match and PVS has not yet been explored but it is quite possible that colour consistency can also be improved.
PVS may also be a useful property as applied to the e-coat product and process, but further work is needed first to look into and verify this.


Significance of Paint Volume Solids and Why is Not Monitored Now

Paint volume solids, (PVS) is one property that people don’t pay much attention to. One reason is that there has never been a practical method of measuring this property. The volume solids content of paint is the property that determines how much cover you will get from a given volume of paint. For example, take two paints at the same price per litre – one with 50% volume solids and the other with 52% volume solids – the paint with 52% PVS paint will cover an area that is 4% more than the other paint. In a situation of tight cost control and competitive bidding this is particularly powerful information to have in a tender situation. If you spend millions on paint this can pay for itself in a couple of months. There is also considerable natural variation in PVS from batch to batch, and having a good handle on this will lead to improved more efficient coating practices. The instrument that measures PVS is now ready for commercial roll out. Our testing covers a wide variety of paint types and shows excellent accuracy and repeatability of measurements.


Principle of Operation (and method of operation)

A drop of paint is placed onto an small aluminum panel, it is smoothed with a doctor blade and the panel is placed onto the sample holder. This part of the process takes about 15 seconds. The measurement cycle is initiated with the press of a button. A high precision actuator (mechanical slide mechanism) moves the sample under the path of a laser sensor with a resolution of 0.1 micrometres. The profile of the smoothed paint droplet is recorded, and the cross sectional area and average thickness are calculated. The paint drop is then transferred into a small IR/convection oven. Solvent is driven off, and the paint is cured. Cure cycles can be adjusted to simulate actual production conditions. Then the sample leaves the oven and enters a short cooling phase. After a predetermined amount of cooling the paint droplet is scanned again to determine its dry film cross sectional area and average thickness. Paint volume solids is calculated by dividing the dry film thickness (or cross sectional area) by the wet film thickness. The test cycle is completed in about 3 minutes, but can be adjusted to simulate any production circumstances.

The principle of operation is very simple and robust. To make this work in practice sophisticated data analysis algorithms and allot of attention to very fine mechanical engineering tolerances is needed. The algorithms eliminate errors due to boundary and wetting effects for the paint’s surface tension, and so on. Making this fairly simple principle work requires a fair amount of ingenuity.


Results

The actual repeatability will depend to some extent on the paint itself. At present the instrument has been tested mainly with coil coating industrial paints, clears, water based, and PVDF paints. Repeatability of results are typically within +/- 0.3%.


Commercial and Technical Significance
  1. From a paint price perspective the actual paint volume solids content becomes more critical for paints with a low PVS value. For example, a one percent variation for a paint with a nominal 20% PVS content represents a 5% difference in applied cost;
  2. If industrial painting procedures have good control of applied wet film build, then PVS values are needed to improve prediction of the final dry film build – having this in control allows operation at lower, but more consistent minimum film build without fear of performance issues or warranty issues. If needed, we have systems under development that will improve control of wet film build during industrial finishing;
  3. Consistent PVS performance from a batch to batch viewpoint will improve batch to batch colour uniformity;
  4. Measuring PVS provides a real tool for checking the performance of any single paint supplier as well as providing a basis for comparing different suppliers.


Cost and Payback Estimation

Payback depends on how much paint is used annually, and the average PVS of the automotive paints used. In rough terms you would expect to save 2-5% of your paint costs by being able to compare and monitor a supplier’s product. Using this factor we estimate a payback period of 4 months based on $3m paint purchased annually. That figure excludes benefits from ultimately achieving better control of the overall painting process and tighter thickness specification. We have expertise in measuring wet film thickness and this can be tailored to automated automotive finishing lines.
  • Tighten control on your industrial coating operation
  • Measure and monitor the volume solids of paint accurately
  • Compare paints and estimate the impact of PVS on cover
  • Measure and calculate the paint volume required for production
  • Estimate the impact of PVS on final paint thickness
  • Non-contact dynamic dry film build measured in real time
  • Monitor consistency of coating quality throughout production
  • Tighten up on painting thickness specifications
  • Reduce waste and maintain thickness with confidence
  • Measure the wet film on the applicator before production commences
  • Predict dry film build during coater set up
  • Quick and easy to use as with all Wolf Innovation products