Application of analytical chemistry to waste minimisation in the powder coating industry.

The results of the audit showed that the most important area for waste reduction in the phosphating line is the waste water stream (extracted phosphating chemicals present in the waste water). Ti concentration profile for OC1 Ti concentration profile for OC1 Concentration profile T] for OC2 Ti concentration profile for OC2 Ti concentration profile for OC3 Ti concentration profile for OC3 Concentration profile T2 for OC1 Concentration profile T2 for OC1 Concentration profile T2 for OC2 Concentration profile T2 for OC2 T2 concentration profile for OC3 T2 concentration profile for OC3 T3 concentration profile for OC1 T3 concentration profile for OC1 T3 concentration profile for OC2 T3 concentration profile for OC2 T3 concentration profile for OC3 T3 concentration profile for OC3 T4 concentration profile for OC1 T4 concentration profile for OC1 T4 concentration profile for OC2 T4 concentration profile for OC2 T4 concentration profile for OC3 T4 concentration profile for OC3

Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure 2.5 Figure 2.6 Figure 2.7 Figure 2.8 Figure 2.9 Figure 2.10 Figure 2.11 Figure 2.12 Figure 2.13 Figure 2.14 Figure 3.1 Figure 3.2 Figure 3.3 Figure 3.4 Figure 3.5 Figure 3.7 Figure 3.8

List of Tables

THESIS STRUCTURE

INTRODUCTION TO POWDER COATING

Breakdown of the Powder Coating Process

The latter wet step in the coating process was developed to ensure that the powder adheres well to the workpiece and to give corrosion resistance to the surface. However, immersing the workpiece in powder, which is forced to flow over the surface in a fluidized bed, is less commonly used than manually spraying the powder directly onto the surface of a moving workpiece.

Surface Preparation - The Cleaning Step

Alkaline Cleaning
Acid Cleaning
Organic Solvent Cleaning
Mechanical Cleaning
Passivating

Phosphates are often used to soften water, and they remove metal oxides and hydroxides from the surface of the workpiece. The surface of the workpiece is cleaned by the scrubbing or abrasive action of the gas bubbles against the surface.

Table 2.1 Properties of light and heavy duty cleaners Cleaner

Surface Treatment - The Phosphate Conversion Coat

An Overview of the Chemistry of Phosphating Solutions
T h e Composition of Phosphating Solutions
The Chemistry of the Phosphate Conversion Coatings
The Chemistry of Zinc and Iron Phosphating
Control of Iron Phosphating Solutions

There have been more reports of phosphate coating analyzes in the literature than analyzes of the phosphating solution. These are deposited on the surface as products of the reactions of the components of the bath, i.e. substrate and phosphates.

Table 2.2 Composition of different phosphating solutions ' Phosphating

An Overview of the Chemistry of Powders

They bind the powder to the surface of the workpiece and form the continuous structure of the coating. Excellent Excellent 12.5-75 Polyesters are defined as all polymers containing repeating units of the ester group (Figure 2.6) in the polymer chain.

Table 2.5 Main properties of the different thermosetting powders Property

Application Principles and Techniques

T h e Phosphating Process
The Immersion Operation
The Spraying Operation

This depends on the type of phosphating (iron or zinc) and on the chemistry of the process solution. The blanks are then passed through each of the solutions in the prescribed order using a conveyor system.

Figure 2.11 Typical immersion system for a zinc phosphating pre-treament process The first process step typically involves cleaning of the substrate using an alkaline cleaner (see Section 2.2.1)

Curing of Powder

The lighter particles remain in the air stream and pass through a central outlet at the top of the chamber to the bag filters. Part of the energy is absorbed in the clothing and transferred to the workpiece, while the rest is reflected by the workpiece.

WASTE MINIMISATION AND THE POWDER COATING INDUSTRY

Waste and Waste Management

Although this definition corresponds to that given in point 1) above, this document continues to give a detailed classification of hazardous waste. It defines hazardous waste as any waste that can cause serious harm to public ... health and the environment due to its inherent toxicological, chemical and physical properties.

Table 3.1 Ratings of hazardous waste Hazard Rating

Raw Materials

Adopting these practices leads to a reduction in the amount of waste generated by the process. Waste minimization can be achieved through material changes {see points 1) and 3) below} or procedural changes {see points 2) and 4) below}.

Product Change

Improved Housekeeping

Waste Minimisation and the Waste Minimisation Programme
Assessment Techniques Used in the Waste Audit Step

Scoping Audit
Mass Balance
Monitoring and Targeting
True Cost of Waste

Prioritizing Waste Minimisation Options
Feasibility Analysis

Technical Evaluation
Economic Evaluation

Waste Minimisation Opportunities and Options in the Powder Coating Industry

Waste minimization opportunities are the sources or areas of waste in the process output stream. The different systems can be defined based on the boundaries (size) and process characteristics (eg open or closed, steady state or non-steady state, batch or continuous). Such waste minimization interventions involve making simple changes to the efficiency of the process runs without requiring large costs.

Figure 3.2 Steps in establishing and running a waste minimisation programme 98,100,104,111,119-121

COMPANY PROCESS AND PROFILE

Company Description

One machine is used only for bending, while the other three are used for bending and punching steel parts. The printing department (see Figure 4.4) is located opposite the phosphating tunnel, which is on the dyeing line. This line is used for bending and punching flat pieces of steel used to make shelves and flooring.

Product Description

These two names refer to the orientation of the brace between the vertical posts (see Figure 4.6). The bottom of the supports is often equipped with a leg to help support the rack system and spread the load on the base. Sloped arms are used for cylindrical objects or loads that tend to roll forward.178 Guides are present on only one side of the rack system.

Figure 4.5 Racking unit made from angled uprights

The Manufacturing Process

Depending on the size and shape of the workpieces, they are hung either vertically or horizontally (see Figure 4.10). There is a spill tray (see Figure 4.11) located between the tunnel and the furnace to collect any excess solution that may have collected on the workpiece exiting the tunnel. The final step in the process is a quality control inspection before the finished product (see Figure 4.12) is shipped to the customer.

Figure 4.9 Flow diagram of the entire powder coating process

The Phosphating Step

There are also two local exhaust fans attached to the top of the spray tunnel. There is a gap between the bottom of the filter and the bottom of the tank. A third pipe attached to the front of the tank brings water from the bottom of the tank into the heat exchanger.

Table 4.1 Structure of the spray system Tank

The Powder Coating Step

The paraffin level is measured manually with a steel scale (see Figure 4.16), which is calibrated in units of 100 L. After the workpiece passes through the drying oven, it is transported to the powder coating booth. Airborne blue dust is collected by a bag filter unit and one cyclone, while orange dust is collected by another bag filter unit and two cyclones (see Figure 4.19).

Figure 4.17 Factory worker spraying powder onto a beam

The Curing Process

Process Control

The quality control of the phosphating step of the powder coating process is carried out by the line manager (in-house). Quality control also takes place on the end product after it has been powder coated. This is an internal function that is performed using a 'Hatch and Impact Test'.77 The Hatch test involves marking squares on the product surface with a box cutter and then placing a piece of tape over the squares.

SCOPES AND AIMS

MONITORING METHODOLOGY

Collection of Existing Data

Monitoring and Targeting Scope Audit Scope Audit Scope Audit Scope Audit Scope Audit Scope Audit.

New Data Collected as derived from Meter Readings and Simple Measurements

This was achieved by consulting the Daily Production Statements (DPS), measuring items and communicating with the line supervisor. A formula for calculating the surface area was derived for each workpiece and used together with the dimensional data to determine the surface area. Other new data collected included a measurement of the solution volume present in the tank by using a tape measure to measure tank dimensions and headroom.

Monitoring Strategy Employed for Collecting New Data by Sampling and Chemical Analysis

Collection of Samples

It was assumed that the returning solution would be completely mixed and thus the sample taken would be representative of the solution in the tank. Furthermore, a layer of foam had built up on the surface of the solution, making it difficult to obtain a uniform set of samples from the bulk tank solution. The wastewater sample was collected from a single wastewater stream located outside the powder coating section of the factory.

Chemical Analyses of Samples using ICP-OES

Principles of Inductively Coupled Plasma Optical Emission Spectrophotometry (ICP-OES)
Preparation of Standards
Preparation of Samples

The operating conditions for ICP-OES used in this analysis for this project are summarized in Table 6.4. For the ICP-OES analysis, seven calibration standards were prepared from a mixed standard solution containing Mo, Mn, Fe, Zn, Na and P. Many samples had to be diluted with an appropriate dilution factor to ensure that the concentrations of metal ions were within the calibration range.

Table 6.4 Specifications and operating conditions for ICP-OES Instrument

Gravimetric Analyses of Samples

Method for Determination of Total Dissolved Solids(TDS)
Method for Determination of Suspended Solids (SS)

The suspended solids in the sample were obtained by subtracting the mass of the filter and the mass of the residue and correcting for void. M2 is the mass of the filter paper and the dry residue after heating (g) V is the volume of the sample solution (mL). The expected SS value, based on the mass of solute dissolved in 250 mL of 100 mg/L Microcrystalline Cellulose solution, is 100.183.

Sludge Analysis

Determination of the Density of Liquid Sludge
Acid Digestion of Sludge

The sample was then cooled to room temperature and then 5 mL of concentrated HNO3 was added. The sample was then refluxed for a further 2 hours without boiling at 98 °C and then cooled to room temperature. The sample was then cooled to room temperature and H2O2 was continuously added until effervescence was minimal.

RESULTS

Results from Existing Data
Results from On-Site Collectable Data

This data is broken down to show the consumption of these raw materials on the paint line for each of the products. The information in Table 7.10 has been compiled from data on invoices and receipts from Waynes Scrap Metal. Tables 7.11 to 7.14 show conductivity, total dissolved solids (TDS), and pH measurements for process solutions in tanks 1 and 2, and rinse solutions in tanks 3 and 4, for the entire monitoring period.

Table 7.1 Workpieces treated on the Paint Line in OC1 Monitoring Period

Direct

Results from Chemical Analysis

Readings taken on standard feet indicated that the sides are generally thinner (50 to 90 \im) than the top (urn 100 to 175). The average elemental concentrations (P, Na, Mo, Zn, Mn, Fe, Cr) determined by ICP-OES for the samples collected by the company for the entire monitoring period are given in tables 7.16 to 7.40. The analysis performed on the effluent (acidified and non-acidified) and water samples are presented in tables 7.44 to 7.46.

Table 7.15 Water meter readings recorded on-site Date

DISCUSSION

Characterisation of the Phosphating Solutions

Characterisation of the Process Solutions
Characterisation of the Rinse Solutions
Characterisation of Effluent Samples
Characterisation of Sludge Samples
TDS, SS and Conductivity Determination

Fe levels in non-acidified samples (around pH 6) are below 1 mg/L for all operating cycles. This is reflected in an increase in concentration on day 11 in acidified samples, but not in non-acidified ones. Na in the non-acidified samples showed slightly higher values than the acidified ones, with the exception of June 1.

Figure 8.3 Concentration profile of Ti for OCl

Scoping Audit

The amount of Chemcoater used on the Paint Line was calculated from the chemical additions (see Table 7.4) and the amount used in the initial make-up and subsequent refilling of the tanks. This value was then used to derive volumes that would have appeared in the first month of 2004 and the remaining seven months of the year. The lifting and removal of the household waste is carried out by the City Engineers - Waste Management Department and the charges appear on the invoices.

Mass Balance Analysis

Total Water Usage and Breakdown

In the Paint Line main, water is used in the two process tanks and the two rinse tanks of the Phosphating Line. In the case of the flush tanks, water can also run through the flush tank. Partial refill volumes were estimated to be approximately half the volume of solution in the tank.

Chemical

Invoiced 1

Drag-out Determination
True Cost of Effluent Waste
Monitoring and Targeting

However, most of the water used on the Paint Line (about 30%) was used in the rinses. The concentrations of the elements in the wastewater were used to determine the raw material waste. PI in the process solution (mg/L) x volume of solution (L) Mass of P in the process solution.

Table 8.6 Estimation of total water usage in factory

CONCLUSIONS AND RECOMMENDATIONS