Alternative coatings and other surface finishing measures
In this guide:
- Engineering business solvents and hazardous waste reduction
- Reducing solvent use during surface cleaning
- Alternative coatings and other surface finishing measures
- Surface finishing better techniques and equipment
- Reducing use of metalworking fluids in engineering
- Reducing use of lubricating and hydraulic oils in engineering
- Engineering cutting oils reduction
- Vehicle refinishing solvent use reduction
- Metal finishing effluent reduction in engineering
- Metal finishing effluent recycling and reuse
- Metal finishing solvent use reduction
Reducing solvent use during surface cleaning
How your manufacturing business can reduce solvent use when cleaning and preparing surfaces of product components.
Degreasing components using organic solvents can be a significant source of emissions and waste for engineering businesses. You can reduce costs, meet solvent emissions legislation and produce a safer working environment by changing your surface cleaning procedures.
Eliminating the need for degreasing
You could eliminate or minimise the need for degreasing by:
- keeping items well protected (eg using covers and stretch-wrap) and free from contamination between processes
- 'spinning-off' excess oils and allowing longer drain times between machining and cleaning components
- stacking components carefully before cleaning to reduce oil retention
Using alternative degreasing methods
You could also consider alternative cleaning methods to traditional acid bath and solvent vapour degreasing. The ban on 1,1,1-trichloroethane (an ozone-depleting substance) and reclassification of trichloroethylene as a Category 2 carcinogen make the following alternative methods more attractive:
- Mechanical cleaning - such as scraping, brushing, blasting, tumbling and vibration to remove dirt and grease.
- Aqueous cleaning systems - these generally have a wash stage (sometimes ultrasonically assisted), combined with rinse and hot air drying stages. This eliminates manual preparation such as hand-wiping with organic solvent.
- Biological cleaning - such as enzymes and surfactant/bacterial remediation systems.
- Controlled pyrolysis ovens - these burn off organic coatings and inks from metal surfaces at temperatures of around 930 °C. These systems have been successfully used to clean paint jigs and hangers, body panels and other metal components.
Improving solvent degreasing
Where you have to use solvent degreasing, consider making the following changes:
- use modern enclosed degreasing machines and hermetically sealed machines - open-topped vapour degreasing plant using higher risk solvents may require approval from a regulatory body
- fit cooling condenser coils below the extraction vent inside the machine to allow internal solvent capture and minimise vapour losses
- retrofit open-topped tanks with a lid - below any rim or other local exhaust ventilation extraction system - and with interlocks to ensure that extraction occurs only when the vessel is open
- rack or jig the items so that there are as few solvent traps as possible and that the items drain freely
- make equipment that transports the components through the degreasing process integral to the machine and don't allow items to carry solvent out of the machine
- turn the work in the freeboard zone to minimise solvent drag-out
- use powered hoists and lifts to ensure that the correct loading and unloading speeds are always used, ensuring minimum disturbance of the solvent surface and minimum solvent carryover
- when topping up the machine, avoid decanting losses by pumping solvents from the supply tank to the degreasing machine through a pipe system - or use sealed drums and a drum pump
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Alternative coatings and other surface finishing measures
How your business can cut solvent use by applying different coatings and employing other surface finishing techniques.
Using alternatives to coatings with high solvent content can save costs, increase quality and help you meet health and safety and environmental legislation.
Examples of alternative coatings
Alternative coating systems include:
- medium and high solids paints - with a range of 40-70 per cent solids and 30-60 per cent volatile organic compounds (VOCs), compared with 20-40 per cent solids for conventional wet paints
- water-based paints - similar solids content to conventional paints but with far less VOCs (typically 10-20 per cent)
- powder coatings - a 100 per cent solids mixture of paint pigment and resin binder
- thermal and plasma coatings - specialist coatings such as metal and polymeric coatings that have to be applied at high temperature
In metal finishing, water-based coatings are now often used as a primer and basecoat with a medium to high solids topcoat. Powder coatings are often applied - electrostatically - without a primer coat.
You could consider other measures such as:
- using pre-mixed coatings to avoid mixing on site
- thinning or mixing coatings in a centralised mixing room, or preferably in an enclosed machine - use trained staff for this task and use automated equipment where possible
- not allowing machine process operators to mix their own coatings at the machine, as this leads to significant emissions into the workplace
- using a brush or sponge rather than a spray gun to apply dyes and stains
- dedicating lines, pots and guns to a particular colour or material, and batch sequence to follow one colour with another of the same or similar colour - this reduces the need for cleaning on changeovers and reduces waste
- optimising spray gun settings and setting procedures for spray gun operators - discourage them from altering spray pressures and other settings without permission
- ensuring that the fan pattern of manual guns is only a little wider than the object being sprayed - movement should be at a constant speed, optimum distance and parallel to the object
- controlling the temperature in the spray area to keep it constant and optimum for spraying
- spraying flat component parts before assembly of a product to avoid over-consumption of the coating
- using paper masking around spray booths to reduce the need for booth cleaning
- controlling the use of cleaning solvents by providing operators with a set amount each day or each shift - use triggered spray containers rather than free access to cans
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Surface finishing better techniques and equipment
How to improve efficiency and reduce waste when using surface finishing techniques such as dipping and spraying.
You can reduce waste and the cost of surface finishing by using better application techniques and equipment. Coatings are applied either by dipping or spraying. Conventional spray guns are typically not more than 50 per cent efficient - for every two litres of paint you use, at least one litre is wasted.
If dipping, consider using electrophoretic and autophoretic dipping for priming and corrosion-resistant coating. Electrophoretic dipping involves the use of electrodes connected to the bath and the jigs to create the attraction between paint and substrate. Autophoretic dipping relies on a chemical reaction to create the attraction. Both techniques offer high material yield and high quality, and are water-based processes with no volatile organic chemical emissions.
If spraying, you should consider replacing conventional spray guns with high volume, low pressure (HVLP) spray guns. These give better control, better coverage of recesses and typically offer efficiencies of 65-85 per cent. HVLP guns typically pay for themselves within weeks.
When using viscous coatings, consider using hot-spray equipment that can produce the correct coating viscosity without the need for excessive use of thinners.
If your business uses higher value coatings, you should consider using electrostatic spraying. With wet paints, this allows the charged paint to be attracted to the earthed piece and gives high transfer efficiency. Combined with HVLP technology, electrostatics can achieve efficiency of 65-95 per cent.
You should consider using powder coating - using either a fluidised bed dip or spraying - as it is a very efficient, high-quality, dry electrostatic process. Unlike wet paints, you can readily collect and recirculate powder.
If using spray guns, you should pump mixed coatings directly or via a ring main to avoid decanting by individual operators. Some low-pressure pumping equipment can supply a number of spray guns directly from one paint container without the need for intermediate pressure pots. This reduces material wastage and the need for cleaning.
Robotic spraying often reduces coating use by 20-30 per cent compared with manual spraying. Although expensive, robotic spraying has advantages for large and complex shapes as it offers high efficiencies, high quality and reduced labour costs.
On robotic spraying equipment, dedicated paint lines often feed a colour changer that, in turn, supplies the gun down a feed line. The closer the colour changer is to the gun, the less waste of paint and cleaning materials on changeover. Alternatively, replace the feed lines with cartridges that can be loaded onto the paint atomiser.
On automatic cleaning systems, you can use pulsed air (in the direction of paint supply) with cleaning materials to improve cleaning and reduce material use. Reversing the direction of the compressed air can drive unused paint back down the supply line into the pressure pot, saving paint and cleaning solvents.
Consider line 'pigging' systems to improve paint recovery and reduce the amount of solvent used for cleaning.
Consider using enclosed gunwashing machines to avoid unnecessary emissions, recover the solvent used in spray-gun cleaning and allow its reuse within the machine.
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Reducing use of metalworking fluids in engineering
An overview of techniques to reduce waste, manage metalworking fluids and cut the quantities of hazardous waste.
Reducing your use of metalworking fluids enables you to cut costs and the quantity of hazardous waste you need to dispose of.
Choosing the right metalworking fluid
Select the correct fluid for the particular operation and metal. Unsuitable fluids waste materials and time, damage machinery, and lead to poor quality products and increased waste-disposal costs. In contrast, a small quantity of specialised fluid, used as a spray mist or for minimal lubrication, can produce large cost savings and increase tool life.
You could choose a less hazardous fluid - based on vegetable oils instead of mineral oils - or an additive-free fluid, eg short-chain chloroparaffins used as lubricating agents, triazine compounds used as biocides, nitrites and secondary amines used as corrosion inhibitors. Alternatively, you could use dry machining to eliminate metalworking fluids.
Good housekeeping with metalworking fluids
Good housekeeping is essential to avoid fluid contamination, extend fluid life, avoid waste and secure safer working conditions. You should:
- Keep fluids clean by labelling all containers, vessels and pipework clearly.
- Keep fluid contact surfaces clean. Do not add clean fluid to a dirty machine or return fluid spills to the machine pump.
- Use biocide to control bacteria and fungicide to control fungi (yeasts and moulds) outside specified limits.
- Remove tramp oils - eg hydraulic and slideways oils from metalworking fluids. The most common forms of contamination are tramp oil leaking from parts of the machine, small metal particles from the cutting process, airborne particles and reuse of fluid recovered from swarf.
- Use only freshly diluted fluid at concentrations recommended by suppliers. Diluting fluids below the recommended level is a false economy as they degrade, machines corrode more easily and the surface finish is poor. If the fluid concentration is too high, this can lead to foam formation and spillages.
Monitoring metalworking fluids
Regular condition monitoring of metalworking fluids, especially for concentration and pH, enables you to extend fluid life and take corrective action at the appropriate time. For example, the build up of particulates allows other contamination to occur. You should:
- record the data on a chart and assess it for trends
- use a check sheet for solid waste to identify sources and types generated
- use a stock rotation scheme to ensure materials are used before their use-by date
- use automatic fluid management systems where appropriate
Disposing of metalworking fluids
You can use on-site treatment to reduce contaminant levels in effluent below the consent levels set by Northern Ireland Water. Treatment is essential as you must not discharge contaminated surface water directly to surface water drains and watercourses.
Spent fluids can be separated into organic and aqueous fluid by adding chemicals. You can discharge the separated water to sewer if it meets the conditions of your trade effluent consent. The sludge produced must be collected by a licensed waste treatment business.
You could consider alternative fluid disposal options such as evaporation, which concentrates spent fluid and produces a residue with potential as a fuel.
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Reducing use of lubricating and hydraulic oils in engineering
Guidance on different methods for engineering businesses to reduce and manage lubricating and hydraulic oils.
Reduced use of lubricating and hydraulic oils enables engineering businesses to cut costs and avoid the need to dispose of these hazardous wastes. You can achieve this through procurement policies, staff training, monitoring and analysing systems and usage, and through improved processes and equipment.
Using one supplier for all oils helps minimise waste, simplifies stock control, makes rationalisation more effective and could lead to discounts for larger orders. Suppliers often offer larger buyers an on-site representative to manage the oil store, manage distribution and monitor usage.
If you do not use such a service, you need to assign responsibility for the oil stock control, distribution and monitoring to key members of your staff. Training may be necessary. You should establish procedures for using and handling different oils, condition monitoring and data analysis, and set targets to reduce use and waste.
You must store oil safely to avoid causing pollution. You may need to comply with the oil storage regulations.
Reducing hydraulic oils waste
Correctly storing and handling oils will avoid waste resulting from damage or contamination. You should clearly label all oil containers so staff can easily identify the oil they require. Waste oil should be labelled and stored separately.
You should respect use-by dates to ensure that the oil performs to its specification. Use devices for handling drums and transferring oil from larger to smaller containers to allow simple movements and to minimise costly spills. Containers should be clean and ideally used for only one type of oil.
Recording and monitoring plant performance and oil use is essential for reducing waste, analysing trends, changes in use and maintenance needs, and identifying problems. For example, analysing oil samples can indicate debris within an oil due to wear of machinery and components, eg bearings.
Reusing and recycling hydraulic oils
You can reuse or recycle waste oils or sell them to cement factories or incinerators as fuel. You need to arrange for decontamination of used oils either on site using small kits (basic filtration and water removal), or by a specialist business which offers a collection, laundering and return service. They normally use a process of filtration, dewatering and then replenishment of the additives, returning oil that is of equal quality to the original.
If you intend to reuse oils, you must reclaim them under low-grade controlled conditions to avoid any degradation of their lubricant quality. The recovery equipment should not come into contact with any oil you intend to dispose of. Make sure the pumps and containers for the oil are free of any contaminants to maintain the quality of the oil that is being reclaimed.
Mixed oils cannot be used for their original application. If you are reclaiming and reusing oil in the same plant item, you should keep it separately from other reclaimed, waste or virgin oils.
Where oil can be recovered but not used for its original application, you could reuse it as lower grade oil. However, it is important you ensure that this will not harm machinery or processes.
Oils often enter the factory drainage system but you should remove them before the water is discharged from the site. Belt skimmers remove oil from water. A number of businesses offer interceptor systems to separate oil and water in the drainage system.
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Engineering cutting oils reduction
An overview of techniques for reducing and managing cutting oils for businesses in engineering industries.
'Swarf' is metal waste contaminated with oil, water and other substances. The waste is considered hazardous but it is also a resource which can be reused either in-house or by another business - for example, a foundry or recycler.
You should reduce the cutting fluid content of swarf to increase its reuse value, make storage easier and safer, and avoid disposal, which has to be carried out by a specialist organisation. There are various methods for doing this:
- Dry machining techniques have been developed to eliminate the need for cutting oils. Dry swarf is produced and the potential hazards associated with handling cutting fluids are removed.
- You can use a centrifuge to separate the liquid from the swarf. Automatic machines have a continuous feed from a conveyor and generally deliver the swarf directly to a bin or a skip. You can send the coolant for cleaning and recycling.
- You can use magnetic separation for steel swarf in systems where the swarf is transported by flowing cutting fluid. The swarf is removed from the fluid by a strong magnet and then scraped mechanically from the magnet. Steel swarf has little value, but you can recycle the cutting fluid.
- You can dry swarf in a kiln to reduce cutting fluid contamination. Waste heat - eg from a compressor - can be used as a source of energy. This technique is normally only worthwhile for a business reusing the swarf itself.
When swarf is left in a bin or a skip, some of the excess cutting fluid will naturally drain under gravity. Use a bin with a mesh layer above the base and a tap to drain off the cutting fluid. Shovelling the swarf out of the bin instead of tipping it will keep the swarf drier. Use a skip with drainage holes, taking care to ensure the skip is within a bunded area to avoid polluting the soil or water sources with cutting fluid.
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Vehicle refinishing solvent use reduction
An overview of various techniques for reducing and managing solvent use in the vehicle refinishing industry.
Reducing the use of solvents and paints in your vehicle refinishing business will cut costs and the amount of hazardous waste requiring disposal and lead to a safer working environment.
You should consider using a powder-based, solvent-free, dry coat system as a guide coat prior to sanding body fillers. There is no need to use expensive aerosol paints or thinners to produce a guide coat, no waiting for the coat to dry and no need to mask the job. There are also no solvent emissions. You could also repair dents that don't need respraying by massaging them from the inside.
You should accurately measure areas to be painted. This avoids you wasting paint, time and money, as well as having to dispose of excess paint. Make sure the mix is correct, otherwise the job may require a complete rework. Using gravity paint cups will help you avoid waste when mixing paint.
Processing paint jobs of the same colour at one time, or one after the other, reduces paint make-up and set-up time, time spent cleaning the spray gun and the use of solvents.
Introducing water-based basecoats for some applications can reduce solvent emissions by around 13 per cent.
High volume low pressure spray guns are one of the most efficient ways of applying paint to surfaces. Fully automatic gun-washing machines ensure you use the correct amount of solvent, reducing wastage.
High-solids paints have less solvent, meaning the paint is more viscous - and more difficult to apply. However, it builds up faster during application, so fewer coats are needed. The lower solvent content results in lower harmful emissions during application.
For cleaning, use dip cans with a plunger pump which allows a small amount of solvent to be pumped onto the cloth. You can also use plastic spray bottles, which allow the solvent to be sprayed onto the item and wiped off with a cloth. Avoid tipping solvent onto a cloth, as the amount of solvent used is often much more than required and the cloth then becomes a health and safety risk when solvent evaporates into the workshop.
You could consider using small solvent recovery machines. These heat up the waste, boil off the solvents and collect the cooled vapours in a separate tank. You can use recovered solvent to clean spray guns.
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Metal finishing effluent reduction in engineering
Methods of reducing effluents in the metal finishing industry to save your business money and improve efficiency.
Metal-finishing effluents are hazardous wastes and costly to dispose of. If you produce metal-finishing effluents you must comply with hazardous waste requirements. Therefore, it will save you money to reduce your use of chemicals, the amount of cleaning you need to do during processing and the volume of effluent.
Good purchasing and stock control are vital. Buying too much stock, or failing to rotate it, may result in waste. You should review your purchases and consider buying stock on a just-in-time basis. You should label containers clearly with the date of purchase and use-by date. Keep an inventory and make sure that old solutions are used before newer ones.
You should also train your staff about the need to reduce waste and to follow your procedures for achieving this. You could link bonus payments with water, chemical and waste disposal costs.
Keep detailed records of chemical and water use, the type, source and amount of aqueous effluent and solid waste, and of treatment, storage and disposal of effluents.
You should reduce drag-out from plating and other treatment baths. It has costly implications, including contamination of subsequent process baths, chemical waste, increased water needed to achieve adequate dilution ratios for rinsing, higher effluent treatment plant costs and additional filter cake and sludge generation.
You can reduce drag-out through:
- slower extraction of a workpiece from the solution
- adjusting the positioning of a workpiece to prevent the solution getting trapped in hollows
- extending drip time
Install drip boards between tanks to capture the run-off as workpieces move between rinse stages and dips. The boards should be tilted so run-off drains back into the tank. If you install an additional drip tank, one batch can drip while another is moved, before the solution is returned to the process bath. Drainage is more efficient when the layers of workpieces are staggered rather than hanging directly above one another.
You should also aim to use only the minimum amount of chemicals for cleaning. Use accurate thermostats, pH probes and measuring devices. Consider installing automatic dosing from larger to smaller containers, as this is safer and more accurate.
Use the minimum amount of water for cleaning as it creates effluent when mixed with chemicals. Pre-programmable water delivery systems ensure that only a specified volume of water is delivered at any one time. Install water meters and flow restrictors on process lines. Manually operated trigger hoses reduce waste by automatically cutting off the water once hand pressure on the trigger is released.
Spray and fog rinsing above the process bath are effective rinsing techniques and water efficient. Countercurrent rinsing uses a series of connected rinsing baths. Water from the bath with the lowest concentration of chemicals flows back into the previous rinse bath and then through the other baths in sequence. The volume of water used is significantly less than in traditional flow rinsing. This method is more effective as concentrations of drag-out chemicals in the rinse baths are kept low.
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Metal finishing effluent recycling and reuse
Techniques to safely reuse and recycle metal finishing effluents to reduce waste and cut engineering business costs.
You can save money and recover materials by treating and reusing metal-finishing effluents (liquid waste).
Polluted effluents can damage the bacterial beds at sewage treatment works, contaminate sewage sludges and lead to pollution of watercourses. You must ensure that your metal-finishing effluents are dealt with appropriately to comply with the conditions of your trade effluent consent and to prevent water pollution incidents.
You can treat your effluents on site to a safe level, or pay a waste-disposal business to remove them.
You could use the following recovery methods:
- Extending drip time after processing allows solutions to drain and be returned to the process bath. Doubling the drip time from 15 seconds to 30 seconds can increase the amount of electrolyte returned to the plating solution by up to 50 per cent.
- Ion exchange can be used for the treatment of cyanide plating baths, nickel, copper, tin and zinc, and aluminium anodising rinse waters. Ion exchange can recover metals and clean water for recycling.
- Electrochemical recovery allows metal to be recovered in powder or solid form. The metal can then be melted down, reused as a soluble anode or regenerated as a concentrated process solution. Electrochemical recovery is a cost-effective method for recovering precious metals from rinsewater and exhausted plating baths. It also reduces the amount of metal sludge requiring disposal.
- An evaporation unit with a pump and evaporative panels of up to 1,000 square metres can recover more than 96 per cent of drag-out chemicals.
- Reverse osmosis uses a semi-permeable membrane to separate water from dissolved salts. This generates water and a concentrated liquid consisting of metals and salts. The liquid can be drawn off for further treatment or returned to the process baths.
- Ultrafiltration can be used to filter out molecules from a contaminated wastewater stream. It is useful for a final cleaning of water before recycling back to the process.
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Metal finishing solvent use reduction
Different ways to reduce solvent use from metal finishing, and how to reuse and dispose of solvents safely.
Reducing solvent use in - or even eliminating it from - your metal-finishing operations will save you money on materials, waste treatment and disposal. Reusing or recycling solvents can also benefit your business.
The following changes in working methods will help you reduce solvent use:
- eliminate cleaning between processes where appropriate
- use alternative measures to keep components, materials and machinery clean - eg when preparing surfaces, use mechanical methods such as brushing, blasting and tumbling to remove dirt or grease
- avoid excessive cleaning by spinning off excess oil prior to degreasing
- install time controllers, alarms and idling cut-outs to schedule cleaning
- ask your component suppliers if they could use less protective greasing in shipping and so reduce your need to clean
- use stock rotation to ensure you use materials before they reach expiry date
- mix only sufficient paint for the job
- schedule colour coatings and products that require the same series of different coatings in batches to minimise the need to clean equipment
Opt for methods which do not involve solvents, such as:
- powder coatings or high-solid, water-based paints
- electrodeposition and autodeposition dipping - which use water-based coatings
- aqueous (water-based) cleaning systems for surface cleaning
- biocleaners - these remove oils, greases, paints and solvents from components
You should choose processes which are appropriate to the task, such as:
- Barrelling - used where only a low quality finish is needed. Items are loaded into a barrel, which is immersed in a bath of coating material and rotated to ensure adequate coverage. The barrel is then withdrawn and allowed to drain.
- Flow coating - suited to large or oddly shaped parts that are difficult or impossible to dip coat. As in dipping, excess coating material is allowed to drain and is collected for reuse.
- Electrostatic spraying and hot spraying - two techniques to help achieve high coating efficiencies.
- An appropriate paint delivery system that will minimise wastage - eg gravity cup feed systems.
- High volume low pressure spray guns - these are efficient, but spray painting can be wasteful. Spray gun and paint manufacturers offer training courses for operators.
Metal finishing solvent reuse
Reusing materials from the cleaning process reduces waste. For example, you may be able to reuse water used to cool trichloroethylene (trike) for rinsing and dry blast media for mechanical cleaning.
In waste plants, reuse can optimise performance, eg using spent alkaline cleaners to adjust the pH of acidic wastewaters prior to treatment, or recovering spent solvent and using treated cleaning water on site.
Solvent recovery machines heat waste, boil off solvent and collect the cooled vapours, which can be used to clean spray guns. You can also recover and recycle solvent in waste on site by distilling the sump contents in the degreaser.
Metal finishing solvent disposal
If further solvent recovery is not possible, you should follow the correct procedure for disposal, including:
- separating, packaging and labelling all spent solvents
- allowing only trained personnel to handle and store spent solvent
- adopting correct handling procedures
- documenting and recording movements of both spent solvent for reclaim and final waste
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