Safety Considerations to Take Note of When Thermal Spraying
Metallisation | 23rd November 2020
Thermal spraying (HVOF)
Please note: The information contained in this blog is offered as a guide to Customers and Metallisation Ltd accept no liability arising from its use. For further information please refer to our specific equipment manuals or get in touch with us to find out more…
What is Thermal Spraying?
The term ‘thermal spraying’ (sometimes referred to as metal spraying) describes a process in which metals or ceramic materials are melted or/and softened and are projected and deposited onto a substrate for use in a broad range of applications. Such applications include, but are not limited to replacement of chrome plating in order to prevent wear, thermal protection, coatings for biomedical implants and coatings to protect against corrosion of steel in many environments.
Thermal spraying can be divided into four processes, Arc Spraying, Flame Spraying, Plasma Spraying and HVOF spraying, all of which we will look at the various health and safety aspects that need to be considered for each process.
Thermal Spraying Safety Considerations
Thermal Spraying is not a dangerous process if equipment is treated with care and correct spraying practices are followed. It is permitted in very safety conscious areas such as oil and gas refineries, proving that with sufficient risk assessments and method statements, coatings can be safely applied in the most hazardous of areas.
As with any industrial process, there are a number of hazards of which the operator should be aware and against which specific precautions should be taken depending on the process being used.
Arc and Flame spraying equipment uses compressed gases which create noise. Sound levels vary with the type of spraying equipment, the material being sprayed and the operating parameters. Typical sound pressure levels taken 1 metre behind the arc spray or flame spray nozzle are 102-104 db(A).
Specially designed enclosures should be used to attenuate these levels. Where this is not possible, operators and passers-by should wear good quality ear defenders.
For Plasma spraying (also known as APS – Air plasma spraying) equipment the sound pressure levels can be upwards to 132 db(A) and for HVOF sound pressure levels can be upwards to 133 db(A) so specially designed enclosures should be used to attenuate these levels as well as ear defenders being worn at all times, especially inside the spray enclosure.
Please refer to the relative Metallisation manual for the generated noise levels of a specific piece of equipment.
Light and Particles
Combustion spraying equipment produces an intense flame which may have a peak temperature in excess of 3,100°C and is very bright. Electric arc spraying produces ultra-violet light which may damage delicate body tissues. Spray booths and enclosures should be fitted with ultra-violet absorbent dark glass. Where this is impracticable operators and others in the vicinity should wear protective goggles containing BS grade 6 green glass. Opaque screens should be placed around spraying areas. The nozzle of an arc pistol should never be viewed directly unless it is certain that no power is available to the equipment.
For Plasma spraying an even higher level of protection is required, typically BS grade 10 green glass, as the Plasma process emits quantities of ultraviolet light, in addition to visible and infrared radiation so extra precaution is required.
UV produced by the Plasma Spray process can affect exposed skin, causing sunburn, sun tanning, and changes in skin cell growth. Repeated exposure to UV may decrease skin elasticity. This can give the appearance of premature ageing and can lead to a higher risk of skin cancer. All skin should be completely covered.
For HVOF and Flame equipment eye protection is also required to protect against particles, when operating or viewing the process. Please refer to the relative Metallisation manual for the generated light and/or radiant energy of a specific piece of equipment.
Dust and Fumes
The atomisation of molten materials produces a certain amount of dust and fumes. Proper extraction facilities are vital, not only for personal safety, but to minimise entrapment of re-frozen particles in the sprayed coatings. The use of breathing masks fitted with suitable filters is strongly recommended where equipment cannot be isolated.
Certain materials offer specific known hazards. All finely divided metal particles are potentially pyrophoric and none should be allowed to accumulate.Certain materials e.g. aluminium, zinc and other base metals may react with water to emit hydrogen. This is potentially explosive and special precautions are necessary in fume extraction equipment.
Fumes of certain materials, notably zinc and copper alloys are unpleasant to smell, and, in certain individuals, may cause a fever-type reaction. This may occur some time after spraying and usually subsides rapidly. If it does not, medical advice must be sought.
Several commonly sprayed substances are subject to statutory exposure limits, please refer to our relevant MSDS sheets for the material to be sprayed.
Combustion spraying pistols use oxygen and fuel gases. The fuel gases are potentially explosive. In particular, acetylene may only be used under conditions approved by the Health and Safety Authorities. Oxygen, while not explosive, will sustain combustion and many materials will spontaneously ignite if excessive oxygen levels are present. Care must be taken to avoid leakage and to isolate oxygen and fuel gas supplies when not in use.
The HVOF and Flame process also produces a flame that presents a burn risk. Also, the workpieces will get hot, particularly when higher melting point materials have been sprayed.
Electric arc pistols operate at low voltages (below 50 vdc) but are relatively high currents. For certain models, they may be safely handheld. The power supply units are connected to 440 volts AC sources and must be treated with the normal caution afforded to such equipment.
The Plasma power supply operates below 120 vdc which is considered safe except in conducting environments. A typical spray booth is a conducting environment. However, the power supply for the equipment will usually be fed from a higher voltage supply, typically 240V or 415V, which must always be considered hazardous
The air supply to spraying pistols is at high pressure. It should not be directed towards people. The motor air supply is lubricated and on no account should it be fitted to breathing apparatus. Any breathing equipment used with the thermal spraying process must be supplied with air of breathing quality.
Some processes also use compress gasses such as propane, acetylene, argon or nitrogren. The normal safety practices associated with handling compressed gasses should be followed. As part of our preventative maintenance programs, Metallisation offer direct customers a CP7 gas safety inspection.
- ASM Thermal Spray Society – Designation SG003-03 - Thermal Spray Booth Design Guidelines
- TSSEA Thermal Spraying & Surface Engineering Association – Code of Practice for the Safe Operation of Thermal Spraying Equipment.
- MSDS – Material Safety Data Sheets - provided by the wire / powder manufacturer.
The Final Finish
Keeping yourself and your employees safe during the process of thermal spraying is vital. When it comes to the different types of thermal spraying such as; arc spray, flame spray, HVOF and plasma spray. The safety considerations may be adapted to suit each process and dependent on your local rules
Want to find out more about the safety considerations to take note of for thermal spraying and how to implement them? Get in touch and speak to the Metallisation team today on +44(0)1384 252 464 or send us an email on firstname.lastname@example.org. Alternatively, you can contact us using the contact form below. We look forward to hearing from you.