Fire risks in a CNC
Introduction
Investing in an industrial CNC milling, turning or grinding center is a smart business choice. A CNC machine can produce parts with amazing speed, accuracy and consistency, which can give you the competitive edge you need to thrive in a tough economy. However, while CNC machines are designed to be as safe as possible, they can be susceptible to fire.
Many CNC/EDM machines operate using oil-based metalworking fluids, coolants and lubricants. These oils and fluids are flammable, with flash points ranging from 170° to 350° Celsius, and are continually exposed to extremely high levels of friction and heat. The fumes created due to the whole process, possess an even greater threat of a fire or a blast within the enclosure. A mistake in programming or a mechanical failure can quickly turn a normal machining operation into a hazardous situation. Even a single spark can turn the ready supply of coolant oil and vapor into a major fire in seconds. The result:
- Lost productivity/ Downtime
- Lost customers
- Lost profits & market share
- Loss of life
- Property Damage and recovery cost
Advantages/ Disadvantages of Oil-Based Fluids
Straight oil-based metalworking fluids, coolants and lubricants offer several advantages over water-soluble fluids. The use of oil-based metalworking fluids in industrial CNC and EDM machines will increase tool life, reduce friction and heat, improve surface finish and help flush dross from the work area. Perhaps the greatest advantage of straight oils is the excellent lubricity or “cushioning” effect they provide between the cutting tool and workpiece. This is particularly desirable for applications that require high quality surface finishing.
The greatest disadvantage of straight oils is their poor heat dissipating properties, which leads to an increased fire risk, which is why they are usually limited to low temperature and low-speed operations.
About Titanium Fires
High tolerance machined titanium parts are always in demand in the aerospace and medical industries. Unfortunately, many shop owners refuse to turn titanium because they are
convinced, it presents a constant and serious fire danger. This is in large part a misconception. While a small percentage of machine fires are sparked by the titanium, the vast majority of fires actually begin in the coolant oils, where the flash point is typically less than half of the flash point of titanium. Once the oil catches fire, it can grow until it becomes hot enough to auto-ignite titanium. The real key to preventing titanium fires is to detect and suppress oil fires quickly, before the heat can build to the titanium flashpoint.
How to Contain the Threat of Machine Fires
Adding an automatic fire detection and suppression system is a reliable and cost-effective way to protect your CNC machines from the threat of fire and the inevitable losses caused by machine downtime. However, not all fire protection systems are equal. The trick is to bring the fire detection and suppression apparatus into the micro-environment of the machine itself in order to quickly detect and extinguish a fire at its source.
One such effective and proven solution by WEFIRE, relies upon heat-sensitive pressurized tubing as detection. The tubing can react to a fire in few seconds and deliver total suppression in less than 15 seconds using a clean agent such as Novec 1230, FK5112, HFC or a CO2. Alternatively, a WEFIRE systems can also be activated manually or using an Industrial grade UV/IR flame detector. The pressure switch mounted on the cylinder of the WEFIRE system can additionally be used to trigger an alarm or used for auto damper shut off, auto door closure etc.
With a WEFIRE system, a machine oil fire is quickly detected and suppressed. Additionally, the clean agent used requires no cleanup and will not contaminate the coolant oil. After rectifying the cause of the fire, most CNC machines can be immediately returned to service.
Case study:
A crank shaft manufacturer based in Pune had WEFIRE automatic fire suppression system installed on their CNC machines. The said CNC was originally using a water-based coolant but for their specific needs, the CNC machine was converted to use an oil-based coolant.
We had 3 nos of 20lb NOVEC 1230 cylinders connected in parallel to make it a 60lb system to suffice the volume of the CNC machine's huge grinding envelope of approximately 28m3. Heat Detection tube was mounted on the roof and walls of the machine along with 6 nos of discharge nozzles, mounted at strategic hazard locations.
One evening, oil fumes within the machining enclosure ignited due to series of sparks erupting from the spindle, followed by a blast due to enough availability of hazardous oil and fumes within the enclosure.
The initial flash fire created a substantial fire in an instant. Within seconds, the heat detection tube installed on the inside roof of the machine detected the fire and activated the WEFIRE system. Novec 1230 extinguishing gas instantly flowed from all 6 discharge nozzles, flooding the whole compartment and extinguishing the fire within seconds.
Post this incident, customer realized the value of installing a WEFIRE system, which not only did suppress the fire in few seconds, but also restricted the damage caused due to fire to minimal, thereby saving the machine, shop floor, downtime and last not but not the least, Human Lives.
Within a few hours, the WEFIRE system was re-instated, and the machine was up and running, doing what it does best, viz: “generating revenue”.
For further information,
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