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Die Casting Lubricant Flash Point and Flammability

Posted by Hill and Griffith Company on Oct 25, 2017 5:18:52 PM

There has been much discussion between the technical staff and customers concerning the application of release agents.

One thing that seems to always seems to be a concern for a customer is the flammability of a product and how flammable our products are compared to the competition. One of the most basic forms of testing the flammability of a product is the flash point.

The die casting lubricant flash point is the lowest temperature at which vapors above a volatile combustible substance will ignite in air when exposed to a flame and is expressed in either Fahrenheit or Centigrade. The test procedure entails filling a prescribed container with the liquid, gradually heating the product and passing a flame over the top of the liquid surface. At such time when the flame causes an immediate flash of fire to occur, the temperature is recorded and is determined to be the flash point. If the material was allowed to continue to heat and a source of ignition was present, the material would eventually ignite and remain on fire until external forces were used to extinguish the fire. This temperature would be titled the fire point. In both cases, a source of ignition is required to cause combustion.

Three types of testing procedures are outlined by the ASTM. The Tag Closed Cup (T.C.C.), the Penske-Martin Closed Cup (P.M.C.C.) and the Cleveland Open Cup (C.O.C.) are all standard test methods. All three will give slightly different results in the temperature of the first flash. In order of lowest temperature flash to highest temperature flash, they would be 1)Penske-Martin 2) Tag and 3) Cleveland Open Cup.

Taking this test information and using it in real-world application is not as difficult as it would seem. The flash point of a material will basically express whether a material will burn or flash at or above a specific temperature. For example, gasoline has a flash point of -36 degrees F. T.C.C. This means that at any temperature above -36 degrees the material will flash or burn. Contrasting, Heptane has a flash point of 25 degrees F. In both instances, the two materials will burn if exposed to an ignition source at room temperature. The bottom line is that it doesn't really matter how low the flash point is for a material, if the operating environment is greater than the flash point, the possibility for ignition will always be present.

The material in this part is extracted from Chapter 1 – Operations – of the book Plant Design and Operations.

This book contains many discussions to do with the control of flammable and combustible materials. The terminology used for this topic — which can be confusing — is explained below.

Flammable Range

Fires require the presence of fuel and air (oxygen) along with a source of ignition. These criteria are often referred to as the fire triangle.

The fuel always has to be in the form of a vapor (liquids and solids do not burn directly — the fire generates flammable vapors at their surface and it is the vapors that actually burn). Moreover, not all fuel vapor/oxygen mixtures will burn — the concentrations have to lie inside the flammable range, which has upper and lower limits for the concentrations of the fuel in the vapor space. The flammability limits vary according to many factors, of which some of the most important are: the pressure and temperature of the mixture and the presence of inert components such as steam, carbon dioxide or nitrogen.

Flammable Limits

The flammable range for a fuel is defined by the Lower Flammable Limit (LFL) and the Upper Flammable Limit (UFL). These terms are also referred to as the Upper and Lower Explosive Limits. Below the Lower Flammable Limit (LFL) there is insufficient flammable material for a fire to occur — the mixture is ‘too lean’. It is the lowest concentration of a flammable vapor in air capable of producing a fire in the presence of an ignition source.

The UFL is similar to the LFL except that there is too high a concentration of vapor for a fire to occur — the mixture is said to be ‘too rich’.

For most flammable hydrocarbons the LFL is around 2 – 5%. For simple alkanes, such as methane and ethane, the UFL is in the 10 – 15% range. Some chemicals, such as hydrogen, ethylene oxide and acetylene, have much higher values for UFL. Values for flammable limit ranges for many flammable materials are provided by NFPA 704 — Standard System for the Identification of the Hazards of Materials for Emergency Response.

Flash Point

The flash point of a flammable material is defined as the temperature at which a vapor that is inside its flammable range that can be ignited. An ignition source such as a flame or spark is needed to make the material actually burn. It is important to recognize that an ignition source is required. The flash point is not the same as the auto-ignition temperature.

The flash point is determined by heating the liquid in test equipment and measuring the temperature at which a flash will be obtained when a small flame is introduced into the vapor zone above the surface of the liquid.

Figure 1.1 illustrates the concepts of ignition temperatures and flashpoints and flammable limits

Figure 1.1
Flammability and Ignition Limits

Flammability Limits

Before a flammable mixture will burn its temperature must be at or above the flashpoint. If the temperature is below this point then the vapor mixture will not burn, even if a source of ignition exists. The left line in Figure 1.1 is the flashpoint line.

Even if the material is above its flashpoint, the ignition source must be of sufficiently high temperature and must contain sufficient energy to ignite the fuel. The minimum energy varies with type of gas and concentration; for hydrocarbon vapors it is low, for high flash point liquids, such as diesel and fuel oil, it is much higher — usually in the form of an existing fire. This is why low energy flashes (such as might be created by a mobile phone or a digital camera) may not ignite a flammable mixture.

If a flammable mixture is heated to a high enough temperature it will spontaneously ignite; an ignition source such as a flame or spark is not needed. Spontaneous ignition occurs at the auto-ignition temperature (AIT), which is also shown in Figure 1.1.

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