Secat was awarded a project to evaluate various protective fabrics in terms of their resistance to molten aluminum. Secat utilized its unique fabric testing machine (photo shown to the right), which was developed based on ASTM F955-15 guidelines.
Test fabrics were provided for possible use as protective garments in the aluminum industry. The fabrics were tested for exposure to molten aluminum using 0.75kg or 1.0kg weights of the designated alloys AA1100, AA5182 or AA6061 chosen by the member company for which the fabrics were tested.
Results from this study are available for purchase from The Aluminum Association’s bookstore.
Secat is currently using this technique for various Aluminum melting facilities and fabric suppliers to help them rate their materials to the standard on an ongoing basis. This allows customers/suppliers in the selection of appropriate garments for use on the plant floor and in the development of the fabrics respectively.
A brief description of the ASTM standard, the development of the test procedure, and the test method utilized for the evaluation of the fabrics is given below.
ASTM Standard F 955 – 15: Standard Test Method for Evaluating Heat Transfer through Materials for Protective Clothing Upon Contact with Molten Substances is used as the reference standard guideline to build the test jig and determine the test parameters.
Workers may be exposed to contact with molten substances. The clothing used should provide some protection.
Whether personal injury results from such contact depends on the resistance of the material from which the clothing is made to molten substance contact and the amount of heat transferred through the material to the wearer.
This test method rates materials that are intended for protective clothing against potential molten substance contact, for their thermal insulating properties and their reaction to the test exposure.
The protective performance, as determined by this test method, will relate to the actual end-use performance only to the degree that the end-use exposure is identical to the exposure used in the test method. Visual inspection of the specimen subjectively notes the material resistance to molten substance contact.
A fabric testing machine built by Secat Inc. is based on the guidelines provided by ASTM Standard F 955 – 15: Standard Test Method for Evaluating Heat Transfer through Materials for Protective Clothing Upon Contact with Molten Substances. Two copper slug calorimeters connected with thermocouples and a National Instruments Data Acquisition System were used to record the temperature variations during the test. The details are shown in Fig 1(a) through Fig 1(c).
The report published by the Aluminum Association “Resistance of Protective Fabrics to Molten Aluminum and Bath Splash and their Comfort Properties, October 2000” is used as an additional reference in determining the test machine construction parameters.
Fig 1(a): Schematic of fabric test machine
Fig 1(b): Macro photographs of the fabric test machine
Fig 1(c): Macro photograph – copper slug calorimeter before & after connection to thermocouple
The thermocouple is pinned into the copper plate
Fabric Test
Tests are carried out at a melting facility using molten aluminum alloy selected by the customer and is melted in an electric resistance furnace.
The tests are conducted under controlled conditions by preheating the test stand crucible prior to pouring and superheating the molten to 156 °C above the liquidus temperature. The pre-heat ensures a slow cool and controlled starting point of pour.
The table below shows the alloy, solidus-liquidus range, pour temperature and minimum superheat. The test crucible preheat is performed in a separate furnace to allow several crucibles to be preheated in case of crucible failure.
Alloy | Solidus-Liquidus Range, °C | Pour Temperature, °C | Minimum Superheat, °C |
Customer | Based on alloy | _+ 56 over Liquidus | + 156 over Liquidus |
After the molten aluminum is poured into the test crucible, a K-type dip thermocouple is used to test the molten temperature and then removed prior to pouring. The A4 size test crucible is made of cement bonded clay graphite and the weight of aluminum tested is up to 1.0 kg.
The temperature on impact is recorded using two copper calorimeters and a video is taken of the entire process. The mass and area are considered when calculating the incident heat.
The molten aluminum is removed from the furnaces by melting facility personnel and then transferred to the test machine. The test is started after the temperature is measured using a dip type thermocouple and the calorimeter readings recording started.
The test stand has 5 interchangeable calorimeter plates that allowed the fabrics to be placed onto the plate prior to insertion into the test stand. The interchangeable plates allow the plates and calorimeters to cool to ambient temperature of the plant for each test.
Fabrics are rated on a 1-5 scale for break-open, char, sticking, and shrinkage with 1 being a minimal rating and 5 being maximal amount or worst rating as described in ASTM F955-15. An indication of ignition and self-extinguish upon exposure to molten aluminum is also recorded.
Calculation Formula
The Calculation Formulas in this report are adopted according to ASTM Standard F 955 – 15: Standard Test Method for Evaluating Heat Transfer through Materials for Protective Clothing Upon Contact with Molten Substances.
Fig 2 and Fig 3 show the Stoll curve and temperature profiles and the tested fabric respectively.
The report will show the test set, behavior of the test fabric as per the test conditions and comparative performance.
Fig 2 – Stoll curve calculations and response
Fig 2 – Stoll curve calculations and response
Fig 3 – Tested Fabric
Fig 3 – Tested Fabric
Fig 2 and Fig 3 show the representative Stoll curve and temperature profiles and the tested fabric respectively.