Material Quality Control
The way of increasing the product quality passes through making no concessions on quality in all details. Foam which doesn’t seem in final products is one of these details. In FINEHOPE Qualiy Control Laboratory which started out with “Quality is under control” slogan, raw materials are subjected to incoming quality control. Also, specimens which are taken after each production are subjected to related tests and their basic technical properties are determined. Quality and reliability of products are tested in accordance with ISO and ASTM standards. In this context, the following physical tests which are explained below in detail are carried out:
Density (ISO 845)
Density is expressed as the mass per unit volume. The SI unit of density is kilogram per cubic meter (kg/m3). It is the major factor, that affects the foam quality and performance. As density of the foam increases, durability and cost also increase.
Hardness – IFD (ISO 2439)
Hardness is a measure of the load bearing capacity of flexible polyurethane foam. It is generally measured as the force (in Newton) required to compress the foam sample to 25, 40 and 65 percent of its initial height. It is possible to produce the foams in accordance with the desired hardness values depending on the area of use. The hardness of the foam does not determine its quality or durability. At this point, what matters most is suitability for use. For instance; in seat cushions, too soft materials provide insufficient support or too hard materials may be comfortless.
SAG Factor (=Support Factor =Compression Modulus) (ISO 2439)
Support is the most important function foam can provide. It means that the cushion is capable of distributing the weight of the person for maximum comfort. Support capability often varies within ranges with different densities and types of foam. The Support Factor is the ratio of 65% IFD to 25% IFD. This number gives an indication of cushioning quality. Higher support factors indicate better cushioning support and comfort.
Tensile Strength (ASTM D 3574)
It is the maximum stress that the material can withstand while being pulled before breaking. It gives information about the foam’s elasticity. Test samples are cut with the help of mold which is specially designed according to the requirements of the standard. Tensile test is performed by means of placing the each of two ends of the test samples in the holders of the test machine and pulling them with force of equal magnitude. Also, besides the tensile strength, percentage of elongation at break is calculated from the ratio of maximum elongation value and the original length of the sample.
Tear Strength (ASTM D 3574)
Tear strength is a measure of the force required to continue a tear in a foam after a split or break has been started and expressed in newton per centimeter (N/cm). This property is important in determining suitability of foam in applications where the material is sewed, stapled, or otherwise anchored to a solid substance.
Resilience (ASTM D 3574)
Resilience is an indicator of the surface elasticity and comfort of the foam. It is measured by dropping a steel ball onto the foam cushion and measuring how high the ball rebounds.
Compression Set (ISO 1856)
Foam sample is compressed under constant load, for a controlled time period and temperature condition. When the compression time is complete, the sample is removed and allowed to recover. The sample height is measured, and the results are given as a percentage of original height. Compression set test correlate with the loss of cushion thickness and it is an indicator of in-use recovery performance.
Dynamic Fatigue (ISO 3385 – ASTM D 3574)
Dynamic fatigue is an indicator of in-use foam softening. Fatigue is measured by compressing the foam sample 8000 (or 80000) times in succession and measuring the change in IFD and thickness. For compression load, an average-weight person (75 kg or 750 N) is taken as a reference. Changes are expressed as percentage. In consideration of this test, lifetime of the foam can be estimated.
Air Flow (ASTM D 3574)
It is the measurement of the volumetric flow rate of the air that is passed through the foam sample at constant pressure. It gives information about whether the foam is open or not.
The number of cells per 1 inch (=2.54 cm) are counted along a straight line with a magnifier that is generally expressed as loupe.
Foam sample is held against a flame source for a length of time, then it is taken away and the change of the position of the flame in unit time is measured.