TECHNICAL TERMS AND DEFINITIONS
Abrasion
Undesirable change of the surface due to loosening of small particles as a result of mechanical stress. Also generally known as wear. The abrasion is determined according to DIN 53516. Here, a specimen is guided with a certain contact pressure on a rotating roller covered with a test emery sheet. The total friction path is approx. 40 m. The loss in mass caused by abrasive wear is measured, taking into account the density of the test specimen and the attack of the emery sheet. The information is given as volume loss in mm?.
Additives
All components in a plastic formulation which are not polymers or their precursors and which are only added in relatively small quantities (UV stabilizers, flame retardants, conductive carbon black, etc.)
Aging
The totality of all chemical and physical processes irreversibly taking place in a material over time. This usually leads to a deterioration of the service properties. Heat, light, high-energy radiation, chemicals, weather, oxygen (ozone) are frequent causes of ageing. The aging condition, mostly surface attack, is monitored by changes in material properties such as toughness, turbidity, molecular weight, etc.
Bending radius
Smallest permissible radius when laying a hose line. The bending radius is given in mm and always refers to the inside of the hose bend.
Compression set
The determination of the compression set DVR [%] according to DIN 53517 is a creep test over 24 hours at 70 ?C and 72 hours at room temperature with constant deformation. The permanent deformation is measured after the specimen is unloaded again.
Elasticity
Means the ability of a material to reshape after removal of an externally applied mechanical stress.
Elastomers
Designation for wide-meshed, cross-linked, macromolecular substances which can be stretched by at least twice their original length by the application of a slight force at room and higher temperatures and which, once the force has been removed, return rapidly and practically completely to their original form.
Flame retardants
Are plastic additives which reduce the flammability and combustibility of plastics. Flame retardants can intervene in the combustion mechanism either physically by cooling, coating and diluting or chemically by reaction in the gas phase (elimination of the energy-rich radicals supporting combustion) or in the solid phase (formation of a protective coal or ash layer).
Flexibility
Force required to achieve the minimum bending radius (the greater the force required, the less flexibility).
Flow / Creep
The delayed but still reversible deformation of a viscoelastic material under constant load is called creep. The irreversible deformation occurring at higher loads is called flow (in cold state). The flow process leads to failure of the component under unchanged load.
Gas permeability
Passage of a gas through a test sample. This takes place in three steps:
Dissolving the gas in the sample.
Diffusion of the dissolved gas through the sample.
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Evaporation of the gas from the sample.
The permeation coefficient is a material constant which indicates which volume of gas passes through a test specimen of known area and thickness at a given partial pressure difference in a given time. It depends on the temperature and is determined according to DIN 53 536.
Halogens
The elements fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) form the group of halogens.
Hardness
Hardness is the resistance of a material to the penetration of a body of a certain shape and defined spring force. The penetration depth of the test body is a measure of hardness. The hardness of elastomers is determined according to Shore A or Shore D in accordance with DIN 53505. It is given as a whole number from 0 to 100 and the letters A and D. The larger the number, the higher the hardness.
Hydrolysis resistance
Hydrolysis = irreversible splitting of the polyester chains in ester polyurethanes. It is caused by prolonged storage in warm water, saturated steam, tropical climate (moisture in combination with heat), aggressive chemicals or aggressive wood dusts. The consequence of hydrolysis is a decrease in mechanical strength properties. Ether polyurethanes are resistant to hydrolysis.
Microbe resistance
Ester polyurethanes can be destroyed by long-term contact with earth-like substances or heavy contamination under conditions favourable to microbes, as the enzymes released by the organisms damage the chemical bonds. Under very unfavourable conditions, initial damage occurred after 8-24 weeks. This time can be delayed by adding toxic fungicides, but later on, by leaching and leaching of the additive, the value may fall below the limit required for protection. It is of the utmost concern that the often toxic fungicides inevitably migrate to the surface and come into contact with the user or conveyed material. Such solutions do not meet our quality level and are therefore not part of our product range. Our hoses made of ether polyurethane are permanently not attacked by microbes and are the clearly better solution here.
Specific volume resistance
According to TRGS 727 the volume resistivity RGES = R?A/S [??m] must be determined. Where R is the measured resistance, A is the surface area of the electrode and S is the thickness of the reed between the plastic and the wire. A piece of hose 100 mm long with a cylindrical electrode inserted on one side is measured, with the counter electrode forming the steel wire helix. The volume resistivity determined thereby must be RGES < 2.5 x 1018 Ohm.
Surface resistivity
The surface resistance (Ro) indicates the insulating capacity of the insulating material surface. Ro is reduced in plastics by the formation of a water film which is created by the action of hydrophilic groups (-COOH, -NH2, -OH), plasticizers and organic fillers. Ro is determined at a test voltage of 1 kV between two electrodes (spring-loaded metal blades) located at a distance of 10 mm. Ro is given either in ohms or as a comparative figure, e.g. 10 = Ro < 10 or comparative figure 6; 10 = Ro < 10 or comparative figure 11.
Permeation
The passage of a gas through a sample is called permeation. It takes place in three steps:
Dissolving the gas in the sample
Diffusion of the dissolved gas through the sample
Evaporation of the gas from the sample
The permeation coefficient Q in m?/(s * Pa) is a material constant which indicates the gas volume
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passes through a test specimen of known area and thickness at a given partial pressure difference in a given time. It depends on the temperature and is determined according to DIN 53536.
Swelling
Absorption of liquid and gaseous substances into solids without a chemical reaction taking place between them. The consequences are an increase in volume and weight combined with a corresponding decrease in mechanical values. After evaporation of the penetrated substance and the associated decrease in swelling, the original properties of the product are almost restored. The swelling is therefore a reversible process.
Peak compressive strength
Resistance to compression of suction and discharge hoses by external load applied at the apex.
Water vapour permeability
It is characterised by the amount of water vapour that passes through 1 m? of sample surface in 24 hours under defined conditions and is approximately inversely proportional to the sample thickness. The water vapour permeability WDD in g/(m?*d) of a plastic is determined according to DIN 53122 sheet 1.
Tear resistance
Tear propagation resistance is the resistance that a notched test piece offers to tear propagation. The test is carried out in accordance with DIN 53515 on angle specimens which are provided with a notch on one side.
UV radiation
Depending on the duration and intensity, plastics can be chemically degraded by the action of UV radiation (ageing). Polyurethanes generally have a good UV resistance. In the course of time, the material turns yellow, which does not automatically cause a decrease in the mechanical properties. With the help of UV stabilizers and/or color pigmentation a certain stabilization can be achieved. We offer special hose solutions for increased and strong UV- exposure. Please contact us in such cases.
