Technical Terms and Definitions

Abrasion

Unwanted alterations of the surface by separation of small particles as a result of mechanical strain. Generally known as abrasive wear. Abrasion is determined according to DIN 53516. By doing this a sample body with a particular contact pressure is guided on a turning roll covered with a testing emery sheet. The complete reaming distance is appr. 40 m. The loss of mass produced by abrasive wear is being measured in consideration of the density of the test body and the active sharpness of the testing emery sheet. It is indicated as loss of volume in mm3.

Additives

All components of a plastic formulation, which are not polymers or their pre-products, and which are only added with relative small quantities (UV-stabilizers, flame protection agents, conductivity carbon black etc.).

Ageing

All chemical and physical processes ocurring irreversibly in a material in the course of time. This usually results in deterioration of the properties of use. Heat, light, high-energy radiation, chemicals, weather, oxygen (ozone) are frequent causes for ageing. The ageing condition, mostly active surface, can be pursued with the alterations of the material properties as toughness, turbidity, molecular weight, etc.

Bending radius

Smallest permissible radius when laying a flexible hose line. The bending radius is indicated with mm and it always refers to the inside of the hose arch.

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 remaining deformation is measured after the sample has been relieved again.

Elasticity

Means the ability of a material for a rebound after mechanical stress from outside has been removed.

Elastomers

Indication for wide-meshed cross-linked, macromolecular materials, which can be stretched at least for the double of their initial length by impact of a banal force at room or higher temperatures, and which return to their original form quickly and almost completely after the force has been removed.

Flame retardant

Are synthetic additives, which reduce the ignitability and flammability of synthetic materials. Flame retardants are able to intervene to the flammability mechanism either physically by cooling, coating or diluting, or by a chemical reaction in the vapor phase (elimination of the high-energy radicals supporting the combustion) or in the solid phase (formation of a protective carbon or ash film).

Flexibility

Required effort for the obtainment of the minimal bending radius (bigger effort results in smaller flexibility).

Flow / creeping

A deformation delayed in time but still reversible of a viscous-elastic material with constant load is indicated as creeping. An irreversible deformation occuring with higher load is indicated as flow (in cold state). The flow process results in failure of the component when the load remains unchanged.

Gas permeability

Flow-through of a gas through a test body. It is performed in three steps:

1. Solution of the gas in the test body.
2. Diffusion of the dissolved gas through the test body.
3. Evaporation of the gas from the test body.

The permeability coefficient is a material constant, which indicates, which gas volume flows through a test body of a known surface and thickness at a given partial pressure difference during a particular time. It is depending of temperature and it is being determined according to DIN 53 536.

Halogens

The elements fluorine (F), chlorine (Cl), bromine (Br) and iodine (J) are the group of the halogens.

Hardness

Hardness is the resistance of a material against the penetration of a body of a particular form and a defined elastic force. The depth of penetration is a measure for the hardness. The determination of the hardness of elastomers is carried out by Shore A or Shore D according to DIN 53505. It is indicated with an integer from 0 to 100 and the letters A and D. A higher number indicates a higher hardness.

Hydrolysis resistance

Hydrolysis = irreversible breakdown of the polyester chains with ester polyurethanes. It is caused by longer storage in warm water, saturated steam, tropic climate (humidity together with heat), aggressive chemicals or also aggressive wooden dust. The result of the hydrolysis is a decrease of the mechanic stress characteristics. Ether polyurethanes are resistant against hydrolysis.

Microbe resistance

Ester polyurethanes may be destroyed during a long-time contact with earth-like substances or a heavy faulting with favourable conditions for the microbes, because the chemical linkages are damaged by the enzymes released by the organisms. Very unfavourable conditions caused a first damage after 8-24 weeks. Although it is possible to delay this time by addition of toxic fungicides, the limit value required for protection may fall below by washout and dealcalization later. It is highly questionable that the often toxic fungicides are migrating inevitably to the surface and there get in contact with users or materials. These solutions do not meet our quality standards and therefore are not part of our delivery program. Our tubes of ether polyurethane are not attacked by microbes permanently and they are a better solution here obviously.

Surface resistance

The surface resistance (Ro) indicates the insulating ability of the insulator surface. Ro is reduced with synthetic materials by the formation of a water skin, which results from the effect of hydrophilic groups (-COOH, -NH2, -OH), plasticizers and organic extenders. Ro is determined with a test voltage of 1 kV between two electrodes at a distance of 10 mm (resilient metal edges). Ro is either indicated in Ohm or as a reference number, e.g. 10 = Ro < 10 or reference number 6; 10 = Ro < 10 or reference number 11.

Permeation

The flow-through of a gas through a test body is indicated as permeation. It is performed in three steps:

1. Solution of the gas in the test body.
2. Diffusion of the dissolved gas through the test body.
3. Evaporation of the gas from the test body.

The permeability coefficient Q in m2/(s * Pa) is a material constant, which indicates, which gas volume flows through a test body of a known surface and thickness at a given partial pressure difference during a particular time. It is depending from temperature and it is being determined according to DIN 53536.

Swelling

Absorption of liquid and gaseous materials in solids, without any chemical reaction takes place between them. The result is an increase in volume and weight together with a corresponding decrease of the mechanic values. After the penetrated material has been vaporated and the decrease of the swelling caused by this the original characteristics of the product are nearly reached again. Swelling is therefore a reversible process.

Vertex compressive strength

Resistance against the compressing of exhausting and pressure hoses by outside load found in the vertex.

Volume resistivity

According to TRGS 727 volume resistivity R_GES = R×A/S[Ω×m] must be determined. Where R is the measured resistance, A  is the lateral surface of the electrode and S is the reed thickness between plastic and wire.
A piece of hose with a length of 100mm is measured by a unilaterally inserted cylindrical electrode, where the counter electrode is forming the steel wire helix. The thus determined volume resistivity must be R_GES < 2,5×10¹⁸ ohm.

Water vapour permeability

It is indicated by the quabtity of water vapour, which is running through 1 m2 test surface, and it is approximately inversely proportional to the test thickness. The water vapour permeability WDD in g/(m2*d) of a synthetic material is determined according to DIN 53122 sheet 1.

Cracking resistance

Cracking resistance means the resistance, which is offered to further cracking by a notched test body. The inspection is carried out according to DIN 53515 with angle tests, which have a single-sided notch.

UV radiation

According to duration and intensity, synthetic materials can be broken down chemically by the action of UV radiation (aging). Polyurethanes have generally a good UV resistance. In the course of time there is a yellowing of the material, what does not automatically cause a decrease of the mechanic property values. With the help of UV stabilizers and/or by colour pigmentation a particular stabilization can be accomplished. We offer special hose solutions for increased and high UV exposure. Please contact us in such cases.