What is the hose/ fitting material wear through erosion and abrasion?

Bulk material handling hoses - Tubes International

Bulk material handling hoses

Bulk material handling hoses – general information

Material handling hoses are used for the transfer of bulk loose materials with high abrasion coefficient. They are used for such applications as sandblasting, shot-blasting, dry-ice blasting, plaster, concrete, cement, sand and gravel transfer but also for grain, granules, feed, seed, sugar, flour (detailed information concerning application are available on catalogue pages of particular hoses).

To match the specific requirements of these applications, the material handling hoses are made of such abrasion-resistant materials as: SBR/NR rubber compound, PU/PVC plastic material or ceramic plates embedded in natural rubber. The inner layer of food grade hoses is made of white rubber. The abrasion resistance of the rubber hose inner layer ranges from 36 mm³ do 80 mm³ according to DIN 53516 (the smaller the value, the higher abrasion resistance of hose material).

The hoses in this group are available in inner diameter range from 13 to 500 mm. The maximum working pressure is 80 bar (hoses for concrete).

The fittings can be assembled on the material handling hoses using either worm drive clamps, bolt clamps, special screwed flanges or they can be crimped with ferrules. For more information see Industrial fittings section.

For other material handling hoses see ducting hoses group and steel stripwound hoses group.

Material handling hoses – for loose bulk materials

Hoses for loose bulk materials are used for the transfer of granules, feed, seed, grain, sugar, flour, powder, cement, lime and sand. These dry bulk materials are conveyed through the hose with the use of compressed air or no pressure (gravity drop). Widely used in warehouses, silos, cement mills, mines, power plants, steel mills, plants manufacturing insulating materials. Commonly used in road and rail transport for loading/unloading operations (cement trucks, feed trucks, flour trucks).

The material handling hoses for loose materials are made of abrasion-resistant SBR/NR rubber compound, PU/PVC plastic material or ceramic. The inner layer of food transfer hoses is made of white rubber. The abrasion resistance of the inner rubber layer is determined by rubber volume loss expressed in cubic millimetres according to ISO 4649 (previously according to DIN 53516) – the smaller the value, the higher abrasion resistance of hose material.

Fittings intended for material handling hoses for loose bulk materials (see INDUSTRIAL FITTINGS) should be mounted with worm-drive clamps, bands and bolt clamps or crimped with ferrules.

For other material handling hoses for loose bulk materials see the following hose groups as well: ductingu hoses and steel stripwound hoses.

Sandblasting

Hoses for cleaning and wet blasting: with sand, steel shot or dry ice.

They are made of extremely abrasion-resistant SBR/NR rubber compound, reinforced with textile cord. The abrasion resistance of the inner rubber layer is determined by rubber volume loss expressed in cubic millimetres according to ISO 4649 (previously according to DIN 53516) – the smaller the value , the higher abrasion resistance of hose material.

They are used with special couplings and nozzles for sandblasting, made of cast iron, aluminium or nylon (see INDUSTRIAL FITTINGS).

Dredge hoses

Delivery and suction-delivery hoses for gravel and sand with water used on suction dredgers and dredger cutters during dredging operations aiming to remove sediment from waterbed or to deepen waterways. They are used for the suction of dredge spoil (pulp) from the bottom and then for the transfer from the dredger to a dump site. Used in gravel pits and sand pits.

The inner layer made of SBR/NR rubber reinforced with textile cord or steel wire braid, with additional steel helix. The outer layer resistant to seawater, oil, abrasion and weather conditions. Supplied as complete hose assemblies with built-in, vulcanised and rubber-protected flanges.

Hose/ fitting material wear through erosion and abrasion

Solid particles, flowing through the hose in a stream of air, water or semi-liquid mass, rub against the walls of the hose or fitting and hit them at different angles, particularly where the flow is turbulent or changes direction (e.g. hose bends, fitting elbows). Wear on the hose or fitting takes the form of material loss, abrasion of the inner layer of the hose, the formation of blisters and pits.

Rubber abrasion standards and their importance
Abrasion testing is carried out by measuring the volume loss (mm3) of a rubber sample in the form of a disc pressed with a specified load against a rotating roller covered with abrasive paper, after a specified abrasion distance (number of rotations). Details are provided in ISO 4649 or the older DIN 53516. The results of such tests, given by manufacturers on the inner layer of each hose, allow only a theoretical comparison of hoses, with a better, more abrasion resistant hose showing a lower abrasion (loss) value given in mm3: 50 mm3 is better than 80 mm3.

But how is it in practice?
The wear will depend on a combination of many factors:

nature of the particles (material, hardness, size, weight, shape of the particles);
speed and angle of impact of the particles against the wall material;
physical properties of the wall (material, its hardness, abrasion resistance and other mechanical properties, surface smoothness);
temperature and its effect on material properties;

The abrasion resistance of the material measured in a lab is therefore only one of many factors in hose or fitting wear characteristics. It is not possible to calculate the service life of a material handling hose: the same hose may function well for a very long or short time depending on, for example, the shape of the granulate grains. The thickness of the inner layer of the hose is of major importance for the service life of the hose.

Rubber or plastic often better than metal
Rubber and some plastics will, in many cases, perform better and show less wear than, for example, steel. But why? The kinetic energy of a solid particle, when it hits a rubber surface, is converted into the energy of elastic deformation of this surface and is largely given back to the particle as it bounces away, without destroying the rubber surface. That is why elbows in steel pipelines are lined with rubber and some steel fittings are mounted on the outside of the hose rather than inserted into the hose. Typical materials used for the inner layer of material handling hoses: natural rubber (NR), natural and synthetic rubber compound (NR/SBR), and plastics – polyurethane (PU).

Static electricity and static electricity hazards

Solid particles, flowing through the hose in a stream of air, fluid or semi-liquid mass, collide with each other and hit against the walls of the hose generating electrical charges and causing static electricity build-up. Static electricity is dangerous because:
• it can attract a charged substance (e.g. dust), which can build up and clog the hose;
• voltage of the accumulated charge can cause a spark and consequently a fire or explosion with catastrophic results!

Flexible hoses are made of rubber or plastic, which generally are insulators – electrical charges cannot move freely in them, dissipate or flow down to the ground. Air is also an insulator, so the problem of static electricity is particularly serious in pneumatic transport. In order for electrical charges to dissipate, the use of:

conductive rubber:
R ≤ 10⁶ Ω

antistatic rubber:
10⁶ Ω < R ≤ 10⁹ Ω

antistatic copper wires
R ≤ 10 Ω

in various combinations (inner layer, outer layer) and depending on the application of the hose. It is absolutely essential to:

when using a hose with a wire – effectively and permanently connect the wire to the fittings and ground it. Inspect. The wire will not fully replace an antistatic inner layer.
for potentially explosive atmospheres (ATEX) – carry out a risk analysis

For other material handling hoses check these chapters: „Ducting hoses” and „Stripwound steel hoses”.

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