High pressure hydraulic hose

High Pressure Hydraulic hose

In  recent years hydraulic has grown steadily and this trends is likely to continue well into the next century. The technological demands made on hydraulic hose manufactures have also increased and will intensify further in parallel  with market requirements for high pressure hoses.

Pressure levels available for high pressure hoses have increased inordinately with improved design and the wire industry has provided a higher strength product to give designer the necessary material to facilitate these advances. Larger diameter wires with very high tensile strengths are now available which have the processing characteristics necessary for hose manufacture.

Aramid textile fiber has also played a significant role in allowing

the production of higher  pressure hoses particularly for the offshore oil industy. Hoses have become slimmer in wall, lighter in weight

and more flexible thus they are able to work at lower bend radii and with capability and because of improvements in compound design and the availability of newer elastomers, at much higher temperatures. The distinction between rubber and plastics has become quite blurred with some thermoplastics having properties that make them virtually indistinguishable from traditional vulcanized rubbers and such material have found a place in the hose manufacturing industry.

Hoses have been combined with electric cables as an integral product to allow the transmission in a single flexible conduit of electric power or communication          signals          and    hydraulic pressure.

Hoses form 5 to 32 mm bore are usually  made on flexible rubber or thermoplasic mandrels. The innerliner is crosshead extruded on the  lubricated mandrel form a cold feed rubber extruder. A short freezing section just prior to the braider ensures that the inner liner is hard enough to withstand the stresses of braiding.

After braiding the hose is covered on a cold feed crosshead extruder frequently the hose is branded at this stage immediately downstream of the crosshead antitack is required is applied and after a period of maturing the hose is either passed through a lead extruder( where a lead sheath slightly smaller than the outside diameter of the hose is applied) or wrapped with nylon fabric on an orbital or concentric wrapping machine. Whether wrapped or leaded the hoses are coiled onto drums which are placed in an autoclave to effect cure. The time and temperature of vulcanization depends on several factors such as mandrel types but it is important  in hydraulic hose manufacture to obtain  a tight cure to minimize compression set, an important property for good end fitting retention. It is also important  property for good end fitting retention. It is also important to have compound that cure at similar rates to ensure good bonding between compounds.

After cure and cooling the lead is stripped off or the wrap is taken off and the mandrel should be loose inside the vulcanized hose. The mandrel loosens  because of the significant thermal expansion differential between the mandrel ( and the inner liner material) and the metal reinforcement.

 During heating in the autoclave the mandrel and the innerliner compounds swell relative to the wire reinforcement. The inner liner material is forced outward into the braid interstices, and bonding to the wire reinforcement takes place. Upon cooling, the mandrel shrinks back to its original size leaving the inner liner bonded to the wire and a gap develops between the mandrel and the inner liner.

         

 It is possible to blow mandrel lengths up to 500 m out of hose in favorable circumstances but a more practical length 200-300 m for smaller sizes and perhaps 150-200 m for 25 and 32 mm bore sizes. Hoses are usually proof tested at this point to pressures recommended in the SAE.

      The water is blown out by air pressure and the finished hose is ready for  dispatch. Cold feed extruders with mixing screws properly fed with consistent and dry compounds and can extrude the innerliner onto the mandrel with a good level of accuracy, especially if the system controlled with the help of a laser or optical micrometer. Covers can be extruded over the wire reinforcement  layer with equipment similar to that used for liner extrusion.

Ultrasonic concentricity equipment which can monitor the concentricity of the innerliner on the mandrel or the cover on the reinforcement and allow adjustments to be made if concentricity is not perfect can be now placed just down stream of the extruder  die.