CA1121123A - Hose manufacture - Google Patents

Abstract

ABSTRACT
HOSE MANUFACTURE

A method of manufacturing a hose comprising a layer of polymeric material having an embedded reinforcement structure. The hose structure is formed on a mandrel and the polymeric material is cured by passing the assembly through a curing unit containing heating fluid at a pressure greater than 100 p.s.i.
The use of pressures greater than 100 p.s.i. ensures the hose components are securely bonded to one another and avoids the use of a conventional outer lead sheath which is expensive and the fitting and removal of which considerably increases the cycle time.
Preferred heating fluids are salts, such as a eutectic mixture of sodium and potassium nitrates, a mixture of sodium nitrate and sodium nitrate or Cassell TR 155. At the vulcanisation temperatures of 170 - 200°C used the temperature of the heating fluids is substantially independent of pressure.
Pressures up to 500 p.s.i. can be used to achieve the necessary bonding of the hose components.

Description

1.
HOSE MANUFACT~RE
This invention relates to a method of rnanuEacture of hose and in particular, though not exclusively, to a method su~table for the continuous manufacture of long length hose. Conventionally, long length hose is manuf~ct-ured by ex~ruding inner lining layer of elastomeric material onto a mandrel, applying a braided wire or cord, or helically wound strip, reinforcement layer by means of a braiding machine or strip winding machine, applying an outer ~overing layer of elastomeric material and vulcanis-ing the assembly. Long lengths of such hose are made on a flexible mandrel, for example a nylon rod, and in this case the assembled hose is covered by a sheath oflead, which is applied by a lead press or lead extruder, to protect the outer cover from marking by steam during vulcanisation and damage by handling. ~he assembly is then coiled up and placed in a curing oven in this coiled state, After curing, the lead sheath is slit and remo~ed whereupon the lead may be re-used.
Whilst produclng good quality hose, the lead sheath method has the di~advantage of requiring the provision of expensive lead coa~ing apparatus7 Surface marking by ~team and damage by handling can to a certain extent be avoided by providing the hose with a temporary wrapping shaath of, for example, helically wound nylon strip material during vulcanisation. This does, however, leave a helically extending imprint on the outer hose ~urface where the hose has been contacted

2.

directly by edges of the nylon ~trip. This imprint is not cor.sidered by customers to be indicative oE a high quality product and it i5 highly desirable to avoid the formation of such markings.
Damage by handl.ing can alternatively be avoided by use of a catenary me~hod o manufacture in whlch following the formation of a cover layer over a reinforcement structure the resulting hose assembly, supported internal.ly by a mandrel, is fed continuousl~ to a steam heating chamber where it is suspended out of contact with the structure of the chamber. The cover and other curable layers of the hose stxucture are cured sufficiently before the hose leaves the chamber so that no surface damage results from contact of the hose with seals at the exit of the ch~mber. This method is cheap to use and also convenient since steam supplies are commonly availabla in factories especially those making use of vulcanisation equipment. In practlae, however, ik has been found that at ~he required vuloani~-ation temperaturQ~ the pres~ure which can be u~ed i5 insuflcient to effectively bond the layers toyether and hoses manufactured by this rnethod have tended to fail by bursting or separation of cvver and reinforcement layers sooner than equivalent hoses made by the lead ~heath method.
According to one asp~ct of the present invention, we provide a method of continuous hose manuacture comprising continuously feeding a long leng$h flexible mandrel supporting a~ ,f~u~ hose assembly comprising an inner liner of i ( ,~7,~-, ~ uncured polymeric material and a reinforcement structure to ~, .,~

3.

an extruder and extru~iny an ou-ter cover of curable polymeric material around said reinforcement structure and continuously fe~ding said mandrel and covered hose assembly through a curing unit in which said covered hose assemhly is surrounded by and in contact with heating fluid at a pressure in the range from lO0 to 500 p.s.i. and a temperatu~ suffic~ent to effect curing of sai~ lin~r and cover materials, said curing temperature being substantially independent of the curing pressure and subsequently removing said flexible mandrel~
By the use of a pressure greater than lO0 p.s.i., it has been found that the resulting hose has a resistance to failure very similar to that of hose manufactured by the lead sheath method. Whilst it is ~ecessary to provide a suitable curing unit and:means for the supply of heating fluid at a high pressure, this will in general be less costly than the provision of lead sheathing and stripping equipment.
Preferably the pre~sure of the heating fluid is greater than : 250 p.s.i. and more preferably is of the order oE 400 p,~.1., though even higher pressures may be used. The use of very high pressures leads to difficulty in ensuxiny~an adequate heatiny 1uid seal be~wee~ the curing unit and hose passing therefrom, and does not result in any improvement in hose quality. Thus the use of pressures greater than in the order of 500 p.s.i.
is not genexally envisaged.
Preferably the heating fluid is a compound having a liquid form at vulcanisation temperatures of the order of 170-200C and the vulcanisation temperature is substantially independent of changes in pressure. Consequently, for a vulcanisation temperature of the order of 170-200C
.; the pressure of the heating fluid can be ',~

,: , ~lAh~ 3 selected ~or example in the range ~rom 100 to 500 p.~,i , 50 that the layers of the hose are sufficiently bonded to one another. ~n this way a hose of similar ~uality to that obtained by the lead sheath process may be obtained without the above-mentioned problems and disadvantages of the lead sheath process.
A partic~llarly suitable heating fluid is a salt, such asa eutectic mixure of sodium and potassium nitrates, or a nitrate such as that identified by the trade mark Cassell TR155 ex I.C.I.
which has a liquid form at temperatures of the order of 170C.
The reinforcement structure may be formed from a layer o~
lapped, s~iralled, or braided reinforcement of metal wire or filaments, strands or yarns made of plastics material or other suitable material for example nylon or an aromatic polyamide such as that identified by the trade mark Kevlar (poly (p-phenylene terephthalamide) ) ex Du Pont.
The invention also provides hose manufactured by method in accordanae wlth the present invention.
One embodiment of the invention will now be described by way of example, with reference to the accompanyiny diagrammatic dr~wing showiny apparatus for the application of a cover layer to a part formed hose assembly and curing of the covered hose assembly.
The apparatus comprises a tubular curing unit 10 curved along its length so as to conform substantially to the catenary curve shape as adopted by the hose being passed through the unit 25 on a flexible mandrel supported only , .i,.

s.

at the end~ of the unit. One end o~ the curing unit surround~
the ou~let of an. extruder 11 provided ~or application o~ a cover layer lS to a part formed ho~e as3emb1y 14, and at the other end o~ the curing unit a water seal 12 is provided to 5 seal again~t the outer ~urface of substantially cured ho~e and re3trict lo~ o~ heating fluid from the curing unit~
The curing unit i~ provided with an inlet 13 in the region of the water qeal for the ~upply of pressurised heatiny fluid to the curing unit, and an outlet 16, for the heat-ing Eluid i~ provided on an upper part of the curing unitclose to the extruder 11. Haul-off means (not shown) i~
provided to draw cured hose from the curing unit.
In use of the apparatus a part fDrmed hose assembly 14 compr~ing a neoprene lining layer and a wire braided reinforaement layer surrounding the li~ing layer and ~upported on an inner flexible nylon mandrel 17 i9 Eed ; to the extruder 11 ~or application oE a rubber covex ~ layer 15 over the braided reinEorcemen.t. On leaving : the extruder the covered ho~e as~emhly immediataly enter~ the tubular curiny unit 10 and pa~es along the length o~ the curing unit to emerge through the water end seal 12 in a substantially cured condition~ Whil~t pa~ing through tho curing unit the covered ho3e a~3embly 15 i8 ~ubjected to heating from a salt mixture of sodium nitrite and 30dium nitrate supplled to the curing unit at a pre3sure in the order of 400 p.s.i~ and temperature of 200C. Subsequent to pa~age through the curing unit the mandrel 17 i~ removed from the covered ho~e 6.

as~embly.
Typically the flexible nylon mandrel has a length in the ord~r of SOO ~eet. Preferably to facilitate ease of continuous operation and to avoid the need for re-threading of the mandrel and covered hose assembly through the water end seal 12, two or ~-ore long length mandrels may be joined together for consecutive passage through the extruder and curing unit and subsequently separated to facilitate mandrel removal and coiling of the manufactured hose.
Whilst in the above-described embodiment reference is made to the use of a nylon mandrel, other materials such as steel may be used, and the mandrel may be of tubular or rod construction. An appropriate selection of the form of the mandxel enables the effect of buoyancy of the heating fluid on hose a3semblies of different diameter and density to be counteracked and thereby ensure that ~or a given haul-of~ ten~ion, the uncured ho~e material lS remain~ out o~ contact with the inner wall o~ ~he curing tube 10. Alternatively, similar mandrel~ may be used for a range of hose thicknesses and material~, and the variation of buoyancy counteracted by suitable adjustment of t~e haul-off tension.
The use of a catenary shaped curing tube is not sssential, and in an alternative apparatus the curing unit may be arranged ~o that the hose passee ~er~ically therethrough. Such an alternative doe3, however, 7.

requirs the provisiozl of a suitably tall building and thus the substantially horizontal catenary process i3 preferrsd as ~eing more .readily per~ormed in conventional factory ~pace.

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of continuous hose manufacture comprising continuously feeding a long length flexible mandrel supporting a hose assembly comprising an inner liner of uncured polymeric material and a reinforcement structure to an extruder and extruding an outer cover of curable polymeric material around said reinforcement structure and continuously feeding said mandrel and covered hose assembly through a curing unit in which said covered hose assembly is surrounded by and in contact with heating fluid at a pressure in the range from 100 to 500 p.s.i. and a temperature sufficient to effect curing of said liner and cover materials, said curing temperature being substantially independent of the curing pressure and subsequently removing said flexible mandrel.

2. A method according to Claim 1 wherein said heating fluid is a eutectic mixture of sodium and potassium nitrates.