FIELD OF THE INVENTION

The present invention relates to the field of hose manufacturing and, in particular, to the coating of flexible mandrels used in the manufacture of hose

BACKGROUND TO THE INVENTION

Flexible thermoplastic mandrels are used to produce rubber hose for applications such as (but not limited to) hydraulic machinery (e.g., earth movers, mining equipment), automotive (e.g., air conditioning) and general industrial uses (e.g., gasoline pump, steam).

Flexible mandrels are used in preference over rigid steel or aluminium mandrels as they enable more efficient production of rubber hose which can be made in very long lengths (e.g., 1000 meters and over). There are significant advantages of very long lengths, including the ability to wind the hoses and mandrels onto cylindrical cores for storage and transportation.

Flexible mandrels are often made from polyamides, polypropylene, thermoplastic elastomer (TPE), or polymethylepentene (TPX) materials, all of which have excellent properties that lend themselves to the mandrel application. One drawback to the use of such materials is that the adhesion and coefficient of friction between them and most industrial rubbers can be significant and the formation of chemical and physical bonds can occur during the curing stage of hose manufacture, thereby creating the challenge of extraction or blow-out of the mandrel from the hose.

Standard practice for use of flexible (and rigid) mandrels includes ensuring the mandrel is coated with a temporary release coating (mandrel lubricant) such as a fluoropolymer or siloxane dispersion/emulsion in water (occasionally in organic solvents). The lubricant is applied to the surface of the mandrel to enable the mandrel to be removed from the moulded hose using a lower force and expending less energy. A shift from solvent to water-based mandrel lubricants has taken place over the last 10+ years primarily driven by issues relating to the use of volatile organic compounds as well as the desirability of minimising the use of flammable materials within the manufacturing process.

The mandrel lubricant is generally applied to the mandrel surface prior to use, to enable the hose manufacturer to remove the mandrel at the end of the manufacturing process. This removal process is normally done by applying high pressure water to one end of the hose - in essence, pushing the mandrel out of the hose.

While solving some issues, the shift of mandrel lubricant from solvent based to water based also created an issue for hose manufacturers due to long dry times required by the water-based system. If the external surface of the mandrel is not sufficiently dry, the residual mandrel lubricant may lead to the creation of pin-holes in the rubber tube lining where residual water is turned to steam at high temperature (an inevitable part of the hose manufacturing process during which the hose is cured/vulcanised in the final step of the process at 140-160°C in an autoclave).

The existence of pin holes in a high-pressure hose will render it unusable and is a well-known cause of hose scrap within the hydraulic hose industry.

The mandrel removal (ejection or blow out) process can often be troublesome within a hose manufacturing plant (in addition to the pin hole issue described above), due to:

Inefficient or poorly applied lubricants can make mandrel removal difficult and time consuming - in effect, the inconsistent application of lubricant can leave the interface between the hose and the mandrel with a higher than ideal coefficient of friction in areas and may enable or allow the creation of chemical and physical bonds. Over long lengths of hose/mandrel, this can cause sticking or non-release of the mandrel.

- Use of high water pressures to blow-out a mandrel from a hose can force out and leave behind the surface of the mandrel inside the hose, creating a plastic residue on the internal surface of the hose (a common issue known as snakeskin). - Hoses may need to be cut into shorter lengths if the mandrel will not move. This is undesirable as the mandrel will need to be re-joined (welded together) prior to being used again (so a long continuous length of hose can be made). Joins/welds are sometime considered defects and can be limited by some manufacturers of hose (e.g., no more than x number of welds in y length of mandrel). This can lead to premature end of mandrel life, scrappage and higher costs for the hose manufacturer.

- Poor or slow mandrel removal can also cause manufacturing constraints or “bottle-necks” in hose plants. Larger factories may have 30+ lines producing hose, but perhaps only 3 mandrel removal stations which can become backlogged quickly if not working efficiently.

It should also be noted that effective mandrel lubricants (release coatings) are considered expensive - and as they are applied at the start of the hose manufacturing process, they create a significant cost burden to hose manufacturers.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a flexible hose mandrel having a surface coating comprising a polysiloxane and a micro or nano size silica.

Preferably, the polysiloxane is a fluorinated polysiloxane, more preferably a fluorinated polydimethyl siloxane.

Preferably, the coefficient of friction between the mandrel and the hose, during manufacture of the hose, is less than that between a traditional flexible mandrel and a hose.

The present invention also provides a method of manufacturing a flexible hose mandrel comprising applying to a mandrel a coating comprising a polysiloxane and a micro or nano size silica.

Preferably, the poly siloxane is a fluorinated poly siloxane, more preferably, a fluorinated polydimethyl siloxane. Preferably, the coefficient of friction between the mandrel and the hose, during manufacture of the hose, is less than that between a traditional flexible mandrel and a hose.

The present invention further provides a method of manufacturing a hose comprising forming the hose with a flexible mandrel coated with a coating comprising a polysiloxane and a micro or nano size silica.

Preferably, the polysiloxane is a fluorinated polysiloxane, more preferably, a fluorinated polydimethyl siloxane.

Preferably, the coefficient of friction between the mandrel and the hose, during manufacture of the hose, is less than that between a traditional flexible mandrel and a hose.

The present invention enables a hose to be made using a flexible mandrel with a coating that enables a lower energy release from the hose during the manufacturing process with no requirement for added lubricant within the process.

The invention relates to a material coating for traditional mandrels that lowers the adhesion and surface energy or coefficient of friction between the mandrel and the hose that is manufactured with the mandrel as its support, thus lowering the force required to remove the mandrel from the hose.

The coating has excellent longevity so that the coated mandrel may be used repeatedly, for instance, up to 50 times in making rubber hose.

The performance of the release coating is managed by controlling film thickness to incorporate wear caused by repeated use. Film thickness is optimised by coating application and in some cases, repeating the coating process.

The traditional mandrel production process is well documented. The application of the coatings to the base material of the mandrel is effected by, for instance, either continuous dip coating or spray coating. During continuous dip coating, the mandrel passes at a constant speed through a reservoir of the coating material. During spray coating, the coating material is converted into a mist by an appropriate spray gun and is sprayed onto the mandrel’s surface. Suitable wiping and drying methods are used to remove solvents and excess coating material from the surface, thereby achieving a smooth and uniform coating layer.

The coating is cured prior to use to create a permanent, durable layer onto the surface of mandrel. Curing happens at ambient conditions and the curing time is preferably 1 to 10 days, more preferably 1 to 7 days and most preferably 1 to 5 days.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are as follows:

Figure 1 is a cross section of a coated mandrel; and

Figure 2 is a schematic diagram of the coating process.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described, by way of example only, with reference to the accompanying drawings.

Referring to Figure 1 of the accompanying drawings, there is shown a coated mandrel 1 comprising the core mandrel 3 and a coating layer 5. Core mandrel 3 is a round cylindrical rod made from a polymeric material such as nylon 6, polypropylene and thermoplastic elastomers. The mandrel 1 may be produced by an extrusion process and it can be used in many industrial applications in addition to hose manufacturing processes. The coating 5 comprises a fluorinated polydimethyl siloxane material mixed with micro or nano size silica. The coating 5 bonds onto the surface of the core mandrel 3. The bond may be a direct bond which is one or more of: a physical interaction at the molecular level, a chemical (e.g., covalent) bond, a polar-polar interaction bond, a Van der Waals bond, and a hydrophobic interaction.

Referring to Figure 2 of the accompanying drawings, the method of manufacturing the coated mandrel comprises the steps of:

1- Coating: the mandrel 1 is fed from a process drum 7 to a coating station 9 where a coating is applied by a suitable coating method such as a dip coating process and a spray coating process. In an example of a dip coating process, the mandrel 1 passes at a constant speed through a reservoir of the coating material. In an example of a spray coating process, the coating material is converted into a mist by an appropriate spray gun and is sprayed onto the surface of the mandrel. 2- Wiping: the mandrel is fed from the coating station 9 to the wiping station 11 where excess solvent/coating material is removed by passing the coated mandrel 1 through a material such as a sponge, fabric or a rubber sheet/cone where the material contacts the mandrel surface.

3- Drying: following the removal of excess coating from the mandrel surface, the coated mandrel is fed to a drying station 13 where the coating is cured either: a. in line by passing the coated mandrel through a sufficiently long heated tunnel (e.g. infra red or hot air); or b. off line by using the method above, or at ambient or at an elevated temperature where the curing time will be reduced Following drying, the mandrel is fed to drum 15.