Hoses and its processing

                                                                   Hoses:

Most hoses are made up of three elements: (1) a tube, (2) reinforcement, and (3) an outer cover.

1.   Tube

2. Reinforcement

3. Outer cover

Each of these components is usually adhered to the adjacent component by the bonding agents or thin layer of specially designed rubber.

Tube:

The tube is the inner most rubber or plastic element of the hose.The  tube may be placed over reinforcing elements. For suitable serive, the tube must be resistant to the materials it is intended to convey. The Characteristics of the rubber or plastic compound from which the  tube is made and the thickness of the tube are based on the service for which the hose is designed.

Reinforcement:

Reinforcement can be textile, plastic or metal alone or in combination, built into the body of the hose to withstand internal pressures, external forces or a combination of both .The type and amount of reinforcing material used depends on the methods of manufacture and on the service requirements.

Cover

The cover is the outer element and can be made. The prime function of the  cover is to  protect the reinforcement form damage and the environment in which the hose will be used, Covers are designed for specific applications and can be made to be resistance to oils, acids, abrasion, flexing, sunlight, ozone, etc.

Manufacturing Materials:

Rubber: To provide a wide range of physical properties for specific service  needs, elastomers are mixed with various chemicals.

                Plastics Materials Used In hose:

ASTM Designation    Common Name

              1.PA      Nylon

              2.PE   Polyethylene

              3.PVC  Polyvinyl chloride

              4.Polyester  

              5. Thermoplastic Rubber

              6.Fluoropolymer(PTFE)

.

                      Fibres Materials Used in Hose

1.       Aramid- para Aramid

2.  Aramid- Meta Aramid

3.   Cotton- Natural cellulose

4.   Glass-  Glass

5.  Nylon- Polyamide

6. Polyester- Polyester

7. PVA – Polyvinyl alcohol

8. Rayon- Regenerated cellulose

Fabrics:

Textile fabrics used as reinforcement in hose construction provide the strength to achieve the desired resistance to internal pressure or to provide resistance to collapse or both. The properties  of a fabric depend on the construction and the material from which the yarn is made and on type of weave used. One common hose fabric is woven from warp yarns which run length wise and filling yarns, which run cross wise. Usually they are woven at right angles to each other. The most common weave is known as plain weave.

Leno Weave

Leno Weave is used mainly where the fabric must be distorted in the hose as in certain types of curved hose. Leno also provides a means for better adhesion than other patterns. Woven cord is a special type of hose reinforcement. The warp cords are strong while the filling yarn is very fine and merely hold the cords in position. This is often called tire cord because this type of construction is commonly used in reinforcing tires. Woven cord provides strength in one direction only. When woven cord is used a minimum of two layers are applied in alternate directions. To adhere to the tube and cover of the hose,the fabic must be rubberized. The fabric is either fabricated or coated with a thin layer of rubber. Before rubberizing  some fabrics are treated with liquid adhesive.

YARNS:

Yarns are used in hose for reinforcement of the tube material to provide the strength to achieve the desired resistance to internal pressure or to provide resistance to collapse, or both. The basic yarn properties required for hose reinforcement are : adequate strength, acceptable heat resistance,dynamic fatigue resistance and satisfactory process ability for the various methods of reinforcing hose. Other special properties such as stiffness, adhesion, conductivity, etc. may be developed depending upon the specific hose application. Yarn is available in two basic forms; Staple( sometimes referred to as spun yarn) and filament.

Staple:

Staple yarn is made by twiating bundles of short fibers to form a continuous yarn. The staple obtains its strength from the binding effect of the twist imparted  to the individual fibers. The base staple yarn is called a singles. It is made from fiber bundles twisted together in one direction to form a single strand.

If two or more single yarn are twisted together usually in a direction opposite that of the single yarn

the result is a plied yarn. Two or more plied yarns may be twisted to form a cable cord. The strength, elongation  and thickness of yarn are a function of the twist level and the number of fibers in the bundle.

Staple yarns may be made  from natural or synthetic fibers or a blend of the two. The cotton count system is normally used to designate staple  yarn size.

The number of  “hanks” in one pound is the yarn number. A cotton hank is 840 yards. Therefore, a 2’s staple  yarn contains approximately 1680 yards in one pound. The cotton count system is an inverse

measure of the linear density of the yarn, i.e., as the yarn number increases the yarn size is decreased.

Filament Yarns

Filament yarn is produced by extruding  synthetic material through a spinnerette containing hundreds of orifices. The monofilaments form each of the orifices are brought together to form a  multifilament yarn.

Filament yarns have higher tenacity ( Strength per unit of weight- grams per denier), in the range of 2 to  3 times that of staple yarn on the same material type and size)

Yarn size is normally designated using the denier system(weight in grams of 1000 meters of yarn) is alos widely used. Both are direct yarn measurements. i.e, as  the number increases the yarn increases.

WIRES:

Reinforcing wire is used in a wide variety of hydraulic and industrial hose, primarily where textiles alone do no satisfy the special engineering requirements or the service conditions for which the hose is designed.

Steel Wire:

Steel wire has strength, high modulus for dimensional stability, fatigue resistance and low cost and is the major reinforcement used in high pressure hose and in most suction hose.

Steel Wire (High Tensile Low Carbon)

Small diameter high tensile steel wire is most commonly used for reinforcement in braided or spiral-wound hose for high pressures and high temperature applications. The wire normally used ranges in size from 0.008 inch to 0.037 inch (0.20 mm to 0.94 mm) in diameter.

Flat wire Braid:

This consists of an odd number of steel wires interwoven to produce a flexible reinforcement. It is used in specialized type of hose, either by itself of in combination  with other shapes of steel wire. Flat braids of standard sizes are composed  of 9,13,17 or 21 strands of wire in an over two under two plain braid pattern.

Wire cable:

Wire cable consists of multiple strands of round wire. It provides high bursting strength without undue loss of flexibility or crush resistance. Sizes range form 0.047 inch to 0.25  inch (1.19 mm to 6.4 mm) in diameter and are made from high tensile carbon steel wire.

Round Wire

Round is the most commonly used wire  shape in hose fabrication. It ranges in size from

0.031 inch to 0.875 inch (0.79 mm to 22.2 mm) in diameter. Round wire is generally made of high tensile carbon steel.

Rectangular Wire

Rectangular wire is most commonly used as a  helical reinforcement on the interior of rough

bore suction hoses to prevent collapse. It is sometimes used in the body of the hose.

Occasionally this type of wire is also used as an external helix embedded in and flush with the

rubber cover to provide protection against cutting and abrasion and to increase crush

resistance. Rectangular wire is generally steel, although aluminum may also be used.

Half-Round Wire

Half round steel wire is used mainly as a protective spiral armor on the exterior of a hose. It is wound with the flat side against the hose cover to provide maximum surface contact. It is available in stainless steel or steel with tin coated or galvanized finishes.

Wire Finishes

Wire finishes for steel wire can be either one  of two types, (1) brass drawn finish, or (2)

coated finish. The most commonly used finish in the hose industry is brass (drawn finish), or

galvanized (coated finish). Other finishes include bronze, liquor, and tin. Helical round

wires used as helical wound in the body of a hose may have a drawn copper finish, or may be

unfinished (bright). Rectangular steel wires used in the bore of a hose usually have a galvanized

finish.

Alloy and Non-Ferrous Wires

Under certain service conditions, carbon steel wire is not suitable. An alloy wire is used instead. One of the most commonly used is stainless steel which offers exceptional resistance to corrosion and heat. Where light weight is essential, alloys of aluminum are used.

Static Wires

Static wires and other conductive materials  are used in hose to prevent static electricity

buildup. Wires can be made from many metals  including copper, steel, monel, aluminum and

tin-coated copper. Static wires may be solid, stranded, or braided.

Manufacturing Methods

The principal methods used to manufacture hose will be described and illustrated in this chapter.  The

three basic methods: (1) non-mandrel, (2) flexible mandrel, and (3) rigid mandrel, describe how the various

components of the hose are supported during processing into a finished product.

THREE BASIC METHODS OF MAKING

HOSE

Hose is manufactured in the unvulcanizedstate by forming a cylindrical tube over which areinforcement and cylindrical cover are applied.n its uncured form, a hose tube will often needsupport to maintain proper internal diameterID) and dimensional tolerances while beingprocessed through the various stages ofmanufacture. Thus, the three basic methods of

making hose have evolved: (1) non-mandrel, (2)lexible mandrel, and (3) rigid mandrel. Inmethods (2) and (3), the mandrels are used forsupport and as dimensional control devices for

the hose tube during processing. Then after thehose building and, if necessary, thevulcanization are complete, the mandrels areremoved, inspected and recycled.

Non-mandrel Style:

The non mandrel method of manufacture is generally used for lower working pressure( less than 500 psi), smaller diameter texile reinforced products not requiring stringent dimensional tolerance. Typical hose products in this category would include garden, washing machine inlet and multipurpose air and water styles.

Essentially the non mandrel technique involves extruding the tube, applying the reinforcing and extruding the cover in the unsupported mode( without a mandrel). Frequently low pressure air is used inside the tube for minimal support, Keeping the tube from flattening during the reinforcing process. In some cases, especially 1 to 2 inch ID, the tube  may be extruded with air injection along with an internal lubricant to prevent adherence to itself.

The non-mandrel tube extrusion process can  be done continuously, if appropriate handling equipment is available, thus providing excellent length patterns for the finished product. In recent years with improvements in die design and cooling, dimensional control of non mandrel

Rubber tube is approaching that of flexible mandrel style.

Most smooth bore thermoplastic hoses are   extruded non-mandrel. The higher rigidity of most thermoplastics eliminates the need for mandrel support. In addition, with advanced  cooling and dimensional sizing equipment, thermoplastic tube dimensions can be maintained quite accurately.

Flexible Mandrel Style

When moderate tube processing support is  needed and more accurate dimensional tolerances are a concern, flexible mandrels may be utilized. These mandrels are rubber or

thermoplastic extrusions, sometimes with a wire  core to minimize distortion. This style process

may be used for mid-range working pressures (up to 5000 psi) with ID’s of 1/8" to 1-1/2".

Of the three flexible mandrel styles, solid rubber offers minimal support, while rubber with wire core and thermoplastic versions provide good dimensional control. In all cases, the flexible mandrel is removed from the hose with either hydrostatic pressure or mechanical push/pull after processing. The mandrel is then inspected for dimensional and cosmetic imperfections, rejoined into a continuous length,

and recycled into the hose making process. Although the flexible mandrel is continuous, limitations of expulsion from the finished hose rarely allow hose lengths above 1000 ft.  Either textile or wire reinforcements may be used. Examples of this style product are power

steering, hydraulic, wire braided and air conditioning hoses.

Rigid Mandrel Style

In larger hose sizes, where flexible mandrels  become quite cumbersome to handle, working

pressures are high, or stringent dimensional control is required, the rigid mandrel process is

the preferred technique.

This method is used for any rubber hose larger than 2" ID and for 1/8" to 2" ID constructions that have higher working pressures, especially wire spiral reinforced products.The rigid mandrels are normally aluminum or steel. For specialty applications where cleanliness is a necessity, stainless steel mandrels are used. Because of weight  considerations the mandrels are usually hollow. Mandrel lengths vary from 10 ft. to 400 ft. with 100 ft. to 200 ft. being the most common. The hose tube may be either extruded on the mandrel, pneumatically pulled onto the  mandrel, or wrapped in sheets onto the mandrel. As with the flexible mandrel style, when the hose manufacturing process is complete, the  mandrel is removed and prepared for recycling.

Manufacturing with rigid mandrels offers two unique production opportunities.  Rigid mandrels can be (1) rotated on a stationary horizontal axis, similar to a lathe, so that material can be applied in bias style or (2) fed horizontally through the tubing, reinforcing and covering operations as the various hose components are spirally fed onto the mandrel.

The former method is often referred to as Hand Built hose. The reference of Wrapped Ply hose

can be associated with either method. Some hand built hoses, depending on the application,

have special ends to accommodate its attachment to existing flanges in the field.

One traditional method of making wrapped ply hose is on a three roll builder. This machine

consists of three long steel rolls, two of which  are in a fixed parallel position in the same

horizontal plane.

The third or top roll is on pivotal mounts so  that it can be raised or lowered. A mandrel

supported hose tube is placed on the trough between the two bottom rolls. 

Then the top roll is rotated down with sufficient pressure to cause the mandrel and

tube to rotate. This enables the reinforcement and cover to be bias wrapped over the tube in

uniform fashion.

. 

SPECIALTY METHODS

Although the three basic methods of hose manufacture just discussed encompass the vast

majority of techniques currently in use, there are still a variety of specialty methods that deserve

attention in this synopsis. Most of these pertain to thermoplastic hose styles.

Thermoplastic Hose Concepts

Thermoplastic products such as vacuum  cleaner hoses, used for very low pressure applications are often manufactured with blow molded or tape forming techniques.

      Blow molded products are shaped into a circumferentially corrugated profile at the tube

extruder when the thermoplastic material is still in the molten state. The corrugations provide a

tremendous improvement in product flexibility and stretch characteristics. The profiling is accomplished by injecting air into the tube pushing it into a series of metal die blocks

corrugated with the intended profile. As the tube cools while traveling along the die block track,

the tube becomes permanently corrugated circumferentially.  A similar process, vacuum

forming, uses the same technique of corrugated die blocks at the extruder, but instead of

blowing air in the tube, a vacuum is drawn through the blocks pulling the molten tube into

the corrugations. The appearance of the final product from each method is quite similar.

However the vacuum forming process generally yields superior corrugation uniformity. 

The corrugated tube from this process may be the final product or used in conjunction with

other hose components. For instance, for higher  pressure applications an adequate reinforcement

may be applied and then a smooth cover extrusion. Combinations of rubber and plastic

layers may provide the best appearance for a specific application.

Tape forming process is a general term to describe a product composed of a narrow

thermoplastic extruded profile helically wrapped with sufficient overlap and adequate

bonding to create a continuous cylinder with hose-like characteristics. The profile can be

varied for best flexibility. Typically swimming pool hoses are of this construction

Helically applied wire at the thermoplastic extrusion point offers another product option

that results in good crush resistance and  flexibility. 

Low pressure gasoline vapor recovery hoses    may use this design.

Continuous Systems

To minimize handling inventory and cost  while maximizing throughput, the continuous

process is common. This process combines tubing, reinforcing, covering and vulcanization

into a single process. To do this, the equipment is merely installed in a tandem fashion thereby

enabling the hose material to flow uninterrupted through each phase. Obviously the system

controls are vitally important to minimize downtime. Since the line output is generally

limited by the reinforcement unit capacity, textile spiraling is the common approach. Also,

since the vulcanization portion of the line is often the most space consuming and expensive,

it is frequently not included. Hoses up to 2" ID with working-pressures up to 400 psi are the most

probable candidates for this process. Flexible  mandrel or non-mandrel methods can be

accommodated on the continuous process.

PROCESS CHARACTERISTICS

As previously mentioned, the basic hose

components are the tube, reinforcement, and

cover. In this section the process methods for

each of these operations will be outlined.

TUBING OPERATION

The two common tube manufacturing  techniques are extruded and wrapped.

Extruded Tubes

For the tube extrusion process, an uncured  rubber or thermoplastic compound ribbon or

pellets are fed into the extruder, through the screw or auger with proper temperature controls

and finally forced through a pair of metal dies, where the cylindrical tube is formed. In the non continuous

process,the tube is then cooled, lubricated to minimize tackiness and stored in coils on

pans, reels,or rigid mandrel poles.

Dimensional control is critical when the tube is being formed. Traditional techniques for maintaining dimensions include die selection, temperature, and line speed adjustments. The

latest innovations include a multi-axis laser micrometer measuring the tube outer diameter

with feedback to the extruder to provide size control. Ultrasonic devices, that can measure

tube ID and OD, are also available.  important to prevent scorch or partial cure of

rubber compounds or burning of the thermoplastics during extrusion and provide

good wall gauge concentricity. The various temperature zones of the extruder provide for a

profile that can be varied for each type of compound to help optimize extrusion characteristics.  For certain applications, to minimize cost or improve flexibility, multiple tube layers may be desirable. In these instances, a tandem or co- extrusion may be preferred. For the tandem method, extruders are installed in series so one tube may be extruded over the other.  For co extrusions, several extruders are mounted in such a way to feed a central die-forming point (extruder head)so that the tubing operation is simultaneous.

These extrusion advancements offer a Good variety of alternatives to use unique polymers or to create hybrid products of thermoplastic and rubber.

Normally, extrusion is the preferred method for the tubing process on hoses with ID’s up to

1-1/2" when built on a flexible mandrel, to 4" for rigid mandrel.  Beyond these dimensions,

wrapped is usually employed. For the larger diameter non-mandrel extrusions, the tube may

be lubricated inside to prevent compound tackiness. Also, an air cushion can be used

internally to prevent tube collapse during

extrusion.

Extruders are often referred to as crosshead or straight head. If the tube is formed in the same

direction as the extruder’s screw orientation, it is a straight head design, whereas if there is an

angle between the tube flow and the screw, it is a crosshead design. Common crosshead designs

are 45° or 90° orientation. Crosshead designs offer more challenges for the process engineer

or rubber chemists since the abrupt change in  rubber flow direction can induce temperature

and pressure anomalies, especially with sensitive compounds.

Hot feed and cold feed extruder terminology is common. In the Hot feed process

the rubber is preheated before it is fed into the extruder, usually on a two-roll mill. This

technique makes the extrusion easier for some compounds since there is less rapid temperature

increase in the rubber. However with high equipment and labor cost, it is almost obsolete

in favor of the cold feed process.

Wrapped Tubes

For the larger diameter rigid mandrel rubber  hose constructions, the wrapped tube process is

utilized. Here, the rubber compound is calendered to a specific thickness and width,

then spirally wrapped on the rigid mandrel with sufficient overlap to form the tube. With the

wrapped process, the challenge is to provide good bonding at the tube overlap area to prevent

tube delamination.

COVERING OPERATION

The covering techniques used for rubber  and thermoplastics are synonymous with the

tubing techniques described previously. In most instances the same equipment is used.

Frequently a hose may have an extruded tube and a wrapped cover. If extruded, covers must

be applied with a crosshead design to allow the reinforced uncured tube to be fed properly into

the extruder covering.

REINFORCEMENT

The strength component of the hose,  designed to handle the entire pressure load with

appropriate safety factors is the reinforcement. In most cases it is located between the tube and

cover. Occasionally there are hose applications  not requiring a cover, in which case the

reinforcement also acts as the outer protective layer. 

When multiple plies of reinforcement are required to meet working pressure performance

levels, typically they are applied one over the other normally separated with a rubber layer

(friction or jacket) to fill voids, prevent adjacent reinforcement abrasion, and to maintain

adequate hose component adhesion levels. Multiple plies may be applied individually or in

a single pass through a multiple deck unit.  

Methods of applying these reinforcements are braid, spiral, knit, wrap, and woven. Combinations, such as

spiral/knit, are available. Selection of reinforcing equipment is dependent on pressure

rating, size, fitting requirements, flexibility, and crush resistance levels.

Braid Reinforcement

Braiding is probably the most common and  traditional method of reinforcing hose. Braiding

machines were available in France and Germany as early as the middle of the l9th

century for braiding textiles used for rope and clothing products. The introduction of the first

braiders for the fledgling hose industry came in America about 1900.

Braiders are described as vertical or horizontal depending on the direction the tube

progresses through the machine during braiding. The two major classifications of braiders are

tubular or “maypole” type and rotary type.

Maypole Type

As the name implies, braid is formed from  multiple carriers each carrying a reinforcement

package traveling in a serpentine maypole fashion generally with a two over-two under

pattern. The common carrier varieties available  are 20, 24, 36, 48, and 64. They are utilized in

vertical or horizontal, single or multiple deck arrangements.

Vertical set-ups are normally a maximum of two decks for convenience and handle nonmandrel  or flexible mandrel hoses up to 1- ½ inches ID .

For vertical braiding,the tube is fed Into the braider From underneath,

Passing through The center of the unit where the braid Is applied and then over a rotating capstan wheel designed to pull the tube through the braider at  a specified rate so the braid is applied at the optimum design angle. For non mandrel style products an air cushion is often used inside the  tube  to prevent collapse at the braid point.

The vertical braider is the most  old fashioned style with few recent advancements. Output speeds are about 30% less than the latest horizontal maypole braider innovations.

Rotary Type

The term rotary braider applies to units  where the carriers holding the reinforcement

package are fixed on two counter-rotating decks and do not move in and out in a serpentine path

like the maypole type. The braiding pattern is achieved by deflecting the reinforcement

strands from the outside deck under and over two carriers on the inside deck, repeating the

motion continuously during rotation. Because of the simpler travel of the carriers, output speeds

can be as much as 200% faster than an equivalent maypole type. Common arrangements are available in 20, 24, 36, 48 carriers, vertical and horizontal, one-, two- or three-deck setups for both textile and wire reinforcement. 

Spiral Reinforcement

Hose spiral reinforcement equipment first  became available in the 1950’s. Since then, it

has evolved into the most economical and efficient method of making certain types of

hose. Spiralling is done horizontally with two  opposing decks revolving in opposite directions

each holding clusters of reinforcement spindles.

Each strand of reinforcement is fed through an array of tensioning devices to the center point of

the decks where they are applied to the tube in a parallel array. In all cases, to have a balanced

hose construction capable of minimal distortion under pressure, the spirals are always in

multiples of two.  Because of the minimal number of moving parts, the spiral decks can

turn at very high rates. State-of-the-art textile spiral units, available at 2000 rpm are

commonly used in continuous lines where tubing, reinforcing and covering are all done in

one pass. Textile spiral is well suited for nonmandrel or flexible mandrel constructions with low to medium pressure ratings. Wire spiral is most common on rigid mandrels designs up to 2 inch ID with very high working pressures.

   Single or double wire spiral applicators may be used in conjunction with a textile braid or

spiral to form a “helix wire” in the hose wall to provide collapse resistance. These are common

for large diameter suction hoses (over 1") or in gasoline pump hose where the “hardwall”

Knit Reinforcement

Rotary knitting machines used for hose  reinforcement were first developed in the early

1900’s. Today their use has declined significantly in favor of textile spiral, but are

still the common method for reinforcing radiator hose because of its good torsional and

circumferential flexibility needed for curved hose products.

Knitting can be horizontal or vertical with textile only. The yarn is fed from cone packages

(usually 4 or 8) through a series of eyelets through latch-type needles onto the hose.

Although the knitted hose is easily shapeable for coolant hose applications, it is a very

inefficient reinforcing method restricted to low pressure applications.

Wrap Reinforcement

Wrap reinforcement is applied spirally to  rigid mandrel hose tube in multiple plies with

the direction of lay reversed with each succeeding ply. The most common fabric

reinforcement is tire cord, which has strength only in the cord direction. To compensate for its

uni-directional strength, plies are usually applied in multiples of two. This may be done

by rotating the mandrel or rotating the reinforcement around the mandrel as described

previously in the “Three Basic Methods of Making Hose”. Wrapping is generally done

with rubberized fabric thereby resulting in hoses in the lower working pressure range. However

for large diameter hoses, generally above 4", it's the only available technique

When needed to prevent collapse or kinking, a wire or thermoplastic helix or helixes

are added to the wrapped construction.  These can be a wide variety of thicknesses, usually

applied at a fairly high helix angle to oppose inward and outward radial stress, but which do

not add significantly to the hose strength in the axial direction.

Woven Hose

The reinforcement for woven hose is a  seamless, tubular textile jacket woven on a

loom. This produces a strong, lightweight hose that is flexible for flat storage. Because the

longitudinal warp yarns are parallel to the axis, woven hose tends to kink more easily than other

hose constructions. Although sometimes used with a rubber cover for industrial applications,

woven discharge hose finds its greatest use as a fire hose where lightweight and high strength are of great importance.

Fire hose consists of a tube and seamless circular woven jacket or jackets, either separate or interwoven. The tube may consist of a rubber or plastic compound. The tube may be extruded, wrapped, or built up by depositing multiple layers of rubber latex. If compounded rubber has been used as a tube,

it may be semi-cured and then backed with a supplemental layer of rubber. This step is

eliminated in the case of plastic tubes. The tube is then drawn into the jacket or jackets and,

when made with rubber compounds, it is cured by internal steam pressure, with the jackets

being the pressure container.  Fire hose is normally made without an outer

rubber cover or protection to the outer jacket. For certain applications, especially in the

chemical industry and at refineries where damage to the jacket would occur from

aggressive liquids, it is normal to use either a rubber covered hose or a hose where the outer

jacket has been impregnated with a rubber type  protective coating.

A great deal of rubber covered fire hose is  made by weaving the jackets on a loom.  Then

the tube and cover are applied simultaneously by pulling the jacket through a special cross

head extruder. This extruder forces the compound through the weave forming a onepiece

tube and cover.

A common loom variety, a Chernack loom,  is a four-shuttle circular loom in which every

alternate fill member may be of different material. 

A hose made with this loom normally would be provided with an inner liner which would be

drawn into the circular woven member simultaneously with the weaving procedure.

The primary use of a hose from such a loom is for suction applications. This construction

would normally have two alternate members of round wire or plastic rods having physical

characteristics which would provide substantial crush resistance in the hose structure. The other

two would be textile yarn.

VULCANIZATION TECHNIQUES

Vulcanization (curing) changes the rubber  product from a plastic to elastic material that is

much stronger and rebounds to its original shape after load deformation. All rubber

products need to go through the “curing” transformation, the final process, whereas with

thermoplastic products, it is not required.

Vulcanization is achieved by heating the rubber products to temperature generally between 280°

F to 400°F. Although pressurized steam is the traditional method, techniques ranging from hot

air, molten eutectic salts, hot glass beads, and high frequency microwaves have been used

quite successfully for certain hose applications. Since the use of steam has become the most

widely used method throughout the rubber industry, the techniques that will be described

here will be lead sheath, wrap, open, and curved. All these methods utilize a steam

vulcanizer for curing the rubber.

The lead sheath is applied as a hot extrusion through a set of dies. Its purpose is to compress the hose components thereby providing good bonding or homogeneous structure with

adequate concentric dimensions. This method can be used for non-mandrel or flexible mandrel

constructions.  For non-mandrel styles, air or water is charged inside the hose for support

during vulcanization.

After curing, the lead is stripped from the hose with a series of knives and melted for recycling.  Although old fashioned and energy consuming, this method is still commonly used for multiple pIy hoses 11/2"

And smaller.However with environmental concerns of the lead this process is becoming obsolete.

Alternate material approaches to lead that  still utilize an extruded sheath include a variety

of heat stabilized thermoplastics. Although the compressive characteristics are not nearly as

good as lead, for lighter weight products, especially single ply, a thermoplastic sheath

cure might be a good alternative to lead.

Wrap Cure

       The wrap cure process uses a closely woven  textile fabric tape generally 2" to 4" in width,

wrapped spirally around the uncured hose and steam vulcanized. This fabric tape, generally

nylon, is overlapped sufficiently that along with the shrinkage properties of the textile, provide

compaction forces to the hose bonding the components during cure. The tape is removed

and recycled after cure. The rough surface of the tape creates a similar rough finish on the

hose. Wrap curing is used for flexible or rigid mandrel constructions in virtually all sizes.

Open Cure

Open or pan cure is the simplest of rubber  hose vulcanization techniques. Essentially, the

hose is taken from the covering operation, coiled either on reels or horizontal pans and

placed directly into the vulcanizer. Obviously, without any protective or compressive sheath

during cure, this process is limited to products of one or two ply and 1" ID or less, either nonmandrel

or flexible mandrel. If non mandrel a water or air charge may be used inside the hose for support during cure.

Curved Hose

For certain applications, such as automotive  coolant hose, a curved or shaped configuration

is required for the hose. In these cases, theuncured hose is cut to the specified length,

installed on a metal mandrel that is the same shape as the finished part, open steam

vulcanized, and then removed from the mandrel. Because the hose is cured in this

configuration, it retains the shape of the mandrel.