Page 46 - 2010-2022 hose manufactureing ability and guide

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. Figure 2-18 shows the
lead extrusion equipment. 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 1-
1/2" and smaller. However with environmental
concerns of the lead, this process is becoming
Figure 2-17 obsolete.
Alternate material approaches to lead that
VULCANIZATION TECHNIQUES still utilize an extruded sheath include a variety
of heat stabilized thermoplastics. Although the
Vulcanization (curing) changes the rubber compressive characteristics are not nearly as
product from a plastic to elastic material that is good as lead, for lighter weight products,
much stronger and rebounds to its original especially single ply, a thermoplastic sheath
shape after load deformation. All rubber cure might be a good alternative to lead.
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.

Lead Cure Figure 2-18
Because of its low melting point and good
ductility, lead has been used in the hose
vulcanization process since early in the 20th
century. After the hose is created, tubed,
reinforced, and covered, if lead curing is
utilized, a lead sheath is applied over the hose,
rolled onto a reel and cured in a steam
vulcanizer.

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