Page 39 - 2010-2022 hose manufactureing ability and guide

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 Figure 2-3
corrugated with the intended profile. As the tube
cools while traveling along the die block track,
the tube becomes permanently corrugated Tape forming process is a general term to
circumferentially. A similar process, vacuum describe a product composed of a narrow
forming, uses the same technique of corrugated thermoplastic extruded profile helically
die blocks at the extruder, but instead of wrapped with sufficient overlap and adequate
blowing air in the tube, a vacuum is drawn bonding to create a continuous cylinder with
through the blocks pulling the molten tube into hose-like characteristics. The profile can be
the corrugations. The appearance of the final varied for best flexibility. Typically swimming
product from each method is quite similar. pool hoses are of this construction. Figure 2-4
However the vacuum forming process generally provides a close-up of this process.
yields superior corrugation uniformity. Figure Helically applied wire at the thermoplastic
2-3 shows a vacuum corrugator extruding extrusion point offers another product option
thermoplastic tubing. that results in good crush resistance and
flexibility.
The corrugated tube from this process may
be the final product or used in conjunction with Low pressure gasoline vapor recovery hoses
other hose components. For instance, for higher may use this design.
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.

Figure 2-4

RMA/IP-2/2003 18