|  Applications
- Plastic Injection
Molding
- Plastic Extrusion
Overview
Certain plastic
resins (hard pellet type - nylon, polyester, polycarbonate, others) must be dried
to a very low moisture content before they can be molded, extruded, etc., in order
that the finished product does not contain surface defects caused by moisture
expanding to steam during the production process. Some resin materials do not
require any drying at all, others can be dried satisfactorily with warm air only.
Critical drying processes must use desiccant dryers. This has traditionally been
an all electric process.
Conair-Franklin
with GRI support developed the first gas unit - a 300 lb/hr model and has since
expanded the line. The unit contains two gas burners - one to heat the "process
air" that heats the plastic resin material and a second to heat the air that
regenerates the desiccant drying medium. The burners are a modulating, "flameless"
ceramic radiant burner that is safe for use with plastics.
Economics
The better applications
for gas-fired dryers are higher volumes of the same material (kind and color)
supplied from a central location where a single dryer can be used. Many processes
are small volume runs where portable electric units are hooked to each machine
for a specific run. There are no gas units to compete with this small operation.
The application should use at least 400 pounds per hour of the same kind and color
material to be considered a viable gas unit application. Single units are available
to about 4,500 pounds per hour. After that, multiple units can be used.
The larger the
dryer (and the higher volume of product), the better the economies of scale. Typical
payback is less than one year for mid to larger end machines, or those that have
a very high load factor.
Gas Input: Conair
CDG400A; 300-500 lbs/hr; 77,000 BTUs
Conair CDG1000A;1000-1800 lbs/hr; 204,000 BTUs
Cost to Operate:
CD400 (Electric) $1.57/hr @ $0.057/kwh (plus $0.17/hr blowers)
CDG400 (Gas) $0.35/hr @ $0.33/CCF (plus $0.21/hr blowers)
Conair also makes
a gas retrofit unit that can convert an existing electric drying system to use
natural gas for regeneration. This makes it possible to reduce operating cost
without having to buy a complete new machine.
Resin
Holding Hoppers
Hoppers hold the
resin material at each molding machine and in bulk distribution areas. The actual
drying of the resin takes place in the hoppers, with the warm, dry air produced
in the dryers.
More
Information
See our Plastics
Consortium web site at www.PlasticsSuite.com
Source:
Energy TechPro
 
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