Diamond Systems Tritan Guia de Resolução de Problemas descarregar pdf (Página 29)

Moisture measurement

Dew point meters measure only the dryness of the air, not the

dryness of the plastic pellets in the hopper. Use of the dew

point meter along with measurements of temperature, airﬂow,

and time can give an accurate indication of whether the plastic

pellets are being dried properly.

Weight loss type moisture meters are instruments that measure

the moisture inside pellets. These meters can give a general

indication of the effectiveness of the drying system in reducing

the moisture level in the plastic pellets. However, most are

usually not accurate enough to use as a quality control method

to ensure adequate dryness of polyesters to prevent degradation

during processing. A moisture level in the range of 0.020%–

0.030% is desired, and this is determined using analytical means

other than the preceding.

Dryer troubleshooting

Dryers require routine checking and maintenance. A good

mechanic that understands dryers and has the time and

support to maintain them is needed. The following information

is provided to help give that understanding. Dryer suppliers can

help also.

Common dryer problems

• Poor airﬂow caused by clogged ﬁlters

• Air passing through the middle of the load rather than

dispersing through the pellets caused by unﬁlled hopper

• Supply/return dry air lines allowing ambient “wet” air to

contaminate dry air

• Wet air contamination through loader on top of hopper

• Lack of cooldown on air returning to the bed in absorption

process. (Air should be cooled below 65°C [150°F] to increase

the desiccant’s afﬁnity for moisture, thus improving efﬁciency.

An aftercooler is required when drying some polymers.)

• Reduced desiccant effectiveness caused by worn-out or

contaminated desiccant

• Nonfunctioning regeneration heater and/or process heater

• Blower motor turning backwards

• Airﬂow not being shifted when controls call for bed change;

one bed stays in process continuously

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Diamond Systems Tritan Guia de Resolução de Problemas Página 29