How to Select Plastics Auxiliary Equipment ─ Drying and Dehumidifying

 

 

With improvement of plastics product quality and enhancement of mechanical automation, plastics auxiliary equipment is attracting more and more attention. To select proper auxiliary equipment not only improve product quality and productivity but also save more invest costs.

 

Automation workshop attracts many investors. How to select suitable auxiliary equipment to add value to your product equipment has puzzled investors and users for a long time.

 

Most engineering plastics have strong hygroscopicity. Once exposing to the air, it starts to absorb moisture from air. The traditional hot air dryer is not suitable for drying hygroscopic engineering plastics, because moisture in heated moist air used to dry plastics can not be evaluated, and plastics will continue to absorb moisture.

 

As the wide use of engineering plastics, traditional hot air dryer has been replaced by dehumidifying hopper dryer gradually.

 

The advantages of using dehumidifying hopper dryer are:

■ Removing moisture from plastics, avoiding appearance of air bubble, to ensure perfect mechanical property electrical property,stability of dimensions and attractive performance.

■ Effectively prevent appearance of defective product and loss because of goods returned, reducing waste material.

■ Because the dehumidifying hopper dryer adopts drying air to dehumidify material, it can shorten drying time and save labor time.

■ Integral circulatory system and filter are adopted by air pipeline, which can effectively keep the workshop clean and provide a dust-free environment.

 

The perfect drying efficiency is affected by: drying temperature, drying time, process air flow and dew-point, which link so close that each change would affect drying efficiency.

 

Drying temperature stands for temperature of air flowing into the drying hopper. The drying temperature of each material is limited by their physical properties including molecular structure, bulk density, specific heat, moisture content ratio and so on. Some additives in material may go bad or lump if the temperature is too high, and crystal material can not reach its desired drying condition if the temperature is too low. For example: the drying temperature of PC is 120℃, and that of PET is 160℃. In addition, thermal insulating hopper should be selected to avoid temperature reduction and energy waste.

 

Drying time stands for pre-drying time before molding. Raw material can go bad, lump or waste energy if drying time is too long, and water ratio may rise if it is too short. For example: the drying time of PC is 2~3 hours, and that of PET is 4~6 hours.

 

Process air flow is the only medium to take water away from raw materials, which also affects the dehumidifying efficiency. Air flow being too large, return air temperature would be high, which affect the stability of dew-point. Air flow being too small, it is hard to remove the moisture from raw materials. Air flow also stands for the dehumidifying ability of dryer.

 

Dry air dew-point temperature means the temperature at which the cooled air get the moisture into dew. It is a unit examines the degree of dry (wet) of air. The less moisture in the air, the lower the dew-point temperature will be. Favorable drying and dehumidifying equipment should have a dew-point temperature below -40℃.

 

Dehumidifying hopper dryer include stand-alone and centralized mode. Stand-alone mode mainly consists of main unit, drying hopper auto loader. It is suitable for drying small amount diversified materials with high efficiency and quick material replacing.

 

Centralized mode consists of main unit and several hoppers, each is equipped with a independent heating controller making several different materials dried at the same time and controlling air flow by flow adjust valve.

 

Factors to be considered when choosing dehumidifying and drying equipment:

 

1. Properties of materials you employ which include: moisture content before and after drying, bulk density, drying temperature and time. All of the above are supplied by material producers.

2. Molding capacity per hour of the equipment.

 

Selection Formula:

Capacity of the dryer (L) =molding capacity (kg/hr) ×drying time (hr)÷bulk density (kg/L)

─ How to choose plastics auxiliary equipment-Feeding & Conveying Series will be published in the 4th View of Shini.