Plastic is a preferred material for making electrical goods
Electrical Items such as Switches, MCBs, Fan Regulators, Switchgear and Electrical Enclosures, etc. are exposed to high voltage electricity and resultant heat. Because of the thermal and electrical insulation properties of plastic materials, they are widely used across electrical goods manufacturing sector. Typical materials used for manufacturing above products are: Acrylonitrile- Butadiene-Styrene (ABS), Nylon (PA), Polycarbonate (PC), Polypropylene (PP) and Polystyrene (GPPS).
Manufacturing Challenges for Electrical Industry
Injection Moulding is the prime process of producing the electrical articles mentioned above. However, producing high quality electrical items with superior finish and desirable properties like structural, impact and tensile strength, poses some unique challenges to manufacturers.
Hygroscopic Nature of Engineering Plastic
Engineering polymers mentioned above have high affinity towards moisture, including Nylon, ABS and Polycarbonate. Polystyrene, do not normally absorb much moisture, but are able to carry significant moisture on their surface when exposed to liquid water. Improper drying of hygroscopic resins can cause loss in tensile strength, surface defects like surface cracks, internal cracks, surface lines, bubbles, etc.
The injection moulding process involves injection of plastic melt into the mould and cooling the melt in the mould to take the desired shape. Water Chillers are used for quick cooling of plastic melts and to reduce the cooling time in a particular cycle. However, when chilled water is used for cooling the plastic melts, the moisture present in air in the vicinity of chilled mould surface condenses, leading to formation of water droplets on the mould surface (mould sweating). Mould Sweating is undesirable, as the condensed water droplets tends to drip on the machine bed and seep into the mould, which causes rusting and severely affects the life of expensive mould and machine bed. Further, condensation in the core and cavity of the mould will lead to defects in the moulded component.
Injection Moulding is a fast process and is used to produce large numbers of identical items continuously which makes handling of resins in the shop floor a complex job. Employing labor to handle resins manually is open to human errors like spillage of resins and delay in changeover of material. Feeding material continuously requires constant monitoring which becomes more tedious manually.
The Bry-Air Solution for Drying – Mould Dehumidification – Conveying
Drying Parameters : • Drying time • Air flow • Temperature • Dew point
While temperature, drying time and air flow are dependent on the type of resin, there is a huge difference in quality of molded component if the dew point can be maintained at minimum –40ºC. Dew point plays a very critical role in creating a lower vapour pressure around the surface of the resin. This lower vapour pressure forces the moisture in the molecular chain to dissipate out to its surface.