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FAQ
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FAQ
What is the difference between injection pressure and holding pressure?
Molding pressure is largely classified into injection pressure (primary pressure) and holding pressure (secondary pressure). Primary pressure is required for pouring the molten resin into the mold. Secondary pressure facilitates the transfer of molten resin in the mold onto the surface of the mold by decreasing the pressure in the cavity, and is also used to prevent shrinkage and deformation of the products.
How many steps are there in the injection molding process?
The injection molding process consists of mold close, injection, cooling/metering and mold open/ejection.
Mold Close
The core, a moving part of the mold, moves to the cavity, a fixed part, and the mold is closed.
Injection
The screw moves forward and the molten resin flows into the mold through the nozzle.
Consistent pressure is applied until the molten resin in the mold hardens.
Cooling/Metering
The molten resin in the mold is cooled and hardened by the cooling water flowing through the cooling channel inside the mold. It is also melted and metered by the rotating screw.
Mold Open/Ejection
The mold is opened and the hardened product ejected out of the mold by the ejector pin.
What is the plastication (metering) process?
The plastication process is the process of heating and melting plastics. At this time, two heat sources are largely used, namely heater band and frictional heat (occurs between the rotating screw and the cylinder wall). It is known that the frictional heat generated by the friction between the rotating screw and the cylinder wall affects 70% of plastication. The plastication time must be shorter than the cooling time, and the holding time in the cylinder for materials that lack heat stability must be shortened by decreasing the plastication time.
What are the characteristics of and process methods for BOPP films?
A BOPP film is Bi-oriented Polypropylene film / Oriented Polypropylene film. The molten film is extruded in the die, which has a straight line shape slit, and is tightly placed onto a cooling roll. After it cools and hardens, it is bi-axially oriented in MD/TD and then the final film is produced. BOPP film improves upon various mechanical properties by arranging the molecular structure of PP in a consistent direction through biaxial orientation. It exhibits the advantages of transparency and gloss and is thus widely used as a packaging material.
What are the characteristics of and process methods for IPP films?
A CPP (Cast Polypropylene) film is a non-oriented film and is widely used as packaging film with various types. CPP film is produced in the following way. A resin fed from the hopper is pushed into the feed section, compression section and metering section and is melted. The molten resin is extruded from the T-die in a consistent shape, and the extruded resin is cooled and solidified without a stretching process. The film that is produced then goes through Corona processing, using an electrical device in order to give polarity to non-polar film. The film obtained from these processes is rolled and marketed in the desired sizes.
What are the characteristics of and process methods for CPP films?
An IPP (Inflated Polypropylene) film is produced with the following procedure. A molten film is extruded in the die, which has the thin cylindrical shape of slit, and is inflated by blowing air into it. Bubbles are formed and the film
We are an injection molding company producing ABS. Is it possible to use polypropylene in an ABS mold?
It would be impossible to do so, due to a difference in shrinkage rate. PP compounds suitable for the shrinkage rate of the existing ABS or a new design mold suitable for the shrinkage rate of PP must be used. Polymer chains move in disorder in a molten state and the volume increases. When the polymer solidifies and its temperature cools down, it returns to its intrinsic arrangement gradually, and thus the chain length decreases. This characteristic is expressed as shrinkage rate. The shrinkage rate varies depending on the type of polymers, and crystalline polymers tend to shrink more than noncrystalline polymers. ABS exhibits a shrinkage rate of between 4/1000 and 5/1000, whereas normal polypropylene exhibits a shrinkage rate of between 14/1000 and 16/1000. If normal polypropylene, therefore, is injection molded in the ABS mold, it shrinks more.
What is impact strength? What is the level of impact strength of PP compared to other resins?
Impact strength is one of the most important characteristics and represents the mechanical properties of a resin. It refers to impact resistance when an object is impacted. In general, the greater the molecular weight and the higher the glass transition temperature (Tg), the lower the impact strength becomes. The strength of a specimen against impact is defined as the total energy used for breaking the specimen or the absorbed breaking energy per unit length. It varies depending on the shape and size of the specimen, and the testing methods. The Izod and Charpy methods are commonly used. The order of universal plastics in terms of impact strength is; LDPE > HDPE > PP (Block copolymer) > PP (Random copolymer) > PP (Homopolymer) > PVC > PS.
When there are inquiries about PP materials, the MI is mostly asked about first. What does MI mean?
The melt characteristic of polypropylene is one of the important characteristics of resins, and affects both the processability and the properties of products. In general, the higher the MI, the better the processability. However, properties such as stiffness and impact resistance tend to decrease. Elements that affect the MI are molecular weight and molecular weight distribution. In general, the MI and the molecular weight are inversely proportional to one another. The measure of melt characteristic is called MI or MFI (Melt Flow Index). It is defined as the mass of resin flowing in for ten minutes through a capillary under a constant load and at a constant temperature. An MI is measured according to the specified load and temperature for each resin. An MI of polypropylene is measured using the method described in the ASTM D1238L standard. A PP resin is heated at 230
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