Blow molding is a technology that blowing plastic into the hollow article. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology has been widely used. Hollow container’s volume can be up to thousands of liters, and some have adopted computer-controlled production. For blow plastics are polyethylene, polyvinyl chloride, polypropylene, polyester, etc. The empty containers are widely used in industrial packaging. According to the production method of the parison, blow molding can be divided into extrusion blow molding and injection blow molding.
Before the parison cools down, a hollow ramrod is injected into its center and pushed to the top of the mold, stretching out the warm plastic preform as it goes. Compressed air is then forced out in controlled low-pressure stages through the hollow ramrod. The plastic form is forced out to the sides of the mold. Because the stretching is performed evenly, the plastic remains uniformly thin and strong. The soda bottle assumes the shape of the mold and is dropped out of the blow molding machine as the two mold halves separate. A new parison is extruded and the entire blow molding process begins again. The actual manufacture of a soda bottle takes only a few seconds.
Since the introduction of bottled water into the market in the 90′s, it has become a household norm. Blow molding a two-liter soda bottle requires a preformed piece called a parison. The parison is mechanically loaded onto a stand and two sides of a bottle-shaped metal mold come together around it and is usually extruded from a plastic injection mouldplaced very close to the blow molding machine. The warm parison looks like an upside-down plastic test tube, with a preformed collar and threads for the cap at the bottom.
When prepare for bottle blow molding, first inject PET chips to preforms. It requires the proportion of second-recycled materials not too high (5%), and the recovery can not be more than two times. Preform mould needs to store more than 48 hours before using. After heating, the preforms did not use must then be stored more than 48 hours before being re-used for heating. Preform storage time should not exceed six months. Injection stretch blow molding is biaxially oriented stretch blow molding is a viscoelastic state of the polymer in the preform is axially stretched by mechanical means, a method using compressed air radially blown molded container preforms, forming characteristics of this method is the same axial and radial stretching ratio, can improve the mechanical properties of the blown container, permeation barrier properties, transparency, reducing the wall thickness, which is the thinnest wall thickness in blow molding a process.
Stretch blow molding is a two-stage process similar to injection blow molding. Firstly, a test-tube like preform is made using plastic injection moulding or a similar process. The neck of the preforms is fully finished but the diameter and length of the body portion are much smaller than the final product. The preform then undergos a stretch-and-blow process.
A small piece of thermoplastic material is preformed to a test-tube shape and installed near the tip of the blow stem. The setup is placed in the closed chamber of a divided mold.
Compressed air is injected into the preform via the blow stem while the blow stem is pushing forward to stretch the preform further into the mold.
The blowing and stretching process continues. The blow stem stops near the far end of the mold.
Compressed air continues to blow in until the preform reaches the wall of the mold.
The plastic piece is removed from the mold after it cools and hardens.
The single most important product made by stretch blow molding is the 2-liter PET bottle for carbonated soft drinks introduced in 1978 and updated to one-piece bottle in early nineties. The PET bottles are virtually unbreakable, lightweight, transparent. They and have various barrier properties. The traditional glass containers cannot compete with PET bottles and are almost extinct from the field of carbonated soft drinks.
A food, beverage, pharmaceutical manufacturers, smaller, they would consider purchasing plastic bottles. However, when the reach a certain size, it will consider the self-built blowing workshop, then you need to buy blow molding machine.
Two blow molding bottle manufacturers, including some of the larger manufacturers of plastic bottles, they need to replace the new blowing machine equipment, some of the newly established plastic bottle manufacturers, they naturally the first step you need to buy a blow molding machine
To sum up, in fact, blow molding machine potential customer base is plastic bottle producers and buyers.
An injection blow molding machine usually has three mould stations, tube-like parisons, or preforms, are injection moulded at the first station, while still hot, these are transferred on mandrels to the blowing station where they are inflated in a set of blow moulds. The blown containers are then transferred to the ejection station.
Because the parisons are injection moulded, injection blown containers have a high quality neck finish and a better surface finish than extrusion blown containers. Tooling costs are high because a preform mould and blow mould are required. The process is usually used for smaller containers and finds its main applications in the pharmaceutical and cosmetics field.