Blow molding (BrE molding ) is a specialized manufacturing process in which hollow plastic parts are formed and can be incorporated: It is also used to form glass bottles or other hollow shapes.. In general, there are three main types of blow molding: extrusion blow molding, injection blow molding, and injection stretch blow molding. The process of blow molding begins by melting the plastic and forming it into parison or in the case of injection and injection stretch blow molding (ISB) of a previous form. The comparison is a piece of plastic like a tube with a hole at one end so that compressed air can pass.
This comparison is then clamped into mold and air is blown into it. Air pressure then pushes the plastic out to match the mold. After the plastic has cooled and hardened the open mold and the part is removed. The cost of the blow molded part is higher than that of the injection molded parts but lower than the rotating part of the mold.
Video Blow molding
History
The principle of the process comes from the idea of ​​glassblowing. Enoch Ferngren and William Kopitke produced blow molding machines and sold them to the Hartford Empire Company in 1938. This was the beginning of the commercial blow molding process. During the 1940s, variations and quantities of products were still very limited and therefore blow molding did not take off until later. After the variety and level of production increases the number of products made immediately following afterwards.
The technical mechanism required to produce hollow hollow workpieces using blowing techniques was established very early. Because glass is very easily broken, after the introduction of plastic, plastic is used to replace glass in some cases. The first mass production of plastic bottles was made in America in 1939. Germany began to use this technology a little later, but today it is one of the leading manufacturers of blow molding machines.
In the United States soft drink industry, the number of plastic containers changed from zero in 1977 to ten billion in 1999. Currently, even more products are being detonated and expected to continue to rise.
For amorphous metals, also known as mass metallic glasses (BMGs), blow molding has recently been shown under pressure and temperature comparable to plastic blow molds.
Maps Blow molding
Typology
Extrusion extrusion blow
In extrusion blow molding ( EBM ), the plastic is melted and extruded into a vacuum tube (parison). This comparison is then captured by closing it into a cooled metal mold. The air is then blown into the parison, inflating it into a bottle, container, or hollow shape. After the plastic is cool enough, the mold is opened and the part is removed. Continuous and Intermittent are two variations of Extrusion Blow Molding. In an advanced extrusion mold, the parison is continuously extruded and the individual parts are cut with a suitable blade. In intermittent blow molding there are two processes: intermittent straight like injection molding where the screw spins, then stops and pushes the melt. With the accumulator method, the accumulator collects the liquid plastic and when the previous mold has cooled and enough plastic has accumulated, the rod pushes the plastic to melt and form the parison. In this case the screws may change continuously or intermittently. With continuous extrusion, parison weight drags parisons and makes calibration of wall thickness difficult. The head accumulator or reciprocating screw method using a hydraulic system to push the exit parison quickly reduces the effects of weight and allows precise control over wall thickness by adjusting the dead gap with the parison programming device.
The EBM process can be either continuous (constant extrusion from parison) or intermittent. The types of EBM equipment can be categorized as follows:
Continuous extrusion equipment
- rotary wheel blow molding system
- shuttle machine
Intermittent extrusion machine
Examples of parts made by the EBM process include most hollow polyethylene products, milk bottles, shampoo bottles, automotive ducting, watering cans and hollowed-out industrial parts such as drums.
The advantages of blow molding include: low tool and die costs; fast production rate; ability to form complex parts; The handle can be included in the design.
The disadvantages of blow molding include: limited to hollow parts, low strength, to improve multilayer pateron barrier properties of different materials used so that it can not be recycled. To make a wide neck grip required trimming.
Rotate pruning
Containers such as jars often have excess material due to the printing process. This is cut by rotating the blade around the container that cuts the material. Excess plastic is then recycled to make new prints. Spin Trimmers are used on a number of materials, such as PVC, HDPE, and PE LDPE. Different types of materials have their own physical characteristics that affect pruning. For example, molds produced from amorphous materials are much more difficult to trim than crystalline materials. Titanium coated blades are often used instead of standard steels to improve life by a factor of 30 times.
Injection blow molding
The injection blow molding ( IBM ) process is used for the production of hollow glass and plastic objects in large quantities. In the IBM process, the polymer is injected into the core pin; then the core pin is rotated to the blow molding station to be cooled and cooled. It is the least used of the three blow molding processes, and is commonly used to make small medical bottles and single bottles. The process is divided into three steps: injection, blowing and ejection.
Injection blow molding machine is based on barrel extruder and assembly screw that melts the polymer. The liquid polymer is inserted into the hot runner manifold where it is injected through the nozzle into the heated cavity and the core pin. The mold cavity forms an external shape and is clamped around the core rod that forms the internal shape of the previous form. The initial form consists of a bottle neck/bottle filled with a thick tube of polymer attached, which will form the body. similar in appearance to a test tube with throat neck.
The preform mold is open and the core rod is rotated and clamped into a hollow and cold molding mold. The end of the core rod is open and allows the compressed air into its previous form, which expands into a completed article form.
After the cooling period the blow mold is open and the core rod is rotated to the ejection position. The completed article is stripped from the core rod and as an option can be tested for leaks before packing. Preform and blow molds can have multiple cavities, usually three to sixteen depending on the size of the article and the required output. There are three sets of core rods, which allow simultaneous injection of preforms, blow molding and ejection.
Advantages: This produces an injection-molded neck for accuracy.
Disadvantages: only fit the small capacity bottle because it is difficult to control the base center during the blowing. There is no increase in barrier strength because the material does not stretch bactially. The handle can not be merged.
Process stretch blow molding injection
It has two different main methods, namely Single-stage and two-stage process. The one-stage process is once again broken down into 3 stations and 4 stations. In a two-stage injection blow molding process, the plastic was first formed into a "preform" using an injection molding process. These preforms are produced with bottle necks, including yarn ("finished") at one end. These preforms are packed, and fed later (after cooling) into the blow blow reheat press. In the ISB process, preforms are heated (usually using infrared heaters) above their glass transition temperature, then blown using high pressure air into the bottle using a metal molding mold. The previous form is always stretched with the core rod as part of the process.
Advantages: Very high volume produced. Small restrictions on bottle design. Preforms can be sold as finished goods to be blown by a third party. Suitable for cylindrical, rectangular or oval bottles. Disadvantages: Capital costs are high. It takes a high floor space, although a compact system is available.
In a one stage process both the preform manufacture and bottle blowing are done in the same machine. Older 4-station injection methods, reheat, stretch blows and expenses are more expensive than 3-station engines that eliminate the reheating stage and use latent heat in the preform, thus saving energy costs for reheating and 25% reduction in equipment. This process explains: Imagine the molecule is a small rounded ball, when together they have a large air gap and a small surface contact, by first flexing the molecule vertically then blowing it to stretch horizontally the biaxial stretch making the cross shape molecule. These "crosses" fit together leaving little space as more surface area is contacted making the material less porous and increasing the barrier strength against permeation. This process also increases the power to be ideal for filling with carbonated beverages.
Advantages: Very suitable for low volume and short run. Because the preform is not released during the entire process, preform wall thickness can be formed to allow wall thickness even when blowing rectangular and not round shapes.
Disadvantages: Limitations on bottle design. Only a champagne base can be made for a carbonated bottle.
See also
- Mold-A-Rama
- Molding
- Plastic-forming machine
References
Bibliography
- Lee, Norman (1990), Plastic Molding Handbook , Van Nostrand Reinhold, ISBN 978-0-442-20752 -6. Lee, Norman (2006), Practical Guide to Blow Molding, Smithers Rapra Technology, ISBN 978-1-85957-513-0.
- Lee, Norman (2008), Blow Molding Design Guide (2nd ed.), Hanser-Gardner Publications, ISBN 978-1 - 56990-426-8.
- Extrusion Blow Molding, Hanser-Gardner Publications, ISBNÃ, 1-56990-334-4
- Ottmar Brandau, Stretch Blow Molding, PETplanet Publisher GmbH, ISBN 3-9807497-2-X
- Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & amp; Children, 2009, ISBN 978-0-470-08704-6
Source of the article : Wikipedia
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