When performing a blow molding plastic extrusion process, a preform is thrust out. The top and bottom are pressed to remove the excess and then blown into the shape of the hollow space. The excess plastic that is squeezed off the top and bottom of the mold’s cavity is called flash.
Minimizing Flash in the Process
Post-molding is when the flash is removed. Removal of flash can be mechanical or manual. These types of operations can damage the parts. It is important to minimize flash to make quality parts.
In the design of a plastic container, the importance of controlling flash has an impact on the part. The container’s size and shape determines how much flash will form during manufacture. As an example, a bottle with a trigger sprayer forms a neck to the side, which will make more flash than a centered neck bottle.
How Flash Impacts the Product
Both appearance and functionality of the container will be impacted by flash. The visual appeal of parts that have the flash methodically removed is far greater than that of parts with ragged and excessive flash. Also, if there is too much flash at the closure to a container or bottle, an improper fit can prevent closing.
Regular Maintenance of Blow Molds is Important
It is very important that regular maintenance of blow molds is done when large areas of flash are required. The flash can be neatly removed by having a raised pinch-off. When a mold has a worn pinch-off, the result will be unacceptable parts. Regular inspections should be done on the mold and the parts to be sure that any excess flash is removed.
The extrusion method of blow molding plastic creates a product with a hollow inside. There are common blow molding materials used such as LDPE, HDPE and PP.
The Most Preferred Blow Molding Technique
If you want the full optical effect from pigments, the extrusion molding method is the preferred option. This method ensures that the pigments are aligned and even.
Co-extrusion is a potent method obtaining high coverage and favorable effects. Pearl luster and other similar effects happen when the inner layer is covered.
What to Consider with the Materials in Production
As is the case with most industrial production, it’s imperative that serious consideration be given to the materials used. The cost, processing, and resin properties are also important items to consider.
There may seem like an endless number of plastic materials available, but a great many of them won’t be the most suitable or appropriate for your product. Knowledge and expertise with blow molding materials is critical to your success.
The Easiest Materials to Use
There are a lot of low cost materials that are also some of the easiest materials to use. Polyethylene (PE) and polypropylene (PP) are very popular resins used for molding. These materials are not only inexpensive but they are chemical resistant. When working with plastics it is important to be cognizant of temperature performance. PP and PE each perform better in different temperatures; PP will perform better in higher temperatures as compared to PE.
Designing the Blow Molding Project
Be certain to use accurate design information for you project. There are a lot of resins that can be used in blow molding, but different resins require different processes to assure success. Many are required to be dry prior to processing but the criterion does differ. Get specific directions from engineering personnel prior to proceeding.
Blow molding plastic is a procedure where hollow 3D articles are produced using various kinds of thermoplastic materials. These materials are usually available in powder or granular form. The simplest blow molded tool has two parts, which are closed and consist of a cavity inside.
Hold Molds Work in Extrusion Blow Molding Technology
A plasticizing cylinder is used by blow molding manufacturers for softening the granular or powder materials, which are then thrust into a parison (vertical tube). An open mold surrounds this parison that is later closed. Thus, the bottom end is sealed effectively and then, the other end is used for sealing it in a pneumatic manner.
The mold’s geometry and the parison’s size determine what the distribution, wall thickness and other dimensions of the manufactured article would be. This makes them important factors, along with the die design, which is affected, by backpressure, land length, melt compression and melt flow pattern. For producing bottles that have uniformity in wall thickness, the wall thickness of the parison is controlled using various pre-stated steps by manufacturers.
Advantages of Extrusion Blow Molding Plastics
Advantages: Because of lower pressure, the mold costs in extrusion blow molding are lower as compared to injection molding and the machinery costs are low as well. Also, it’s easy to mold external threads. Making open-ended parts that are large can be done by splitting open a closed molding.
Disadvantages of Using Extrusion Blow Molding
Disadvantages: As the diameter of the mold increases, the corners and areas with the thinnest walls have close tolerance. Plus, extrusion molding has longer cooling times than injection molding. Also, it is not possible to mold in holes except after the molding.