plastic machine for raw milk bottle
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Plastic machine for production of raw milk storage bottle by blow molding

Plastic machine for production of raw milk storage bottle by blow molding
Blow Molding Plastics containers

What do plastic beverage bottles, toy dolls, fuel tanks, stadium seating, milk jugs, biohazard waste containers, and skin cream bottles have in common?

They are all plastic products produced by a process called blow molding.

Blow molding is a fast, cost-effective way to manufacture hollow plastic products and packaging. Essentially, blow molding fills a heated plastic cylinder with air,

causing the plastic to expand like a balloon and evenly fill a shaped mold. Then the plastic is cooled and the finished bottle, jug or tank is removed from the mold press.

Blow Molding vs. Other Types Of Molding

Blow molding and injection molding are the two most commonly used plastic molding methods.

Blow-molded products are typically hollow and more often than not used to hold liquids. Injection molding, on the other hand, can be used to make solid

plastic parts, pipefittings, toys, utensils, bottle caps and a wide variety of intricately designed plastic tools, parts and products.

The process of extrusion blow molding takes place in two stages: The first step involves fabricating a tube of soft, molten plastic called a parison.

The parison is positioned between two halves of a mold press. The mold is then closed around the parison and a blow pin is inserted at the bottom of the mold.

During the second step, air is forced in through the blow pin, causing the parison to inflate until it fills the mold cavity. After the plastic cools, the finished

product is ready for use.

Injection molding does not use an air blower of any sort. Instead, heated plastic is injected under high pressure into a mold. The pressure ensures

that every space within the mold is filled with plastic. Because no air is used, products made with injection molding are typically not hollow.

Other, less common types of molding include compression molding and rotational molding. Compression molding uses two heated mold halves to

press a slug of hard plastic into shape.

Rotation molding essentially turns a mold slowly, using gravity to coat the cavity walls of the mold with molten plastic.

Which Plastic Resins Work Best With Blow Molding?

Certain polymer resins are not conducive to blow molding. Polystyrene (better known as Dow Chemical’s Styrofoam™), for example, is not commonly used

in blow molding. Custom-Pak Design & Blowmolding’s article, A Guide to Plastics Commonly Used in Blow Molding, lists the following polymers as well-suited to blow molding:

High-Density Polyethylene (HDPE) – The #1 most common resin for blow molding, HDPE is used to bottle liquids ranging from motor oil and fuel to shampoo,

in consumer-sized bottles or industrial drums.

Low-Density Polyethylene (LDPE) – When a high level of stress-crack resistance is required, LDPE is preferred due to its flexibility. Common applications

include squeeze bottles and blown film for plastic bags. Polypropylene (PP) – One of the most popular plastics in the world, PP is very similar to HDPE.

But PP’s lower density and high heat resistance lends itself to medical parts, food containers, and milk jugs.Polyvinyl Chloride (PVC) – Another incredibly popular

polymer, PVC is tough and flexible. Traffic cones, soft equipment parts, durable plastic jars, and household cleaner containers are all products of blow molded PVC.

Polyethylene Terephthalate (PET) – Injection blow molding, which injects plastic into the blow mold in lieu of using a parison, turns PET plastic into water

and soft drink bottles.

Some other common blow molding polymers include thermoplastic elastomers (TPE), Acrylonitrile Butadiene Styrene (ABS),

Polyethylene Oxide (PPO), Polycarbonate (PC) and polyurethane.

Features & Application
Why plastic bottles widely used on  milk storage

Keeping milk chilled is critical to keeping it fresh. Whether you are storing raw milk or pasteurized milk, you should always keep it in the refrigerator.

It should never sit out at room temperature. If all you plan to do with your milk is drink it, then store it in clean glass jars, 2-quart size or smaller.

Every time a jar is opened and exposed to air, there is the possibility of contamination.

For now, plastic container for raw milk storage is most popular in the world.

Plastic milk containers are plastic containers for storing, shipping and dispensing milk. Plastic bottles, sometimes called jugs, have largely

replaced glass bottles for home consumption. Glass milk bottles have traditionally been reusable while light-weight plastic bottles are designed for single trips

and plastic recycling.

Packaging of milk is regulated by regional authorities. Use of Food contact materials is required: potential food contamination is prohibited.

Strict standards of cleanliness and processing must be followed.

The most common material in milk packaging is high density polyethylene (HDPE), recycling code 2. Low density polyethylene (LDPE), and polyester (PETE),

are also in use. Polycarbonate had been considered but had concerns about potential contamination

Blow molded plastic milk bottles have been in use since the 1960s.[2] [3] [4] HDPE is the primary material but polyester is also used. A wide variety of milk bottle

designs are available. Some have a round cross section while others have a more square or rectangular shape. A special flat-top square milk jug was recently

developed to maximize shipping and storing efficiency but had some difficulties in dispensing. Many milk bottles have integral handles.

Milk bags are also in use. The milk is sold in a plastic bag and put into a pitcher for use.Small individual containers of milk and cream are often thermoformed

or injection molded and have a peelable lid. These are often used in restaurants.

The shelf life of pasteurized milk in HDPE bottles and LDPE pouches has been determined to be between 10 and 21 days when stored at 4-8 °C. Other factors

such as light and temperature abuse have effects. Shelf life can be extended by ultrapasteurisation and aseptic processing.

Milk containers for retail sale must contain the same amount of milk as indicated on the label. To be acceptable to consumers, the containers must also appear

to be completely full. Therefore, the volume of the container must be precisely controlled.

The designer of a die for a blow moulded bottle can never be completely sure of how much the finished bottle will hold. Shrinkage always occurs after the item

is released from the mould. The amount of shrinkage depends upon many factors, including cycle time, inflation air pressure, time in storage prior to filling, storage

temperature, and more.

A volume adjuster insert is one way to slightly adjust the volume of a bottle, without building a completely new mould. A volume insert attaches to the inside of

a mould, creating a circular indentation on the side of the finished bottle. Different size inserts can be used as manufacturing circumstances change,

for example mould temperature or cooling rate. The volume of finished bottles is periodically measured, and volume inserts are changed as needed.

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