When did blow molding start?

Manufacturing process for forming and joining together hollow plastic parts

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Blow molding (or moulding) is a manufacturing process for forming hollow plastic parts. It is also used for forming 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 blow molding process begins with softening plastic by heating a preform or parison. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can enter.

The plastic workpiece is then clamped into a mold and air is blown into it. The air pressure inflates the plastic which conforms to the mold. Once the plastic has cooled and hardened the mold opens and the part is ejected. Water channels within the mold assist cooling.

History

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The process principle comes from the idea of glassblowing. Enoch Ferngren and William Kopitke produced a blow molding machine and sold it to Hartford Empire Company in 1938. This was the beginning of the commercial blow molding process. During the 1940s the variety and number of products were still very limited and therefore blow molding did not take off until later. Once the variety and production rates went up the number of products created soon followed.

The technical mechanisms needed to produce hollow-bodied workpieces using the blowing technique were established very early on. Because glass is very breakable, after the introduction of plastic, plastic was used to replace glass in some cases. The first mass production of plastic bottles was done in America in 1939. Germany started using this technology a little bit later but is currently one of the leading manufacturers of blow molding machines.

In the United States soft drink industry, the number of plastic containers went from zero in 1977 to ten billion pieces in 1999. Today, an even greater number of products are blown and it is expected to keep increasing.

For amorphous metals, also known as bulk metallic glasses, blow molding has been recently demonstrated under pressures and temperatures comparable to plastic blow molding.[1]

Typologies

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Extrusion blow molding

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In extrusion blow molding, plastic is melted and extruded into a hollow tube forming a tube like piece of plastic with a hole in one end for compressed gas - known as a parison. The parison is captured by closing it into a cooled metal mold. Air is blown into the parison, inflating it into the shape of the hollow bottle, container, or part. After the plastic has cooled, the mold is opened and the part is ejected.[2]

"Straight extrusion blow molding is a way of propelling material forward similar to injection molding whereby an Archimedean screw turns, feeding plastic material down a heated tube. Once the plastic is melted the screw stops rotating and linearly moves to push the melt out. With the accumulator method, an accumulator gathers melted plastic and after the previous mold has cooled and enough plastic has accumulated, a rod pushes the melted plastic and forms the parison. In this case the screw may turn continuously or intermittently.[3] With continuous extrusion the weight of the parison drags the parison and makes calibrating the wall thickness difficult. The accumulator head or reciprocating screw methods use hydraulic systems to push the parison out quickly reducing the effect of the weight and allowing precise control over the wall thickness by adjusting the die gap with a parison programming device.

Continuous extrusion equipment includes rotary wheel blow molding systems and shuttle machinery, while intermittent extrusion machinery includes reciprocating screw machinery and accumulator head machinery.

Spin trimming

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Containers such as jars often have an excess of material due to the molding process. This is trimmed off by spinning a cutting blade around the container which separates the material. The excess plastic is then recycled to create new moldings. Spin Trimmers are used on a number of materials, such as PVC, HDPE and PE+LDPE. Different types of the materials have their own physical characteristics affecting trimming. For example, moldings produced from amorphous materials are much more difficult to trim than crystalline materials. Titanium nitride-coated blades are often used rather than standard steel to increase life by a factor of 30 times.

Injection blow molding

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The process of injection blow molding (IBM) is used for the production of hollow glass and plastic objects in large quantities. In the IBM process, the polymer is injection molded onto a core pin; then the core pin is rotated to a blow molding station to be inflated and cooled. This is the least-used of the three blow molding processes, and is typically used to make small medical and single serve bottles. The process is divided into three steps: injection, blowing and ejection.

The injection blow molding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a hot runner manifold where it is injected through nozzles into a heated cavity and core pin. The cavity mold forms the external shape and is clamped around a core rod which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body. similar in appearance to a test tube with a threaded neck.

The preform mold opens and the core rod is rotated and clamped into the hollow, chilled blow mold. The end of the core rod opens and allows compressed air into the preform, which inflates it to the finished article shape.

After a cooling period the blow mold opens and the core rod is rotated to the ejection position. The finished article is stripped off the core rod and as an option can be leak-tested prior to packing. The preform and blow mold can have many cavities, typically three to sixteen depending on the article size and the required output. There are three sets of core rods, which allow concurrent preform injection, blow molding and ejection.

Injection stretch blow molding

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Injection Stretch Blow Molding has two main different methods, namely Single-stage and Double-stage process. The Single-stage process is then again broken down into 3-station and 4-station machines.

In the single-stage process, both preform manufacture and bottle blowing is performed in the same machine. The older 4-station method of injection, reheat, stretch blow and ejection is more costly than the 3-station machine which eliminates the reheat stage and uses latent heat in the preform, thus saving costs of energy to reheat and 25% reduction in tooling. The process explained: Imagine the molecules are small round balls, when together they have large air gaps and small surface contact, by first stretching the molecules vertically then blowing to stretch horizontally the biaxial stretching makes the molecules a cross shape. These "crosses" fit together leaving little space as more surface area is contacted thus making the material less porous and increasing barrier strength against permeation. This process also increases the strength to be ideal for filling with carbonated drinks.

In the two-stage injection stretch blow molding process, the plastic is first molded into a "preform" using the injection molding process. These preforms are produced with the necks of the bottles, including threads (the "finish") on one end. These preforms are packaged, and fed later (after cooling) into a reheat stretch blow molding machine. In the ISBM process, the preforms are heated (typically using infrared heaters) above their glass transition temperature, then blown using high-pressure air into bottles using metal blow molds. The preform is always stretched with a core rod as part of the process.

See also

The company is the world’s best Automatic Bottle Blowing Machine supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

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References

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Bibliography

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The blowing of plastics

has its roots in

glass blowing

.

The invention of blown glass

was born in the same period of

the birth of the Roman Empire in the 1st century BC

, which promoted the spread of this new technology. Glass blowing was supported by the Roman government, and glass artifacts were produced in many areas of their empire, on the eastern borders for instance, where now there are the countries of Lebanon, Israel and Cyprus, the Phoenician people created the first large blowing factories.

1935: The blow molding industry born in Italy

Actually, the process for obtaining #packaging by "#blowing" a #thermoelastic material, was known since 1920, but had just a little use and only to produce cellulose objects.

From the 1930 there is a report of the first patents in this field, but we must wait the 40s to see the first successes of this technology, mainly due to the introduction of #polyethylene and #PVC which allowed the large-scale production of #blown #bottles.

The first #EBM (#Extrusion #BlowMoulding) technology for hollow bodies was initially applied only for small bottles, later also for large containers up to 5 liters.

Afterwards, the #IBM (#Injection Blow Molding) technology was developed and used above all to produce flacons and bottles for pharmaceutical or cosmetic markets.

1940s and 1950s: The first manufacturer

The history of blowing hollow bodies began in Italy with Giuseppe Moi, originally from Sardinia, who created an empire between 1937 and 1987. #Moi, in fifty years had managed to allow thirty companies start the blow moulding business in Italy and abroad. In 1951 the first half-liter Italian blow molding machine was manufactured, equipped with double screw extruders for the production of bottles for detergents. The first blow molder was followed, in 1962, by machines of different sizes, from 2 to 10 Lt. with either heads in continuous extrusion and with an #accumulation #head.

1960s: The first large Italian blow molding industries

Just after the second word war, two other companies started the development of these technologies: F.lli Moretti and Co-Mec.

The Moretti was founded in 1957 by the brothers Domenico and Giorgio Moretti as: "Mechanical workshop for the construction of machines and moulds for plastic hollow bodies". F.lli Moretti beyond the machines built also #extruders, extrusion heads, dies and small towings. One of the first #blowing machine, built in 1959, was continuous extrusion type with #pneumatic movements to blow 2 Lt. containers for detergents.

The Co-Mec was founded in 1960 by Herberto Hauda, and until 1965 it built blowers with pneumatic movements with a maximum capacity of 5 Lt., while, in 1966, the first #hydraulic type machine see the light, it could be equipped either with single head for 5 Lt container or a double head for up to 1 Lt. bottle.

Towards the end of the 1960s, the first special heads  were manufactured (for PVC and PE), with the possibility, in some case, to color the bottles in stripes.

We must also remember Piero Giacobbe founding in 1960 the ASCO - Association of plastics machinery manufacturers. The first blowing machine was called Mini Magic, and equipped with a 38mm / 22D extruder driven by an hydraulic motor and an accumulation head with a control unit panel and 3 thermoregulated heating zones. (The complete line cost at the time 3,558 liras, approximately 1,700 euros today).

The ASCO, in 1965, was changed in #MagicMP and quickly became a leader among the Italian blow moulding manufacturers for containers up to 200 liters, thanks to the #Miniblow and #Maxiblow models – the first for processing rigid PVC for food markets with automatic deflashing and neck calibration and the second for the production of larger containers up to 50 liters, with accumulation head and adjustment of parison weight and thickness.

...But the story continues.

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