Injection Molds and Rotational Molds

Tag : Plastic Injection Process
The world has become very dependent upon plastic products. Fromhousehold items to industry and aerospace, plastic in its manyformulations has transformed modern manufacturing and createdconveniences and economies unimagined in the early decades of the20th century.

Injection Molds
The injection molding industry took hold in 1946 when James Hendrybuilt a screw injection molding machine. But, his technology wasbased on an earlier invention by John Wesley Hyatt who, in 1868injected hot celluloid into a mold to make billiard balls. Hyatt'smethod used a plunger to force the material inside a mold. Hendry'simprovement was revolutionary because it eliminated the plunger andreplaced it with an auger-type action that better distributedmaterial and facilitated the use of plastic inside molds.

Today's injection molds use much the same process and produce awide variety of products from car panels to outdoor furniture,small toys and tools. Injection molding is ubiquitous inmanufacturing and uses many different materials from polymerplastics to aluminum, copper and other metals. The plastic bottlesand kitchen implements people use in everyday life are products ofthe injection process.

Because the metal molds are generally expensive to produce,injection molding is most economically used when thousands ofpieces are being manufactured. Molds are made of hardened steel or,more recently, aluminum which is less expensive.

The Injection Process
Described very simply, molten plastic is injected into the moldunder high heat and pressure. The goal is to have the moltenplastic material evenly flow to all parts of the mold, creating anexact, consistent, solid plastic replica of the mold cavity. Aftera brief cooling cycle, the mold or tooling mechanically ejects theplastic part which then moves on through the manufacturing process.In the injection molding industry, this is a completely automatedprocess that's very fast and extremely efficient.

Rotational Molding
Rotational molding is yet another method of producing multipleproducts, most often made with a variety of plastic powders. Thisprocess is usually used in making hollow products such as trafficcones, canoes, kayaks, bicycle helmets and giant tanks used forwater or chemical storage.

Like Injection molding, rotational molding had its roots in the1940s. But it was not until the technology was more sophisticatedand new polymer and plastic formulations became available that therotational process became a mainstream manufacturing method.

Rotational Process
The two processes are quite different. Let's consider, for example,a 300 gallon water storage tank made of polyethylene. Picture amaster mold made of aluminum or steel. The plastics manufacturerpours poly resin powder into the mold that is fitted inside anoven. Once sealed, the mold is mechanically turned on at leastthree axes, moving much like a gyroscope. At the same time, theoven is raised to an appropriate temperature and the polymer - orother material - tumbles inside and slowly coats the inner walls ofthe mold, melting as it rotates.

Once the optimal temperature is reached, the mold is cooled. As thetemperature of the mold itself falls, the product on the insideshrinks away from the inner walls and is easily removed. This isnot always the case with injection molds that are often moredifficult to successfully remove. The shrinking action ofrotational molding is particularly desirable when the product isvery large and awkward to handle.

Rotational molding is also more economical for some productsbecause less material is used. In addition, the polymer that isleft over from one mold can be used in another. The method itselfis more streamlined than injection molding, which requires moreinterlocking parts.

Materials Improve and Expand
Most products made with the rotational molding method are from thepolyethylene family. Other materials include nylons, polypropyleneand PVC plastics. Some manufacturers have developed formulas thatintegrate the use of natural materials such as sand and chips ofstone to make products.

Plastic and resin products are now an integral part of everydaylife and supply us with items as tiny as paper clips and as big asstorage tanks. As the industry developed, so too has environmentalawareness about the safety and use of these petrochemical-basedproducts. Today, materials can meet the specifications of FDArequirements, and other health and safety related regulations.Producers are also cooperating to create products that can berecycled.
The injection molding industry took hold in 1946 when James Hendrybuilt a screw injection molding machine. But, his technology wasbased on an earlier invention by John Wesley Hyatt who, in 1868injected hot celluloid into a mold to make billiard balls. Hyatt'smethod used a plunger to force the material inside a mold. Hendry'simprovement was revolutionary because it eliminated the plunger andreplaced it with an auger-type action that better distributedmaterial and facilitated the use of plastic inside molds.

Today's injection molds use much the same process and produce awide variety of products from car panels to outdoor furniture,small toys and tools. Injection molding is ubiquitous inmanufacturing and uses many different materials from polymerplastics to aluminum, copper and other metals. The plastic bottlesand kitchen implements people use in everyday life are products ofthe injection process.

Because the metal molds are generally expensive to produce,injection molding is most economically used when thousands ofpieces are being manufactured. Molds are made of hardened steel or,more recently, aluminum which is less expensive.

The Injection Process
Described very simply, molten plastic is injected into the moldunder high heat and pressure. The goal is to have the moltenplastic material evenly flow to all parts of the mold, creating anexact, consistent, solid plastic replica of the mold cavity. Aftera brief cooling cycle, the mold or tooling mechanically ejects theplastic part which then moves on through the manufacturing process.In the injection molding industry, this is a completely automatedprocess that's very fast and extremely efficient.

Rotational Molding
Rotational molding is yet another method of producing multipleproducts, most often made with a variety of plastic powders. Thisprocess is usually used in making hollow products such as trafficcones, canoes, kayaks, bicycle helmets and giant tanks used forwater or chemical storage.

Like Injection molding, rotational molding had its roots in the1940s. But it was not until the technology was more sophisticatedand new polymer and plastic formulations became available that therotational process became a mainstream manufacturing method.

Rotational Process
The two processes are quite different. Let's consider, for example,a 300 gallon water storage tank made of polyethylene. Picture amaster mold made of aluminum or steel. The plastics manufacturerpours poly resin powder into the mold that is fitted inside anoven. Once sealed, the mold is mechanically turned on at leastthree axes, moving much like a gyroscope. At the same time, theoven is raised to an appropriate temperature and the polymer - orother material - tumbles inside and slowly coats the inner walls ofthe mold, melting as it rotates.

Once the optimal temperature is reached, the mold is cooled. As thetemperature of the mold itself falls, the product on the insideshrinks away from the inner walls and is easily removed. This isnot always the case with injection molds that are often moredifficult to successfully remove. The shrinking action ofrotational molding is particularly desirable when the product isvery large and awkward to handle.

Rotational molding is also more economical for some productsbecause less material is used. In addition, the polymer that isleft over from one mold can be used in another. The method itselfis more streamlined than injection molding, which requires moreinterlocking parts.

Materials Improve and Expand
Most products made with the rotational molding method are from thepolyethylene family. Other materials include nylons, polypropyleneand PVC plastics. Some manufacturers have developed formulas thatintegrate the use of natural materials such as sand and chips ofstone to make products.

Plastic and resin products are now an integral part of everydaylife and supply us with items as tiny as paper clips and as big asstorage tanks. As the industry developed, so too has environmentalawareness about the safety and use of these petrochemical-basedproducts. Today, materials can meet the specifications of FDArequirements, and other health and safety related regulations.Producers are also cooperating to create products that can berecycled.