Plasticstrends

  • Increase font size
  • Default font size
  • Decrease font size

News Flash

Researchers gather to discuss advances in organic photovoltaics (OPV)

For the first time, IBM researchers showed 3D molecular structure could be observed

McMaster university (Canada) researchers developed flexible solar cell technology

How computer modelling & 3D printing create fracture resistant composites – reports Stratasys and MIT researchers

James Cropper Speciality Paper touts recycling of disposable coffee cups

Are you interested in self-healing polymers – must read reviews

Brazilian scientists are actively pursuing bioplastics research and innovation

A novel technique to manufacture continuous twisted yarn from aligned PAN nanofibers

Japanese scientists report a unique, smart and self-healing polymer nanocomposite hydrogels

World’s first all-plastic LED lamp comes from Japan

Nanoparticle coating prevents ice build up

ZogglesTM earns Invention of the year 2010 award and keeps the fog away

Yale scientists develop high performance thin film composite membrane

Plastrec, a Quebec recycler unveils recycled PET production combining two plastics technologies

Sabic Innovative Plastics unveils its newly developed a clear flame retardant Polycarbonate copolymer

IKV researchers report thermoplastic/metal hybrid materials for Direct manufacturing electronic part

Self-healing plastics healing like human skin

MIT researchers develop first Solar Thermal Fuel storage platform in solid-state

Polymers can be used to package insulin into a pill for diabetes treatment reports Indian scientists

Canadian researchers claim world’s most efficient “inverted” OPV solar cells

Austrian scientists claim to be the first to have developed an image sensor that is fully transparent

Bayer uses PC film Makrofol? for it's new Innosec Fusion? technology to stop counterfeiting

Norner touts major research project on polymers based on carbon dioxide

GM recycles oil soaked booms from the Gulf of Mexico for its Chevrolet Volt under hood parts

Will your windows generate power one day?

Scientists from Sweden and USA showed electronics can truly be organic or say truly be plastics

Current trends and future prospects for flame retardants in polymeric materials

Work of North Carolina State Univ. researchers shows how to remove radioactive elements from drinking water

Arkema unveils a range of "green" polymers for its textile market

MIT researchers show how to draw Polyethylene as nanofibers and get a very high thermal conductivity

Alberta scientists help to make Canada’s first bio-composite based electric vehicle body design

Plastic Logic sees mass production of flexible display in 2008

NIST develops greener solution to challenge commercial fire retardants

Carbon3D, a Canadian company unveils a breakthrough technology for layerless 3D printing

If you follow plastics electronics - follow Unidym’s innovative product lines

Current status in graphene based polymer nanocomposites – a review

Oil-SAP, a novel development to clean-up oil spill & recovery from Penn State University, USA

3D systems introduces non-halogenated flame retardant for aircraft applications

Polymers help Addidas to launch lightest soccer boots and 2010 FIFA World cup match ball never seen before in the field

UCLA scientists showed how simple it could be to make conducting polymer thin films

Wax could be green too – touts GreenMantra Technolgies!

Polymer bank notes on the rise to avoid counterfeit paper currencies

New ambipolar polymer beats others: reports US researchers

Rutgers Univ researchers moves plastic electronics with graphene based PS thin films

UC Berkley researchers have developed paper thin e-skin that responds to touch

Singapore researchers touts corn starch can help solve body armour and protective sports padding

Stanford university researchers detect mercury ions in sea water using organic polymer transistor sensor

Block copolymers could create hard disks with 10 tera-bit-per-Square-inch:Researchers predict

Work of North Carolina State Univ. researchers shows how to remove radioactive elements from drinking water

Non-toxic, liquid bandage from Chesson Labs of Durham, NC is ready for the healthcare market

Mannigton converts large stickers from 2010 winter games into commercial flooring

Siver nanowire electrodes for flexible electronics

Cima NanoTech flexes mussels with its non-Indium Tin Oxide, high performance transparent conductors

Researchers develop unique printable thin film supercapacitor using SWCNT

Can you 3D print yourself? TwinKinds of Germany shows just that!

Can you “Cool Your Roof” - reports researchers from Chinese Academy of Sciences, Beijing

Umass, Amherst researchers find ways to hold 300 kilograms of weight using sticky tape

A new microcellular injection molding process for polycarbonate using water

Can polycarbonate be replaced with another polymer? Click chemistry might provide the answer!

Harvard University researchers design stretchable, transparent ionic conductors

It is time to make “Perfect Plastic” reports UK researchers

How blood can clot to heal a wound - Science reports

Innovations in design come from plastics to win several 2009 International Design Excellence Awards

Can Gas Jet process challenge electrospinning in producing polymeric nanofibers?

Braskem S.A. is leading the way to manufacture biobased polyethylene using catalytic dehydration

Using biodegradable polymer, University of Basque country researcher report on bone regeneration

Princeton university researchers embedded piezoelectric material onto polymer as energy harvester

USA researchers report polymeric blood-resistant surgical glue that can repair minimally invasive heart defects

Scientists from IBM and Stanford University are developing new plastics recycling process

Austrian researcher reports new opportunities from Silicon oxide Nanofilms

Univ of Texas @ Austin scientists reported method to produce a large scale reduced graphene oxide

Stanford Univ researchers make Jell-O-like conducting polymer hydrogels

MIT researchers develop first Solar Thermal Fuel storage platform in solid-state

Harvard Univ researchers show how soft robotics could navigate a difficult obstacle

A team of researchers demonstrate plastics and graphene can work together to make touch screen device a reality

Stratasys touts World’s first color multi-material 3D printer for rubber & plastics products

Practical Devices provide useful power from the body

Chinese researchers made a bendy polymer that could separate aromatics hydrocarbons from aliphatic

University of Texas at Austin researchers show use of polymer membranes for fracking in shale gas

Something old... Something new.... produces an interesting marriage

Strain Paint: an alternative to strain gauges

German researchers unveiled a green approach to electrospinning technique for making biodegradable nanofibres

Korean scientists provide a different twist to the “Smart Window” technology

In Milan, art and science get together to showcase Vegetal, weather resistant designer chair

Bio-succinic acid is becoming new green platform chemical for plastics

Battelle researchers are improving PLA for injection molding applications

Japanese researchers are developing stereo-block type PLAs for high performance materials

Advanced nanocomposite membrane technology of NanoH2O turns it to a Global clean technology company

Plastics help design non-shatter pint glass to prevent pub attacks

Can polymer reinforced aerogel make a space mission? University of Akron researchers think so!

Swedish researchers show highest reported charge capacities for all polymer paper-based battery

Prof. Alan Heegers group demonstrated the potential of plastics solar cells

Stanford researchers use cheap plastics film to make safe lithium batteries

Can you “Cool Your Roof” - reports researchers from Chinese Academy of Sciences, Beijing

Kyoto researchers are upbeat about cellulose nanofibers based composites for auto parts

Researchers review how to characterize polymer nanocomposites by different microscopicy techniques

Rice Univ (USA) researchers grew high quality graphene from polystyrene, cookies, grass, cockroach leg & dog feces

Are you an injection moulder, you may want to read the ultimate in mould cooling article

AMI unveils the North American Bioplastics technology agenda

Binder free multilayer graphene based polymer composite for high performance supercapacitor electrodes

Green Composites - all you wanted to know about

USA researchers develop all-polymer multilayer coating to retard fire and to suppress smoke

Polymer helps to designing higher capacity Li-ion battery

Electric Glue: Another twist to make controlled polymer-surface adhesion

Teijin Techno Products claims to be world’s first mass producer of aramid nanofibers

How Collagen nanofibers could find use in Tissue Engineering

Researchers show stretchy battery for flexible and stretchable electronics

A review on polymer/bioactive glass nanocomposites provides current trends in polymer research

Can polymer reinforced aerogel make a space mission? University of Akron researchers think so!

How plastics helping revolutionize stretchable electronics applications – a review, not to be missed!

Caltech researchers show through telechelic polymers how to produce a safer and a cleaner fuel

US and South Korean researchers develop a printing technique to make high performance CNT transistors

US researchers develop shape memory polymer nanocomposites exhibiting fast actuation speed

French scientists tout first use of nano-structured assemblies that could revolutionize dentistry

MIT team aims to develop application specific surgical adhesives to seal tissues

The Evolution of Screw Design Technology for the Injection Molding Process – Part 2

E-mail Print PDF

tmw2 figure 1  Part 1 of this paper discussed the origins of the injection molding process and the development and use of the helical screw for conveying and melting polymers.

The plasticating unit used for melting and mixing on an injection moulding machine performs the same basic functions as the plasticating unit of an extruder. The difference lies in the fact that the screw moves backwards in injection moulding and thus the plasticating unit in an injection moulding machine can be considered to be a reciprocating extruder.

While screw design was considered to be important in extrusion, it was often considered to be less import in injection moulding. The major difference is that in a reciprocating system, the process is cyclic instead of continuous and the screw design plays a key role in maintaining cycle to cycle consistency for the resulting, molded plastic parts.

This second part of this paper discusses the use of barrier / mixing screw technology for the plasticating of polymers in the injection molding process from the early 1960’s to today’s sophisticated injection molding equipment.                                                          

The Need

As Part 1 of this paper explained, simple three-zone screws like the one shown in Figure 1, are commonly known as ‘General Purpose (GP) Screws’, which are designed to process as much thermoplastic material as possible in an injection molding process, while providing a reasonable level of quality.

tmw2 figure 1

Figure 1

 

This screw design was adequate in the early years and in many situations still today, but it did have and frequently still has its drawbacks, for example when the parts that are being manufactured have specific quality requirements especially if high throughput is required.

Another situation in which GP screws provide is when masterbatches are mixed with virgin resins. The use of these color concentrates is more economical than using pre-colored resins, since this reduces waste and reduces a company’s inventory costs. Blending the virgin resins with color concentrates required more mixing than the GP screw geometry could readily provide, because the three zone screws lack shear and mixing elements. As a consequence of the inadequacy of these screws in this application, many believed that GP was an abbreviation for ‘Generally Poor’ and not ‘General Purpose’.

The Conair Auto-color™ blender provided one of the earliest attempted solutions. This piece of equipment automatically pre-blended the materials at the throat of the injection molding machine. Prior to the development of the Auto-Color™ many processors would simply put the neat resin and the color concentrate pellets in a drum and tumble them together often by just rolling the drum across the shop floor. With the introduction of the Auto-color™ blender, better mixing was possible.

This automatic pre-blending gave significant improvements in the color uniformity of the molded part, but it would still be necessary for the machine operator to make processing adjustments to obtain color shade uniformity. Most often this was done by increasing the back pressure on the injection unit.

As time passed, it became more apparent that the need for improved mixing quality was a necessity for the injection molding process. Various workers used ideas developed for plastics extrusion screws, attempting to obtain further improvement by incorporating additional mixing devices into the injection molding screw design.

Carl F. Schnuck and his colleagues, at the Farrel-Birmingham Company developed one of the earliest extrusion screw mixers (figure 2) in 1952 for which they were granted US Patent 2,680,879.

tmw2fig 2

Figure 2

 

Screw designers at other plastics machinery manufacturers who understood plastics processing, screw design and mixing began to develop other types of mixers. Individuals such as Street, LeRoy, Maddock, Gregory and Hsu developed several different types of distributive and dispersive mixers, some of which are shown in Figure 3. For example, in 1968, R.B. Gregory showed that the introduction of mixing sections lowered melt temperature, allowed faster production rates and yet gave an extrudate with improved properties.

tmw2fig 3

Figure 3

 

Most of these mixers adopted from the extrusion process into the injection molding process. Most of this work was done in the late 1960’s and 1970’s.

As the injection molding industry started to really grow in the 1970’s, individuals, such as, Bill Willert and Paul N. Colby, started to develop new mixing elements and also started to use barrier screw technology for injection molding screws.

In principle, barrier screws used for injection molding operate in the same way as in extrusion. The screw channel is divided into a solids channel and a melt channel. The barrier flight essentially separates both the channels and helps to homogenize the melt.

Maillefer introduced the barrier screw for extrusion in 1959, in which the screw design included a barrier in the transition section of the screw (Swiss Patent 82,535/59). Bill Willert patented a barrier-type screw in his US Patent 4,330,214 (Figure 4), which was granted on May 5, 1982, and was eventually used for injection molding applications.

After the expiration of the Dray-Lawrence US Patent 3,650,652 on March 22, 1989, Paul N. Colby started to use the Dray-Lawrence barrier screw technology for injection molding applications.

With the development of the two U.S. patents described above, the injection molding industry stepped into the 20th century in the area of plasticating of polymers. The new barrier screw technology, provided a way to increase plasticating rates and thus throughput by15 to 20%.

tmw2fig 4

Figure 4

 

At this time many new barrier mixing sections were developed. LeRoy at Union Carbide Corporation patented a dispersive mixer in US Patent 3,485,192. This mixer eventually became known as the Maddock Mixer (Figure 5) and was the first device that was used for improving the melt quality of the polymer before it was injected into the mold.

tmw2fig5

Figure 5

This was a period of innovation (late ‘70s through early ‘90s) for the injection molding industry. Paul N. Colby was responsible for a great amount of the development that was done in the United States. One of the most popular and well-known mixers in the injection molding industry was the Spirex Pulsar® Mixer. The Pulsar® mixer, shown in Figure 6 was granted on June 21, 1988. This new distributive mixing device was a break through in screw design for injection molding which was the market area that Spirex primarily pursued.

tmw2fig 6

Figure 6

 

Following the development of screw technology by Dulmage, Saxton, Le Roy, Maddock, Kruder, Gregory and others, there was a mad race by many other inventors in the United States to develop new mixing devices. Robert Dray provided the “Dray Mixer” (3,788,612). Jim Frankland invented the StrataBlend® Mixer (4,639,143). Spirex patented the Z-Mixer (5,318.357). Westland Corporation patented the Eagle® Mixer (5,215,764). Womer patented the V-Mixer (5,798,077), Pulsar®II (5,816,698), StrataBlend®II (6,488,399) and Nano™Mixer (6,497,508) while at Spirex and at Xaloy. Also, Womer patented the MeltStar II Mixer (6,547,431) for Milacron.


Conclusions

Over the past 50 years, starting with Bill Willert’s innovation of using barrier technology for the injection molding process, along with the advancements by Paul N. Colby and others, the injection molding of plastics has gone through great improvements to increase the product quality and production rates for the plastics industry.

Although simple three zone screws for injection molding must function with a wide range of requirements and materials, the sophistication of today’s plastics business has put enormous pressure on the homogeneity (melt quality) of the melt such that the needs cannot be achieved with GP screws.

New developments in screw designs will continue to provide molders with exciting opportunities to increase their productivity. As long as plastics continue to be injection molded, innovators of the plastics industry will continue to develop newer screw designs for processing a wide variety of plastic materials.

 

Timothy W. Womer, CPlasT

Tim Womer, is the President of TWWomer & Associates, LLC and was the 2006-2007 President of the Society of Plastics Engineers and a member of the SPE Extrusion Board of Directors for the past 20 years.  At the Society of Plastics Industries (SPI) NPE 2012, Tim has been inducted into the Plastics Hall of Fame.

Tim is a recognized authority in plastics technology and machinery with a career spanning over 35 years; having worked for other companies like Xaloy, Inc., Spirex Corporation, Conair Group and NRM Corporation.

Tim has designed thousands screws that have been used in all areas of single-screw plasticizing such as extrusion, blow/injection molding. Numerous patents have been issued for his inventions of screws, mixers, processes and other products.