design began to \"get some respect\", injection screw design has long been a neglected topic.
However, as more and more molds are required to provide faster cycles and tighter tolerances, this situation begins to change.
As more and more molesters meet new families
High performance resin for key applications, requiring stricter temperature control and a more gentle mixing, screw design is becoming more and more important.
Most material suppliers customize their resin based on what is usually accepted as standard screws for good operation.
However, equipment suppliers are developing a number of key areas specifically designed to improve plastic performance.
Most of these new designs are the result of a surge in new polymers, including enhanced compounds, ultra-high molecular weight polymers, and high-quality high molecular weight polymers
Heat resin for particularly demanding applications.
The above types of resin are required to be low
If they are to maintain their desired physical properties, shear treatment and strict temperature control. General-Purpose, single
Flighted screws typically provide relatively high shear rates and fluctuating temperatures, which in many cases lead to overheating and degradation problems.
Shear problem the traditional screw creates a high shear between the barrel and the solid mass of the resin during the screw flight, which results in uncontrolled degradation of high melting temperature and resin properties.
In addition, since the solid mass eventually breaks down when the solid mass becomes too small to maintain cohesion, part of the unmelted resin can be mixed with the molten pool.
This unmelted resin is finally located at the center of the melting channel and can enter the mold.
The problem, therefore, is twofold: excessive melting temperatures plus incomplete and poor mixing.
To solve these problems, barrier screws have been in use for more than 20 years.
Barrier screws reduce the \"unmelted\" problem to some extent and reduce the melting temperature.
But barrier screws rely on the same type of melting mechanism as conventional screws
High Shear included in the solid bed to melt the resin.
Because of this, it is still difficult for some screw manufacturers to run low enough melting temperatures to properly handle many emerging materials.
Screw and barrel suppliers, machinery manufacturers, and even processors themselves are working to design screws that bypass these problems.
In this article, we will take a closer look at some of these new designs.
The examples given are intended to represent trends, rather than an exhaustive list of each vendor that conducts technology development in this area.
Robert Barr developed an improved melting mechanism a few years agoT. (Energy Transfer)
Unlike traditional screws or barrier screws, screws use a melting mechanism other than solidbed melting.
Melting mechanism of E. T.
Screws are similar to the ones seen in many twinsScrew extruder.
The initial melting follows a traditional solid-
The bed mechanism, but at the end of the relatively short transition section, only about half of the resin is melted and it enters the E. T.
Part, intended to intentionally break the solid bed and disperse the unmelted resin into the melting pool.
The melting is then completed by conducting the heat from the melted mass to the unmelted solid.
It is said that the melting rate is larger than the melting rate of the solid.
The bed layer melts as the mixture is fully stirred by flow profiles and back and forth on obstacles with clearance of at least resin particle size.
According to Barr, the melting rate is as high as 20-in some cases-30% higher.
In addition to the higher melting capacity, E. T.
The energy transfer from the molten resin to the solid reduces the melting temperature, which is advantageous for many emerging resins. The Barr E. T.
Screws are available from the Great Lakes Feedscrews. S. President Jeffrey Kuhman, the user of the report. T.
Reduced recovery time by 50% and reduced the entire cycle by 25-
30% and reduce the melting temperature by 40-50[Degrees]F. Spirex Corp.
Recently, pulse helix was developed to solve some problems caused by emerging engineering resin (see PT, Feb. \'86, p. 49).
Marketing manager Mike Durina said that perhaps its biggest advantage is that it provides
Compression and low
Compression type of screws.
Flight screws do a reasonable job in mixing plastic melts, but mixing plastic melts by high shear, which often results in excessive melting temperatures.
This can lead to low productivity and poor quality of parts. Low-
The compression screw can provide more output, but the mixing and parts are of poor quality and may even allow unmelted resin particles to pass through.
In the case of little or no temperature rise and low shear, the pulse provides excellent mixing, Durina said.
Pulsars have a metering part that is divided into changing parts that are deeper or shallow than the average metering depth.
This requires all material to pass back and forth from shallow depth and slightly higher shear to a deeper channel of low shear many times.
The deeper parts always contain larger resins because these are low-shear areas.
Each time the plastic changes from one part to another, it experiences a gentle mixing action.
This interrupts the poor flow, which is said to result in excellent distribution and melting uniformity without high shear.
Van Dorn Plastic Machinery offers its own patent \"highperformance\" (HP)
The main purpose is to provide better melting uniformity, but it is also indicated that faster circulation and energy saving can be provided.
This is a barrier type, which is said to be 25% higher than general van doen\'s production. purpose screw.
The barrier in the flow channel selectively adds more energy to the lower part
Temperature particles (or \"mini-masses\")
Plastic, due to its high viscosity or stiffness.
At the same time, both macro and micro dispersion are happening.
All resin can get the benefit of this selective increased energy as needed, as all plastics have to go through the barrier to get to the front of the screw. Mixing-
Part of the channel is opened alternately upstream and downstream, so the material must pass through the barrier to continue along the screw.
The design also has a forwarding feature that facilitates material and color change, and has a long barrier that minimizes pressure generation.
Behind the obstacles.
Another advantage is reported to be energy saving.
Since there is less heat used to melt the plastic, it is possible to produce a uniform melting at a lower temperature, which requires less cooling in the mold.
Chicago npe\'88, Sumitomo Plastic Machinery (
Represented by SPM company. )
Its new subflight screw is shown, which is said to provide accelerated plasticization speed due to no alternative flight of resin.
It is said that in order to melt more evenly, this speeds up the separation of solids and melting particles.
It is also claimed to have a higher injection and kneading capacity.
Xaloy developed a dispersion/distribution mixing device for injection molding, which is said to be mild to the degradation material.
Laura Turner, director of marketing, says this \"G1\" device is its own
Clean and clean, conducive to the change of color, and provide a high mixing.
The G1 mixer is added to the discharge end of the screw and allows deeper screw flight by enhancing the mixing function.
This helps to reduce the melting temperature before the mixing part, thus reducing the possibility of material degradation.
Decentralized mixing (
Separation of large particles)
Through moderate shear (
About the shear rate. 250 sec (1))
When mixing is assigned, the material flows through the mixer (
Random spatial distribution of particles in matrix)
It is done through the material through the inlet and discharge channels.
For the processor, this means uniformity of temperature, color, and viscosity, Turner said.
The spiral angle of the G1 mixer is greater than the square spacing, resulting in a delivery rate greater than the rest of the screw, which makes the G1 mixer self-
Clean and clean.
The new castle industry also has new mixing heads.
Its Stratablend equipment is designed to maximize distribution and/or dispersion mixing. Its a free-
Flow mixer for selective application of formation
According to marketing manager Jim Frankland, the cut is layered on an intermittent basis, while creating an unlimited number of melt flow departments.
Stratablend is said to provide static mixing capability
Mix the part with little temperature rise.
The New Castle recommends mixing different resins or processes that require a high degree of color or additive.
Non-uniformity of screw diffusion
Robert Nunn of Lowell University, Massachusetts.
Research and development of company manager Stephen Gao Dao HPM.
The screw configuration jointly developed is as follows (left)
Promotes mixing behavior in which elements of non-uniformity can be distributed throughout the lens. Called the Two-
Its basic features include multiple parallel spiral channels, providing compression and decompression regions (
Shallow and deep channel section)
, And weaken on the flight tip to allow forward and backward flow between parallel channels.
In fact, the mixing part consists of a series of repeated unit geometry, each providing compression, decompression, and forward and return mass transfer.
The mixing of the screws is due to the positioning of the compression and decompression areas in the two channels relative to the flight cut.
The compressed area in one channel is combined with the reduced pressure area in the other channel and separated by the weakened flight area.
Therefore, the pressure difference due to the flow between material elements in each channel leads to the mass transfer of materials between each channel.
These cross flows produce a mixture of forward and backward.
When local non-uniformity enters the compressed area, the part is transferred to another channel by cross-flow, either forward or backward, depending on the local geometry.
In subsequent compression areas, other parts of non-uniformity are also transmitted from the Channel to the channel.
The range of the final mix depends on the number of cross flow paths present throughout the mix-
The number of materials transferred depends on the cross flow rate, which is a function of geometry, flow rate and polymer viscosity that can be specified by the screw designer.
In addition to the mixed action already described, Dr.
Nunn said that due to the impact of what he and Koh Dao call a \"leak\" flow, there is a potential additional flow complexity.
The first one is the flow of resistance at each bottom cut caused by screw rotation, always oriented backwards, the second is the flow of pressure at each weakening caused by the overall pressure gradient of the mixing segment, which can be directed backwards or forwards, depending on whether the pressure gradient is positive or negative.
The size of this leakage flow can also be specified by the screw designer.
At least one injection molding machine manufacturer seems to be applying the groove-feed-
The concept of throat, has been shown to improve the screw feed in the polyolene extrusion.
Battenfeld in the United States provides a new design, company officials said, this design provides the advantages of a wider range of processing, higher plasticization rate at lower screw speeds, good reduction of wear and tear, etc. The so-
The first launch at the k\'86 show at W. Dusseldorf was called LT screw.
Germany is different from the traditional screws because LT is equipped with a barrel that has a rectangular feed throat and a small groove in the feed area.
It is said that these grooves can improve the filling of the spiral channel without the need to build-up of pressure.
According to Battenfeld officials, this improved feeding brings higher throughput per revolution, although the channels in the feeding area are lighter.
It is said that the process of material compression and melting will begin faster.
At the same time, the melting process is strengthened in the shallow feeding section.
According to Battenfeld, this means that mixing and homogenization will be further improved in the case of the same screw length.
The metering part of the LT screw is cut deeper.
It is said that even in the case of \"difficult\" materials, an uncontrollable high level of shear can be avoided.
LT screws are reported to provide a wider range of processing in the case of controlling the melting temperature.
Although the output has increased by about 25%, the LT screw allows the installation of the mixing head;
As a result, not only can the ability to increase the molding, but also can improve the mixing performance.
On conventional plastic-increasing devices, the barrel or wall temperature along the screw is usually increased or constant.
However, with a plastic-adding device equipped with LT screws, it is said that it can also work with fewer and fewer barrel walls
The barrel temperature at the Hopper throat can be significantly higher than the screw tip that sets the desired melting temperature.
It is reported that this operation method is not possible for traditional screw processing materials such as PP, PS and PE;
The result is a sharp drop in throughput.
The higher the barrel temperature of the LT screw feed part, means that the material starts melting much faster.
At the same time, Battenfeld officials reported that experiments have shown that reducing the distribution of barrel temperature can help achieve better mixing and provide a more uniform melting temperature in the metering chamber.
Battenfeld offers LT screws from 16 to 150mm in diameter as an option (0. 62-5. 85 in. ).
In order to increase the yield and/or reduce the melting temperature, it is especially recommended for olefin.
Possible applications include high density polyethylene barrels and PP dishwasher barrels.
Husky Injection Molding system is specially used for PET pre-forming in the field of PET bottle molding specialty, and it has developed screws for significantly reducing aldehyde (AA)levels.
AA is a harmless by-product of thermal degradation, but it affects the taste of bottled products.
France\'s leading minerals
The tap water company has set the standard to allow the highest AA content in PET bottles of 2 micrograms per liter
Less than half what major American airlines allowS. soft-Beverage manufacturers
To limit the AA level, PET screws must be designed to minimize the processing temperature.
For a specific melting temperature, AA is produced at a linear rate over time, but this relationship becomes exponentially when the melting temperature exceeds 510 F.
Therefore, it is important to prevent temperature rise during injection molding.
Husky claims that its screw design achieves a 33% reduction in the AA level, providing a wider operating window than the standard screw design.
Husky officials say the mixing head is an integral part of the special screw structure, which is said to provide high productivity and very gentle mixing.
New use for ventilation Spirex has applied for a patent for ventilation
The barrel system that enables the injection molding machine and the extruder to process the poly resin (
Surlyn of DuPont)
In a \"wet\" state without pre-drying, special two-
Stage screw design.
This method is useful, as it is reported that polyethylene Poly such as Surlyn cannot be dried in the traditional way.
The system needs to starve-
Feed to allow the evaporated moisture to be discharged from the back of the partially filled screw and through the barrel vent.
The patent application name is DuPont.
Being the sole licensee of the process and further stipulating that DuPont grants re-licensing to its customers.
Spirex supplies both.
Stage screws, exhaust cylinders and hunger feeders.
Bmc machine has mixed screws at the JP \'88 trade show in Osaka, Japan, Yubu Industrial Co. , Ltd.
A machine specially used for long molding is introduced. glass-
Fiber reinforced hot solid compounds (PT, Jan. \'89, p. 64).
The Ubemax LM series machine has a screw that is said to combine the best features of the reciprocating screw and the piston.
It has a wider material Channel area between the barrel and the screw, and the length of the screw is kept to a minimum.
Yubu officials said that by adopting these concepts, the mixing and kneading of the resin was reduced during the metering process, minimizing the loss of material impact strength.
In Dearborn, Michigan, a processor strives to achieve a new approach to zero rejection, custom molder Wolf engineering.
, Designed its own \"heat compensation\" screw.
This system \"reuses\" by transferring excess friction heat from the front end of the screw to the transition area, where it can help melt and increase the plastic.
It is said that the hot conductor inside the screw provides the necessary precise compensation to prevent random overheating and overheating of the melt caused by conventional reciprocating screws.
Roger Holtslander, maintenance director at Wolf Engineering, said that the net effect is to remove all unmelted resin from traditional melts.
He added that the internal thermal conductor stabilized the melting temperature in the critical frontier area and allowed to reduce the temperature in the area below the temperature used with the uncompensated screws, increasing the effect of the cycle speed.
Hot compensation screws can control the front better, says Holtslander
Usually only increase, but not decrease.
It is said that both heat compensated screws are possible.
He said that about 20 other barrel areas can run [degree]
F cooler because the previously uncontrolled friction heat is controlled by the compensation screw.
Another benefit of the internal heat transfer provided by the screws is reported to be a significant reduction in screw and barrel wear.
A wolf engineer described the abrasion resistance of heat.
The compensation screw on the filling material is \"eliminate grinding effect \".
Holtslander said the material is now in a \"fluid flow mode\" and there is much less wear in the compression zone compared to standard screws.
He added that the tests show that the integrity of the fibers in the filling material is preserved better, thus enabling the production of stronger parts.
The thermal compensation screw is limited by its thermal conductor and the upper temperature limit is about 600 F, Holtslander said. IMS Co.
Chin Falls, Ohio, is licensed by Wolf Engineering to provide heat compensated screws, or to retrofit existing screws with internal heat transfer.
Conversion options for Wayne machines and molds
The screws have been modified for the customer to reduce the stay time in the bucket.
Wayne calls it a \"quick lead on the Screw \".
For example, put one. 75-in. lead on a 1. 5-in. -Diameter screw-
There is usually a 1. 5 in.
Lead, also known as Square Court
It is reported that degradation is avoided by reducing dwell time, and faster shooting cycles are facilitated by delivering the melt to the nozzle faster.
Wayne also modified the screws in other ways.
For example, customers who want to run PVC in a low density polyethylene machine need a screw with a lower compression ratio.
Other companies active in conversion include Xaloy and Spirex.
Photo: Van doen\'s HP mix screw ion in the oven-
Nitrogen treatment (opposite page).
The main purpose of HP screws is to improve the melting uniformity, but it is said that it can also provide faster circulation and energy saving.
On the right is the ET screw of bar.
It is said that this will save energy and reduce the melting temperature.
Photo: it is said that the thermal compensation of the screw interior developed by injection of Molde Wolff engineering reciprocating screw thermal conductor provides the precise compensation needed to prevent random overheating and overheating.
Photo: basic feature part of HPM dual threaded Channel
The method of mixing the screw includes multiple parallel screw channels, compression and decompression areas, and the bottom of the flight tip to allow forward and backward flow between parallel channels.
Photo: The expansion channel of the pulse mixing part pulse mixing screw from Spirex is designed to provide high-
Compression and low
Compression screw type.
Figure: depicted with tables and charts (acetaldehyde)
AA level customized with standard screws and screws-
Designed by Husky Injection Molding system.
Feed polymers such as PP and ET.
Bar E Festival. T.
Screws are used at the end of a conventional cone or transition segment.
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