Industry News • Paul Murphy Plastics

Plastics.jpg

May 15, 2019

Thermoplastic polymer resins are extremely common, and we come in contact with thermoplastic resins constantly. Thermoplastic resins are most commonly unreinforced, meaning, the resin is formed into shapes and have no reinforcement providing strength.

Examples of common thermoplastic resins used today, and products manufactured by them include:

  • PET – Water and soda bottles
  • Polypropylene – Packaging containers
  • Polycarbonate – Safety glass lenses
  • PBT – Children’s toys
  • Vinyl – Window frames
  • Polyethylene – Grocery bags
  • PVC – Piping
  • PEI – Airplane armrests
  • Nylon – Footwear

Many thermoplastic products use short discontinuous fibers as a reinforcement. Most commonly fiberglass, but carbon fiber too. This increases the mechanical properties and is technically considered a fiber reinforced composite, however, the strength is not nearly as comparable to continuous fiber reinforced composites.

In general, FRP composites refers to the use of reinforcing fibers with a length of 1/4″ or greater. Recently, thermoplastic resins have been used with continuous fiber creating structural composite products. There are a few distinct advantages and disadvantages thermoplastic composites have against thermoset composites.​

Advantages of Thermoplastic Composites

There are two major advantages of thermoplastic composites. The first is that many thermoplastic resins have an increased impact resistance of comparable thermoset composites. In some instances, the difference is as high as 10 times the impact resistance.

The other major advantage of thermoplastic composites is the ability reform. See, raw thermoplastic composites, at room temperature, are in a solid state. When heat and pressure impregnate a reinforcing fiber, a physical change occurs; not a chemical reaction as with a thermoset.

This allows thermoplastic composites to be reformed and reshaped. For example, a pultruded thermoplastic composite rod could be heated and remolded to have a curvature. This is not possible with thermosetting resins. This also allows for the recycling of the thermoplastic composite at end of life. (In theory, not yet commercial).

Properties and Benefits of Thermoset Resins

Traditional Fiber Reinforced Polymer Composites, or FRP Composites for short, use a thermosetting resin as the matrix, which holds the structural fiber firmly in place. Common thermosetting resin includes:

  • Polyester Resin
  • Vinyl Ester Resin
  • Epoxy
  • Phenolic
  • Urethane

The most common thermosetting resin used today is a polyester resin, followed by vinyl ester and epoxy. Thermosetting resins are popular because of uncured, at room temperature, they are in a liquid state. This allows for convenient impregnation of reinforcing fibers such as fiberglass, carbon fiber, or Kevlar.

As mentioned, a room temperature liquid resin is easy to work with. Laminators can easily remove all air during manufacturing, and it also allows the ability to rapidly manufacture products using a vacuum or positive pressure pump. (Closed Molds Manufacturing) Beyond ease of manufacturing, thermosetting resins can exhibit excellent properties at a low raw material cost.

Properties of thermoset resins include:

  • Excellent resistance to solvents and corrosives
  • Resistance to heat and high temperature
  • Fatigue strength
  • Tailored elasticity
  • Excellent adhesion
  • Excellent finishing (polishing, painting, etc.)

In a thermoset resin, the raw uncured resin molecules are crossed linked through a catalytic chemical reaction. Through this chemical reaction, most often exothermic, the resin creates extremely strong bonds with one another, and the resin changes state from a liquid to a solid.

A thermosetting resin, once catalyzed, it can not be reversed or reformed. Meaning, once a thermoset composite is formed, it cannot be remolded or reshaped. Because of this, the recycling of thermoset composites is extremely difficult. The thermoset resin itself is not recyclable, however, there are a few new companies who have successfully removed the resin through pyrolization and are able to reclaim the reinforcing fiber.

Disadvantages of Thermoplastics

Because thermoplastic resin is naturally in a solid state, it is much more difficult to impersonate reinforcing fiber. The resin must be heated to the melting point, and pressure is required to impregnate fibers, and the composite must then be cooled under this pressure. This is complex and far different from traditional thermoset composite manufacturing. Special tooling, technique, and equipment must be used, many of which are expensive. This is the major disadvantage of thermoplastic composites.

Advances in thermoset and thermoplastic technology are happening constantly. There is a place and a use for both, and the future of composites does not favor one over the other.

Original Source


plastic-resin.jpg

May 9, 2019

There are thousands of plastics on the market that can be used for rapid prototyping or low-volume manufacturing—choosing the right one for a given project can be overwhelming, especially for first-time inventors or new entrepreneurs. Each material has trade-offs when it comes to cost, strength, flexibility and surface finish. Consideration must be given not only to the application of the part or product, but also to the environment in which it will be used.

Overall, engineering plastics have advanced mechanical properties that offer greater durability and that won’t be compromised during the manufacturing process. Modifications also can be made to some types of plastics to improve their strength as well as their impact and heat resistance. Let’s delve into the different plastic materials to consider depending on the final part or product’s function.

Mechanical parts

One of the most common resins used to make mechanical parts is nylon, aka polyamide (PA). When PA is mixed with molybdenum it has a slippery surface for easy motion. However, using nylon-to-nylon gear trains is not recommended, as similar plastics tend to stick together. PA is highly resistant to wear and abrasion and has good mechanical properties at elevated temperatures. Nylon is ideal as a filament for 3D plastic printing, but it absorbs water over time.

Polyoxymethylene (POM) is also a great option for mechanical parts. POM is a type of acetal resin, used to make Dupont’s Delrin, a valuable plastic for gears, screws, wheels and more. POM has high flexural and tensile strength, stiffness and hardness. However, POM can degrade with alkali, chlorine and hot water and can be difficult to bond together.

Plastic containers

If your project is a vessel of sorts, polypropylene (PP) is best. PP is used for food-storage containers because it is heat resistant, is impervious to oils and solvents and doesn’t leach chemicals, making it food safe. PP also has a superior balance of stiffness and impact strength and can be easily formed into a hinge that can be bent repeatedly without breaking. It can also be used for applications in pipes and hoses.

Another option is polyethylene (PE). The most common plastic in the world, PE has low strength, hardness and rigidity. It usually has a milky white color and is the plastic found in medicine bottles and milk and detergent containers. PE is highly resistant to various chemicals, but has a low melting point.

Tool cases and hardware

For any project needing high impact resistance and strong resilience to tearing and breaking, acrylonitrile butadiene styrene (ABS) is ideal. ABS is lightweight and can be strengthened by adding glass fibers. It is more expensive than styrene, but lasts much longer due to its hardness and toughness. ABS is used for 3D fused deposition modeling of rapid prototypes.

Given its properties, ABS is a good option for wearable devices. At Star Rapid, we created a smart watch case for E3design with black, pre-colored ABS/PC plastic resin using plastic injection molding. This material choice allows the overall device to stay relatively light, while also providing a shell that can endure accidental impacts, such as when the watch hits a hard surface. If you need something that is versatile and impact resistant, high-impact polystyrene (HIPS) is a good option. This material is suitable for creating tough cases for power tools and tool boxes. While HIPS is economical, it is not considered environmentally friendly.

Rubber

Many projects call for injection molding of resins that have the soft, elastic properties of rubber. Thermoplastic polyurethane (TPU) is a great option, as it comes in many special formulas to achieve high elasticity, low-temperature performance and durability. TPU is also used in power tools, caster wheels, cable insulation and sporting goods. As it is solvent resistant, TPU can be found in many industrial environments due to its high abrasion resistance and shear strength. However, it is notorious for absorbing moisture from the atmosphere, so it can be difficult to process during manufacturing. For over-molding, there’s thermoplastic rubber (TPR), which is inexpensive and easy to handle for applications like cushioned rubber grips.

Transparent parts

If your part requires clear lenses or windows, acrylic (PMMA) is best. This material is used to make shatterproof windows like Plexiglass because of its rigidity and abrasion resistance. PMMA also takes a high polish, has good tensile strength and is economical in large volumes. However, it is not as impact or chemical resistant as polycarbonate (PC).

If you need something stronger for your project, PC is more durable than PMMA and has excellent optical properties, making it an appropriate choice for lenses and bulletproof windows. PC also can be bent and formed at room temperature without shattering. It’s useful for prototyping work, since it does not require expensive mold tools to shape. PC is more expensive than acrylic and may release harmful chemicals when exposed to hot water for extended periods of time, so it’s not food safe. Due to its impact strength and resistance to scratches, PC is ideal for a variety of applications. At Star Rapid, we used this material to create covers for handheld point-of-sale terminals for Muller Commercial Solutions. The part was CNC machined from solid blocks of PC; since it needed to be completely transparent, it was then hand sanded and vapor polished.

This is just a quick look at some of the most commonly used plastics for manufacturing. Most can be altered with various glass fibers, UV stabilizers, lubricants or other resins to achieve specific engineering properties based on the needs of the project and the manufacturing process being used—whether it’s injection molding, vacuum casting or 3D printing.

Original Source


fundamentals-of-extrusion.jpg

May 1, 2019

In the plastics extrusion process, raw thermoplastic material, or resin, is gravity fed from a top mounted hopper into the barrel of an extruder. Additives, such as colorants and UV inhibitors, in either liquid or pellet form are often used and can be introduced into the resin below arriving at the hopper. The process has much in common with plastics injection molding though differs in that the process is usually continual. While injection molding can offer many similar profiles in continuous lengths, usually with added reinforcing, the finished product is pulled out of a die instead of extruding the fluid resin through a die.

As the material enters the feed throat near the rear of the barrel it comes in contact with the screw. The rotating screw forces the plastic resin forward into the barrel that is heated to the desired melt temperature depending on the resin. In most processes, a heating profile is set for the barrel utilizing three or more independent PID (proportional-integral-derivative controller) controlled heat zones that gradually increase the temperature of the barrel from the rear where the resin has entered to the front. This allows the plastic resin to melt gradually as it is pushed through the barrel and lowers the risk of overheating which may cause degradation in the polymer.

At the front of the barrel, the resin leaves the screw and travels through a reinforced screen to remove any contaminants.  A breaker plate generally reinforces screens because the pressure at this point can exceed 5000 psi (34 MPa).

After passing through the breaker plate resin enters the die. The die is what gives the final product its profile or shape and must be designed so that the molten plastic evenly flows from a cylindrical profile, to the product’s profile shape. Uneven flow at this stage would produce a product with unwanted stresses at certain points in the profile. These stresses can cause warping upon cooling. Almost any shape imaginable can be created so long as it is a continuous profile.

The product must now be cooled which is usually achieved by pulling the extrudate through a water bath. Plastics are excellent thermal insulators and are therefore very difficult to cool quickly. Compared with steel, plastic conducts its heat away 2000 times more slowly. In a tube or pipe extrusion line, a sealed water bath utilizes a carefully controlled vacuum to keep the newly formed and still molten tube or pipe from collapsing. A set of cooling rollers is generally used in the sheet extrusion process to cool sheet as it exits the extruder.

Sometimes, on the same line, a secondary process may occur before the product has finished its run. In the manufacture of adhesive tape, a second extruder melts adhesive and applies this to the plastic sheet while it’s still hot. Once the product has cooled, it can be spooled, or cut into lengths for later use.

Plastic extruders are also extensively used to prepare recycled plastic waste and/or raw materials after cleaning, sorting and/or blending into filaments suitable for blending into the resin pellet stock used by the plastics industry at large.

Original Source


Polyethylene-.jpg

April 17, 2019

The model above is an image of the pdb model you can view
by clicking here or you can just click on the image itself.
Either way, be sure to close the new window that opens up
with the 3D model in it when you are ready to come back here.


Polyethylene is probably the polymer you see most in daily life. It is one of the polymers called polyolefins, which is an odd name. Many names from the past have nothing to do with the actual chemical compositions of the molecules, but that’s a story for another time.
Polyethylene is the most popular plastic in the world. This is the polymer that makes grocery bags, shampoo bottles, children’s toys, and even bullet proof vests. For such a versatile material, it has a very simple structure, the simplest of all commercial polymers. A molecule of polyethylene is nothing more than a long chain of carbon atoms, with two hydrogen atoms attached to each carbon atom. That’s what the picture at the top of the page shows, but it might be easier to draw it like the picture below, only with the chain of carbon atoms being many thousands of atoms long:

Sometimes it’s a little more complicated. Sometimes some of the carbons, instead of having hydrogens attached to them, will have long chains or branches of polyethylene attached to them. This is called branched, or low-density polyethylene, or LDPE. When there is no branching, it is called linear polyethylene, or HDPE. Linear polyethylene is much stronger than branched polyethylene, but branched polyethylene is cheaper and easier to make. It is also more flexible and works great for sandwich wrap.

Linear polyethylene is normally produced with molecular weights in the range of 200,000 to 500,000, but it can be made even higher. Polyethylene with molecular weights of three to six million is referred to as ultra-high molecular weight polyethylene, or UHMWPE. UHMWPE can be used to make fibers which are so strong they replaced Kevlar for use in bullet proof vests. Large sheets of it can be used instead of ice for skating rinks.

Polyethylene is vinyl polymer, made from the monomer ethylene. Here’s a model of the ethylene monomer. It looks like some sort of four-legged headless animal if you ask me.

The model above is an image of the pdb model you can view by
clicking here or you can just click on the image itself.
Either way, be sure to close the new window that opens up
with the 3D model in it when you are ready to come back here.

Branched polyethylene is often made by free radical vinyl polymerization. Linear polyethylene is made by a more complicated procedure called Ziegler-Natta polymerization.UHMWPE is made using metallocene catalysis polymerization.

But Ziegler-Natta polymerization can be used to make LDPE, too. By copolymerization ethylene monomer with a alkyl-branched comonomer one gets a copolymer which has short hydrocarbon branches. Copolymers like this are called linear low-density polyethylene, or LLDPE. BP produces LLDPE using a comonomer with the catchy name 4-methyl-1-pentene, and sells it under the trade name Innovex¨. LLDPE is often used to make things like plastic films.


Other plastic polymers include: Other fiber polymers include:
Polypropylene Polypropylene
Polyesters Polyesters
Polystyrene Nylon
Polycarbonate Kevlar and Nomex
PVC Polyacrylonitrile
Nylon Cellulose
Poly(methyl methacrylate) Polyurethanes

Original Source


Plastics.jpg

April 3, 2019

Plastics extrusion is a high volume manufacturing process that melts and forms raw plastic material into a continuous profile. Plastic extrusion is a process that creates two-dimensional shapes on length providing the third dimension tubing, edging, moldings fence, deck railing, window frames, weather stripping, adhesive tape and wire insulation and similar products in continuous lengths or short sections. Extruded products can be utilized as it is, or may be transforming into more complex assemblies by punching, molding, forming and other techniques. The extruded products can provide a cost effective solution to your product fabrication and assembly needs.

The two different fundamental methods of extruding film are below extrusion and slit die extrusion. While the design and operation of the extruder during die is the similar in both methods.

In the form of small beads known for gravity, raw thermoplastic material fed from a top mounted hopper into the barrel of the extruder. Also in the extrusion of plastics additives such as colorants and UV inhibitors either in liquid or in pellet form are often used and can be mixed into the resin prior to arriving at the hopper. Through the feed throat and rotating screw plastic beads are forced forward into the barrel where it is heated to the desired melt temperature of the molten plastic. This leads plastic beads to melt gradually as they are pushed through the barrel and lowers the risk of overheating which may cause degradation in the polymer.

Innovative Extrusion Pvt Ltd is a specialist manufacturer and supplier of products like rigid PVC profiles, thermal breaker, injection moulded components, Dies and Moulds and dies and moulds.

Vinayak Plastic Industries is engaged in Manufacturing and Exporting of HDPE / PP Solid Extruded Sheets and PP Corflute Sheet / PP Corrugated Sheets / PP Hollow Profile Sheets & HDPE Pipes. The sound infrastructure furnished with Hi-Tech Machinery that facilitates bulk production of the products that includes extrusion process.

In the recent days, plastics extrusion has seen conventional and unconventional ideas those made lot of difference to the process and the sector. It is not only about process and machinery involved, but also the market demand for it. As per a research report, US demand for extruded plastics is forecast to expand 2.6% annually through 2013.

BASF’s plastics extrusion technology has manufacturing of films, fibers, monofilaments, profiles, sheets, semi-finished products and a wide range of plastic materials plays important role in this process. The mechanical, thermal, chemical and electrical properties are information on fields of use on applications, which as well process information by extrusion or other processing techniques.

Custom Complex Profile Plastic Extrusions

Creating and generating custom plastic extrusions needs unique skills and talents, while it adds value and innovation to the current product.

Plastic Extrusion Technologies is recognized for its products and services in custom plastic profile and plastic tubing needs. Here over 25,000 square feet of plastic extrusions facility is filled with the most state-of-the-art production machinery. Plastic Extrusion Technologies has the technology, and more importantly, the knowledge to help you get your extruded plastic product into your customers’ hands. The clientele is from window manufacturers to adhesives producers, use Plastic Extrusion Technologies custom extrusions. The applications are prevalent in brush products, refrigeration, HVAC, cable and wire, safety products, point of purchase displays and commercial construction.

Eaton’s industrial plastics business provides custom complex profile plastic extrusions for a wide variety of customers and industries. The company’s value-added fabrication such as length cutting, hole punching, texture, and tape backing for mounting applications provide customers with the capabilities to complete any production. Custom profile extrusion products and solutions for a variety of applications and industries.

Crafted Plastics Inc has new approaches to the plastics extrusion process of making the specialized extruded plastic product. The approaches include

  • Co-Extrusion process is used when two materials and colors must be joined into one part.
  • Dual Durometer provides the making of a plastic extrusion where the same family of plastics, but with different hardness, is combined in various combinations-flexible and rigid, flexible and flexible, rigid and rigid. The term also applies when two different opaques are used in combination to make a part.
  • The Tri-Extrusion is a process that involves combining three materials or colors when needed in one plastic extrusion.
  • Value Added Operations after a plastic profile is extruded, additional work can be done. This work includes drilling, punching, notching, creating round or oval holes, cutting mitres, and doing precise tolerance cutting.

In the process, profile extrusion can be completed followed by adding tape like, film, foam, or magnetic, printing, or close tolerance cutting. Every year many events, exhibitions and conferences take place on plastics extrusion. An ongoing research and development has brought in improved applications and approaches to the plastics extrusion process. A lot of production lines via plastics extrusion machineries already lined up and this is the evidence of the demand for plastics extrusion technologies and the raw material.

Original Source


Polypropylene-.jpg

March 20, 2019

The model above is an image of the isotactic polymer you can view
by clicking here or you can just click on the image itself.
The image below is of the atactic version with random backbone stereochemistry.
Either way, be sure to close the new window that opens up
with the 3D model in it when you are ready to come back here.

Polypropylene is one of those rather versatile polymers out there. It serves double duty, both as a plastic and as a fiber. As a plastic it’s used to make things like dishwasher-safe food containers. It can do this because it doesn’t melt below 160oC, or 320oF. Polyethylene, a more common plastic, will anneal at around 100oC, which means that polyethylene dishes will warp in the dishwasher. As a fiber, polypropylene is used to make indoor-outdoor carpeting, the kind that you always find around swimming pools and miniature golf courses. It works well for outdoor carpet because it is easy to make colored polypropylene, and because polypropylene doesn’t absorb water, like nylon does.

Structurally, it’s a vinyl polymer, and is similar to polyethylene, only that on every other carbon atom in the backbone chain has a methyl group attached to it. Polypropylene can be made from the monomer propylene by Ziegler-Natta polymerization and by metallocene catalysis polymerization.

This is what the monomer propylene really looks like:

The model above is an image of the pdb model you can view
by clicking here or you can just click on the image itself.
Either way, be sure to close the new window that opens up with
the 3D model in it when you are ready to come back here.


Wanna know more?

Research is being conducted on using metallocene catalysis polymerization to synthesize polypropylene. Metallocene catalysis polymerization can do some pretty amazing things for polyolefins like polypropylene. Specifically, it allows polypropylene to be made with different tacticities. Most polypropylene we use is isotactic. This means that all the methyl groups are on the same side of the chain, like this:

Isotactic polypropylene has a high enough melting point that you can put it in your dishwasher and it won’t come out as a new form of plastic art. But sometimes we use atactic polypropylene. Atactic means that the methyl groups are placed randomly on both sides of the chain like the 3D image above or the figure below:

Atactic polypropylene has no commercial application because it’s pretty much a gooey, messy blob. However, by using special metallocene catalysts, it’s believed that we can make polymers that contain blocks of isotactic polypropylene and blocks of atactic polypropylene in the same polymer chain, as is shown in the picture:

This polymer is rubbery, and makes a good elastomer. This is because the isotactic blocks will form crystals by themselves, acting as physical crosslinkers. But because the isotactic blocks are joined to the atactic blocks, the little hard clumps of crystalline isotactic polypropylene are tied together by soft rubbery segments of atactic polypropylene, as you can see in the picture on the right.

To be honest, atactic polypropylene would be a very soft rubber without help from the isotactic blocks, but it wouldn’t be very strong. The hard isotactic blocks hold the rubbery isotactic material together, to give the material more strength. Most kinds of rubber have to be chemically crosslinked to give them strength, but not polypropylene elastomers.

Elastomeric polypropylene, as this copolymer is called, is a kind of thermoplastic elastomer. However, until the research is completed, this type of polypropylene will not be commercially available.

The polypropylene that you can buy off the shelf at the store today has about 50 – 60% crystallinity, but this is too much for it to behave as an elastomer. It does make it an excellent polymer for applications in plastic storage containers and bottles. Take a look on the bottom of what you use to store leftovers in the fridge. If it has a recycle number of “5,” it’s isotactic polypropylene.


Other polymers used as plastics include: Other polymers used as fibers include:
Polyethylene Polyethylene
Polyesters Polyesters
Polystyrene Nylon
Polycarbonate Kevlar and Nomex
PVC Polyacrylonitrile
Nylon Cellulose
Poly(methyl methacrylate) Polyurethanes

Original Source

 


images.jpg

March 4, 2019

By plasticizing, there are dry extrusion and wet extrusion processes and by pressurizing there are continuous and intermittent extrusion processes

Continuous production yields a high efficiency, simple operation for a wide range of applications, such as tubing extrusion, sheet/film extrusion etc.

Profile Extrusion

The Profile Extrusion process, such as drinking straws and medical tubing, is manufactured the same as a regular extrusion process up until the die. Placing a pin or mandrel inside the die extrudes hollow sections, and in most cases positive pressure is applied to the internal cavities through the pin.

Tubing with multiple lumens (holes) must use tooling made for specialty applications. For these applications, the tooling is made by placing more than one pin in the center of the die to produce the number of lumens necessary. In most cases, these pins are supplied with air pressure from different sources. This way, the individual lumen sizes can be adjusted by adjusting the pressure of the individual pins.

Co-Extrusion

Co-Extrusion is the extrusion of multiple layers of material simultaneously. This type of extrusion utilizes two or more extruders to melt and deliver a steady volumetric throughput of different viscous resins to a single die and extrude the resin in the desired form. This process can be used in a variety of extrusion processes (blown film, profile or sheet).  The layer thicknesses are controlled by the relative speeds and sizes of the individual extruders delivering the materials.

There are a wide range of reasons why a manufacturer may choose co-extrusion over single layer extrusion. One example is in the vinyl fencing industry, where co-extrusion is used to tailor the layers based on whether they are exposed to the weather or not. Usually a thin layer of compound that contains expensive weather resistant additives are extruded on the outside while the inside has an additive package that is more suited for impact resistance and structural performance.

Extrusion Coating

Extrusion coating is used in a blown or cast film process to coat an additional layer onto an existing roll stock of paper, foil or film. For example, this process can be used to improve the characteristics of paper by coating it with polyethylene to make it more resistant to water. The extruded layer can also be used as an adhesive to bring two other materials together.

Sheet/film Extrusion

For products such as plastic sheet or film, cooling is achieved by pulling material through a set of cooling rolls, usually 3 or 4 in number. Running material too fast creates an undesirable condition called “nerve” which is basically inadequate contact time given to dissipate the heat present in the extruded plastic. In sheet extrusion, these rolls not only deliver the necessary cooling but also determine sheet thickness and surface texture.

Often co-extrusion is used to apply one or more layers on top of a base material to obtain specific properties such as UV-absorption, soft touch or “grip”, matte surface or energy reflection where it is needed.

A common post-extrusion process for plastic sheet stock is thermoforming where the sheet is heated until soft and then formed via a mold into a new shape. Thermoforming can range from line bended pieces to more complex shapes such as computer housings.  These more complex forms which often resemble injection molded parts and can be attributed to the various possibilities in thermoforming, such as inserts, undercuts and divided molds.

Plastic sheet and film extrusion onto paper is the basis of the liquid packaging industry.  Juice cartons, wine boxes as well as the food packaging industry utilize this process.

Blown film Extrusion

This process is used to manufacture plastic film for products such as shopping bags .  Blown film is imilar to any regular extrusion until it reaches the die. The die is an upright cylinder with an annular opening similar to a pipe extrusion die. The molten resin is pulled upwards from the die by a pair of nip rolls high above the die.  Changing the speed of these nip rollers will change the gauge or wall thickness of the film. Around the die sits a cooling ring that blows air onto the film tube as it travels past. The airflow cools the film as it travels upwards. In the center of the die is an air outlet trough which compressed air can be forced into the inside of the extruded cylindrical profile, adjusting the bubble volume.  The film can then be slit, spooled, printed on or cut into shapes and heat sealed into bags or other items.

Compound Extrusion

Compound extrusion is a process that mixes one or more polymers with additives to create a plastic compound. The feed stock may be pellets, powder and/or liquids, but the product is usually in pellet form and used in other plastic-forming processes such as extrusion and injection molding. Machine size varies from tiny lab machines to the biggest extruders in the industry, running as much as 20 tons per hour, as used by the chemical companies that make base resins. Usually twin-screw extruders are preferred because they offer superior mixing at lower melt temperatures. Most of these have screws and barrels comprised of smaller segments (mixing, conveying, venting and additive feeding) so that the design can be changed to meet the production and product needs. Single-screw extruders can be used for compounding as well, especially with appropriate screw design and static mixers after the screw. Selection of the components to be mixed (viscosities, additive carriers) is as important as the equipment.

3-D Printer Filament Extrusion

Low-cost 3-D printers use extrusion to fabricate 3-D plastic objects. The filament used as feedstock in these 3-D printers is itself extruded either conventionally through industrial high-rate extruders or other common extruders.

Original Source


Extruder-Screw.jpg

February 5, 2019

I teach a one-day Intro to Extrusion seminar, and many of my participants are new to extrusion. Therefore, I explain the basic principles of screws for thermoplastics. That’s good for the newbies, but sometimes I get more experienced extrusion people thanking me for these basics, which they had never learned way back when. So here goes. I hope you all find it useful.

The screw is a conveyor. As it turns, it tries to screw itself backward out of the barrel, but a bearing keeps it from going out the back. Because every action has a reaction—remember Isaac Newton?—it pushes the other way, too, in the forward direction, and that’s what pushes the material out of the die.

Material needs to get soft to go through the die. Any thermoplastic will get soft and moldable (plastic) with heat (thermo). The feed is sometimes preheated (usually for drying), but it gets most of the heat from internal friction as it moves against the barrel walls and screw surfaces. The clearances from flights to barrel are where most heat is generated. Exceptions: Some twin screws, small machines, high-temp resins and PE coatings, where barrel heat is important, too.

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Plastic-Testing.jpg

February 5, 2019

The term ‘plastics’ is used to describe a variety of synthetic and natural compounds, and many plastic variants are used in different products and industries.

Plastics can contain an assortment of reinforcing materials and fillers additives. The combination of these products along with the manufacturing process can significantly affect the mechanical properties of the finished product. Industries such as automotive engineering and aerospace have a huge demand for advanced plastics, making it imperative to assess and monitor the performance of such materials.

Testometric’s precision testing system has invaluable capabilities that help ensure that the selected material has the performance and characteristics to fulfill the necessary specification for the specific product or component. Packages are provided to cover the entire range of plastic materials. These comprise of grips, software, and other accessories for all test protocols covering compression, shear, creep, tensile, tear, flexural, puncture, peel, ring stiffness, friction, adhesion, hardness, etc.

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Drive-Flow.jpg

February 5, 2019

Molecular orientation occurs when melted polymer is sheared or stretched. If cooled quickly, this orientation is largely retained until the extrudate is reheated to a temperature that allows the molecular chains to move to their relaxed state.

Orientation can be beneficial or troublesome. It can be desirable when it is deliberately added to the extrudate. For example, it provides property improvements such as unidirectional strength in fibers, hoop strength in oriented extrusion blow molded bottles, and tear strength in oriented films. But in many extruded parts orientation can cause post-extrusion problems from non-uniform shrinkage and warpage.

Orientation occurs in every extrusion process due to the inherent strain applied to the long-chain molecules as the polymer is shaped and flows through the die. Some orientation through the die is unavoidable, and the magnitude depends on output rate for a given die design. A secondary annealing process is about the only way to reduce all orientation in extruded parts.

Polymer orientation can be measured for transparent polymers in the amorphous state by birefringence, and in both the amorphous and semi-crystalline state by infrared spectroscopy. The simple field test for orientation, often referred to as the “Chrysler test,” calls for cutting

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